* Corresponding author. E-mail addresses: shehab@dmu.ac.uk(E.M.Shehab),ha@dmu.ac.uk (H.S. Abdalla).  http://www.eng.dmu.ac.uk/concurrent/ Robotics and Computer Integrated Manufacturing 17 (2001) 341}353 Manufacturing cost modelling for concurrent product development E.M. Shehab*, H.S. Abdalla Department of Design Management & Communication, De Montfort University, Leicester, UK Abstract This research work aims to develop an intelligent knowledge-based system that accomplishes an environment to assist inexperi- enced users to estimate the manufacturing cost modelling of a product at the conceptual design stage of the product life cycle. Therefore,aquickerresponsetocustomers' expectationsisgenerated.Thispaperdiscussesthedevelopmentprocessoftheproposed system for cost modelling of machining processes. It embodies a CAD solid modelling system, user interface, material selection, process/machineselection,andcostestimationtechniques.Themainfunctionofthesystem,besidesestimatingtheproductcost,isto generate initial process planning includes generation and selection of machining processes, their sequence and their machining parameters. Therefore, the developed system di!ers from conventional product cost estimating systems, in that it is structured to support concurrent engineering. Manufacturing knowledge is represented by hybrid knowledge representation techniques, such as production rules, frames and object oriented. To handle the uncertainty in cost estimation model that cannot be addressed by traditional analytical methods, a fuzzy logic-based knowledge representation is implemented in the developed system. Based on the analysisofproductlifecycle,theestimatedcostincludedmaterial,processing,machineset-upandnon-productivecosts.Acasestudy is discussed and demonstrated to validate the proposed system.  2001 Elsevier Science Ltd. All rights reserved. Keywords: Feature-baseddesign;Concurrentengineering;Manufacturingcostmodelling;Object-orientedprogramming;Processoptimisation;Fuzzy logic 1. Introduction The current trend forces companies to produce low- costandhigh-qualityproductsinordertomaintaintheir competitiveness at the highest possible level. There is no doubt that, reducing the cost of a product at the design stage is more e!ective than at the manufacturing stage. Therefore, if the product manufacturing cost can be esti- matedduringtheearlydesignstage,designerscanmodify a design to achieve proper performance as well as a rea- sonable cost at this stage and encourage designers to design to cost. Past studies showed that over 70% of the production cost of a product is determined during the conceptual design stage [1]. However, the design phase itself ac- counts for only (6%) of the total development cost [1]. Therefore, devoting a greater e!ort to design to cost is a necessary step towards optimising product costs. Fig. 1 illustrates the percentage of product costs set and incurred in di!erent phases. Cost can be employed as an evaluation criterion in design in two ways. It can be used either in a design- to-cost or design-for-cost context. Design-for-cost is the conscious use of engineering process technology to re- ducelifecyclecostwhiledesign-to-costprovidesadesign satisfying the functional requirements for a given cost target. 2. Literature review Cost estimation is concerned with the predication of costs related to a set of activities before they have act- ually been executed. Cost-estimating approaches can be broadly classi"ed as intuitive method, parametric techniques, variant-based models, and generative cost estimating models. However, the most accurate cost estimates are made using the generative approach. Among the many methods for cost estimating, at the design stage, are those based on knowledge bases, fea- tures,operations,weight,material,physicalrelationships and similarity laws. 0736-5845/01/$-see front matter  2001 Elsevier Science Ltd. All rights reserved. PII:S0736-5845(01)00009-6