The module of the machine tool rack is 2mm, the number of teeth is 12, and the material is 40Cr steel. Heat treatment technical requirements: Quenching and tempering hardness is 18-22HRC, and heat treatment distortion requirements are small.
(1) Original technology and distortion issues. The quenching and tempering process is: (850±5)℃ The hardness requirement after tempering is 18-22HRC. During production, it was found that the quenched and tempered racks had large distortion during cold processing (plane milling, tooth milling, keyway milling) and could not meet the technical requirements, resulting in many racks being scrapped and the process unstable.
(2) Countermeasures. The main cause of rack distortion during cold working is the thermal stress generated during the quenching and tempering process. In order to eliminate the thermal stress of the rack, the following process measures can be taken:
1) Cool the oil after quenching and tempering at high temperature to prevent the second type of temper brittleness caused by slow cooling of the rack. After the rack is oil-cooled, the thermal stress is small and the impact toughness value is high.
2) After the rack is quenched and tempered, a medium-frequency induction heating machine is used for additional tempering to further reduce the thermal stress of the rack. The process is: (430±5)℃x4-8h heating and then air cooling. The test results show that after gear milling, the △ab value drops to 0.006-0.010mm, which can meet the technical requirements of high-precision racks.
(3) Effect. After adopting the improved technology, the rack distortion is greatly reduced, which meets the technical requirements. The product quality is excellent and the production is stable.
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GS-ZP-1200
