500 has the ability to setup outside process operations on the routing.  In newer versions you can setup either Inventory Items or Non-Inventory Items that represent the outside service that is being preformed.  (In older versions the item had to be an Inventory Item.)

Once you do this, you can add a step to your routing that references the outside service item.  After creating a work order to produce your finished good you can create a purchase order for the service which can be linked to the associated work order step.  Doing so will cause the auto-issue of the service to the work order upon posting the receipt of goods.  If you do not establish the link, you can manually issue the service to the work order.

As always, it would be suggested that you review this in a test environment to ensure that the process and costing is working the way you would like.

Thanks Russ