21 4 p.515-5212003

1.

2

0.2mm

Laser Focussed Arc Welding1,2

YAG

* 14 9 514

** J F E Mem b e r , J F E S t e e lCorporation

*** JFEJFE Steel Corporation

**********

Laser- Arc Hybrid Welding of Thin Steel Sheets

By ONO Moriaki**, SHINBO Yukio**, YOSHITAKE Akihide*** and OHMURA Masanori***

In recent years, laser welding has begun to be used for assembly welding of automotive bodies and parts, although it has not yetto be used widely. One restraint is that in laser lap welding, the gap between the lapped sheets must be controlled very tightly. Ifthe gap is wide, burn-through occurs, and, if the gap is excessive, the two sheets cannot be welded together. For this reason, the gapis generally restricted to 0.2 mm or less for laser welding. Laser lap welding of zinc-coated sheets poses additional problems. Whenlap welding of zinc-coated sheets is performed without any gap, the zinc evaporated between the sheets tends to blow off weldmetal, or the zinc vapor tends to remain in the weld metal and form blowholes. Laser-arc hybrid welding was developed to solvethese problems. This newly developed welding method maintains the features of laser welding, in that it is highly efficient and doesnot cause much thermal deformation due to its low heat input. Its proven characteristics are as follows:1 The gap tolerance in hybrid lap welding is nearly equivalent to the thickness of the sheets to be welded, which is significantlylarger than with laser welding.2 The hybrid lap-welded joint can attain a strength that exceeds that of the base metal, because the bead width is wider than thatin laser welding.3 In hybrid lap welding of zinc-coated steel sheets, the formation of blowholes is restrained significantly compared to laserwelding, even when the gap is 0 mm, so that a sound welded joint can be obtained.

Key Words:Hybrid welding, Laser welding, Lap welding, Zinc-coated steel sheet, Blowhole

2.

Fig.1

YAG

1 3mm

YAGYAG

Fig.1 Configuration of laser beam and arc electrode in laser-arc hybrid welding.

516

3.

3.1

0.8mm1.6mm 300

1200MPa

Table1

3.2

4.5kWYAGLuminics

MAG

0.8mm

0.8mm1.6mm

GA

Table2

3.3

3.4

4.

4.1

Fig. 2

3kW100A2m/min

020V

10ms

Fig.2 Time dependence of arc voltage with and without laserirradiation.

Table 2Welding conditions of laser-arc hybrid welding

Table 1Mechanical properties and chemical compositionsof the materials

Fig.3 Appearances of hybrid and arc welded bead surface.Fillet joint upper thickness 0.8mmlower thickness1.2mmWelding conditionLaser output 2kWArc current100ASpeed 2m/min

2120034517

50 100ms

Fig.3

Fig.4

7

1.54.0 1017/cm3 3

1mm

Fig.5

Fig.6

Fig.4 Welding speed limit without humping in arc weldingand that in hybrid welding.

Fig.6 Cross sections of hybrid, laser and arc welded beads.Laser output 3kW, Arc current 100A, Welding speed1m/min

Fig.5 Mechanism of arc discharge with and without laserbeam irradiation.

518

4.2

4.2.1

Fig.7

0.8mm

0.20.4mm

Fig.8

4.2.2

Fig.9 0mm

4.3

Fig.10

1.2mmt

Table

3

Fig.8 Cross section of hybrid and laser welded joints.Laser output 3kW, Arc current 100A, Welding speed3.0m/min

Fig.7 Gap tolerance of lap joint in hybrid and laser welding.

Fig.9 Bead width of hybrid and laser welded joints.

2120034519

Table 3Tensile strength of lap joints by hybrid and laserwelding

Fig.10 Testing specimen for tensile shear strength of lapwelded joint.

Fig.11 Relation between static tensile strength of lap jointand bead width.

Fig.12 Relation between static tensile strength of lap jointand base metal.

Fig.13 Relation between fatigue strength of hybrid, laser andspot welded joint.

Fw

N4

Fw = 1.9W hHv

Wmmmm

Hv

TS=650MPa

250Fig.11

Fig.121.2mmt

520

Fig.14 Appearance of lap joint of zinc coated steel sheetwelded by hybrid welding method.

Fig.15 Appearance and longitudinal cross section of lap jointof zinc coated steel sheet welded by hybrid and laserwelding.

2

590MPa

590

MPa

Fig.13 1.2mm590MPa

2

4.4

9001500

Fig.1445g/m2

2.52.7kW100A

2m/min

3.23.7kW

100A2m/min

Fig.1545g/m2

3.2kW100A

2m/min

3.2kW

2m/min

2120034521

5.

Laser Focussed

Arc Welding

1

2

3

0mm

1M.Hamazaki et.al: Effect on Welding current in TIG-Lasercombined welding, High Temp. Society,19-21983, 79-83inJapanese

2U.Dilthey et al: Prospects by Combining and Coupling LaserBeam and Arc Welding Processes,IIW Doc. XII-15651999

3M.Ono, S.Kosuge, K.Nakada: An Investigation on CO2 La-ser-Induced Plasam Study on CO2 laser Welding PhenomenaReprt --,Quar.J.JWS,10-21992, 31-37. in Japanese

4M.Ono, M.Kabasawa, M.Ohmura:Static and Fatigue Strebgthof Laser Welded Lap Joints, Quar.J.JWS, 14-31996, 586-591in Japanese