JP7139218B2 - Weld point evaluation method for indirect spot welding - Google Patents

Description

The present invention relates to a method for evaluating weld points formed by indirect spot welding.

In the automobile assembly process, a vehicle body is assembled by joining a plurality of parts made of metal plates by spot welding. As spot welding, direct spot welding is often used in which a plurality of metal plates are sandwiched between a pair of electrodes and energized. However, depending on the shape of the part, it may not be possible to sandwich a plurality of metal plates between a pair of electrodes, and direct spot welding may not be applied. In this case, indirect spot welding is applied, in which welding is performed by applying pressure to the overlapped portions of a plurality of metal plates with a welding electrode and applying an electric current between the electrodes while a ground electrode is in contact with a portion different from the overlapped portion. be.

However, in indirect spot welding, the welding electrode and the ground electrode are often placed apart, and the current flowing through the contact portion between the metal plates (for example, the previously welded welding point) other than the overlapping portion The problem is that it is difficult to form a good nugget because (reactive current) is likely to occur.

For example, in Patent Literature 1 below, a bearing surface is provided in advance on a metal plate, and by pressing the bearing surface while crushing it with a welding electrode, the contact area between the metal plates is reduced and the current density is increased. A method is presented to facilitate nugget formation.

Further, Patent Document 2 below discloses an indirect spot welding method capable of stably obtaining a nugget by controlling the applied pressure and the current value.

Japanese Patent Application Laid-Open No. 2002-239742 JP 2010-194609 A

However, since there was no method for quantitatively evaluating the ease of forming a nugget at a welding point, there was no choice but to search for suitable welding conditions for nugget formation by repeating trial and error while trying the above methods.

Therefore, the present inventors separately measured the resistance value of the active current path that contributes to welding and the resistance value of the reactive current path that does not contribute to welding, and set the active current based on these resistance values. An attempt was made to evaluate the susceptibility to nugget formation at weld points based on the rate.

Specifically, as shown in FIG. 4A, a first metal plate 101, a second metal plate 102 having a hat-shaped cross section, and a first metal plate 101 and a second metal plate 102 and a third metal plate 103 having a hat-shaped cross section arranged in a hollow portion, the first metal plate 101 and the top plate portion 103b of the third metal plate 103 A description will be given of an evaluation method when indirect spot welding is applied to the overlapped portion P with. Note that pre-welded points Q1 and Q2 are provided between the respective metal plates.

First, the resistance value _RB of the reactive current path that does not contribute to welding is measured. Specifically, one terminal 131 of the resistance measuring device 130 is brought into contact with the overlapped portion P of the workpiece 100 from above, which is a portion of the workpiece 100 to which the welding electrode is brought into contact during welding. In addition, the other terminal 132 of the resistance measuring device 130 is brought into contact with one already-welded point Q2 of the work 100, which is a portion of the workpiece 100 to which the ground electrode is brought into contact during welding, from below. In this state, the resistance value of the current path between both terminals 131 and 132 is measured without pressurizing the overlapping portion P of the workpiece 100 . Since the overlapped portion P is not pressurized, the overlapped portion P of both metal plates 1 and 3 is not substantially in contact with each other, and almost no current flows through the overlapped portion P even without insulation. Therefore, one terminal 131 → first metal plate 101 → already welded point Q1 → second metal plate 102 → the other terminal 132, which is a current path that does not pass through overlapping portion P (interface between both metal plates 101 and 103). C1 is formed, and this current path C1 can be regarded as a current path of reactive current that does not contribute to welding.

Next, the resistance value _RA of the effective current path contributing to welding is measured. Specifically, as shown in FIG. 4B, one terminal 131 of the resistance measuring device 130 is inserted into the slit S provided in the first metal plate 101, and the third metal plate 103 is It is brought into contact with the vicinity of the overlapping portion P of the top plate portion 103b from above. Also, the other terminal 132 of the resistance measuring device 130 is brought into contact with one of the welded points Q2 from below. As a result, a current path C2 of one terminal 131→third metal plate 103→pre-welded point Q2→second metal plate 102→other terminal 132 is formed, and the resistance value of this current path C2 is measured.

Based on the resistance values _RB and _RA measured as described above, the likelihood of forming a nugget at the welding point can be evaluated. For example, the sum of the resistance value R _A of the active current path and the resistance value R _B of the reactive current path is defined as the total resistance R _T (=R _A +R _B ) _. It is obtained as a ratio of the resistance value R _B of the path (K'=R _B /R _T ). The effective current rate K' is an index representing the ease with which an effective current flows. Based on the value of the effective current rate K', the ease with which a nugget is formed in the overlapping portion P can be evaluated.

However, in the above measurement method, only the resistance value between both terminals 131 and 132 can be measured. Therefore, as shown in FIG. Alternatively, even if the resistance value of each path can be measured when the current is flowing in only one of the effective current paths C2, the welding electrode presses the overlapped portion P as in actual welding, When the first metal plate 101 and the top plate portion 103b are in contact with each other, current flows through both the reactive current path C1 and the effective current path C2, and in a situation where the paths are partially common, each path It was not possible to separate and measure the resistance value, and it was not possible to calculate the effective current rate.

However, the resistance value of the metal plate changes as the current flows and heat is generated. Therefore, when the overlapping portion P is pressurized and the current flow changes, the resistance value of each path also changes. In other words, there is a deviation between the resistance values _RB and _RA measured by the above measurement method and the resistance values during actual welding. I can't say that I was able to evaluate it accurately.

In view of such circumstances, an object of the present invention is to accurately evaluate the likelihood of forming a nugget at a welding point.

In order to solve the above problems, the present invention provides indirect spot welding in which overlapping portions of a plurality of workpieces are pressurized by a welding electrode, and a ground electrode is brought into contact with a portion different from the overlapped portion to energize between the electrodes. A method for evaluating a weld point formed by a part to be measured of the workpiece and a part to be measured of the workpiece at a position different from the part to be measured, or between the welding electrode and the ground electrode At least a current detection means is provided at a position where the current value of the welding electrode can be detected, and the current flowing through the part to be measured during the indirect spot welding , or the welding electrode, which is detected using a plurality of the current detection means and a step of calculating an active current value and a reactive current value based on the strength of the magnetic field formed by the current flowing between the ground electrode and the active current value and the reactive current value based on the current value. and a step of evaluating the welding point based on the effective current rate.

In the present invention, a current detecting means is provided in the portion to be measured of the workpiece, and the value of the current flowing through the specific portion of the workpiece is detected by a method of measuring the current value based on the strength of the magnetic field formed by the current flowing through the portion to be measured. Can be measured individually. In other words, even if a current flows in each of the active current path and the reactive current path, and both paths are partially common, the value of the current flowing through each of the active current path and the reactive current path is It can be measured or calculated, and the effective current rate can be calculated based on the current value. Therefore, the effective current rate can be calculated based on the actual current value during welding, and the likelihood of forming a nugget at the welding point can be accurately evaluated.

According to the present invention, it is possible to accurately evaluate the likelihood of forming a nugget at a welding point.

FIG. 4 is a schematic diagram showing how current values flowing during welding are measured using current detection means according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1; It is a sectional view showing a toroidal coil. FIG. 4 is a diagram showing how the resistance value of each current path of a work is measured using a resistance measuring instrument;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

This embodiment shows an indirect spot welding method performed in the assembly process of an automobile body. Specifically, for example, as shown in FIG. 1, a case of welding a bracket 2 as a second work to a pillar-to-pillar member 1 (hereinafter referred to as a PP member 1) as a first work will be described.

The PP member 1 is a cylindrical member made of steel and arranged between pillars of the vehicle body, and has a cylindrical shape in this embodiment. A plurality of brackets including a bracket 2 are welded to a plurality of locations in the longitudinal direction on the outer peripheral surface side of the PP member 1, and various in-vehicle parts (for example, steering-related parts, passenger airbags, etc.) are attached to each bracket. ) is attached.

Bracket 2 has a flange portion 2 a welded to PP member 1 . The flange portion 2 a extends in the longitudinal direction of the PP member 1 .

an indirect spot welding device 10 including a welding electrode 3, a holding part 4, a first ground electrode 5, a multi-axis robot 6 supporting the holding part 4, etc.; The overlapped portion P of the PP member 1 and the flange portion 2a is welded by equipment having a control device (not shown) for controlling the applied pressure and the current value between the welding electrode 3 and each ground electrode. The indirect spot welding device 10 includes pressurizing means (such as an air cylinder or an electric cylinder) that drives the welding electrode 3 in the axial direction to pressurize the overlapped portion.

The first ground electrode 5 has a cylindrical shape, and the PP member 1 is inserted into the inner peripheral surface of the first ground electrode 5 . The first ground electrode 5 is provided with a gripping mechanism (not shown) that grips the first ground electrode 5 from its outer peripheral surface side. are in contact.

As shown in FIG. 2 , the first ground electrode 5 is composed of a knitted body 51 and a plate member 52 . The knitted body 51 has a two-layer structure of a first layer 51a on the outer peripheral surface side and a second layer 51b on the inner peripheral surface side. A plate member 52 is inserted. The braided body 51 can be formed by loosening and softening a commercially available flat braided copper wire by hand and forming it into a tubular shape. The plate member 52 is provided along the longitudinal direction of the first ground electrode 5 (horizontal direction in FIG. 1).

The cylindrically formed first ground electrode 5 contacts the PP member 1 so that the copper wire forming the second layer 51b follows the outer peripheral surface of the PP member 1 . As a result, the contact area between the copper wire forming the second layer 51b and the PP member 1 can be increased, preventing the current density of the current flowing through the first ground electrode 5 from becoming excessive, and It is possible to prevent the electrode from being damaged, and to suppress seizure and deformation of the surface of the PP member 1 . In this embodiment, the first ground electrode 5 has a tubular shape covering the entire outer peripheral surface of the PP member 1, but may have an arcuate shape covering a part thereof. In addition, by providing the plate member 52 between the first layer 51a and the second layer 51b, compared to the case where the copper wires forming the first layer 51a and the second layer 51b are in direct contact with each other, each layer By increasing the number of contact points between the copper wire constituting the plate member 52 and the plate member 52, the thermal conductivity of the first ground electrode 5 can be enhanced.

As shown in FIG. 1, the holding part 4 grips one end of the bracket 2 and is positioned so that the bracket 2 can be welded to the PP member 1, that is, the flange part 2a faces the outer peripheral surface of the PP member 1. holding in position.

The holding part 4 has gripping arms 41 and 42 for gripping one end of the bracket 2 . The gripping arm 42 comprises a conductive portion 42a (see the cross-hatched portion in FIG. 1) as a second ground electrode and an insulating base portion 42b. Also, the gripping arm 41 is made of an insulating member.

The holding part 4 is attached to the tip of the multi-axis robot 6 . A position where a member to be welded to the PP member 1, such as the bracket 2, can be gripped and welded by driving the multi-axis robot 6 and rotating the gripping arm 41 around the spindle (see the arrow in FIG. 1). can be moved to and held and fixed at that position.

During welding, the welding electrode 3 presses the flange portion 2a of the bracket 2 to form an overlapping portion P between the flange portion 2a and the PP member 1, and the welding electrode 3→bracket 2→overlapping portion P→PP member. The overlapped portion P is welded by passing a current through the path R1 from 1 to the first ground electrode 5. In addition, the conductive portion 42a, which is a part of the gripping arm 42, functions as a second ground electrode, and current also flows through the route R2 from the welding electrode 3→bracket 2→conductive portion 42a. Furthermore, since the bracket 2 is also in contact with the PP member 1 at the end portion 2c, which is a portion different from the overlapping portion P, the welding electrode 3→bracket 2→end portion 2c→PP member 1→first ground electrode 5 A current is also flowing through the route R3. A route R3 is a route that diverges from the route R2 and merges with the route R1, and is partly shared with the routes R1 and R2. The current flowing through path R1 is an active current that contributes to welding of overlapping portion P, and the currents flowing through paths R2 and R3 are reactive currents that do not directly contribute to welding.

Next, a method of measuring the current value flowing through the PP member 1 and the bracket 2 during welding and evaluating the ease of forming a nugget at the welding point will be described.

Welding electrode 3 , first ground electrode 5 , and conductive portion 42 a are electrically connected, and power is supplied to welding electrode 3 via transformer 71 . A first toroidal coil 72 is wound around a location where the total current value flowing during welding can be measured, such as an electric wire connected to the welding electrode 3 .

A second toroidal coil (current detection means) 73 is wound around the portion 2b to be measured, which is a predetermined position on the vertical wall portion of the bracket 2. As shown in FIG. The measured portion 2b is a portion through which the active current path R1 does not pass and all the reactive current paths R2 and R3 pass.

As shown in FIG. 3, the second toroidal coil 73 forms an annular shape by connecting a pair of fasteners 731, and is wound around the measured portion 2b so as to cover the entire circumference of the measured portion 2b. be.

As shown in FIG. 1, a second toroidal coil 73 may be provided on the gripping arm 41, for example. Specifically, the second toroidal coil 73 is provided with a base (not shown), and the grasping arm 41 holds the second toroidal coil 73 via this base. Then, the second toroidal coil 73 may be wound around the measured portion 2b of the bracket 2 by the gripping arm 41 rotating to grip one end of the bracket 2 .

The toroidal coils 72 , 73 are connected to a current measuring device 74 . The current measuring device 74 measures the current flowing through each conductor based on the strength of the magnetic field generated by the conductor around which each toroidal coil is wound (the electric wire connected to the welding electrode 3 or the measured portion 2b). . Specifically, the current passing through the conductor around which each toroidal coil is wound produces a magnetic field, and the current measuring device 74 integrates the voltage induced across each toroidal coil by this magnetic field. Measure the value of the current flowing through the conductor.

In the method of measuring the current value of this embodiment, the flange portion 2a is pressed by the welding electrode 3, and the distance between the welding electrode 3 and each ground electrode (the first ground electrode 5, the conductive portion 42a), that is, the paths R1, R2, Each current value is measured by the current measuring device 74 while current is flowing through R3. Specifically, based on the magnetic intensity detected by the toroidal coil 72, the current measuring device 74 measures the total current value I _T flowing from the welding electrode 3 to each ground electrode. Also, the current measuring device 74 measures the current flowing through the measured portion 2b based on the strength of the magnetic field detected by the toroidal coil 73 . As described above, the measured portion 2b is a portion through which all reactive current paths R2 and R3 commonly pass, and the current value flowing through this portion can be measured as the total reactive current value _IB . can.

Also, since the total current value I _T is the sum of the total active current value I _A and the total reactive current value I _B , the total reactive current value I _B is subtracted from the total current value I _T to obtain the total active current value I _A can be determined (I _A =I _T -I _B ). Thus, in this embodiment, even if the total active current value _IA cannot be directly measured, the total active current value _IA can be calculated from the total current value _IT and the total reactive current value _IB . can.

Then, for example, it can be obtained as an effective current rate K (=I _A /I _T ) during welding, and the ease of forming a nugget in the overlapped portion P can be evaluated from the magnitude of this effective current rate K. .

As described above, according to the current measuring method of the present embodiment, even in the case where the active current path and the inactive current path are partly common, such as the path R1 and the path R3, welding The total active current value _IA and the total reactive current value _IB at the time of welding can be measured or calculated, respectively, and the effective current rate K under the conditions at the time of welding can be calculated. Therefore, it is possible to quantitatively and accurately evaluate the likelihood of forming a nugget at an arbitrary welding point. Therefore, it is possible to improve the welding quality by adjusting the welding conditions (pressure and/or current value) and the design and assembly process of each workpiece (position, number, welding order of welding points, shape of metal plate, etc.). can.

Further, as described above, even when the reactive current path diverges to the path R3 and joins the active current path, the effective current rate K can be calculated. Regardless of whether the PP member 1 is in contact or not, each current value can be measured and the effective current rate K can be calculated. In this way, the effective current rate K can be calculated regardless of the contact state between the PP member 1 and the bracket 2 . Note that the measured portion 2b is not limited to the position in the present embodiment, and can be set at an appropriate position until the path R2 and the path R3 split.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

Further, in the above-described embodiment, the effective current rate K is the ratio of the total effective current value _IA to the total current value _IT , but it is not limited to this. For example, the active current rate K may be the ratio (I _A /I _B ) of the active current value I _A to the total reactive current value I _B . Also, although the effective current rate K is determined as the ratio of each current value, it may be determined as the ratio of the resistance values of the paths calculated from the respective current values.

In the above embodiment, the total current value I _T and the total reactive current value I _B are measured, and the difference between them is used to calculate the total active current value I _A . However, the present invention is not limited to this. For example, a plurality of toroidal coils may be used to measure the current value of the portion common to the routes R1 and R3 and the value of the current flowing through the route R3, and the effective current value _IA may be calculated from the difference. Thus, in the present invention, current detection means are appropriately provided at necessary measurement locations according to the current path of the workpiece to be welded, and the total reactive current value _IB and the total active current value _IA are determined based on the measurement results. It can be measured or calculated.

1 PP member (first work)
2 Bracket (second workpiece)
2a flange portion 2b portion to be measured 3 welding electrode 4 holding portion 5 first ground electrode 6 multi-axis robot 10 indirect spot welding device 41 gripping arm 42 gripping arm 42a conductive portion (second ground electrode)
42b base 71 transformer 72 first toroidal coil (current detection means)
73 second toroidal coil 74 current measuring device P overlapping portion R1, R2, R3 path

Claims (1)

A method for evaluating weld points formed by indirect spot welding in which overlapping portions of a plurality of works are pressurized by a welding electrode, a ground electrode is brought into contact with a portion different from the overlapping portion, and an electric current is passed between the electrodes. and
At least a current detection means is provided at a portion to be measured of the work, a portion to be measured at a position different from the portion to be measured of the work, or a portion capable of detecting a current value between the welding electrode and the ground electrode. ,
Based on the strength of the magnetic field formed by the current flowing through the portion to be measured or the current flowing between the welding electrode and the ground electrode during the indirect spot welding, which is detected using the plurality of current detection means. and calculating an active current value and a reactive current value ;
calculating an active current rate represented by an active current value and a reactive current value based on the current value;
and a step of evaluating the welding point based on the effective current rate.

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