When you design a part, the first step is to determine what material it should be made of. When you decide that the part should be plastic and CNC machined, but does the choice end there? No, there are too many plastics to choose from, each with its own combination of properties.
In this article, we help you combine your project needs with the right plastic materials for the job, narrowing down your choices to just a few commonly used plastic materials.
ABS is a comprehensive general-purpose plastic. It provides high impact strength, toughness and electrical resistance at a low price. It’s also easy to finish, as it can be easily painted, glued, or welded together. If machined as is, it will have a matte finish.
Advantages: ABS is the best choice for general purpose prototypes, pre-formed prototypes, parts that are subject to impact and need toughness, or when low cost is required.
Cons: ABS does not have good abrasion or chemical resistance and will melt in acetone. It’s also not a particularly strong plastic. also.
Common Applications: The most common application for ABS is injection molding, which is used to make electronic enclosures, home appliances, and even iconic Lego bricks.
Nylon is a strong and durable plastic that is suitable for many purposes.
Advantages: Nylon has high strength and stiffness, can be maintained over a wide temperature range, has good electrical insulation, and good chemical and abrasion resistance. Nylon is ideal for applications that require low cost, robust and durable components.
Cons: Nylon will absorb moisture, causing it to swell and lose some dimensional accuracy. Due to the inherent internal stress of the material, distortion can also occur if a large amount of asymmetric material is removed during processing.
Common Applications: Nylon is most commonly found in medical devices, circuit board mounting hardware, automotive engine compartment components, and zippers. It is used as an economical replacement for metals in many applications.
PMMA is acrylic, also known as plexiglass. It is tough, has good impact strength and scratch resistance, and can be easily bonded with acrylic cement.
Pros: It’s perfect for any application that requires optical clarity or translucency, or as a less durable but less expensive alternative to polycarbonate.
Disadvantages: PMMA is a brittle plastic that will fail by cracking or shattering rather than stretching. Any surface finish on a piece of acrylic loses its transparency, giving it a frosted, translucent appearance. Therefore, it is usually best to pay attention to whether the PMMA part should remain stock thickness to maintain transparency. Polishing can be done as an additional post-processing step if the machined surface requires transparency.
Common Applications: After processing, PMMA is transparent and is most often used as a lightweight replacement for glass or light pipes.
POM is a special brand of acetal homopolymer with a smooth, low friction surface, excellent dimensional stability and high stiffness.
Advantages: POM is a good plastic for these or any other applications where a lot of friction is required, tight tolerances are required, or high stiffness materials are required.
Cons: POM is difficult to bond. The material also has internal stresses that make it prone to warping in areas where thin or large amounts of asymmetric material are removed.
Common Applications: POMs are commonly used in gears, bearings, bushings and fasteners, or in the manufacture of jigs and fixtures for assembly.
HDPE is high density polyethylene
Advantages: HDPE is a very low density plastic, it also has excellent chemical resistance, electrical insulation and a smooth surface. It is ideal for making plugs and seals due to its chemical resistance and slip properties, but is also a good choice for weight-sensitive or electrically-sensitive applications.
Disadvantages: The main disadvantage of HDPE is its poor strength, especially in stretching and bending.
Common Applications: HDPE is commonly used in fluid applications such as fuel tanks, plastic bottles and fluid flow pipes.
PC is our most durable plastic.
Pros: It has high impact resistance and stiffness and remains functional over a wide temperature range. It is also optically clear and can be tinted black if opacity is desired. PC is best suited for applications that require very hard or very strong plastics, or require optical clarity. Therefore, PC is one of the most used and recycled plastics.
Disadvantages: Pure PC does not have good wear resistance and is easy to scratch. If desired, an anti-scratch coating and vapor polishing can be added as post-processing steps to improve abrasion resistance or optical clarity. It also doesn’t have readily available two-inch-thick parts,
which limits the size of PC parts.
Common applications: PC’s durability and transparency mean it can be used to make optical discs, safety glasses, light pipes, and even bulletproof glass.