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EN
In the paper the methods of laser hardening of external tool corners on the example of bending tools for press brakes were presented. The disadvantages and limitations of the most commonly used techniques for guiding a hardening laser light beam are presented, i.e.: (i) in one pass parallel to the tool corner plane symmetry, (ii) in two passes perpendicular to the surfaces adjacent to the corner, and (iii) in one pass perpendicular to the surface adjacent to the corner by using two diode lasers. The microstructure of the tool material after laser and induction hardening was compared. A significant influence of the heating method on the microstructure of the tool material after hardening was demonstrated. The original method of hardening the outer corners of bending tools using a hardening laser beam splitter was subject to a more detailed analysis. The analysis of material heating in simultaneously hardened corner area and adjacent surfaces was carried out using the Marc/Mentat software based on the finite element method. By analyzing the temperature distributions it was shown that if a beam splitter was used, obtaining a continuous and uniform hardened layer (i.e. with comparable hardness, depth, without tempered or non-tempered areas) in the area of the outer corner and adjacent surfaces was possible. In practice, achieving such a layer is conditioned by the correct selection of the size of the k parameter which determines the distance between the separated beams of laser light. Depending on the geometry of the hardened tool corner and the parameters of the hardening laser beam, this distance can be determined experimentally or on the basis of numerical simulation.
EN
The negative refractions are discussed in detail to demonstrate two different two-dimensional photonic crystal structures that undergo negative refractions associated with the backward-wave and forward-wave phenomenon, respectively. The presentation of the left-handed property of effective negative index photonic crystal is followed by a discussion of a backward flowing phase and causality. The forward-wave negative refraction occurs in photonic crystals as a result of anisotropy. This paper is based on the theoretical analysis and is illustrated with the results of finite element method simulations.
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