MITO Collision Repair L4 cheat sheet
MITO Collision Repair L4 · Keep the key ideas within reach.
Collision Repair
Unibody vs body-on-frame: unibody uses the body shell as the structural frame and absorbs impact through crumple zones; body-on-frame isolates the load in a separate ladder frame, so straightening and measuring procedures differ.
Three measuring planes: length (fore-aft), width (side-to-side) and height (vertical). A vehicle is only confirmed straight when all three reference planes match the OEM datum dimensions.
Datum points are OEM-specified reference locations; centreline is the fore-aft axis. Control points must be within OEM tolerance (commonly ±3 mm) before any panel is fitted.
Repair sequence rule: measure and pull the structure first, then align bolt-on panels, then refinish. Refinishing before structural alignment traps misalignment under paint.
High-strength and ultra-high-strength steels (boron/martensitic) must not be heat-treated or straightened; OEM repair information dictates replacement. Heat above roughly 200 °C can destroy the martensitic structure.
Common structural steel classes: mild steel (easy to reform), high-strength steel (HSS, moderate), ultra-high-strength steel (UHSS), and press-hardened/boron steel (replace-only in most OEM procedures).
Crumple zones are designed to deform; occupant cell (safety cage) is designed to resist deformation. Any deformation of the occupant cell requires measurement and OEM-approved repair.
Sectioning rule: only in OEM-approved locations, with the specified joint type (butt, lap or insert), and with corrosion protection restored inside and outside the joint.
Pre-repair vehicle protection: disconnect the battery on HV and modern vehicles, disable SRS per OEM procedure, and record pre-existing damage before any work starts.
Squeeze-type resistance spot welding is the standard for panel joining; parameters (current, time, electrode force, tip size) must match the OEM weld schedule, and destructive test coupons are recommended.