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Laser welding of zinc-coated steels in an overlap setup is prone to weld defects and seam expulsion reducing in particular the properties in mechanical loading and in general the deployability of such weldments in industry. Several laser welding process technologies failed to created defectfree welds in zinc-coated steels. This paper renders the welding of zinc-coated steels by the novel technology of bifocal hybrid laser welding. The zinc-coated steels under consideration are DX56D ? Z, DC04 ? ZE, and HXT700D. The bifocal hybrid laser system is realised by combining an Nd:YAG laser with a high power diode laser, both of 3 kW maximum output power. The beam parameter product (BPP) of the employed Nd:YAG laser of 25 mm mrad translates with an optical system of focal length f = 150 mm into a circular focus of diameter 0.45 mm, whereas the BPP of the HPDL of 85 mm 9 200 mm mrad can achieve a rectangular focus of 0.9 mm 9 3.7 mm. The optical system allows the respective focal plane and relative position of the foci to be independently vertically and horizontally positioned. This paper presents research into the causes of instabilities in laser welding of zinc-coated steels. Experimental evidence is considered and presented to establish the need for an empirical process model for stable laser welding of zinc-coated steels. The increase of process robustness is discussed.

The laser is widely used in additive layer manufacturing for producing parts on the basis of polymer and metal powder. In the metal area, the capacity of laser technologies is noticeably exhausted. The electron beam (eb) technology offers higher power density and beam velocity and therefore seems more suitable for sintering high-tensile steel powder in an economic way. In this paper, a comprehensive method is implemented to develop the eb sintering. In comparison to laser-based applications, different physical effects occur and have to be controlled. Therefore, the paper focusses on those physical effects and the measures, which have to be taken in order to achieve a reliable process. The result of this work is a prototype machine, in which the eb is used for sintering high-tensile steel directly from CAD files to three-dimensional, non-porous parts.

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SUMMARY:In slab milling the quality of the machined surface is directly influenced by the dynamic behaviour of the machine tool. In addition to the cycloidical microgrooves, the dynamic relative motion between the workpiece and tool is superimposed on the machined surface. In general these vibrations cannot be directly identified by investigat~ng the machined surface. By the application of a special purpose milling cutter, microgrooves are generated which are identifiable and from which the relative motions in the cutting zone can be determined by surface topography measurement. It is shown how the groove structure is produced as a function of the kinematics of the process and the relative motions in the zone of cutting. An example based on experimental investigation is used to illustrate the procedure used to determine these relative motions based on analysis of the workpiece surface.