The Mechanism And Key Technology Research On The Decrease Of Residual Tensile Stress In SKD11 Caused By Pulse Magnetic Treatment

Stamping dies are important machine tools which are widely used in metal forming field. They always work under high cyclic stress and contact pressure which make their life shorter than expected. Although heat treatment is the primary method to improve die life, it can't work well in some problems. Pulse magnetic treatment(PMT)is widely used to optimize the stress state of cutting tools as an alternative to treatment. However, the application of PMT in improving working life of stamping die is rarely reported and has no mature theories. This article focuses on revealing the mechanism of PMT and studying the application of PMT in stamping dies. Specific studies are summarized as follows:(1)A PMT device was developed. The pulse frequency was adjustable from 0 ~ 30 Hz while the magnetic field intensity from 0 ~ 2T. The main work included two aspects. Firstly, the parameters of magnetizer was tested and optimized by the finite element analysis software MAXWELL. Secondly, a pulse power with a single-chip controller was developed.(2)The influences of the magnetic field parameters on residual tensile stress of the SKD11 specimens were analyzed by single factor experiments. The micro-hardness of SKD11 before and after PMT was compared.(3)Some experimental results were explained from the ways of magnetostriction and system energy. The development of the residual stress under the magnetostrictive cyclic strain and the change of energy were analyzed. All experiment phenomena were explained by an innovative theory of dislocation. The process of PMT was divided into two stages in the new theory. The first stage was un-piling of the dislocation pile-up group and the second was multiplication of dislocation.Formula of was deduced and was the critical magnetic field strength which determined the un-piling of dislocation pile-up group in the first stage. Formula of and ? were also deduced. In the second stage, was the critical magnetic field strength which determined multiplication of a single Frank-Read dislocation source and ? determined a single dislocation overcoming the lattice resistance.(4)The principals of PMT in the application on stamping dies were established based on the experiments and the analysis.