hot stamp
An impression made in a hot metal forging.
hot stamp: permanent mark pressed into heated metal
A hot stamp is an impression die pressed into a metal workpiece while it is still at forging temperature, typically between 700 and 1100 degrees Celsius depending on the alloy. The heat softens the metal enough that the die sinks in under pressure, creating a permanent raised or recessed mark without the need for secondary machining. This is distinct from cold stamping, which requires either softer metals or significantly higher press force.
The process serves both functional and practical purposes. Functionally, hot stamps create identification marks, serial numbers, or part designations directly into components. They also serve as alignment guides or handling marks during subsequent manufacturing steps. On the practical side, hot stamping while the metal is malleable means lower press tonnage requirements compared to cold work, and the mark typically has better definition because the metal flows into the die cavity more completely.
Common applications and limitations
Hot stamping is routine in forging shops for marking billets, ingots, and finished forgings. It appears frequently on automotive components, turbine blades, and industrial fasteners. The mark is permanent and cannot be accidentally removed by handling or corrosion, making it superior to painted or adhesive identification for traceability in harsh environments. However, the impression must be designed carefully: too sharp or too deep and the die will stick or cause cracking in the cooling metal; too shallow and the mark becomes illegible after light corrosion.
The die itself is made from tool steel, typically H13 or similar heat-resistant grades, because it experiences rapid thermal cycling. Die life varies widely depending on die depth, metal temperature, and part geometry, but dies generally last for thousands of impressions before requiring rework. Improper die cooling or misalignment between die and workpiece can lead to chipping or uneven impressions.
Hot stamping differs from other marking methods in the trade. Stamping done at room temperature requires either much higher force or pre-work-hardened soft metals. Electric marking, laser etching, and chemical etching are alternatives when the workpiece cannot tolerate the heat input or when the mark must be applied after hardening or plating. However, mechanical hot stamping remains fast, cheap, and reliable for high-volume production where the part is already hot.