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2020.4.26
Plastic parts need to be cut when it is difficult to form directly or high precision is required. Considering the plastic types, cutting tool materials, and processing characteristics, how to process plastics with CNC machines for high quality and productivity. From the problem of material pullout, we introduce how to achieve perfect surface finish on plastic and the tips for CNC plastic machining.
A common problem seen during CNC machining of thermoplastics is material pullout, it’s most commonly experienced in darker plastics, how to solve the problem and achieve a perfect finish on engineering plastic products? This phenomenon can be caused by various improper machining techniques but not related to the plastic quality. For preventing the plastic material pullout, proper machining is the key. And the following tips can ensure successful machining and smooth surface finish on plastic.
– Tool geometry. Make sure to use a cutting tool with the correct geometry, which allows the tool to cut the material properly. Unlike CNC metal machining, engineering plastics require a slightly positive or neutral tool geometry, too much positive geometry will cause the cutter to dig at the material and result in the pullout effect.
– Proper fixturing/clamping. Firmly securing the part or fixturing is another key step in successful machining. Improper fixturing may cause vibration between the CNC parts and tool, which make the tooling dig or walk as it travels across the surface of the part. Correct holding will ensure the right contact between the workpiece surface and tool, so as to achieve a desirable finish.
– Correct feed rate and tooling speed. The recommended feed rate and tooling speed settings vary from material and material. Ensure your cutting equipment is set to match the appropriate machining rates, which also extends the life of your tools without sacrificing production speed or efficiency.
Related Read: Different Types of Plastic for CNC Machining and Uses
Generally, metal processing equipment can be used for cutting plastic parts. Due to the large difference between the properties of plastics and metals, and the wide variety, the properties of different plastics also have great differences, improper machining will lead to many problems. For example, the local overheating due to the small heat capacity, poor thermal conductivity, and elastic deformation caused by excessive pressure of plastics, the surface quality and dimensional accuracy of plastics will be affected. In serious cases, it may even cause accidents in the machine shop. To avoid these issues and confirm success plastic CNC machining, here are some tips as below.
1. Cutting Tool Material
The cutting tools are mainly made of high-speed steel, cemented carbide, diamond, etc. For cutting general plastics, the first two cutting tool materials can be selected. In comparison, high-speed steel has a better grind ability, choose the high-speed steel tool and grind carefully, the cutting edge of the tool will be sharper, but its durability is lower than that of the carbide tool.
2. Cutting Tool Parameters
Reduce the cutting force and temperature as much as possible, select appropriate front angle, back angle, main angle, minor cutting edge angle, tip arc radius, etc., to improve the productivity and tool durability, save the machining cost. Keep the cutters sharp and freeze the material when it’s not rigid enough.
3. Part Workholding
Clamp the plastic block with properly, avoid too much pressure to cause breakage. It is recommended to use pads made from soft materials between the fixtures and the part to avoid leaving marks on the surface.
4. Minimize the Chip Effect
Keep the cutting tool moving all the time(avoid staying in one place for too long) to prevent the chip from melting to the machined part. Coolant or cutting fluid can be used to reduce the temperature and remove chips.
5. Machining Feed
Apply large feed rate and fast spindle speed, the approximate estimation is about 3 times as aluminum feeds and a corresponding cutting speed.
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