Introduction

Introduction

Copyright: © 2020 |Pages: 19
DOI: 10.4018/978-1-7998-1546-4.ch001

Abstract

This chapter introduces the application background and characteristics of five kinds of grinding processing methods, briefly describes the enhanced heat transfer mechanism and tribological properties of nanofluids, and points out that nanofluids minimum quantity lubrication (NMQL) solves the technical bottleneck, namely minimum quantity lubrication (MQL) heat transfer capacity is insufficient and opening a new path for application of MQL to grinding process. The current status of exploratory research on the mechanism of minimum quantity lubrication grinding using nanofluids as cooling lubricants is analyzed. The research characteristics of the new green NMQL grinding technology are described, and the chapter puts forward some key problems such as the heat transfer enhancement process of NMQL, the anti-friction and anti-wear tribological mechanism of nanoparticles, and the controlled transport strategies of minimal quantity of lubricating droplets. It will be of great scientific significance and pragmatic value to perfecting NMQL grinding technical system.
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Introduction

Grinding is one of the most fundamental machining modes. It’s especially important that final precision and surface quality of most parts are guaranteed by the grinding technology. The most significant features of grinding are high circular velocity of grinding wheel and high energy consumption (specific grinding energy). Grinding is negative rake cutting of abrasive grain on the grinding wheel surface, and the energy consumed to remove unit volume of materials is far greater than other machining methods (Xu & S, 2001). Most energy generated in the grinding area is converted into heat quantity which is dispersed on abrasive dust, grinding wheel and workpiece (Deng, Liu, & Zhang, 2010). As grinding is different from other machining forms, the contact time between each abrasive grain and workpiece is extremely short under the effect of circular velocity of grinding wheel, and meanwhile, the volume of abrasive dust generated in the grinding process is very small and the ratio of the generated heat quantity which is carried away by abrasive dust is very low. High-energy density in the grinding area has a great bearing on surface quality and usability of the workpiece. Especially when temperature in the grinding area exceeds critical value, this will cause thermal injury (surface oxidation, burning, residual tension and crack) on the workpiece surface so as to degrade anti-fatigue performance and anti-wear performance of parts, and consequently, service life and reliability of parts will be reduced, so will grinding performance and machining precision of grinding wheel (Guo, Yin, Li, & Chen, 2009; Yuan et al., 2010). With heat accumulation on the workpiece surface, its dimensional accuracy and form accuracy will become very poor under the influence of grinding heat (Chen, Shen, Huang, & Xu, 2010). Generally speaking, grinding is the final parts machining procedure and grinding technology and process decide their final precision and surface quality. To effectively control the temperature of the grinding zone and reduce the thermal damage on the surface of the workpiece, large flow grinding fluid is often injected into the grinding zone during processing,which is called cast cooling. Due to the existence of the “gas barrier layer” around the high-speed moving grinding wheel, it is often difficult for the pouring type liquid supply to enter the grinding zone, and the “effective flow rate” (the ratio between the liquid volume that enters the grinding interface actually and the total supply liquid volume) is only 5%-40%. Therefore, most of the grinding fluid can not actually reach the grinding interface, but only acts to cool the workpiece base in the periphery, resulting in insufficient cooling capacity of the conventional liquid supply method and futher leading to the grinding burns and deterioration of the surface integrity of the workpiece. Additionally, the supply of a large amount of grinding fluid will form a fluid introduction force and a fluid dynamic pressure at the wedge-shaped gap of the grinding wheel workpiece, thereby causing deflection of the spindle of the grinding machine and furtherly reducing the actual depth of cut. therefore, the traditional pouring type liquid supply method not only causes large shape and size errors in the processed workpiece, but also wastes a lot of grinding fluid. Green development is an international trend. The current environmental and resource issues have become a common challenge for mankind, and an international consensus has been reached on how to achieve sustainable development. Green manufacturing is undoubtedly the only way for industrial upgrading and transformation. China is a big manufacturing country in the world,there are still “three highs” problems of high emissions, high consumption and high investment. Both energy consumption and pollution emissions are far from the world's advanced manufacturing levels. The Ministry of Industry and Information Technology issued the “Industrial Green Development Plan”, and the green manufacturing of basic manufacturing processes to promote the technology of “green manufacturing” with less cutting fluid green processing is the key development direction of the National 13th Five-Year Plan. The development of quasi-dry green manufacturing technology is conducive to alleviating the current environmental resource eastward problem, facilitating the rapid cultivation of new economic growth points, and has a profound historical significance for accelerating the transformation of economic development mode, promoting industrial transformation and upgrading, transforming old and new kinetic energy, and enhancing the international competitiveness of manufacturing industry.

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