Sheet Metal 2007

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Authors: Till Laumann, Markus Pfestorf, Andreas Beil, Manfred Geiger, Marion Merklein
Abstract: The increasing call for significant safety improvements of new cars requires, among other important relevant aspects, the application of high strength materials for the body in white. Quenchable manganese boron alloyed steels like 22MnB5 offer superior strength values, complex shapes and enhanced accuracy. For the evaluation of the crash appropriateness specimens in different annealed states are deformed in a so called drop test bench and hereupon judged in terms of absorbed energy, maximum deformation and other aspects like wrinkling behaviour. Microscopic analysis complements the evaluation of crash-appropriateness.
Authors: Johan De Keuster, Joost R. Duflou, Jean Pierre Kruth
Abstract: In this paper, the development of a monitoring system for high-power CO2 laser cutting of thick steel plates (>15 mm) is reported. The aim of this system is to increase the robustness and autonomy of the laser cutting process of thick plates, which is still characterized by more narrow process windows compared to cutting of thin sheets. The applicability for monitoring purposes of two types of sensors is investigated: the acoustic microphone and the photodiode. For both types, correlation between the sensor output and the cut quality is investigated. Both contour cutting and piercing are covered in the study. The full penetration of the piercing can be monitored by both sensors. Furthermore quantitative relations between cut quality parameters and photodiode signal parameters could be determined: the mean level of the photodiode signal correlates well with the drag of the striations and dross formation, whereas the standard deviation proves to correlate well with the occurrence of burning defects and the cut edge roughness.
Authors: Dong Gyu Ahn, Hyung Jun Park
Abstract: The objective of this paper is to investigate the influence of process parameters on kerfwidth and the melted area in sharp corners for cutting of a low carbon (CSP 1N) sheet using a high power Nd:YAG laser with a continuous wave for net shape manufacturing. In order to investigate the effects of the power of laser, the cutting speed of the laser and the thickness of the material on the kerfwidth, several linear cutting tests have been carried out. From the results of experiments, the relationship between the effective heat input and kerfwidth has been obtained. In addition, it has been shown that the kerfwidth ranges from 0.47 mm to 0.79 mm. In order to investigate the influence of the corner angle and size of the loop on the melted area in sharp corners for each cutting condition, angular cutting tests and loop cutting tests have been performed. From the results of angular cutting tests, the relationship between the corner angle and the melted area has been obtained and it has been found that the melted area is nearly zero at the corner angle of 150 o. Through the results of loop cutting experiments, the relationship between the corner angles on the melted area in the corner according to the size of the loop has been obtained. In addition, a proper size of loop for each corner angle has been obtained. The above empirical results have been applied in the development of a knowledge-based path generation program for laser cutting with algorithms of the offset generation and the path modification.
Authors: Massimiliano Annoni, Michele Monno
Abstract: The internal geometry of water jet orifices is important to determine water velocity and structure of the jet: the geometrical features of orifices, such as diameter, rounding of the entrance edge, taper angle of internal walls and so on, play an important role under the fluid-dynamic point of view and, consequently, on water velocity and jet behaviour in air, which are responsible for the available value of specific power on the workpiece. The aim of this study is to experimentally evidence possible differences among performances of orifices coming from different manufacturers in order to point out the effects of orifices geometrical features on water velocity and cutting capability in case of abrasive water jet cutting of Aluminium.
Authors: Janina Adamus
Abstract: In this paper, the influence of the cutting method on the cut-surface quality is analysed. A WT1-0 titanium sheet was cut in three different ways: using a guillotine, a laser and an abrasivewaterjet. The cut-surface’s appearance, microstructure, microhardness and the roughness of the cutsurface were tested. Moreover, a numerical simulation of the banking process of a titanium disk was carried out with the ADINA System v.8.3 based on the finite element method. The influence of the radius of the cutting edge and the clearance on the surface quality was analysed.
Authors: Alberto Boschetto, Armando Ruggiero, Francesco Veniali
Abstract: In sheet metal processes the burrs cannot be completely eliminated during the process but can be minimized by optimization of the process parameters. Hence the deburring often becomes an essential secondary operation. Most of the deburring operations are hand-made and therefore several manufacturers tend to eliminate these tedious and labor-intensive operations due to time and cost issues. Moreover, clamping problems can arise which, together with the deburring forces, can induce dimension alterations and local deformations, particularly for thin sheets. Barrel finishing is an old technique commonly used to improve the surface roughness of complicated parts, but can find interesting applications also in the deburring. Aim of this work is to present an experimental investigation on the deburring of sheet metal performed by barreling. A technological model has been developed in order to assess the height of the burr as a function of the initial burr and of the working time.
Authors: Bernd Arno Behrens, Kanwar Bir Sidhu
Abstract: Ductile fracture processes for discrete crack propagation using nodal release approach is well established for modelling crack in metal sheet. In this method, the crack is assumed to initiate or propagate along the element edges; hence, a new crack is implemented in the FE mesh. In Blanking process, the crack trajectory is unknown; therefore a very fine mesh is required to simulate a realistic crack propagation using the nodal release method. Consequently, the nodal release method has to be modified in which first the direction of crack extension is calculated and then, accordingly, the local element topology near the crack-tip is modified such that the nodes of elements are moved to predicted crack-tip in order to accommodate the crack extension. The advantage of this method is that it is possible to model the predicted crack with only slight modification in the local mesh near to the crack tip. However, it is necessary to transfer history variables from old local elements of previous increment to the new local elements of the current increment at the vicinity of crack-tip. But this method can lead to slight loss of accuracy to predict the subsequent crack extension due to interpolations. However, the advantage of this method is that remeshing can be either completely eliminated or reduced to a greater extend during the simulation. Therefore, in this paper, modified nodal release method for modelling ductile crack propagation in blanking process with the uncoupled damage approach is presented, and is further implemented in commercial FE software - MSC.Marc® together with predefined user-subroutines
Authors: Jussi A. Karjalainen, Kari Mäntyjärvi, Martti Juuso
Abstract: Flat-end tools are the most general types used in sheet metal punching and nibbling. They are geometrically simple and easy to sharpen but, on other hand, their cutting forces are relatively large, and hence the cutting process is frequently noisy. In order to reduce both cutting force and noise tools with one-way or two-way shearing have been utilised. The major drawbacks of these tools are the asymmetry of cutting easily causing non-circular holes with round tools, lateral forces with one-way shearing, excessive forming during cutting and more complex tool geometry to maintain. Here a new geometry for a punch is employed. The shearing edge is a sinus curve with several peaks making the cutting edge circularly symmetric and the phenomenon totally balanced. This means smaller forming forces, particularly in cases when also the radial form is concave. The geometry is without doubt more complex compared to the flat-end tool but rather easy to produce by multi-axis milling and electro-discharge machining. In the current work a set of experimental punches has been designed, manufactured and tested. A simple analytical theory for cutting force has also been derived and compared with the test results. The results show that the new geometry produces very precise hole geometry with a lower cutting force compared to conventional flat-end tools. Of course, more theoretical and experimental work is required to optimise the tool geometry including the tool clearance for each pair of material strength and thickness.
Authors: Hartmut Hoffmann, Florian Hörmann
Abstract: In blanking operations the cut edge of the sheet metal is not clear due to fracturing and burr formation by the shearing process. For precision parts with high quality and dimensional accuracy, often secondary machining is necessary. Shaving, in particular, counter-shaving, is a shearing operation to improve the cut edge quality of a blanked part or punched hole in two stages. This paper introduces a progressive die tool to realize the counter-shaving process on a single acting press. In order to realize the shaving operation in the opposite punching direction, the punch needs to move in counter direction. The burr and fracture zone left on the sheet metal after the first stage will be removed by the counter-shaving operation. By choosing the right process parameter a sharpedge transition is formed, without any rollover, between the upper surface of the sheet metal and the sheared-edge. Different punch geometries as well as the corresponding process parameters were part of the research work in order to improve the cut edge. Experimental and FEM results are presented for two sheet metal materials at three thicknesses.
Authors: Ralf Kolleck, Stefan Pfanner, E.P Warnke
Abstract: Two central topics of modern automotive constructions refer to automotive lightweight constructions and safety; this is best indicated by the most various developments in the context of body constructions. The consistent evaluation of cars by means of crash tests has led to the fact that new manufacturing variants combined with the use of high and ultra high strength materials represent a fundamental part of the body in white. One possibility to form such materials is given by the hot forming process. An innovative approach, namely to improve this procedure in economic and technological terms, is represented by the new tool system for tempered forming processes carried out at the Institute Tools & Forming (T&F). The integration of most complex cooling duct geometries by casting integral tube networks into the tool represents an innovative possibility to improve the cooling performance combined with the reduction of the cycle times.

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