The heat treatment deformation of the industrial sewing machine frame can be easily dealt with by the medium frequency induction heating machine

The tooth frame is an important part of the industrial sewing machine and is made of 20Cr cast steel. The tooth frame is subjected to rapid movement contact stress during work, which requires it to have high wear resistance. The tooth frame is a precision fitting component and requires high dimensional accuracy. The part was originally carburized and quenched. The depth of the carburized layer was 0.3-0.5mm. The hardness after quenching was 55-60HRC. After treatment, the warpage deformation of both sides of the workpiece was ≤0.1mm. The parallelism tolerance and expansion and contraction between the forks were even. ≤0.1mm. During production, it was found that the warping deformation of the bracket after carburization was so serious that it often failed to be finely ground to a size that met the technical requirements and the workpiece was scrapped. At the same time, it was very difficult to correct and shape the deformed bracket because the parts were complex and thin in size. The waist fork shoulders are easily broken during correction and shaping, and the scrap rate is very high during production.

The size of the frame deformation and casting stress are related to the as-cast structure. The coarser the grains, the smaller the yield strength, and the easier it is for the workpiece to deform after quenching. Therefore, to reduce casting deformation, it is necessary to eliminate casting stress and refine the cast structure, as well as eliminate the network structure that reduces the yield strength. The analysis shows that the bracket is a thin and long plate-shaped complex part, and the preparatory heat treatment of the workpiece is crucial to control its heat treatment deformation. The original preliminary heat treatment is normalizing treatment. Because the workpiece is thin and small, and the normalizing cooling speed is fast, new internal stress will be generated in the workpiece after cooling. Experiments and practice have proven that annealing is the best method for heat treatment of brace preparation. In order to reduce the deformation of the workpiece, the final heat treatment of the bracket is carried out in a medium frequency induction heating machine, which has better results. In terms of process parameters, cooling media, cooling methods and operating methods, technical corrections and improvement measures have been made to improve the process. During the quenching of the workpiece, the greater the difference between the quenching heating temperature and the cooling medium temperature, the greater the thermal stress and structural stress of the workpiece, and the greater the deformation of the workpiece. Therefore, the temperature of the quenching medium is increased and hot oil quenching with an oil temperature of 120-140°C is used. The loading and cooling methods of the racks have a significant impact on the deformation of the workpiece. To this end, a special spreader is designed and produced so that each rack is in a vertical and free hanging state without touching each other. After quenching and cooling, the oil is quickly poured into the oil and suspended. Hanging cooling, cooling effect is good.

After the bracket is treated with an improved heat treatment process, the surface hardness reaches 596-687HV (56-60HRC), the plane warpage is ≤0.1mm, and the parallelism and expansion and contraction of the fork part meet the technical requirements. The surface structure of the workpiece is fine granular carbonitride, nitrogen-containing tempered martensite and retained austenite, the transition zone metallographic structure is tempered martensite + retained austenite, and the core structure is lath martensite.

After the dental rack is produced using an improved process, the product quality is excellent and the performance is stable. The workpiece surface hardness, hardened layer depth, deformation amount and metallographic structure qualification rate are greater than 98%, saving a lot of correction and shaping man-hours, and the technical and economic benefits are obvious. If you still don’t understand anything about the improved heat treatment process, you can read more books on heat treatment. I believe you will gain a lot.