Sheet metal assembly is a common assembly process for several products such as automobiles and airplanes. Since all manufacturing processes are affected by variation, and products need to have a high geometric quality, geometry-related production problems must be analyzed during early design phases. This paper discusses two methods of performing this analysis. One way of performing the simulations relatively fast is to establish linear relationships between part deviation and assembly springback deviation by using the method of influence coefficient (MIC). However, this method does not consider contact between the parts. This means that the parts are allowed to penetrate each other which can affect the accuracy of the simulation result.
Over the past years, several approaches for variation simulation of sheet metal assemblies have been presented. However, there are few reports on validation of the methods compared to real production inspection data. Often, the validation consists of comparing the simulation result from different methods against each other and not to real inspection data. In practice, variation simulation methods are difficult to use due to practical implications. This paper illustrates some of the implications and modeling aspects related to sheet metal assembly variation analysis. The tolerance analysis and validation is done by analyzing a real sheet metal assembly with the production inspection data that is used to monitor the process. The aim is to analyze how consistent the result from the tolerance analysis is with the inspection data. Finally, some modeling aspects and techniques will be discussed.
Compliant sheet metal assemblies are often used as support structures in automobiles, airplanes and appliances. These structures not only provide a metrology frame for other modules to be assembled, but also give the product its aesthetic form. For this reason, the dimension quality of the assemblies is a very important factor to control, in order to make sure that the product will function as planned and continuously keep the product cost low. The assembly is influenced by variations in the component parts and the assembly processes. Tolerance analysis, as conducted in most industries today, is normally based on the assumption of rigid parts and is thus not always valid for sheet metal assemblies, due to their compliance. This paper will present a method, based on finite element analysis (FEA) and design of computer experiments, of identifying the influence of input variables on the final geometry variation of the assembly. The influence and the interactions among the input variables are analyzed with a response model that has been constructed, using the simulation results. This response model could be used to identify the important variables that need to be controlled in assembly. An example application is included, in order to demonstrate the simulation model and response model construction. Analysis of the results from the simulations can facilitate the design of the assembly process, in order to control the dimensional quality of the product.
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