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What is Plastic CNC Machining?
Plastic CNC machining is a subtractive manufacturing process in which computer numeric control (CNC) machines carve plastic to create parts using a CAD file. It works by placing a plastic block or sheet into the CNC machining device and removing plastic layer by layer across the surface until it reaches its desired shape.
Unlike additive processes, where parts are printed layer by layer, CNC machining uses sharp cutting tools to cut the desired shape from a solid block of plastic. This is why CNC machining is a preferred method for creating parts that are durable, precise, and repeatable. Engineers and manufacturers rely on CNC machining to create prototypes, production parts, functional components, and end-use products.
It is capable of performing operations such as CNC milling, turning, drilling, and routing. It provides manufacturers with the ability to create simple shapes to highly complex geometries. It also provides assurance of tight tolerances and consistent quality of every part produced.
Common Plastics Used in CNC Machining
Here are the common plastics used in CNC machining:
ABS
Acrylonitrile Butadiene Styrene (ABS) is the most popular plastic to machine using CNC, as it offers high strength, flexibility, and a low price. ABS is a low-density material, and it machines to a nice, clean finish without much post-processing.
ABS is very tough but lightweight enough to provide a proper design for functional prototypes, automotive interior parts, and many electronics enclosures. Manufacturers also select ABS because it can absorb impacts and withstand continuous wear under regular use.
Nylon
Nylon has excellent strength, wear resistance, and loss of length. When manufacturing beveled parts, such as gears, pulleys, and bearings, wherein the components are in constant motion, the strength and fatigue resistance of the parts are critical.
Unlike other plastics, nylon offers good fatigue resistance and can withstand repeated loads without developing cracks. Also, many plastics will survive abrasion; nylon, instead of wrapping around itself, will wear like a button, which is necessary in many situations and environments.
Polycarbonate
Polycarbonate is a see-through plastic that combines transparency with a high toughness level. Polycarbonate is stronger than glass and much lighter, which means it will essentially not shatter like glass would.
Thus, it allows it to be used in protective covers, face shields, safety goggles, and machine guards. When CNC machining polycarbonate components, it will make strong parts that can take an amazing amount of impact without breaking.
Acrylic
Acrylic (also called PMMA, which stands for Polymethyl Methacrylate) is a medium plastic, meaning it has large amounts of clarity and allows for outstanding smooth surfaces. Many markers of quality often look to work with a design concept that uses acrylic, as it is lightweight and can be used as a replacement for glass in displays, lenses, or light fixtures.
In comparison to glass, acrylic will shatter far less easily and is more resistant to scratching than many types of plastics.
Polypropylene
Polypropylene is an excellent choice for CNC machining applications due to its remarkable chemical resistance properties. Polypropylene is resistant to acids, solvents, and cleaning agents, making it an excellent material for laboratory equipment, medical containers, and industrial applications.
It is lightweight and flexible and can bend without cracking. The machining process for polypropylene yields smooth and durable parts, which do not typically soak up moisture or chemicals. This property makes polypropylene an excellent option for food-safe applications, fluid handling components, and packaging applications.
Advantages of Plastic CNC Machining
There are many advantages of plastic machining over alternatives like injection molding, and here are some of them:
Lightweight Performance
Because plastics are lighter than metals, industries can significantly reduce the weight of devices with strength. Lighter components in aerospace and automotive applications have less drag, meaning better fuel efficiency and improved handling.
Lighter components in consumer products mean easier transportation, portability, and comfort. CNC machining allows manufacturers to precisely shape plastics into components that help maintain the durability of the materials while keeping the components lightweight and strong.
Cost-effective Manufacturing
Plastic machining is often less expensive than metal machining. The raw materials for plastics are less expensive, and machining with plastics frequently means less tool wear and less time machining. All of this, in turn, means lower overall production costs while delivering excellent quality.
The cost savings of plastic machining can be beneficial for companies making prototypes, small batches, or even large amounts of production. All while delivering cost-effective machining services without compromising on accuracy.
Excellent Chemical Resistance
Many plastics – including polypropylene and PEEK – have chemical resistance, solvents, and cleaning agents. The value of plastic machining appeals to many industries, including medical devices, food processing, and laboratory equipment.
While metals don’t have corrosion resistance, plastics maintain their structure and function under harsh conditions due to their amazing chemical resistance properties.
Insulating Properties
Nylon and ABS have good electrical insulation properties. This natural quality gives plastics characteristics of excellent electrical and electronic applications.
CNC machining of plastics can utilize these features to produce circuit housing, switch components, and insulating barriers in the electrical engineering landscape. Since plastics aren’t conductive, they present some safety factors in the design of electrical systems.
Challenges of CNC Plastic Machining
While plastic CNC machining has its advantages, it also has some challenges that come with it. Here are some of the challenges:
Heating sensitivity
One of the challenges of working with plastics, as compared to metals, is that plastics tend to have much lower melting points. In CNC machining, the rotary cutting tool generates heat through friction as it cuts through the plastic.
If the heat is not controlled through proper means, the plastic may melt, warp, or potentially adhere to the tool. This impacts accuracy and destroys finish, requiring extra surface treatment.
Dimensional Stability
Plastics tend to expand and contract more than metals in response to temperature excursions. The changes in dimensional stability make for very tight tolerances difficult in CNC machining. A plastic part may measure perfectly in one set of circumstances, having a conforming or non-conforming measurement under new delivery or end-use conditions.
Moisture Absorption
Moisture uptake. Some plastics, such as nylon, can absorb moisture from the air. This makes them swell, warp, and lose their strength over time. In CNC machining, moisture uptake also produces accuracy, as well as reduced strength in the finished part.
To minimize this, machinists often store plastics in dry conditions and sometimes pre-dry the plastics before machining.
Surface Finish Issues
Some plastics are hard to get clean surfaces. Some plastics, like acrylics, scratch easily, and others leave burrs when cutting. A poor finish reduces the appearance and the function of the part. In some industries, including medical or consumer products, these are big problems. A clean surface may require additional finishing steps like sanding, polishing, or flame treating.
Applications of Plastic CNC Machining
Below are the many applications of plastic machining:
Medical Industry
Plastic machining is especially important in the medical field. Plastics are lightweight, biocompatible, can be sterilized, and are perfect for medical tools, surgical guides, and device housings. For example, PEEK (polyether ether ketone) and acrylic are often machined into implants, diagnostic components, and clear covers.
Automotive Industry
The automotive industry relies on plastic machining for prototypes and production parts. The benefit of plastic is the weight savings with strength improvements; weight savings help save fuel. The industry is using plastics for dashboards, brackets, housings, and fluid system parts, with a strong trend in the use of engineering plastics.
Aerospace
In aerospace, reducing weight must be priority one. CNC plastic-machined parts and equipment can produce lightweight but very strong components like ducts, panels, and insulation parts. Ultem and PEEK are both structurally dynamic and handle a high temperature and stress variation. CNC machining is able to provide precision final products that can satisfy an industry’s exacting standards for safety and liability.
Prototyping and Product Development
When plastics are being machined, it is important to use sharp cutting tools. Dull tools will create chipping, stress markings, or have a rough finish. High-speed steel or carbide tools are the most commonly used because they will separate easily without introducing excessive friction. Tools should be routinely inspected or replaced to maintain quality control.
Best Practices for Plastic CNC Machining
Follow these guidelines for the output of plastic machining:
Choose the Correct Plastic Material Properties
The first step toward achieving success with CNC machining involves choosing the correct plastic material. Each plastic has specific properties; some are better suited to resist heat, some are better for handling impact, and others provide clarity.
If you need a high-performance part, then PEEK would certainly be able to handle it; however, if you require a clear cover, acrylic may be a better choice.
Control Heat During Machining
The mechanical properties of plastic are different from those of metal, and plastics are more sensitive to heat than metal parts are. If the cutting speed is relatively high, the plastic might melt, warp, or stick to the CNC tool.
Machinists today typically choose sharp tools, a relatively slow spindle speed, and utilize the proper coolant. Controlling heat will achieve a smooth surface finish and, more importantly, no deformation of the part.
Optimizing Feeds and Speeds
The feed rate against the spindle speed is critically important in machining plastic. If the feed rate is too slow, it could possibly chip the material; if too fast, it can overheat the material, causing possible disintegration.
Each plastic has its ideal machining specifications. Softer plastics like nylon will not go as fast, whereas for a harder plastic like PEEK, a cutting rate may be higher.
Finish and Polish Carefully
Surface finish is an essential consideration for plastics, particularly in consumer products and medical devices. After the machining operation, parts may require deburring, sanding, or polishing to achieve the optimum finish. Different polishing techniques, such as flame polishing and vapor polishing, are also common for transparent plastics such as acrylic, providing a clear glass-like finish.
Conclusion
Plastic CNC machining is a flexible and effective process for manufacturing precision plastic parts for a wide of industries and applications. Plastic machining offers accuracy, flexibility, and efficiency. The versatility and accuracy of machining plastic make it a great process for a number of industries, including automotive, medical, aerospace, and electronics.
If a manufacturer uses the correct material, machining, and finishing processes, they can produce finished plastic parts that meet strict operational requirements for performance. If you need top-notch CNC machining services, then AT-Machining is your go-to. They offer quality and cost-effective services. Contact us today to get started.
