RU2181647C2 - Method of press welding of workpieces heated by magnetic field controlled arc - Google Patents

Abstract

FIELD: mechanical engineering; welding. SUBSTANCE: invention can be used in automotive industry, construction of hot-water boilers, industrial and civil engineering, construction of pipelines using small and medium diameter pipe4s, welding of workpieces of solid and developed section, and T-joints. In process of heating, controlled shifting of workpieces to be welded is provided. Clearance between end faces of workpieces is maintained constant. Value of voltage across welding arc is considered as clearance control parameter. Required temperature on end faces of workpieces to be welded is determined by value of relative displacement of workpieces. When preset displacement values are obtained, speed of arc travel along end faces of workpieces under welding is programmed. EFFECT: improved quality of welded joints made by press welding with heating by magnetic field controlled arc. 2 cl, 1 dwg, 1 ex

Description

 The proposed method relates to methods of press welding, in which the source of heating of the welded products is a welding arc controlled by a magnetic field, and can be used in such sectors of the economy as automotive, boiler building, construction, in the construction of pipelines for connecting tubular and continuous sections, as well as for connecting parts to brands.

 A known method of welding by an arc controlled by a magnetic field, in which, in order to improve the quality of the obtained joints, audio signals are generated that are generated when the arc moves along the ends of the parts to be welded. In the process of arc burning, the frequency and strength of the sound change, the signal of the mismatch of the values of these parameters with the previously set ones is a criterion for controlling the current strength, voltage and the gap between the edges of the welded parts (GDR "Schweisstechnik" 6, 1980).

 The disadvantage of this method is the complexity of the control system, low repeatability of the method due to the acoustic properties of the measuring equipment and the premises in which the equipment is operated.

 Also known is a method of controlling the welding process by the energy input into the edges of the products (ZIS - Mitteilungen 10, 1982, pp. 1051-1055). The essence of the method is as follows.

 The converted voltage and current signals during heating are fed to a computing device, where the calculation of the power released at the edges of the parts to be welded takes place. Values are read every 0.1 s.

 In the process of heating, the accumulated values of power are reduced, reduced to the thermal energy released at the edges. The accumulated energy equivalent is analyzed in a computer and, as the calculated value is reached, serves as a parameter for controlling the heating process. The control system analyzes the compliance of the accumulated energy with the reference value obtained by calculation. If the accumulated energy deviates by more than 10% from the reference, the connection is rejected.

 The disadvantage of this control method is that during the heating of the edges the voltage and current do not remain constant, their value depends on the position of the arc relative to the section of the edges of the welded products. It was experimentally established that the voltage across the arc changes throughout the entire welding cycle, and this change has a characteristic dependence.

 In the course of laboratory studies, it was found that at the initial moment of the arc movement along the edges of the products, it moves from the outer edge of the section (for tubular products) to the inner one. In this case, the voltage deviations on the arc can reach 20% of the initial value, which is established at the time of the beginning of the stable movement of the arc along the ends of the products. It was also established that the quality of the compounds obtained largely depends on the position of the arc during heating relative to the cross section of the welded product. Thus, with the same energy spent on reaching the plastic state, the quality of the resulting compounds can have significant deviations.

 As a prototype of the claimed invention, a method of press welding with an arc controlled by a magnetic field is adopted, in which the parts to be welded are heated, the moment of reaching the required heating temperature at the ends of the parts being welded is determined, then the welding current is increased and the draft is produced (A.S. USSR 1692785 , 23 K, 9/08 of December 23, 1987. Authors: S. I. Kuchuk-Yatsenko, V. Yu. Ignatenko et al., Published on November 23, 91. Bull. 43). According to this method, the moment when the ends of the welded products reach a plastic state is determined by the magnitude of the voltage on the welding arc. The nature of the change in arc voltage during heating was experimentally determined (V.D. Taran, Yu.G. Gagen, M., Mashinostroenie, 1970, "Magnetically controlled arc welding").

 The method selected for the prototype is as follows.

 The method is based on the principle of thermal expansion, in which there is a decrease in the arc gap. With a single gap between the parts to be welded, the minimum arc voltage corresponding to the beginning of the melting of their ends is determined experimentally. At the moment when the minimum voltage on the arc, corresponding to the achievement of the plastic state of the ends of the products, is reached as the heating is achieved, the welding current (boost) is increased and the draft is made (compression of the welded products).

 The disadvantage of this welding method is the low stability of the process of moving the arc, which is especially important at the final stage of heating before upsetting to obtain high-quality compounds. In addition, the nature of the movement of the arc, and hence the stability of heating, is greatly affected by the condition of the ends of the welded products (the presence of braid, rust, etc.). It should also be noted the limited application of the method for welding tubular parts with a wall thickness of more than 5 mm due to thermal expansion and shortening of the arc gap during heating.

 The basis of the invention is the task of improving the method of press welding with heating by an arc controlled by a magnetic field, by controlling the movement of the parts being welded during the heating process and controlling the gap between their ends, which ensures a constant value of the welding voltage during the welding process and thereby increases the stability of movement of the welding arc along the edges of the products, allows you to maintain the value of the arc gap between the ends of the welded products and thereby exclude the influence of the state of their blood Mok, and also to eliminate a short circuit between the edges of the welded parts during their thermal expansion during heating, thereby ensuring the possibility of welding tubular parts with a wall thickness of more than 5 mm.

 The essence of the invention is that a method of press welding with an arc controlled by a magnetic field, in which the welded parts are heated, the moment of reaching the required heating temperature at the ends of the welded parts is determined, then the welding current is increased and the draft is produced, according to the invention, the heating process is carried out controlled continuous relative movement of the parts to be welded, while the gap between the ends of the parts is kept constant, using They determine the value of the magnitude of the voltage at the welding arc, and the moment of reaching the required heating temperature at the ends of the parts to be welded is determined by the value of the relative displacement of the parts, and upon reaching the set values of displacement, the arc speed along the ends of the parts to be welded is programmed.

 It was found that at the beginning of the heating process, the arc voltage increases with increasing speed of the arc. After some time, the voltage begins to decrease and decreases before the melting of the ends of the welded products begins. The nature of the change in arc voltage is identical for different materials and is determined by the fraction of thermal energy used to heat the products. The nature of the voltage change during heating depends on the physical and structural characteristics of the material (cross-sectional area, coefficient of linear thermal expansion, etc.).

To implement the proposed method, a device was manufactured, a block diagram of which is shown in the drawing, where
1, 2 - parts to be welded;
3 - movable clamping device;
4 - fixed clamping device;
5 - block voltage measurement on the arc;
6 - power amplifier UEGS;
7 - block UEGS.

9 - magnetic system;
8 - welding arc;
10 - block displacement sensor;
The method was carried out as follows.

 Initially, the products 1, 2 are installed end-to-end in the clamping devices 3, 4 of the welding installation. At the time of supplying the welding current, the voltage measuring unit on the arc 5 generates a motion control signal for the moving part 3 of the installation. Motion control is carried out through the interaction of blocks 6 and 7. The direction of movement in the initial phase of the process is determined as follows. If at the moment of supply of the welding current there is a short circuit mode, the movable part 3 of the installation moves back until the burning mode of arc 8 is established, until the voltage on the arc becomes equal to the reference, pre-set value in block 5, if it has place idle, there is a forward movement to a short circuit. The speed of movement of the moving part 3 is determined by the magnitude of the signal of the voltage mismatch on the arc 8 and the reference. With this method of controlling the excitation of the welding arc, a 100% stable initial phase of the welding process is achieved.

 After excitation, the welding arc begins to move along the edges of the parts to be welded under the action of the magnetomotive force created by the magnetic system 9. After a time of 1-2.5 s, the movement of the arc passes from the acceleration phase to the phase of steady motion along the edges of the parts.

 At the beginning of this stage, the displacement sensor unit 10 measures the amount of movement of the moving part of the installation relative to the initial position (the moment of arc excitation). The obtained value is stored in the block of the motion sensor 10.

 As the ends of the welded products are heated by block 5, the arc voltage is monitored and maintained constant within 1 - 5% of the reference value. The speed of the system for measuring the voltage on the arc and controlling the movement of the movable part 6, 7 allows you to track and work out disturbances lasting less than 0.2 s, which contributes to the stable movement of the arc.

 According to the invention described in the prototype, as the products are heated due to thermal expansion, the arc gap decreases. In the proposed technical solution due to the continuous movement of the movable part 3 of the installation according to the magnitude and sign of the error signal, it is kept constant, which is especially important at the final stage of heating, when at the time of reaching the required heating temperature of the welded products due to thermal expansion, especially when welding tubular products with a thickness walls of more than 5 mm, shorting of the arc gap begins.

 At the moment determined by the thermal expansion of the products, and accordingly by the relative displacement of the movable part 3 of the installation, by the value of the displacement determined by the displacement sensor unit 10, an abrupt increase in the welding current (forcing) occurs, accompanied by an intense discharge of liquid metal from the gap between the parts to be welded, leads to a sharp increase in the arc gap, at a time when the total shortening of the parts is 0.5 ... 4.5 mm (this value depends on the sizes and material from division, which is controlled by the displacement sensor unit 10 of the movable part of the installation 3, there is a draft and after a time of 0.1 ... 0.3 s, the welding current is turned off.

 An example implementation of the method.

 The parts to be welded, in this case, pipes with a diameter of 42 mm and a wall thickness of 4 mm from Steel 20, were installed end-to-end in the clamping devices of the laboratory unit.

 When the welding current was applied, the movable clamp moved backward, forming a gap between the parts to be welded, at which the voltage on the excited welding arc reached 24 V. The arc, under the action of the magnetomotive force created by the magnetic system, began to move along the ends of the pipes being welded. To stabilize the movement of the arc at the initial stage of the welding process, the movable clamp of the installation moved according to the value of the monitored voltage on the welding arc.

 The position of the movable clamp at the time of stabilizing the movement of the arc along the edges of the parts was monitored by a displacement sensor and served as the basis for measuring the relative displacement of the movable clamp during heating. When the relative displacement equal to 0.8 mm is reached during heating, due to the thermal expansion of the pipes, the control unit issued a command to jumpwise increase the welding current (boost). The position of the movable clamp, measured at that moment by the displacement transducer, served as the basis for determining the moment of upset. During forcing, when the total shortening of the parts to be welded due to the intense ejection of liquid metal from the arc displacement zone was 2.5 mm, a command was issued to compress the parts (draft). After a time of 0.3 s, the welding current was turned off.

 This ended the welding process. The control circuit tracked the expansion of the welded parts and the opening of the clamps. The magnitude of the shortening of the welded parts was 6 mm. Parts were compressed at a speed of at least 150 mm / s with a force of 25,000 N. The total welding time was 10 s.

 Tests of welded samples of parts were carried out in accordance with applicable standards and rules.

 Analysis of the welded joints of pipes made using the prototype and the proposed method showed that the quality of the joints made by the proposed method is higher.

 Improving the quality of joints was achieved by a more accurate determination of the moment when the edges of the welded parts reach a plastic state and more stability of the process of moving the arc, especially at the final stage of heating, before forcing.

The proposed method has the following compared with the prototype advantages:
1. High process stability in the initial phase (arc excitation).

 2. Stable uniform heating of product edges over the entire cross-sectional area.

 3. High accuracy in determining when the edges reach a plastic state.

 4. Stable arc movement.

5. High accuracy of determining the moment of start of precipitation
6. Low requirements for the preparation of the edges of the parts to be welded (rust and braid up to 1.5 mm are allowed).

 7. A wider range of welded products due to the possibility of welding parts with a larger cross-sectional area.

Claims (2)

 1. A method of press welding with heating by an arc controlled by a magnetic field, in which the parts to be welded are heated, the moment of reaching the required heating temperature at the ends of the parts to be welded is determined, then the welding current is increased and a draft is produced, characterized in that the process is controlled continuously the relative movement of the parts to be welded, while the gap between the ends of the parts is kept constant, as a parameter for controlling the magnitude of the gap, use the value of tension on the welding arc.  2. The method according to p. 1, characterized in that the moment of reaching the required heating temperature at the ends of the parts to be welded is determined by the relative movement of the parts, and upon reaching the set values of movement, the arc speed along the ends of the parts to be welded is programmed.