Specific grinding energy as an in-process control variable for ductile-regime grinding

This article addresses the problem of monitoring the material removal regime (ductile versus brittle) that occurs during the grinding of brittle materials. Often a ductile grinding regime is desired, but currently there is no way to measure the grinding ductility “in process.” A model is developed to describe the dependence of the specific grinding energy on the material removal regime. It is found that the specific grinding energy will remain relatively constant for ductile-regime grinding but will decrease in a power-law relationship with an increasing material removal rate for brittle-regime grinding. Experimental confirmation of the proposed model is presented. The potential for using measurements of specific grinding energy to control the grinding ductility is established, and the benefits of such a closed-loop feedback system in ductile-regime grinding are explained.     

部分稳定氧化锆PSZ高效深磨磨削力试验研究

本文对部分发稳定氧化锆陶瓷（Panialy stabilized Zirconia，PSZ）在高效深磨条件下的磨削力进行了试验研究，分析了各种因素对磨削力的影响，并与其它磨削方式的PSZ陶瓷作了比较和综合分析。分析表明：PSZ陶瓷在高效深磨条件下，当比材料去除率一定时，工作台速度的变化对磨削力的影响比切深的变化对磨削力的影响大；磨削力与普通磨削相比较大，比材料去除率是普通磨削的几十倍；材料去除模式以显微塑性去除为主，磨削工件表面质量较好。     

基于声发射信号的外圆切入磨削去除率监测

针对精密外圆切入磨削加工的在线监测需求,提出一种采用声发射信号实现轴类零件材料去除率在线监测的方法。根据声发射信号强度与磨削力之间的联系,建立了声发射信号均方根曲线的预测模型,利用该预测模型研究了砂轮进给阶段和驻留阶段磨削系统时间常数的理论计算方法,推导了声发射信号均方根曲线与工件材料去除率的关系;编写了在线监测软件,利用声发射传感器实现了精密外圆切入磨削的材料去除率预测。实验证明,所建立的声发射信号均方根曲线模型具有良好的预测精度,基于该模型能够实现磨削系统时间常数在线评估,并实现精密轴类零件材料去除率的实时在线监测。     

Real-time fuzzy-clustering and CART rules classification of the characteristics of emitted acoustic emission during horizontal single-grit scratch tests

During the unit event of material iteraction in grinding three phenomena are involved, namely: rubbing, ploughing and cutting. Where ploughing and rubbing essentially mean the energy is being applied less efficiently in terms of material removal. Such phenomena usually occurs before or after cutting. Based on this distinction, it is important to identify the effects of these different phenomena experienced during grinding. Acoustic emission (AE) of the material grit interaction is considered the most sensitive monitoring process to investigate such miniscule material change. For this reason, two AE sensors were used to pick up energy information (one verifying the other) correlated to material measurements of the horizontal scratch groove profiles. Such material measurements would display both the material plastic deformation and material removal mechanisms. Accurate material surface profile measurements of the cut groove were made using the Fogale Photomap Profiler which enables the comparison between the corresponding AE signal scratch data. By using short-time Fourier transforms (STFT) and filtration, the salient features for identifying and classifying the phenomena were more distinct between the three different levels of single-grit (SG) phenomena. Given such close data segregation between the phenomenon data sets, fuzzy clustering/genetic algorithm (GA) classification techniques were used to classify and verify the demarcation of SG phenomena. After the cutting, ploughing and rubbing gave a high confidence in terms of classification accuracy, the results from the unit/micro-event to the multi/macro-event, both 1-μm and 0.1-mm grinding test data, were applied to the named classifier for classification. Interesting output results correlated for the classifier signifying a distinction that there is more cutting utilisation than both ploughing and rubbing as the interaction between grit and workpiece become more involved (measured depth of cut increases). With the said classifier technique it is possible to get a percentage utilisation of the grit and material interaction phenomena. In addition, optimised fuzzy clustering was verified against a classification and regression tree (CART) rule-based system giving transparent rule classification. Such findings were then realised into a Simulink model as a potential control system for a micro-grinding simulation or, for real-time industrial control purposes.     

Study of grinding tool profiling for robotic processes

In the fabrication and maintenance of hydroelectric turbines, the reconstruction by grinding of certain high-curvature surfaces such as junctions has not yet been robotized and must now be done manually. The problem is related to the very fast grinding wheel wear and the difficulty in controlling the position and orientation of the robot's grinder to adjust to changes in wheel shape. If the grinding wheel orientation is kept constant with respect to the workpiece, wheel-workpiece conformity increases, specific energy increases, the material removal rate drops and glazing of the wheel may occur. This article presents a method for controlling simultaneously the profile of both the workpiece and the grinding wheel. The orientation of the wheel is oscillated to maintain a constant wheel profile throughout its life and thus achieve better control in material removal. Research results provide the basis for robotic grinding tool profiling.     

A magnetorheological polishing-based approach for studying precision microground surfaces of tungsten carbides

Surface features of tungsten carbide composites processed by bound abrasive deterministic microgrinding and magnetorheological finishing (MRF) were studied for five WC–Ni composites, including one binderless material. All the materials studied were nonmagnetic with different microstructures and mechanical properties. White-light interferometry, scanning electron microscopy, and atomic force microscopy were used to characterize the surfaces after various grinding steps, surface etching, and MRF spot-taking. It was found that the peak-to-valley (p–v) microroughness of the surface after microgrinding with rough or medium abrasive size tools gives a measure of the deformed layer depth. MRF spots revealed the true depth of the grinding-induced deformed surface layer.     

超音速火焰喷涂WC-17Co涂层的高速磨削机理试验研究

针对超音速火焰喷涂WC-17Co高硬涂层的加工难题,对WC-17Co涂层进行了高速/超高速磨削试验。通过考察不同金刚石砂轮和磨削工艺参数对磨削力、磨削温度和表面残余应力、表面/亚表面微观形貌和表面粗糙度的影响,讨论了最大未变形切屑厚度与比磨削能的内在关系,分析了磨削温度对表面残余应力的作用规律,探讨了法向磨削力对涂层亚表面损伤的作用规律。结果表明：WC-17Co涂层磨削去除是脆性和延性去除并存;提高砂轮线速度将使磨削力先快速减小后缓慢增大,磨削温度持续升高,涂层磨削从脆性去除转为延性去除的趋势也逐渐增强,表面残余应力由压应力逐渐转变为拉应力,而磨削高温引起涂层热塑性变形是表面残余应力状态转变的根本原因。涂层亚表面磨削损伤层平均深度随法向磨削力的增大而变大。提高砂轮线速度、降低工作台速度和减小磨削深度均能增大涂层磨削塑性去除的比例。     

TEMPERATURE AND ENERGY PARTITION IN HIGH-SPEED GRINDING OF ALUMINA WITH A BRAZED DIAMOND WHEEL

An investigation is reported on the temperatures and energy partitions for high speed grinding of alumina with a brazed diamond wheel. The grinding temperature at the wheel-workpiece interface was measured using a pair of grindable foil thermocouples. The energy partition to the workpiece was evaluated by matching the analytical temperatures to the measured results. The influences of the grinding conditions, including wheel speed, the depth of cut, workpiece velocity, and material removal rate, on the temperatures and energy partitions were investigated. In all tests, the maximum grinding zone temperature rise was below 260°C. The energy partitions to the workpiece obtained under different grinding conditions varied from 30% to 75%. The calculated diamond tip temperature might be over 1000°C if the circular grain contact radius of contact was less than a critical value.     

超高速磨削的比磨削能研究

阐述了超高速磨削的机理，介绍了磨削中的尺寸效应和比磨削能。对超高速磨削条件下比磨削能的影响因素进行了分析，得出了在超高速磨削下，比磨削能与未变形的磨屑厚度的关系。同时，比磨削能随工作台速度、磨削速度、实际磨削深度以及材料的去除率的增加而降低，而良好润滑的磨削液可使比磨削能保持在低水平，在同样的磨削参数条件下，工件的材料对比磨削能也有一定的影响。采用超高速磨削，对改善磨粒的切削状态，降低比磨削能是非常有利的。     

Effect of parameters on grinding forces and energy while grinding Al (A356)/SiC composites

Abstract

Grinding processes require a high energy input per unit volume of material removed, which is converted to heat at the grinding zone, resulting in increased force and wear. In the present study, the influence of grinding parameters like work speed and depth of cut on grinding forces and energy was studied. An attempt has been made to study the forces and energy involved while grinding aluminium alloy (A356)/silicon carbide (SiC) composite material with different grinding wheels. Experiments were carried out on a surface grinding machine. Three different types of wheels like SiC, cubic boron nitride (CBN) and diamond wheels were used. The grinding forces increased with increase in depth of cut and work speed. SiC exhibited high grinding force compared to the CBN wheel. In the case of the diamond wheel, it was even less. The specific grinding energy was highest for the diamond wheel followed by CBN and SiC wheels. The specific grinding energy decreased with increase in depth of cut and work speed.     

Vibro-impact dynamics of material removal in a robotic grinding process

This paper studies the vibratory dynamics governing material removal performed by a compliant robot. The objective is to understand whether metal removal at a target rate or to a target depth of cut is possible given the unavoidable significant and sustained vibrations inherent to the process. Robotic grinding by the SCOMPI robot developed at Hydro-Québec’s research institute for field maintenance work on hydroelectric equipment is studied. A test rig is developed to investigate the instantaneous process of material removal. The setup employs the methodology of angular analysis to detect and locate the discrete cutting events with respect to the instantaneous angular position of the spindle. Test results confirm that the grinding wheel exhibits cyclic impacting oscillations while removing material. This vibro-impact behavior is explained by the nonsmooth nature of the system arising from the substantial difference between process stiffness and stiffness of the robot. Grinding force and power are formulated based on the impacting dynamics of material removal (impact cutting). Parameters of the impact-cutting model are determined experimentally. The impact-cutting model is found well-suited to predicting the grinding power required to remove metal at a target rate. The conclusion is reached that metal removal to a target depth and with acceptable surface waviness is possible despite high-amplitude vibro-impacts between the grinding wheel and workpiece.     

DETECTION OF DUCTILE TO BRITTLE TRANSITION IN MICROINDENTATION AND MICROSCRATCHING OF SINGLE CRYSTAL SILICON USING ACOUSTIC EMISSION

Machining of brittle materials entails two modes of material removal: pure plastic deformation and brittle fracture. The mode of material removal is generally identified by surface quality observations in a scanning electron microscope (SEM) or an atomic force microscope (AFM) after machining. Hence, there is a need for the development of in-process monitoring technology in order to detect whether the mode of material removal is ductile or brittle, and thereby predict surface quality. In the present paper, acoustic emission (AE) is proposed as a means of monitoring the ductile to brittle transition. Microindentation and microscratching tests of single crystal silicon were conducted using an ultrafine-motion table with very small motion error. The obtained AE signals were correlated with crack initiation and the ductile to brittle transition. The critical force f_c defined as the force at which AE was induced during the microindentation and microscratching tests was measured to be 40 ∼ 50 mN. AFM observations revealed the critical depth of cut d_c to be 0.20 μm in the microscratching test.     

Research on constant grinding depth model for cam grinding

In order to mitigate the problems in CNC grinding of a camshaft caused by varying grinding depth along the periphery of the cam, a novel grinding strategy is proposed to keep the grinding depth constant during the process. In comparison with the current cam grinding strategy, analysis results derived from the modelling of the process indicate that it is applicable to keep the grinding depth constant. Consequently, in combination with a constant grinding infeed speed, the material removal rate (MRR) is also kept stable. With the same grinding depth, the volume of removed material in a certain single revolution with the new processing strategy is less than the conventional process. This new strategy can increase the grinding depth without causing grinding burns. Therefore, the total number of grinding revolutions/steps decreases dramatically. Moreover, experiments for comparison of both the single revolution machining and the whole cam grinding have been carried out on a CNC8325B camshaft grinder. The results show that the new process improves machining efficiency dramatically while ensuring the machining quality.     

小切深磨削条件下工件表面硬化机理

以位错运动造成塑性变形的理论为基础,深入分析了小切深条件下磨削力机械作用硬化机理和材料热相变硬化机理。通过不同磨削参数的小切深磨削硬化试验,分析磨削硬化过程中不同磨削参数条件对工件表面强化层形成的影响及其金相组织转变的情况,深入研究磨削强化层组织的形成机理。试验结果表明,小切深条件下磨削加工试件表面的硬化主要以位错运动而产生的强化层为主,提高磨削深度和降低工件进给速度会增大工件表面显微残余应力,增强试件表层硬化层的形成效果。     

磨削参数对超细硬质合金磨削表面粗糙度的影响

在使用金刚石砂轮的平面磨床上对超细硬质合金进行了磨削试验研究。通过扫描电子显微镜观察磨削表面形貌和用表面粗糙度测定仪测量磨削表面粗糙度,分析了磨削参数对超细硬质合金磨削表面粗糙度的影响。研究结果表明,同一切深下,超细硬质合金磨削表面粗糙度随砂轮粒度的增大而增大。采用相同粒度砂轮磨削,切深较小时,超细硬质合金磨削表面粗糙度随切深的增加而增大,当切深增大到一定值后,磨削表面粗糙度值逐渐降低。     

Deformation analysis of micro/nano indentation and diamond grinding on optical glasses

The previous research of precision grinding optical glasses with electrolytic in process dressing (ELID) technology mainly concentrated on the action of ELID and machining parameters when grinding,whic...     

A new approach to investigate tool condition using dummy tool holder and sensor setup

The industrial demand for automated machining systems to enhance process productivity and quality in machining aerospace components requires investigation of tool condition monitoring. The formation of chip and its removal have a remarkable effect on the state of the cutting tool during turning. This work presents a new technique using acoustic emission (AE) to monitor the tool condition by separating the chip formation frequencies from the rest of the signal which comes mostly from tool wear and plastic deformation of the work material. A dummy tool holder and sensor setup have been designed and integrated with the conventional tool holder system to capture the time-domain chip formation signals independently during turning. Several dry turning tests have been conducted at the speed ranging from 120 to 180?m/min, feed rate from 0.20 to 0.50?mm/rev, and depth of cut from 1 to 1.5?mm. The tool insert used was TiN-coated carbide while the work material was high-carbon steel. The signals from the dummy setup clearly differ from the AE signals of the conventional setup. It has been observed that time-domain signal and corresponding frequency response can predict the tool conditions. The rate of tool wear was found to decrease with chip breakage even at higher feed rate. The tool wear and plastic deformation were viewed to decrease with the increased radius of chip curvature and thinner chip thickness even at the highest cutting speed, and these have been verified by measuring tool wear. The chip formation frequency has been found to be within 97.7 to 640?kHz.     

Grinding wheel wear monitoring based on wavelet analysis and support vector machine

A novel grinding wheel wear monitoring system based on discrete wavelet decomposition and support vector machine is proposed. The grinding signals are collected by an acoustic emission (AE) sensor. A preprocessing method is presented to identify the grinding period signals from raw AE signals. Root mean square and variance of each decomposition level are designated as the feature vector using discrete wavelet decomposition. Various grinding experiments were performed on a surface grinder to validate the proposed classification system. The results indicate that the proposed monitoring system could achieve a classification accuracy of 99.39% with a cut depth of 10?μm, and 100% with a cut depth of 20?μm. Finally, several factors that may affect the classification results were discussed as well.     

Experimental investigation on electrochemical grinding (ECG) of alumina-aluminum interpenetrating phase composite

The present paper focuses on the evaluation of material removal rate (MRR), surface finish, and cutting forces during electrochemical grinding of Al₂O₃/Al interpenetrating phase composite. The effect of electrolyte concentration, supply voltage, depth of cut, and electrolyte flow rate on machining performances has been studied. The characteristic features of the electrochemical grinding (ECG) process are explored through Taguchi-design-based experimental studies with various process parametric combinations and finally the process has been optimized. The mechanism of material removal and surface characteristics under different grinding conditions have been studied through SEM micrograph. Besides, another set of experimental investigation has been carried out in order to identify the influence of different type of electrolytes and degree of reduction in grinding force in ECG. Finally, a comparative study of conventional and electrochemical grinding of this special class of material has been carried out.     

纳米结构Al2O3/13TiO2涂层精密磨削的材料去除机理的研究

应用扫描电镜对纳米结构Al2O3/13TiO2(n-Al2O3/13TiO2)涂层精密磨削后的表面/亚表面形貌进行观察和分析,结合对n-Al2O3/13TiO2精密磨削的单颗磨粒磨削力、磨削力分力比和比磨削能的磨削实验结果的分析,揭示了n-Al2O3/13TiO2涂层精密磨削的材料去除机理.研究表明,在大多数磨削条件下,n-Al2O3/13TiO2陶瓷涂层磨削的材料去除机理主要是以材料碎裂和材料压碎等脆性去除方式为主,同时也存在一定的材料粉末化以及极少的显微塑性变形等方式.研究结论对纳米结构陶瓷涂层的工业化应用具有重要的理论和实用价值.