L-PBF of 4340 Low Alloy Steel: Influence of Feedstock Powder, Layer Thickness, and Machine Maintenance

Laser powder bed fusion (L-PBF) is an additive manufacturing process in which a 3D part is fabricated by fusing metal powder together layer by layer. L-PBF has many variables which contribute to part performance, which include powder properties, process parameters, and machine condition. L-PBF is a relatively expensive process compared to traditional manufacturing. Feedstock material and build time are two major factors which contribute to the cost of the L-PBF process. Various methods were explored as ways to reduce the cost of 4340 steel parts manufactured by L-PBF, including fabricating the parts with thicker powder layers and expanding the allowable powder particle size range. In addition, the effects of powder porosity and recoater condition on producing consistent material properties in the manufactured part were also explored. The experimental results showed that allowing a larger powder particle size range and thicker powder layers was a possible method for reducing the cost of L-PBF-fabricated 4340 steel parts without significantly degrading the mechanical properties. Methods for measuring the allowable loose particle porosity will be emphasized in this report. Furthermore, the study also revealed the importance of the recoater condition because variation in the machine condition can negatively influence the part quality.