激光模具修复锤击消除应力方法研究

发布时间：2018-09-03 12:58

【摘要】：热作模具在交变应力下长期服役,其表面容易产生裂纹,造成疲劳失效。小功率脉冲激光填丝焊接能改善焊接区组织,获得良好的力学性能,在模具修复中得到广泛应用。激光填丝焊接能量密度高,金属熔化和冷却迅速,焊接区存在较大焊接残余应力,其拉应力对裂纹萌生和扩展有促进作用,加快修复模具的失效。锤击可降低残余拉应力,并可在锤击区产生残余压应力,提高修复模具的使用寿命。但锤击至今没有形成相关工艺规范,在模具修复中的使用主要建立在经验的基础上,限制了锤击在模具修复中的应用。本文通过Marc有限元软件模拟计算并与实验相结合的研究方法,分析锤击对激光填丝焊接模具修复产生的焊接残余应力的消除状况;旨在为锤击在模具修复中的应用提供数据支持和合理的锤击方案,推广锤击在模具修复消除应力方面的应用。本文通过建立的高斯面热源和旋转体热源复合热源模型模拟小功率脉冲激光焊接的热传导过程,通过实验验证误差在合理范围内,可利用此复合热源模型模拟小功率激光填丝焊接模具修复过程。有限元模拟和实验表明,激光填丝模具修复在模具修复区存在较高残余拉应力,接近热作模具材料的屈服强度,熔合区残余应力以拉应力为主;实验表明熔合区组织以淬火马氏体和回火马氏体为主,组织粗大,力学性能较焊缝和母材差,裂纹容易在此处萌生和扩展。通过构建的锤击力采集系统对锤击力进行测量,测得普通成人利用标准1 b手锤轻击、用较小力,中等力气和稍大力锤击时锤击力的大小和变化过程,锤击力的作用时间和峰值停留时间极短,作用时间分别为0.02 s和0.002 s,峰值分别为254 N、848 N、2096 N和4806 N。利用Marc有限元模拟计算和实验表明,锤击可降低模具修复中产生的焊接残余应力,当锤击应力超过材料的屈服强度时,模具表面产生残余压应力;锤击后模具表面等效塑性应变较小,最大值为0.00675。锤击通过消除模具修复区焊接残余应力和产生残余压应力,将有效降低模具修复后使用过程中在修复区疲劳裂纹的萌生和扩展。
[Abstract]:Low power pulsed laser wire-filling welding can improve the microstructure of the welding zone and obtain good mechanical properties. It is widely used in die repair. Laser wire-filling welding has high energy density, rapid metal melting and cooling, and large welding area. Hammering can reduce the residual tensile stress, produce residual compressive stress in the hammering zone, and improve the service life of the repairing die. However, hammering has not formed the relevant technical specifications, and the use in the repair of the die is mainly based on experience. Based on this, the application of hammering in die repair is limited. In this paper, the elimination of welding residual stress caused by hammering in laser wire-filling welding die repair is analyzed by the method of Marc finite element simulation and experiment. The purpose is to provide data support and reasonable hammering for the application of hammering in die repair. In this paper, the heat conduction process of low power pulsed laser welding is simulated by using the combined heat source model of Gaussian surface heat source and rotating body heat source. Finite element simulation and experiments show that there is a high residual tensile stress in the repair zone of the laser-filled die, which is close to the yield strength of the hot-working die material, and the residual stress in the fusion zone is mainly tensile stress. The hammering force is measured by the hammering force acquisition system. The magnitude and variation process of the hammering force are measured when ordinary adults use standard 1b hand hammer to strike lightly with small force, medium force and slightly strong hammering. The action time and peak residence time of the hammering force are very short. The results of finite element simulation and experiment show that hammering can reduce the welding residual stress produced in the repair of the die. When the hammering stress exceeds the yield strength of the material, the residual compressive stress is produced on the die surface; the equivalent plastic strain of the die surface after hammering is higher than that after hammering. The hammering can effectively reduce the fatigue crack initiation and propagation in the repair area of the die after repair by eliminating welding residual stress and generating residual compressive stress in the repair area of the die.
【学位授予单位】：哈尔滨理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG76

【相似文献】