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.

The purpose of this study was to measure the change in joint energy of the hip,knee and ankle of the right and left leg, in the sagittal plane during the delivery phase of the rotational shot put. We hypothesized that (1) throwers who produced a greater total hip energy change would have greater horizontal displacement and (2) throwers who produced a higher ratio of hip energy, in each leg independently, would produce greater horizontal displacement. Subjects (n = 8) must have been right-handed, collegiate or post collegiate level throwers trained in the rotational technique. Vicon Nexus System (Denver, CO, USA) used six MX13+, two F20, two T20 cameras recorded at 240 Hz, and the body Plug-in Gait model to track the body position during each trial. Two AMTI force plates (OR-6, Watertown, MA, USA) were used for collecting ground reaction force data at 960 Hz. A linear regression analysis was performed to determine a relationship between total hip energy change and horizontal displacement. A mixed model regression was used to determine any correlation between horizontal distance and left and right energy change ratios. Athletes who produced a greater total hip energy change had the greatest horizontal displacement (p = .022). Also throwers who produced a higher ratio of left hip energy change to total left leg energy produced the greatest horizontal displacement (p = .02). The ratio of right hip energy change to right leg energy change was found to not be significant to horizontal displacement (p = .955). We feel the findings on the left leg energy change are an attempt by the athlete to both accelerate the shot put as well as stop the rotational progression to allow the athlete to complete a fair throw. The athlete extending both the right and the left hip rapidly during the delivery phase can help explain the combined right and left hip energy change. This action accelerates the ball in a proximal-distal sequence, which allows athletes to reach high final shot put velocities. The higher the final velocity on the shot put positively correlates with the horizontal displacement.