Weld fairing apparatus and welding method using the same

A weld fairing apparatus and a welding method using the apparatus effectively prevent a weld metal zone from forming a humping bead. The welding method includes: butting first and second object pieces together; heating the butted first and second object pieces using a heating device, thus forming a weld metal zone; and placing a fairing device such that the fairing device comes into contact with the weld metal zone and fairs the weld metal zone.

TECHNICAL FIELD

The present invention relates to a weld fairing apparatus and a welding method using the apparatus.

BACKGROUND ART

Hereinbelow, as an example of the related art of the present invention, a welding technique for producing welded products using high energy density beams such as laser beams will be described. The high energy density beams have high energy input per unit area of beam, thus effectively increasing the weld strength of weld metal zones in welded products. In recent years, as shown inFIG. 16andFIG. 17, a laser beam is preferably used for welding a plurality of pieces of sheet material1X and2X together to produce a welded product.

Japanese Patent Publication No. Hei. 2-43590 (first cited patent document) discloses a butt seam welding technique, in which ends of thin steel sheets are butted and welded together using a laser beam. In the butt seam welding technique, welding is executed under the condition that the laser beam is transmitted through an optical fiber, with the spot diameter of the beam set to two or more times the thickness of each of the steel sheets, or ten or more times the gap between the butted ends of the steel sheets, and the energy density of the beam set lower than a level capable of generating plasma.

In addition, Japanese Patent Laid-open Publication No. Sho. 62-101382 (second cited patent document) discloses a method of welding the flanges of a pulley to each other, in which an electrode is placed to come into contact with the outer circumferential surfaces of the flanges (the outer diameter end surfaces of the flanges) from the outside, ring-shaped compression discs, which are made of a nonconductive and heat-resistant ceramic material, are placed outside the side surfaces of the respective flanges and compress the flanges in the thickness direction of the flanges, and, thereafter, a welding current flows to the electrode, thus generating Joule heat to weld the flanges together.

According to the above-mentioned related art, as shown inFIG. 17, a weld metal zone5X is formed between the butted surfaces of the pieces of sheet material1X and2X. Further, it is necessary to increase the weld strength and the weld reliability of the weld metal zone5X. However, when the heat input by a laser beam is increased in order to increase the depth of weld penetration in the weld metal zone5X, humping is generated in the weld metal zone5X, as shown inFIG. 18, and thus a humping bead may be formed in the weld metal zone5X. The technical term “humping bead” means a bead that may be formed in a weld metal zone when molten weld metal in the weld metal zone is humped, thus causing uneven thickness of the weld metal zone in a welded product.

Described in brief, the first and second cited patent documents are problematic in that an increase in the heat input by the laser beam undesirably forms a humping bead in the weld metal zone.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a weld fairing apparatus and a welding method using the apparatus, which effectively prevent a humping bead from being formed in a weld metal zone.

In order to achieve the above object, according to one aspect of the present invention, there is provided a welding method, in which a first object piece and a second object piece are butted together and are heated by a heating device, thus forming a weld metal zone, the method comprising: placing a fairing device such that the fairing device is in contact with the weld metal zone, thus fairing the weld metal zone. Because the weld metal zone is faired by the fairing device, the formation of a humping bead in the weld metal zone can be prevented. Thus, although the heat input by a laser beam is lower or higher than a reference level, the formation of the humping bead in the weld metal zone can be prevented. Because the formation of the humping bead in the weld metal zone can be prevented even when the heat input by the laser beam is higher than the reference level, the heat input can be increased so as to increase the depth of weld penetration in the weld metal zone and improve the weld reliability of the weld metal zone.

According to another aspect of the present invention, there is provided a weld fairing apparatus, which is used for fairing a weld metal zone that is formed by heating butted first and second object pieces using a heating device, the weld fairing apparatus comprising a fairing device having a contact surface for coming into contact with the weld metal zone and fairing the weld metal zone. Because the weld metal zone can be faired by the fairing device, the formation of the humping bead in the weld metal zone can be prevented, so that, although heat input by a laser beam is lower or higher than a reference level, it is possible to prevent the formation of the humping bead in the weld metal zone. As described above, the humping bead is prevented from being formed in the weld metal zone even when high heat is input, so it is possible to increase the depth of weld penetration in the weld metal zone and improve the weld reliability of the weld metal zone by increasing the heat input by the laser beam.

Advantages of the Invention

According to the weld fairing apparatus and the welding method using the apparatus according to the present invention, the weld metal zone can be faired by the fairing device, so that the humping bead can be prevented from being formed in the weld metal zone. Thus, even when a step is defined between a first object piece and a second object piece, or the heating conditions for welding are varied, desired weld metal zones can be formed, thus increasing the freedom of welding conditions.

BEST MODE FOR CARRYING OUT THE INVENTION

Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

In the present invention, a heating device may be selected from conventional means, such as high energy density beams, electric arcs, electric currents and gases. Examples of the high energy density beams are laser beams or electron beams. Examples of the laser are a YAG laser, a CO2laser, a ruby laser, an Ar laser and a glass laser. The first object piece and the second object piece are preferably made of metal, which can be melted and welded together by heat, and which may be selected from ferrous metals or nonferrous metals. The ferrous metals may be mild steels, hard steels, or alloy steels. Examples of the alloy steels are stainless steels. Examples of the stainless steels may be ferrite steels, austenite steels, and martensite steels. When the welded product is a ferrous product, the carbon content in the product is 1.0% or less, 0.8% or less, 0.5% or less, or 0.3% or less by mass of the product, and further, 0.1% or less or 0.05% or less by mass of the product. When the welded product is the ferrous product, it is preferred that the carbon content in the product be limited, to thus limit over-tempering.

In the present invention, each of the first object piece and the second object piece is preferably configured as sheet material. Thus, the welded product may be configured as a structure, fabricated by welding a plurality of pieces of metal-based sheet material together. Described in detail, to produce a welded product in the present invention, it is preferred that the ends of a plurality of pieces of sheet material be butted together and that the butted ends of the pieces of sheet material be heated to form a weld metal zone, thus welding the plurality of pieces of sheet material to each other.

The fairing device is preferably placed behind part of the butted ends of the pieces of sheet material, heated by the heating device, in a welding direction. In the above state, the distance between the part of the butted ends of the pieces of sheet material, heated by the heating device, and the fairing device may be a variable distance. When the distance is a variable distance, the extent of fairing of the weld metal zone can be controlled. When the distance is too long and thus the weld metal zone becomes too cold, the extent of fairing of the weld metal zone will be limited. Further, when the distance is too short and thus the molten weld metal in the weld metal zone is too abundant, the molten weld metal may flow out. Thus, it is preferred that the distance between the part of the butted ends of the pieces of sheet material, heated by the heating device, and the fairing device be determined in consideration of the circumstances.

The fairing device may be formed as a compression unit having a contact surface coming into contact with the weld metal zone. For example, the compression unit may be formed as a rotary unit. When the compression unit is configured as a rotary unit, the rotary unit is advantageous in that the weld metal zone can be continuously faired by the rotary unit. The rotary unit may comprise a roller or an endless unit, such as a caterpillar or a belt. The rotary unit may be configured as a driven type or a drive type unit. For example, the fairing device may comprise a first compression unit and a second compression unit, which are contactable with the weld metal zone and compress the weld metal zone. At least one of the first compression unit and the second compression unit may be configured as a roller, having a contact surface coming into contact with the weld metal zone.

Further, the distance between the first compression unit and the second compression unit in the thickness direction of the weld metal zone may vary. In the above state, it is possible to properly respond to a variation in the thickness of the weld metal zone. Further, the variation in the distance between the first and second compression units in the thickness direction of the weld metal zone can control the forging effect of the weld metal zone.

Further, the fairing device may comprise an endless assembly, having contact surfaces that come into contact with the weld metal zone, and a support for supporting the endless assembly. The endless assembly is rotated with the rotary unit of the compression unit while the contact surfaces of the endless assembly come into contact with the weld metal zone. The endless assembly may be configured as a belt or a chain. The endless assembly may be configured as a driven type or a drive type unit.

According to the present invention, although high heat is input, the fairing device prevents the formation of a humping bead in the weld metal zone, thus realizing a high welding speed and increasing the depth of weld penetration in the weld metal zone by increasing the heat input by the laser beam. In the above case, when the first object piece and the second object piece are pieces of sheet material, the depth of weld penetration into the weld metal zone is set to HA millimeters and the thickness of the first sheet material is set to t1 millimeters, HA/t1=2 to 20, so that the ratio of the depth of weld penetration of the weld metal zone to the thickness of the first sheet material can be preferably determined to be a large ratio. The ratio of HA to t1 (HA/t1) can be determined according to the kind of a welded product. For example, the ratio of HA to t1 is preferably included within a range of 2.5 to 20, a range of 2 to 19, a range of 2 to 18, a range of 2 to 15, or a range of 2 to 10. Further, the lower limit value of the ratio of HA to t1 is set to, for example, 2.2, 2.5, 3, 3.5, 4 or 5. Further, the upper limit value of the ratio of HA to t1, which is set in consideration of the lower limit value, is set to, for example, 20, 15, 10 or 8.

When the width of the weld metal zone in the thickness direction is denoted by W, the relationship between W and t1 may be expressed as W≧t1, wherein the width W of the weld metal zone in the thickness direction is expressed as W=t1×2. Thus, the width W of the weld metal zone in the thickness direction may be expressed as W=(t1×2)×α, wherein α=0.85 to 1.15 or 0.95 to 1.05.

After the fairing of the weld metal zone, the weld metal zone may have an exposed surface, which is exposed in the direction of the depth of weld penetration. Particularly, after the fairing of the weld metal zone, the weld metal zone may have two exposed surfaces, which are exposed outwards in opposite directions. In other words, the weld metal zone after the fairing may include a first exposed surface, which is exposed outwards and faces one thickness direction of the first sheet material, and a second exposed surface, which is exposed outwards and faces the opposite thickness direction of the second sheet material. In the above case, the first exposed surface and the second exposed surface of the faired weld metal zone are exposed outwards, and thus it is possible to observe the depth of weld penetration in the weld metal zone from the first exposed surface and the second exposed surface with the naked eyes, or using an image pickup device, thus desirably increasing the strength and reliability of the weld metal zone.

In a preferred embodiment of the present invention, when the first object piece and the second object piece are pieces of sheet material, the thickness of the first sheet material is set to t1, and the thickness of the second sheet material is set to t2, the first exposed surface of the weld metal zone may be defined within a range of t1/5 millimeters inside or outside a line extending the surface of an edge of the first sheet material in the thickness direction of the weld metal zone, and the second exposed surface of the weld metal zone may be defined within a range of t1/5 millimeters inside or outside a line extending the surface of an edge of the second sheet material in the thickness direction of the weld metal zone.

Thus, in a preferred embodiment of the present invention, the first exposed surface of the weld metal zone may be defined along the line extending the surface of a first edge of the first sheet material, while the second exposed surface of the weld metal zone may be defined along the line extending the surface of a second edge of the second sheet material. Further, the first and second exposed surfaces of the weld metal zone may have respective traces, formed by the fairing device. When the traces are concave or convex traces, it is possible to increase the strength of adherence of paint after painting.

Further, the weld metal zone may comprise an exposed surface, which is exposed outwards and face outwards from one of the first and second pieces of sheet material, wherein the remaining one (non-welded sheet material) of the first and second pieces of sheet material is exposed at the side opposite the exposed surface of the weld bead. The above-mentioned state may be easily generated when the heating position of a heat source, such as a laser beam, deviates from a desired heating position, or when the first sheet material and the second sheet material have different thicknesses.

First Embodiment

Hereinbelow, a first embodiment of the present invention will be described in detail with reference toFIG. 1throughFIG. 6. The drawings are schematic views, in which the construction is not shown in detail. The first embodiment is adapted to welding the edges of object pieces together. As shown inFIG. 1, a first piece of sheet material1, made of metal, is used as the first object piece, and a second piece of sheet material2, made of metal, is used as the second object piece. To weld the edges of the pieces of sheet material together, a first edge11of the first piece of sheet material1overlaps a second edge21of the second piece of sheet material2. Each of the first piece of sheet material1and the second piece of sheet material2includes a ferrous metal (for example, having a carbon content of 0.3% or less by mass, and more preferably, 0.1% or less by mass). The thickness of the first edge11of the first piece of sheet material1is denoted by t1, while the thickness of the second edge21of the second piece of sheet material2is denoted by t2, wherein t1=t2, t1≈t2, t1<t2 or t1>t2.

As shown inFIG. 1, before a laser beam7is applied to the overlapping edges11and21, the first end surface13of the first edge11of the first piece of sheet material1and the second end surface23of the second edge21of the second piece of sheet material2are set flush with each other, thus forming a flat surface. Therefore, the laser beam7can be evenly applied to the overlapping edges11and21and the weld strength of the weld bead5is increased. However, in the present invention, a step may be defined between the first end surface13and the second end surface23.

Further, as shown in the schematic view ofFIG. 1, the YAG laser beam7, which is a high energy density beam used as the heating device, is applied from a laser source72to the end surfaces13and23of the first edge11and the second edge21, thus melting the end surfaces13and23. Therefore, a molten weld metal6is created and solidified to form a weld bead5as the weld metal zone. Here, laser beam welding is executed with high heat input per unit area of beam, thus resulting in quick heating, and is cooled quickly, thus resulting in quick cooling. Further, while welding, the laser beam7is moved relative to the first edge11and the second edge21in the direction of the arrow X1(welding direction, seeFIG. 4). The welding direction means the direction in which the welding is conducted. In the present invention, the laser beam7may be moved while the first edge11and the second edge21are fixed. Alternatively, the first edge11and the second edge21may be moved while the laser beam7is fixed.

As schematically shown inFIG. 4, the fairing device4is placed behind a heat input position7cof the laser beam7in the welding direction. In other words, the fairing device4is placed at the location on which the laser beam7has been applied. The fairing device4comprises a first rotary unit41(first compression unit), having a first flat roller surface43(first contact surface), and a second rotary unit42(second compression unit), having a second flat roller surface44(second contact surface). As shown in the schematic view ofFIG. 3, the first rotary unit41is rotatably held in a first support46, while the second rotary unit42is rotatably held in a second support47. In the embodiment, the first rotary unit41and the second rotary unit42are configured as driven type units, which are not connected to a drive motor, thus being rotatably idle. However, as desired, the first rotary unit41and the second rotary unit42may be configured as drive type units connected to a drive motor.

The first rotary unit41and the second rotary unit42have the same diameter. The central axis P1of the first rotary unit41is parallel to the central axis P2of the second rotary unit42in a vertical direction. In the present invention, each of the first rotary unit41and the second rotary unit42may be configured as a structure having a cooling channel therein to cool the rotary unit. However, it should be understood that the first rotary unit41and the second rotary unit42may be configured as structures that lack cooling channels. Further, the first rotary unit41and the second rotary unit42may be made of a metal or ceramic material. When the first rotary unit41and the second rotary unit42are made of metal, the metal rotary units41and42have high thermal conductivity, so that they can quickly cool the molten weld metal or the weld bead5in a short period of time. The metal of the rotary units41and42may be, for example, ferrous metal, or copper-, titanium- or aluminum-based metal. The ceramic material of the rotary units41and42may be, for example, alumina, silica, silicon carbide, silicon nitride or zirconium oxide.

According to the first embodiment, the distance L1(seeFIG. 4) between the heat input position7cof the laser beam7and the fairing device4is capable of being varied. In the above case, the location of the first support46and the second support47may be moved relative to the heat input position7cof the laser beam7in the welding direction (the direction of the arrow X1). Here, when the first piece of sheet material1and the second piece of sheet material2are fixed, the heat input position7cof the laser beam7may be moved relative to the fixed first and second pieces of sheet material1and2. When the heat input position7cof the laser beam7is moved as described above, it is preferred to make the first rotary unit41and the second rotary unit42follow the heat input position7cof the laser beam7.

Further, when the heat input position7cof the laser beam7is fixed, the first piece of sheet material1and the second piece of sheet material2may be moved relative to the heat input position7cof the laser beam7. In the above case, the first rotary unit41and the second rotary unit42may fixed at their locations. Alternatively, the first and second rotary units41and42may be movable relative to the heat input position7cof the laser beam7, so that the distance L1can vary.

The distance L1(seeFIG. 4) is equal to the distance between the heat input position7cof the laser beam7and the position LB, whereas the distance LA between the first rotary unit41and the second rotary unit42is minimized. In the present invention, the distance L1may be appropriately determined in accordance with the welding conditions. For example, the distance L1may be set within the range of 0<L1<100 mm or 0<L1<50 mm, and particularly 0<L1<30 mm. In the present invention, it is possible to select the fairing temperature of the weld bead5by changing the distance L1while the weld bead5is fairing by the fairing device4. For example, the weld bead5may be faired by the fairing device4while the outer surface and the interior of the weld bead5become solidified. Alternatively, the weld bead5may be faired by the fairing device4while the outer surface of the weld bead5becomes solidified, but the interior of the weld bead5remains in a molten state. As a further alternative, the weld bead5may be faired by the fairing device4while the outer surface of the weld bead5is in a half-solidified state.

Further, according to the first embodiment, the distance LA (seeFIG. 4) between the first roller surface43of the first rotary unit41and the second roller surface44of the second rotary unit42in the thickness direction of the weld bead5varies. Thus, the thickness of the weld bead5can be controlled. When the distance LA is controlled as described above, a forging effect of the weld bead5can be expected. The forging effect of the weld bead5is advantageous in that it preferably increases the strength of the weld bead5and reduces the number of pinholes in the weld bead5.

When the weld bead5is formed as described above, the fairing device4properly comes into contact with the weld bead5and fairs the weld bead5, as schematically shown inFIG. 3throughFIG. 5. In the above case, as shown in the schematic view ofFIG. 3, the first roller surface43of the first rotary unit41comes into contact with a first exposed surface51of the weld bead5, which is a first side surface of the weld bead5in the thickness direction of the weld bead5. Further, the second roller surface44of the second rotary unit42comes into contact with a second exposed surface52of the weld bead5, which is a second side surface of the weld bead5in the thickness direction of the weld bead5. As described above, the first and second exposed surfaces51and52of the weld bead5are faired by the fairing device4, so that the present invention can provide a good weld bead5having an excellent appearance. During the fairing of the weld bead5, as schematically shown inFIG. 3, the first roller surface43of the first rotary unit41comes into contact with a first surface14of the first piece of sheet material1, while the second roller surface44of the second rotary unit42comes into contact with a second surface24of the second piece of sheet material2. Thus, the thickness of the weld bead5can be limited.

In the first embodiment, although the heat input by the laser beam7is lower or higher than a reference level, the weld bead5can be efficiently faired by the fairing device4, thus preventing the formation of a humping bead. As described above, because the formation of the humping bead in a weld metal zone can be prevented even when the heat input by the laser beam7is higher than a reference level, the heat input can be increased to increase the depth of weld penetration in the weld metal zone, increase the strength of the weld bead5and improve the weld reliability of the weld bead5.

FIG. 6schematically illustrates a cross-section of the weld bead5after fairing. As shown inFIG. 6, the weld bead5after fairing is provided with the first exposed surface51, which is exposed outwards and faces one thickness direction of the first piece of sheet material1, the second exposed surface52, which is exposed outwards and faces the opposite thickness direction of the second piece of sheet material2, and a third exposed surface53, which crosses both the first exposed surface51and the second exposed surface52. Further, the first and second exposed surfaces51and52are formed by extending in the direction of weld penetration (laser beam applying direction), so that the exposed surfaces51and52can be viewed by the naked eyes from the outside.

As schematically shown inFIG. 6, the first exposed surface51and the second exposed surface52of the faired weld bead5face outwards in opposite thickness directions of the weld bead5. The first exposed surface51of the weld bead5is faired by the first roller surface43of the first rotary unit41and is defined to be flat along the first surface14of the first edge11of the first piece of sheet material1. The second exposed surface52of the weld bead5is faired by the second roller surface44of the second rotary unit42and is defined to be flat along the second surface24of the second edge21of the second piece of sheet material2.

As described above, the first exposed surface51and the second exposed surface52of the weld bead5are faired by the first roller surface43and the second roller surface44, respectively, so that the first exposed surface51and the second exposed surface52can have respective traces formed by the first roller surface43and the second roller surface44. When the traces are concave or convex traces, it is possible to increase the strength of adherence of paint after painting.

According to the first embodiment, as shown in the schematic view ofFIG. 6, the first exposed surface51of the weld bead5is defined along a line extending the first surface14of the first edge11of the first piece of sheet material1. Further, the second exposed surface52of the weld bead5is defined along a line extending the second surface24of the second edge21of the second piece of sheet material2.

In other words, when the thickness of the first piece of sheet material1is set to t1, and the thickness of the second piece of sheet material2is set to t2, the first exposed surface51of the weld bead5is defined within a range of t1/5 millimeters inside or outside the line extending the first surface14of the first edge11of the first piece of sheet material1in the thickness direction of the weld bead5. Further, the second exposed surface52of the weld bead5is defined within a range of t2/5 millimeters inside or outside the line extending the second surface24of the second edge21of the second piece of sheet material2in the thickness direction of the weld bead5.

In the first embodiment, the depth of weld penetration of the weld bead5can be increased by increasing the heat input by the laser beam7, so that, when the depth of weld penetration of the weld bead5is set to HA mm, and the thickness of the first edge11of the first piece of sheet material1is set to t1 mm, the ratio of HA to t1 (HA/t1) can be determined in the range of 4 to 13, particularly, in the range of 4 to 11 or the range of 4 to 8. Thus, the ratio of the depth of weld penetration of weld bead5to the thickness of the first piece of sheet material1is determined as a large ratio. The increase in the depth of weld penetration of the weld bead5cannot be accomplished through a conventional welding technique.

Further, according to the first embodiment, when the width of the weld bead5in the thickness direction of the weld bead5is denoted by W (seeFIG. 6), the relationship between W and t1 may be expressed as W≧=t1. When t1+t2=t3, the width W may be expressed as W=t3 or W≈t3. Thus, W/t3 is determined within the range of 0.85 to 1.15, particularly, a range of 0.95 to 1.05.

As described above, the weld bead5, having the increased depth of weld penetration, can firmly weld the first edge11of the first piece of sheet material1and the second edge21of the second piece of sheet material2together. Therefore, it is possible to produce a container900(seeFIG. 9), which has a chamber901defined inside the first piece of sheet material1and the second piece of sheet material2.

As described above, according to the first embodiment, the first rotary unit41and the second rotary unit42, which constitute the fairing device4, fair the weld bead5, thus preventing the formation of a humping bead. Thus, even if the heat input by a laser beam is lower or higher than a reference level, a humping bead is prevented from being formed during a welding process.

In the embodiment, the formation of a humping bead can be prevented even when the heat input by the laser beam is higher than a reference level. Thus, the heat input can be increased in order to increase the depth of weld penetration of the weld bead5and improve the weld reliability of the weld bead5. Further, unlike a conventional welding technique, the embodiment of the present invention can provide an increased ratio (HA/t1) of the depth HA of weld penetration of the weld bead5to the thickness t1 of the first piece of sheet material1.

Further, the first exposed surface51and the second exposed surface52of the faired weld bead5are exposed outwards, so that it is possible to observe the depth of weld penetration of the weld bead5from the outside with the naked eyes, or using an image pickup device, thus desirably increasing the weld strength and weld reliability of the weld bead5. Particularly, according to the first embodiment, the thickness of the weld bead5is determined as the sum total t3 of the thicknesses t1 and t2 of the first edge11of the first piece of sheet material1and the second edge21of the second piece of sheet material2. Thus, the weld bead5has a desired thickness, increasing the strength of the weld bead5and thus increasing the reliability of the weld bead5, and improving the appearance of the weld bead5.

According to the first embodiment, although the weld bead5is somewhat deformed, both the first roller surface43of the first rotary unit41and the second roller surface44of the second rotary unit42of the fairing device4can quickly fair the deformed weld bead5. Thus, when a step is defined between the first end surface13(seeFIG. 1) of the first edge11of the first piece of sheet material1and the second end surface23of the second edge21of the second piece of sheet material2before the laser beam7is applied to the overlapping edges11and21, a weld bead5may be formed in a course to compensate for the effect of the step. In the above state, a good weld bead5can be formed. Further, the heat input by the laser beam in the welding method according to the present invention can be increased, as described above, so that, when a step is defined between the overlapping edges, the weld bead5can be formed in the course to compensate for the effect of the step. Thus, the present invention greatly increases the freedom of welding conditions.

Further, while welding, the heat input position of the laser beam7can be moved the direction of the arrow X1(welding direction) relative to the first piece of sheet material1and the second piece of sheet material2, thus continuously welding the pieces1and2together. In the above state, when the fairing device4follows the movement of the heat input position of the laser beam7relative to the first and second pieces of sheet material1and2such that the fairing device4is moved relative to the first and second pieces of sheet material1and2, the weld bead5can be continuously faired. Thus, the productivity of welded products can be increased and the production cost of the welded products can be reduced.

According to the first embodiment, the weld bead5, which is in a high temperature state, can be quickly cooled both by the first roller surface43of the first rotary unit41and by the second roller surface44of the second rotary unit42of the fairing device4. Thus, the oxidation of the weld bead5is restricted, thus improving the anticorrosion property of the weld bead5. Therefore, it is preferred that both the first roller surface43of the first rotary unit41and the second roller surface44of the second rotary unit42be made using a high conductive metal, for example, copper or a copper alloy.

Experimental Example

FIG. 7is a photograph illustrating the cross-section of a weld bead according to an experimental example of the first embodiment of the present invention. The welding conditions in the experimental example are set as follows: the laser source is a YAG laser, the laser output power is 4.5 kW, the diameter of beam concentration is 0.6 mm, and the material of the first and second pieces of sheet material1and2is stainless steel. Further, the thickness of the first piece of sheet material1is 0.6 mm, the thickness of the second piece of sheet material2is 0.6 mm, the welding speed is 3 m/min, and the distance L1is 8 mm. Further, the material of the first and second rotary units41and42is a copper alloy, the outer diameter of the first rotary unit41is 45 mm, and the outer diameter of the second rotary unit42is 45 mm. In the experimental example, the depth HA of weld penetration of the weld bead5is 3.8 mm, so that HA/t1=3.8 mm/0.6 mm≈6.3.

According to the experimental example, the ratio (HA/t1) of the depth of weld penetration of the weld bead5to the thickness of the first piece of sheet material can be set to a large ratio. Further, when the width of the weld bead5in the thickness direction of the weld bead5is denoted by W, and the width W is about 1.2 mm, the relationship between the width W and the thickness t1 is expressed as W≧t1 and W≈t1×2.

As shown in the photograph ofFIG. 7, the first exposed surface of the weld bead is exposed outwards, and is defined along the line extending the first surface of the first edge of the first piece of sheet material. Further, the second exposed surface of the weld bead is exposed outwards, and is defined along the line extending the second surface of the second edge of the second piece of sheet material.

Second Embodiment

FIG. 8throughFIG. 10are views schematically illustrating a second embodiment of the present invention. The basic construction of the second embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the second embodiment will be described based on the differences from the first embodiment. As shown inFIG. 10, the fairing device4according to the second embodiment comprises a first rotary unit41, having a first flat roller surface43(first contact surface), and a second rotary unit42, having a second flat roller surface44(second contact surface). The first rotary unit41is rotatably held in a first support46, while the second rotary unit42is rotatably held in a second support47. In the second embodiment, both the first rotary unit41and the second rotary unit42are configured as driven type units, which are not connected to a drive motor, thus being idly rotatable. Further, the first rotary unit41and the second rotary unit42have the same diameter. The central axis P1of the first rotary unit41is parallel to the central axis P2of the second rotary unit42in a horizontal direction.

To weld pieces of sheet material together according to the second embodiment, as shown inFIG. 8, the first and second pieces of sheet material1and2are placed horizontally such that the first edge11of the first piece of sheet material1and the second edge21of the second piece of sheet material2overlap each other before a laser beam7is applied to the overlapping edges11and21. The first and second end surfaces13and23of the overlapping first and second edges11and21of the first and second pieces of sheet material1and2form a level surface. Thus, the laser beam7can be evenly applied to the first and second end surfaces13and23, thereby increasing the weld strength of the weld bead5. However, it should be understood that a step may be defined between the first end surface13and the second end surface23.

As shown inFIG. 8, a YAG laser beam7, which is a high energy density beam used as the heating device, is applied from a laser source72to the end surfaces of the overlapping first and second edges11and21in a horizontal direction, thus melting the first and second end surfaces13and23. Therefore, a molten weld metal6is formed and solidified, thus forming a weld bead5as a weld metal zone.

When the laser beam7is applied to the horizontally overlapping first and second edges11and21in the horizontal direction, the weld bead5may sag downwards due to gravity, and thus only one rotary unit may be used to support the weld bead5upwards in the second embodiment. Described in detail, the second rotary unit42is placed under the weld bead5, while the first rotary unit41may be removed from the top of the weld bead5. In the above state, it is possible to reduce the production cost of welded products and simplify the construction of a welding jig.

As described above, when the weld bead5is formed, the fairing device4is placed on each side of the weld bead5to fair the weld bead5, as shown inFIG. 10. In the above state, the first roller surface43of the first rotary unit41comes into contact with the first exposed surface51of the weld bead5, while the second roller surface44of the second rotary unit42comes into contact with the second exposed surface52of the weld bead5. Because the exposed surfaces51and52of the weld bead5are faired by the fairing device4, it is possible to provide a weld bead5having a good appearance. Thus, even if the heat input by the laser beam is lower or higher than a reference level, the formation of a humping bead can be prevented. Because the formation of the humping bead can be prevented even when the heat input by the laser beam is higher than the reference level, the heat input can be increased to increase the welding speed, increase the depth of weld penetration of the weld bead and thus improve the weld reliability of the weld bead.

In the second embodiment, it is possible to prevent the formation of the humping bead, so that the heat input by a laser beam can be increased to increase the depth of weld penetration and improve the weld reliability of the weld bead5. Therefore, unlike a conventional welding technique, the second embodiment of the present invention can provide an increased ratio (HA/t1) of the depth HA of weld penetration of the weld bead5to the thickness t1 of the first piece of sheet material1.

Third Embodiment

FIG. 11is a view schematically illustrating a third embodiment of the present invention. The basic construction of the third embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the third embodiment will be described based on the differences from the first embodiment. In the third embodiment, the fairing device4comprises a first rotary unit41, having a first flat roller surface43(first contact surface), and a second rotary unit42, having a second flat roller surface44(second contact surface). Further, a release agent spraying unit90is placed to spray a release agent91onto both the first roller surface43and the second roller surface44. In the third embodiment, the release agent91allows easy removal of the first rotary unit41and the second rotary unit42from the weld bead5. Further, the release agent91effectively prevents the first rotary unit41and the second rotary unit42from overheating.

Fourth Embodiment

FIG. 12is a view schematically illustrating a fourth embodiment of the present invention. The basic construction of the fourth embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the fourth embodiment will be described based on the differences from the first embodiment. In the fourth embodiment, the fairing device4comprises a first rotary unit41, having a first flat roller surface43, and a second rotary unit42, having a second flat roller surface44. The first rotary unit41is rotated by a first drive motor41m, which is a drive unit supported by a first support46. In the same manner, the second rotary unit42is rotated by a second drive motor42m, which is a drive unit supported by a second support47. Further, there may be a difference in rpm between the first rotary unit41and the second rotary unit42. Thus, the fourth embodiment can easily respond to differences in the length of a weld line between the first exposed surface51and the second exposed surface52of the weld bead5. Further, in the fourth embodiment, the first rotary unit41and the second rotary unit42may sometimes be rotated synchronously.

Fifth Embodiment

FIG. 13is a view schematically illustrating a fifth embodiment of the present invention. The basic construction of the fifth embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the fifth embodiment will be described based on the differences from the first embodiment. In the fifth embodiment, the thickness t2 of the second piece of sheet material2is greater than the thickness t1 of the first piece of sheet material1. The weld bead5is extended and formed in the direction of the depth of weld penetration of the weld bead5. The weld bead5has an exposed surface51, which is exposed outwards from the first piece of sheet material1. In the above state, the surface24(non-welded surface) of the second piece of sheet material2is exposed at the side opposite the exposed surface51of the weld bead5. As shown inFIG. 13, the first rotary unit41comes into contact with the first exposed surface51of the weld bead5, while the second rotary unit42comes into contact with the surface24of the second piece of sheet material2. In the above state, the weld bead5is interposed between the first rotary unit41and the second rotary unit42, so that the first exposed surface51of the weld bead5can be properly faired by the fairing device4.

Sixth Embodiment

FIG. 14is a view schematically illustrating a sixth embodiment of the present invention. The basic construction of the sixth embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the sixth embodiment will be described based on the differences from the first embodiment. In the sixth embodiment, the fairing device4comprises a first rotary unit41, which has a first flat roller surface43and is used for primary fairing of a weld bead5, and a second rotary unit42, which has a second flat roller surface44and is used for primary fairing of the weld bead5. The fairing device4further comprises a first rotary unit410, which has a first flat roller surface430and is used for final fairing of the weld bead5, and a second rotary unit420, which has a second flat roller surface440and is used for final fairing of the weld bead5. In the sixth embodiment, the final fairing is executed after the primary fairing, so that the weld bead5can be effectively faired to realize a good appearance.

Seventh Embodiment

FIG. 15is a view schematically illustrating a seventh embodiment of the present invention. The basic construction of the seventh embodiment remains the same as that of the first embodiment, thus providing the same operational effect as that of the first embodiment. Hereinbelow, the seventh embodiment will be described based on the differences from the first embodiment. As shown inFIG. 15, the fairing device4B comprises a first endless unit81B and a second endless unit85B, which are placed such that the thickness of the weld bead5is interposed between the two endless units81B and85B.

The first endless unit81B comprises a first endless assembly82B and a first rotary unit83B, which acts as a first support for supporting the first endless assembly82B. In the same manner, the second endless unit85B comprises a second endless assembly86B and a second rotary unit87B, which acts as a second support for supporting the second endless assembly86B.

As shown inFIG. 15, the first endless assembly82B comprises a plurality of segments820, which are arranged in an endless arrangement and are coupled to each other, thus forming a caterpillar structure in which the segments820are movable with respect to each other. The first endless assembly82B comprises first contact surfaces84B, which come into contact with the weld bead5. In response to the rotation of the first rotary unit83B, the first endless assembly82B is rotated while the first contact surfaces84B are in contact with the weld bead5. The second endless unit85B has the same construction as that of the first endless unit81B, and is operated in the same manner as the first endless unit81B.

In the seventh embodiment, when a weld bead5is formed by the laser beam7, the fairing device4B fairs the weld bead5, as shown inFIG. 15. In other words, the first contact surfaces84B of the first endless assembly82B come into contact with the first side surface of the weld bead5in the thickness direction of the weld bead5. In the same manner, the second contact surfaces88B of the second endless assembly86B come into contact with the second side surface of the weld bead5in the thickness direction of the weld bead5.

Because the weld bead5can be faired by the fairing device4B, as described above, the seventh embodiment provides a weld bead5having a good appearance. Thus, even if the heat input is lower or higher than a reference level, the formation of a humping bead can be prevented. Because the formation of the humping bead can be prevented even when high heat is input, it is possible to increase the depth of weld penetration, increase the strength of the weld bead5and, at the same time, improve the weld reliability of the weld bead5by increasing the heat input.

Other Embodiments

In the first embodiment, the rotary units41and42, which constitute the fairing device, compress the entire length of the weld bead5in the bead height direction. However, part of the overall length of the weld bead5in the bead height direction (for example, at least 40% or at least 50% of the overall length of the weld bead5in the bead height direction) may be compressed by the rotary units41and42, without affecting the functioning of the present invention. While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Industrial Applicability

As apparent from the above description, the present invention is preferably used in the production of welded products or in welding methods. Particularly, the present invention is preferably used in producing welded products using a heating device, for example, high energy density beams, such as laser beams, or in welding methods.