Manufacturing and production systems: machining, forming, joining, organisation
This domain mixes process knowledge with calculation and production management: cutting parameters, forming and joining choices, tolerances, and how a plant is organised to meet demand.
Machining
- Turning: v_c = π·D·n/1000 in m/min (D in mm); feed f in mm/rev; machining time t = L/(f·n).
- Milling uses feed per tooth and number of teeth; drilling uses the same v_c formula with the drill diameter; grinding gives fine Ra and tight tolerances.
- Material removal rate ≈ v_c·f·a_p for turning.
Forming and casting
Rolling, forging, extrusion, stamping, bending (neutral fibre, bend allowance, springback) and deep drawing. Sand casting needs pattern allowances for shrinkage, draft and machining; die casting suits non-ferrous alloys in large series.
Joining
- Permanent: SMAW (electrode), MIG/MAG (consumable wire with gas), TIG (tungsten electrode, inert gas), resistance spot welding (sheets), brazing and soldering (filler melts, base does not), adhesives, rivets.
- Detachable: threaded fasteners, keys, pins, clamps.
Tolerances and metrology
ISO 286 fits: H7/g6 is a clearance fit, H7/p6 an interference fit. Surface finish Ra in µm, measured against a profiler; tolerances must be functional, not gratuitously tight.
Production organisation
- Takt time = available time/demand. Bottleneck governs throughput (theory of constraints).
- Push (MRP) versus pull (JIT, Kanban); layouts by process, product (line), fixed position or cellular; lean tools 5S, SMED, SPC control charts; scheduling with Gantt charts and CPM critical path.
Worked example
Turning a 200 mm long, Ø60 mm shaft at n = 800 rpm, f = 0.2 mm/rev, depth of cut a_p = 2 mm. v_c = π × 0.060 × 800 = 150.8 m/min. Time per pass t = 200/(0.2 × 800) = 1.25 min. Removal rate = 150 800 mm/min × 0.2 mm × 2 mm = 60 320 mm³/min ≈ 60 cm³/min.
Traps that cost marks
- Feeding D in mm into a formula that expects metres.
- Confusing feed per revolution with feed per minute (multiply by n).
- Forgetting the approach and exit length when timing a cut.
- Calling a welded joint detachable, or a bolted joint permanent.
- Tightening a tolerance without a functional reason, raising cost.