Parametric Thermal FE Analysis on the Laser Power Input and Powder Effective Thermal Conductivity during Selective Laser Melting of SS304L

Abstract

A low-cost parametric finite element thermal model is proposed to study the impact of the initial powder condition, such as diameter and packing density, on effective thermal conductivity as well as the impact of the laser power input on the final temperature distributions during selective laser melting (SLM). Stainless steel 304L is the material used, since it is not yet commercially available in SLM equipment and our main goal was to show the capabilities of the finite element method in the evaluation of power input in the process. The results from our sensitivity analysis showed that packing density has a greater impact on the final temperature distributions compared with powder diameter variance. However, overall the thermal conductivity of the powder only showed significant effects below the melting point, otherwise the thermal conductivity no longer affected the temperature distributions. Among the three different power inputs analyzed, the temperature profile demonstrated that power inputs of 100 and 200 W are recommended when printing SS-304L rather than 400 W, which generates too high temperature in the powder bed, a non-favorable behavior that can induce high residual stresses and material evaporation.

Transient Powder Melting in SLM Using an Analytical Model with Phase Change and Spherical Symmetry in a Semi-Infinite Medium

“…(2) An approximate analytical solution of the melting radius as a function of time is obtained by assuming a single material, i.e., solid powder, and by locating the radius where the temperature is at the melting temperature, as in [37]. (3) This simple approximation has the same steady-state result as the numerical solution, and also provides transient results close to the numerical solution, although the numerical solution includes the latent heat, and a higher heat capacity and conductivity for the fluid similar to the finite element analyses conducted by [34,35] for a moving heat source (Figure 4). The reason for this is that the heat conduction process is controlled by the material with the lower thermal diffusivity, i.e., the solid powder, and that the melt pool has small dimensions.…”

“…In the existing literature, time-intensive thermal models of the transient temperature distribution during SLM processing are presented using equivalent heat sources on the basis of the finite element analysis [34,35]. In this work, we focus exclusively on the transient heat transfer effects during the phase change, i.e., the melting, of solid powder to liquid, by proposing an analytical model.…”

The Influence of Powder Size and Packing Density on the Temperature Distribution in Selective Laser Melting

“…The packing density affects the contact radius, consequentially influencing the emissivity and finally the final effective thermal conductivity of the powder bed. Below are the porosity-dependent emissivity for all packing densities and the final effective thermal conductivity of all cases from 300K until of SS304L [7]. Figure 3 -Effective thermal conductivity of powder for SC, BCC and FCC with 20, 60 and 100μm of powder diameter for SS304L [7] In this study, it is considered three different packing densities, SC, BCC and FCC, with porosity of 0.2424, 0.3571 and 0.467 respectively, along with three powder diameters analysed, 20, 60 and 100μm.…”

“…Below are the porosity-dependent emissivity for all packing densities and the final effective thermal conductivity of all cases from 300K until of SS304L [7]. Figure 3 -Effective thermal conductivity of powder for SC, BCC and FCC with 20, 60 and 100μm of powder diameter for SS304L [7] In this study, it is considered three different packing densities, SC, BCC and FCC, with porosity of 0.2424, 0.3571 and 0.467 respectively, along with three powder diameters analysed, 20, 60 and 100μm. On previously work the effects of powder packing in the bed was not analyzed and a general value of 0.400 in porosity was adopted [3].…”

“…The thermal radiation term is highly influenced by the powder diameter, temperature and emissivity of the powder bed. In the other hand, the thermal conductivity due the contact between particles will vary according to the contact ratio and the initial solid thermal conductivity, since the value of the fractional contact area, Λ, is less than 3x10⁻⁴ [7].…”