The Engineering Change Analysis And Evaluation Methods In Product Design

To reduce the cost and time of new product development,many manufacturing enterprises adopt the change pattern to finish new product design based on the existing old products,which causes engineering changes(EC)to become an important business activity.How to quickly deal with ECs is always a disturbing problem that troubles the industrial and academe community.Engineering change impact assessment(ECIM)is one of bottleneck factors of restricting the engineering change process,and the accuracy of the EC impact assessment is very important for engineers to reasonably choose the right EC from a group of EC plans.Therefore,manufacturing enterprises urgently need the engineering change impact analysis evaluation methods or the auxiliary tools of EC impact assessment.Aiming at the need,this dissertation considers two types of ECs(part level change and product level change)as the research objects to study the methods of EC impact assessment.For the part change,a change feature-based approach is proposed to evaluate the EC impact.For the product change,this dissertation proposes a feasible change path search and optimization method based on the model of product parameters-driven associated network.The main contents of the dissertation are presented as follows:(1)An EC similarity calculation method is proposed.Adopting past EC knowledge to assess the impact of EC requires a method to compute the similarity between EC cases.Firstly,the concept of change feature is introduced in the second chapter of this paper,which aims to address the issue about EC impact assessment.Change features are utilized to describe the change attitudes of part CAD models including the part model before change and the part model after change.Afterwards,the engineering change feature data model(ECFDM)is constructed,which aims to provide an analysis model that can capture,save and reuse the knowledge of EC.Finally,the similarity between ECs is computed based on the change feature similarity.This method not only provides a new thought for EC theory study,namely EC similarity is computed from the perspective of feature;but also establishes theoretical basis that helps achieve the reuse of much EC case knowledge in enterprises,especially including the information and knowledge of part model.(2)A change feature-based method for predicting the EC impact is presented.Building the EC impact prediction model of part level is always difficult.Firstly,the relationship between change features and EC impact is analyzed in the third chapter of this paper.Then,according to the relationship an EC impact evaluation method is proposed based on change feature.Finally,according to the Bayes rule and the minimum cross entropy principle,the mathematics prediction model of EC impact is constructed.The model built using our method can address the problem on the quick impact evaluation of part level EC.(3)An EC impact analysis model of product driving parameters is constructed.The feasible change path analysis of product level EC requires accurate product analysis model.Firstly,on the basis of traditional product parameter modeling technology,the concept of product driving parameter is introduced in the forth chapter of this paper.And then we define three modeling rules: product driving parameter modeling,assembly constraint relationship promotion,and the five-step termination principle.Finally,according to the relationship between product parameters,the EC impact analysis model is established with three modeling rules.Compared with the traditional product model,the node number of the product drive parameters model decreases significantly and greatly improves the analysis efficiency.Meanwhile,using the broken-ring rule can effectively avoid change into the infinite loop problem in EC propagation analysis.(4)A change path search and optimization method is presented.Chapter 5 is based on the part model of Chapter 4.Firstly,according to the EC impact analysis model,the product parameter information is saved as the node of graph.Secondly,the depth first search algorithm is used to find feasible change path.Then,based on such evaluation indexes as change cost and change efficiency,an unified evaluation criterion is established.Finally,the optimal change plan is selected based on the criteria.The method of this chapter provides a theoretical basis for the realization of computer automatic analysis,search of the feasible change pathes and selection of the optimal feasible change path.Based on the above researches,a prototype system of EC impact evaluation(ECIES)for helping engineers analyze and evaluate the EC impact quickly has been developed,and experiment results that include the part level EC impact evaluation instance and the change path search and optimization instance of the product level change are given.Meanwhile,some experiments are utilized to verify the feasibility and effectiveness of the proposed theories and approaches.