Topic 5 of 6 · Form 6
Casting, forming and sheet metal work
Marking out with developments; cutting (guillotine, snips, nibblers); bending allowances; folding (box and pan folders); wired edges and seams; joining by riveting, soldering and spot welding.
Notes for this topic 1 file, in order
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Casting
- Sand casting: pattern, moulding box (cope and drag), cores, runners, risers and gates; allowances for shrinkage, machining and draft.
- Die casting (pressure and gravity) for high volumes of aluminium and zinc parts.
- Investment (lost-wax) casting for precision and art castings.
- Defects: blowholes, cold shuts, shrinkage cavities and misruns.
Forming
- Forging: hand forging (drawing down, upsetting, bending, punching) and drop forging – improves grain flow and strength.
- Rolling (hot and cold), extrusion, drawing (wire and tube), pressing and deep drawing.
Sheet metal work
Marking out with developments; cutting (guillotine, snips, nibblers); bending allowances; folding (box and pan folders); wired edges and seams; joining by riveting, soldering and spot welding.
Powder metallurgy
Compacting metal powders and sintering – used for self-lubricating bearings and complex small parts.
Process selection
Consider material, shape complexity, quantity, accuracy, surface finish and cost.
Exam tip: Compare casting and forging by grain structure: forging produces continuous grain flow and greater toughness.
Check yourself
- Why is a pattern made slightly larger than the finished casting?
- Give one advantage of drop forging over casting.
- What is sintering?
Show answers
- To allow for shrinkage as the metal cools (and for machining).
- Better grain flow, giving greater strength and toughness.
- Heating compacted metal powder below its melting point so the particles bond together.
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