Quality control of large-sized alloy steel parts fabricated by multi-laser selective laser melting (ML-SLM)

Additive manufacturing of large-sized parts remains challenging due to large residual stress and performance consistency. In this paper, a method of combining process, structure and performance was proposed to control the forming quality, and the brake disc for high-speed railways was chosen as a validation example. Meanwhile, multi-laser selective laser melting (ML-SLM) was adopted to prepare large-sized products. Research mainly includes process parameters optimization, mechanical properties distribution, and structural design. Process parameters of 24CrNiMo were optimized by exploring the influence of laser power and scanning speed on porosity, pore characteristics, and forming efficiency. Results show excessive heat input could reduce forming quality, causing an increase in either porosity or pore size. Mechanical properties research reveals that 24CrNiMo parts fabricated by ML-SLM have good consistency and overcome the strength-toughness tradeoff. The ultimate tensile strength reached 1255.25 MPa and impact energy was 101 J for single-laser regions. Furthermore, the new brake disc was redesigned with an innovative hollow self-supporting heat rib structure to enable a lightweight design and simplify post-processing. Finally, the qualified product was produced, and bench tests showed SLM-disc had higher performance. The work shows this method is effective and provides an engineering example for large-sized parts fabricated by ML-SLM.