CNC machining is a common rapid prototyping manufacturing process due to its accuracy, precision, compatibility with complex design, etc. It is a subtractive process that involves a computer controlling a CNC tool via techniques such as milling, turning, etc., to remove part of a workpiece used to form the required product.
CNC machines are compatible with many materials such as metals, plastics, and wood. However, recently, many plastic products manufacturers now use plastic CNC machining, which involves manufacturing plastic products using different CNC machine techniques. There are many things to plastic CNC machining. Therefore, this article will introduce seven essential things you need to know about the process.
Can Plastic Be CNC Machined?
Yes, plastic can be CNC machined. For most people conversant with the process, soft metals are the most common workpiece materials in major CNC shops. This is because most rapid prototyping service providers will rather use injection molding and 3D printing for manufacturing plastic products.
However, this does not mean plastic polymers cannot be machined. Currently, many CNC machinists love working with plastics as the advantages of the process complement the inherent properties of plastics. For example, plastics are easier to cut, which improves precision, accuracy, and tight tolerance. Consequently, plastics are becoming popular among businesses that care about better quality.
What Plastic is Best for Machining?
Thermoplastics are the most common plastic polymers used in CNC plastic machining. This is because they retain their original properties after reforming and remodeling on melting. For a better view and understanding of what plastic polymer to use, you can check through our list of CNC materials. However, below are some common plastics suitable for many products.
· Delrin (POM)
Delrin is a thermoplastic known for its rigidity and strength. It is a good plastic CNC machining material as it can function well in high tensile stress situations. It is heat resistant (however, it cannot withstand temperatures greater than or equal to 121°C (250°F).
· Nylon (Polyamide)
Nylon is a high purity semi-crystalline CNC plastic machining material known for its excellent thermal, mechanical, and chemical resistance. CNC machining nylon is easy as the material offers tight tolerance due to its physical properties and dimensional stability. It also behaves like a metal, evident in the popular saying, “machining nylon is like machining brass.” CNC tools used in working nylon material should be tungsten carbide alloy tools.
· Acrylic
Acrylic is a suitable plastic CNC material with lightweight, great tensile strength, wear resistance, and rigidity. It has high machinability although there are some conditions you should look at. For example, for CNC cutting, the cutting tool must be a carbide tool with an aggressive and razor-sharp edge to give a perfect surface finish.
· PTFE
PTFE (Polytetrafluoroethylene) or Teflon is a thermal, water, electrical, and chemical resistant plastic known for its extremely high tensile strength. It is a common CNC plastic due to its density and softness. However, it has a high coefficient of friction and stress creep properties which makes it hard to achieve tight tolerances. Therefore, you or the rapid prototyping service you employ should know about the implications of its properties and the required tools before machining.
· PEEK
PEEK or Polyether ether ketone is a group of high-performance plastics known for their high melting point, corrosion resistance, and excellent mechanical properties. PEEK is more popular in 3D printing; however, its inherent properties and the accuracy, repeatability, tight tolerances, and other advantages of a CNC machine make them highly suitable for machining. While PEEK is popular as a plastic CNC machining material, you should know about its properties so as to reduce cracking as a result of heat and internal stress.
· UHMW
Ultra-high molecular weight polyethylene is another CNC plastic machining material with high tensile strength, corrosion resistance, and other excellent mechanical properties. These properties make it a likable material in rapid prototyping. However, machining UHMW is not an easy task due to its instability. Since it is impossible to mold the material, machining is still the better option. Therefore, it is better to outsource to a service with high experience of working with the material.
How are Plastics Machined?
Plastic machining involves several processes depending on the material and the product to make. Of the many processes used in popular rapid prototyping services, below are the three most popular plastic machining processes:
· CNC Turning
CNC turning involves spinning the plastic polymer on a CNC lathe while a fixed CNC tool removes part of it to create the needed shape. The process is ideal for working with many shapes, although the most common workpiece shape is cylindrical. Choosing whether CNC turning is the right process requires you or the prototyping service to understand several factors, such as the desired productivity, outer diameter of the plastic polymer, etc.
· CNC Milling
CNC plastic milling is the opposite of CNC turning, as the tools rotate while the material is fixed. Like CNC turning, it has high precision and accuracy and a uniform production rate due to the corresponding cutting speed of the tools. CNC milling is also suitable for working with flat and irregular shapes. The process involves using a single-point cutting tool that works on many axes (the common one is the 3-axis). The number of axes supported determines the flexibility of the process and its suitability in making complex components.
· CNC Drilling
CNC Drilling involves boring a hole in a material using cutting tools in the form of drills. Holes of different sections are created in the material depending on the kind and shape of the drill. CNC machines used in drilling are multi-purpose since they also perform some milling and turning operations. They also come in different sizes and require an expert to ensure cost-effectiveness when making plastic components.
How to Achieve a Perfect Finish on Plastic Parts?
Achieving a perfect finish in CNC plastic machining depends on the techniques employed and the understanding of the properties of the material. To avoid this (i.e., obtain a perfect finish) for your plastic product, follow the following guidelines:
- Avoid using any cutting tool with complex geometries.
- Do not go beyond the recommended feeding rate of the material in use.
- Plastic materials to be machined must be properly held in place. Improper clamping of materials will lead to vibration, which further results in an imperfect finish of the plastic.
- The cutting speed must also be within the recommended range, and it also varies for different plastics.
These factors depend on the understanding of the different properties of plastic materials. However, you can further improve the surface finish of any plastic product by using finishing techniques such as annealing, sandblasting, powder coating etc. You can contact us on how to choose the perfect finish technique for your product.
Why Do People Prefer CNC Plastic Machining Over Other Methods?
Plastic polymers are often used with other rapid prototyping methods, such as injection molding and 3D printing. However, there has been a recent shift to CNC plastic machining due to its advantages. The three methods are fast and common, with each having its advantages, but many people now prefer CNC plastic machining abilities due to the following:
· Precision and Accuracy
CNC plastic machining has an unmatched precision and accuracy among the three rapid prototyping methods. The high precision and accuracy ensure high repeatability as the quality of different plastic products made by the process are similar.
· Suitable for Complex Designs
Plastic polymers are used in making both complex and simple products. CNC plastic machining is suitable for making plastic products with complex designs. Although 3D printing also boasts of an insane capability of complex designs, the precision and accuracy offered by CNC machine tools give the process an edge.
· Tight Tolerance
CNC plastic machining is the best of the three methods for making products with tight tolerances. This is also due to its high accuracy and precision and makes it an important process for most plastics manufacturers.
· Compatible with Different Plastic Polymers
All the methods are compatible with various materials. However, CNC plastic machining works well with a broader range of plastics, especially tough ones, without many issues.
What Are the Common Applications of CNC Plastic Parts?
Plastic polymers come in different properties and, consequently, different uses. Below are a few common applications of CNC plastic parts:
- Production of medical appliances and implants.
- Use in the manufacturing of plastic parts used in food and beverages industries.
- Manufacturing the insulating parts of electrical devices
- Manufacturing parts of automobiles and aircraft
- Production of lenses (e.g., Acrylic is known for its optical activity)
Conclusion
Plastic polymers are used in making different industrial and domestic-grade products. For some products, there is a need for a high level of precision, accuracy, tight tolerance, etc. Therefore, CNC plastic machining has been a top choice for many people who want durable and quality plastic polymers for use.
Do you have a machined plastic parts project that requires high-quality plastic CNC machining services? Reach out to us at AT Machining. AT Machining is a reputable CNC machining service provider that provides professional solutions and can help you manufacture high-quality plastic products. We also offer an instant quote and DfM feedback which improves our manufacturing process. Are you confused about plastic machining? Contact us, and our expert team can help you.
