Splicing of load-bearing chassis parts

Some damage does not justify either a complete replacement of a body panel or simple patching. Here scarfing comes into play: a technique where only the damaged part of a panel or load-bearing construction part is replaced while the rest is preserved. The body technician training regulations require that you can plan and perform scarfing tasks both on non-load-bearing structures and – with stricter requirements – on load-bearing parts of the vehicle's structure, including proper corrosion protection and sealing.

With scarfing the damaged section is cut out and a new section of the same material is put in its place and joined along a defined cut. The advantage is that you only replace what is actually damaged which saves material and time compared to replacing the whole part. The disadvantage is that the cut must be placed very precisely — too far from the damage and you remove unnecessarily much original structure; too close and you risk the joint in an area that is still weakened.

Non-load-bearing parts like outer panels and certain fittings allow more flexibility in where and how you splice. Load-bearing parts — those that are part of the collision structure and carry forces through the body in a crash — instead require that you only cut and assemble at the points the manufacturer has approved as 'splice zones'. These points are chosen because they lie outside the most stressed areas and because the original material strength is easier to restore there.

The factory's cathodic dip coating (KTL) protects the body from inside out, but that protection is broken when you cut into the plate. Therefore, the new joint must be treated with primer, sealant, and cavity wax so the exposed metal does not become a starting point for rust. If you skip this step, otherwise correctly executed welding can still develop rust from inside within a few years.

• 01Remove all old paint and any rust around the cut edge before assembly is carried out.
• 02Choose joining method (welding or adhesive) based on manufacturer's material specification.
• 03Apply primer to exposed metal immediately after joining.
• 04Seal the joint externally and fill relevant cavities with cavity wax.
• 05Check sealing visually before coating begins.

After welding the geometry is measured against reference points, often using a layout table, to confirm that the part is correctly positioned in all three dimensions. Welds or glued joints are checked according to the criteria of the chosen method, and the seal is checked before the plate goes on to primer preparation. Only when all three checks are passed is the joint ready for the final surface treatment.