Metal and Engineering

If your focus area is Metal and Engineering, Sections I and II of your written paper are about the metal and engineering industries (fabrication, machining, foundry, sheet metal and manufacturing): 10 multiple-choice marks and about 15 marks of short answers (roughly six items, at least one worth 4–6 marks), 25 of the 40 written marks. They test Industry Related Manufacturing Technology: the materials, tools, machines, processes, WHS and environmental practices of the industry.

• Materials: ferrous and non-ferrous metals and alloys, their properties, forms of supply (sections, sheet, bar, tube).
• Heat treatment: annealing, normalising, hardening, tempering, case hardening; work hardening.
• Joining: MMAW, GMAW (MIG), GTAW (TIG), oxy-acetylene, brazing and soldering; rivets, bolts, screws and threads.
• Machining and measuring: lathe and drilling operations, cutting speeds, cutting fluids, marking out, micrometers and callipers.
• Forming: sand and die casting, forging, sheet metal work and developments, bending and rolling.
• Finishing: galvanising, powder coating, painting, anodising, electroplating; corrosion.
• CNC and emerging technologies: plasma, laser and waterjet cutting, CNC machining, robotic welding, 3D metal printing.
• WHS: welding hazards, machine guarding, pre-operational checks, fumes, noise, manual handling.

Section II most often asks you to name a machine or tool, give WHS precautions, describe a process step by step (casting, brazing, marking out) or explain why a material or finish suits a product; it sometimes asks you to calculate speeds, masses or costs.

Key properties: ductility (stretch into wire), malleability (hammer or roll into sheet), hardness (resist wear and indentation), toughness (absorb impact), tensile strength, brittleness, conductivity, corrosion resistance. Steel is supplied as flat bar, round and square bar, angle, channel, RHS and SHS (rectangular and square hollow sections), tube, plate and sheet.

Temper colours on polished steel: pale straw (about 230 °C) for scribers and lathe tools; dark straw to brown (about 240–260 °C) for drills and taps; dark straw to purple (about 240–270 °C) for chisels and punches; blue (about 300 °C) for springs and screwdrivers.

Work hardening: cold working (bending, hammering, rolling) makes metal harder and less ductile; annealing restores it. Copper is annealed by heating to a dull red and can then be cooled quickly, unlike steel.

• MMAW ('stick'): a flux-coated consumable electrode; the flux gives shielding gas and slag. Portable, works outdoors; slag must be chipped off.
• GMAW (MIG): continuous wire fed through the gun with shielding gas (often argon and CO₂). Fast and easy to learn; production fabrication.
• GTAW (TIG): non-melting tungsten electrode, argon shield, filler added by hand. Precise, clean; thin sheet, stainless steel and aluminium.
• Oxy-acetylene: a flame for welding, brazing, heating and cutting. Cylinders stored upright and secured, with flashback arrestors fitted.
• Brazing: filler (brass or silver alloy) melts above about 450 °C, below the parts' melting point, and flows into the joint by capillary action; joins dissimilar metals with little distortion. Soft soldering uses filler below 450 °C.
• Mechanical fasteners: bolts, nuts and washers; machine screws in tapped holes; blind (pop) rivets where only one side can be reached; solid rivets.

Threads: ISO metric coarse threads are written M10 × 1.5 (major diameter × pitch). Tapping drill ≈ major diameter − pitch, so M10 × 1.5 needs an 8.5 mm drill. A single-start thread advances one pitch per turn.

Lathe operations: facing, parallel turning, taper turning (compound slide or taper attachment), centre drilling and drilling, boring, parting off, knurling and thread cutting.

Spindle speed:

with $N$ in rpm, cutting speed $V$ in m/min (about 25–30 m/min for mild steel with high-speed steel tools) and diameter $D$ in mm. Smaller diameters need higher speeds. Machining time = length ÷ (feed per revolution × N).

Worked example: drilling a 12 mm hole in mild steel at 24 m/min.

Cutting fluid cools, lubricates, flushes chips and prevents rust. Drilling: centre punch first, use a pilot hole for large drills, clamp the work, correct speed.

Marking out: clean and coat with marking fluid; work from datum edges checked with an engineer's square; scribe lines with a scriber and rule, odd-leg callipers or a height gauge on a surface plate; dot punch then centre punch hole centres. Measuring: steel rule (±0.5 mm), vernier callipers (0.02 or 0.05 mm), outside micrometer (0.01 mm), feeler gauges, dial indicators.

Mass of steel: mass = volume × density (steel about 7850 kg/m³; aluminium about 2700 kg/m³). Convert all dimensions to metres. Worked example: a 1.2 m length of 40 × 6 mm flat bar.

Sand casting: make a pattern (oversize for shrinkage and machining, with draft so it lifts out) → ram sand around it in the drag and cope → form the sprue, runners, gates and riser → remove the pattern, place any cores, close the mould → melt, skim and pour → cool, break out (fettle), cut off the sprue and riser, clean and machine. The riser feeds metal as the casting shrinks.

Pressure die casting forces molten zinc, aluminium or magnesium alloy into steel dies: accurate, fast and smooth, but the dies are expensive, so it suits large runs. Investment (lost wax) casting gives fine detail for jewellery, turbine blades and sculpture.

Forging shapes hot metal by hammering or pressing; the grain flow follows the shape, so forged parts (crankshafts, spanners, hammers) are tough and fatigue resistant. Other forming processes include rolling, extrusion (aluminium sections) and pressing.

Sheet metal: mark out a development (flat pattern), cut with tin snips or a guillotine, fold on a pan brake or folder, roll curves on rollers, and join by spot welding, riveting, seaming or soldering. Hems and wired edges stiffen and make edges safe; their allowance must be added to the development.

• Hot-dip galvanising: dip in molten zinc (about 450 °C); barrier plus sacrificial protection at scratches. Posts, trailers, structural steel.
• Powder coating: dry powder sprayed electrostatically and baked; tough, even film; needs good surface preparation (blasting, pretreatment).
• Paint systems: primer (often zinc-rich) then top coats.
• Anodising: thickens the oxide layer on aluminium; can be dyed.
• Electroplating: deposits chromium, nickel or zinc for corrosion resistance and appearance.
• Galvanic corrosion: dissimilar metals in contact in an electrolyte (such as seawater) make the more active metal corrode faster; insulate them or choose compatible metals.

Parts are drawn in CAD, nested on the sheet and cut by CNC machines:

• Plasma: fast, good on thick mild steel; rougher edge and a heat-affected zone (HAZ).
• Laser: very accurate, fine detail, small HAZ; best on thinner sheet.
• Abrasive waterjet: cuts almost any material with no HAZ; slower.
• CNC lathes and machining centres repeat parts precisely; robotic welding gives consistent welds in mass production; metal 3D printing (powder bed fusion) makes complex, light parts.

These raise accuracy, productivity and material use, but need capital, programming skills and maintenance.

Under the _Work Health and Safety Act 2011_ (NSW) and the WHS Regulation 2017, businesses must identify hazards, assess and control risks, keep Safety Data Sheets for chemicals such as paints, solvents and gases, and consult workers; SafeWork NSW enforces these laws. Always follow the hierarchy of control (eliminate, substitute, isolate or engineer, administrative, PPE) and do pre-operational checks: guards, tooling, work clamped, correct speed, PPE and a clear area.

• Confusing annealing (slow cool, soft) with hardening (quench, hard), or saying tempering makes steel harder.
• Saying mild steel can be hardened by quenching (it has too little carbon; case harden it).
• Mixing up MIG (wire through the gun) and TIG (tungsten electrode), or brazing (above 450 °C) and soldering.
• Swapping brass (zinc) and bronze (tin), or ductility and malleability.
• Forgetting the 1000 or π in the spindle speed formula, or using the bar diameter when drilling.
• Leaving millimetres in a volume calculation with density in kg/m³.
• Giving only PPE as the control for every hazard.

• Describe a process: give the stages in order with the tools, materials and checks at each step.
• Explain a choice: link each property to the product's requirement (for example corrosion resistance for a boat trailer).
• In calculations, write the formula, convert units first, show substitution and give the unit asked for.
• Use precise terms ('quench', 'temper colour', 'heat-affected zone', 'sacrificial protection', 'datum edge').

• Industry Study (Section III): use metal and engineering examples such as CNC and robotic welding replacing manual work, steel prices and imported fabricated steel, apprenticeships (Certificate III in Engineering – Fabrication Trade or Mechanical Trade), the AMWU, welding fume and silica hazards, and recycling of scrap steel and aluminium.
• Major Project: your project's materials testing, processes and WHS procedures are evidence for your folio.