# Calculation of torque in friction welding

1. Feb 20, 2009

### robkm

Hi all.
As part of a Uni project I need to calculate the torque required to rotate one pipe relative to another stationary pipe so the two ends of the pipes are in contact with each other and therefore the rotation and the axial force of the rotation pipe causes friction and melt.

I know at first, when there is no melt and the surfaces are dry, the friction force F is
F=N*μ and therefore Torque, T= ∫ Nμdr (with boundary conditions of r inner and r outer (sorry, not sure how to put them on in equ))

But what I am unsure about is how to calculate Torque when friction has caused the pipes to melt and therefore im guessing the torque is dependent on the melt.

Any ideas would be greatly appreciated.

 Attachment is pic of configuration of pipes 

#### Attached Files:

• ###### friction welding diagram.doc
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2. Feb 20, 2009

### Dr.D

Assuming that the interface actually melts all the way across at the same time (I think this is what is supposed to happen in this operation, isn't it), then it would seem reasonable to model this as a viscous friction, a distributed force proportional to the relative velocity across the interface. With that assumption, I think you have a basis for making a calculation. Whether or not it is a really good model is another matter altogether!

3. Feb 20, 2009

### skeleton

Friction welding does not melt the materials since the temperature is controlled and kept below the melting temperature. It maintains a solid phase during the heat and pressure sequence, which underlay the principles of forging. It is true that the materials will soften (plasticize) at the faying surface and experience some extrusion.

A crude estimate of the required energy for friction welding:
- Identify coefficient for dynamic friction between the two materials.
- Identify coefficient of thermal conductivity of materials.
- Require that (say) 1 mm thickness of each material at faying surface must reach melting temperature (this is upper bound).
- Write energy balance equation.

.. Solve.