What is the reason why grinding cracks occur when the ball screw is quenched and heat treated using an intermediate frequency heating power supply?

After the surface of the ball screw is induction quenched by a medium frequency induction heating power supply and the thread is ground, through coloring or magnetic particle inspection, sometimes axial or network cracks appear on the arc of the thread raceway. In severe cases, even during the thread grinding process Visible to the naked eye. Grinding cracks are generally the result of a combination of problems in raw materials, heat treatment and grinding, but sometimes problems in one aspect are the main cause.

Generally speaking, the occurrence of ball screw grinding cracks can be avoided by taking measures in three aspects: raw materials, heat treatment and grinding.

(1) Raw materials. The quality of raw materials for ball screws should strictly comply with relevant material standards. During production, physical and chemical inspections of steel materials entering the factory should be carried out. If the network carbide exceeds the standard, normalizing + spheroidizing annealing should be performed; if the microstructure is unqualified, spheroidizing annealing should be performed.

(2) Heat treatment. When the screw uses a medium frequency induction heating power supply for induction quenching, the quenching inductor, the gap between the inductor and the screw should be correctly selected, the electrical parameters (such as current, voltage, output power) and moving speed should be correctly formulated, and the induction heating temperature and The heating time is to avoid overheating and coarse structures caused by excessive heating temperature, and to ensure that the screw is fully tempered after quenching. If the raw materials are qualified and the quenching temperature is not high, and even if the grinding specifications are adjusted during grinding, grinding cracks cannot be avoided, it should be considered to add one tempering after quenching, that is, two temperings after quenching, in order to more effectively release, Eliminate the internal stress generated during quenching of the screw and reduce the tendency of wear and tear. If grinding cracks are found during the grinding process, grinding should be stopped immediately and the remaining grinding amount should be measured. Depending on the remaining grinding amount, tempering or low-temperature aging can be performed again, which is very helpful in avoiding cracks during re-grinding. efficient.

(3) Grinding. Correctly formulate the grinding process to minimize grinding heat, such as rationally selecting the type, particle size, hardness and speed of the grinding wheel, reducing the feed amount each time, and selecting a cutting fluid with good cooling performance. At the same time, the operator should strictly implement the ball wire Rod grinding operating procedures.