Electric heating – Metal heating – By arc
Reexamination Certificate
1999-01-21
2001-04-03
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S061000
Reexamination Certificate
active
06211489
ABSTRACT:
The proposed method belongs to press welding processes in which the source of heating of the parts being welded is the magnetically impelled welding arc, and it can be applied in such industries as car-making, boiler-construction, building industry, in the construction of pipelines, for joining parts of the tubular and solid cross-section, as well as for parts joining to form a tee-joint.
Known is the process of welding by the magnetically impelled arc, in which the sound frequency signals are used in order to improve the quality of the produced joints, the signals being generated during the arc displacement along the edges of parts being welded. The sound frequency and volume change during arcing, the signal of mismatch between the values of these parameters and the preset ones, is the criterion for controlling the current, voltage and size of the gap between the edges of parts being welded (GDR, “Schweisstechnik”, #6, 1980).
The disadvantage of this method is the complexity of the control system, low repeatability of the process because of the acoustic properties of the instrumentation and premises in which the equipment is operated.
Also known is the method of controlling the welding process by the energy Input into the item edges (ZIS -Mitteilungen #10, 1982, pages 1051-1055). The essence of the process is as follows. The converted signals of voltage and current during heating arrive to the computer where the power evolved in the edges of parts being welded, is calculated. The readings are taken every 0.1 s. During heating the derived power values reduced to the thermal energy evolved on the edges, are accumulated. The accumulated energy equivalent is analyzed by the computer, and, as the calculated value is reached, it serves as a parameter for controlling the process of heating. The control system analyzes the correspondence between the accumulated energy and the reference value derived through calculations. In the case of deviation of the accumulated energy value by more than 10% from the reference one, the joint is rejected.
The disadvantage of this control process is the fact that during the edges heating, neither the voltage, nor the current remain constant, their value depends on the arc position relative to the cross-section of the edges of items being welded. It is experimentally established that the arc voltage varies during the entire welding cycle and that this change has a characteristic dependence.
During laboratory studies, it was found that at the initial moment of the arc displacement along the items edges, it shifts from the outer edge of the section (for tubular items) to the inner one. Here, the arc voltage deviations can reach 20% of the initial value, which is established at the moment of the start of the stable arc movement along the item edges. It was also established that the quality of the produced joints is largely dependent on the arc position during heating relative to the section of the item being welded. Thus, with the same energy spent to achieve the plastic state, the quality of the produced joints can have vary considerably.
Taken as the prototype of the claimed invention, is the process of magnetically impelled arc butt welding in which the parts to be welded, are heated. Here, the moment of achievement of the required heating temperature on the edges of the parts being welded, is determined, and then the welding current is increased, and upsetting is performed (USSR A.C. # 1692785 V23 K 9/08 of 23.12.87. Authors: S. I. Kuchuk-Yatsenko, V. Yu. Ignatenko, et al., publ. 23.11.91. Bul. #43). According to this method, the moment of achievement of the plastic state by the edges of items being welded, is determined by the value of welding arc voltage. The nature of arc voltage variation during heating was experimentally determined (V. D. Taran, Yu. G. Gagen, M. Mashinostrojenie, 1970, “Magnetically impelled arc welding”). The process taken as the prototype, is implemented as follows:
The process is based on the principle of thermal expansion which leads to the arc gap narrowing. The minimal arc voltage corresponding to the start of part edges melting, is determined experimentally with the same gap between the parts being welded. When during heating, the minimal arc voltage is reached, which corresponds to achievement of the plastic state of the items edges, the welding current is increased (boosting) and upsetting is performed (pressing together of the items being welded).
The disadvantage of this welding process is the low stability of the process of arc displacement, which is especially important at the final heating stage prior to upsetting for production of sound joints. Furthermore, the nature of arc displacement, and, therefore, the heating stability, are greatly influenced by the condition of the edges of items being welded (presence of skewing, rust, etc.). Note also the limited applicability of the process for welding tubular parts with more than 5 mm wall thickness, because of thermal expansion and shorting of the arc gap during heating.
The invention is aimed at improvement of the process of magnetically impelled arc butt welding, by controlling the displacement of the parts being welded during heating and monitoring the size of the gap between their edges, thus providing the constant value of welding voltage during welding, and, thereby, improving the stability of the welding arc displacement along the items edges, allowing the arc gap between the edges of the items being welded to be kept constant, and thus eliminating the influence of the condition of their edges, as well as preventing the short-circuiting between the edges of the parts being welded at their thermal expansion during heating, thereby providing the capability of welding the tubular parts with more than 5 mm wall thickness. The essence of the invention consists in that the process of magnetically impelled arc butt welding, in which the parts being welded are heated, with determination of the moment of achievement of the required heating temperature on the edges of the parts being heated, then the welding current is increased and upsetting is performed, according to the invention during heating the controlled continuous displacement of the parts being welded is carried out, here the gap between the edges of the parts is kept constant, the welding arc voltage being used as the parameter for the gap size adjustment, and the moment of achievement of the required heating temperature on the edges of parts being welded, is determined by the value of relative displacement of the parts, and when the preset displacement values have been achieved, the speed of the arc movement along the edges of parts being welded, is programmed.
It is found that at the start of the heating process, the arc voltage rises with the speed of the arc displacement. After some time, the voltage starts decreasing, and keeps dropping until the start of melting of the edges of parts being welded. The nature of the arc voltage variation is identical for various materials and is determined by the share of thermal energy consumed in the items heating. The nature of voltage variation during heating depends on the physical and structural characteristics of the material (cross-sectional area, linear thermal expansion factor, etc.).
REFERENCES:
patent: 5117084 (1992-05-01), Kuchuk-Yatsenko et al.
Ignatenko Vadim Yurjevich
Kachinskii Vladimir Stanislavovich
Koval Mikhail Pavlovich
Kuchuk-Yatsenko Sergei Ivanovich
E.O. Paton Electric Welding Institute of the National Academy of
Jacobson Price Holman & Stern PLLC
Shaw Clifford C.
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