Plasma Electron Beam Welder for Space Vehicles Final Report

Feasibility of developing plasma electron beam welding system for earth orbiting vehicl

DC-DC Power Converter Design for Application in Welding Power Source for the Retail Market

The purpose of this study is to design and analyze a DC-DC power converter for application in a welding power source that is cost-competitive with the more traditional, lower-tech welding power source topologies. This thesis first presents a background study of recent design approaches to DC-DC power converters, as they relate to application in welding power converters. The background study also surveys recent design approaches to welding power source controls. Evaluation of available options in DC-DC converter topologies and switching schemes for application in a welding power source is presented. Design methodology of a low-cost DC-DC converter for application in a welding power source is explained in detail. The design criteria are presented, and systematically solved for using a combination of electrical theory and computer-based modeling. The power converter design is modeled and verified through simulation. An economic analysis of the design proves it to be economically feasible, but still not as inexpensive as traditional, lower-tech solutions currently in use in the arc welding retail market. The most expensive component of the design is the power switching components, which have the potential for further cost reduction, and is recommended as future wor

Arc behaviour and metal transfer of the VP-GMAW process

This project evaluated the metal transfer behaviour of the variable polarity (VP) GMAW process. Analysis was performed using high speed video that was synchronised with high speed data acquisition. Melting rate measurements were found to be very dependent on current waveform, polarity, and droplet size, and metal transfer if it occurred, for each waveform period. The transient conditions of current waveform and metal transfer produced rapid changes in arc behaviour which influenced the melting at the electrode tip and growing droplet. The concentrated melting theory was developed to explain the significant increase in electrode extension burnoff and droplet growth rate that occurred at short EN time as a function of current, and during EP peak pulse when the pre-pulse droplet volume was small. The highest electrode extension burnoff and droplet growth rate occurred when the arc was permitted to climb over the solid electrode tip producing rapid concentrated melting. Likewise, large molten droplets were found to promote a negative electrode extension burnoff and a decreased droplet growth rate. The arc rooted on large droplets providing additional heating but limited electrode melting. The droplet burnoff rate (DBR) method was developed and found to yield good experimental measurements for the arc and resistive heating coefficients used in a 2nd order melting rate equation developed for a complex waveform process, like VP-GMAW. For the EN period, the EN time affected the melting rate as a function of EN current. The greater melting rate that occurred at low EN time was measured by the changes in the resistive heating coefficient. Concentrated arc melting of the electrode extension at low EN time caused the slope of the burnoff diagram to increase, which represented the resistive heating coefficient. The melting rate of the EP pulse was related to the pre-pulse droplet volume. Large pre-pulse droplets decreased the arc heating coefficient, which could be negative, which meant the electrode extension was increasing and the arc length was decreasing in that waveform period. VP-GMAW power supplies offered stable operation for welding sheet structures on both carbon steel and stainless steel. Higher travel speeds were required as the %EN of the waveform increased to produce acceptable constant deposit area fusion. Welding speeds were up to 300% higher with VP-GMAW compared to the GMAW-P process when welding lap joints on 1.8 mm thick material with a 1.8 mm gap. VP-GMAW heat input was up to 47% less than GMAW-P for the same melting rate

Systems to Control Molten Metal Transfer in Arc Welding

The paper analyzes the systems used for controlling molten wire metal droplets during the arc welding process in shielding gases. The variations for implementing the relevant systems are given, with the positive and negative aspects of such implementation taken into account. Electrical systems are currently investigated to the fullest extent possible and implemented in different power sources for pulsed welding arc. Mechanical systems are represented by different types of feeders that provide the pulsed wire feeding process. The feed mechanisms driven by electric motors and electromagnets are analyzed. In addition to the mechanical and electrical systems, the examples of combined control systems are given

A two-stage power converter for welding applications with increased efficiency and reduced filtering

The power supply technology used in welding applications changed dramatically from manually tap-controlled 50Hz bulky transformers which had large leakage inductance to provide stable arc burn to switch-mode fast controlled highfrequency power electronics. Nowadays, the typical converter configuration consist of a diode rectifier supplying via a large electrolytic capacitor a smooth DC-link voltage to a high switching frequency H-bridge inverter that steps down the voltage and provides isolation via a high frequency transformer whilst operating with adjustable dutycycle to maintain the output current constant. This topology allows for important size reduction since the size of magnetics decreases rapidly with the increase of the frequency. This paper proposes a more complex two-stage configuration with a buck DC/DC converter operating at a reduced switching frequency to feed adjustable voltage to an H-bridge inverter, which is operating always with the required voltage at 50% dutycycle, enabling in addition the minimization of the output filter size and of the switching losses

Control and Power Supply for Resistance Spot Welding (RSW)

In the automobile industry, Resistance Spot Welding (RSW) is widely used for its low cost, high speed, simple mechanism and applicability for automation. RSW has become the predominant means of auto body assembly, resulting in two to six thousands spot welds performed on each manufactured car. In the North American automobile industry there are approximately 100 billion spot welds, which are done every year. RSW is the joining of two or more metal parts together in a localized area by resistive heating and pressure. Small Scale RSW (SSRSW) is commonly used for medical devices and electronic components, because the welded parts are thinner and smaller compared to common RSW applications, such as automotive applications. According to a study of Edison Welding Institute, 20% of the welding quality issues are the weld schedule or power supply related. Therefore, to contribute to weld quality improvement, the study of different weld schedules or power supplies and control schemes needs to be improved by doing further studies in this area. Thus a novel power supply, which can provide a testing bench for these studies, was designed and developed in 2005 by L. J. Brown and J. Lin. This research study will focus on studying and improving weld power supplies, weld schedules and control modes. One of the goals for this research is to improve the consistency of weld nugget size and strength by using different control parameters, which will be weighted geometric averages of voltage and current. These control parameters are fed back to a Proportional Integral Derivative (PID) controller that is designed to control the Direct Current (DC) power supply for the RSW to come up with the best control parameters that will improve the consistency of the RSW spot welds. Another goal for this research is it to further develop the existing DC power supply that was designed for SSRSW by L. J. Brown, to include tip voltage measurements, and Large Scale Resistance Spot Welding (LSRSW). This goal will lead to build additional weld modules to construct a 6000A welder in the future

A two-stage power converter for welding applications with increased efficiency and reduced filtering

The power supply technology used in welding applications changed dramatically from manually tap-controlled 50Hz bulky transformers which had large leakage inductance to provide stable arc burn to switch-mode fast controlled highfrequency power electronics. Nowadays, the typical converter configuration consist of a diode rectifier supplying via a large electrolytic capacitor a smooth DC-link voltage to a high switching frequency H-bridge inverter that steps down the voltage and provides isolation via a high frequency transformer whilst operating with adjustable dutycycle to maintain the output current constant. This topology allows for important size reduction since the size of magnetics decreases rapidly with the increase of the frequency. This paper proposes a more complex two-stage configuration with a buck DC/DC converter operating at a reduced switching frequency to feed adjustable voltage to an H-bridge inverter, which is operating always with the required voltage at 50% dutycycle, enabling in addition the minimization of the output filter size and of the switching losses

Metal Transfer in Arc Welding

A double pulse welding current method is disclosed for the generation and transfer of droplets of welding metal from an electrode wire to a workpiece in an arc welding process. A suitable background direct current level is specified to deliver a desired number of droplets to the weld site. During each cycle of droplet formation and transfer, a first increased current pulse is applied to the electrode and arc to generate a droplet on the tip of and electrode and then a second further increased current pulse is applied to timely separate the droplet from the electrode for transport in the arc to the workpiece. This double-pulse current application reliably produces one droplet per cycle of pulses to deliver a specified number of droplets to the weld site for improved weld quality and reduced spatter or waste of weld metal