Evaluation of cutting fluid application in surface grinding

Highlights

• The coolant flow rate is more influential than it’s velocity on grinding performance.

• Scraper board or air barrier to be used proximate to the grinding zone.

• Flood cooling with effective removal of air-layer improves machining and reduces production cost.

• Distance between nozzle and grinding zone also governs the cooling and lubrication.

• Flood cooling with scraper board is superior to dry, MQL, high-speed jet and nozzle positioning.

Abstract

The application of cutting fluid performs a significant role in improving the grinding efficiency. It also ensures the considerable improvement of workpiece quality by reducing the friction coefficient between the wheel and workpiece. The present study is aimed carefully to evaluate the various fluid application methods towards improving grinding performance. Five various techniques of fluid application such as traditional flood cooling, flood cooling at different angular locations of the nozzle, flood cooling in the presence of scraper board (SB) at distinct angular positions, application of fluid at different velocities and pressures through an indigenously made nozzle, and minimum quantity lubrication (MQL) have been typically employed. The techniques are evaluated by assessing the output variables such as grinding forces, surface roughness, surface texture, wheel loading and chip formation. The results confirm that the technique of using the scraper board proximate to the grinding zone can appreciably reduce the grinding force, wheel loading and produces favourable chips and surface texture than other methods of application of the fluid. In particular, positioning scraper board at 57.5° along with the Nozzle at 42.5° reduces the tangential force by 48%, 18%, 12%, compared to dry grinding, MQL and grinding by positioning nozzle at 42.5° respectively. However, the ground surface roughness in MQL succeeds in other methods of application. The findings also reveal that the increase in the fluid flow rate is more important than the velocity towards improving productivity and product quality.

Introduction

Grinding is an abrasive machining process associated with high heat generation which leads to thermal damages to the workpiece. Therefore, the use of cutting fluid becomes essential to typically improve the process performances. It improves product quality and productivity. These actions of the cutting fluid chiefly depend upon the type of fluid used and their methods of application. The proper use of the grinding fluid can meaningfully improve the machinability and machining quality to a great extent [1]. Therefore, the study of the actions of cutting fluid in various methods of application is important to find the most effective one.

Several application methods of cutting fluid have been studied to improve the cooling and lubrication of the grinding zone. The minimum quantity lubrication (MQL) philosophy has been developed primarily to reduce the cost of production by utilizing the less amount of lubricant [2], [3]. The MQL method, where oil is utilized as cutting fluid is found to improve the lubrication to a considerable extent and the specific energy requirement becomes less compared to the conventional jet cooling method. But the cooling capacity of the tool and work surface is poor. Saberi has found the cooling capacity of MQL is as low as 5% with comparison to cold air [4]. Also, the cleaning of chips arrested between the abrasive grits and cooling ability is poor in MQL [1], [5], [6]. As a result, abrasion and rubbing on the material surface and consequently temperature increases and surface quality and integrity decrease [6], [7]. In terms of surface finish, jet cooling is more proficient than MQL. However, better surface finish is reported by MQL on the hardened material than the soft [8].

Various optimization techniques such as genetic algorithm, ant colony optimization, flower pollination algorithm, etc. have been developed and used to evaluate the optimum grinding conditions. However, authors have only suggested the better method of optimization which gives the closure values to the experimental results [9], [10], [11], [12], [13], [14], [15], [16], [17]. Many researchers have reported that the useful flow rate of the cutting fluid through the grinding zone is critically important to improve the machining quality [18], [19], [20], [21]. The round nozzle has been reported to be more effectual over flat nozzle [22]. Mao et al. have shown the angular position of the nozzle is more effective in improving the process performance than the tangential position and toward the grinding wheel position [23]. Engineer et al. has tested the useful flow rate for two different positions of the nozzle, changing its position both horizontally and vertically. A 26% increase in useful flow rate has been reported when the nozzle is positioned at zero distance from the wheel surface. But positioning the nozzle at the surface of the wheel may give rise to excessive splashing, hence gives rise to an unhealthy working environment and wastage of cutting fluid [24].

Thus, the method of application of coolant has been observed to be a key factor in suggestively improving productivity and product quality. In a recent study, Baumgart has found that at 770 kPa fluid pressure and the speed of the coolant jet at 37% of the wheel speed issued through a flat nozzle can overcome the effect of the boundary-layer airflow around the grinding wheel. But flood cooling by high-pressure jet not only increases the pumping cost but also upsurges the splashing of fluid at the surrounding [22]. Thus, it is required to devise a process to increase the lubrication and cooling by overcoming the consequences of air boundary and without augmenting the pumping cost simultaneously. Numerous techniques of fluid applications such as traditional flood cooling, flood cooling for different nozzle positions, flood cooling at high jet speed and MQL have been studied earlier. But whether they can demand their supremacy over flood cooling at various velocities of fluid jet and flood cooling with optimized angular positions of the scraper board without increasing the production cost at once has not been examined. Between the low flow rate at high velocity and high flow rate at low-velocity jet which one is more effective is correspondingly required to be understood. In the present investigation, all these cutting fluid application methods have been studied. The evaluation analysis has been carried out based on the output variables such as grinding forces, surface roughness, surface texture, wheel loading and chip formation. Finally, the best application method has been suggested.