Biuletyn Instytutu Spawalnictwa No. 01/2012

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of energy in one pulse, particularly through defining the value and location of the peak power sector of a pulse. The shape of a laser beam pulse influences the geometry of a weld and the conditions of weld crystallisation. The manner of this influence varies depending on materials, their chemical composition and state of delivery. Changing a pulse shape can help limit or eliminate welding imperfections characteristic of some metals and their alloys. The selection of pulse shape is conditioned by the rate of the change of power in time, particularly in a pulse section of descending characteristic. Pulses of complex characteristic in the area of gradual power decrease may prove their usability in the welding of numerous materials. References 1. Tzeng Y-F.: Parametric analysis of the pulsed Nd:YAG laser seam-welding process. Journal of Materials Processing Technology 102 (2000). 2. Banasik M., Dworak J., Stano S.: Badania procesu spawania laserem impulsowym wybranych materiałów konstrukcyjnych /Tests of welding selected structural materials with pulse laser. Praca badawcza nr /Research work no./ Ci-18 (ST-279/10). Instytut Spawalnictwa, Gliwice, 2010. 3. Zhang J., Weckman D.C., Zhou Y.: Effects of temporal pulse shaping on cracking susceptibility of 6061-T6 aluminium Nd:Yag laser welds. Weld.J., 2008, nr 1. 4. Naeem M. Controlling the Pulse in Laser Welding. weldingdesign.com/equipment-automation/news/wdf_11036. 5. Lienert T.J., Lippold J.C.: Improved weldability diagram for pulsed laser welded austenitic stainless steels. Science and Technology of Welding and Joining, 2003, vol 8, nr 1. 6. Laser beam welding: benefits, strategies and applications. Weld., J., 2007, nr 5. 7. Tzeng Y-F.: Pulsed Nd:YAG Laser Seam Welding of Zinc-Coated Steel. Weld., J., 1999, nr 7. 8. Tzeng Y-F.: Effects of operating parameters on surface quality for the pulsed laser welding of zinc-coated steel. Journal of Materials Processing Technology 100 (2000). 9. Bley H., Weyand L., Luft A.: An alternative approach for the cost-efficient laser welding of zinc-coated sheet metal. Annals of the CIRP, 2007,vol., 56, nr 1. 10. Malek Ghaini F., Hamedi M.J., Torkamany M.J., Sabbaghzadeh J.: Weld metal microstructural characteristics in pulsed Nd: YAG laser welding. Scripta Materialia 56, (2007). 14 BIULETYN INSTYTUTU SPAWALNICTWA NR 01/2012
Antoni Sawicki Modified Habedank and TWV hybrid models of a variable length arc for simulating processes in electrical devices Introduction The multiplicity, complexity, and problematic measurability of the characteristics of processes in arc discharges entails the necessity of applying various methods of mathematical description and quantitative analyses. Numerous physical processes including electromagnetic, thermal, gasodynamic, and acoustic as well as the mechanical processes take place in the plasma and electrodes. The complexity of such processes results from significant nonlinearities of static and dynamic characteristics, collectiveness, and interaction of plasma components as well as from the very short relaxation times of the elementary processes. Difficulties in measurability are caused by high temperatures, strong heat (and light) emission, significant gas flow rates, high quantity gradients in state variables, very high chemical reaction rates, occasional difficulties in accessing sensors (including optical ones) to a discharge area because of its small size or the fact of being closed. Due to this and depending on the needs in designing the power-supply and control systems of elecrotechnological devices, one adopts various simplifying assumptions leading to various degrees of approximation of physicochemical phenomena using mathematical models. The simplest and most commonly applied models include those of Cassie-Berger and Mayr-Kulakov. However, approximations obtained using these models are often considered to be very rough in relation to needs connected with designing and building various measuring, supply, and control systems; this being caused by a necessity to apply various electric excitations and various conditions of arc burning in devices. For this reason, various modifications of equations and new mathematical models of arcs have been proposed. Most of the existing arc models (i.e. also those by Cassie-Berger and Mayr-Kulakov) take into consideration only one manner of heat transfer, either conduction or convection, regarding each of them as dominant in a variety of technological conditions. The Cassie-Berger model provides more satisfactory results in cases when strong currents are required, whereas the Mayr-Kulakov model is preferred when weak currents are preferred. Such an approach to modelling is justified by an experimentally confirmed assumption, according to which there is a boundary between a column of thermal plasma and a turbulent gas flow around it [1]. The extension of the applicability area of widely known simplified Cassie-Berger and Mayr-Kulakov models required the development of several associations. One of them is the series connection of two resistances corresponding to the nonlinear Cassie-Berger and Mayr-Kulakov models suggested by Habedank. This combined model, however, lacks appropriate physical interpretation of phenomena present in the column. A more rational solution to the issue of generalisation of description of processes taking place in the arc Dr hab. inż. Antoni Sawicki, professor at Częstochowa University of Technology – Częstochowa University of Technology, Faculty of Electrical Engineering NR 01/2012 BIULETYN INSTYTUTU SPAWALNICTWA 15
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Page 3 and 4: Summaries of the articles J. Dworak
Page 5 and 6: Jerzy Dworak Research Impact of las
Page 7 and 8: cess being carried out at a specifi
Page 9 and 10: pulses up to several dozen millisec
Page 11 and 12: ectangular pulse, P i max =702 W, p
Page 13: ectangular pulse, P i max =1752 W s
Page 17 and 18: 1 dr r dt - in the resistance form
Page 19 and 20: The conditions of the selection of
Page 21 and 22: Similarly as previously (37), one c
Page 23 and 24: Eugeniusz Turyk, Agnieszka Żydzik-
Page 25 and 26: gical weldability, confirmed by the
Page 27 and 28: Damage was also caused to the welde
Page 29 and 30: Initial selection of method for wel
Page 31 and 32: Fig. 19. Assembly table with fixed
Page 33 and 34: Agnieszka Kiszka, Tomasz Pfeifer Va
Page 35 and 36: Fig. 4. Course of changes in curren
Page 37 and 38: extreme, the process was less stabl
Page 39 and 40: Fig. 13. Macrostructure of T-shaped
Page 41 and 42: L=1 mm, I=25 A L=1 mm, I=50 A L=1 m
Page 43 and 44: case of TIG welding (for similar we
Page 45 and 46: Other, equally important research i
Page 47 and 48: tion of a function connected with t
Page 49 and 50: The intensity of arc radiation was
Page 51 and 52: On the basis of calculations (Table
Page 53 and 54: NR 01/2012 BIULETYN INSTYTUTU SPAWA
Page 55: INSTYTUT SPAWALNICTWA The Polish We

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