Material removal in grinding sapphire wafers with brazed–diamond pellet plates

Grinding is an important abrasive machining process in many manufacturing chains. In order to improve the material removal in the grinding of sapphire wafers, this study presents two brazed-diamond pellet (BDP) plates developed with different BDP surface textures, i.e., a non-grooved BDP plate and a grooved BDP plate. Their performances were tested in the coarse grinding of sapphire wafers. The surface topography, surface roughness, material removal rate (MRR) were comprehensively investigated. The experimental results show that sapphire is removed in its brittle mode. However, the grooved BDP plate can produce lower surface roughness under a higher MRR. The improvement in surface roughness is mainly due to the better coolant flowability and chip removal facilitated by the grooves. The higher MRR is partly due to the increased pressure in the sapphire-plate contact zone. It is found that the grooved BDP plate can increase MRR by about 45.7%.     

Experimental Investigations of Abrasive Mixed Electro Discharge Diamond Grinding of Nimonic 80A

This paper presents a novel hybrid machining process (HMP) called abrasive mixed electro discharge diamond grinding (AMEDDG) in which abrasive powder is mixed in dielectric fluid to perform electro discharge diamond grinding (EDDG) action on a workpiece. In-house-fabricated AMEDDG setup was used to experimentally evaluate the performance of the process during the machining of Nimonic 80A. The effects of wheel speed, powder concentration, current, and pulse-on-time (POT) were investigated on the material removal rate (MRR). The surface morphological properties of the machined workpiece were investigated based on some quality surface indicators. The experimental results show that MRR of the workpiece was influenced by wheel speed, current, and powder concentration, and optimum MRR can be achieved at a wheel speed of 1400 RPM, a powder concentration of 4 g/L, a current of 10 A, and a POT of 26 µs.     

材料特性对亲水性固结磨料研磨垫加工性能的影响

为研究材料特性对亲水性固结磨料研磨垫的加工性能影响,本文研究了K9玻璃和硅片两种材料在不同加工顺序下研磨过程中的声发射信号和摩擦系数特征,采用扫描电镜分析磨屑的尺寸与形态.结果表明:不同加工顺序下工件的材料去除速率差别很大.与直接研磨硅片相比,先研磨K9玻璃再研磨硅片,硅片的材料去除速率大幅下降;相反,先研磨硅片再研磨K9玻璃,与直接研磨K9玻璃相比,K9玻璃的材料去除速率变化不大.无论采用哪种加工顺序,后研磨的工件表面粗糙度均比直接研磨的同种工件要大.扫描电镜的分析表明,硅片的磨屑尺寸集中在600 nm~1.5μm,磨屑大部分都棱角完整;而K9玻璃的磨屑尺寸集中在300 nm~500 nm左右,无明显棱角.硅片磨屑较大的尺寸与完整的棱角促进了研磨垫的自修正过程,所以硅片这类脆性较大的材料有利于研磨垫的自修正过程.     

On machining of hard and brittle materials using rotary tool micro-ultrasonic drilling process

The present paper reports on a recently developed rotary tool micro-ultrasonic drilling (RT-MUSD) process. The RT-MUSD process was utilized for machining of micro-holes in zirconia, silicon and glasswork materials. The effects of work material properties on the performance characteristics (material removal rate (MRR), depth of hole and hole overcut) of RT-MUSD process were investigated by varying the power rating, rotation speed, abrasive size and slurry concentration. Additionally, machined micro-holes and tool surface were analyzed considering microscopic images. The experimental results revealed that the MRR and depth of hole increased by increasing the power rating. An increase in rotation speed up to 300 rpm, abrasive size up to #1200 mesh and concentration up to 20% increased the MRR, depth of hole and decreased hole overcut. The maximum machining rate and hole overcut were observed during machining of silicon followed by glass and zirconia. The fracture toughness and hardness of the work material affected the MRR and tool wear, respectively. Pure brittle fracture mode of material removal was observed in all the work materials during RT-MUSD process. Eventually, the RT-MUSD process was optimized using desirability approach and a micro-hole of depth 4355 µm was achieved using optimal parameter settings.     

Fixed Abrasive Diamond Wire Saw Slicing of Single-Crystal Silicon Carbide Wafers

This article investigates the slicing of single-crystal silicon carbide (SiC) with a fixed abrasive diamond wire. A spool-to-spool rocking motion diamond wire saw machine using a 0.22 mm nominal diameter diamond wire with 20 µm average size diamond grit was used. The effect of wire downfeed speed on wafer surface roughness and subsurface damage was first investigated. The surface marks generated by loose diamond grit and stagnation of the wire during the change of the wire-cutting direction were studied. The use of scanning acoustic microscopy (SAcM) as a nondestructive evaluation method to identify the subsurface damage was explored. Effects of using a new diamond wire on cutting forces and surface roughness were also investigated. Scanning electron microscopy has been used to examine the machined surfaces and wire wear. This study demonstrated the feasibility of fixed abrasive diamond wire cutting of SiC wafers and the usage of a SAcM to examine the subsurface damage.     

旋转超声磨削Si3 N4陶瓷用金刚石磨具磨损行为研究

热压烧结Si₃N₄陶瓷材料常应用于航天飞行器中关键耐高温零部件,但由于高硬度和低断裂韧性,其加工效率和加工表面质量难以满足制造需求。为了提高热压烧结Si₃N₄陶瓷旋转超声磨削加工质量,减小由于金刚石磨具磨损带来的加工误差,开展了磨具磨损行为研究。基于热压烧结Si₃N₄陶瓷旋转超声磨削加工实验,分析了金刚石磨具磨损形式;基于回归分析建立了金刚石磨具磨损量数学模型,揭示了加工参数及磨具参数与金刚石磨具磨损量间映射关系;并研究了磨损形式与磨具磨损量及加工表面粗糙度影响规律。结果表明：磨粒磨耗是旋转超声磨削Si₃N₄陶瓷用金刚石磨具最主要磨损形式,比例超过50%;主轴转速和磨粒粒度对磨具磨损量影响最为显著;且磨损量较小时,加工表面粗糙度值反而增加。以上研究可为提高旋转超声磨削Si₃N₄陶瓷加工精度和加工质量提供指导。     

On theoretical substantiation of the choice of effective grain profile shape in modeling of diamond layer in dressing tools. Part 1. Electroplating

The paper gives theoretical substantiation of the phenomenon of a circular shape of a scratch cross-section averaged over a set of cuts produced by far-from-round tips of diamond grains of electroplated dressing tools that work on the abrasive material of grinding wheels. This cross-sectional shape is identified as an effective shape of the grain that produces the scratch. Information on the scratch parameters and their relationship with the diamond grain size in the tool is needed for calculating individual and total cross-sections of cuts, dressing forces, and surface roughness of workpieces upon grinding with abrasive wheels dressed by a diamond roll.     

Optimization of photochemical machining process parameters for manufacturing microfluidic channel

In the present study, the investigation on photochemical machining (PCM) of stainless steel (SS-304) by ferric chloride as etchant is reported. SS-304 is machined by PCM process to obtain accurate dimensions and better geometrical features. Weighted grey relational analysis (WGRA) technique is used in optimization of PCM process parameters. DoE (L₂₇) orthogonal array is applied to evaluate machining parameters, such as concentration of etchant, etching time, and temperature of etchant. The multiobjective optimization technique is used to optimize material removal rate (MRR), surface roughness (R_a), undercut (U_c) and etch factor (EF). Weighted grey relational grade is calculated to minimize U_c and surface roughness and to maximize MRR and EF. The quality characteristics MRR, EF, U_c, and R_a are reporting the improvement after the confirmatory test. The optimum machining parameters are processed to manufacture the microfluidic channel used in biomedical applications. The microfluidic channels and its assembly with Y-type for mixing of fluid with a size of 100 µm, 200 µm, and 300 µm are developed and investigated.     

Twyman effect mechanics in grinding and microgrinding

In the Twyman effect (1905), when one side of a thin plate with both sides polished is ground, the plate bends: The ground side becomes convex and is in a state of compressive residual stress, described in terms of force per unit length (Newtons per meter) induced by grinding, the stress (Newtons per square meter) induced by grinding, and the depth of the compressive layer (micrometers). We describe and correlate experiments on optical glasses from the literature in conditions of loose abrasive grinding (lapping at fixed nominal pressure, with abrasives 4-400 μm in size) and deterministic microgrinding experiments (at a fixed infeed rate) conducted at the Center for Optics Manufacturing with bound diamond abrasive tools (with a diamond size of 3-40 μm, embedded in metallic bond) and loose abrasive microgrinding (abrasives of less than 3 μm in size). In brittle grinding conditions, the grinding force and the depth of the compressive layer correlate well with glass mechanical properties describing the fracture process, such as indentation crack size. The maximum surface residual compressive stress decreases, and the depth of the compressive layer increases with increasing abrasive size. In lapping conditions the depth of the abrasive grain penetration into the glass surface scales with the surface roughness, and both are determined primarily by glass hardness and secondarily by Young's modulus for various abrasive sizes and coolants. In the limit of small abrasive size (ductile-mode grinding), the maximum surface compressive stress achieved is near the yield stress of the glass, in agreement with finite-element simulations of indentation in elastic-plastic solids.     

CVD‐Diamantschleifstifte für den Werkzeug‐ und Formenbau. Abrasive Pencils for Tool and Die Making Coated by Diamond CVD

Recently developed compeDIA®‐ abrasive pencils have been produced and tested for the machining of cemented carbide molding tools. In order to produce abrasive pencils, carbide base plates have been grinded and coated with a diamond layer by a Hot‐Filament‐CVD‐process. The testing of the abrasive pencils took place with an ultra‐precision grinding machine on carbide workpieces. Surface roughness of the workpiece and its wheel life were the criteria for evaluation. For the specific adjustment of the grain size of the abrasive pencils, the adequate coating parameters were worked out, and the dependencies on basic influencing variables at coating procedures, such as nominal diameter and grinding length, were calculated. In order to be able to coat the grinded base plates with enough film adhesion, a practical pre‐treatment method was developed and tested, which removes the fringe zone, that was damaged during the grinding process. At present, the costs for the coating process are uneconomically high, though. By means of large‐scale production in connection with an automated pre‐treatment and coating it would be possible to lower the costs so far that they are on the same cost level with other coatings like TiN or TiAlN. The CVD‐Diamond abrasive pencils are very appropriate for tool and die making. It is to be expected that through further development of tools and through process optimization, the quality of the wrought workpiece can be ameliorated and surface finishes of R_a < 0,3 μm can be reached. The wheel life could be increased to appropriate values by optimization of the coating technology. The range of the machining parameters, in which the grinding process can be accomplished expediently without leading to a broken die, have been worked out. Afterwards, a die‐casting component with typically shaped elements was designed and an adequate molding tool prototype was crafted. With that, the basic conditions for tool‐ and die‐making were worked out in order to put into practice a fast and flexible machining of cemented carbide molding tools with the aid of those innovative abrasive pencils. In contrast to the traditional molding tool material made of brass, clear advantages in tool life can be made in the production of miniature serial‐parts by drawing, deep‐drawing or extrusion.     

On theoretical substantiation of the choice of effective grain profile shape in modeling of diamond layer in dressing tools. Part 2. Electroforming

The paper describes, from the statistical standpoint, the mechanism of formation of spherical shape of the averaged cross section of scratches produced by flat faces of diamond grains in abrasive material of grinding wheels during their dressing with diamond rolls manufactured by electroforming. The distribution of parameters of orientation of diamond grain cutting faces has been determined and a brief comparative analysis of characteristics of dressing tools manufactured by electroforming and electroplating has been performed. A notion of the reduced effective diameter has been introduced into the model representation of a diamond cutting grain; a relationship between this diameter and the tool grain size has been found, which is needed for calculating individual and total cross-sections of cuts, dressing forces, and surface roughness of workpieces ground with pre-dressed abrasive wheels.     

Experimental investigation of surface topography in photochemical machining of Inconel 718

Surface topography is one of the important aspects of micro-components manufacturing. Photochemical machining (PCM) is the most commonly used method in the low-cost micro-manufacturing process. The present investigation focused on the study of the effect of process parameters on the surface topography in PCM of Inconel 718 of two different grain sizes using ferric chloride (FeCl₃). For this work, the input parameters considered are concentration, time and temperature of the etchant. The temperature of the etchant was found to be the most dominant parameter in the PCM of Inconel 718. Moreover, in this study, the effect of grain size of samples on surface roughness was considered. The average increase in surface roughness is 1.227 times due to variation in grain size from 59?µm to 42?µm.     

Improving the machining performance characteristics of the µEDM drilling process by the online cryogenic cooling approach

Productivity and surface quality would significantly affect the performance of the micro electrical discharge machining process (µEDM). Thus, the machining performance would be enhanced by improving the material removal rate (MRR) and surface quality. In this investigation, cryogenic LN₂ cooling was introduced to the conventional µEDM setup for developing an innovative process of cryogenically cooled µEDM process (CµEDM). The favorable outcomes of this process were estimated by selecting discharge current (I_p) and pulse on duration (T_on) for determining the effects of the machining performance including MRR and surface integrity. Surface quality was also analyzed by microstructural analysis and a scanning electron microscope (SEM) for evaluating the effects of the cryogenically cooled µEDM process. The experimental result shows 54–62% improvement in MRR and 22–36% improvement in average roughness values. Hence, it is suggested that cryogenically cooled µEDM facilitates improvement in productivity and surface quality.     

Constrained multi-objective optimization of EDM process parameters using kriging model and particle swarm algorithm

This paper investigates the highly nonlinear relationship between process parameters and machining responses, including material removal rate (MRR), surface roughness (SR), and electrode wear rate (EWR) of electric discharge machining (EDM) using Kriging model. Subsequently, an emerging multi-objective optimization algorithm called particle swarm is used to determine the best machining conditions that not only maximize the machining speed but also minimize the EWR with a constraint of the SR. The experiment was carried out with P20 steel on a CNC EDM machine using copper electrode. The research result shows that the MRR increases sharply when increasing the discharge current just like other researches pointed out. However, the relationship between EWR and current is complicated. EWR appears the minimum value when the current is around 30?A. The speed of change of MRR per unit of EWR is the highest when the SR is around 14.5?µm. The combination of Kriging regression model and particle swarm optimization is considered as an intelligent process modeling and optimization of EDM machining. The proper selection of process parameters helps the EDM operator to reduce the machining time and cost.     

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.     

Experimental investigation on carbon steel micro-rod machining by LS-WEDT

This article proposed for the first time the method of the low-speed wire electrical discharge turning (LS-WEDT) combined with the multiple cutting strategy to fabricate carbon steel micro-rods. First, the rotating apparatus submerged in working fluid is designed and manufactured to enable the low-speed wire electrical discharge machine to generate cylindrical geometries. Besides, material removal rate, surface roughness, and machining precision of the micro-rod manufactured by the LS-WEDT are, respectively, investigated. Moreover, the surface microstructure and surface chemical reaction of micro-rods are characterized using scanning electron microscopy and energy-dispersive spectroscopy analysis. Experimental results display that the micro-rod of 70?µm diameter and 1000?µm length can be successfully fabricated. More importantly, the mean absolute diameter deviation of the micro-rod fabricated by LS-WEDT is 0.65?µm and the surface roughness is 0.53?µm, which identified the high machining precision and good surface quality of the micro-rod.     

Feasibility study of a flexible grinding method for precision machining of the TiAl-based alloy

This study presents detailed experimental investigations on precision machining of the TiAl-based alloy with an abrasive belt flexible grinding method. Subsequently, the feasibility of this precision machining method is evaluated with respect to the material removal rate, abrasive wear, machined surface roughness, and residual stress. The material removal rate and surface roughness were determined as experimental indicators and were measured via a three-coordinate measuring instrument and surface profiler, respectively. Micro-morphologies of the machined surface and worn abrasive belt were investigated via a scanning electron microscope. The residual stress distributions in the machined surface layer were detected by using an X-ray diffractometer. The experimental results revealed that the aforementioned evaluation indicators satisfied the desired requirements, thereby indicating that the abrasive belt flexible grinding technique was suitable for precision machining of the TiAl-based alloy. Additionally, the optimal combinations of grinding parameters were determined to obtain desirable material removal rate and machined surface roughness. The basic wear processes and characteristics of the abrasive belt were thoroughly examined. The formation of desirable residual compressive stresses in the machined surface layer was mainly attributed to low frequency and small amplitude vibration knocking at the grinding interface.     

The characteristics of machined surface controlled by multi tip arrayed tool and high speed spindle

In this study, we propose one of the ultra-precision machining methods that can be adapted brittle material as well as soft material by using multi arrayed diamond tips and high speed spindle. Conventional machining method is too hard to control surface roughness and surface texture against brittle material because particles of grinding tools are irregular size and material can be fragile. Therefore we were able to design tool paths and machine controlled pattern on surface by multi arrayed diamond tips which has uniform size made in MEMS fabrication and high speed spindle of which maximum speed is about 300,000 rpm. We defined several parameters that can have effect on machining surface. Those are multi array of diamond tips (n * n), speed of the air spindle, and feeding rate. Surface roughness and surface texture can be controlled by those parameters for micro machining.     

Surface and porous recast layer analysis in µ-EDM of MWCNT-Al2O3 composites

Machining of ceramic materials has been a major challenge owing to high hardness and brittleness. The reinforcement of a conducting filler allows permissible machining in electrical discharge machining (EDM) process. The current effort analyses the impact of multi-walled carbon nanotubes (MWCNT) of concentrations of 2.5 and 5 vol. %, as conducting filler towards machinability of alumina composites in µ-EDM process. The influence of tool materials and its rotation are closely analyzed. A successful machining process is observed in both the two composites, with a higher material removal rate (MRR) in 5 vol. % MWCNTs. When the tool starts to rotate at 750 rpm, an increment of around 60–65% is observed in MRR for both the two composites. Similarly, the surface roughness (R_a) decreases by a factor of 20?25%. The brass tool is observed to yield better machining capabilities due to the frequent initiation of sparks. A highly porous machined surface is observed in both the two composites. This scenario depicts the spalling effect as more dominant than melting-evaporation effect. The extent of porous recast layer on the drilled edges is found to reduce with increasing the speed of tool rotation.     

Parametric Optimization of Centrifugal Force-Assisted Abrasive Flow Machining (CFAAFM) by the Taguchi Method

Extrusion honing, known as abrasive flow machining (AFM), deburrs, polishes, and radiuses surfaces and edges by flowing an abrasive-laden media over these areas. The process is particularly used on internal shapes that are difficult to process by other nonconventional machining processes. Because abrasive action occurs only in areas where the flow is restricted, tooling is used to direct the media to the appropriate areas. Like other nonconventional machining processes, AFM has the limitation of lower material removal rates. The application of centrifugal force (by using rotating rectangular rod inside the hollow workpiece) has been explored for the productivity enhancement of the process. This article reports that centrifugal force enhances the material removal rate (MRR) and improves the scatter of surface roughness (SSR) value in AFM. It outlines the development of a system that determines sets of viable process parameters for a new process called centrifugal force-assisted abrasive flow machining (CFAAFM). Cylindrical workpieces of brass are used for the experiment. During the experiments, parameters, such as rotational speed of rectangular rod, extrusion pressure, and grit size, were varied to explore their effect on material removal and scatter of surface roughness. Taguchi's parameter design strategy has been applied to investigate the effect of process parameters on the MRR and SSR values.