4T焊接滾輪架機(jī)械設(shè)計(jì)
4T焊接滾輪架機(jī)械設(shè)計(jì),焊接,輪架,機(jī)械設(shè)計(jì)
A new generation of power supplies for electron beam welding machines
Jerzy Doraa, Jan Felbab, , and Wiktor Sielankoc
aDORA POWER SYSTEM, ul. Wyszyńskiego 110, 50-307 Wroc?aw, Poland
bFaculty of Microsystem Electronics and Photonics, Wroc?aw University of Technology, ul. Grabiszyńska 97, 53-439 Wroc?aw, Poland
cIndustrial Institute of Electronics, ul. D?uga 44/50, 00-241 Warszawa, Poland
Received 31 August 2004;? accepted 10 September 2004.? Available online 10 November 2004.
Abstract
Widely used electron beam welding machines are equipped with heavy power supplies, located in a special oil tank and connected with an electron gun to a high-voltage cable. A special system detects electric discharges in the electron gun space, which may arise during welding and then it tries to switch off the high voltage to interrupt an electric arc. Such disadvantages have been eliminated with the novel power supply described here. The Q of resonance circuit of this supply is stabilized and as a result circulating power appears. During an electric discharge in the gun, power is not sent to the electron gun but circulates between the electronic parts of the resonance circuit without losses and “waits” for the break in the short circuit. The power supply is much smaller and lighter than supplies of similar rating used nowadays. It is connected directly to the electron gun chamber without a high-voltage cable. The first construction of the supply was designed for electron beam welding machine of 5?kW power and 60?kV accelerating voltage. Tests of the new power supply in laboratory and industrial conditions have shown its usefulness for electron beam welding.
Keywords: Electron beam; Electron beam welding; Power supply
Article Outline
1. Introduction
2. State-of-the-art of a power supply
3. Power supply consideration
4. Model of the new power supply
5. Power supply in use
6. Conclusions
References
1. Introduction
Since the pioneering work on the development of high-power electron beam welding, the main effort of welding machine designers and constructors has been concentrated on the design of the electron beam generator. It consist of three distinct parts: the electron gun, where electrons are emitted, accelerated and formed into an electron beam, the gun power supplies and a beam transport system.
These requirements of electron beam technology and possibility of modelling the electron trajectories defined the principles of electron gun construction. Free electrons (emitted or extracted from heated, cold or plasma cathodes) acquire kinetic energy when they cross the electric field created between cathode and anode, which is usually connected to the ground. An additional electrode influences the shape of the electric field and controls the current of the electron beam. The gun's electrodes receive energy and power from a power supply unit. The beam transport systems facilitate the concentration of the energy of the beam to provide the deep penetration, necessary for welding, and play an important role in electron beam technology. The system deflects the beam and is able to acquire information from the welding point to give automatic focusing, seam tracing and power control of the beam. The progress in systems operation has been determined mainly by the developments in modern electronic devices and controlling computers.
Possible discharges in the electron gun space are some of the most important problems of electron beam welding. As a result of arcing a weld process may be discontinued. The repair of welded parts (if possible) is time and labour consuming. In order to prevent interruptions caused by arcing, constructors have proposed methods which limit the flow of metal vapour and gas into the gun space [1]. Much more effective results seem to be attainable if the power supply functions properly. This problem is driving the progress in constructions of power supply design for the next generation.
2. State-of-the-art of a power supply
The discharge between gun electrodes can be classified as micro-arcing, single or multi-arcing and a soft vacuum discharge. Conventional power sources are already practically resistant to micro-arcing. Also single and multi-arcing do not interrupt the welding process. Almost all charges are discharged in the output filter capacitors of such supplies and soon the gun recovers. Unfortunately, during a soft vacuum discharge, the breakdown has not been recovered by the time the power supply is restarted (several milliseconds) and the process of welding can be stopped. Prevention of interruptions because of such a discharge has been possible by making the arcing as short as possible, having lower stored energy and by resupplying power to the gun in a very short time.
There have been some systems constructed which meet the requirements. Paton Electric Welding Institute proposed a system in which the surge energy at arcing is absorbed by a vacuum tube [2]. The regulating lamp is controlled along a channel which protects the source of accelerating voltage and restricts the beam current. Such power sources have been used extensively in recent years [3]. As an alternative to a power supply with a tube, high frequency or switch-mode systems to decrease arcing energy were developed. MELCO proposed a system in which the period of interruption of power supply by arcing was extremely short. The system consists of a high-frequency power source to decrease the arcing energy and a transient signal controller which controls feedback signals at arcing and supplies power continuously and stably [4]. A switch mode accelerating voltage regulator, developed by Ferranti Sciaky, enabled a fast response and low-stored energy power supply to withstand arcing [5].
Generally, power supplies for welding machines working according to the above-mentioned principles have been in common use. The high-voltage part of the main and auxiliary supplies are located in a special heavy oil tank connected with an electron gun by a high-voltage cable. A large source of new high sophisticated electronic components and the idea of transferring some auxiliary supplies directly into the gun (e.g. TWI, Cambridge [6]) has made units become smaller, more reliable and resistant to arcing. Nevertheless, stored energy in a high-voltage tank and a cable is very detrimental to the operation of an electron beam gun and may have an influence on the welding process. Such disadvantages have been eliminated with the novel power supply described below.
3. Power supply consideration
The new power supply for electron beam welding machines is absolutely resistant to arcing, has exceptionally low dimensions and operates without a heavy oil tank, high-voltage cable or any special system to detect electric discharges.
The novelty of the presented supply is based on the resonance circuit [7]. In high-frequency resonance circuits, as a result of non-matching, reflected power is created. In the present case, the so-called circulating power appears due to the substitution of the reflected power by DC power which returns to the power supply.
If no stabilization of the resonance circuit takes place, the power circulates between the electronic parts of the resonance circuit and causes almost no losses in it. In the case of the electron beam welding process, all the power supply is used as the effective power. Each mismatch between the electron gun and the output of the power supply reflects circulating power. The maximum value of this power is when the soft vacuum discharge in the gun chamber occurs. This arcing may arise between cathode or control electrode and anode, as well as between all possible parts of the gun and insulator at high-voltage potential and the ground. As the power is not sent to the electron gun but circulates and is stored in the supply, the short circuit is immediately quenched.
The power supply has two parts. The high-voltage part, in the form of a cylinder filled with silicon oil, is joined mechanically with the electron gun chamber and connected with gun electrodes by vacuum culverts. The low-voltage unit can be installed directly within reach of the operator. Both parts are connected using an optical waveguide and conductors with breakdown voltage isolation less than 500?V.
The supplies of the indirectly heated cathode and control electrode are located in the high-voltage cylinder. For cathode heating a resonance circuit has also been used but, in this case, it is only there to give the possibility of calculating the feedback resonance between the primary and secondary winding of the heating transformer into the resonance circuit. Thus, the control electrode takes energy from the cathode supply. A schematic diagram of all units is presented in Fig. 1. The circuit diagram is available on the internet site [8].
Display Full Size version of this image (46K)
Fig. 1.?Schematic diagram of power supply.
4. Model of the new power supply
The new unit was designed with a power supply of 5?kW and 60?kV accelerating voltage for a triode electron gun with a directly heated cathode. The shapes of gun electrodes and distances between them had been optimized by measuring the electron beam emittance, which is a very sensitive figure-of-merit to detect any influence of geometrical and electrical gun factors on the quality of the electron beam [9]. The optimization procedure (applying the Taguchi method of experimental design) was to decrease the normalized emittance of the electron beam [10]. The heating of the tantalum cathode with 2×2?mm emitting surface in the gun needs power of 150?W, while the control electrode is supplied up to 2?kV. The power supply was constructed in the form of a cylinder of 160?mm diameter and 600?mm long (the high-voltage part) and 6U standard unit. Tests were performed on an electron beam welding machine of 10?kW and 80?kV designed and constructed by Wroclaw University of Technology. The results of the tests are given in Table 1.
Table 1.
Results of the tests
Type of test
Test result
Short-time stabilization test (60?kV, 3.6?kW, 15?min)
Voltage stability ?0 to +0.3%,
Short-time stabilization test (60?kV, 3.6?kW, 15?min)
Current stability ?0.5% to +0
Long-term stabilization test (60?kV, 1.2?kW, 1?h)
Voltage stability ?0.2% to +0
Long-term stabilization test (60?kV, 1.2?kW, 1?h)
Current stability ?0.5% to +0
Repeatability in cyclic work (60?kV, 4.5?kW, 2?min work +1?min break, 90?min)
Voltage stability ?0.3% to +0
Repeatability in cyclic work (60?kV, 4.5?kW, 2?min work +1?min break, 90?min)
Current stability ?0.2% to +0
Shape of welds (60?kV, different beam power, different welding speed, stainless steel)
Statistically the same as with standard power supply (400?Hz frequency motor generator) of the welding machine
Resistance to arcing (even with welding of high-pressure-vapor alloys, e.g. brass)
Short brakes in generating of electron beam have been visually observed, but without interrupting of the welding process, and with no disadvantageous effects to the weld.
All tests show the usefulness of the new power supply for electron beam welding. A power supply of 15?kW power and 120?kV accelerating voltage is now under design. It is estimated that it will be located in a cylinder of 300?mm×600?mm (the high-voltage part) and two 6U standard units.
5. Power supply in use
The power supply was adapted to the new electron beam welding machine, constructed by the Industrial Institute of Electronics in Warsaw. It is a fully automated unit for welding torsional vibration dampers for crankshafts of diesel engines with a yield of 50?000 pieces a year [11]. The device was installed in industry for mass production in 2001 and until now the reliability of the power supply is very high.
6. Conclusions
After testing the new power supply in laboratory and industrial conditions, it can be concluded that:
? all operating data of the supply are at least not worse than those for supplies presently in use,
? it is resistant to every kind of arcing which may appear in the electron gun space during the welding process,
? it operates without both a heavy oil tank and costly high-voltage cable,
? it is much smaller, lighter and cheaper than supplies of similar output presently in use.
References
[1] Fritz D, Nazarenko OK, Irie H, Abe N, Ohmine M. Proceedings of the sixth international conference on welding and melting by electron and laser beams, Toulon, 1998, p. 1.
[2] O.K. Nazarenko, A.A. Kayalov and C.N. Kovbasnko et al., Electron beam welding, Naukova Dumka, Kiev (1987) [in Russian].
[3] Kazakov VA, Zuev IV. Proceedings of the fifth international conference on beam technologies, Varna, 1997. p. 90.
[4] Kita H, Satoh S, Matsui S, Yasunaga S, Irie H. Electron and laser beam welding. Oxford: Pergamon Press; 1986, p. 149. Published on behalf of the International Institute of Welding.
[5] Ferrario JD, Kyselica SP, Lawrence GS. Proceedings of the fourth international colloquium on welding and melting by electron and laser beams, Cannes, 1988. p. 69.
[6] Sanderson A, Ribton CN. Proceedings of the sixth international conference on welding and melting by electron and laser beams, Toulon, 1998. p. 611.
[7] Dora J, Polish Patent nr 178285, 2000.
[8] www.lipec.info/powersupply.pdf.
[9] J. Felba, Vacuum 55 (1999), pp. 223–233. SummaryPlus | Full Text + Links | PDF (311 K) | View Record in Scopus | Cited By in Scopus
[10] Felba J, Friedel KP. Proceedings of the sixth international conference on welding and melting by electron and laser beams, Toulon, 1998. p. 603.
[11] W. Sielanko, A. Czopik, J. Felba and M. J?drzejczyk, Elektronika 12 (2002) (XLIII), pp. 36–39 [in Polish].
Corresponding author. Tel.: +48?71?3324488; fax: +48?71?3283504
收藏