Cutting principles of plastic materials
The most remarkable feature of plastics in processability is its poor stiffness and easy bending and deformation. In addition, thermoplastics also have poor thermal conductivity and are easy to heat up and soften. All these have caused certain difficulties in cutting.
When cutting plastic workpieces, it is best to use high-speed steel or cemented carbide tools, with a feed rate of 0.1 to 0.5 mm per revolution and a higher cutting speed. For the problem of heat generation in processing, the tool front angle of 10 degrees to 30 degrees and the tool back angle of 5 degrees to 15 degrees can be used. As long as the tool is sharp enough, it can produce banded chips and take away most of the heat. In addition, compressed air can also be used for effective cooling. Only celluloid material is an exception. Because it is easy to catch fire during cutting, it must be cooled with water.
During machining, if excessive short chips and dust are generated, the tool will become blunt and pollute the machine tool. The exposed parts and guide rails on the machine tool are the most vulnerable to pollution, so they must be protected.
Turning of plastic materials
Cemented carbide cutting tools are suitable for turning plastics, and the cutting speed varies with the thermosetting plastic box and thermoplastic. When turning thermosetting plastics such as phenolic plastic, amino plastic and adhesive tape board, the cutting speed should be 80 to 150 meters per minute; When turning PVC, nylon, bakelite and other thermoplastics, the cutting speed should be 200 to 600 meters per minute.
Milling of plastic materials
When milling plastics, if high-speed steel cutters are used, the milling speed is generally 35 to 100 meters per minute; If cemented carbide tools are used, the milling speed can be increased by 2 to 3 times. Therefore, cemented carbide tools are undoubtedly a better choice.
Drilling of plastic materials
For plastic drilling, a fried dough twist drill with a large spiral angle can be used, and when the hole diameter is greater than 30mm, a nesting drill can be used. Due to the obvious expansibility of plastic, when the drill bit is withdrawn after drilling, the hole diameter often shrinks, which is smaller than the diameter of the drill bit. Therefore, the diameter of the drill bit used should be larger than the required aperture, and the increase is generally between 0.05 and 0.1 mm. When using high-speed steel bits, the common cutting speed is between 40 and 80 meters per minute. When drilling, a piece of hardwood should be placed under the plastic to prevent the plastic from falling around the hole wall at the outlet of the drill.
Other cutting methods of plastic materials
In general, the processing methods of planing and slotting should not be used for plastics, because the cutting speed of these two processes is too low. But sometimes you can also use a woodworking planer for leveling and chamfering. When tapping plastic, high-speed steel wire cones with wide grooves can be used, and pay attention to the lubrication of asking price lubricating oil; External threads can be cut with a thread comb.
For thermosetting plastics such as nylon, bakelite and bakelite, they can be ground with loose white corundum or silicon carbide grinding wheel, or polished with abrasive cloth, but they need to be cooled with water. The grinding method is generally not recommended for the processing of thermoplastic because the grinding debris is easy to block the grinding wheel.