Effect of machining parameters on surface integrity of silicon carbide ceramic using end electric discharge milling and mechanical grinding hybrid machining

A novel hybrid process that integrates end electric discharge (ED) milling and mechanical grinding is proposed. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and fine working environmental practice. The polarity, pulse on-time, and peak current are varied to explore their effects on the surface integrity, such as surface morphology, surface roughness, micro-cracks, and composition on the machined surface. The results show that positive tool polarity, short pulse on-time, and low peak current cause a fine surface finish. During the hybrid machining of SiC ceramic, the material is mainly removed by end ED milling at rough machining mode, whereas it is mainly removed by mechanical grinding at finish machining mode. Moreover, the material from the tool can transfer to the workpiece, and a combination reaction takes place during machining.     

Micro-EDM milling of zirconium carbide ceramics

Surface characteristics and machining performances of micro-pockets manufactured by μEDM as a function of different process conditions are studied in this paper. The micro-pockets were obtained using different combinations of process parameters on different ultra-high temperature ceramics (UHTCs) with the same base matrix (ZrC) and different volume fraction of the second phase (MoSi₂). This work presents an analysis of the process performances with different machining approaches, from pre-roughing down to fine-finishing. Microstructure analysis of the as-sintered and machined materials was conducted to identify materials modification due to the electrical discharges. A removing material mechanism during the μEDM process has been hypothesized, correlating the ED-machined surface structure and the main process performances.     

超声辅助磨削碳化硅陶瓷的工具磨损试验研究

为探究超声辅助磨削过程中不同工具的磨损特征,采用电镀和钎焊两种金刚石磨头对碳化硅陶瓷进行了超声辅助磨削和普通磨削对比试验,研究了超声振动作用、工具类型对磨粒磨损形式及其变化过程的影响,在此基础上分析了磨粒磨损形式对工件表面质量的影响.试验结果表明:对于电镀磨头,普通磨削和超声辅助磨削过程中的磨粒磨损形式均以磨耗磨损和宏观破碎为主,超声振动作用可有效改善加工表面质量;而对于钎焊磨头,普通磨削的磨粒磨损形式主要是磨耗磨损和宏观破碎,超声辅助磨削的磨粒磨损形式主要是磨耗磨损和微破碎,初始阶段超声振动作用可改善表面质量,但随着磨削行程的增加,微破碎形式的占比增高,超声辅助磨削时的工件表面粗糙度值高于普通磨削时的工件表面粗糙度值.     

碳化硅衬底超精密加工技术

通过对比不同的加工方法获得最佳工艺:切片采用多线切割或者多线切割与超声切割相结合;磨削采用双面研磨获得较低翘曲度的表面或ELID磨削实现高速、高效、高质量磨削;抛光工艺使用化学机械抛光方法,通过粗抛提高加工效率,精抛提高表面质量,从而获得超光滑表面。分析了碳化硅衬底加工存在的问题并指出超精密加工的发展趋势。     

Wear of diamond grinding wheel in ultrasonic vibration-assisted grinding of silicon carbide

It is recognized that grinding efficiency and ground surface quality are determined by grinding wheel performance. Additionally, the investigation on wear behavior is essential for evaluating the grinding wheel performance. There is a lack of research on the tool wear behavior during ultrasonic vibration-assisted grinding (UAG), whose grain motion trajectory differs from that in conventional grinding (CG). In the present work, CG and UAG tests of silicon carbide (SiC) were conducted in order to investigate the effects of ultrasonic vibration on the tool wear through tracking observation of grains. Meanwhile, the grinding forces and ground surface roughness correlated to the tool wear stages were studied. The results demonstrated that the main wear types during UAG were micro-fracture and macro-fracture which caused the wheel sharpening, while during CG, the main wear type was attritious wear that made the wheel blunt. As a result, UAG obtained lower and more stable grinding forces while slightly rougher ground surface in comparison with CG.     

介绍一种刨铣磨通用加工镶条夹具

一、前言机床、轧机及锻压等设备的导轨移动机构中的镶条制造精度 ,直接影响到机床、轧机及锻压等设备的加工精度。镶条通常采用的加工工艺为 :锻造毛坯→钳工划线→夹持在虎钳上 ,用牛头刨床按划线刨出一定的倾斜角→在装配过程中工人反复配刮 ,直达到 2 5ｍｍ× 2 5ｍｍ内有 12点以上为止。这种制造方法的缺点是 :由于镶条细长 ,刚性差 ,在牛头刨床上加工时 ,虎钳装夹困难 ,倾斜面难控制 ,工人配研劳动强度大 ,质量差 ,效率低。为保证镶条加工的精度、高效率和减轻工人体力劳动 ,在机床、轧机、锻压等设备制造和大修中 ,可采用图 1所示的…     

Fiber-reinforced composites in milling and grinding: machining bottlenecks and advanced strategies

Fiber-reinforced composites have become the preferred material in the fields of aviation and aerospace because of their high-strength performance in unit weight. The composite components are manufactured by near net-shape and only require finishing operations to achieve final dimensional and assembly tolerances. Milling and grinding arise as the preferred choices because of their precision processing. Nevertheless, given their laminated, anisotropic, and heterogeneous nature, these materials are considered difficult-to-machine. As undesirable results and challenging breakthroughs, the surface damage and integrity of these materials is a research hotspot with important engineering significance. This review summarizes an up-to-date progress of the damage formation mechanisms and suppression strategies in milling and grinding for the fiber-reinforced composites reported in the literature. First, the formation mechanisms of milling damage, including delamination, burr, and tear, are analyzed. Second, the grinding mechanisms, covering material removal mechanism, thermal mechanical behavior, surface integrity, and damage, are discussed. Third, suppression strategies are reviewed systematically from the aspects of advanced cutting tools and technologies, including ultrasonic vibration-assisted machining, cryogenic cooling, minimum quantity lubrication (MQL), and tool optimization design. Ultrasonic vibration shows the greatest advantage of restraining machining force, which can be reduced by approximately 60% compared with conventional machining. Cryogenic cooling is the most effective method to reduce temperature with a maximum reduction of approximately 60%. MQL shows its advantages in terms of reducing friction coefficient, force, temperature, and tool wear. Finally, research gaps and future exploration directions are prospected, giving researchers opportunity to deepen specific aspects and explore new area for achieving high precision surface machining of fiber-reinforced composites.     

Ultrasonic slot machining of a silicon carbide matrix composite

Rotary ultrasonic slot machining (RUSM) of ceramic matrix composites is explored. A comparison is made between RUSM and conventional diamond grinding by studying the effects of material removal rate (MRR) on process forces, tool wear and surface roughness. It was shown that RUSM leads to a significant decrease in process cutting forces and tool wear in comparison to the conventional machining process. Furthermore, the influences of diamond tool characteristics on surface roughness and tool wear are also ascertained.     

普通磨床超精度磨削工艺及工艺参数选择

通过对超精度磨削机理的研究和分析，在ME1432B普通外圆万能磨床上．采用精、细修整砂轮．使砂轮上的同一颗粒等高微刃数增多的方法，达到磨削抛光作用，并对磨床导轨、砂轮主轴与轴瓦间隙进行修刮和调整，同时合理选择磨削工艺参数等方面达到超精磨削的目的。     

Influence of dielectric and machining parameters on the process performance for electric discharge milling of SiC ceramic

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD).     

An economic machining process model with interval parameters

The primary objective of a machining economics model is to determine the optimal cutting parameters that minimize production costs while satisfying some design constraints. When the parameters in a machining economics model have interval values, the associated problem becomes an interval machining economics problem, and the objective value will also have interval value; that is, lying in a range. This paper develops a solution method that is able to derive the interval unit production cost of a machining economic model with interval parameters. A pair of two-level machining economics problems is formulated to calculate the upper bound and lower bound of the unit production cost. Based on the duality theorem, the two-level machining economics problem is transformed into the one-level conventional geometric program. Solving the corresponding pair of geometric programs produces the interval of the unit production cost. The results indicate that the cost interval contains more information for making decisions.     

Parametric analysis on electrochemical discharge machining of silicon nitride ceramics

The electrochemical discharge machining (ECDM) process has a potential in the machining of silicon nitride ceramics. This paper describes the development of a second order, non-linear mathematical model for establishing the relationship among machining parameters, such as applied voltage, electrolyte concentration and inter-electrode gap, with the dominant machining process criteria, namely material removal rate (MRR), radial overcut (ROC) and thickness of heat affected zone (HAZ), during an ECDM operation on silicon nitride. The model is developed based on response surface methodology (RSM) using the relevant experimental data, which are obtained during an ECDM micro-drilling operation on silicon nitride ceramics. We also offer an analysis of variance (ANOVA) and a confirmation test to verify the fit and adequacy of the developed mathematical models. From the parametric analyses based on mathematical modelling, it can be recommended that applied voltage has more significant effects on MRR, ROC and HAZ thickness during ECDM micro-drilling operation as compared to other machining parameters such as electrolyte concentration and inter-electrode gap.     

A new chip-thickness model for performance assessment of silicon carbide grinding

The chip-thickness models, used to assess the performance of grinding processes, play a major role in predicting the surface quality. In the present paper, an attempt has been made to develop a new chip-thickness model for the performance assessment of silicon carbide grinding by incorporating the modulus of elasticities of the grinding wheel and the workpiece in the existing basic chip-thickness model to account for elastic deformation. The new model has been validated by conducting experiments, taking the surface roughness as a parameter of evaluation .     

The optimisation of the grinding of silicon carbide with diamond wheels using genetic algorithms

Modelling and optimisation are necessary for the control of any process to achieve improved product quality, high productivity and low cost. The grinding of silicon carbide is difficult because of its low fracture toughness, making it very sensitive to cracking. The efficient grinding of high performance ceramics involves the selection of operating parameters to maximise the MRR while maintaining the required surface finish and limiting surface damage. In the present work, experimental studies have been carried out to obtain optimum conditions for silicon carbide grinding. The effect of wheel grit size and grinding parameters such as wheel depth of cut and work feed rate on the surface roughness and damage are investigated. The significance of these parameters, on the surface roughness and the number of flaws, has been established using the analysis of variance. Mathematical models have also been developed for estimating the surface roughness and the number of flaws on the basis of experimental results. The optimisation of silicon carbide grinding has been carried out using genetic algorithms to obtain a maximum MRR with reference to surface finish and damage.Nomenclature C constant in mathematical model - C₁ constant in surface roughness model - C₂ constant in the number of flaws model - d depth of cut, m - dof degrees of freedom - f table feed rate, mm/min - M grit size (mesh) - MRR material removal rate, mm³/mm width-min - N_c number of flaws measured - R_a surface roughness measured, m - Y machining response - depth of cut exponent in mathematical model - ₁ depth of cut exponent in surface roughness model - ₂ depth of cut exponent in number of flaws model - feed rate exponent in mathematical model - ₁ feed rate exponent in surface roughness model - ₂ feed rate exponent in number of flaws model - grit size exponent in mathematical model - ₁ grit size exponent in surface roughness model - ₂ grit size exponent in number of flaws model     

Parametric analysis on electrochemical discharge machining of silicon nitride ceramics

The electrochemical discharge machining (ECDM) process has a potential in the machining of silicon nitride ceramics. This paper describes the development of a second order, non-linear mathematical model for establishing the relationship among machining parameters, such as applied voltage, electrolyte concentration and inter-electrode gap, with the dominant machining process criteria, namely material removal rate (MRR), radial overcut (ROC) and thickness of heat affected zone (HAZ), during an ECDM operation on silicon nitride. The model is developed based on response surface methodology (RSM) using the relevant experimental data, which are obtained during an ECDM micro-drilling operation on silicon nitride ceramics. We also offer an analysis of variance (ANOVA) and a confirmation test to verify the fit and adequacy of the developed mathematical models. From the parametric analyses based on mathematical modelling, it can be recommended that applied voltage has more significant effects on MRR, ROC and HAZ thickness during ECDM micro-drilling operation as compared to other machining parameters such as electrolyte concentration and inter-electrode gap.     

Effect of machining parameters on the milling process of 2.5D C/SiC ceramic matrix composites

Abstract

The C/SiC ceramic matrix composites are widely used for high-value components in the nuclear, aerospace and aircraft industries. The cutting mechanism of machining C/SiC ceramic matrix composites is one of the most challenging problems in composites application. Therefore, the effects of machining parameters on the machinability of milling 2.5D C/SiC ceramic matrix composites is are investigated in this article. The related milling experiments has been carried out based on the C/SiC ceramic matrix composites fixed in two different machining directions. For two different machining directions, the influences of spindle speed, feed rate and depth of cut on cutting forces and surface roughness are studied, and the chip formation mechanism is discussed further. It can be seen from the experiment results that the measured cutting forces of the machining direction B are greater than those of the in machining direction A under the same machining conditions. The machining parameters, which include spindle speed, feed rate, depth of cut and machining direction, have an important influence on the cutting force and surface roughness. This research provides an important guidance for improving the machining efficiency, controlling and optimizing the machined surface quality of C/SiC ceramic matrix composites in the milling process.     

Evaluation of the effects of machining parameters on MQL based surface grinding process using response surface methodology

Journal of Mechanical Science and Technology - Grinding is a precision machining process widely used for close tolerance and good surface finish. Due to aggregate of geometrically undefined cutting...     

An experimental investigation on the process parameters influencing machining forces during milling of carbon and glass fiber laminates

Milling is the most feasible machining operation for producing slots and keyways with a well defined and high quality surface. Milling of composite materials is a complex task owing to its heterogeneity and the associated problems such as surface delamination, fiber pullout, burning, fuzzing and surface roughness. The machining process is dependent on the material characteristics and the cutting parameters. An attempt is made in this work to investigate the influencing cutting parameters affecting milling of composite laminates. Carbon and glass fibers were used to fabricate laminates for experimentations. The milling operation was performed with different feed rates, cutting velocity and speed. Numerically controlled vertical machining canter was used to mill slots on the laminates with different cutting speed and feed combinations. A milling tool dynamo meter was used to record the three orthogonal components of the machining force. From the experimental investigations, it was noticed that the machining force increases with increase in speed. For the same feed rate the machining force of GFRP laminates was observed to be very minimal, when compared to machining force of CFRP laminates. It is proposed to perform milling operation with lower feed rate at higher speeds for optimal milling operation.