Engineering Materials and Workshop Technology
This domain covers what parts are made from and how they are cut, formed and finished in the workshop. Expect classification of ferrous and non-ferrous metals, the purpose of each heat treatment, tool selection, and cutting calculations for drilling and turning.
Materials
- Plain carbon steel by carbon content: low (<0.30 % C, ductile, weldable), medium (0.30–0.60 %, hardenable), high (0.60–1.4 %, springs and tools).
- Cast iron holds 2–4 % C: grey iron is cheap, castable and damps vibration but is brittle.
- Non-ferrous: aluminium (light, corrosion-resistant, soft), copper (excellent conductor), brass (Cu-Zn, machinable), bronze (Cu-Sn, bearings).
Heat treatment
Annealing softens and relieves stress by slow cooling; normalizing refines grain structure; hardening quenches (water, oil, air) to form martensite; tempering reheats after quenching to trade some hardness for toughness. Never leave a hardened part untempered.
Workshop practice
Marking out precedes cutting. Hacksaw blade pitch: coarse (14–18 TPI) for thick solid stock, fine (24–32 TPI) for tube and thin sheet. Tapping drill size = major diameter − pitch. Turning speed follows N = 1000v/(πD).
Worked example. Tap an M10 × 1.5 thread: drill = 10 − 1.5 = 8.5 mm. Then drill a 20 mm hole in mild steel at v = 25 m/min: N = (1000 × 25)/(π × 20) ≈ 398 rpm, rounded down to the nearest available machine speed.
Traps. Confusing annealing (soften) with tempering (toughen after hardening); using a coarse blade on thin tube and stripping teeth; drilling the full major diameter before tapping; forgetting that the cutting-speed formula uses diameter in mm and speed in m/min.