The Ultimate Guide to CNC Machining Plastics
CNC machining is a subtractive manufacturing process that uses rotating tools and drills to systematically remove material from solid blocks of material to create parts. CNC machining is a versatile and efficient rapid manufacturing process that features high precision, high quality, fast turnaround and compatibility with many different materials. Metal, wood, composites, and plastics are all suitable for CNC machining, with plastic being the most common one. CNC machining is more precise than injection molding when it comes to manufacturing custom plastic parts, quickly producing thousands of uniform and precise parts with extremely tight tolerances. There are many types of plastics suitable for CNC processing, so how to choose the right one? This is not an easy question to answer and it depends on a range of different factors. This article will explain the properties that must be kept in mind when working with plastics and give examples of the most commonly used plastics.
Common process for CNC machining plastics.
CNC Turning Plastic
CNC turning refers to the process of rotating plastic raw materials on a CNC lathe while stationary CNC tools remove parts of it to form the desired shape. Although the most common plastic workpiece shapes are conical or round, the CNC turning process is well suited to machining a wide variety of shapes.
CNC Milling Plastic
CNC milling is the opposite of CNC turning because the tool rotates while the material is stationary. CNC milling is suitable for machining flat and irregularly shaped parts. The number of axes in 3-axis, 4-axis, 5-axis CNC milling determines the flexibility of the process and its suitability for manufacturing complex components.
CNC Drilling Plastic
CNC drilling refers to the drilling of holes in materials using cutting tools in the form of different drill bits. Depending on the type and shape of the drill bit, holes with different cross-sections are formed. CNC machines used for drilling also perform some milling and turning operations. Choosing the right CNC drilling machine ensures cost-effectiveness.
Advantages of CNC Machining Plastic Parts
AN-Prototype is the trusted expert in CNC machining plastics parts.
4 Factors to Consider in CNC Machining Plastic Materials
As explained in our article on CNC machining materials, the physical properties of a material can affect its machinability. Therefore, the results you get from your workpiece will vary depending on the material. With plastics, the size and shape of the workpiece may change during or even after CNC machining. Therefore, design engineers need to consider the characteristics of various plastics to ensure the manufacturability of their designs.
#1 Thermal Expansion and Heat Deflection Temperature (HDT)
According to the principle of thermal expansion and contraction, almost all materials expand and increase in volume at high temperatures. In CNC machining, the tools used generate heat when they come into contact with the material. In the case of plastics, they have a higher coefficient of thermal expansion than metals. Therefore, their dimensions change more significantly after processing. Therefore, it is critical to understand how each plastic reacts to heat input during CNC machining. These factors will directly affect the tolerances of CNC plastic parts. Additionally, a material’s Heat Deflection Temperature (HDT) indicates when a material is prone to begin deforming due to exposure to high temperatures. You may want to consider this when making your final material selection to ensure the part is suitable for its intended application.
#2 Hardness and strength of plastic
You should consider the hardness and strength properties of the plastic for your part to ensure it will meet the requirements of the end application. However, these characteristics also affect the tolerance of the part during CNC machining. The tensile strength of a plastic material affects how it is CNC chipped and thus the final surface finish of the part. Hardness also affects how chips are formed, and with very soft materials, gouging can occur if the operator does not take proper precautions. In general, the hardness and tensile strength of plastic materials do not affect the wear life of the CNC tools used. However, this is often a more important consideration when machining metals and ceramics.
#3 Reaction of Moisture Chemicals in the Air with Plastics
Certain plastics absorb moisture from the air or coolant, or are adversely affected by certain chemicals in the air. They may even need to be kept in an air-conditioned room or in a sealed bag. The effects of moisture and chemicals can cause dimensional changes in plastic materials, affecting the ability to meet precise tolerances. Moisture and chemicals can even completely reduce the strength and stability of plastics.
#2 Hardness and strength of plastic
Appearance and related properties such as light transmission can be an important factor in the design. If so, this limits the amount of plastic material you have available. Additionally, care needs to be taken during CNC machining to ensure that the rough surface finish does not affect light transmission or clarity.
Rapid Manufacturing Plastic Parts
Why Choose AN-Prototype CNC Plastic Machining Services
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AN-Prototype has passed ISO9001 & ISO13485 certification. Our advanced quality control process complies with the quality management system.
Advanced CNC machines
3-axis, 4-axis, 5-axis CNC machines from the United States and Japan ensure that we can execute complex machining tasks on time and can handle any type of CNC plastic project
Fully understand the properties of various plastics
AN-Prototype can produce plastic parts from various types of plastics. Extensive knowledge of the properties of different plastics and extensive testing and experimentation.
15 years of experience in CNC machining plastics
Since 2009, we are good at CNC machining plastic parts. Our team will quickly manufacture precision plastic components and custom machine them to your specifications.
Plastic Types for CNC Machining
CNC machining plastics can be used to create a range of parts from prototypes to end-use assemblies. Because plastics are usually lightweight and dense, CNC machining is a better process for processing plastics than 3D printing or injection molding. Many engineering materials are very durable, have high fatigue resistance, inertia and shock absorption, such as POM. Some plastics are general purpose materials suitable for testing designs at low cost, such as ABS. According to the needs of your project, AN-Prototype lists 12 common plastic properties to choose the best material for your custom parts.
Acrylonitrile butadiene styrene (ABS) is an engineering thermoplastic known for its impact resistance, strength and good machinability. ABS has low chemical stability and is sensitive to grease, alcohol and other chemical solvents. However, pure ABS is less thermally stable because the plastic polymer burns even when the flame is removed. Common applications include electronic housings, keyboard covers, and dashboard components in automobiles.
Nylon, also known as polyamide (PA), is a low-friction engineering thermoplastic with high impact strength, high abrasion and chemical resistance, and overall excellent mechanical properties. Nylon can withstand a lot of wear and tear and is resistant to oil and fuel damage. However, nylon 66 has poor hygroscopic dimensional stability and is very easy to absorb moisture. Nylon 66 is particularly suitable for CNC machining, and common applications include many industries including automotive and medical equipment.
PEEK is a high performance engineering thermoplastic that is lightweight, resistant to chemicals, abrasion, creep, fatigue, liquids and temperatures up to 260°C (480°F). Additionally, PEEK is recyclable and biocompatible. PEEK can replace some metals in part manufacturing. It is one of the most expensive CNC machined plastics on the market. For all its advantages, PEEK is not UV resistant and does not maintain good performance in the presence of halogens or sodium. Common applications include piston devices, critical aircraft engine parts and dental syringes.
POM (Delrin) is the easiest of all CNC plastics to process. It is a high-strength, high-rigidity plastic with excellent heat resistance, abrasion resistance, weather resistance, chemical resistance and fuel resistance. Delrin 570 and 150 are the most commonly used POM grades in CNC machining because they have excellent dimensional stability and are ideal for manufacturing precision parts with tight tolerances. However, POM has poor acid resistance. Plus, it can be difficult to glue. Common applications for POMs include seat belt components, electronic cigarettes, insulin pens, and water meters.
PC is a tough yet lightweight thermoplastic polymer that is naturally heat resistant and has excellent electrical insulating properties. PC is naturally transparent, can transmit light like glass, and can replace glass. Common applications include goggles, surgical instruments, and CD/DVDs. Unfortunately, the good mechanical properties of PC degrade after prolonged exposure to water above 60°C. Additionally, while PC is resistant to dilute acids, oils, and greases, it is susceptible to abrasion from hydrocarbons and can turn yellow over time after prolonged exposure to UV light.
PTFE, commonly known as Teflon, has the lowest coefficient of friction of all solid materials and is particularly suitable for CNC machining. Teflon has chemical resistance, temperature resistance, light resistance, UV resistance, water resistance, weather resistance and fatigue resistance. It is important to note that there is a limit to the thickness of parts made from PTFE, as it is usually only available in two-inch thick plates or rods. PTFE is also sensitive to creep and wear. Known for its excellent anti-stick properties, PTFE is most commonly used in non-stick pan coatings, but it is also used in gaskets, semiconductor parts.
Polyethylene is a lightweight, strong CNC plastic material known for its impact resistance, stiffness and flexibility. It has excellent dielectric properties. It is available in different grades, each with unique applications, including LDPE, HDPE and UHMW PE.
PMMA is a hard thermoplastic that is popular in plastic CNC machining due to its optical properties. It is tough, lightweight and resistant to most laboratory chemicals especially toughness and impact resistance. Compared to polystyrene, PMMA transmits light better and is more weather and UV resistant. However, PMMA is not as good in heat resistance, impact resistance, abrasion resistance or wear resistance. In addition, this material is prone to cracking under heavy loads and it breaks down when used with chlorinated or aromatic hydrocarbons, ketones or ethers. Therefore, designers should only consider PMMA for low stress applications such as light pipes, greenhouse canopies, automotive light covers, etc.
LDPE is a tough and flexible CNC plastic material with good chemical resistance and low temperature resistance. LDPE's low coefficient of friction, high insulation resistance and durability make it an ideal material for high performance applications. It is easy to weld and heat seal, and is widely used in medical parts, prosthetics, orthotics, gears and mechanical parts, electrical parts (such as insulators and housings for electronic equipment), and parts with a polished or glossy appearance.
HDPE is a flexible, easily processable thermoplastic that is resistant to stress cracking, chemicals and corrosion even at low temperatures. It has the same superior impact strength as low density polyethylene (LDPE), but with four times the tensile strength. But this material has poor UV resistance. In addition, it is a good material for gears due to its low coefficient of friction and high wear resistance, and it is a good material for bearings because it is self-lubricating and chemically resistant, and it is inexpensive.
PVC is a highly durable and versatile plastic material that is resistant to moisture, chemicals and abrasion and is easy to CNC machine. It cuts, drills, mills and turns with ease to create precise parts and assemblies. PVC is chemically non-reactive, which makes it widely used in several industries. Rigid PVC is suitable for making parts such as rings, rollers, pads, pipes and valve components. Additionally, PVC is a low-cost material compared to other plastics, making it an economical choice for many applications.
UHMW is a tough, versatile and CNC-friendly plastic with high wear resistance. When product teams need a durable, low-friction plastic for their industrial applications, UHMW is the answer. However, UHMW is not suitable for high load applications as it is highly prone to creep and should not be used at temperatures above 80°C. UHMW is commonly found in truck bed liners, food processing machinery parts, wear strips and ship dock fender pads.
Which plastic should you choose for your CNC project?
As you’re probably aware, there are a variety of plastics to choose from. But which one is best for your CNC project? If you are looking for a strong plastic with transparent properties, you may have to choose between PC, PMMA or PET, but you should keep their thermal limitations in mind.Maybe you need a plastic with good chemical resistance? ABS, PEEK, POM, PVC, HDPE may be good choices for CNC machining.
CNC machining plastic parts tips
When CNC machining plastics, some parameters need to be set to ensure the quality and efficiency of machining. The following are some commonly used parameter settings:
When you are setting up your CNC programming it is important to remember that plastic is not metal. If the blank is clamped hard, it is easy to leave large marks on the surface. In fact, parts may break if too much force is applied.
Selecting the best cutting tool for CNC plastic parts is a complex endeavor. The reason for this is that the composition of plastics and composites varies greatly. Some plastics are reinforced with hard carbide particles or contain additives to enhance flexibility, heat resistance or some other parameter. All of this changes the way plastics respond to processing. Therefore, the appropriate cutting tool should be selected for processing plastic parts according to the characteristics of different plastics.
Let us take the case of CNC milling plastic as an example to understand the choice of plastic cutting process. The main issues you have to watch out for are excessive friction and plastic deformation of the part. To avoid these problems, keep your knives sharp at all times during cutting. If the material you are using is not firm enough, freeze it. However, you should be careful as plastic becomes hard and brittle at low temperatures.
To keep chips from melting into a CNC plastic part, you need to keep the tool moving and prevent it from staying in one place for too long. Remove the chip as soon as possible. Therefore, the feed rates for plastic processing must be large, even aggressive. When the feed speed parameter is large, the spindle speed must also be fast. A rough estimate is about 3 times the aluminum feed rate and corresponding cutting speed.
Cutting speed refers to the moving speed of the tool during processing. A tool speed that is too high may cause tool wear or damage, and a speed that is too slow may reduce machining efficiency. Tool speed settings must be adjusted based on factors such as the specific plastic material, tool type, machine tool performance, and more.
Feed rate refers to the speed at which the workpiece moves during machining. Feeds that are too high may result in rough surfaces or excessive heat generation, while feeds that are too slow may reduce machining efficiency. The setting of the feed rate must be adjusted according to factors such as plastic material, tool type, and machine tool performance.
Depth of cut refers to the depth of each tool. Too much depth of cut will cause tool wear or workpiece deformation, and too small will affect processing efficiency. The setting of depth of cut must be adjusted according to factors such as plastic material, tool type, machine tool performance, etc.
Cutting clearance (step distance):
Cut gap is the distance between two adjacent cuts. Too much clearance may result in rough workpiece surfaces, and too little clearance may increase tool wear. The setting of the cutting gap needs to be adjusted according to the plastic material, tool type and machine performance.
Coolant reduces the heat generated during machining, thereby reducing the risk of tool wear and deformation of the workpiece. In plastic CNC processing, it is necessary to select the appropriate type of coolant and add it regularly during the processing.
Why CNC Machining Plastic Instead of 3D Printing
1. Wide range of CNC machining plastic materials. For rapid manufacturers, CNC machining, not 3D printing, is the first thing that comes to mind when making custom plastic prototypes. Certain plastic materials, such as plastic parts such as PVC, POM, PEI or PEEK, cannot be 3D-processed. Because there are no reliable and affordable plastic formulations for these plastics. CNC machining can easily manufacture any type of plastic part according to the customer’s specifications.
2. Cost-effectiveness. 3D printing specialty materials is usually more expensive, and manufacturing costs are priced based on the quantity of material used, which means larger parts or higher numbers of parts cost more, while CNC plastic is a more convenient and cost-effective process, Especially suitable for small batch manufacturing.
3. CNC machining for smoother surface of plastic parts. The 3D printing process leaves a hard-to-remove pattern on plastic parts. 3D printing is not suitable when there is a need to manufacture conceptual models or functional prototypes with a high-quality surface finish. We use a CNC milling process to ensure the parts have a high quality finish. When it comes to making plastic parts with greater dimensional accuracy, 5-axis CNC milling machines can help you meet your toughest manufacturing challenges by high-precision machining of more complex parts.
Application of CNC Machining Plastic Parts
Industrial Plastic Parts
CNC machined plastic parts can be used in industrial areas such as pulleys and levers. CNC machining is also economically beneficial in manufacturing plastics in small batches.
Automotive lighting prototypes for the automotive industry rely heavily on CNC milled PMMA parts. It can be used to make outer lens covers and light guides. CNC machined parts leave no marks and look better.
CNC machining is one of the most common methods of manufacturing medical plastic parts, including electronic medical device components and surgical tools. PEEK\PTFE is a commonly used material in the manufacture of medical plastic parts.
Electronic Plastic Parts
The manufacture of electronic plastic prototype parts relies heavily on CNC machining, such as semiconductors, inside plastic housings for gaming devices.
CNC plastic machining is a widely accepted process among designers because of its precision, speed, and suitability for manufacturing parts with tight tolerances. This article discusses the properties of different CNC machining materials and the range of applications for plastic parts.
Choosing the right CNC machining technology can be very challenging, so it is recommended that you entrust your CNC plastic project to a fast fabricator. At AN-Prototype, we offer custom plastic CNC machining services that can help bring your designs to life.
We have a wide range of plastic materials suitable for CNC machining and are strictly certified to provide Rosh certification. In addition, AN-Prototype’s engineering team can provide professional material selection advice and design advice. Upload your design today and get a free quote and a free DfM analysis at a competitive price.