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     

Multiple-response optimisation of electrochemical grinding characteristics through response surface methodology

This paper comprehensively evaluates the influence of voltage and cutting speed on electrochemical grinding of composite carbide inserts. A complete 4² factorial experiment was planned and carried out where each treatment combination has been replicated twice to achieve an acceptable degree of precision. Mathematical models have been developed for the major performance indices like current density, material removal rate (MRR) and surface finish of the job by multiple linear regression analysis. Then multiple-response optimisation has been carried out to find the optimum parameter settings to get a desired yield both by desirability functions as well as by contour overlapping method. It has been found that passivation occurs increasingly at higher voltages and it is removed almost instantaneously at higher speed leading to higher current density and MRR. The surface finish is not very much dependent on grinding speed. The optimum surface finish is obtainable at 12 to 13 V (app.) in electrochemical grinding of composite carbides.     

Ceramic Response to High Speed Grinding

Material response was investigated with respect to normal grinding forces, surface roughness, and removal mechanisms in grinding of alumina, silicon carbide, silicon nitride, and zircona with a resin-bond 160 μm grit diamond wheel at the grinding speeds of upto 160 m/s. The results reveal that the normal grinding forces decreased significantly with an increase in grinding speed; they also increased substantially with an increase in a complex relation of the ceramic hardness and toughness. High speed grinding produced a reduction in surface roughness for silicon carbide and alumina but gave no improvement for zirconia and silicon nitride. Also the surface roughness in high speed grinding was found to be material-dependent that the ground silicon nitride exhibited much smoother than the other ground ceramics. The influence of grinding speed on material removal mechanisms was analyzed in terms of grinding geometry and ceramic material properties.     

Factors affecting surface finish when grinding titanium and a titanium alloy (Ti-6Al-4V)

Under conventional grinding conditions redeposition which degrades surface finish occurs when grinding titanium and a titanium alloy (Ti-6Al-4V). To prevent redeposition and hence to obtain optimum surface finish the following grinding conditions are required: a soft grade (H) silicon carbide wheel running at 10 m s^?1, a sulphur-chlorinated cutting oil grinding fluid and a relatively high table speed (0.2 m s^?1), and the wheel should be re-dressed prior to taking the finishing passes (about ten) at a wheel downfeed of 2.5 μm.     

Predictive Modeling of Surface Roughness in Grinding of Ceramics

The surface roughness represents the quality of ground surface since irregularities on the surface may form nucleation for cracks or corrosion and thus degrade the mechanical properties of the component. The surface generation mechanism in grinding of ceramic materials could behave as a mixture of plastic flow and brittle fracture, while the extent of the mixture hinges upon certain process parameters and material properties. The resulting surface profile can be distinctively different from these two mechanisms. In this article, a physics-based model is proposed to predict the surface roughness in grinding of ceramic materials considering the combined effect of brittle and ductile material removal. The random distribution of cutting edges is first described by a Rayleigh probability function. Afterwards, surface profile generated by brittle mode grinding is characterized via indentation mechanics approach. Last, the surface roughness is modeled through a probabilistic analysis of ductile and brittle generated surface profile. The model expresses the surface finish as a function of the wheel microstructure, the process conditions, and the material properties. The predictions are compared with experimental results from grinding of silicon carbide and silicon nitride workpieces (SiC and Si₃N₄, respectively) using a diamond wheel.     

Soft computing models and intelligent optimization system in electro-discharge machining of SiC/Al composites

In this paper, a multi-variable regression model, a back propagation neural network (BPNN) and a radial basis neural network (RBNN) have been utilized to correlate the cutting parameters and the performance while electro-discharge machining (EDM) of SiC/Al composites. The four cutting parameters are peak current (I_p), pulse-on time (T_on), pulse-off time (T_off), and servo voltage (S_v); the performance measures are material remove rate (MRR) and surface roughness (Ra). By testing a large number of BPNN architectures, 4-5-1 and 4-7-1 have been found to be the optimal one for MRR and Ra, respectively; and it can predict them with 10.61 % overall mean prediction error. As for RBNN architectures, it can predict them with 12.77 % overall mean prediction error. The multivariable regression model yields an overall mean prediction error of 13.93 %. All of these three models have been used to study the effect of input parameters on the material remove rate and surface roughness, and finally to optimize them with genetic algorithm (GA) and desirability function. Then, an intelligent optimization system with graphical user interface (GUI) has been built based on these multi-optimization techniques, in which users can obtain the optimized cutting parameters under the desired surface roughness (Ra).     

A study on the surface grinding of 2D C/SiC composites

This paper aims at studying the machinability of 2D C/SiC composite with 0°/90° woven carbon fibers using a resin bond diamond grinding wheel. The effects of grinding parameters on the grinding force, force ratio, specific grinding energy, surface topography, surface roughness, and grinding chips were investigated. And the grinding mechanism of the 2D C/SiC composite was discussed by analyzing the chip components and material removal characteristics. The results indicate that the grinding force and surface roughness increase with the increase of feeding speed and depth of cut, while decrease with the increase of wheel speed. The force ratio F _n /F _t and the specific grinding energy of 2D C/SiC composite were lower than those of conventional ceramics under the defined experimental conditions. Additionally, the grinding chips were composed of carbon powder, carbon fiber fragments, and SiC matrix debris. It can be deduced that the dominant removal mechanism of the 2D C/SiC composite was brittle fracture mode during grinding process.     

Taguchi-based grey relational analysis for modeling and optimizing machining parameters through dry turning of Incoloy 800H

The present research focused on the optimization of machining parameters and their effects by dry-turning an incoloy 800H on the basis of Taguchi-based grey relational analysis. Surface roughness (Ra, Rq and Rz), cutting force (Fz), and cutting power (P) were minimized, whereas Material removal rate (MRR) was maximized. An L ₂₇ orthogonal array was used in the experiments, which were conducted in a computerized and numerical-controlled turning machine. Cutting speed, feed rate, and cut depth were set as controllable machining variables, and analysis of variance was performed to determine the contribution of each variable. We then developed regression models, which ultimately conformed to investigational and predicted values. The combinational parameters for the multiperformance optimization were V = 35 m/min, f = 0.06 mm/rev and a = 1 mm, which altogether correspond to approximately 48.98 % of the improvement. The chip morphology of the incoloy 800H was also studied and reported.     

Optimal designing of multiple deferred state sampling plan for assuring percentile life under Weibull distribution

Continuous carbon fiber reinforced silicon carbide ceramic matrix composites (C/SiC) are promising materials in aerospace and space optical fields due to their excellent properties. However, poor machining quality resulted from surface/subsurface breakage is hard to meet precision requirements of some components. With an objective to study surface/subsurface breakage formation mechanism and improve machining quality of C/SiC composites, ultrasonic assisted grinding (UAG) and conventional grinding (CG) tests with a defined diamond grain distribution brazed grinding wheel were conducted. The surface/subsurface breakage types and formation mechanism were studied by comparative analysis of grinding force, micro-morphology of grinding surface/subsurface, and ground surface roughness. The results showed that main breakage types of different angle fibers in ground surface were lamellar brittle fracture and pit group originating from fracture and pullout of fibers, while breakage types of different angles fibers in ground surface were brittle fracture. Compared to CG, these breakages were reduced by UAG in varying degrees because it can reduce grinding force that determined fiber breakage. Consequently, because of the lower fiber breakages, the ground surface roughness Sa obtained by UAG was lower than CG and the maximum reduction was 12%.     

基于不同磨料的氮化硅陶瓷球精研工艺研究

为探究磨料对氮化硅陶瓷球精研加工的影响,从而提高氮化硅陶瓷球的表面质量和材料去除率,以基液种类、磨料种类和研磨盘转速为主要影响因素设计正交试验,并分析各因素对表面粗糙度Ra的影响程度。以表面粗糙度Ra和材料去除率为评价指标,通过单因素试验优化研磨参数。根据正交试验结果,得到精研加工过程中各影响因素对于表面粗糙度Ra的影响程度,从大到小排列依次为:磨料种类>基液种类>研磨盘转速。综合考虑陶瓷球精研加工的要求,确定最佳的研磨参数组合为:煤油基液、碳化硅磨料以及150 r/min的研磨盘转速。在金刚石、碳化硅、氮化硼、氧化铬和氧化铁这5种磨料中,氧化铁磨料修复粗研过后的氮化硅陶瓷球表面缺陷的效果最好。     

Sustainability analyses of cutting edge radius on specific cutting energy and surface finish in side milling processes

The aim of this work is to determine the influence of cutting edge radius on the specific cutting energy and surface finish in a mechanical machining process. This was achieved by assessing the direct electrical energy demand during side milling of aluminium AW6082-T6 alloy and AISI 1018 steel in a dry cutting environment using three different cutting tool inserts. The specific energy coefficient was evaluated as an index of the sustainable milling process. The surface finish of the machined parts was also investigated after machining. It was observed that machining with the 48.50-μm cutting edge radius insert resulted in lower specific cutting energy requirements when compared with the 68.50 and 98.72-μm cutting edge radii inserts, respectively. However, as the ratio of the undeformed chip thickness to cutting edge radius is less than 1, the surface roughness increases. The surface roughness values gradually decrease as the ratio of undeformed chip thickness to cutting edge radius (h/r _e) tends to be 1 and at minimum surface roughness values when the ratio of h/r _e equalled to 1. However, the surface roughness values increased as h/r _e becomes higher than 1. This machining strategy further elucidates the black box and trade-offs of ploughing and rubbing characteristics of micro machining and optimization strategy for minimum energy and sustainable manufacture.     

单晶硅纳米级磨削过程的理论研究

对内部无缺陷的单晶硅纳米级磨削过程进行了分子动力学仿真,从磨削过程中瞬间原子位置、磨削力、原子间势能、损伤层深度等角度研究了纳米级磨削加工过程,解释了微观材料去除、表面形成和亚表面损伤机理。研究表明：磨削过程中,单晶硅亚表面损伤的主要形式是非晶结构形式,无明显的位错产生,硅原子间势能的变化是导致单晶硅亚表面损伤的重要原因;另外,发现磨粒原子与硅原子之间有黏附现象发生,这是由于纳米尺度磨粒的表面效应而产生的。提出了原子量级条件下单晶硅亚表面损伤层的概念,并定义其深度为沿磨削深度方向原子发生不规则排列的原子层的最大厚度。     

Experimental study on micro electrical discharge machining of porous stainless steel

Various cutter strategies have been developed during milling freeform surface. Proper selection of the cutter path orientation is extremely important in ensuring high productivity rate, meeting the better quality level, and longer tool life. In this work, finish milling of TC17 alloy has been done using carbide ball nose end mill on an incline workpiece angle of 30°. The influence of cutter path orientation was examined, and the cutting forces, tool life, tool wear, and surface integrity were evaluated. The results indicate that horizontal downward orientation produced the highest cutting forces. Vertical downward orientation provided the best tool life with cut lengths 90–380 % longer than for all other orientations. Flank wear and adhesion wear were the primary wear form and wear mechanisms, respectively. The best surface finish was achieved using an upward orientation, in particular, the vertical upward orientation. Compressive residual stresses were detected on all the machined surfaces, and vertical upward orientation provided the minimum surface compressive residual stress. In the aspect of tool wear reduction and improvement of surface integrity, horizontal upward cutter path orientation was a suitable choice, which provided a tool life of 270 m, surface roughness (R _a ) of 1.46 μm, and surface compressive residual stress of ?300 MPa.     

A state-of-the-art review of ductile cutting of silicon wafers for semiconductor and microelectronics industries

Silicon is a typical functional material for semiconductor and optical industry. Many hi-tech products like lenses in thermal imaging, solar cells, and some key products of semiconductor industry are made of single crystal silicon. Silicon wafers are used as substrate to build vast majority of semiconductor and microelectronic devices. To meet high surge in demand for microelectronics based products in recent years, the development of rapid and cost efficient processes is inevitable to produce silicon wafers with high-quality surface finish. The current industry uses a sequence of processes such as slicing, edge grinding, finishing, lapping, polishing, back thinning, and dicing. Most of these processes use grinding grains or abrasives for material removal. The mechanism of material removal in these processes is fracture based which imparts subsurface damage when abrasive particles penetrate into the substrate surface. Most of these traditional processes are extremely slow and inefficient for machining wafers in bulk quantity. Moreover, the depth of subsurface damage caused by these processes can be up to few microns and it is too costly and time consuming to remove this damage by heavy chemical–mechanical polishing process. Therefore, semiconductor industry requires some alternative process that is rapid and cost effective for machining silicon wafers. Ductile cutting of silicon wafer has the potential to replace the tradition wafer machining processes efficiently. If implemented effectively in industry, ductile cutting of silicon wafers should reduce the time and cost of wafer machining and consequently improve the productivity of the process. This paper reviews and discusses machining characteristics associated with ductile cutting of silicon wafers. The limitations of traditional wafer fabrication, the driving factors for switching to ductile cutting technology, basic mechanism of ductile cutting, cutting mechanics, cutting forces, surface topography, thermal aspects, and important factors affecting these machining characteristics have been discussed to give a systematic insight into the technology.     

Multi-objective optimization for surface grinding process using a hybrid particle swarm optimization algorithm

Optimization for the surface grinding process is a problem with high complexity and nonlinearity. Hence, evolutionary algorithms are needed to apply to get the optimum solution of the problem instead of the traditional optimization algorithms. In this work, a hybrid particle swarm optimization (HPSO) algorithm which combines the dynamic neighborhood particle swarm optimization (DN-PSO) algorithm with the strategy of mutation considering constraints is presented to handle multi-objective optimization for surface grinding process. Such four process parameters as wheel speed, workpiece speed, depth of dressing, and lead of dressing are considered as the variables for optimization, and the following three objectives such as production cost, production rate, and surface roughness are used in a multi-objective function model with a weighted approach. Meanwhile, the constraints of thermal damage, wheel wear, and machine tool stiffness are considered. Computational experiments are conducted on cases of both rough grinding and finish grinding, and comparison results with the previously published results obtained by using other optimization techniques shows the efficiency of the proposed algorithm.     

On the mechanism of material removal by free abrasive grinding of glass and fused silica

The dependence of the rate of material removal from glass and fused silica specimens on the carrier fluid used in free abrasive grinding was observed and other abrasion parameters, i.e. surface roughness, bed thickness and drag force, were measured. The similarity between the damage produced by silicon carbide particles during free abrasive grinding and that found after indentation with a sharp point encouraged the formulation of a rotation/ indentation model of abrasion. This semi-quantitative model showed good agreement with the experimental data.     

An investigation into parallel and cross grinding of BK7 glass

Conventional grinding of BK7 glass will normally result in brittle fracture at the surface, generating severe sub-surface damage and poor surface finish. The precision grinding of BK7 glass in parallel and cross grinding modes has been investigated. Grinding process, maximum chip thickness, ductile/brittle regime, surface roughness and sub-surface damage have been addressed. Special attention has been given to the condition for generating a ductile mode response on the ground surface. A polishing–etching method has been used to obtain the depth of sub-surface damage. Experiments reveal that the level of surface roughness and depth of sub-surface damage vary differently for different grinding modes. This study gives an indication of the strategy to follow to achieve high quality ground surfaces on brittle materials.     

Wear study of carbon–silicon carbide couples

This experimental study concerns the tribological properties of different carbon/porous silicon carbide couples. The aim of this is to characterize the optimum friction couple (carbon/silicon carbide) for dynamic sealing elements in automotive water pumps. A tribometer was used to determine the wear of these material couples. The parameters able to influence the wear, namely the surface finish of the porous silicon carbide material, the quality of the carbon material, the normal load, the surroundings and the speed (in the case of dynamic friction), have been studied. It is evident from this study that the estimated average wear calculated by an empirical mathematical model is reliable except under conditions of extreme friction. This revised version was published online in July 2006 with corrections to the Cover Date.     

ELID镜面磨削硬质合金的工艺参数实验研究

随着国防尖端技术的迅速发展,许多具有独特性能的新材料得到了日益广泛的应用,如光学玻璃、硬质合金。但采用传统磨削工艺加工这些材料很难得到良好的表面质量。在线电解砂轮修整(ELID)磨削技术是一项新的、高效的磨削方法,它有效地实现了许多难加工材料的超精密加工和高效加工。针对硬质合金的特性,用ELID磨削方法应用于硬质合金的精密加工,通过实验研究ELID磨削中工艺参数对加工表面的影响规律,找到了在一定条件下优化的工艺参数。     

Role of the strengthening phases in abrasive wear resistance of laser-clad NiCrBSi coatings

The influence of the strengthening phases on the tribological characteristics (wear intensity, specific work of wear, coefficient of friction) and the wear mechanisms in two-body abrasion tests with abrasives of different hardnesses (corundum Al₂O₃, ~2000 HV and silicon carbide SiC, ~3000 HV) has been investigated for PG-SR2 (Cr₂₃C₆, 1000–1150 HV), PG-10N-01 (Cr₇C₃, 1650–1800 HV; CrB, 1950–2400 HV), and 75% PG-SR2 + 25% TiC (TiC, 2500–2900 HV; (Cr,Ni)₂₃(C,B)₆ and (Ti,Cr)(C,B), ~2000 HV) coatings. The dominant role of the strengthening phases (compared with the role of the metal matrix) in the abrasive wear resistance of laser-clad NiCrBSi coatings has been estimated. Different wear mechanisms have been identified and, accordingly, different levels of coatings wear resistance have been achieved depending on the ratio between the hardness of the strengthening phases (carbides, borides, carboborides) and abrasive particles.