Welding assistance member and spot-welding method using welding assistance member

1. A spot-welding method for spot welding performed by sandwiching between a first electrode and a second electrode using a welding assistance member that has electrically-conductive properties and is used for spot-welding performed by sandwiching a non-electrically-conductive member between a first electrically-conductive member disposed on a side in contact with the first electrode during welding and a second electrically-conductive member disposed on a side in contact with the second electrode during welding and composed of a different kind of material from the non-electrically-conductive member, the welding assistance member being fitted into a hole extending through the non-electrically-conductive member so as to allow for spot-welding of the first electrically-conductive member and the second electrically-conductive member to each other including the non-electrically-conductive member from opposite sides in an area of the hole, the welding assistance member including:

a main body that is made from a plate-shaped material being smaller than an inside size of the hole and has a size and shape that allow a gap extending in an axial direction of the first electrode and the second electrode used during spot welding and formed between the main body in a plane direction and an inner side surface of the hole of the non-electrically-conductive member when the main body is fitted in the hole, and a thickness of the main body is formed equal to the thickness of a second member, and the main body is held between the first electrically-conductive member and the second electrically-conductive member in the axial direction of the first electrode and the second electrode; and

a position maintaining component surrounding an outer periphery of the main body; comprises a non-foamed foaming agent configured to foam in accordance with heat generated during the spot-welding, and, after foaming, has heat insulating, heat resisting, and electrically insulating properties to maintain the main body in a separated state from the inner side surface of the hole and from the non-electrically-conductive member of equal thickness to the main body, the spot-welding method comprising:

hole forming that forms the hole extending through the non-electrically-conductive member;

foaming-agent that provides for providing a non-foamed foaming agent at an outer side of the main body, a thickness of the main body is formed equal to the thickness of the non-electrically-conductive member;

fitting that stacks the non-electrically-conductive member having the hole onto one of the first electrically-conductive member and the second electrically-conductive member and fits the main body having the non-foamed foaming agent on the outer side of the main body into the hole;

sandwiching that sandwiches the welding assistance member by stacking the first electrically-conductive member onto an upper surface of the second electrically-conductive member fitted with the main body having the non-foamed foaming agent on the outer side of the main body; and

welding that applies electric current to the first electrically conductive member and the second electrically-conductive member sandwiching the non-electrically-conductive member in a state where the first electrically-conductive member and the second electrically-conductive member are sandwiched and pressed from opposite sides in a stacking direction by the first electrode and a second electrode and fusion-bonds the first electrically-conductive member and the second electrically-conductive member to each other by forming the nugget connecting each of the first electrically-conductive member and the second electrically-conductive member to the main body to cause a force to sandwich the non-electrically-conductive member between the first electrically-conductive member and the second electrically-conductive member while simultaneously thrilling a foam component by causing the non-foamed foaming agent to foam in accordance with heat generated as a result of the applied electric current from the welding to keep the main body in a separated state from the non-electrically-conductive member of equal thickness to the main body.

2. A spot-welding method for spot welding performed by sandwiching between a first electrode and a second electrode using a welding assistance member that has electrically-conductive properties and is used for spot-welding performed by sandwiching a non-electrically-conductive member between a first electrically-conductive member disposed on a side in contact with the first electrode during welding and a second electrically-conductive member disposed on a side in contact with the second electrode during welding and composed of a different kind of material from the non-electrically-conductive member, the welding assistance member being fitted into a hole extending through the non-electrically-conductive member so as to allow for spot-welding of the first electrically-conductive member and the second electrically-conductive member to each other including the non-electrically-conductive member from opposite sides in an area of the hole, the welding assistance member including:

a main body that is made from a plate-shaped material being smaller than an inside size of the hole and has a size and shape that allow a gap extending in an axial direction of the first electrode and the second electrode used during spot welding and formed between the main body in a plane direction and an inner side surface of the hole of the non-electrically-conductive member when the main body is fitted in the hole, and a thickness of the main body is formed equal to the thickness of a second member, and the main body is held between the first electrically-conductive member and the second electrically-conductive member in the axial direction of the first electrode and the second electrode; and

a position maintaining component surrounding an outer periphery of the main body, comprises a non-foamed foaming agent configured to foam in accordance with heat generated during the spot-welding, and, after foaming, has heat insulating, heat resisting, and electrically insulating properties to maintain the main body in a separated state from the inner side surface of the hole and from the non-electrically-conductive member of equal thickness to the main body, the spot-welding method comprising:

forming a nugget between the main body and each of the first electrically-conductive member and the second electrically-conductive member in a region of the hole such that the first electrically-conductive member and the second electrically-conductive member are welded together to hold the non-electrically-conductive member therebetween;

pressing the first electrically-conductive member and the second electrically-conductive member and the second electrically-conductive member at a central position of the hole with sandwiching the welding assistance member consists of the main body and the position maintaining component by the first electrode and the second electrode of a spot welding device, and

forming the position maintaining component outside of the main body by resistance heat generated by pressing fuses the first electrically-conductive member and the second electrically-conductive member and the main body forming a foam component by causing the non-foamed agent to foam in accordance with heat generated as a result of the applied electric current from the welding to keep the main body in a separated state from the non-electrically-conductive member of equal thickness to the main body.