Meaning
Cold-forming processes create complex cavity shapes by pressing a hardened master tool into a softer steel blank. This technique, known as hobbing, is often used to produce multiple identical cavities for small parts like gears or buttons. The master hob carries the inverse of the desired shape and is forced into the block under hydraulic pressure.
It produces a dense and highly polished surface that requires minimal finishing.
Process Pressure
Generating the force required to displace solid steel demands specialized hydraulic presses. During hobbing, the blank is usually confined in a heavy ring to prevent it from splitting as the metal flows.
Cavity Consistency
Producing many identical cavities is the primary advantage of using a master tool for the process. Every cavity created through hobbing shares the exact dimensions and surface finish of the original master. This ensures that the parts moulded in a multi-cavity tool are interchangeable and consistent.
Steel Selection
Choosing a blank with good flow characteristics is essential for a successful outcome. Steels used for hobbing must be soft enough to deform under pressure but capable of being hardened later. After the shape is formed, the block is heat-treated to provide the durability needed for the injection moulding process.
Low-carbon alloys allow for deeper penetration of the master tool during the pressing phase. Final hardness is achieved through carburizing or vacuum heat treatment once the machining is complete.
