Optimal Fixture Location Design Research Of Compliant Sheet Metal Workpiece Based On Rigid Variation Modelling Method

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. Fixture locating scheme is one of the key elements which have direct influence to product demision quality, the traditional fixture scheme designing method need designer design it by using experience, which lacks theory data support. As the flexible sheet metal parts often use"N-2-1"locating scheme, finite element modeling method is used to calculate variation, the method has high precision, but due to the complexity of the model, making the calculation less efficient.To address the above problems, this paper first proposed a fixture locating stability index to evaluate the quality of fixture locating, the locator-searching algorithm is used to design the deterministic fixture location scheme based on stability index; Then a rigid combination modeling method is used for positioning deviation of sheet metal parts and sub-variety of conditions with the finite element method are compared and analyzed; Then analyze the characteristics of the locators and clamps of a fixture and put forward the design methods for laying out locators and deciding the clamping sequence. The main content of this paper can be divided into four parts:(1) Presenting a stability index for evaluating a deterministic locating layout and proposing a new locator-searching algorithmBased on deterministic variation model, A stability index for evaluating a deterministic locating layout is presented and a new locator-searching algorithm is proposed to optimize fixture locating design which has been validated by a fixture locating design case of automobile dashboard.(2) Establishing compliant parts assembly variation model based on the combination of rigid variation modelA compliant parts variation analysis based on the combination of rigid variation model is established, the scope of the rigid variation model and the variation influence between different rigid model is analyzed; Then the variation results are compared and analyzed with the finite element method in different conditions.(3) Optimization of clamping sequenceThe clamping modes and clamping process of measuring fixture is analyzed, then the clamping sequence optimization model is established. The heuristic algorithm is introduced in the optimization of clamping sequence, which can greatly improve the optimization speed and make the optimization more meaningful for engineering application.(4) Application and validation of frontbodyDesigning the fixture location of frontbody. The deterministic locating layout is designed by using the locator-searching algorithm based on the available locating positions, then the clamping sequence of fixture is designed by using the heuristic algorithm. The variation of the gaps and flushes between different parts of frontbody is compared under the optimized location scheme and the current location scheme by using the combination of rigid variation modeling method. The results show that the variation control level of the optimized location scheme has greatly improved .