Shaping and Forming
Shaping and Forming tests how sheet metal is moved into shape without cracking, thinning or losing its intended crown. Exam questions cover stretching, shrinking, planishing, hammer-and-dolly work, English wheels, bead rollers, press work, springback and heat.
Core rules
- Metal moves by stretching (thinning) or shrinking (thickening). A dent is usually reversed by stretching low areas and shrinking high areas, not by random hammering.
- Use a dolly behind the work for support; hammer off-dolly to raise a low area and on-dolly to planish.
- Work in small increments and check shape with a template or profile gauge.
- Anneal work-hardened aluminium carefully; overheating can melt it. Steel may need controlled heat to relieve stress.
- Springback must be allowed for in bending; over-bend slightly and test.
- Use a lubricant on forming tools and keep tools polished to avoid marking.
Worked example
A low-crown aluminium panel has a shallow stretched area. The repairer cleans the panel, supports it on a dolly and uses light hammer blows around the perimeter of the low area to draw metal inward, then planishes with a flat hammer. Heat is avoided because the alloy is thin and easily overheated. Reasoning: controlled stretching around the perimeter raises the low area while preserving thickness.
Traps
Do not hammer directly on a high spot without support; it worsens the stretch. Do not overheat aluminium until it collapses. Do not use a shrinking hammer on an already-thin area. Do not skip planishing; it leaves hammer marks.