S-K RO, C-J Kim, J-S Oh, S-C Lee, J-Y Shim, S-H Han
Korea Institute of Machinery and Materials,
Keywords: mobile machine tools, crawler mechanism, 3D position measurement with absolute distance laser interferometry, spindle with cutting force cancelation
Summary:For machining features on large workpieces of aerospace, maritime and plant industry with conventional machines, the machine tool system should be large enough to hold large workpieces. These large conventional machines consume energy, space, cost and time including setting up and transferring large works. The mobile machines, which have light configuration and mobility to reach to working position, or on the workpiece, are considered for substitution of conventional large machines. There are efforts to apply mobile machines for on-site processing in large parts of aerospace, shipbuilding and energy industries. Despite of obvious benefits of the mobile machines in manufacturing, there are still technological barriers to reach required performances and productivities. Machining accuracy may suffer in such a machine tool due to the limited structural stiffness, lack of measurement methods in open space and varying gravity directions with machine orientations. This study proposes technologies for a new concept for in-situ machine tools walking on large workpieces including machine mechanisms, machining tools, measurement methods and compensations. A machine with walking mechanism was developed for drilling holes on curved surface with local and global movement. Applying motion tracking camera as global referencing system, sub-mm position accuracy of drilled holes could be demonstrated. As component technologies for future use of mobile machines, spindle with multiple cutters was developed for canceling cutting forces to reduce reaction force affecting machine structure. A novel spindle system with active controlled gyroscopes could absorb torques during drilling process. For measuring global positions with high precision, multi-literation based coordinate measurement system was developed. This system utilized four laser-tracking systems of absolute distance interferometers with femto-second lasers, and 3-dimentional measurement errors less than ±80 ㎛ in 1 m^3 volume were demonstrated.