Manufacturing and Production Processes
This domain covers how a finished part is produced: casting and moulding, bulk and sheet forming, joining, machining, and the production-system choices behind them. Questions favour allowances, process selection and defect recognition.
Shaping processes
- Sand casting: the pattern is larger than the part by the shrinkage allowance, plus draft and machining allowance. Die casting suits high-volume non-ferrous parts with fine detail.
- Hot working (rolling, forging, extrusion) needs less force and refines grain; cold working gives better surface finish and tolerance but causes work hardening.
- Sheet drawing blank diameter for a cup: D = √(d² + 4dh), where d is cup diameter and h is cup height.
Joining
SMAW uses a flux-coated consumable electrode; MIG uses a continuous wire with shielding gas; TIG uses a non-consumable tungsten electrode with filler added separately. Soldering melts below 450 °C, brazing above it - neither melts the parent metal. Weld defects: porosity (gas), undercut (excess current or travel speed), slag inclusion (poor cleaning between passes).
Systems
Job, batch and mass production differ in volume and repeatability; jigs guide the tool, fixtures hold the work. CNC programs use G-codes for motion and M-codes for machine functions.
Worked example. A cup 50 mm diameter and 40 mm high: D = √(50² + 4 × 50 × 40) = √(2500 + 8000) = √10500 ≈ 102.5 mm blank diameter.
Traps. Applying shrinkage to the casting instead of the pattern; confusing brazing with soldering temperature ranges; assuming a jig and a fixture are the same; ignoring machining allowance on a cast surface that must be finished.