Tool wear, surface integrity and spheroidal chip analysis in micromilling of AISI H13 fabricated by additive manufacturing

Micromilling was used as a post-processing technique for additive manufactured AISI H13 (UNS T20813) tool steel produced by laser-beam direct energy deposition. Despite the increasing interest in micromilling, studies related to the micromilling of additively manufactured tool steels remain limited, particularly with respect to achieving low surface roughness. The influence of cutting speeds (12.57 m/min and 25.14 m/min) and cutting fluid on the tool wear mechanisms, wear evolution, cutting force, surface roughness, chip morphology and top burr formation was investigated. Moreover, the cutting conditions under dry and MQL machining were compared. The tests consist of the micromilling the microchannels using a 2-flute (Al, Ti)N-coated carbide microtool with a diameter of 0.4 mm. Tool wear was quantified based on tool diameter reduction and microchannel width. The average force of the peaks of the collected Fx signals, corresponding to the maximum cutting force at the maximum uncut chip thickness, was analyzed. Wear mechanisms, surface quality, chip morphology, and burr formation were evaluated using SEM images. Additionally, the amplitude roughness parameter Ra and the hybrid roughness parameter RΔq were evaluated using a profilometer for surface characterization. The results depicted that microchipping and adhesion at the cutting-edge were predominant. The roughness Ra values are lower than those reported by previous works on micromilling of additive manufactured steels. The spherical chips exhibit a smoother structure under MQL conditions and a layer-like texture under dry conditions. In dry machining, the cutting force and top burr width on the up-milling side were lower than in MQL machining.