Manufacturing Processes and Engineering Materials
Core content
Know the process families and what each is good for: casting (sand, die, investment), forming (forging, rolling, extrusion, sheet metal), machining (turning, milling, drilling), joining (welding, brazing, bolting, adhesives) and additive manufacturing. Die casting suits thin, complex non-ferrous parts; forging gives toughness and favourable grain flow; investment casting gives fine detail and finish. Heat treatment of steel: annealing softens and relieves stress, normalising refines grain, quenching forms martensite, and tempering restores toughness. Distinguish strength, hardness, ductility, toughness, fatigue resistance, weldability and corrosion resistance as separate properties. Steel designations often encode carbon content (1045 ≈ 0.45 % C). Non-destructive testing: visual, dye penetrant, magnetic particle (ferrous only), ultrasonic and radiography.
Traps: treating hardness and toughness as interchangeable; assuming quenched martensite is a usable part without tempering; using magnetic particle inspection on austenitic stainless steel; confusing weld defects (porosity, lack of fusion, undercut) with design errors; and ignoring machinability and cost when selecting a material.
Worked example. On a lathe, spindle speed n = 1000V/(πD). For V = 120 m/min and D = 50 mm, n = 1000 × 120/(π × 50) ≈ 764 rpm. Halving the diameter to 25 mm doubles the speed to about 1528 rpm. The trap is dropping the 1000 factor when V is in m/min and D in mm.
Rule of thumb: roughing uses slower speeds and deeper cuts; finishing uses higher speed and light cuts, because surface finish is set mainly by feed per revolution.