Optimization of multi-response processes using the VIKOR method

Design of experiments and Taguchi methods are extensively adopted as off-line quality improvement techniques in industry. However, these methods were developed to optimize single-response processes. In many situations, multiple responses must be optimized simultaneously, since some product designs, especially in the integrated circuit industry, are becoming increasingly complex to meet customers’ demands. Although several procedures for optimizing multi-response processes have been developed in recent years, the associated quality measurement indices do not consider variations in the relative quality losses of multiple responses. These procedures may therefore result in an optimization in which quality losses associated with a few responses are very small but those associated with others are very large, even if the overall average quality loss is small. Such an optimization with a large variation of quality losses among the responses is usually unacceptable to engineers. Accordingly, this study employs the VIKOR method, which is a compromise ranking method used for multicriteria decision making (MCDM), to optimize the multi-response process. The proposed method considers both the mean and the variation of quality losses associated with several multiple responses, and ensures a small variation in quality losses among the responses, along with a small overall average loss. Two case studies of plasma-enhanced chemical vapor deposition and copper chemical mechanical polishing demonstrate the effectiveness of the proposed method.     

Multi-response optimisation of WEDM process using principal component analysis

Like many other processes, the wire electrical discharge machining (WEDM) process has several performance characteristics. Determination of the optimal process settings with respect to all these performance measures (responses) is an important issue. Taguchi’s robust design method can only be applied to optimise a single-response problem. Some researchers have attempted to optimise WEDM operations using a multi-response signal-to-noise (MRSN) ratio and constraint optimisation methods. Both these methods suffer from some weaknesses. The principal component analysis (PCA)-based approach for multi-response optimisation can effectively overcome those weaknesses. In this paper, some modifications in the PCA-based approach are suggested and two sets of experimental data published by the past researchers are analysed using this modified procedure. It is observed that the PCA-based optimisation can give better results than the constrained optimisation and MRSN ratio-based methods, which can be attributed to the fact that the possible correlation among the multiple responses is taken care in the PCA-based approach.     

Improving yarn quality through multi-response optimisation of electronic yarn clearer in winding machine

One of the essential post-spinning operations of yarn is winding. In winding machine, ring yarn (i.e. the yarn produced in ring frame) is passed through electronic yarn clearer (EYC) and wound into empty conical-shaped packages called cones. The purpose of EYC is to improve the yarn quality as much as possible by eliminating the various types of faults or irregularities, e.g. thin places, thick places and neps from the ring yarn. The process engineer in an Indian spinning mill was facing the problem of inaccurate detection of faults by the EYC, which led to higher number of winding breaks as well as yarn irregularities. Aiming to tackle the problem, Taguchi’s L₂₇ orthogonal array experimentation was carried out. The experimental data are analysed using weighted principal component (WPC) method and principal component analysis-based grey relational analysis that take care of correlation among multiple responses. The WPC method is found to give better optimisation. By using the optimal settings, sensitivity of the EYC to detection of faults increased and thus, yarn quality improved substantially.     

The effect of the cutting parameters on performance of WEDM

In this study, variations of cutting performance with pulse time, open circuit voltage, wire speed and dielectric fluid pressure were experimentally investigated in Wire Electrical Discharge Machining (WEDM) process. Brass wire with 0.25 mm diameter and AISI 4140 steel with 10 mm thickness were used as tool and work materials in the experiments. The cutting performance outputs considered in this study were surface roughness and cutting speed. It is found experimentally that increasing pulse time, open circuit voltage, wire speed and dielectric fluid pressure increase the surface roughness and cutting speed. The variation of cutting speed and surface roughness with cutting parameters is modeled by using a regression analysis method. Then, for WEDM with multi-cutting performance outputs, an optimization work is performed using this mathematical models. In addition, the importance of the cutting parameters on the cutting performance outputs is determined by using the variance analysis (ANOVA).     

Optimisation of multiple responses for WEDM processes using weighted principal components

Taguchi method is widely used for optimisation of various processes. Using Taguchi method, the parametric settings can be optimised with respect to one performance characteristic (response) at a time, whereas wire electrical discharge machining (WEDM) processes require optimisation of multiple performance characteristics. Researchers have attempted several approaches but determination of the optimal process settings that can optimise multiple performance measures (responses) of WEDM operations still remains an important issue. In this paper, weighted principal component (WPC) method is used to optimise the multiple responses of WEDM processes. The results show that the WPC method offers significantly better overall quality than the other approaches.     

Experimental study on energy consumption of energy-saving pulse power for WEDM

Wire electrical discharge machining (WEDM) is widely used in aerospace, mold manufacturing, automotive, and other fields. But now, traditional WEDM pulse power contains current-limiting resistor, and its energy utilization rate is low. Meanwhile, discharge energy of WEDM pulse power cannot be accurately controlled, and there is no unified understanding of distribution about discharge energy. In this paper, the pulse power improves energy utilization rate by removing current-limiting resistor and adopting single-arm pulse width modulation control method which controls peak current and modulates long short-circuit pulse width. Experiments proved that the energy-saving pulse power improves energy utilization rate by, approximately, 67.6 % than traditional pulse power. The paper analyzed a single-pulse energy waveform of the energy-saving pulse power and calculated each spark pulse energy and total energy provided by pulse power. It found that gap spark discharge energy only accounted for about 51 % of the energy provided by the pulse power, and other energy was mainly consumed in switching loss of power switch and parasitic resistance of pulse power.     

A unique solution for principal component analysis-based multi-response optimization problems

A procedure to find a unique solution for multi-response optimization problems based on indexing is presented. The procedure utilizes principal component analysis to map the original data to a new vector of component scores, transforming the original response variables into uncorrelated principal components. This process involves loadings that are the elements of the eigenvectors corresponding to the eigenvalues of response variables in the correlation matrix. It is shown that for a given eigenvalue λ, its corresponding eigenvectors are not unique, which could lead to different “optimal” parametric (factor-level) settings and will further mislead the process or product improvement strategy. The proposed indexing method will determine a unique optimal solution in the presence of (2^p)(p!) combinations of eigenvectors.     

A hybrid approach for multi-response optimization of non-conventional machining on AlSiCp MMC

In this study, investigation on machinability characteristic of aluminum silicon carbide composite on electrical discharge machine is carried out. The composites are prepared through powder metallurgy route. The influence of four machining parameters (discharge current, pulse duration, duty cycle, and flushing pressure) and two material parameters (weight fraction of silicon carbide in the composite and mesh size) on selected responses are studied. The responses considered, in this work, are material removal rate, tool wear rate, surface roughness and circularity. In actual machining application, it is desirable to find a parametric combination that leads to simultaneous optimization of all the responses. Classical Taguchi method can optimize a single response but not multiple responses. In order to simultaneously optimize multiple responses, a hybrid approach combining principal component analysis (PCA) and fuzzy inference system is coupled with Taguchi method. The influence of each parameter on the responses is established using analysis of variances (ANOVA) at 5% level of significance. It is found that pulse duration, duty cycle, discharge current and flushing pressure contribute significantly to the multiple performance characteristic index. The four responses at optimal parameter setting have been reported.     

A comparative study on the performance of boric acid with several conventional lubricants in metal forming processes

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. The lubricating action of boric acid is due to its layered crystalline structure, and is similar to the structure of MoS₂ and graphite. However, boric acid lubrication could offer distinct advantages in terms of its application prior to forming and removal after a forming operation since it can be dispensed using water and alcohol solutions, raising the possibility of being environmentally friendly. Its effectiveness under actual conditions of metal forming operations such as rolling, forging, and sheet metal drawing and stretching has been evaluated in this study with both ferrous and non-ferrous work materials. It was found that boric acid provided lowest friction in sheet drawing and stretching operations, which is attributed to its lattice layer structure that facilitates easy sliding between molecular layers. Under predominantly compressive conditions of forming, liquid or semi-solid lubricants have performed better as they could squeeze out along with forwarding workpiece surfaces. The findings presented in this paper increase the prospect for developing boric acid as an effective lubricant in the cold forming of materials under certain conditions.     

The principal component analysis (PCA)-based approaches for multi-response optimization: some areas of concerns

Over the years, Taguchi method for process optimisation has become very popular among the engineers. However, Taguchi method focuses on the optimisation of a single-response variable only, whereas most of the modern manufacturing processes demand for simultaneous optimisation of multiple response variables, and some of these responses are often correlated. Several methods have been proposed in literature which aims at making the Taguchi method useful for solving multi-response optimisation problems too. However, only few of these methods take into account the possible correlations that may exist among the response variables. Among these, principal component analysis (PCA)-based approaches are quite popular among the practitioners. However, we find that the PCA-based approaches suffer from some weaknesses, e.g. problem due to using signal-to-noise ratios as input data, problem due to scaling of the input data, problem due to difference in PCA results given by different software. This article aims at drawing attention of the researchers/practitioners to these problem areas of the PCA-based approaches so that appropriate research initiatives can be taken up by the researchers/practitioners to overcome those weaknesses.     

基于DK7740P电火花线切割机床多次切割研究

在国内电加工界对电火花丝线切割的研究基础上,结合DK7740P线切割机床的应用,阐述高速走丝多次切割的基本条件,以及多次切割过程中各种工艺参数的确定。详细分析了在线切割机床上进行单次和多次切割加工时尺寸精度的对比实验,表明在高速走丝线切割机床上采用多次切割技术,可以明显提高加工精度,带来显著的经济效益。     

A numerical study on parameter control for remelted coating processes

A parametric finite element analysis was carried out to investigate the relation between processing parameters in remelted coating processes (e.g. remelting power, beam diameter, and scanning speed) and thermal behavior of the coating/substrate system such as dilution, melt pool, and heat affected zone. In the simulation, nickel-based alloys and alumina are studied as coatings deposited on AISI 1040 carbon steel substrate. A wide range of processing parameters are investigated. Scanning speed ranges from 5 to 100mm/s. Machining beam radius is taken from 0.5 to 3mm. It is found that the dilution is very sensitive to the re-melting power, scanning speed and machining beam radius. The role of the preheating temperature of the coating/substrate system is also considered. Significant reductions in remelting power of around 20%, 30% and 40% can be seen when the coating/substrate system is preheated at 250, 500 and 750°C, respectively. Numerical results provide useful suggestions for a re-melting process in practice.     

电火花线切割加工工艺研究

电火花线切割加工的用途已越来越广泛，主要介绍了其加工原理；薄工件的加工方法；减少和防止工件的变形和开裂的措施；加工表面的黑白条纹产生的原因，同时还提出了限制黑白条纹的对策。本文能针对这些常见加工工艺问题，结合自己的实践提出一些解决办法，以期给使用电火花线切割加工者带来一些参考办法和经验。     

复杂曲面零件电火花线切割加工系统研究

开发了以新型翻转式自动分度数控回转工作台为核心的复杂曲面电火花线切割加工系统。阐明了系统的运动规律,建立了通用数学模型,并进行了计算机仿真和样件加工实验研究。利用该数控回转工作台,采用二维加工信息流控制技术,与国产高速走丝电火花线切割机床相结合,从根本上解决复杂曲面零件高速走丝电火花线切割加工的关键技术问题,大幅度提高了线切割加工的加工质量和生产效率。该方法在模具制造中得到了良好的应用。     

工业过程智能控制策略的研究

智能控制策略的提出是以仿人的智能控制思想为基础的控制方法.该文针对具有不确定性、建模困难的系统,结合智能控制的思想,提出了一种方便、快速、精确的智能控制策略.     

Comparison of performances of five prospective approaches for the multi-response optimization

The Taguchi method of experimental design is widely used for optimization of process performance. However, this method has been developed to optimize single-response processes. But, in many situations, the engineers are required to determine the process settings that can simultaneously optimize multiple responses. In the recent past, researchers have proposed several systematic procedures for multi-response optimization. Most of these methods use complicated statistical/mathematical models and are, therefore, not easily comprehendible to the engineers who do not have a strong background in mathematics. Only a few methods, e.g. weighted signal-to-noise (WSN) ratio, Grey relational analysis, multiple-response signal-to-noise ratio, VIKOR (VlseKriterijumska Optimizacija I Kompromisno Resenje in Serbian), and weighted principal component methods, use relatively simpler procedures. In this paper, the computational procedures for these five methods are standardized. Three sets of experimental data are analyzed using these standardized procedures and the predicted optimization performances of the five methods are compared. The results show that no method can give better optimization than the WSN method.     

A study on the thermal behavior in microaccelerometer manufacturing processes

Single crystal silicon (SCS) is used in a variety of microsensor applications in which stresses and other mechanical effects may dominate device performance. One of major problems associated with the manufacturing processes of the microaccelerometer based on the tunneling current concept is temperature gradient and thermal stressess. This paper deals with finite element analyses of residual stresses causing popping up, which are induced in micromachining processes of a microaccelerometer. The authors model temperature-dependent mechanical properties during focused ion beam (FIB) cutting and Pt deposition processes. The maximum thermal strain of 0.0012 occurred at the readout gap of the microaccelerometer during the Pt deposition process. The stress produced during the heating process of FIB cut was also found to be about 33–36 MPa and cooling process the maximum equivalent stress of about 34MPa still at the right corner of readout gap. The calculated maximum displacement occurred at the readout gap was 0.14 μm. This is still smaller than the popping up of about 2 μm observed in the experiment. The reason for this popping up phenomenon in munufacturing processes of microaccelerometer may be the bending of the whole wafer or it may come from the way the underetch occurs. Different SOI material and a new geometry of the accelerometer are under investigation. We want to seek after the real cause of this pop up phenomenon and diminish this by changing munufacturing processes of microaccelerometer.     

A tolerancing optimisation method for product design

Although extensive research has been carried out in the area of tolerancing techniques for product design, concurrent engineering is still very seldom used in this context. This paper introduces a unique tolerancing method which applies the concept of concurrent engineering. The proposed method essentially allocates the required functional assembly tolerances to the component tolerances by formulating the tolerancing problem into a mathematical model and solving the model using a linear programming approach. The component tolerances are first represented in terms of the process tolerances, assigned by process planners at an early stage of the product design. The objective function of the mathematical model, which is to maximise the residual tolerances of the processes, is then established and the constraints formulated based on the assembly requirements and process constraints. The model is subsequently solved using a linear programming approach. Finally, the proposed method is tested on a practical example.     

A cost-tolerance model for process sequence optimisation

This paper concerns the modelling of cost-tolerance data for various manufacturing processes and the optimisation of process sequences based on minimum production cost. A natural spline model representing the cost-tolerance relationship is introduced. A methodology to optimise the process sequences is developed using an expert system approach. An example to illustrate the methodology and the optimisation model is presented