Improving the process of layerwise laser welding of metal parts by controlling residual stresses

Abstract

Background. Layerwise laser welding of metal parts allows you to get a weld in layers. As a result of the heating of the surface, thermal stresses sharply increase, caused by a non-stationary temperature field. The purpose of the study is to improve the process of layerwise laser welding of metal parts by controlling residual stresses by obtaining a product prototype on a 3D printer. The combination of rapid prototyping technology with a 3D scanning module and the prediction of residual stresses by digital technologies allow you to quickly make changes to a 3D computer model or lay the optimal path for a laser beam, analyze the stress-strain state of prototype parts, reducing financial costs in production. Materials and methods. Analytical and computer methods for studying thermal stresses in flat metal parts are used, digital models of the distribution of residual stresses over the surface and depth of the part are built. The results are verified experimentally by metallographic pilot studies. Results. The maximum load from thermal stresses during cyclic heating falls on the surface layer of the part, the amplitude of fluctuations in the deep layers is lower than the amplitude of stress fluctuations on the surface. The higher the intensity of heat transfer, the faster the part will collapse from fatigue, the smaller should be the value of the amplitude of fluctuations in the temperature of the medium, at which the part adapts to a given thermal loading cycle. The durability of the part depends on the frequency of temperature fluctuations. Conclusions. During the simulation, it was revealed that the additive mechanics of the laser can go through sinusoidal, rectangular, sawtooth cycles with the same duration of the cooling period and the heating period. The limits of change in thermal stresses on the surface of the part depend significantly on the specific type of temperature cycle of the medium. The maximum value of the amplitude of thermal stresses and the minimum value of the adaptive thermal loads occurs with a rectangular cycle. Moreover, vice versa, the minimum thermal stresses - with a sawtooth. With asymmetric periodic heating of the part, the amplitude of fluctuations of thermal stresses on the surface x = R does not depend on the intensity of heat transfer on the surface x = 0 and takes place only at small values of ωR2/a. For a large value of ωR2/a, there is no dependence of the amplitude of thermal stresses on the surface x = R on the intensity of heat transfer on the surface x = 0. The conducted pilot tests have shown that the additive layer-by-layer technology for welding a steel sheet with a laser beam and the analysis of the metallographic structure of the metal are consistent with the obtained data on the change in stresses over the section of the part. This confirms the accuracy of the theoretical and digital experiments. The technology can be used in stationary and mobile installations.

Keywords

• layerwise laser welding
• weld seam
• thermal stresses
• non-stationary temperature field
• rapid prototyping
• computer model
• metallographic analysis