Background Downsizing of machine tools can improve space utilization factor, and reduce the price...

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

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


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 )

2

Z-axis drive mechanism


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

3


NC System overview

Notebook PC

Video monitor

Milling machine

Spindle driveNC with console

CAD/CAM system

4

Step response


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m/sDisplacement

Velocity50mm

2m/s2

Max. velocity

Max. Acceleration

Servo gain

Ruling law changes depending

on the step size!

5

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


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

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


7

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


8

Machined examples


4

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

9

Conclusions


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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Background Downsizing of machine tools can improve space utilization factor, and reduce the price...

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