Abstract: In order to improve the simulation accuracy of air conditioner and enable simulation to be widely applied in product development. Take the bottom plate of outdoor air conditioning units as the research object and analyzes the applicability of four common spot welding simulation units. Firstly, conduct free mode testing on the physical object to measure the natural frequencies of each order. Secondly, four types of spot welding FEM are established at the actual spot welding positions, and free mode simulations are performed to calculate the natural frequencies of each order. Finally, based on experimental testing, compare the error results of four simulation units. The results show that the ACM unit was used to simulate the bottom plate welding which got the highest accuracy, the average error of the first five orders of the mode is 1.09%, the average error of the first 5 modes simulated by RBE2 unit is 2.55%. the average error of the first 5 modes simulated by Beam element is 3.78%, the average error of the first 5 modes simulated by CWELD unit is 1.48%, the research results can provide reference for the application of welding constraints in simulation.

Key words: Sheet metal, Spot welding, Natural frequency, Modal