CNC machining is a perfect match for various metals. It’s known to expertly craft a range of durable components for assorted industries, from aluminium to steel to copper, but metal isn’t the only suitable material.
In fact, CNC machining is compatible with plenty of plastics. Acrylic, ABS, and polycarbonate are all ideal for various applications, forming parts that offer similar strength and precision to metal, especially when paired with the precision and accuracy of CNC mills, drills, lathes, and other plastic CNC machines.
Reasons to choose plastic
The best part about plastic machining is that there are so many kinds of plastic that you can use. Each type of plastic offers its own properties and benefits, meaning there’s almost always one to suit your project needs. This makes it a popular option for various industries and applications, especially in sectors searching for practical alternatives to metal.
Applications
While plastics’ uses vary, they’re often found in medical appliances, automobiles, aircraft, and insulating components for electrical devices.
That said, there are specific plastics that are better for certain applications. For instance, while polycarbonate is a good option for safety glasses, CDs and DVDs, and transparent panels in garages, greenhouses and bike sheds, polypropylene is better suited to both flexible and rigid food packaging, plastic bottles and bottle caps, and mechanical components.
Versatility
Different plastics are defined by their physical properties and chemical makeup. These factors play a significant role in determining which plastics are suitable for specific applications and which don’t meet the criteria.
Plenty of plastics are compatible with CNC machining, but six standard options are ABS, acrylic, nylon, HDPE, polypropylene and polycarbonate.
- ABS: ABS (Acrylonitrile Butadiene Styrene) is a popular general-use plastic with high impact strength and toughness. Components are easily cut and engraved with CNC mills and lathes, then finished with a matte or shiny coat and painted after the fact. ABS also offers high electrical resistance while remaining affordable, making it perfect for prototyping and household appliances. However, it’s not the most UV-resistant and may present difficulties in machining due to its high coefficient of thermal expansion.
- Acrylic: Like ABS, acrylic is suited to CNC milling and turning, offering a range of tough, high-impact-strength parts. Its UV stability prevents yellowing in sunlight, perfect for outdoor applications and those needing glass substitutes. These include transparent tanks, panels, and automobile components. Even so, some types of acrylic can scratch easily and aren’t heat-resistant.
- Nylon: Nylon is a durable and versatile option with good chemical and heat resistance. It can keep its shape and is ideal for various applications, including insulations and circuit breakers. It can be machined using CNC mills and lathes. Nylon has a range of grades available, though nylon 6/6 is one of the most popular for CNC machining with its strength, durability and low price point. It’s important to note that nylon is hygroscopic, which means it absorbs moisture and may swell or deteriorate in humid or wet environments.
- HDPE: Its high chemical resistance, electrical insulation and waxy finish are only a few properties that make HDPE (High-density Polyurethane) so popular. HDPE also has a low coefficient of friction while being durable and affordable, which means its components are suited to a range of fluid applications, as well as those that are weight- and electrically sensitive. Despite its benefits, it often lacks UV stability and can be prone to stress in certain environments.
- Polypropylene: Polypropylene is an excellent option for packaging, medical equipment and machine parts that require good chemical resistance, particularly when exposed to corrosive environments, cleaning agents, solvents and moisture. It is easy to machine and offers good dimensional stability that maintains its shape. However, it’s not ideal for parts that need painting or sit in direct UV light, so you may want to consider something else for those applications.
- Polycarbonate: Polycarbonate is one of the most common CNC plastics, with transparent surfaces that offer high-impact strength, toughness, and recyclability. It can be machined using CNC mills and lathes to craft safety glasses, transparent panels, and even CDs and DVDs. While pure polycarbonate doesn’t have the best scratch resistance, it can be coated for added wear resistance.
Other plastics include Delrin, PEEK (Polyetheretherketone), and PTFE (Polytetrafluoroethylene). Each is advantageous in its own way.
Derlin offers high machinability and strength with fantastic wear, weather, heat, fuel, and chemical resistance. PEEK has a lightweight structure that is durable enough to withstand harsh conditions and chemicals and is insoluble in common solvents. Lastly, PTFE has excellent anti-adhesion properties and can resist wear, light, chemicals and temperatures.
Surface finishes
Plastic machined parts can offer different surface finishes depending on their physical properties and manufacturing processes. Pick the appropriate cutting speed and feed rate for the type of plastic used for a good surface finish. You should also hold the workpiece securely; vibrations can cause imperfections.
If your plastic components require a more advanced surface finish, annealing, powder coating, or sandblasting can achieve this.
Do CNC machining and plastics work well together?
One of the biggest appeals of plastics is their variety. Each type of plastic offers a different structure with different physical properties, rendering them perfect for forming various components.
While plastics’ lightweight structures and denseness might make processes like 3D printing and injection moulding more challenging, these attributes suit different CNC machining processes, including milling, drilling, and turning.
CNC machining makes it even easier to manufacture plastic parts — especially when high precision is required for complex designs with tight tolerances. This is because, once given the correct G-code and instructions, CNC machines easily and quickly cut away at the plastic workpiece and produce designs that can be repeated in batches. As a result, CNC plastic components are manufactured consistently and accurately, making them ideal for prototypes and custom parts. This means that CNC plastic machining boosts production and limits the physical labour required for manual machining methods.
The benefits of plastic CNC machining
As mentioned, plastic is a versatile material. Not only is there a vast assortment of plastics on the market, each meeting the needs of different industries, customers, and designers, but they each present a typically lightweight, corrosion-resistant, and insulative alternative to metals. They produce parts for applications in specialised environments, electronic and electrical devices, and places where heavy components are unsuitable.
Plastics are generally cheaper than metals, too. They offer good corrosion resistance and durability and often require low maintenance, making for long-lasting, cost-effective parts. Plastics are typically more flexible, outperforming more rigid materials like metal and glass, and many can be recycled after use.
When combined with the accuracy and precision of CNC machining, plastics produce high-quality shapes and designs. Parts can be easily machined with minimal human error, waste and labour costs while improving finishes due to precise cutting tools, optimised speeds and feed rates, and reduced vibration.
Drawbacks of plastic CNC machining
Plastic CNC machining can pose a few problems. Since many plastics are soft and melt at lower temperatures than metal, they aren’t always best suited to high-load and high-stress applications. The heat formed in plastic machining processes can also cause warping, deformities, and chipping.
Burring and cracking are common challenges in plastic CNC machining, especially where sharp corners, thin cross-sections and soft structures are present. Not only does this prevent you from achieving tight tolerances and smooth finishes, but the plastic chips often gather and stick to parts of the machine, too. Any inconvenient build-ups of material can hinder the cutting process further, as changing out worn tools can cost you extra money and time, causing delays.
Luckily, there are some easy fixes to the challenges plastics can present. When machining plastic, the appropriate cutter and tool path must be selected to reduce cracking and chipping. As for burring, burrs can be removed using de-burr operations or by machining extra passes.
You can also consider:
- Hardness and strength: To reduce the risk of warping, consider the softness of your material. The chosen plastic should be strong and hard enough to withstand the machining process and application. Otherwise, the machined plastic parts won’t last.
- Chemical and moisture resistance: Certain plastics absorb moisture or react badly to chemicals, impacting dimensions and tolerances. They can also cause the components to deteriorate or reduce their strength and durability. Chosen plastics should always be suitable for their environment.
- Thermal expansion: Since many plastics have a higher coefficient of thermal expansion than metals, their size can vary during machining. To prevent this, heat deflection temperatures should be considered to determine which plastics deform in the high heat from cutting tools and work environments.
- Physical appearances: Some applications require materials that let light through. This is why transparent plastics like polycarbonate and acrylic should be considered. Rough surface finishes can affect their optical clarity, so care should be taken when machining plastics.
Is plastic CNC machining worthwhile?
In this guide, we’ve discussed plastic CNC machining and its benefits. These include precision, repeatability, and compatibility with several plastic materials to produce complex designs with tight tolerances and high standards. We’ve also covered plastic CNC machining’s drawbacks, like thermal expansion, warping and burring, and how these risks can be reduced with appropriate material selection, tool paths and machining parameters.
There’s no doubt that plastic CNC machining proves a versatile and cost-effective way to manufacture high-quality plastic parts for a wide range of industries, especially for applications where corrosion resistance and lightweight structures are a must. So, whether you’re looking to produce prototypes or final products, CNC machining plastic is a worthwhile choice.
Supporting UK businesses
Are you looking for support with your project? Sheldon Precision is here to help. With a full CNC manufacturing facility, we provide premium service that meets exact customer specifications, whether that’s for plastic machining services or various metal options.
Contact us today for more information.