Dear Sir,

It would be ideal , if the strain gauge is applied adjacent to the clamped area( referably radially outwards from the bore)

The clamping force in this case is a function of the axial travel of the mandrel which in turn is a function of the elasticity of : a) the mandrel material, b) collet material, c) clamped material  .

For force balance :

F = F1 + F2 + F3

F = force due to hydraulic pressure, ( pressure x area)

F1 = horizontal component of friction force between the mandrel and collet.

F2 = force required for elastic expansion / deflection (consider the collet as a cantilever beam).

F3= clamping force.( This will be a function of the clamped material modulus)

Or

For displacement balance:

D= d1 +d2+d3.

D = axial travel of the mandrel after zero clearance between the collet and the workpiece.

D1 = contraction in the mandrel

D2 = contraction in the collet.

D3 = expansion in the clamped component.

D1 and D2 can be calculated from the elastic properties of the materials and knowing the clamping pressures.

Thanks a lot for your kind reply.

My question was as a result of my ongoing PhD. work.

Your answer is very supportive. I am exactly working as per your answer. Regarding force F as you mentioned, F1 is known or say it is decided by designer. F2 is not known but I have derived deflection equation for a stepped and taper cantilever beam with uniform loading. F3 is not yet know. I have again mechanics to solve F3 but unless really I measure F3, I can't validate it.  That's why I need to measure it.

Thanks again.

Hi

A low tech way to measure the axial travel of the mandrel might be to take a fixed thin diameter object, e.g. a steel wire and use a fixed position light source to cast a shadow across the dimension pattern you have on the mandrel. Alternatively, you can tape a mm scale to the mandrel. This would show mandrel extension.

On the same note, a scale that is able to stretch taped to the mandrel can be compared with an unloaded scale attached at one of the ends to show relative displacement. This might be implemented by printing a pattern on a plastic sheet.

As stated, low tech, but maybe enough to get at least part of the job done.

If you  wish to go more high tech. Why not use a FE model, measure deflection e.g. using image analysis or multiple measurement locations of your measurement clock (if the process is static) and work loads out from inverse analysis, i.e. apply displacements as loads and compute force/stress?

Sincerely

Claes

Sir, 

i think that to measure the clamping force you will have to make slight modifications in the setup.  Inplace of the clamped item, place a internally expanding ring connected to  a hydraulic setup which can be pressurised, The hydraulic pressure in the expanding ring must be measured .( you will need six small pistons, actuated by the collet ).

By this setup  you can calibrate the clamping arrangement,  by developing a equation relating the input pressure and the clamping force.

Mr. Claes and Mr. Pramod.

Thanks for your guidance and help. I am working on that.