General Information On Repair Of Vehicles With Ultra-Strength Steels - AH60.00-P-0024-01N

MODEL 117, 156, 166, 176, 177, 190, 197, 204, 205, 207, 212, 213, 216, 217, 218, 221, 222, 231, 238, 242, 246, 253, 257, 292 

It is essential to observe the notes when straightening/repairing, separating, preparing bonding points, joining/connecting, resistance spot welding and MIG soldering.

Ultra high-strength steels and their joints can otherwise be severely damaged.

Straightening/repairing ultra-high-strength steels 

Planishing and straightening work:

• Do not heat above 300 °C.
• Use a commercially available pulling tool to planish the side longitudinal member, for example. Observe the suitability for resistance welding when installing the pulling adapter (e.g. shims) on ultra high-strength steels.
• Straightening work on ultra high-strength steels can only be accomplished in the event of minor damage (dents).

Cutting ultra-high-strength steels 

Observe the following points:

• Spot welds must be drilled out using special drill bits.
• Spot welds must be milled off using special spot weld milling cutters.
• Cut using special cutting disks Ø 30 mm.
• Use suitable machines for the individual tools.
• Warming up of bonding points:
  • The maximum permissible temperature for heating the flange connection to be released is 200 °C.
  • The ideal temperature for releasing the flange, e.g. using a chisel, is approx. 100 to 120 °C.
  • To preserve adhesive bonds consisting of 3 sheets of metal without permanent damage, do not heat the adhesive bonds to temperatures exceeding 200 °C.
  • After the component has cooled down, the adhesive resumes its original strength.
  • A heat gun is recommended as a heat source.

Prepare gluing points 

The detailed work description included with glue set must be strictly observed.

Otherwise adhesion problems may occur.

Observe pretreatment of bonding surfaces.

Joining/connecting ultra-high-strength steels  Rivet joints:

• Rivet holes must be drilled using special drill bits.
• When processing ultra-high-strength materials, use only high-strength rivets approved by Daimler AG.
• A riveter with increased draw-off strength is required for this purpose.

Resistance spot welding 

The following points must be observed in order to form an optimum weld joint:

• The electrode arms (inverter technology) must be approved for these materials.
• The extension of the electrode arms is limited to the short standard electrode.
• To determine the optimum welding parameter settings and the electrode pressure, perform a snap-out test on a sample plate before performing resistance spot welding on the vehicle (see the following picture below).

MIG soldering 

MIG soldering is only permissible at the repair points described in the workshop information.

Snap-out test on sample panel (old part) on ultra high-strength steels to determine the optimal welding parameter setting  Procedure:

• Determine suitable welding parameters on sample panel (to be removed from old part) in combination with approved spot welders. By completing spot-weld specimen (with adhesive) and performing snap-out test with measurement of weld nugget Ø using formula 4x √t (t = panel thickness).
• The weld nugget diameter (a) should be at least 5 mm. The adhesive should be removed from an adhesive cartridge without mixing tube (mixed by hand).