Vacuum heat treatment for die manufacturing

Vacuum heat treatment technology is a new type of heat treatment technology developed in recent years. Its characteristics are urgently needed in die manufacturing, such as preventing heating oxidation and decarbonization, vacuum degassing or degassing, eliminating hydrogen embrittlement, thereby improving the plasticity, toughness and fatigue strength of materials (parts). The factors such as slow vacuum heating and small temperature difference between inside and outside of parts determine the small deformation of parts caused by vacuum heat treatment process.

According to the different cooling medium used, vacuum quenching can be divided into vacuum oil quenching, vacuum gas quenching, vacuum water quenching and vacuum nitrate isothermal quenching. Vacuum oil quenching, vacuum gas quenching and vacuum tempering are the main applications of vacuum heat treatment of dies. In order to maintain the excellent characteristics of vacuum heating of workpieces (such as dies), the selection and formulation of coolant and cooling technology are very important. Oil-cooled and air-cooled are mainly used in the quenching process of dies.

For the die working face which is no longer machined after heat treatment, vacuum tempering is adopted as far as possible after quenching, especially for the vacuum quenched workpiece (die). It can improve the mechanical properties related to surface quality, such as fatigue performance, surface brightness, and corrosiveness.

Successful development and application of computer simulation technology for heat treatment process (including structure simulation and performance prediction technology) make it possible to intellectualize heat treatment of dies. Because of the characteristics of small batch (or even single piece) and multi-variety in mould production, as well as the high requirement of heat treatment performance and the characteristics of no waste products, intelligent heat treatment of mould becomes necessary. Intelligent heat treatment of dies includes: defining the structure, material and heat treatment performance requirements of dies; computer simulation of temperature field and stress field distribution in the heating process of dies; computer simulation of temperature field, phase transformation process and stress field distribution in the cooling process of dies; simulation of heating and cooling process; formulation of quenching process; automatic control technology of heat treatment equipment. In the field of vacuum high pressure gas quenching, developed countries, such as the United States and Japan, have carried out research and development in this field, aiming mainly at dies and moulds.