Welding Processing in Die Correction

If the velocities between the outside of the profile and the central portion are close to

being equal and the pressure within the die is great enough then a eutectic weld between

consecutive billets will be achieved. The outer friction, as already discussed, is generated by

the bearing surface.The velocity of the extrusion is zero at the end the cycle and the

Aluminium adheres to the bearings. The longer the bearings the greater the force required

to give any change in velocity. The greatest change will be to get the profile moving from rest

at the bearing surface. Therefore, the greatest shearing will occur between the central portion

and the outer portion. The joint weld at this point will be weak and will probably break

during stretching.

If the friction can be reduced at the bearing surface then a more homogeneous

extrusion will be produced. This can easily be achieved by reducing the length of the

bearings. However, there will now be insufficient pressure generated by the bearings to

achieve a weld. If the welding were to take place before the bearings the problem could be

solved.The bearings would then only have to give the profile the correct dimensions.

This can be achieved with a minimal bearing length. The introduction welding chambers and

ports before the die itself will increase pressure within the tool. The design suggested has two

more integral concepts to further generate homogeneous and eutectic welding conditions.The

small port openings generate higher pressures and the fact that they do not feed directly into

the bearings help to give a rise in operating pressures.

The higher number of ports is to optimise the flow and improve the strength of the die, because of the minimal web thickness used to obtain better internal welding. The insides

of the ports and all internal features of the die that come into contact with the Aluminum

should have a low coefficient of friction. A highly polished surface should be sufficient for

this purpose.

This design of die should dramatically reduce " pick-up " and " coring " and give rise to a

strong welded join between billets. It is further likely that higher production speeds are obtainable.