
Title: An investigation into improving weld strengths during spot welding
Author: Arumugam, Aravinthan.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2003
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Spot welding is a process that is widely used in industries worldwide. This project aims to research and develop a control system to improve the strengths of the spot welds. Conventional (pneumatic) spot welding systems do not lend themselves towards in-process control specifically controlling the forging force during welding. The importance of the forging force is that it is related to the dynamic resistance and hence to the rate of heating of the weld as has been shown in this work. The use of the forging force to control weld strengths was investigated by converting the electrode actuating system of a pneumatic spot welder to a motor driven servo system. This enabled the electrode forging force to be varied during welding. The control system was used to vary the forging force during welding by means of various preset force profiles in order to vary the heating during welding. The effects of the various force profiles to heat generation and weld growth were studied by using the dynamic resistance curve. The relationship between resistance and force enables the dynamic resistance to be used as an indicator for weld performance. Experiments were carried out to propose the force profile that will give the highest weld strength. Results obtained from this project shows that two changes in the characteristics of the force profile, viz, the delay time before ramping and the rate of ramping, affects the amount of heat supplied to the weld during welding which causes change in the weld strength. Statistically significant differences between average weld strengths due to the changes in these characteristics are presented. Forging force control was also found to produce stronger welds compared to the conventional electrode clamping force (ECF) condition, which was found to be statistically significant. It was also found possible to extend the weld lobe region of the electrode clamping force (ECF) condition by using forging force control, to produce improved weld strengths at the no weld and expulsion regions of the lobe. The profile that starts with a lower force and ends with a higher force with a longer ramping delay and slower ramping rate was the profile that produces the strongest weld strength among all the profiles tested. This profile with a welding current below the expulsion limit was suggested as the strategy to produce stronger welds at a faster rate.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Forging force profile Manufacturing processes Reliability (Engineering) Robotics