Assembly Sequence Optimization Of Auto-Body Parts Based On Compliant Assembly Variation Analysis

The dimensional quality of car body directly related to vehicle appearance, wind noise, shut door effection and drive stationarity, is influenced by parts design, assembly techniques and manufacture variations. Further improvement of quality of auto-body product depends on leverage of better design methods rather than merely support from advanced manufacturing tools and technology, of which the capability limit has been reached. During assembly processes of compliant parts, assembly sequence, welding position and fixture configuration influence assembly variation of auto-body product character. Most scholars mainly adopted one dimension variation analysis model, and took qualitative analysis on the butt joint, lap joint of the parts in the research field of assembly sequence optimization which targets was dimension quality. But the sheet metals of auto-body have complex assembly relationship, and they are easy to distort, so the traditional rigid body variation analysis model is on longer fit for flexible sheet medal parts.For compliant assemblies, an algorithm of assembly sequence optimization was presented. Assembly sequence planning is proposed based on multi-property directed graph, which can remove unfeasible sequences in engineering according to assembly constraints. Afterwards, the assembly variation analysis modeling is established, which can applied to analyze assembly tolerance of key characteristics in different sequences. The paper proposes assembly sequence optimization with two stages. For improving the efficiency of assembly sequence optimization, a software is developed for assembly sequence generation and optimization. Some cases are used to illustrate the algorithm such as the auto-body side and the rear lamp bracket assemblies. The main researches are as follows:(1) Proposing an algorithm of assembly sequence planning based on multi-property directed graphThe current algorithms of assembly sequence planning generate assembly sequences based on precedence relationships among components, which can not assure they are all used in engineering. The paper proposes an algorithm based on multi-property directed graph. Assembly modeling not only describes the relationships among components, but also appends matching features and assembly constraints. Moreover, the paper completes the subassembly types through importing loop subassemblies and classifying the three types into subgroups. Finally the algorithm removes unfeasible assembly sequences in engineering, which can improve the efficiency of assembly sequence generation.(2) Establishing modeling of multi-station compliant assembly variation analysisTraditional assembly variation analysis modeling mainly focus on the relationship between part variation and assembly variation; fixture variation is very important to assembly variation during the assembly processes of compliant parts. The paper establishes modeling of multi-station compliant assembly variation analysis. The sensitivity matrices are given according to the process of variation propagation for two locating principles of"N-2-1"and"3-2-1". Moreover, different assembly models are deduced for adapting each fixture layout and locator release.The modeling can be used to analyze prorogation of assembly variation in different sequences.(3) Proposing assembly sequence optimization with two stagesFor reducing the complexity of assembly sequence optimization, two stages are employed to optimize assembly sequences, which include: (1) optimizing assembly sequences based on rigid model; (2) optimizing schemes of fixture and welding points. In the first stage, the genetic algorithm is used to optimize matching features among parts. In the second stage, the paper proposes the response surface modeling based on radial basis function, which can well simulate nonlinear problem of deformable sheet metals. For improving the efficiency of fixture locating design, the paper uses the heuristic algorithm and the orthogonal design to optimize locating layout. The heuristic and orthogonal design algorithms are presented to select optimal assembly operations among components, whose advantages are that the search efficiency can be improved.(4) Developing the software of assembly sequence optimizationBased on the above researches, a software is developed for improving the efficiency of assembly sequence generation and optimization. The software uses the ACCESS database, utilizes the developing tool of VC++ and shows 3D data model of parts through the model of OpenGL. The software includes assembly modeling, assembly sequence planning, assembly variation analysis and assembly sequence optimization, which can automatically generate and optimize assembly sequences.