Robust Design Methodology Research Articles

The importance of robust design methodology: case study of the infamous GM ignition switch recall

While a systematic quality strategy is of crucial importance for the success of manufacturing companies, the universal applicability and effectiveness of implemented quality management practices were called into question by a number of major product recalls in recent years. This article seeks to illustrate how already simple analyses and early stage design methods can help to better understand one of the potential reasons for these failures, namely the variation inherent in manufacturing, assembly, and use processes. Usually thoroughly controlled in production, it seems as if particularly the risk of unanticipated variation effects remain largely underestimated and thus unaccounted for in design practice, sometimes with disastrous consequences. To foster the awareness of this variation and to illustrate the benefits of its early consideration in product development, this paper reviews one of the most infamous recalls in automotive history, that of the GM ignition switch, from the perspective of Robust Design. It is investigated if available Robust Design methods such as sensitivity analysis, tolerance stack-ups, design clarity, etc. would have been suitable to account for the performance variation, which has led to a number of fatal product defects and the recall of 30 million vehicles. Furthermore, the disclosed legal case files were examined, offering a unique opportunity to examine how technical malfunctioning of the ignition switch could stay undetected long enough to result in fatalities.

Optimal Design of Injection Molding Process using the Mahalanobis Taguchi System

Warpage is a major defect frequently found in the injection molding process, and the reduction of warpage is a very challenging problem because of the uncontrollable factors, such as variations in the process parameters. Without any countermeasure against these noises, attempts to reduce the defects often lead to failure. In this research, a new robust design methodology, based on the Mahalanobis Taguchi System (MTS) to reduce warpage, is presented. The MTS performs the orthogonal array experiments and uses the signal-to-noise (SN) ratio of the Mahalanobis distance as a performance metric. The validity of the proposed method is illustrated through an optimal design of the injection molding process of a CPU base plate.

Robust approximation-free design for tracking and fault tolerance in the presence of arbitrarily switched unknown nonlinearities

This paper presents a robust approximation-free design methodology of tracking problem for a class of uncertain switched nonlinear systems under arbitrary switching. Switched nonlinearities, switched control coefficient functions, and external disturbances are assumed to be unknown. Based on the performance function and the common Lyapunov function method, the common robust approximation-free tracking controller is constructed to ensure that all error surfaces are preserved within the predefined performance bounds and finally converge to a preselected neighborhood of the origin. Then, the fault-tolerant tracking problem of uncertain switched nonlinear systems with faults in both an actuator and switched nonlinearities is addressed without any reconstruction of the proposed control structure. Differing from the existing results in the literature, the proposed control scheme can be implemented without computing repeated time derivatives of certain signals and solving any differential equations for adaptive laws to compensate for unknown nonlinearities and external disturbances, and can guarantee transient performance of the tracking error at the moments when switching or faults occur.

Optimization and influence of process parameters on surface roughness in turning of titanium alloy

Surface finish plays vital role in service life of components and it ensures a great reliability of sensitive aerospace components. Therefore, it is required to optimize process parameters for better surface finish. Titanium alloys have high strength to weight ratio, high toughness even at extreme temperatures, extraordinary corrosion resistance and ability to withstand extreme temperatures. However, the high cost of both raw materials and processing limits their use in aircraft, spacecraft, medical devices and military applications. This paper deals the optimization of process parameters to minimize surface roughness in turning of Titanium alloy (Ti-6Al-4V) under dry machining with different tool materials using Taguchi's robust design methodology. The results reveal that uncoated tool is suitable at low cutting speeds whereas PVD coated tools is suitable at high cutting speeds. It is observed from Analysis of variance (ANOVA) that feed rate is contributed more to minimize surface roughness for both uncoated and PVD coated tools. Interaction plots are generated to study the influence of process parameters on surface roughness. Mathematical models are developed to predict the surface roughness using a regression model.

Optimization and Influence of Process Parameters on Surface Roughness in Turning of Titanium Alloy under Different Lubricant Conditions

In any machining process, large amount of heat is generated due to plastic deformation of work material, friction at the tool – chip and tool - work piece interface. In dry machining, the heat generated adversely affects the quality of the products. Therefore, effective control of heat generated in the cutting zone is essential to ensure good surface quality of the work piece in machining. Cutting fluids have been the conventional choice to deal with this problem. Cutting fluids are introduced in the machining zone to improve the tribological characteristics of machining processes and to dissipate the heat generated. The advantages of cutting fluids however been questioned later on due to the negative effects on product cost, environment and human health. Later on Minimum Quantity Lubrication (MQL) has been tried as a possible alternative to the use of flooded coolants. Minimum Quantity Lubrication machining refers to the use of a small amount of cutting fluid, typically in order of 300 ml/hr or less, which are about three to four orders of magnitudes lower than that used in flooded lubricating conditions.This paper deals with the optimization and influence of process parameters on surface roughness in turning of Ti-6Al-4V alloy under dry, flooded and Minimum Quantity Lubrication (MQL) conditions using Taguchi’s robust design methodology. The results have been compared among dry, flooded and MQL conditions and it reveals that MQL shows better performance and improvement in reduction of surface roughness as compared to dry and flooded lubricant conditions. The CVD coated tool shows better performance as compared to the uncoated and PVD coated tools. It is also observed from the ANOVA that, feed rate has major influence on surface roughness.

Simultaneous automated design of structured QFT controller and prefilter using nonlinear programming

SummaryThis paper describes a nonlinear programming‐based robust design methodology for controllers and prefilters of a predefined structure for the linear time‐invariant systems involved in the quantitative feedback theory. This controller and prefilter synthesis problem is formulated as a single optimization problem with a given performance optimization objective and constraints enforcing stability and various specifications usually enforced in the quantitative feedback theory. The focus is set on providing constraints expression that can be used in standard nonlinear programming solvers. The nonlinear solver then computes in a single‐step controller and prefilter design parameters that satisfy the prescribed constraints and maximizes the performance optimization objective. The effectiveness of the proposed approach is demonstrated through a variety of difficult design cases like resonant plants, open‐loop unstable plants, and plants with variation in the time delay. Copyright © 2016 John Wiley & Sons, Ltd.

Optimization of production time in the multi-pass milling process via a Robust Grey Wolf Optimizer

In order to optimize multi-pass milling process, selection of optimal values for the parameters of the process is of great importance. The mathematical model for optimization of multi-pass milling process is a multi-constrained nonlinear programing formulation which is hard to be solved. Therefore, a novel robust meta-heuristic algorithm named Robust Grey Wolf Optimizer (RGWO) is proposed. In order to develop a RGWO, a robust design methodology named Taguchi method is utilized to tune the parameters of the algorithm. Therefore, in contradiction to previous researches, there is no need to design costly experiments to obtain the optimal values of the parameters of the GWO. In addition, an efficient constraint handling approach is implemented to handle complex constraints of the problem. A real-world problem is adopted to show the effectiveness and efficiency of the proposed RGWO in optimizing the milling process within different strategies. The results indicated that the RGWO outperforms the other solution methods in the literature as well as two novel meta-heuristic algorithms by obtaining better and feasible solutions for all cutting strategies.

Cobalt carbonate and cobalt oxide nanoparticles synthesis, characterization and supercapacitive evaluation

Taguchi robust design methodology was used to optimize direct precipitation reaction conditions for simple and fast synthesis of cobalt carbonate nanoparticles. The effects of several parameters that influence on particle size of prepared cobalt carbonate were investigated. The significance of these parameters on the size of cobalt carbonate particles were quantitatively evaluated by using of analysis of variance (ANOVA). The results showed that flow rate and the concentrations of cobalt and carbonate solutions have significant effect on the size of cobalt carbonate nanoparticles. Also, optimum conditions for synthesis of cobalt carbonate nanoparticles via precipitation reaction were achieved. The ANOVA demonstrated that under optimum condition, cobalt carbonate nanoparticles will have of 39.6 ± 2.2 nm sizes. In addition, the solid state thermal decomposition reaction of precursor was used for preparation of Co3O4 nanoparticles. The results showed that the Co3O4 nanoparticles synthesized by thermal decomposition of cobalt carbonate nanoparticles have 53 nm sizes. Cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy were used to investigate the supercapacitive property of the Co3O4 electrode. The Co3O4 electrode shows high specific capacitance of 396 F g−1 at scan rate of 2 mV s−1 in 2.0 M H2SO4 electrolyte. Thus, the prepared electrode could be used for supercapacitor.

Rapid development of xylanase assay conditions using Taguchi methodology

ABSTRACTThe present investigation is mainly concerned with the rapid development of extracellular xylanase assay conditions by using Taguchi methodology. The extracellular xylanase was produced from Aspergillus niger (KP874102.1), a new strain isolated from a soil sample of the Baramura forest, Tripura West, India. Four physical parameters including temperature, pH, buffer concentration and incubation time were considered as key factors for xylanase activity and were optimized using Taguchi robust design methodology for enhanced xylanase activity. The main effect, interaction effects and optimal levels of the process factors were determined using signal-to-noise (S/N) ratio. The Taguchi method recommends the use of S/N ratio to measure quality characteristics. Based on analysis of the S/N ratio, optimal levels of the process factors were determined. Analysis of variance (ANOVA) was performed to evaluate statistically significant process factors. ANOVA results showed that temperature contributed the maximum impact (62.58%) on xylanase activity, followed by pH (22.69%), buffer concentration (9.55%) and incubation time (5.16%). Predicted results showed that enhanced xylanase activity (81.47%) can be achieved with pH 2, temperature 50°C, buffer concentration 50 Mm and incubation time 10 min.

Optimization of Tape Winding Process Parameters to Enhance the Performance of Solid Rocket Nozzle Throat Back Up Liners using Taguchi’s Robust Design Methodology

The throat back up liners is used to protect the nozzle structural members from the severe thermal environment in solid rocket nozzles. The throat back up liners is made with E-glass phenolic prepregs by tape winding process. The objective of this work is to demonstrate the optimization of process parameters of tape winding process to achieve better insulative resistance using Taguchi’s robust design methodology. In this method four control factors machine speed, roller pressure, tape tension, tape temperature that were investigated for the tape winding process. The presented work was to study the cogency and acceptability of Taguchi’s methodology in manufacturing of throat back up liners. The quality characteristic identified was Back wall temperature. Experiments carried out using L 9 ′ (34) orthogonal array with three levels of four different control factors. The test results were analyzed using smaller the better criteria for Signal to Noise ratio in order to optimize the process. The experimental results were analyzed conformed and successfully used to achieve the minimum back wall temperature of the throat back up liners. The enhancement in performance of the throat back up liners was observed by carrying out the oxy-acetylene tests. The influence of back wall temperature on the performance of throat back up liners was verified by ground firing test.

Interactive robust optimal design of plastic injection products with minimum weldlines

A new robust optimal design methodology has been developed and applied to the design of plastic injection molding products. Taguchi’s robust design method and an optimal design search algorithm are integrated with a commercial CAE simulation tool. A direct search-based optimization procedure is implemented with the considerations of process variations as well as uncontrollable noise variables. The Interactive Design Space Reduction Method (IDSRM) based on orthogonal arrays for design of experiments is developed as a general optimization tool. Using the system, designers can interactively adjust the design space during the searching process for the optimal solution based on the outcomes of the experiments. The developed methodology is applied to an industrial application: a molding process design of an automobile front bumper to minimize the weldline, a form defect of plastic parts. Compared with the initial design solution, the optimized design aided by the proposed methodology shows a more efficient and better result in terms of design robustness against process variations.

Mechanisms and coherences of robust design methodology: a robust design process proposal

Although robust design (RD) methods are recognised as a way of developing mechanical products with consistent and predictable performance and quality, they do not experience widespread success in industry. One reason being the lack of a coherent RD process (RDP). In this contribution we analyse commonly used RD methods to identify their mechanisms and coherences and propose a RDP that is connected to the actual design tasks of the design engineer. The presented RDP comprises four main activities: (1) design and modification of the conceptual design solution, (2) measuring and modelling the robustness of the design, (3) processing and evaluation of the robustness data and (4) scaling of the design to optimise parameter and tolerance values. For each of the activities, the set of relevant RD methods is presented. The main objective of the RDP is to provide the design team with a better overview and understanding of the RD toolbox and to support the application of RD continuously throughout the product development by providing a sequential description of when to apply the methods and how they affect the robustness of the design.

Improving sleep quality using weighted blankets among young children with an autism spectrum disorder

Background/Aims: Sleep and rest disturbances in children with an autism spectrum disorder and sensory over-responsivity are challenging issues to address. These are important self-care challenges that are commonly faced by many individuals with an autism spectrum disorder, with a high percentage of individuals with an an autism spectrum disorder reporting sleep disturbances. Many health-related professions, including occupational therapy, use weighted blankets to assist children with an autism spectrum disorder to calm, fall asleep and remain asleep. The purpose of this study was to explore the efficacy of weighted blankets with children with an autism spectrum disorder and sleep disturbances using a single case, multiple baseline design. Methods: This pilot study included two children with an autism spectrum disorder and sensory over-responsivity. Results: Using a single subject design found that there were minimal changes reported via caregivers, indicating that weighted blankets assisted in improving the overall quality of sleep for their child with an autism spectrum disorder, specifically time to fall asleep, number of wakings in the night, duration of sleep and behaviour in the morning. Using visual analysis, changes were noted in the variability of data points but not with abrupt changes in the slope of trend lines. Conclusions: This study provides a valuable springboard justifying the necessity for additional research studies related to improving the quality of sleep in children with an autism spectrum disorder and sensory over-responsivity using more robust single subject design methodology and objective measurement resources.

마하라노비스 다구찌(Mahalanobis Taguchi) 시스템을 이용한 박판 성형 공정의 최적화

Wrinkle, spring-back, and fracture are major defects frequently found in the sheet metal forming process, and the reduction of such defects is difficult as they are affected by uncontrollable factors, such as variations in properties of the incoming material and process parameters. Without any countermeasures against these issues, attempts to reduce defects through optimal design methods often lead to failure. In this research, a new multi-attribute robust design methodology, based on the Mahalanobis Taguchi System (MTS), is presented for reducing the possibilities of wrinkle, spring-back, and fracture. MTS performs experimentation, based on the orthogonal array under various noise conditions, uses the SN ratio of the Mahalanobis distance as a performance metric. The proposed method is illustrated through a robust design of the sheet metal forming process of a cross member of automotive body.

Robust design principles for reducing variation in functional performance

ABSTRACTThis paper identifies, describes and classifies a comprehensive collection of variation reduction principles (VRP) that can be used to increase the robustness of a product and reduce its variation in functional performance. Performance variation has a negative effect on the reliability and perceived quality of a product and efforts should be made to minimise it. The design principles are identified by a systematic decomposition of the Taguchi Transfer Function in combination with the use of existing literature and the authors’ experience. The paper presents 15 principles and describes their advantages and disadvantages along with example cases. Subsequently, the principles are classified based on their applicability in the various development and production stages. The VRP are to be added to existing robust design methodologies, helping the designer to think beyond robust design tool and method application, towards forming product variation management strategies.

A life cycle approach to robust design methodology

This paper proposes a new practice of robust design methodology (RDM); to adopt a life cycle approach to noise factor identification. Such practice expands the boundary of traditional use of robust design where noise factors are generally known, observable and experimentally controllable. By exploiting information from claim data of a medium-sized Swedish manufacturing company, several other noise factors were identified and classified into product life cycle stages; factors that are often uncontrollable,unobservable, or unknown. Exploratory data analysis, interviews, and internal documents are used in this study. The results show that by analysing the claims data, the product’s failure modes can be identified and classified into various product life cycle stages. This enables identification of noise factors in each product life cycle stage. The use of a life cycle approach has two major implications. One is to expand the focus of RDM to encompass all product life cycle stages instead of being limited to a product development process. The other implication is that the practice proposed facilitates consideration of more stakeholders, in addition to one single customer by looking at consequences for society at large once the product is in use. Hence, the proposed RDM practice can be supportive of sustainable product development.

Parametric design for quality improvement of injection-moulded product in a consumer electronics conglomerate

Current global market trends place an enormous amount of pressure on the process engineers to deliver functional products at the lowest possible cost. Taguchi's robust design methods provide a systematic and efficient method for developing improved products at reduced cost. This paper presents an application of Taguchi's parametric design methodology which is popularly known as robust design methodology to achieve improvements in product quality through process optimisation in a manufacturing context undertaken at the automation division of one of India's largest consumer electronics conglomerate. Plastic-moulded components are manufactured using automatic injection moulding machines to meet the needs of the entire group. During the preliminary investigation it was observed that sink mark on the surface of the moulded plastic component was the main contributor for rejection of the components and hence was selected as a measure for quality improvement. Taguchi's methods were applied and significant improvements in quality levels followed leading to an improvement of 84.95% reduction in current rejection rates. The authors advocate the need for manufacturing organisations to adopt Taguchi's robust design methodologies for process optimisation so as to achieve higher levels of quality on a continuing basis to sustain the intense global competitive pressures.

Experimental investigations on tool wear in turning of Ti-6Al-4V alloy under different machining environmental conditions

This paper deals with the study of tool wear on different cutting tool materials under scanning electron microscope (SEM) and optimisation of process parameters to minimise tool wear in turning of Ti-6Al-4V under different machining environments such as dry, flooded and MQL machining. Optimisation of process parameters is carried out using Taguchi's Robust Design Methodology to minimise tool wear. The results reveal that MQL machining is shown less tool wear as compared to dry and flooded machining. Moderate cutting speed, high feed rate, moderate depth of cut are found to be the optimum conditions and uncoated tool is outperformed as compared to CVD and PVD coated tools. The SEM analysis has been carried out on the worn tools to evaluate the wear mechanisms. [Received 24 June 2016; Accepted 24 June 2016]

Robust design methodology for simultaneous feedforward and feedback tuning

This study presents a control design methodology to address simultaneous robust feedforward and feedback tuning. A tuning guideline including tuning rules based on the time-domain response is introduced. Then, an optimisation algorithm is used in the frequency domain to find the optimal feedback–feedforward controller. Detailed simulations covering a wide range of industrial process models are carried out to demonstrate the validity of the proposed methodology and its advantages over other approaches.

Robust Observer Design of Tire Forces in Heavy-Duty Vehicles

This paper presents a robust observer design methodology to estimate tire forces in heavy-duty vehicles. The proposed methodology uses low-cost sensors and observer-based numerical differentiators. In addition to the already available sensors, low-cost sensors from the CAN bus are employed to get additional measurements. Sliding mode differentiators are used to optimize the sensors' configuration. Validation of the proposed estimation methodology is made by comparing the results with that generated using the PROSPER software simulator. The finite-time convergence with small estimation error suggests that the proposed methodology is valid and can be applied in real time.