CNC Machinable Plastic Selection Guide
You know how it goes. You’re designing that next big product and it’s time to choose the plastic. Suddenly you’re staring at a spreadsheet packed with plastics you’ve never heard of. Acrylic, acetal, nylon – it’s enough to make your head spin!
Well stress no more my friend. This handy guide breaks down the most common plastics used for CNC machining. We’ll explore their key properties so you can find the perfect plastic for your application.
Whether you need a material that’s rigid and heat resistant or one that’s flexible and chemical resistant, we’ve got you covered. We’ll even look at handy tips for getting the most out of each material when it comes time for machining.
What Is Plastic Machining?
Plastic machining refers to the process of cutting and shaping plastic materials to create custom parts for machinery and components for machinery. Unlike metal, plastics can be heated and machined at high speeds without losing their material properties which is why they’re commonly used in machinery.
Top 7 Common Plastics Used in CNC Machining
In 2024, there is a wide variety of machinable plastic available, each with a unique set of qualities.
ABS(Acrylonitrile Butadiene Styrene)
ABS is a highly versatile thermoplastic polymer known for its toughness, rigidity, and impact resistance. It’s commonly used to make automotive components, medical devices, and consumer goods.
Benefits
ABS is an inexpensive, durable plastic that can withstand high temperatures. It has good chemical resistance and dimensional stability, meaning parts of machinery made from ABS will hold their shape even under stress. ABS can also be machined and fabricated in many of the same ways as metal, using techniques like milling, turning, and drilling.
Drawbacks
While ABS has excellent mechanical properties, it does have some downsides. It can warp or deform under high heat, so parts may require annealing to stabilize their shape. ABS also has poor UV resistance and will degrade in sunlight over time, resulting in fading and loss of mechanical strength. It is not well suited for outdoor uses where resistance to weathering is important.A
BS requires high molding temperatures, so processing must be able to reach over 400°F. This can increase costs for cooling. Recycling ABS can also be difficult due to the variety of additives used in different formulations and grades. Some of used equipment, formulations and grades of ABS can emit hazardous fumes when overheated, so ventilation and protective equipment are needed during processing.
Applications
Some common applications of ABS include:
Legos and other children’s toys
Helmets and protective gear
Appliance housings like refrigerators and vacuum cleaners
Pipes, valves, and fittings
Car bumpers, dashboards, wheel covers
Computer keyboards, monitors, and printers
Medical devices like blood pressure cuffs, surgical tools, and test tube racks
Acetal/POM(Polyoxymethylene)
Acetal, also known as polyoxymethylene (POM), is an engineered thermoplastic polymer known for its high strength elasticity, hardness and rigidity. Acetal has the ability to withstand repeated impact and abrasion. It maintains its mechanical properties even in cold temperatures and has a low coefficient of friction, which provides an excellent bearing surface.
Benefits
Acetal is a lightweight, low-friction plastic that resists wear and abrasion. It has good chemical resistance to solvents and fuels. Acetal can be machined accurately and holds tight tolerances. It has a high stiffness-to-weight ratio, which means it can replace metal parts to reduce cost and weight.
Drawbacks
While acetal has good chemical resistance, it can degrade from exposure to strong acids and oxidizing agents. It is also susceptible to stress cracking in the presence of certain chemicals. Acetal has a limited temperature range, softening at 176°F and melting around 390°F. It may require post-machining to improve dimensional stability. Acetal can be difficult to bond using adhesives and requires surface treatment for painting.
PC(Polycarbonate)
Polycarbonate, or PC, is a popular machinable plastic known for its high impact resistance and durability. PC is a great choice if you need a strong yet lightweight material for your CNC project.
Benefits
Benefits include:
Highly Durable：PC is extremely impact-resistant, even at low temperatures. It can withstand drops, impacts, and shocks that would crack most other plastics. This makes it ideal for where durability and impact resistance are important, like machine guards, power tool housings, and sporting equipment.
Dimensional Stability：PC has good dimensional stability, meaning it retains its shape well over time and under stress. It resists warping, shrinking, and expansion, even with temperature changes. This is important for precise CNC machining and for parts that need to maintain strict tolerances.
Machinability：While PC is a hard, durable plastic, it machines surprisingly well. It can be cut, shaped, and engraved using conventional woodworking tools and CNC routers. Sharp cutters are recommended to achieve a clean cut. PC does require fast machining speeds compared to softer plastics.
Weather Resistance：PC offers good weatherability and UV resistance. It can be used outdoors without significant degradation for many years.
Cost：PC tends to be more expensive than other plastics, especially in small quantities for shop only. For larger CNC projects and machines, the increased cost of PC may be justified by its excellent properties. However, for small hobby machine, the cost can be prohibitive.
Drawbacks
Lubrication and cooling are often needed to avoid melting.
Its mechanical properties may change slightly over time with sun exposure. UV-stabilized PC grades are available for maximum weather resistance.
Acrylic/PMMA
Acrylic, also known as PMMA (Polymethyl Methacrylate), is a popular plastic for CNC machining machine part. It has several benefits that make it suited for a variety of machine parts.
Benefits
Acrylic glass is transparent, impact-resistant, and weather-resistant. Its optical clarity makes it perfect for applications like signage, displays, and lighting fixtures. Acrylic glass also has a high strength-to-weight ratio, so parts can be very durable without adding a lot of weight.
Acrylic is easy to machine and shape using CNC equipment. It cuts and engraves cleanly without chipping or cracking. Acrylic parts can also be bent, molded, or thermoformed into different shapes. Its machinability allows for the creation of complex parts with tight tolerances.
Acrylic is also non-toxic, odorless, and chemically resistant. It does not react with most chemicals and is safe for use in medical devices, containers, and other applications where chemical contact is a concern.
Drawbacks
While acrylic has many useful properties, it also has some significant drawbacks to consider for your application. Acrylic can scratch and stain easily if not properly handled and maintained. It is also flammable and will burn in the presence of high heat or flame. Acrylic loses a significant amount of its properties above 170°F, so it should not be used in high-temperature.
Acrylic parts may require secondary finishing operations like polishing, painting, or coating to achieve the desired appearance or surface properties. Acrylic also has a high coefficient of thermal expansion, so parts can warp or change dimensions in extreme heat or cold.
For some, acrylic may not have enough strength or durability. It can fracture on impact or stress and may deform over time under load. In these cases, a higher-performance plastic like polycarbonate may be a better choice.
HDPE(High-density polyethylene)
HDPE is a versatile, durable plastic known for its high strength-to-density ratio. As the name suggests, it has a high density.
Benefits
Benefits include:
Strength and durability: HDPE is an extremely durable plastic that can withstand high impacts and abrasion. It has high tensile strength and chemical resistance, making it suitable for demanding applications like maritime equipment, fuel tanks, and playground equipment. HDPE pipes and fittings are also popular because they can withstand high pressures and temperature extremes.
Low cost: HDPE is an inexpensive plastic to produce and machine. It is made from petroleum, and improvements in production technology have made it even more affordable and widely used. The low processing costs of HDPE have allowed it to compete with traditional materials like wood, metal, and concrete in some applications.
Easy to machine: HDPE can be easily machined, welded, and thermoformed using standard woodworking tools and techniques. It can be cut, routed, and drilled with common tools. HDPE sheets can also be bent and shaped when heated, allowing for the creation of more complex forms. The machinability and formability of HDPE have made it a popular choice for applications like furniture, signs, and recreational equipment.
Weather resistance: HDPE has excellent weathering properties and is resistant to moisture, UV radiation, and environmental stress cracking. Products made from HDPE can be used outdoors without significant degradation from exposure to the elements. HDPE is also resistant to many chemicals like acids, alkalis, and solvents. Its combination of chemical resistance and weatherability make it well-suited for uses such as chemical tanks, outdoor furniture, and marine equipment.
Drawbacks
Its poor heat resistance and tendency to scratch and stain. By understanding the unique properties of HDPE, you can determine if it meets your needs or if another plastic may be more suitable.
PEEK (Polyether Ether Ketone)
PEEK is a high-performance engineering plastic that offers exceptional mechanical and thermal properties. Its high strength-to-weight ratio and heat resistance make it suitable for components in harsh environments. However, it can be more difficult to machine compared to other plastics.
Benefits
PEEK is an extremely durable and stiff material that maintains its properties even at high temperatures. It has the highest strength and stiffness of any thermoplastic up to 500°F. This allows PEEK to replace metal parts in some applications, reducing weight and improving corrosion resistance.
PEEK also has excellent chemical resistance and is inert to nearly all organic and inorganic chemicals. It is also naturally flame retardant and resistant to weathering. These properties make PEEK ideal for components exposed to harsh chemicals, high heat, or outdoor conditions.
Drawbacks
While PEEK offers exceptional performance, it can be more difficult and expensive to machine compared to other plastics. PEEK is abrasive and requires tooling made of extremely hard materials like polycrystalline diamond (PCD). Machining PEEK also generates significant heat, requiring flood cooling and slower feed rates.
The high-performance properties of PEEK come at a cost, as it is significantly more expensive than most other plastics. PEEK can cost 5 to 10 times as much as nylon or acetal. The high cost of PEEK materials may be prohibitive for some applications, especially those requiring large volumes of material.
Nylon/PA
Nylon is one of the most popular plastics for CNC machining. It’s a tough, durable polymer that can handle high heat and stress. Nylon parts have a smooth finish and low friction, so they work great for bearings, bushings, and other sliding parts.
Benefits
Benefits include:
Strength and Durability: Nylon has excellent mechanical properties. It’s strong, stiff, and impact resistant. Nylon parts can handle thousands of cycles without breaking down or deforming. The material is also chemically resistant to oils, greases, and solvents. However, nylon will absorb moisture over time, which can slightly soften and cause parts to swell.
Easy to Machine: Nylon machines quickly and produces chip-free cuts, even at high speeds. It has a low melting point, so tools require high rake angles and sharp cutting edges. Nylon parts have an excellent surface finish right off the machine with little or no post-processing required. The material is also easy to paint, plate, or print on for marking and identification.
Drawbacks
While nylon has many benefits, it does have some significant downsides to consider. Nylon parts may warp or change dimensions over time due to moisture absorption and stress relaxation. The material is also sensitive to UV light which can cause parts to become brittle. Nylon is not suitable for high-temperature uses since its properties start to degrade around 150°C. It also has a low chemical resistance to some solvents like acetone.
5 Factors To Consider For Seletion CNC Machining Plastics
Below are some of the data, the factors to consider when selecting CNC Machining Plastics
Materials Machinability
The machinability of a plastic refers to how easily it can be cut, shaped and processed using CNC machining. Some plastics like acrylic and polypropylene are highly machinable, while others like PVC and nylon can be more difficult to work with.
Consider how complex your part geometry is and how precise the tolerances need to be. Highly machinable plastics allow for more intricate details and tighter tolerances.
Materials Shrinkage
All plastics shrink slightly as they cool after processing. The amount of shrinkage depends on the plastic and can range from 0.001 inches per inch to over 0.060 inches per inch. For critical dimensions, you’ll want to choose a plastic with minimal shrinkage and account for any shrinkage in your part design. Polycarbonate and ABS are examples of low-shrinkage plastics.
Appearance, Light Transmittance, and Transparency
The appearance of your plastic parts may be an important factor depending on your application. Consider properties like color, clarity (how transparent the plastic is), and light transmittance (how much light passes through).
Acrylic is highly transparent and transmits over 90% of visible light, while many plastics are opaque or translucent. Some plastics can be dyed in different colors or painted for custom appearances.
Temperature Resistance
The maximum temperature a plastic can withstand is an important property to consider based on your application and operating environment. Plastics are rated for both continuous use (long term) and peak (short term) temperatures.
For high-heat applications, consider plastics like polyetheretherketone (PEEK) or polytetrafluoroethylene (PTFE) which can withstand over 300°C continuously. For most applications, plastics like acrylic, ABS, and polypropylene with temperature resistance up to 100°C would work well.
Plastic Cost
Cost is always a factor when selecting materials. Plastic prices can range from $1 to $100 per pound depending on the polymer. In general, plastics that are more durable, heat-resistant, and chemically inert tend to be on the higher end of the price spectrum.
For low-cost parts, plastics like HDPE, polypropylene, and polystyrene are good options. For high-performance parts where cost is less of a concern, plastics like PEEK, polyimide, and PTFE would be suitable. Consider your priorities and how critical the properties of your plastic are to determine a budget-friendly option.
Conclusion
So there you have it – a quick guide to selecting the right CNC machinable plastic for your next project. With so many options out there, it can get overwhelming fast. But keeping the key factors like mechanical properties, temperature resistance, and machinability in mind will help narrow down your choices.
Don’t be afraid to ask your plastic supplier for recommendations too based on your specific application. They’ll be able to point you in the right direction based on years of experience.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.