Production method for welded structure
A method of production of a welded structure by butt welding two steel sheets ( 51, 52 ) by laser welding ( 11 ) while supplying assist gas ( 12 ) to a back surface of a melt pool ( 13 ), whereby it is possible to prevent formation of a through hole in the melt part ( 53 ), characterized in that a thickness of at least one steel sheet ( 52 ) of the two steel sheets ( 51, 52 ) is 0.6 mm or less, the assist gas ( 12 ) is a mixed gas ( 12 ) containing 10 to 50 vol % of O 2 gas, and, when an O 2 concentration in the mixed gas ( 12 ) is C (vol %), a flow rate L of mixed gas ( 12 ) (liter/min) satisfies 30 (liter/min)−C(vol %)×1 (liter/min/vol %)≤L (liter/min)<40 (liter/min).
1. A method of producing a welded structure comprising the steps of:
butt welding two steel sheets by laser welding, and
supplying assist gas to a melt pool surface during said butt welding,
wherein a thickness of at least one steel sheet of said two steel sheets is 0.6 mm or less,
said assist gas is a mixed gas containing 10 to 50 vol % of O 2 gas;
when the O 2 concentration in said assist gas is C (vol %), a flow rate L of assist gas (liter/min) is
30
-
C
1
vol
%
≤
L
1
liter
/
min
<
40
,
and
L
1
liter
/
min
≥
10
;
and
when a welding speed is V (m/min), an average thickness of two steel sheets is “t” (mm), and a spot area of the laser is A (mm 2 ), an output of the laser is
1.45
kW
×
V
1
m
/
min
×
t
1
mm
×
A
1
mm
2
to
1.83
kW
×
V
1
m
/
min
×
t
1
mm
×
A
1
mm
2
.
2. The method of producing the welded structure according to claim 1 , wherein a front surface melt width of a melt part of said two steel sheets is made 2.3 times or less a thickness of a thinner steel sheet among the two steel sheets and a back surface melt width is made 0.5 to 1.2 times the melt width of the front surface.
3. The method of producing the welded structure according to claim 2 , wherein the O 2 concentration in said assist gas is 15 to 30 vol %.
4. The method of producing the welded structure according to claim 2 , wherein said assist gas is air.
5. The method of producing the welded structure according to claim 2 , further comprising, supplying said assist gas to said melt pool surface so as to flow in a direction opposite to a weld advancing direction.
6. The method of producing the welded structure according to claim 1 , wherein the O 2 concentration in said assist gas is 15 to 30 vol %.
7. The method of producing the welded structure according to claim 6 , wherein said assist gas is air.
8. The method of producing the welded structure according to claim 6 , further comprising, supplying said assist gas to said melt pool surface so as to flow in a direction opposite to a weld advancing direction.
9. The method of producing the welded structure according to claim 1 , wherein said assist gas is air.
10. The method of producing the welded structure according to claim 9 , further comprising, supplying said assist gas to said melt pool surface so as to flow in a direction opposite to a weld advancing direction.
11. The method of producing the welded structure according to claim 1 , further comprising, supplying said assist gas to said melt pool surface so as to flow in a direction opposite to a weld advancing direction.
12. The method of producing the welded structure according to claim 11 , further comprising, supplying said assist gas so as to intersect the melt pool surface.
13. The method of producing the welded structure according to claim 11 , further comprising, supplying said assist gas so as to intersect the steel sheet in front of said melt pool in the weld advancing direction.
14. The method of producing the welded structure according to claim 1 , wherein said welded structure is a tailored blank material.