Optimization of adaptive control for spot welding

Sammanfattning: In December 2015 Scania Oskarshamn started production in their new facility for the body in white (BiW) production. Heat capacity control (HCC) is used to control the RSW process for all the welding robots in this facility for BiW at Scania Oskarshamn. HCC is a relatively new adaptive control system and Scania wants to optimize the process times for their RSW process using HCC. HCC is an adaptive control system which means that it changes parameters using input from data gathered in real time in order to form a weld of good quality with minimized occurrence of spatter. The drawback is that the process time cannot be set to a specific value. The process times can therefore get relatively long for difficult conditions. The purpose of this project was to investigate if Scania’s program for mild steels with a combined sheet thickness of under 3mm using the adaptive control system HCC could be optimized to reduce the process time for each weld by changing the welding parameters weld time and pause time.Four different research questions were formulated based on how the weld time and pause time affects the process time and quality of the welds. Demands in Scania’s standard for resistance spot welding STD4429 should also be fulfilled. • How does shorter weld times than used today affect the weld quality according to Scania standard STD4429, and how is total process time influenced? • How does longer weld times than used today affect the weld quality according to Scania standard STD4429, and how is total process time influenced? • How does shorter pause times than used today affect the weld quality according to Scania standard STD4429, and how is total process time influenced? • How does longer pause times than used today affect the weld quality according to Scania standard STD4429, and how is total process time influenced? Four different sheet combinations were tested in order to answer the research questions. Different test phases were conducted with both One-factor-at-a-time testing and design of experiments testing. Weld quality was assessed using peel testing, shear testing, metallography and hardness testing. Experimental results showed that the weld times could be reduced while still fulfilling the strength requirements set by Scania’s standard STD4429. The pause time could also be changed but results showed that sufficiently high pause times tend to give less variation in process time due to less variation in amounts of pulses used in the process. The results showed that approximately 17% shorter process times could be achieved with maintained strength in the welds.