JP2011104628A - Resistance welding method, resistance welding material, resistance welding device and control device for the same, control method and program for resistance welding device, and evaluation method and program for resistance welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resistance welding method capable of efficiently stabilizing the welding quality even in the case of the presence of various disturbances. <P>SOLUTION: The resistance welding method includes: a melt starting time detection step of detecting a melt starting time which is when at least one part of the welding portions of an object to be welded starts melting by Joule heating using electric power applied from a pressure-welded electrode; a first electric power amount calculation step of calculating the amount of the first electric power which has been applied to the object to be welded from the start of melting; and a first determination step of determining whether or not the amount of the first electric power has reached a first predetermined amount. The resistance welding method is characterized in that Joule heating is continued until the amount of the first electric power reaches the first predetermined amount. A high correlation exists between the amount of electric power which has been applied since the object to be welded started melting and a nugget to be formed. Therefore, suppressing the amount of electric power after the start of melting can efficiently stabilize the welding quality even in the case of the presence of various disturbances. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method, apparatus, program, and resistance-welded member related to resistance welding such as spot welding.

  When joining a plurality of materials, welding that is easy to ensure strength at low cost is often used. In particular, spot welding, which is one type of resistance welding, is frequently used for efficiently welding stacked steel plates (a plurality of objects to be welded) at a plurality of points (spots) such as an automobile body or a car body. In this spot welding, generally, a large current is allowed to flow from the electrodes sandwiching the outer sides of the work piece to the work piece for a short time to melt and solidify the joining portion (welded part) inside the work piece. This is a welding method for joining weldments.

By the way, unlike arc welding or the like, spot welding is difficult to observe the welded portion directly because the welded portion is located inside the workpiece. In addition, it is not realistic for a mass production process that an operator inspects the spot welding state with a jig or the like.
Thus, various methods have been proposed for stabilizing the welding quality by making the size of the nugget (melted and solidified portion of the workpiece) uniform while performing spot welding. For example, the following patent document 1 has a related disclosure.

JP-A-62-264483

(1) Patent Document 1 discloses that resistance welding is performed by flowing a welding current until the actual energy actually supplied matches the total energy of the target value.
However, in an actual welding site, welding is performed under various situations (disturbances) different from the assumptions. For example, when resistance welding is performed on two steel plates that are to be welded, there is a gap between the steel plates joined by welding, the steel plate is inclined, or the tip of the electrode pressed against the steel plate is It can wear out. When such a disturbance exists, the contact state (particularly the contact area) between the steel plates changes. For this reason, the amount of Joule heat and heat radiation generated in the welded portion also change due to disturbance, and the amount of heat effectively used for welding varies. For this reason, as in the above-mentioned Patent Document 1, it is possible to stabilize the welding quality even if attention is paid to the total energy (total electric energy) input from the start of energization to the workpiece without considering disturbance. Was difficult in reality.

(2) The present invention has been made in view of such circumstances, and when actually welding the workpiece, the situation of the welded portion (between the joints of the workpiece) and the workpiece and the electrode. It is an object of the present invention to provide a resistance welding method capable of stabilizing the quality of resistance welding and a resistance welding member obtained thereby, even when there is a disturbance in the contact state or the like. It is another object of the present invention to provide a spot welder suitable for carrying out such a spot welding method, a control method thereof, a control device thereof, and a control program thereof. Furthermore, it aims at providing the evaluation method of spot welding, and its evaluation program.

  As a result of extensive research and trial and error, the present inventor has conducted various trials and errors, and even when various disturbances exist at the welding site, the disturbances will be prevented after the Joule-heated workpiece starts melting. It is new that resistance welding proceeds according to the input energy (input power amount) and a desired nugget can be formed by adjusting the input energy (input power amount). I found it. By developing this result, various inventions related to resistance welding as described below have been completed.

《Resistance welding method》
(1) The resistance welding method of the present invention is a method for detecting a melting start time, which is a time when at least a part of the welded portion of the work piece is Joule-heated by the electric power input from the pressure-welded electrode and starts melting. A start time detection step, a first power amount calculation step of calculating a first power amount that is an integrated value of the power input to the workpiece through the electrodes from the start of melting, and the first power amount Alternatively, a first determination step of determining whether or not a welding index value indicating a welding state of the weld corresponding to the first power amount has reached at least a first set value, and the first time from the start of melting. A heating step of performing the Joule heating until the electric power amount or the welding index value reaches at least the first set value, and the formation of a nugget in which the welded portion is melted and solidified can be stabilized.

(2) According to the present invention, after the resistance welding of the workpiece is started, that is, after the electrode is energized for Joule heating of the workpiece, first, at least a part of the welded portion of the workpiece is welded. The time when melting starts after Joule heating (at the start of melting) is detected. Starting from this melting start time, the energy (input power amount) input to the workpiece is calculated.
If attention is paid to the first power amount that is the input power amount after the start of melting, the reason and mechanism are not necessarily clear, but even in the presence of various disturbances, it is formed in the welded portion of the work piece. The size of the nugget can be controlled appropriately. Specifically, a first power amount obtained by integrating the input power amount after the start of melting or a welding index value obtained by converting the first power amount into a nugget size (nugget diameter) is a predetermined value. By performing Joule heating until at least the set value (first set value) is reached, welding quality can be stabilized even at welding sites where various disturbances exist.

In this specification, “at least reach the set value” includes the case where the target value falls within a specific range. The set value may be an upper limit value (final target value) or a minimum reached value (lower limit value). In the case of the present invention, the heating process may be stopped when the calculated first power amount or its welding index value reaches the first set value, or the range exceeding the first set value. The heating process may be continued within.
The “welding index value” may be any value that accurately indicates the state of resistance welding, and a representative example is a nugget diameter.
Furthermore, the calculation method of “electric energy” in this specification is not limited. As for the amount of electric power referred to in this specification, the specific numerical value itself is not important, and it should be a clear index correlated with the start of melting of the work piece or the size of the nugget diameter to be formed. It's enough.

(3) In the resistance welding method of the present invention, detection or identification (estimation) at the start of melting is also important in order to stabilize the welding quality of the work piece based on the first electric energy calculated from the start of melting. Become.
In the first place, the start of melting is when the welded part of the work piece changes from the solid phase to the liquid phase, so pay attention to changes in the physical properties of the work piece such as the temperature and volume of the melted part. It is conceivable to detect.
However, the present inventor has newly found a method that can detect the start of melting with high accuracy and simpleness regardless of the type of disturbance even when various disturbances exist in the vicinity of the workpiece and the electrode. It was. That is, the present inventor determined that the integrated value of the electric power supplied to the work piece according to the elapsed time from the start of energization, which is the time when energization of the electrode is started for Joule heating of the welded portion. A second power amount calculating step for calculating the second power amount, and a predetermined time corresponding to an elapsed time from the start of energization, and at least a part of the welded portion is put in before actually starting melting. A second determination step for determining that the melting start time is when the second power amount reaches at least a melting start power amount that is a predetermined power amount or a second set value set based on the melting start power amount. The present inventors have found that detection at the start of melting (that is, the configuration of the detection process at the start of melting described above) is possible. The reason is as follows.

If there is a “disturbance” in which the arrangement state of the workpieces to be welded or the contact state between the workpieces and the electrodes deviates from the assumed original state (standard state), the actual melting start time varies. This is supported by test results obtained by examining the amount of input power accumulated from the start of energization of the electrodes and the formed nugget diameter (see FIG. 2). For this reason, at first glance, it seems that it is difficult to detect the melting start time with high accuracy in a situation where an unspecified disturbance exists.
However, when the melting start time of the workpiece was examined under various disturbances, it was found that there was a difference between the energization time until the melting start time and the amount of power input until the melting start time (melting start power amount). Were found to be correlated. That is, it became clear that the accumulated electric energy (melting start electric energy) necessary for the start of melting of the workpiece is expressed as a function of the elapsed time after the start of energization (initial energization time).
More specifically, when the workpiece starts melting in a short time after energization, the input power amount is small, and when the workpiece starts melting in a long time after energization, the input power amount increases. . That is, it was found that the melting start electric energy has a monotonically increasing relationship with respect to the initial energization time.
Therefore, even if the type of disturbance is not specified, the amount of electric power (second electric energy) calculated according to the elapsed time after the start of energization (initial energization time) is the same as the elapsed time after the start of energization (initial energization time). If at least the time of reaching the melting start power amount determined according to (1) is detected, melting of the workpiece is started at that time, and it can be determined that the time of melting starts.

  Incidentally, the reason why the initial energization time and the melting start electric energy have the above-described relationship is as follows. When there is a disturbance, the contact resistance and current density of the welded portion change, and the heat generation amount (heat generation rate) per unit time in the welded portion also changes accordingly. For this reason, for example, when the contact resistance and current density are large and the heat generation rate of the welded portion is also large, the temperature of the welded portion is increased and melted in a short time. On the other hand, when the contact resistance and current density are small and the heat generation rate is small, it takes a long time to raise the temperature and melt the weld.

(4) In the present invention, the current value and the voltage value when energizing the electrode in contact with the workpiece to be resistance welded are not necessarily constant. While the first power amount reaches the first set value set corresponding to the desired nugget diameter or the like, or even for each welding spot, the current value or the voltage value applied to the work piece may be changed as appropriate. Good. Therefore, the heating step according to the present invention may include a heating change step of changing the heating condition of the workpiece to be welded based on the determination result of the first determination step.
The same can be said for detection at the start of melting of the workpiece. The detection at the start of melting is performed by calculating the energization time until the workpiece starts to melt, the second power amount calculated corresponding to the energization time, and the melting start power amount determined corresponding to the energization time. Contrast is important. Therefore, the current value and the voltage value applied to the workpiece may be appropriately changed during the calculation of the second electric energy, and for each welding spot.

  The contents described here are also applied as appropriate to the resistance welding machine and its control device, the resistance welding machine control method and its control program, and the resistance welding evaluation method and evaluation program, which will be described later. In that case, the “process” in the above-described invention configuration may be appropriately read as “step” or “part”.

《Resistance welding member》
When the above resistance welding method is used, it is possible to obtain a product in which defective welding is suppressed and welding quality is stabilized. Therefore, the present invention can be grasped not only as a resistance welding method but also as a stable resistance welding member having each nugget shape and the like.

<Resistance welding machine and its control device>
Moreover, this invention can be grasped | ascertained also as a resistance welding machine and its control apparatus which implement | achieve said resistance welding method.
(1) That is, the present invention is a resistance welding machine control device comprising an electrode circumscribing an object to be welded and a power supply device for supplying a heating current for Joule heating the welded portion of the object to be welded to the electrode. ,
A melting start detection unit for detecting a melting start time, which is a time when at least a part of the welded portion is Joule-heated by the electric power supplied from the electrode to the workpiece and starts melting; A first power amount calculation unit that calculates a first power amount that is an integrated value of the power input to the workpiece through the electrodes, and the welding corresponding to the first power amount or the first power amount. A first determination unit that determines whether or not a welding index value that indicates a welding state of the part has reached at least a first set value; and at least the first power amount or the welding index value from the start of melting. A resistance welding machine control device comprising: a heating unit that performs the Joule heating until reaching one set value.

(2) Further, the present invention provides an electrode that is pressed against the workpiece, a power supply that supplies a heating current for Joule heating the welded portion of the workpiece, and the workpiece from the power supply. And a resistance welding machine including the above-described control device that controls the amount of electric power input to the power source.

<< Control method and control program for resistance welding machine >>
Furthermore, this invention can be grasped | ascertained also as a control method of said resistance welding machine, or its control program.
(1) That is, the present invention is a control method for a resistance welding machine including an electrode circumscribing a workpiece and a power supply device that supplies a heating current for joule heating the welded portion of the workpiece to the electrode. ,
A melting start detection step for detecting a melting start time which is a time when at least a part of the welded portion is Joule-heated by the electric power supplied from the electrode to the workpiece and starts melting; A first power amount calculating step of calculating a first power amount that is an integrated value of power input to the workpiece through the electrodes; and the welding corresponding to the first power amount or the first power amount. A first determination step for determining whether or not a welding index value indicating a welding state of the part has reached at least a first set value; and at least the first power amount or the welding index value from the start of melting. And a heating step of performing the Joule heating until reaching one set value.

(2) The present invention may also be a resistance welding machine control program characterized in that the resistance welding machine control method is executed by causing a computer to function.

<Evaluation method for resistance welding>
In addition, the present invention can be grasped as a resistance welding evaluation method and its evaluation program.
(1) That is, according to the present invention, detection at the start of melting is detected when at least a part of the welded portion of the work piece is Joule-heated by the electric power input from the pressure-contacted electrode to start melting. A first power amount calculating step of calculating a first power amount that is an integrated value of power input to the workpiece through the electrodes from the start of melting, and the first power amount based on the first power amount. An estimation step of estimating a welding state of a welded portion, and a resistance welding evaluation method characterized by comprising:

(2) Further, in the present invention, in addition to the above-described resistance welding evaluation method, energization of the electrode is started in order to Joule-heat the welded portion of the workpiece to be welded by the electric power supplied from the pressure-welded electrode. A second power amount calculating step for calculating a second power amount that is an integrated value of the electric power input to the workpiece according to an elapsed time from the start of energization, and an elapsed time from the start of energization Corresponding to the melting start power amount that is an amount of power that is input until at least a part of the welded portion actually starts melting, or a second set value that is set based on the melting start power amount. A second determination step of determining at the time when the second electric energy reaches at least as the time of melting start, and detecting at the time of melting start when at least a part of the workpiece to be resistance-welded starts melting Resistance solution It may be of evaluation methods.
However, the latter resistance welding evaluation method may be incorporated into the “melting start detection step” of the former resistance welding evaluation method.

(3) Further, the present invention may be a resistance welding evaluation program characterized in that the resistance welding evaluation method is executed by causing a computer to function.

(4) In the estimation step, the welding state is determined based on whether the calculated first power amount or a welding index value indicating the welding state of the weld determined from the first power amount is within a predetermined range. It may be an evaluation step for evaluating pass / fail. The estimation step is more preferably a nugget estimation step for estimating the size of a nugget formed by melting and solidifying the welded portion based on the first electric energy.

It is explanatory drawing explaining the various disturbance which may arise in the case of resistance welding. It is a graph which shows the correlation with the amount of input electric power from the time of the energization start to the to-be-welded object in presence of various disturbances, and the nugget diameter formed. It is a graph which shows the correlation with the energization time to a to-be-welded object in presence of various disturbances, and input electric energy. It is a graph which shows the correlation with the amount of input electric power to a to-be-welded object after the time of the melting start of to-be-welded object, and the nugget diameter formed. It is a schematic diagram of a spot welder. It is a schematic diagram near the welding part of a work to be welded. It is a flowchart of the spot welding method which concerns on the Example of this invention.

DESCRIPTION OF SYMBOLS 11 Electrode 20 Welding robot 30 Control apparatus 40 Power supply apparatus 100 Spot welding machine W Workpiece (to-be-welded object)
R1 first electric resistance value R2 second electric resistance value X electric energy

  The present invention will be described in more detail with reference to embodiments of the invention. In the following, the resistance welding method of the present invention will be mainly described and described. However, the contents include not only resistance welding methods, but also resistance welding members, resistance welding machines, resistance welding machine control devices, resistance welding machine control methods, resistances. The present invention is appropriately applied to any of a welding machine control program, a resistance welding evaluation method, and a resistance welding evaluation program. And what added one or two or more structures arbitrarily selected from the structure enumerated below to the structure mentioned above can also be this invention. The configuration to be added can be selected in a superimposed manner or arbitrarily across categories. Note that which embodiment is the best depends on the target, required performance, and the like.

《Resistance welding and disturbance》
First, resistance welding and disturbance, which are important preconditions in understanding the present invention, will be described.
(1) In resistance welding, when an electrode pressed against a workpiece is energized, a part of the workpiece itself is generated from resistance heating (joule heating) generated by various resistances existing in the welded portion. This is a joining made by cooling and solidifying after the temperature of the welded part of the work to be welded rises and melts due to the difference in heat quantity subtracting the amount of heat dissipated to the electrode and the electrode.
As an example, let us consider a case where a set of a plurality of metal plates are resistance-welded. A set of plate materials to be welded is first pressed with an electrode or the like to be brought into close contact. Then, the electrodes are energized, large Joule heat is generated between the contact surfaces of adjacent plate members (between the joints), and the vicinity of the contact surfaces is preferentially melted. And by the cooling after completion | finish of electricity supply, the fusion | melting part will solidify and a nugget will be formed and the resistance welding will be complete | finished.

By the way, in this resistance welding, the melting preferentially occurs in the vicinity of the contact surfaces of two or more workpieces to be joined because the contact resistance in that region is larger than the resistance of other portions. However, the contact resistance greatly depends on the contact state between the workpieces, and moreover, deviation (disturbance) from the contact state (standard state) initially assumed at the actual welding site often occurs. For this reason, even if conditions, such as the electric current value and time to supply with electricity, are the same, the form of the welding part formed may change.
Of course, even in the presence of disturbance, stable welding can be performed if the amount of heat released accurately can be calculated and the necessary amount of heat necessary for welding can be input to the contact part. Have difficulty. For this reason, in conventional resistance welding, it has been difficult to perform stable welding efficiently because variations occur in the form of the welded portion or an excessive amount of electric power is input.

(2) However, as described above, the influence of the disturbance remains until the contact portion of the work piece starts melting, and the reason is not clear, but the influence of the disturbance after the start of melting is small or almost none. .
Therefore, as in the present invention, if attention is paid after the start of melting of the workpiece, it is possible to optimize the amount of electric power supplied to the workpiece depending on the desired welding situation (for example, the size of the nugget). This makes it possible to stabilize the welding quality efficiently.
However, the amount of electric power that is input at the start of melting and before the start of melting of the workpiece to be premised depends on the type of disturbance, and simply by the amount of electric power that is input to the workpiece from the start of energization, It is difficult to accurately determine or specify when welding starts.

  For example, comparing the case where the disturbance of the pattern III shown in FIG. 1 is present and the case where the disturbance of the pattern IV is present, the former has a smaller contact area at the contact portion and a larger contact resistance. Even if the overall current value flowing through the electrodes is the same, in the former case, since the resistance at the contact portion is large and the current density flowing through the contact portion is also large, the contact portion generates heat rapidly (that is, the heat generation rate increases). And the temperature of the contact portion rises rapidly. Furthermore, with this temperature rise, the specific resistance value having temperature dependence also rises rapidly. As a result, the former starts to melt in a considerably shorter time than the latter, and wasteful heat radiation is reduced, and the amount of input electric power until the start of melting is also reduced.

<< Electricity calculation process >>
The electric energy calculation process of this invention is calculated based on the electric current etc. which flow through the electrode press-contacted to the to-be-welded object. The amount of electric power is obtained as an integral value of current, voltage and time, but may be obtained from a modified expression thereof. The energization of the electrodes may be direct current or alternating current, and in the case of alternating current, the amount of power may be calculated based on the effective value.

<< Judgment process >>
The determination step of the present invention is performed by comparing the power amount calculated in the power amount calculation step or an index value corresponding to the power amount with a set value. An appropriate set value is selected depending on whether the comparison target is an electric energy or an index value. A typical index value is the size (nugget diameter) of the nugget formed by melting and solidifying the welded portion of the workpiece.
However, since no nugget is formed before the start of melting of the work piece, the input power amount calculated as needed according to the energization time and the melting start power amount determined according to the energization time or a set value based on it are briefly explained. It is preferable to contrast with.

《Workpiece》
There is no limitation on the shape and material of the workpiece. A typical workpiece is a laminated steel plate. For example, a mild steel sheet having a thickness of about 0.5 to 3 mm and a carbon content (C) of 0.05 to 0.2% by mass is used for resistance welding. In addition, materials such as high-strength steel (high tensile), galvanized steel, stainless steel, aluminum (Al), Al alloy, copper (Cu), Cu alloy, nickel (Ni), and Ni alloy may be used as the workpiece. . Furthermore, the workpiece may be a combination of different materials.
Depending on the material of the work piece, the amount of power required to obtain a desired form of weld varies. Therefore, the set value compared with the electric energy calculated during resistance welding, the melting start electric energy, and the like vary depending on the material and form of the workpiece, the lamination state of the workpiece, the pressure applied by the electrodes, and the like.

"electrode"
The shape and material of the electrode are not limited. The electrodes are usually made of columnar or cylindrical copper. In the case of a cylindrical electrode, it is preferable that cooling water is supplied to the inside of the electrode and the electrode is forcibly cooled to prevent wear of the electrode.
The end face of the electrode that circumscribes the workpiece is often circular or a gentle cone. If resistance welding is good, the shape of the nugget formed in the welded part often follows the shape of the electrode end face and is almost circular. In this case, the size of the nugget is indicated by its diameter (nugget diameter). In this specification, the size of the nugget is also referred to as a nugget diameter for convenience.

<Power supply unit>
The power supply device may be an AC power supply or a DC power supply. AC power supplies include single-phase power supplies and three-phase power supplies. The power supply device may be a constant current power supply or a constant voltage power supply. A constant current power supply is preferable because the amount of Joule heat generated increases as the work piece is heated and heated, and a nugget in which the work piece is melted and solidified is reliably formed. In addition, the preferable electric current value etc. which are supplied to a to-be-welded object from an electrode differ with the materials of a to-be-welded object, the desired nugget diameter, electricity supply time, etc.

The present invention will be described more specifically with reference to examples.
《Power input and nugget formation》
The inventor performed resistance welding (spot welding) under various disturbances on a cut model of a workpiece (workpiece to be welded) made of two stacked steel plates, and photographed the situation with a high-speed camera. This observed the formation process of nuggets that could be spot welded.
(1) Specifically, spot welding was performed by setting five typical patterns I to V as shown in FIG.
“No disturbance” in the pattern I shown in FIG. 1 is a case where the two stacked steel plates are pressed and in close contact with the electrode, and the central axis of the electrode is a normal line passing through the welded part of the workpiece. is there. Pattern II “straightening” is when the workpiece is inclined 3 ° from the horizontal direction with respect to the standard state of pattern 1. The “plate gap” of pattern III is a case where a gap is formed around the weld. Specifically, a spacer having a thickness of 1 mm was interposed at positions 15 mm (φ30 mm) on both sides from the weld center of the stacked steel plates. The pattern IV “electrode wear” is when the tip end surface (contact surface with the workpiece) of the electrode is expanded from de = φ6 mm to de = φ7 mm. Incidentally, the tip surface of the electrode is connected to the peripheral side surface of the electrode by a curved surface having a curvature radius of 40 mm. “V shunt” of pattern V is when the current supplied from the electrode flows not only to the current welding spot but also to another spot (pre-welded point) where welding has been completed in the previous process.

(2) Spot welding was performed with the workpiece and electrode set to the above-described patterns. At this time, the input power amount Q, which is an integrated value of the power input to the workpiece, was calculated. Further, the nugget diameter D formed on the work according to the input power amount Q was also measured. The correlation between the input electric energy Q and the nugget diameter D is shown in FIG.
In addition, the workpiece | work provided to spot welding is what laminated | stacked two sheets of cold rolled mild steel plates (JIS: SPC270) of thickness 2mm. The electrode used was cylindrical, and spot welding was performed while water-cooling the inside. The shape of the tip of the electrode is as described above. The electrode was spot welded while being pressed against both outer sides of the workpiece. The pressure of the workpiece by the electrode was 3430N. A 60-cycle single-phase alternating current was used as the power source. The effective current value at this time was 11 kA. The energization time of this heating current was controlled in units of cycle time Ct (1/60 seconds).

(3) The input power amount Q calculated here is an integrated value of the current applied to the electrode x the voltage x time between the electrodes (between both ends of the work). Therefore, the input power amount Q is also a function of time. Therefore, the relationship between the elapsed time from the start of energization (energization time) and the input power amount Q obtained for each of the patterns described above is shown in FIG. In FIG. 3, the energization time is indicated by the number of energization cycles (1 cycle time Ct: 1/60 seconds).
Furthermore, the point (melting start point) at which the workpiece of each pattern described above started to melt was estimated with reference to FIG. 2 and superimposed on FIG. This melting start point was specified by the timing when the flow due to melting could be confirmed on the cross section of the cut model.

A melting start curve is obtained by connecting the five melting start points obtained for each pattern (thick solid line in FIG. 3). In other words, the intersection of the curve (energization time-input power amount curve) indicating the relationship between the energization time and the input power amount when spot welding is actually performed becomes the melting start point. Therefore, the melting start point is given as the intersection of the energizing time-input power amount curve and the melting start curve drawn when spot welding is actually performed without specifying the presence or absence of disturbance and the disturbance pattern. The energization time is when melting starts, and the amount of power input at that time is the melting start power amount.
More realistically, the calculated input power amount and the melting start power amount stored corresponding to the energization time are calculated for each energization time (number of energization cycles) without worrying about the disturbance pattern. Contrast. Then, when the input power amount reaches the melting start power amount or exceeds the melting start power amount, it is determined that the melting starts.

(4) A first power amount Q1 (= Q-Qm) obtained by subtracting a melting start power amount Qm from an input power amount Q (power amount calculated from the start of energization) when each workpiece is spot welded, and a nugget diameter D The relationship is shown in FIG. In short, FIG. 4 is obtained by translating the respective curves shown in FIG. 2 by an amount corresponding to the melting start electric energy Qm.
As is apparent from FIG. 4, it can be seen that the relationship between the first electric energy Q1 after the start of melting and the nugget diameter D formed is substantially the same regardless of the disturbance pattern. In other words, if attention is paid after the start of melting of the workpiece, the formed nugget diameter D is substantially determined by the first electric energy Q1 with almost no influence of disturbance.

《Spot Welder》
(1) FIG. 5 shows a spot welder 100 which is an embodiment according to the resistance welder of the present invention. The spot welder 100 includes an articulated welding robot 20, a control device 30 that controls the welding robot 20, and a power supply device 40.

  The welding robot 20 is a six-axis vertical articulated robot. The base 21 is fixed to the floor so as to be rotatable about a first axis in the vertical direction, the upper arm 22 following the base 21, and the forearm following the upper arm 22. 23, a wrist element 24 rotatably connected to the front end portion of the forearm 23, and a spot welding gun 10 attached to the end portion of the wrist element 24. The upper arm 22 is connected to the base 21 so as to be rotatable about a second axis in the horizontal direction. The forearm 23 is connected to the upper end of the upper arm 22 so as to be rotatable around a third axis in the horizontal direction. The wrist element 24 is connected to the distal end portion of the forearm 23 so as to be rotatable around a fourth axis parallel to the axis of the forearm 23. The spot welding gun 10 has a sixth axis perpendicular to the fifth axis via another wrist element (not shown) that is rotatable around a fifth axis perpendicular to the axis of the forearm 23 at the tip of the wrist element 24. It is mounted so that it can rotate around.

  The spot welding gun 10 includes an inverted L-shaped gun arm 12 and a servo motor 13. The gun arm 12 is provided with a pair of electrodes 11 (a movable electrode 11a and a counter electrode 11b).

The movable electrode 11a is driven by the servo motor 13 so as to be able to contact with and separate from the workpiece W, which is a workpiece, and cooperates with the counter electrode 11b arranged coaxially in the plate thickness direction of the workpiece W. Is held at a desired pressure.
The movable electrode 11a and the counter electrode 11b are made of a bottomed cylindrical copper alloy, and the inside thereof is forcibly cooled by circulating cooling water.

  The control device 30 includes a robot drive circuit (not shown) and controls driving of the welding robot 20 and the spot welding gun 10. The control device 30 includes a power circuit (not shown), and controls power (at least one of voltage or current) supplied to the workpiece W via the electrode 11. By these circuits, the current value applied to the workpiece W, the energization time, the energization timing, the clamping force (pressing force) by the electrode 11 of the workpiece W, and the like are controlled. Conditions necessary for the control are input from the operation panel 31.

  The power supply device 40 is an AC constant current device that can boost a single-phase power supply or a three-phase power supply and stably supply a large constant current. The power supply device 40 is controlled by the control device 30.

(2) The spot welder 100 is operated and operated as follows.
A workpiece W to be spot welded is placed on a holding table (not shown). Welding spot of workpiece W, physical property value of workpiece W, clamping force of workpiece W by electrode 11, current value supplied to electrode 11, energization time, target value (first set value) corresponding to desired nugget diameter, etc. The conditions are input and set to the control device 30.

  When the spot welder 100 is subsequently operated, the welding robot 20 controlled by the control device 30 sequentially moves the spot welding gun 10 to each welding spot. The electrode 11 provided in the spot welding gun 10 is driven by the servo motor 13 controlled by the control device 30 and sandwiches the workpiece W with the set pressure. In this state, a predetermined constant current is supplied from the power supply device 40 to the workpiece W. The work W (welded member) spot-welded is completed by repeating this operation at a plurality of spots set.

(3) A schematic diagram of spot-welded welding spots is shown in FIG. If spot welding is good, a nugget N in which the workpiece W is melted and solidified is obtained inside the workpiece W (work Wa and workpiece Wb) made of a mild steel plate. In addition, the part heated while being pressurized by the electrode 11 is a welded portion Y. Normally, the nugget N is included in the welded portion Y, and the maximum diameter of the nugget N is the nugget diameter.

<< Control Device and Control Method for Spot Welder >>
(1) The control apparatus 30 which is an Example which concerns on this invention is further provided with the monitoring circuit (not shown) which monitors the welding condition of a welding spot.
This monitoring circuit includes a melting start detection unit that detects a melting start time, which is a time when at least a part of the workpiece W is joule-heated by the electric power input from the electrode 11 and starts melting, and the workpiece via the electrode 11 A first power amount calculation unit that calculates the first power amount Q1 input to W, and whether or not the integrated first power amount Q1 has reached the first set value X1 (that is, whether Q1 ≧ X1) A first determination unit. Further, the monitoring circuit supplies power to the workpiece W through the above-described power circuit and joule-heats the workpiece W (heating unit) until the first power amount Q1 reaches the first set value X1.

  The melting start detection unit of the monitoring circuit further includes a second electric energy Q2 input to the work W via the electrode 11 with respect to an initial energization time t that is an energization time from the start of energization from the electrode 11 to the work W. A second power amount calculation unit that calculates (t), and a melting start power amount X2 (t) (second power amount that is determined when the workpiece W actually starts melting and corresponds to the initial energization time t. A second determination unit that determines whether or not the second power amount Q2 (t) has reached the set value (that is, whether Q2 ≧ X2).

(2) A specific control method of the spot welder 100 by the control device 30 is shown in the flowchart of FIG. By executing the control method shown in FIG. 7, each step of the resistance welding method of the present invention is realized, and the resistance-welded workpiece W (welding member) is manufactured.
First, in step S11, various welding conditions are input and set (setting step). Specifically, the material and plate thickness of the workpieces Wa and Wb, the number and positions of welding spots, the tip shape of the electrodes 11a and 11b, the pressure applied to the workpiece W by the electrodes 11, the heating current value I1 for spot welding , Cycle time Ct, first set value X1 corresponding to the desired nugget diameter, and melting start electric energy X2 (t) which is a function of initial energization time t. Incidentally, the melting start power amount X2 (t) is sufficient if it is derived from the melting start curve shown in FIG. 3, and may be in the form of an empirical formula, or the melting start power amount X2 correlated with the initial energization time t. Numerical data (array data) of (t) may be used.

In step S12, the welding robot 20 and the spot welding gun 10 are operated, and the electrode end surfaces (electrode tips) of the electrodes 11a and 11b abut (externally contact) both outer sides of the workpiece W. Based on the setting in step S11. The electrode 11 pressurizes the workpiece W (pressurizing step).
In step S13, heating energization for spot welding is performed. That is, the current value I1 for heating is supplied to the electrode, and spot welding is started (heating step, heating process).

  In step S14, the second power amount Q2 (t) input to the workpiece W is calculated according to the energization time (initial energization time) t from the start of energization (second power amount calculation step, second power amount calculation). Process). Specifically, when the heating current is alternating current, the second electric energy Q2 (t) is calculated based on the effective current value and the effective voltage value supplied through the electrode 11 for each cycle time Ct of heating energization. Is calculated. Note that 1 Ct is one period of alternating current to be supplied. For example, if the alternating current is 60 cycles, 1 Ct = 1/60 sec.

  In step S15, the melting start power amount X2 (t) corresponding to the calculated cycle time Ct of the second power amount Q2 (t) is compared with the second power amount Q2 (t) calculated in step S14 ( Second determination step, second determination step). If the second power amount Q2 (t) is smaller than the melting start power amount X2 (t), that is, if the second power amount Q2 (t) has not reached the melting start power amount X2 (t), step S13 is performed. Continue heating and energizing. On the other hand, if the second power amount Q2 (t) has reached the melting start power amount X2 (t), the process proceeds to the next step S16, and the melting start time t0 is specified (melting start time detection step, melting start time). Detection step).

In step S17, as in step S14, the first electric energy Q1 supplied to the workpiece W is calculated according to the energization time from the melting start time t0 (melting energization time: t−t0) (first Power amount calculating step, first power amount calculating step).
In step S18, the first power amount Q1 calculated after the melting start time t0 is compared with the first set value X1 corresponding to the desired nugget diameter (first determination step, first determination step).

  If the first power amount Q1 is smaller than the first set value X1, heating energization to the workpiece W is continued. Conversely, if the first power amount Q1 has reached the first set value X1, the process proceeds to step S19, and after the heating energization to the work W is completed, the electrode 11 is separated from the work W, and at that position. Finish spot welding (heating step, heating process).

  Although not shown in the flowchart of FIG. 7, when step S17 and step S18 are repeated a predetermined number of times or time (number of cycle times), the heating energization condition may be corrected or changed ( Heating change step, heating change step).

<Evaluation method of spot welding>
In order to evaluate the welding situation of spot welding, it can carry out by step S14-18 shown in FIG. If only the quality of the welding situation is to be evaluated, it can be evaluated from the magnitude relationship between the first power amount Q1 and the first set value X1 as in step S18 (estimation step, evaluation step). Of course, if a database associating the first electric energy Q1 and the nugget diameter D as shown in FIG. 4 is prepared in advance, the nugget diameter formed in the welded portion from the actually accumulated first electric energy Q1. D can be estimated (nugget estimation step).

  Moreover, if it is the detection at the time of a melting start, it can carry out by step S13-16 shown in FIG. That is, it is possible to determine the melting start time by comparing the magnitude relationship between the second power amount Q2 (t) and the melting start power amount X2 (t) as in step S15 for each energization time (estimation step). , Evaluation step).

Claims (13)

A melting start detection step for detecting a melting start time, which is a time when at least a part of the welded portion of the work piece is Joule-heated by the electric power input from the pressure-welded electrode and starts melting;
A first power amount calculating step of calculating a first power amount that is an integrated value of power input to the workpiece through the electrodes from the start of melting;
A first determination step of determining whether or not a welding index value indicating a welding state of the weld corresponding to the first power amount or the first power amount has reached at least a first set value;
A heating step of performing the Joule heating until the first power amount or the welding index value reaches at least the first set value from the start of melting,
A resistance welding method, wherein the formation of a nugget in which the weld is melted and solidified can be stabilized. The melting start detection step includes
A second electric energy that is an integrated value of electric power supplied to the workpiece according to an elapsed time from the start of energization, which is the time when energization of the electrode is started for Joule heating of the welded portion. A second electric energy calculating step for calculating;
Based on the melting start power amount or the melting start power amount that is determined in advance corresponding to the elapsed time from the start of energization and that is the amount of power that is input until at least a part of the weld actually starts melting. 2. The resistance welding method according to claim 1, further comprising: a second determination step of determining when the second electric energy reaches at least the set second set value as the melting start time.   The resistance welding method according to claim 1, wherein the heating step includes a heating change step of changing a heating condition of the workpiece to be welded based on a determination result of the first determination step.   A resistance welding member welded by the resistance welding method according to claim 1. A resistance welding machine control device comprising: an electrode circumscribing an object to be welded; and a power supply device for supplying a heating current for Joule heating the welded portion of the object to be welded to the electrode,
A melting start detection unit for detecting a melting start time, which is a time when at least a part of the welded portion is Joule-heated by the electric power input from the electrode to the workpiece and starts melting;
A first power amount calculation unit that calculates a first power amount that is an integrated value of power input to the workpiece through the electrodes from the start of melting;
A first determination unit for determining whether or not a welding index value indicating a welding state of the weld corresponding to the first power amount or the first power amount has reached at least a first set value;
A heating unit that performs the Joule heating until the first power amount or the welding index value reaches at least the first set value from the start of melting;
A resistance welding machine control device comprising: An electrode pressed against the work piece;
A power supply device for supplying a heating current for Joule heating the welded portion of the workpiece to the electrodes;
A control device according to claim 5;
A resistance welding machine comprising: A resistance welding machine control method comprising: an electrode circumscribing an object to be welded; and a power supply device that supplies a heating current for Joule heating the welded portion of the object to be welded to the electrode,
A melting start detection step for detecting a melting start time which is a time when at least a part of the welded portion is Joule-heated by the electric power supplied from the electrode to the workpiece and starts melting;
A first power amount calculating step of calculating a first power amount that is an integrated value of power input to the workpiece through the electrodes from the start of melting;
A first determination step of determining whether or not a welding index value indicating a welding status of the weld corresponding to the first power amount or the first power amount has reached at least a first set value;
A heating step in which the Joule heating is performed until the first power amount or the welding index value reaches at least the first set value from the start of melting;
A control method for a resistance welder, comprising:   A control program for a resistance welder according to claim 7, wherein the control method for the resistance welder is executed by causing a computer to function. A melting start detection step for detecting a melting start time, which is a time when at least a part of the welded portion of the work piece is Joule-heated by the electric power input from the pressure-welded electrode and starts melting;
A first power amount calculating step of calculating a first power amount that is an integrated value of power input to the workpiece through the electrodes from the start of melting;
An estimation step of estimating a welding state of the weld based on the first electric energy;
A resistance welding evaluation method comprising:   The resistance welding evaluation method according to claim 9, wherein the estimation step is a nugget estimation step of estimating a size of a nugget formed by melting and solidifying the welded portion based on the first electric energy. The melting start detection step includes
A second electric energy that is an integrated value of electric power supplied to the workpiece according to an elapsed time from the start of energization, which is the time when energization of the electrode is started for Joule heating of the welded portion. A second power amount calculating step for calculating;
Based on the melting start power amount or the melting start power amount that is determined in advance corresponding to the elapsed time from the start of energization and that is the amount of power that is input until at least a part of the weld actually starts melting. A second determination step of determining when the melting starts at the time when the second electric energy reaches at least the set second setting value;
The method for evaluating resistance welding according to claim 9 or 10. Input to the work piece according to the elapsed time from the start of energization, which is when the energization of the electrode is started in order to joule-heat the welded part of the work to be welded by the electric power input from the pressure-welded electrode A second power amount calculating step of calculating a second power amount that is an integrated value of the generated power;
Based on the melting start power amount or the melting start power amount that is determined in advance corresponding to the elapsed time from the start of energization and that is the amount of power that is input until at least a part of the weld actually starts melting. A second determination step of determining when the second electric energy reaches at least the set second setting value as the melting start time,
A resistance welding evaluation method characterized in that it can detect a melting start time at which at least a part of a workpiece to be resistance welded starts melting.   The resistance welding evaluation program according to claim 9, wherein the resistance welding evaluation method according to claim 9 is executed by causing a computer to function.

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