| Selective Laser Melting(SLM)can be used to directly manufacture complex parts made out of metal,it’s one of technologies which have the best development prospects in Additive Manufacturing field.During SLM construction process,the materials melt and solidify rapidly under the influence of high-energy laser;so selective laser melted parts easily accumulate high temperature gradients,a large amount of residual stress and distortions.Residual stress and distortions are deleterious to SLM parts’ mechanical properties,dimensional accuracy,and applied ranges.Therefore,the study on the distortions of parts in SLM process is very important to enhance the prototyping quality and improve SLM basal techniques.Distortions of overhanging parts which manufactured based on supports during SLM process have been researched in this paper.The main research contents as follows:(1)Principles and features of SLM manufacturing process were analyzed.Parts and structures which have different angles of inclination were analyzed from the viewpoints of layered slicing,horizontal distribution long stripe structures which have different lengths are the fundamental elements of SLM parts,so researches on the distortions of horizontal distribution long stripe structures are the basel of control on the distortions of parts which has different angles of inclination.(2)Distortions of long stripe parts under the influence of different types of re-melting,outer structures,and supports were researched in the experiments.For the displacements in the height direction at the two ends of long stripe parts,contant sections partial re-melting can reduce the displacements to 60-80% compared to formal part without any treatments,variable sections partial re-melting reduce the displacements to 10-40%;outer structures can restrain the displacements in the height direction at the two ends of long stripe parts absolutely.(3)Based on theories of temperature field and thermal expansion,a three-dimensional distortions finite element model of 316 L processed by SLM was developed.The mechanisms of distortions on unilateral fixed overhanging parts and bilateral free overhanging parts were researched under the influence of different re-melting ways.The evolution of long stripe parts’ distortions and stress field during the SLM construction and removing supports process was studied.(4)Based on the results of SLM experiments and simulations,a new way which can decrease the distortions of overhanging parts which manufactured based on supports was proposed.When the forming height less than 0.5 millimeter,extending of the parts at the direction of length by using outer structures can compensate the shrinkage;when the forming height exceed 0.5 millimeter,different ways of re-melting can be used to reduce the distortions.Composite combination of re-melting,outer structures,supports and heat treatment can reduce the distortions most effectively.To sum up,features of SLM manufacturing process were analyzed in this paper,an opinion that horizontal distribution long stripe structures which have different lengths are the fundamental elements of SLM parts were put forward.Mechanisms of distortions were analyzed based on SLM construction experiments and finite element simulations.Finally,some effective ways which can decrease the distortions of SLM overhanging parts were proposed. |
