JP4854920B2 - Spot welding method and spot-welded steel plate member - Google Patents

Description

The present invention relates to a steel plate member which is spot welding method and spot welding, in particular, to a locally spot welding technique in a laminated state only three steel plates to each other.

  In recent years, there has been a demand for further increasing the strength of members in which steel plates are welded to each other without increasing the weight thereof. For example, with the stricter standards for improving safety at the time of automobile collision, it is required to increase the rigidity of the body (vehicle body) constituting the automobile and the structural parts constituting the automobile.

On the other hand, research to improve the material strength of the steel sheet has been advanced, and a high-tensile material (high-tensile steel) having a tensile strength of 340 MPa or more and a steel sheet having a tensile strength of 980 MPa or more prepared by a hot press method have been proposed. It is being applied to applications such as shock absorbing members. In addition, a steel plate part having a sufficient strength by increasing the thickness of the steel plate or welding a reinforcing plate in a portion where strength is required by design has been proposed and is being applied to applications such as an impact absorbing member. For the welding, continuous welding such as arc welding, plasma welding, laser welding, and mash welding using a welding wire can be suitably used, but spot welding is the most excellent in terms of work efficiency. In particular, in the case of welding with each other in a laminated state only three steel plates that spot welding is optimal.

  For example, Patent Document 1 discloses a nugget that is a region in which three thin steel plates are overlapped with each other and sandwiched between a pair of electrode tips and a current is passed through the pair of electrode tips to melt and solidify between the steel plates. And a technique of locally spot welding the three thin plates to each other.

Japanese Patent Laid-Open No. 10-249537

By the way, since the steel plate parts welded in the conventional spot welding method are actually often combined with press-formed parts, a gap is usually generated between them. As the strength increases and the plate thickness increases, the gaps are less likely to collapse during welding, and the repulsive force of the steel plate parts may increase, leading to the occurrence of weld defects such as weld cracks and blowholes. there were. Particularly, when the movable spot welding machine provided on the robot arm is used, when superimposed on the three as described above, the total plate thickness than two stacked with two or more gap is formed Since it becomes large, it becomes easier to generate | occur | produce the said welding defect. For this reason, when the strength is increased and the increase in the thickness of the steel sheet is large as in the case of a reinforcing member of an automobile, the above inconvenience tends to be significant.

  On the other hand, it is conceivable to use a spot welder that increases the pressure of the pair of electrode tips or changes the front and back so as to crush the gap during spot welding. However, there is a disadvantage that the apparatus becomes large and expensive and the welding operability and workability are lowered.

State The present invention has been completed with the above view in mind, it is an object of repeated only three steel sheets stably even with a movable spot welding machine without causing welding defects It is an object of the present invention to provide a spot welding method capable of spot welding with each other.

By the way, high-tensile materials contain a large amount of chemical components such as additive elements Si, Mn, Cr, etc., so that they have high electrical resistance and are more likely to generate heat than other steel plates, and hot pressed materials also have a surface oxide layer. since liable to generate heat than other steel high surface resistance, the high-tensile outwardly in contact with the electrode tip of the spot welding machine to form a good nuggets when subjected to spot welding to the three steel plates stacked together Generally, a material and a hot press material are arranged. However, when such a general spot welding method is actually applied in the production of steel plate parts, spot welding is not always successful, and the welding quality may become unstable.

The present inventors have, as a result of various research to achieve the above object, in spot welding in a state in which only three steel containing high strength material superimposed on each other, the conventional general spot welding method On the other hand, it has been found that spot weldability is improved when a steel plate located on the outer side has a relatively low material strength or a low plate strength having a thin thickness. In other words, the higher the steel sheet coefficient value represented by the product of the hardness (Hv) and the plate thickness (mm) of the steel sheet, the better the spot weldability by positioning it on the inner side in the thickness direction so as not to contact the electrode tip. Found the fact that it will be improved. That is, according to the analysis of the present inventors, the above conventional common spot welding method when there is no gap between the steel plate when only a spot welding three steel plates stacked is suitable, practical When manufacturing steel plate parts, most of them are pre-pressed on each steel plate, so when spot welding is performed with a gap formed between the stacked steel plates, it is rather located outside. It is preferable to use a steel plate having a relatively low material strength or a low plate strength having a relatively small thickness. The present invention has been made based on such findings.

That is, it is an gist of the invention according to claim 1, a spot welding method for localized welding overlapped state only three steel plates which are pressed into one another, of (a) the three steel plates and superimposing step of superimposing the steel sheet of the maximum intensity of the out mutually so as to be positioned between the other steel sheet, sandwiched only by the pair of electrode tips (b) the three steel plates overlaid by the overlapping step, the pair high strength and welding step, wherein, the steel sheet of the maximum intensity of the (c) the three steel plates are in the process of being molded by hot press method to another spot welded portion sandwiched between at the electrode tip Steel plate having a Vickers hardness of 350 Hv or more.

Further, it is an gist of the invention according to claim 2, the steel sheet of the maximum intensity among the three steel plates, steel coefficient values represented by the product of the steel hardness and plate thickness of a steel plate is the maximum is there.

Further, it is an gist of the invention according to claim 3, the steel sheet of the maximum intensity of the above three steel is one having an iron zinc alloy layer on the surface.

  A gist of the invention according to claim 4 is a steel plate member spot-welded by any one of the above-described inventive methods.

  The gist of the invention according to claim 5 is that the steel plate member constitutes a part of a vehicle body or a component thereof.

According to the spot welding method according to claim 1, of the three superimposed on each other as steel of the maximum intensity of the three steel plates which are press-formed superimposed on one another is located between the other steel plate Since the steel plate is sandwiched between a pair of electrode tips and the portions sandwiched between the pair of electrode tips are spot welded together, the thickness direction is such that a relatively low strength steel plate is brought into contact with the pair of electrode tips. since the high strength steel plate is allowed to lie outside the are is located inside in the thickness direction, stable quality even with a movable spot welding machine without steel superimposed on three generates the weld defects It is preferably spot welded. Further, the steel sheet of the maximum intensity of the three steel plates which are press-formed superimposed on said another, because in the process of being molded by hot press method is a high strength steel sheet, hot pressing and at the same time By using the steel plate member having increased strength, wear of the mold or the like is suitably suppressed and processing costs are reduced as compared with the case of pressing the steel plate after increasing strength. Also, high-tensile steel is additive elements Si, Mn, has a high electrical resistance to general steel because it contains a large amount of steel chemical components, such as Cr, the steel sheet of the maximum intensity of the three steel plates which are superimposed on the cross When the high-tensile material is used, heat generation due to the welding current is concentrated on the high-tensile material, and it is difficult to sufficiently form nuggets on the general steel layered on the top and bottom of the high-tensile material, which may cause poor welding. hand, if the high-strength steel sheet in the course of the steel sheet of the maximum intensity is formed by hot-press method of the three steel sheets as described above is used, generally steel and electrical resistance so the difference of Therefore, a good nugget having a sufficient size is formed even in the general steel. Further, the steel sheet of the maximum intensity of the three steel plates which are press-formed superimposed on the cross, since those having a hardness of at least 350Hv of Vickers hardness, after spot welding the steel plate member having high rigidity is obtained .

Further, the invention according to claim 2, the steel sheet of the maximum intensity of the three steel plates which are superimposed on the mutually steel coefficient values K represented by the product of the steel hardness and thickness of at most Since it is a certain steel plate, using this steel plate coefficient value K has an advantage that the steel plate having the maximum strength can be easily selected or specified without requiring strength measurement.

Further, the invention according to claim 3, since the steel sheet of the maximum intensity is located on the inside of the three steel plates which are superimposed on the cross is one having an iron zinc alloy layer on the surface, the maximum intensity Oxidation scale is not generated during the heat treatment for the heat treatment for obtaining the steel sheet, and spot welding can be performed without performing a surface cleaning process such as shot blasting after forming.

  Further, according to the invention according to claim 4, since it is a steel plate member spot-welded by any one of the above inventive methods, a steel plate member having stable welding quality and high rigidity or high corrosion resistance can be obtained.

  Further, according to the invention according to claim 5, since the steel plate member constitutes a part of a vehicle body or a component thereof, the welding quality is stable, and high rigidity or high corrosion resistance is achieved. A car body or its components can be obtained.

  Here, the strength of the steel sheet indicates the degree of strength of the steel sheet and correlates with the rigidity indicating the ability to withstand bending and twisting, that is, the ability to hardly deform. It can also be called a steel plate. The strength of the steel sheet should be originally expressed by the tensile strength T (MPa) of the steel sheet, but is proportional to the Vickers hardness Hv in the cross section at the thickness center of the steel sheet (T = 3.1 × Hv). As such, it can be expressed using the Vickers hardness Hv. Further, the strength of the steel plate is proportional to the plate thickness. Therefore, the strength of the steel sheet is preferably indicated by a steel sheet coefficient value K represented by the product (= Hv × t) of the hardness Hv and the thickness t (mm) of the steel sheet. Can be used instead of other strengths, but other values may be used.

The method for steel coefficient values K is high strength of a steel sheet which is the maximum, i.e. a method for increasing the strength for obtaining the steel sheet of the maximum intensity among the three steel plates are overlaid for spot welding In addition to quenching by hot pressing, a rapid cooling method such as induction quenching is also preferably used. Further, the strength can be increased by increasing the hardness of the steel sheet by nitride coating or carburization.

  High-tensile steel made high-tensile steel by containing many steel plate chemical components such as additive elements Si, Mn, Cr, etc., and hot-pressed in the austenite region heated to a temperature of Ac3 point or higher A hot press material that has been quenched by being rapidly cooled to a temperature below the Ms point in a press mold and causing martensitic transformation corresponds to the high-strength steel sheet having a Vickers hardness of 350 or more. . The strength of a high-strength steel plate is determined by the carbon equivalent calculated from the contents of carbon, manganese, chromium, and boron contained therein, and 1180 MPa class, 1470 MPa class, and the like are known. As a special case such as the above hot press, a part of the steel plate part having a low strength may be used by providing a locally slow cooling part by partially applying a heat insulating material during quenching. . This is a steel sheet in which the carbon equivalent is partially lowered by the tailored blank method, or the hardness after quenching is partially reduced by slowing the cooling rate to 150 Hv (Vickers hardness). Spot welding may be performed with the low strength portion of such a steel plate as the outside, or spot welding may be performed with the high strength portion as the inside.

  The iron-zinc alloy layer is generated on the surface of a steel plate after the steel plate having an alloyed hot-dip galvanized coating or electrogalvanized coating is quenched by hot pressing. The alloyed hot dip galvanized film is formed by a so-called hot dip plating method. Electrogalvanized films and plated films formed by so-called hot dipping are zinc-based, zinc-iron-based, zinc-aluminum-based, zinc-nickel-based, zinc-cobalt-based coatings, and the like. As a steel material having the iron-zinc alloy layer on the surface, for example, an alloyed hot-dip galvanized steel sheet (GA) and a hot-dip galvanized steel sheet (GI) are known. The iron-zinc alloy layer is generally an iron-zinc solid solution phase, an iron-zinc intermetallic compound phase, or the like, but they may be constituted singly or in a mixed state.

Only the three steel plates for nipping between a pair of electrode tips during spot welding, pneumatic cylinder, hydraulic cylinder, the electrode tip clamp actuator for driving the electric motor or the like provided in the spot welding apparatus. The spot welding apparatus may be either a stationary type (stationary type) or a movable type (portable type or portable type). Also, either C type gun type or X type gun type may be used. As the material of the electrode tip, a copper alloy such as chromium copper, alumina-dispersed copper, zirconium copper or the like is preferably used, but any material having low electrical resistance and high wear resistance may be used in order to pass a large current.

The present invention, by spot welding in a state of overlapping three press parts molded from steel plate to each other, for example, a vehicle body of an automobile, or a part of its components frames, panels, side members, It is applied to manufacture steel parts such as doors, reinforcements, pillars such as center pillars and front pillars, and door impact beams. The steel parts constituting a part of the automobile body or its components obtained by applying the method of the present invention are stable in welding quality, and are highly rigid or highly corrosion resistant automobile bodies or their components. can get. Hereinafter, experimental examples performed by the present inventors and the evaluation results thereof will be described below.

Explanation of Experimental Sample Each sample No. used in the experiment 1 to No. Reference numeral 5 denotes a three-ply steel plate part in which a steel piece (30 mm width × 100 mm length) is spot-welded under the following conditions . Each of these sample Nos. 1 to No. The hardness of the three steel plates used in 5, the plate thickness t, the steel coefficient value K is that shown in Figure 1. Each sample No. 1 to No. Reference numeral 5 denotes a combination of the steel plates 1 to 3 shown in FIG. In each sample, the maximum strength steel sheet having a steel sheet hardness of 350 Hv or more, that is, the steel sheet with the maximum steel sheet coefficient value K, has a steel chemical composition of 0.21% C (carbon) and 0.2% Si. (Silicon), 1.2% Mn (manganese), 0.007% P (phosphorus), 0.002% S (sulfur) hardened steel sheet alloyed hot dip galvanized layer (plating) Within 10 seconds after the heat treatment of holding a 900 ° C.-5 minute test piece of a steel sheet having an adhesion amount of 60 g / m ² ) at a temperature of Ac 3 point or higher in a heating furnace, the temperature inside the Ms point or less is within 10 seconds. This is a hot-pressed steel sheet that has been quenched by quenching at the same time as pressing with a pressurizing force of 5 MPa using a flat-pressed metal mold cooled with water. The maximum strength steel sheet is sample No. 1 to No. No. 3 is a steel plate 2 and sample no. 4 and no. 5 is a steel plate 3 .

Welding machine DR type spot welding machine Electrode tip: made of chrome copper, tip original diameter is 16mmφ, tip diameter is 6mmφ, tip curvature radius is 40mmR.
・ Pressure: 3920N (400kgf)
・ Welding current: 9000A
-Energization conditions: 10 cycles of preliminary energization, 40 cycles of main energization, 1 cycle hold (60 Hz)
・ Cooling water flow: 3L / min

Welding process As shown in FIG. 2, in order to form the same gap condition and current condition as those of an actual product, three steel plate pieces 1, 2 and 3 are connected via a plate-like spacer 10 made of general steel. The electrode chips 12 and 14 are overlapped in order and positioned between the pair of electrode chips 12 and 14 (stacking step), and then pressed (clamped) between the pair of electrode chips 12 and 14 as shown in FIG. 3 or FIG. Thus, the gap S between the steel plates is filled and brought into contact with each other, and then the welding current is energized according to the energization conditions set in advance between the pair of electrode tips 12 and 14 (welding process), and then the pair of electrodes The pinching pressure by the chips 12 and 14 is released.

Evaluation criteria Each sample No. 1 to No. For the spot welded state of No. 5, the cross section where the spot weld nugget appears is observed using an optical microscope, and if the nugget is well formed, a circle mark is formed around the boundary of the steel plate. When a blow hole having a diameter of 20% or more of the diameter of the nugget is present, a Δ mark is attached to the result column of FIG.

Evaluation Results As shown in FIG. 1, the maximum strength steel plate having a hardness of 350 Hv or more among the three steel plate pieces 1, 2, and 3 stacked on each other is positioned between the other steel plates, and the inner side in the thickness direction. In the sample No. to which the method of the present invention is applied. 1, no. 2, no. Sample No. 3 is a comparative example in which the nugget is well formed, whereas the steel plate with the maximum strength is located outside. In No. 4 , blow holes and cracks were observed in the nugget, and the welding quality was unstable. Sample No. 4 and sample no. 5 is sample No. 5 above. 1 and sample no. It is indicated that the nugget evaluation effect is larger as the steel plate coefficient value K is larger because the evaluation of the nugget is x and 2 levels lower than 3. Further, in the overlapping process, the state shown in FIG. 1, no. 2, no. 3, the deformation and distortion of the outer steel plates 1 and 3 are small as shown in FIG. 4, as shown in FIG. 4, the deformation and distortion of the outer steel plate 1 on the opposite side to the steel plate having the maximum strength is increased. As a result, the nugget formation becomes unstable or difficult to form.

Therefore, according to this embodiment, a pair while being superimposed on one another so as to be located a maximum steel sheet strength 2 of the three steel plates 1-3 which are superimposed on each other between the other of the steel plate 1 and 3 Are sandwiched between the electrode tips 12 and 14 and the portions sandwiched between the pair of electrode tips 12 and 14 are spot-welded to each other, so that the steel plates 1 and 3 having relatively low strength or low plate rigidity are paired with each other. since is is positioned outside in the thickness direction to be brought into contact with the electrode tip 12 and 14 are steel plates of the maximum intensity or a maximum rigidity is caused located inside in the thickness direction, the steel plate 1-3 is welded superimposed on three Even if a movable spot welder is used without causing defects, spot welding is suitably performed with stable quality.

Further, according to this embodiment, the steel plate 2 of the maximum intensity of the three steel plates 1-3 which are superimposed on each other, the steel sheet hardness Hv and the steel plate coefficient values K represented by the product of the thickness t (= Since this steel plate has the maximum Hv × t), using this steel plate coefficient value K has an advantage that a steel plate having the maximum strength can be easily selected or specified without requiring strength measurement.

Further, according to this embodiment, the steel plate 2 of the maximum intensity of the three steel plates 1-3 which are superimposed on each other, because it is a high strength steel sheet in the process of being molded by hot press method, By using a steel plate member that has been strengthened at the same time as hot pressing, the consumption of the mold and the like is suitably suppressed and the processing cost is reduced compared to the case of pressing the steel plate after strengthening. . Also, high-tensile steel is additive elements Si, Mn, has a high electrical resistance to general steel steel 1,3 because it contains a large amount of steel chemical components, such as Cr, the three steel plates are superimposed above one another When the high-tensile material is used as the steel plate 2 having the maximum strength, heat generated by the welding current is concentrated on the high-tensile material, and it is difficult to sufficiently form nuggets on the general steel layered on the top and bottom of the high-tensile material. while there is a possibility that poor welding occurs, as in the present embodiment, a high strength steel sheet in the course of the steel sheet 2 of the maximum intensity is formed by hot-press method of the three steel sheets used In this case, since there is not much difference in electrical resistance from the steel plates 1 and 3 made of general steel, there is an advantage that a good nugget having a sufficient size is formed in the steel plates 1 and 3.

Further, according to this embodiment, since the maximum strength steel sheet 2 of the three steel plates 1-3 which are superimposed on one another is one having a hardness of at least 350Hv of Vickers hardness, high rigidity after spot welding The steel plate member is obtained.

  Further, since the steel plate member obtained by the spot welding method of this embodiment has a stable welding quality and a steel plate member having high rigidity or high corrosion resistance can be obtained, it constitutes a part of a vehicle body or a component thereof. By being applied to the manufacture of a steel plate member, a car body or a component thereof of an automobile having stable welding quality and high rigidity or high corrosion resistance can be obtained.

  As mentioned above, although the Example of this invention was described in detail based on drawing, these are one Embodiment to the last, This invention is implemented in the aspect which added the various change and improvement based on the knowledge of those skilled in the art. be able to.

It is a graph which shows the evaluation result of the steel plate component manufactured according to the spot welding method of one Example of this invention in contrast with the evaluation result of the steel plate component manufactured according to the conventional spot welding method. It is a figure explaining the spot welding method of one Example of this invention, Comprising: It is a figure which shows the overlap process. It is a figure explaining the spot welding method of one Example of this invention, Comprising: It is a figure which shows the welding process. It is a figure explaining the welding process of the conventional spot welding method, Comprising: It is a figure which shows the welding process.

1: Steel plate 2: Steel plate 3: Steel plate
10: Spacer 12, 14: Electrode tip

Claims (5)

In a laminated state only three steel plates which are pressed into a mutual a spot welding method for localized welding,
And superimposing step of superimposing one another so as to position the steel sheet of the maximum intensity among the three steel plates during the other steel sheet,
Interposing only the three steel plates overlaid by polymerization it processes a pair of electrode tips, and a welding step of another spot welded portion sandwiched between at the pair of electrode tips, comprising,
Steel of the maximum intensity among the three steel plates, characterized in that in the process of being molded by hot press method are those having a high strength has been a steel plate and a hardness of more than 350Hv of Vickers hardness Spot welding method. 2. The spot welding method according to claim 1, wherein the steel plate having the maximum strength among the three steel plates is a steel plate having a maximum steel plate coefficient value represented by a product of steel plate hardness and plate thickness. 3. The spot welding method according to claim 1 or 2, wherein the steel plate having the maximum strength among the three steel plates has an iron-zinc alloy layer on the surface.   A steel plate member that is spot-welded by the method according to any one of claims 1 to 3.   The steel plate member according to claim 4, wherein the steel plate member constitutes a part of a vehicle body or a component thereof.

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