Manufacturing and production systems: machining, forming, joining and metrology
What the exam tests
Process selection for a shape/material/volume, machining parameters, forming and joining, and metrology with tolerances.
Machining
Turning: the workpiece rotates and a single-point tool feeds; cutting speed v = πDN/1000 (m/min), feed f (mm/rev), depth of cut. Milling: multi-tooth cutter, table feed v_f = f_z·z·N. Drilling uses feed per revolution. CNC uses G-code (G01 linear, G02/G03 circular, M03 spindle on). Higher speed raises tool wear; coolant controls heat.
Forming and casting
Rolling (plates, profiles), forging (grain flow, strength), extrusion (constant cross-section), drawing (wire), stamping/deep drawing (sheet). Casting gives complex shapes but can have porosity and shrinkage; sand casting for large parts, die casting for non-ferrous high volume. Powder metallurgy for small precise parts.
Joining
Welding: fusion (MIG/MAG, TIG, arc), resistance spot, laser. The heat-affected zone can reduce strength. Soldering/brazing occur below the parent melting point. Rivets, bolts and adhesives suit disassembly or dissimilar materials.
Metrology
Calliper resolution is typically 0.02 mm; micrometer 0.01 mm; dial gauge 0.01 mm. Vernier reading = main scale + (coincident line × least count). Tolerance = upper − lower limit; fits are clearance, interference or transition. ISO fits: H7/h6 is a clearance location fit; H7/p6 is interference. Surface roughness Ra is in µm. GD&T controls flatness, position, etc.
Worked example
A shaft is specified Ø40.00 ±0.02 mm. The lower limit is 39.98 mm and the upper limit is 40.02 mm. A micrometer reads 40.031 mm. Deviation is +0.031 mm from nominal, so it exceeds the upper limit by 0.011 mm and is rejected. If the fit were H7/g6, the shaft would be smaller than the hole, giving clearance.
Traps
- Mixing diameter and radius in calliper readings.
- Confusing tolerance with allowance.
- Selecting a process before considering batch size and material.
- Forgetting the heat-affected zone or distortion after welding.
- Reading a vernier from the wrong zero.