Is it possible to make over mold on teflon?

I wouldn't expect anything to chemically/physically stick to the Teflon, but, by using undercuts or thru-holes in key areas of the Teflon part, you should be able to get another material to stay wrapped around the Teflon. Basically you should design the overmold interfaces such that the Teflon part is physically-constrained inside the over-molded polymer/elastomer. Hope that helps. Regards.

There are ways to treat the surface of the PTFE, so you can stick anything on it.
Terribly expensive, but not impossible.

It is definitely possible to etch PTFE to provide good adhesion. DuPont can, I imagine, give precise details of the “witches’ brew” that is required, as I cannot recall the details. I once dealt with a problem in which a PTFE pad had been bonded into an ABS component that was part of a ski binding and the joint was coming apart. My instinctive reaction then had been that it must be the PTFE surface that was at fault. How wrong I was! The joint had actually failed by tearing a very thin layer (invisible to the naked eye) from the surface of the ABS in a so-called cohesive (rather than adhesive) failure, due to its very high orientation. I suggested a change to moulding conditions for the ABS part, to minimise the shear stresses in mould-filling. It worked. Similar delamination is often the cause of localised lifting of chrome plating, often seen only upon inspection by electron microscopy. Worth checking if plasma can also activate the surface.

Hi John.
Indeed, the surface of PTFE can be treated, so you can glue on it, even paint it. Almost 20 years ago, I made parts for Daimler like this.

Indeed, as Mr. Vandenbosch already told, you have to treat the surface with plasma or electron beam.
I'm not totally agree with you. The cost is depending on how high your production rate should be.
We have both processes in our portfolio, if you want more information just drop me an e-mail with some more details.

Kind Regards

Maybe someone can provide information on the "recipe" for the witches' brew I alluded to? It changed the colour of the PTFE to a brown, I recall (around thirty years ago, so beyond my detailed memory)?

Indeed, the surface was brown. Actually they made another material of it (at the surface only)
I think to remember they etched the surface with a gas, so not with a liquid chemical.
All my PTFE components had to go in a barrel/conclave to be treated with the gas.