CNC Plastics: Choosing the Right Plastic for Your Project

Why Choose CNC Plastics?

CNC technology is reputable for its reliable solutions in different applications. Product designing teams consistently choose plastics as the suitable material for several machined parts due to their extensive material options, range of surface finishes, low cost, and extended lifespan. As such, plastics have become an increasingly important and widely embraced choice for various machined parts.

CNC plastics allow you to create precise customized parts that match the design specifications while minimizing costs. Moreover, the plastic CNC machining process offers faster lead times and preferred tight tolerances. As a result, these engineering plastics are ideal for high-precision machined products.

Common Plastic Materials used in CNC machining

Plastics offer varying results due to their difference in physical properties. Below are the common machinable plastics:

ABS (Acrylonitrile Budatine Styrene)

ABS is a widely used engineering plastic with low weight, good machinability, and remarkable resistance to impact and high heat. Manufacturers commonly use ABS for rapid prototyping because it is cheap and offers impressive results. It is a suitable material for electrical applications due to its good insulation properties and maintains mechanical stability over time.

ABS is suitable for making machined plastic components like interior components of vehicles, electronic enclosures, and keyboard caps. Despite its high impact strength, certain greases, alcohols, and solvents make ABS highly susceptible to wear.

PC (Polycarbonate)

Polycarbonate is popular for its toughness, excellent electrical insulation, and lightweight and natural heat-retardant properties. Unlike most engineering plastic, polycarbonate is a highly efficient material. PC offers good transparency and light transmittance similar to glass. Hence, product designers commonly use PCs for plastic parts such as surgical tools, CDs /DVDs, safety goggles, and circuit breakers.

PC resists greases, oils, and diluted acids. However, extended exposure to water over 60ºC compromises the good mechanical properties of this transparent thermoplastic. It is also vulnerable to hydrocarbon wear, and extended exposure to ultraviolet rays changes its appearance to yellow.

PVC (Polyvinyl chloride)

PVC is a rigid, lightweight, and durable thermoplastic polymer with excellent corrosion resistance. It is a readily available, low-cost, and very strong plastic. Product engineers commonly use PVC due to its ability to resist deformation. It has impressive flame resistance due to its high chlorine content, making it a popular material across industries.

It exhibits poor heat stability due to its 176°F working temperature, producing toxic fumes when melted. PVC is commonly found in plumbing, construction, and automotive industries due to its incredible versatility.

PMMA (Polymethyl methacrylate)

PMMA or acrylic is a rigid thermoplastic with good toughness, resistance to most chemicals, and lightweight. Although it exhibits good shatter resistance, it breaks down when exposed to ketones, ethers, chlorinated, or aromatic hydrocarbons. Acrylic is commonly found in solar panels, automotive parts such as indicator light covers, greenhouse canopies, and drug testing devices.

PMMA exhibits good light transmittance and resistance to ultraviolet rays. In terms of design, acrylic accepts extensive coloring options and offers a refractive index of 1.49. Nevertheless, this plastic material has poor abrasion, wear, impact, and heat resistance, making it crack easily under heavy loads. Therefore, it is advisable to consider acrylic for low-stress applications.

PEEK (Polyetheretherketone)

PEEK is a popular semi-crystalline thermoplastic with unique mechanical properties that make it suitable for many applications. It can resist fatigue, liquids, chemicals, wear, and temperatures of about 260ºC (480ºF). PEEK is biocompatible, recyclable, and insolvent in common solvents and exhibits high-temperature resistance. Its corrosion resistance and low moisture absorption make it ideal for different applications that subject machined plastic parts to corrosive substances.

PEEK’s excellent strength and flame resistance make it a suitable alternative for metal in CNC machining. Dental syringes, critical airplane engine components, piston units, etc., are typical PEEK applications. However, PEEK exhibits poor UV resistance and is highly susceptible to sodium or halogen exposure. It is also one of the most costly CNC plastics on the market; therefore, it is advisable to consider PEEK for demanding applications.

POM (Polyacetal polyoxyethylene)

POM or Delrin (its commercial name) is one of the highly machinable plastics with high stiffness and strength. It offers excellent fuel, wear, heat, weather, and chemical resistance. Common grades of POM that product teams commonly use are Delrin 150 and 579. Delrin exhibits excellent dimensional stability and is suitable for making precise plastic CNC machined parts with desired tolerances.

However, Delrin can be challenging to bond, and it exhibits poor resistance to acids. Common applications of POM include water meters, seat belt components, insulin pens, and electronic cigarettes.

PTFE (Polytetrafluoroethylene)

PTFE, also called Teflon, is a commonly used polymer due to its excellent properties that make it ideal for designing different commercial products. This high-performance polymer exhibits excellent resistance to fatigue, temperature, water, chemical, light, weathering, and ultraviolet rays. PTFE/Teflon is widely used as coatings for non-stick pans due to its excellent anti-adhesion properties. It is also used for semiconductor parts, gaskets, and heart patches.

PTFE is one of the standard corrosion-resistant CNC plastics with a low coefficient of friction. Generally, Teflon’s properties are inferior compared to other plastics and it generates toxic fumes when heated above 450ºC. It would be best to add appropriate fillers to remedy this condition. However, PTFE material is only available in 2” thick rods or plates, which limits the thickness of PTFE machined parts.

Nylon 66

Nylon or polyamide (PA) is a low-friction engineering plastic with high-impact strength, and good chemical and high abrasion resistance. Nylon 66 is a widely used CNC plastic due to its high strength and durability, which make it suitable for various applications in many industries, including medical devices and automotive parts. Nylon can be CNC machined because it is a strong plastic.

Nylon 66 can withstand extreme wear and tear and prevents oil and fuel damage. However, nylon 66 absorbs water very easily and exhibits low dimensional stability when it absorbs moisture. Also, it is susceptible when exposed to strong mineral acids.

HDPE (High-Density Polypropylene)

High-density polyethylene is a flexible, easy-to-machine plastic with excellent stress-cracking and good chemical resistance, even at low temperatures. It works great in corrosive environments. Its high impact strength and tensile strength make it ideal for common applications such as seals, electrical insulations, and plugs. However, HDPE exhibits poor UV resistance, making its surface fade and lose color.

UHMW (Ultra-high molecular weight polyethylene)

UHMW is a versatile engineering plastic famous for its high machinability, toughness, excellent abrasion, and wear resistance. It is an ideal option for industrial applications that require durable and low-friction plastics.

It would help to know that UHMW is highly susceptible to creep and isn’t ideal for use in working environments with temperatures exceeding 80 to 100ºC. Hence, it is incompatible with high-load applications. UHMW applies to making food processing machinery parts, marine dock fender parts, and truck bed liners.

Typical Industries that Use CNC Plastics

Product teams in many industries use plastics for several applications due to their excellent material properties. Here are common industries that use these plastic materials:

Automotive Industry

Automotive manufacturers use CNC-machined plastics to replace metals. Common polymers such as ABS, PVC, and PC are used for interior and exterior vehicle parts like bumpers, handles, and lighting components. Machined plastic parts are commonly used in vehicles due to properties such as impact resistance, low weight, and durability.

Medical Sector

Manufacturing experts in the medical sector utilize high-grade CNC plastics like Polyethylene, ABS, and acrylic to make medical instruments and implants like enclosures for medical devices, syringes, and pacemakers. Most plastic materials are biocompatible and can undergo various sterilization procedures, and most plastics, like PEEK, are biocompatible, making them suitable for implants.

Aviation and Aerospace

The aviation and aerospace sector uses CNC plastics such as PTFE and PEEK to make different aerospace parts and components due to their remarkable resistance to impact and corrosion. Engineers use these plastics for structural components because they can withstand heavy loads.

Food Processing

Food processing is one of the most popular industries that use CNC plastics. They use food-grade plastics like PC, PP, and HDPE for primary and secondary food packaging since they have high impact resistance and are a safe choice for storing food items.

Consumer Electronics

CNC plastics are suitable for making different components for electrical and electronic appliances. Product designers and engineers in this field use plastics like ABS and polycarbonate to create LCD screens and wire enclosures for devices such as laptops, TVs, smartphones, keyboards for remote, mobile phones, and laptops.

Helpful Considerations in Choosing the Right Material for Your Plastic Machining Projects

This section discusses factors to consider in choosing a suitable plastic for your project since material properties influence the machinability of these plastics. Here are some of them:

Hardness and Strength

It would be best to consider the hardness and strength of plastic to determine if it matches the requirements of the intended application. A material’s hardness and tensile strength affect the chip formation and surface finish during plastic machining.

For example, the high tensile strength of HDPE influences how it forms chips and its surface finish when machining. Manufacturers may experience gouging with low-rigidity plastics, such as polypropylene and PMMA. Hence, it is critical to take the necessary precautions.

Reaction to Chemicals and Moisture Absorption

Plastics like nylon, acrylic, ABS, and PC may absorb moisture from the air or react negatively with certain chemicals. As a result, you may have to store them in air-conditioned spaces or sealed bags. A plastic material’s dimensions may change due to the influence of chemicals and moisture, hindering the ability to meet precise tolerances. These factors can also deteriorate the strength and stability of these plastics.

Appearance, Light Transmittance, and Transparency

Appearance and other related properties like light transmittance and transparency are pivotal to a product’s design. As such, there are limits to compatible plastics for use in such situations because not all are transparent or transmit light.

Examples of plastics with light transmittance or optical transparency properties include acrylic, PC, and PE. In contrast, PEEK and PP are typical non-transparent plastics. However, taking precautions when machining these plastics would be best to avoid compromising the light transmittance or transparency with a rough surface finish.

Thermal Expansion and Heat Deflection Temperature (HDT)

Elevated temperatures affect almost all CNC materials, increasing their volume. Most plastics, including PE, PTFE, and ABS, have a higher coefficient of thermal expansion than metallic materials. Hence, a significant change in size is likely to occur due to the machining operations.

A plastic’s heat deflection temperature (HDT) represents the point at which it begins to deform easily when subjected to high temperatures. As a result, it would help to examine how the intended plastic would react to heat input from cutting tools during plastic machining and heat exposure in the working environment.

Conclusion

CNC plastics are readily available, cost-effective, and compatible with standard manufacturing processes such as CNC machining, 3D printing, and injection molding. However, it is essential to consider the material properties of these plastics during the material selection stage.

AT-Machining is the machining expert to consult whenever you need help choosing the suitable CNC plastic for your project. Our product designers, machinists, and quality control experts offer high-quality parts and components. We leverage our sophisticated 3-, 4-, and 5-axis CNC machines and machining experience to bring your design to reality precisely to your design specifications. Upload CAD files today for instant quotes!