Lätt UHS Repair spot welding Anna de Try och Arne Melander Swerea KIMAB.
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Transcript of Lätt UHS Repair spot welding Anna de Try och Arne Melander Swerea KIMAB.
Aim:
• To determine how different conditions typical to a repair work shop influence spot welding of UHSS.
• To produce corresponding welding diagrams
Five different conditions were investigated in this project:
• The effect of shunt spots • The effect of grinding of the surface of electro coated
steel sheets • The effect of epoxy and rubber-based adhesives• The effect of different misalignments between two
sheet material combinations.• The effect of different electrode forces
Shunt spot effecs
Study with one, two and three spots
with different distance between spots:
(10*t= 15, 20*t=30, 30*t=45, t=1,5mm).
DP1000 Z100 1,5mm
DX54 Z100 1,5mm
Influence of distance between the three spots
DP 1000 Z100 1,5mm
5
5.2
5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
5.8 6 6.2 6.4 6.6 6.8 7
Weld current [kA]
Plu
gg
dia
met
er [
mm
]
0*t one spot
10*t three spots
20*t three spots
30*t three spots
Approved plugg
Linjär (0*t one spot )
Linjär (10*t three spots)
Linjär (20*t three spots )
Linjär (30*t three spots)
DX54 Z100 1,5mm (Three spots)
3
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
7
7.2
7.4
7.6
7.4 7.6 7.8 8 8.2 8.4 8.6 8.8
Weld current [kA]
Plu
gg
dia
met
er [
mm
]
0*t one spot
10*t three spots
20*t Three spots
30*t Three spots
Approved plugg
Linjär (0*t one spot)
Linjär (10*t three spots)
Linjär (20*t Three spots)
Linjär (30*t Three spots)
-0,30
-0,20
-0,10
0,00
0,10
0,20
0,30
0,40
0,50
0,60
0,70
0,80
0,90
1,00
1,10
1,20
str
pun
Avs
*pun
Avs
pun*
str
Avs
*str
Eff
ects
Investigation: svets (MLR)Effects for pluggdiameter
N=52 R2=0,910 R2 Adj.=0,898DF=45 Q2=0,880 RSD=0,1233 Conf. lev.=0,95
Weld
cu
rren
t
Nu
mb
er
of
weld
sp
ots
Effect plot of weld current: Dogal 1000
Nu
mb
er
of
weld
sp
ots
Weld
cu
rren
t
Dis
tan
ce
betw
een
w
eld
sp
ots
cu
rren
t*D
ista
nce
Effect plot of weld current: DX54
Compensation for shunts
• UHSS less sensitive to shunt effects than mild steel• Compensation must however be made when going
from data without shunt to data with shunt• Compensation by increasing current
Effect of ED coat on outside surfaces on spot welds
Two sheets of Dogal 1000DPX Z100 fully ED coated
The contacting surfaces between sheets contain ED coat
The outside surfaces towards electrodes are in three conditions:
Moderately groundWell ground
ED coat condition
Effect of different levels of grinding DP1000 Z100 1,5mm
5
5,2
5,4
5,6
5,8
6
6,2
6,4
6,6
6,8
7
6,2 6,4 6,6 6,8 7 7,2
Weld current [kA]
Plu
gg
dia
me
ter
[mm
]
One spot parent material
Good grinded
Bad grinded
Combination good and bad grinded
Approved plugg
• It is possible to weld with ground outer surface and ED beween sheets but
• Spatter observed originating between sheets in all cases. This is main cause of scatter and difficulty to reach large spot size.
Two cases • Case I
– TDPX1000Z100(1,5mm)-DPX1000Z100(1,5mm)
– Welding through cured and non cured adhesive (one shunt)
• Case II– DPX1000Z100(1,5mm)-
DPX1000Z100(1,5mm)-DX54(0,8mm)
– Welding through cured adhesive ( two shunts)
Effects of epoxy adhesives for DP1000
1,2,3 = weld sequence
Coupon without adhesive Dogal 1000 DPX Z100 1,5mm
Hardening of adhesive
1 2 3
Shunt spot for spot no 2
• Elektrode force = 2,4kN • Elektrode force = 5,0kN
6,8kA/200ms/450ms
D=3mm, Interfacial, ss
6,8kA/200ms/450ms
D=6,0mm, Interfacial, s
8kA/200ms/450ms+6,8kA/200ms/450ms
D=6,9mm, Interfacial, s
8kA/200ms/450ms+6,8kA/200ms/450ms
D=7,8mm, Interfacial, ss
Adhesive – DP1000 Epoxy
• It is possible to weld through adhesive ( cured and non cured) if shunt exist
• Non cured adhesive usually no problem• Problems with spatter for cured adhesive• Larger electrode force -> less risk of spatter• Interfacial failure frequent.• Pre pulse with large current to ”evaporate” cured
adhesive or is often required
1,2,3 = weld sequence
Coupon without adhesive Dogal 1000 DPX Z100 1,5mm
Coupon without adhesive DX54 Z100 0,8mm
Hardening of adhesive
1 2
Shunt spot for spot no 1
Shunt spot for spot no 2
3
Epoxy adhesive – 2*DP1000(1,5mm) + DX54(0,8mm)
Weld data • Electrode force: 2,4kN• Upslope: 200ms• Weld pulse: 700ms• Hold: 400ms • Current: 6,8 – 8,2kA
DX54 0,8mm
DP 1000 Z100 med härdat epoxy lim + två
shuntpunkter
Svetsat utan lim Svetsat i ohärdat lim
Svetsat i härdat lim, treplåts komb.
Three sheet material combination with harden epoxy
4
4,2
4,4
4,6
4,8
5
5,2
5,4
5,6
5,8
6
6,2
6,4
6,6
6,8
7
7,2
7,4
7,6
6,8 7 7,2 7,4 7,6 7,8 8
Weld current [kA]
Plu
gg
dia
met
er [
mm
]
Epoxy
Approved plugg
Spatter avoided at weld time 700ms
Effect of dissplacement on plugg diameter
4
4,2
4,4
4,6
4,8
5
5,2
5,4
5,6
5,8
6
6,2
6,4
6,6
6,8
5,8 6 6,2 6,4 6,6 6,8 7
weld current [kA]
Plu
gg
dia
met
er [
mm
]
a=1mm
a=1,5mm
a=2mm
a=2,5mm
a=0
Approved plugg
Spatter interval a=1,5mm
Spatter interval a=1mm
Spatter interval a=2,0mm
Spatter interval a=2,5mm
Misalignment gives spatter which gives scatter in weld size
Misalignment
• Misalignment gives problems with spatter which can produce scatter in weld size due to loss of weld size
• Increase electrode force might be solution
High electrode force gives small weld size
Effect of different levels of elektorde force
4
4,2
4,4
4,6
4,8
5
5,2
5,4
5,6
5,8
6
6,2
6,4
6,6
6,8
5,8 6 6,2 6,4 6,6 6,8 7
Weld current [kA]
Plu
gg
dia
met
er [
mm
]
190daN
240daN
350daN
550daN
Approved nugget
Electrode force
• Higher electrode force is not always solution to good results since contact resistance is reduced with smaller weld size as result
• Higher electrode force can however be solution to reduce misalignment or reduce spatter from obstacles between sheets such as ED or cured adhesive
Conclusions•Dogal 1000DPX not sensitive to number (1 or more) or distance between shunt spots
•DX54 more sentitive to shunt effect than Dogal 1000DPX
•It is possible to weld through ED coat on inside. No large effect of quality of grinding on outside for Dogal 1000DPX. Large risk of spatter with loss of weld size.
•It is possible to weld through cured and non cured epoxy adhesive if shunt spot is present. Pre pulse or long weld pulse can be needed for cured adhesive. Large risk of spatter
•Misalignment produces problems with spatter
•Difficult to obtain large spot sizes with high electrode force only