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Groche P.,Institute for Production Engineering and Forming Machines PtU | Kloepsch C.,Lech Stahlwerke GmbH | Moeller N.,Institute for Production Engineering and Forming Machines PtU
Production Engineering | Year: 2012

Deep drawing is one of the most important forming procedures for the economic production of sheet metal components. Especially for high-volume parts, deep drawing is a very efficient method of fabrication with high utilization of semi-finished parts. Certainly, conventional deep drawing processes are restricted by forming limits due to part failure during the drawing process. The process force is one of the most important factors for this restriction. The narrow process window, especially for deep drawing of light-weight materials, can be extended by reducing the friction forces at the die radius, using hydrostatic pressure lubrication. After the numerical analysis of the appearing loads of deep drawing processes, the optimal position for the insertion of pressurized lubricant was identified and the potential of the hydrostatic pressure lubrication was predicted. With experimental tests, the results of the simulations were approved. Both, the simulations and the experimental tests showed a significant reduction of the process forces. © 2012 German Academic Society for Production Engineering (WGP). Source

Turk M.,Institute for Production Engineering and Forming Machines PtU | Groche P.,Institute for Production Engineering and Forming Machines PtU
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The Institute for Production Engineering and Forming Machines at the Technische Universität Darmstadt examines the reduction of uncertainty of bar structures by integrating adaptive components into the bars. As sensors, these components allow a monitoring of appearing loads, as actuators they allow an active influencing on appearing disturbances. One approach for producing those structures is given by incremental forming processes. They feature the advantage to combine the forming of the parts as well as the integration of the active components in one process. The research contains numerical analyses and experimental tests. © 2010 SPIE. Source

Groche P.,Institute for Production Engineering and Forming Machines PtU | Moeller N.,Institute for Production Engineering and Forming Machines PtU | Hoffmann H.,Institute of Metal Forming and Casting utg | Suh J.,Institute of Metal Forming and Casting utg
Wear | Year: 2011

The usage of high-strength instead of mild sheet metals leads to increased wear of forming tools. Especially deep-drawing tools are of high economic relevance. Due to their good corrosion resistance zinc-coated sheet metals are often used in deep drawing operations. In order to enable the design of a sufficiently wear resistant tool which is not unnecessarily overdesigned a prediction of tool wear is desirable. So far, the usage of Archard's law is state of the art. This law does not imply any influence of the contact pressure or the gliding speed on the wear coefficient.The subject of this paper is the influence of different process parameters on the wear of forming tools when zinc-coated sheet metals are processed. Strip drawing tests are used for experimental investigations. In the strip drawing test, the practical conditions of the deep-drawing process can be reproduced while process parameters such as gliding speed, surface pressure and load history can be varied individually. A gray cast iron tool, which is prevalent in automotive industries for forming processes, is used in the tests. For the ascertainment of the impact of the parameter variations on the amount of wear, single parameters are altered under the condition that the cumulative work of friction is kept constant for all tests. The worn surfaces of the tools are analyzed by a confocal white light microscope in order to quantify the wear progress at fixed intervals during the tests. Additionally, EDX-analyses showed the chemical composition of the surface layers. The derived experimental data are used to proof and improve Archard's law.This paper focuses on the influence of gliding speed and contact pressure on the abrasive and adhesive wear of forming tools. It will be shown that the prediction of tool wear under different geometrical and process conditions is possible when finite element simulations and a modified Archard's law are combined. © 2011 Elsevier B.V. Source

Groche P.,Institute for Production Engineering and Forming Machines PtU | Moller N.,Institute for Production Engineering and Forming Machines PtU
ASME 2012 International Manufacturing Science and Engineering Conference Collocated with the 40th North American Manufacturing Research Conference and in Participation with the Int. Conf., MSEC 2012 | Year: 2012

Deep-drawing is one of the most important processes for the economic production of sheet metal parts, especially for high quantities. The forming forces during the process are a limiting factor for the producible shapes. A particular importance is associated with the tribology, because the percentage of friction forces on the total forces is relatively high. The friction between sheet metal and tool is influenced by several factors, such as surface characteristics of the work piece and the tool, lubrication conditions and process parameters, like the contact pressure and the sliding speed. Controlling these parameters will expand the process window for deep-drawing. Lately, servo presses provide the possibility of controlling the process speed in dependency of the process progress. The subject of this paper is the tribological investigation of deep-drawing processes. The friction coefficient decreases with an increasing sliding speed. Investigating this correlation and utilizing it for the application with modern servo technology for industrial use is the main objective of the presented research works. First of all the dependency of the friction coefficient on the sliding speed is investigated by the use of the strip drawing tests, which allows the control of every parameter independently. The dependencies are implemented in a FEM-simulation, evaluating the potential for real deep-drawing processes. Deep-drawing experiments are then used to validate the results of the simulation with a speed-dependent friction coefficient as well as for the verification of the force reduction due to the influencing of process speed. In the end, the numerical simulated results in comparisons to the experimental measured results are discussed. Copyright © 2012 by ASME. Source

Groche P.,Institute for Production Engineering and Forming Machines PtU | Christiany M.,Institute for Production Engineering and Forming Machines PtU
Wear | Year: 2013

The increasing relevance of lightweight design intensifies the use of advanced high strength steels (AHSS). However, the use of AHSS causes higher stresses on the forming tools, thus reducing tool life and making it impossible to achieve the aspired process reliability.Since there is no reliable information on the wear behavior of tool materials for the forming of AHSS, this study aims to investigate wear and wear development of different tool materials. For this purpose, a strip drawing test with drawbead geometry is used as a model test. Continuous measurements of forces, temperatures of tool and sheet metal, and the roughness of sheet metal allow accurate and detailed analyses of wear.The investigation shows distinct differences in wear resistance of the tested tool materials and reveals characteristic wear development. Furthermore, the results of this study broaden knowledge on dependencies between tool wear, process temperature, and surface changes. © 2013 Elsevier B.V. Source

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