JP3223065B2 - Pre-energization control device for resistance welding and method for determining pre-energization conditions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-energization control device and a pre-energization condition determining method for resistance welding, particularly spot welding.

[0002]

2. Description of the Related Art Resistance welding, particularly spot welding, has been used for welding various products using steel sheets, and in recent years, defective welding tends to increase. In other words, welding of unsuitable materials to be welded, such as pressed parts having complicated shapes and variations in welding positions, causes only a part of the apparent contact between the plates only by pressing the electrodes, resulting in a concentration of current density. This causes initial dust and electrode welding.

Further, materials that are difficult to deform and adhere to, such as high-strength steel and various surface-treated steel sheets, have been used.
Increasingly, the above problems were exacerbated. Therefore, for the purpose of sufficiently softening the material to be welded or bringing the electrode and the material to be welded into close contact with each other and smoothing the actual energization, pre-energization before the main energization has been adopted.

[0004] However, there is no means for determining an effective pre-energization current or pre-energization time according to the welding situation, and the actual situation is that the pre-energization conditions are determined at the welding site by experience and intuition.

As a current control method including pre-energization, there are the following methods (I) and (II). (I) Welding quality is improved by performing preheat slope control.
A control method disclosed in Japanese Patent No. 4676. (II) To improve the welding quality by selecting a current pattern suitable for the welding conditions of the work to be welded.
A control method disclosed in Japanese Patent Publication No. 80.

[0006]

SUMMARY OF THE INVENTION Among these methods,
In the conventional method (I), from the viewpoint of pre-energization as preheating, the up slope control (conventionally increasing the call angle so as to realize a current gradient such that the current is sequentially increased one cycle at a time) is conventionally performed. Control method). No means for determining the optimal pre-energization condition is shown. Further, the up-slope control includes a time during the pre-energization time that does not contribute to heat generation and softening of the material to be welded.
In other words, a time period during which there is no effect as the preliminary energization is included.
When welding hard or poorly matched materials, the pre-energization time must be increased, causing problems such as increased dead time and tact time.

The above-mentioned conventional method (II) does not specifically mention a current pattern itself suitable for welding conditions. As described above, the conventional pre-energization method and apparatus do not show the optimization, and the operator is empirical,
The pre-energization conditions had to be intuitively determined.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for determining the most effective and efficient pre-energization conditions in resistance welding in consideration of the above conventional problems.

[0009]

In order to achieve the above object, the present invention provides a welding current between electrodes sandwiching a material to be welded, and a current between electrodes.
Current detector with means for measuring pressure directly or indirectly
And voltage detectors, and physical quantities detected by both detectors
Temperature distribution in the material to be welded using a heat conduction model
Output the parameter temperature required for changing the pre-energization conditions.
Calculation unit and preliminary welding conditions according to the parameter temperature are recorded.
The stored storage unit and the parameter temperature output from the calculation unit
Observe the temperature and nugget according to the temperature parameter in the storage unit
Output section that outputs the optimal pre-welding conditions that do not cause cracking
And a control unit for controlling the pre-energization based on the pre-welding conditions output from the comparison output unit .

[0010]

In the above configuration, the temperature distribution of the material to be welded is
Extracts parameter temperature and its parameter temperature variation
In this way, the optimum pre-energization is performed in accordance with the condition, and the material to be welded is brought into close contact with the preheating so that welding can be performed smoothly.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. (Embodiment 1) FIG. 1 shows the configuration of a pre-energization control device for resistance welding according to Embodiment 1. As shown in FIG.
Detects the end of welding from the start of welding at the welding portion 3 of the welding machine 2 as one hit point, and stores the output signal from the detecting portion 1 as a hit point count and the first storage section 4 as the total number of hit points. The second storage unit 5 stores optimum pre-energization conditions for each hit point,
That is, the optimum pre-energization conditions according to the electrode wear state are stored. The condition changing unit 6 outputs the total number of spots of the welded portion 3 output from the first storage unit 4 to the second storage unit 5, and the optimum number according to the number of spots output from the second storage unit 5. The preliminary welding conditions are output to the control unit 7. The control unit 7 outputs a control signal so as to perform welding under the changed pre-welding conditions, and the welding machine 2 determines the optimum pre-welding conditions according to the number of spots in the welding part 3, that is, in accordance with the wear condition of the electrode. Perform welding.

(Embodiment 2) FIG. 2 shows the configuration of a pre-energization control device for resistance welding according to Embodiment 2. In FIG. 2, a welding current necessary for numerical analysis for optimum pre-welding conditions in the welding portion 8 is detected by a current detecting portion 9, a voltage between electrodes in the welding portion 8 is detected by a voltage detecting portion 10, and a calculating portion 11 Is output to The calculation unit 11 calculates the temperature distribution in the material to be welded by simulation using a heat conduction model.

More specifically, according to the flow chart shown in FIG. 3, welding is started by inputting the sheet thickness, the number of sheets to be overlapped, and the material. Next, the inter-electrode voltage and the welding current are detected, and the energizing diameter indicating the energizing path is determined from the detected inter-electrode voltage and the welding current,
The potential distribution is estimated, and the temperature distribution in the material to be welded is calculated from a heat conduction model obtained by differentiating the resistance heat generation in the material to be welded and the heat conduction equation. By repeating this process during energization, the temperature distribution in the material to be welded is calculated every moment from the start of energization to an arbitrary time.

The temperature distribution in the material to be welded immediately after the completion of the pre-energization is calculated by using the simulation using the heat conduction model, and a necessary portion is extracted as a parameter temperature. It is output to the comparison output unit 12. The pre-energization condition and the allowable range of the parameter temperature, which are obtained in advance, are stored in the storage unit 13.
The comparison output unit 12 compares the parameter temperature output from the calculation unit 11 with the allowable range, and when the parameter temperature exceeds the allowable range, selects an optimal preliminary welding condition from the storage unit 13 and outputs it to the control unit 14. The control unit 14 outputs a control signal so as to perform welding under the changed pre-energization condition, controls the power source 15 of the welding machine, and performs welding under the optimal pre-energization condition according to the situation.

(Embodiment 3) Next, an embodiment of a method for determining a pre-energization condition will be described with reference to FIGS. 4, 5 and 7 and Table 1.

FIG. 4 shows a flowchart of a method for determining the pre-energization condition. Hereinafter, a method for determining the pre-energization condition realized according to this flowchart will be described in detail. First, the temperature distribution of the material to be welded is calculated, and the parameter temperature is extracted. After confirming the number of data, the parameter temperature variation calculation is performed. If the number of welding conditions is satisfied, the parameter temperature variation is compared to determine the pre-energization condition.

More specifically, FIG. 5 illustrates a process of calculating a temperature distribution in a material to be welded by a simulation using a heat conduction model from the detected welding current and resistance between electrodes, and calculating a parameter temperature. is there.

As an example, the up-slope was selected for the pre-energization, and the welding conditions were 1.2 mmt × 2 galvanized steel sheet, 10 kA of main energizing current, 320 kgf of pressurization, and 20 cycles of welding time. The resistance between the chips and the welding current obtained from the detected voltage between the electrodes sandwiching the material to be welded are respectively a1
In the welding current a2, the section of a5 is shown as a preliminary energizing section which is an up slope portion, and the remaining section of a6 is shown as a main energizing section. From the measured chip voltage a1 and welding current a2, (Example 2)
From the temperature distribution calculated by the simulation using the heat conduction model shown in the above, the central temperature a3 between the materials to be welded and the melting portion diameter which is the maximum diameter in the radial direction from the range of the melting temperature or higher (hereinafter referred to as the nugget diameter a4) ) Is shown in the figure. It is explained that when the center temperature a3 rises with time and eventually reaches the melting temperature, a melted portion appears, and the change in diameter is a curve of the nugget diameter a4.

The center temperature a7 immediately after the pre-energization section a5 is selected as a parameter temperature for explaining this embodiment, and the description of each embodiment will be made using the center temperature a7. In the initial stage of energization, the resistance a1 between the tips is measured as a different change for each hitting point due to the contact between the materials to be welded or the state of wear of the electrodes, and the center temperature a3 calculated by the simulation also reflects those states. Show different changes.
In the pre-energization, which is used for the purpose of pre-heating the materials to be welded and bringing the welding current smoothly through,
The change in the central temperature a3 of the main energizing section a6 is stable for each hit point, that is, the smaller the variation of the central temperature a7 immediately after the preliminary energizing section a5, the more the above purpose is satisfied.

In this embodiment, when the standard deviation of the center temperature a7 is selected as an indicator of the degree of variation, the center temperature a7 immediately after the pre-energization, which is the parameter temperature, is calculated for each dot by simulation using a heat conduction model. From the point data that can be statistically processed to the center temperature a7
By obtaining the standard deviation of, the variation can be obtained. Similarly, the standard deviation of the center temperature a7 is obtained for any pre-welding conditions, and the standard deviation is smaller when each is compared in consideration of external factors such as occurrence of dust during pre-energization or tact time. The pre-energization condition is a more optimal pre-energization condition, that is, a condition for achieving the purpose of the pre-energization described above.

[0021]

[Table 1]

Table 1 is an example illustrating the present invention. The main energizing current value was set to 10 kA in the welding of two galvanized steel sheets of 1.2 mmt.
I chose. The above-mentioned variation of the center temperature a7 is represented by the standard deviation from the average center temperature of data for 50 dots under each pre-energization condition. The results of Table 1 clearly show that the preliminary welding condition D has the smallest standard deviation, and is the most effective among the preliminary welding conditions shown in this example. Further, in the preliminary welding conditions A, B, and C, that is, in the conventional pre-energization using the upslope, there is a section where the effect is not present as shown in FIG. Not only is it impossible to obtain, but also wasteful energizing time is wasted. At sites where a large amount of spot welding is used, such as in the automobile industry, this time loss, even if the current is low, causes a large power loss. According to the present invention, the most effective and rational pre-welding conditions can be selected for any pre-welding conditions.

(Embodiment 4) Another method of determining the pre-energization condition will be described in detail with reference to FIGS. FIG.
In the case of, the standard deviation of the parameter temperature when the pre-energization current value (Ip in FIG. 8) is changed while the pre-energization time (tp in FIG. 8) is kept constant in the welding of 1.2 mmt galvanized steel sheet and two laps Is to compare. In this embodiment, the temperature at the center of the material to be welded was selected as the parameter temperature as described above. The abscissa indicates the current value of the pre-energization, and the ordinate indicates the standard deviation of the center temperature after the pre-energization obtained by the above-described method. I have. In this embodiment, the pre-energization time tp is 1
The cycle was constant, and the pre-energization current value Ip was also constant at the value shown on the horizontal axis in the figure. In the example, the standard deviation of the central temperature increases as the preliminary energizing current value decreases at about 8 kA or less, and the standard deviation of the central temperature increases at 11 kA, and it is confirmed that dust occurs during the preliminary energizing. It can be seen that the current value of 7 to 8 kA is the most effective pre-energizing condition in the pre-energizing condition of the embodiment. That is, according to the present invention, by using the above-described pre-energization determination method, the most effective pre-energization current value can be obtained when the pre-energization time is constant. This is effective when the welding time is limited.

Further, another method of determining the pre-energization will be described in detail with reference to FIGS. In the case of FIG. 7, the standard deviation when the pre-energization time (tp in FIG. 8) is changed while the pre-energization current value (Ip in FIG. 8) is constant at 8 kA in the welding of 1.2 mmt galvanized steel sheet and two laps. Is to compare. In this embodiment, the center temperature of the material to be welded after the pre-energization was selected as the parameter temperature in the same manner as described above. From this embodiment, the standard deviation decreases as the pre-energization time increases, and the standard deviation is substantially constant between the third cycle and the fourth cycle, and the effect of the close contact by preheating is substantially the same. It can be seen that three cycles of the pre-energization time are the most effective and rational conditions for the pre-energization time within the range of the present embodiment. That is, according to the present invention, the most effective and rational pre-energization time can be obtained when the pre-energization current value is constant by using the pre-energization condition determination method of the above-described (Example 3). And, in particular,
This is effective when dust is likely to occur at the beginning of energization, such as when the materials to be welded are bad at the welding site or when a hard material is welded.

As described above, the pre-energization control device and the pre-energization condition determining method for resistance welding according to the present embodiment determine the most effective and efficient pre-energization conditions for bringing the workpieces into close contact by preheating. Can be determined rationally regardless of Also, with respect to a change with time such as electrode wear during continuous hitting, a stable preheating effect can always be obtained by selecting a pre-energization condition corresponding to the welding state.

It should be noted that the present invention is not limited to the above embodiment, and various modifications may be made without departing from the scope of the present invention, such as the parameter temperature and the pre-energization current pattern required for determining the pre-energization conditions. Needless to say, this is possible.

[0027]

As is apparent from the above description of the embodiment, the resistance welding pre-energization control device and the pre-energization condition determination method of the present invention bring the workpieces into close contact by preheating, which is the main purpose of pre-energization. For this reason, the most effective and efficient pre-energization conditions can be rationally determined by comparing the standard deviation of the observed parameters with the environment and conditions used. By appropriately setting the energizing conditions, a stable adherence of the material to be welded can always be obtained, and an excellent effect of improving the quality and reliability of welding can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pre-energization control device for resistance welding according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a pre-energization control device for resistance welding according to another embodiment of the present invention.

FIG. 3 is a flowchart for explaining a simulation using a heat conduction model in the method for determining a pre-energization condition for resistance welding according to the present invention.

FIG. 4 is a flowchart illustrating a method for determining a pre-energization condition for resistance welding according to the present invention.

FIG. 5 is an explanatory diagram of a method for determining pre-energization conditions for resistance welding according to the present invention.

FIG. 6 is an explanatory diagram of another method for determining a pre-energization condition of resistance welding according to the present invention.

FIG. 7 is an explanatory diagram of another method for determining a pre-energization condition of resistance welding according to the present invention.

FIG. 8 is an explanatory diagram of another method for determining a pre-energization condition of the resistance welding according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detecting part 2 Welding machine 3 Welding part 4 First storage part 5 Second storage part 6 Condition changing part 7 Control part a1 Curve indicating resistance change between electrodes a2 Curve indicating change in welding current a3 Center between materials to be welded Part temperature a4 Curve indicating change in nugget diameter a5 Preliminary energizing section a6 Main energizing section a7 Parameter temperature

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-75633 (JP, A) JP-A-63-154276 (JP, A) JP-A-62-240180 (JP, A) JP-A-6-240180 47563 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 11/24 394 B23K 11/24 398

Claims (4)

(57) [Claims] 1. A welding current between electrodes sandwiching a material to be welded,
Current detection with means for measuring the voltage directly or indirectly
Output part and voltage detection part, and physical parts detected by both detection parts
Temperature distribution in the material to be welded using the heat conduction model
Output the parameter temperature required for changing the pre-energization conditions
And the preliminary welding conditions according to the parameter temperature
Stored storage unit and parameters output from operation unit
Observe the temperature and adjust the nugget according to the temperature parameter in the storage unit.
Output section that outputs the optimal pre-welding conditions that do not cause heat
And a control unit for controlling the pre-energization based on the pre-welding conditions output from the comparison output unit . 2. A welding current between electrodes sandwiching a material to be welded and a voltage between the electrodes are detected, and the detected physical quantity is converted into a heat conduction model.
After pre-energization using simulation based on
Numerical analysis of the temperature distribution in the material
The required temperature or temperature distribution immediately after
Extraction as a data temperature, and
Repeatedly repeat the data
Parameter temperature for the parameter
Determining the temperature variation of the meter;
Under any pre-energization conditions, parameters after pre-energization
From the step of comparing temperature variations, an acceptable
Among the power supply conditions,
A method for determining the pre-energization conditions for resistance welding with the small ones being the optimal pre-energization conditions . 3. When the pre-energization time is fixed,
3. The pre-energizing condition according to claim 2,
It is necessary to determine using the
Characteristic method for determining pre-energization conditions for resistance welding. 4. The resistance welding method according to claim 2 , wherein when the pre-energization current is constant, an optimum pre-energization time is determined by using the pre-energization condition determination method according to claim 2 , and the pre-energization condition is set. How to determine pre-energization conditions.