Spot welding process using welding auxiliary element

Abstract

A spot welding method using a welding auxiliary element (10) having electrically conductive properties and used for spot welding performed by placing a second element between electrically conductive first elements composed of a different type of material from the second element, wherein the welding auxiliary element (10) is inserted into a hole (18) extending through the second element to allow the first elements to be spot welded together from opposite sides in the region of the hole (18), wherein the welding auxiliary element (10) comprises: a main body (10a) having a size and shape that allow a gap to be formed between the main body (10a) and an inner surface of the hole (18) when the main body (10a) is inserted into the hole (18); and a position-holding component provided on an outer side of the main body (10a), having heat-insulating, heat-resistant and electrically insulating properties and holding the main body (10a) in a state separated from the inner surface of the hole (18), where the spot welding process comprises: hole forming a hole (18) extending through the second element (14); Foaming agent providing means for providing a non-foaming foaming agent to an outer side of the main body (10a); Setting which stacks the second member (14) having the hole (18) on one of the first members (12-1, 12-2) and sets the main body (10a) having the non-foamed foaming agent on the outside of the main body (10a) into the hole (18); Interposing the welding auxiliary member (10) by stacking the other first member (12-1, 12-2) on top of the second member (14) provided with the main body (10a) having the non-foamed foaming agent on the outside of the main body (10a); and Welding, which applies electric current to the first elements (12-1, 12-2) sandwiching the second element (14) in a state, in which the first elements (12-1, 12-2) are interposed and pressed by electrodes (108-1, 108-2) in the stacking direction from opposite sides, and the first elements (12-1, 12-2) are fusion-bonded to each other while simultaneously forming a foam component (10b) by causing the non-foamed foaming agent, according to the heat generated as a result of the applied electric current, foams up.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2015-034848, filed on February 25, 2015, the entire contents of which are hereby incorporated by reference. BACKGROUND 1. Technical field

[0002] The present invention relates to a spot welding method using a welding auxiliary element. More particularly, the present invention relates to a spot welding method using a welding auxiliary element used when joining different types of materials by spot welding. 2. Related technology

[0003] When spot welding is performed by sandwiching an element between two electrically conductive elements composed of a material different from that of the sandwiched element, there is a known technology which involves forming a hole extending through the sandwiched element, inserting a welding auxiliary element composed of an electrically conductive material similar to that of the two electrically conductive elements into the hole, and performing spot welding from opposite sides in the region of the hole.

[0004] US 2014 / 0 294 489 A1 discloses a method for connecting components comprising the steps of forming an opening in an intermediate component which consists of one part or at least two parts arranged one above the other, embedding an insert component made of metal in the opening, arranging an outer skin component made of metal on an outer surface of the intermediate component so that the intermediate component is held on an inner side of the outer skin component, and connecting the outer skin component to the insert component.

[0005] US 6 037 559 A discloses a method for lap joining two types of metal parts with different melting points, in which a circular blank made of a steel plate is placed on an Al-based plate in lapped areas of the Al alloy plate and another steel plate. The three members are then pressed through a pair of electrodes, and a welding current is passed between the two electrodes, thereby sequentially melting a current-carrying portion of the Al alloy plate and a portion near the current-carrying portion, removing a molten portion by partially bead-deforming the blank toward the Al alloy plate, applying the bead-deformed portion to the steel plate, and resistance welding between the bead-deformed portion and the steel plate.

[0006] JP 2014-104502 A discloses a method in which a blank made of a first metal material is superimposed on a second member made of a second metal material having a lower melting point than that of the first metal material and placed on an upper surface of a die to form a drill. The blank material is driven into the second member by vertically moving a punch to form the drill, and a portion overlapping the blank material of the second member is punched out, forming a hole in the second member. At the same time, the blank material is caulked and fixed to the hole of the second member, and the structure for the dissimilar joint body is manufactured. SUMMARY OF THE INVENTION

[0007] Because in this type of spot welding, the hole equipped with the welding auxiliary element is located between two electrically conductive elements, the seating condition of the welding auxiliary element inserted into the hole, i.e., the seating position, cannot be checked. Therefore, if the welding auxiliary element is not seated in the center of the hole, or if the position of the welding auxiliary element inserted in the center of the hole moves during the process, the spot welding process may not be performed in the center of the welding auxiliary element, causing fusion at an off-position. This could result in reduced strength after the welding process, leading to a loss of accuracy.

[0008] Japanese Unexamined Patent Application Laid-Open No. 2014-104502 relates to a technology developed in view of the above circumstances, and discusses a spot welding method that involves inserting and caulking the welding auxiliary member into the hole extending through the interposed member. According to this technology, a pair of plate-shaped members composed of iron as the main component are stacked on opposite surfaces of the plate-shaped interposed member composed of the other type of material, in which the welding auxiliary member is inserted and caulked, and spot welding is performed from opposite sides in the hole region. Thus, the welding auxiliary member is positionally stabilized in the hole, and spot welding is performed in this stable state. Consequently, the welding process is performed accurately without deviation.

[0009] However, in the technology according to JP 2014-104 502 A, the electrically conductive welding auxiliary element is in direct contact with the intermediate element.

[0010] The following problem arises particularly when this technology is applied using carbon fiber reinforced plastic (hereinafter referred to as "CFRP") as the intermediate member. When spot welding is performed in the above-described state, resistance heat generated when electricity is applied to the two members and the welding auxiliary member is transferred to the intermediate member in direct contact with it. This could cause the intermediate member to break, for example, by igniting, or by absorbing the electricity. In this case, the quality of the weld may deteriorate.

[0011] It is desirable to provide a spot welding method using the welding auxiliary element, which can avoid deterioration of fasteners while achieving stable installation of the welding auxiliary element.

[0012] A first aspect of the present invention provides a spot welding method using a welding auxiliary member. The welding auxiliary member is used for spot welding, which is performed by placing a second member between electrically conductive first members composed of a different type of material from the second member. The welding auxiliary member is inserted into a hole extending through the second member to allow the first members to be spot welded together from opposite sides in a region of the hole. The welding auxiliary member includes a main body and a position-holding component. The main body is composed of an electrically conductive material and has a size and shape that allow a gap to be formed between the main body and an inner surface of the hole.when the main body is inserted into the hole. The position-holding component is provided on an outer side of the main body, has heat-insulating, heat-resistant, and electrically insulating properties, and keeps the body separated from the inner surface of the hole. The spot welding process includes: hole-forming, which forms a hole extending through the second member; foam-providing, which provides a non-foaming foaming agent on an outer side of the main body; setting, which stacks the second member having the hole on one of the first members and places the main body, which has the non-foaming foaming agent on the outer side of the main body, into the hole; interposing, which interposes the welding auxiliary member by stacking the other first member on top of the second member equipped with the main body.which has the non-foamed foaming agent on the outside of the main body; and welding, which applies electric current to the first elements sandwiching the second element in a state where the first elements are sandwiched and pressed by electrodes in the stacking direction from opposite sides, and melt-bonds the first elements to each other while simultaneously forming a foam component by causing the non-foamed foaming agent to foam according to the heat generated as a result of the applied electric current.

[0013] The position-holding component may be formed from a foam component. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a perspective view of a welding auxiliary element according to an example, and Fig. 1B is a cross-sectional view of the welding auxiliary member in its thickness direction; Fig. 2A shows a method of manufacturing a main body and shows its state before a punching process, and Fig. 2B similarly shows the method of manufacturing the main body and shows its state after the punching process; Fig. 3 shows a method of wrapping a foam tape around the main body; Fig. 4A shows a method of inserting a non-foamed welding auxiliary member into a hole in a second member stacked on a first member, and shows a state of the non-foamed welding auxiliary member before insertion, and Fig. 4B similarly shows the method of inserting the non-foamed welding auxiliary member into the hole, and shows an inserted state of the non-foamed welding auxiliary member; Fig. 5A is a partial cross-sectional view showing a method of stacking a first member on top of the second member provided with the non-foamed welding auxiliary member to sandwich the non-foamed welding auxiliary member, and Fig. 5B is a partial cross-sectional view showing a method of fusing connecting elements together and showing a pre-electrified state; and Fig. 6 is a partial cross-sectional view showing a method for causing a foam tape to foam simultaneously with the melt-bonding of the fasteners. DETAILED DESCRIPTION

[0014] A welding auxiliary element according to an example will be described below with reference to the drawings.

[0015] The Fig. 1A and Fig. 1B show the configuration of a welding auxiliary element 10 according to an example. In particular, Fig. 1A a perspective top view, and Fig. 1B is a cross-sectional view in the thickness direction. In this example, the welding auxiliary member 10 is composed of a substantially disc-shaped main body 10a and a foam component 10b as a position-holding component, which is attached around the outer surface of the main body 10a. The main body 10a is composed of an electrically conductive material, such as a metallic material with iron as the main component. In this example, the main body 10a is composed of the same type of material as the first members 12-1 and 12-2. In this example, the main body 10a has an outer diameter of approximately 10 mm. The thickness of the main body 10a is substantially equal to the thickness of a second member 14 to be described later.The material used for the foam component 10b is synthetic resin foam, which has heat-insulating, heat-resistant and electrically insulating properties and is selected according to various conditions such as the melting point of the first elements 12-1 and 12-2.

[0016] The Fig. 2A and Fig. 2B show a presumed process for manufacturing the welding auxiliary element 10. In particular, Fig. 2A shows a method of manufacturing the main body 10a and shows its state before a punching process, and Fig. Fig. 2B similarly shows the method for manufacturing the main body 10a and shows its state after the punching process. For example, as in Fig. 2A, a plate-shaped material 110 used to manufacture the main body 10a and composed of the same type of material as the first elements 12-1 and 12-2 is placed on a punching base 100, and a punch 102 is lowered together with a guide 104. Then, as shown in Fig. 2B, a punching process is performed on the plate-shaped material 110 by means of the punch 102 to thereby form the main body 10a.

[0017] Fig. 3 shows a method for wrapping a foam tape 16 around the aforementioned main body 10a formed by punching. A vertically movable support 106 is placed in the center of the punching base 100. When the aforementioned main body 10a formed by punching falls downward, the upper end surface of the support 106 receives the main body 10a. By lifting the support 106 with the main body 10a arranged thereon, the main body 10a is sandwiched between the support 106 and the punch 102 from opposite sides. With the main body 10a sandwiched between them, the main body 10a is fixed at a higher position than the upper surface of the plate-shaped material 110.

[0018] Then, in this state, the main body 10a is rotated by rotating the punch 102 and the support 106 together in the same circumferential direction. During the rotation of the main body 10a, the foam tape 16 is wound around and attached to the outer surface of the main body 10a. Although this example refers to a case where the foam tape 16 is wound and attached, a foaming agent may alternatively be applied to the main body 10a. By heating the foam tape 16 to cause the foam tape 16 to foam, the foam component 10b is formed, whereby the welding auxiliary member 10 according to this example can be manufactured.

[0019] A spot welding method according to an example of the present invention using the welding auxiliary element 10 will be described below with reference to the Fig. 4A to 6.

[0020] The spot welding method according to this example involves sandwiching the second member 14 between two electrically conductive first members 12-1 and 12-2 composed of a different material from the second member 14, and then spot-welding the members together. Each of the first members 12-1 and 12-2 is composed, for example, of an electrically conductive material with iron as the main component and is a plate-shaped metallic member with a thickness of approximately 0.5 mm. The second member 14 is composed of carbon fiber reinforced plastic (hereinafter referred to as "CFRP") and is a plate-shaped member with a thickness of approximately 1.0 mm.

[0021] First, a hole 18, which is a cylindrical through-hole, is formed in each weld point of the second member 14. The inner diameter of the hole 18 is approximately 14 mm. In one example of the present invention, this process may be referred to as "hole forming."

[0022] Fig. 4A shows a state where the second member 14, in which the holes 18 have been previously formed as described above, is stacked on the first member 12-2. Fig. 4B shows a state where a member (hereinafter referred to as "non-foamed welding auxiliary member 20") obtained by wrapping and attaching the foam tape 16 around the outer surface of the aforementioned main body 10a is inserted into each hole in the above-described state. The manufacturing of the non-foamed welding auxiliary member 20 is as described above. In one example of the present invention, this process may serve as "foaming agent provision."

[0023] In this state, the outer diameter of the non-foamed welding auxiliary element 20 is smaller than the inner diameter of the hole 18. Therefore, this insertion process can be easily performed. In one example of the present invention, this process can be referred to as "setting."

[0024] Fig. 5A shows a state where the non-foamed welding auxiliary element 20 (see Fig. 4B) is inserted into the hole 18, and the first element 12-1 is stacked on top of the second element 14. In one example of the present invention, this process may serve as "interleaving."

[0025] The Fig. 5B and Fig. 6 show a state where the connecting elements are fusion-bonded. First, as shown in Fig. As shown in Figure 5B, the aforementioned connecting elements are pressed from opposite sides in the stacking direction with two electrodes 108-1 and 108-2 at the center position of the hole 18 provided with the non-foamed welding auxiliary element 20, in a state where the connecting elements are interposed. By applying an electric current in this state, resistance heat is generated on the main body 10a, so that the fusion of the first elements 12-1 and 12-2 and the main body 10a begins.

[0026] This example is characterized in that the foam tape 16 wound around the outside of the main body 10a is heated using the aforementioned resistance heat to cause the foam tape 16 to foam.

[0027] Fig.6 shows a method for causing the foam tape 16 to foam simultaneously with the fusion bonding of the connecting elements. The foam tape 16 foams in a gap between the main body 10a and the inner surface of the hole 18 to fill the gap between the main body 10a and the inner surface of the hole 18. Thus, the foam component 10b can be easily formed without providing an additional process for forming a foam component, and the main body 10a can remain in a separate state from the inner surface of the hole 18. Moreover, because the foam component 10b has pores, it has high heat resistance properties to reduce the transmission of the resistance heat generated in the main body 10a through the second member 14. Consequently, deterioration of the second member 14 caused by a temperature rise can be prevented.

[0028] The material of the foam component 10b is prepared to have sufficient heat resistance properties to prevent it from being ignited by heat generated during spot welding.

[0029] Furthermore, because the foam component 10b has electrical insulating properties, the foam component 10b can prevent electric current from flowing distributed among the second member 14 while electricity is supplied to the main body 10a. The first members 12-1 and 12-2 and the main body 10a are fused in this state, and the fused portions solidify and become weld nuggets 112, so that connecting members can be joined together. In one example of the present invention, this process may serve as "welding." Consequently, spot welding can be performed stably with high quality without deteriorating the quality of the second member 14.

[0030] The present invention is not limited to the scope defined in the above example, and various modifications are possible within the scope of the invention. For example, although in this example, the foam tape 16 is caused to foam within the hole 18 by utilizing the heat generated during spot welding, the foam component 10b may also be attached to the main body 10a in a preliminarily foamed state and inserted into the hole 18.

[0031] Furthermore, although the foam component 10b is described as an example of the position holding component, various types of materials can be used as long as the material used has heat insulating, heat resistant and electrical insulating properties and can be inserted into the gap between the main body 10a and the inner side surface of the hole 18.

[0032] Furthermore, although in this example, the foam component 10b is provided as the position-holding component around the entire outer side surface of the substantially disc-shaped main body 10a, the main body 10a is not limited to the approximate disc shape and can have various shapes as long as the main body 10a has a size that can be inserted into the hole 18. Furthermore, although the position-holding component is formed around the entire outer side surface of the main body 10a, the position-holding component can also be partially provided on the outer side of the main body 10a as long as the main body 10a can be stably positioned in the hole 18.

Claims

[1] A spot welding method using a welding auxiliary element (10) having electrically conductive properties and used for spot welding carried out by placing a second element between electrically conductive first elements composed of a different type of material from the second element, the welding auxiliary element (10) being inserted into a hole (18) extending through the second element to allow the first elements to be spot welded together from opposite sides in the region of the hole (18), the welding auxiliary element (10) comprising: a main body (10a) having a size and shape that allow a gap to be formed between the main body (10a) and an inner surface of the hole (18) when the main body (10a) is inserted into the hole (18); and a position-holding component provided on an outer side of the main body (10a), having heat-insulating, heat-resistant and electrically insulating properties and holding the main body (10a) in a state separated from the inner surface of the hole (18), where the spot welding process comprises: hole forming a hole (18) extending through the second element (14); Foaming agent providing means for providing a non-foaming foaming agent to an outer side of the main body (10a); Setting which stacks the second member (14) having the hole (18) on one of the first members (12-1, 12-2) and sets the main body (10a) having the non-foamed foaming agent on the outside of the main body (10a) into the hole (18); Interposing the welding auxiliary member (10) by stacking the other first member (12-1, 12-2) on top of the second member (14) provided with the main body (10a) having the non-foamed foaming agent on the outside of the main body (10a); and Welding, which applies electric current to the first elements (12-1, 12-2) sandwiching the second element (14) in a state, in which the first elements (12-1, 12-2) are interposed and pressed by electrodes (108-1, 108-2) in the stacking direction from opposite sides, and the first elements (12-1, 12-2) are fusion-bonded to each other while simultaneously forming a foam component (10b) by causing the non-foamed foaming agent, according to the heat generated as a result of the applied electric current, foams up. [2] Spot welding method according to claim 1, wherein the position holding component is formed from a foam component (10b).

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