hotworking

Hotworking, or hot forming, is a metal forming process conducted at elevated temperatures above the recrystallization temperature and below the melting point. Heating lowers flow stress, enabling large plastic deformations and the shaping of complex geometries that are difficult to achieve at room temperature. It reduces work hardening but can cause grain growth and surface scale if not controlled.

Common hotworking methods include forging (open-die, closed-die, and drop forging), extrusion, rolling, and upsetting. Heated blanks are formed between dies, forced through shaped openings, or rolled to thinner sections. Heating is typically accomplished in furnaces or by other heat sources, often with lubricants or protective atmospheres to reduce wear and oxidation.

Operating temperature ranges depend on the alloy and are chosen to balance formability with microstructural control. Key process parameters include temperature, strain rate, and lubrication, all of which influence defect formation and grain size. Post-processing may include heat treatments such as annealing or normalization to refine the microstructure.

Advantages of hotworking include lower forming forces and the ability to produce complex shapes. Disadvantages include grain growth, surface scaling and oxidation, and potential dimensional changes from heating. Safety concerns are significant due to high temperatures, requiring protective equipment, fire controls, permits, ventilation, and appropriate equipment design to manage heat, fumes, and scale.

Applications span automotive components, aerospace parts, gears and shafts, and various structural shapes produced by forming at high temperature.