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).
Grinding is considered one of the last processes in precision parts manufacturing, which makes it indispensable to have a reliable monitoring system to evaluate workpiece surface integrity. This paper proposes the use of the electromechanical impedance (EMI) method to monitor the surface grinding operation in real time, particularly the surface integrity of the ground workpiece. The EMI method stands out for its simplicity and for using low-cost components such as PZT (lead zirconate titanate) piezoelectric transducers. In order to assess the feasibility of applying the EMI method to the grinding process, experimental tests were performed on a surface grinder using a CBN grinding wheel and a SAE 1020 steel workpiece, with PZT transducers mounted on the workpiece and its holder. During the grinding process, the electrical impedance of the transducers was measured and damage indices conventionally used in the EMI method were calculated and compared with workpiece wear, indicating the surface condition of the workpiece. The experimental results indicate that the EMI method can be an efficient and cost-effective alternative for monitoring precision workpieces during the surface grinding process.
Energy consumption, air pollution and industrial waste have received special attention from public authorities in recent years. The environment has become one of the most important subjects in the context of modern life, for its deterioration impacts the quality of life populations. Driven by pressure from environmental agencies, politicians have drawn up ever stricter laws aimed at protecting the environment and preserving energy resources. All these factors have led industry, research centers and universities to focus their efforts on researching alternative production processes, creating technologies to minimize or avoid the production of environmentally aggressive residues. Up to a few years ago, the main objective of manufacturing plants was to produce goods aimed at satisfying technological and economic aspects. Green, or "dry" machining and Minimum Quantity Lubricant (MQL) machining have caught the attention of researchers and technicians in the area of machining as an alternative to traditional fluids. Thus, this work proposes to explore the MQL concept in the grinding operation. Although its advantages allow one to predict a growing range of applications for MQL, the variables of influence to be considered and the effects on the results of the process have so far been little studied. Grinding involves several input parameters but, to date, little attention has been focused on the form and quantity of cutting fluid applied to the process. The condition and rate of cutting fluid applied directly influences some of the process's output variables. This work, therefore, analyzes the behavior of the MQL technique under different lubrication and cooling conditions, developing an optimized fluid application methodology based on the creation of a special nozzle through which a minimum amount of oil is pulverized in a compressed air stream. The evaluation of the technical performance of MQL in grinding, using aluminum oxide and superabrasive CBN (cubic boron nitride) grinding wheels, consisted of an experimental analysis of the behavior of the tangential cutting force, G ratio, roughness and residual stress. The results presented herein allowed us to evaluate the behavior of the MQL technique in the grinding process, thus contributing toward an environmentally friendly technology
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