Improved Feasible-Set Method for Removing Mesh Inversion

This paper presents a new computational method based on the feasible-set method (Berndt, Kucharik, and Shashkov, 2010, “Using the Feasible Set Method for Rezoning in ALE,” Procedia Comput., 1(1), pp. 1879–1886 and Vachal, Garimella, and Shashkov, 2004, “Untangling of 2D Meshes in ALE Simulations,” J. Comput. Phys., 196, pp. 627–644) for removing inverted elements in surface and volume meshes. The proposed method calculates a region for each node called a “feasible set” in which the node can reside without creating an inverted element. The node is then relocated within the region so that the number of inverted elements is reduced. Unlike the original feasible-set method, it is applicable to nonplanar surface meshes, volume meshes, and also has a step for recovering a feasible set when the set is empty. While various useful mesh optimization techniques have been proposed over several decades, many of them do not work well if the initial mesh has inverted elements. Additionally, some mesh optimizations create new inverted elements when the mesh topology is highly irregular. The goal of the proposed method is to remove mesh inversion without creating a new inverted element. The proposed method is useful for preconditioning for conventional smoothing techniques, which require that the initial mesh be inversion free. It is also useful for correcting inverted elements created by conventional smoothing techniques. The effectiveness of the improved method has been verified by applying it to the facet-repair and the boundary-layer generation problems.

Concave Diffraction Gratings by High-Precision Injection Moulding

As an example of the applicable process chain, a concave grating (1175 grooves/mm) with an active area of approx. 24 mm to 24 mm has been replicated by means of electroplating and further by injection moulding with polycarbonate, resulting in a surface accuracy even below 4 µm peak-to-valley (PV). The obtained moulds were further metallised with bare aluminium to obtain components for optical applications. To our knowledge, this is the first time that such a large nanostructured nonplanar surface has been manufactured by injection moulding in such an accuracy.

Selective Surface Sintering Using a Laser-Induced Breakdown Spectroscopy System

Titanium metal injection molding allows creation of complex metal parts that are lightweight and biocompatible with reduced cost in comparison with machining titanium. Laser-induced breakdown spectroscopy (LIBS) can be used to create plasma on the surface of a sample to analyze its elemental composition. Repetitive ablation on the same site has been shown to create differences from the original sample. This study investigates the potential of LIBS for selective surface sintering of injection-molded titanium metal. The temperature created throughout the LIBS process on the surface of the injection-molded titanium is high enough to fuse together the titanium particles. Using the ratio of the Ti II 282.81 nm and the C I 247.86 nm lines, the effectiveness of repetitive plasma formation to produce sintering can be monitored during the process. Energy-dispersive X-ray spectroscopy on the ablation craters confirms sintering through the reduction in carbon from 20.29 Wt.% to 2.13 Wt.%. Scanning electron microscope images confirm sintering. A conventional LIBS system, with a fixed distance, investigated laser parameters on injection-molded and injection-sintered titanium. To prove the feasibility of using this technique on a production line, a second LIBS system, with an autofocus and 3-axis translation stage, successfully sintered a sample with a nonplanar surface.