Browsing by Subject "homopolar pulsed welding"
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Item Application of Homopolar Pulsed Power to Metals Joining(1983-04) Aanstoos, T.A.; Keith, R.E; Weldon, W.F.Homopolar generators (HPGs) presently being developed at the Center for Electromechanics are capable of delivering megampere pulses of electric current in a controllable manner. One application for these machines is as the power supplies for an industrial welding process. During the past five years, several research projects have been carried out to explore the welding capabilities of HPGs. Among the materials that have been welded are carbon and low alloy steels, several varieties of stainless steels, tool steels, nickel-base and molybdenum-base alloys, aluminum, and several dissimilar-metal couples. Among the shapes that have been welded are bars, sheets, plates, tubes, pipe, angle sections, and rails. The largest cross sections that have been welded to date are 9 in. 2 (2.9 tm2), and the smallest have been less than 0.3 in. (0.58 cm). Welding is accomplished in times approximating a second. Unique advantages of the homopolar pulse welding process are that it can be scaled upward to indefinitely large cross sections and that it does not impose a sudden load on the mains.Item Five-Megajoule Homopolar Upgrade(1981-06) Bullion, T.M.; Zowarka Jr, R.C.; Aanstoos, T.A.; Weldon, W.F.; Rylander, H.G.; Woodson, H.H.The five-megajoule homopolar generator (5-MJ HPG) designed and built in 1974 by the Center for Electromechanics at the University of Texas at Austin (CEM-UT) was the result of an engineering feasibility study that examined alternate means of pulsed energy storage for controlled thermonuclear fusion experiments. The machine proved very reliable and useful in a variety of applications, notably pulsed resistance welding, and was modified in 1978 to improve its flexibility and ease of maintenance. CEM-UT is now completing a major upgrading of this HPG to a hydraulically motored, 10-MJ, 47-V, 1.02-MA device capable of welding large-section, high-carbon railroad rail. This report considers the design and fabrication of the new rotor, shaft, brush mechanisms, field coil, making switch, busbar system, and control system, as well as the addition of the 31-MPa (4,500 psi) hydraulic motoring system. Future applications of the 10-MJ HPG are also discussed.Item Homopolar Pulse Welding of High Strength Steel Line Pipe(1988-04) Aanstoos, T.A.; Weldon, W.F.Item Homopolar Pulse Welding of Rail(1983-11) Aanstoos, T.A.; Weldon, J.M.The homopolar pulse welding process uses a single unidirectional, high current electrical pulse from a homopolar generator to heat the interface between two workpieces in solid contact. When the interface reaches an optimum temperature, forging pressure is applied, and the workpieces coalesce without melting and without use of either a flux or a filler. The weld is completed in from 1 to 2 s. Because current distribution and heat generation can be made uniform throughout the workpiece section, irregular sections such as rails can be welded. Ninety lbm/yd rail has been welded with the process using a 10 MJ homopolar generator. The welds were excellent metallurgically, but there were fixturing problems with mechanical clamping, alignment, and current delivery. A through-feeding fixture for welding pipe has been designed and built that successfully addresses these fixturing problems, and electrical contacts and clamps for welding rails are presently being designed. A compact system that could serve as the power supply for an in-track rail welding system has recently become commercially available.Item Homopolar Pulsed Welding for Offshore Applications(1990-02) Aanstoos, T.A.; Gully, J.H.; Harville, M.W.As a low impedance energy storage device, the pulsed homopolar generator (HPG) is capable of delivering a multimegawatt, megampere-current pulse into a resistive or inductive load with high efficiency. Such HPGs have been used for over ten years as power supplies for research in high energy, high-rate processing of metal alloy components and systems. Most of these processes rely on resistive heating during the current pulse to rapidly heat the material as required for a particular process. One such application is homopolar pulsed welding (HPW), a solid state, forged welding process in which heat generation is concentrated at the interface between workpieces as homopolar current is conducted between them. Because of the very high peak current and power (from 8 to 20 kA/cm2 and 50 to 100 kWfcm2), weld time is very short, reducing time-at-temperature exposure and related microstructural changes. Welding is accomplished in air, no flux or filler is used, and the interface disappears completely in a good weld. This paper reports on recent and ongoing research into the weldability by HPW of various alloys applicable to offshore systems, including stainless steel and titanium alloys, but primarily focusing on various grades of high strength steel pipe. The research includes an investigation of weld parameters, sensitivity of the process to the weld parameters, metallurgical and mechanical evaluation of weld quality, and the development of a real time quality assurance capability that can certify nondestructively an HPW weld before it is removed from the welding fixture. The research presented here is sponsored by the National Science Foundation (NSF) and various private industry companies.Item Homopolar Pulsed Welding for Offshore Applications(1991-09) Harville, M.W.; Trevisan, R.E; Gully, J.H.Item Homopolar Pulsed Welding for Offshore Applications(1990-10) Harville, M.W.; Gully, J.H; Aanstoos, T.A.As a low impedance energy-storage device, the pulsed homopolar generator (RPG) is capable cif delivering a multimegawatt, megampere-current pulse into a resistive or inductive load with high efficiency. Such HPGs have been used for over ten years as power supplies for research in high energy, high-rate processing of metal alloy components and systems. Most of these processes rely on resistive heating during the current pulse to rapidly heat the material as required for a particular process. One such application is homopolar pulsed welding (HPW), a solid state, forged welding process in which heat generation is concentrated at the interface between workpieces as homopolar current is conducted between them. Because of the very high peak current and power (from 8 to 20 kNcm2 and 50 to 100 kW/cm2), weld time is very short, reducing time-at-temperature exposure and related microstructural changes. Welding is accomplished in air, no flux or filler is used, and the interface disappears completely in a good weld. This paper reports on recent and ongoing research into the weldability by HPW of various alloys applicable to offshore systems, including stainless steel and titanium alloys, but primarily focusing on carbon-steel pipe. This research includes an investigation of weld parameters, sensitivity of the process to the weld parameters, metallurgical and mechanical evaluation of weld quality, and the development of a real-time quality assurance capability that can certify nondestructively an HPW weld before it is removed from the welding fixture. The research presented here is sponsored by the National Science Foundation (NSF) and various private industry companies.Item Homopolar Pulsed Welding for Offshore Applications(1991-11) Harville, M.W.; Trevisan, R.E; Gully, J.H.Item Homopolar Pulsed Welding of Steel Pipe: Effects of Controlled Parameters on Weld Properties(1992-06) Trevisan, R.E.; Harville, M.W; Gully, J.H.This paper reports on recent and continuing research into the optimization of the homopolar pulsed weld (HPW) process for welding 89-mm diameter, ASTM 1035 steel pipe. Present study characterizes the typical macro- and microstructure found in HPW and seeks to identify causes of low toughness. Metallurgical and mechanical evaluation indicated nonuniform heating around the circumference of the pipe. New electrodes were fabricated and shown to reduce circumferential nonuniformity in the weld specimens, and improve the weld repeatability. Several experiments were performed that varied process control parameters, one at a time, and identified the effects on weld properties. However, the process control parameters investigated did not improve the weld toughness. The reduced toughness at the weld line of the HPW process is attributed to the large grain size present on this region.Item Homopolar Pulsed Welding: Interface Properties of High Strength Steel Pipe, a Technical Note(1992-01) Trevisan, R.E.; Harville, M.W; Gully, J.H.This note discusses the microstructure, hardness, and toughness of a homopolar weld (HPW) performed on API 5L grade X-52 line pipe (90 mm diameter and 10 mm wall thickness). Homopolar welding is a solid state welding process made possible by a large pulse of direct current from a homopolar generator (HPG) The heat generated by electrical resistance leads to complex phase transformations resulting in different structures with different characteristics. The results show the weld properties are affected by the pipe materials and that HPW is a promising process for joining high strength steel pipe.Item Resistance Welding Using Homopolar Generators as Power Supplies(1976-11) Grant, G.B.; Brennan, M; Weldon, W.F; Rylander, H.G; Woodson, H.H.The University of Texas Center for Electromechanics (CEM) was originally formed to address the pulsed power requirements in the nuclear fusion research areas. It was determined that inertial energy storage using homopolar conversion could effectively meet these requirements. Two homopolar generators have been built and tested by the CEM; one is under construction and several others are scheduled to begin construction in mid-1977. The machines have been so successful that the CEM is now investigating other areas requiring high energy pulses. Many of these applications have previously been limited by availability of peak power, either by reason of existing technology or economics. One such area is resistance welding where we feel the present generation of homopolar generators offers the potential to significantly extend the limits of cross-sectional areas that can be successfully and economically resistance welded. Since homopolar generators are used effectively as energy storage devices, storing energy (inertially) slowly and then discharging it very quickly, they are ideal sources for the high power inputs required for resistance welds. This energy storage capability can eliminate demand charges when used in-plant and makes on-site resistance welding possible without requiring excessively large prime movers. The CEM has done some welding feasibility experiments using the 5 MJ homopolar generator. Thus far, one-inch bars (both 1018 steel and 304 stainless) , four-inch Schedule 80 304 SS pipe and four-inch Schedule 40 steel pipe have been welded. The pipe welds were completed in under one second at peak currents of up to 170 kA using less than 30% of the available energy in the 5 MJ machine. The design and construction of larger homopolars that could supply sufficient power and energy to resistance weld cross sections on the order of 100 in2 on the same time scale is a straightforward extrapolation of the existing technology.