CN117359070A - Method for estimating nugget diameter of resistance spot welding - Google Patents

Abstract

The present invention discloses an estimation method for estimating a nugget diameter using a predetermined estimation value using a welding parameter that affects the size of a nugget diameter formed in resistance spot welding as an explanatory variable and using an estimated value of the nugget diameter as a target variable, wherein the estimation method comprises: a resistance value obtaining step of obtaining, as a welding parameter, a second half resistance value which is a resistance value of a second half of an energization period at the time of welding and which is a resistance value of an entire energization circuit including a welding object; and a nugget diameter calculation step of substituting the acquired second half resistance value into the estimated value to calculate the nugget diameter.

Description

Method for estimating nugget diameter of resistance spot welding

Technical Field

The present disclosure relates to a method of estimating nugget diameter for resistance spot welding.

Background

Conventionally, resistance spot welding has been used as a means for joining a plurality of metal plates to each other in the manufacture of a body frame or the like of a vehicle. In the resistance spot welding, a welding target (a plurality of metal plates) is energized while being sandwiched by a pair of electrodes, and the metal plates are fused and joined to each other by joule heat generated by the resistance of the welding target itself or the like. In order to improve the bonding strength of the welded portions between the metal plates, it is necessary to sufficiently secure the weld nugget diameter obtained by the resistance spot welding. Thus, a method of estimating whether the welding nugget diameter is successfully ensured is demanded.

For example, in the method for estimating the nugget diameter in the resistance spot welding apparatus described in japanese patent application laid-open No. 2020-171942, preliminary energization for registering the main mode is performed under a welding condition set in advance. Then, when the main welding is performed under the preset welding conditions, the nugget diameter obtained by the main welding is estimated based on the resistance value in the main mode and the amount of deviation of the resistance value at the time of the main welding. In such an estimation method, for example, information on the entire energization period from the start of energization to the stop of energization is used as the resistance value.

Disclosure of Invention

However, in the case where there are various disturbances in the welding site, for example, a gap between steel plates, inclination of the steel plates, abrasion of the tip end portion of the electrode pressed against the steel plates, or the like, there is a problem in that the correlation between the resistance value and the nugget diameter is not high throughout the entire energization period, and the estimation accuracy of the nugget diameter is poor.

The present disclosure may be implemented as follows.

(1) According to one aspect of the present disclosure, a method of estimating a nugget diameter is provided. The method for estimating the nugget diameter is a method for estimating the nugget diameter by using a predetermined estimated value, which uses a welding parameter that affects the size of the nugget diameter formed in resistance spot welding as an explanatory variable and uses the estimated value of the nugget diameter as a target variable, wherein the method comprises: a resistance value obtaining step of obtaining, as the welding parameter, a second half resistance value which is a resistance value of the second half of the energization period at the time of welding and which is a resistance value of the entire energization circuit including the welding object; and a nugget diameter calculation step of substituting the acquired second half resistance value into the estimated value to calculate the nugget diameter.

According to this aspect, the nugget diameter is estimated using the second half resistance value, which is the resistance value of the second half of the current flow, as the welding parameter. The inventors of the present application have found that the second half resistance value has a higher correlation with the nugget diameter than the first half resistance value of the current application. By estimating using the latter half resistance value having a high correlation with the nugget diameter as the welding parameter, the accuracy of estimating the nugget diameter can be improved.

(2) In the above aspect, the energization period during the welding may include an initial energization period and a main energization period that is performed at an interval after the initial energization, and the second half resistance value may be a resistance value of a second half of the main energization period. According to this aspect, when the energization period includes the initial energization and the main energization, the accuracy of estimating the nugget diameter can be further improved by using the resistance value of the latter half of the period of high correlation, that is, the main energization period, as the welding parameter.

(3) In the above aspect, the estimation may be a first order equation calculated by linearly regressing a plot point where the second half resistance value and the nugget diameter are associated with each other. According to this aspect, the correlation between the second half resistance value and the nugget diameter can be expressed uniquely. Further, the estimated value can be easily created by using the plot points in which the second half resistance value and the nugget diameter are associated.

Drawings

Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals refer to like elements.

Fig. 1 is a schematic configuration diagram showing a nugget diameter estimating system as a first embodiment of the present disclosure.

Fig. 2 is a block diagram showing a schematic configuration of the control device.

Fig. 3 is a flowchart showing steps in the method of estimating the nugget diameter.

Fig. 4 is a graph showing a time change in resistance value.

Fig. 5 is an enlarged view of a portion surrounded by a two-dot chain line in the graph in fig. 4.

Fig. 6 is a graph showing a relationship between the resistance value of the second half of energization and the nugget diameter.

Fig. 7 is a diagram for explaining the effect when the nugget diameter is estimated using the latter half resistance value as a welding parameter.

Fig. 8 is a diagram for explaining the effect when the nugget diameter is estimated using the latter half resistance value as a welding parameter.

Fig. 9 is a diagram showing a change in welding current in the second embodiment of the present disclosure.

Detailed Description

A. First embodiment:

A1. the nugget diameter estimating system 1 is integrally constituted:

in describing the method of estimating the nugget diameter in the first embodiment of the present disclosure, first, the configuration of the nugget diameter estimating system 1 (hereinafter, also simply referred to as "estimating system 1") will be described. Fig. 1 is a schematic configuration diagram showing a nugget diameter estimating system 1 as a first embodiment of the present disclosure. The estimation system 1 is a system for estimating the nugget diameter of a welded portion formed on a welded member W by resistance spot welding performed by the resistance spot welding apparatus 10. The estimation system 1 includes a resistance spot welding apparatus 10, a control apparatus 100, and a measurement mechanism 9.

The resistance spot welding apparatus 10 is an apparatus for joining together by melting a welded member W in which a plurality of metal plates W1, W2 are stacked. The resistance spot welding apparatus 10 includes a welding gun G and a robot arm RA.

The welding gun G includes a gun body 11, upper and lower electrodes 2 and 3 as a pair of electrodes, an electrode lifting device 4, a pressurizing device 5, and a current adjusting device 6. The gun body 11 is held by the robot arm RA. The lower electrode 3 is a fixed electrode arranged in a state of being fixed to the lower portion 11b of the gun body 11. The upper electrode 2 is a movable electrode movable in a direction along the opposing direction of the upper electrode 2 and the lower electrode 3. The upper electrode 2 is mounted on the upper portion 11a of the gun body 11 via the electrode lifting device 4. The upper electrode 2 and the lower electrode 3 each have a flow path, not shown, formed therein for circulating cooling water.

The electrode lifting device 4 is an electric device that holds and lifts the upper electrode 2. The electrode lifting device 4 is mounted on the tip of the upper portion 11a of the gun body 11. The electrode lifting device 4 includes a servomotor 41 and a lifting member 42 coupled to a drive shaft of the servomotor 41. The electrode lifting device 4 operates the servomotor 41 in accordance with a lifting command from the control device 100 to lift the lifting member 42.

The pressurizing device 5 presses the upper electrode 2 and the lower electrode 3 in a direction in which the upper electrode 2 and the lower electrode 3 approach each other. Specifically, the pressurizing device 5 is a device for pressurizing the welding member W with a predetermined pressurizing force in a state where the welding member W is sandwiched between the upper electrode 2 and the lower electrode 3, and applying a force to the upper electrode 2 and the lower electrode 3, respectively. The pressurizing device 5 applies a predetermined force to each of the upper electrode 2 and the lower electrode 3 in response to a pressurizing command from the control device 100.

The current adjustment device 6 adjusts the value of the welding current (hereinafter, current value) flowing between the upper electrode 2 and the lower electrode 3 according to the current command sent from the control device 100. The current adjustment device 6 is, for example, a device provided with a variable resistor or a device provided with a converter.

Fig. 2 is a block diagram showing a schematic configuration of the control device 100. In the present embodiment, the control device 100 has a function as an estimating device for estimating the nugget diameter in resistance spot welding in addition to a function of controlling the operation of the resistance spot welding device 10. The estimation device may be configured to be separated from the control device 100 and perform data communication by wire or wireless.

The control device 100 includes a communication unit 30, a display 40, an input operation unit 50, a storage unit 60, and a CPU 20. The control device 100 is, for example, a computer having the respective constituent elements 20 to 60. The communication unit 30 connects the resistance spot welding apparatus 10 and the measuring mechanism 9 to the control device 100 in a communicable manner. The display 40 is, for example, a liquid crystal display, and displays information according to instructions from the CPU 20. The input operation unit 50 has, for example, a keyboard and a mouse, and receives an instruction from a user.

The memory unit 60 stores various programs for controlling the operation of the resistance spot welding apparatus 10 and various data of the estimated expression 670. The storage unit 60 includes RAM, ROM, rewritable nonvolatile memory, and the like. The estimation formula 670 is a relational formula prepared in advance for calculating an estimation value of the nugget diameter. Specifically, the estimated expression 670 is a relational expression in which a welding parameter that affects the size of the nugget diameter is used as an explanatory variable and an estimated value of the nugget diameter is used as a target variable. In the first embodiment, as the welding parameter, the estimated expression 670 uses the second half resistance value, which is the resistance value of the entire current carrying circuit including the welding object, as the resistance value of the second half of the current carrying period at the time of welding, and is shown by the following equation (1). The details of the "second half resistance value" will be described later.

Nugget diameter=c1× [ second half resistance position ] +c2 (C1 C2 is a predetermined constant), formula (1)

The CPU 20 functions as the operation control unit 200, the acquisition unit 210, and the estimation unit 290 by expanding various programs stored in the storage unit 60.

The operation control unit 200 controls the operation of the resistance spot welding apparatus 10. The operation of the resistance spot welding apparatus 10 is controlled based on preset parameters (hereinafter, welding parameters) at the time of welding. That is, the welding parameters are welding conditions set in advance when welding is performed. The welding parameters include, for example, a current value, a voltage value, a resistance value, an inter-electrode displacement amount, an expansion amount, and pressurizing forces of the electrodes 2 and 3. The operation control unit 200 comprehensively controls the operations thereof. The operation control unit 200 controls the operation of the resistance spot welding apparatus 10, for example, based on the set values of the welding parameters set in advance by the user via the input operation unit 50.

The obtaining unit 210 obtains the second half resistance value at the time of welding. The estimating unit 290 calculates an estimated value of the nugget diameter by substituting the latter half resistance value into an estimated expression (1) above). Details of each function are described later together with a method of estimating the nugget diameter. Further, at least a part of the functions of the CPU 20 may be realized by a hardware circuit.

The measuring means 9 measures an actual measurement value of a welding parameter as a physical quantity required for welding using the resistance spot welding apparatus 10. The "actual measurement value of the welding parameter" referred to herein is a value of the welding parameter actually observed when welding is performed in accordance with an instruction concerning the welding condition, that is, a set value of the welding parameter set in advance, transmitted from the operation control unit 200. The actual measurement value of the welding parameter measured by the measuring means 9 is transmitted to the CPU 20 via the communication unit 30.

In the present embodiment, the measuring means 9 includes a current value measuring unit 91, a voltage value measuring unit 92, a resistance value calculating unit 93, a pressurizing force measuring unit 95, an inter-electrode displacement measuring unit 96, and an inter-electrode displacement calculating unit 97. The structure and function of the measuring mechanism 9 are not limited to this. The measuring means 9 may also be provided with other means for measuring welding parameters, for example. The function of at least a part of the measuring means 9 may be realized as a function of the CPU 20.

Each of the constituent elements 91 to 97 included in the measuring means 9 measures an actual measurement value of the welding parameter for each predetermined measurement time at the time of welding. The current value measuring unit 91 measures the value of the current flowing between the upper electrode 2 and the lower electrode 3. The current value measuring unit 91 is, for example, a current sensor. The voltage value measuring unit 92 measures the voltage value (potential difference) between the upper electrode 2 and the lower electrode 3. The voltage value measuring unit 92 is, for example, a voltage sensor.

The resistance value calculating unit 93 calculates a value of the resistance (hereinafter, resistance value) using the measured value of the current value and the measured value of the voltage value measured at the time of energization. Specifically, the resistance value calculating unit 93 calculates the resistance value by dividing the voltage value by the current value. In this case, the current value and the voltage value at the same measurement time point are used for calculation of the resistance value.

The pressurizing force measuring unit 95 measures the pressurizing force of each electrode 2, 3 on the welding target member W. The pressurizing force measuring unit 95 is, for example, a load cell housed in the electrode lifting device 4. The inter-electrode displacement amount measuring unit 96 includes a first displacement amount measuring unit 961 for measuring the displacement amount of the upper electrode 2 (hereinafter, first displacement amount) and a second displacement amount measuring unit 962 for measuring the displacement amount of the lower electrode 3 (hereinafter, second displacement amount).

The first displacement amount measuring unit 961 measures, for example, the position of the upper electrode 2 to be raised and lowered at a first measurement time point and the position of the upper electrode 2 to be raised and lowered at a second measurement time point after a predetermined measurement time has elapsed from the first measurement time point, and calculates the first displacement amount from the difference between the measured values. The first displacement measuring unit 961 is, for example, an encoder housed in the electrode lifting device 4, and detects the rotational angle position of the output shaft of the servomotor 41 to measure the lifting position of the upper electrode 2.

The second displacement amount measuring unit 962 measures a second displacement amount. Specifically, the gun body 11 is fixed to the lower portion 11b thereof. Thus, in the case where a force is applied due to thermal expansion, the lower electrode 3 is deformed without moving. Therefore, the second displacement amount measuring unit 962 measures the force (deformation value) applied to the lower electrode 3 as the second displacement amount. The second displacement measuring unit 962 is, for example, a strain sensor for measuring a strain value of the lower electrode 3.

The inter-electrode displacement amount calculating unit 97 calculates the displacement amount between the upper electrode 2 and the lower electrode 3 (hereinafter, inter-electrode displacement amount) using the first displacement amount measured and calculated by the first displacement amount measuring unit 961 and the second displacement amount measured by the second displacement amount measuring unit 962. In this case, the value at the same measurement time point is used for calculating the inter-electrode displacement amount. The inter-electrode displacement amount calculating unit 97 calculates the inter-electrode displacement amount during energization by adding the first displacement amount and the second displacement amount during energization, for example. The method for calculating the inter-electrode displacement is not limited to this.

A2. The method for estimating the nugget diameter comprises:

next, a method for estimating the nugget diameter in the first embodiment of the present disclosure using the estimation system 1 described in detail above will be described. Fig. 3 is a flowchart showing steps in the method of estimating the nugget diameter. As shown in fig. 3, the method for estimating the nugget diameter includes a resistance value acquisition step (S101) and a nugget diameter calculation step (S102).

In the resistance value obtaining step (S101), the obtaining unit 210 obtains the second half resistance value. In the resistance value estimation step (S101), the estimation unit 290 substitutes the second half resistance value into the formula (1) as an estimation formula to calculate an estimation value of the nugget diameter.

Next, in the first embodiment, the second half resistance value used as the welding parameter will be described in more detail. Fig. 4 is a graph showing a time change in resistance value. Fig. 5 is an enlarged view of a portion surrounded by a two-dot chain line in the graph in fig. 4. Fig. 5 shows a time change in the resistance value at the end of the energization period. In fig. 4 and 5, the current values are shown in thick solid lines, and the resistance values of test patterns 1 to 4 in a plurality of (4 in the present embodiment) test welds are shown in thin solid lines, broken lines, one-dot chain lines, and two-dot chain lines, respectively.

As shown in fig. 4, the energization start time T1 is 100ms, and the energization stop time T4 at which energization to the welding target W is stopped is 300ms. The energization intermediate time point T2 is an intermediate time point between the energization start time point T1 and the energization stop time point T4, and is 200ms. The "second half of the energization period" here means from the energization intermediate time point T2 to the energization stop time point T4. Hereinafter, the "latter half of the energization period" will also be simply referred to as "latter half of the energization". The current-supply end time point T3 is set to, for example, several tens of ms before the current-supply stop time point T4, between the current-supply intermediate time point T2 and the current-supply stop time point T4. The energization end time point T3 corresponds to, for example, a time point at which 10 to 20% of the energization period is traced back from the energization stop time point T4. The period from the energization end time point T3 to the energization stop time point T4 is referred to as "energization end period S". That is, the power-on end period S is included in the latter half of the power-on period.

As a result of the study by the inventors of the present application, a characteristic amount having a correlation with the nugget diameter was searched for among the resistance values, and it was found that the correlation between the resistance value of the latter half of the period of energization and the nugget diameter was higher. The larger the nugget diameter is, the smaller the resistance value is. In particular, the correlation between the resistance value in the end period S of energization and the nugget diameter is large. This is considered because various disturbances may occur in the welding field, but in the first half of the energization, the influence of the disturbance is difficult to appear, and in the period S at the end of the energization, the influence of the disturbance appears more remarkably. The interference is, for example, a gap between steel plates, inclination of the steel plates, abrasion of the distal end portion of the electrode pressed against the steel plates, or the like. As shown in fig. 5, in the power-on end period S, a change in resistance value due to the influence of disturbance can be significantly read as compared with other periods in the power-on period.

The present inventors have found that the accuracy of estimating the nugget diameter can be improved by using the resistance value during the period of greater correlation. In addition, in the latter half of the energization period, a molten pool is formed by welding, and the molten pool reaches a size close to the target nugget diameter, and the molten state becomes a stable state compared with the initial energization.

Fig. 6 is a graph showing a relationship between the resistance value of the second half of energization and the nugget diameter. In the production of the above-described estimated expression, a first current value of the nugget diameter of the production target and a second current value of the nugget diameter which is smaller than the first current value and is intentionally reduced by the current value are set, and the second half resistance value and the nugget diameter are measured at the respective current values to obtain a plurality of data. In fig. 6, a plurality of acquired data are plotted. The second half resistance value is an average resistance value in the current-carrying end period S. Based on these data, a single regression analysis was performed to produce the above-described estimation formula. The estimation formula is a first-order formula calculated by linearly regressing the plot points in which the second half resistance value and the nugget diameter are associated with each other, and shows a straight line in fig. 6.

Fig. 7 and 8 are diagrams for explaining the effect of estimating the nugget diameter using the second half resistance value as a welding parameter. In fig. 7, the result is plotted with the measured nugget diameter (hereinafter, also referred to as "measured diameter") on the horizontal axis and the estimated nugget diameter (hereinafter, also referred to as "estimated diameter") on the vertical axis. In fig. 8, the horizontal axis represents the estimation accuracy, the vertical axis represents the measured diameter, and the results are plotted. In fig. 7 and 8, when the estimated diameter matches the measured diameter, the plot point is located on an ideal line L1 shown by a one-dot chain line in the drawing. In fig. 7 and 8, the plot points are located on the ideal line L1 or in the vicinity of the ideal line L1. The plot points are each located in a range of ±20% or less of the estimated error shown by the broken lines L2 and L3 in each of the figures. That is, it was confirmed that the estimated nugget diameter was highly accurate.

According to the method for estimating the nugget diameter of the first embodiment, the nugget diameter is estimated using the resistance value of the second half, that is, the second half resistance value, as the welding parameter. The latter half resistance value has a higher correlation with the nugget diameter than the resistance value of the first half of the energization. By estimating using the latter half resistance value having a high correlation with the nugget diameter as the welding parameter, the accuracy of estimating the nugget diameter can be improved as compared with the case where the resistance value throughout the entire energization period is used, for example.

The estimation method for estimating the nugget diameter according to the first embodiment is a first-order equation calculated by linearly regressing the plot points where the second half resistance value and the nugget diameter are associated with each other. Thus, the correlation between the second half resistance value and the nugget diameter can be expressed uniquely. Further, the estimated value can be easily created by using the plot points in which the second half resistance value and the nugget diameter are associated.

B. Second embodiment:

next, a second embodiment will be described with reference to fig. 9. In the second embodiment, the current-carrying mode is different from the first embodiment only, and the other configurations and estimation methods are the same, so that a detailed description thereof is omitted. Fig. 9 is a diagram showing a change in welding current I in the second embodiment of the present disclosure. As shown in fig. 9, in the resistance spot welding according to the second embodiment, after the initial energization is performed for a predetermined time, the energization is stopped for a predetermined period, and then the main energization is performed. That is, the energization period includes a period of initial energization and a period of regular energization performed at intervals after initial energization.

In the second embodiment, the latter half resistance value is an average value of the resistance values of the latter half (time T5 to T6) in the period of the main energization. In the second embodiment, the same effects as those of the first embodiment can be achieved.

C. Other embodiments:

(C1) In each of the above embodiments, the estimated expression is set to include only the second half resistance value as the welding parameter as shown in expression (1), but other welding parameters such as the expansion amount may be included.

(C2) In the first embodiment, the second half resistance value is an average resistance value in the current-carrying end period S, but the present invention is not limited to the current-carrying end period S, and any average resistance value in any period in the second half of the current-carrying after the current-carrying intermediate time T2 may be used. Further, the integrated value of the resistance value may be used for the whole of any period after the second half of the energization, instead of the average value. They are all referred to as "the latter half resistance value".

The present disclosure is not limited to the above embodiments, and may be implemented in various configurations within a range not departing from the gist thereof. For example, the technical features of the embodiments corresponding to the technical features of the embodiments described in the summary of the invention may be replaced or combined as appropriate to solve part or all of the above-described problems or to achieve part or all of the above-described effects. Note that, this feature may be appropriately deleted unless described as an essential feature in the present specification.

Claims (3)

1. A method for estimating a nugget diameter using a predetermined estimated value having a welding parameter that affects the size of a nugget diameter formed in resistance spot welding as an explanatory variable and the estimated value of the nugget diameter as a target variable, the method comprising:

a resistance value obtaining step of obtaining, as the welding parameter, a second half resistance value which is a resistance value of the second half of the energization period at the time of welding and which is a resistance value of the entire energization circuit including the welding object; and

and a nugget diameter calculation step of substituting the acquired second half resistance value into the estimated value to calculate the nugget diameter.

2. The method for estimating a nugget diameter according to claim 1, wherein,

the energization period at the time of the welding includes a period of initial energization and a period of regular energization performed at intervals after the initial energization,

the second half resistance value is a second half resistance value in the period of the main energization.

3. The method for estimating a nugget diameter according to claim 1 or 2, wherein,

with respect to the above-mentioned presumption,

is a first order equation calculated by linearly regressing the plot points where the second half resistance value and the nugget diameter are associated.