Improving minimum quantity lubrication in CBN grinding using compressed air wheel cleaning

Abstract

a b s t r a c tThe application of minimum quantity lubrication (MQL) in grinding has emerged as an alternative for reducing the abundant flow of cutting fluids, thus achieving cleaner production. Although considered an innovative technique in grinding operations, its widespread application is hindered due primarily to the high heat generation and wheel pore clogging caused by machined chips, harming the final product quality and increasing tool wear on the machine. This study sought to improve MQL use in grinding. In addition to the conventional MQL injected at the wheel/workpiece interface, a compressed air jet was used to clean the mixture of MQL oil and machined chips from clogged wheel pores. Experiments were conducted using external cylindrical plunge grinding on AISI 4340 quenched and tempered steel, and a vitrified cubic boron nitrite (CBN) wheel. The cooling-lubrication methods employed were the conventional flood coolant application, MQL (without cleaning), and MQL with a cleaning jet directed at the wheel surface at different angles of incidence. The main goal of these experiments was to verify the viability of replacing the traditional abundant flow of cutting fluid with MQL and wheel cleaning. The analyses were conducted by measuring the following output variables of the process: workpiece surface roughness and roundness errors, diametrical wheel wear, acoustic emission generated by the process, and metallographic images of the ground surface and subsurface. Results show the positive effects of implementing the cleaning jet technique as a technological improvement of minimum quantity lubrication in grinding in order to reduce the usage of cutting fluids. The MQL technique with cleaning compressed air jet, for a specific angle of incidence (30 • ), proved to be extremely efficient in the improvement of the surface quality and accurate workpiece shape; it also reduced wheel wear when compared to the other cooling-lubrication methods that were tested (without a cleaning jet).

Utilization of minimum quantity lubrication (MQL) with water in CBN grinding of steel

“…The air flow rate was monitored using a turbine-type meter, calibrated to a pressure of 8.0 × 10 5 Pa. Figure 2 presents the nozzle for MQL application turbulence of the air-oil mixture, enhancing penetration at the wheel/workpiece interface. A wheel cleaning system using compressed air (at a flow rate of 8.0 × 10 -3 m 3 /s and pressure of 7.0 bar) was also used 23 . The nozzle was placed at 1 mm in relation to the wheel cutting surface.…”

“…Recently a study was done about the use of compressed air jet for wheel cleaning, when applying MQL in grinding with CBN wheel. The results showed that an air jet incidence angle of 30º turns its penetration in the cutting zone more efficient, providing a better cleaning of the wheel, improving surface roughness, roundness errors and wheel wear, when compared to traditional MQL (without cleaning) 23 . Reduction of fluid flow associated with better results indicate that this improvement of cooling-lubrication conditions in grinding may reduce environment and health hazards, contributing to a cleaner, faster, and more cost-effective manufacturing process.…”

Retificação cilíndrica do aço VP50 utilizando o rebolo de carbeto de silício verde com a técnica de MQL

“…Assim, como há pouco fluido de corte, a peça sai praticamente limpa e permite o monitoramento visual do processo [3]. O ar carrega o óleo diretamente (com elevada velocidade) para a zona de corte, o que faz com que esse seja um método bastante eficiente de lubrificação [14]. Embora chamada também de sistema de névoa, ou ainda usinagem próxima a seco, a técnica MQL apenas aproveita a velocidade do ar para conduzir o lubrificante até o ponto desejado e não para criar uma névoa ao redor da peça.…”

“…Oliveira et al [14] afirmam que a emissão acústica está relacionada com a condição do processo de retificação e com as condições da superfície do rebolo e da peça. Todos os fenômenos físicos que ocorrem no processo (atrito, deformação plástica e elástica e remoção de cavaco) podem gerar emissão acústica.…”

State in the art of cooling and lubrication of the machining zone in grinding processes

“…Ta bardzo mała ilość PCS doprowadzana do strefy szlifowania pozwala w znacznym stopniu zredukować tarcie w strefie kontaktu CPS z powierzchnią obrabianą oraz ogranicza adhezję produktów szlifowania do powierzchni ściernicy [28]. Wydajne smarowanie jest zapewnione ponieważ strumień powietrza przenosi krople PCS bezpośrednio do strefy szlifowania, natomiast w przypadku obróbki z użyciem konwencjonalnej metody zalewowej należy stosować szczegól-ne procedury, aby PCS skutecznie dotarł do strefy szlifowania [29].…”