The CWM Die Cast Component OEM Quick Guide to Surface Finishing

A Condensed Resource on Die Cast Part Surface Finishing for OEM Design Engineers & Specifiers

A preliminary guide for evaluation of die cast surface finishing alternatives for product appearance, durability and protection to aid in cost-effective specification of parts produced in Aluminum, Magnesium & Zinc—and ZA-8—die casting alloys.

A companion piece to the CWM Comprehensive Surface Finishing Guide and Sample Portfolio, which contains detailed finishing recommendations and die cast plates in the most widely used alloys, with surface finishes applied.

Chicago Browse CWM’s DC2 ® White Metal (Die Cast Design Center) Casting, Inc. Over 70 die casting design guides & bulletins are available to OEM product designers and engineers for download 24/7 at our website: http://dc2.cwmdiecast.com CONTENTS Introduction to Surface Finishing here. Advanced die casting processing has the for Die Cast Parts unique ability to deliver extremely close tolerances as-cast, with machining often entirely eliminated; Introduction to The three main reasons for the application of spe- where such as-cast processing is not feasible, Surface Finishing for cific coatings and finishes to die cast components pre-die-design consultation with CWM is essential Die Cast Parts are these: to assure successful post-casting machining 2 ■ Meet cosmetic/decorative appearance require- results. ments Surface finishing test results, executed under How Die Cast Part controlled laboratory conditions, are available to ■ Enhance resistance to wear Features Impact CWM customers for many of the finishing opera- Surface Finishing: ■ Provide a protective barrier against environ- tions outlined in this Quick Guide. Contact the Design Guidelines mental or galvanic corrosion CWM Sales Department regarding your specific for Enhancing In certain cases, die castings are also called upon finishing questions. Finishing Results to meet very special shielding specifications or 2-3 special pressure tightness requirements: How Die Cast Part Features ■ Special EMI/RFI shielding requirements Surface Impact Surface Finishing Die cast housings and components, in all Finishing alloys, provide assured built-in EMI/RFI shielding. Superior as-cast cosmetic surface finishes char- Steps and Coating When shielding requirements are particularly criti- acterize die castings produced by today’s Alternatives cal, with special designs or products subject to advanced technology. To consistently achieve 4 extreme abuse, surface plating can be used to such results at the lowest cost per part, it is achieve such optimum specifications. The result- essential that early discussions clarify precisely Die Cast Finishing ing plated surface finish will also provide an how the part will mate with other components in Cost-Performance enhanced appearance. When specialized EMI the final product assembly. This analysis is as Comparison Table gasketing must be used, plating may also be important to final surface finish quality as it is to 5 required. meeting tolerance specifications. Those sections of the die casting which will be ■ 100% pressure tightness requirements “hidden” from view, and cosmetically non-critical, Surface Finishing Impregnation is a post-casting sealing process can be considered for placement of the part’s Requirements for which, under vacuum, brings organic material into gating for metal entry and for its required parting 9 Typical the surface and subsurface pores of a die cast- lines. The presence of either of these features of Die Cast Parts: ing, providing highest pressure tightness. It is rou- die construction can create a severe cost penalty and suggested tinely recommended for critical air or water if they fall on a viewable, cosmetic surface of the coatings for each sealing applications, and, in addition, assures part. Likewise, a potential sink mark on a non- 6-7 high output for any final surface finishing required. cosmetic surface can be largely ignored, or steps can be taken to overcome its possible appear- The CWM This CWM Condensed Quick Guide, or its com- ance by wall redesign—for example, internal sup- Surface Finishing panion—the CWM Comprehensive Surface port features which will be invisible to the user. Portfolio: Finishing Portfolio with sample finished plates— While the exterior finish is dictated by the Comprehensive should not be viewed as self-selection tools for required appearance specifications, the specific descriptions and specifying precise finishes for die cast parts. They surface preparation called for is usually more sample library are published as aids to understanding the range, dependent on functional design features. Critical of coated die cast characteristics and relative costs of the post-cast- edges may require a shave trim, followed by spe- plates ing finishing operations available to OEMs from cial polishing, a chromate coating and then final 8 CWM to meet final product requirements. painting. Specified tight-tolerance holes may call Over 70 years of CWM experience, and that of for acid etching or chromating followed by ream- its surface finishing production partners, are CWM Design ing, milling or boring. reflected in their content, to aid in assuring that Resources for OEMs The type and quality of the final finish produced CWM Al, Mg and Zn die cast housings and com- Summary listing is impacted by the geometry of the design of spe- ponents meet stringent protection, durability and of CWM sales and cific part features. Minor modifications of critical decorative specifications. surfaces, edges, and mounting features can engineering The final decision on any post-casting finishing change a costly finishing scenario to highly cost- resources for operation should always be made in advance of efficient processing with minimum surface prepa- designers and die casting die design and only after detailed con- ration prior to application of a final coating. specifiers sultation with CWM engineering. The specific Preplanning, well before the final component 8 design features of your die cast part in almost design is locked in, is the essential step. Design every case have a direct impact on achieving your consultation on post-casting machining, as well precise surface finish specifications. © 2012 Chicago White as final surface finishing, prior to tooling design, Metal Casting, Inc. This is also true in the case of any post-casting die construction and die cast production, is the All Rights Reserved. machining requirements, a subject not treated recommended guideline.

2 CWM Surface Finishing Quick Guide Design Guidelines for Enhancing ■ Die Cast Bosses Finishing Results Include correctly designed gussets to improve Design modifications to aid surface finishing qual- die fill and avoid resulting sink marks on Class “A” ity are not always feasible. Where they can be surfaces. Short and stocky bosses are preferable made, significantly improved results will follow. to tall, thin designs to optimize metal flow and insure integrity of the feature (Figs. 4a & 4b). ■ Die Cast Part Edges Part designs which hide any trimmed edges within the final product assembly will eliminate any need for post-casting edge polishing. Early CWM consultation on cosmetic features will assure that necessary parting lines will be placed to conceal trimmed visible edges (Fig. 1).

Fig. 4a Tall bosses can lack Fig. 4b Shorter bosses with integrity for support. gussets optimize designs.

■ Die Cast Corners Use the maximum allowable radius for all inter- nal and external corners to permit vibratory deburring media to reach all part surfaces. This design guideline for die cast corners of housings is also vital to assuring the complete filling of the Fig. 1 A plastic bumper joining this 2-part case will con- ceal all parting lines, thus avoiding any edge polishing. die cavity and maintaining the integrity of the cor- ners of the part (see Fig. 5). ■ Die Cast Holes for Machining Design in chamfers (countersinks) or counter bores on holes to assure integrity of the surface edge of tapped holes. Leading threads will be pro- tected from deburring or polishing. (Figs. 2a & 2b).

Fig. 5 While advanced technology can execute most corner designs, gentle radii, as above, will reduce finishing steps.

■ Die Cast Surfaces Fig. 2a A cast-in counter- Fig. 2b A counter bore also Subtle textured surfaces can be produced, as- sink protects lead threads. serves as a thread protector. cast, on selected areas of a component by spe- cial preparation of the die casting die. These ■ Die Cast Mounting Features cast-in textures are created by photoengraving Wherever possible, create raised “shoulders” techniques during die construction and are some- on bosses which will receive painting masks; times recommended for use on the underside of scuffing can thus be avoided on surrounding complex parts to aid in smooth die fill (Fig. 6). painted surface areas during fastener torquing and mounting of mated parts (see Figs. 3a & 3b).

Fig. 3a Flush bosses for Fig. 3b Cast-in boss shoul- mounting mated parts may ders protect adjacent paint- Fig. 6 The addition of cast-in surface textures, as in this cause adjacent paint damage. ed areas during assembly. internal frame, can aid smooth filling of the die cavity.

CWM Surface Finishing Quick Guide 3 Finishing Steps and Alternatives parts produced in other production processes. Depending on requirements to meet durability, pro- These final die cast finishes include powder coat- tection and cosmetic appearance specs, most Al, ings applied electrostatically in finishes from fine to Mg and Zn die cast components will receive from coarsely textured in a variety of chemistries, to liq- one to three standard post-casting finishing steps: uid paint polyurethane and water-based finishes deburring, conversion or combined conversion- applied at various thickness/texture levels by elec- functional coating, and a final surface finish coating. trostatic or conventional means. Component masking is an essential part of vir- Post-Trim Deburring tually all cosmetic surface finish applications, Vibratory processes including highly automated required to assure that part areas that must not operations, using a range of media types, can receive finish coatings are protected during pro- round sharp edges, remove burrs, loose flash and cessing. Required protective masks must be debris, and smooth and brighten part surfaces. applied during finishing production and later Liquid, selective media, calibrated vibration, and removed from each part. Costs are proportional to special compounds to cushion against damage part complexity and the resulting masking are employed. Virtually all CWM die castings go required. Unique to die cast parts, special fixtures through a mechanical deburring operation prior to mated to the die castings can be constructed, in post-trim finishing. For 100% burr-free specifica- the case of longer finishing runs and those parts tions, an additional operation may be required. suited to such fixturing. If feasible, such fixture Surface Conversion Coating masks can reduce finishing production costs. Deburring is usually followed by a conversion Painting: Powder or Liquid. Electrostatically coating that removes any remaining oil, die cast applied, non-solvent-based powder coatings are part release agents and other contaminants. environmentally friendly, enabling non-toxic waste Where final painting is specified, this coating disposal. Powder coatings for die castings pro- serves as preparation and primer. In many non- duce a durable, uniform surface finish, from matte cosmetic applications, this conversion coating can to semi-gloss, with a wide variety of standard col- serve as the component’s final finish. ors available in a range of surface textures. Trivalent Clear Chromate (TCP). Environment- Custom colors can be formulated at extra cost. ally friendly Trivalent clear chromium is now a Powder coating is the only recommended proven, economical alternative to widely used painting process for die cast parts specified for hexavalent chromium coatings, offering high cor- operation in the field at temperatures over 300° F rosion resistance for Al, Mg & Zn die cast parts in (148.8° C). Custom formulations are available to a wide range of applications. With a bright, cos- enable maintenance of coating integrity at even metically pleasing finish, it meets stricter EPA reg- higher product operating temperatures. ulations and RoHS European Union mandates. Polyurethane and other wet paint chemistries avoiding concerns with prohibited toxic hexavalent are the most common final color finishes per- chromates. ASTM test results demonstrate salt- formed on die cast components, and have now spray protection up to 168 hours on Al 380. been joined by water-based wet paints. Finishes from matte to high-gloss are available. Combined Conversion Coatings/Functional Finishes Total production costs and lead times for most Where a die cast component has a specific func- liquid paints are lower than for powder coating, tional requirement, such as added corrosion pro- especially for short production runs—particularly tection, the need for added durability, and/or a those projects requiring a custom formulation. semi-decorative appearance, one of the com- Plating. Electro-deposition of a metallic coating bined conversion-functional finishes is often rec- on a die casting can provide the most attractive, ommended. A combined coating replaces the use durable and wear- and corrosion-resistant finish of of a surface conversion coating. It can serve either any surface treatment, at proportionately as a paint base or, in many applications, as the added cost. While die castings offer excellent part’s final finish. built-in EMI-RFI shielding, as cast, internal board Final Cosmetic Surface Finish design sometimes indicates additional plating to While final painting or plating of die cast housings achieve maximum possible shielding protection. and components is most often specified for cos- Additional Post-Casting Operations metic purposes, and to sustain their decorative Cosmetic parts routinely receive graphic identifica- appearance over the life of the part, other func- tion and labeling, by silkscreening or pad printing, tional purposes of a final applied finish may be of and “soft-touch” clear coatings in areas where equal, or of even greater, importance. These portable housings will be gripped. include: maximizing corrosion resistance, heat dis- With pressure-tight specifications for air- or sipation, and surface performance under abuse, water-sealed applications, die castings may and adding greater insulation properties. require resin impregnation. A wide range of painting applications are avail- Elastomer overmolding can also be used for able for die castings in matching finished, mating premium product ruggedization.

4 CWM Surface Finishing Quick Guide CWM Surface Finishing Cost/Performance Comparison Table for Al, Mg & Zn Die Cast Parts Values shown are relative within categories. They are not based on specific die cast part designs, features or surface specifications, which can greatly influence costs. Rating Code Key: L = Low M = Medium H = High VH = Very High

PLATE COATINGSURFACE RELATIVERELATIVEWEARCORROSIONPORTFOLIO CODE✻ FINISH COSTAPPEARANCERESISTANCERESISTANCESUBSECTION✻ 1. POST-TRIM DEBURRING Tumble Deburring Rough Deburr — Cutting-type media LL ------1.A1 Polished Deburr — Plastic media MM ------1.A2a Polished Deburr — Ceramic media MH ------1.A2b Aluminum Oxide Deburr ML ------1.A3 Ball Burnishing (Cost varies by media shapes) M-H H ------1.A4 Mechanical/Pressure Deburring Bead Blasting — Al Oxide media ML ------1.B1a Bead Blasting — Glass media ML ------1.B1b Automated Bead Blasting –- Al Oxide media LL ------1.B2a Automated Bead Blasting –- Glass media ML ------1.B2b WheelabratingTM — Al Oxide Shot media LL ------1.B3a WheelabratingTM — Steel Shot media LL ------1.B3b 2. CONVERSION COATINGS & COMBINED CONVERSION/FUNCTIONAL FINISHES Surface Conversion Coatings SC-A1 Trivalent Clear Chromate✽ ✽ (for Al, Mg, Zn parts) ML L L SC-A Yellow Chromate (for Al parts only) LL LL2.A SC-B Clear Chromate (for Al parts only) LL LL2.B SC-C NH-35 (for Mg parts only) LL LL2.C SC-D1 Alodine 5200 (for Al parts) MLLL2.D1 SC-D2 Alodine 5200 (for Mg parts) ML L L 2.D2 Combined Conversion/Functional Finishes (Combined Coatings replace use of Surface Conversion Coatings) CC-E1 Anodize: Black (for Al parts only) MM L L 2.E1 CC-E2 Anodize: Clear (for Al parts only) MM L L 2.E2 CC-E3 Anodize: Clear Hard Coat (for Al parts only) MM MM2.E3 Anomag (for Mg parts only) MM HH CC-G Dow 7 (for Mg parts only) HMLM2.G CC-H Dow 9 (for Mg parts only) HMLM2.H CC-I Gold Irridite/Chromate (for Zn parts only) LMLL2.I 3. COSMETIC FINISHES Painting (for Al, Mg & Zn die cast parts) CF-A1a Powder Coat — Fine Surface Finish L-M HHH3.A1a CF-A1b Powder Coat — Medium Surface Finish L-M MHH3.A1b CF-A1c Powder Coat — Coarse Surface Finish L-M LHH3.A1c CF-A2a Liquid Paint — Fine Surface Finish L-M H M-H M 3.A2a CF-A2b Liquid Paint — Medium Surface Finish L-M MMM3.A2b Plating CF-B1 Electroless Nickel Plate (for Al, Mg & Zn parts) HMMM3.B1 CF-B2 Copper, Nickel, Chrome Plate (for Zn parts) MH HH3.B2 CF-B3 Polish & Buff (Copper, Nickel, Chrome Plate) (for Zn parts) VH VH HH3.B3 CF-B4 Bright Acid Tin Plate (for Zn parts) MM MM3.B4

✽ The Coating Codes and page references refer to finished die cast sample plates & coating descriptions in CWM’s Comprehensive Resource Portfolio (see back cover). ✽ ✽ Trivalent Clear Coating (TCP) is U.S. EPA compliant & RoHS compliant with European mandates. (See page 4) © 2012 Chicago White Metal Casting, Inc. All Rights Reserved

CWM Surface Finishing Quick Guide 5 9 Typical Die Cast Parts, Their Surface Finishing Requirements and Suggested Coatings for Each This table is presented to enable OEM engineers & specifiers to better understand the factors involved in die cast coating selection. Coating & finishing recommendations will always depend on specific part designs and features, and discussion with CWM Engineering.

1 2 3 4 Basic Functional High Durability Cosmetic High Cosmetic Die Cast Part (Al) Die Cast Part (Al) Die Cast Part (Mg) Die Cast Part (Zn)

Internal bracket for a External electronic Functional housing Functional housing commercial/industrial housing for commercial components for com- components for pre- housing. application. mercial power tool. mium indoor modular Requirements: Good Requirements: Requirements: Good lighting fixture. durability and strength. (A) High durability. Non- appearance. Good Requirements: Premium Normal corrosion expo- cosmetic. Corrosion durability. Good drop appearance. High Standard sure. Non-cosmetic exposure above aver- strength. Light weight. durability. Good Post-Casting surface. age. Good strength. Above-average corro- strength. Normal Surface Finishing Relatively thick walls. sion exposure. corrosion exposure. (B) As above, but addi- Steps for tional cosmetic surface Die Cast Parts requirement.

DEBURRING (A & B) Tumble Polished Deburr — Polished Deburr — Polish Deburr — Deburring Plastic media Ceramic media Ceramic media (recommended to Mechanical/Pressure Automated Bead protect machined surfaces) Deburring Blasting — Al Oxide Shot media

CONVERSION None required COATINGS & FUNCTIONAL FINISHES

Conversion Coating Yellow Chromate for Al (B) Yellow Chromate Trivalent Clear Chromate (Note: With environmen- for Al (TCP) tally-sealed housing, no conversion coat needed) Combined Conversion- (A) Clear Hard Coat Functional Finish Anodize (plus nickel acetate and sodium dichromate seal)

COSMETIC FINISH None required (A) None required Painting (B) Fine Finish Medium-Textured Finish Powder Coat Powder Coat to match plastic parts to match company color and plastic parts Plating Copper, Nickel, Chrome Plate (For very high cosmetic appearance, wear & corro- sion resistance, a series of polish and buffing opera- tions would be substituted for polish deburring)

The nine hypothetical die cast examples above illustrate typical finishing steps. CWM publishes a Comprehensive Surface Finishing Resource Portfolio which details recommended uses, advantages and limitations for all coatings listed in this Quick Guide (see back cover). 6 CWM Surface Finishing Quick Guide 5 6 7 8 9 Anti-Corrosion High Anti-Corrosion EMI Shielded High Cosmetic/EMI Internal EMI Shielded Die Cast Part (Zn) Die Cast Part (Mg) Die Cast Part (Al) Die Cast Part (Mg) Die Cast Part (Mg)

Functional housing/heat Functional housing Housing components Housing components Functional internal EMI sink component for out- component for marine for an electronic mea- for electronic hand-held electronic door application. application. suring device designed medical device with shield/stiffener frame. Requirements: High Requirements: Light with good board-level limited board-level Requirements: 100% corrosion exposure. weight. High corrosion shielding. shielding. fail-safe EMI/RFI shield- Good appearance. High exposure. Premium Requirements: Fail-safe Requirements: 100% ing. Excellent rigidity durability and strength. appearance. High EMI-RFI shielding. Good fail-safe shielding. Good and drop strength. Mild Relatively light weight. durability & strength. appearance. Excellent appearance. Excellent corrosion exposure. drop strength. Good drop strength. Good Non-cosmetic. durability. Above-aver- durability. High age corrosion exposure. corrosion exposure. Relatively light weight. Light weight.

Polished Deburr — Rough Deburr — Polished Deburr — Polished Deburr — Aluminum Oxide Deburr Ceramic media Cutting type media Ceramic media Plastic media

Gold Irridite/Chromate Yellow Chromate for Al Trivalent Clear Chromate None required for Zn (TCP)

Anomag

Medium-Textured Finish Fine Finish Powder Fine Finish Liquid Paint Fine Finish Powder Coat Liquid Paint Coat to match company color to match plastic parts (with catalyst added for in a two-coat application for and plastic parts ("Soft-Touch" clear coat higher durability in outdoor added durability applied to handle grip. EMI use) finger gaskets for shielding Electroless Nickel Plate integrity)

CWM Surface Finishing Quick Guide 7 Contact your CWM The CWM Surface Finishing CWM Design Resources for OEMs Sales-Engineering Representative, or the Portfolio with sample finished plates To aid OEM product design engineers and speci- fiers in making all of the right design-for-die cast- CWM Sales Dept., to This Quick Guide is based on CWM’s Compre- access a copy of the ing decisions early in the product concept stage, hensive Surface Finishing Portfolio, which includes CWM Comprehensive Chicago White Metal offers a variety of resources. a library of finished die cast “plates.” The Portfolio Die Cast Surface CWM Sales/Engineers Finishing Portfolio, contains detailed information on the most widely . As an arm of our engineer- companion to this used post-casting surface coatings and finishing ing and sales departments, CWM sales/engineer Quick Guide. alternatives available for die cast components in representatives are located in most major design aluminum, magnesium and zinc. and production centers throughout the U.S., and The recommended uses, advantages and limi- in Canada & Mexico. They can answer your initial tations outlined in the Portfolio for each coating questions on designing for die casting, provide Shown below are provide a clear picture of what can be expected you with specific information on CWM capabilities samples of the from CWM in performance from alternate surface and arrange a visit to our modern 136,000 sq. ft. 4.25 x 3 x .1875 in. facility; all can be located through our website (10.79 x7.62 x .476 cm) finishes. In evaluating finished appearance, die cast plates, with however, there is no substitute for examining a (www.cwmdiecast.com), or by calling CWM. individual coatings finishing alternative applied under production con- 60+ Design Aids from CWM by 24/7 Download. applied, which are ditions to the actual die cast alloy surface to be Valuable design and specification guides, refer- part of CWM’s used for your product. Such cast and ence manuals, case studies and online Webinars Surface Finishing are available in the OEM Resource Center at the Portfolio. finished samples are pro- vided as die cast plates, in CWM website: www.cwmdiecast.com/ OEM the appropriate alloy, with design engineers can also obtain a copy of the each described coating 211p NADCA Product Specification Standards applied. manual from CWM at a special discount. For Portfolio informa- Profile CWM Capabilities. To profile CWM’s die tion, contact your CWM casting design and production capabilities, go to Sales-Engineering Repre- the CWM website’s virtual “Tour” section. You can sentative, or the CWM also download or request a free copy of the CWM Sales Dept. This surface full-color Capabilities brochure. finishing resource, and For a detailed look at CWM’s CNC Precision those listed at the right, Machining and Contract Manufacturing capabili- are further examples of ties, see the additional websites below. how CWM strives to assure OEMs better-per- forming, lower-cost die cast parts. Founded in ® 1937, CWM is one of the leading custom die casting producers in North America. Certified Aluminum, Magnesium & Zinc Die Casting and Miniature Zinc & ZA-8 Die Cast Parts Our Quality Management & Environmental Management Systems are ISO 9001 and ISO 14001 Registered EXCELLENCEISEXPECTED A GREEN BIZ COMPANY

649 N. Route 83 Bensenville, Illinois 60106-1340 U.S.A. Phone: 1 (630) 595-4424 Fax: 1 (630) 595-4474 CWM E-mail: [email protected] CWM Website: www.cwmdiecast.com CWM-CNC Website: www.cnc-technology.com DISCLAIMER CWM-CM Website: www.cwm-contractmfrg.com Every effort has been made to Sales & Engineering Representation throughout North assure the accuracy of data America and in Central America. See our Websites. presented in this Surface Finishing Quick Guide, but Chicago White MEMBER: Metal Casting cannot be responsible for results obtained with this data. North American Die Casting Association CWM disclaims any liability arising out of use of this material. No war- International Magnesium Association ranties, express or implied, are given in connection with this publication. © 2012 Chicago White Metal Casting, Inc. All Rights Reserved. The CWM symbol is a U.S. registered trademark of Chicago White Metal Casting, Inc. 8 Printed in the U.S A. on Recycled Paper