Forging and Smithy: Hot Working Operations
Forging and smithy shape metal in the hot plastic state by hammer blows or press pressure, producing parts with continuous grain flow and good strength. The exam tests forge operations, tools, temperature colours and the reason for heating.
Heating and temperatures
Steel is heated in an open hearth with a blower. Colour indicates temperature: dull red about 550 °C, cherry red about 800 °C, bright red about 900 °C, orange about 1000 °C, yellow about 1100 °C, white about 1300 °C. Forge at orange to yellow; never strike below a low red heat, because cold steel cracks.
Operations
Upsetting (increasing thickness while reducing length), drawing down (reducing section while increasing length), bending on the horn, twisting, punching and drifting a hole, fullering and swaging, flattering, cutting with a hot or cold chisel, and forge (scarf) welding.
Tools
Anvil with face, horn and hardy hole; hearth and tuyere; tongs (flat, pickup, hollow-bit) matched to the section; sledge for the striker and cross-peen or straight-peen hammer for the smith; hot and cold chisels, punch, drift, fuller, flatter and swage block.
Worked example
Reduce the end of a 20 mm bar to 12 mm over 80 mm. Heat the end to bright orange, hold it on the anvil face and strike with the cross peen along the length, rotating the bar a quarter turn between blows. This is drawing down, and the cross peen stretches metal faster than a flat face. Reheat whenever the colour falls to cherry red, because working below that causes surface cracking, then true the section with light flatter blows.
Traps
Thinking forging only shapes metal - it also improves grain structure. Confusing upsetting with drawing down. Using the anvil horn for flat work. Holding hot work with bare hands or the wrong tongs. Quenching a high-carbon forging straight from the fire without a planned heat treatment.