Experimental Study of Micromilling of H13 Tool Steel Manufactured by Directed Energy Deposition

Parts manufactured by additive manufacturing (AM) processes have rough surface finish and poor dimensional accuracy, therefore, post-processing must be required. Among the post-processing techniques, micro-milling is popular. Since machinability of materials manufactured by AM differs from those manufactured conventionally, this work investigates the micromilling of AISI H13 tool steel manufactured by the laser-beam directed energy deposition (LDED) and compares it with the micromilling of the same steel obtained by hot rolling and annealing heat treatment. Both quality of the machined surface and the cutting force were analyzed to assess the machinability. The force signals were acquired using a Kistler dynamometer and signal amplifier, and a National Instruments acquisition board and a computer with LabView Signal Express software. Roughness of a micromilled channel was measured using a Taylor Hobson profilometer. Micromilling was performed with the Minitech micromilling system with a maximum speed of 60,000 rpm. Mitsubishi’s (Al,Ti)N coated carbide tool, with a cutting diameter of 400 µm were used. The cutting parameters included a cutting speed of 12.6 m/min, feed per tooth of 10 µm/tooth, axial depth of cut of 40 µm and radial depth of cut equal to 400 µm. Longer milling time caused a reduction of surface roughness Ra and an increase in the cutting force. No statistically significance differences between the Ra values and the cutting force obtained for micromilling the hot rolled versus LDED samples. However, the wear results of the microtools were compatible with the differences in the hardness of the analyzed samples.