CNC machining plastic is one of the popular machining processes across different industries. Manufacturers often make machined parts for diverse applications because of plastic material availability. Besides, the CNC machining process is more accurate and fast and offers the preferred tolerances in plastic machined parts since it uses computer numerical control to execute tasks.
However, there is a wide range of plastics with varying properties and chemical composition, hence the need to understand the process and determine the ideal plastic for your projects. This article discusses everything you need to know about plastic CNC machining, common engineering plastics, and standard machining processes.
What is Plastic CNC Machining?
Plastic CNC machining is a standard industrial process that uses Computer Numerically Controlled (CNC) technology to cut plastic materials into desired shapes and dimensions. This efficient and versatile machining process provides reliable results in making plastic parts that fit the intended applications. As such, manufacturers often use this process when alternative methods, such as 3D printing and injection molding, are unsuitable.
Common Plastics for CNC Machining
There are various machinable plastics compatible with CNC machining processes. Here are the typical plastics used for CNC machining.
Acrylic, also called PMMA or plexiglass, is a transparent thermoplastic material with remarkable impact resistance, and good tensile and impact strength. Its optical clarity or translucence property makes it an ideal material for light components, display screens, and intraocular lenses.
Moreover, due to its high transparency, polymethyl methacrylate (PMMA) is an ideal substitute for traditional glass. However, its brittleness makes it susceptible to cracking or shattering. Therefore, acrylic is unsuitable for CNC parts requiring very thin wall thickness.
Polytetrafluoroethylene (PTFE or Teflon)
Teflon is a high-performance plastic compatible with CNC machining processes. It exhibits a low coefficient of friction and anti-adhesive properties, making it a perfect material for different commercial products.
PTFE is commonly used for coating surgical equipment, making non-stick cookware, and making abrasion-resistant automobile coating. It has excellent cold and heat resistance and is available in a longer-lasting coating form. However, it can be quite costly and deforms easily under pressure.
ABS (Acrylonitrile Butadiene Styrene)
ABS is a versatile engineering thermoplastic polymer with broad applications due to its cost-effectiveness, high toughness, impact strength, and electrical resistance. It also provides good strength and chemical and thermal stability.
Product designers commonly use machining ABS for general-purpose plastic prototyping and machined parts such as control panels, keyboards, pipes, etc. However, ABS melts in organic compounds such as acetone. Heating ABS beyond 400 degrees Celsius can be harmful. Likewise, it exhibits poor weather resistance and response to ultraviolet rays.
PEEK (Polyether ether ketone)
It is a popular semi-crystalline organic thermoplastic with good mechanical properties suitable for various engineering applications. PEEK has no color in its pure form and has a melting point of 343 degrees Celsius. Its high melting point makes it a perfect material for CNC machining PEEK.
PEEK exhibits remarkable heat and chemical resistance and outstanding strength. As such, it is ideal for aerospace and automotive parts, medical implants, and pump bearings requiring chemical resistance and good strength. However, PEEK can be quite expensive and degrades in UV light.
POM (Polyoxymethylene) is one of the commonly used plastics in CNC machining. Its other names include Acetal and Delrin. This plastic is easily machinable and offers appealing physical properties. The typical applications of machining Delrin include bushings, fittings, safety restraints, and screws.
Manufacturers in most industries often use Delrin 150 and 570 for applications that require higher dimension stability and longer lifespan. However, it corrodes quickly in acids even though this plastic provides good resistance to chemical, weather, heat, and impacts.
Glass Filled Nylon（PA+GF)
Glass-filled nylon (PA+GF) is another popular engineering thermoplastic that easily meets the demands of several application areas. This material offers high creep strength, excellent dimensional stability, high mechanical damping, and good fatigue strength.
It can be challenging for CNC machine glass-filled nylon due to its high abrasive properties, resulting in increased tool wear. However, you can attain the desired results by machining the material carefully and correctly using carbide tools. Typical applications of this material include windshield wiper parts, speedometer gears, water purifiers, and wire housings.
Factors to Consider When Choosing Plastics for CNC Machining
This section discusses helpful considerations for choosing the right material for your CNC plastic machining projects. Here are some of them:
Appearance, Transparency, and Light Transmittance
When choosing compatible plastic materials for your project, you may have limited options when physical properties such as light transmittance or transparency are crucial parts of your design because most plastics are not transparent. Polypropylene and PEEK are apt examples of opaque or non-transparent plastics.
However, you must be careful with the machining process not to affect the material’s light transmittance or transparency in plastic such as acrylic, PE, or PC with a rough surface finish.
Moisture Absorption and Reaction to Chemicals
Some plastics like acrylic, nylon, and PET can take in moisture from the air or CNC coolants or can be adversely affected by certain solvents. Therefore, you may even have to store these plastics in air-conditioned rooms or enclosed bags.
Besides, moisture and chemicals can influence a material’s dimensions, hindering the ability to meet required tolerances. The stability and strength of the plastics may deteriorate.
Strength and Hardness
The intended plastics’ strength and hardness properties are crucial when choosing the ideal plastic for your project to ensure your machined parts meet the required standards. However, these material properties may influence the behavior of the plastic workpiece during machining.
The tensile strength of plastic such as HDPE may affect how the chip forms during machining, influencing the final surface finish. Similarly, the hardness of a material can impact the way chips form. As such, gouging can occur if a machinist refuses to take necessary precautions when machining less-rigid or softer plastics like acrylic, PP, PE, etc.
Thermal Expansion and Heat Deflection Temperature (HDT)
CNC machine tools used in machining plastic materials generate heat. Plastic materials like PC and PVC have a higher coefficient of thermal expansion than metals. Hence, their size can change significantly due to machining.
Therefore, examining how each intended plastic reacts to heat input during CNC machining is essential. Similarly, you should consider the amount of heat the machined plastic parts will be subjected to to determine their heat deflection temperature.
Different Plastic CNC Machining Techniques
Product designers and machinists adopt different CNC plastic machining processes in plastic fabrication. Below are some of these processes:
CNC plastic milling is a common rapid prototyping technique in machining plastic components. It involves rotating the tool cutter while the workpiece material maintains a fixed position. The corresponding speed of the cutting tools allows this machining process to offer high precision and accuracy cuts as it removes plastic material at a uniform production rate.
The CNC milling process is ideal for milling plastic parts with flat and irregular shapes since it uses a single-point cutting tool capable of working on many axes. However, the number of axes a CNC mill supports will determine its flexibility and ability to make complex parts.
CNC turning is a process that uses a fixed CNC tool to cut material from a rotary plastic workpiece on a CNC lathe to form the desired shape and dimension. Although this process is commonly used to machine cylindrical-shaped workpieces, it is suitable for working different shapes in plastic workpieces.
CNC drilling involves making holes in different sections in a plastic material with cutting tools such as CNC drills. However, the type and shape of the CNC drill determine the sections made in plastic workpieces.
Manufacturers often use multipurpose CNC machines in drilling because they can perform certain turning and milling operations. Hence, you need an expert like XC Machining to operate these CNC drilling machines for a cost-effective CNC drilling of plastic components.
Surface Finishes for Machined Plastic Parts
Various surface finishes are suitable for improving your CNC-machined plastic parts’ surface aesthetics and performance. Here are some of these finishes:
Machined plastic parts with this finish often bear minor visible tool marks since that’s how they come out of the CNC machine; they often have the standard surface roughness (Ra) of 3.2, 1.6, 1.8, and 0.8µm. This surface finish helps manufacturers to keep CNC machining costs at a minimum. It is perfect for manufacturers working with a tighter budget.
Powder coating provides additional wear and corrosion resistance to the surface of plastic parts. It offers higher impact resistance properties and a wide range of color options.
Vacuum metalizing or vacuum deposition is a process that adds vaporized metal material like aluminum on the surface of machined plastic parts in a vacuum chamber.
It involves shooting abrasive media, such as tiny fine glass beads, at high pressure against the surface of CNC plastic parts to improve its visual appearance.
It involves applying liquid paints (polyurethane and lacquer) on plastic parts with different colors. This surface finish is well-suited for improving the lifespan of machined plastic parts by preventing corrosion and abrasion.
Advantages of Using CNC Machining Plastic
CNC machining plastic is a versatile plastic prototype and final product manufacturing method. Manufacturers often use this process in different industries due to the diverse benefits. Below are some of the expected benefits of CNC plastic machining.
Dimensional Accuracy and Precision
CNC machining plastic process provides high accuracy and precision for producing your plastic parts. The method uses multi-axis CNC machines to achieve the desired engineering tolerance. Since a computer controls this process, you can quickly achieve intricate designs in CNC machined plastic parts with the utmost precision for industries like healthcare and aerospace.
Compatible with Several Plastic Materials
CNC plastic machining processes are compatible with a wide range of engineering-grade polymers. These machining processes are often suitable for machining different material textures, including rigid or flexible plastic materials, for various applications.
Suitable for Handling Complex Designs
CNC plastic machining processes are suitable for making plastic components with complex or simple designs. Plastic CNC machine tools offer the required precision and accuracy to effectively handle intricate designs in fabricating plastic parts. Besides, plastic CNC machining facilitates the production of custom plastic parts for specialized purposes.
Faster Turnaround Time
The processes involved in CNC machining plastic ensure an optimized production cycle and faster time-to-market of your machined plastic parts. The machining process is fast and efficient since it machines parts directly from plastic sheets and rods. Unlike other techniques, CNC machining doesn’t require mold creation. Hence, you can make plastic machined parts faster with CNC machining than alternative methods.
Challenges and Tips for Plastic CNC Parts
Although you can easily machine CNC plastic parts with the desired precision and accuracy, here are some likely challenges you may encounter.
Usually, polymers have about one-tenth the melting point of metals. These plastic parts will likely build up heat, resulting in higher temperatures since they do not conduct heat like metals.
However, use water or oil coolant and lubricant to mitigate heat. Likewise, adjust the feed rate and speed of the tooling. You can also use sharp CNC cutting tools with polished upper surfaces to reduce heat build-up.
Deflection during Machining
Plastic polymers such as polyethylene and polycarbonate become more elastic than metals when machining at elevated temperatures. Hence, deflection occurs instead of cutting when machining plastic CNC parts.
To address this, you can use the appropriate CNC fixtures to hold the plastic workpiece in position during CNC machining. Use sharp CNC tools with lubricated flutes and optimized speed and feed for better cuts. Similarly, apply lubricants or coolants to minimize friction and heat.
Burring is one of the common faults or flaws of machining plastic CNC parts due to the softness of plastics. Burrs are tiny raised edges on plastic components that occur when cutting tools fail to neatly remove materials from the workpiece. Therefore, it impacts the surface finish and accuracy of the machined plastic parts. However, you can easily eliminate these burrs by deburring or machining extra passes.
Poor Chip Extraction
Plastic materials can generate chips that can glue the flutes of milling and drilling tools when they are not extracted immediately from the cutting zone. Poor chip extraction hinders cutting efficiency, increasing the surrounding plastic’s temperature. However, CNC machining coolants effectively remove chips quickly and reduce heat during machining.
Applications of CNC Machined Plastic Parts
CNC-machined plastic parts have a broad range of applications. Here are its typical applications.
CNC-machined plastic medical parts such as implants, disposable syringes, blood bags, heart valves, etc., are commonly used in the healthcare sector.
Similarly, high-grade plastics such as ABS, PMMA, and polyethylene are used to make CNC-machined enclosures of medical devices such as vitals monitoring and pacemakers. These CNC-machined plastic parts possess surface finishes that resist wear and stress cracking.
Engineers and product designers in the automobile sector often use CNC-machined plastic parts and prototypes. CNC-machined plastic automotive components are used to reduce weight and as a suitable alternative to metal in certain situations.
These parts are often used for interior vehicle parts like dashboards, handles, and lining. At the same time, the exterior parts used include bumpers and lighting components. Electronic housing and engine covers are other miscellaneous machined plastic parts used in automobiles.
Most plastic polymers such as PEEK, PVDF, and PTFE exhibit high corrosion and impact resistance required in aerospace applications. Hence, some structural components used in the aerospace sector are made with thermosetting polyimide since they can withstand extreme pressure.
Oil and Gas Industries
Plastic materials such as PTFE, nylon, PEEK, PC, etc., are commonly used plastics in the oil and gas sector due to their remarkable chemical resistance. Manufacturers often create containers and seals for oil extraction and storage with plastic polymers. Likewise, CNC-machined plastics are used as electrical connectors in heavy mining machinery.
Electrical and Electronics Appliances
CNC-machined plastic parts are used for casing, device keypads, LCD screens, and wire enclosures for electrical and electronic appliances like TVs, smartphones, laptops, remotes, etc. In addition, circuit breakers for electronic devices often feature nylon spacers, which provide insulation against electricity and moisture.
Plastic is a popular choice in the food processing industry for primary and secondary packaging. CNC-machined food-grade plastic containers are a safe option for storing food items. At the same time, plastic parts like food trays offer impact-resistance transportation for food items.
How to Find a Reliable Partner for Plastic Machining Services?
Partnering with a reputable CNC shop that specializes in precision plastic machining is crucial to the success of your plastic parts machining project.
Such a partner must have experience handling custom plastic fabrication and advanced CNC technology capable of handling the complexities of your project design. Ensure the shop has required ISO certifications and can deliver quality plastic CNC machined parts within the required time.
XinCheng is an expert with a team of skilled machinists and engineers with experience machining various materials, including metals and plastics. We provide reliable and one-stop CNC machining services to ensure make your machined parts on time and within your budget. Contact us to learn more about our plastic machining services and get a quote for your project!
Plastic CNC machining is a relevant machining process in every significant industry since CNC-machined parts are used everywhere. However, there are different plastic CNC machining materials with varying material properties. Therefore, it is critical to understand the various factors involved in plastic CNC machining to execute your project.
What are the alternative processes to plastic machining?
Injection molding, vacuum casting, and 3D printing are the standard alternative processes to CNC plastic machining.
What are the common limitations of plastic CNC machining?
It might be challenging to achieve tight tolerances in plastic CNC machining due to plastic material’s thermal expansion. Likewise, CNC machining processes often generate heat, which could lead to warping, cracking, melting, and deformation of CNC plastic parts.
Which plastic material Is mostly used for CNC machining?
Polyoxymethylene (POM) or acetal is the most widely embraced plastic material for CNC machining due to its remarkable stiffness, strength, and dimensional stability. As a result, electronics, industrial machinery, and automotive manufacturers use acetal for precision CNC plastic parts.