Hybrid additive/subtractive manufacturing (ASHM) is recently developed to fabricate complex structures. High thermal gradient during the SLM process leads to large residual stresses, which could affect the surface quality of subjacent milled surfaces. This paper focuses on the surface quality of overhang features in selective laser melting (SLM)-based ASHM. An ASHM experiment with overhang feature was conducted for 6511 steel. A 3D thermo-mechanical coupled finite element (FE) model of SLM considering phase transformation of 6511 was established. The effects of volumetric change due to phase transformation on surface quality were studied. The predicted overhang surface quality was compared with that from the experiment. This paper could provide guidance to the process planning of ASHM with overhang features.
White light scanning interferometry (WLSI) is a fast, noncontact, high-precision method to measure three-dimensional (3D) surface profile and extensively used in roughness measurement of ultra-precision machined surface. However, due to Rayleigh criterion, the lateral resolution of WLSI is limited to hundreds of nanometers. It is hard to measure rough surfaces with delicate details that adjacent distance less than lateral resolution. Also, WLSI can’t measure profiles with large surface gradient for no light reflected and received by objective lens. In this work, with a proposed simulation measurement model, surface gradient error and lateral resolution error on measuring result of WLSI is studied by simulating the response characteristics of sinusoidal signal, square signal, sawtooth signal and actual surface profile of grinding silicon wafer measured by AFM respectively. The effectiveness of the simulation model is verified by comparing the simulation results with the experimental results. The mechanism of surface gradient error and lateral resolution error is revealed from the perspective of simulation analysis, which has certain guiding significance for the future research of error analysis on white light scanning interference.
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