Engineering Materials and Manufacturing Processes
This section covers Engineering Materials and Manufacturing Processes: ferrous and non-ferrous metals, polymers, composites, properties, casting, forming, welding, machining and heat treatment. The exam tests material selection and process sequencing.
Core rules
- Ferrous metals contain iron; carbon steel properties depend on carbon. Low-carbon steel (about 0.1–0.3% C) is ductile and weldable; high-carbon steel (about 0.6–1.0% C) is hard and wear-resistant but less weldable.
- Cast iron has high compressive strength and damping but low tensile strength; it is brittle. Aluminium is light, corrosion-resistant and a good conductor but has lower strength than steel.
- Casting fills a mould with liquid metal; forging shapes hot metal by compressive force and improves grain flow; rolling reduces thickness; extrusion forces metal through a die; welding joins by heat or pressure.
- Annealing softens and relieves stress; normalising refines grain; hardening produces martensite; tempering reduces brittleness after hardening.
- Machining uses relative tool-work motion: turning on a lathe, drilling with a rotating drill, milling with a rotating cutter.
Worked example
A shaft needs a tough core and a hard, wear-resistant surface. Choose low-carbon steel, carburise the surface, quench, then temper. Carburising adds carbon to the skin; quenching hardens it; tempering relieves stress and retains toughness. Choosing 0.9% carbon through-hardened steel would make the whole section hard and brittle.
Traps
Hardness is not toughness. Cast iron is not generally welded easily. Do not temper before hardening. Do not call rolling a casting process.