We design CAD structures for our customers. What Intellectual Property do we own?

We are a small enterprise in Japan. As part of our services, we design 3d-printable CAD-structures to client specifications. Sometimes, the design of these layouts involves some significant Engineering work. Therefore, we do not merely product 3D models of ready-made parts. Rather, we design 3-dimensional objects from scratch. Because there is so much design & Engineering work involved, what Intellectual Property do we have in the CAD models and the finished printed products? Do we automatically have a Copyright in the design? And what sort of license must we give our customers?