The major differences between a rolled and ground ballscrew are the manufacturing process, the lead error definition and geometrical tolerances.
Chinese FBT Rolled ball screw threads are created by pushing each uncut bar stock blank through rotating tool dies in a single operation. The driving principle behind this process is a cold work deformation process where the blank material is literally shaped by rolling tooling dies which are designed to form both the internal and external threads of the lead screw and ball nut. The rolling process is highly efficient because no material is physically removed from the cut blanks, as would be the case in any cutting or grinding process. The process is widely used throughout the industry because it can be easily automated to achieve high rates of production.
Chinese FBT Ground screw threads are fabricated through an abrasion process that typically occurs in a horizontal setup where the material blanks rotate on their long axis between two machining centers while extremely hard abrasive cutters that are designed to cut a few threads at a time, carve out the threads from the cut blanks. A similar process is employed for both internal and external thread cutting of the lead screw and ball nut. This progressive abrasive machining process requires the material blanks to be cut to final length before grinding. Varying cutter sizes and styles are used to grind the internal vs external threads, but the conceptual process is the same.
The combination of rolled ballscrews and ground nuts has replaced the traditional ACME screws and trapezoidal screws. This makes for a smoother operation while lowering friction and backlash. Moreover, the new technology has the advantage of faster production speed and lower prices.