BMW 7 Series: Welding Steel Components

IMPORTANT: Comply with the following topics from "Body, General": Safety regulations.

Handling electrical/electronic equipment, airbags and restraint systems.

1. General information

• The following procedures are used for repairs:
  • MAG welding (M etal Ac tive G as welding)
  • Resistance pressure spot welding (referred to in the following and in the repair instructions as spot welding).
• Take the number and location of weld spots and MAG weld seams from the separated part. Replace areas inaccessible to spot-welding tongs with MAG plug/spot welds at the same distance. Diameter of bores for plug/spot welds 8 mm.
• In the case of emissions extraction, observe a minimum distance of 30 cm for MAG welding during the welding process. Otherwise the inert gas would be drawn off.
• Follow the equipment manufacturer's instructions for use.

2. Work materials

• MAG welding:
  • Steel welding apparatus (see WORKSHOP EQUIPMENT ).
  • Steel welding wire - G3SI1 (SG2) or alternatively G4SI1 (SG3)
  • Welding mask
  • Gas bottle containing inert gas (82 % argon, 18 % CO 2)
• Resistance pressure spot welding:
  • Spot-welding apparatus (see WORKSHOP EQUIPMENT ).
  • Protective goggles

3. Preparations for MAG and spot-welding

• Remove the paint coating in an area of approx. 30 mm around the weld seam or spot.
  • The zinc coating underneath must be removed during the MAG welding operation.
  • It is not necessary to remove the zinc coating underneath during spot-welding.
• Remove the paint coating on the reverse side of the weld seam or spot.
  • Contaminants will otherwise enter the weld pool via the root of the weld seam.
  • An insufficient electron flow prevents an optimum spot-weld joint.
• Coat all metal overlaps and weld spot flanges with welding primer.
• To determine the optimum electrode contact force for spot-welding, carry out spot-weld shear tests on sample metal sheets.
• In order to keep the electron flow short during MAG welding on the body, you must if possible attach the ground terminal directly to the component to be welded.

4. Welding

• During MAG welding, the weld gap must be kept as small as possible. The larger the weld gap, the lower will be the strength of the joint.
• During spot-welding, the metal flanges to be joined must be placed as close together as possible without gaps.

  The larger the gap, the lower will be the strength of the joint.

  Minimum gap between welding spots 25 mm.

5. Subsequent treatment of weld joints

• When grinding a weld seam, do not grind thin the base material next to the seam.
• After joining, clean all weld seams and spots with a stainless steel wire brush.
• Remove burnt paint with a stainless steel wire brush.
• All weld joints sealed off with body sealing compound in original state must be primed and sealed off again thoroughly after repairing. Replace damaged or removed anti-drumming layers.

Working With 2-Component PU Cavity Foam

Sourcing reference for cavity foam, refer to BMW Parts Service.

Properties of cavity foam:

• 2-component PU foam, solvent-free.
• Excellent flow capacity, enabling complete sealing of cavities.
• Good strength, preventing slipping in cavities.
• Low water absorption, preventing corrosion.
• Ideal for use as insulating and sealing compound

Information on dangers/hazards

• Avoid eye and skin contact.

  Wear protective goggles, solvent-resistant protective gloves and protective clothing.

• Do not inhale.

  Apply in well ventilated rooms only.

WARNING: Application time after mixing: within 8 minutes!

• Completely empty open can after use.
• Remaining amounts which are not used can cause the can to explode on account of a chemical reaction (buildup of heat)! Alternatively, cool the can containing the non-removed remaining amount for several hours in cold water.
• Do not eat, drink or smoke during this operation.
• Keep heat and ignition sources well away.
• Read the manufacturer's information on hazards/dangers (printed on the can) prior to application.

Application instructions

• Use by date on can.

  Do not use the spray can after the Use by date on the can has expired. After the Use by date the properties of the cavity foam will no longer meet the requirements of the BMW Group.

• Cavity sealing of repair area possible after an air drying time of 1 hour.
• Backing surface must be
  clean and free from
  dust,
  grease,
  oil and stripping agent.
• Application temperature at least 15ºC. Optimally 20ºC.
• Remove fresh, non-hardened PU foam with adhesive cleaner 208.

  Sourcing reference: BMW Parts Service.

  Hardened PU foam can only be removed by mechanical means (machine).

• Excess, hardened PU foam can be disposed of as residual waste.

  Cans which are not entirely empty and unused whose Use by date has expired are classed as hazardous waste.

  Observe country-specific waste-disposal regulations.

• Observe the manufacturer's application instructions (printed on the can).
• IMPORTANT: Foam expands many times over as it sets (change in volume).
• Setting takes approx. 30 minutes. Mechanical processing (e.g. drilling, cutting, etc.) is then possible.

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