Process measures to reduce deformation of machine tool guide rails during high-frequency induction quenching

A factory produces small machine tools, and the machine tool guide rail material is HT200 cast iron. Heat treatment uses high-frequency induction quenching and quenching heat treatment to strengthen the surface of the workpiece. The high-frequency induction heating quenching temperature is 900-950°C, and the quenching hardened layer is ≥1mm. The technical requirement is that the hardness of the workpiece after quenching is ≥44HRC. U-shaped inductors are used in production for continuous high-frequency Heating water spray cooling quenching method, after quenching, residual heat self-tempering heat treatment is performed. During production, it was found that after high-frequency induction heating annealing and quenching of the workpiece, the hardness and strength indicators are easy to ensure, but guide rail deformation is a common defect and problem. The deformation characteristics are smooth as both ends are lifted, and the tailstock is slightly lifted when broken.

Analysis shows that the rigidity of the workpiece and the heat treatment process are the main reasons for the deformation of the guide rail. The rigidity of the workpiece depends on the guide rail material and design structural factors. It is generally determined during processing and is not easy to change. The heat treatment process is a variable process. The size and distribution of the thermal stress and tissue stress caused by the deformation of the workpiece can be changed through process improvement or parameter adjustment. wait. In order to achieve the purpose of reducing and controlling the deformation of the workpiece. Generally speaking, the structural stress caused by the specific volume change caused by the quenching martensite transformation increases the volume of the workpiece, and the thermal stress caused by the temperature difference between the guide rail heating and quenching cooling and the uneven surface temperature cause the workpiece to shrink. , the surface area decreases; the warpage change of the guide rail surface is the result of the combined effect of these two stresses.

Tests have found that if the surface of a high-frequency heated workpiece is quickly cooled below 700°C, the rapid cooling of the guide rail will produce thermal stress that will deform the workpiece, which is opposite to the quenching deformation. This thermal stress can be used to offset the tissue stress generated during quenching of the workpiece, making the guide rail The disguise is greatly reduced. During the production test, high-frequency induction heating and normalizing treatment were used as preparatory heat treatment, and then the stress was mainly thermal stress. At the same time, normalizing and preparatory heat treatment could reduce and improve the casting defects of the workpiece, refine the pearlite, and improve the strength and hardness of the workpiece. , shorten the high-frequency heating time, and improve the quality and efficiency of subsequent high-frequency induction absolute heat machine quenching. Production tests also tried the fine planing and pressure method and the fixed pressure at both ends of the guide rail to reduce deformation, but the effect was not significant. Time has shown that high-frequency induction heating for quenching and normalizing using high-frequency induction heating is an effective process.