Studies On The Post Processing Of Selective Laser Melting

Selective laser melting(Selective Laser Melting,SLM)is an important part of the Addition Manufacturing,which uses the high energy laser beam to directly acts on the metal powder to form high density parts.SLM can produce complex shape structure,and has widely been applicated for in aerospace,biomedical and complex mold.SLM processing is a process of layer by layer accumulation and rapid temperature change,the uneven distribution of crystal structure will reduce the ductility of the material,and the internal accumulation of residual stress will lead to deformation and crack.In this paper,research the SLM processing of 316 L powder molding parts as the object,the ductility of the forming parts was improved by different post-processing methods,and the influence of different processing parameters on the crack is discussed.Different heat-treatment schemes of SLM forming part were formulated,and a heat-treatment method aiming to improve the toughness of parts effectively was proposed based on the schemes.The experimental results showed that the maximum tensile strength enhanced by 10.8% and elongation improved by 20% after the combination of solid solution and aging treatment compared with the unheated 316 L stainless parts.In addition,the improvement of heat-treatment on properties of tensile strength and elongation were further expounded via organizational change of forming part during heat-treatment process.Surface fissures and the cracks caused by stress release on SLM forming part were analyzed,and concluded that the forming defects aroused by SLM processing technology and stress concentration were the main reasons of causing cracks.Based the above research results,a method of reducing cracks and its impacts by surface treatments and adjusting SLM processing technic was came up with.Experiments indicated that the cracks after stress release under laser power of 200 W reduced by 54.5% compared with laser power of 160 W,and the cracks on the parts with personalized supports reduced by 20% contrasted to the parts with columned supports.Based on the single channel and thin section experiments,the forming effects of different SLM processing technology were discussed,and the reasonable processing parameters of SLM were obtained combined with the post processing effects.The experimental results showed that the higher laser power had better quality,but it was difficult to control the forming effect.