JP2006142380A - Resistance projection welding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that losses of the mechanical properties of a base material are large because warp and distortion of a metal plate caused by the thermal effect of the resistive heat generation and squeeze of the expand metal are large in a conventional welding of the expand metal. <P>SOLUTION: An expand metal overlaps the surface of a metal plate, and an overlapped projection-shaped contact part is held between a pair of electrodes 2, 3. In a resistance welding machine to perform the projection welding of the projection-shaped contact part formed between the plate and the expand metal by applying the pressure required for the welding between the electrodes by an actuator unit, and allowing the welding current of large capacity to run from a capacitor power supply, the expand metal is firmly melted and joined while the projection-shaped contact part is less squeezed and the original shape of a base material of the expand metal is maintained by performing the correction-control of the pressure during the projection welding so that the mesh height of the expand metal after the welding is matched with the reference value of the preset mesh model height h. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resistance projection welder when connecting expanded metal to a metal plate.

  As a conventionally known method for welding steel expanded metal to a metal plate, for example, there is a welding method described in Patent Document 1.

  In this conventional method, the spot spot of the expanded metal is press-molded prior to welding to make it completely flat, and then normal spot welding is performed in a state of surface contact with the mating metal plate.

JP 62-137183 A (page 2, left column, lines 3-8, Fig. 1-2)

  The problem to be solved by the present invention is that, when the expanded metal is joined to the metal plate, the conventional welding method cannot take advantage of the mechanical properties without destroying the original mesh shape of the expanded metal.

  Therefore, in order to solve the above-mentioned problem, the invention of claim 1 superimposes the expanded metal on the surface of the metal plate, and sandwiches the protrusion contact portion of the work to be welded formed between the pair of electrodes, Resistance welding is performed by applying welding force required for welding between the electrodes by the actuator unit, and by projecting the projection contact portion formed between the plate and the expanded metal by supplying a large-capacity welding current from a capacitor power source. A resistance projection welding characterized in that the applied pressure is corrected and controlled during the projection welding so that the mesh height dimension of the expanded metal after welding coincides with a preset reference value of the mesh model height h dimension. Provide a machine.

  The invention of claim 2 has a pair of positive and negative electrodes, one of which is a movable electrode, and an actuator unit comprising a system that converts the rotational motion of the electric motor into linear motion by a ball screw and nut. One axis of the actuator unit is controlled by a controller in a closed loop system, and the pressurizing force between the electrodes, welding current, energizing time, electrode positioning, moving speed, and other parameters necessary for energizing welding are controlled by the controller. Recorded and set in the main control unit, one electrode clamps the welded portion with the other fixed side electrode according to the main control unit, the torque current of the electric motor and the pulse signal from the encoder A resistance projection welder characterized in that synchronous control is reproduced by Provide.

  Next, the invention of claim 3 is provided with a motor amplifier that drives one or two axes of the actuator unit, a welding power source controller, and a contactor that controls an electronic switch of a welding transformer of the welding machine, The electric storage type welding power source of the welding machine has a charging circuit, the charging circuit has an inverter circuit and a rectifier circuit, and the capacitor group is charged to a voltage value that can be arbitrarily set by the charging circuit, Provided is a resistance projection welding machine that performs welding by performing on / off switching with a discharge switch and discharging electric power accumulated in a capacitor group to a clamp portion between the electrodes through a welding transformer.

  Next, the invention according to claim 4 receives the mesh model height h dimension of the designated reference value and the torque current stop position command, commands torque control of the target position and motor speed of the electric motor, The target value of the mesh model height h dimension of the workpiece to be welded is detected from the pulse signal from, and when the target value is reached, the energization stop and torque limit or torque control are turned off to the welding power source control unit. Position control switching to the vertical position is commanded to the motor amplifier, the position detection of the movable side electrode is read by an encoder pulse built in the electric motor, and the β reference value corresponding to the mesh model height h dimension of the work to be welded Alternatively, the α reference value taken before the mesh model height h dimension is set in the welding position calculation control unit of the controller, and the stroke displacement amount of the electrode is preset. Whether or not the model height dimension is β value or α value is read by the welding position calculation control unit from the number of pulses output from the encoder every moment, whereby the mesh height dimension after welding is A resistance projection welder characterized in that it is positioned within a value.

  According to the first aspect of the present invention, the ratio of the mesh height dimension of the expanded metal after welding to the mesh height H dimension of the expanded metal before welding is a reference value corresponding to the mesh model height h dimension. By welding so as to reach 60 to 85%, the contact point of the expanded metal is not completely flattened, and the mesh material can be firmly and uniformly melt bonded.

  According to the second aspect of the present invention, the optimum welding current can be made to flow evenly over the entire contact surface of the expanded metal that is always welded. Since there is little deformation and crushing of the metal, the loss of mechanical properties of the base metal can be reduced.

  According to the third aspect of the present invention, the torque current of the electric motor 4 and the encoder 8 can be clamped between the one electrode 2 and the other fixed-side electrode facing each other according to the main control unit 7. Since the synchronous control is reproduced by the pulse signal from the welding power source control unit when the mesh model height h dimension is detected from the pulse signal from the encoder 8 of the motor 4 and the target value is reached. 10 is switched off to the model height position, the electrode position is kept at the reference position, and the weld height is maintained at a value corresponding to the product accuracy.

  According to claim 4 of the present invention, the detected value is not detected from the pulse signal from the encoder of the electric motor 4 during the welding process, but rather the pressure is unilaterally applied to the welding position set to the target value by the torque control. When the β reference value or α reference value of the target position is detected, the welding current between the electrodes is stopped, and at the same time, the torque limit or torque control is turned off by a command from the welding position calculation control unit 13 and the mesh model height h β Control is performed until the current weld height finally matches the mesh model height h dimension by the position control that is switched to the reference value or position control to the α reference value in the vicinity thereof while the torque is released. In addition, it is possible to reliably detect the normal position and ensure product accuracy.

  This is an effective method for connecting expanded metal for mounting brake pads for automotive disc brakes, and crushes the flat contact portion formed by overlapping the metal plate (backing plate) and expanded metal completely flat. In this case, the embodiment is optimal when the protruding contact portion is firmly joined in a state in which the base shape of the expanded metal is left.

  FIG. 1 is a plan view showing a mesh shape defined in JIS G 3351 (expanded metal). Symbols S and L are the lengths in the vertical and horizontal directions of the product. FIG. 2 is an enlarged partial view of the same. Symbol T: plate thickness, W: step width, SW: mesh width direction distance, LW: mesh length direction distance. FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2 and shows a protruding contact portion that overlaps the metal plate. Symbol H in the figure shows the mesh height of the expanded metal. FIG. 4 is a plan view in which expanded metal divided into three parts is integrated into a metal plate in the present invention. FIG. 5 is a photograph showing the details of the appearance of a welded part in which one expanded metal is integrated with a metal plate in the projection welding machine of the present invention. FIG. 6 shows a block diagram of a capacitor type resistance projection welding machine for carrying out the present invention. FIG. 7 is an explanatory view comparing the mesh height before and after welding by the welding machine of the present invention. FIG. 3A shows the height H dimension of the mesh before welding by the welding machine of the present invention. FIG. 7B shows the mesh model height h dimension after welding by the welding machine of the present invention.

  In FIG. 6, a capacitor type resistance projection welding machine 1 of the present invention has a pair of positive and negative electrodes 2 and 3 in a part of main components, and one of the electrodes 2 serves as a movable side electrode as a ball screw B and a nut N. Is driven by an actuator unit 5 constituted by a system that converts the rotational motion of the electric motor 4 (servo motor) into a linear motion.

  One axis of this actuator unit 5 is controlled by the controller 6 in a closed loop manner, and the pressurizing force between the electrodes, welding current, energizing time, electrode positioning, moving speed, and other parameters necessary for energizing welding are all those of the controller 6. Recorded and set in the main control unit 7. Synchronous control is reproduced by the torque current of the electric motor 4 and the pulse signal from the encoder 8 so that the welding portion can be clamped between one electrode 2 and the other fixed-side electrode facing each other according to the main control portion 7. It is the composition which becomes.

  The welding machine of the present invention includes a motor amplifier 9 that drives one or two axes of the actuator unit 5, a contact power supply control unit 10, a contactor 11 that controls an electronic switch of a welding transformer of the welding machine, a work jig ( (Not shown).

  Although not shown in the figure, the electric storage type welding power source device 12 has a charging circuit, and this charging circuit has, for example, an inverter circuit and a rectifier circuit, and the capacitor group has a voltage value that can be arbitrarily set by this charging circuit. Charged. Electric power stored in the capacitor group by switching on and off by a thyristor serving as a discharge switch is discharged to the electrode clamp connected to the secondary coil of the welding transformer via the primary coil of the welding transformer and welding is performed.

  The welding position calculation control unit 13 receives the mesh model height h dimension of the commanded reference value and the torque current stop position command, and commands torque control such as the target position and motor speed of the electric motor 4 to the motor amplifier, The mesh model height h dimension is detected from the pulse signal from the encoder 8 of the motor 4, and when the target value is reached, the energization stop and torque limit or torque control are turned off to the welding power source control unit 10, and the model height position The motor amplifier 9 is instructed to switch the position control to.

  In the welding machine 1, the contactor 11 is interposed in the main circuit of the power source and the electric storage type welding power source device 12, and operates the electronic switch in response to the energization signal from the main control unit 7 when conducting the electric welding. The main current of the apparatus 12 is controlled, and the magnitude and energization time of the heating current passed between the pair of electrodes 2 and 3 through the secondary conductor of the welding machine are directly controlled.

The position of the movable electrode 2 is detected by an encoder pulse built in the electric motor 4. In this case, the electrode origin setting is performed with the position where the torque current flows as a result of the air pressure being applied to the stationary electrode 3 from the fully open origin position of the movable electrode 2 as a base point (zero).

  Explaining the setting of the reference value in the welding process, the mesh height H dimension of the expanded metal before welding is obtained from the tip origin position by back calculation. For example, if the mesh height H dimension is 2 mm, the movable electrode 2 is The electrode movement is decelerated just before the mesh height H reaches 2 mm, and the positioning of the soft landing is detected by the encoder pulse. If the mesh model height h dimension of the quality target is 1.2 mm, a target value corresponding to 1.2 mm is detected from the encoder pulse as the β reference value.

  Further, in the case of the α reference value, the amount of penetration is determined by back-calculating the distance slightly ahead of the model height h dimension, for example, a distance of about 0.1 to 0.3 mm before α target value. Thus, the β reference value corresponding to the model height h dimension of the product or the α reference value taken before the model height h dimension is set in the welding position calculation control unit 13 of the controller. The calculation unit of the welding position calculation control unit 13 determines whether or not the stroke displacement amount of the electrode 2 is a β value or α value of a preset model height dimension from the number of pulses output from the encoder 8 every moment. read.

  When correcting the amount of displacement between electrodes due to electrode wear, the origin of the chip is defined as the base point (zero) at which the torque current flows when the stationary electrode 3 is air-pressed from the fully open origin position of the movable electrode 2. Do the set.

  6 and 7, the main control unit 7 has the above-mentioned target position (the β reference value or α reference value) of the welding sequence and the welding pressure, welding current value, energization time, and other necessary welding. Patterns and parameters are set, and commands are issued according to those parameters.

Based on the mounting method of the present invention, a sample was prepared to confirm the actual performance. Experimental values are shown below.
-Workpiece and material Metal plate: Material SAPH440, plate thickness 8mm, plate width 86mm
Length 106mm
Expanded metal: Material SPHC Wire diameter 0.8mm, width 80mm,
Length 100mm Height 2mm
・ Welding condition table Applied pressure kN: 20 to 25, Capacity kW: 15 to 20,
Welding current kA: 160 to 180, energization time ms: 10 to 20

Next, the operation of the present invention will be described with reference to FIGS.
First, before performing projection welding, insert a reference material between the movable side electrode 2 and the fixed side electrode 3 or between the electrodes 2 and 3 and clamp them without inserting a workpiece between the electrodes 2 and 3 by an automatic device. The origin and zero base of the electrode are detected by the encoder 8 from the amount of electrode movement on the movable side when stopped, and the data is stored in the controller 6.

  The controller 6 of the resistance projection welder teaches various parameter operations on the sequence such as electrode speed and electrode positioning as well as various operations such as a pressurizing pattern, a current pattern, and an energizing pattern necessary for welding the actuator unit 5. The expanded metal to be welded is fixed at a set position provided in advance on the work jig.

  Next, in response to a command from the main control unit 7 of the controller 6, the welding position calculation control unit 13 instructs the motor amplifier 9 to control the torque current such as the target position and the motor speed, and the electric motor 4 of the actuator unit 5 is actuated. By transmitting the rotational motion of B to the ball nut N, the movable shaft 14 moves linearly and lowers the movable electrode 2 toward the fixed electrode 3.

  During this time, the amount of electrode movement is detected by receiving an encoder pulse from the electric motor 4. The speed of the movable side electrode 2 set in the main control unit 7 can operate quickly up to the mesh height H dimension where the electrode tip is in contact with the welded portion, and therefore the moment when the movable side electrode 2 is in contact with the welded portion. Thus, the speed is reduced, and the welding part is substantially contacted by a soft touch. The weld is sandwiched between the fixed side electrode 3 and pressurized.

Thereafter, a torque current for obtaining a high pressurization force of, for example, 20 kN to 25 kN is generated between the fixed-side electrode 3 and the movable-side electrode 2 as a pressurizing force, and the welded part is mechanically operated within a current-carrying time of 10 to 20 ms. Press. In response to a setting command from the main control unit 7, an energization start command is received from the welding power source control unit 10 to operate the switch of the contactor 11. In this case, a large current of about 160 kA to 180 kA flows from the storage welding power source 12 during the energization time of 10 to 20 ms, for example, according to the setting data of the main control unit 7.
Thus, when a welding current is supplied to the movable electrode 2 and the fixed electrode 3, the welded portion can be heated and melted at an accelerated speed to be pressed.

  The welding indentation amount is detected by the encoder pulse of the motor from the electrode displacement, and the penetration amount gradually progresses, and these data are sequentially monitored at each hit point to compare whether the target standard value has been reached or not by a calculation unit. Calculated. When the calculation result does not reach the reference value, the difference is feedback-controlled, and correction control is performed such as increasing or decreasing the pressure until the target α reference value or β reference value is reached.

  In this case, the welding portion is not unilaterally pressurized to the welding position set to the target value by torque control, but the welding portion is crushed by the pressure of the movable electrode 2 during this welding process, and the electric motor 4 When the detected value detects the β reference value or α reference value of the target position from the pulse signal from the encoder, the contactor 11 causes the welding current between the electrodes in response to a command from the welding position calculation control unit 13 to the welding power source control unit 10. At the same time, the torque limit or torque control is turned off by a command from the welding position calculation control unit 13 and the motor amplifier 9 is commanded to switch the position control to the β reference value of the mesh model height h dimension or the α reference value in the vicinity thereof. To do.

  Thus, when the torque current and the welding current are interrupted almost simultaneously, the weld is held between the electrodes until the hold time (for example, 0.5 to 20 cycle range) is completed. During this time, the electric motor torque is maintained at the reference position while the holding torque is maintained, and the height of the welded portion is maintained constant. In other words, the present invention cancels the torque limit or torque control at a predetermined position during welding and performs position control, thereby reducing the tolerance of the mesh model height h dimension of the welded portion to the accuracy of motor encoder disassembly (for example, 1/100 or less). ).

  After welding is completed, one cycle of projection welding is completed when the electric motor 4 of the actuator unit 5 rotates in reverse according to a command from the main control unit 7 and the movable electrode 2 opens to the origin.

  Next, the next new workpiece is taken in and out between the electrodes, and the welding cycle is repeated in the same manner.

  Note that the amount of wear of the chip is determined by performing blanking pressurization with the positive and negative electrodes 2 and 3 once at an arbitrary number of times (10 times) according to the wear amount, and resetting the base point as described above.

  In this case, it is possible to control the position of the current welded portion to be finally matched with the mesh model height h dimension by the position control which is switched in a state where the torque is released halfway, and to detect and hold the normal position reliably. it can.

  On the other hand, in the conventional concept where welding was performed by pressurizing continuously or empirically to the target mesh model height h dimension by air pressurization control, the dimensional accuracy of the parts was not stable. Therefore, by improving the monitoring accuracy of the mesh model height h dimension, the quality control for improving the component accuracy is improved, the tact time can be shortened, and the productivity can be increased.

  As the welding method for determining the mesh model height h dimension, the position control and torque control by the servo motor have been mentioned. However, in addition to the first embodiment, the movable side electrode may be mechanical, for example, pneumatic or hydraulic. The moving speed and / or moving distance of the movable side electrode when a pressure is applied to the movable part including the movable shaft, arm, secondary conductor, or the fixed side electrode when the pressure is applied by the cylinder of the type When the value detected by the displacement sensor reaches a predetermined movement speed and / or a predetermined movement distance corresponding to the model height dimension, the welding current and pressure between the electrodes are stopped and welding is performed. To complete. Further, when the value detected by the displacement sensor does not reach a predetermined moving speed or moving distance during the welding process, the movable side electrode can be switched to a stop and / or open operation. In this case, it is useful for ensuring safety by detecting the presence / absence of an object to be welded to prevent poor welding in advance and detecting the insertion of foreign matter into the welded portion.

  As shown in FIG. 4, the welding method using the resistance projection welder shown in the first embodiment is effective for connecting an expanded metal for mounting a brake pad of an automotive disc brake, and a metal plate (backing plate) and Without causing the expanded metal base metal shape to remain flat, the expanded metal base metal shape is retained without causing the expanded metal base material to be crushed. be able to.

  As a result of welding the metal plate and expanded metal within the above experimental values, according to the projection welding method, which is one of the resistance welding methods, the entire surface of the expanded metal material is less likely to be crushed uniformly and melted and welded firmly. It was possible to integrate. In this welding experiment, an electrode having a flat pressure surface having a width of 25 mm and a length of 80 mm was used. The expanded metal was superimposed on the metal plate and sandwiched between the upper and lower electrodes, and was welded by a capacitor power source in several times under welding conditions of a pressurizing force of 20 kN, a welding current of 164 kA, and an energization time of about 10 ms.

  In this experiment, a single piece of expanded metal was welded once, and then the first welded mesh was wrapped in the next welding to lap and perform split welding. According to this welding result, the mesh height H dimension after welding of the expanded metal before the welding was 2 mm, and the mesh model height h dimension after welding could be secured within the range of 1.2 mm to 1.7 mm. As a result of performing a pliers peeling test after welding, the mesh model height h dimension after welding is within a range of 1.2 mm to 1.7 mm, that is, the ratio of the h dimension is within 60 to 85% with respect to the H dimension. In other words, it was confirmed that the expanded metal was cut from each projection weld and sufficient mechanical strength was obtained, and that the metal plate was not warped or deformed. In this experiment, even when the capacity of the power source was small, the results of a pliers peel test on the welded part by split welding in the same way confirmed that a strong peel strength was obtained in terms of welding quality.

  On the other hand, when the height h dimension of the mesh model after welding is 1.1 mm or less, it is found that a lot of dust is generated in the expanded metal weld, resulting in insufficient weld strength, warping and distortion of the metal plate due to the decrease in molten metal. did. In addition, it can be confirmed that when the mesh model height h dimension after welding is 1.8 mm or more, the welding area of the expanded metal is small, so that the weld area of the molten metal is reduced and sufficient weld strength cannot be obtained. It was.

  In the experiment of the present invention, if the expanded metal is divided into three in the vertical direction in advance and the backing metal is overlapped at equal intervals and projection welding is performed, the mesh material is divided and welded in advance, so that the welding time for each sheet is reduced. A large current can flow in a short time. This expanded metal welding method allows the optimum welding current to flow evenly over the entire surface of the expanded metal that is always welded in capacitor welding, and because of the short-time heat generation, warpage and distortion of the metal plate due to thermal effects, and material alteration of the expanded metal.・ Since there was little crushing, it was confirmed that there was little loss in the mechanical properties of the base metal.

  In this welding experiment, the expanded metal divided into three parts was tested by split welding. However, in the case of overlapping welding, the same invention effect can be obtained by welding by wrapping the first row or by wrapping multiple rows. Needless to say, it is also possible to weld the entire expanded metal weld at the same time.

  With other resistance welding power sources, for example, with a single-phase AC power source, a large current cannot be flowed in a short time. In addition, an inverter power supply cannot flow a large current in as short a time as a single-phase AC power supply, so the warpage and distortion of the metal plate are large, and the expanded metal material is greatly deformed and crushed, resulting in mechanical strength. There wasn't.

  In the present invention, since a large current can flow in a short time for welding, there is little collapse of the base metal original form of the expanded metal, and it can be melt-welded firmly. In addition, in this experiment, the strength test of a sample made by capacitor projection welding of a metal plate and expanded metal was verified by a pliers peel test. As a result, a strong peel strength at which the expanded metal side could be cut was obtained, confirming improved weld quality.

  The expanded metal integrated by the welding process described above is applied to the pad in the next pad forming process, a biscuit-like mixed powder is put into the mold, and heat-molded at several hundred degrees to be incorporated into the pad shape. In this case, the pad base material penetrates to the entire area of the expanded metal mesh, so that a metal reinforcing material, that is, a steel expanded metal is embedded in the pad material.

  The brake pad is hardened and fixed to the metal plate through a series of processing steps such as a pad forming / curing step. Thus, the vibration force and impact force imposed on the brake pad are finely dispersed and absorbed along the mesh of the mesh material, and the frictional heat generated in the brake pad is finely conducted in a mesh by the expanded metal inside the pad.・ Dispersed and can greatly extend the durability of adhesive strength.

  As an example of the resistance projection welding machine of the present invention, the brake pad mounting method after the projection metal is projected on the backing plate of the automotive disk brake is mentioned, but the steel expanded metal and the metal plate of the standard product by the capacitor type resistance welding are mentioned. Can be firmly fixed without losing mechanical properties, so that it can be used for welding other parts that require expanded metal.

It is a top view which shows the mesh shape prescribed | regulated to JISG3351 (expanded metal). It is an enlarged partial view of expanded metal. It is a figure which shows the protrusion contact state of the overlapping part formed by overlapping the expanded metal on the metal plate in this invention. It is a top view which integrated the expanded metal divided into three in the metal plate in this invention. It is a photograph which shows the external appearance detail of the welding part which integrated one sheet of expanded metal with the metal plate in the resistance projection welding machine of this invention. It is a side view showing the appearance concept of the capacitor type resistance projection welding machine of the present invention. It is explanatory drawing which compared the mesh height of the expanded metal before welding with the welding machine of this invention, and after welding. FIG. 3A shows the mesh height H before welding by the welding machine of the present invention. FIG. 7B shows the mesh model height h dimension after welding by the welding machine of the present invention.

Explanation of symbols

1 Capacitor-type resistance projection welding machine 2 One electrode (movable side)
3 The other electrode (fixed side)
DESCRIPTION OF SYMBOLS 4 Electric motor 5 Actuator unit 6 Controller 7 Main control part 8 Encoder 9 Motor amplifier 10 Welding power supply control part 11 Contactor 12 Power storage type welding power supply device 13 Welding position calculation control part 14 Movable shaft

Claims (4)

Expanded metal is placed on the surface of the metal plate, and the projection contact part of the work to be welded is placed between a pair of electrodes, and the actuator unit applies the pressure required for welding between the electrodes. At the same time, in a resistance welding machine in which a projection welding portion formed between the plate and the expanded metal is projected by flowing a large-capacity welding current from a capacitor power source, the mesh height dimension of the expanded metal after welding is previously set. A resistance projection welding machine, wherein the applied pressure is corrected and controlled during the projection welding so as to coincide with a reference value of a set mesh model height h dimension. It has a pair of positive and negative electrodes, one of which is a movable electrode and is driven by an actuator unit composed of a system that converts the rotational motion of an electric motor into linear motion by means of a ball screw and a nut. The axis is controlled by the controller in a closed loop manner, and the pressurizing force between the electrodes, welding current, energizing time, electrode positioning, moving speed, and other parameters necessary for energizing welding are recorded and set in the main controller of the controller. One electrode clamps the welded portion with the other fixed side electrode according to the main control unit, and the synchronous control is reproduced by the torque current of the electric motor and the pulse signal from the encoder The resistance projection welder according to claim 1, wherein: A power amplifier for driving one or two axes of the actuator unit, a welding power source control unit, and a contactor for controlling an electronic switch of a welding transformer of the welding machine are provided. Has a charging circuit, and this charging circuit has an inverter circuit and a rectifying circuit. The capacitor group is charged to a voltage value that can be arbitrarily set by the charging circuit, and is switched on and off by a discharging switch. 3. The resistance projection welding machine according to claim 2, wherein welding is performed by discharging electric power accumulated in the group to a clamp portion between the electrodes through a welding transformer. The mesh model height h dimension and torque current stop position command of the specified reference value are received, the torque control of the target position and motor speed of the electric motor is commanded, and the welding target is determined from the pulse signal from the encoder of the electric motor. When the target value of the model height h dimension of the object is detected and the target value is reached, the welding power source control unit is turned off and torque limit or torque control is turned off to the target position of the mesh model height h dimension. The position of the movable electrode is detected by an encoder pulse built in the electric motor, and the β reference value or mesh corresponding to the mesh model height h dimension of the workpiece is commanded. The α reference value taken before the model height h dimension is set in the welding position calculation control unit of the controller, and the stroke displacement amount of the electrode is preset. Whether or not the model height h dimension is within the β value or α value is read by the welding position calculation control unit from the number of pulses output from the encoder every moment, whereby the mesh height h dimension after welding is determined. The resistance projection welding machine according to claim 3, wherein the resistance projection welding machine is positioned within the reference value.

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