Avaliação do aumento da resistência à abrasão do ferramental de estampagem com folhas metálicas

• Ano de defesa: 2019
• Autor(a) principal: Augusto, Arnaldo
• Orientador(a): Vatavuk, Jan
• Banca de defesa: Couto, Antonio Augusto , Andrade, Arnaldo Homobono Paes de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Presbiteriana Mackenzie
• Programa de Pós-Graduação: Engenharia de Materiais e Nanotecnologia
• Departamento: Escola de Engenharia Mackenzie (EE)
• País: Brasil
• Palavras-chave em Português: folha metálica; revestimento duplex; desgaste abrasivo
• Área do conhecimento CNPq: CNPQ::ENGENHARIAS::ENGENHARIA DE PRODUCAO
• Link de acesso: http://dspace.mackenzie.br/handle/10899/24253

Wear is the factor that causes most faults and reduces the life of forming tools, as well as resulting in products with intolerable surface conditions. The increasing demand of the industry for lower costs, higher productivity and better quality are among the justifications for finding ways to increase performance in forming tools (punches, dies, reliefs and extractors). In this context, the objective of this work was to evaluate surfaces designed for wear resistance, observing characteristics necessary for their use in cold forming tools. The focus on wear resistance is due to the fact that when making grooves in the tool, it must be removed for polishing, edging and radius correction, reducing its life. For this, a comparative characterization and behavior study was performed on the abrasive wear of two types of steel: AISI D6 and S790 Microclean®. AISI D6 steel is produced by conventional metallurgy, having been tempered and tempered to HRC 60-62 hardness range, receiving no further treatment. The S790 Microclean® alloy is sintered and produced by HIP (hot isostatic pressing), with initial microstructure tempered and annealed for hardness in the range of HRC 61-63. This alloy received surface treatment in two stages, initially low pressure gaseous nitriding, followed by the application of a coating of AlCrN (chromium and aluminum nitride) by the process of physical deposition of plasma assisted steam. This technology is called the Duplex process. The stamping process used as a raw material the chromium foil used in the manufacture of caps for glass packaging. The chromium sheet consists of a laminated "sheet" of low carbon steel, with chromium deposition by the electrolytic process. This surface does not have a high resistance to corrosion, but is very resistant to sulphuration with excellent adherence to certain varnishes and compared to tinplate is lower cost for products of low acidity such as metal caps for glass pots for peas and vegetables in general. Initially the VF800AT steel supplied in annealed state was tested for comparison to AISI D6 steel. The VF800AT steel is applied in tools for stamping, pressing, extrusion, cutting, thread rolling rolls, cold forming and all material processing applications below 250°c, especially at room temperature, where they are High tensions are involved. The VF800AT Steel has a chemical composition specially developed to provide good wear resistance associated with high toughness. It has high temperability and can be tempered in air or in oil, including heating in a vacuum furnace. Compared to the D-series steels, the VF800AT is less prone to cracks induced by machining or EDM process, because thanks to its lower carbon and chromium content, it has smaller primary carbides and a lower volumetric fraction. This alloy was subjected to heat treatment of tempering within the range 1,020 º C to 1,040 º C, followed by two tempers of 1 hour at the temperature of 520 º C. Subsequently, a new machining was performed for dimensional corrections, followed by coating application through the PVD (Physical Vapor Deposition) process. In this stage of manufacture it was found that the VF800AT steel did not present good dimensional stability varying around 0, 015mm, after the heat treatment and after a period of one week in operation the coating presented cracks and began to yield and Unfeasible to use this alloy in this application. To achieve the objective in terms of the performance of the tools, it was necessary a material in which there was good adhesion of the chosen coating, in addition to a high dimensional stability, because with each sharpening the material is subjected to 450 ℃ for new application of the PVD coating. The option was the steel S790 Microclean®, steel manufactured by sintering, with high resistance to wear and toughness, compressive strength and that had good dimensional stability, achieved with the thermal cycle of quench and tempering employed in this Study. The choice of this material also took into account operational problems such as the presence of black soots or foreign bodies adhered to the sheet metal, with great potential for the generation of risks in the finished product. The increased surface hardness of the tool was achieved by applying coating by the PVD process well adhered to the nitreted surface. The nitriding followed by deposition by the PVD process, carries the duplex name, and the higher hardness of the nitreted layer in relation to the base metal makes it decrease the hardness difference between the deposited layer and its substrate. The puncture of S790 Microclean® proved to be effective for the intended purpose, reducing the production waste that was ± 10 hours in a period of 24 hours, for ± 1 hour in a period of 16 hours and the number of defective parts that was 0.3% of the production (± 1,600) to 0 1% (± 620), preventive maintenance of punctures went from bimonthly to semiannual and the labor for classification of non-conforming products was also reduced by around 38%.