[Munis]

How can I add extruder as an external axis in Fanuc robot (Fanuc RJ3 post processor).

[Albert]

This section of the documentation shows how you can model and synchronize external axes in RoboDK:
https://robodk.com/doc/en/General.html#ModelRobot

When you generate a program for a Fanuc robot controller, RoboDK will already output the required code for the robot controller. However, you should make sure you properly model the axes and the relationship between the robot and the external axes to match your real setup. You can also configure if you want to use your additional axes as a separate motion group. You can find some configuration flags for the Fanuc RJ3 controller here:
https://robodk.com/post/Fanuc-RJ3