Hard alloy tool machining methods

The hardness of cemented carbide inserts is high, they are brittle, have poor thermal conductivity, and a large thermal contraction rate. Diamond grinding wheels are typically used for sharpening, but due to their high cost and difficulty in repairing after wear, many factories still use conventional grinding wheels. During the sharpening process, because of the high hardness of cemented carbide, the abrasive grains of conventional grinding wheels dull easily, and the intense friction generates localized high temperatures on the insert surface, creating additional thermal stress. This can easily lead to thermal deformation and thermal cracks, directly affecting the tool's service life and machining quality. Therefore, necessary measures should be taken to prevent the generation of grinding cracks. Through processing practice, the following process measures have been summarized as effective in preventing or reducing grinding cracks:

1. Negative rake grinding method: The negative rake grinding method involves grinding a negative rake land on the rake face or flank face of the tool before sharpening. Cemented carbide is a hard and brittle material, and during sharpening, vibrations from the grinding wheel can subject the tool to impact loads, causing vibration cracks. At the same time, the instantaneous temperature rise and cooling in the grinding zone can generate thermal stresses that may exceed the strength limit of the cemented carbide, leading to thermal cracks. Adopting the negative rake grinding method can improve the strength of the insert, enhance its resistance to vibration and impact loads, and increase the heated area, preventing the grinding heat from being directed to the insert in large quantities, thereby reducing or preventing the generation of cracks.

2. Infiltrating the grinding wheel with molybdenum disulfide: In a normal temperature state, a mixed solution is prepared from powdered molybdenum disulfide and anhydrous ethanol. Then, in a sealed container (to prevent ethanol evaporation), a new conventional grinding wheel is immersed in the mixed solution for 14 hours before being removed and allowed to dry naturally for 18-20 hours until the grinding wheel is completely dry. The internal pores of the grinding wheel treated in this way are filled with molybdenum disulfide, which lubricates the abrasive grains, allowing the grinding wheel to discharge chips well without clogging easily. Tests have shown that when using a grinding wheel infiltrated with molybdenum disulfide to grind cemented carbide inserts, the grinding is sharp, the abrasive grains do not dull easily, the workpiece deformation is small, the chip discharge is smooth, and the chip shape is mostly ribbon-like, taking away most of the grinding heat and thus improving the grinding effect and increasing the yield of finished inserts.

3. Reasonable selection of grinding parameters: If the friction during the sharpening process is too high, it can cause the grinding temperature to rise sharply, leading to bursting of the insert. Therefore, it is very important to select reasonable grinding parameters. Commonly used reasonable grinding parameters are: circumferential speed v=10-15 m/min, longitudinal feed rate f_long=0.5-1.0 m/min, and cross feed rate f_cross=0.01-0.02 mm/pass. When sharpening manually, neither the longitudinal nor the cross feed rate should be too large.

4. Other process measures: Insufficient rigidity of the tool holder, unstable clamping of the tool, and runout of the machine tool spindle can all cause grinding cracks. Therefore, the machining system consisting of the machine tool, grinding wheel, fixture, and tool should have sufficient rigidity, and the axial and radial runout of the grinding wheel should be controlled. There are many factors that can cause grinding cracks in cemented carbide tools. Only by selecting a suitable grinding wheel and adopting a reasonable grinding process can cracks be effectively avoided and the sharpening quality be improved. SGS cemented carbide milling cutter.