Development of New Preheating Methods for Hot Forging Tools Based on Industrial Case Studies and Numerical Modeling
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G many metal-forming technologies, hot forging is commonly applied in the production of parts for the machine-building, agricultural, extractive, aircraft and, above all, automotive industry. At present, the main directions of forging industry development are concentrated on improving the quality of the forgings, among others, with the use of precision forging,
MAREK HAWRYLUK, PAWEŁ WIDOMSKI, MARCIN KASZUBA, and JAKUB KRAWCZYK are with the Department of Metal Forming, Welding and Metrology, Wroclaw University of Science and Technology, Lukasiewicza Street 5, 50-370 Wrocław, Poland. Contact e-mail: [email protected] Manuscript submitted September 17, 2019. Article published online July 9, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
improving the efficiency of the forging processes through their automatization, robotization and use of advanced production monitoring systems as well as lowering the production costs.[1,2] Therefore, optimizing the amount of forging material and the whole forming process using FEM as well as increasing the durability of the forming tools used is being pursued.[3] The tools used in hot forging processes are exposed to many detrimental factors, the most important of which is friction (abrasive wear), as well as varying temperatures and pressures (thermomechanical fatigue).[4–7] The occurrence of these destructive mechanisms is inevitable, and they can only be limited by controlling the tool material and tool production technology.[8] Additionally, in hot forging processes, during the tool’s contact with the hot material of the forging, irregularities are seen, such as overheating or cracking as a result of
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non-uniform accelerated heating of the tool material. These problems should be eliminated by following proper tool cooling and performing preheating before the forging process begins to avoid non-uniform heating and its accompanying stresses.[9,10] Proper preheating greatly increases the durability of the tool because it reduces the stress and thus directly helps avoid brittle fractures.[11,12] The preheating of forging tools commonly takes place after they have been mounted on the forging aggregate (press or hammer), or directly before this, and the beginning of the forging process. In this field, the following methods are commonly used (Figure 1). The dies are usually heated using one or several gas flame burners. Often, the gas burners are arranged in a way to generate a diffused heat source on the surface of the dies (Figure 1(a)). Typical problems encountered in this heating method are carbon deposits, high noise, very significant temperature inhomogeneities and a large temperature difference between the upper and lower surface of the forging tools in the vertical configuration. Preheating is mainly carried out using thermal oil, electrical heat and guidance through the channels in the mold, or direct firing on the back of the mold, and dies using gas flames. Depending on the size of the tool, it can take several hours, which leads to huge produc
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