What effect does grinding have on plastic bottle cap moulds?

The essence of the grinding process of the plastic bottle cap mold is that the metal surface of the workpiece is ground, deformed under the instantaneous extrusion and friction of countless abrasive grains, and then turned into abrasive debris, and the process of forming a smooth surface. Grinding The whole process is manifested as the action of force and heat. What is the effect on the plastic bottle cap mold during the grinding process?

① During the grinding process, the processed surface generates thermal expansion under the action of cutting heat. At this time, the temperature of the base metal is low, so the surface generates thermal compressive stress. When the grinding ends, the surface temperature of the workpiece decreases, because the surface has produced a thermal state The plastic deformation is limited by the matrix, so the surface produces residual tensile stress, and the inner layer produces residual compressive stress.

② During grinding, the grinding wheel and the workpiece are in contact with the arc surface. When the grinding wheel is cutting, the workpiece produces plastic deformation and severe frictional resistance between the grinding wheel and the workpiece, thus forming a grinding force of equal size and opposite direction between the grinding wheel and the workpiece. When the material is plastically deformed, the relative displacement between the metal molecules inside the workpiece material will form internal friction and generate heat, and the external friction between the grinding wheel and the workpiece will also generate heat. High temperature, and the grinding wheel is not easy to conduct heat, so 80% of the heat is transmitted to the workpiece and grinding debris, and the metal changes from one lattice to another with the change of temperature in the solid state, and the transformation of metallographic structure occurs. , when grinding hardened steel, the cooling is sufficient, secondary quenching occurs on the surface layer, part of the retained austenite is transformed into martensite, and the specific volume of martensite is large, the specific volume increases, and compressive stress occurs on the surface. If the cutting cooling is not good, or no coolant is used, the surface will be tempered, martensitic transformation will occur, and tensile stress will be generated on the surface (for example, the volume of iron will expand by 1% when γFe is transformed into α-Fe), these stresses (residual stress can be 500~1000MPa), if the yield limit of the material is exceeded, grinding cracks will occur. In addition, the mold is not tempered immediately after heat treatment and quenching, the quenching temperature is too high, there is network carbonization, and untempered martensite after tempering Or too much residual austenite, phase transformation will occur during grinding, and stress will cause cracks on the surface of the workpiece. Grinding cracks are very fine surface cracks. There are generally three types of grinding cracks: parallel lines, Network cracks and eight-shaped cracks. The direction of the cracks is related to the shape of the mold, and the development direction of the cracks is related to the grinding direction of the grinding wheel on the surface of the workpiece. The depth is within 0.03mm.

③ During grinding, the grinding wheel is not sharp, the amount of feed is large, and the cooling is poor, which makes the surface of the workpiece reach a temperature of 300 ° C, causing burns on the surface of the workpiece.

A little bit of inappropriateness in the grinding process will damage the workpiece produced by the plastic bottle cap mold.