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In sheet metal stamping, galling is initiated and developed aggressively at the mould radius, where sheet metal undergoes large plastic deformation. This study sheds light on correlating the level of sheet plastic deformation with galling initiation on the mould surface. The 3D topography facilitated the observation of galling evolution process on the surface of quenched/tempered mould. The observation on the sliding sheet counterpart showed that with larger plastic deformation, zinc-coated surface tended to become rough and a large number of intermittent micro-cracks formed, leading to earlier initiation of galling. Furthermore, the surface of mould was treated by physical vapour depositing (PVD) of CrN. In the specific sliding tests under the same level of plastic deformation, critical total slid distance at which galling initiated was increased significantly. The major factor causing galling initiation on the PVD(CrN)-coated mould was identified.

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We propose a bi-layer 5-tip edge coupler in a multilayer silicon nitride-on-silicon (SiN-on-Si) waveguide platform. The coupler is used for the integration between a monolithic 1550 nm laser and a single-mode SiN waveguide. The simulated coupling efficiency is 92.8%. The vertical 1-dB-loss misalignment tolerance is as large as 0.5 µm. Broad 1-dB-drop bandwidth (1338 nm to 1700 nm) and small footprint (total length: 38.2 µm) are achieved simultaneously. A broadband bi-layer SiN-Si adiabatic transition cascaded to the edge coupler is designed to couple the laser power into a single-mode Si waveguide at an efficiency of 90.6%. Lowcomputation-cost electromagnetic numerical simulation and optimization strategies are applied to improve the reverse design of the complex couplers.