Rajat Roy

Supply chain modelling using fuzzy sets

Abstract This paper considers a production supply chain (SC) with all facilities in a serial connection. The SC includes inventories and production facilities between them. It is assumed that the SC operates in an uncertain environment. Uncertainty is associated with: (1) customer demand, (2) supply deliveries along the SC and (3) external or market supply. Uncertainties are described by vague and imprecise phrases that are interpreted and represented by fuzzy sets. The SC fuzzy model described in this paper is developed to determine the order quantities for each inventory in the SC in the presence of uncertainties, that give an acceptable service level of the SC at reasonable total cost. Two control concepts of the SC are treated: (1) decentralised control of each inventory and (2) partial coordination in the inventories control. A special purpose simulator has been developed for examining the dynamics and performance of all the parts of the SC and the SC as a whole. Various simulation tests have been carried out to assess particularly the effects of uncertain external supply on the SC service level. Different approaches to improve SC performance in an uncertain environment have been simulated and analysed.

Modelling and simulation of a supply chain in an uncertain environment

This paper describes fuzzy modelling and simulation of a supply chain (SC) in an uncertain environment, as the first step in developing a decision support system. An SC is viewed as a series of facilities that performs the procurement of raw material, its transformation to intermediate and end-products, and distribution and selling of the end-products to customers. All the facilities in the SC are coupled and interrelated in a way that decisions made at one facility affect the performance of others. SC fuzzy models and a simulator cover operational SC control. The objective is to determine the stock levels and order quantities for each inventory in an SC during a finite time horizon to obtain an acceptable delivery performance at a reasonable total cost for the whole SC. Two sources of uncertainty inherent in the external environment in which the SC operates were identified and modelled: customer demand and external supply of raw material. They were interpreted and represented by fuzzy sets. In addition to the fuzzy SC models, a special SC simulator was developed. The SC simulator provides a dynamic view of the SC and assesses the impact of decisions recommended by the SC fuzzy models on SC performance.

Re-engineering the construction process in the speculative house-building sector

The UK house-building industry has often been criticized for failing to meet the housing needs of the country. The traditional craft-based build process is labour intensive with a long lead-time and is difficult to control for product quality. It is also not suitable for configurable designs that would help to customize the home, and the industry has been criticized for excessive standardization of its products. Attempts at industrialization, usually employing frame or panel-based build methods seen in many countries, have failed due mainly to lack of clear objectives. A change in build technology is also only one step in addressing the concerns of poor quality and lack of product variety. The paper presents a programme of work that is being carried out with a major house builder towards re-engineering of the build process through a combination of new technology, product engineering and changes in working practices.

Documentation, standardization and improvement of the construction process in house building

There is growing interest in the industrialization of house building methods in the UK. Much of the focus has been on the use of manufactured structural components, which addresses the inherent problems of reliance on ‘wet trades’ but not of the quality and efficiency of the assembly and ‘fitting’ processes on site. The house building process has tended to develop more through custom and practice rather than formal analysis of methods. There is a lack of standards, and of mechanisms for process review or sharing knowledge and good practice. The result is significant process variability on site. Process documentation is a rigorous description of a process, procedure or policy to facilitate training, and development of consistency of operations and standards. The paper presents work on a process documentation system, and discusses the organizational changes needed to create the cultural environment for process standardization and improvement.

Modelling distortion induced in an assembly by the self piercing rivet process

Traditionally, prediction of the dimensions of an assembly has concentrated on the variation of the constituent components and fixtures. Although recent methods have accounted for both statistical variation and flexibility of sheet metal components, the impact of the joining process has largely been ignored for riveted and spot-welded assemblies. The self-piercing rivet (SPR) has been used increasingly in the automotive industry for joining lightweight aluminium body structures, but the localized distortion around an SPR has been shown to be greater than that associated with the spot weld commonly used in steel body constructions. Consequently incorporation of such distortion into the simulation process for predicting the overall distortion of assemblies would be useful. This paper presents a simulation method based on a local/global approach where the distortion occurring around a single SPR is projected on to a global assembly at each rivet location. The results for both flat sheet assemblies and a simple top-hat assembly are presented for comparison and show that the method can be valuable in the early design stages by predicting the distortion from the joining process. Some suggestions for improving the method are also discussed.

Simulation of distortion induced in assemblies by spot welding

Abstract Maintaining dimensional tolerances during the manufacture of vehicle bodies is important to the automotive sector. With the industrys drive towards continuous improvement there is increasing focus on the effect of the joining process on the final assembly. A simulation tool that can predict the distortion resulting from assembly offers potential time- and cost-savings throughout design and manufacture. Although individual spot welds have been studied in detail, to-date methods to predict the distortion of a final assembly have concentrated on the variation of the constituent components. In the current paper simulation is used to predict the distortion of an assembly owing to spot welding using a local/global approach where the local distortion occurring around a single spot weld is projected onto a global assembly at each of the weld locations. The comparisons of the simulations of the assemblies with coordinate measuring machine (CMM) data under different clamping conditions suggest sufficient agreement with experimental data to be of value to engineers. A number of possible enhancements are suggested to improve the accuracy of final shape prediction.

Detecting subtle cosmetic defects in automotive skin panels

Abstract Cosmetic defects, such as ‘hollows’, are deviations in topology of automotive skin panels that form as a result of springback at the end of the forming process. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem. The first is the springback of the panel, the second is the optics of the painted panel, and the third is the ability of human sight to perceive a defect. In particular, it is argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a way to relate the geometry of a hollow to the resulting optical distortion. The transform was applied to two physical parts and the paper will discuss the effectiveness of the transform in locating and quantifying the relative severities of the defects that were present.

Alloy Development through Rapid Solidification for Soft Magnetic Application

This chapter describes different rapidly solidified processing routes of soft magnetic alloys and their properties and applications in different areas. Section-2 explains the details of process mechanism. The functions of different alloying elements are discussed with the alloy design of soft magnetic alloys in section-3. The structureproperty correlation is described in section-4. Section-5 highlights different types of rapidly solidified soft magnetic alloys, like high permeability alloys, high induction alloys, Fe-6.5 wt% Si steel and GMI alloys. In the last section-6, the applications of different types of soft magnetic alloys are mentioned.

Determining a probabilistic forming limit curve

Forming Limit Curves are surrounded by uncertainty - in particular the uncertainty surrounding the calculation of limit strains from experimental data. The position dependent method outlined in ISO12004-2 is known to make assumptions regarding the behavior of sheet metal at the onset of necking. Recent time dependent methods better utilize measured strain data from digital image correlation (DIC) techniques to determine the onset of localized necking. Both approaches generate a series of forming limit strains which require subsequent interpretation to produce a deterministic forming criterion. By acknowledging the inherent heterogeneous plastic deformation behavior of sheet metal, a new statistical approach to quantifying formability is proposed. Gaussian Mixture Models are used to characterize DIC-measured strain data and to determine both onset of localized necking and the size and location of the neck itself. By avoiding any pre-conceptions regarding the size or characteristics of the localized neck, a more realistic and robust probabilistic forming criterion is attainable.

Subtle cosmetic defects in automotive skin panels

Cosmetic defects such as ‘hollows’ are the result of deviations in a skin panel. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem: the springback or buckling of the panel, the optics of the painted panel and the ability of an observer to perceive the defect. In particular, it will be argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a simple way of locating and quantifying the severity of these defects. The transform was applied to two physical parts and a simulation model.