Manufacturing Processes
Manufacturing Processes covers material removal, casting, molding, forming, and joining, plus the economics and capability metrics used to choose among them. The exam tests whether you can select a process for a given material, tolerance, and volume - and then defend the choice with numbers.
Process families and what they buy you
- Machining (turning, milling, drilling, grinding): tight tolerances, no tooling amortization, but material waste and longer cycle times. Grinding is for hardness and finish, not bulk removal.
- Casting (sand, die, investment): complex geometry and internal passages; sand uses cheap tooling at low volume, die casting is high volume with high tooling cost.
- Forming (forging, stamping, rolling, extrusion): grain flow, strength, and speed at volume; limited geometry and heavy tooling.
- Joining (arc, laser, resistance welding, brazing, adhesive): arc for structure, laser and resistance for speed, adhesives for dissimilar materials and heat-sensitive parts.
Selection rules that show up on the exam
Tolerance and surface finish narrow the list first; annual volume then decides the tooling investment. Cost per part ≈ (tooling / volume) + material + cycle time × rate. Each process has a capability ceiling: sand casting typically holds about ±0.8 mm on small features, investment casting tighter, and machining can reach ±0.025 mm.
Worked example
A turned shaft: 60 mm diameter, cutting speed 90 m/min, feed 0.25 mm/rev, depth of cut 1.5 mm. Spindle speed n = 1000V/(πD) = 90,000/(3.1416 × 60) ≈ 477 rpm. Material removal rate = 1000 × V × f × d = 1000 × 90 × 0.25 × 1.5 = 33,750 mm³/min. If 405,000 mm³ must be removed, cycle time ≈ 12 min per pass set. Reasonable - but the tolerance callout, not the time, is what rules out casting here.
Traps
Mixing feed units (mm/rev versus mm/min) - multiply feed per revolution by spindle speed. Forgetting that a coarse primary process can be finished by a second one. Confusing blanking (shearing) with punching. Overlooking that heat treatment changes machinability and can shift tolerances after the last cut.