KR101729607B1 - Resistance Spot Welding System Using Dynamic Resistance Characteristics for Weld Quality Improvement and Method for Power Supply for Resistance Spot Welding System - Google Patents

Abstract

According to the present invention, to obtain a more stable welding quality, power for welding is supplied to a current carrying a front half portion of which contact resistance before a dynamic resistance critical point is greatly changed with constant-voltage control or constant power control. Moreover, in a current carrying a rear half portion of which contact resistance after the dynamic resistance critical point is relatively and constantly changed, an optimal welding state is able to be obtained with constant-current control from external effects.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding system and a resistance spot welding apparatus,

The present invention relates to a resistance spot welding system in which resistance spot welding is performed by supplying power in constant voltage or constant power control to the power supply front part in order to obtain more stable welding quality in the resistance spot welding, And a power supply technique for a resistance spot welder.

Resistance spot welding is a method in which a large current is passed through a contact resistance generated between the base materials after sufficiently pressurizing the base materials to be welded with welding electrodes, and the base material is melted and bonded by resistance heat generated at this time.

The change in resistance that occurs during welding is due to the resistance that occurs when the welding current passes through the base material, the resistance increases as the temperature of the base material rises due to heat generation, and the nugget is formed by melting the base material. This phenomenon is generally referred to as dynamic resistance, and Figure 1 shows a typical dynamic resistance curve that varies with time during welding.

The dynamic resistance and the dynamic resistance critical point will be described with reference to Fig.

① Section: The initial contact resistance is drastically reduced as the base material is softened by resistance heating while being pressed by the pressing force.

② Section: The resistance increases with the temperature rise of the base material. At t2, the interface between the base materials begins to melt and nugget begins to be generated.

③ Section: As the nugget grows, the resistance decreases due to the increase of the energized area.

④ Section: As the growth of nugget slows down, the magnitude of contact resistance also decreases slowly.

⑤ Section: The growth of the nugget is stopped, and the contact resistance is slightly reduced as the pressing portion increases due to the pressing force.

Point A: The dynamic resistance value at the point when the dynamic resistance value does not increase any more or begins to decrease (when the growth of the nugget starts) after entering the section ③ after increasing the dynamic resistance value in the section ②, ) Is referred to as "dynamic resistance critical point ".

Although many studies have been made on the dynamic resistance characteristics of such resistance spot welding, there have been no reports of improvement in welding quality by changing the power supply technique using dynamic resistance characteristics.

In the actual industrial field, the contact resistance changes due to the change of the shape or physical properties of the base material surface, the change of the thickness of the plating layer, the wear of the electrode, and the sorting effect that a part of the welding current flows in the adjacent welding portion. It is difficult to keep it stable. In order to maintain stable welding quality, an effective method is needed to detect the change of welds in real time by these external factors.

On the other hand, conventional resistance spot welding supplies a welding power source only by a single control method by the constant voltage control mode or the constant current control mode, and controls the voltage or current flowing through the base material constantly during the energization time. However, such a single control method has the following problems.

In the case of controlling only by the constant current control method, the initial heat generated due to the high contact resistance at the initial energization causes the expansion force of the molten metal to be higher than the pressing force of the base metal, so that initial ripples may occur. Even when the contact resistance between the electrodes is changed, the calorific value changes and stable welding quality can not be obtained.

In the case of control by only the constant voltage control method, even though the contact resistance is high at the initial stage of the energization, a constant voltage is applied, and the current gradually changes, so that the initial current does not flow. However, since the resistance of the nugget grows in the latter period, There is a problem in maintaining constant welding quality due to the occurrence of warpage

In addition, when control is performed only by the constant power control method, even if the contact resistance between the base materials changes during the welding operation, the power is controlled so as to maintain a constant calorific power and is stably welded. However, since the resistance is decreased in the latter half of the welding, there is a problem.

Japanese Patent Application Laid-Open No. 10-2013-00092476 entitled " Power Control Method of Spot Welding System and Spot Welding System Using the Same " Registered Patent No. 10-0482487 "Spot Welding Quality Evaluation System" (Registered on April 1, 2005)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art as described above, and it is an object of the present invention to provide a welding power source, A new type of resistance spot welding system and a resistance spot welding power supply technique capable of obtaining an optimal welding condition even under external influence by controlling the constant current in the latter half of the energization with a relatively constant change in contact resistance after the dynamic resistance critical point I would like to propose.

In order to solve the above problems, the present invention provides a resistance spot welding machine comprising: a resistance spot welder having a pair of welding electrodes; A power supply for supplying welding power to the welding electrode; A voltage detector for detecting a voltage value of welding power supplied to the welding electrode; A current detector for detecting a current value of a welding power supply supplied to the welding electrode; A dynamic resistance calculating section for calculating a dynamic resistance value by dividing the voltage value detected by the voltage detecting section by the current value detected by the current detecting section; and a dynamic resistance calculating section for calculating a dynamic resistance value from the dynamic resistance calculated by the dynamic resistance calculating section, Wherein the power supply unit supplies a constant voltage mode to the welding electrode from the start of energization to the point of time when the dynamic resistance threshold search unit finds the dynamic resistance threshold, Wherein the power supply device controls the power supply device to supply the welding power supply in the constant power mode, and the power supply device supplies the welding electrode with a welding power source in a constant current mode until the copper resistance threshold point finds the copper resistance threshold, A welding power supply control unit for controlling the power supply unit A control device comprising: Wherein the control apparatus further includes a dynamic resistance critical point occurrence time interval storage unit for storing information on a dynamic resistance critical point occurrence expected time interval and wherein the dynamic resistance critical point searching unit includes a dynamic resistance critical point occurrence time interval The welding power source control unit controls the welding power source to supply the welding power source in the constant current mode to the welding electrode from the end of the estimated time period of the dynamic resistance critical point occurrence time until the end of energization, And controls the power supply unit.

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According to another aspect of the present invention, there is provided a power supply technique for supplying power for welding to a welding electrode of a resistance spot welder, wherein the power supply device is a constant voltage mode or a constant power mode Wherein the welding power supply supplies welding power to the welding electrode, wherein the power supply device supplies welding power to the welding electrode in a constant current mode from a critical point of time until the end of energization, Wherein the dynamic resistance threshold value is a time point at which the dynamic resistance value of the power supply divided by the current value increases and starts to decrease or does not increase any more and the dynamic resistance threshold does not exist in the predetermined dynamic resistance threshold occurrence time interval The threshold time point may be set to a time point at the end of the predefined dynamic resistance critical point occurrence time period And it characterized in that.

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In the above, it is preferable that the information on the dynamic resistance critical point occurrence time interval includes information on standard dynamic resistance critical points and information on the distance between the standard dynamic resistance points.

As described above, in order to obtain a more stable welding quality, the welding power is supplied to the power supply front part where the change of the contact resistance before the resistance threshold is severe by the constant voltage control or the constant power control, and the contact resistance The resistance spot welding system and the resistance spot welding apparatus are provided with a power supply technique for a resistance spot welding machine in which the constant current is controlled in the latter half of the welding process.

Figure 1 shows a typical dynamic resistance curve that varies with time during welding,
2 is a block diagram of a resistance spot welding system according to the present invention;
FIG. 3 is a graph showing a dynamic resistance curve showing the standard dynamic resistance critical point and the front / rear spacing interval information,
4 to 6 are graphs showing nugget sizes according to Comparative Example, Experimental Example 1 and Experimental Example 2,
7 is a block diagram of the control measuring section of the present embodiment,
8 shows a main screen of the PC program,
9 is a data search screen of a PC program,
10 is a screen showing a welding waveform of a PC program.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention in the drawings, portions not related to the description are omitted, and like reference numerals are given to similar portions throughout the specification.

Throughout the specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

2 is a block diagram of a resistance spot welding system according to the present invention.

The resistance spot welding system, which is one embodiment according to the present invention, comprises a resistance spot welder 100, a power supply device 200, and a control device 300.

The resistance spot welder 100 has a pair of welding electrodes, and presses the base material with a pair of welding electrodes. That is, the resistance spot welder 100 can be interpreted as a kind of pressure device.

In addition, the power supply device 200 supplies a welding power source, that is, a large current capable of melting the base material, to a pair of welding electrodes.

An AC power source device, a DC power source device, a capacitor discharge energy device, an inverter power source device, or the like may be employed as the power source device 200 for resistance spot welding. In this embodiment, an inverter power source device is adopted.

The inverter power supply 200 rectifies the commercial AC power and then generates a high-frequency alternating current. Since the switching frequency is much higher than that of the conventional AC power supply system, the control cycle is much shorter than that of the power supply having a different control period. Since the current flowing in the base material flows through the DC having a very small ripple, it is possible to concentrate the heat and obtain good welding quality as compared with other power supply devices.

The inverter power supply 200 of the present embodiment includes a diode rectifier, an L-C filter, an IGBT inverter, a step-down transformer, and a diode for rectifying the secondary side.

In other words, 60Hz 3-phase AC 220V input is converted to DC power through a 3-phase diode rectifier, and the rectified voltage is mixed with ripple component, so it makes smooth DC input to inverter side through L-C filter.

The DC link voltage is converted to alternating alternating voltage at a high frequency of 2 kHz by the phase-shift PWM technique of a single-phase full-bridge inverter.

The alternating current output converted by the inverter becomes an alternating current of low voltage and large current through the intermediate tap transformer for stepping down. Then, through the secondary rectifying diode, finally, a very large direct current is supplied to the base material through the electrode for welding.

On the other hand, a voltage detector 401 and a current detector 402 are provided to detect the voltage value and the current value of the welding power source supplied to the welding electrode, respectively.

The control device 300 controls the power supply device 200 based on the voltage value and the current value detected by the voltage detection unit 401 and the current detection unit 402. [

The control device 300 is provided with a dynamic resistance calculating unit 310, a dynamic resistance threshold searching unit 320, a dynamic resistance threshold occurrence time period storing unit 330, a welding power supply controlling unit 340, and the like.

The dynamic resistance calculation unit 310 receives the voltage value detected by the voltage detection unit 401 and the current value detected by the current detection unit 402 and uses the detected voltage value to detect the voltage value detected by the voltage detection unit 401, ), And the dynamic resistance value is calculated in real time.

Using the dynamic resistance value calculated in real time by the dynamic resistance calculating unit 310, the dynamic resistance threshold searching unit 320 finds the dynamic resistance threshold.

Here, the dynamic resistance critical point means the point at which the dynamic resistance value increases, and no longer increases or begins to decrease.

Meanwhile, the welding power source control unit 340 controls the welding power source of the power source device 200.

The welding power supply controller 340 controls the power supply 200 to supply welding power from the start of energization to the end of energization, and is divided into a first control mode and a second control mode based on a critical point.

First, the case where the critical-point of time is the dynamic resistance critical point found by the dynamic resistance critical point searching unit 320 will be described.

In the first control mode, that is, from the start of energization to the dynamic resistance critical point, the welding power source control unit 340 controls the power supply device 200 to supply welding power to the welding electrode in the constant voltage mode or the constant power mode.

That is, in the first control mode, the power supply device 200 is controlled in the constant voltage mode or the constant power mode.

In the second control mode, that is, from the dynamic resistance critical point to the end of energization, the welding power source control unit 340 controls the power source device 200 to supply the welding electrode with the welding power source in the constant current mode.

That is, in the second control mode, the power supply 200 is controlled in the constant current mode.

The constant voltage mode, the constant power mode, and the constant current mode mean that the voltage value, the power value, and the current value are controlled to be a predetermined value or a value within a predetermined range.

In order to control the power supply device 200 in the constant voltage mode, the constant power mode, and the constant current mode, the welding power controller 340 controls the voltage value detected by the voltage detector 401 and / or the voltage detected by the current detector 402 Feedback control may be performed based on the value.

In a further embodiment of the present invention, the controller 300 may further include a dynamic resistance critical point occurrence time interval storage unit 330.

The dynamic resistance critical point occurrence time interval storage unit 330 stores information about the dynamic resistance critical point occurrence time interval.

The information on the estimated time period of occurrence of the dynamic resistance critical point may be composed of the standard dynamic resistance threshold information and the back and forth spacing information from the standard dynamic resistance threshold.

In this case, the standard copper resistance critical point means the most standard point at which the copper resistance critical point can appear, which can be regarded as the most preferable copper resistance critical point predicted in advance for a specific welding situation.

That is, in order to obtain the nugget size most suitable for the base material desired to be welded, after adjusting the welding current, the energization time, and the pressing force, optimum conditions are found while welding, and then the dynamic resistance curve obtained under the optimum condition In the case of the dynamic resistance curve, the standard dynamic resistance threshold information corresponds to the "A" point, and the back and forth spacing information from the standard dynamic resistance threshold refers to the width of the "B" interval.

In addition, the forward / backward interval information from the standard dynamic resistance threshold means information on a time interval that is spaced back and forth from the standard dynamic resistance threshold, which can be set as a ratio to the total energizing time or set to an absolute time amount.

The forward and backward separation interval information from the standard copper resistance threshold is given as a constant, as opposed to the standard copper resistance critical point being changed according to a specific welding situation. That is, the estimated time interval of the dynamic resistance threshold is basically changed by the standard dynamic resistance threshold.

For example, if the total energizing time is 100ms and the distance information from the standard copper resistance threshold is set to 10% of the total energizing time, this corresponds to 10ms as an absolute amount of time.

Therefore, if the standard dynamic resistance threshold is 40ms, the estimated time interval of dynamic resistance threshold corresponds to 30ms ~ 50ms.

(40 ms - 10 ms = 30 ms, 40 ms + 10 ms = 50 ms)

When the dynamic resistance critical point occurrence time interval storage unit 330 is provided as described above, the dynamic resistance critical point searching unit 320 finds the dynamic resistance critical point only within the dynamic resistance critical point occurrence expected time interval.

That is, the dynamic resistance threshold is not found for the interval of 0 ms to 30 ms and the interval of 50 ms to 100 ms.

Accordingly, when the dynamic resistance critical point search unit 320 finds the dynamic resistance critical point within the dynamic resistance critical point occurrence time interval, the welding power source control unit 340 changes the control method.

In addition, if the dynamic resistance critical point search unit 320 can not find the dynamic resistance critical point within the dynamic resistance critical point occurrence time interval, the welding power control unit 340 determines the end point of the dynamic resistance critical point occurrence time period The power supply apparatus 200 controls the power supply apparatus 200 to supply welding power to the welding electrodes in the constant current mode.

<Comparative Example>

4 shows the nugget size formed as a result of controlling the constant current control method over the entire energization time while changing the magnitude of the pressing force to 60 kg, 75 kg, and 95 kg.

As can be seen in FIG. 4, it can be seen that the nugget size largely changes in response to a change in the contact resistance.

<Experimental Example 1>

5 shows the nugget size formed as a result of controlling the constant force control from the beginning of the energization to the critical point and the constant current control from the critical point to the end of energization while changing the magnitude of the pressing force to 60 kg, 75 kg, and 95 kg.

As can be seen in FIG. 5, it can be seen that stable welding can be performed because the nugget size does not change even when the contact resistance changes. However, the scattering of the nugget size at the same contact resistance is somewhat large.

<Experimental Example 2>

6 shows the nugget size as a result of controlling the constant voltage from the initial stage to the threshold point and the constant current control from the critical point to the end of the energization while changing the magnitude of the pressing force to 60 kg, 75 kg and 95 kg.

As can be seen from FIG. 6, it can be seen that the variation of the nugget size is small even in the change of the contact resistance, the stable welding is possible, and the scattering of the nugget size at the same contact resistance is also small.

Meanwhile, the control device 300 of the present embodiment may be implemented by being divided into a control measurement unit and a PC connected to the control measurement unit through Ethernet communication.

The control measuring unit can be described as a block diagram as shown in FIG.

The control part consists of the control MPU of the Cortex M3 (STM32F103VCT6) and is composed of (1) a part for measuring the welding power source voltage and the welding power source voltage part, (2) a part for driving the inverter for the power supply device, and ) Ethernet communication that communicates with the PC for configuration and monitoring.

In order to process the welding current and welding voltage, which are measured in real time, the analog signal transferred from the sensor is converted into a digital value by using the ADC module embedded in the MPU. The converted value is used for the important It is used to find the dynamic resistance in real time.

In addition, the generation of the switching signal for controlling the inverter power supply uses a PWM module. More specifically, the DC link voltage is switched to control the power supply 200 by using the TIM_CH1, TIM_CH1N, and TIM_CH2 , TIM_CH2N are used.

An Ethernet module using SPI1 is used for communication between the control unit and the program running on the PC.

The PC connected to the control unit via Ethernet communication displays data of welding current and welding voltage measured in real time and can set various conditions for driving the inverter for the power supply unit 200.

The PC program includes a dynamic resistance calculating unit 310, a dynamic resistance threshold searching unit 320, a dynamic resistance threshold occurrence time interval storage unit 330, and a welding power supply control unit 340.

The welding power supply control unit 340 of the PC program determines whether the control measuring unit operates the constant voltage / constant power mode and the constant current mode. Accordingly, the control measuring unit controls the welding power supply control unit 340 of the PC program Thereby driving the inverter for the apparatus. Accordingly, it can be understood that the welding power source control unit 340 of the present embodiment is dispersedly provided in the PC program and the control measuring unit.

The PC program sets various conditions and control types for driving the inverter for the power supply device 200, displays the welding data at each welding, stores the data, and searches for and analyzes the stored data using various search conditions. It is a monitor program that operates.

FIG. 8 shows a main screen of the PC program. When the operation start button is clicked, it is connected to the control measuring section and is clicked when the operation stop button is clicked. When the DATA view button is clicked, the screen is switched to the screen for searching the stored welding data as shown in FIG. 8, and various conditions for welding are stored when the storage button is clicked. The LIST value in the main screen displays the average current, average voltage, average resistance, maximum current, maximum voltage, maximum resistance, and energization time in the order of up to 300 recently welded data.

FIG. 9 is a data search screen, which shows welding data within a search date range specified by various search conditions and displays the data in a list form, displays the maximum value, minimum value, average value, and standard deviation of the detected weld data, Format.

Search date can be specified by date and time. It is possible to search by condition by setting upper and lower limit values of welding data to be searched. The retrieved data shows average current, average voltage, average resistance, maximum current, maximum voltage, maximum resistance, and energization time in the order of date and time.

If one of the searched data is selected and double-clicked, the welding waveform screen of Fig. 10 is displayed.

10 is a screen showing a welding waveform and has various functions for analyzing a waveform. Clicking the View button displays the measured value and time of the clicked area of the weld waveform on the left side of the screen. The Adjust button adjusts the range that displays the welding current, welding voltage, and welding resistance. The Restore button moves to the original welding waveform before the magnification function is used. The left arrow button moves to the previous enlarged welding waveform, and the right arrow button moves to the welding waveform after being enlarged. The magnification button is used to specify the magnification range using the mouse and then click the right mouse button to enlarge the waveform. The calculation button calculates the welding current, welding voltage, welding resistance average value, maximum value and minimum value. .

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the embodiments described above are intended to be illustrative, but not limiting, in all respects. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

100: Resistance spot welder
200: Power supply
300: Control device
310: Copper resistance calculating section
320: Dynamic resistance critical point searching section
330: Estimation time interval of dynamic resistance critical point storage section
340: welding power source control unit
401:
402:

Claims (5)

A resistance spot welder having a pair of welding electrodes;
A power supply for supplying welding power to the welding electrode;
A voltage detector for detecting a voltage value of welding power supplied to the welding electrode;
A current detector for detecting a current value of a welding power supply supplied to the welding electrode;
A dynamic resistance calculating section for calculating a dynamic resistance value by dividing the voltage value detected by the voltage detecting section by the current value detected by the current detecting section; and a dynamic resistance calculating section for calculating a dynamic resistance value from the dynamic resistance calculated by the dynamic resistance calculating section, Wherein the power supply unit supplies a constant voltage mode to the welding electrode from the start of energization to the point of time when the dynamic resistance threshold search unit finds the dynamic resistance threshold, Wherein the power supply device controls the power supply device to supply the welding power supply in the constant power mode, and the power supply device supplies the welding electrode with a welding power source in a constant current mode until the copper resistance threshold point finds the copper resistance threshold, A welding power supply control unit for controlling the power supply unit A control device comprising:
And,
The control apparatus according to claim 1, further comprising a dynamic resistance critical point occurrence time interval storage section for storing information about a dynamic resistance critical point occurrence expected time interval, wherein the dynamic resistance threshold point searching section includes a dynamic resistance threshold The welding power source control unit controls the power supply unit so that the power supply unit supplies welding power to the welding electrode in the constant current mode from the end of the estimated time period of the dynamic resistance critical point occurrence time until the end of energization And a resistance spot welding system using the dynamic resistance characteristic for improving the welding quality.
delete A power supply technique in which a power supply supplies welding power to a welding electrode of a resistance spot welder,
Wherein the power supply device supplies welding power to the welding electrode in a constant voltage mode or in an electrostatic mode from a start of energization to a critical point,
Wherein the power supply apparatus supplies power for welding to the electrode for welding in a constant current mode from a critical point to an end of energization,
Wherein the critical point is a dynamic resistance critical point which is a point at which the dynamic resistance value of the welding power supply supplied to the welding electrode divided by the current value increases and starts to decrease or decrease no more.
Wherein when the dynamic resistance critical point does not exist within a predetermined dynamic resistance critical point occurrence expected time interval, the critical point corresponds to an end time of the predetermined dynamic resistance critical point occurrence expected time interval. Power Supply Technique for Resistance Spot Welder Using Characteristics.
delete The method of claim 3,
Wherein the information on the dynamic resistance critical point occurrence time interval information includes standard dynamic resistance critical point information and front and rear separation interval information from the standard dynamic resistance critical point. Power supply technique.

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