JP2002263878A - Butt weld method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which is capable of efficiently forming a defectless butt welded joint which is less rugged on bead surfaces and wide in back bead width while achieving a good bead surface shape and reducing a cost required for assist gas. SOLUTION: In but-welding a weld zone by using a high-energy beam while supplying the assist gas to the weld zone, the welding is performed by blowing the assist gas from the rear side in the progression direction of the beam, or by dividing the high-energy beam into two spectral components so that a line for connecting centers of the two and more divided beams is set within a range of 10 to 80 degree of angle relative to the butt surface of a welding raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for butt welding metal materials using a high energy beam.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved butt welding method that can efficiently and reliably provide a defect-free high quality welded joint.
The high energy beam used in the present invention includes:
A laser beam, an electron beam, a plasma beam, and the like can be mentioned. Of these, the features of the present invention are most effectively utilized when performing laser beam welding. Therefore, the following description mainly focuses on welding using a laser beam. This will be explained. However, the present invention is not limited to the laser beam welding, and can be similarly applied to other high energy beam welding.

The butt welding method of the present invention can be widely applied to iron-based metals such as steel and other non-ferrous metals, and the shape thereof can be applied to plates and pipes. A description will be given mainly of a case where the present invention is applied to a simple steel sheet.

[0003]

2. Description of the Related Art When butt welding metal materials such as steel plates using a laser beam, the type of laser beam, laser output,
Optimization of the focus position of the laser beam, welding speed, type of assist gas, flow rate, etc. are being performed.

[0004] Defects found in butt-welded joints such as steel sheets include cross-sectional defects such as undercuts and underfills, porosity, and weld cracks. High-energy beams such as laser beams are used. The most important thing to pay attention to when doing is non-penetration welding. That is, the non-penetration welding means a state in which the molten portion does not penetrate the steel sheet. If such non-penetration welding occurs in a thin plate material, the non-penetration welding part becomes a serious defect when performing press working after welding. This causes cracking due to insufficient strength.

Further, it is known that the width of the bead on the back surface becomes narrower as the state from the through welding to the non-through welding state is approached. Therefore, at the actual site, the backside bead width is adopted as a management value of the through-hole welding, and by ensuring an appropriate backside bead width, non-through-hole welding is eliminated to guarantee through-hole welding. Although it is effective to increase the laser output in order to eliminate the non-penetration welding state and to realize the reliable penetration welding, if the output is increased unnecessarily, the weld metal may burn off. In addition, by lowering the welding speed, penetration welding can be ensured, but a decrease in welding efficiency is inevitable. Further, when the welding speed is increased, the molten portion becomes unstable, and welding defects such as humping beads are likely to occur. Therefore, in actual welding, welding conditions with good productivity are determined in a range in which the quality of the welded joint can be satisfied while balancing the laser output and the welding speed.

On the other hand, in CO ₂ laser beam welding, metal vapor is generated by high energy at the time of welding. This metal vapor is generally easily converted into plasma, and the generated plasma easily absorbs the CO ₂ laser beam. And
The plasma that has absorbed the laser beam grows increasingly and causes a reduction in the laser beam reaching the weld, possibly causing non-penetrating welding.

[0007] For this reason, the plasma is usually removed from the beam welding position by spraying a gas called an assist gas to the welding portion so that the laser beam can efficiently reach the welding portion.

For example, FIG. 1 is a schematic side view illustrating a laser welding method using the above assist gas. In the figure, reference numeral 1 denotes a laser beam, 2 denotes an assist gas nozzle,
Is a welding base material (butting surface), 4 is a keyhole formed by a laser beam, 5 is a molten metal, 6 is a welding metal,
Reference numerals 7, 7 'denote plasmas, respectively. As shown in the figure, when performing butt welding by the laser welding method, the welding base materials 3 and 3 are butt-jointed, and the converged laser beam 1 is projected toward the butt-joining portion, and the laser beam 1 is directed in the welding direction shown by the arrow. Is moved and the welding base material is heated and melted to perform welding. The molten metal 5 generated on the butt surface by heating is rapidly cooled and solidified by heat transfer to the base metal around the welded portion, forming a weld metal 6, that is, a weld joint.

At this time, heat generated by the laser beam 1 generates a metal vapor. Since the metal vapor is easily turned into a plasma as described above, a plasma 7 is generated near the beam projecting portion, and the plasma 7 absorbs the laser beam 1. As a result, the energy of the laser beam 1 reaching the welded portion is further reduced, and as a result, non-penetration welding due to insufficient heat input is caused.

Therefore, in order to prevent such an obstacle caused by the plasma 7, an assist gas is blown from the assist gas nozzle 2 disposed on the front side in the welding direction toward the plasma 7 generating position, so that the plasma 7 is welded as indicated by a broken line 7 '. Of the laser beam 1 from the projection position of the laser beam 1.

At this time, it can be easily inferred that the plasma is removed from the beam directing position by increasing the flow rate of the assist gas. For example, FIG. 2 is a graph showing the relationship between the flow rate of the assist gas and the increase rate of the backside bead width. As the flow rate of the assist gas increases, the backside bead width clearly increases. This is thought to be because as the assist gas flow rate increases, the amount of plasma movement from the welding position increases, the amount of beam absorption by the plasma decreases, and as a result, the amount of heat input to welding increases. It can be seen that increasing the assist gas flow rate is effective in removing plasma.

In order to remove the plasma efficiently, the moving speed of the welding device, that is, the relative speed difference between the moving speed of the plasma and the moving speed of the plasma by the assist gas spraying, is determined by the following formula.
It is considered effective to blow the assist gas from the front in the welding progress direction as shown in FIG.

On the other hand, there is a relationship as shown in FIG. 3 between the assist gas flow rate and the irregularities generated on the bead surface, and the irregularities on the bead surface become more remarkable as the assist gas flow rate increases. Originally, when realizing stable penetration welding (that is, enlarging the backside bead width), it is desirable to increase the flow rate of the assist gas for plasma removal. However, if the flow rate of the assist gas is increased, the shape of the weld bead is increased. (The unevenness becomes remarkable), the gas supply amount must be increased in order to increase the assist gas flow rate, and the cost increases due to the increase in the gas usage amount.

Therefore, usually, the back bead width, the surface shape,
Considering the balance of cost, etc., set the assist gas flow rate to 2
Although the control is performed in the range of 0 to 30 liter / min, further improvement is required in terms of improving the quality of the welded joint (particularly, increasing the width of the backside bead).

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a welded joint while improving the bead surface shape and reducing the cost required for assist gas. It is an object of the present invention to provide a welding method that can improve the quality of a part.

It is a further object of the present invention to establish a welding method capable of increasing the width of the backside bead as compared with the conventional method and improving the welding efficiency (productivity).

[0017]

A first butt welding method according to the present invention which can solve the above-mentioned problems uses a high energy beam, particularly a CO ₂ laser beam, and blows an assist gas to a welding portion. However, in performing the butt welding, the gist is that the assist gas is supplied from the rear side in the traveling direction of the beam. The preferred assist gas flow rate when performing butt welding using this method is 5
１５15 liters / min.

In the second butt welding method according to the present invention, when performing butt welding using a high energy beam,
The high-energy beam is split into two or more beams, and a straight line connecting the centers of the two or more beams is one to the butted surface of the welding base material.
The gist is that the beam is set to be within the range of 0 to 80 degrees, one beam split is used for preheating the weld metal, and the other beam is used for welding so that welding can be performed efficiently. are doing.

The third butt welding method according to the present invention is a method combining the first welding method and the second welding method,
When performing butt welding while blowing an assist gas onto the weld using a high energy beam, especially a CO ₂ laser beam, the assist gas is supplied from the rear side in the beam traveling direction and the beam is split into two or more beams. The point is that the butt welding is performed by setting the straight line connecting the centers of the two or more beams to be within a range of 10 to 80 degrees with respect to the butt surface of the welding base material.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the conventional butt welding using a CO ₂ laser beam as a heat source, in order to suppress the absorption of the laser beam by the plasma generated in the welding portion by the beam projection and the reduction of the heat input by the welding. In this method, an assist gas is supplied from the front side of the beam projection position to shift the plasma to the rear of the welding position.

On the other hand, plasma generated directly above the welded portion by laser beam welding is usually at a high temperature of about 8000 ° C. or more. Depending on the state of the plasma, the welding base material may be heated by radiant heat from the plasma or retained heat. It seems possible enough. However, the above-mentioned conventional method adopts a method in which the plasma generated immediately above the welded portion is shifted to the rear side of the welded portion by the assist gas. However, radiant heat or retained heat of the plasma cannot be positively used.

The inventors of the present invention have thought that if the radiant heat and retained heat of the plasma are effectively used for preheating the welding base material, the welding efficiency can be further improved. Was. As a result, instead of supplying the assist gas from the front side of the welding position, instead of spraying from the rear side of the welding position toward the front side, and adopting a method of welding while shifting the plasma to the front side of the welding position, It was confirmed that not only the absorption of the laser beam projection energy by the plasma could be prevented, but also that the radiant heat and retained heat of the plasma shifted forward could be effectively used for preheating the welding base metal, and the first aspect of the present invention described above. It is the one that came to the configuration.

FIGS. 4 and 5 are conceptual views showing an embodiment for realizing the technical idea of the first method. The laser output mechanism 8 for projecting a laser beam emits a laser beam 1 from a laser output mechanism 8 toward a welding portion. When performing butt welding while converging and projecting the laser beam, an assist gas nozzle 2 is arranged behind the laser beam 1 projection position, and the assist gas is supplied from the nozzle 2 toward the front side in the welding direction of the welding position. The welding is performed while moving the plasma 7 generated immediately above the welded portion to the position immediately before the welding direction.

If this method is adopted, the base material 3 immediately before welding is preheated by the retained heat or radiant heat of the plasma 7 ′ pushed forward in the welding direction by the assist gas, and welding is performed by the laser beam 1 immediately thereafter. Will be.

That is, if this method is adopted, the plasma 7 generated at the position immediately above the welded portion is pushed forward and is removed from the position where the laser beam 1 is projected. Not only all of the energy is effectively used as welding heat input, but also the plasma 7 'pushed forward is effectively used for preheating the welding base metal 3 immediately before the welding position as described above. Therefore, the combined effect of these effects allows the amount of heat input by the laser beam 1 to be utilized most effectively, and welding can be performed extremely efficiently.

On the other hand, in the conventional example, the plasma 7 'pushed to the rear side of the welding position as shown in FIG.
Since only the surface of the weld metal 6 already welded can be heated, it is not used at all for improving weldability.

FIG. 6 shows that the inclination angle between the central axis of the laser beam 1 and the central axis of the assist gas nozzle 2 is 45 degrees, and the assist gas is sprayed from the front side in the welding direction at a rate of 20 l / min by the conventional method. Based on the backside bead width at the time, when the assist gas flow rate is 10 l / min in the conventional spraying from the front, and when the assist gas flow rate is blown from the rear in the welding direction according to the present invention is 10 l / min. 7 is a graph showing the back bead width formed in FIG. In this figure,
The distance between the tip of the assist gas nozzle 2 and the welded portion (reference numeral L shown in FIG. 5) was set to 12 mm, and the same distance was set to 20 mm.
An example in the case of mm is shown.

As is apparent from this figure, in the conventional method in which the assist gas is blown from the front of the welded portion, the gas flow rate is set to 1
At 0 liter / min, the backside bead width is greatly reduced, whereas the backside bead width is significantly larger in the method of the present invention in which the assist gas is blown from behind the welded portion than in the conventional method. Can be confirmed. This means that even with the same laser beam output, the energy was effectively used as heat input for welding due to the preheating effect of the base metal by the plasma shifted to the front of the weld. are doing.

FIG. 7 shows that the inclination angle between the center axis of the laser beam 1 and the center axis of the assist gas nozzle 2 is 30 degrees.
And the assist gas flow rate is 10 l / min.
Similarly, the back bead width is compared, and it can be seen that the back bead width can be increased by the present invention even when the inclination angle is 30 degrees.

FIG. 8 shows that the inclination angle between the center axis of the laser beam 1 and the center axis of the assist gas nozzle 2 is 45 degrees.
The distance L was set to 12 mm, and the assist gas was blown from the front (conventional method) and the back gas was blown from the rear (method of the present invention). However, according to the method of the present invention, the irregular shape of the bead surface is improved in both cases where the assist gas flow rate is set to 10 l / min and 20 l / min. As is apparent from this figure, according to the present invention, by blowing the assist gas forward from the rear of the welded portion, not only can the bead width be enlarged and the non-penetration welding can be eliminated, but also the bead surface can be eliminated. It can be seen that the unevenness on the side can be reduced, and the joint quality can be improved from both the front and back surfaces of the weld bead.

The blowing angle of the assist gas (FIG. 9)
Angle θ) can be arbitrarily adjusted as long as the plasma can be moved in front of the welded portion. However, in consideration of the structure of the welding equipment and adaptability to various welding parts, the most feasible angle θ range Is 30 degrees or more and 60 degrees or less, more preferably 35 degrees or more and 55 degrees or less. The angle θ is
It is desirable to appropriately adjust taking into consideration the moving speed of the welding device. When the moving speed is high, the blowing angle θ of the assist gas is set relatively large, and when the moving speed is low, the angle θ is set relatively. It is better to make it smaller.

The supply amount of the assist gas is about 20 to 30 liter / min which is generally adopted in the conventional method of supplying from the front side of the welded portion, but is supplied from behind the welded portion. A preferable gas flow rate when the method of the present invention is employed is 5 to 10 liter / min, and it has been confirmed that the use amount of the assist gas can be reduced according to the present invention.

FIG. 10 shows another embodiment in which the shape of the assist gas nozzle 2 is changed, and shows an example in which the nozzle 2 is curved and directed to a welded portion. As described above, in the present invention, the shape of the nozzle 2 itself is not limited at all. In short, any shape and structure of the nozzle can be used as long as the assist gas can be supplied from the rear side to the front side of the welded portion. You can use it. In particular, a curved nozzle as shown in FIG. 10 is advantageous because the entire welding apparatus including the nozzle can be made more compact.

Next, a second butt welding method according to the present invention will be described.

In the first method, as described above, the assist gas is blown from the rear side to the front side of the welded portion, so that the plasma generated immediately above the welded portion is shifted to the front side, so that the radiant heat of the plasma is reduced. Although the actual heat input was increased by preheating the welding base metal with the retained heat, in the second method, the laser beam projected to the weld was split into two or more by a reflector or the like, and the split beam was A part of the beam is used for welding and another beam is used for preheating to improve welding efficiency.

FIG. 11 is an explanatory view exemplifying this method. The laser beam 1 emitted from a laser oscillator (not shown) is split into two by a reflecting mirror 9 and each beam is converged by a convex mirror 10. Is directed to the welded portion as the welding beam 1a, and the other is directed to the base metal portion immediately before the welded portion as the preheating beam 1b. If this method is adopted, the welding base material (weld to be welded) 3 is preheated by the beam 1b for preheating, and immediately thereafter is welded by the beam 1a for welding, so that the amount of penetration during welding is increased. Reliable penetration welding becomes possible.

However, the present inventors have further studied and found that even when such a method is employed, the welding efficiency is deteriorated depending on the positional relationship between the preheating beam 1b and the welding beam 1a, and the bead spectroscopy is performed. In order to make the preheating effect by the expansion of the backside bead width more effective, the line between the center of each bead 1a, 1b to be split and the welding line W, that is, the butted surface of the welding base material 3, 3 'is required. We have found that it is effective to have a moderate angle.

FIG. 12 is an explanatory view exemplifying this state, in which the welding base materials 3 and 3 ′ are welded in the direction of the arrow along the welding line W formed by butting to form a weld joint (weld metal) 6. Shows the situation. In carrying out the second method according to the present invention, as described with reference to FIG. 11, the beam is split into two beams, ie, a welding beam 1a and a preheating beam 1b, and the welding base material is heated to perform butt welding. Do
In FIG. 12, a straight line S connecting the centers of the welding beam 1a and the preheating beam 1b and the welding line W (that is, the butt surface) have an appropriate angle B, and the welding beam 1a is directed on the welding line W. On the other hand, the preheating beam 1b is directed to a position slightly displaced from the welding line W in the direction of the welding base material 3. In this case, as shown by a broken line in FIG.
Of course can be shifted to the side of the welding base material 3 '.

In order to more effectively take advantage of the method of welding with the welding beam 1a immediately after preheating by the preheating beam 1b, both beams 1a and 1b should be directed to the welding line W. Seems to be the most effective. However, the present inventors have confirmed that:
As shown in the drawing, it was found that directing the welding beam 1a and the preheating beam 1b to positions slightly shifted in the width direction is effective for improving the quality of the welded joint.

FIG. 13 shows a case where the angle B formed by the beams 1a and 1b is variously changed when performing butt welding with the arrangement of the beams 1a and 1b as shown in FIG. 9 is a graph showing the results of examining the effects on the front surface dent ratio and the back surface bead width ratio. Here, the dent ratio of the surface of the welded portion represents the ratio of the thickness Y of the central portion of the welded joint to the thickness X of the base material to be butt-welded as shown in FIG. 14 (that is, the degree of the dent at the center of the welded portion). The back bead width ratio is a back bead formed when both beads 1a and 1b are arranged in a straight line along the welding line W and welding is performed (that is, when the angle B is set to zero). Width 1
00 and the ratio to this is shown.

As is apparent from FIG.
It can be seen that the larger the angle B between a and 1b, the smaller the dent ratio of the surface of the welded portion (that is, the more the dent becomes remarkable), whereas the ratio of the back side bead width tends to increase as the angle B increases. Can be In other words, if the back bead width is increased to achieve more reliable penetration welding, the recess at the welded portion becomes larger.

Therefore, in order to obtain a sound weld joint by simultaneously increasing the width of the backside bead and reducing the depression of the welded portion, it is desirable to control the angle B formed by the beam to an optimum range, as shown in FIG. As a result of repeated examinations based on such a tendency, the angle B was 10 to 80 degrees, more preferably 30 to 80 degrees.
It was confirmed that the range of 60 degrees was optimal.

FIG. 12 shows an example in which the welding bead 1a is directed on the welding line W and the preheating bead 1b is directed slightly shifted from the welding line W. For example, as shown in FIG. , 1b can be directed to both sides across the welding line W. Also, the beads can be split into three or more, two or more beads can be used for welding or preheating, and the remaining beads can be used for preheating,
Alternatively, as shown in FIG. 16, for example, by additionally projecting another laser beam 1A in addition to the split beams 1a and 1b, the melting width can be enlarged so that a sounder welded joint can be obtained. Is also possible.

In any case, according to the second method of the present invention, the separated welding and preheating beams are arranged to be spread in the welding width direction, and as a result, the welding bead width is reduced. Since the width of the backside bead is expanded, the penetration of the backside bead becomes wider, so that more reliable penetration welding is performed. In addition, in the case of the method of performing preheating and welding in parallel by splitting the beam in this way, in addition to laser beam welding, it is also possible to adopt other high energy beam welding such as electron beam welding and plasma beam welding. The effect of can be obtained.

In the third method according to the present invention, the first method and the second method, that is, the plasma generated immediately above the welding portion is generated by blowing the assist gas from the rear side in the traveling direction of the beam. Welding efficiency improvement effect (first method) by shifting to the front of the weld and preheating, and separating the high-energy beam into two or more beams, and a straight line connecting the centers of the two or more beams is the By setting the angle to be in the range of 10 to 80 degrees with respect to the abutting surface, the effect of obtaining a sound welded joint by simultaneously increasing the width of the backside bead and reducing the depression of the welded portion is obtained (second method). The additive or synergistic effect of these increases the efficiency of butt welding and enables the formation of a sound weld joint. The individual methods are described in the first and second methods. Do the same as Bayoku, also can be carried out in the same variant.

As described above, according to the present invention, the butt welding using a high-energy beam as a heating source can be performed by carrying out the first method and the second method individually or in combination. It is possible to provide a sound welded joint that can be implemented efficiently and realizes reliable penetration welding.

Therefore, the method of the present invention can be widely used for butt welding of plate-like or tubular objects made of iron-based alloys such as steel or other metal materials, and the characteristics thereof can be effectively exhibited. In particular, the method of the present invention is particularly suitable for tailored blanks (Tailored Blanks:
This technology can be effectively used for welding techniques such as a technique of joining and integrating steel materials having different wall thicknesses or different types of steel materials to form an automobile body by welding.

[0048]

The present invention is configured as described above. When performing butt welding using a high energy beam as a heat source, the direction of spraying the assist gas is devised, or the beam is split into two or more beams. By utilizing one for welding and the other for preheating, or by implementing these methods in combination, the backside bead width can be enlarged to enable more reliable penetration welding, and the bead surface can be welded. Irregularities are suppressed as much as possible, and a sound welded joint can be efficiently performed.

[Brief description of the drawings]

FIG. 1 is an explanatory side view illustrating a conventional laser beam welding method using assist gas blowing.

FIG. 2 is a graph showing a relationship between a flow rate of an assist gas and a width of a backside bead when performing butt welding using a laser beam.

FIG. 3 is a graph showing a relationship between an assist gas flow rate and unevenness generated on a front side bead when performing butt welding using a laser beam.

FIG. 4 is an explanatory side view illustrating a state in which the butt welding of the present invention is performed.

FIG. 5 is an enlarged explanatory diagram of the diagram shown in FIG. 4;

FIG. 6 is a graph showing a comparison of a back side bead width ratio formed when the conventional method and the method of the present invention are employed.

FIG. 7 is a graph showing another example in which the ratio of the rear bead width formed when the conventional method and the method of the present invention are adopted is compared.

FIG. 8 is a graph showing an unevenness ratio of a surface bead formed when the conventional method and the method of the present invention are adopted.

FIG. 9 is an explanatory side view showing a modification of the assist gas blowing direction when the present invention is carried out.

FIG. 10 is an explanatory side view showing a modified example of the assist gas nozzle implemented in the present invention.

FIG. 11 is an explanatory side view showing an example in which a laser beam is split into two and projected.

FIG. 12 is an explanatory plan view showing an embodiment of the present invention in which welding is performed by splitting a laser beam into two parts.

FIG. 13 is a graph showing the effect of the angle B on the rear surface bead width ratio and the weld dent ratio when the angle B between the two split beams is changed.

FIG. 14 is an explanatory diagram showing a calculation standard of a dent ratio of a welded portion.

FIG. 15 is an explanatory plan view showing another example in which welding is performed by skewing two split beams.

FIG. 16 is an explanatory plan view showing another embodiment of the present invention in which a beam is split into two or more beams.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser beam 2 assist gas nozzle 3 welding base metal 4 keyhole 5 molten metal 6 weld metal (weld joint) 7,7 ′ plasma 8 laser oscillator 9 reflecting mirror 10 concave mirror 1a, 1b dispersed bead W welding line (butting surface)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4E066 BA06 BA11 BF08 CA02 CA03 CA08 CB00 4E068 BE00 CD03 CG01 CH06 CH07 DA14 DA15 DB01 DB06

Claims (7)

[Claims] 1. A butt welding method wherein a butt welding is performed from the rear side in a traveling direction of a beam when performing butt welding while supplying an assist gas to a welding portion using a high energy beam. 2. An assist gas flow rate of 5 to 15 liters /
The welding method according to claim 1, wherein the welding time is min. 3. The welding method according to claim 1, wherein a CO ₂ laser beam is used as the high energy beam. 4. When performing butt welding using a high-energy beam, the high-energy beam is split into two or more beams, and a straight line connecting the centers of the two or more beams is defined as 10 to 10 with respect to the butt surface of the welding base material. A butt welding method characterized in that welding is performed with the angle set within 80 degrees. 5. When performing butt welding while supplying an assist gas to a welding portion using a high energy beam, the assist gas is blown from the rear side in the traveling direction of the beam, and the high energy beam is split into two or more beams. , Said 2
A butt welding method, wherein a straight line connecting the centers of the above-mentioned beams is set within a range of 10 to 80 degrees with respect to a butt surface of a welding base material, and welding is performed. 6. An assist gas flow rate of 5 to 15 liters /
The welding method according to claim 5, wherein the welding time is min. 7. The welding method according to claim 5, which is applied to a CO ₂ laser beam welding method.