Metal manufacturing - Managing inventory of unfinished goods during inventory transfer

Hi All!,  We are a metal manufacturer that does CNC machining and fabrication that does mostly special order components.  Currently, all of our "final products"are assembly items and components are the raw materials used to compile the final product.  We've run into a situation where 2 or more of our components may get joined together before the "final product" is made (i.e. before the assembly item is built).  Sometimes we need to send this widget out for services like heat treat, coatings, etc before it gets joined with the rest of the components in the final assembly.  We're struggling to