Analysis Of DMLS With Various Scanning Patterns And Ultrasonically Aided DMLS Using Finite Element Method

Selective laser sintering (SLS) of metal powder is an important branch of fast archetypal manufacturing technology. However, limited by the factors of material and process, metal parts prepared by SLS possess a few disadvantages such as balling, curling and low compactness. The investigation of the effect of temperature field, stress field and the adscititious physical field on the SLS can lead to the systematical analysis and elimination of the disfigurements existed in the metal parts prepared by SLS. In this thesis, ANSYS, which is finite element simulation software, was used to numerically simulate the temperature field and stress field in the SLS of 316 stainless steel. In addition, this software was also used to qualitatively simulate the effect of ultrasonic vibration on the melting pool. The numerical calculating results by using this program are basically in agreement with the experimental results, thus the process factors could be fixed on through this simulation of SLS. In this thesis, the 2 dimensional (2D) and 3 dimensional (3D) models of the SLS of 316 stainless steel powder were constructed. APDL (ANSYS Parameter Design Language) was used to control the density of thermal flow, velocity and path of scanning. The temperature field and stress field of the single-layer-multiple-paths and multiple-layers-single-path sintering were studied. The simulation results suggest that, at the end of the scanning line, the dissymmetric temperature field and the great temperature gradient result in the balling phenomenon and great thermal stress, which could lead to the destruction of the sintering samples in this region. Because of the Coupling effect between scanning lines, the balling phenomenon is increased as the increase of the scanning lines, thus the over short scanning lines should be avoided in the sintering process. Different scanning strategies have significant influence on the sintering. Alternant scanning would decrease the quality of the samples, thus unidirect-scanning strategy should be adopted in practical manufacture.In this thesis, the response of melting pool of laser sintering under ultrasonic vibration was investigated. The results indicate that forced vibrations of the melting metal in the melting pool occurred under the ultrasonic vibration leading to the decrease of the viscosity of melting metal, which promotes the infiltration between melting pool and powder. The vibration causes the destruction of the dendritic crystal, the reorganization/rearrangement of the crystals and the distribution of the temperature field...