Residual Stress Testing Of Machine Tool Lathe Bed And Research And Evaluation Of Vibratory Stress Relief

The important reason for the deformation of large parts of the machine tools and the reducing of the machining accuracy and accurate retentivity of the whole machine tools is residual stress in casting. It has been an issue for the whole machine tool industry in method to detect and eliminate the residual stress of large machine tool castings. How to eliminate the residual stress of castings has become an important research field in mechanical-building technology.Detection of residual stress of castings can provide data support for the selection of the process parameters of Vibratory Stress Relief. However, there are two important the strain release coefficients A and B to detect residual stress by blind-hole method. This article addresses the studies about the strain release coefficients of HT300, which is widely used by KUNMING MACHINE TOOL OF SHENGJI GROUP, and the accurate values and trends of Stress release coefficients A and B will be listed. The research shows that:(1) The elasticity modulus and Poisson ratio of HT300 about KUNMING MACHINE TOOL OF SHENGJI GROUP are 198GPa and 0.28. (2) The strain release coefficients of HT300 is loaded and demarcated hierarchically, the value of A of the strain release coefficients has a smaller increased, in the subsequent loading process, it is increased with the decrease of loads. But the value of B of the strain release coefficients is decreased with the increase of loads. (3) The error due to the patch and borehole deviation was enlarged with the increase of tensile stress.The blind hole method is used to test residual stress of the important work of machine tool bed surface. The measurement results show that:the distribution of two guide rails’residual stress is scattered, the values of all checkpoints’residual stress are relatively large, eighteen of the all values are over 100MPa, and the maximum principal stress and the minimum principal stress of all points are positive values. Which prove the machine tool bed surface has the large residual stress in the process of casting, the stress state of the most guide surface location is the tensile stress, and for the brittle material as cast iron, which can have an adverse impact to the casting.On this basis, the best process parameters of Vibratory Stress Relief were obtained by the simulate of finite-element analysis and the experiment of Vibratory Stress Relief, and the blind hole method was used to test the residual stress before and after Vibratory Stress Relief. The study shows that the support points of vibrating aging process and the position of exciting point are determined based on the result of machine tool bed’s modal analysis:the position of exciting point in the distance 0.6m of machine head and in the distance 0.7m of machine tail. According to the harmonic response analysis, the excitation forces is 40KN, and the exciting frequency is 55Hz, on the basis of the quality of the machine tool bed, we choose the excitation time for 40 minute. The aging parameters are applied to the experiment of Vibratory Stress Relief, the experimental results show that after the Vibratory Stress Relief, the residual stress of the most measurement points on the guide rail are decreased, the bandwidth of the overall stress level is narrowed, and the residual stress is homogenized. The stress state of the most measuring position from tensile stress state into compressive stress state, the tensile stress is harmful to the brittle materials such as cast iron parts, but the compressive stress is good for the brittle materials, so the overall performance of casting is improved after the Vibratory Stress Relief.In the process of Vibratory Stress Relief test, there are three acceleration time curve in (30-70) mm/s2 Which prove the aging parameters have a better effect on the elimination of residual stress.