7.1 Definition

Cold hubbing is a cold bulk forming process where a hardened punch (male hub) penetrates a workpiece at a low speed (slower than extrusion).

7.2 Application of the Process

For the production of cavities in dies for moulding, stamping, injection moulding, plastic moulding and drop forging.

For example:

Screw and bolt production (Figure 7.1 )

Figure 7.1: a) cold hubbed bolt die, b) hub, c) carriage bolt produced by upsetting

The hubbing of screw and bolt head shapes in punches and dies.

Production of cutlery (Figure 7.2 )

Figure 7.2: Forging die for cutlery handle, a) hub, b) hubbed stamping die

The hubbing of cutlery cavities in stamping dies.

The production of forging dies (Figure 7.3 )

Figure 7.3: Cold hubbed cavity in a drop forging die,
a) hub,
b) hubbed cavity

Hubbing cavities in drop forging dies.

7.3 Permissible Deformations

The limits for cold hubbing are derived from the deformability of the tool steels and the permissible maximum surface pressure of the hub. As yet there is, however, no precise method of calculation for this.

7.4 Calculation of Force and Mechanical Work

7.4.1 Hubbing force

equivalent diameter d

• F in N hubbing force

• A in mm ² hub area

• d in mm diameter of the hub

• t in mm hubbing depth

• p _max in N/mm ² specific hubbing force

(from Table 7.1)

Table 7.1: Specific hubbing force p _max in N/mm ² =

t/d