ALUMINIUM PANEL REPAIR




Precautions upon sheet metal processing


1.Major difference in processing between sheet metal and steel sheet (On the basis of general body shop)
Work description
Aluminium alloy panel
Steel sheet
Hammering
Mallet or plastic hammer
Sheet metal hammer
Washer welding
Not possible
Possible
Gas welding
Not good workability but possible
Possible
Spot welding
Not possible
Possible
MIG welding
Possible by a welding machine for aluminium and argon gas
Possible by a general welding machine and CO2 gas
2.If strong impact is given under low temperature, its strength becomes low and cracking occurs.
3.The springback (returning force to the original condition) is large due to high elastic modules.
4.The thermal effect is large due to high heat conductivity.
5.When excessively heated, its strength will be deteriorated. When heated additionally, it will be melted without discolouration. (The heating temperature is approximately 250°C.)
Material
Melting point
Aluminium
475 to 660 °C (varying with the alloy content)
Steel sheet
1 500 to 2 500 °C
6.
caution Weld and repair it if the side sill reinforcement front is damaged.
Because the material is soft, choose an abrasive carefully. Wear a dustproof mask and safety glasses, because earth particle is light and tends to float in the air.
7.If a disk sander is strongly pressed against the aluminium plate, friction heat is generated, resulting in exfoliation of the aluminium alloy and clogging of the disk sander with the exfoliated particles.
8.Because the clogged disk sander will damage the aluminium alloy panel, replace it with a new one as soon as possible.
9.General tools and sanding tools shall not be shared for both aluminium alloy and steel panels. (Iron powder remaining on the surface may cause electric corrosion with a different type of metal.)
10.During MIG welding, protect the vicinity because the spatters are hard to see and spread father than expected.

Correction of uneven surface



Basically, the same as the steel panel. However, give a consideration to the aluminium alloy characteristics.


1.Repair of sheet metal
(1) Heat with a burner.
caution
  • Heat-up the panel until you feel heat with a keplar work glove on the reverse side of the panel.
  • Keep moving the burner evenly to prevent heat from concentrating in one point.
(2) Because hammering may stretch the panel, use a mallet or plastic hammer.
caution Minimize the stretch and hardening, and give no hammer dent.

2.Distortion check: Grind the surface with #80 to #120-grit sandpaper and then check for distortion.

3.Straightening: Remove distortion by the draw correction procedure with a flattening hammer and a burner.
caution
  • The heating temperature should be approximately 250 °C.
  • Pay particular attention to heating, because it is melted without discolouration by heat.
  • Cover the vicinity of the area to be heated with a wet rag or the like to prevent temperature rise and influence of heat (distortion).
  • Do not use a draw hammer for steel sheets because it may cause the panel crack.

4.Sanding: Grind the surface with a disk sander or a double-action sander.

  • Disk sander: #100 to #120
  • Double-action sander: #150 to #180
caution Aluminium plates are softer than steel sheets, therefore select an appropriate abrasive to prevent the surface from deeply scratched. The heating temperature should be approximately 250 °C.


Correction of cuts and cracks



If cuts, cracks, or holes occur in a steel sheet panel, MIG welding with CO2 is used for repair. However, for an aluminium panel, use MIG or TIG welding with argon gas (inert gas) as shielding gas for repair.

DEGREE OF DISTORTION CAUSED BY WELDING


Gas welding (a large amount of distortion) > TIG welding > MIG welding (a small amount of welding). This manual explains the operation procedure of MIG welding which causes a small amount of distortion by welding heat.

Operation procedure of MIG welding




1.
caution
  • Be careful to avoid excessive stretch of or damage to the panel.
  • Minimise the gap of the butt joint.
Correct the damaged area by hammering lightly while heating it. If any area is stretched by hammering, grind it off with a pneumatic saw.

2.
caution To minimise distortion and meltdown, divide a welding area into several short segments, and weld one segment at a time.
Welding: Use an aluminium dedicated welding machine or a shared welding machine for aluminium and steel sheet for the operation.
Wire diameter: 0.8 or 1.0 mm
(1) Degrease the welding area by white gasoline or the like.
(2) Remove the oxide coat from the welding area, including its back, with a stainless steel wire brush just before welding. Welding shall be started as soon as the oxide coat is removed.

3.
caution Do not over-grind the base of the panel.
Refinish the welding area by a 100-grit disk sander, and then check for any faulty welding by the visible dye penetrate testing.

4.Check for distortion: Grind the surface with #80 to #120-grit sandpaper and then check for distortion.
5.
caution
  • The heating temperature should be approximately 250 °C.
  • Pay particular attention to heating, because it is melted without discolouration by heat.
  • Cover the vicinity of the area to be heated with a wet rag or the like to prevent temperature rise and influence of heat (distortion).
  • Do not use a draw hammer for steel sheets because it may cause the panel crack.
Remove distortion by the draw correction procedure with a flattening hammer and a burner.


6.
caution Remove any spark spot or carbon residue on the surface by a stainless steel wire brush, because they will cause improper painting in the following process.
Finishing: Finish it with a 100- to 120-grit disc sander.

Other welding



TIG WELDING



1.This welding is conducted by the same arc welding method as for MIG welding, however, it uses a welding rod instead of electrode wire.
Wire diameter: 1.6 mm
caution
  • Be careful to avoid excessive stretch of or damage to the panel.
  • Minimise the gap of the butt joint.

GAS WELDING (OXIDE - ACETYLENE)



If gas welding is allowed, the welding can be conducted using a welding rod and flux (oxide coat remover). However, before the welding work, do sufficient practice to avoid distortion by welding heat or poor welding.
Wire diameter: 1.6 mm
1.Heat the welding rod and bond the flux to it.

2.
caution Keep the welding surface as horizontal as possible, because the melted welding rod flows readily.
While melting the flux with the burner to remove the oxide coat, conduct the welding.
3.Remove the flux residue from the panel with a stainless steel wire brush.

Finish with putty




1.Grind the putty-applied area with a 150- to 180-grit double-action sander.
2.Degrease and clean the putty-applied area.
3.Apply 2-liquid type epoxy primer or a pretreatment agent for aluminium.
4.Grind with a 180-grit double-action sander for cutting action.
5.Degrease and clean the putty-applied area.
6.Apply putty for metal sheets, and dry it naturally.
caution Do not dry it forcibly at 60°C or higher.

7.Grind with a 180-grit sander.