| Auto-body assembly is a complex sheet metal assembly process in multi-station. The parts variation, locating variations etc. will influence the auto-body dimensional variation. The dimensional quality of car body directly relates to vehicle performance, appearance and competitive power on market, so automotive companies pay close attention to auto-body assembly quality. Function Evaluation (FE) is a critical process in launching a vehicle which evaluates prototype parts on checking fixtures. But physical validations increase investment in tooling and manpower and more importantly, lengthen the vehicle development process.To solve these problems, digital panel assembly is proposed in this paper in order to reduce cost and shorten lead time. First, digital matching flow and method of compliant parts is presented after physical FE is reviewed and discussed, then two key techniques-flexible parts variation analysis using finite element methods and variation model based on influence coefficient method are established, last two virtual variation simulation models are validated their reliability by calculating a rear lamp bracket assembly variation of an automotive company. The main content of this paper can be divided into four parts:(1) Proposing a method of evaluating assembly variation based on compliant parts digital matchingConsidering features of automotive compliant parts assembly and FE, the paper proposed a digital matching method to evaluate assembly variation, which includes three stages: parts features identification and extraction, virtual assembly simulation and assembly quality assessment. Firstly, measuring data, locating and welding information are obtained through identifying and extracting parts features, secondly, virtual assembly is established through finite element method, and lastly, assembly quality is evaluated. Digital matching evaluation will largely shorten auto-body development process and reduce cost.(2) Establishing compliant parts assembly variation analysis model based on finite element methodA compliant parts variation analysis based on finite element method is established from meshing of assembly parts, adding boundary conditions, calculating assembly model and assess assembly quality. Physical parts mesh are generated from ideal model and physical parts measuring data, several nodes are used to constraint compliant parts, welding model and interference model are established after finishing these conditions.(3) Establishing assembly variation model based on influence coefficient methodFor reducing time and improve efficiency of finite element method, influence coefficient method is introduced to solve this problem. Influence coefficient method analyzes the assembly variation statistically considering parts variations and fixtures variations, a model based on influence coefficient method is established considering both parts variations and fixtures variations, and an example has been calculated to explain how to establish this model.(4) Application and validation of rear lamp bracketTwo variation models are applied on rear lamp bracket assembly which is supported by an automotive company. In finite element analysis model, parts mesh is generated after treating point clouds measured by white light scanning, assembly model is simulated after adding boundary conditions and establishing welding model. Influence coefficient model is applied on first station, and the assembly variations are gained after inputting parts variations and fixtures variations. The results of two models are in accordance with the manufacturing data, which show virtual assembly method can solve compliant parts variation analysis. |
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