Ingeniare. Revista chilena de ingeniería, vol. 17 Nº 2, 2009, pp. 267-274

TEMPERATURE AND HEAT FLOW WHEN TAPPING OF THE HARDENED STEEL USING DIFFERENT COOLING SYSTEMS 

TEMPERATURA Y FLUJO DE CALOR AL ROSCAR CON MACHOS ACERO ENDURECIDO UTILIZANDO DIVERSOS SISTEMAS DE LUBRICACIÓN

Lincoln Cardoso Brandão¹               Reginaldo Teixeira Coelho²

1 Departamento de Engenharia Mecânica. Universidade Federal de São João del Rei. São João del Rei. Minas Gerais, Brasil. E-mail: lincoln@ufsj.edu.br
2 Departamento de Engenharia de Produção. Universidade de São Paulo. São Carlos, São Paulo, Brasil. E-mail: rtcoelho@sc.usp.br

RESUMEN 

Trabajar los aceros endurecidos siempre ha sido un desafío para el corte de metales, particularmente en las operaciones de roscado. En el presente trabajo se mide la temperatura del acero AISI H13 endurecido, realizándose ensayos  sin lubricación (seco) y dos sistemas con lubricación: aceite lubricante en grandes cantidades y mínima cantidad de líquido (minimum quantity of fluid MQF) a 20 ml/h, en ambos casos se utilizó aceite integral mineral. El roscado se realiza sobre probetas de prueba de 100 x 40 mm con 14mm de espesor y dureza de 55 HRc. Para medir la temperatura se utiliza la técnica de termocuplas situadas muy próximas al diámetro mayor del hilo de rosca (a 0.1, 2.5 y 5 mm de distancia). Se utiliza tres termocuplas a lo largo del espesor de la probeta de prueba a 3.0, 7.0 y 11.0 mm desde la entrada del roscado. Se hacen dos réplicas del registro de la temperatura para cada condición de corte ensayada. Se utilizan un modelo teórico-analítico de conducción de calor para evaluar la temperatura en la interfase de la probeta de prueba, determinar el flujo de calor y el coeficiente de  convección. El menor incremento de la temperatura y del calor se observa al utilizar el método lubricante en grandes cantidades, seguido por el de MQF, al comparar con la condición en seco. El efecto es directamente proporcional a la cantidad de lubricante aplicado, siendo también significativo con el sistema MQF al compararlo con el corte en seco. 

Palabras clave: Roscado, conducción del calor, cantidad mínima del líquido (MQL), acero AISI H13, temperatura.

ABSTRACT 

Machining hardened steels has always been a great challenge in metal cutting, particularly for tapping operations. In the present paper, temperature was assessed when tapping hardened AISI H13. Dry machining and two cooling/lubrication systems were used: flooded and minimum quantity of fluid (MQF) with 20ml/h, both using mineral oil. The tapping operation was performed on 100 x 40 mm, 14 mm thick workpieces with 55 HRc. An implanted thermocouple technique was used for temperature measurement at distances very close to the highest thread diameter (at 0.1, 2.5 and 5.0 mm). Three thermocouples were used for each distance along the workpiece diameter at 3.0, 7.0 and 11.0 mm from the tap entrance. Measurements were replicated twice for each condition tested. An analytical theoretical heat conduction model was used to evaluate the temperature at the tool-workpiece interface and determine the heat flow and convection coefficient. The smallest temperature increase and heat flow were observed when using the flooded system, followed by the MQF, compared to the dry condition. The effect was directly proportional to the amount of lubricant applied, as well as with the MQF system, when compared to dry cutting. 

Keywords: Tapping, heat flow, minimum quantity of fluid (MQF), steel AISI H13, temperature.

ACKNOWLEDGMENTS 

We extend our sincere thanks to all who contributed to the present work, in particular to Titex-Prototype in Brazil (Eng. Marcos Soto Ice) and Frankfurt (Dr.Ing. Roland Heiler), Gerdau Açominas Brazil and also FAPESP – Brazil. 

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Received: May 9, 2007, Accepted: June 4, 2009