1. Background Downsizing of machine tools can improve space utilization factor, and reduce the price and energy consumption including air conditioning and facility investment. The agility in reconfiguring the manufacturing lines in the factories will be elevated. Furthermore, location of the machines can be spread off the factory floor, to the design office, classrooms and distributed to small manufacturing laboratories, even in residential areas. As technical aspects, the downsizing makes it easier to achieve high-speed machining and high-precision/rigidity motion control due to reduce inertia, and in turn, it leads to higher precision, quality and productivity. With these objectives, a desktop NC milling machine has been developed, using a miniature high-speed spindle. The purpose of the development is to evaluate the technical possibility of extremely downsized machine tools in practice. Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) 1

2. Mechanical design Compact: 450x300 (base)x380(H) Ultra-high speed spindle: 200krpm XY+Z slides: 0.2G, 50mm/s max. feed Rugged: “Housing” construction Custom NC: Full-closed 0.1µm resolution/DNC compatible Low power consumption: 120W Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) Specification of axis mechanisms AxisX (lower)Y (upper)Z (top) Guides Crossed roller guides (2) Crossed roller guides (4) Travel60mm100mm30mm Feed mechanism Ball screw (lead: 2mm) Ball screw (lead: 1mm) Lead screw (lead: 1.5mm) Actuator AC servomotor (30W) DC torque motor (57W) Maximum feed rate 50mm/s 3mm/s Command acceleration 2mm 2 /s 0.5mm 2 /s Encoder (resolution) Optical linear scale (50nm) 2

3. Z-axis drive mechanism Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) Spindle unit High-frequency AC motor up to 200krpm 2 ceramic-ball bearings Collet chuck at the spindle end (1mm dia.) Mist-air coolant for both spindle and cutting point 3

4. Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) NC System overview Notebook PC Video monitor Milling machine Spindle drive NC with console CAD/CAM system 4

5. Step response Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) 2m/s 2 Max. velocity Max. Acceleration Servo gain Ruling law changes depending on the step size! 5

6. NAK55 d = 0.05mm F = 50mm/s Pf= 0.05mm N = 200,000rpm R0.2 WC Downcut Surface finish Sa=0.255µm, Pt=1.35µm Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) A7075 d = 0.05mm F = 12.5mm/s Pf= 0.05mm N = 200,000rpm R0.2 diamond Reciprocating cut Sa=0.106µm, Pt=0.61µm 6

7. Surface finish A7075 Pf = 0.05mm d = 0.05mm F = 50mm/s N = 200krpm Upcut Sa=0.211, Pt=1.22 Reciprocating cut Sa=0.214, Pt=1.26 feed pickfeed feed Surface texture depends on cutting direction Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) 7

8. High-aspect ratio machining Work material ： A7075, Tool: Square end mill Φ0.5, Depth of cut: 0.02mm×100 times=2mm Feedrate: 50mm/s  200 krpm 50 krpm  Fin thickness: 80µm x 2mm x 6mm φ0.5 0.5 Work material: A7075 Tool: Square End mill Φ 0.5 Feedrate: 50mm/s, Depth: 0.02mm x 100times=2mm 50µm 20µm (Inclined! Higher rpm for less damage) Alternatively machined on both sides Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) 8

9. Machined examples Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) 4 0.1 Work material: A7075, Tool: Tapered ball end mill R0.2mm ， 5deg Feed rate: 50mm/s Pick feed: 0.1mm, 0.025mm Depth: 0.05mm x 40 times = 2mm Helical milling Φ150µm x 2mm Workpiece: A7075 (20x20mm) Tool: Ball end mill, R0.2 Max. feedrate: 50mm/s Pick feed: 0.1mm Cutting depth: 0.1mm x 2times Duration: 130 seconds 9

10. Conclusions Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST) Fine Manufacturing System Research Group http://unit.aist.go.jp/imse/finemfg/ (former Mechanical Engineering Laboratory, AIST,Tsukuba) Taking advantages of downsized machine tool, the developed milling machine features high acceleration due to the reduced moving mass even using small actuators, and minimized power consumption, Furthermore, ultra-high speed spindle enables high speed milling on hard materials. High aspect ratio machining was also performed. 10