JP2021079417A - Spot welding method, spot welding control device and control program - Google Patents

Abstract

To provide a spot welding method that can reduce excessive power distribution and efficiently stabilize quality of a welded product.SOLUTION: The spot welding method, in which power is distributed from a pair of opposing electrodes contacting an outer surface of a polymer to the polymer in which a plurality of materials to be welded overlap, comprises: a first step of obtaining an index value for electric resistance of the polymer by performing power distribution so that the materials to be welded are not melted; and a second step of performing power distribution so that the materials to be welded are welded to each other inside the polymer, along a power distribution pattern set based on the index value. The second step comprises an increasing process in which amounts of power distribution increase, a main power distribution process following the increasing process, and a decreasing process following the main power distribution process, in which the amounts of power distribution decrease, for instance. The power distribution pattern is adjusted based on a rate of increase of the amounts of power distribution in the increasing process and/or current values in the main power distribution process or the index value for electric resistance.SELECTED DRAWING: Figure 5

Description

The present invention relates to a spot welding method and the like.

The car body and the like are manufactured by spot welding a plurality of plate materials (bonded materials). Spot welding is a type of resistance welding that utilizes Joule heating, and is performed by applying a large current for a short time from an electrode that is pressed against the outer surface of the superposed material to be joined. By this energization, a molten pool is formed in the vicinity of the contact interface (joint portion) inside the superposed materials to be joined, and the molten pool is cooled and solidified to become a welded portion (so-called nugget). In this way, the materials to be joined are joined by spot-shaped nuggets to form a welded product (joint body).

By the way, in the case of spot welding, since the welded portion is inside the material to be joined, it is not possible to judge the quality of welding from the appearance. Moreover, considering productivity, it is not possible to inspect each of a large number of welding points one by one. Therefore, a proposal that enables stable spot welding even when there are various disturbances (for example, fluctuations in the contact state between the electrode to be joined or the materials to be joined) that occur during spot welding is, for example, the following patent. It is done in the literature.

JP 2011-31277 JP 2011-104628 JP 2012-183550 WO2013 / 31247 WO2015 / 49998

However, none of the patent documents describes that the main energization for melting the jointed portion is performed after the surface condition, contact state, etc. of the bonded material at the jointed portion are evaluated at any time in advance.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a spot welding method or the like capable of stabilizing spot welding by a method different from the conventional method.

As a result of diligent research to solve this problem, the present inventor evaluates the electric resistance value of the polymer, which reflects the surface state and contact state of the material to be joined before the main energization, for each welding spot, and based on the evaluation. The idea was to perform proper main energization. By embodying this and developing it, the present invention described below has been completed.

《Spot welding method》
(1) The present invention is a spot welding method in which a polymer in which a plurality of materials to be welded are superposed is energized from a pair of opposing electrodes in contact with the outer surface of the polymer, and the materials to be welded are not melted. Energization that welds the materials to be welded inside the polymer according to the first step of energizing to obtain an index value of the electrical resistance of the polymer and the energization pattern set based on the index value. This is a spot welding method including a second step of performing the above.

(2) In the spot welding method of the present invention (also simply referred to as "welding method"), first, in the first step, the electrical resistance of the polymer that reflects the surface state, contact state, etc. of the material to be joined before the main energization. I know the index value of. Next, in the second step, energization is performed according to the energization pattern set based on the index value, and the materials to be joined are welded to each other. Therefore, even when the surface state or contact state of the material to be joined changes, efficient (or energy-saving) spot welding can be appropriately performed for each welding spot.

<< Spot welding control device or control program >>
The present invention also provides a spot welding control device for executing the above-mentioned spot welding method by controlling at least the amount of electricity applied to a pair of opposing electrodes in contact with the outer surface of a polymer in which a plurality of materials to be joined are superposed. I can grasp it.

It is also grasped as a spot welding control program executed by the spot welding control device.

In the control device or the control program, the component "-process" related to the above-mentioned method may be read as "-means" or "-part" and grasped as a component related to an object. Further, the present invention may be grasped as a control method in which "-process" and "-process" are read as "-step" and the control program is executed by a computer.

<< Other >>
(1) The "index value of electrical resistance" referred to in the present specification is not only the electrical resistance value itself and its time change rate, but also, for example, a set current value (primary current value) and an actual current value actually flowing with respect to the set current value (primary current value). It may be a difference or ratio with the secondary current value). That is, the index value of the electric resistance may be any value as long as it can be grasped by energizing the polymer from the electrode.

(2) Unless otherwise specified, "x to y" in the present specification includes a lower limit value x and an upper limit value y. A range such as "ab" may be newly established with any numerical value included in the various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value. Further, unless otherwise specified, "x to ymm" in the present specification means xmm to ymm. The same applies to other unit systems.

It is a schematic diagram which shows the outline of spot welding. It is a graph which shows the electric resistance value of various plate sets. It is a photograph which shows the explosion which occurred in the plate assembly which concerns on a sample 23. It is a photograph which shows the cross section of the plate assembly which concerns on a sample 11. It is explanatory drawing which shows the range of the resistance value between electrodes and the limit current value which can perform good spot welding. It is a graph which shows the relationship between the pressing force and the resistance value between electrodes. This is an example of a time chart related to spot welding. This is an example of a flowchart relating to spot welding (first step). This is an example of a flowchart relating to spot welding (second step).

One or more components arbitrarily selected from the present specification may be added to the components of the present invention described above. The contents described in the present specification may be appropriately applied to a product (welded product, etc.) as well as a welding method, a control device, a control program, and the like. Which embodiment is the best depends on the target, required performance, and the like.

《Electrical resistance》
The electrical resistance of the polymer between the electrodes (also referred to as R / “resistance between electrodes”) occurs, for example, at the contact interface between the outer surface of the material to be joined and the electrode, as shown in FIG. The contact resistance (Ro = Ro ₁ + Ro ₂ ), the contact resistance (Ri) generated at the contact interface between the inner surfaces of the material to be bonded inside the polymer, and the electrical resistance of the material to be bonded (Rm = Rm ₁ + Rm). _{It is} the sum of 2). When the contact resistance (Ro1) on one surface side of the polymer and the contact resistance (Ro2) on the other surface side are substantially equal (Ro1≈Ro2), Ro≈2Ro1≈2Ro2. Similarly, when the electrical resistance of each material to be joined is substantially equal (Rm1≈Rm2), Rm≈2Rm1≈2Rm2.

On the other hand, when direct current is applied from the electrodes to the polymer, the electric resistance (R) is set to R = V / I according to Ohm's law from the applied voltage (V) between the electrodes and the actual current value (I) between the electrodes. I want it.

Good spot welding can be expected when the heat generation on the outer surface of the material to be joined is small and the heat generation on the inner surface of the material to be joined is large. Therefore, Ri should be sufficiently larger than Ro. If Ri is too small, a sufficient weld (nugget) is not formed inside the polymer. However, if Ri is excessive with respect to the current value between the electrodes, the amount of Joule heat (Qi = Ri · I ² ) inside the polymer is also excessive, and the material to be bonded melts to the surface side or explodes (explosion (Qi = Ri · I 2). (Including dust) may occur. By the way, if Ro is excessive, formation or welding of an intermetallic compound is likely to occur between the material to be bonded and the electrode.

By the way, the resistance between electrodes (R) can change between the spot welding points. Not only when the material and form of the material to be joined change, but also when the material to be joined has the same material and form, each contact resistance (Ri, Ro) can change between the hitting points. Such factors (disturbance factors) include foreign matter biting between the contact surfaces, contamination of the contact surfaces (oil film, etc.), gaps between the contact surfaces (plate gaps, etc.), electrode center misalignment, and inclination of the electrodes with respect to the material to be welded. (Face collapse, etc.), current branching to existing welding points, etc.

In order to efficiently perform stable spot welding at each hitting point, it is desirable to control the amount of energization between the electrodes according to R (particularly Ri) at each hitting point. By the way, only Ri cannot be measured for each spot welding spot, but Ro is usually sufficiently smaller than Ri. Therefore, it can be considered that the inter-electrode resistance (R) mainly indirectly reflects Ri.

<< First step >>
In the first step, the electrical resistance (index value) of the polymer can be grasped (sensing, monitoring, monitoring) through the electrodes in contact with the polymer before the second step of melting and solidifying the bonded portion. As long as the index value of electrical resistance can be grasped, the amount of energization in the first step does not matter. The energization should be performed at least within a range that does not melt the material to be joined.

The material to be bonded may be preheated (preheated) by the energization within a range that does not melt. By this energization heating, the material to be bonded is softened, and the contact state between the materials to be bonded and the contact state between the material to be bonded and the electrode may change. That is, so-called "familiarity" may occur between the materials to be joined or between the materials to be joined and the electrodes. Therefore, the first step may include a softening process in which the material to be joined is energized and heated to soften it. The current value or energization to the extent that the material to be bonded does not soften (to the extent that the electrical resistance is measured) is appropriately referred to as a search current value or search energization. A current value or energization that softens the material to be joined without melting it is appropriately referred to as a pre-current value or pre-energization.

Preheating causes the material to be joined to become hot and its electrical resistance increases. Therefore, when preheating, it is preferable that the resistance between the electrodes is measured (evaluated) after at least cooling the jointed portion. That is, the first step may include a cooling step of cooling the material to be joined after the softening process. As a result, even when energized and heated, the index value of the electric resistance related to the setting of the energization pattern in the second step can be accurately grasped.

<< Second step >>
By the second step, a molten pool in which the material to be joined is melted is formed in the portion to be joined. The superposed materials to be joined are joined (welded) by a joint (nugget) in which the molten pool is solidified.

The energization in the second step is performed according to the energization pattern set based on the index value of the electric resistance obtained in the first step. If the index value of electrical resistance is as expected, for example, energization may be performed based on a reference energization pattern (reference energization pattern / master curve). When the existence of various disturbances (changes in the contact state between the materials to be joined and the contact state between the materials to be joined and the electrodes, etc.) is assumed from the index value of electrical resistance, at least a part of the reference energization pattern is changed (adjusted). It is preferable that the energization in the second step is performed based on the energization pattern.

Incidentally, there may be various methods for specifying the index value of the electric resistance which is the setting reference of the energization pattern. For example, the index value of electrical resistance when the fluctuation range (time change rate, etc.) falls within a predetermined value (nearly zero) may be used as a reference. Further, the minimum value of the electric resistance value within a predetermined time may be used as a reference. It should be noted that the index value of electrical resistance is sufficient as a criterion for selecting an energization pattern, and the accurate index value itself is not important. If you dare to say it, you may use the index value that is arithmetically averaged within the predetermined time as a reference, starting from the time when the rate of change is within the predetermined value.

In the second step, at least the main energization (process) of applying the amount of heat for melting the material to be joined to the portion to be joined may be performed. Therefore, the second step may be, for example, an energization step in which the current value suddenly rises to a predetermined value, the predetermined current value is maintained for a predetermined time, and then the current value suddenly drops to substantially zero.

However, a sudden increase in the current value causes dust and the like to be generated inside the polymer (near the contact interface between the materials to be bonded) and on the outer surface of the polymer (near the contact interface between the electrode and the material to be bonded). Therefore, the second step may include an ascending process for relaxing the rate of increase in the amount of energization before the main energizing process. Further, a sudden drop in the current value causes welding cracks (solidification cracks due to solidification shrinkage of the molten pool, hot cracks that may occur near the recrystallization temperature, etc.). Therefore, the second step may include a processing process for alleviating the reduction rate of the energization amount after the main energization process. That is, in the second step, in addition to the main energization process, an ascending process (upslope process) in which the energizing amount gradually increases before reaching the main energizing process, and a descending process in which the energizing amount gradually decreases after the main energizing process. (Downslope process) should be provided. The energization pattern set based on the index value of the electric resistance grasped in the first step may reflect those processes. In the present specification, energization in the ascending process (upslope process) is referred to as upslope energization, and energization in the descending process (downslope process) is referred to as downslope energization as appropriate.

Of course, in the energization pattern, the current value (particularly the limit current value) in the main energization process may be adjusted based on the index value of the electric resistance. The limit current value is the maximum current value that can be applied to the polymer (between the electrodes) within a range that does not cause explosion (including dust).

《Adjustment of pressing force》
The contact state between the electrode and the material to be bonded and the contact state between the materials to be bonded can be adjusted by the pressure applied to the polymer by the electrode. The pressing force may be substantially constant from the first step to the second step, or may be changed (changed) during each step. If the pressing force is adjusted or changed before the energization pattern is set, that is, before the second step, spot welding is stably performed. Therefore, before the second step, it is advisable to perform a pressurization adjustment step of adjusting the pressurization of the polymer by the electrodes. Further, the pressing force adjusting step may be performed as a part of the first step. Thereby, the energization pattern can be set based on the index value of the electric resistance after the pressurizing adjustment step, and the energization in the second step can be stably performed along the energization pattern.

By the way, when the pressing force increases, the electric resistance tends to decrease, and when the pressing force decreases, the electric resistance tends to increase. For example, if the electrode and the material to be joined have poor contact, it is advisable to reduce the contact resistance between the two by increasing the pressing force. As a result, the generation of surface dust is suppressed. On the contrary, if the contact resistance between the materials to be joined is increased by reducing the pressing force, it is possible to secure the calorific value (Joule heat amount) of the joint while suppressing the increase in the current value.

<< Material to be bonded / Polymer >>
The material and form of the material to be joined do not matter. The material to be joined may be, for example, an iron base material (steel material or the like) or an aluminum base material or the like. The material to be joined may be a molten material (extended material or cast material) or a sintered material. The material to be joined is not limited to a plate shape, but may be a non-plate shape such as a block shape. The material of the material to be welded may be the same type or different types.

At least one of the materials to be joined is usually plate-shaped. When joining plate-shaped materials to be joined, the plate thickness of each material to be joined may be the same or different. The number of materials to be bonded may be 3 or more. In other words, there may be a plurality of bonded portions inside the polymer with respect to the electrode center direction.

"electrode"
(1) Form The electrode for resistance spot welding may be detachable from the shank (cap tip type) or integrated with the shank (integrated type). Usually, a cap tip type electrode (also referred to as a “tip”) that can reduce welding costs is used.

The electrode (chip) has, for example, a bottomed substantially cylindrical tip portion and a substantially cylindrical body portion continuous from the tip portion. The outer surface (pressure contact surface) of the tip portion may be concave or non-concave with respect to the material to be joined. The size of the electrodes does not matter. The outer diameter (B / original diameter / nominal diameter) of the body portion is, for example, φ10 to 20 mm and further φ15 to 19 mm.

Refrigerant (coolant / cooling water) may be introduced into the inner cylinder of the electrode inside the tip of the electrode. When the refrigerant is forcibly circulated, the temperature rise of the electrode is suppressed and the material to be joined is cooled stably through the electrode.

Many basic shapes of the tips of electrodes (particularly convex electrodes) are specified in JIS C9304 (1999). For example, there are a flat type (F type), a radius type (R type), a dome type (D type), a dome radius type (DR type), a truncated cone type (CF type), a truncated cone radius type (CR type), and the like. Any shape may be used, but the DR type or F type electrode has a good balance between cooling capacity and strength.

(2) Material The electrode (at least the tip) is preferably made of a material having excellent thermal conductivity, conductivity, strength and the like. For example, an electrode made of a copper alloy having a conductivity of 75 to 95% IACS and further 80 to 90% IACS is used. Copper alloys include, for example, chromium copper, zirconium copper, chromium-zirconium copper, alumina-dispersed copper, beryllium copper and the like.

By exemplifying the fact that the electric resistance value between electrodes (electrical resistance value of a polymer) can fluctuate depending on the surface state of the material to be bonded and the contact state of each part, and a spot welding method corresponding thereto, the present invention is described below. Will be specifically described.

"Overview"
FIG. 1 shows a state in which a plate assembly (polymer) in which two plate materials (materials 1 and 2 to be joined) are laminated is sandwiched between a pair of opposing electrodes (1 and 2) and spot welding is performed. The contact resistance value at each contact interface before spot welding (before the second step) and the electrical resistance value of each plate material itself will be described as appropriate using the reference numerals shown in FIG.

In this embodiment, it is assumed that the energization from the electrodes to the plate assembly is performed by direct current control. The applied voltage (V) is adjusted according to the set current value (I ₀ ), and the current value (I) actually flowing at that time is measured. The electric resistance value (R) of the plate set between the electrodes is calculated from the voltage (V) and the current value (I). In this embodiment, R was monitored while the electrode was energized.

<< Materials to be joined and electrical resistance >>
(1) As an example of measuring the electric resistance value of the plate set to be joined, two types of aluminum alloy plates (Al alloy plates) to be joined were prepared. One Al alloy plate is a wrought material (equivalent to JIS A6022), and the other Al alloy plate is a die-cast material (equivalent to JIS ADC10). Each Al alloy plate had a thickness of 2.5 mm (thickness of the plate assembly: about 5 mm).

Further, a plurality of types of Al alloy plates having different surface conditions were prepared, and Al alloy plates in the same state were laminated to form a plate assembly. Specifically, for Al alloy plates (equivalent to A6022), a plate set (sample 10) of Al alloy plates (denoted as "standard") that have been rolled to a predetermined thickness and their Al alloy. A plate set (Sample 11) of Al alloy plates (denoted as "double-sided polishing") in which the plates were double-sided polished with water-resistant polishing paper was prepared.

For Al alloy plates (equivalent to ADC10), a plate assembly (sample 21) of Al alloy plates (denoted as "alkaline cleaning") obtained by cauterizing the casting (die-cast product) taken out from the mold and the casting are water-resistant polished. An Al alloy plate ("Sample 22") made of Al alloy plates polished on both sides with paper (denoted as "double-sided polishing") and an Al alloy plate ("" Plates (indicated as "outside and outside polishing") and Al alloy plates (indicated as "inside and outside polishing") in which only one side of the casting (inner surface of the plate to be joined) is polished. (Sample 24) was prepared.

(2) Electrical resistance value Fig. 2 shows the results of measuring the electrical resistance value (R) between the electrodes by energizing the plate assembly of each sample sandwiched between the pair of electrodes. This energization (corresponding to pre-energization) was performed with a current value of I: 8 kA and a pressing force of F: 5 kN. The horizontal axis (time) shown in FIG. 2 is the time measured from the time when the electrodes are brought into contact with each plate assembly. The pressing force applied to the plate set by the electrodes is substantially constant during the time zone mainly shown in FIG.

Each Al alloy plate has a strip shape (30 mm × 100 mm). As the electrodes, a pair of DR type (JIS C9304) commercially available chips (manufactured by OBARA Corporation) were used. The tip diameter was φ16 mm, and the thickness of the tip bottom was 12 mm. Cooling water (flow rate: 4 L / min) that was forcibly circulated was supplied to the inside (inner cylindrical portion) of the chip to forcibly cool the chip. The electrodes were made of chromium copper (Cr: 1% by mass, Cu: balance) and had an electrical conductivity of 80% IACS.

(3) Evaluation As is clear from FIG. 2, it can be seen that even with the same material, the electrical resistance value of the plate assembly differs greatly depending on the surface condition. Specifically, the sample in which both sides of the Al alloy plate were polished had a small R and was stable. On the other hand, the sample in which only one side of the Al alloy plate was polished had a large R. It was also found that R is likely to fluctuate if the contact interface with the electrode is not polished as in sample 24. It was also found that if the contact interface between the Al alloy plates was not polished as in sample 23, R tended to decrease with the passage of time. It is considered that this is because the contact state between the two Al alloy plates changes (that is, becomes familiar) as a result of the Al alloy plates being heated and softened. It is considered that the reason why R becomes large due to the presence of the non-polished surface is that the surface of the Al alloy plate is rough or a thick oxide film is present on the surface.

FIG. 3A shows a state when the main energization (I: 30 kA, F: 5 kN, t: 100 ms) was applied to the sample 23 having a large R. Further, FIG. 3B shows a cross section of the plate set in which the sample 11 having a small R was subjected to the main energization (I: 35 kA, F: 5 kN, t: 100 ms).

As is clear from FIG. 3A, when the amount of electricity applied to the plate set having a large R is applied, the jointed portion is rapidly heated, and it can be seen that explosion is likely to occur. On the contrary, as is clear from FIG. 3B, when the amount of electricity applied to the plate set having a small R is insufficient, the heat generation at the jointed portion becomes insufficient, the nugget is not formed or grown, and welding failure is likely to occur. Therefore, as shown in FIG. 3C, in order to realize stable spot welding, it is desirable to energize with an appropriate current value corresponding to R.

《Pressure and electrical resistance》
Using the plate set of sample 10, energization (I: 35 kA, t: 100 ms) was performed while changing the pressing force (F) by the electrodes. The relationship between each pressing force (F) obtained by this and the resistance value between electrodes (R) is shown in FIG.

As is clear from FIG. 4, it was confirmed that R decreased as F increased. However, the effect of the pressing force on the resistance value between the electrodes was not so large.

《Spot welding》
An example of a time chart related to spot welding is shown in FIG. Further, an example of the flowchart relating to spot welding is shown in FIGS. 6A and 6B (both are collectively referred to as “FIG. 6”).

Spot welding according to this embodiment is roughly classified into step I (first step) and step II (second step). In step I, energization is mainly performed to measure (monitor) the electric resistance value (R) between the electrodes (polymer) that reflects the surface state, contact state, and the like of the material to be joined. In step II, energization is mainly performed according to an energization pattern set based on the electric resistance value. Specifically, it is as follows.

(1) Step I
In step I, the pressurizing process S11, the pre-energization process S12 (softening process), and the interval process S13 (cooling process) are performed in this order. In the pressurizing process S11, the pressing force on the polymer by the electrode is increased at a constant rate until the time change rate (ΔR) of R becomes less than a minute predetermined value (ε). When | ΔR | <ε, the pressing force (F1) at that time is maintained (steps S111 to S113). Further, R at that time is measured and set to R1 (step S114). If R1 is within a suitable range, the process may jump to step II (step S21).

In the pre-energization process S12, pre-energization having a larger current value than the search energization (step S112) is performed (step S121). This is continued until | ΔR | <ε (step S122). By the pre-energization process S12, the material to be joined is heated and softened, and the contact property of each part is improved. That is, familiarity occurs in the vicinity of each contact interface.

In the interval process S13, the search energization having a current value smaller than that of the pre-energization (step S121) is continued until | ΔR | <ε (steps S131 and S132). When | ΔR | <ε, R at that time is measured and set to R2 (step S133). By the interval process S13, the material to be bonded heated in the pre-energization process S12 is cooled through the electrodes, and R under appropriate conditions is measured. If R2 is within a suitable range, the process proceeds to step II (step S21), and energization is performed according to the energization pattern set based on R2.

If R2 is out of the preferable range, the pressing force adjusting step S14 may be further performed. In this case, as in the pressurizing process S11, the pressing force is increased or decreased until the desired R is measured (steps S141 to S143). In step S143 (“R adjustment”), it is determined whether or not the R measured when | ΔR | <ε is within the desired range, and when R is within the desired range, the R is set to R3. Is also included. Then, the conventional pressing force is updated by the pressing force (F2) when R is within the desired range (step S144). Subsequent steps II are performed by the thus adjusted F2 and R3.

(2) Step II
In step II, the upslope process S21 (upward process), the main energization process S22, the downslope process S23 (downward process), and the cooling process S24 are performed in this order.

In the upslope process S21, the current value is increased to a predetermined set value at a predetermined rate of change along the energization pattern determined based on the R measured in the step I.

In the main energization process S22, energization according to the set current value defined by the energization pattern is continued until a desired amount of heat is applied to the bonded portion (steps S221 and S222).

In the downslope process S23, the current value is lowered at a predetermined rate of change along a predetermined energization pattern. As a result, the molten pool formed in the jointed portion solidifies while being slowly cooled, and solidification cracking is suppressed. In addition, the temperature of the solidified portion also drops at a predetermined rate, and hot cracking is suppressed.

In the cooling process S24, energization is stopped (static elimination) while the electrodes are in pressure contact with the polymer. As a result, the temperature of the polymer drops to around room temperature, and the welded product is completed.

By spot welding as described above, the quality of the welded material can be efficiently stabilized while reducing excessive energization.

Claims (7)

A spot welding method in which a polymer in which a plurality of materials to be bonded are superposed is energized from a pair of opposing electrodes in contact with the outer surface of the polymer.
The first step of obtaining an index value of the electric resistance of the polymer by applying electricity without melting the material to be bonded, and
A second step of energizing the materials to be welded to each other inside the polymer according to an energization pattern set based on the index value, and
Spot welding method including. The spot welding method according to claim 1, wherein the first step includes a softening step of energizing and heating the material to be joined to soften the material to be joined. The spot welding method according to claim 2, wherein the first step includes a cooling step of cooling the material to be joined after the softening step. The second step includes an ascending process in which the amount of energization increases, a main energizing process succeeding the ascending process, and a descending process in which the energizing amount decreases following the main energizing process.
The spot welding method according to any one of claims 1 to 3, wherein the energization pattern is an increase rate of an energization amount in the ascending process and / or a current value in the main energization process is adjusted based on the index value. The spot welding method according to any one of claims 1 to 4, further comprising a pressure adjusting step of adjusting the pressing force of the polymer by the electrode before the second step. A spot for performing the spot welding method according to any one of claims 1 to 5, at least controlling the amount of electricity applied to a pair of opposing electrodes in contact with the outer surface of a polymer in which a plurality of materials to be joined are superposed. Welding control device. A spot welding control program executed by the spot welding control device according to claim 6.

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