Tool, Die, Mold and Fixture Making
Tool, die, mold and fixture making is the core of the trade. Exam questions cover die clearance, die sets, bending and drawing calculations, mold design basics, locating principles, and the tool steels that suit each application.
Blanking and piercing
Clearance is applied per side and is a percentage of material thickness - typically 5–10% for mild steel, less for harder alloys, more for soft aluminium. Cutting clearance creates the fracture zone and controls burr height and tool wear. Punch and die edges must be sharp; a worn edge increases burr and stripping force. Strippers hold the strip flat and pull it off the punch. Shear angles on large punches reduce tonnage.
Bending and forming
Bend allowance accounts for the neutral axis: BA = θ × (π/180) × (R + K·T), with K typically 0.33–0.5 depending on R/T. Springback increases with higher-strength material and larger R/T, and is compensated by overbending or coining.
Molds
Every molded part needs draft, usually 1–2° per side, so it releases without scuffing. The parting line is chosen to keep the part in the moving half. Shrinkage is added to the mold cavity, not the part print. Gates, runners, ejector pin locations, and cooling channels are designed around uniform shrinkage and ejection.
Jigs, fixtures and locating
The 3-2-1 rule: three points locate the primary plane, two the secondary, one the tertiary, removing all six degrees of freedom. Clamps should sit over support points, not over air. Fool-proofing prevents wrong-part loading, and chip clearance prevents location error.
Tool steels
O1 is oil-hardening and dimensionally stable for gauges and small punches. A2 air-hardens with minimal distortion for complex dies. D2 offers high wear resistance for long-run blanking. M2 is used for cutting tools. H13 hot-work steel suits die casting and forging; P20 is a pre-hardened mold steel.
Worked example
A 2.0 mm mild steel part is blanked with 6% clearance per side. Per-side clearance = 0.06 × 2.0 = 0.12 mm. If the punch is 30.00 mm, the die opening = 30.00 + 2(0.12) = 30.24 mm. Reasoning: the blank is punched to punch size, so the die is larger by twice the per-side clearance; applying 6% once to the die gives half the required clearance and heavy burring.
Traps
Applying clearance to one side only; forgetting springback; omitting draft in molds; and using K = 0.5 for every bend.