Manufacturing Processes, Materials, and Welding
This domain asks you to connect a process to a material and a defect mode. Expect cutting-parameter arithmetic, weld process selection, heat treatment terminology and steel designation recognition.
Core rules
- Turning: cutting speed V = πDN/1000 (m/min, D in mm). Machining time = L/(f·N) with f in mm/rev.
- Casting: riser design follows Chvorinov's rule, t = k(V/A)²; a riser must freeze later than the casting it feeds.
- Welding processes: SMAW for site work and dirty steel; GMAW for production speed; GTAW for thin sheet and stainless; SAW for thick plate and long straight seams.
- Common Iranian/DIN steel grades: St37 (≈ S235, weldable structural), St52 (≈ S355). Carbon equivalent CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 predicts weldability; CE > 0.4 needs preheat.
- Heat treatment: annealing softens and relieves stress; normalising refines grain; quenching plus tempering trades hardness for toughness.
Worked example
Turning a 100 mm diameter bar at N = 400 rpm with feed f = 0.2 mm/rev over L = 300 mm. V = π × 100 × 400/1000 = 125.7 m/min. Machining time = L/(f·N) = 300/(0.2 × 400) = 3.75 min per pass.
Traps
- Using radius rather than diameter in V = πDN/1000.
- Choosing GTAW for thick plate where deposition rate is uneconomic.
- Ignoring preheat on a CE above 0.4 and then attributing hydrogen cracking to the filler metal.
- Confusing St37 with a stainless grade; it is plain carbon structural steel.