background downsizing of machine tools can improve space utilization factor, and reduce the price...
TRANSCRIPT
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)
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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
Axis X (lower) Y (upper) Z (top)
GuidesCrossed roller
guides (2)Crossed roller
guides (2)Crossed roller
guides (4)
Travel 60mm 100mm 30mm
Feed mechanism
Ball screw (lead: 2mm)
Ball screw
(lead: 1mm)
Lead screw
(lead: 1.5mm)
ActuatorAC servomotor
(30W)AC servomotor
(30W)DC torque motor
(57W)
Maximum feed rate
50mm/s 50mm/s 3mm/s
Command acceleration
2mm2/s 2mm2/s 0.5mm2/s
Encoder (resolution)
Optical linear scale (50nm)
Optical linear scale (50nm)
Optical linear scale (50nm )
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Z-axis drive mechanism
Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST)
送りねじ
Encoder head Spindle unit
Crossed roller guides Slide Ball bearing
DD motor
Nut
Lead screw
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
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Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST)
NC System overview
Notebook PC
Video monitor
Milling machine
Spindle driveNC with console
CAD/CAM system
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Step response
Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST)
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Time ms
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Velocity
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Velocity
Displacement
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Time ms
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t µ
m-0.2
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DisplacementVelocity
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DisplacementVelocity
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Vel
ocity
mm
/sDisplacepent
Velocitty
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Vel
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/sDisplacepent
Velocitty
-1000
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Time ms
Dis
pla
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ent µ
m
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Velo
city
m
m/sDisplacement
Velocity50mm
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Time ms
Dis
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Velo
city
m
m/sDisplacement
Velocity50mm
2m/s2
Max. velocity
Max. Acceleration
Servo gain
Ruling law changes depending
on the step size!
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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
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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)
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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)
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Machined examples
Institute of Mechanical Systems Engineering (IMSE), National Institute of Advanced Science and Technology (AIST)
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0.1
Work material: A7075, Tool: Tapered ball end mill R0.2mm , 5deg
Feed rate: 50mm/sPick feed: 0.1mm, 0.025mm Depth: 0.05mm x 40 times = 2
mm
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
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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.
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