alroplastics.com 800-877-ALRO 2 5 7 6 Plastics Processing Getting Started, Coolants ............................................................ 298 Tips, Threading, Tapping, Reaming ............................................ 299 Saw Cutting, Milling, Turning, Drilling .................................300-301 Post Annealing & Adhesive Bonding .......................................... 302 Machining Guidelines Chart ........................................................ 303 Trouble Shooting, Plastic Drilling ............................................... 304 Trouble Shooting, Turning & Boring ........................................... 305 Processing Saw Cutting, Kerf Line ................................................................. 306 Plastics Standard Edge Finishes ............................................................... 307 Processing Introduction .............................................................. 308 Saw Cutting, Sheet/Plate .............................................................. 309 Saw Cutting, Rounds .................................................................... 310 Waterjet Cutting ............................................................................ 311 CAD/CAM Programming .............................................................. 312 CNC Routing ................................................................................. 313 CNC Milling .................................................................................... 314 Drilling and Tapping ..................................................................... 315 Plastic Welding ............................................................................. 316 Bending and Gluing ...................................................................... 317 297 alroplastics.com 800-877-ALRO 2 5 7 6 Fabrication Guidelines The following guidelines are presented for those machinists not familiar with the machining characteristics of plastics. They are intended as guidelines only, and may not represent the most optimum conditions for all parts. The troubleshooting quick reference guides in this section should be used to correct undesirable surface finishes or material responses during machining operations. All Quadrant materials are stress relieved to ensure the highest degree of machinability and dimensional stability. However, the relative softness of plastics (compared to metals) generally results in greater difficulty maintaining tight tolerances during and after machin- ing. A good rule of thumb for tolerances of plastic parts is +/-.001" per inch of dimension although tighter tolerances are possible with very stable, reinforced materials. When machining Plastic stock shapes, remember... ● Thermal expansion is up to 10 times greater with plastics than metals ● Plastics lose heat more slowly than metals, so avoid localized overheating ● Softening (and melting) temperatures of plastics are much lower than metals ● Plastics are much more elastic than metals Because of these differences, you may wish to experiment with fixtures, tool materials, angles,speeds and feed rates to obtain optimum results. Getting started Plastics ● Positive tool geometries with ground peripheries are recommended Processing ● Plastics Carbide tooling with ground top surfaces is suggested for optimum tool life and surface finish. Polycrystalline diamond tooling provides optimum surface finish when machining Celazole® PBI. ● Use adequate chip clearance to prevent clogging ● Adequately support the material to restrict deflection away from the cutting tool Coolants Coolants are generally not required for most machining operations (not including drilling and parting off). However, for optimum surface finishes and close tolerances, non-aromatic, water soluble coolants are suggested. Spray mists and pressurized air are very effective means of cooling and cutting interface. General purpose petroleum based cutting fluids, although suitable for many metals and plastics, may contribute to stress cracking of amor- phous plastics such as PC 1000 Polycarbonate, PSU 1000 Polysulfone, Ultem® 1000 PEI, and Radel® R PPSU. Continued on next page 298 alroplastics.com 800-877-ALRO 2 5 7 6 Fabrication Guidelines Machining Tips ● Coolants are strongly suggested during drilling operations, especially with notch sen- sitive materials such as Ertalyte® PET-P, Torlon® PAI, Celazole® PBI and glass or carbon reinforced products. ● In addition to minimizing localized heat-up, coolants prolong tool life. Two (flood) cool- ants suitable for most plastics are Trim 9106CS (Master Chemical Corp. - Perrysburg, OH) and Polycut (Tullco -Savannah, GA). A generally suitable mist coolant is Astro-Mist 2001A (Monroe Fluid Technology - Hilton, NY). Threading and Tapping Threading can also be completed on conventional machinery such as automatic or semi- automatic equipment, and self-opening dies with high-speed chasers. In general, lubricants or coolants are not needed but they can be of assistance on extremely high speed opera- tions. A slightly oversized tap is recommended to overcome the tendency toward recovery, although this property may be used to produce a self-locking thread. When threading long lengths of rod stock, a follow rest or support should be used to hold the work against the tool. When threading cast nylon on a lathe using conventional single- pointed tools, several successive cuts of .005 -.01" should be made. Finished cuts should Processing not be less than .005" because of cast nylon's resilient nature. Plastics Threading should be done by single point using a carbide insert and taking four to five 0.001" passes at the end. Coolant usage is suggested. For tapping, use the specified drill with a two flute tap. Remember to keep the tap clean of chip build-up. Use of a coolant during tapping is also suggested. Reaming Most of the engineering plastics can be reamed with either hand or collar reamers to produce holes with good finish and accurate dimensions. Expansion type reamers and standard .001-.002" oversize stub machine reamers can also be used. Helical flute reamers are rec- ommended if there is an interruption in the I.D.. Cuts made with a fixed reamer tend to be undersized unless at least .005" is removed by the final reaming. With a .01-.02" per revolution feed rate and a .005-.01" depth of cut, reamer speeds of 250-450 fpm are recommended. Reaming PTFE / TFE is generally not recommended. The operation causes the material to compress, especially if the reamer is not exceptionally sharp. Also, PTFE's elasticity will cause holes to "fall in" creating undersize holes. If necessary, special reamers with a pri- mary relief (clearance) angle can produce accurate holes. The use of an oversized reamer can correct undersized holes. Where hole diameter permits, a single point boring tool is recommended to finish the hole to close tolerances. Continued on next page 299 alroplastics.com 800-877-ALRO 2 5 7 6 Fabrication Guidelines Saw Cutting Band sawing is versatile for straight, continuous curves or irregular cuts. Table saws are convenient for straight cuts and can be used to cut multiple thicknesses and thicker cross sections up to 4" with adequate horsepower. Saw blades should be selected based upon material thickness and surface finish desired. Engineering plastics can be cut with band and circular saws. Blades should be very sharp and have sufficient kerf to clear the cut and allow chips to evacuate. For best results, use high speed steel rip or combination type circular saw blades having a 0o rake angle and a 3-10 tooth set. A carbide blade is recommended for production sawing. Bimetaloy or skip tooth saw blades with 2-4 teeth per inch are recommended for band saws. Hook or claw tooth blades are not recommended. ● Rip and combination blades with a 0o tooth rake and 3o to 10o tooth set are best for general sawing in order to reduce frictional heat. ● Hollow ground circular saw blades without set will yield smooth cuts up to 3/4" thickness. ● Tungsten carbide blades wear well and provide optimum surface finishes. Milling Sufficient fixturing allows fast table travel and high spindle speeds when end milling plastics. When face milling, use positive geometry cutter bodies. Milling tip, climb milling is recom- mended over conventional milling Plastics Processing Turning A tool-geometry of 0-5o back rake angle, 15-20o end relief angle and end cutting edge, and a 2-20o side relief angle with a slight nose radius will give good turning results. Although a rake angle of 0-5o is recommended, it is sometimes necessary to vary the angle to 0-5o. Varying is done to balance the cutting tool pressure on the material and results in better finish and size control. Surface speeds from 200-500 fpm with feed rates of .002-.010"/revolution do not require flood coolants and are most appropriate for fine finish turning. Higher speeds can be used with very low feeds for rougher cuts if a coolant is used. If a finishing cut is desired from a high speed operation, the feed must be dropped to a correspondingly lower value. Directing the chips/curl away from the work is often neces- sary to prevent it from restricting turning and boring operations. This can be accomplished by using an air jet or some other mechanical means. When turning a large diameter cast nylon, light cuts .625-.125" deep and light feeds .003-.007" per revolution are suggested. Satisfactory results can be obtained, however, using heavy cuts up to 3/8" deep and feed of .015" per revolution. Continued on next