WO2007029170A1 - A spot welding machine with control circuit for determining the magnitude of weld current to be applied on load circuit - Google Patents

A spot welding machine with control circuit for determining the magnitude of weld current to be applied on load circuit Download PDF

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Publication number
WO2007029170A1
WO2007029170A1 PCT/IB2006/053108 IB2006053108W WO2007029170A1 WO 2007029170 A1 WO2007029170 A1 WO 2007029170A1 IB 2006053108 W IB2006053108 W IB 2006053108W WO 2007029170 A1 WO2007029170 A1 WO 2007029170A1
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WO
WIPO (PCT)
Prior art keywords
current
circuit
welding machine
weld current
welding
Prior art date
Application number
PCT/IB2006/053108
Other languages
French (fr)
Inventor
Salih Arslantas
Ozkal Bayir
Original Assignee
Arcelik Anonim Sirketi
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arcelik Anonim Sirketi filed Critical Arcelik Anonim Sirketi
Publication of WO2007029170A1 publication Critical patent/WO2007029170A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/24—Electric supply or control circuits therefor
    • B23K11/25—Monitoring devices
    • B23K11/252—Monitoring devices using digital means
    • B23K11/256—Monitoring devices using digital means the measured parameter being the inter-electrode electrical resistance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • B23K11/115—Spot welding by means of two electrodes placed opposite one another on both sides of the welded parts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/12—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to investigating the properties, e.g. the weldability, of materials
    • B23K31/125—Weld quality monitoring

Definitions

  • the present invention relates to a spot welding machine.
  • the spot welding being a type of resistance welding, is a frequently used method for welding of metal pieces.
  • the high temperature created by the current that is passed through the metal pieces to be joined and the pressure applied on the metals provide the metals to melt and to coalesce.
  • the welding machine used in the application of spot welding basically provides the low current and high voltage delivered by a power supply to be converted into a low voltage and high current in the secondary side of a transformer.
  • a control circuit triggers the thyristor with a certain phase angle on the primary side of the transformer for a certain period of time to control the magnitude of the welding current on the secondary side.
  • the resulting current is transferred to the pieces to be joined by means of electrodes that apply pressure above and below a spot.
  • the load circuit is made up of the workpiece and resistances resulting from the transitions. These resistances are of significance since the voltage on the secondary side of the transformer is low. Therefore the quality of the welding changes depending on the features of the load circuit.
  • the welding current is increased as the number of weldings done by the welding machine increases, in order to compensate the surface deteriorations in the electrodes with time.
  • the quality of the welding cannot be increased as expected since the conditions that affect the quality of the welding like the material, coating and surface variations, changes in resistance in the pieces to be joined by welding, the differences in the pressure applied by the electrodes are not taken into account.
  • a current sensor is used on the secondary side of a transformer and the actual welding current measured by this sensor while the welding is carried out is adjusted until the actual current substantially equals the commanded current which is triggered by a thyristor in the primary side of the power supply.
  • the object of the present invention is to design a welding machine wherein the welding quality is enhanced by determining the weld current based on the resistance of the load circuit.
  • the welding machine of the present invention there is a measurement circuit on the primary side of the transformer and a control circuit in connection with this measurement circuit.
  • the said control circuit applies a very small sized test current for a very short time while the electrodes are clamped on the workpiece but before the weld current is applied.
  • the measurement circuit measures the resistance of the load circuit on the secondary side that corresponds to this test current.
  • the measured resistance value of the load circuit is compared with the pre-measured load circuit resistances and the corresponding weld current values to determine the magnitude of the weld current that has to be applied for the said resistance. This value is transferred to the thyristor circuit to provide the application of welding with the determined current value. Consequently a constant weld current can be applied that is conformable with the load resistance during the said welding process.
  • test current is applied for a time period that can't be perceived by the person applying the weld, for example for a duration of 5 - 50 milliseconds.
  • the current values recorded in the processor are values determined numerically for certain load resistances.
  • the current values recorded in the processor are composed of values that correspond to certain load resistances of the quality welds that have been implemented previously.
  • Figure 1 - is the schematic view of the welding machine.
  • the welding machine (1) of the present invention comprises:
  • the load circuit is comprised of all the intermediary parts together with the workpiece (P), through which the weld current passes as well as the electrodes (9).
  • the material, coating and surface features of the workpiece (P) and the deterioration rate of the electrodes (9), the pressure applied after the workpiece (P) is clamped on them are all factors affecting the resistance value of the load circuit. This resistance value varies even with two consecutive welding processes applied by the same person on the same workpieces (P) by the same electrodes (9).
  • the welding machine (1) of the present invention takes into account these factors in determining the weld current by means of applying the test current before each welding.
  • the load circuit values derived from previous quality welding processes or determined by numerical/analytic means and the corresponding weld current values are recorded in the control circuit (6).
  • the control circuit (6) measures the load resistance between the electrodes (9) by the measurement circuit (7) by means of applying the test current just before the start of the welding process and thereafter provides the application of a thus determined constant weld current on the workpieces (P) during the welding process.
  • the features of the load circuit varies due to reasons like the pressure applied by the electrodes (9) in even two consecutive welding processes, the application of the test current before the application of each current provides the possibility of determining a weld current value that takes into account the features of the load circuit.
  • the test current is applied for a very short time period, for example 5 - 50 milliseconds.
  • the test current is applied for the purpose of measuring the load resistance that is relevant for the conditions of that moment, only on the point of welding, not for making the welding. Since the test current is very small, welding is not done during the testing phase.
  • the control circuit (6) applies a test current.
  • the measurement circuit (7) measures the load circuit resistance that corresp onds to this test current.
  • the weld current value that corresponds to this load circuit resistance in the control circuit (6) is applied on the workpiece (P).
  • a weld current is determined taking into account the features of the effective load circuit at that moment and this weld current is provided to be applied on the workpieces (P) during the welding process without being changed.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Quality & Reliability (AREA)
  • Lining Or Joining Of Plastics Or The Like (AREA)
  • Resistance Welding (AREA)

Abstract

The present invention relates to a spot welding machine (1) . In this welding machine (1) , a constant test current of a very small magnitude is run for a short period of time before the weld current is applied. The load circuit resistance value measured with a measurement circuit (7) in response to this current is compared with the load circuit resistance measured previously and the relative corresponding weld current values recorded in a control circuit (6) to determine the magnitude of the weld current that has to be applied on the said load circuit.

Description

Description
A SPOT WELDING MACHINE WITH CONTROL CIRCUIT FOR DETERMINING THE MAGNITUDE OF WELD CURRENT TO BE APPLIED ON LOAD CIRCUIT
[1] The present invention relates to a spot welding machine.
[2] The spot welding, being a type of resistance welding, is a frequently used method for welding of metal pieces. The high temperature created by the current that is passed through the metal pieces to be joined and the pressure applied on the metals provide the metals to melt and to coalesce. The welding machine used in the application of spot welding, basically provides the low current and high voltage delivered by a power supply to be converted into a low voltage and high current in the secondary side of a transformer. A control circuit triggers the thyristor with a certain phase angle on the primary side of the transformer for a certain period of time to control the magnitude of the welding current on the secondary side. The resulting current is transferred to the pieces to be joined by means of electrodes that apply pressure above and below a spot. However the magnitude of the welding current depends on the load circuit aside from the winding features of the transformer and the losses. The load circuit is made up of the workpiece and resistances resulting from the transitions. These resistances are of significance since the voltage on the secondary side of the transformer is low. Therefore the quality of the welding changes depending on the features of the load circuit.
[3] In state of the art, the welding current is increased as the number of weldings done by the welding machine increases, in order to compensate the surface deteriorations in the electrodes with time. However in this implementation, the quality of the welding cannot be increased as expected since the conditions that affect the quality of the welding like the material, coating and surface variations, changes in resistance in the pieces to be joined by welding, the differences in the pressure applied by the electrodes are not taken into account.
[4] In the welding machine described in the state of the art United States Patent no.
US4849601, a current sensor is used on the secondary side of a transformer and the actual welding current measured by this sensor while the welding is carried out is adjusted until the actual current substantially equals the commanded current which is triggered by a thyristor in the primary side of the power supply.
[5] In the welding machine described in another state of the art document, the United
States Patent no. US6064029, wherein a voltage is applied to the primary circuit to generate a welding current which is measured by a current sensor to obtain a dynamic resistance curve. The calculation of the nugget size and nugget penetration is based on this curve and the weld current is controlled accordingly by using the dynamic resistance curve. [6] In the welding machine described in the United States Patent no. US5938947, the current value measured on the primary side is controlled whether it is within a predetermined allowable range. If the detected value of the primary current exceeds the predetermined allowable range, then it is decided that the secondary current is erroneous and the applied current is changed.
[7] In state of the art, changing the weld current values based on the current sensor measurements while the welding process is carried out that takes only milliseconds is not sufficient. However it is not possible to take into account all the factors like material, coating and surface variations, resistance changes, variations in the pressure applied by the electrodes in such a short period of time.
[8] The object of the present invention is to design a welding machine wherein the welding quality is enhanced by determining the weld current based on the resistance of the load circuit.
[9] The welding machine designed to fulfill the object of the present invention is explicated in the attached claims.
[10] In the welding machine of the present invention, there is a measurement circuit on the primary side of the transformer and a control circuit in connection with this measurement circuit. The said control circuit applies a very small sized test current for a very short time while the electrodes are clamped on the workpiece but before the weld current is applied. The measurement circuit measures the resistance of the load circuit on the secondary side that corresponds to this test current. The measured resistance value of the load circuit is compared with the pre-measured load circuit resistances and the corresponding weld current values to determine the magnitude of the weld current that has to be applied for the said resistance. This value is transferred to the thyristor circuit to provide the application of welding with the determined current value. Consequently a constant weld current can be applied that is conformable with the load resistance during the said welding process.
[11] The test current is applied for a time period that can't be perceived by the person applying the weld, for example for a duration of 5 - 50 milliseconds.
[12] In an embodiment of the present invention, the current values recorded in the processor are values determined numerically for certain load resistances.
[13] In another embodiment of the present invention, the current values recorded in the processor are composed of values that correspond to certain load resistances of the quality welds that have been implemented previously.
[14] The welding machine designed to fulfill the object of the present invention is illustrated in the attached figures, where:
[15] Figure 1 - is the schematic view of the welding machine.
[16] Elements shown in the drawings are numbered as follows: [17] 1. Welding machine
[18] 2. Power supply
[19] 3. Transformer
[20] 4. Primary side
[21] 5. Secondary side
[22] 6. Control circuit
[23] 7. Measurement circuit
[24] 8. Thyristor circuit
[25] 9. Electrode
[26] The welding machine (1) of the present invention comprises:
[27] - a power supply (2),
[28] - a transformer (3) having a primary (4) and a secondary side (5), converting the high voltage and low current electricity applied on the primary side (4) into low voltage and high current electricity on the secondary side (5),
[29] - two electrodes (9) that transmit the weld current formed on the secondary side (5) of the transformer (3) to the workpieces (P),
[30] - a thyristor circuit (8) that controls the energy in conformance with the value of the current to be transmitted to the primary side (4) of the transformer (3),
[31] - a measurement circuit (7) situated on the primary side (4) of the transformer (3), and measuring the load resistance on the secondary side (5),
[32] - a control circuit (6) wherein the load resistance values and the corresponding weld current values determined by the producer are recorded, that applies a very small sized test current before every welding process for a very short time period while the electrodes (9) are clamped on the workpiece (P) but just before the weld current is applied, and compares the resistance value of the load circuit measured by the measurement circuit (7) in relation to this current with the recorded resistance values and transfers the corresponding weld current value to the thyristor (3) to be applied on the workpiece (P).
[33] The load circuit is comprised of all the intermediary parts together with the workpiece (P), through which the weld current passes as well as the electrodes (9). The material, coating and surface features of the workpiece (P) and the deterioration rate of the electrodes (9), the pressure applied after the workpiece (P) is clamped on them are all factors affecting the resistance value of the load circuit. This resistance value varies even with two consecutive welding processes applied by the same person on the same workpieces (P) by the same electrodes (9). The welding machine (1) of the present invention takes into account these factors in determining the weld current by means of applying the test current before each welding.
[34] In this embodiment, the load circuit values derived from previous quality welding processes or determined by numerical/analytic means and the corresponding weld current values are recorded in the control circuit (6). The control circuit (6) measures the load resistance between the electrodes (9) by the measurement circuit (7) by means of applying the test current just before the start of the welding process and thereafter provides the application of a thus determined constant weld current on the workpieces (P) during the welding process. Furthermore since the features of the load circuit varies due to reasons like the pressure applied by the electrodes (9) in even two consecutive welding processes, the application of the test current before the application of each current provides the possibility of determining a weld current value that takes into account the features of the load circuit.
[35] The test current is applied for a very short time period, for example 5 - 50 milliseconds. The test current is applied for the purpose of measuring the load resistance that is relevant for the conditions of that moment, only on the point of welding, not for making the welding. Since the test current is very small, welding is not done during the testing phase.
[36] In the welding machine (1) of the present invention, first the electrodes (9) are clamped on the workpieces (P). Afterwards, the control circuit (6) applies a test current. The measurement circuit (7) measures the load circuit resistance that corresp onds to this test current. The weld current value that corresponds to this load circuit resistance in the control circuit (6) is applied on the workpiece (P).
[37] By way of the welding machine (1) of the present invention, a weld current is determined taking into account the features of the effective load circuit at that moment and this weld current is provided to be applied on the workpieces (P) during the welding process without being changed.

Claims

Claims
[1] A welding machine (1) comprising a power supply (2), a transformer (3) having a primary (4) and a secondary side (5), converting the high voltage and low current electricity applied on the primary side (4) into low voltage and high current electricity on the secondary side (5), two electrodes (9) that transmit the weld current formed on the secondary side (5) of the transformer (3) to the workpieces (P), a thyristor circuit (8) that controls the energy in accordance with the value of the current to be transmitted to the primary side (4) of the transformer (3), and characterized by a measurement circuit (7) situated on the primary side (4) of the transformer (3), measuring the load resistance on the secondary side (5), and a control circuit (6) wherein the load resistance values and the corresponding weld current values determined by the producer are recorded, that applies a very small sized test current before every welding process for a very short time period while the electrodes (9) are clamped on the workpiece (P) but just before the weld current is applied, and compares the measured resistance value of the load circuit in relation to this current with the recorded resistance values and transfers the corresponding weld current value to the thyristor circuit (3) to be applied on the workpiece (P).
PCT/IB2006/053108 2005-09-05 2006-09-05 A spot welding machine with control circuit for determining the magnitude of weld current to be applied on load circuit WO2007029170A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
TR200503543 2005-09-05
TR2005/03543 2005-09-05

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WO2007029170A1 true WO2007029170A1 (en) 2007-03-15

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2389590C2 (en) * 2008-07-28 2010-05-20 Открытое акционерное общество "Новосибирский завод химконцентратов" Power supply for contact welding
RU2421311C2 (en) * 2009-04-08 2011-06-20 Александр Александрович Шевцов Power supply of contact welding machine
JP2022134917A (en) * 2021-03-04 2022-09-15 トヨタ自動車株式会社 Resistance spot welding method and resistance spot welding device

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56160885A (en) * 1980-05-14 1981-12-10 Nippon Abionikusu Kk Resistance welding equipment
US4634828A (en) * 1984-09-21 1987-01-06 Dengensha Manufacturing Company Limited Control method of resistance welding
JPH07266059A (en) * 1994-03-30 1995-10-17 Nippon Avionics Co Ltd Welding quality control method and apparatus
US5523541A (en) * 1993-10-14 1996-06-04 Miyachi Technos Corporation Method and apparatus for controlling constant current for resistance welding

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56160885A (en) * 1980-05-14 1981-12-10 Nippon Abionikusu Kk Resistance welding equipment
US4634828A (en) * 1984-09-21 1987-01-06 Dengensha Manufacturing Company Limited Control method of resistance welding
US5523541A (en) * 1993-10-14 1996-06-04 Miyachi Technos Corporation Method and apparatus for controlling constant current for resistance welding
JPH07266059A (en) * 1994-03-30 1995-10-17 Nippon Avionics Co Ltd Welding quality control method and apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2389590C2 (en) * 2008-07-28 2010-05-20 Открытое акционерное общество "Новосибирский завод химконцентратов" Power supply for contact welding
RU2421311C2 (en) * 2009-04-08 2011-06-20 Александр Александрович Шевцов Power supply of contact welding machine
JP2022134917A (en) * 2021-03-04 2022-09-15 トヨタ自動車株式会社 Resistance spot welding method and resistance spot welding device
JP7435505B2 (en) 2021-03-04 2024-02-21 トヨタ自動車株式会社 Resistance spot welding method and resistance spot welding device

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