Warm Forming

Warm forming occupies the process window between cold forming (room temperature) and hot forging (above recrystallization temperature). Metal is heated to a controlled temperature that increases its ductility and reduces its flow stress — making it easier to form — without triggering recrystallization, grain growth, or metallurgical fracture.

The Temperature Window

The warm forming range is typically 200 °C to 850 °C, depending on the material. The key constraint is that the temperature must remain below the material’s recrystallization temperature — the point at which new, stress-free grains form. Above recrystallization, work hardening is eliminated and the mechanical property improvements of cold forming are lost.

Temperature Range	Process	Key Characteristics
Ambient (20 °C)	Cold forming	Max work hardening, highest tooling loads, limited to ductile materials
200–850 °C	Warm forming	Increased ductility, reduced load, suitable for difficult materials
Above recrystallization	Hot forging	No work hardening, large deformations possible, scale formation

Above 600 °C, coolant systems and tooling clearances must be modified to account for material expansion and altered lubrication behaviour.

Why Warm Form?

Warm forming is chosen when:

• The material is insufficiently ductile at room temperature — titanium, Inconel, Waspalloy, FA 286 stainless, high-strength alloy steels
• The forming geometry exceeds cold forming limits — very large heads, deep holes, extreme L/D ratios
• Part specifications require warm forming — aerospace standards often specify forming temperature for certain alloys
• Tool life at cold temperature is uneconomically short — reducing temperature reduces flow stress and tooling load

Materials Suitable for Warm Forming

The aerospace and defence industries drive most warm forming applications, due to the prevalence of difficult-to-form high-temperature alloys:

• Stainless steels: commercial grades and FA 286 (iron-nickel-chromium)
• Titanium alloys: Ti 6-2, Ti 6-4 (aerospace fasteners, structural fixings)
• Nickel superalloys: Inconel, Waspalloy (jet engine and gas turbine fasteners)
• High-carbon and alloy steels: grades that work-harden rapidly at room temperature

Induction Pre-Heating

The standard method for warm forming on progressive headers is electronic induction pre-heating of the wire before it enters the machine. An induction coil surrounds the wire path and heats the wire by electromagnetic induction to the target temperature before cutoff.

Induction heating advantages:

• Heats the wire deep inside the core, not only the surface — uniform temperature through the cross-section
• Computer-controlled by the machine — temperature follows production speed automatically
• Reaches target temperature in very short time — high production speed is maintained
• Water-refrigerated coil — safe and reliable in production environments
• No open flame, no combustion products in the work area

On Manzoni machines, the Electronic Induction Pre-Heating System is an optional accessory, applicable to the MC, ME, and MF series for wire diameters from 20 mm to 42 mm.

Process Considerations

Warm forming introduces process variables that cold forming does not have:

• Thermal expansion: tooling clearances must account for the expanded wire diameter at temperature
• Lubrication: standard cold forming lubricants may not function above 300–400 °C; high-temperature lubricants are required
• Scale formation: some materials form an oxide layer at elevated temperature; die design and lubrication must address this
• Cooling between stations: on multi-station machines, the part may cool between stations; tooling must be designed for the actual temperature at each station