Late answer for future researchers.
A tool is created from scratch in two steps (at least).
First you have to create or import the geometry. You can use CATIA for example, to create a product composed by some parts.
Constraints created in the Assembly Design have effect further on the design, but not the Joints, that have to be created in DELMIA.
Do not set up a constraint where you have to define a joint afterwards.
Once you finish your design in CATIA, you have to open the tool in the Device Building workbench in DELMIA. There you are able to define the Frames of Interest, where you must configure the base frame and the tool center point. These two frames are references you will use to show the robot where to pick up the tool and which is the specific point the tool apply its force, spot weld, etc.
Also, you have to define the tool joints and mechanisms, and create the commands to control the tool movements. At this point, you can also create home positions for the tool, that will be useful for positioning for example, the open and close states of a spot welding machine.
Once you completed this tasks, the tool is ready to import into a DELMIA Process as a resource. To be able to use it as a robot tool, you have to "Set Tool" in the Robot Management toolbar. There you will be asked for the base frame and the tool center point. It is also important to create a Tool Profile, that you can use when you are teaching a task to your robot, to specify him which tool his is using at every moment (specially important when you change tools during a process).
A tool can also mounted / unmounted, that is in case you have for example a quick exchanger.