JP6214376B2 - Evaluation method of welded joint state - Google Patents

Description

  The present invention relates to a welded joint state evaluation method for evaluating the quality of a welded part in which a pair of electrodes are brought into contact with two super-high-strength steel plates that are superposed to perform spot welding.

  Conventionally, as shown in FIG. 7, electrodes 51 a and 51 b are placed in contact with predetermined welding portions of two metal plates 50 a and 50 b, and spot welding (resistance welding) is performed by energizing both electrodes 51 a and 51 b, As a method for inspecting the quality of the welded state of the welded part 52 called a nugget, as shown in FIG. 8, a chisel 53 is driven between the two metal plates 50a and 50b toward the welded part 52, for example, a nugget diameter. When D (see FIG. 7) is smaller than a desired value and peeling or the like occurs in the welded portion 52, it is determined that the connection is poor, and the metal plate 50a is slightly deformed as shown in FIG. If not, it is determined that a good weld 52 having a nugget diameter (see FIG. 7) of a desired value or more is formed. If it is determined that the welded portion 52 is good, then the deformed metal plate 50a is restored to its original shape by hitting it with a hammer 54 and used in a product as shown in FIG.

  At this time, if the tensile strength of the metal plates 50a and 50b is a high-strength steel plate exceeding 270 MPa and these welds 52 are inspected, the metal plates 50a and 50b are not easily deformed as shown in FIG. Therefore, as shown in FIG. 11, due to the impact when driving the chisel 53, there is a problem that stress concentration occurs on the side where the chisel 53 of the welded portion 52 is driven and cracks 55 are likely to occur.

  Therefore, for example, as described in Patent Document 1, inspection is performed using a specially shaped chisel formed by forming a notch portion that is larger than the width of the welded portion at the blade tip portion that is tapered toward the tip. It is considered to be.

  However, in the case of a very hard steel plate called ultra-high tensile material (hereinafter referred to as ultra-high tensile material) having a tensile tension of 590 MPa or more, the ultra-high tensile material becomes even more difficult to deform. Even a specially shaped chisel is not suitable for inspection of a welded portion of a super high tensile material having a tensile tension of 590 MPa or more.

  Therefore, after the current flowing between the electrodes is increased to the welding current value so that the spot welded portion of the super high tensile material having a tensile tension of 590 MPa or more can be inspected in a non-contact manner, the electrode immediately after the current value is increased. If the resistance value decreases, it is determined that a good weld has been formed, and if the resistance value between the electrodes decreases after a while after increasing the current value, it is determined that the joint state of the weld is poor. Has been proposed (for example, Patent Document 2).

JP 2011-47738 A (refer to paragraphs 0002-0004, 0009 and FIGS. 1 and 2) JP 2011-177722 A (see abstract, paragraphs 0012-0014)

  However, in the case of the method as described in Patent Document 2 mentioned above, since the inspection (non-destructive inspection) can be performed without destroying the joining state of the welded portion, there is no possibility that the welded portion may crack at the inspection stage. Since a device for constantly monitoring the resistance value between them is required, the inspection cost is high, and the resistance value data must be analyzed for each welded portion, which requires time and labor.

  An object of the present invention is to make it possible to easily evaluate the joining state of a welded portion of a super high tensile material (tensile tension of 590 MPa or more) without incurring inspection costs.

  In order to achieve the above-described object, the welded state evaluation method of the present invention is based on whether the welded state of a welded part that is spot-welded with a pair of electrodes in contact with two super-high-strength steel plates superimposed In the welding state evaluation method of the welded portion, the non-high strength steel sheet is further superposed on one of the ultra-high strength steel sheets, and the thickness of the non-high strength steel sheet, The reference point is compared with the distance from the reference point to the boundary surface of both the ultra-high-strength steel plates, with a reference point being a half point of the total thickness of both ultra-high-strength steel plates and the non-ultra-high-strength steel plates. Is set so that the distance from the one ultra-high strength steel sheet to the boundary surface between the non-ultra high-strength steel sheet is increased, and the both ultra-high-tensile steel sheets and the non-ultra-high-strength steel sheets are overlapped with each other. Welded and said one ultra-high strength steel and said non-high strength steel The chisel for inspection is characterized by evaluating the quality of the bonding state of the welded portion are implanted toward the welded portion between the (claim 1).

  In the case of spot welding, two electrodes are brought into contact with both sides of the welded portion and energized, and the metal is melted from the inside using heat generated by electric resistance to form a welded portion called a nugget where the molten metal is solidified. The nugget is formed from a position that is half the total thickness of the object to be welded.

  Therefore, even if two ultra-high strength steel sheets thinner than this are superposed and spot welded, one ultra-high strength steel sheet and a non-high-tensile steel sheet can be used in addition to the boundary between both ultra-high strength steel sheets. A nugget that straddles both of the boundaries can be formed. At this time, as the thickness of the non-ultra high strength steel sheet, a reference point is a half of the total thickness of the both ultra high strength steel sheets and the non-ultra high strength steel sheet, and the boundary between the ultra high strength steel sheets from the reference point. By setting the distance from the reference point to the interface between one ultra high strength steel sheet and the non-high strength steel sheet, the nugget diameter at the boundary between both ultra high strength steel sheets is larger than the distance to the surface. Can be made larger than the nugget diameter at the boundary between one ultra-high strength steel sheet and a non-ultra-high-strength steel sheet, It is possible to evaluate the quality of the joining state of the nugget at the boundary between both ultra-high-strength steel sheets by inspecting by a conventional method using the above.

  Therefore, according to the first aspect of the present invention, two super high strength steel plates having a tensile tension of 590 MPa or more are superposed, and a non-super high strength steel plate that is thinner than these super high strength steel plates is further superposed on one of the spots. Welding and driving a test strip between one ultra-high strength steel plate and a non-high-strength steel plate toward the weld to evaluate the quality of the welded joint. Therefore, it is possible to easily determine the quality of the joining state between the super-high strength steel sheet and the non-super high-strength steel sheet that are easily deformed and superposed. If it can be evaluated as good, it can be evaluated that the joining state between both ultra-high-strength steel plates is also good, and the joining state of the welded portion of the ultra-high-strength steel plate having a tensile tension of 590 MPa or more can be easily performed without incurring inspection costs. It becomes possible to evaluate.

It is sectional drawing for operation | movement description at the time of welding in one Embodiment of the joining state evaluation method of the welding part which concerns on this invention. It is sectional drawing in the middle of a test | inspection of the joining state of the welding part in one Embodiment. It is sectional drawing for the evaluation principle description of one Embodiment. It is sectional drawing for the evaluation principle description of one Embodiment. It is a perspective view of a modification. It is a perspective view of another modification. It is sectional drawing for description of general spot welding. It is sectional drawing in a state with the welding part of FIG. It is sectional drawing in the state from which the welding part of FIG. 7 differs. It is sectional drawing in the state with another prior art example. It is sectional drawing of the welding part of FIG.

  An embodiment of the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 1, first and second welded members 1a and 1b made of two super high tensile materials (ultra high strength steel plates) having thicknesses T1 and T2, respectively, are superposed, and one super high tensile material is used. A plate 2 made of a non-ultra-high-strength steel plate having a thickness t3 is superimposed on a certain second member 1b, and spot welding electrodes 3a and 3b are brought into contact with the first welding member 1a and the plate 2 so that both electrodes 3a and 3b are brought into contact with each other. Spot welding is performed with current passing between them.

At this time, as shown in FIG. 2, when a current is passed between the electrodes 3a and 3b, half of the total thickness T (= T1 + T2 + t3) of both the welding members 1a and 1b and the backing plate 2 due to heat generated by electric resistance (= The position of T / 2) is defined as a reference point P (marked with x in FIG. 2), and the weld 5 is formed by melting the metal starting from the reference point P and spreading to the periphery, and solidifying the molten metal called a nugget. Is done. Therefore, the relationship between the thickness t3 of the backing plate 2 and the total thickness T is
T / t3 ≧ 3 (1 formula)
3, that is, if the thickness t3 of the backing plate 2 is made thinner than one third of the total thickness T, as shown in FIG. 3, the nugget diameter D1 at the boundary between the two welding members 1a and 1b is 2 The nugget diameter D2 at the boundary between the welding member 1b and the contact plate 2 is greater than or equal to D2 (D1 ≧ D2).

  More preferably, as the thickness t3 of the contact plate 2, as shown in FIG. 2, the distance from the reference point P to the boundary surface of the first and second welding members 1a, 1b is compared with the first point from the reference point P. The distance y to the boundary surface between the two members 1b and the contact plate 2 may be set to be large (x <y).

  Then, as shown in FIG. 4, when the chisel 7 is driven toward the welded portion 5 at the boundary between the second welding member 1b and the contact plate 2, the contact plate 2 made of a non-ultra high strength steel plate is easily deformed. Therefore, the joining state of the boundary between the second welding member 1b and the contact plate 2 can be determined by a well-known ratchet inspection. As a result of the ratchet inspection, the second welding member 1b and the contact plate 2 If the joining state of the boundary is good, it is evaluated that the joining state of the boundary between the two welding members 1a and 1b having a nugget diameter D1 equal to or larger than the nugget diameter D2 of the boundary between the second welding member 1b and the contact plate 2 is good. it can. The deformed backing plate 2 may be restored to its original shape by hitting with a hammer afterwards, as in the conventional case.

  Therefore, according to the above-described embodiment, both the welding members 1a and 1b are overlapped, and the contact plate 2 made of a non-ultra-high strength steel plate having the thickness t3 is further overlapped with the second welding member 1b and spot-welded, Since the inspection chisel 7 is driven toward the welded portion 5 between the overlapped second welded member 1b and the backing plate 2, the quality of the welded state of the welded portion 5 is evaluated. 7, the contact plate 2 that is a non-ultra-high-strength steel plate is easily deformed, so that the joining state between the second welded member 1b and the contact plate 2 can be determined by the same technique as the well-known steel sheet inspection. Whether the quality is good or not can be easily determined, and the joining state between the second welding member 1b and the contact plate 2 is good, the joining state between the two welding members 1a and 1b can be evaluated as good. . As a result, the joining state of the welded portions 5 of the two welded members 1a and 1b having a tensile tension of 590 MPa or more can be easily evaluated without incurring inspection costs as in the prior art.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the example in which the contact plate 2 made of a non-ultra-high-strength steel plate is further superposed on the two welding members 1a and 1b and spot welding is described, but the specific product is used for a vehicle body. As an example of evaluating the joining state when spot welding is performed on the super high tensile material, as shown in FIG. 5, for example, as shown in FIG. 5, the flange portions on both sides of the first member 11a having a cross-sectional hat shape made of super high tensile material having a tensile tension of 590 MPa or more In addition, the flat plate 11b made of a super high tensile material having a tensile tension of 590 MPa or more is superposed on each other, and when spot welding is performed at several locations (marked with x in FIG. 5) of the flange portion, below the both flange portions of the flat plate 11b. Spot plate welding is performed by further overlapping a contact plate 12 made of a long non-super high strength steel plate along the flange portion, and the flat plate 11b and the contact plate By implanting chisel toward the welded portion at the boundary between the 2 may be evaluated the quality of the bonding state.

  At this time, the contact plate 12 may be a flat plate having the same shape as the flat plate 11b (however, the thickness is different), and the contact plate 12 is arranged for each spot welding point. Also good.

  Further, the contact plate 2 in the above-described embodiment and the contact plate 12 in FIG. 5 are used exclusively for evaluation of the joined state, and are examples of cases where the product is not a member constituting the product. The present invention can be similarly implemented even when a member made of a non-ultra-high-strength steel plate that constitutes is further superposed on two ultra-high strength materials.

  That is, as shown in FIG. 6, in the vehicle, a pillar P in which an inner panel and an outer panel made of a super high tensile material having a tensile tension of 590 MPa or more are superposed, and a side outer panel S made of a non-super tensile steel plate is further superposed. In the configuration to be reinforced, the present invention is similarly carried out even when spot welding is performed at a plurality of welding points indicated by x marks in the same figure and the quality of the joint state of the spot welded portions is evaluated. Can do.

1a, 1b ... 1st, 2nd welding member (ultra high strength steel plate)
2,12 ... Contact plate (Non-high strength steel plate)
5 ... welded part 7 ... chisel 11a ... 1st member (ultra high strength steel plate)
11b ... 2nd member (super high strength steel plate)
P ... Pillar (super high strength steel plate)
S: Side outer panel (non-super high strength steel sheet)

Claims (1)

In the welded state evaluation method for evaluating the quality of the welded state of the welded portion where spot welding is performed by bringing a pair of electrodes into contact with the two super high strength steel plates that are superimposed,
Further superimposing a non-ultra high strength steel plate on one of the ultra high strength steel plates of the both ultra high strength steel plates,
As the thickness of the non-ultra high strength steel sheet, a reference point is a half of the total thickness of the both ultra high strength steel sheets and the non-ultra high strength steel sheet. Compared to the distance to the boundary surface, the distance from the reference point to the boundary surface between the one ultra high strength steel sheet and the non-super high strength steel sheet is set to be large,
Spot welding in a state in which the both ultra-high strength steel plates and the non-high strength steel plates are overlapped,
Welding characterized in that an inspection chisel is driven toward the welded portion between the one ultrahigh-strength steel plate and the non-ultrahigh-strength steel plate to evaluate the quality of the welded state of the welded portion. Of bonding state of a part.

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