How do I create a part model "machined.prt" using a portion (25 mm of 250 mm bar)of bar-stock.prt Model (Extruded bar) as material. I want the Stock model drive the machined part profile. I also need to report in structure

A couple of ideas come to mind...

If by reporting in the structure, you are referring to WTPart Structure in Windchill then there are a couple of trade-offs to consider:

• You could set the stock up as a flexible part with flexible length, constant profile and add it in as a child to machines.asm (rather than machined.prt).  Upside is that this will "build" the structure you want, although you'll probably still want to manipulate the WTPart Structure to remove the each occurrence of stock.prt and replace it with Quantity = XXX and Unit = [length measure].  The disadvantage here is that all of your "machined" features are assembly features which (in my experience) do not publish into the Creo-View Viewable (this is a royal pain with machined weldments where the weldment is modelled as an assembly with material modelled as parts)
• You can set the association type to Contributing Image and manually construct your WTPart Structure.  If you're okay with this, then you could use a merge inheritance feature or imported data (first geometry feature).  This has the advantage of machined features being published in the viewable.  The downside is that you're probably importing a full length of stock and removing a large amount which makes the model bounding box larger than need be.

Are you using a bar-feed machine or cutting the 25mm piece off before doing the machining.

There really is no clean way to show the raw stock part in a structure.

If the part is being cut off first, use a family table with the generic as the full length and dash numbers for different cut off lengths. Then pull the dash number into machine.asm and machine away the chips. One caution is that an assembly cut cannot add material. In a part file, you can add a fillet, but in an assembly, the fillet has to be modeled as the revole feature being subtracted.