Controlling the porosity of 316L stainless steel parts manufactured via the powder bed fusion process

Abstract

Purpose: The Pulsed Laser Powder Bed Fusion (PBF) process is an additive manufacturing technology that uses a laser with pulsed beam to melt metal powder. In this case Stainless Steel SS316L alloy is used to produce complex components. To produce components with acceptable mechanical performance requires a comprehensive understanding of process parameters and their interactions. This study aims to understand the influence of process parameters on reducing porosity and increasing part density. Design/methodology/approach: The Response Surface Method (RSM) is used to investigate the impact of changing critical parameters on the density of parts manufactured. Parameters considered include: point distance, exposure time, hatching distance and layer thickness. Part density was used to identify the most statistically significant parameters, before each parameter was analysed individually. Findings: A clear correlation between the number and shape of pores and the process parameters was identified. Point distance, exposure time and layer thickness were found to significantly affect part density. The interaction between these parameters also critically affected the development of porosity. Finally, a regression model was developed and verified experimentally and used to accurately predict part density. Practical and Research limitations/implications: The study considered a range of selected parameters relevant to the SS316L alloy. These parameters need to be modified for other alloys according to their physical properties. Originality/value: This study is believed to be the first systematic attempt to use RSM for the design of experiments (DOE) to investigate the effect of process parameters of the pulsed-laser PBF process on the density of SS316L alloy components.

Investigations on the Effect of Layers’ Thickness and Orientations in the Machining of Additively Manufactured Stainless Steel 316L

“…At the same time, the same energy density is appropriate for LT-60 resulting in low porosity, as shown in Figure 7 b. In the LT-80, the energy density becomes insufficient to penetrate into the powder layer to the pre-solidified layers due to the thermal loss to voids, which leads to un-melted powder particles and lack of fusion/joining with the previous layer, as shown in Figure 7 c. The degree of lack of laser penetration is further increased in the case of LT-100 resulting in an increased lack of fusion (welding between layers/poor connectivity) and higher porosity and voids [ 45 , 59 ], as shown in Figure 7 d. This is because varying surface roughness and porosity is encountered for L-PBF parts produced with different LTs [ 60 , 61 ]. The differences in porosity and lack of fusion can be noted between the side and top faces for LTs 30, 60, 80 and 100 μm, as shown in Figure 8 .…”

“…At the same time, the differences are 1.7% for LT-60. The reason of LT-60 eliminates the effect of L-PBF part orientation concerning the milling TFD due to the enhanced fusion/consolidation of the L-PBF layers, low porosity and lesser differences between the side and top faces [ 45 , 59 ]. Since the same energy density was used for all LTs.…”

“…To study the exclusive effect of the layer thickness on machining, the energy density was kept constant by changing the exposure time according to the relation shown in Equation (1). The L-PBF parameters listed in Table 2 were determined using previous research [ 45 ]. Energy density = (laser power)/(hatching distance × scan speed × layer thickness), …”

“…The diameter of the laser beam was 70 ± 5 µm and the build volume capacity of the unit was 250 × 250 × 300 mm 3 . The scan strategy used in this study was Meander where the scan direction of a layer rotates 67 degrees from the previous layer [45,46]. Four samples were fabricated with four different layer thicknesses (LT), as shown in Figure 1a for the actual parts, and the schematics parts, as shown in Figure 1b.…”

Porosity Analysis of Additive Manufactured Parts Using CAQ Technology

“…It was stated that this low pore volume did not affect the mechanical properties of the parts produced by the additive technology from 316L material. Al Faifi [ 29 ] identified the most statistically significant parameters of laser processing. The article identified the relationship between the number of pores and the parameters of the sintering process.…”