JP2014113618A - Resistance welding inspection method and resistance welding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique that can predict a volume of a welding part.SOLUTION: Fig. (b) corresponds to a curve b, and a large welding parts 36, 36 are recognized. Fig. (c) corresponds to a curve c, and the welding parts 36, 36 smaller than that in Fig. (b) are recognized. Fig. (d) corresponds to a curve d, and the welding parts 36, 36 are extremely small. From the above knowledge, temperature curves b, c, d of Fig. (a) are acquired, and the presence or absence of a rise in temperature generated immediately after separation of a main electrode from one steel plate is inspected. It can be determined that the welding parts 36, 36 have not reached the necessary size because the rise in temperature is not recognized in the curve d. Also, it can be determined that the welding parts 36, 36 have sizes larger than necessary because a sufficiently large rise in temperature δb is recognized in the curve b. Also, it can be determined that the welding parts 36, 36 have the necessary sizes because a sufficiently large rise in temperature δc is recognized in the curve c. Therefore, the volume of the welding parts can be predicted without performing destructive inspection.

Description

  The present invention relates to a spot welding technique for joining at least two steel plates.

Spot (point) welding is employed in a vehicle body production line for joining thin steel plates. In spot welding, since the size of the welded portion called a nugget affects the joint strength, it is required to confirm the size of the welded portion.
In addition to a destructive inspection method for cutting a sample and observing a welded portion appearing on a cut surface, various nondestructive inspection methods that do not damage a work have been proposed (see, for example, Patent Document 1 (FIG. 1)).

  As shown in FIG. 1 (c) of Patent Document 1, a pair of electrodes (1a, 1b) (the numbers in parentheses indicate the symbols described in Patent Document 1. The same applies hereinafter), the work piece (S1, After the nugget (N) is generated during S2), the size of the nugget (N) is obtained by photographing the welding trace with the infrared camera (2).

100% inspection is possible because of non-destructive inspection.
Since the image is taken by the infrared camera (2), only the area (plane area) of the nugget (N) is obtained.
On the other hand, in the destructive inspection, the cut surface is observed. With this observation, the area (vertical area) of the nugget (N) (in the thickness direction) straddling the workpiece (S1) and the workpiece (S2) is obtained. The vertical area as well as the planar area greatly affects the bonding strength.

That is, the bonding strength by the nugget (N) has a strong correlation with the volume of the nugget (N), and the reliability of the inspection result is lowered only by obtaining the flat area as in Patent Document 1.
Therefore, a technique capable of predicting and evaluating the volume of the nugget (welded portion) is required.

Japanese Patent Laid-Open No. 7-63694

  This invention makes it a subject to provide the technique which can estimate the volume of a welding part.

The invention according to claim 1 is characterized in that at least two steel plates are laminated, a main electrode and a ground electrode are applied to one steel plate, and the main electrode is energized from the main electrode to the ground electrode through the steel plate. A resistance welding inspection method for inspecting the generation state of the weld portion in a resistance welding operation in which a weld portion is generated in the vicinity of the main electrode and the ground electrode from the one steel plate,
Until the main electrode is separated from the one steel plate until after it is separated, the temperature measurement step of continuously measuring the temperature of the one steel plate at the site where the main electrode is hit or hit,
In the temperature curve obtained in this temperature measurement process, after the main electrode has moved away from the one steel plate, a determination is made to determine whether or not the temperature rises and the generation state of the welded portion based on the magnitude of the temperature rise Process.

According to a second aspect of the present invention, there is provided a device frame that is held in a relatively movable manner with respect to a workpiece made of at least two laminated steel plates, and a main electrode that is held in the device frame through a main moving means. And a ground electrode that is movably held on the apparatus frame via a sub-moving means, and a welding power source that is connected to the main electrode and the ground electrode, and the main electrode and the ground electrode on one steel plate In the resistance welding apparatus for generating a weld portion in the vicinity of the main electrode by energizing the ground electrode through the steel plate from the main electrode,
The resistance welding apparatus includes a temperature measuring unit that measures the surface temperature of the one steel plate in the vicinity of the welded portion, and inputs temperature information from the temperature measuring unit and acquires a threshold value corresponding to the workpiece in advance. A determination unit that determines whether or not the temperature rises above the threshold immediately after the main electrode is separated from the one steel plate is provided.

  The invention according to claim 3 is characterized in that the temperature measuring means is a non-contact type radiation thermometer that measures the intensity of radiant energy radiated from one of the steel plates and converts it into temperature.

The method according to claim 1 focuses on the fact that the molten metal becomes a welded portion after releasing the heat of solidification, and if the molten metal cannot be formed or is slight as one of the welding defects, The temperature rise after the separation from the steel plate is zero or slight. On the other hand, the greater the amount of welded portion generated, the more heat of solidification is released, and the temperature rise after the main electrode is separated from the steel plate increases.
That is, according to the present invention, the volume of the welded portion can be predicted.

  In the apparatus according to the second aspect, similarly to the first aspect, the volume of the welded portion can be predicted. In addition, the resistance welding apparatus according to the present invention is inexpensive because only a temperature measuring means and a determination unit are added to a normal spot welding apparatus.

  In the invention according to claim 3, since the temperature measuring means is a non-contact type radiation thermometer, it is not necessary to apply it to the measurement object as in the case of the contact temperature measuring means. Can be achieved.

It is a perspective view of the apparatus movement means holding the resistance welding apparatus which concerns on this invention. It is a principle figure of the resistance welding apparatus which concerns on this invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 2. It is an effect | action figure of a resistance welding apparatus. It is a figure which shows the main electrode and electric current which concern on resistance welding. It is a figure explaining the production | generation process of a welding part. It is a figure which shows the temperature of one steel plate. It is the figure which investigated the correlation of the magnitude | size of an electric current and a welding part. It is a determination flowchart of a welding part.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the resistance welding apparatus 10 is held by apparatus moving means 11 represented by a robot and is appropriately moved. Details of the resistance welding apparatus 10 will be described with reference to the next figure.

  As shown in FIG. 2, the resistance welding apparatus 10 includes an apparatus frame 15 held above the work 12, a main moving means 16 provided at the center of the apparatus frame 15, and extends downward from the main moving means 16. A main electrode 18 attached to the rod 17; earth electrodes 19 and 19 disposed on both sides of the main electrode 18; and sub-moving means 21 and 21 provided on the apparatus frame 15 for moving the earth electrodes 19 and 19. And a welding power source 22 connected to the main electrode 18 and the ground electrodes 19, 19.

The main moving means 16 is preferably a cylinder unit using a servo motor as a drive source. The sub moving means 21 is the same.
The welding power source 22 is preferably mounted on the apparatus frame 15, but the installation position is arbitrary.

In the most common spot welding apparatus, a pair of electrodes are arranged vertically on a straight line.
In the resistance welding apparatus 10 of this example, since the main electrode 18 and the ground electrodes 19 and 19 are both disposed on one side of the workpiece 12, it is also called a one-side spot welding apparatus and falls into the category of a special spot welding apparatus. In other words, it is not necessary to place a ground on the back side (lower side in the embodiment) of the work 12, and the degree of freedom in welding is increased.

As shown in FIG. 3, a radiation thermometer 25 is disposed as a temperature measuring means so that the center of the visual field comes to a point 24 where the center line 23 of the main electrode 18 and the upper surface of the work 12 intersect. The installation position of the stand 26 that supports the radiation thermometer 25 is arbitrary.
Temperature information is sent from the radiation thermometer 25, and this temperature information is displayed on the display 27 and sent to the determination unit 28. The determination unit 28 performs determination described later.

  In addition to the radiation thermometer, the temperature measuring means 25 is a contact-type thermometer that measures the temperature by changing the resistance by bringing a resistor into contact with one steel plate, an optical thermometer that converts the wavelength of light into temperature, and infrared heat rays. Various means such as an infrared thermometer for converting the temperature into temperature can be adopted.

The operation of the resistance welding apparatus 10 described above will be described next.
As shown in FIG. 4A, the workpiece 12 is formed by laminating one steel plate 32 on the other steel plate 31, pressing the main electrode 18 against the one steel plate 32 and applying the ground electrodes 19, 19. The pressing force of the ground electrodes 19 and 19 is set smaller than the pressing force of the main electrode 18.

FIG. 4B is an enlarged view of part b of FIG. 4A, and the other steel plate 31 and one steel plate 32 are deformed so as to protrude downward. From the inflection points 33 and 33 of one steel plate 32, in the center-side range A, the other steel plate 31 is in close contact with the one steel plate 32, and the electrical resistance is reduced. In the outer ranges C and C from the inflection points 33 and 33, a gap is formed between the other steel plate 31 and the one steel plate 32, and therefore, conductivity cannot be expected.
Ranges B and B in the vicinity of the inflection points 33 and 33 have intermediate properties between the ranges A and C, and the electrical resistance is much larger than the range A, although the conductivity is ensured.

That is, in FIG. 5A, the pressing force of the main electrode 18 is increased to a predetermined value from the point P1 to the point P2. The form at the point P2 is the above-described FIGS. 4 (a) and 4 (b).
While maintaining this state, power supply is started at a point P3 shown in FIG.
Then, as shown in FIG. 4C, a current flows from the main electrode 18 through the work 12 to the ground electrodes 19 and 19.

This current hardly flows in the ranges C and C in FIG. The current flows in range A and ranges B and B. Joule heat corresponding to IR ² (I: current value, R: resistance value) is generated by the current. Since the resistance values in the ranges B and B are much larger than those in the range A, a large Joule heat is generated in the ranges B and B.

  When this Joule heat exceeds the heat of fusion of the workpiece, a melting phenomenon occurs at the excess portion. That is, as shown in FIG. 6A, melting portions 34 and 34 called molten pools appear at the boundary between the other steel plate 31 and one steel plate 32. At this time, the other steel plate 31 is heat-softened, the portion under the main electrode 18 is pushed and flows horizontally, and a part rises along the main electrode 18.

  When the energization is stopped, the energy supply by the energization is lost, so that heat is transferred from the workpiece 12 to the main electrode 18 as shown in FIG. 6B. This phenomenon occurs because the main electrode 18 has a lower temperature than the workpiece 12 and the heat capacity of the main electrode 18 is larger than that of the workpiece 12. This heat transfer stops when the main electrode 18 is separated from one steel plate 32.

  As shown in FIG. 6C, when the main electrode 18 moves away from one steel plate 32, the form of heat transfer changes. That is, heat moves from the hottest melted portions 34, 34 to lower temperature surroundings (one steel plate 32 and the other steel plate 31). This heat corresponds to the heat of solidification (or heat of aggregation) released when the liquid transforms into a solid, and is sufficiently large. When the melted parts 34 and 34 are solidified, they become welded parts 36 and 36, but the temperature in the vicinity of the welded parts 36 and 36 rises due to the heat of solidification.

The form of this temperature rise will be described with reference to the next figure.
7 (a) and 7 (b) are the same graphs as FIGS. 5 (a) and 5 (b), but are re-displayed for explanation of the temperature graph of FIG. 7 (c).
When energization is started at a point P3 in FIG. 7B, as shown in FIG. 7C, the temperature of one steel plate in the vicinity of the main electrode rapidly increases due to Joule heat. When the energization is stopped at the point P4, the heat moves to the main electrode (see FIG. 6B), so the temperature decreases. This temperature drop continues to point P5 shown in FIG. At the point P5, the pressing force becomes zero, and the main electrode is separated from one steel plate.

  After the point P5, as described in FIG. 6C, the temperature rises by δ due to the heat of solidification. An experiment was conducted to confirm the magnitude of δ.

(Experimental example)
Experimental examples according to the present invention will be described below. Note that the present invention is not limited to experimental examples.

○ Test material:
・ One steel plate: thickness 0.7 mm, 270 MPa class galvanized steel plate ・ The other steel plate: thickness 2.0 mm, 980 MPa class high strength steel plate

○ Resistance welding equipment: According to FIG.
○ Temperature measurement: According to FIG.

○ Resistance welding conditions:
・ Pressure of main electrode: 60kg
・ Pushing force of earth electrode: 40kg
・ Power value: 5.5 kA, 6.5 kA or 7.5 kA
・ Energization time: 0.5 seconds ・ Energization cycle: 25 times / second

○ Experimental results:
As shown in FIG. 8A, temperature curves b, c, and d were obtained. However, the curve b set the current value to 7.5 kA, the curve c set the current value to 6.5 kA, and the curve d set the current value to 5.5 kA.
In curve b, an increase in temperature of δb was observed. Further, in curve c, an increase in temperature of δc was observed. δc was about 1/3 of δb. Further, no increase in temperature was observed in curve d.

The obtained three types of test materials were cut and the cut surfaces were observed.
FIG. 8B corresponds to the curve b, and large welds 36 and 36 were observed.
FIG. 8C corresponds to the curve c, and welds 36 and 36 smaller than those in FIG.
FIG. 8D corresponds to the curve d, and the welded portions 36 and 36 were extremely small.

Based on the above knowledge, the temperature curves b, c, and d in FIG. 8A are obtained, and the presence or absence of a temperature rise that occurs immediately after the main electrode is separated from one steel plate is examined.
Since the temperature rise is not recognized in the curve d, it can be determined that the welded portions 36 and 36 have not reached the required size.

Further, in the curve b, a sufficiently large temperature rise δb was recognized, so that it can be determined that the welded portions 36 and 36 have reached a size larger than necessary.
Further, since a large temperature increase δc is recognized in the curve c, it can be determined that the welded portions 36 and 36 have reached a necessary size.

  From the above knowledge, from the time before the main electrode is separated from one steel plate until after it is separated, the temperature measurement step of continuously measuring the temperature of one steel plate at the site where the main electrode is hit or hit, and this In the temperature curves b, c, and d obtained in the temperature measurement process, the generation state of the welded portion is determined based on whether the temperature rises and the magnitude of the temperature rise after the main electrode is separated from the one steel plate. A resistance welding inspection method comprising a determination step is provided.

The determination step is performed by the determination unit 28 shown in FIG. 3, and it is recommended that the determination unit 28 perform the next step.
Prior to the determination, one steel plate and the other steel plate are overlapped, welded, cut, the size of the welded portion is measured, and the correlation with the temperature difference δ at that time is examined. Then, a threshold value Ts is determined from a temperature difference when a weld portion having a strength required is obtained.
This Ts is determined for each combination of thicknesses of one steel plate and the other steel plate. If necessary, Ts is determined by adding the steel grade to the parameters.

  As shown in FIG. 9, first, a threshold value Ts, which is a pass criterion value, is input to the determination unit (ST01). This Ts is, for example, δc in FIG. This ST01 is performed only when the plate thickness condition and the steel type condition change, and can pass when there is no change.

  One steel plate and the other steel plate are overlapped, welded, and the temperature of one steel plate is measured. The temperature at point P5 in FIG. 7C (this temperature is defined as T1) is specified. When it is necessary to save the time for examining the temperature curve, the temperature at the start of the main electrode rise may be applied (ST02).

  Next, the maximum temperature T2 in the temperature curve up to n seconds (for example, 3 seconds) is specified (ST03). In ST04, ΔT = T2−T1 is calculated.

  In ST05, it is checked whether or not ΔT is positive. If it is zero or negative, no temperature rise is observed. Therefore, it is considered that there is no welded portion or is minute (ST06), and a failure is determined (ST07).

  When ΔT is positive, it is checked whether ΔT is equal to or greater than a threshold value Ts. If not, an increase in temperature is recognized and the formation of a weld is predicted, but this weld is considered small (ST09) and a failure is determined (ST07).

    If ΔT is positive and greater than Ts, it is predicted that a sufficiently large welded portion has been generated (ST10), and a pass determination is made (ST11).

  When the above flow is applied, the size of the welded portion can be predicted only by measuring the temperature of one steel plate. Since it is a non-destructive inspection, the total number of welded products can be inspected.

  In the embodiment, two steel plates are laminated, but three or more steel plates may be laminated.

  In the embodiment, one steel plate 32 is placed on the other steel plate 31, but the other steel plate 31 may be placed on one steel plate 32. In addition, the plates 31 and 32 may be arranged horizontally or vertically or diagonally. The one electrode 18 and the other electrode 19, 19 may be brought into contact with or separated from the steel plate 32 from above, from below, or from the side in accordance with the orientation of the plates 31, 32, and the orientation of the components is arbitrary. .

  The present invention is suitable for a technique of joining two thin steel plates by a one-side spot welding method.

  DESCRIPTION OF SYMBOLS 10 ... Resistance welding apparatus, 11 ... Apparatus moving means, 12 ... Work, 15 ... Apparatus frame, 16 ... Main moving means, 18 ... Main electrode, 19 ... Ground electrode, 21 ... Sub moving means, 22 ... Welding power supply, 25 ... Temperature measuring means (radiation thermometer), 28 ... determining part, 31 ... steel plate (the other steel plate), 32 ... steel plate (one steel plate), 36 ... welding part.

Claims (3)

Laminating at least two steel plates, applying a main electrode and a ground electrode to one steel plate, and energizing the ground electrode from the main electrode through the steel plate, thereby generating a welded portion in the vicinity of the main electrode. In a resistance welding operation in which the main electrode and the ground electrode are separated from the one steel plate, a resistance welding inspection method for inspecting a generation state of the weld portion,
Until the main electrode is separated from the one steel plate until after it is separated, the temperature measurement step of continuously measuring the temperature of the one steel plate at the site where the main electrode is hit or hit,
In the temperature curve obtained in this temperature measurement process, after the main electrode has moved away from the one steel plate, a determination is made to determine whether or not the temperature rises and the generation state of the welded portion based on the magnitude of the temperature rise A resistance welding inspection method comprising a process. A device frame held relative to a workpiece made of at least two laminated steel plates, a main electrode held movably on the device frame via a main moving means, and a sub-movement to the device frame Consisting of a ground electrode held movably through means, and a welding power source connected to the main electrode and the ground electrode,
In the resistance welding apparatus for generating a welded portion in the vicinity of the main electrode by applying the main electrode and the ground electrode to one steel plate and energizing the ground electrode from the main electrode through the steel plate,
The resistance welding apparatus includes a temperature measuring unit that measures the surface temperature of the one steel plate in the vicinity of the welded portion, and inputs temperature information from the temperature measuring unit and acquires a threshold value corresponding to the workpiece in advance. A resistance welding apparatus comprising: a determination unit that determines whether or not the temperature rises above the threshold value immediately after the main electrode is separated from the one steel plate.   3. The resistance welding apparatus according to claim 2, wherein the temperature measuring means is a non-contact type radiation thermometer that measures the intensity of radiant energy radiated from the one steel plate and converts it into temperature.

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