Computer numerical control machining is a popular manufacturing method for plastic parts. It’s an example of subtractive manufacturing that uses a specialized CNC machine with a guided cutting tool to carve a block of plastic into the intended component.
Using CNC machining for plastics can produce durable, precise components, but achieving excellent outcomes requires knowing and implementing effective techniques. Continue reading to learn more.
Plastic is an ideal material for CNC machining because it is affordable, durable and versatile. However, since plastics come in different varieties with distinct pros and cons, you must make the correct choice for your CNC machining operation.
Consider the function of the part you’re machining to select a plastic that fits your needs. Ensure you know the pros and cons of various plastics for CNC machining. These CNC machining plastic guidelines and features will help you choose the correct material for the job.
Acrylics: Good for transparency and transmitting light. High impact resistance, but vulnerable to cracks and scratches.
High-density polyethylene: Resistance to impact, corrosion, chemicals and moisture. High tensile strength. Lacks UV resistance.
PVC: Accessible, affordable, durable and acid-resistant. Toxic and unstable at high heat.
PVDF: Rigid resistance to abrasion, chemicals and flames. Requires clean processing machines to retain purity. Vulnerable to acids.
Polycarbonate: Bulletproof strength and fire resistance. Easy to work with. Lacks UV resistance.
Polypropylene: Resistant to chemicals and fatigue. Susceptible to heat and UV radiation.
Teflon: Extreme resistance to heat and most chemicals. Sensitive to abrasion and limited in flexibility.
UHMW: Ultimate impact resistance and good resistance to chemicals and odors. Vulnerable to heat.
ABS: Tough and affordable. Sensitive to heat, UV light and abrasions.
Whichever equipment you use, you should familiarize yourself with your machine and select the proper cutting tool for your material. Here are guidelines for CNC machining plastic with four of the most popular machines.
Three-axis mills work for simpler plastic parts, but multi-axis mills offer advanced precision cuts for more complex components. High-speed steel tooling is sufficient for most plastics. Choose carbide tools for reinforced materials.
Controlling heat is critical when drilling plastics. Ensure the drill is sharp. For most plastics, aim for a slower drill speed with a 90- to 118-degree drill bit and 9- to 15-degree lip angle. Acrylic drilling requires a zero-degree rake.
When using a lathe, protect the plastic from rubbing with generous relief angles and negative back rakes.
Laser-cutting CNC machines work for most plastics, but not PVC, which releases toxic fumes. Using nitrogen gas for your laser cutter produces clean cuts and smooth edges when cutting plastic.
You must tailor the CNC machine’s cutting speed to the material. Most plastics are vulnerable to melting, so a slower cutting speed to minimize heat is usually advisable.
Save on materials: Plastics vary in price. If more than one material could work for you, choose the most affordable one. Budget-friendly plastics include acrylics, polypropylene and ABS.
Design rounded corners: If possible, design your plastic part with rounded internal edges to allow the cutting tool to run more efficiently. Larger radii of at least one-third the cavity depth will also help reduce cutting costs.
Keep cavities shallow: Plastic part designs without deep pockets will result in a quicker cut and more efficient material use.
Expand thin walls: Plastic component designs with walls thicker than 1.5 millimeters allow easier, faster cutting and are safer from error and damage.
Decimate the decimals: The more decimal points you include in your dimension specifications, the more intricate and costly the machining becomes. Unless a tight CNC machining tolerance is essential to your component, reduce decimals to the minimum you need and leave tolerance unspecified. The machine will cut within the standard tolerance of 0.010 thousandths or better, which is sufficiently accurate for most parts.
As-machined: Parts fresh off the line with no added finish have improved uniformity and precise dimensions. A technician can CNC machine any plastic with an as-machined finish. However, this technique leaves minor visible tool marks. Softer plastics may be vulnerable without a protective coating.
Bead blasting: A pressurized air gun blasts plastic parts with glass beads for a smooth matte or satin finish. This method offers pleasing aesthetics but only works for plastics with enough impact resistance.
Wet sanding: Moistened fine-grit silicon carbide sandpaper smooths plastic to prepare for paint or polish. Be sure to apply a plastic-safe polish.
Fire polishing: An open flame partially melts the plastic to smooth the surface for a polished look. This technique only applies to plastics that can tolerate the heat, never to those that melt easily or become toxic when heated, like polypropylene or PVC.
Vapor polishing: A chemical vapor can polish dull plastic surfaces to a smooth sheen. It can enhance the properties of polycarbonate and acrylic but requires strict safety measures and is not ideal for all plastics.
Make American Micro Industries Your Plastic Machining Partner
If you need an expert in effective CNC techniques for plastics, American Micro Industries has the knowledge, experience and cutting-edge equipment to exceed your expectations.
Your requirements are all we need to know. Our expert engineers and machinists will:
Assist with your design
Recommend and supply plastics
Fabricate your parts to precise specs
Turn the product around quickly at a competitive price
