Machining Plastics: Case Study Polycarbonate
In this Series of discussions, we will explore some past projects that involved some trouble shooting and some machining tips that were learned along the way. This might help you set your mind when certain problems arise in your next project.
PC 1000: Case Study
In this study we are going to talk about Polycarbonate materials and where we used them. Polycarbonate is available in many transparent, translucent and opaque colors from the generic to name brand options to select from. We are going to list a few of them here and a brief discussion about them, but our main focus will be PC 1000 and where we used this material.
Note to Reader: It is important to note that this data is only of an indicative nature, derived from all sorts of literature related to the chemical resistance of plastics. Therefore, in practice it is strongly recommended carrying out tests on a prototype, to determine the final suitability of a plastics material for the application.
Excelon PC: For the clarity of glass and the impact resistance of metal, specify Excelon™ PC tubing. Excelon PC provides extraordinary design and fabrication opportunities Made from FDA-approved materials, UL rated, Superior clarity, High Tensile Strength over a wide temperature range, High impact strength - even at low temperatures. Excellent high temperature resistance, Flame-resistant, Self-extinguishing, can be machined, drilled, cut and sawed. Easily joined with solvents or adhesives. Polycarbonate Tubes can be ordered from stock in 1/4" - 3 3/4" I.D., in 8 ft. lengths. Custom orders are also available in sizes up to 8" O.D. and in a variety of wall thicknesses. Specific formulations are available for tints and colors with performance additives for ultraviolet stabilization, flame retardant (94VO) and radiation resistance.
Common Applications for Excelon PC:
Protection for Delicate Instruments and tools
High pressure fluid or gas transfer
Hygard BR1000: ballistic grade sheet is a 1.000”, 4-ply polycarbonate laminate that conforms to UL 752 Level 2 rating for 0.357 Magnum ballistic attack and HP White TP 0500 Level IV. Unlike glass-clad products, this all-polycarbonate laminate resists spalling and white-out after repeated high force and ballistic impacts, an advantage in maintaining visibility of a threat during an attack. All Hygard products incorporate TUFFAK polycarbonate sheet produced for high optical quality in security glazing laminates. Exterior surfaces have a proprietary TUFFAK AR hard coat that facilitates cleaning and resists marring, chemical attack, and graffiti.
Common Applications for Hygard Polycarbonate:
Government and Detention facilities
24 hour convenience stores
Cash transaction windows
Zelux (PC): Zelux polycarbonate is a transparent engineering plastic with excellent dimensional stability and good mechanical and electrical properties. It is used for structural applications when clarity and impact strength are essential including lenses, manifolds, site glasses, and machine guards. Zelux is used for a wide range of electrical applications since it has low moisture absorption and good insulating properties. Other grades like Zelux W is a window grade (optically clear) material while Zelux M is a machine grade, stressed relieved, easy to machine, easy to fabricate, paint and bond (available in natural and black). Zelux M-GF is a glass filled FDA compliant grade that is available in a variety of blends and colors. Benefits include excellent impact resistance, excellent dimensional stability, low moisture absorption, good strength and stiffness over a wide temperature range and good electrical insulating properties. These Zelux grades are available in sheets
Common Applications for Zelux Polycarbonates:
Fluid handling components
Scientific and analytical instrument components
Housing and covers
ZELUX® SD-P (Static-dissipative Polycarbonate): Carbon-powder-filled material with resistivity levels in the 107 - 1011 range with high flexural strength and good thermal stability to 270° F. UL94 V-O rated at .030”, this material is thermo formable in .010” - .060” gauges and has low out gassing properties.
ZELUX® CN-P and CN-SS (Conductive Polycarbonate): The CN-P material is carbon-powder filled, while the CN-SS is filled with small non-sloughing stainless steel fibers. Both have high flexural strength and good thermal stability to 275° F. The CN-SS material has excellent impact strength, while the CN-P is UL94 V-0 rated at .030” and is thermo formable in thinner gauges (.010” - .060”).
Common Applications for Zelux SD-P, CN-P and CN-SS:
Explosives handling equipment
Zelux (GF Polycarbonate): is an engineering plastic with excellent dimensional stability and good strength and stiffness over a wide range of service temperatures. Zelux is used for a wide variety of electrical applications since it has low moisture absorption, good insulating properties, and an excellent flammability rating. Zelux is easy to fabricate, paint, and glue.
Common Applications for Zelux GF Polycarbonate:
Scientific and analytical instrument components
Fluid handling components
Housings and covers
Zelux GS (Gamma Stabilized): Medical grade Zelux GS polycarbonate is produced from resin formulated to meet the stringent performance characteristics and requirements of the healthcare industry. Suitable for gamma, E Beam, ETO gas and limited autoclaving sterilization, the resin utilizes proprietary color enhancement technology to reduce color shift caused by gamma radiation. Advantages of Zelux GS include excellent impact resistance, lot controlled and traceable. Easy to machine, has optical clarity and meets the requirements of USP VI and ISO 10993 biocompatibility requirements for non-implantable medical applications. Available in standard rods of 1" to 3" diameter up to 48" long, non-standard rod sizes of less than 1" and greater than 3", non-standard slabs of 1/2" to 6" thick in blue tinted clear color. The special transparent tint is formulated to offset post gamma yellowing and polymer stabilizers help maintain physical properties.
Common Applications for Zelux GS:
Housings and covers
Polycarbonate Sheet: Polycarbonate is a shatter resistant thermoplastic that features higher impact resistance and better light transmission versus many types of glass. Polycarbonate is a safe, durable and lightweight plastic that features many specialty grades. Polycarbonate is easily worked, molded and thermoformed. It can undergo large deformations without cracking or breaking. Available in machine, twin wall (48" x 288", 48" x 192", 48" x 96"), multiwall. Full sheets 48" x 96" from 0.060" to 1.5" thick and rods from 0.250" to 4" diameter. Polycarbonate sheet is cost-effective in a wide range of industrial glazing, design and structural applications, as well as thermoformed and fabricated components.
Common Applications for Polycarbonate Sheet:
Flat and curved glazing
Indoor and outdoor signage
Safety and security glazing
Construction equipment (Cab glazing and guards)
PC 1000: machine grade polycarbonate (PC) is a transparent amorphous thermoplastic which offers very high impact strength and high modulus of elasticity. The material has a 290°F (145°C) heat deflection temperature at 264 psi, absorbs very little moisture and resists acidic solutions. These properties, in addition to good electrical characteristics, make PC 1000 machine grade polycarbonate stock shapes an excellent choice for electrical/electronic applications (See Figures 12 and 13). Its strength, impact resistance and transparency also make it an ideal material for certain transparent structural applications such as sight glasses and windows.
This machine grade polycarbonate is stress relieved making it ideal for close tolerance machined parts. Stock shapes are produced from polycarbonate resins which meet the requirements of ASTM D 3935. A food grade polycarbonate that is compliant with FDA, NSF, Canada AG and USP Class VI regulations is also available. Clear shapes available in rod 0.062" to 6" diameters and plate 0.250" to 3" thick in widths of 24" x 48" long.
If buying and storing PC 1000 keep indoor in a normal environment (air at 50 - 86°F / 30 - 70% relative humidity) and kept away from any source of degradation such as sunlight, UV-lamps, chemicals (direct or indirect contact), ionizing radiation or flames. Dimensional changes (camber, warpage, shrinkage) as well as slight color shifts of the external surfaces can occur with time. This generally does not pose a problem in case of semi-finished products since the surface layer is mostly removed during machining into finished parts. Avoid temperatures above 536°F (Standard industrial safety recommendations shall be observed) suitable extinguishing media like water, foam, dry chemical, CO2.
Common Applications for PC 1000:
Parts for processing lines
Medical equipment components
Machining PC 1000:
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. Troubleshooting should be used to correct undesirable surface finishes or material responses during machining operations. This Quadrant material is 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 machining. 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.
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 the cutting interface. General purpose petroleum based cutting fluids, although suitable for many metals and plastics, may contribute to stress cracking of amorphous plastics such as Quadrant PC 1000, Quadrant PSU, Duratron® U1000 PEI, and Quadrant PPSU.
Drilling Tip: The insulating characteristics of plastics require consideration during drilling operations, especially when hole depths are greater than twice the diameter. For small diameter holes high speed steel twist drills are generally sufficient for small holes. To improve swarf removal, frequent pull-out (peck drilling) is suggested. A slow spiral (low helix) drill will allow for better swarf removal. For large diameter holes a slow spiral (low helix) drill or general-purpose drill bit ground to a 118°-point angle with 9° to 15° lip clearance is recommended. The lip rake should be ground (dubbed off) and the web thinned.
Milling Tip: Sufficient fixturing allows fast table travel and high spindle speeds when end milling plastics. When face milling, use positive geometry cutter bodies. Climb milling is recommended over conventional milling. To ensure finished part flatness, always machine a plate flat to start. Do not force a plate flat with a vice or vacuum.
Threading and Tapping Tip: 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 coated tap. Remember to keep the tap clean of chip build-up. Use of a coolant during tapping is also suggested. Use of a coated tap will create radii at the root of the threads resulting in a stronger and tougher thread which is less prone to cracking from over-torquing.
Turning Tip: Turning operations require inserts with positive geometries and ground peripheries. Ground peripheries and polished top surfaces generally reduce material build-up on the insert, improving the attainable surface finish. Fine grained C-2 carbide is generally best for turning operations.
Post Machining Annealing: In our experience and parts we have produced this step was avoidable with a roughing in machine stage and leaving parts unclamped for 1 to 2 days. This worked great for critical tolerance work. Here is some information on the annealing process that we feel is important to at least mention.
Finale Note: PC 1000 polycarbonate is machine grade, not optically clear. It can be both mechanically and vapor polished to improve optical clarity. Caution: During machining, never use coolants with an aromatic base.
Case Study #: Material Replacement for Ultem
Customer was mainly looking for a material to replace several Ultem housings, chemical level glass sights made from glass and a few Acrylic plastic parts in their custom testing equipment. Customer stressed the Ultem housings where working fine but there high cost was pushing there budget to near exhaustion. There were several upper tanks that had tubular glass inserts that made tank level easily to view; the problem here is the availability of these custom cut glass tubes lead times where to long. Customer asked if there is alternative to glass that will resist the chemicals in the tanks and still be acceptably clear. Last where three (3) manifolds made from Acrylic material, customer complained that these manifolds where getting cracked from various impact incidents can we review and try an alternate material.
Challenge: Replace Ultem Housings with a lower cost alternative material. Replace the glass tank level sight glass with a material readily available; last review three (3) manifolds that are being damaged during scheduled maintenances.
Solutions: We began this study with the main objective to this project and that was the high cost of the Ultem housings. These housing where large and had a lot of machining detail in and out on five (5) surface faces. Several faces had machined O-ring grooves to seal out moisture. After a review of the requirements of this housing we had several options but opted to use PC 1000 for its high heat deflection, absorb very little moisture and resists chemical solutions. PC 1000 has good electrical characteristics which will work well here; the housing contains several electronic circuit board assemblies. PC 1000 also has great strength and very impact resistant, and though not optically clear customer did not like the transparency of the material but was willing to try it since the lower cost of the material brought the project budget lower than required.
Just a quick note here, customer asked us to prototype a housing in black polycarbonate so they can do further testing outside the machine and concluded a standard black polycarbonate worked fine. Sometimes over engineering your specifications and requirements isn't necessary and can greatly impact your costs. Not in all cases but in this case an example of where little experimentation, trial and error helped reduce the costs of an over engineered component.
Next item was the tank level tubes that were made from thick glass. PC 1000 was also selected to use as a replacement here due to its resistance to acidic solutions. We must mention however that we couldn't achieve glass clarity when the tubes where mechanically polished, it was a combination of vapor polishing that brought the tubes to a desirable clarity. Being readily available and easily machined, customer appreciated the reduction in lead time and cost here.
Last item or items where the three (3) Acrylic manifolds. PC 1000 was again chosen here for its impact and acidic resistant characteristics, this area of the machine is also slighted heated, and this material has good heat deflection for the required manifold psi. There were several impact studies that we had to conduct here, and although we achieved better impact results with PC 1000 vs. the Acrylic counterpart. We where able to still damage the manifolds with a much higher impact force, it was suggested and implemented to install a polycarbonate impact shield to deflect and prevent any falling objections from initially damaging the manifolds. Easy fix right?
All trademarks and service marks are property of their respective manufactures. All statements, technical information and recommendations contained in this publication are presented in good faith and are, as a rule, based upon tests and such tests are believed to be reliable and practical field experience. The reader, however, is cautioned that Diversified Designs does not guarantee the accuracy or completeness of this information and it is the customer’s responsibility to determine the suitability of any information provided by Diversified Designs in any given application.