JP2005169429A - Resistance welding method, and resistance welding power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistance welding equipment and a resistance welding method in which melting deformation, thermal deformation, degradation of base metal characteristics, and degradation of strength do not occur, and the quality and reliability of welding are not degraded between dissimilar metal components or even between similar metal components when the heat capacity is small or the heat capacity is considerably different from each other. <P>SOLUTION: In the resistance welding, the welding current including the high frequency components with the skin effect runs while maintaining the pressure applied to a component to be welded so as to keep the contact resistance of considerably high value in order to concentrate the heat to a welding surface, and the welding is performed by locally and instantaneously performing heating, melting and bonding of a surface layer of the welding surface by these two synergistic effects. By the local and instantaneous heating effect, high quality and high reliability can be obtained in the welding of dissimilar metal components, or the welding of similar metal components of small heat capacity or similar metal components considerably different in heat capacity from each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a resistance welding power supply apparatus and a resistance welding method for resistance welding of dissimilar metal parts, similar metal parts having greatly different heat capacities, or similar metal parts having a small heat capacity.

  Generally, resistance welding is performed as follows. A part to be welded is sandwiched between a fixed electrode and a movable electrode attached to a pressure shaft driven by an electric motor, a pneumatic cylinder or the like, and is held for an appropriate time while applying an initial pressure. Next, a welding current is applied to the parts to be welded from a welding power source connected between the fixed electrode and the movable electrode while applying a pressing force for heating. The welding current generates Joule heat due to the specific resistance of each welded part and the contact resistance of the joint surface, and the welded part is melted and welded. Thereafter, energization of the welding current is terminated, and the cooling and solidification are waited while applying a pressurizing force for cooling and holding. As described above, welding is completed through a series of steps.

The quality and reliability of resistance welding depend on the pressurizing pattern applied to the parts to be welded during the series of welding processes described above, the welding current conduction pattern, and their interrelationships, and the execution accuracy of each. Therefore, various methods have been devised for controlling the pressing force and the welding current. For example, Patent Document 1 discloses a device that controls an air cylinder with an electropneumatic proportional valve in order to ensure that the applied pressure at the start of welding current energization matches the set applied pressure. Patent Document 2 discloses a resistance welding machine that performs pressurization while detecting a conduction state between electrodes in order to perform pressurization control while avoiding detection of foreign object pinching. Patent Document 3 discloses a resistance welder that, when a gap is generated between workpieces, pressurizes with a predetermined pressure after setting the gap to zero. Further, Patent Document 4 discloses a resistance welding machine that measures the conduction resistance of the entire part to be welded before welding, and sets a larger pressure as the conduction resistance increases. Further, Patent Document 5 discloses a pressure control method for controlling the armature current of a servo motor to increase the pressure continuously or intermittently.

The power source used for resistance welding is generally (1) a DC power source in which electric charge is stored in a capacitor, and (2) a commercial AC current of 50 Hz or 60 Hz is subjected to conduction angle control with a semiconductor element such as a thyristor element or a triac element and transformed (3) 50Hz or 60Hz commercial alternating current is converted into direct current by a rectifier circuit and smoothing circuit, and the direct current is switched by a semiconductor switching element such as a power transistor and converted to alternating current, and it is stepped down by a transformer. Inverter AC type power supply etc. are used. Patent Document 6 discloses an inverter AC resistance welding method in which the welding current frequency is changed in accordance with welding conditions such as a plate thickness and a material of a welded part for the purpose of suppressing an excessive change in current during welding energization. It is disclosed. However, in any of these power supplies, the frequency of the AC component having the largest amplitude included in the welding current is at most about 400 Hz, and none of the present invention has about 800 Hz to 1000 Hz or more. Further, the frequency of the AC component having the largest amplitude included in the welding current during energization is not arbitrarily changed with a certain purpose.
Japanese Patent Laid-Open No. 9-277063 JP 2002-205174 A JP 2000-218379 A JP 2002-28790 A JP-A-9-85456 JP 2001-105155 A

  When resistance welding of dissimilar metal parts, the electrical resistivity of each metal is different, so the specific resistance of each part to be welded is different, and the amount of Joule heat generated by the welding current is different. Moreover, even if the generated Joule heat amount is the same, the specific heat and the thermal conductivity of each metal are different, so that the temperature at which each welded part rises is different. Further, even if the parts to be welded are at the same temperature and the melting points of the metals are different, welding is not possible unless the temperature is about the melting point of the metal having a high melting point. Thus, in order to weld dissimilar metal parts, it is necessary to overcome the differences in electrical resistivity, specific heat, and thermal conductivity and raise the temperatures of both parts to be welded to the melting point of a metal having a high melting point.

However, if the temperature of both parts to be welded is raised to the melting point of the part to be welded with a high melting point, the part to be welded with the lower melting point will be overheated, and melting and thermal deformation will occur at and near the weld surface. However, the heat-affected zone expands in a wide range, and the base material characteristics are deteriorated and the strength is lowered due to the coarsening of crystal grains, so that the quality and reliability of welding are lowered.

When the same kind of metal parts having greatly different heat capacities are resistance-welded, if the parts to be welded having large heat capacities are heated to an appropriate welding temperature, the parts to be welded having small heat capacities are overheated, and the above-described problems occur.

When welding the same kind of metal parts with small heat capacity such as thin wire rod parts, the heat capacity is small, so not only the welding surface but the whole part is heated, melting deformation and heat deformation occur, and the heat affected zone Expanding over a wide area, deterioration of base material properties and strength reduction due to coarsening of crystal grains, etc. occur, and the quality and reliability of welding deteriorate.

The problems to be solved by the present invention are these problems.When the heat capacity is small or the heat capacities are different even between different metal parts or between the same kind of metal parts, melting deformation, heat deformation, deterioration of base material characteristics, strength Provided are a resistance welding apparatus and a resistance welding method that do not cause deterioration and do not deteriorate the quality and reliability of welding.

  The present invention does not cause melting deformation, heat deformation, deterioration of base material characteristics, and strength reduction as in the case where the heat capacity is small or the heat capacity is greatly different even between dissimilar metal parts or between the same metal parts. The following technical measures are taken by resistance welding without reducing the properties. A welding power source is connected between the two electrodes while two parts facing each other are sandwiched between the parts to be welded between the electrodes and a pressing force is applied, and welding is performed by passing a welding current to the workpiece. In the resistance welding method, the applied pressure applied to the welded part during energization of the welding current is smaller than the applied pressure applied to the welded part during cooling and holding after the energization of the welding current, and is supplied from the welding power source. The welding current is characterized in that the AC component included in the welding current is relatively large with respect to the DC component, and the frequency of the AC component having the largest amplitude is about 800 Hz or more. And

By taking the above-described means, (1) a welding current is applied while maintaining a large contact resistance of the weld surface, and I ² R Joule heat concentrates on the surface layer of the weld surface of the welded part. (2) Due to the skin effect of the welding current including the high frequency component in which the alternating current component is relatively large with respect to the direct current component and the amplitude of the alternating current component having the largest amplitude is about 800 Hz to about 1000 Hz or more, Two physical phenomena that the current density of the surface layer of the surface increases and the I ² R Joule heat concentrates only on the surface layer occur at the same time. Heat, melt, and fuse. As a result, in the welding of dissimilar metal parts, small homogeneous metal parts with small heat capacities, and similar metal parts with greatly different heat capacities, melting and thermal deformation may occur in the welded part and the entire part, and there is a wide range of heat affected parts. Thus, the base material characteristics are not deteriorated and the strength is not reduced due to the coarsening of crystal grains, and welding with high quality and reliability is possible.

  That is, the resistance welding of the present invention includes a high-frequency component having a skin effect while maintaining the pressure applied to the parts to be welded at such a level that the contact resistance can be maintained at a considerably large value in order to concentrate heat on the welding surface. A welding current is passed, and the surface layer of the welding surface is locally, instantaneously heated, melted, and fused by these two synergistic effects to perform welding. Due to this local and instantaneous heating action, high quality and high reliability can be obtained in welding of dissimilar metal parts, small-sized similar metal parts having a small heat capacity, and similar metal parts having greatly different heat capacities.

The present invention drives a servo motor to sandwich a part to be welded between a fixed electrode and a movable electrode attached to a pressure shaft driven by a servo motor, applies pressure, and welds between the electrodes. This is performed in a resistance welding method in which a power source is connected and welding is performed by passing a welding current through the workpiece. Further, an inverter AC power source is used as the welding power source. Embodiments according to the present invention will be described below in detail with reference to the drawings.

  An overall configuration diagram of a resistance welding apparatus for carrying out the present invention is shown in FIG. The servo motor 1 is connected to the linear motion unit 2, the pressure shaft 3 is attached to the unit 2, and the movable electrode 4 is attached to the pressure shaft 3. A fixed electrode 5 is installed at a position facing the movable electrode 4. The servo motor 1 is connected to a servo motor control circuit 8 via a servo motor drive circuit 7. The servo motor 1 has both a speed control mode that rotates at a specified speed and a torque control mode that generates a specified armature current, that is, generates a specified torque, and operates according to a signal from the servo motor control circuit 8. The mode selection, speed magnitude and torque magnitude are determined. The linear motion unit 2 is provided with an origin position detection sensor 9 at the origin position and a mode switching position detection sensor 10 for switching between the speed control mode and the torque control mode at a position where the movable electrode 4 contacts the workpiece 6b. An output terminal of the resistance welding power source device 12 of the present invention is connected between the electrodes 4 and 5. The overall control instruction device 11 of the resistance welding device receives welding conditions and controls and manages a series of welding processes. The operation instruction signal, the control signal, or the The welding condition information signal is output.

A series of welding process conditions for carrying out the present invention are shown in the time chart of FIG. The movable electrode lowering step 21 is started by the start signal 26 from the overall control instruction device 11 of the resistance welding apparatus, the servo motor 1 operates in the speed control mode, and the movable electrode 4 is operated at the specified speed from the origin position. It goes down until the signal of the switching position detection sensor 10 is detected. Next, in the initial pressurizing step 22, the servo motor 1 switches to the torque control mode and generates a designated torque. As a result, the movable electrode 4 applies the parts to be welded 6a and 6b with the designated pressure. Press. Next is an energization heating process 23. In this process as well, a pressure is applied to the parts to be welded 6a and 6b with a specified pressure, and the resistance welding power source device 12 of the present invention passes through both electrodes 4 and 5 through the electrodes. The welding voltage of the designated welding voltage frequency pattern 28 and the designated welding voltage duty ratio pattern 29 is applied to the welding parts 6a and 6b, a welding current is passed, and the parts to be welded 6a and 6b are heated and melted. Next, in the cooling and holding step 24, the welding current energization is finished, and the cooling and solidification are waited while applying the specified pressurizing force. Next, in the movable electrode rise return step 25, the servo motor 1 is switched to the speed control mode, the movable electrode 4 is raised at a designated speed, and is stopped when the signal of the origin position detection sensor 9 is detected. Depending on the material and size of the parts to be welded 6a and 6b, the pressure application patterns 27a, 27b and 27c applied in each process are properly used. The welding voltage frequency pattern 28 sets the frequency and its pattern according to the size, material, or shape of the parts to be welded 6a, 6b. As described above, welding is completed through a series of steps.

  In the resistance welding method of the present invention, in order to concentrate heat on the welding surface and instantaneously heat and melt the surface layer of the welding surface, the following two methods are simultaneously performed during the energization heating process 23, and the synergistic effect of the interaction is performed. It is characterized by drawing out an effect.

The first method is that the pressure applied to the parts to be welded 6a and 6b during the current heating process 23 is made smaller than the pressure applied to the parts to be welded 6a and 6b during the cooling holding process 24. is there. By applying the pressurizing force, the contact resistance of the welding surface is kept large, and local heating in the surface layer of the welding surface is performed.

In the second method, the welding current supplied from the resistance welding power source 12 is such that the AC component included in the welding current is relatively large with respect to the DC component, and the frequency of the AC component having the largest amplitude is about 800 Hz. That is, the frequency is about 1000 Hz or higher. A welding current including such a high-frequency component flows in a concentrated manner on the surface layers of the parts to be welded 6a and 6b due to the skin effect. That is, current concentrates on the surface layer of the weld surface.

By simultaneously performing the above two methods, the resistance value of the surface layer of the welding surface is increased, and the welding current is concentrated there, so that Joule heat is locally applied to the surface layer of the welding surface. Generates and instantaneously heats, melts and fuses the surface layer of the welding surface. As a result, in the welding of dissimilar metal parts, small homogeneous metal parts with small heat capacity, and homogeneous metal parts with greatly different heat capacities, the welded part or the entire part may be melted or thermally deformed, and there is a wide range of heat affected parts. Thus, the base material characteristics are not deteriorated and the strength is not lowered due to the coarsening of crystal grains, and high quality and highly reliable welding is possible.

  In the cooling and holding step 24, in order to improve the adhesion degree of the joint surface, the cooling and solidifying process is awaited while applying a constant applied pressure equal to or higher than the applied pressure in the energizing and heating step 23.

Prior to describing the resistance welding power supply device 12 of the present invention, a conventional power supply circuit will be described. FIG. 3 shows a conventional power supply block wiring diagram. This conventional inverter power supply uses a single-voltage method by inserting a diode on the secondary side of the transformer. The welding current is distorted by the inductance component included in the wiring from the secondary side of the transformer to the welding jig, and becomes a current close to direct current as shown in FIG.

  FIG. 4 also shows a conventional power supply block wiring diagram. Since no diode is inserted on the secondary side of the transformer, it can be used with both voltages. However, even in this case, the polarity of the voltage is different for each switching in the inverter circuit. Therefore, the voltage polarity applied to the transformer does not change every switching. Therefore, as shown in FIG. 4B, the welding current becomes a low-frequency alternating current including ripples, that is, since the high-frequency component is not included, the present invention cannot use the power supply device. At the ripple level, the power as a high frequency component is small.

Therefore, the resistance welding power source device 12 of the present invention is arranged on the secondary side of the transformer with a high frequency in which the AC component is relatively large with respect to the DC component and the frequency of the AC component having the largest amplitude is about 800 Hz to about 1000 Hz. The circuit configuration allows a current containing many components to flow. FIG. 5 is a block diagram showing the resistance welding power source device of the present invention, characterized in the following four points.
(1) In the inverter circuit of the power supply device, the voltage polarity is changed for each switching, the voltage polarity applied to the transformer is changed for each switching, and the high-frequency component contained in the current flowing on the secondary side of the transformer is increased.
(2) The inductance of the power supply transformer is made as small as possible. That is, in a resistance welding power source transformer, by using two or more parallel windings or a litz wire as a winding, the inductance of the transformer is reduced and a large current flows easily. .
(3) The wiring from the secondary side of the transformer to the electrode of the resistance welding apparatus is composed of two or more parallel wirings or litz wires.
(4) The waveform of the inverter is basically one-pulse width modulation, but it may be two pulses or more, and may be a positive voltage-negative voltage, or conversely, a negative voltage-positive voltage, as in this embodiment.

  Conventionally, in resistance welding using high-frequency current, it has been considered that a large current required for welding cannot be flowed due to the inductance of a transformer or wiring. However, the present invention has the above (1), (2), (3 ) And (4), it is possible to flow a large current at a high frequency.

  The operation of the resistance welding power source apparatus of FIG. 5 will be described. A three-phase AC 51 is rectified by a rectifier circuit 52 and smoothed by a smoothing capacitor 53 to produce a DC power source. The DC power source is converted to AC by an inverter circuit 54 constituted by a power transistor, and the primary side of the transformer 55 is energized. The secondary side becomes a large current and can be used as a welding current. Here, the inverter circuit 54 is driven by the control circuit 60 through the drive circuit 61 with the switching frequency, duty ratio, and energization time of the inverter set by the input unit 58 and stored in the storage unit 59.

  The input unit 58 is a part for setting welding conditions such as a switching frequency, a duty ratio, and an energizing time, and receives a welding condition information signal from the overall control instruction device 11. The storage unit 59 is a part that stores the welding conditions input to the input unit 58. The display part is a part for displaying the stored welding conditions. The control circuit 60 is a part that outputs a signal to the drive circuit 61 of the inverter, and sends a drive signal to the drive circuit 61 of the inverter based on the switching frequency, duty ratio, energization time, and the like that are input and stored.

  The drive circuit 61 amplifies the drive signal from the control circuit 60, drives the power transistor of the inverter circuit 54, and is energized to the primary side of the transformer 55. 62 shown in the figure is a current detection circuit, which detects each current on the primary side and secondary side of the transformer 55 to determine whether there is an abnormality. FIG. 6 shows a primary side voltage waveform 65 and a secondary side current waveform 66 entering the transformer 55. In this power supply apparatus, the voltage polarity applied to the transformer 55 is switched by the inverter circuit 54 at every switching, and the welding current on the secondary side can be greatly pulsated positively and negatively.

  In the resistance welding of the present invention, the frequency is generally set to about 800 Hz to about 1000 Hz or more, and an extremely high frequency current flows as compared with a conventionally used seam welder having a frequency of about 400 Hz. In the present invention, the length of the winding of the transformer 55 and the length of the lead wire 56 (wiring) from the transformer 55 to the electrode terminals 57a and 57b are shortened, and the lead wire 56 is bundled in parallel wiring or thin wires. By using a litz wire, a high-frequency large current generated on the secondary side can be guided to the electrode terminals 57a and 57b for resistance welding.

  As described above, the resistance welding power source apparatus and the resistance welding method of the present invention are configured to allow a large current containing a high frequency component to flow.

The whole resistance welding apparatus block diagram. Time chart of resistance welding process. The power supply circuit and voltage waveform and current waveform of a conventional resistance welding apparatus. The power supply circuit and voltage waveform and current waveform of a conventional resistance welding apparatus. The block diagram of the resistance welding power supply device of this invention. Transformer primary voltage waveform and secondary current waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Servo motor 2 Linear motion unit 3 Pressurization shaft 4 Movable electrode 5 Fixed electrode 6 Parts to be welded 7 Servo motor drive circuit 8 Servo motor control circuit 9 Origin position detection sensor 10 Mode switching position detection sensor 11 Overall control instruction device 12 Resistance welding Power supply device 21 Movable electrode lowering step 22 Initial pressurizing step 23 Current heating step 24 Cooling and holding step 25 Movable electrode rising return step 26 Start signal 27 Pressure application pattern 28 Welding voltage frequency pattern 29 Welding voltage duty ratio pattern 51 Three-phase AC 52 Rectifier circuit 53 Smoothing capacitor 54 Inverter circuit 55 Transformer 56 Lead wire 57 Electrode terminal 58 Input unit 59 Storage unit 60 Control circuit 61 Drive circuit 62 Current detection circuit 65 Primary side voltage waveform 66 Secondary side current waveform

Claims (8)

A welding power source is connected between the two electrodes while two parts facing each other are sandwiched between the parts to be welded between the electrodes and a pressing force is applied, and welding is performed by passing a welding current to the workpiece. In the resistance welding method, the applied pressure applied to the welded part during energization of the welding current is smaller than the applied pressure applied to the welded part during cooling and holding after the energization of the welding current, and is supplied from the welding power source. The welding current is characterized in that the AC component contained in the welding current is relatively large with respect to the DC component, and the frequency of the AC component having the largest amplitude is about 800 Hz or more. The welding current supplied from the welding power source is such that the AC component included in the welding current is relatively large with respect to the DC component, and the frequency of the AC component having the largest amplitude is about 1000 Hz or more. Item 2. The resistance welding method according to Item 1. The welding current supplied from the welding power source is such that the AC component included in the welding current is relatively large with respect to the DC component, and the frequency of the AC component having the largest amplitude is arbitrarily changed during the energization of the welding current. The resistance welding method according to claim 1. A resistance to weld by placing a welding power source between the two electrodes facing each other and sandwiching the part to be welded between the two electrodes while applying pressure, and applying a welding current to the work piece In a resistance welding power source apparatus of a welding machine, after converting a DC power source to an AC power source, it is connected to the primary side of the transformer, the secondary side current of the transformer is set as a welding current, and the AC component included in the welding current is A resistance welding power supply device characterized in that the frequency of an alternating current component that is relatively large with respect to the direct current component and has the largest amplitude is about 800 Hz or more. The resistance welding power source device according to claim 4, wherein the frequency of the AC component having the largest amplitude is about 1000 Hz or more. 5. The resistance welding power source device according to claim 4, wherein the frequency of the AC component having the largest amplitude can be arbitrarily changed during energization of the welding current. 7. The resistance welding power supply device according to claim 4, wherein the winding of the transformer is two or more parallel windings or each winding is a litz wire. The resistance welding power supply device according to claim 4, 5, 6, or 7, wherein the wiring from the transformer to the electrode of the resistance welding machine is two or more parallel wirings or the wiring is a litz wire.

Images