Manufacturing Processes and Production Engineering: Casting, Welding and Machining
Casting and joining
- Casting: pattern allowances for shrinkage, draft and machining; riser sized by Chvorinov's rule t = B(V/A)² and placed at the hottest section; gating ratio controls turbulence.
- Welding: arc welding uses a consumable or tungsten electrode; TIG suits thin, clean sections, MIG is faster on thicker plate; resistance welding relies on I²Rt at the interface.
- Weld defects: porosity, slag inclusion, lack of penetration, undercut and hot cracking.
Machining and forming
- Cutting speed V = πDN/1000 m/min; feed in mm/rev; depth of cut in mm; MRR ≈ V × f × d.
- Taylor's tool life VT^n = C, with n ≈ 0.1–0.2 for HSS and higher for carbides.
- Merchant circle: 2φ + β − α = 90°, with shear angle φ, friction angle β and rake α.
- Rolling, forging, extrusion and drawing are bulk forming; blanking and piercing are sheet-metal shearing.
Worked example
A tool lasts 60 min at 100 m/min. With n = 0.2, find the speed for 240 min life. C = 100 × 60^0.2 = 100 × 2.268 = 226.8. V₂ = 226.8/240^0.2 = 226.8/2.993 = 75.8 m/min. Quadrupling tool life cuts speed by about 24%, which is the economic trade-off in tool-life selection.
Traps
- Interchanging feed (mm/rev) and depth of cut in MRR.
- Using diameter in mm with V in m/min without dividing by 1000.
- Confusing blanking (slug is the product) with piercing (hole is the product).
- Assuming a positive rake always helps; negative rake strengthens the edge but raises forces.