Archive for Technical Enquiries

Extrusion dies with split nibs (I). Concentricity

Tungsten carbide dies can have different sizes: from very large to very small. For quite some time, tooling manufacturers have succeeded on developing its technology for cutting the nibs on long enough dies, thus reducing manufacturing costs. Of all tungsten carbide dies, the most demanding for this technology are the extrusion dies, because of the high pressures they are submitted to, which can cause that the upper nib is expelled from the casing.


Is it possible to split the upper nibs?


TEMSA does it quite frequently and with very good results. The nib is cut at a suitable distance above the extrusion. Many customers ask how we can overcome the concentricity problems between the upper and the lower nib. Any small variation will cause the material to grip and eventually breaking the die. TEMSA solves this problem by smoothing the sharp edges on both tungsten carbide nibs creating a small bevel on both edges. This problem can also be solved by making a small radius. Furthermore, the joint of both nibs can be used for adding air events. With this simple method, we can solve those concentricity problems that could appear on the nibs.


Detalle de unión entre núcleos de metal duro para evitar desconcentricidad

Detalle de unión entre núcleos para evitar evitar desvíos de concentricidad

Extrusion dies without a reduction ring

Quite often, the designer of a cold forging process has to bear in mind so many small details that some other really important ones, that could compromise the whole project, can be inadvertently overlooked. We have sometimes noticed this in complex extrusion dies where the designer has forgotten to include a back relief after the extrusion.

If reduction is performed without a reduction ring, then there will be too much friction surface between the material and the die. We must prevent this situation because, due to the pressures and frictions involved, the material will tend to grasp and glue to the internal surface of the extrusion die and this will consequently crack. If the reduction diameter is open few microns, the friction surface will be considerably reduced and the calibrating zone will have a much longer span life. About 2 mm length should be enough.

This we call the reduction ring of an extrusion die.

Extrusion dies without a reduction ring
Design of an extrusion die with the modified by TEMSA

Hexalobular dies with reduction problems

In Hexalobular dies, also called Torx-type dies, we have sometimes found tool designs where the material could not completely fill the calibrating zone down to the desired depth and, consequently, some remained out of it.

When the reduction percentage of the wire in the calibrating zone is equal or higher than 30%, then the wire has a natural tendency to expand itself lengthswise just like a cork in a bottle, meaning that it tends to spring out.
As it is seen in the drawing, this problem can occur when the reduction in the die is not guided. Therefore, if we add a small guide of about 1 mm depth before the hexalobular reduction, the material will not expand lengthwise and thanks to the crosswise pressure, we will force it to enter into the calibrating zone down to the desired depth.

For this kind of dies, having a reduction and an hexalobular profile, TEMSA recommends the TEM4F quality, as this is the carbide quality having the best combination of resilience and hardness required for this application.

Reduction in a Hexalobular die TEMSA

Reduction in a Hexalobular die TEMSA