Allocating buffer storages in a pull system

This report proposes a method of estimating the amount of safety stock needed in each station of a production line due to variation in processing times, machine breakdowns and demand fluctuation in order to meet a predetermined desired level of performance. The production line is assumed to operate as a pull system and the measure of performance is the average percentage of demand backlogged. Multiple machines and different batch sizes in the stations are included in the model. Dynamic production control is used and is based on the current inventory level in every station of the system. Simulation results are used to test the performance of the system in which the maximum inventory level allowed in each station is based on the estimation given by our method.     

智能材料与结构在汽车行业的应用

智能材料与结构在汽车行业有着重要的潜在应用.大力研究与发展智能材料与结构,可为汽车向轻型化、节能化、自动化、智能化和舒适化方向发展提供强有力的材料支撑,发展前景广阔.本文对智能材料与结构在汽车业的应用进行了阐述.     

Algorithm for agile assembling-to-order in the automotive industry

Traditional automotive assembly initiates the assembly of a vehicle based on a specific order and keeps that order coupled with the vehicle as it moves through the plant. However, due to parallel stations and rework loops in the plant, the build sequence becomes scrambled by the time it enters final assembly. The sequence that reaches final assembly may not be suited for efficient assembly because it might cause very unlevel material usage and workload. Conventional scheduling optimizes the build sequence before the body shop, attaches an order to a physical vehicle as it enters the body shop, and keeps the order and vehicle coupled throughout the plant. Decoupled assembly allows the plant to change the customer order associated with a particular physical vehicle. An algorithm is presented for scheduling and matching customer orders to vehicles to take advantage of this decoupling and quantify its advantages via simulation.     

Thermomechanical design in the automotive industry

In this paper thermomechanical fatigue assessment in the automotive industry is discussed. The design strategy is based upon a consistent approach of the thermomechanical loading, the mechanical constitutive law of the material, the damage parameters and the fatigue strength criteria. The good understanding of these different steps allows one to perform predictive calculations of automotive parts subjected to thermomechanical loading. The main hypotheses and modelling choices are presented and results are illustrated by a series of computations on real 3D structures. Cracked area and lifetime prediction are described in the case of aluminium alloy cylinder heads subjected to transient thermal loadings.     

An analysis of designing for quality in the automotive industry

The paper is based on the authors' experiences in devising and conducting continuing education courses on Designing for Quality for design, development and manufacturing engineers in a large automotive company. Participants in the courses brought forward a wide range of quality problems encountered in their day-to-day professional activities. Methods for classifying and defining these problems are developed as a prelude to examination of the product development process and its management to fulfil quality objectives. The technique of quality function deployment which has recently received wide publicity in automotive engineering is investigated in the context of established design theory. Conclusions are drawn relating to the practice of engineering design in industry and the need for the effective dissemination of the work of design researchers.     

Determination of unit load sizes in an AGV-based material handling system for an FMS

Unit load size is a key factor in an automated guided vehicle based material handling system for a flexible manufacturing system. Highlighting this aspect and its importance at the design stage, this paper presents an integer programming formulation of the problem of finding the optimal unit load size. Using an existing analytical model to decide the number of AGVs required, an algorithm based on branching and implicit enumeration and a heuristic have been developed. Revised computations due to dynamic system conditions such as changes in part mix are also possible with the proposed algorithms. The methodologies have been demonstrated using numerical examples.     

Polyester moulding materials in automotive underbonnet environments

This paper describes investigations which have been carried out to characterize the behaviour of polyester moulding compounds when subjected to tests in environments encountered in automobile underbonnet situations. The tests contrast the behaviour of various polyester resin types in aqueous and hydrocarbon media; and show that the materials which best resist water and antifreeze exhibit the greatest degradation in petrol. The resistance of a range of polyester types to dry heat at 130°C and 180°C is discussed. Combinations of resin and glass fibre types have been tested in boiling water: the results show that the correct choice of resin and glass fibre can improve the onset of blistering from within one week to over 12 months. Single surface exposure of moulded plaques is shown to result in a far higher level of strength retention than total immersion of the material. A comparison has been made of the effect of different types of motor fuel, including methanol additives and ethanol, on the strength retention of dough moulding compound and sheet moulding compound throughout a 12 month ageing period.     

The effect of push and pull lot splitting approaches on lot traceability and material handling costs in stochastic flow shop environments

This study evaluates how the procedures followed in splitting job lots on the shop floor influence both material handling and lot integrity in stochastic flow shop environments. Former work has shown that lot splitting improves flow time and customer service performance, but with an increased number of transfers along with a corresponding increase in material handling costs. Physical lot integrity, which is important to lot tracing, has not been considered in prior literature. In order to overcome these limitations and address material handling concerns better, we define a new measure of performance called the lot integrity loss exposure (LILE). We use this and other measures to show that the traditional 'push' approach that has been followed in modelling lot splitting complicates lot traceability in the shop and leads to an excessive number of transfers. As an alternative, we propose a 'pull' approach in which an order is split between any successive pair of machines only on an as-needed basis. The push and pull approaches for lot splitting are compared under a range of conditions characterized by factors such as machine utilization levels within the shop, setup-to-processing time ratios, and number of splits created in job lots. Our results indicate that relative to the push approach, pull lot splitting helps significantly in reducing the number of transfers incurred and in maintaining a greater degree of physical lot integrity. At the same time, there is no significant difference in the two approaches with respect to improvements in flow time and customer service measures. Both the degree to which lot integrity is preserved, and the extent of savings in material handling that result from using the pull approach, are shown to be most pronounced under conditions characterized by high machine utilizations rates and setup-to-processing time ratios. Managerial implications of our study along with further research directions in this area are also discussed.     

Supply chain planning in the German automotive industry

Following the evolution in the computer industry, quite a lot of car manufacturers currently intend to move from a built-to-stock oriented production of standardized cars towards a customized built-to-order (BTO) production. In the premium segment of Germanys automotive industry, the share of customized BTO cars traditionally is comparatively high. Nevertheless, German car manufacturers have spent a lot of efforts in recent years to further increase this share in order to realize short delivery times, high delivery reliability and a fast responsiveness. Surprisingly, comprehensive overviews of the short- and mid-term planning landscape of car manufacturers cannot be found in the scientific literature. Thus, the first part of the paper discusses supply chain planning, as traditionally established in the premium segment of the German automotive industry, and reviews methods of Operations Research (OR) that are able to support the various planning tasks involved. In the second part, the major change in strategy, currently to be observed in the German automotive industry, is briefly summarized in order to derive its impacts for the planning system and for the respective planning methods. In this way, challenges for a future application of OR methods in the automotive industry can be identified.     

A two-phase heuristic algorithm for determining buffer sizes of production lines

In-process inventories are often used in many manufacturing systems to smooth and balance work flow. The buffer design problem of determining the best size of storage space between operations (or workstations) is one that has been approached in past and current research issues. Although past research attempted to apply traditional optimization methods to the buffer design problems, the applications revealed that some fundamental drawbacks were occurring due to the unique characteristics of the buffer design in the production lines. This paper addresses the unique characteristics involved in the buffer design, discusses drawbacks of traditional optimization methods applied, and finally presents an efficient two-phase heuristic method using a dimension reduction strategy and a buffer utilization-based beam search method, fn addition, numerical results show sensitivity analyses for the performance of the heuristic method with respect to parameters involved in the second phase of the method.     

Environmental and economic prospects of biomaterials in the automotive industry

Clean Technologies and Environmental Policy - This study provides an overview of the application of biomaterials in automotive industries and their economic and environmental implications. It also...     

Pyrolysis of glass-hardened polyamides used in the automotive industry

Thermogravimetry and on-line flash pyrolysis–gas chromatography–mass spectrometry were used for studying thermal decomposition processes in filled polyamides deriving from used cars. The thermal decomposition of each polymer begins at about 350 °C and proceeds with a weight loss of 100% for the non-glass fibres, under nitrogen atmosphere. The analysis of the pyrolyzate compounds shows that from polyamide 66, the most abundant product volatile at degradation temperatures is cyclopentanone, while from polyamide 6 there is a considerable yield of ε-caprolactam. This revised version was published online in November 2006 with corrections to the Cover Date.     

Approaches for fatigue assessment of welded joints in automotive industry

The numerical fatigue assessment of seam welded joints is of significant importance in automotive industry. In order to use the fatigue concepts, which are available in the literature, in series calculations, they usually have to be implemented into commercial software programmes. In the following contribution the possibilities available are discussed with respect to the needs in automotive industry. No specific commercial software will be discussed in detail. At the end open questions for developments necessary in the future will be addressed.     

Requirements management: an enabler for concurrent engineering in the automotive industry

Defining and agreeing the product requirements is especially important when the design and manufacture of a system is part of an Extended Enterprise. To realize an all-inclusive concurrent engineering process, tools for the upstream design activities are needed. In practice, it is often difficult for the companies to have a shared understanding of what needs to be developed, and so specifications contain ambiguities in describing the product requirements. This paper clarifies the problem domain in the context of a complex product, designed and manufactured in a pan-national Extended Enterprise and serving a highly competitive market. The authors show how the challenge can be addressed through the application of ontology. A model of a requirements-management tool is proposed that will allow the various systems and associated levels of a product to be described and then shared through the supply chain. A prototype system is presented and illustrated through a case study from the automotive industry.     

A prototype knowledge-based system for material selection of ceramic matrix composites of automotive engine components

A prototype knowledge based system (KBS) for material selection of ceramic matrix composites (CMC) for engine components such as piston, connecting rod and piston ring is proposed in this paper. The main aim of this research work is to select the most suitable material for the automotive engine components. The selection criteria are based upon the pre-defined constraint value. The constraint values are mechanical, physical properties and manufacturing techniques. The constraint values are the safety values for the product design. The constraint values are selected from the product design specification. The product design specification values are selected from the past design calculation and some values are calculated by the help of past design data. The knowledge-based system consists of several modules such as knowledge acquisition module, inference module and user interface module. The domains of the knowledge-based system are defined as objects and linked together by hierarchical graph. The system is capable of selecting the most suitable materials and ranks the materials with respect to their properties. The design engineers can choose the required materials related to the materials property.     

Dispatching rules and flexible environments: the influence on buffer behaviour

Frequent production requirements are linked to effective and profitable strategies for the management of queues, e.g. input buffers of machining centres and selection of rough workpieces from central storage. As a matter of fact, management policy performances must be evaluated by focusing not only on induced queue lengths or customer waiting times, but also on the future composition of the queues themselves, this being a consequence of the dispatching rule adopted. The question acquires further importance when flexible environments and buffer capacity constraints are considered. The aim of the present study is to illustrate an analytical procedure, based on the Markov chains theory, able to forecast the composition of buffers starting from any initial configuration. Attention is given to the buffer behaviour during the transient period and the steady state: results are offered for sequential and prioritized dispatching of items, together with application examples derived from common industrial situations. In the final sections, the possible extension of the procedure is considered and outlined with regard to particular management rules, thus introducing a further development of the present research.