CNC Plastic Material Selection Comprehensive Guide

Do you often need to choose the right CNC machining technology for custom plastic parts in your projects? Plastic materials that can be manufactured using CNC machining each have their own unique advantages, and choosing the right plastic can be overwhelming. The right plastic can improve the durability, precision, and performance of your parts. Let’s delve into the world of CNC plastics and learn how to find the ideal material to meet your machining needs.

What is CNC plastic machining?

CNC machining of plastics is a process that uses computer programs to control the cutting of plastic materials instead of relying on manual cutting. This removal process is also known as subtractive manufacturing because the machine removes plastic material from the part. This plastic material is then cut into the desired shape. Machining is a primary technology used in the manufacturing processes of many custom precision plastic parts . Computer Numerical Control (CNC) machining technology is widely used in the mass production of all kinds of plastic parts in many industries , especially for parts requiring precise dimensions. This computer-aided machining technology is particularly common in the military and aerospace fields because these fields have high precision requirements for plastic materials. CNC machining brings significant advantages to the manufacturing industry. Due to the automation of the machining process, each cut is consistent, thus ensuring quality control of mass-produced plastic products. These machines can operate almost automatically, so workers can be away from the machines while operating them. At the same time, the automation of the production process can also significantly promote business growth.

How to choose plastic materials for producing custom parts using CNC machining technology ?

CNC machining is a method for automating the mass production of precision plastic parts. These machines can process not only plastics , but also a variety of materials such as metals and wood, and produce parts more efficiently than other technologies. People are using these machines to create complex shapes while ensuring every detail is flawless. Time and again, businesses are choosing plastics. Plastic is a primary material for manufacturers to produce their products. Plastic materials remain a popular choice for manufacturers due to the following characteristics: cheaper and more durable. Compared to other options, manufacturing plastic parts using CNC machine tools allows you to manufacture the parts you need precisely to specifications at a lower cost. In addition to being more economical, using plastic materials also offers faster turnaround times and tighter tolerance control. This characteristic makes it ideal for high-precision manufacturing, especially when prototyping is crucial. These advantages make plastic a popular material for prototyping and custom parts. Even manufacturers with little experience with machinable plastics find these materials easier to handle when using CNC machining. For most manufacturers, the choice of plastic material is critical.

Commonly used plastic materials, properties, and applications in the production of custom parts using CNC machining technology

The most popular types of plastics on the market today include several common materials listed in the table below. The table not only summarizes the properties of the relevant materials, but also summarizes Elimold’s experience in manufacturing different parts using different plastic materials over the years.

Application scenarios	Recommended materials	reason
Gears, bushings, sliding parts	POM (Synergy)	POM is the easiest engineering plastic to process, has a low coefficient of friction, is dimensionally stable, and has a moderate cost. It is sufficient for 80% of plastic structural components.
Wear-resistant liners, guide rails, and pads	UHMWPE	It has excellent abrasion resistance, is extremely lightweight (density 0.93), and costs significantly less than PTFE. Food-grade is available.
Bearings, pulleys, load-bearing structural components	PA66 (Nylon)	It has good toughness, wear resistance, and higher strength than POM. However, its tendency to swell after absorbing water is a major drawback, so precision parts must be dried in advance.
High-temperature resistant structural components (200°C+)	PEEK	It can be used continuously at 260°C and has good chemical stability. However, the material is expensive (more than 10 times that of POM) and causes significant tool wear.
Electrical insulation + High temperature (170°C)	PEI (Ultem)	Flame retardant with high dielectric strength. Cheaper than PEEK. Commonly used in PCB substrates and electrical enclosures.
Seals, low-friction bushings	PTFE (Teflon)	It has the lowest coefficient of friction (0.04) and unparalleled chemical resistance. However, it is extremely difficult to machine; if injection molding is possible, avoid machining.
Transparent components, protective covers, viewing windows	PC (Polycarbonate)	Highly transparent and impact-resistant. However, it is easily scratched and not resistant to chemical solvents.
It needs to be insulating, transparent, and impact-resistant.	PC	It’s much tougher than acrylic and less likely to break. Aircraft windows and safety masks are made of PC.
Semiconductors / Medical Implants / Aviation	PEEK	Biocompatible, sterile resistant, and certified levels are available. However, lead times are long and prices are high, so please confirm whether it is truly necessary first.
Limited budget + large volume	POM or HDPE	POM has the highest processing efficiency (saving machine time), while HDPE has the lowest material cost. For large-volume production, injection molding is more cost-effective.

How to choose the right plastic for your CNC machining project

When selecting the right engineering plastic for your project, you should consider the following factors;

Hardness and strength

The hardness and strength properties of specific plastics are important considerations for ensuring their performance meets the requirements of their end applications. High-hardness plastics generally have better abrasion resistance, while high-strength plastics can withstand greater mechanical loads. Furthermore, these properties affect how the material behaves during processing. Plastics with higher hardness and strength, such as POM, PEEK, and glass fiber reinforced PA, tend to produce short, regular parts and achieve high surface finishes. However, cutting is more challenging, and tool wear occurs more quickly. In contrast, softer or lower-strength plastics such as PP, PVC, and PTFE produce long, gritty scraps during processing that can easily entangle tools . These materials are prone to adhesion and digging, leading to surface quality issues.

Absorption of moisture and reaction to chemicals

Unlike most metals, which do not absorb moisture from the air under normal conditions, many plastics (such as PA and PC) do absorb moisture from the atmosphere or coolant. This can cause dimensional expansion, affecting CNC machining accuracy. Moisture can also soften plastics, reducing their toughness or releasing internal stress, all of which affect the durability of parts. To prevent brittleness or machining defects, these plastics may need to be stored in air-conditioned rooms, sealed bags, or dried beforehand. On the other hand, plastics are generally resistant to most acids, alkalis, and salts. For example, PTFE is virtually inert to all chemicals, even in harsh environments. However, some plastics (such as ABS) are susceptible to solvents, such as acetone, which can dissolve surfaces, while PC may crack in alcohol or alkaline solutions.

Thermal expansion and thermal deflection temperature (HDT)

Plastics expand when exposed to heat, a property measured by their coefficient of thermal expansion (CTE). Plastics typically have a higher CTE (50–250 × 10⁻⁶/°C) compared to metals, while for materials like steel and aluminum, plastics typically have 10–25 × 10⁻⁶/°C. A higher CTE results in greater dimensional changes due to heat during CNC machining, which can affect accuracy. For high-precision applications, such as aerospace and medical devices, plastics with high CTE (such as POM and PTFE) may require design compensation to maintain accuracy. Conversely, low-expansion materials (such as PEEK or glass fiber-reinforced composites) can help minimize thermal distortion.

Additionally, thermal deflection temperature (HDT) measures a material’s resistance to deformation under load at elevated temperatures. Generally, the HDT of plastics corresponds to their stiffness , and materials with higher stiffness (such as glass fiber reinforced plastics and polyimides) tend to have higher HDT values, while more flexible polymers (such as PE and PP) have lower HDT values. Plastics with higher HDTs maintain dimensional stability at higher temperatures, ensuring parts function as intended. However, most plastics have significantly lower HDTs than metals. Their range typically falls between 50°C and 250°C, with only a few high-performance engineering plastics (such as PEEK and PAI) reaching around 300°C.

Mechanical properties

Understanding the mechanical properties of the plastics used in CNC machining projects is crucial. For example, polymers like PEEK and nylon offer high strength and good abrasion resistance, making them suitable for load-bearing components. On the other hand, acrylic is a polymer designed for flexibility and transparency, not thumb resistance. Therefore, choose materials that meet the mechanical requirements of the application.

Corrosion resistance

If your project involves chemicals, moisture, or extreme conditions, then CNC-machined plastics with extremely high corrosion resistance are recommended. Chemicals are best handled with PTFE (Teflon) and PVC plastics, while high-density polyethylene is best suited for high-humidity areas. Choosing the right plastic ensures reliability and functionality for many years.

thermal expansion

Let’s examine the behavior of the plastics under discussion in response to temperature changes. For example, PEEK materials have low thermal expansion, making them suitable for high-temperature applications. On the other hand, some CNC materials, such as PP, may expand more than expected due to temperature changes.

Cost and availability

Cost and material availability are typically key factors influencing decisions. General-purpose plastics like ABS and PP are cheaper and more readily available. Specialty materials such as PEI or PEEK are more expensive but offer specific advantages. A good balance between performance and budget is important.

Surface finish requirements

When visually inspecting anything, aesthetics and surface quality must be considered. In terms of ease of use, high tensile strength materials like POM are suitable for applications requiring simplicity. The final result must be harmoniously balanced in terms of function and aesthetics.

Cost considerations

The cost of materials can vary significantly depending on the type and quantity you need. Plastics generally offer better budget options compared to metals . Budgeting is crucial. It helps you choose what you can afford and stay on track. CNC machining is relatively expensive and time-consuming. Therefore, in projects involving different plastic materials, money and time are influenced by many factors , including the complexity of the work, the type of resources used, and the machines required. Choosing cheaper tools that can still get the job done can help reduce the overall cost of manufacturing the product. Therefore, the cost of the materials chosen also affects the quality of the final product. Cheaper options may have problems or break down faster than more expensive ones. Therefore, choosing high-quality materials and managing your budget wisely is essential to ensuring the final product is durable and meets high standards.

Other factors to consider when selecting CNC plastic materials

The paragraphs above describe the basic factors to consider when selecting plastic materials for CNC machining projects. In addition, other factors need to be considered, including the following three points.

Required tolerance

Achieving accurate tolerances in CNC machining is crucial. It significantly impacts our choice of plastic materials. The required acceptance levels for a project dictate the quality of the material, and some applications demand very strict limitations. Generally, more rigid plastic materials are chosen because of their mechanical strength, which allows them to remain stable during the manufacturing process. Their behavior is highly predictable. These plastic materials are stable and provide accurate results. This makes them suitable for projects requiring precise adherence to measurements. Understanding how plastic materials react to hot or cold weather is also important . This is particularly useful during the manufacturing process, such as when heat affects how things are properly assembled.

Post-processing

Considering what happens after the machine has worked is crucial to ensuring the finished product meets the requirements of all CNC plastic parts projects. Different plastic materials may require additional steps or treatments to improve their quality or meet industry regulations. These processes can include surface changes, heat treatment, covering, or further machine work after the machine has finished its job. Choose a suitable plastic material that matches what you will be doing after using the machine . Consider whether it fits the specific processes and requirements of the entire project. Factories such as automakers, aircraft manufacturers, and medical device manufacturers often require these additional steps to meet high-quality standards. This demonstrates how important the choice of plastic material is throughout the manufacturing process.

Environmental conditions

plastic materials for projects using CNC machine tools , environmental factors must be considered. Different places present different challenges. Therefore, we need exceptional plastic products that can perform well and last a long time in these environments. Corrosion resistance is crucial, especially in areas where parts are near water, chemicals, or harsh weather. In these cases, different plastic materials are often chosen to prevent them from deteriorating over time. Another important consideration is temperature stability, particularly for tasks in extreme environments, whether hot or cold. For these applications, plastic materials must possess thermal stability to perform well at varying temperature levels. In fields such as marine engineering, plastic parts are frequently in contact with saltwater and must be protected from rust, making it essential to withstand the challenges posed by nature. In certain applications, such as medical devices or parts that come into contact with the human body, it is crucial to make the material conform to the body. Materials like PEEK , which conform well to the body, are indispensable. They prevent adverse reactions and ensure the safety and proper functioning of medical components.

Why should the working conditions be considered first when selecting engineering plastics for CNC machining?

Engineering plastic parts are not necessarily “the stronger the better,” nor are they “the more expensive the more stable.” Different materials have different strengths in rigidity, toughness, heat resistance, water absorption, friction performance, and processing stability. For precision CNC plastic parts, the truly suitable material should match the part’s usage environment, assembly method, dimensional requirements, and production volume. In engineering plastic CNC machining, the Elimold team typically starts with drawings, samples, and application scenarios, combined with the part’s structure, wall thickness, hole positions, tolerances, and appearance requirements to help customers establish a clearer initial material selection direction before prototyping, reducing repeated trial and error.

Advantages and disadvantages of commonly used CNC plastics

These plastic types can meet the needs of almost any customer in any situation. Manufacturers can choose from a variety of plastics for machining, each with its own advantages. Since one of the primary considerations when selecting materials for machining is ensuring that the chosen plastic has the appropriate properties, it is essential to understand the main advantages and disadvantages of commonly used CNC machining plastics.

Acrylic resin (PMMA)

Acrylic, commonly known as “plexiglass,” is a synthetic polymer of polymethyl methacrylate (PMMA). It has high impact resistance and is not easily broken. Acrylic has a higher transmittance of visible light than glass. However, it is also prone to cracking and scratching. This material is often used because of its optical transparency or as a more economical, though slightly less durable, alternative to polycarbonate. This is partly why it is only suitable for low-stress applications such as solar panels.

High-density polyethylene (HDPE)

High-density polyethylene (HDPE), sometimes also called high-density polyethylene (PEHD), is a thermoplastic polymer in the polyethylene family. This material is impact-resistant, corrosion-resistant, and chemically resistant, with low moisture absorption and high tensile strength. Due to its high density and impact resistance, HDPE is often used to manufacture building components such as pipes. It is also used in the development of commercial containers and household goods, such as cutting boards, trash cans, and laundry detergent cartons. While this plastic material has many advantages, its UV resistance is relatively poor. In CNC machining, it is often used for prototyping and casing manufacturing.

PVC

Polyvinyl chloride (PVC) is a rigid thermoplastic polyvinyl chloride polymer with excellent acid resistance. Furthermore, PVC is generally readily available, high in density, and inexpensive. Its excellent resistance to deformation is one of the main reasons for its widespread popularity. However, PVC has a working temperature of 176°F (approximately 80°C), meaning it has poor thermal stability and releases toxic gases when melting. Due to its remarkable versatility, PVC is used in numerous industries, including construction, automotive, and plumbing.

polyvinylidene fluoride

PVDF is a robust polyvinylidene fluoride polymer commonly used in high-tech applications, such as chemical processing equipment. Due to its high purity, it possesses wear resistance, chemical corrosion resistance, and flame retardant properties. Any machine processing this plastic must be kept clean to ensure its purity. Because of its corrosion resistance, PVDF is used as a pipe and internal coating.

Polycarbonate (PC)

Polycarbonate is a type of thermoplastic polyester with flame-retardant and virtually indestructible properties. Its lightweight nature makes it sustainable and easy to process. However, it is susceptible to degradation by ultraviolet (UV) radiation. This plastic is ideal for manufacturing products such as bulletproof glass, bumpers, and LED screens because these products require plastics with high strength and high transparency.

Polypropylene (PP)

Polypropylene (PP) is a thermoplastic polymer with excellent chemical resistance and fatigue resistance. It is widely used in many applications because it can be used as both a plastic material and a fiber. PP plastic is readily available and inexpensive, and is commonly used in consumer product packaging and automotive manufacturing.

Polytetrafluoroethylene® (PTFE)

Teflon is a synthetic fluoropolymer of polytetrafluoroethylene with extremely high resistance to both high and low temperatures. It is commonly used in bushings and bearings and has high dielectric strength. However, it is susceptible to creep, cold flow, and compressive stress, all of which can affect seal integrity. Due to its high machinability, Teflon is well-suited for manufacturing oil pans, lubricants, seals, and gears.

Ultra-high molecular weight polyethylene (UHMWPE)

Ultra-high molecular weight polyethylene (UHMW) is a thermoplastic with excellent toughness, boasting the highest impact strength of all thermoplastics. Due to its high strength, chemical resistance, and extremely low coefficient of friction, UHMW’s performance is comparable to Teflon. UHMW is widely used in the food and beverage industry due to its chemical resistance and odor resistance.

CNC machining techniques for plastics

In CNC machining of plastics, there are several common techniques, including milling, turning, and drilling. Each method has its advantages and best practices:

CNC Milling

CNC Milling is a versatile machining method that can create complex shapes and features. When milling plastics, sharp cutting tools are used, and proper chip removal is maintained to prevent material buildup and melting.

CNC milling process

The CNC milling process can be divided into three main steps:

Step 1: Prepare a 2D or 3D CAD model	Your program will determine how to set up the CAD file for CNC machining. The finished product can be designed in 2D or 3D and then machined using CAD/CAM software.
Step 2: Convert your design to a CNC-compatible file format.	CAD/CAM programs require you to export your CAD model to a CNC-friendly file format. The converted file will indicate the machine tool’s rotational and linear motions, cutting sequence, toolpath, and machine and workpiece speeds.
Step 3: Configure and run the CNC milling machine	After the workpiece is placed on the worktable, the operator mounts the cutting tool onto the spindle. The machine tool is then configured to start the machining program and milling begins.

CNC Turning

CNC Turning is suitable for manufacturing cylindrical parts. When turning plastics, ensure the tool geometry and depth of cut are correct to minimize friction and heat generation.

CNC plastic turning process

CNC turning processes can be very complex. However, we will provide you with a simplified, step-by-step overview of the process from design to production.

Step 1: Convert CAD design files into CNC programs	The first stage requires preparing to convert the CAD files into CNC lathe language. Production engineers can then use this program to test the manufacturability of components.
Step 2: Install the CNC lathe	The machine setup process is the next stage. Although most operations are automated, an operator is still required. Because incorrect estimations can affect the final product, the machinist must calculate the appropriate speed and feed rate of the machine. Furthermore, incorrect calculations when using specific materials can lead to permanent damage to the workpiece or uneven surface finish.
Step 3: Manufacturing CNC-machined parts	Manufacturing the product is the final stage. Depending on the desired result, you can choose from a variety of turning programs. The raw materials used throughout the manufacturing process will determine the final product. The function and surface roughness of plastic parts will differ from those of metal parts.

CNC drilling

CNC Drilling is used to create holes in plastic materials. When drilling plastic, use a slow auger bit with wide helical flutes to effectively remove chips and ensure an appropriate cutting speed to prevent melting.

CNC plastic drilling process

Step 1: Create a CAD file	Creating CAD files for CNC-drilled parts using software such as Autodesk Inventor or SolidWorks is the first stage of the drilling process. Technical details of the component, such as tolerances and dimensions, are sent to the operator via the CAD file.
Step 2: Convert your design to a CNC-compatible file format	CNC machine tools can only understand formats such as STEP and STL. Therefore, you must convert the generated CAD file to the appropriate format. This function is integrated into some applications. For those who don’t do this, you can use internet services to perform the file conversion. This conversion will adjust the machine tool’s speed, toolpath, rotation, linear motion, and other characteristics.
Step 3: Configure and run the CNC machine tool	Connect the CNC drill bit to the drilling machine and set it up. Next, attach the workpiece to the machine. Finally, begin the drilling process and watch the machine work. After drilling is complete, inspect the part for any defects or faults.

Industrial applications of CNC plastic parts

With the advent of CNC machining, cross-industry CNC machining of plastic parts has become easier while ensuring accuracy and robustness. The choice of plastic material depends on the application and industry. CNC plastics are suitable for various industries, including aerospace, medical, defense, automotive, electronics, and marine. The requirements for products vary across these industries, so some plastics are more suitable than others. Some plastics are better suited for extreme durability environments, while others are better suited for everyday applications.

healthcare industry	The use of plastic processing techniques meets the demands of producing surgical instruments, heavy-duty prostheses, and medical tools. These methods also ensure compliance with stringent safety requirements while enabling the production of intricately sculpted details.
Automotive parts	Plastic parts such as dashboards and vents can be machined using computer numerical control (CNC). This can reduce the weight of the car body and improve the performance of the machined parts.
Aerospace parts	The prototypes, internal structures, and components are all heat-resistant and lightweight, making plastic the preferred material for the aerospace industry. This process is crucial because the plastic details processed using these methods are subjected to immense stress and require extremely high precision.
Electronics industry	In the electronics industry, machined plastic components such as connectors, housings, and keyboards are used. Overmolding connectors with plastic enhances the insulation and robustness of precision systems.

Start using Elimold Plastics CNC Machining Services now

CNC plastic machining is a reliable method for manufacturing precision CNC plastic parts with good tolerances and high-quality specifications. It is constantly expanding due to its accuracy, speed, and adaptability. Working quickly and directly with a service provider is very helpful in selecting the right technology and the right materials. We offer custom CNC plastic machining to meet prototyping and production requirements. The machinable plastic materials we use are not chosen arbitrarily but are carefully selected to achieve the desired results. Furthermore, our engineering department will advise on the best materials and designs. Uploading your design will get you an instant quote, free Design for Manufacturing (DfM) analysis, and competitive pricing.

Elimold’s support methods for CNC machining of engineering plastics

In precision CNC machining projects of engineering plastics, material selection is only the first step. Subsequent steps involve tool selection, cutting parameters, clamping methods, temperature control, and inspection standards. Elimold leverages its multi-axis CNC machining capabilities and specialized engineering plastics processes to provide continuous support from initial contact to finished product delivery.

Drawing and sample matching	Perform DFM optimization, structural analysis, and process evaluation to help clarify material direction.
Processing plan formulation	Select 3-axis, 4-axis, or 5-axis machining paths based on the part shape to reduce the risk of deformation and clamping errors.
Engineering Plastics Special Process	By using vacuum adsorption, specialized cutting tools, and constant temperature processing, problems such as sticking to the tool, melting edges, and thermal deformation are minimized.
Precision Inspection and Delivery	Combining 2D measuring instruments, height gauges, roughness gauges, and coordinate measuring machines, complete full inspection and cleaning packaging as required.

If you are evaluating your choice of POM, PEEK, PA6, or PA66, Elimold can leverage its expertise in precision CNC machining of engineering plastics to provide application-specific recommendations for your parts, facilitating sample verification and subsequent custom machining. For projects requiring stable delivery, controllable precision, and cost-effective solutions, this kind of early assessment can significantly improve communication efficiency and project progress.

Conclusion

After reading this article, you will have a clear understanding of most of the information in the field of CNC plastic machining, providing you with basic references, analytical information, and rationale for selecting appropriate plastic materials in your subsequent CNC plastic parts projects. Based on Eliimold’s many years of experience, we understand that in some cases, CNC plastics have unique advantages over metals, including lower density, superior chemical resistance, excellent electrical insulation, and cost efficiency. Furthermore, they are compatible with a variety of manufacturing processes, such as CNC machining, 3D printing, and injection molding. We hope this guide will provide valuable insights to help you make informed decisions when selecting CNC plastics for your projects.

Furthermore, advancements in modern plastics materials science have made careful selection of plastic materials increasingly crucial for CNC machining. At Elimold , we offer a wide range of plastic materials, from popular common plastics to premium engineering plastics , and we specialize in CNC machining services, including CNC milling and turning. Our team’s experience and 5-axis machining capabilities enable us to provide our clients with unparalleled quality and precision. Contact us today! We are committed to providing the best customer service to help our clients achieve their goals and reduce costs. Our technicians can help you select the best materials for your project and offer free professional advice. Whether you have a specific project or need custom CNC machined parts, we can assist you at every stage. Get a quote to get started!