Highly Efficient Grinding of Ceramic Parts by Electrolytic In-Process Dressing (ELID) Grinding

In the manfacture of structural ceramic components, it has been well documented that the grinding costs can be as high as 90% of the total cost. Grinding costs of ceramics can be reduced by maximizing the material removal rates (MRR). A novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels, known as Electrolytic In-Process Dressing (ELID) has been developed (1) which can significantly increase the MRR. This technique uses a metal bonded grinding wheel that is electrolytically dressed, during the grinding process, for continuous protrudent abrasive from superabrasi ve wheels. The principle of ELID grinding technology will be discussed in this paper as will its application for rough grinding. The effects of various parameters such as wheel bond type and type of power supply on the ELID grinding mechanism will also be addressed in this paper.     

Highly Efficient and Precision Fabrication of Cylindrical Parts from Hard Materials with the Application of ELID (Electrolytic In-Process Dressing)

The ELID (Electrolytic In-Process Dressing) grinding process, which incorporates in-process dressing of metal bonded superabrasive wheels, was applied for efficient and precision grinding of hard materials such as ceramic, hard metals, and quenched steels. Addressed in this paper are some of the typical applications of ELID Grinding for cylindrical machining. The significant advantages, performances, and characteristics of mirror surface grinding for external surface, internal surface, and end-face Finish processes of cylindrical components are described.     

Ductile streaks in precision grinding of hard and brittle materials

Ductile streaks produced during diamond grinding of hard and brittle materials have aided the subsequent process of polishing. Two novel techniques were used to study the formation of ductile mode streaks during diamond grinding (primary process) of germanium, silicon, and glass. In the first technique, aspheric surfaces were generated on Ge and Si at conventional speeds (5000 rpm). In the second technique, diamond grinding of plano surfaces on glass and Si surfaces using high speed (100,000 rpm) was carried out. Form accuracy, surface finish and ductile mode grinding streaks are discussed in this paper. It was found that resinoid diamond wheels gave more ductile streaks than metal-bonded wheels but better form accuracy was obtained with the latter. Ductile streaks were obtained more easily with pyrex rather than with BK 7 glass thus necessitating very little time for polishing. Ductile streaks appeared in abundance on germanium rather than silicon. Both the novel grinding techniques were used on CNC machining centres.     

Grinding Characteristics of Hard and Brittle Materials by ELID-Lap Grinding Using Fine Grain Wheels

In this investigation, ceramics such as zirconia and silicon carbide were ground by lap grinding using the ELID (electrolytic in-process dressing) method and using various-sized metal bonded wheels (mesh sizes of #1200-#8000). Differences in the ground finish, according to the wheel grain size, and surface roughness were investigated through the use of a Scanning Electron Microscope (SEM). It was found that the ground surface roughness improved proportionally to the grain size. The SEM observations also showed that the ground surfaces using wheels over #4000 were very smooth with several minute ground grooves crossing each other without brittle fracture. Brittle-ductile transition was studied using these wheels and the removal mechanisms of silicon and tungsten carbides were also investigated. It was found that for silicon, brittle-ductile transition was obtained using wheels over #8000 and for tungsten carbides, transition was achieved using wheels over #4000. Therefore, the work materials affect the changes in the removal mechanism.     

Ductile Regime Mirror Finish Grinding of Ceramics with Electrolytic In-process Dressing (ELED) Grinding

Advanced structural ceramics, such as silicon nitride based materials, are of interest owing to their unique physical and mechanical properties. However the cost of grinding these ceramics, which is an integral part of their fabrication, is very high. Moreover, grinding can result in surface and sub-surface damage in the material and these defects can significantly reduce the strength and reliability of the finished components. Grinding damage is sensitive to grinding parameters. Two types of silicon nitride based ceramic materials were ground with Electrolytic In-Process Dressing (ELID) using different grit sized metal bonded diamond grinding wheels. With the application of ELID technology, mirror surface finish was realized with a #4000 mesh size wheel (average grain size = 4μm). Differences in ground surface topography caused by wheel grain size were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM studies reveal that material was predominantly removed in the ductile mode when ELID grinding was performed with a #4000 grit size wheel or finer.     

Influence of dressing parameters on grinding performance of CBN/ Seeded Gel hybrid wheels in cylindrical grinding

Wide use of vitrified bond CBN grinding wheels in today's production grinding is due to their higher grinding efficiency and longer wheel life compared to other types of CBN wheels or conventional wheels. Trueing and dressing, however, strongly affect these advantages, since superabrasive wheels usually act dull after a dressing operation and require an initial break-in period. In this study, a rotary trueing and dressing process was investigated for vitrified bond CBN/ Seeded Gel wheels to determine optimum parameters required to eliminate the initial break-in period and to grind at steady-state right after dressing. This paper describes the effects and importance of dressing factors on wheel grinding performance. A limiting factor for useful wheel life between dresses is also suggested.     

A Study of the influence of plasma treatment on the working surface of superabrasive grinding wheels

The paper addresses the effect of plasma treatment on the working surface of polymer- and metal-bonded superabrasive grinding wheels. The investigation has shown a change in hardness of the wheel surface treated with a plasma jet. The paper provides some data on the performance of plasmatreated grinding tools.     

高强度铸铁基cBN砂轮修整实验研究

消失模铸造制备的奥-贝球墨铸铁基cBN砂轮具有胎体强度高、胎体对磨粒把持力大等优点,但也存在着铸造砂轮毛坯尺寸精度不高、磨削层修整余量大、修整较为困难等不足之处.本文针对铸造铸铁基大粒度cBN砂轮毛坯,分别进行机械修整、电解修整和电解-机械-电解复合修整试验,探究不同修整方式下的最优工艺参数和修整效率,以及修整后磨粒的破碎和出刃情况.研究结果表明:采用Si C修整轮修整,当转速比为+0.3时修整效率最高,但修整效率随着时间的增加逐渐减小,修整至120 min才能够达到砂轮的目标精度;采用电解修整,砂轮在最优工艺参数下修整30 min后将产生钝化,电解修整难以继续进行;采用电解-机械-电解复合修整,不仅其修整效率比机械修整有所提高,而且砂轮表面磨粒破碎较少,磨粒出刃高度较大.     

The specific cost of grinding R6M5F3 steel with various dressing methods and electric discharge actions on Kubonit wheel working surface

A comparative study of grinding R6M5F3 steel with metal-bonded Kubonit wheels in various dressing methods and with electric discharge action on the wheel working surface is carried out based on the minimum specific cost criterion. The electric discharge dressing method has been found to provide a reduction in specific grinding cost by one order of magnitude in comparison to an abrasive method. Electric discharge actions on the wheel working surface in the course of grinding result in a higher specific machining cost; therefore, it is advisable to perform grinding with periodic in-process electric discharge dressing.     

Experimental investigations on nanogrinding of RB-SiC wafers

Nanogrinding experiments are performed to investigate the processing characteristics and material removal mechanism of reaction-bonded silicon carbide (RB-SiC) wafers on an ultraprecision grinder using the cup wheel. #120, #600 diamond wheels are used as coarse and semifinished grinding wheels, while #2000 and #12000 diamond wheels are selected as fine and finish grinding wheels, respectively. The experimental results indicate that an ultrasmooth surface with roughness value R_a less than 3?nm and groove depth about 5?nm can be achieved using a diamond wheel whose mesh size exceeds 2000. In addition, R_a less than 1?nm and groove depth about 2?nm will be obtained with a #12000 diamond wheel. The present study reveals the feasibility of ultraprecision grinding RB-SiC materials in the ductile regime and provides technological insights into nanogrinding of hard materials with an ultrasmooth surface.     

THE SIGNIFICANCE OF CONTINUOUS DRESSING IN PRECISION GRINDING OF HARD AND BRITTLE MATERIALS

The precision grinding of hard cemented carbides and brittle ceramics using diamond wheels with continuous electrochemical dressing is considered. A novel grinding apparatus, the electrochemical dressing Miskolc (ECDM), was developed and used. Higher grinding efficiency was observed as compared to grinding using mechanically dressed wheels.     

GRINDING OF SILICON AND GLASS USING A NEW DRESSING DEVICE AND AN IMPROVED COOLANT SYSTEM

Ductile mode machining of brittle materials such as ceramics is recognized as an emerging technology with important applications. Ductile machining is possible if the depth of cut is less than the critical depth of cut of the machined material. By using a new device for dressing a resin-bonded diamond wheel and an improved coolant system proposed here, ductile mode grinding of silicon and glass was achieved using an inexpensive, conventional surface-grinding machine. The low-cost dressing device also ensured minimum disruption to the grinding operation and a higher level of safety. A flooding supply of coolant at the grinding zone provided better cooling performance and lubrication. A relationship appeared to exist between the surface finish and the lightness values of ground silicon surfaces.     

Study on grinding of pre-sintered zirconia using diamond wheel

Zirconia-based ceramics are the most preferred materials used in implants due to their excellent mechanical properties compared with other alternatives. These materials available in the pre-sintered form are appropriate to grind due to their soft nature. However, it is challenging to achieve a required surface finish in grinding these ceramic materials owing to chipping, which limits its usage in industries. In this work, the pre-sintered yttria stabilized tetragonal zirconia (Y-TZP) component was ground using a resin-bonded diamond-grinding wheel under different cooling environments. The components ground under the minimum quantity lubrication conditions exhibited a reduced grinding force with better surface finish compared to wet (flood coolant) and dry conditions. The resultant specific energy was reduced with the increase in maximum chip thickness for different cooling conditions. The critical depth of cut estimated from the pre-sintered zirconia was witnessed to be higher, which indicated that the initiation of ductile to brittle transition occurred at a deeper depth of cut. The material removal mechanism observed in the pre-sintered zirconia was dominated by brittle fracture. This was evident from the obtained chips and ground surface morphology.     

Comparative analysis of performance of cubic boron nitride and microcrystalline alumina tools in profile grinding of form cutters

A comparative analysis of performance of cubic boron nitride, microcrystalline alumina, and white fused alumina wheels has been carried out in profile grinding of long-length HSS profile broach under production conditions. In a particular case, where grinding is accompanied by impact loading and the wheel has to be frequently dressed to provide precise profiling, the vitrified cubic boron nitride wheel has demonstrated an essentially better performance in terms of removal rate, minimum time for dressing cycles, and overall labor input in shaping a working profile of the broach.     

Grinding forces and the machining of magnesium oxide crystals

The forces acting on magnesium oxide crystals during a surface grinding operation have been studied as a function of rate of material removal and crystal orientation, using two different conventional grinding wheels.The results are discussed in terms of the resulting surface and subsurface damage and the geometry of the wheel-workpiece interaction. The results are consistent with the observations that chip formation occurs by plastic flow under a 46-grit alumina wheel, while material is removed completely by brittle fracture under a 100-grit diamond wheel. It is demonstrated that the stress on an individual chip is within an order of magnitude of the theoretical shear strength of the workpiece, thus accounting for the presence of both surface and subsurface plastic deformation.     

CBN grain wear and its effects on material removal during grinding of FGH96 powder metallurgy superalloy

Grinding with cubic boron nitride (CBN) superabrasive is a widely used method of machining superalloy in aerospace industries. However, there are some issues, such as poor grinding quality and severe tool wear, in grinding of powder metallurgy superalloy FGH96. In addition, abrasive wheel wear is the significant factor that hinders the further application of CBN abrasive wheels. In this case, the experiment of grinding FGH96 with single CBN abrasive grain using different parameters was carried out. The wear characteristics of CBN abrasive grain were analyzed by experiment and simulation. The material removal behavior affected by CBN abrasive wear was also studied by discussing the pile-up ratio during grinding process. It shows that morphological characteristics of CBN abrasive grain and grinding infeed direction affect the CBN abrasive wear seriously by simulation analysis. Attrition wear, micro break, and macro fracture had an important impact on material removal characteristics. Besides, compared with the single cutting edge, higher pile-up ratio was obtained by multiple cutting edges, which reduced the removal efficiency of the material. Therefore, weakening multiple cutting edge grinding on abrasive grains in the industrial production, such as applying suitable dressing strategy, is an available method to improve the grinding quality and efficiency. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00412-2     

Technological aspects of controlling structural orientation of the working layer in superabrasive wheels

The authors of the paper discuss the importance of taking into account the structural orientation of a working layer in grinding wheels of superhard materials—superabrasive grinding wheels. Some manufacturing methods to be used in pressing and sintering of a wheel working layer are put forward, which permit controlling the layer’s structural orientation.     

Laser-assisted Grinding Wheel Dressing (Ⅱ)-Experimental Researches

Most of the mechanical dressing technologies for resin bonded superabrasive grinding wheels are time consumingand costly. Based on the outcomes of the simulations in the previous study, this paper demonstrates the comprehensive researches on the laser-ass     

Grinding of Toroidal and Cylindrical Surfaces on SiC Using Diamond Grinding Wheels

This paper presents the methods and experimental results for grinding toroidal and cylindrical surfaces made of silicon carbide using diamond grinding wheels and an inexpensive CNC machining center. The mirrors were successfully obtained by automatic grinding operations with good shape accuracy, mirror surface finish, and low roughness heights. The time consumed in the process is very short. Industrial manufacture of lenses usually involves three operations — grinding without dressing, lapping, and polishing. In the laboratory studies, however, mirrors and lenses have been manufactured only with grinding process, because of 100% ductile-mode material removal in grinding with dressing. These processes were individually evaluated for surface roughness and surface integrity using surface roughness testers and a scanning electron microscope.     

The use of bearing elements in the structure of superabrasive wheel working layer to improve the wheel performance

A study is performed to find ways for efficient use of bearing elements in the form of layered compacts or milled Kiborite in the working layer of superabrasive wheels in order to improve the wheel performance in grinding processes.