JP4296648B2 - Electrode displacement control method and apparatus for resistance welding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a resistance welding electrode displacement control method and apparatus for obtaining a workpiece having high welding quality while preventing weld crack failure.
[0002]
[Prior art]
The current resistance welding method is a method of welding by fixing the pressurizing force, welding current, and energization time, which are the three major elements of resistance welding. In this current method, when a material to be welded that is likely to crack is resistance-welded, a workpiece with stable and sound welding quality cannot be obtained due to changes in the surface state of the welding electrode and changes in the properties of the workpiece. . Therefore, in the recent resistance welding method, in order to stabilize the work crushing amount (electrode displacement amount) due to the applied pressure of the electrode and thereby obtain a work with sound welding quality, a preset electrode displacement amount is obtained. immediately electrode displacement amount control method for stopping the energization when it reaches the came to be performed. In the conventional resistance welding control method, since the electrode displacement stop time is delayed due to the inertia shown in FIG. 7, the amount of collapse cannot be suppressed depending on the pattern of the electrode displacement amount at one electrode hit point. Therefore, defects such as weld cracks are generated in the workpiece.
[0003]
[Problems to be solved by the invention]
In resistance welding, many welding work factors and workpiece properties affect welding quality. When the workpiece (material to be welded) is a material that is particularly susceptible to weld cracking, such as phosphor bronze, among the welding work factors, the electrode surface condition (change over time) and the variation in workpiece properties are welded to the workpiece. Generate cracks. In particular, when the surface state of the electrode changes with time, in a mass production process, welding defects such as weld cracks of workpieces continuously occur, and there is a risk that many poorly welded parts are manufactured.
[0004]
Accordingly, it is an object of the present invention to provide a resistance welding electrode displacement control method and apparatus for supplying a welded part which prevents a product defect due to weld cracking and has a reliable welding quality.
[0005]
[Means for Solving the Problems]
In the present invention, in the resistance welding control method, paying attention to the fact that there is a strong correlation between the amount of electrode displacement (the amount of workpiece crushing) and the welding current, the amount of electrode displacement is measured at each electrode hit point. When a deviation occurs between the measured electrode displacement amount and the set electrode displacement amount by comparing with the preset upper limit and lower limit electrode displacement amounts, the deviation is caused to flow to the electrode at the next electrode hitting point according to this deviation. The above problem is solved by controlling the electrode displacement by increasing or decreasing the welding current.
[0006]
The reason why the electrode displacement can be controlled by adjusting the welding current flowing through the electrode is as follows. An increase in the amount of electrode displacement during resistance welding means an increase in the amount of heat input to the workpiece (workpiece). Since the conventional welding power source is set to a constant current, the electrode surface state changes as the number of electrode hits increases. Therefore, the contact resistance changes as the contact area between the electrode surface and the material to be welded changes, and as a result, the amount of heat between the electrode surface and the material to be welded changes. Here, the amount of heat is represented by Q = 0.24 × I ² × R × t, where I is the welding current (A), R is the contact resistance (Ω), and t is the time (sec). Corresponding to the increase / decrease of the contact resistance, the welding current flowing through the electrode is increased / decreased to make the amount of heat supplied to the material to be welded constant. As a result, the amount of electrode displacement can be controlled. Note that the contact resistance can be controlled even if the applied pressure is changed, but if the applied pressure is reduced, there is a possibility that sputtering or the like may occur. Therefore, in the present invention, the amount of electrode displacement is controlled by increasing or decreasing the welding current flowing through the electrode at a predetermined electrode hitting point while keeping the applied pressure constant.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The object is achieved by the resistance welding control method and resistance welding apparatus of the present invention described below.
As shown in FIG. 1, the resistance displacement electrode displacement control device of the present invention has first means 21, second means 22, third means 23, fourth means 24, and fifth means 25. A welding power source feedback control device 9 is provided.
[0008]
Since the first means 21 of the present invention includes the electrode displacement measuring circuit B, the electrode displacement amount upper / lower limit setting circuit C, the arithmetic circuit J, the comparison circuit K, and the arithmetic circuit L, the method of the present invention can measure the electrode displacement. The output of the circuit B and the set value of the electrode displacement amount upper / lower limit setting circuit C can be compared and calculated using the calculation circuit J, the comparison circuit K, and the calculation circuit L. The second means 22 of the present invention includes a continuous NG count setting circuit D, an electrode hitting count measurement circuit E including an arithmetic circuit O and a comparison circuit P, and a continuous NG count correction circuit G, whereby the method of the present invention. Can input the electrode hit point number and the continuous NG number set value to the continuous NG number correction circuit G. Since the third means 23 of the present invention includes the comparison circuit M and the current control circuit H that compare the outputs of the first means 21 and the second means 22 , the method of the present invention has been continuously removed. When the number of electrode hitting points reaches a preset number of consecutive electrode hitting points, it becomes possible to energize the electrode via the current control circuit H with the welding current adjusted for excess or deficiency at the next electrode hitting point.
[0009]
In the apparatus of the present invention, as shown in FIG. 1, the welding power source feedback control device 9 includes the fourth means 24, that is, the electrode spot number setting circuit F. Thereby, the present invention enables a method of correcting a preset number of electrode hits as the number of electrode hits increases. Further, in the apparatus of the present invention, the welding power source feedback control device 9 includes the fifth means 25, that is, the NG rate setting circuit I as shown in FIG. Accordingly, the present invention enables a method of stabilizing the control of the electrode displacement amount by adjusting the welding current depending on the number of non-set electrode hit points within a certain period after the preset electrode hit points.
[0010]
The resistance welding example of a phosphor bronze joint that is likely to cause weld cracking, which is the subject of the present invention, will be described more specifically by comparing it with a conventional example.
An example of resistance welding of a joint of a phosphor bronze coil terminal and a phosphor bronze connector terminal is shown. A joint obtained by joining a 1.5 mm diameter phosphor bronze wire coil terminal 10 and a 0.64 mm thick phosphor bronze plate connector terminal 11 by resistance welding is shown in FIGS. In conventional resistance resistance welding of phosphor bronze, as shown in FIG. 2 b, weld cracks 12 are likely to occur particularly in the vicinity of the welded portion 13 of the coil terminal 10 as well as insufficient welding strength. As shown in FIG. 3, the weld crack 12 in the vicinity of the welded portion of the coil terminal generates a weld crack when the electrode displacement amount L increases, that is, when the coil terminal collapse amount increases. Since this electrode displacement changes with changes in the electrode surface state and workpiece properties, various controls are required to maintain the electrode displacement in the stable region. In particular, since the surface state of the electrode changes as the number of electrode hits increases, the amount of crushing of the coil terminal increases as the surface state of the electrode changes, and as a result, weld cracks occur near the welded portion of the coil terminal. As a countermeasure for preventing the change in the electrode displacement amount, an electrode displacement amount control method is considered in which the current flowing through the electrode is stopped when a preset electrode displacement amount is reached. However, in this case, since there is a delay time of about 4 ms from when the set electrode displacement amount for stopping energization is reached to when the energization is actually stopped, the collapse amount of the coil terminal is not suppressed so much and stable electrode displacement is achieved. It is difficult to secure the amount.
[0011]
Therefore, in the present invention, when resistance welding is performed as shown in FIGS. 4A and 4B, the actual electrode displacement amount is measured for each electrode hitting point, and the upper limit set displacement amount 14 and the lower limit of the preset electrode displacement amount are measured. Compared with the set displacement amount 15, the number of electrode hit points of the actual electrode displacement amounts 16, 17, 18 deviating from both of these set displacement amounts 14, 15 is measured. Then, the number of electrode hit points deviating continuously from these set displacement amounts is calculated. This control method stabilizes the amount of electrode displacement by increasing / decreasing the welding current flowing to the electrode at the next electrode hitting point by a predetermined rate when the number of electrode hitting points that have been continuously removed becomes the preset electrode hitting point number. For example, when the measured electrode displacement amount (as indicated by reference numeral 16 in FIG. 4b) deviates to the preset number of electrode hits continuously on the upper limit set displacement amount side, the welding current at the next electrode hit point Is reduced by a predetermined rate, resistance welding is performed, and the amount of displacement of the workpiece is improved by controlling the amount of electrode displacement.
[0012]
In the following, a method and apparatus for adjusting the welding current of the present invention to stabilize the control of the electrode displacement amount, a schematic diagram of the method and apparatus for measuring the electrode displacement amount and the number of electrode hit points in the resistance welding of FIG. 6 will be described in more detail with reference to a flowchart showing the control contents of the present invention.
In the present invention, all electrode hit points after resistance welding start (start), electrode hit point number N is the potential difference between the fixed electrode 3 and the movable electrode 4 sandwiching the materials 1 and 2 to be welded. Measurement is performed by inputting to the electrode spot number measurement circuit E via the interelectrode voltage detection line 8 (electrode spot number measurement 26 in FIG. 6). The electrode displacement amount L is detected by attaching a displacement sensor 7 such as a linear gauge to the holding portion of the movable electrode 3 and is measured by the electrode displacement amount measurement circuit B (electrode displacement amount measurement 27 in FIG. 6). In the present invention, the applied pressure applied to the electrode is applied by the pressurizing cylinder 5, and the applied pressure is controlled to be constant. Further, both the electrode hitting point count measurement and the electrode displacement amount measurement may be performed at the same time or at the same time.
[0013]
Next, in order to calculate the number of electrode hit points deviating from the upper limit / lower limit setting value from the measured electrode displacement amount, first, the output from the electrode displacement amount measurement circuit B via the arithmetic circuit J is the electrode displacement amount upper / lower limit setting circuit C. Is compared with the output from the comparator circuit K and calculated by the arithmetic circuit L (electrode displacement amount 30 in FIG. 6) . On the other hand, the output electrode RBI frequency measurement circuit E for measuring the electrode RBI number, via a computing circuit O and comparison circuit P are entered in successive NG count correction circuit G. At this time , the set value of the electrode hitting point setting circuit F is inputted to the comparison circuit P (the set electrode hitting point number 28 in FIG. 6), and the result is obtained as the continuous NG number correcting circuit G and the NG rate setting circuit I (see FIG. 6). It is input to the electrode displacement amount NG rate calculation 29). Additionally, the set value of the continuous NG count setting circuit D is also input to the consecutive NG count correction circuit G (consecutive NG count n operation 34). The output of the continuous NG count correcting circuit G is compared with the output from the arithmetic circuit L by the comparison circuit M (continuous NG count 31 in FIG. 6) and input to the current control circuit H (current value calculation in FIG. 6). 32) As a result, the welding current (control current value output 33 in FIG. 6) adjusted for excess or deficiency can be supplied to the electrode via the welding power source 6.
[0014]
When the number of electrode hits increases, that is, when the electrode changes over time, or when the number of electrode hits increases and the electrode surface becomes rough, it is somewhat higher than adjusting the welding current with a small number of continuous NG electrode hits. The control of the electrode displacement is more stabilized by adjusting the welding current according to the number of electrode hits. Therefore, as shown in FIG. 1, in the method of the present invention, the relationship between the number of electrode hits and the number of consecutive NGs is set in advance in the continuous NG number setting circuit D, for example, the relationship shown in FIG. (The electrode displacement amount NG rate calculation and the continuous NG count n calculation in FIG. 6) can be set, and the preset continuous NG electrode hit count can be corrected as the electrode hit count increases.
[0015]
Further, after reaching the preset number of electrode hits, the control of the electrode displacement can be stabilized by adjusting the welding current depending on the number of non-set electrode hits that are NG within a predetermined period. . That is, the amount of electrode displacement is controlled by adjusting the current flowing through the electrode depending on the NG rate expressed by the following equation (current value calculation in FIG. 6).
NG rate = Number of non-set electrode hits (N _OU ) / Number of all electrode hits within the set period (N _IN )
However, in the above equation, the total number of electrode hits NIN within the set period is appropriately set according to the electrode surface state.
[0016]
Therefore, as shown in FIG. 1 in the process of the present invention, Ru set Teisu in advance NG rate setting circuit I the relationship between the total electrode RBI number within a set period and set out electrode RBI count. The output of the electrode hitting point measurement circuit E that has passed through the arithmetic circuit 0 and the comparison circuit P is input to the NG rate setting circuit I (electrode displacement amount NG rate calculation 29 in FIG. 6 ) , and then the current is controlled via the comparison circuit M. In the circuit H, the welding current is adjusted depending on the number of non-set electrode hit points within a predetermined period (current value calculation 32, control current value output 33 in FIG. 6). In the present invention, the NG rate is preferably constant.
[Brief description of the drawings]
FIG. 1 shows a schematic diagram of a method and apparatus for measuring the amount of electrode displacement and the number of electrode hit points in resistance welding according to the present invention.
2 shows a joint in which a phosphor bronze wire coil terminal and a phosphor bronze plate connector terminal are joined by resistance welding. FIG. 2a is a partial perspective view of the joint, and FIG. 2b is a partial cross-sectional view of the joint. is there.
3 shows a relationship between an electrode displacement amount L and a welding current of a joint between a coil terminal and a connector terminal shown in FIG.
FIG. 4a shows the relationship between the number of electrode hits and the welding current, and FIG. 4b shows the relationship between the number of electrode hits and the amount of electrode displacement.
FIG. 5 shows the relationship of the number of consecutive NG times to the number of electrode hit points.
FIG. 6 shows a flowchart showing the control contents of the present invention. FIG. 7 shows the relationship between the amount of electrode displacement and the energization time in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Material to be welded 2 ... Material 3 to be welded ... Movable electrode 4 ... Fixed electrode 5 ... Pressure cylinder 6 ... Welding power supply 7 ... Displacement sensor 8 ... Interelectrode voltage detection line 9 ... Welding power supply feedback control device 10 ... Coil terminal 11 ... Connector terminal 12 ... Weld crack 13 ... Welded portion 14 ... Upper limit set displacement 15 of electrode displacement amount ... Lower limit set displacement amount 16 of electrode displacement amount ... Actual electrode displacement amount 17 deviating from set displacement amount ... From set displacement amount Deviated actual electrode displacement 18 ... Actual electrode displacement 21 deviated from set displacement 21 ... First means 22 ... Second means 23 ... Third means 24 ... Fourth means 25 ... Fifth means 26 ... electrode spot count measurement 27 ... electrode displacement measurement 28 ... set electrode spot count 29 ... electrode displacement NG rate calculation 30 ... electrode displacement 31 ... continuous NG count 32 ... current value calculation 33 ... control current value output 34 ... continuous NG The number n operation

Claims (8)

In the electrode displacement control method for resistance welding,
Set the upper limit setting displacement amount and lower limit setting displacement amount of the electrode displacement amount in advance,
Measure the number of electrode hits (N) when resistance welding, measure the amount of electrode displacement in the pressurization direction for each number of electrode hits,
When the number of electrode hit points where the electrode displacement amount has continuously deviated from the upper limit set displacement amount and the lower limit set displacement amount is calculated, and the continuously deviated electrode hit number reaches the preset continuous electrode hit number By passing the welding current adjusted to the excess or deficiency at the next electrode hit point to the electrode, and stopping the current flowing to the electrode when the pre-installed electrode displacement amount is reached,
An electrode displacement amount control method for resistance welding, wherein the electrode displacement amount of the electrode is controlled. The electrode displacement amount control method according to claim 1, wherein the electrode displacement amount of the electrode is controlled by changing the preset number of consecutive electrode impact points (N _VA ) as the number of electrode impact points increases. After the preset number of electrode hits,
NG rate = Number of non-set electrode hits (N _OU )
/ Number of all electrode hits within the set period (N _IN )
The electrode displacement amount control method according to claim 1, wherein the electrode displacement amount of the electrode is controlled by applying a welding current adjusted for excess or deficiency to the electrode in accordance with the NG rate indicated by the following. 2. The electrode displacement amount control method according to claim 1, wherein phosphor bronze is welded. 2. The electrode displacement amount control method according to claim 1, wherein a phosphor bronze wire coil terminal having a diameter of 1.5 mm and a phosphor bronze plate connector terminal having a thickness of 0.64 mm are welded. In an electrode displacement control device for resistance welding,
First means (21) for measuring individual electrode displacement amounts in the pressurizing direction and comparing them with preset upper and lower limit electrode displacement amounts;
A second means (22) for measuring the number of electrode hit points (N) and calculating the number of electrode hit points continuously deviating from a preset upper and lower limit electrode displacement amount; and When the set number of continuous electrode hits has been reached, the third means (23) for causing the welding current adjusted to be excessive or insufficient at the next electrode hit to flow to the electrode,
An electrode displacement amount control device for resistance welding, characterized by a welding power source feedback control device (9) comprising: The electrode displacement amount control device according to claim 6, further comprising fourth means (24) for changing the preset number of continuous electrode hits as the number of electrode hits increases. After the preset number of electrode hits,
NG rate = Number of non-set electrode hits (N _OU )
/ Number of all electrode hits within the set period (N _IN )
The electrode displacement amount control device according to claim 6, further comprising fifth means (25) for supplying the electrode with a welding current adjusted for excess or deficiency in accordance with an NG rate indicated by:

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