ROTARY TRUING OF VITREOUS BOND DIAMOND GRINDING WHEELS USING METAL BOND DIAMOND DISKS

Experiments on rotary truing of vitreous bond diamond grinding wheels were conducted to investigate the effects of truing speed ratio, type of diamond in the metal bond truing disks (synthetic versus natural), and diamond grit size in the grinding wheel on the wear of truing disk and on the cylindrical grinding of zirconia. Similar to G-ratio, a new parameter called D-ratio is defined to quantify the wear rate of the diamond truing disks. Experimental results show that, under the same truing condition, the truing disk with blocky, low friability synthetic diamond has a higher D-ratio than the truing disk with natural diamond. Diamond wheels trued by the disk with synthetic diamond also generate lower grinding force and rougher surface finish. High truing disk surface speed, 1.8 times higher than the surface speed of the grinding wheel, was tested and did not show any improvement in D-ratio. This study indicates that μm-scale precision form truing of the vitreous bond diamond wheel is difficult due to excess wear of the metal bond diamond truing disk.     

ROTARY TRUING OF VITREOUS BOND DIAMOND GRINDING WHEELS USING METAL BOND DIAMOND DISKS

Abstract

Experiments on rotary truing of vitreous bond diamond grinding wheels were conducted to investigate the effects of truing speed ratio, type of diamond in the metal bond truing disks (synthetic versus natural), and diamond grit size in the grinding wheel on the wear of truing disk and on the cylindrical grinding of zirconia. Similar to G-ratio, a new parameter called D-ratio is defined to quantify the wear rate of the diamond truing disks. Experimental results show that, under the same truing condition, the truing disk with blocky, low friability synthetic diamond has a higher D-ratio than the truing disk with natural diamond. Diamond wheels trued by the disk with synthetic diamond also generate lower grinding force and rougher surface finish. High truing disk surface speed, 1.8 times higher than the surface speed of the grinding wheel, was tested and did not show any improvement in D-ratio. This study indicates that μm-scale precision form truing of the vitreous bond diamond wheel is difficult due to excess wear of the metal bond diamond truing disk.     

A study on wear mechanism and wear reduction strategies in grinding wheels used for ELID grinding

Metal-bonded superabrasive diamond grinding wheels have superior qualities such as high bond strength, high stability and high grindability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the grinding wheel. Electrolytic in-process dressing (ELID) is an effective method to dress the grinding wheel during grinding. The wear mechanism of metal-bonded grinding wheels dressed using ELID is different form the conventional grinding methods because the bond strength of the wheel-working surface is reduced by electrolysis. The reduction of bond strength reduces the grit-depth-of-cut and hence the surface finish is improved. The oxide layer formed on the surface of the grinding wheel experiences macrofracture at the end of wheel life while machining hard and brittle workpieces. When the wheel wear is dominated by macrofracture, the wheel-working surface is free from loaded chips and worn diamond grits. When the oxide layer is removed from the wheel surface, the electrical conductivity of the grinding wheel increases, and that stimulates electrolytic dressing. The conditions applied to the pulse current influence the amount of layer oxidizing from the grinding wheel surface. Longer pulse ‘on’ time increases the wheel wear. Shorter pulse ‘on’ time can be selected for a courser grit size wheel since that type of wheel needs high grinding efficiency. Equal pulse ‘on’ and ‘off’ time is desired for finer grit size wheels to obtain stable and ultraprecision surface finish.     

超硬磨料砂轮的激光修锐技术研究

激光修整超硬磨料砂轮的原理,利用Ｎｄ：ＹＡＧ固体脉冲激光器进行激光修锐青铜结合剂和树脂结合剂硬磨料砂轮的试验,用扫描电镜观察了激光修锐前后砂轮表面的微观表貌,对激光作用下砂轮表面不同结合剂材料的去除机理进行了分析,通过磨削陶瓷试验,研究激光修锐的金刚石砂轮的磨削性能,并与普通砂轮磨削肖修锐的金刚石砂轮进行对比。结果表明,采用试验所确定的激光参数可选择性地去除砂轮表面的结合剂材料,而不损伤超硬磨粒,     

The optimal diamond wheels for grinding diamond tools

Grinding is the most suitable process for manufacturing good quality diamond tools. In this paper, diamond wheels have been studied. From the grinding of polycrystalline diamond (PCD) insets, the effects of certain factors such as the bonding material, the grit size and structure of a diamond wheel have been investigated. It is concluded that vitrified bond diamond wheels are the most suitable for grinding PCDs and the recommended grit size is mesh number 1000, which can get a good surface quality within an appropriate time. The wheel structure is another important factor. Rougher wheels (mesh #800, #1000) with the softer grade scale P yield a higher material removal rate (MRR) than scale Q. However, a finer wheel (mesh #1200) needs a tougher structure to promote its grinding ability and to have a higher MRR.     

Mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating

Diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses that problem in that it proposes an effective dressing technique—mist-jetting electrical discharge dressing (MEDD) of nonmetal bond diamond grinding wheels using conductive coating. A conductive phase is coated on the wheel surface to increase the conductivity of the nonmetal bond. Electrical discharge model was built to analyze feasibility and select optimized parameters of MEDD. Experiments were conducted to evaluate the dressing performance of MEDD in terms of surface morphology of the wheel surface, grinding force, and surface roughness of the workpiece. Experimental results show that abrasive grains on the wheel protrude are satisfied. The discharge parameters have an important influence on the dressing result. The grinding force and the surface roughness of the workpiece significantly reduced after dressing.     

Wear mechanism of metal bond diamond wheels trued by wire electrical discharge machining

The stereographic scanning electron microscopy (SEM) imaging was used to investigate the wear mechanism in wire electrical discharge machining (EDM) truing of metal bond diamond wheels for ceramic grinding. A piece of the grinding wheel was removed after truing and grinding to enable the examination of wheel surface and measurement of diamond protrusion heights using a SEM and stereographic imaging software. The stereographic SEM imaging method was calibrated by comparing with the profilometer measurement results. On the wheel surface after wire EDM truing and before grinding, some diamond grain protruding heights were measured in the 32 μm level. Comparing to the 54 μm average size of the diamond grain, this indicated that over half of the diamond was exposed. During the wire EDM process, electrical sparks occur between the metal bond and EDM wire, which leaves the diamond protruded in the gap between the wire electrode and wheel. These protruding diamond grains with weak bond to the wheel were fractured under a light grinding condition. After heavy grinding, the diamond protrusion heights were estimated in the 5–15 μm range above the wear flat. A cavity created by grinding debris erosion wear of the wheel bond could be identified around the diamond grain.     

Grinding damage of BK7 using copper-resin bond coarse-grained diamond wheel

Coarse-grained wheels can realize high efficient grinding of optical glass. However, the serious surface and subsurface damage will be inevitably introduced by the coarse-grained wheels. In this paper, the grinding damage of a copper-resin bond coarse-grained diamond wheel with grain size of 150μm was investigated on optical glass BK7. The wheel was first properly trued with a metal bond diamond wheel, then pre-dressing for the wheel and grinding experiments are carried out on a precision grinder assisted with electrolytic in process dressing (ELID) method. The surface roughness (Ra) of ground surface was measured using an atomic force microscope (AFM) and the surface topography were imaged by a white light interferometer (WLI) and the AFM. The subsurface damage level of ground surface was evaluated by means of both MRF spot method and taper polishing-etching method, in term of the biggest depth of subsurface damage, distribution of micro defects beneath the ground surface, the cluster depth of subsurface damage, relationship between subsurface damage (SSD) and PV surface roughness (SR), propagating distance and pattern of cracks beneath the ground surface. Experimental results indicate that a well conditioned copper-resin bond coarse-grained diamond wheel on a precision grinder can generate good surface quality of Ra less than 50nm and good subsurface integrity with SSD depth less than 3.5ε for optical glass BK7.     

Wear of the blade diamond tools in truing vitreous bond grinding wheels: Part II. Truing and grinding forces and wear mechanism

Truing and grinding forces and the wear mechanism of particle and rod diamond blade tools used to generate precise and intricate forms on rotating vitreous bond silicon carbide grinding wheels are presented. A Hall effect sensor was used to measure the change of grinding spindle power during truing and grinding. A signal processing procedure was developed to identify individual truing passes and to extract the average, peak-to-valley, and standard deviation of the variation of truing force for each pass. The truing force data and SEM micrographs of worn surfaces on blade tools reveal micro- and macro-fracturing of the diamond. The attritious and erosion wear of the diamond rod and particle, erosion of the metal bond, and pulling-out of the diamond particle are also identified. Grinding force data shows that, for the same truing parameters, a wheel trued by the rod diamond blade tool has higher grinding forces than one trued by a particle diamond blade tool.     

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.     

The mechanism and application of bronze-bond diamond grinding wheel pulsed laser dressing based on phase explosion

This paper presents a theoretical analysis of the surface bond removal mechanism for bronze-bond diamond grinding wheels using a pulsed laser. For the first time, the existence of a phase explosion phenomenon during the process of grinding wheel laser dressing is proposed, and the negative effects of a phase explosion on laser dressing are analyzed. Additionally, a theoretical study on phase explosion is conducted. The mechanism of bronze-bond diamond grinding wheel laser dressing is improved, and theoretical guidance for bronze-bond diamond grinding wheel laser dressing is provided. In the experiment, the processing parameters of the laser during phase explosion are studied, and a grinding test under the corresponding conditions is conducted. A high-speed camera is used to observe phase explosion in the laser dressing process. An ultra-depth 3-D microscope system is used to observe the topography of the bronze-bond diamond grinding wheel after dressing and grinding as well as the bronze wheel surface quality. It is concluded that to avoid phase explosion from occurring in the laser dressing of the bronze-bond grinding wheel, chip space around the bond must exist for the abrasive particle protrusions. The processing parameters of laser dressing under certain condition are optimized, and the desired dressing effect is achieved.     

Wear of the blade diamond tools in truing vitreous bond grinding wheels: Part I. Wear measurement and results

The wear of stationary blade diamond tools used to generate a precise and intricate form on the vitreous bond grinding wheel is presented. Two types of blade tools made of rod and particle diamond were used. A method to measure the wear of the blade diamond tool in the μm-scale range using the size difference of two parts ground before and after truing was introduced. Two sets of experiments with four truing feeds and four tool traverse speeds across the grinding wheel were conducted on the rod and particle blade diamond tools, respectively. Experimental results showed the wear rate of blade diamond tools was improved at higher truing feeds and traverse speeds due to the brittle fracture of the abrasive and vitreous bond.     

Genetic Algorithm (GA) for Multivariable Surface Grinding Process Optimisation Using a Multi-objective Function Model

A genetic algorithm (GA) based optimisation procedure has been developed to optimise the surface grinding process using a multi-objective function model. The following ten process variables are considered in this work: wheel speed, workpiece speed, depth of dressing, lead of dressing, cross-feedrate, wheel diameter, wheel width, grinding ratio, wheel bond percentage, and grain size. The procedure evaluates the production cost and production rate for the optimum grinding conditions, subject to constraints such as thermal damage, wheel-wear parameters, machine-tool stiffness and surface finish. A worked example is used to illustrate how this procedure can be used to produce optimum production rate, low production cost, and fine surface quality for the surface grinding process.     

A novel technique for dressing metal-bonded diamond grinding wheel with abrasive waterjet and touch truing

The dressing of metal-bonded diamond grinding wheels is difficult despite their availabilities on hard and brittle materials. In this paper, a novel compound technology that combines abrasive waterjet (AWJ) and touch truing is proposed for dressing metal-bonded diamond grinding wheel precisely and efficiently. The dressing experiments of a coarse-grained and a fine-grained bronze-bonded diamond grinding wheel were carried out on a surface grinder with a developed AWJ system. The feasibility of this method was verified by analyzing the wheel runout, the truing forces, and the wheel surface topography. The variations of 3D surface roughness of wheel surface topography during the compound dressing process were quantitatively analyzed. The mechanism of AWJ and touch compound dressing is also discussed. Further, a reaction-bonded silicon carbide block was ground to validate the dressing quality. The experiment results indicate that the grinding wheels that were well dressed by the proposed technique leads to a smaller grinding force and a smaller surface roughness than that of undressed wheels.     

Some effects of dressing on grinding performance

This paper presents a review of dressing from the work of Pahlitzsch in 1953 up to the present day and concentrates on the single-point diamond dressing of vitreous bonded wheels. Particular emphasis is made of the role of dressing on cutting forces, specific energy, wheel wear and the surface finish of the workpiece. The extent to which an optimum wheel condition is a compromise is discussed together with the practical methods of achieving and monitoring such a condition.     

基于修整力的树脂结合剂金刚石砂轮机械修整

研究了树脂结合剂金刚石砂轮修整过程中修整力与修整效果的关系,基于修整力的变化表征了砂轮的表面形貌及磨削性能。首先,对碳化硼、碳化硅、白刚玉3种砂轮修整工具进行实验,并采集了修整过程中修整力的变化;然后,利用白光干涉仪观测修整后砂轮的表面形貌;最后,对修整后砂轮进行磨削验证实验,得到不同修整工具修整后砂轮的磨削性能。基于上述实验,分析并验证了修整力的变化与砂轮表面形貌和砂轮磨削性能的关系。结果表明,法向力Fn能够表征砂轮的磨粒切削刃密度以及磨粒突出高度;修整比率β反映了砂轮的锋锐程度,当β稳定时,砂轮达到充分修整。因此修整力反映了砂轮表面形貌和磨削性能,根据修整力的变化可以把握砂轮的修整进程。     

金属结合剂砂轮精密成形磨削T15工具钢零件的实验研究

采用金属结合剂金刚石砂轮对T15工具钢进行成形磨削加工实验,获得了形面精度保持性好的成形磨削砂轮,并用其进行长时间磨削加工,得到了满足形面加工精度要求的加工试件.实验表明,采用电火花修形方法对金属结合剂砂轮进行精密修形,可获得满足成形磨削加工要求的砂轮轮廓;在成形磨削过程中,凹槽侧面磨损率始终最大,而砂轮回转面的磨损最为稳定.     

树脂结合剂金刚石砂轮磨削铁氧体陶瓷表面粗糙度的试验研究

通过磨削对比试验研究了树脂结合剂金刚石砂轮的特性参数和磨削用量对铁氧体陶瓷表面粗糙度的影响;通过砂轮速度、磨削深度、横向进给速度和纵向进给速度等四因素及各因素之间交互试验的数据分析和金相显微图像比较,探讨了各因素对陶瓷表面粗糙度的影响规律,并优化了降低表面粗糙度的磨削参数。     

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151 μm (D151), 91 μm (D91) and 46 μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.     

IN SITU TRUING/DRESSING OF DIAMOND WHEEL FOR PRECISION GRINDING

An application for achieving on-machine truing/dressing and monitoring of diamond wheel is dealt with in dry grinding. A dry electrical discharge （ED） assisted truing and dressing method is adopted in preparation of diamond grinding wheels. Effective and precise truing/dressing of a diamond wheel is carried out on a CNC curve grinding machine by utilizing an ED assisted diamond dresser. The dressed wheel is monitored online by a CCD vision system. It detects the topography changes of a wheel surface. The wear condition is evaluated by analyzing the edge deviation of a wheel image. The benefits of the proposed methods are confirmed by the grinding experiments. The designed truing/dressing device has high material removal rate, low dresser wear, and hence guarantees a desired wheel surface. Real-time monitoring of the wheel profile facilitates determining the optimum dressing amount, dressing interval, and the compensation error.