Polytetrafluoroethylene material is a polymer of tetrafluoroethylene, and the color is white. PTFE has the following characteristics.

1) Non-hygroscopic, non-flammable, stable to oxygen and ultraviolet rays, and good weather resistance.

It is hardly corroded by any chemical reagents.

3) Good insulation performance, low dielectric loss, self-lubricating.

4) The coefficient of friction between plastics is small, making it an ideal oil-free lubricating material.

5) The material is soft and easy to cut. It is a kind of easy-to-process material.

PTFE materials are widely used in nuclear energy, aerospace, electronics, electrical, chemical, machinery, instrumentation, construction, textile and food industries.

2. Problems and causes in the processing of PTFE boxes

The PTFE material at the bottom of the box is very thin, only 1mm. The original processing technology is to press the surrounding area with a pressing plate, and cut from the inside to the outside with a φ6mm end mill. At 2mm, because the PTFE material is softer, the bottom surface becomes thinner and thinner, and the strength gradually decreases. Under the action of cutting force, vibration will be generated, and the bottom surface will be pulled up or torn when processing continues. The entire part is scrapped.

According to analysis, due to the soft material of the part, after the material of the part is gradually removed, when the cutting force is greater than the strength of the material, the bottom surface of the part will be pulled up or torn.

3. Improved process plan

According to the characteristics of the materials, a set of processing schemes were reworked.

1) Divide the inner cavity of the part into 4 small pieces, reserve <6mm ribs in the middle, the main purpose is to reduce the area of one-time cutting. Through the reinforcing ribs in the middle, the strength of the processing area at the bottom of the part is enhanced, so that the bottom surface of the part is not easy to be pulled up or torn.

2) Change the cutting path and cutting depth, as shown in Figure 3. Cut the knife from the middle position of the 4 small cavities, and the machining depth is directly to -9mm in the Z direction. No layered progressive processing is used to keep the thickness of the surrounding materials at 9mm. When the strength of the material is greater than the cutting force, the bottom surface will not be pulled up or torn.

3) Use circular machining tool path from inside to outside, and cut the edge of the part into a circle in a clockwise direction. When cutting clockwise, the cutting force is downward, which has the effect of pressing down the parts. When the part margin is reduced, the bottom surface will not pull up.

4) The tool speed is generally controlled at 3000r/min, and the feed speed is 500mm/min. This set of cutting parameters is obtained after verification. The speed of the tool matches the feed speed. During the machining process, the heat and cutting force of the parts can be reduced. After the parts are disassembled, there will be no excessive stress or deformation.

5) After processing 4 small cavities, when removing the middle stiffener, the key technology is to flatten the bottom of the part through the action of 4 magnets and fix it with a workbench, as shown in Figure 4. For the layer-by-layer treatment of the ribs, the middle ribs are removed through 3 incisions.