Patent Description:
Patent Document <NUM> discloses a joint structure in which a first metal material and a dissimilar material that is difficult to be welded to the first metal material overlap each other, and a filler material (welding wire) is arc-welded through a through-portion of the dissimilar material.

A part of the melted filler material forms a flange so as to cover an upper peripheral area of the through-portion of the dissimilar material. Accordingly, the dissimilar material and the first metal material are fixed to each other by a compressive fixing force between the flange and the first metal material due to solidification shrinkage of the filler material onto the first metal material.

However, according to the invention of <CIT>, which is a basis for the preamble of claim <NUM>, moisture may enter from outside through a gap between overlapped surfaces of the flange of a third metal material and a second metal material. Electrolytic corrosion may thus occur in an area where the flange of the third metal material and the second metal material overlap each other due to the entry of the moisture, and joint strength between the materials may decrease.

In view of the foregoing, it is an object of the present invention to reduce occurrence of electrolytic corrosion in an area where a metal material and a dissimilar material overlap each other.

A first aspect is directed to a joining method of joining a first member made of a metal material and a second member made of a material difficult to be welded to the first member with the first member and the second member overlapping each other, the second member including a through-portion penetrating toward the first member, the joining method including: a first step of forming a third member for compressing and fixing the second member between the first member and the third member by welding a first filler material, which is weldable to the first member, to the first member through the through-portion; and a second step of forming a fourth member by covering a surface of the third member with a second filler material, which is weldable to the second member, and welding the second filler material to the second member.

According to the first aspect, the first step includes forming the third member by welding the first filler material to the first member through the through-portion of the second member. The second step includes forming the fourth member by covering the surface of the third member with the second filler material and welding the second filler material to the second member.

In this manner, the fourth member covers the surface of the third member and is welded to the second member, thereby closing the gap between the second member and the third member with the fourth member. Thus, moisture can be kept from entering an area where the second member and the third member overlap each other from the outside.

It is therefore possible to reduce occurrence of electrolytic corrosion in the area where the second member and the third member overlap each other and secure joining strength.

A second aspect is an embodiment of the first aspect. In the second aspect, the first step includes forming the third member by short-circuit arc welding of the first filler material to the first member, and the second step includes forming the fourth member by pulse welding of the second filler material to the second member.

According to the second aspect, in the first step, the first filler material is welded to the first member by short-circuit arc welding. In the second step, the second filler material is welded to the second member by pulse welding.

In the first step, short-circuit arc welding with a small spread of arc, in which the short-circuit state and the arc state are repeated, is performed in welding the first filler material to the first member through the through-portion. It is therefore possible to form the third member with a smaller amount of heat input to the second member. The short-circuit arc welding includes a welding method employing wire feed control in which forward feed and backward feed are repeated.

In the second step, pulse welding with straight polarity or AC pulse welding with a large spread of arc is performed. It is therefore possible to form the fourth member by spreading the melted second filler material so as to cover the entire surface of the third member.

A third aspect is an embodiment of the first or second aspect. In the third aspect, the second filler material has an outer diameter equal to an outer diameter of the first filler material or larger than the outer diameter of the first filler material.

According to the third aspect, the second filler material has the outer diameter equal to the outer diameter of the first filler material or larger than the outer diameter of the first filler material.

Specifically, the first filler material is welded to the first member through the through-portion. Thus, the first filler material preferably has a small diameter so as to be easily inserted in the through-portion. For example, if the through-portion has a hole of <NUM> to <NUM>, the outer diameter of the first filler material may be selectable from <NUM>, <NUM>, <NUM>, and <NUM>.

On the other hand, the second filler material is welded over the entire surface of the third member. Thus, the second filler material preferably has a large diameter so as to spread the arc easily. The second filler material with a large outer diameter is preferred because buckling is reduced. For example, relative to the first filler material with the diameter described above, the outer diameter of the second filler material may be selectable from <NUM>, <NUM>, and <NUM>.

A fourth aspect is an embodiment of any one of the first to third aspects. In the fourth aspect, the second step includes: periphery formation of forming a peripheral portion of the fourth member by welding the second filler material along an outer peripheral edge of the third member; and after the periphery formation, center formation of forming a central portion of the fourth member welded to the peripheral portion, by welding the second filler material to cover a central area of a surface of the third member.

According to the fourth aspect, the fourth member is formed by separately forming the central portion and the peripheral portion in the second step.

Specifically, the peripheral portion is formed by welding the second filler material to cover the peripheral area of the surface of the third member, and the second filler material is welded thereafter to the central area of the surface of the third member. Thus, the central and peripheral portions of the fourth member can conform to each other.

Since the center formation is performed after the periphery formation, the peripheral portion can block the outflow of the second filler material melted in the central area of the third member in the center formation.

A fifth aspect is an embodiment of any one of the first to third aspects. In the fifth aspect, the second step includes: center formation of forming a central portion of the fourth member by welding the second filler material to cover a central area of a surface of the third member; and after the center formation, periphery formation of forming a peripheral portion of the fourth member welded to the central portion and the second member, by welding the second filler material along an outer peripheral edge of the third member.

According to the fifth aspect, the fourth member is formed by separately forming the central portion and the peripheral portion in the second step.

Specifically, the central portion is formed by welding the second filler material to cover the central area of the surface of the third member, and the peripheral portion is formed thereafter by welding the second filler material along the outer peripheral edge of the central portion. Thus, the central and peripheral portions of the fourth member can conform to each other.

A sixth aspect is an embodiment of any one of the first to fifth aspects. In the sixth aspect, the first step includes: first joining of forming a first joint in the through-portion by welding the first filler material to the first member through the through-portion; and after the first joining, second joining of forming a second joint that projects radially outward from the through-portion and presses a peripheral edge of the through-portion, by welding the first filler material to the first joint under a welding condition different from a welding condition in the first joining.

According to the sixth aspect, in the first step, the third member is formed by separately forming the first j oint and the second j oint, thereby making it possible to use different welding methods or different welding conditions, depending on the material characteristics of the second member.

For example, short-circuit arc welding with a small spread of arc in which the short-circuit state and the arc state are repeated may be performed in welding the melted first filler material to the first member through the through-portion with heat input necessary for welding, thereby forming the first joint. After that, pulse welding with straight polarity or AC pulse welding with a large spread of arc may be performed with a low heat input that does not melt the second member, thereby forming the second joint. It is therefore possible to form the second joint with a smaller amount of heat input to the second member.

The welding conditions include, for example, a change in the outer diameter of a filler material, in addition to a switch between the short-circuit arc welding and the pulse welding.

According to the aspects of the present invention, it is possible to reduce occurrence of electrolytic corrosion in an area where a metal material and a dissimilar material overlap each other.

Embodiments of the present invention will be described in detail with reference to the drawings. Note that the following description of embodiments is merely an example in nature, and is not intended to limit the scope, applications, or use of the present invention. as defined by the claims.

<FIG> shows a joint structure for joining together a first member <NUM> made of a metal material, a second member <NUM> made of a material that is difficult to be welded to the first member <NUM>, and a third member <NUM> made of a first filler material <NUM>.

The first member <NUM> is a plate-shaped member made of the metal material.

The second member <NUM> is a plate-shaped member made of the material that is difficult to be welded to the first member <NUM>. The second member <NUM> is arranged to overlap with an upper side of the first member <NUM>. The second member <NUM> has a circular through-portion <NUM>.

In the present embodiment, the through-portion <NUM> is described as a circular through-hole, but may be an elliptical or elongated through-hole.

The third member <NUM> is made of the first filler material <NUM> that is a metal material of the same type as the first member <NUM>. The metal materials of the same type are metals that can be welded to each other, and are not only metal materials of an identical quality but also metal materials satisfactorily weldable to each other, such as ferrous metal materials or nonferrous metal materials. In other words, the metal materials of the same type are materials of the same type that are compatible with each other in welding.

Specifically, examples of a combination of the first member <NUM> and the third member <NUM> for welding include the following. For example, combinations of ferrous metal materials include mild steel and mild steel, stainless steel and stainless steel, mild steel and high-tensile steel, high-tensile steel and high-tensile steel, etc. Examples of combinations of nonferrous metal materials include aluminum and aluminum, aluminum and aluminum alloy, aluminum alloy and aluminum alloy, etc..

The second member <NUM> as a dissimilar material is a material of different quality from the quality of the first member <NUM> and the third member <NUM> as metal materials of the same type, and is difficult to be welded to the first member <NUM> and the third member <NUM>.

For example, when the first member <NUM> and the third member <NUM> as metal materials of the same type are ferrous metal materials, the second member <NUM> as a dissimilar material is a nonferrous metal material such as a copper material or an aluminum material.

The third member <NUM> is welded to the first member <NUM> through the through-portion <NUM>. The third member <NUM> is provided with a flange <NUM> that presses the peripheral edge of the through-portion <NUM>. The third member <NUM> then solidifies and shrinks on the first member <NUM>, whereby the second member <NUM>, which is a dissimilar material, is compressed and fixed between the flange <NUM> and the first member <NUM>.

Moisture may enter the area where the flange <NUM> of the third member <NUM> and the second member <NUM> overlap each other, thereby causing electrolytic corrosion.

In the present embodiment, the gap in the area where the second and third members <NUM> and <NUM> overlap each other is closed with a fourth member <NUM>.

Specifically, the fourth member <NUM> is made of a second filler material <NUM> as a filler material which is a metal material of the same type weldable to the second member <NUM>. The fourth member <NUM> covers the surface of the third member <NUM>. The fourth member <NUM> is welded to the second member <NUM>.

In the following description, the first member <NUM> is made of a mild steel material; the second member <NUM> is made of an aluminum material; the third member <NUM> that is a filler material for the first member <NUM> is made of a mild steel material; and the fourth member <NUM> that is a filler material for the second member <NUM> is made of an aluminum material. The through-portion <NUM> has a hole diameter of <NUM>. The first filler material <NUM> has an outer diameter of <NUM>. The second filler material <NUM> has an outer diameter of <NUM>.

An arc welder <NUM> includes a nozzle <NUM> and a tip <NUM>. The nozzle <NUM> supplies a shielding gas or the like to a welding point of a welding target. The tip <NUM> supplies a welding current to the third member <NUM>.

The arc welder <NUM> performs metal active gas (MAG) welding using a mixed gas of argon (Ar) and carbon dioxide (CO<NUM>) as a shielding gas or CO<NUM> gas shielded arc welding using carbon dioxide (CO<NUM>) as a shielding gas, in welding the first filler material <NUM> which is a mild steel material.

The arc welder <NUM> performs argon gas welding using argon (Ar) as a shielding gas in welding the second filler material <NUM> which is an aluminum material.

The arc welder <NUM> performs a first step. In the first step, the first filler material <NUM> as a welding electrode is welded to the first member <NUM> as a base material through the through-portion <NUM>. Short-circuit arc welding is performed at this time in which a short-circuit state where the first filler material <NUM> and the first member <NUM> are short-circuited and an arc state where an arc is generated between the first filler material <NUM> and the first member <NUM> are repeated. The short-circuit arc welding causes a small spread of an arc <NUM>.

The arc welder <NUM> supplies a welding current, while feeding the first member <NUM> with the first filler material <NUM> (i.e., the third member <NUM>) as a welding electrode through the through-portion <NUM>, thereby releasing the short-circuit between the first filler material <NUM> and the first member <NUM> and generating the arc <NUM> between the first filler material <NUM> and the first member <NUM>.

The arc <NUM> thus generated in the arc state generates droplets at the end of the first filler material <NUM>. On the other hand, in the short-circuit state, the droplets generated at the end of the first filler material <NUM> are brought into contact with, and transferred to, the first member <NUM>.

The third member <NUM> melted by the arc welding is melt-bonded to the first member <NUM> and is laminated in the through-portion <NUM>. Then, the melted third member <NUM> fills the through-portion <NUM> up, flows out to an upper peripheral edge of the through-portion <NUM>, and spreads in a flange shape.

In the process in which the melted third member <NUM> turns into a bead, the third member <NUM> is provided with the flange <NUM> that presses the peripheral edge of the through-portion <NUM>. The flange <NUM> projects radially outward from the through-portion <NUM> on a surface (an upper surface in <FIG>) of the second member <NUM> facing opposite to the first member <NUM>.

The third member <NUM> then solidifies and shrinks on the first member <NUM>, whereby the second member <NUM>, which is a dissimilar material, is compressed and fixed between the flange <NUM> and the first member <NUM>.

In this manner, the welding wire as the filler material, which is the third member <NUM>, is melted and supplied to the first member <NUM> through the through-portion <NUM> of the second member <NUM>. Accordingly, a flange-shaped bead for securing a strength is formed on the second member <NUM> to fasten the second member <NUM> between the first member <NUM> and the bead by compression fixing.

The second member <NUM> and the third member <NUM> do not have to be fusion welded. An intermetallic compound, if any is formed through the fusion welding, does not cause any problem, since the fusion welding aims at the compression fixing in the flange shape.

The arc welder <NUM> performs a second step. In the second step, the second filler material <NUM> (i.e., the fourth member <NUM>), which is weldable to the second member <NUM>, is used to cover the surface of the third member <NUM> and is welded to the second member <NUM>. Specifically, in welding the second filler material <NUM> to the second member <NUM>, the arc welder <NUM> performs pulse welding in a pulse waveform with a peak current and a base current alternately repeated in DC straight polarity welding or AC welding with alternating polarity. In the pulse welding, the spread of the arc <NUM> is increased with a low heat input that does not melt the second member <NUM>, thereby increasing the amount of heat input to the second filler material <NUM> as the welding electrode and increasing the amount of welding.

In the pulse welding, the droplets generated at the end of the second filler material <NUM> are detached from the second filler material <NUM> once per pulse consisting of the peak current and the base current, and are detached and transferred toward the flange <NUM> and the second member <NUM>.

Here, the "DC straight polarity welding" is welding using DC, in which the second filler material <NUM> as the welding electrode serves as a negative pole and the first member <NUM> and the second member <NUM> as the base material serve as a positive pole, thereby increasing the heat input to the second filler material <NUM> as the welding electrode. This welding reduces the heat input to the base material and promotes melting of the second filler material <NUM> as the welding electrode.

On the other hand, the "AC welding with alternating polarity" is welding using AC, in which, for example, electrode-positive (reverse polarity) welding is performed at the waveform with a peak current, and electrode-negative (straight polarity) welding is performed at the waveform with a base current. At the time of the peak current of the reverse polarity, the first member <NUM> and the second member <NUM> as the base material serve as the negative pole, and the second filler material <NUM> as the welding electrode serves as the positive pole. At the time of the base current of the straight polarity, the first member <NUM> and the second member <NUM> as the base material serve as the positive pole, and the second filler material <NUM> as the welding electrode serves as the negative pole.

Thus, in the "AC welding with alternating polarity," welding is performed with a larger heat input to the first member <NUM> and the second member <NUM> as the base material at the time of the peak current of reverse polarity, and with a larger heat input to the second filler material <NUM> as the welding electrode at the time of the base current of straight polarity. Thus, the heat input to the base material is reduced compared to the DC welding, which promotes melting of the second filler material <NUM> as the welding electrode.

An example in which the pulse welding with straight polarity is performed has been described. However, short-circuit arc welding in which the arc state and the short-circuit state are repeated may be performed as a welding method that causes a small spread of the arc <NUM> but a smaller amount of heat input to the second member <NUM>.

The arc welder <NUM> supplies a welding current while feeding the surface of the third member <NUM> with the second filler material <NUM> (i.e., the fourth member <NUM>), thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding is melt-bonded to the second member <NUM> and is laminated to cover the surface of the third member <NUM>.

As described above, in the joining method according to this embodiment, the fourth member <NUM> is used to cover the surface of the third member <NUM> and is welded to the second member <NUM>. Accordingly, the fourth member <NUM> closes the gap between the second member <NUM> and the third member <NUM> to reduce the entry of moisture from the outside. This keeps moisture from entering an area where the second member <NUM> and the third member <NUM> overlap each other from the outside.

It is therefore possible to reduce the occurrence of electrolytic corrosion in the area where the second member <NUM> and the third member <NUM> overlap each other and secure joint strength.

The second welding is performed in this manner, using the second filler material <NUM> (i.e., the fourth member <NUM>) as a filler material of the identical quality with the second member <NUM> and different from the third member <NUM>, thereby welding the molten metal so as to cover the flange-shaped bead made of the third member <NUM> and creating a bead larger than the size of the flange shape. Accordingly, the fourth member <NUM> can be fusion welded to the second member <NUM> of the identical quality with the fourth member <NUM>.

Fusion welding the materials of the identical quality can reduce the entry of moisture or other substances from the outside and can reduce the electrolytic corrosion, without typically used other means, such as an adhesive, a sealant, or a sealing agent.

Basically, the first and third members <NUM> and <NUM> are made of a material with a higher melting point than the second and fourth members <NUM> and <NUM>. Thus, the interface between the third and fourth members <NUM> and <NUM> is not fusion welded or slightly fusion welded.

Accordingly, the bead of the fourth member <NUM> can be formed on the bead of the third member <NUM> of the flange shape without influence, such as deformation of the flange shape of the third member <NUM>.

In the following description, the same reference characters designate the same components as those of the first embodiment, and the description is focused only on the differences between this embodiment and the first embodiment.

As shown in <FIG>, the second member <NUM> has the through-portion <NUM>. The through-portion <NUM> has a tapered portion <NUM> that is tapered toward the first member <NUM>.

The arc welder <NUM> performs a first step. In the first step, the first filler material <NUM> (i.e., the third member <NUM>) is melted by short-circuit arc welding. The melted third member <NUM> flows along the tapered portion <NUM> of the through-portion <NUM> to gather to the central area of the through-portion <NUM> and is melt-bonded to the first member <NUM>.

The melted third member <NUM> fills the through-portion <NUM> up, and spreads in a flange shape on the upper surface of the tapered portion <NUM>.

In the process in which the melted third member <NUM> turns into a bead, the third member <NUM> is provided with the flange <NUM> that presses the tapered portion <NUM> of the through-portion <NUM>.

The arc welder <NUM> performs a second step. In the second step, a welding current is supplied, while feeding the surface of the third member <NUM> with the second filler material <NUM> (i.e., the fourth member <NUM>), thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding is melt-bonded to the second member <NUM> and is laminated to cover the surface of the third member <NUM>.

As described above, in the joining method according to this embodiment, the through-portion <NUM> has the tapered portion <NUM>, and the flange <NUM> is solidified in the shape along the tapered portion <NUM>, thereby reducing the thickness of the flange <NUM> protruding from the second member <NUM>. Accordingly, the thickness of the fourth member <NUM> protruding from the second member <NUM> can also be reduced.

As shown in <FIG>, the second member <NUM> has a stepped portion <NUM> open to the surface (i.e., the upper surface in <FIG>) opposite to the first member <NUM>, and a through-portion <NUM> in the bottom of the step <NUM>.

The arc welder <NUM> performs a first step. In the first step, the first filler material <NUM> (i.e., the third member <NUM>) is melted by short-circuit arc welding. The melted third member <NUM> is melt-bonded to the first member <NUM>.

Then, the melted third member <NUM> fills the through-portion <NUM> up, flows out to the upper peripheral edge of the through-portion <NUM>, that is, the bottom of the stepped portion <NUM>, and spreads in a flange shape.

In the process in which the melted third member <NUM> turns into a bead, the third member <NUM> is provided with the flange <NUM> that presses the peripheral edge of the through-portion <NUM>.

The arc welder <NUM> performs a second step. In the second step, a welding current is supplied, while feeding the surface of the third member <NUM> with the second filler material <NUM> (i.e., the fourth member <NUM>), thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding is melt-bonded to the stepped portion <NUM> of the second member <NUM> and is laminated to cover the surface of the third member <NUM>.

As described above, in the joining method according to this embodiment, the flange <NUM> of the third member <NUM> is disposed in the stepped portion <NUM>, thereby making it possible to reduce the protrusion of the flange <NUM> from the second member <NUM>. The thickness of the fourth member <NUM> protruding from the second member <NUM> can also be reduced.

As shown in <FIG>, the second member <NUM> has a stepped portion <NUM> open to the surface (i.e., the upper surface in <FIG>) opposite to the first member <NUM>, and a through-portion <NUM> in the bottom of the stepped portion <NUM>. The bottom of the stepped portion <NUM> is inclined toward the through-portion <NUM>.

The arc welder <NUM> performs a first step. In the first step, the first filler material <NUM> (i.e., the third member <NUM>) is melted by short-circuit arc welding. The melted third member <NUM> is melt-bonded to the first member <NUM>. If the melted third member <NUM> reaches the inclined surface of the stepped portion <NUM>, such a third member <NUM> flows along the inclined surface of the stepped portion <NUM> toward the through-portion <NUM> and is melt-bonded toward the first member <NUM>.

Then, the melted third member <NUM> fills the through-portion <NUM> up, flows out to the upper peripheral edge of the through-portion <NUM>, that is, the bottom of the stepped portion <NUM>, and spreads in a flange shape on the inclined surface of the stepped portion <NUM>.

In the process in which the melted third member <NUM> turns into a bead, the third member <NUM> is provided with the flange <NUM> that presses the inclined surface of the stepped portion <NUM>.

The arc welder <NUM> performs a second step. In the second step, a welding current is supplied, while feeding the surface of the third member <NUM> with the second filler material <NUM> (i.e., the fourth member <NUM>), thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding flows along the inclined surface of the stepped portion <NUM>. More specifically, the fourth member <NUM> flows effectively to close the gap between the second and third members <NUM> and <NUM> from the outside. Then, the melted fourth member <NUM> is melt-bonded to the second member <NUM> and laminated to cover the surface of the third member <NUM>.

As described above, in the joining method according to this embodiment, the stepped portion <NUM> has the bottom inclined toward the through-portion <NUM>, thereby allowing the melted third member <NUM> to flow easily toward the through-portion <NUM>.

The melted fourth member <NUM> flows along the inclined surface of the stepped portion <NUM>, allowing the gap between the second and third members <NUM> and <NUM> to be closed effectively from the outside and the fourth member <NUM> to be melt-bonded to the second member <NUM>.

Further, the flange <NUM> of the third member <NUM> is disposed in the stepped portion <NUM>, thereby making it possible to reduce the protrusion of the flange <NUM> from the second member <NUM>. The thickness of the fourth member <NUM> protruding from the second member <NUM> can also be reduced.

As shown in <FIG>, the second member <NUM> has a stepped portion <NUM> open to the surface (i.e., the lower surface in <FIG>) overlapping the first member <NUM>, and a through-portion <NUM> in the bottom of the stepped portion <NUM>.

The first member <NUM> has an expansion <NUM> toward the stepped portion <NUM>. The expansion <NUM> is fitted into the stepped portion <NUM>.

Then, the melted third member <NUM> fills the through-portion <NUM> up, flows out to an upper peripheral edge of the through-portion <NUM>, and spreads in a flange shape.

As described above, in the joining method according to this embodiment, the first and second members <NUM> and <NUM> can be aligned easily by making the stepped portion <NUM> fitted with the expansion <NUM> in overlapping the first and second members <NUM> and <NUM>.

Further, a penetration bead can be sufficiently formed on the back surface of the first member <NUM>, which is opposite to the second member <NUM>, by utilizing an empty space on the back of the expansion <NUM> of the first member <NUM> in melting the third member <NUM> with respect to the first member <NUM> by arc welding. The strength can be further increased by the so-called "penetration welding" by which a weld bead is formed as if it were welded from the back of the first member <NUM> as well.

The empty space on the back of the expansion <NUM> of the first member <NUM> can provide a space for a weld bead partially protruding as a penetration bead from the back surface of the first member <NUM>.

As shown in <FIG>, the second member <NUM> has a through-portion <NUM>.

The arc welder <NUM> performs a first step. The first step includes first joining and second joining. In the first joining, a first joint <NUM> is formed inside the through-portion <NUM> by welding the first filler material <NUM> to the first member <NUM> through the through-portion <NUM>.

Specifically, short-circuit arc welding with a small spread of the arc <NUM>, in which a short-circuit state and an arc state are repeated, is performed in welding the melted third member <NUM> to the first member <NUM> through the through-portion <NUM> with heat input necessary for welding, thereby forming the first joint <NUM>.

In the second joining, the first filler material <NUM> is welded to the first joint <NUM> under welding conditions different from those in the first joining. Specifically, pulse welding with straight polarity or alternating polarity AC pulse welding is performed, with a low heat input that does not melt the second member <NUM>, to increase the spread of the arc <NUM> and the amount of heat input to the first filler material <NUM> as the welding electrode, thereby forming the second joint <NUM>. It is therefore possible to form the flange <NUM> with a smaller amount of heat input to the second member <NUM>.

The welding conditions include, for example, a change in the outer diameter of the first filler material <NUM>, in addition to a switch between the short-circuit arc welding and the pulse welding. For example, in a case in which the first filler material <NUM> to be used in the first joining has an outer diameter of <NUM>, <NUM>, <NUM>, or <NUM>, the first filler material <NUM> to be used in the second joining may have an outer diameter of <NUM>, <NUM>, or <NUM>. If the outer diameter of the first filler material <NUM> is changed, the second joining may be performed by the short-circuit arc welding.

In this manner, in the process in which the melted third member <NUM> turns into a bead, the first joint <NUM> and the second joint <NUM> are formed to form the third member <NUM>. The first joint <NUM> is melt-bonded to the first member <NUM>. The second joint <NUM> is melt-bonded to the first joint <NUM> and forms a flange <NUM> that presses the peripheral edge of the through-portion <NUM>.

Preferably, the first joint <NUM> is welded to have its upper portion depressed at the center. Such an upper portion facilitates the determination of the welding position in welding the second joint <NUM> to the first joint <NUM>. It also facilitates the gathering of the melted second joint <NUM> at the depressed center of the first joint <NUM> and finer shaping of the second joint <NUM>.

As described above, in the joining method according to this embodiment, the third member <NUM> is formed by separately forming the first joint <NUM> and the second joint <NUM>, thereby making it possible to use different welding methods or different welding conditions, depending on the material characteristics of the second member <NUM>.

The shapes of the first and second members <NUM> and <NUM> are mere examples and may be in any other suitable combination.

The arc welder <NUM> performs a first step. In the first step, the first filler material <NUM> (i.e., the third member <NUM>) is melted by short-circuit arc welding. The melted third member <NUM> is melt-bonded to the first member <NUM>. The melted third member <NUM> fills the through-portion <NUM> up, flows out to an upper peripheral edge of the through-portion <NUM>, and spreads in a flange shape.

The arc welder <NUM> performs a second step. The second step includes center formation and periphery formation. In the center formation, the second filler material <NUM> is welded to cover a central area of the surface of the third member <NUM>, thereby forming a central portion <NUM> of the fourth member <NUM>.

Specifically, a welding current is supplied, while feeding the central area of the surface of the third member <NUM> with the second filler material <NUM> (i.e., the fourth member <NUM>), thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding is laminated to cover the surface of the third member <NUM>. The central portion <NUM> of the fourth member <NUM> is formed in this manner.

In the periphery formation, the second filler material <NUM> is welded along the outer peripheral edge of the third member <NUM>, thereby forming a peripheral portion <NUM> of the fourth member <NUM>. The peripheral portion <NUM> is welded to the central portion <NUM> and the second member <NUM>.

Specifically, the nozzle <NUM> of the arc welder <NUM> is turned along the outer peripheral edge of the central portion <NUM> to supply the melted fourth member <NUM> to the outer peripheral edge of the central portion <NUM>. The melted fourth member <NUM> is welded to the central portion <NUM> and the second member <NUM>. The peripheral portion <NUM> of the fourth member <NUM> is formed in this manner.

The center formation and the periphery formation may be performed by either the short-circuit arc welding or the pulse welding.

As described above, in the joining method according to this embodiment, the central portion <NUM> is formed by arc welding to cover the central area of the surface of the third member <NUM>, and the peripheral portion <NUM> is formed thereafter by arc welding along the outer peripheral edge of the central portion <NUM>. Thus, the central portion <NUM> and the peripheral portion <NUM> can conform to each other.

The arc welder <NUM> performs a second step. The second step includes periphery formation and center formation. In the periphery formation, the second filler material <NUM> is welded along the outer peripheral edge of the third member <NUM>, thereby forming a peripheral portion <NUM> of the fourth member <NUM>.

Specifically, the nozzle <NUM> of the arc welder <NUM> is turned along the outer peripheral edge of the flange <NUM> to supply the melted second filler material <NUM> (i.e., fourth member <NUM>) to the outer peripheral edge of the flange <NUM>. The melted fourth member <NUM> is welded to the second member <NUM> along the outer peripheral edge of the flange <NUM>. The peripheral portion <NUM> of the fourth member <NUM> is formed in this manner.

In the center formation, the second filler material <NUM> is welded to cover the central area of the surface of the third member <NUM>, thereby forming a central portion <NUM> of the fourth member <NUM>. The central portion <NUM> is welded to the peripheral portion <NUM>.

Specifically, a welding current is supplied, while feeding the central area of the surface of the third member <NUM> with the fourth member <NUM>, thereby generating an arc <NUM>. The fourth member <NUM> melted by the arc welding is melt-bonded to the peripheral portion <NUM> and is laminated to cover the surface of the third member <NUM>. The central portion <NUM> of the fourth member <NUM> is formed in this manner.

As described above, in the joining method according to this embodiment, the peripheral portion <NUM> is formed by arc welding to cover the peripheral area of the surface of the third member <NUM>, and the central portion <NUM> is formed thereafter by arc welding in the central area of the surface of the third member <NUM>. Thus, the central portion <NUM> and the peripheral portion <NUM> can conform to each other.

Since the center formation is performed after the periphery formation, the peripheral portion <NUM> can block the outflow of the second filler material melted in the central area of the third member <NUM> in the center formation.

The embodiments described above may be modified as follows.

While the first member <NUM> is subjected to arc welding in the embodiments, the welding is not limited thereto. Specifically, the filler material as the third member <NUM> is grouped into a consumable electrode type and a non-consumable electrode type. For example, laser filler welding may be performed in which the welding wire as a filler material of the consumable electrode type used as the third member <NUM> may be replaced with a filler wire as a filler material of the non-consumable electrode type to perform laser welding on the first member <NUM>.

In the laser filler welding, the first member <NUM> is irradiated with a laser to ensure sufficient penetration in the surface of the first member <NUM>, and then, the laser is emitted only to the to-be-supplied filler wire, thereby melting the filler wire that is the third member <NUM>. Accordingly, the third member <NUM> fills the through-portion <NUM> up with a smaller amount of heat input to the second member <NUM>.

Further, a larger beam diameter is secured by defocusing and lowering the power density of the laser, thereby making it possible to preheat the second member <NUM> by utilizing the peripheral area of the beam diameter of the laser. This method allows the melted filler wire, which is the third member <NUM>, to conform to the second member <NUM> more easily. Due to the effect of this method, the gap between the second member <NUM> and the third member <NUM> is closed so as to prevent the entry of moisture from the outside, thereby keeping the moisture from entering an area where the second member <NUM> and the third member <NUM> overlap each other from the outside.

The third member <NUM> and the fourth member <NUM> may be formed by hybrid welding of arc welding and laser welding. Specifically, the hybrid welding may be performed in which the third member <NUM> is formed by laser filler welding and the fourth member <NUM> is formed by arc welding.

Alternatively, the hybrid welding may be performed in which the third member <NUM> is formed by arc welding using a filler material of the consumable electrode type and the fourth member <NUM> is formed by laser filler welding using a filler wire as a filler material of the non-consumable electrode type.

These laser welding processes may be combined. For example, the output of the laser is relatively lowered by defocusing and reducing the power density of the laser, or by changing the continuous output of the laser to a pulse oscillation output, or by lowering the duty, which is the ratio of ON and OFF of the pulse oscillation output; and at least one or more points on the periphery of the through-portion <NUM> of the second member <NUM> and on the upper part of the third member <NUM> may be preheated by being irradiated in advance with such a lower output laser. This method can increase the conformity of the second member <NUM>, the third member <NUM>, and the fourth member <NUM> in welding. It is therefore possible to keep moisture from entering an area where the second member <NUM>, the third member <NUM>, and the fourth member <NUM> overlap each other from the outside.

In this embodiment, the first member <NUM> is made of a mild steel material, while the second member <NUM> is made of an aluminum material. Alternatively, the first member <NUM> may be made of an aluminum material, while the second member <NUM> may be made of a mild steel material. In this case, it is not necessary to perform short-circuit arc welding in welding the third member <NUM> to the first member <NUM>, since the mild steel material of the second member <NUM> has a higher melting point than the aluminum material of the first member <NUM>.

Claim 1:
A joining method of joining a first member (<NUM>) made of a metal material and a second member (<NUM>) made of a material difficult to be welded to the first member with the first member and the second member overlapping each other,
the second member including a through-portion (<NUM>) penetrating toward the first member, the joining method comprising:
a first step of forming a third member (<NUM>) for compressing and fixing the second member between the first member and the third member by welding a first filler material (<NUM>), which is weldable to the first member, to the first member through the through-portion; the joining method being characterized by
a second step of forming a fourth member (<NUM>) by covering a surface of the third member with a second filler material (<NUM>), which is weldable to the second member, and welding the second filler material to the second member.