Avaliação dos fluidos de corte classificados pelo ponto de Leidenfrost durante o torneamento do aço SAE 52100
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Data
2022-02-10
Autores
Gonçalves, Daniel da Motta
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Universidade Estadual Paulista (Unesp)
Resumo
Introdução: Fluidos de corte são amplamente aplicados pelo método convencional com a finalidade de lubri-refrigerar a interface cavaco-ferramenta, onde a transferência de calor ocorre por convecção forçada em baixa pressão. Logo, a menor capacidade refrigerante deste método em relação aos demais provavelmente ocorre devido ao efeito Leidenfrost, responsável pela formação de uma película de vapor, que impede o contato entre o fluido e a superfície aquecida. Embora o efeito Leidenfrost seja amplamente estudado em diversas aplicações, no qual o rápido resfriamento é necessário, existe a carência de trabalhos que estudem a influência deste efeito na usinagem dos materiais. Objetivo: Diante do exposto, o presente trabalho tem o objetivo avaliar, durante o torneamento do aço SAE 52100 recozido e esferoidizado, o efeito lubri-refrigerante dos fluidos de corte previamente classificados pelo ponto de Leidenfrost. Métodos: Para tanto, corpos de prova foram torneados com parâmetros de corte constantes e submetidos a lubri-refrigeração convencional por tipos de fluidos de corte variados em Emulsões, fluidos Sintéticos e Semissintéticos, aplicados em três concentrações diferentes para cada tipo. Os resultados da temperatura de usinagem, desgaste da ferramenta de corte e da integridade superficial das amostras foram analisados e relacionados com a Temperatura de Leidenfrost (TLF) dos respectivos fluidos de corte. Resultados: Como resultado geral, os fluidos Sintéticos apresentaram maior capacidade de refrigeração, seguido pelos Semissintéticos e Emulsões. Entretanto, o fluido Semissintético em concentração de 1,25% resultou na menor temperatura de usinagem com redução 37,9% em relação a Emulsão 2,5% que resultou na maior temperatura. As Emulsões resultaram em menor desgaste da ferramenta de corte, seguido pelos fluidos Semissintéticos e Sintéticos. Ambas as Emulsões a 5% e 10% reduziram em 38,8% o desgaste em relação ao fluido Sintético a 4%, que resultou no maior desgaste. Ao comparar diferentes tipos de fluidos com mesma TLF, a temperatura de usinagem apresentou diferença de 10% a 15% nos resultados, e o desgaste apresentou diferença 25% a 62% nos resultados. A análise por tipo de fluido mostrou que apenas para fluidos Semissintéticos, quanto maior a TLF, menor a temperatura de usinagem. Com relação ao desgaste da ferramenta, para Emulsões e fluidos Sintéticos, quanto maior a TLF, maior o desgaste. As Emulsões a 5% e 10% e o fluido Sintético a 10% resultaram na menor rugosidade, com redução de 17%. A análise microestrutural e de microdureza mostraram ausência de alterações em decorrência do uso dos diferentes fluídos de corte. Conclusões: Para as condições de usinagem empregadas neste trabalho, todos os fluidos são capazes de remover calor da interface e evitam significativas alterações microestruturais no material usinado. Devido a diferença de condutividade térmica dos fluidos, não há relação da TLF com a temperatura de usinagem para fluidos de mesma TLF. Dadas as diferentes propriedades tribológicas, também não há relação com o desgaste da ferramenta quando fluidos de mesma TLF são aplicados. Por fim, os resultados indicaram que fluidos de corte com maior TLF nem sempre promovem menor temperatura de usinagem e desgaste da ferramenta de corte.
Introduction: Cutting fluids applied by the conventional method are widely used to lubricate and cool the tool-chip interface, when the heat transfer occur in forced convection at low pressure. Therefore, the conventional method has a lower refrigerating capacity than the other methods, probably caused by Leidenfrost effect, that is the phenomenon in which is formed a vapor layer of low thermal conductivity, which prevents the contact between the cutting fluid and the tool-chip interface. Although the Leidenfrost effect is widely studied in several applications where fast cooling is necessary, there is a lack of researches concerning the influence of this effect on machining of materials. Objective: Given the above, the present work aims to evaluate the lubrication-cooling effect of cutting fluids previously classified by Leidenfrost point, during turning of spheroidized and annealed SAE 52100 steel. Methods: For this purpose, specimens were turned with fixed cutting parameters, using conventional method to apply varied cutting fluids conditions (Emulsions, Synthetic and Semi-synthetic), which were applied in three different concentrations for each type of fluid. Then, the results of machining temperature, tool wear and surface integrity of the samples were analyzed and correlated with the Leidenfrost Temperature (LFT) of the respective cutting fluids. Results: As a result, in general, Synthetic fluids application provided lower machining temperatures followed by Semi-synthetics and Emulsions. However, the semi-synthetic fluid at concentration of 1.25% resulted in lowest machining temperature, with 37.9% reduction in relation to Emulsion at concentration of 2.5% (higher machining temperature). Emulsions resulted in lowest wear of the cutting tool, Semi-synthetic fluids in intermediate wear and Synthetics in highest wear. Both 5% and 10% Emulsions reduced 38.8% of wear compared to 4% Synthetic fluid, which resulted in highest tool wear. When compared different types of fluids with the same LFT, the results of machining temperature showed a difference between 10% and 15%, and the tool wear results showed a difference between 25% to 62%. The analysis based on the type of cutting fluid showed that only the Semi-synthetic fluids with higher LTF provided lower machining temperature. With respect to tool wear, both the Emulsions and Synthetic fluids with higher LFT provided higher tool wear. Emulsions at 5% and 10%, and Synthetic fluid at 10% resulted in the lowest roughness, with a reduction of 17%. The microstructural and microhardness analysis showed no significant differences due to the use of different cutting fluids. Conclusions: All analyzed cutting fluids were capable of remove heat from tool-chip interface and had avoided microstructural changes in workpiece material. Due to the thermal conductivity difference of the fluids, there is no correlation between the TLF and the machining temperature when fluids with same TLF are applied. Given the different tribological properties, there is also no correlation between the TLF and tool wear when fluids with same TLF are applied. Finally, the results indicated that cutting fluids with higher TLF do not always promote lower machining temperature and cutting tool wear.
Introduction: Cutting fluids applied by the conventional method are widely used to lubricate and cool the tool-chip interface, when the heat transfer occur in forced convection at low pressure. Therefore, the conventional method has a lower refrigerating capacity than the other methods, probably caused by Leidenfrost effect, that is the phenomenon in which is formed a vapor layer of low thermal conductivity, which prevents the contact between the cutting fluid and the tool-chip interface. Although the Leidenfrost effect is widely studied in several applications where fast cooling is necessary, there is a lack of researches concerning the influence of this effect on machining of materials. Objective: Given the above, the present work aims to evaluate the lubrication-cooling effect of cutting fluids previously classified by Leidenfrost point, during turning of spheroidized and annealed SAE 52100 steel. Methods: For this purpose, specimens were turned with fixed cutting parameters, using conventional method to apply varied cutting fluids conditions (Emulsions, Synthetic and Semi-synthetic), which were applied in three different concentrations for each type of fluid. Then, the results of machining temperature, tool wear and surface integrity of the samples were analyzed and correlated with the Leidenfrost Temperature (LFT) of the respective cutting fluids. Results: As a result, in general, Synthetic fluids application provided lower machining temperatures followed by Semi-synthetics and Emulsions. However, the semi-synthetic fluid at concentration of 1.25% resulted in lowest machining temperature, with 37.9% reduction in relation to Emulsion at concentration of 2.5% (higher machining temperature). Emulsions resulted in lowest wear of the cutting tool, Semi-synthetic fluids in intermediate wear and Synthetics in highest wear. Both 5% and 10% Emulsions reduced 38.8% of wear compared to 4% Synthetic fluid, which resulted in highest tool wear. When compared different types of fluids with the same LFT, the results of machining temperature showed a difference between 10% and 15%, and the tool wear results showed a difference between 25% to 62%. The analysis based on the type of cutting fluid showed that only the Semi-synthetic fluids with higher LTF provided lower machining temperature. With respect to tool wear, both the Emulsions and Synthetic fluids with higher LFT provided higher tool wear. Emulsions at 5% and 10%, and Synthetic fluid at 10% resulted in the lowest roughness, with a reduction of 17%. The microstructural and microhardness analysis showed no significant differences due to the use of different cutting fluids. Conclusions: All analyzed cutting fluids were capable of remove heat from tool-chip interface and had avoided microstructural changes in workpiece material. Due to the thermal conductivity difference of the fluids, there is no correlation between the TLF and the machining temperature when fluids with same TLF are applied. Given the different tribological properties, there is also no correlation between the TLF and tool wear when fluids with same TLF are applied. Finally, the results indicated that cutting fluids with higher TLF do not always promote lower machining temperature and cutting tool wear.
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Palavras-chave
Usinagem, Fluidos de corte, Efeito Leidenfrost, Torneamento, SAE 52100, Machining, Leidenfrost efect, Cutting fluids, Turning