RU2191099C2 - Method or resistance arc welding of fasteners - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: invention can be used at manufacture of automobiles, cases of instruments and outer equipment. After striking of welding arc, welding voltage and current are measured to determine instantaneous power and evaluate amount of energy liberated in arc gap. After forming of liquid metal pool, part is moved trill contact with workpiece surface with simultaneous application of pressure. At obtaining mismatch with preset definite values, parameters are corrected to bring energy to nominal value. Integrated value of instantaneous power is determined additionally and result obtained is compared with threshold value for combination "part diameter - sheet thickness". Signal is generated to complete welding cycle. Welding current is switched off after a certain period of time from reception of signal on short circuit. EFFECT: provision of high quality of welded joints at variations of operating conditions. 3 cl, 1 ex, 2 dwg

Description

 The invention relates to the field of welding and can be used for welding fasteners (bolts, studs, pins, etc.) to various products in the manufacture of car bodies, control cabinets, instrument housings and equipment at enterprises of various industries.

 A known method of electric arc welding of studs, including the excitation of the auxiliary arc between the stud and the product when lifting the studs, moving the studs towards the product, the excitation of the main arc between the product and the end face of the studs, immersion of the studs in the molten metal bath formed on the surface of the product, and during the process of moving the studs towards the part measure the voltage drop in the arc gap of the auxiliary arc, the sum of the voltage drops in the pin contact is subtracted from the obtained value the part and at the moment when the calculated difference is 10-90% of the initially obtained voltage drop, the capacitor begins to discharge [1].

 In this method of electric arc capacitor welding, the amount of energy that must be released in the arc gap in advance is set by the value of the charging voltage of the capacitors. The ignition of the main welding arc (discharge of capacitors) occurs when the desired value is reached by the voltage drop on the auxiliary arc, which is controlled by the control system. In this case, the process of discharge of capacitors is uncontrollable, and the value of real heat input is not regulated.

 A known method of controlling the process of welding bolts, providing for the issuance during the general operating cycle of the position of the bolt holder in a control device, where it is compared with a given dependence of the path on time, after which the difference signal controls the lifting magnet, which releases the spring when the latter brakes the holder subject to the given ratio [ 2]. When compressing the bolt, you can save the specified length of the welding arc using the position sensor, regardless of the tolerances of the bolt.

 In this method, the controlled parameter is the amount of movement of the movable pistol rod with a bolt holder attached to it. This makes it possible to stabilize the length of the arc gap (i.e., arc voltage) and the arc burning time, irrespective of fluctuations in the length of the bolts being welded. However, the value of the welding energy (arc current, voltage, time) is set in advance and is not regulated during the welding process. The true value of energy during the welding process can be affected by various disturbances, for example, a change in contact resistances in different parts of the welding circuit.

 A known method of welding bolts, providing for registration before welding and the supply of bolts to the welding head typical parameters for a bolt, such as the length and / or diameter of the ignition tip, cone of the bolt head, diameter and material of the bolt, and storing them with the possibility of interrogation on an auxiliary device, mounted on a bolt or directly on a bolt, interrogation of the specified parameters before feeding the bolt, reading them in the welding control device, calculation and installation in it based on these parameters necessary for each bolt and source material of variable parameters and control accordingly the welding process [3]. In this method, welding parameters, such as the charge voltage of welding capacitors, welding energy and the speed of immersion of the bolt, are set, and, if necessary, adjusted using an electronic device, providing a high-quality welding result.

 This method of electric arc capacitor welding is aimed at improving the quality of welding by eliminating the subjective errors of welding machine operators when evaluating welding conditions and choosing the initial process parameters. The combination of parameters for each welding case is selected from the databank of the plant control system. The real value of the energy released in the arc gap, while not being estimated and not adjusted.

 A known method of arc-contact welding of fasteners to the product, including the excitation of the arc between the part and the product when lifting the part, the formation of a bath of molten metal and moving the part to contact the surface of the product with the simultaneous application of pressure, and after the excitation of the preliminary welding arc measure arc voltage, and after excitation of the main welding arc measure the arc current, welding time and the time of lowering the bolt, the data obtained are recorded in the memory of the control circuit scooter, after the end of the welding cycle, they are compared with predetermined limit values and the results of the comparison give a conclusion on the correctness of the passage of the welding cycle [4].

 In this method, the welding cycle is carried out by working out predetermined welding parameters (current, voltage, welding time), the value of which is constant during the welding cycle. If necessary, changing the parameters for the next welding cycle is carried out manually by the operator, using the controls of the installation. The past welding cycle is considered satisfactory, i.e. providing conditions for obtaining a welded joint of satisfactory quality, if all the controlled parameters have not gone beyond their maximum permissible values.

 In this welding method, the quality of the welded joint is evaluated after completion of the process. The parameters of the mode are determined on the basis of a subjective assessment by the operator of the conditions for welding and largely depend on the experience and qualifications of the operator. During the process itself, the heat input of the arc is not evaluated and not regulated.

 A known method of arc-contact welding of fasteners, including the excitation of the arc between the product and the part when lifting the latter, the formation of a bath of molten metal and moving the part to contact the surface of the product with the simultaneous application of pressure, and after the excitation of the welding arc, measure the voltage and welding current, which are used to determining the instantaneous power and estimating the amount of energy released in the arc gap, then compare it with a predetermined value, generate th process control system, and when receiving the error correction to produce the parameters adjusting the power value to the rated [5].

 In this method, the energy value is only one of the recorded parameters, allowing after the end of the process to evaluate its stability and to a certain extent to predict the quality of the welded joint.

 The present invention solves the problem of maintaining the quality of welded joints under various perturbations: fluctuations in the voltage of the network, fluctuations in the welding current due to changes in the length of the arc, etc. by maintaining within the specified limits the thermal power of the arc and, consequently, the size of the weld pool, which allows to ensure the stability of the dimensions of the weld and, therefore, the strength properties of the welded joint.

 To solve the aforementioned problem in the proposed method of arc contact welding of fasteners, including the initiation of an arc between the part and the product when lifting the part, the formation of a bath of molten metal and moving the part to contact the surface of the product with the simultaneous application of pressure, and after arc excitation, the voltage and current of welding are measured which are used to determine the instantaneous power and estimate the amount of energy released in the arc gap, then compare it with a predetermined their assignment, produced by a process control system, and when receiving the error correction produce parameters with bringing to the rated power value.

 The process can be adjusted either by changing the arc burning time at a constant welding current, or by changing the welding current.

 An additional definition of the integrated instantaneous power value allows the use of a simple method for evaluating the energy parameters of the welding process. Tracking the thermal power of the arc, in contrast to tracking separate parameters (current and voltage), allows you to more accurately evaluate their resulting effect on the process of forming a weld pool.

 Comparison of the integrated value of instantaneous power with the threshold value for this combination "part diameter - sheet thickness", sufficient to form the weld pool, and issuing a signal to complete the welding cycle makes it possible to obtain data on the need to complete the welding process. Turning off the welding current after a certain period of time after a short circuit signal is received ensures that the fastener is immersed in the weld pool until it crystallizes and thereby ensures the quality of the welded joint.

 Making adjustments to the welding process when receiving a mismatch signal of the above values with bringing the values of the welding energy to the nominal values ensures the optimality of the welding process.

 Making process adjustments by changing the arc burning time at a constant welding current makes it possible to simplify the welding process control system.

 Making adjustments to the process by changing the welding current makes it possible to more quickly compensate for deviations from the normal course of the welding process.

 The proposed method is illustrated by drawings, which depict: in FIG. 1 is an electrical block diagram of a welding installation, and FIG. 2 is an electrical block diagram of a control system.

 The installation diagram (Fig. 1) shows a block 1 of thyristor switches, a welding transformer 2, a controlled rectifier 3, a current and voltage sensor 4, a welding gun 5 with a controlled electromagnet, while the outputs of the current and voltage sensor 4 and a welding gun 5 are connected to the input unit 6 of the electronics, and the outputs of the latter are connected to the inputs of unit 1 of the thyristor switches and controlled rectifier 3.

 Block 6 (figure 2) of the electronics contains a two-channel pre-amplifier 7, one output of which is connected to the device 8 integration and multiplication, the second to the sensor 9 short circuit, the third to the timer 13, the input of which is also connected to the sensor 9 short circuit. The outputs of the integration and multiplication device 8 are connected to the comparison device 10, and the latter, together with the outputs of the short circuit sensor 9 and the timer 13, is connected to the logical comparison unit 11, the outputs of which are connected to the key unit 12.

 Sensor 9 short circuit is made on the comparator. In the integration and multiplication device 8, the integration function is carried out using integrating microcircuits based on operational amplifiers, and the analog multiplication function is performed using integrated multiplication circuits of the K525PS2A type. The comparison device 10 is made on comparators. Block 11 logical comparison is made on logic circuits.

 The method is as follows. A part, for example, a bolt, a hairpin, etc., is installed in a holder rigidly connected to the electromagnetic mechanism for raising and settling the gun 5. The gun 5 is mounted on the product, while the head of the part rests on the product. Block 6 of the electronics, after receiving the signal "START" from the gun 5, turns on the current in the welding circuit and at the same time lift the part above the product. In the gap, first the preliminary, and then the main welding arc is excited. Next, the control system using the sensor 4 current and voltage measures the current and voltage of the welding during the burning of the main arc. The received signals are amplified by a preamplifier 7 and fed to a short circuit sensor 9, to a timing device 13, to an integration and analog multiplication device 8.

Next, the integrated signals of current, voltage and power are supplied to the comparison device 10, in which the comparators compare these signals with the calculated values for this combination "part - sheet thickness" values obtained from the built-in reference voltage sources. After comparison, the comparison device 10 generates discrete signals to the logical comparison unit 11, in which the compliance of the received discrete signals (power, time, short circuit time) with a given control system operation algorithm is evaluated. Upon receipt of a signal from the comparison device 10 about the achievement of a threshold value by power, the block 11 gives a signal to the key block 12 to turn off the electromagnetic coil of the gun 5 and lower the fastener into the weld pool. Upon receipt of a signal that the permissible value of the welding time has been exceeded, a signal is issued to shut down the installation and, with some delay, a signal to turn off the electromagnet,
The control system 6 captures the moment of arc extinction (short circuit of the part with the weld pool) using the short-circuit sensor 9 and gives a signal to turn off after a certain period of time of the welding current.

 Example. The fastener is welded - an M6 bolt 22 mm long, with a head diameter of 7 mm, from steel 10 to the product, which is used as a shield on the front end of the VAZ-2110 car with a wall thickness of 0.9 mm.

 Welding of this part was carried out using a portable arc contact welding machine in the following modes: welding current 630 A, arc voltage 27 V, welding time 25 ms, productivity 15 pcs / min.

The quality of welding of the bolts was evaluated by testing by repeated bending at an angle of 45 ^o relative to the axis of the bolt. A welded joint is considered to be of high quality if a bolt breaks out of the sheet according to the diameter of the cast core, while the breakout diameter should be at least 80% of the diameter of the bolt.

 During the test, the molten core was torn from the sheet. The diameter of the breakout was 6.2 mm, which meets the requirements for the quality of the welded joint.

Sources of information
1. Japan Application 2-60435, CL B 23K 9/20, 9/22, 1990

 2. German application 4307325, cl. B 23 K 9/20, 1996

 3. German application 4236527, cl. B 23K 9/20, 9/095, 1994

 4. Installation of NTR 800G f. "TRW Nelson" (Germany).

 5. WO 82/03033 A1, B 23 K 9/20, 09/16/1982

Claims (3)

 1. The method of arc contact welding of fasteners, including the excitation of the arc between the product and the part when lifting the latter, the formation of a bath of molten metal and moving the part to contact the surface of the product with the simultaneous application of pressure, and after the excitation of the welding arc, measure the voltage and welding current, which use to determine the instantaneous power and estimate the amount of energy released in the arc gap, then compare it with a predetermined value generated by the system process control, and when a mismatch is obtained, the parameters are adjusted to bring the energy value to the nominal one, characterized in that the integrated instantaneous power value is additionally determined and this value is compared with the threshold value for this combination of "part diameter - sheet thickness" to form a welding baths, after which they give a signal to complete the welding cycle, while the welding current is turned off after a certain period of time after the receipt of the signal about com circuit.  2. The method according to claim 1, characterized in that the process is adjusted by changing the arc burning time at a constant welding current.  3. The method according to claim 1, characterized in that the process is adjusted by changing the welding current.

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