Finite-element analysis of effects of the laser-processed bimaterial component size on stresses and distortion

Abstract

Processing of bimaterial parts via a moving laser beam has been investigated using three-dimensional (3D) finite-element modeling. Effects of the size of parts on the temperature distribution, thermal transient stresses, residual stresses, and distortion have been evaluated. The result indicates that the size of the part to be processed has strong influence on the transient temperature, transient stresses, residual stresses, and distortion of the part. Distortion is small when the size of the part is small and can be predicted from the thermal-expansion mismatch between the two materials. However, when the size of the part becomes large, both distortion and residual stresses increase. Furthermore, both distortion and residual stresses, in this case, cannot be predicted based on the thermal-expansion mismatch alone. The distortion, in this case, is mainly determined by the asymmetrical plastic deformation driven by transient thermal stresses, while residual stresses are dictated by the thermal-expansion mismatch and the temperature gradient of the part before and during cooling.

Texture characterisation of hexagonal metals: Magnesium AZ91 alloy, welded by laser processing

“…The origin of residual stresses and their evolution within a welded joint is difficult to evaluate because they are the result of a number of competing mechanisms: shrinkage changes in phase and microstructure [30]. In our case, the magnesium does not undergo a phase transformation, as is the case for aluminium alloys.…”

“…Their behaviour in tension and their variation have in part been explained by the influence of the thermal cycle on the origin of residual stresses and their evolution within the material [38,39]. The residual stresses on the face exposed to the laser beam are elevated (up to 80 MPa) whereas the opposite face creates stresses of only 23 and 7 MPa respectively for the longitudinal and transverse stresses.…”

Simulation of metallic powder bed additive manufacturing processes with the finite element method: A critical review

“…Other studies utilize a uniform mesh for the whole model. 36,50,52,[59][60][61][62] In the two previous cases, the mesh thickness is usually equal to the layer thickness. 37 The solid substrate can be meshed with larger element size than the overlying layers in order to reduce simulation time, 40,43,51,63,64 as shown in Figure 6.…”

“…34 However, in a number of studies, the density has been considered to be constant, in order to reduce the complexity of the analysis. 34,41,49,51,52,59–62,69 Other studies consider two different densities for the powder and the solid state. 35–37,42,44,70 In those studies, the powder density can vary from 40% to 60% of the solid density, depending on which assumption for the powder packing is followed.…”

“…As in the case of the thermal conductivity, several studies use pre-defined values for the heat capacity and the value for any given temperature point is calculated by linear interpolation or extrapolation. 34,41–47,49,51,52,59–62,64,69,73,78 The specific heat capacity of powder beds can be found taking into account the powder bulk density or for powder mixtures applying the law of Kopp–Neumann. 63 Other studies consider constant specific heat.…”