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Abstract(s)
Actualmente os cárteres das caixas de embraiagem utilizados na indústria automóvel são de ligas de alumínio. Estas ligas metálicas leves têm o grande inconveniente de possuírem elevados coeficientes de expansão térmica e suas alterações dimensionais requerem especial atenção durante o seu processamento. Assim é usual que a maquinação de alta velocidade de ligas de alumínio implique a prévia estabilização térmica das peças de forma a evitar que alterações dimensionais ultrapassem as tolerâncias admissíveis.
Com este trabalho pretende verificar-se a possibilidade de evitar a estabilização térmica numa estufa, de um cárter de embraiagem em alumínio, antes da sua maquinação. A estabilização dimensional do cárter será feita no interior do centro de maquinação, recorrendo à “duchagem” das peças com o óleo de corte refrigeração a uma temperatura estabilizada.
Foi desenvolvido uma extensa metodologia experimental aplicada a um sistema de maquinação e usando um sistema de “duchagem” com temperatura controlada, analisando-se cerca de 35 características em mais de 40 peças. Este estudo exaustivo foi efectuado através da determinação das temperaturas das peças antes de entrarem no centro de maquinação, da temperatura no interior do centro de maquinação, das cotas, seus limites e seus desvios em função do intervalo de confiança do lote de referência.
Os resultados obtidos permitiram verificar quais as características em que a correlação com a temperatura é mais sensível e constatar que as cotas de profundidade são as que apresentam maiores desvios. Sendo este um trabalho de aplicação prática verificou-se que através duma regulação sistemática de algumas cotas e da sequencia de maquinação se podia aplicar o método desenvolvido aumentando a eficiência e alcançando uma importante poupança de energia e de manutenção.
At the present time both clutch and mechanism housings, which are the main components from automotive gear boxes, are made of special aluminium alloys. These alloys are extremely light when compared with steel, making them a perfect choice to mitigate the cars weight and machining costs. Nonetheless they possess a high thermal expansion coefficient, which can be considered a major disadvantage since it makes necessary to pay extraordinary attention to dimensional variations during the production cycle due to temperature deviations. High speed machining of precision components made of aluminium requests thus their temperature to become previously stable. This procedure is the only way to force dimensions to stay inside its tolerance intervals. The main purpose of the work presented herewith was to assess the possibility to avoid the use of special ovens to make the clutch housing temperature become stable prior to machining. The experimental methodology was carefully outlined by exploring the existence of a cooling oil showering system with controlled temperature, installed in the loading chamber. The dimensional stabilization of 40 sample parts, pre-heated at 3 temperature levels, was accomplished through the use of this system. The achieved results were made possible by analysing the part’s temperature at the machine’s entrance, the machine’s interior temperature, 35 measured dimensions and their tolerance intervals as well as the average temperature deviations of each of the 5 considered batches. By analysing the obtained results in detail it was possible to determine which dimensions show high sensitiveness to temperature (high correlation between dimension’s variation and temperature). Among this dimensions we can point out the ones related with depth, since they display the highest deviations due to temperature. Being a work with practical application it was possible to confirm the benefit of using this methodology by achieving significant enhancements on production efficiency, energy savings and reduction on maintenance costs, through the application of small adjustments to the machining sequence and by adopting a systematic tuning of certain dimensions.
At the present time both clutch and mechanism housings, which are the main components from automotive gear boxes, are made of special aluminium alloys. These alloys are extremely light when compared with steel, making them a perfect choice to mitigate the cars weight and machining costs. Nonetheless they possess a high thermal expansion coefficient, which can be considered a major disadvantage since it makes necessary to pay extraordinary attention to dimensional variations during the production cycle due to temperature deviations. High speed machining of precision components made of aluminium requests thus their temperature to become previously stable. This procedure is the only way to force dimensions to stay inside its tolerance intervals. The main purpose of the work presented herewith was to assess the possibility to avoid the use of special ovens to make the clutch housing temperature become stable prior to machining. The experimental methodology was carefully outlined by exploring the existence of a cooling oil showering system with controlled temperature, installed in the loading chamber. The dimensional stabilization of 40 sample parts, pre-heated at 3 temperature levels, was accomplished through the use of this system. The achieved results were made possible by analysing the part’s temperature at the machine’s entrance, the machine’s interior temperature, 35 measured dimensions and their tolerance intervals as well as the average temperature deviations of each of the 5 considered batches. By analysing the obtained results in detail it was possible to determine which dimensions show high sensitiveness to temperature (high correlation between dimension’s variation and temperature). Among this dimensions we can point out the ones related with depth, since they display the highest deviations due to temperature. Being a work with practical application it was possible to confirm the benefit of using this methodology by achieving significant enhancements on production efficiency, energy savings and reduction on maintenance costs, through the application of small adjustments to the machining sequence and by adopting a systematic tuning of certain dimensions.
Description
Keywords
Maquinação do alumínio Alumínio - Aplicação Alumínio - Cárter de embraiagem Maquinação de cárteres Maquinação de peças - Alumínio - Temperatura
Pedagogical Context
Citation
Publisher
Universidade da Beira Interior