This paper details the failure analysis of deformed passenger car door lock case and presents a solution to avoid the part deformation during caulking process. This failure was observed during the assembly of case and its cover by caulking process. Mechanical properties and chemical composition of case (Zn Al4 material) has been checked by universal testing machine and spectra material analyser. The material composition having less aluminium content leads to the casting strength and cast ability losses. In order to get the exact load requirement for caulking process, analysis has been carried out by using finite element method. In finite element method, the case and case cover model has created by AUTODESK INVENTOR and stress analysis was carried using same software. The induced stress and deflection are obtained for various load conditions. The experimental measurement was taken from the machine by using load cells. By comparing the experimental data with FEM data we found that the problem happened due to the overload. From this result data the machine design was optimized by changing booster and cylinder which is used to generate the load. The hydro pneumatic circuit of the caulking machine has been optimized and redesigned to avoid future problems.