Research On Elimination Of Stress By Hammering In Laser Die Repair

Hot work dies in the process of long-term by the alternating stress,the mold surface prone to fatigue crack.Pulsed laser welding of low power and fill wire is widely used in die repairing because of its improved welding zone organization and getting good mechanical properties.High power density and fast cooling rate of laser fill wire welding;there is a large welding residual stress after welding.Welding residual tensile stress will promote the initiation and expansion of cracks and accelerate the repair of mold failure.Hammering can reduce welding residual tensile stress,and in the hammer area to produce residual compressive stress to improve the service life of the mold after repair.However,the hammering has not formed the relevant process specification and the use of die repair is mainly based on experience,limiting the use of hammering in the mold repair.In this paper,the welding residual stress produced by the hammering elimination of the laser filler die is analyzed by finite element method and experimentally verified;through the Marc finite element software simulation and experimental research methods.The purpose of this paper is to provide data support and reasonable hammering scheme for the application of hammering in die repair,and to promote the application of hammering in mold repair and eliminate stress.In this paper,the heat transfer process of low power pulsed laser welding is simulated by a compound heat source model of Gaussian surface heat source and a rotating body heat source combined.The error is within the reasonable range by experimental results.This composite heat source model can be used to simulate the die repairing process of pulsed laser welding of low power and fill wire.The finite element simulation and experimental data show that there is a high welding residual tensile stress in the repairing zone of the laser filler wire repairing die,which is close to the yield strength of the material.Residual tensile stress is also the main residualstress in the fusion zone.Experimental results show that the microstructure of the weld zone is mainly martensite and tempered martensite,the structure is coarse and the mechanical properties are worse than those of weld and base metal.Here,the crack initiation and propagation is easy.The hammering force is measured by the hammer force acquisition system.The size and change process of hammering force of ordinary adult using the standard 1 b hand hammer are measured with small force,moderate force and slight force.The interaction time and peak residence time of the hammering force were 0.02 s and 0.002 s,and their peak values were 254 N,848 N,2096 N and 4806 N.Finite element simulation analysis and experimental verification show that hammering can reduce the welding residual stress in the hammering area.When the hammer stress exceeds the yield strength of the material,the residual compressive stress will be generated on the mold surface.The equivalent plastic strain of the die surface after hammering is small,and the maximum equivalent plastic strain ε is 0.00675.The elimination of the welding residual stress and the residual compressive stress produced by the hammering on the die repairing area effectively reduce the initiation and propagation of the fatigue crack in the repairing area after the die is repaired.