Milling investigations and yield strength calculations for nickel alloy Inconel 625 manufactured with laser powder bed fusion process

Abstract

Additive manufacturing processes such as laser powder bed fusion (LPBF) are progressively implemented in industry due to increased flexibility and ability to produce complex geometries. However, the required dimensional and surface quality cannot be achieved even tough nearly fully dense net-shaped components are manufactured. Precision surfaces for design requirement can only be achieved with subsequent machining processes. Therefore, in this paper, milling investigations on nickel alloy Inconel 625 workpiece samples that were built using LPBF-based additive manufacturing process have been conducted. The samples were fabricated using different layer-to-layer scan strategy rotations. The side milling experiments were performed on machining of surfaces in horizontal (XY) and vertical (Z) orientations. It was observed that machining forces were influenced by the relative engagements of cutter feed direction and workpiece built directions. When milling cutter was fed against the vertical direction, lower peak forces with higher deviations were recorded. On the contrary, feeding the milling cutter along the vertical build direction resulted in higher peak forces with lower deviations. By using metal cutting principles, shear yield stress and yield strength at each milling case and relative engagements were identified. The results indicate that the yield stress is higher along the horizontal (XY) orientation and affects the milling forces and it is lower vertical (Z) build direction however, a scan strategy rotation of 90° layer-wise built provides an increase in yield strength as well as at higher cutting speeds due to strain-hardening behaviour of additively fabricated Inconel 625 material.