Fixture configuration design for sheet metal assembly with laser welding

Sheet metal laser welding has gained acceptance for meeting the increasing demands for high weld quality in the assembly process. Current stamping processes cannot meet the metal fit-up specification that laser welding requires. Assembly fixture will play a critical role in both control of assembly variation and improving Degree of Metal Fit-up (DMF). A new assembly system using OCMM and flexible fixtures for laser welding is proposed. Different cycles of the same assembly will result in different fixturing schemes that can be accommodated by adjusting the flexible fixtures. A new locating scheme with both total locating and direct locating for welds is proposed. The total locating scheme is used to locate the entire sheet metal assembly. The direct locating scheme is used to locate the weld joints to meet the metal fit-up requirement.; A finite-element (FE) model and a prediction and correction method for direct locator configuration are developed in the general fixture design. In the optimization for fixture configuration design, both number and location of the locators concerned are taken as design variables. Genetic algorithm (GA) is employed as the optimal procedure. In order to reduce the sensitivity of the performance characteristic of DMF to the location fluctuation of designed locators, a generic robust design method, a two-stage response surface methodology, is developed for the robust fixturing design. An optimal objective combining both robustness and performance is derived to determine the robust design space. Instead of the experience-based determination of the weld pattern a new design approach of the assembly weld pattern is developed. At last, a case study with the cross member assembly is presented, the results of the case study show that the proposed fixturing methodologies are effective in meeting the requirement of sheet metal assembly with laser welding.