A vee block - also known as a female die - is used in combination with a top blade or knife, to bend metal plate.
The figure below shows a multiple vee block.
Vee blocks come in various lengths. The most common is a full length that matches the length of the press brake bed.
When pressing a conical shape you must select the vee block size and length to suit the material thickness and length of the object you are forming.
Two measurements are needed for a pressing operation
The vee block width and bend radius can be calculated but are usually found by referring to a chart on the machine or a data sheet provided by the manufacturer.
If no pressing guide is available, the minimum width (W) of the vee block opening for pressing mild steel is found using this formula:
W = 8 x thickness of plate
Other types of metals will require a wider vee opening.
Using 5mm plate
W = 8 x thickness
= 8 x 5
You can use a narrower vee opening for pressing a conical shape but more tonnage per linear metre is required. This could cause the material to fracture along the outside of the bend.
A larger die opening will create a larger bend radius.
Bending to 90 degrees
Using mild steel and a vee opening of 40mm you would need 47.8 tonnage whereas with a vee opening of 25mm you would need a tonnage of 68.4.
Therefore when pressing a conical shape, the size of the vee block opening will depend on the capability of the press brake you are using.
Recommended vee opening for stainless steel, aluminium and bisalloy is 12 x the material thickness.
The minimum bend radius is calculated by:
Inside radius = 1.5 x thickness of plate
Bend radius = 1.5 x thickness
= 1.5 x 5mm
Data sheets from machine manufacturers give pressing information relating to:
The following chart relates to a 80 tonne hydraulic press brake.
V = vee block opening
IR = inside radius
B = minimum flange length
F = force required to bend
t = material thickness