Mold Design ~ Guidelines A NINE-PART SERIES SPONSORED BY
Copper Development Association . ~-
Reprinted by permission from Modern Mold & Tooling March 1999 - February 2000
Copper Development Association CDA Sponsors Mold Design
Look for ideas Guidelines that will allow faster processing of plastic and production of in MM&T higher-quality parts
eep an eye out for coming the moldmakers, molders and issues of Modern Mold and manufacturers to improve the KTooling, which will contain processing of plastic materials. injection mold design guide The task group, supported by lines developed to make you the trade associations of the ~~ more productive. These infor copper industry, is dedicated to HUSSEY COPPER n• ~::ff} · mative and collectable fact research and disseminating the filled design guidelines are information you need to take being developed for the injec advantage of the superior per tion molder, mold designer formance of molds containing and mold builder. The informa copper-alloys. Also, the associa tion contained in the guide t ion is dedicated to developing lines will maximize the mold's an infrastructure of copper pro cycle time and improve part ducers, fabricators, suppliers •••• • quality with the use of copper and mold makers who are in the ••• alloys in the mold. plastics chain. I\ The articles will begin in the Research work, performed at THYSSEN ~ May issue. western Michigan University, is . These information packed conducted to address technical COPPER AND BRASS SALES Injection Mold Design issues and remove barriers to GZt. Guidelines are being developed the use of copper alloys for DMliotiofTllyal«ilnc.,NA and generated by The Copper plastic processing. The develop Alloy Molds Marketing Task ment of these Injection Mold Group. The group is a network Design Guidelines is a result of of copper-alloy suppliers, dis- this research and in addition to tributors, and fabricators who empirical data derived from have joined together to assist industry applications.
Companies and representa HUSSEY MARINE ALLOYS LTD, IL 60632 . Phone 773 .376.0100 tives, with contact informa H. Russell Garrett, 100 Washington BOOOA tion, serving on the Task Street, Leetsdale, PA 15056-1099. FABRICATORS Group include: Phone 800.767 .0550 BOOOA 50 YEARS NONFERROUS PRODUCTS, INC., 1946-1996 (For more informataion NGK METALS CORPORATION, Glade Denis B. Brady (1999-2000 Chairman • from these companies, F. Nelson , P.O. Box 13367, Reading, of the Task Groupl, 401 East 14th write in the reader service PA 19612-3367. Phone 800.237.9526 Street, Franklin, IN 43131. number on the reader service card BOOOA Phone 800.423.5612 BOOOA or fax-back pagel REVERE COPPER PRODUCTS, INC. PERFORMANCE ALLOYS & SER COPPER ALLOY PRODUCERS Michael Decker, 24 North Front VICES, INC. , Cliff Moberg, N116 AMPCO METAL INCORPORATED, Street, New Bedford, MA 02740. W18515 Morse Drive, Germantown, Wayne Jakusz. 1745 South 38th Phone 800.831 .1801 BOOOA WI 53022 . Phone 800.288.7747 Street, Milwaukee, WI 53201 . Phone SIP/ METALS CORPORATION, Mike BOOOA 800.844.6008 BOOOA Smith, 1720 North Elston Avenue, WELDALOY PRODUCTS COMPANY, BRUSH WELLMAN ENGINEERED Chicago, IL 60622 -1579. Phone Leland Thomas, 11551 Stephens MATERIALS, J. Scott Smyers, 17876 800.621 .8013 BOOOA Drive, Warren , Ml 48090-1047 . St. Clair Avenue, Cleveland , OH SPEC/ALLOY, INC., Karl P. Lebert, Jr.. Phone 800.597 .8634 44110. Phone 800.321 .2076 BOOOA 4025 South Keeler Avenue, Chicago, BOOOA continued DISTRIBUTORS Menomonee Falls. WI 53051 . and Manufacturing Engineering, CAD/ COMPANY INC. Ronald P. Pratt, Phone 414.255 .0205 BOOOA College of Engineering and Applied P.O. Box 81053, Rochester. Ml 48308- SNIDER MOLD COMPANY INC., Sciences, Kalamazoo, Ml 49008-5061 . 1053. Phone 248.375 .2224 BOOOA James L. Meinert, 6303 West Phone 616.387.6527 BOOOA COPPER & BRASS SALES, INC. John Industrial Drive, Mequon. WI 53092 . CONSULTANTS M. Perryman. Jr. 400 Renaissance Phone 414.242 .0870 BOOOA DEALEY'S MOLD ENGINEERING, Center. Suite 1800, Detroit Ml 48243. ASSOCIATIONS Robert Dealey, 351 Forest Drive, Phone 313.566.7425 BOOOA COPPER DEVELOPMENT Williams Bay, WI 53191. Phone MOLDMAKERS ASSOCIATION, INC., Dr. Harold T. 414.245.5800 BOOOA ELECTROFORMED PRODUCTS INC., Michels, 260 Madison Avenue, New ISORCA INCORPORATED, William Vecere. 1921 Bellaire Avenue, York, NY 10016. Phone 800.232 .3282 Kenneth C. Apacki , 1226 Weaver Royal Oak, Ml48067-1587. Phone BOOOA Drive, Granville, OH 43230. Phone 248.548.9164 BOOOA INTERNATIONAL COPPER 740.587.3262 BOOOA METALLAM/CS, INC., Robert R. ASSOCIATION, Johan Scheel, 260 WISCONSIN WIRE WORKS INC, Carl McDonald, Ph .D., 13795 Seven Hills Madison Avenue, New York, NY W. Dralle, 17975 Continental Drive, Road , Suite A, Traverse City, Ml 10016. Phone 800-232-2382 BOOOA Brookfield, WI 53045. Phone 49686 -9378. Phone 616.223 .9423 RESEARCH UNIVERSITY 414.781.1042 BOOOA BOOOA For information regarding participation in WESTERN MICHIGAN UNIVERSITY, THE COPPER-ALLOY MOLDS MARKETING TASK OMEGA TOOL, INC., Andy Lehner, Dr. Paul Engelmann, Associate GROUP, contact: N93 W14430 Whittaker Way, Professor, Department of Industrial Dr. Harold T. Michels at 800.232.3282. BOOOA
several molds, funded by the Tooling. The greatest benefit to
ENGINEERED MATERIALS task group, were built and test the people who deal with molds ed to conduct research under and molding will be to collect actual production conditions. each issue to use as a reference one studied the cycle time in both the applications of the HUSSEY advantage the copper alloys copper alloys and the mold _.. ~ offered over traditional mold design principles. steels. Additionally, due to the Subjects for the Injection Mold MARINE ALLOYS superior thermal conductivity Design Guidelines will include: Where the customwork is always right of the copper alloys, part quali 1. Sprue Bushings and Runner ty improvements including less Bars warpage, better dimensional 2. Mold cores, core Pins and stability and more uniform Chill Plates mold temperatures resulted. 3. Mold Cavities and "A" Side Other research and testing con Inserts centrated on eliminating mold 4. Slides, Lifters and Raising sweating under humid operat Mold Members ing conditions. This is accom 5. Ejector Pins, Ejector Sleeves plished by running higher mold and Ejection P PERFORMANCE ALLOYS operating temperatures with 6. Mold Temperature control A COPPER ALWYS FOR MOLDMAKING copper alloy mold cores. The Systems. Bubblers. Baffles, s 1-800-272-3031 test results prove that better Diverters and Plugs part dimensional stability can 7. wear plates, Slide Gibs, be obtained at shorter mold Interlock Plates, Leader pins and cooling times without mold Guided Ejector Bushings sweating when compared with 8. Plating and Coating of Copper mold steels. Alloys Exhaustive wear 9. Application of Copper Alloys study is under way in Injection and Blow Molds An exhaustive wear study is under way testing the effects of These guidelines will include electroless nickel, hard chrome, properties of the various cop titanium nitriting, thin dense per alloys most commonly uti chrome and thin dense chrome lized for their thermal and bear with diamond particulate in ing properties, compared with extending the mold life of the traditional mold steels. Charts, copper alloys. graphs, formulas and descrip As a service to the plastics tions will provide the user with industry, the Task Group is fund pertinent data not available ing the publication of these from other sources. • guidelines in Modern Mold and Injection Mold Design
Guidelines By Dr. Paul Engelmann and Bob oealey for the Mold Marketing Task croup of the Copper Maximizing Development Association Performance Using Copper Alloys
copper Ac lloys f or onveying and runner faster, allowing Radius s Plastic in Injection Molds more efficient ejection or ~ ~ removal by sprue pickers or 1/2" .3125 The high thermal conductivity robots. of copper alloys makes them 3/4" .5625 ideal materials for the injec Sprue Bushing Radius tion mold sprue bushing and In North America two injection runner bars. Three alloys typi mold nozzle and sprue bushing cally are utilized for the mold radii are used, 112 and 3/4 inch. components, which will have To insure proper fit up, the R contact with plastic. The cop nozzle radius is nominal -.015 per alloys are: inch, while the sprue radius is nominal+. 015 inch, required • C17200, high hardness tolerances to use. Illustration I, SprH Radius beryllium-copper alloy • C17510, high conduct Swing points and tolerances beryllium-copper alloy used in establishing the radius • C18000, NiSiCr hardened high on a sprue bushing are shown conductivity copper alloy in illustration I.
These Copper alloys have six to Sprue Bushing Orifice nine times greater heat trans Machine nozzle orifices come fer rates than conventional in nominal 1/16" fractional inch mold steels as indicated by the sizes. To insure that the slug thermal conductivity. in the nozzle will pull through the sprue, the orifice must be .031 !1/32 inch> larger in diame Mold Thermal ter. This dimension is referred Material conductivity to as the "O" dimension. The !Btu/Hr/Ft2/°Fl relationship is shown in thi.s C-17200 60 chart. C-17510 135 C-18000 125 H-13 17 Nozzle "O" Sprue "O" P-20 20 1/16" 3/32" 420 SS 14 1/8" 5/32" The sprue or runner system 3/16" 7132" must never control the cooling 3/8" 9/32" phase and/or overall molding 5/16" 11/32" cycle. Plastic in contact with copper alloys will set the sprue Nominal + 1/32" Primary Runner Sizing Calculation Sprue Bushing Taper Also, a sprue bushing that is 02 = 0 1 + L ( TAN 2.386° ) To aid in the removal of the not keyed will rotate creating sprue from the bushing, a misalignment with the runner taper of one-half inch per foot machined into the face of the is normally used in injection sprue bushing and the runner molding. Calculate the sprue system. To prevent these orifice at the parting line face, problems, retain and key the multiply the tangent of the sprue into position with the taper angle times the length, use of a cap screw as illustrat plus the "o 2" . Knowing this ed in figure IV. dimension, informed decisions can be made on primary run ner sizing. Sprue Fit Heat must be transferred from The sprue frequently controls the sprue through the copper Illustration II, Sprue taper the molding cycle when larger alloy sprue bushing to the mold orifice conventional steel plates. Interference fit is rec sprue bushings are used. The ommended for optimum cool Pressure in Sprue * application of a copper alloy ing. The bore through the "A" sprue bushing cools the sprue plate should be nominal size to more quickly and efficiently, plus .0005 inches with a surface allowing the molding cycle to finish of at least 16 RMS. The be controlled by the piece shank of the sprue bushing part. should be the nominal size, plus .0005 to plus .001 inches. Pressure loss is high in the sprue. This is the only place in standard Sprue Bushing -+- 3/32 _2000 t--t----t---::;..._...,=r---; the feed system where the Availability ..... 5/32 channel progresses from a ! 1600 +------b-"=---+--+------+-~ I! smaller area to larger. Copper alloy sprue bushings ..... 7/32 Frequently, smaller orifices are with patented stainless steel - 9/32 i ,- t-F=-t=::l~H used on long sprue bushings nozzle seats are commercially II. 600 t--J:::§::F=~;;:;;::=t-1 --11132 in an effort to reduce the available. An insulator mass. This results in extreme between the nozzle and sprue 3 4 • For Polystyrene Length of Sprue ly high injection pressure loss is beneficial in controlling the es, making the part hard to fill. flow of heat from the nozzle Illustration Ill, Pressure, Sprue Length to the sprue. Special sprue The chart in illustration 111 is a bushings may be constructed -lllliiiiii;;::-, Illustration IV, guide for determining the to suit using standard 112 inch Anti- rotation screw effect that the specific "O" per foot sprue bushing dimension has on the pres tapered drills and reams. sure required to deliver plas Sprue bushings with tapers of tic through the length of a up to 3/4 inch per foot have sprue. Note that the differ been used for difficult to ence between a 3/32 and remove plastics. Care must be 9/32-inch sprue is about 1,000 taken to insure that the taper PSI over a short sprue and is draw polished and free from almost 1,500 pounds on a long undercuts or rough surfaces sprue. that could hinder sprue removal. Using a copper alloy sprue bushing allows for an Conventional Injection Mold A Illustration v, increased size orifice, thus Runner Systems ER= Formula reducing pressure loss while p runner system maintaining reasonable cooling The shape of the runner, full times. round or trapezoidal, or other configuration, is dictated by ER = Efficiency Ratio Sprue Retention and mold design. The most effi Anti-Rotation cient runner cross section is A = Area of runner Pressure acting on the parting full round. The efficiency of the cross section line face of the sprue, due to runner cross section can be projected area of the runner calculated with a formula, P = Periphery of runner system or part detail, exerts Figure V, the larger the ratio cross section pressure on the sprue bushing. the better. Runner Bar Straight Threaded Injection Mold Runner Bars runner with one-half the area is Runner systems for high cavita not the same as a runner of one tion molds normally have larger half the diameter...... , ~ diameters due to runner balanc ing. The runner system extends Formulas for calculating the area the molding cycles as heat is of the runner: slowly transferred from the thick Runner Bar Mating plastic to steel mold plates. Best results are obtained by Inserting copper alloy runner bars Full Round Runner Illustration VI, Runner Bars in the mold "A" and "B" plates. A= 0.7854 d2 cooling the runner faster, is ben Trapezoidal Runner eficial. in reducing the overall A = (W1 + W2l h/2 molding cycle. A= area, d = diameter, I = length, w =width. h = height Runner Sizing Runner sizing is dependent on designing and building the run many things, including: plastic ner bars to have zero to negative material; part size, weight and contact with each other when wall thickness; molding machine the mold is closed. This will pre capabilities and processing para vent any deformation on the meters and, the number and parting line surfaces that could placement of the cavities. result from high clamping pres Illustration VII sures exceeding the compressive cooling arrangements. larger Each mold is unique and the strength of the alloy. To accom diameter runners can be used in a designer must consider all parame plish this, the "A" and "B" runner mold equipped with copper alloy ters and options available on an bars should be flush to minus .001 runner bars. Almost without individual case by case basis. inch on each side of the mold. exception, runner diameters one several mold design software pack This allows the mold base and/ or or two sizes larger can be set up ages are available, including Mold cavity and core inserts to receive quicker with the copper alloys, Flow and C-Mold, which address machine clamp force, not the over traditional mold steels. sizing of the runner system. runner bars. Sprue Puller one method of runner sizing and care must be taken to under A reverse taper sprue puller, 3° for balancing used by mold design stand the characteristics of the stiffer materials and 5° for flexible ers· starts at the sprue and then plastic being molded and clear materials, is recommended to works toward the gate. Other ance should be short of allowing insure sprue removal. To rapidly designers start with the part wall the runner system to flash. cool the undercut machine. the thickness and work back to the Additionally, it is important to puller directly into the runner sprue outlet orifice. The normally insure that the mating halves of bars or a copper alloy insert. recommended procedure is that, the runner system are in perfect Illustration VII gives more details. in the direction of plastic flow. alignment. with no mismatch at the runner area always goes from the parting line, to maximize plas Acknowledgements larger to smaller. Never from a tic flow efficiency. The injection mold design guidelines were smaller area to a larger area . written by Dr. Paul Engelmann, Associate Professor, western Michigan University and Runner Bar Cooling Bob Dealey, Dealey's Mold Engineering, with When the primary runner diame The runner system must never the support of Dr. Dale Peters, for the Mold ter is known. the sum of the areas control the molding cycle. To Marketing Task Group of the copper Development Association. Kurt Hayden, of the multiple connecting run insure proper temperature control graduate research assistant, WMU , generat ners must be equal or smaller in of the runner bars. cooling chan ed the Illustrations. Research conducted by area than the preceding runner. nels should be placed directly into WMU students in the plastics program. When working back from the part. the both the "A" and "B" side Disclaimer some designers size the final run inserts. The cross-drilled holes These guidelines are a result of research at ner channel size !that runner should be blocked with a plug con WMU and industry experience gained with the use of copper alloys in injection mold which feeds the gatel to equal the taining an "O" ring and a straight ing. While the information contained is thickest wall section in the part. thread plug. Due to the high ther deemed reliable, due to the wide variety of Each runner intersection then is a mal conductivity of the copper plastics materials, mold designs and possi function of the area of that run alloys and the tendency to thermal ble molding applications available, no war ranties are expressed or implied in the ner times the number of connect cycle rapidly, tapered thread sys application of these guidelines. ing runners, usually two. tems must be avoided in the cop Therefore. the area of the per alloys to prevent cracking. Contact Information upstream runner is always at least Information regarding copper alloys for molds and molding is available from the equal to or larger in area than the With the increased cooling rate of Copper Development Association, sum of the branches. Note that a the copper alloys and proper 1-800-232-3282. Injection Mold Design
Guidelines By Dr. Paul Engelmann and Bob Dealey for the Mold Marketing Task croup of the Copper Maximizing Development Association Performance Using Copper Alloys
The Injection Mold Core plastic molding due to the mater A mold core is any member that ial shrinking around the standing forms the interior of a plastic features of the mold. part. usually on the "B" side of the mold parting line. Mold copper alloys have adequate cores can be machined from a hardness levels to hold up against solid piece of copper alloy or normal injection pressures found inserted to aid in construction or in conventional injection molding allow for easier machines. The normal press !pos replacement if a com itive interference, or crush> is not ponent would ever be used due to the higher ductility damaged in molding. of copper alloys and to avoid any peening or hobbing at shut offs This picture shows a and at the parting line. Rather large copper alloy zero to negative press is recom core,about24inches mended. Negative press or clear long and seven inches ance of the mating components high, used to mold a must obviously be less than that PVC bezel for a where plastic will flash. Hardness Kitchen Aid dishwash levels of the copper alloys and er manufactured by mold steels are listed in the fol Whirlpool corporation. lowing chart: Findlay Ohio. The cop per alloy was specified primarily to eliminate warpage on the part. Hardness Levels Copper Hardness Steel Hardness which is both func Alloy Alloy Picture of Whirlpool mold: Acore built from a tional and esthetic in copper alloy for a large dishwasher part nature. The cycle time advantage C17200 41 Re H·13 38/ 52 Re of about 20% by using the high C17510 96 Rb P-20 28-48 Re thermal conductive copper alloy C18000 94 Rb 420 SS 27 -50 Re was an added bonus to the improved part quality, which was the main objective. The copper alloys normally selected for mold cores. core Properly designed molds with pins. inserts. slides and raising copper alloys used in strategic mold members are; C17200 a high locations. usually the core, have hardness beryllium-copper alloy; proven to reduce injection mold C17510 a high conductivity beryl ing cooling cycles by 20 to 50 per lium-copper; And. C18000 a NiSiCr cent. The mold core is responsi hardened high conductivity cop ble for removing from 65 to 75 per alloy. These alloys, with six per cent of the heat from the to nine times greater heat trans- fer rates than steels !see that for a mold material. The cop Injection Mold Design per alloys exhibit a good combi Guidelines, number 1 for nation of tensile strength and details! have proven over ductility, making them tough and time to be the best choices ideal candidates for mold compo for plastic forming mold nents, not withstanding the high components. Other copper thermal conductivity properties. alloys, including the alu Tensile strength of the three cop minum bronzes, have per alloys and three common attributes consistent with mold steels are compared in the specific applications in the following tensile strength table. mold not associated with plastic forming. These Tensile strength
The Injection Mold cavity ease of insert installation and A mold cavity forms the exterior leak free operation. of the plastic part and almost always is located on the "A" side Mono Block Construction of the mold. However, there are Frequently in low run single situations where the cavity is impression and/or large molds located on the opposite side of the cavity is machined directly the parting line or occasions into the "A" plate. This type of where the injection mold construction is referred to molded part is sym as "Mono-Block" construction and metrical and the cavity eliminates the step of machining is on both sides of the an insert pocket into the plate. parting line. In these Additionally, it offers a very rigid instances it is called a type mold construction with "B" side cavity. opportunities for excellent cool ing channels surrounding the cavity Inserts cavity. Molds containing more that one cavity, cavity cooling multiple impression cooling channels of appropriate molds, are usually diameter or channel size should constructed individu be incorporated into the mold ally, or if small, ganged cavity block. Placement of these into cavity blocks, and channels should follow similar inserted into the mold recommendations made for the "A" or cavity plate. core of the mold. The coolant separate inserting channel should be placed about Illustration A: Edge gate showing gate width 1w1, allows for ease of two times the diameter away depth 101 and gate land Ill. manufacturing the cavity from a from the cavity with a pitch of variety of mold materials and three to five times the diameter. makes replacement easier should While it is common practice to damage ever occur. Round run the cavity warmer than the inserts are a natural, as round core for aesthetic reasons, the insert pockets are easy to best running molds are those machine with great accuracy into where even surface temperatures mold plates. The round insert is and good temperature control an ideal application for "sur can be maintained. round" cooling of the insert. "O" rings are used to seal the water To insure turbulent water flow in channels and prevent coolant mold cooling circuits a mold cool leakage. They should be ing analysis is conducted prior to designed to be placed in com mold building. This analysis pression and not in shear, for checks and determines place- ment. number and size of run molds. P-20 or Number 3 coolant channels required. steel is used for long run After the mold is built coolant molds and when part detail is flow can be measured to machined into the mold plate. determine if adequate flow When a heat-treated mold rates are being maintained. plate is required, some cavity The following table lists pipe detail can be formed on the size and minimum amount of mold plate and the cavity built flow in gallons per minute up with laminations, H-13 is a which guarantees turbulent logical choice for these high flow. run molds. Another material used for high volume and long Nominal Channel Min. running molds or with corro Pipe Size Size Flow sive plastics is type 420F stain !NPTl !diameter>
£'Flats
Acknowledgements Collector/ The injection mold design guidelines were written by Dr. Paul Engelmann. Associate Ring ~Spiral Professor, western Michigan University and Bob Dealey, Dealey's Mold Engineering, Bleed with the support of Dr. Dale Peters. for the Mold Marketing Task Group of ttie Copper Development Association. Kurt Hayden, graduate research assistant, WMU , Offs generated the illustrations. Research conducted by WMU plastic program under graduate students.
Illustration F: Method of venting at ejector or core pins. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information con tained is deemed reliable, due to the wide variety of plastics materials, mold designs and possible molding applications available, no warranties are expressed or implied in the application of these guidelines. contact Information Information on copper alloys is available from the Copper Development Association. 1-800-232-3282. Injection Mold Design
Guidelines By or~ Paul Engelmann FOURTH IN A SERIES: Nomenclature and Bob oealey for the Mold Marketing Task croup of the Copper Ma~imizing Development Association Performance Using CofJper Alloys
Nomenclature for the types of one probe to feed plastic for the molds is somewhat diverse but mold to be a true runnerless mold usually follows an order describ ing system. Often hybrid systems ing the type of runner system, are used, especially on small parts mold action and ejection method where one probe is used to feed a used. A mold is considered a conventional runner system, which standard mold when it has a con then feeds multiple parts. Copper ventional runner system, the part alloy probes have proven to hold is pulled without any action and more even temperature profiles the mold only has an than steel alloys, especially at the opening at the parting tip end. Ejection line. Occasionally we actuation D hear the term two-plate Internally heated systems incorpo not shown. d applied to this type of rate a manifold with balanced and conventional mold. This streamlined passages installed for is not necessarily a cor the plastic to flow from the inlet to {Stripper rect description and per the nozzles. Nozzles normally haps is only used to dif equipped with coil heaters around \ Ring ferentiate it from a the periphery and a thermocouple three-plate mold. to control the temperature, feed plastic from the manifold to the A three-plate mold has gate. A very popular divergent flow the runner system style incorporates a copper alloy installed between a sepa tip, usually made from C17200 or rate parting line and the c1sooo copper alloy, to aid in main parts are gated with a pin taining an even temperature profile point gate. The advan at the gate entrance to the cavity. tage is that the cold run- The melt flow typically diverges mustration A: Stripper ring ejection of ner is separated from the from the center flow passage an undercut. parts on mold opening. This type through orifices allowing the cop of mold was popular for top gating per alloy tip to extend down to or parts and now frequently a runner into the gate orifice. The tip then less molding system is used in its maintains control of the gate area, place. freezing the gate during part removal and maintaining the cor Runnerless molding systems IRMSl rect temperature to open the gate account for nearly 30% of the for the next cycle. molds built today. RMS can be internally or externally heated. If Molds can have many actions, internally heated, the mold has dis depending on what has to be tributor tubes and/or probes with accomplished, to free undercuts electric heaters placed in the distri and remove the part from the mold. bution channels to maintain the External threads for example, if not melt temperature of the plastic as strippable, utilize slide action or it flows around the tubes toward expandable cavities to free external the gate. Each cavity needs at least features. Internal threads can be formed on side of the mold, require that collapsible cores or in unscrewing the core be removed prior to molds. several methods are used attempting to free even the for unscrewing molds, including slightest undercut, as the flexing hydraulic motors, splines, various plastic must have a place to gearing methods and for large compress or expand into if the multiple cavity molds, racks and part is manufactured without pinions are used. moving mold members. When the undercut is too great, the Other mold actions include mold cavity can be split or mov lifters, wedges or slifters !a new ing cams installed to release the terml, raising members and undercut. These plastic part fea slides !sometimes referred to as tures with details connected to splits, cams and side action!. the main wall tend to have the Mold nomenclature then typical thickest sections. Copper alloys ly describes the type of ejector with their ability to cool faster Illustration B: Alifter shown with the mold closed. system used, normally ejector than conventional mold steels Lifter angle Is exaggerated, should not exceed 5°. pins, sleeves, stripper rings or have proven to be the best plates. Therefore. molds are choice of mold materials in normally refereed to as "a three these areas. Copper alloys will plate, slide action sleeve ejected provide the most even surface mold", or "runnerless collapsible temperatures necessary to take core, stripper plate mold". the heat away from the molding surfaces. Frequently, the front Mold Slides of the slides are faced or insert Undercuts, features on the plas ed. A copper alloy is inserted on tic part that are not in line with a steel slide carrier and coolant normal mold opening, are fre channels are machined through quently encountered. When the the carrier into the copper alloy undercut is small, typically insert. With this design, the cop defined as a percentage of the per slide face acts as a watered overall part dimension, the best heat sink, drawing heat away and least expensive option is to from the part. determine if the part will flex enough to strip off the cavity or In all other designs the slide core without the use of a mold should be designed with the action. Freeing the plastic same concept and mold coolant undercut is first dependent channel as the molds cores and upon the plastic material, its cavities. The coolant channels flexibility and hardness. The could include looping flow, baf Illustration C: Lifter actuation shown during ejection. greater the flexibility and more fles or bubbles. A coolant-circu compressive the plastic the lating cascade is available from a Lifter angle Is exaggerated, should not exceed 5°. greater the undercut can be. number of standard mold com The stiffer and more rigid the ponent supplies and is ideal for plastic material, the less the getting coolant into hard to undercut must be. Undercuts reach areas like those found on a are defined as the percentage slide. The best practice is to difference between "d", the place these coolant lines about amount of the undercut, and "D" two diameters of the cooling the diameter or dimension that channel away from the molding the undercut has to snap off surfaces. This standard works !see Illustration Al. well with the copper alloys, as well as mold steels. However, if Seals are molded from flexible you cannot get that close to the PVC with undercuts greater than mold surface, the more efficient .375 inch and a 1.500 diameter, copper alloys, with their higher resulting in undercuts of 25%. thermal conductivity, will per Modified Closure Manufacturer's form well when the coolant lines Association !CMAl threads are are not ideally located. frequently stripped on closure sizes above 24mm in polyethyl Mold Lifters ene and polypropylene, especial A lifter is a component in the ly in co-polymers. Acme or but mold that is normally attached tress threads typically will not to and actuated by the ejector strip due to the sharp and flat system and moves at an angle to thread profile perpendicular to free internal molding detail !see the direction of draw. Illustrations B and Cl. They are typically attached between the External part features, those ejector retainer and ejector normally found on the cavity plates with some mechanism allowing the fixed end to slide or but when moved forward free pivot to compensate for the move themselves from the pocket to ment of the lifter position as it move away from the plastic wall moves at the desired angle. Lifters !see Illustrations o and El. They are frequently used when segment have a guiding system allowing ed plastic undercuts !raised mold them to move forward and away core detaill is necessary. The lifter from internal or external undercuts has to move out of the mold core at on the plastic part. The wedges an angle, typically 5° or less, to clear are normally located on the "B" the plastic from the mold lifter side of the mold and are either detail. This angle is critical for two pulled with a mechanical attach reasons. First, if the angle were too ment from the "A" side of the great the forward motion of the mold, or pushed by the ejector sys ejector system would put too much tem or cylinders. While less com pressure against the lifter body. mon, wedges can be installed on This pressure would create binding the "A" side of the mold. of the lifter and lead to excessive wear or premature failure. Should The wedge must be guided as it the angle be too shallow, the ejector moves forward. The two guide sys Illustration D: Wedge/"slifter" with the mold closed. plate travel would be excessive. tems most frequently encountered Therefore, careful engineering and are the "T" slot or dovetails. Molds installation of coolant channels due good judgement has to be made. with wedges utilizing dovetails to to their contour and shape. guide and hold the wedge in posi Placement of the coolant channels Due to their function, lifters are nor tion are being called "slifters" in the can be far from ideal. lVPically a mally long and narrow. coolant tooling community. Wedges or tool steel core member in these channels are nearly impossible to slifters have a commonality with applications results in areas where machine into them. The C17200, lifters. The angle in which they raise cooling is compromised. Copper C17510 and C18000 copper alloys, nor must be steep enough to free the alloys have proven time and again mally used in the mold cavity and undercut within the movement that they will, due to their high core, will remove the heat efficiently range and yet shallow enough so as cooling rates, run cooler and have from the lifter. However, because this not to bind or be exposed to condi more evenly distributed surface is a high wear area and when the tions where excessive wear could temperate than a steel counterpart mold core is built from one of the occur. would have. The plastic product alloys already, aluminum bronzes almost always has less warp, twist, make excellent choices for lifter By design, these mold members sink and is more dimensional consis materials. More information on alu have large areas in contact with the tent, due to improved temperature minum bronzes will be included in plastic part. Therefore it is necessary control of this raising mold member. article eight of this series. To avoid to build them with coolant channels seizing the lifter, one copper alloy and from materials with high ther Other Mold Movements riding against another copper alloy is mal conductivity rates. While these The injection-molding machine pro not good engineering practice. one wedges and slifters are ideal candi vides one movement when the of the components should be plated dates for the C17200, C17510 and machine platens separate. The sub or coated. The plating or coating C18000 copper alloys for the plastic sequent mold opening provides the should be carefully chosen, as it must forming contact areas, they are not mold designer with motion that can provide a low coefficient of friction the best choices for the "T" or dove be used to mechanically create between the two surfaces. Surface tail guiding systems. Therefore, sev movement in another plane. Plate treatments should provide dry lubri eral options should be considered in movement, commonly referred to cation and not be affected by con their construction. One preferred as floating of the plates, creates the tact with the plastic material and method is to laminate hardened conditions where the desired mold thermal cycling of the mold compo tool steel to the copper molding actions can be incorporated. nent due to the molding process. face and install the guiding system in the tool steel. Aluminum bronze One example is the movement of As the lifters have to move inward materials can be laminated to the conventional mechanical slides on from the inside wall of the plastic opposing member of the mold to the "B" side of the mold with an part to free the undercut, the part reduce friction and avoid common angle pin !see Illustration Fl. The must be devoid of any detail that tool steels acting as bearing sur angle pinlsl is located on the · ~ A" would prohibit or impede lifter faces. side of the mold and when the part movement. Should the part design ing line separates the pin, due to not allow this required movement Raising Mold Members the angle, moves the slide out. If the only choice to form this part Occasionally plastic parts will have the same movement is required on detail may be with the aid of inter extreme contours. Automotive "A", the "A" side of the mold the prob nal or hidden slides. The problem "B" and "C" pillars, for example, lem of clearing the undercut prior with internal slides is the amount of which have geometry where the to the main parting line must be room they take to position and only way to free the part is to raise overcome. one solution may be to move them in a core. it out of the mold and physically or pull the slides with hydraulic or mechanically flex the plastic to pneumatic cylinders prior to the Wedges or Moving Members remove it from the mold core. mold opening. If the slide has plas Wedges are mold components that These molds are frequently consid tic forming projected area against it have a shape that allows them to ered raising core molds. This type the cavity pressure must be over fit tight in the molding position of arrangement complicates the come by some locking method. Should the area and pressures dard mold is straight forward, be small the cylinder may have the sequence of events is that enough force to prevent move the mold closes, plastic is inject ment. If the pressures are great. ed, the plastic is cooled, the Wear then a locking cylinder must be mold opens, the parts are eject Plate used. In any event, the timing of ed and the cycle continues. the cylinder retraction and When mold actions, items like advancement must be tied into slides. lifters, wedges. floating Dove the molding machine and mea plates, etc. are incorporated, Tail_._...,..... sures taken to insure that the the sequence of events must be Guide slide is in the proper position on pre-determined and the mold mold opening and closing. designed and built to insure that the proper event happens To move the "A" half slides and that the plate or movement mechanically a mold movement has traveled the correct amount has to be established where the prior to the next sequence "A" plate floats !retaining the starting. Additionally, it is plastic partl creating forward important that the mold actions Illustration E: Slitter actuation during ejection, showing the movement so that angle pins return in the proper order. wear plates and dove tall guides. mounted in the top clamp plate over the years, almost any can actuate the slides away from action or movement has been the part and clearing the under installed in production molds. cut. once the part is clear from We are only limited by our the slide the plate movement is imagination on how to positive positively stopped, normally ly insure that the proper mold with shoulder or stripper bolts. action will take place at the cor and the main parting line is rect time and then reverse the allowed to open. process to prepare for the next molding cycle. The movement of plates is typi cally accomplished with a puller There is no room for error in mechanism. Frequently external sequencing of mold actions. mounted commercially available Each operation must be pre latch lock devices are mounted cisely carried out in the proper on the mold. These mechanisms sequence with the movement are solidly attached to the mold required exactly carried out. If member that will be actuating any plate or action is left to the plate and the opposite end chance, damage will occur Fasteners and wa ter~ of the device will contact and sometime during the molding connections are not shown.(-:_ lock the plate when moving it run. The correct way to design Illustration F: Copper faced slide showing the use of an and release when the desire trav the mold is to positively angle pin. The cooling circuit path and "O" rings between el has been reached. achieve the desired movement copper and steel are not visible in this view. at the right time, while provid Timing ing a method of determining The expression used to describe that the sequence has the proper sequence of events occurred prior to allowing the in mold action is timing. The mold process to continue to opening and closing of a stan - the next step. •
Acknowledgements The injection mold design guidelines were written by Dr. Pau l Engelmann, Associate Professor, Western Michigan University and Bob Dealey, Dealey's Mold Engineering, with the support of Dr. Dale Peters. for the Mold Marketing Task Group of the Copper Development Association. Kurt Hayden. graduate research assistant, WMU, generated the Illustrations. Research conducted by WMU plastic program students. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information con· tained is deemed reliable, due to the wide variety of plastics materials, mold designs and possible molding applications available, no warranties are expressed or implied in the application of these guidelines. Contact Information Information on copper alloys is available from the Copper Development Association, 1-800-232 -3282. Technical clarification of the guidelines can be made by contacting Bob Dealey, Dealey's Mold Engineering at 262 -245·5800. Area code 414 until mid September 1999 Injection Mold Design
Guidelines By or. Paul Engelmann FIFTH IN A SERIES and Bob oealey for the Mold Marketing Task Group of the Copper Maximizing Development Association Performance Using CoJJper Alloys
Copper Alloy core Pins The fastest, easiest and quickest method of proving benefits from the high thermal conductivity properties of Where: copper alloys is to replace a core pin in H = Quantity of heat in a troublesome application. Core pin, as Btu's conducted the name implies, forms the interior of K = Thermal conductivity a plastic part feature. Problem areas in factor of mold material in the mold that will benefit from the Btu/hr/ft2/ooF/ft core pin replacement A =Surface area in contact with include heavy wall sections the plastic part in square feet that control cycle time, inte T = Time in hours rior part features that can t2 =Temperature of injected not be cooled efficiently, plastic sections prone to sink t 1 =Temperature of circulating marks and features that medium require tighter and more L = Distance from the plastics consistent dimensional con surface to the circulating trol. Ullustration Al medium
The principles of heat flow It is apparent from this equation that to should be understood and remove Btu's more rapidly the mold applied in the injection mold design should use materials with the design as the mold acts as a highest thermal conductivity (copper heatexchangerdunngthe alloys, C17200, C1 7510 and C18000 have molding cycle. Those princi six to nine times greater thermal con Illustration A: care pin forming a hale in the plas ples are: 1. Radiation, con ductivity than conventional mold steelsl. tic part. The care pin transfers heat to a chill plate duction and convection The lowest temperature possible of the transfer heat. (Conduction is circulating medium is a good option. for faster cooling cycles. the main method of heat However, especially with semi-crystalline transfer in a mold and is the materials, mold temperatures cannot be most efficient means of coolingl 2. Heat extremely low or the proper formation flows from the body with the higher of the crystalline structure will not be temperature to a body of lower tem formed in the plastics. Basically it is not perature. (You cannot transfer coldl. possible to increase the area in contact 3. The temperature difference, not the with the core pin and increasing "T" , the amount of heat contained, determines cycle time, is opposed to our objective flow of heat. 4. The greater the differ of achieving the shortest possible cycle ence in temperatures between the time. bodies, core and plastic, the greater the flow of heat. s. The thermal conductivi Copper alloy core pins are then ideal for ty of the mold materials will have a use in cooling plastic in a mold as they dominant affect on the amount of heat are in contact with the plastic and will energy transferred. remove heat by conduction. The copper alloy core pin can transfer heat rapidly to The following mold-cooling formula is an area of cooler temperature, insuring normally used for engineering mold flow from the plastics through the core designs for efficient operation: pin, due to the greater temperature dif - ference between them. The fit had less warpage than the part mold dimensions and tolerances of core ed with a steel core with water circu Steel Core wih Steel Chil Plate pins are critical to the success in lating, even at a 22% longer molding 2.0 their function in the injection mold. cycle. 'E 1e Core fit at its mounting surface, is .S Watered Steel Core typically an interference fit of -.0000 From the western Michigan il.1.2 ~ ,,. to -.0005 depending on its size and University test data one can conclude .f Copper Core 'NTth '- ~ o.e Steel Chill Plate ---:i\, frequency of removal from the that "L" is rather insignificant when ~ Copper Core 'Nith mold. As a general rule the length of the combination of the copper alloy Copper Chit Pla t e ~- 04 - - the fit area should be at least twice core pins and chill plate of the same ~.,,.;:.~~~~~~~~ the diameter. material and thermal conductivity is O.O Watered Copper Core____. used in a mold design. This is an 5 6 7 6 9 10 11 12 .As the core pin forms its detail in the important discovery and technology Cycle Time (Seconds) surrounding plastic, the heat given improvement in the efficiency of Chart B: Chart illustrates advantages of copper alloys in off from the plastic must be mold building and injection molding. reducing part warpage and cycle times. absorbed and transferred through the core pin to an area of the mold coefficient of Thermal Expansion where the heat can be transferred The coefficient of thermal expansion into cooling lines. As with tool steel must be considered when designing cores, the most efficient method of molds with materials that expand at different rates. The degree of ther mal expansion is critical in both the Mold Material Coefficient of Applications in Molds fit of the components and the cor and Description Thermal Expansion rect dimensions to design and build 10-6/F the mold core, components and cavi 420 SS 6.1 High Gloss cavities ty. Copper alloys have larger expan Stainless steel sion coefficients than tool steels and H-13 Tool steel 7.1 Hardened cavities and cores are listed in Illustration c. P-20 Tool steel 7.1 Pre-Hard cavities Both the plastic material shrink rate C17200 9.7 cores, core Pins, cavity and thermal expansion of the mold 2% BeCu Inserts, Slides, Etc. Where cavity and core must be taken into Higher Hardness is Desired consideration in the design of close C17510 9.8 cores, core Pins, cavity tolerance molds. Plastic shrink rates, .5% Becu Inserts, Slides, Etc. Where Higher when using copper alloys in the Thermal conductivity is Desired mold, may be reduced when com C18000 9.7 cores, core Pins, cavity pared with steel components. If the CuNiSiCr Inserts, Slides, Etc. Where Higher plastic material shrink rate is affected Thermal conductivity is Desired by mold temperature, then compen C62400/C95400 9.0 Lifters, Bushings, Bearings, sation must be made. l'{pically, the Al Bronze Wear Plates, Gibs and High mold surface temperature will be wear Areas more consistent and lower with the use of copper alloys. If the mold will C62500/C95900 9.0 Ejector Sleeves, Bushings, be run at elevated temperatures, as Al Bronze Bearings, Wear Plates, Gibs and Load Bearing Areas is the case with many of the new engineering grades of materials, the thermal expansion of mold cavities Illustration C: Chart listing various mold materials, coefficient of thermal expansion and and cores must be considered when applications 11 Injection molds. specifying mold sizes. This same con sideration should be taken into account when inserting a copper removing the heat is with an internal alloy into a steel retainer. The final fit coolant passage with cooling medi should be calculated at operating um circulating in the core itself. temperatures.
Tests at western Michigan University Ejector Sleeves and core Pins have proven the effectiveness of core pins fitting into ejector sleeves transferring heat from the plastic requires special considerations. through a copper alloy core pin and Standard off the shelf ejector sleeves then into a copper alloy chill plate. are built to accept pins with toler (Chart Bl. In this illustration, the ances applicable to ejector pins and results of exhaustive testing in the not core pins. Apparently when ejec same mold are shown; steel and cop tor sleeves were first introduced the per core pins with and without water only close tolerance pins available circulating in them were tested. The were ejector pins and the precedent tests prove the effectiveness of core was established. As ejector sleeves pins made from copper alloys, with are utilized to force plastic off mold higher thermal conductivity rates detail, it implies that a core pin than tool steels, will cool a part faster should be used in the application. with far less warpage at shorter cycle The core pin must rapidly transfer times than their steel counterparts. heat removed from the plastic to Note that the warpage of a part another part of the mold. The high molded with copper alloy core pins, thermal conductivity of copper alloys resting on a copper alloy chill plate, performs this function efficiently and results in a very consistent and uniform and foremost, the ejector compo shot-to-shot component temperature. nent must push the plastic off the mold member. Placing an ejector care must be taken to provide the prop pin on a surface that creates a er clearance between the ejector sleeve pulling action on a plastic wall and copper alloy core pin. Always check results in greater resistance to your ejector sleeve supplier's dimensions the removal of the part. and tolerances, the ejector sleeve has an internal tolerance of the nominal dimen Ejector and sprue puller pins built sion + .0005 -.0000 inches. The copper from the copper alloys, C17200, alloy core pin should have approximately C18000, C62400 and C62500 are .0010 to .0015 clearance, depending upon successfully used in high volume the diameter and at what clearance plas molds. The copper alloy ejector tic will flash. Copper alloy core pins can pins require slightly greater clear not just automatically be used with stan ances between the pin and the dard ejector sleeves as the tolerances do ejector pinhole to compensate not allow enough clearance and galling for their higher thermal expan of the components will result. Proper sion. These pins work well when Illustration D: Bearing length of ejector sleeves should consideration must be made in providing additional heat must be taken the proper sliding fit. away and have proven beneficial be no greater than two times the diameter. when used in thick wall applica The other design necessity is to insure tions for reducing or eliminating sink contact surface is accommodated nicely that the proper bearing length between marks. by the high thermal conductivity of the the ejector sleeve and core pin is used. copper alloys. !Illustration DJ Bearing length should be one of the most impressive success sto a function of the core pin diameter. The ries involves the use of a copper alloy Ejector bars, similar to ejector rings but general rule of thumb is that the bearing sprue puller pin. !Illustration El Problems straight, are being used to contact long length should be two times the diameter. are frequently encountered in cooling wall sections and are replacing the large we think when the bearing length the sprue puller enough to efficiently pull number of small diameter ejector pins exceeds one-half to three-quarters of an the sprue. The use of the copper alloy commonly used. This concept, using the inch, problems will occur as a result of sprue puller is highly effective and rec low friction properties of the aluminum too great of a bearing length. Experience ommended when flexible materials are bronze copper alloys, provides a robust in the mode of failure between the molded and problems pulling the sprue means of ejecting on large surface areas. sleeve and pin show that 90% of the time are encountered. Again, the bearing Fewer ejector pin impression marks are the bearing length is too long. Standard length on the sprue puller pin should be encountered at shorter cooling and cycle ejector sleeves are provided will two times the diameter of the pin. times with the use of ejector bars. allowances for cutting to the desired length and the bearing length is pur The most common mode of failure of an Head Clearances for Ejector Sleeves and posely long to accommodate all possible ejector pin is galling created by overly Pins sleeve lengths in that size range. long bearing lengths. This failure mode is To allow for any misalignment in machin Therefore, when the sleeve is cut for just typically observed when a tensile failure ing of the multiple plates in the mold and a short length, the bearing length is long occurs. !Illustration Fl to compensate for any adverse thermal and that is generally when problems Buckling of ejector pins is the second expansion, clearances must be provided occur. most common mode of failure. for the ejector components in the mounting area. The counter bore depth Copper Alloy Ejector Sleeves When small diameter pins are used, in the ejector retainer plate for the sleeve Thin wall ejector sleeves built from whether in steel or copper alloy, stepped or pin head should be .001 inch greater C65900 aluminum bronze and then plated ejector pins should be used for maximum than the actual head dimension. This are successfully utilized in high speed resistance against bending. Euler's allows the fixed end of the column to and high cavitation unscrewing molds. Formula for long and slender columns seek its proper alignment in relationship The sleeves offer advantages over their can be used to determine how long an to the corresponding hole in the mold H-13 counterparts as they provide an ejector pin can be in relation to its diam core. extremely low coefficient of friction. eter. Most ejector pin failures occur, due More importantly, they hold their round to the column being slender where The head counter bore diameter should ness better in thin wall sleeve applica bending or buckling action predominates be .015 inch larger than the sleeve or pin tions. Diameters of 2.000 inch with wall over compressive stresses. head diameter. Through clearance in the thickness of .040 inch in the ejection area ejector retainer plate for the sleeve or have been known to run 1,000,000 cycles. Ejector Rings, Bars and Air Poppets pin shank should be .005 inch. These When the plating begins to show evi When concerns regarding wear of ejector clearances will hold the head end of the dence of wear or exposes the copper components are encountered, copper ejector component secure, vet allow alloy, the mold components are stripped, alloy stripper rings or bars can be used. enough movement to not create binding refit and plated again. Due to similar The ductility of the copper alloys, along when the device tries to seek its own materials, it typically is not a good prac with the low coefficient of friction location. tice to run copper against copper in ejec between them and tool steels make tor sleeve applications. However, with them ideal candidates for these mold Clearances through the support and "B" the proper plating on both components, components. Stripper rings inserted into plate should be .032 inch greater than the success has been achieved in high vol guided steel stripper plates designed ejector component diameter. Each plate ume molds. with minimal clearance results in long leading edge should be countersunk with maintenance-free operation. In the event a 45 degree taper for ease of assembly and Copper Alloy Ejector and Sprue Puller of the plate cocking or shifting of the to prevent damage to the outside edge of Pins core, damage to the expensive mold the ejector component. The mold should The placement of ejector pins, sleeves, component can be minimized with the be assembled with the ejector plate sepa rings or bars in the mold is crucial to the use of the copper alloys. Additionally, the rated from the ejector retainer plate. efficient removal of the plastic part. First hard-to-cool area of the stripper plate Each ejector sleeve or pin should be indi- vidually positioned and loaded into its ejector plate and the tip located at proper location. The components, the parting line, only ensures full once committed to a location, should return when the mold is closed. be properly identified and always Frequently, it is desired to either take returned to that position. the load off the return pins or assist in the return of the ejector system. Guided Ejector System connecting the ejector system to the Every mold that utilizes small diam machine's hydraulic knock out plates eter ejector pins or is heavy with an ejector rod is common. enough to cause the pins to flex When the machine ejector system should be equipped with a four returns, the ejector plate and ejector post-guided ejector system. The system also returns. most efficient systems utilize hard surface grooveless leader pins and Many molds incorporate compression C95400 or C95900 aluminum bronze springs to aid in the return of the bushings. The guides should be ejector system. Four springs, often located on the four corners of the located around the return pins, are ejector system to provide the most used. care must be taken not to over Illustration E: copper alloy sprue puller pin used to firm up accurate alignment of the compo compress the springs and cause pre puller and reduce molding cycles. nents to the mold core. The objec mature failure. This method is not tive is to remove any load from the entirely fool proof. The ejector sys ejector components. Debates tem is not positively returned after range if the leader pins should be each cycle and should never be used installed in the ejector housing or as the only means of return if dam through the support plate. we pre age will result should an ejector com fer installing the guide pins in the ponent not be returned prior to mold support plate as this allows the closing. Ejector return springs should ejector retainer plate to be held in be replaced in sets. never individually, position when the ejector compo to ensure that even pressure is sup nents are loaded. plied against the ejector plate. In those instances when the support plate will be subjected to greater When the ejector system must be thermal expansion than the ejector absolutely and positively returned plate, additional clearances can be prior to the mold closing, early ejec accommodated in the fit of the bush tor system mechanisms are used. EJec~ ings to the ejector and ejector retain small molds sometimes use internally Pm er plate. Placement of the guide pins mounted early ejector return sys in the ejector housing removes the tems. Medium and large molds use element of thermal expansion from externally mounted toggle mecha the equation, but makes it more diffi· nisms to ensure that the ejector cult to assemble the mold. plates have been positively returned so they will not prevent the mold Ejector System Return from closing. Every mold should have ejector we believe that having a limit switch return pins to insure that the ejector or electrical signal to ensure the posi system has positively returned for of tive return of the ejector system is an Illustration F: Bearing length ejector pins is crucial to the start of the next cycle. The most important safety consideration. mold life. common method is using the stan Using a switch alone. without the dard four return system found on assistance of an early return system, every standard mold base. This posi can be dangerous and result in mold tive method of ejector plate return, damage should a system electrical with the pin head resting on the failure or false signal occur. • Acknowledgements The injection mold design guidelines were written by Dr. Paul Engelmann, Associate Professor, western Michigan University and Bob Dealey, Dealey's Mold Engineering, with the support of Dr. Dale Peters, for the Mold Marketing Task Group of the copper Development Association. Kurt Hayden, graduate research assistant, WMU , generated the illustrations. Research conducted by WMU plastic program students. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information con· tained is deemed reliable, due to the wide variety of plastics materials, mold designs and possible molding applications available, no warranties are expressed or implied in the application of these guidelines. Contact Information Information on copper alloys is available from the Copper Development Association. at 800·232·3282. Technical clarification of the guidelines can be made by contacting Bob Dealey, Dealey's Mold Engineering at 262-245·5800 Injection Mold Design
Guidelines By Dr. Paul Engelmann SIXTH IN A SERIES and Bob Dealey for the Mold Marketing Task croup of the Copper Ma~imizing Development Association Performance Using Copper Alloys
cooling With Copper Alloys ejected correctly without harming lVPically the C17200, C17510 and the part. Normally we think of the c1sooo copper alloys are used in process as just cooling of the mold, plastic forming areas of molds but sometimes the mold is heated. because of their high thermal con our ultimate objective is to control ductivity and unique abilities to mold temperature within a range attain a more even molding surface that yields a product within specifi temperature. cations at acceptable cycle times.
The key to obtaining and maintain- Placement of coolant Channels ing plastic part Ideal placement of water channels dimensional sta in copper alloys will enhance an bility and already good mold temperature repeatability, crit control material. Good design ical in three and practice calls for the edge of the six sigma mold channels to be placed two times ing, is to expose the diameter of the channel away each and every from the molds plastic forming cavity and mold surfaces, see Illustration A. This ing cycle to distance has proven t o be effective exactly the same in providing enough su pport to conditions. The prevent deformation of the mold molding machine ing surface and ideal for providing and/or process an even mold surface temperature. controls provide Closer placement to the plastic the ability to forming surface could result in control melt greater temperature variation temperatures, across the mold surface by over screw recovery, cooling areas in closer proximity. injection rates Illustration A: water channel placement showing position and pressures, The pitch. distance between coolant betwee1 channel and edge of cavity cycle time and channels, is also an important forming alloy. other parame design consideration. Th~ recom ters associated mended distance between these with the process. control of both channels is two to five times the the mold surface temperature and diameter of the coolant channel. then the range of these tempera These recommendations have tures is a separate and frequently proven effective in mold applica overlooked process. tions using copper alloys. Frequently, in similar situations with After cavity filling, mold tempera molds built from tool steels. the ture control is the single most recommendations are to place the important factor influencing dimen coolant channels closer to the sur sional control of the molded part. face with reduced pitch distances. All thermoplastics have to be cooled The superior thermal conductivity from their melt temperature to a of the copper alloys allows greater temperature where they can be freedom in channel placement. A fluid circulating systems using water appears in pump with capability Injection Molding Handbook, of achieving turbulent edited by Dominick v. Rosato and flow rates is an impor Donald V. Rosato. It takes into tant part of the equa account the fluid velocity in feet tion. When using cold per second times the diameter mold temperatures, of the coolant passage times a typically below 50 constant of 7740 divided the vis degrees F, closed sys cosity of water. water viscosity tems with mixtures of changes as temperatures water and ethylene increase. At 32°F the viscosity of glycol are typically water is about 1.8 centistokes, at used. These systems 100°F it has changed to about 0.7 require higher horse and at 200°F about 0.3. This power motors to explains why, on occasion, achieve the same flow increasing coolant temperature rates as water as the reduces part warpage and cycle viscosity of the fluid time. Lessons learned in produc Illustration B: Baffle in series coolant circuit, positioned to force changes. Temperature tion molding have shown that flow up and over baffle and not around. ranges between 50 and with the use of copper alloys 210 degrees F usually higher coolant temperatures can use plain water. be used, reducing sweating of Processes over the the mold and supply lines, while boiling point of water producing a better part at lower generally rely on oil cycle times. and usually the mold is being heated, even Normally mold cool programs though the mold has are used to analyze effectiveness to cool the plastic to of heat transfer in the mold due eject it. to number of variables affecting the calculation. While better Reynolds Numbers cooling is achieved with higher A method used in mold Reynolds numbers, a point of design to describe the diminishing returns will be mold temperature con reached. When the circulating trol fluid flow in a media has the capability of mold, either laminar or removing heat faster than the turbulent. is by a plastic will give it up, which is dimensionless number. typically the case with the proper The Reynolds number application of copper alloys, takes into account the energy in cooling or heating and pressure. volume and pumping the circulating media is viscosity of the coolant, wasted. correctly designed the resistance to flow, coolant systems are important length and diameter of factors in obtaining fast and eco the channels and the nomical cycle time. The higher pressure loss in the cir thermal conductivity of the cop cuit. Laminar flow in a per alloys allows more freedom Illustration C: Bubbler in parallel coolant circuit. Area of center of plastic mold, described in this design over traditional tube should equal area of return. by Reynolds numbers tool steels. below 2,000, indicates conditions whereby An effective method of testing heat is not efficiently existing mold temperature con transferred from the trol systems is to remove an exit channel wall to the cir- line and measure the coolant culating media. Turbulent flow. flow through that circuit. The Reynolds numbers above 5,000, following table lists the flow describe conditions where effi nominal size !pipel, drilled whole cient transfer of heat is made diameter and the minimum from the coolant channel wall to water flow required insuring tur the circulating media. Heat trans bulent flow. fer during turbulent conditions can be as much as three to five times greater than with laminar flow. Numbers falling between Pipe Size Drilled Min. Flow 2.000 and 3,500 describe a transi Channel !gal/mini tion phase and typically is inef Diameter fective in closely controlling 1/ 16-NT .250 .33 mold surface temperatures. 1/ 8-NPT .3125 .44 1/ 4-NPT .4375 .55 A simplified formula for deter 3/ 8-NPT .562 .75 mining the Reynolds number for 1/2-NPT .6875 1.3 Chill Plates insure that the out Earlier injection mold design guide let temperature lines describe the effective use of a does not exceed the Straight Threaded Plug chill !temperature control> plate inlet temperatures l made from the same copper alloy to by more than 3°to 0 Separate Plug :\ insure the same thermal conductivi S F. High tempera ty. Testing at Western Michigan ture differentials with 0-Ring ~ University has proven the effective between individual ness of cooling multiple small cores cavities or their that have small diameters prevent mold sections ing water passages. It is necessary results in undesir that the core pin heads be firmly able part consisten seated against a clean and oxidation cy. Therefore, series free plate surface to insure efficient circuits typically transfer of heat. have a maximum of six to eight baffles. Temperature Control Channels with Baffles Spiral baffles are use Channels that divert temperature ful in long slender Illustration D: Recommended straight threaded pressure plug control fluids from one level to areas cores as the coolant where heat is concentrated in the flows around the and seal. mold can use baffles, Illustration B, baffle, exposing the to positively direct the flow through diameter of the coolant channel to cuits and must be avoided to the channel. This type of coolant more even temperatures than what achieve optimum mold cooling. direction is referred to as series flow could result from having up one side when multiple baffles are used. and down the other side of a core. Drilling and Plugging Coolant Proper mold design starts with the Incorrect assumptions have been Channels diameter and area of the inlet chan made that spiral baffles create tur Long coolant channels are typically nel. The hole for the baffle, after tak bulent flow. the fact is that spiraling gun drilled in mold plates, cavities ing the area occupied by the baffle water does not create turbulent and cores. lVPically, even with accu into account, must be twice the area flow or result in higher Reynolds rate gun drilling, the hole can wan of the inlet channel, to prevent flow numbers. by the fact that the der and the tolerance of hole loca restrictions and high-pressure loss coolant is turning. tion is normally understood to be es. Remember when calculating .0.001 per inch of length. Smaller flow channels that twice the area is Temperature control Channels with diameter drills tend to wander more not the same as twice the diameter. Bubblers than larger diameters. care must be Bubblers are also used to step taken when coolant lines pass close Brass baffle and pressure plugs, coolant into areas of the mold that to holes in the mold and adequate which resists the build up of water require heat removal. The major dif clearances must be allowed to pre deposits, work best in copper alloys. ference between the bubbler and vent break though or leaving a weak Most standard off the shelf baffles the baffle is that water flows up a section of the mold. With copper use a dry seal design, where stan tube in the center of the coolant alloys the minimum recommended dard pipe taper is 3/4 inch/foot. the channel and cascades down the out distance is approximately .100", dry seal design features 718 side to the outlet, Illustration c. depending upon coolant diameter. inch/foot taper. To prevent high These cooling circuits, when more distance from drill start and the size hoop stresses on the copper alloys than one bubbler is used are called and location of the cross hole. straight thread pressure plugs must parallel circuits. The inlet has to Coolant channels should not run be used instead of either tapered or have greater volume than the sum parallel or in close proximity with dry seal pressure plugs. of the bubbler internal diameters to sharp cavity corners to guard against insure that each circuit will have the premature failure. Another important consideration is same flow rates. the clearance area between the tip The coolant channels, Illustration D, of the baffle and the drilled hole. Design of the coolant channel and should be blocked with a fabricated General design practice is to allow the bubbler is important to success straight threaded brass plug to avoid the same gap as the diameter of the ful mold temperature control. The excessive hoop stresses on the cop baffle hole. Make sure that the baffle area of the internal diameter of the per alloys. An effective method in is installed at a 90° angle to the flow bubbler tube, 02 must be exactly the leak prevention is to counter bore of the coolant to positively force the same as 03 to insure that high-pres the plug hole and then use an a-ring flow up and over the baffle. sure losses are not encountered. installed in compression. The a-ring Otherwise leakage around the baffle Critical to the calculation is deter should be replaced each time the will result in inefficient cooling. An mining the bubbler wall thickness. plug is removed or at major mold effective method is to braze the baf 01 and the area it occupies. The maintenance cycles. Cross-drilled fle blade to the pressure plug and coolant inlet must feed the bottom connecting channels should have mark the outside of the plug with a of the bubbler tube. The outlet for the drill point run out in the con line indicating the blade orientation. the coolant is around the outside necting channel, avoiding stress ris Check to insure that the blade is diameter of the bubbler tube. Each ers. properly positioned when the pres mold coolant channel inlet and out sure plug is tight. let must be clearly marked to insure series and Parallel Channels that outside connections are cor Coolant channel placement has to As temperature control fluid flow is rectly made, insuring the proper be considered and engineered into positively directed through each flow. Excessive looping can result in the mold design from the onset. channel, care must be taken to high-pressure losses with these cir- Efficient mold temperature control has to have the same priority in a mold operation temperature. On mold design as gating and part occasion a reaction can occur ejection; it cannot be an after between copper alloys, in the thought. Coolant circuits can presence of water and/or other loop inside the mold with con fluids and certain mold steels necting channels or outside the where corrosion or pitting could mold with external connections. take place. To prevent the possi bility of this electrolytic action When the mold design calls for taking place, the copper alloy can series internal looping, and the be chromium or nickel-plated in coolant could flow in more than the o-ring area. The objective is one direction, flow must be posi to prevent direct contact tively routed in the desired chan between the two materials by nel. A number of diverter plugs using a third compatible materi are commercially available to al. If the copper alloy compo block the unused channels and nent will have a coating or plat direct flow though the designat ing applied to the molding sur Illustration E: Looped water circuit with dlverter. ed route. However, a simple and face anyway, covering the whole recommended method is to component will normally suffice. machine a brass plug .003/.005 A separate or different coating smaller than the coolant channel for the o-ring area should not be with the plug length twice the necessary. diameter, Illustration E. The plug should be inserted into the chan All water Lines are Not Straight nel with a light press fit to insure Through Mold Components it remains firmly in the correct The design and routing of position. The location should be coolant channels can be chal Fastners not shown measured by inserting a rod into lenging, especially in mold the coolant channel and the cores. Straight through drilled for clarity entire circuit water tested to passages are not always possi insure that proper routing with ble due to mold configuration, out restriction has been achieved. mounting and ejector pin holes and other obstacles. O·Rings for Sealing Coolant Machining or drilling channels Channels that intersect and direct o-rings, when placed in com coolant flow to the desired pression, have proven to be the location, Illustration F, should most effective method of provid be considered. The use of inno ing a seal between two joining vative design methods, includ components in a mold. They are ing baffles and bubblers, to placed between mating compo insure proper mold tempera nents when baffles or bubblers ture control is achieved pays are used. Additionally, o-rings handsome rewards in obtaining are placed between cavity and an efficient running mold. Illustration F: Intersection drilled coolant channels in hard core components when coolant coupling these design princi to reach locations. is directed through the "A", "B" ples with the use of copper and support plates. The o-ring alloys and their superior ther material type must have a com mal conductivity provides the patible temperature rating with best opportunity in achieving in the range of the coolant and optimum molding conditions • Acknowledgements The injection mold design guidelines were written by Dr. Paul Engelmann. Associate Professor. Western Michigan University and Bob Dealey, Dealey·s Mold Eng jneering, with the support of Dr. Dale Peters. for the Mold Marketing Task Group of the copper Development Association. Kurt Hayden. graduate research assistant. WMU, generated the illustrations. Research conducted by WMU plastic program students. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information con· tained is deemed reliable, due to the wide variety of plastics materials. mold designs and possible molding applications available. no warranties are expressed or implied in the application of these guidelines. Contact Information Information on copper alloys is available from the Copper Development Association. at 800·232-3282. Technical clarification of the guidelines can be made by contacting Bob Deal ey, Dealey·s Mold Engineering at 262 -245 -5800 Injection Mold Design
Guidelines By or. Paul Engelmann SEVENTH IN A SERIES and Bob oealey for the Mold Marketing Task croup of the copper Maximizing Development Association Performance Using Copper Alloys
Leader Pins and Bushings pin length should be at least the
Recommended nominal leader pin and bushing diameter by mold base size Width Mold base lengths cup toJ 8 9 10 12 14 16 18 24 26 30 36 7 7/ 8 .75 .75 .75 .75 9 7/ 8 .75 .75 .75 1.00 1.00 1.00 1.00 10 7/ 8 1.00 1.00 1.00 1.00 1.00 11 7/ 8 1.00 1.00 1.00 1.00 1.00 13 3/ 8 1.00 1.00 1.00 1.00 1.00 1.00 14 7/ 8 1.25 1.25 1.25 1.25 1.25 1.25 15 7/ 8 1.25 1.25 1.25 1.25 1.25 1.25 161/2 1.25 1.25 1.25 1.25 1.25 1.25 17 7/ 8 1.25 1.25 1.25 1.25 1.25 191/2 1.25 1.25 1.25 1.25 1.25 23 3/ 4 1.50 1.50 1.50 1.50 25 7/ 8 1.50 1.50 1.50 To 36 2.00 Table A: Nominal diameter of bushings by mold size. HS and a HB for the dimension bushings, the shoulder is between the gibs and a g 4 to an placed closer to the mid f 7 for the slide carrier. As always, dle of the bushing. when providing clearances in A counter bore is injection molds the overriding fac machined in the ejector tor is to insure against flash while plate to trap the bushing holding the required product between it and the ejec dimension. When those two con tor retainer plate. The siderations have been accounted bushing should be for, only then can the application designed to extend the of normal clearances be incorpo full thickness of both the rated to the mold to achieve the ejector and ejector desired condition. retainer plates. The side wall of the bushing The second function is for the gib should be one-fourth of to retain the sl ide and keep it from an inch to provide derailing. Clearance up and down strength. As the guided can be greater than side to side if ejector system is difficult the opposite mold side will hold to access in the assem Illustration D: Four aluminum bronze bushings with mid the slide in position in molding. If bled mold, a method to busing flange used to guide ejector system. no contact will be made when the lubricate from the out mold is closed, than the slide gibs side of the mold is rec- must provide that assistance. ommend. Grease fittings into connecting spiral grooves expansion created by the normal Gibs have two surfaces that could machined into the bushing is the practice of running the cavity side be used to assist in guiding the preferred method of providing of the mold warmer. Larger molds slide carrier. Only one surface lubrication to the bearing surfaces. use a double tapered interlock sys should be used as the bearing tem where the interlocks are guide, typically the top surface. Angle Interlock Face Plates machined directly into the mold The other surface should be Injection mold leader pins and base, or in mono-block construc cleared an additional .001 of an bushings act as a rough alignment tion, the cavity and core blocks. inch or more to reduce friction. system. Interlocks are used to provide the final and precision Aluminum bronze wear plates, Aluminum bronze Guided Ejector mating of the cavity and core. Two Illustration E, mounted on the face System Bushings styles of interlocks are used. The of one of the interlock serve three High-speed molds using small first is straight interlock and its extremely important functions. diameter ejector pins require sup function is to line up the two mold First, they prevent galling, com port for the ejector and ejector halves prior to the mold closing. mon when two similar steel inter retainer plate to insure smooth These interlocks are either mount faces would normally contact each operation. Another effective use ed on the side of the mold base other, due to the differential in of aluminum bronze is in the and are called straight side locks hardness and material composition bushings used in conjunction with or mounted on the face of the while providing low friction char groveless leader pins installed on mold at the parting line and called acteristics. Next, the aluminum the ejector side of the mold. top mount interlocks. straight bronze faceplates provide an effi Leader pins, with nominal diame interlocks normally align the entire cient method of fitting and adjust ters of .750, 1.00, 1.25, 1.50 and mold rather than individual cavi ing during mold construction or at 2.00 inches, are placed at the four ties and cores and the interlocking mold maintenance intervals. Last, corners in the ejector housing. concept and is used when align they are less expensive to replace The greater the mold length and ment is necessary on mold closing. should any damage to the inter the heavier the mold plates, the This system is mandatory when locking system occur over the life larger the nominal diameter of using vertical shut offs or tele of the mold. Aluminum bronze the leader pin should be. scoping cores. faceplates should be at least one Guidelines By or. Paul Engelmann .... EIGHTH IN A SERIES and Bob oealey fOr the Mold Marketing Task croup of the copper Ma~imizing Development Association Performance Using Co1Jper Alloys Protecting Copper Alloys With rough surface finish will improve Plating slightly when plated and a smooth Frequently various coatings or highly polished surface will appear platings are used in injection less polished. The plating process molds to prevent corrosion or will not cover scratches, nicks and erosion from the plastics attack surface imperfections. Any mold ing the mold. Coatings can defects must be removed prior to reduce mold maintenance inter plating. vals while extend mold life. Copper alloys, C17200, C17510 and While it is a common and accept c1sooo utilized for their high ther able practice to sample a mold mal conductivity prior to plating, it is necessary to properties to remove all traces of plastic from improve part quality the component and notify the and reduce cycle plater that the mold is used. Mold times, are no differ drawings, indicating the molding ent than tool steels surfaces to be plated, should when protection is accompany the components to desired. the plater. Masking surfaces where the plating is not desired Copper alloys in the can and should be noted on the presence of some mold drawings, if there is a good plastic residues will reason for not applying plating. react with mating However, masking can be a time steel components consuming and expensive opera and create an elec tion and it is normally a better tric current flow, choice to plate the entire compo similar to a battery. nent when it will not interfere Isolating the cop with the molding process. per- to-steel con tact. Illustration A, Choices for Protecting Copper Illustration A: use of copper alloy in cavity tor thermal conductiv- with plating elimi- Alloys and plated to Isolate it from the steel cavity. nates the galvanic A wide variety of platings and ity action between the coatings are available to protect two materials and your mold components. Some are prevents the formation of small more effective than others and amounts of tarnish that could individual choices will vary transfer to the plastic part. depending upon the application lVPically the insert is completely and experiences with your type of covered with the plating. applications. Additionally, the quality of a given plating or coat Preparing Surfaces for Plating ing may be very dependant upon The desired SPI surface finish, A-1 the company that did the work. through D-3, should be applied to the copper alloy prior to shipment Based on studies taking place at to the plating source. The plating Western Michigan University two will generally duplicate t he sur types of platings are showing the face where it is applied. A very most promise depending upon the specific application, nents !for forming ribs on the chrome electroplating plastic partl create problems in Electroplated Outside Corners and electroless nickel. electroplating. When the The first and most depth is greater than one half effective protection the width, plating thickness will against wear caused by vary considerably and diminish impingement of glass on the sides of the walls as the filled nylon against depth increases. Illustration D cores is a variety of shows a typical condition electroplated chrome encountered in molds. The platings. These sharp outside and inside cor Correct chrome platings fall ners, coupled with the depth into one of four cate of the channels prevents the gories; standard indus chrome from building up even trial hard chrome, ly. Illustration E exhibits a industrial hard chrome more ideal construction Improper with its structure filled method using an insert elimi with a polymer, densi nating the channel depth-to fied chrome platings width problem. Additionally, Illustration B: outside corners illustrating build up on out and chrome compos the generous outside radius side sharp corners along with the correct application of ites like Armoloy·s eliminates the problem of radii. XADC a nodular chromi excessive outside corner build um containing nano up, while the inside radius composite of diamond. reduces corner starvation. When mold components can Electroplated Inside Corners Chrome Electroplating not be modified to optimize The electroplating the electroplating process then process uses electrical anodes have to be built to get current to deposit the the plating down into deep chrome on the mold channels. component surface. Both ferrous and non Benching of Electroplated Mold ferrous materials con components duct current around Mold components must be the outside of the benched after electroplating. component and as a Any overhanging chrome result the process deposits must be removed attracts more chrome prior to sampling the mold or Correct to outside sharp cor- the plastic will form around the ners than flat surfaces. build up and the results will However, the copper either be sticking of the plastic Improper alloys are such great part or the chrome tree break electrical conductors ing off or chipping exposing Illustration C: Sharp Inside corners on channels without that corner build up is the parent material. Illustration draft results in uneven plating. Draft on the walls and radii accentuated over com F shows chipping of chrome in on the Inside corners allow for an even build up of chrome. parable steel compo a gate area. lWo methods are nents. see Illustration normally used to remove the B. To reduce the build chrome build up. The first is up, sometimes referred to as with a hard 600 grit stone and chrome trees or dog bones, carefully stoning the surface in the use of generous outside the direction of draw, remov radius is recommended on the ing any chrome build up which components outside corners. would create an undercut. Obviously, the plastic part and its function must be able to The second method, per accept the radius without formed by a skilled mold maker, detrement. Normally a gener uses a nylon brush mounted in ous radius, outside edge on the a rotary tool operating at a mold component and inside slow speed with light pressure edge of the plastic part, adds and a chrome polish. The sur great strength to the part and face is gently worked, carefully is typically a great benefit. removing only the overhand so as not to destroy the intended This electroplating process also plating thickness or reducing creates problems on sharp adhesion to the mold compo inside corners of the mold nent. caution has to be used, component. see Illustration c. as to much pressure and/or A sharp corner, due to current high removal rates can cause flow, will be starved of chrome. chipping and exposure of the A generous radius on the inside parent material. corners allows for a more even build up and will prevent chip Electroless Nickel ping at the corners. The second category of protec Channels cut into mold compo- tion is electroless nickel applied by an auto catalytic !with Deposition Thickness out current! process. The advan The best thickness to tage of electroless nickel is that apply a coating to a mold the surface is covered to a uniform component is an age-old thickness compared to most of the question and opinions electroplating processes. As the differ widely. Experience deposition is applied uniformly and extensive testing at and without current due to the western Michigan electroless process. special draft University shows that a angles are not necessary and the thin layer of protection is process is forgiving on both inside extremely effective. The and outside corners. The disadvan first consideration has to tage is that the hardness of nickel betoinsurethatthe is in the 50 Re range, a lower hard plating will adhere to the ness than many of the other plat patent metal. This favors ings available. Additionally, nickel a thin layer over a thick is not a great bearing material and layer. The second consid it should not be used in applica eration is to the reason tions with moving parts. why the plating was Illustration D: Illustration shows the uneven plating build applied in the first place resulting from typical mold construction practices. Chrome Plating of Holes and if a thicker layer will build up is thick on the outside corners and thin to non-exis Electroless nickel has the advan provide better protec tent in the channels. tage of covering side surfaces of tion. holes or channels with large aspect ratios. Sharp inside corners Table 2 lists plating thickness, for extended times can be detri on blind holes are difficult to cover which have proven to be effec mental to their properties. and a radius is recommended on tive in protecting copper alloys any blind hole. on holes up to .125 used in plastic forming applica Reasons for Plating Mold inch in diameter the depth is limit tions. components ed to about .750 inch due to prob Copper alloys are plated to extend lems associated with getting the Deposition Temperatures periods between maintenance or gases out of the hole. There is no care must be taken to avoid component replacement intervals practical limit to the depth of plat exposing all materials used in mold and to improve part quality. Most ing electroless nickel in holes construction to excessive heat plating is applied to protect plastic greater than .125 inch on conven which could stress relieve or forming components from erosion tional molds. !Table 1l anneal the component. The cop and premature failure resulting per alloys should not be exposed from running glass or mineral Electroplating chrome into holes is to temperatures above recom filled plastics. Testing underway at more difficult than applying nickel. mended manufacture specifica western Michigan University, using Frequently, anodes have to be tions, typically around 400 degrees 33% glass filled type 6 nylon in an built to assist in the application F. The electroless nickel process is eight cavity mold, has shown that process. The cost of constructing typically less than 200 degrees F. copper alloy cores protected with the anode can be a significant Chrome electroplating usually has some of the chrome processes additional cost not encountered a process temperature of 185 have extended component life up with electroless nickel. degrees F or less. PVD or CVD to 20 times longer when compared Maintaining the proper position of process can run up to and some to non-plated P-20 cores. the anode also adds difficulty in times exceed 400 degrees F. the plating process. Not with considerations must to be given The second reason is to protect standing the cost and difficulty, to the use of processes that against corrosion. The copper one plater uses the information expose copper alloys to tempera alloys are naturally resistant to listed in the following table as a tures approaching 900 degrees F, attack from most plastics. guide to maximum depths of such as those found in some tita However, to prevent tarnish and chrome plating into blind or nium nitride processes. Exposing the transfer of residue created by through holes. copper alloys and some other the interaction with steel, plating mold alloys to high temperatures of copper alloys is an effective prac- TABLE 1. Depth of Electroplating Chrome in Holes TABLE 2. Hole Diameter Blind Hole Through Hole Plating Ideal Maximum Typical Maximum Typical Maximum Process Thickness Thickness Range Depth Range Depth Electroless .0005-.0007 .001 .125 0.00-0.75 1.00 0.00-1.50 2.00 Nickel .250 0.00-1.50 2.00 0.00-3.00 4.00 Flash .0001-.0003 .001 Chrome .500 0.00-6.00 8.00 0.00-12.00 16.00 Thin Dense .000050-.0005 .0005 .750 0.00-12.00 18.00 0.00-24.00 36.00 Chrome 1.00 0.00-24.00 36.00 0.00-48.00 72.00 Thin Dense .000050-.0005 .0005 *All dimensions are in inches Chrome with Diamond *All dimensions are in inches tice. Nickel is recommended machining marks and stoning Fastener over chrome when molding or polishing in the direction of Not Shown polyvinyl chloride. as draw with the proper grits, Insert hydrochloric acid will strip prior to applying the desired chrome from the component surface finish. surface. Chrome works well with most other plastics. The plating should only be applied after the plastic form Another reason for applying ing mold surfaces have the plating is for wear associated proper finish. A coating or with stripping abrasive plastic plating will not resolve all parts from cores. As chrome release and ejection problems; has a higher hardness level, it especially those created by proves to be more effective improper mold finishes. than nickel. In mold areas where components are in Affect on Thermal conductivity moving contact, the nodular of copper Alloys Illustration E: Tllis Illustration shows a suggested method chromes tend to work best. Extensive laboratory testing on of manufacture tbat results in a component that can be The sliding coefficient of fric the affect of nickel or chrome tion of non-lubricated nodular plating on thermal conductivity plated to an even thickness. chrome against nodular is scheduled by the CDA. At chrome is around 0.14. This this time the experience gained compares to a rating of 0.20 of in running thermal studies indi steel against steel. Nickel does cates that there is no measur not hold up as well in rubbing able loss in cooling effective applications. ness when comparing the same plated and non-plated The last reason for plating is to mold cores. Similarrly, no sig improve mold release. Nickel nificant change in cycle time, and chrome with impregnated have been reported in situa polymers are offered by a tions where molds are sampled number of companies as a without plating and then plat solution in reducing friction ed and run in production. one and improving part release. theory is that the high thermal Other companies offer wide conductivity of the copper ranges of platings and coat alloy overcomes any reduction ings in which they claim suc in heat flow from the plastic cess in resolving release prob part that the thin layer of plat lems. Due to the wide range ing could create. of mold conditions and plastic part design, it is difficult to Allowing for Plating Thickness Illustration F: Chipping in gate area caused by improper qualify what process works In certain situations the thick removal of chrome build up at tbe corners. better. However, if is safe to ness of the plating has to be say that the first priority has to taken into account in mold be to allow adequate draft design. Fits of inserts, for exam angles and provide proper ple, should allow for the increase ejection mechanisms as a first in size due to plating thickness step to insure part release. insuring proper mold function. Next, the mold component These allowances are typically in must be benched properly. the range of tenths to a few This includes removing all thousands of an inch. • Acknowledgements The injection mold design guidelines were written by Dr. Paul Engelmann, Associate Professor, western Michigan University and Bob Dealey, Dealey's Mold Engineering, with the support of Dr. Dale Peter,;, for the Mold Marketing Task Group of the Copper Development Association. Kurt Hayden, graduate research assistant, WMU, generated the illustrations. Research conducted by WMU plastic program students. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information con· tained is deemed reliable, due to the wide variety of plastics materials, mold designs and possible molding applications available, no warranties are expressed or implied in the application of these guidelines. contact Information Information on copper alloys is available from the Copper Development Association, at 800·232-3282. Technical clarification of the guidelines can be made by contacting Bob Dealey, Dealey's Mold Engineering at 262 -245 -5800 Injection Mold Design By Dr. Paul Engelmann GuidelinesThis Ninth Design Guideline will address applications of copper alloys in molds and Bob Dealey for the Mold Marketing Task croup of the Copper Maximizing Development Association Performance Using Copper Alloys Injection Mold core Applications smaller mold cavity and cores Copper alloys, specifically c 17200, !Picture Bl, where installing cooling c 17510 and c 18000 continue to channels in the proper position is a enhance performance, reduce common problem, benefit from the cycle time and cost, and improve high thermal conductivity of the part quality in injection molding copper alloys. When coolant cannot applications. The injection mold be circulated through the small core is responsible for removing mold core, channels surrounding the majority of the heat from the the core provide an excellent injected plastic and mold materials method of extracting the heat from with high thermal conductivity the plastic part, allowing for faster consistently outperform those cycles. materials with low thermal con ductivity. High cavitation, high-speed molds benefit from the rapid heat removal Advantages of mold materials with characteristics of the copper alloys. high thermal conductivity include These fast cycling molds frequently not only reduction of the cooling running in single digit seconds, ben phase of the molding process, but efit greatly from the rapid transfer also contribute to dimensional of heat from the molding surface control with less tolerance devia through small diameter cores. Due tion, less part warpage, fewer to the size of many of these mold molded-in stresses and reduced components coolant channels are incidence of sink marks. impossible to install in the normally recommended proximity to the Copper Alloys for Cycle Reduction molding surfaces. The high thermal The tremendous thermal conduc conductivity of the copper alloy tivity, along with their high density cores transfer heat effectively while and excellent tensile strength, maintaining even mold surface tem makes copper alloys an ideal choice peratures. Multiple small diameter for a core material. Molders are core pins, !Picture Cl, in contact reporting between 20 and 50% with chill plates have proven to be reductions in the cooling portion an extremely effective method of of the molding cycle. Kodak, for cooling cores in studies conducted example in a recent article, report at western Michigan University. ed that in a test mold "copper alloy While results from mold-to-mold cores ran 18 deg F cooler than the will vary, the test mold at WMU 420 stainless steel cores." The cop using the chill plate cooling per alloys are used in both large method, with no coolant circulating and small molds. In large molds, in the cores, runs at less than a six !Picture Al, coolant channels are second cycle time. This compares machined into the core similar to to 15 seconds with tool steel cores ferrous materials. The higher ther and a steel chill plate. mal conductivity, up to nine times greater than some tool steels, con Sink Mark Reduction trols the mold temperature evenly Sink marks on injection mold parts, Picture c and closer to the temperature of resulting from the delayed solidifi the circulating media. cation in heavy part sections after the gate has frozen off, can be to the cooling system. reduced by application of high thermally conductive copper Core, Sprue Puller and Sucker alloys in strategic positions Pins around the heavy sections. In Standard off the shelf pins made thick wall and boss sections, cor from c 17200, c 17510 or c 18000 ing out sections of plastics with !Picture El have enjoyed huge copper alloy core has proven to success in molds with their abili be an effective method of both ty to transfer heat from the con reducing the incidence of sink tact area to the base of the pin. marks and cooling times. A sprue puller pin made from copper alloys rapidly set the Tighter Tolerances puller end of sprue and provides When product designs call for an excellent surface area to hold tight dimensional tolerances the sprue on the ejector side of with quality levels demanding the mold. three or six sigma molding, all molding parameters must be Material saver core pins utilized closely held. A constant and uni to remove plastic and cool desig form mold surface temperature nated areas are the most inex will provide for the greatest pensive applications of copper opportunity to produce parts alloys while perhaps providing with the narrowest tolerance the greatest benefit in reducing range. The copper alloys, with the mold cycle time. Three plate their great thermal properties molds, where the sucker pins coupled with good mold tem must hold the gate drop firmly perature control, provide the to allow the gate to break, cycle right combination for tolerance faster when the plastic under cut control in injection molds. area sets up quicker. Injection Mold cavities Cladding or Bimetal Inserts In situations where plastic When the properties of both fer shrinks away from cavity sur rous and copper alloys are faces, cooling conditions are less required for a particular applica demanding and the copper tion, swaging of copper alloys alloys are used more in applica around materials like 420 ss have tions where "A" side coring is been used !Picture Fl. The swag required. Television backs, for ing process insures complete example, have large amounts of thermal contact without the detail cored from the cavity side. worries of oxidation forming In these molds, cooling cycle between the two materials. time reductions of 25% have been reported by replacing fer Blow Molds rous inserts with copper alloys. Copper alloys, c 17200, c 17510 Entire sections of cavities have and c 18000 have superior corro been inserted prior to final sion resistance in the presence machining and the finished cavi of polyvinyl chloride and is the ty detail has been machined in material of choice for clear blow assembly, reducing mold build molded cavities !Picture Gl. ing, benching and finishing costs. Again the high thermal conduc tivity rates of the copper alloys, Injection Mold Slides coupled with their high densi coolant channels are typically ties, produce the best molding difficult to install in slides and cycles. Another advantage is the moving members of molds. high degree of luster possible These internal mold actions are with the alloys. usually in locations where proper cooling is paramount for the In other applications where neck dimensional stability and/or and tail pinch offs are inserted, function of the plastic part. With the copper alloys are normally the sophisticated plastic part specified because of their excel design levels demanded from lent tensile and compressive today's injections molds, mold strengths. These materials con surface temperature control is tinue to prove superior to alu mandatory in the molding minum in pinch off applications. process. !Picture DJ, shows the Additionally, blow molds that use of copper alloys in a four require tight dimensional control cavity mold, where due to multi and long mold life specify copper ple core draws the part interior alloys for their mold material. is formed entirely by slides. The copper alloys are ideal choices Ejector Sleeves for these slides, as most of the The aluminum bronze materials, heat from the plastic must be c 62400, c 95400, with their excel transferred through the alloys lent wear characteristics and low the damage, rather than an expen sive slide. Slide Gibs Guiding slides with "L" gibs built from aluminum bronze !Picture Kl has become the standard mold of the mold industry. The gibs with their low coefficient of friction against lubricated steel provide an exceptional bearing surface allowing for a close running fit between it and the slide. This close fit insures proper slide to core and/or cavity alignment and guarantees a preci sion fit. Sprue Bushings When a large diameter sprue is nee- Picture I essary for maximum injection pres- sure the molding cycle could be Picture H controlled by the thick mass of plas- tic. Sprue bushings !Picture u. built from high thermal conductive cop- per alloys, remove heat more effi coefficient of friction make excellent ciently setting the sprue quicker. ejector sleeves !Picture Hl. As the Other applications use the copper alloys do not require heat treatment alloy sprue bushing to purposely after machining, ejector sleeves increase the orifice diameter reduc maintain roundness better than ing pressure loss in the feed system. most ferrous alloys. The secret of holding close tolerances on thin Runner blocks walled ejector sleeves is to machine Long and large diameter runner sys the internal diameter first and then tems used in fully balanced high cav mount the sleeve on a mandrel and itation molds typically have huge pri complete the outer diameters. With mary runners. These large diameter this method, ejector sleeves with runners concentrate large amounts wall thickness as low as .040 inch are of heat in a small area and the mold routinely built. ing cycle must be lengthened to enable runner ejection. The c 17200, Lifters c 17510 and c 18000 copper alloys, Internal undercuts requiring lifters inserted on both the "A" and "B" !Picture ll can prove to be trouble mold side with coolant circulating in some. These components typically the runner bars. sets the runner have narrow cross sections prohibit faster while reducing the overall Picture J ing the installation of coolant chan molding cycle. nels. As they are in direct contact with large plastic surface areas mas Leader Pin Bushings sive amount of heat must be The four leader pin bushings in an removed from the lifter. The alu injection mold are crucial to initial minum bronze materials c 62400 and mold alignment and grooved steel C 95400 work well in these applica leader pins against steel bushings tions providing that thin wall sec can rapidly deteriorate. Aluminum tions are avoided. While the thermal bronze leader pin bushings !Picture conductivity is not as good as the Ml running against groveless leader copper alloys recommended for pins have proven to be one of the mold cores, it is superior to the fer most ideal and long life combina rous alloys. tions in mold applications. wear Plates Guided Ejector Bushings Number one through five mold base A smooth operating ejector system materials make poor bearing sur is mandatory in long running and faces for ferrous slides and carriers. high-speed injection molds. Utilizing Inserting the mold base !Picture Jl aluminum bronze guided ejector with one-quarter to one-half inch bushings !Picture Nl results in mini aluminum bronze plates provide one mal wear even in installations where of the best wear combinations avail lubrication is hard to apply. able for injection molds. Symmetrically designing the wear unscrewing Rack Guide Bearings plates doubles the life, by allowing it Moving mold components, such as to be inverted should damage occur. unscrewing racks and cam bars Picture K Additionally, if a burr or chip gets which require high speed and close between the wear plate and slide running fits, benefit by aluminum surfaces the wear plate will suffer bronze flat bearings inserted between the component and mold base. A light coating of high temperature non-migrating lubri cant will provide an excellent low friction surface. Runnerless Molding Systems Components Runnerless molding systems, fre quently referred to as hot runners, probes, drops and bushing diver Picture L gent tips, benefit from the fast heat transfer provided by copper alloys !Picture OJ. Materials with high rates of thermal conductivity allow the heat source to be some distance from the tip while main taining and controlling tempera tures within a close range. The importance of maintaining uni form tip temperatures in the gate area on an RMS cannot be empha sized enough. Plating of the probe or bushing will extend com ponent life when molding abrasive matena~. • Picture M Picture N Picture o Acknowledgements The injection mold design guidelines were written by Dr. Paul Engelmann, Associate Professor. western Michigan University and Bob Dealey, plastic consultant with Dealey·s Mold Engineering, with the support of Dr. Dale Peters, for the Mold Marketing Task Group of the Copper Development Association. Kurt Hayden, graduate research assistant, WMU, generated the illustrations. Research conducted by WMU plastic program students. Special thanks to Whirlpool Corporation, Findlay Ohio, for the use of photographs of their molds for this article. Omega Tool, Menomonee Falls, WI , Progressive components; Wauconda, IL and Performance Alloys, Menomonee Falls, WI also provided components and photographs for this ninth injection mold design guideline. We appreciate all of their contributions. Disclaimer These guidelines are a result of research at WMU and industry experience gained with the use of copper alloys in injection molding. While the information contained is deemed reliable, due to the wide variety of plastics materials, mold designs and possible molding applications available, no warranties are expressed or implied in the application of these guidelines. All coating or plating processes have not been evaluated at WMU . contact Information Information on copper alloys is available from the Copper Development Association, at 800-232·3282. Technical clarification of the guidelines can be made by contacting Bob Dealey, Dealey's Mold Engineering at 262·245-5800 When it comes to injection mold materials, nothing exceed most production requirements. And for speeds production like copper alloys. Copper's extreme conditions, such as long runs of 30% thermal conductivity is 3 to 9 times greater than glass-filled nylon, copper alloy cores thinly coated stainless and tool steels' so it offers faster, more with hard, dense chromium last as long or longer uniform heat dissipation. That means 16% to 20% than P-20 steel cores. shorter cycle times. And up to 4 times less Higher profits sound good to you? Get faster parts warpage. production. Fewer rejects. Longer mold life. Give But speed isn't the only thing. Mold life is copper alloys a shot - they'll pay off. To find out important, too. Current research at Western more, call 800-232-3282 or visit our Web site at Michigan University shows copper alloy cores http: //molds.copper.org. ~~ A7023-XX/OO ~ Copper Development Association