machine tool spindle Technology development and future ...sme-japan.org/journal1-nakamura-eng.pdf · case of multitasking lathe, the trend toward speeding up Figure 1:Transition of

© Journal of SME-Japan

TechnologyTechnologyTechnologyTechnology developmentdevelopmentdevelopmentdevelopment andandandand futurefuturefuturefuture challengechallengechallengechallenge ofofofofmachinemachinemachinemachine tooltooltooltool spindlespindlespindlespindle

ShinyaShinyaShinyaShinya NakamuraNakamuraNakamuraNakamuraNSKNSKNSKNSK Ltd.,Ltd.,Ltd.,Ltd., JapanJapanJapanJapan

E-mail: [email protected][Received November 16, 2012; Accepted September 30, 2012]

AbstractAbstractAbstractAbstractIn this paper, the history for this 40 years of spindle speeding up and future technological challenge are

described, at the same time, the latest spindle technology is introduced.

Keywords: Machine tool spindle, Oil-air lubrication, 5-axis machine, Grease replenishing lubrication,Intelligent spindle

1 INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONThe machine tool spindles have been developed with afocus on high-speed technology as the reason behind thatthey aimed the improvement of cutting efficiency by thedevelopment of machining center on 1975 or later, inaccordance with the demand of speeding up wasincreased rapidly.After that the wide range of needs such as higheraccuracy, higher stiffness, and improvement of reliabilityetc. is come out. In addition, the needs in response toenvironment, saving energy, 5-axis machine, multitaskingmachine and intelligent machine are come out. In thisarticle, the history of spindle speeding up and futuretechnological challenge are described, at the same time,the latest spindle technology is introduced.

2222 SPEEDINGSPEEDINGSPEEDINGSPEEDING UPUPUPUP OFOFOFOF SPINDLESPINDLESPINDLESPINDLE2.12.12.12.1 HistoryHistoryHistoryHistory ofofofof spindlespindlespindlespindle speedingspeedingspeedingspeeding upupupupFigure 1 shows the history of spindle speeding up. Thedmn value of spindle bearing has been increased

spectacularly in response with the cutting needs with thetimes. As the key technologies making progress ofspeeding up, the improvement of lubrication method suchas grease lubrication, oil-air lubrication, and jetlubrication, the application of new material to bearings(rolling elements , inner and outer rings and cage) suchas ceramic balls, and the advancement of designapproach and technique of analysis are mentioned.Figure 2 shows the investigation results of high-speedspindle (10000min-1 over) displayed in Japan InternationalMachine Tool Fair (JIMTOF) since 1982. In JIMTOF2010,the progress of speeding up is standstill in recent years,and the maximum rotating speeds are focused on around12000min-1 and 20000min-1. As the features of wholemachines, speaking of machining center, the exhibits of5-axis machining center which has the turning mechanismof spindle(tool side) and table(work side) are increased,and in the case that they are used as processing machineof aircraft components or dies, in order to attain high-efficiency process, high-speed spindle is equipped. Incase of multitasking lathe, the trend toward speeding up

Figure 1: Transition of speeding up of machine tool spindles

Machine processing Automotive components etc.

High-speed processing

for die

50

100

150

200

250

300

350

400

1970 75 949080 85 98 2002

Tapered roller bearing(Forced-circulation oiling)

Angular contact ball bearing

Cylindrical roller bearing

(Grease lubrication) 　

Hybrid

angu

lar co

ntact

ball b

earin

g

(Oil-a

ir lub

ricati

on)

Lathe Milling machine

Machining center NC lathe 　NC milling machine

High-speed machining center

Built-in motor

Ultrahigh -speedHigh-stiffness machining center

Hybrid angular contact ball bearing

(Grease lubrication)

Under

race l

ubric

ation

,

Preloa

d vari

able

spind

le

High-speed specification Small diameter ballCeramic ball bearing

Neobrid angular contact ball

bearing(Grease lubrication)

Hybrid cylindrical roller

bearing(Oil-air lubrication)


Bearing (Oil -air lubrication)

ROBUST Series angular

contact ball bearing


ROBUST Series

Grease

replen

ishing sy

stem

Aircraft components, High-speed aluminum processing

Robust design bearing

Super lean lubrication

Constant pressure built - in spindle

Development era


contact ball bearing,


Oil-air

Spinshot

bearing

Constant p

ressu

re built

-in sp

indle

d mn

valu

e of

mai

n sp

indl

e be

arin

g（×

10４）

2006

New ROBUST Series angular


Oil-air

NEW ROBUST



High-speed・High-stiffness

NC lathe

NEDO

Super lean oil -air lu

brication

Preload shifting built -

in spindle

2010

Cera

mic

angu

lar co

ntac

t ball

bea

ring

Cylin

drica

l rol

ler b

earin

g(Je

t lub

ricat

ion)

Machine processing Automotive components etc.

High-speed processing

for die

50

100

150

200

250

300

350

400

1970 75 949080 85 98 2002

Tapered roller bearing(Forced-circulation oiling)

Angular contact ball bearing


(Grease lubrication) 　

Hybrid

angu

lar co

ntact

ball b

earin

g

(Oil-a

ir lub

ricati

on)

Lathe Milling machine

Machining center NC lathe 　NC milling machine

High-speed machining center

Built-in motor

Ultrahigh -speedHigh-stiffness machining center

Hybrid angular contact ball bearing


Under

race l

ubric

ation

,

Preloa

d vari

able

spind

le

High-speed specification Small diameter ballCeramic ball bearing


bearing(Grease lubrication)

Hybrid cylindrical roller

bearing(Oil-air lubrication)


Bearing (Oil -air lubrication)




ROBUST Series

Grease

replen

ishing sy

stem

Aircraft components, High-speed aluminum processing

Robust design bearing

Super lean lubrication

Constant pressure built - in spindle

Development era


contact ball bearing,


Oil-air

Spinshot

bearing

Constant p

ressu

re built

-in sp

indle

d mn

valu

e of

mai

n sp

indl

e be

arin

g（×

10４）

2006

New ROBUST Series angular


Oil-air

NEW ROBUST



High-speed・High-stiffness

NC lathe

NEDO

Super lean oil -air lu

brication

Preload shifting built -

in spindle

2010

Cera

mic

angu

lar co

ntac

t ball

bea

ring

Cylin

drica

l rol

ler b

earin

g(Je

t lub

ricat

ion)


of milling spindle is remarkable.The so-called built-in motor spindle which the drivingmotor is integrated inside the spindle is become regularuse as it is indispensable technology for high-speedspindle, for the attainment of ultrahigh-speed rotation,further speeding up, high output, and downsizing of therotor and stator are expected. Recently in response toenvironment and saving energy, additional speeding upand improvement of reliability of grease lubrication beginto be required.

2.22.22.22.2 High-speedHigh-speedHigh-speedHigh-speed bearingbearingbearingbearing technologytechnologytechnologytechnologyAs for the high-speed spindle of recent machine tool, inorder to make the inertia of rotating parts, the adoption ofbuilt-in motor spindle which integrates compact and highoutput rotor is increasing. However, in case of suchspindle structure, at the transition period of rapidrotational fluctuation, ambient environmental variation(heat generation change of motor and outer cylindercooling) becomes significant, and the bearing of spindle isexposed under the harsh thermal fluctuation condition.For the spindle bearing, it is the most important to havethe characteristics of seizure resistance under suchenvironmental condition, and it is necessary to havetemperature robust performance (against thermal loadfluctuation, the bearing itself shows small fluctuation of

heat generation value, more specifically, against thethermal disturbance, the bearing has a characteristic ofthermal insensitivity). For these high-speed spindles, torespond the demands described above, the ultrahigh-speed bearings “ROBUST Series”, which bearing internaldesign was optimized as described below are adopted1).(Refer to Figure 3)Under the processing conditions with various cuttingconditions and rotational fluctuation, the temperaturechange inside the spindle is significant and thetemperature difference between inner and outer ringsinvolved, it causes the decrease of bearing internalclearance, the contact angles between balls and racewaygroove of inner and outer rings change rapidly, and theinternal preload of bearing increases, the PV value (P:Contact surface pressure, V: Sliding speed) of rollingcontact area between the raceway groove of inner andouter rings and balls increases. The internal specificationof ROBUST Series bearings is that the change of PVvalue is minimized under the conditions described aboveon the basis of analytical results by the computer as theaffectors such as ball diameter, raceway groove curvatureof inner and outer rings, and contact angle etc. areconsidered the parameters. And the application of specialcarbonitrided steel (SHX steel) and the adoption of high-strength plastic cage of special configuration that has

Figure 2: JIMTOF High-speed spindle display situation (10000min-1 over)Investigated by NSK

Figure 3 : Examples of various ROBUST Series

Ultrahigh-speed angular contact ball bearing Spinshot II bearing Ultrahigh-speed single-row cylindrical roller bearing

1013

1518

2225

2835

4060

100

25th (2

010)

24th (2

008)

23th (2

006)

22th (2

004)

21th (2

002)

20th (2

000)

19th (1

998)

18th (1

996)

17th (1

994)

16th (1

992)

15th (1

990)

14th (1

988)

13th (1

986)

12th (1

984)

11th (1

982)

0

10

20

30

40

50

60

70

SPEEDx1000min-1

Machine processing (Drill, Milling processing)Automotive components etc.

Lathe milling shaft

Aircraft componentsHigh-speed

aluminum

processing

High-speed

processing for die

Internal grinding process

Oil-air lubrication

Built-in spindle

Shaft center cooling

Hybrid cylindrical roller bearingCeramic roller

Hybrid angular Ceramic ball

Ball guided plastic cage TY type

Neobrid angular contact

ROBUST Series

Grease replenishingCylindrical roller

bearingDouble-row cylindrical roller bearing with TB cage

Preload adjustable spindle

Small diameter ball BNC Series

Technologies for speeding upGrease replenishingAngular contact ball bearing

1013

1518

2225

2835

4060

100

25th (2

010)

24th (2

008)

23th (2

006)

22th (2

004)

21th (2

002)

20th (2

000)

19th (1

998)

18th (1

996)

17th (1

994)

16th (1

992)

15th (1

990)

14th (1

988)

13th (1

986)

12th (1

984)

11th (1

982)

0

10

20

30

40

50

60

70

SPEEDx1000min-1

Machine processing (Drill, Milling processing)Automotive components etc.

Lathe milling shaft

Aircraft componentsHigh-speed

aluminum

processing

High-speed

processing for die

Internal grinding process

Oil-air lubrication

Built-in spindle

Shaft center cooling

Hybrid cylindrical roller bearingCeramic roller

Hybrid angular Ceramic ball

Ball guided plastic cage TY type

Neobrid angular contact

ROBUST Series

Grease replenishingCylindrical roller

bearingDouble-row cylindrical roller bearing with TB cage

Preload adjustable spindle

Small diameter ball BNC Series

Technologies for speeding upGrease replenishingAngular contact ball bearing


excellent heat resistance and wear resistance improveseizure resistance additionally. Also, the Spinshotbearings that the lubricating oil is replenished effectivelyunder the condition of high-speed operation by optimizingthe bearing configuration are developed.

3333 TECHNICALTECHNICALTECHNICALTECHNICAL CHALLENGECHALLENGECHALLENGECHALLENGE OFOFOFOF SPINDLESPINDLESPINDLESPINDLEFigure 4 shows the technologies required from themachine tools in Japan in the future. To begin with, thetechnologies required from the machine tools, secondlythe technologies required from the spindle and thebearings were summarized. Until recently thedevelopment of high speed, high accuracy, and highstiffness was focused but recently the durability and theimprovement of reliability are required, especially in thepast several years, the environmental responsiveness,saving energy, and advanced grease lubrication formaintenance-free operation are required. And therequirement of Intelligent and Smart by applying thesensor is increasing.

3.13.13.13.1 MeasuresMeasuresMeasuresMeasures forforforfor highhighhighhigh speedspeedspeedspeed andandandand highhighhighhigh accuracyaccuracyaccuracyaccuracyAs the lubrication method used generally for spindle of

machine tool, grease lubrication,oil-air lubrication and oilmist lubrication etc. are quoted. Depending on the methodof supplying or retaining the lubrication oil or thedifference of quantity, their features are differentrespectively. For the spindle of machine tools, from theaspect of the improvement of machining accuracy, as thebasic characteristics, low heat generation and lowtemperature rise are required.3.1.13.1.13.1.13.1.1 Oil-airOil-airOil-airOil-air lubricationlubricationlubricationlubricationThe oil-air lubrication was developed and put to practicaluse as the suitable lubrication method for ultrahigh-speedrotation by adopting advantages of grease lubrication andoil mist lubrication and by eliminating disadvantagesrespectively. As shown in Figure 5, the oil-air lubricationsystem is that high-pressure air and tiny oil droplet are fedfrom bearing side face to bearing inside with the use of oilfeeding nozzle. In this system, the air curtain which isgenerated by high-speed rotation (the air curtain in thiscase means the wall of circumferential high-speed airstream generated by the friction between the air and high-speed rotating outside surface of inner ring.) blocks the oilflow from the nozzle. As the result, the lubrication oil wasnot fed into the bearing inside certainly, it was likely thecause of seizure. There was the lack of stability in therange where the dmn value exceeding (200-250)x104 .

3.1.23.1.23.1.23.1.2 SpinshotSpinshotSpinshotSpinshot bearingbearingbearingbearingNew bearing “Spinshot II”2) as shown in Figure 6, wasdeveloped to solve the problem described above, and ithas the design specification of improved temperaturerobust performance described in the section 2.2 andspecial bearing structure additionally that the width ofinner ring is wider than that of outer ring and the outsidesurface of inner ring is tapered configuration. By thisconfiguration, the lubrication oil assisted with air, issprayed from the outer ring spacer to the tapered surfaceof outside surface of inner ring, as shown in Figure 7, thelubrication oil is moved on the tapered surface bycentrifugal force of rotation and guided to the inside ofbearing and fed to the rolling elements certainly. Andsince the structure is that the air is not blown to the insideof bearing directly, it is able to control harsh air noise ofhigh frequency due to the air generated by high-speedrotation. In addition, as it is free from the blocking of oil bythe air curtain, it is not necessary to speed up the flowrate of air and it was possible to reduce the air pressure.For the amount of air and oil, it is 10L/min(Normal) perone nozzle, in comparison to conventional oil-airlubrication, about 60% reduction in air consumption wasattained. And in case that the lubrication oil is fedexternally, to realize the stable rotation at ultrahigh-speedrotation, it is important to attach the sensor, which ismonitoring whether the lubrication oil is fed fromlubrication equipment to spindle side certainly or not.3.1.33.1.33.1.33.1.3 DevelopmentDevelopmentDevelopmentDevelopment ofofofof supersupersupersuper leanleanleanlean oil-airoil-airoil-airoil-air lubricationlubricationlubricationlubricationIn order to make further speeding up of oil-air lubrication,as the lubrication method feeding much less quantity oflubrication oil, the super lean oil-air lubrication wasdeveloped. The super lean oil-air lubrication is thesystem feeding lubrication oil by use of air as well as oil-air lubrication, but it is possible to control the dischargerate of 0.001cc or less for one shot. As the spindleadopted the super lean oil-air lubrication, the spindle of

Figure4: Technologies required fromJapanese machine tools in the future

Figure 5: Conventional oil-airsystem

Figure 6: Spinshot system

Figure 7: Lubrication principle of Spinshot II

Needs required fromNeeds required fromNeeds required fromNeeds required frommain spindlemain spindlemain spindlemain spindle Needs required from bearingNeeds required from bearingNeeds required from bearingNeeds required from bearingTechnological needs Technological needs Technological needs Technological needs

required from machinerequired from machinerequired from machinerequired from machine

Measures for Measures for Measures for Measures for environmentenvironmentenvironmentenvironment

Saving energySaving energySaving energySaving energyNo maintenanceNo maintenanceNo maintenanceNo maintenance

Technological advance of grease lubricationTechnological advance of grease lubricationTechnological advance of grease lubricationTechnological advance of grease lubrication・Ultra long life greaseUltra long life greaseUltra long life greaseUltra long life grease・Highly reliable life calculation formulaHighly reliable life calculation formulaHighly reliable life calculation formulaHighly reliable life calculation formula

GeneralGeneralGeneralGeneral----purposepurposepurposepurpose

processingprocessingprocessingprocessing

IntelligentIntelligentIntelligentIntelligent Fusion of main spindle and Fusion of main spindle and Fusion of main spindle and Fusion of main spindle and peripheral technologiesperipheral technologiesperipheral technologiesperipheral technologiesIntelligent main spindle Intelligent main spindle Intelligent main spindle Intelligent main spindle

Intelligent bearing selfIntelligent bearing selfIntelligent bearing selfIntelligent bearing self----inclusivelyinclusivelyinclusivelyinclusively・Bearing with sensorBearing with sensorBearing with sensorBearing with sensor・Establishment of sensing technologyEstablishment of sensing technologyEstablishment of sensing technologyEstablishment of sensing technology

Common Common Common Common technologytechnologytechnologytechnology

　Improvement ofImprovement ofImprovement ofImprovement of　　　　processed processed processed processed 　　surface qualitysurface qualitysurface qualitysurface quality

Tough main spindleTough main spindleTough main spindleTough main spindle

Processing technologyProcessing technologyProcessing technologyProcessing technologyfor difficultfor difficultfor difficultfor difficult----totototo----MachineMachineMachineMachinematerialmaterialmaterialmaterial

Speeding up and high Speeding up and high Speeding up and high Speeding up and high accuracy level of accuracy level of accuracy level of accuracy level of main spindlemain spindlemain spindlemain spindle

Improvement of Improvement of Improvement of Improvement of durability and antidurability and antidurability and antidurability and anti----shocshocshocshockkkk　characteristicscharacteristicscharacteristicscharacteristics

High capacity, High capacity, High capacity, High capacity, high stiffness, high stiffness, high stiffness, high stiffness, and high torqueand high torqueand high torqueand high torque

Improvement of accuracy as Improvement of accuracy as Improvement of accuracy as Improvement of accuracy as bearing selfbearing selfbearing selfbearing self----inclusivelyinclusivelyinclusivelyinclusively

Bearing of high stiffness, antiBearing of high stiffness, antiBearing of high stiffness, antiBearing of high stiffness, anti----shock shock shock shock and antiand antiand antiand anti----vibration,vibration,vibration,vibration,High accuracy of large size bearingHigh accuracy of large size bearingHigh accuracy of large size bearingHigh accuracy of large size bearing

Bearing improved indentation Bearing improved indentation Bearing improved indentation Bearing improved indentation resistance andresistance andresistance andresistance andseizure resistanceseizure resistanceseizure resistanceseizure resistance

ProcessingProcessingProcessingProcessingof dieof dieof dieof die

Processing Processing Processing Processing of aircraft of aircraft of aircraft of aircraft

componentscomponentscomponentscomponents

Processing Processing Processing Processing of automotiveof automotiveof automotiveof automotivecomponentscomponentscomponentscomponents

Needs required fromNeeds required fromNeeds required fromNeeds required frommain spindlemain spindlemain spindlemain spindle Needs required from bearingNeeds required from bearingNeeds required from bearingNeeds required from bearingTechnological needs Technological needs Technological needs Technological needs

required from machinerequired from machinerequired from machinerequired from machine

Measures for Measures for Measures for Measures for environmentenvironmentenvironmentenvironment

Saving energySaving energySaving energySaving energyNo maintenanceNo maintenanceNo maintenanceNo maintenance

Technological advance of grease lubricationTechnological advance of grease lubricationTechnological advance of grease lubricationTechnological advance of grease lubrication・Ultra long life greaseUltra long life greaseUltra long life greaseUltra long life grease・Highly reliable life calculation formulaHighly reliable life calculation formulaHighly reliable life calculation formulaHighly reliable life calculation formula

GeneralGeneralGeneralGeneral----purposepurposepurposepurpose

processingprocessingprocessingprocessing

IntelligentIntelligentIntelligentIntelligent Fusion of main spindle and Fusion of main spindle and Fusion of main spindle and Fusion of main spindle and peripheral technologiesperipheral technologiesperipheral technologiesperipheral technologiesIntelligent main spindle Intelligent main spindle Intelligent main spindle Intelligent main spindle

Intelligent bearing selfIntelligent bearing selfIntelligent bearing selfIntelligent bearing self----inclusivelyinclusivelyinclusivelyinclusively・Bearing with sensorBearing with sensorBearing with sensorBearing with sensor・Establishment of sensing technologyEstablishment of sensing technologyEstablishment of sensing technologyEstablishment of sensing technology

Common Common Common Common technologytechnologytechnologytechnology

　Improvement ofImprovement ofImprovement ofImprovement of　　　　processed processed processed processed 　　surface qualitysurface qualitysurface qualitysurface quality

Tough main spindleTough main spindleTough main spindleTough main spindle

Processing technologyProcessing technologyProcessing technologyProcessing technologyfor difficultfor difficultfor difficultfor difficult----totototo----MachineMachineMachineMachinematerialmaterialmaterialmaterial

Speeding up and high Speeding up and high Speeding up and high Speeding up and high accuracy level of accuracy level of accuracy level of accuracy level of main spindlemain spindlemain spindlemain spindle

Improvement of Improvement of Improvement of Improvement of durability and antidurability and antidurability and antidurability and anti----shocshocshocshockkkk　characteristicscharacteristicscharacteristicscharacteristics

High capacity, High capacity, High capacity, High capacity, high stiffness, high stiffness, high stiffness, high stiffness, and high torqueand high torqueand high torqueand high torque

Improvement of accuracy as Improvement of accuracy as Improvement of accuracy as Improvement of accuracy as bearing selfbearing selfbearing selfbearing self----inclusivelyinclusivelyinclusivelyinclusively

Bearing of high stiffness, antiBearing of high stiffness, antiBearing of high stiffness, antiBearing of high stiffness, anti----shock shock shock shock and antiand antiand antiand anti----vibration,vibration,vibration,vibration,High accuracy of large size bearingHigh accuracy of large size bearingHigh accuracy of large size bearingHigh accuracy of large size bearing

Bearing improved indentation Bearing improved indentation Bearing improved indentation Bearing improved indentation resistance andresistance andresistance andresistance andseizure resistanceseizure resistanceseizure resistanceseizure resistance

ProcessingProcessingProcessingProcessingof dieof dieof dieof die

Processing Processing Processing Processing of aircraft of aircraft of aircraft of aircraft

componentscomponentscomponentscomponents

Processing Processing Processing Processing of automotiveof automotiveof automotiveof automotivecomponentscomponentscomponentscomponents

Air pressure is Air pressure is Air pressure is Air pressure is reduced by groove reduced by groove reduced by groove reduced by groove on theon theon theon the circumferencecircumferencecircumferencecircumference


Flaking point of Flaking point of Flaking point of Flaking point of oil dropletoil dropletoil dropletoil droplet

Centrifugal forceCentrifugal forceCentrifugal forceCentrifugal forceAir flowAir flowAir flowAir flowSurface tensionSurface tensionSurface tensionSurface tension

Oil dropletOil dropletOil dropletOil droplet

Bearing outer ringBearing outer ringBearing outer ringBearing outer ring



Flaking point of Flaking point of Flaking point of Flaking point of oil dropletoil dropletoil dropletoil droplet

Centrifugal forceCentrifugal forceCentrifugal forceCentrifugal forceAir flowAir flowAir flowAir flowSurface tensionSurface tensionSurface tensionSurface tension

Oil dropletOil dropletOil dropletOil droplet

Bearing outer ringBearing outer ringBearing outer ringBearing outer ring


Spindle end taper HSK-E50

Maximum rotatingSpeed (dmn value)

50000min-1(dmn380x104)

Bearing bore diameter Front side Ф60mm,Rear side Ф50mm

Lubrication Super lean oil-air lubrication

Preload type Constant pressure preload

(DT+DT arrangement)

Preload shifting 3 steps preload shifting

the highest speed in the world was developed. Thespecification is that the taper of spindle end is HSK-E50,spindle diameter is 60mm, the maximum rotating speed is50000min-1 (dmn 380x104).In Table 1, the specification is listed and the features of

this spindle are shown in Figure 83). As the first feature,new oil supply and drainage system was adopted. For theoil supply side, by using the super lean oil-air lubricationdescribed above, as shown in Figure 9, in comparisonwith the oil-air lubrication, the flow of oil droplet insidepiping is able to be stabilized and it is possible to controlthe heat generation of bearing and the change oftemperature rise. Also, for the drainage side, newly oilsuction and oil drainage system was adopted. By thismechanism, even if the spindle goes up and down orturns, the lubrication oil does not stay inside the bearingand to be drained easily the change of heat generationinside spindle is controlled and it is possible to stabilize

the temperature rise. Figure 10 shows the flow pattern oflubrication oil supply and drainage inside the bearing.As the second feature, by using tandem duplex bearings(DT+DT) with constant pressure preload, the preloadshifting mechanism (Figure 11) that can control thepreload such as heavy preload at low speed, mediumpreload at medium to high speed, and light preload athigh to ultra-high speed, was adopted. By this preloadshifting system, it can bring about the realization of heavycutting at low speed to ultrahigh-speed cutting. As thethird feature, by attaching MEMS (Micro electromechanical System) temperature sensor inside of thebearing, the temperature around heat source of bearingwas measured. By adopting MEMS temperature sensors,it was able to improve the responsiveness of temperaturemeasurement. And for the needs of speeding up and highrigidity of spindle, the higher speed spindle, the moretechnologically advanced measures are required such asmulti balance control at high-speed rotation and highaccuracy of bearing etc. In addition, in the case of built-inmotor, when the channel of stator cooling oil is not linesymmetry channel to the shaft center of spindle, thethermal displacement in radial direction occurs easily, andthe shaft elongation affects heavily the quality of finishedsurface, so that it is looking forward to the arrival of high-speed bearing and motor with excellent heat generationproperties, and material of low linear expansioncoefficient.

3.23.23.23.2 MeasuresMeasuresMeasuresMeasures forforforfor highhighhighhigh rigidityrigidityrigidityrigidityMeantime, for the aluminum processing profiler asrepresented by aircraft components, since the aluminummaterial has a good machinability, high-speed (high feed)

Figure 8: Features of 50000min-1 Spindle

Figure 9: Comparison result of oil droplet quantitypassing through piping

Figure 10: Flow of lubrication oil inside bearing

Figure 11: Constant pressure 3 steps preload shifting

Table 1: 50000min-1 Spindle specification

1.1.1.1.Adoption of new oil supply and drainage systemAdoption of new oil supply and drainage systemAdoption of new oil supply and drainage systemAdoption of new oil supply and drainage system

①Super lean oil-air lubrication

② Oil suctionOil suctionOil suctionOil suction・OOOOil drainage systemil drainage systemil drainage systemil drainage system

3. 3. 3. 3. Adoption of MEMSAdoption of MEMSAdoption of MEMSAdoption of MEMS

2. 2. 2. 2. Adoption of preload Adoption of preload Adoption of preload Adoption of preload shifting mechanismshifting mechanismshifting mechanismshifting mechanism

1.1.1.1.Adoption of new oil supply and drainage systemAdoption of new oil supply and drainage systemAdoption of new oil supply and drainage systemAdoption of new oil supply and drainage system

①Super lean oil-air lubrication

② Oil suctionOil suctionOil suctionOil suction・OOOOil drainage systemil drainage systemil drainage systemil drainage system

3. 3. 3. 3. Adoption of MEMSAdoption of MEMSAdoption of MEMSAdoption of MEMS

2. 2. 2. 2. Adoption of preload Adoption of preload Adoption of preload Adoption of preload shifting mechanismshifting mechanismshifting mechanismshifting mechanism

Outer ringOuter ringOuter ringOuter ringspacerspacerspacerspacer

Outer ringOuter ringOuter ringOuter ring

Inner ring Inner ring Inner ring Inner ring

Suction holeSuction holeSuction holeSuction hole

Suction groove

BallBallBallBall

CageCageCageCage

Inner ring spacerInner ring spacerInner ring spacerInner ring spacer

Oil supply holeOil supply holeOil supply holeOil supply hole

Outer ringOuter ringOuter ringOuter ringspacerspacerspacerspacer

Outer ringOuter ringOuter ringOuter ring

Inner ring Inner ring Inner ring Inner ring

Suction holeSuction holeSuction holeSuction hole

Suction groove

BallBallBallBall

CageCageCageCage

Inner ring spacerInner ring spacerInner ring spacerInner ring spacer

Oil supply holeOil supply holeOil supply holeOil supply hole

0

20

40

60

80

100

120

140

160

180

200

00:00 05:00 10:00 15:00 20:00 25:00 30:00 35:00 40:00

経過時間 m:s

配管

内通

過油

粒数

/10s

スーパーリーンオイルエア

通常オイルエア

Discharge interval of normal oilDischarge interval of normal oilDischarge interval of normal oilDischarge interval of normal oil----airairairair

Oil droplet image inside piping of normal oilOil droplet image inside piping of normal oilOil droplet image inside piping of normal oilOil droplet image inside piping of normal oil----airairairair

Oil droplet image of super lean oilOil droplet image of super lean oilOil droplet image of super lean oilOil droplet image of super lean oil----airairairair

Qua

ntity

of o

il dr

ople

t pas

sing

thro

ugh

pipi

ngQ

uant

ity o

f oil

drop

let p

assi

ng th

roug

h pi

ping

Qua

ntity

of o

il dr

ople

t pas

sing

thro

ugh

pipi

ngQ

uant

ity o

f oil

drop

let p

assi

ng th

roug

h pi

ping

/103

Normal oilNormal oilNormal oilNormal oil----airairairair

Super lean oilSuper lean oilSuper lean oilSuper lean oil----airairairair

Elapsed timeElapsed timeElapsed timeElapsed time　　(ms) (ms) (ms) (ms)

0

20

40

60

80

100

120

140

160

180

200

00:00 05:00 10:00 15:00 20:00 25:00 30:00 35:00 40:00

経過時間 m:s

配管

内通

過油

粒数

/10s

スーパーリーンオイルエア

通常オイルエア

Discharge interval of normal oilDischarge interval of normal oilDischarge interval of normal oilDischarge interval of normal oil----airairairair

Oil droplet image inside piping of normal oilOil droplet image inside piping of normal oilOil droplet image inside piping of normal oilOil droplet image inside piping of normal oil----airairairair

Oil droplet image of super lean oilOil droplet image of super lean oilOil droplet image of super lean oilOil droplet image of super lean oil----airairairair

Qua

ntity

of o

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ople

t pas

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ugh

pipi

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uant

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let p

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Qua

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t pas

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/103

Normal oilNormal oilNormal oilNormal oil----airairairair

Super lean oilSuper lean oilSuper lean oilSuper lean oil----airairairair

Elapsed timeElapsed timeElapsed timeElapsed time　　(ms) (ms) (ms) (ms)

0

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0 5 10 15 20 25 30 35 40 45 50

回転数 ×1000 min-1

設定

予圧

荷重

N

3000 N

2100 N

1400 N

Pre

load

set

ting

(N

)P

relo

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g (

N)

Pre

load

set

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N)

Rotating speed (x1000minRotating speed (x1000minRotating speed (x1000minRotating speed (x1000min----1111 )

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3500

0 5 10 15 20 25 30 35 40 45 50

回転数 ×1000 min-1

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N

3000 N

2100 N

1400 N

Pre

load

set

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(N

)P

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g (

N)

Pre

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(N

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N)

Rotating speed (x1000minRotating speed (x1000minRotating speed (x1000minRotating speed (x1000min----1111 )


(1) Shortening of overall length (2) Reliability of bearing lubrication structure

●Selection of number of bearing row●Downsizing of bearing system●Downsizing of built-in motor●Shortening of tool clamping mechanism

●Smooth drainage of lubrication oil●User friendliness of piping●Control of grease drop out●Prevention of ingress of coolant

processing is mainstream, and for the spindle, in additionto the speeding up, the high rigidity that is conflictingperformance is required. In addition, for this type ofmachine, the work tends to increase in size, and theturning spindle type is general. In this case, in order toattain fine profile processing of complex and smallcircular arc, the downsizing of spindle is moreadvantageous, but to ensure the compatibility with highrigidity, higher technology level is required.

3.33.33.33.3 MeasuresMeasuresMeasuresMeasures forforforfor 5-axis5-axis5-axis5-axis machinemachinemachinemachine andandandand multitaskingmultitaskingmultitaskingmultitaskingmachinemachinemachinemachine

3.3.13.3.13.3.13.3.1 RequiredRequiredRequiredRequired functionfunctionfunctionfunction inininin casecasecasecase ofofofof tooltooltooltool sidesidesideside turningturningturningturningFor the machine tools of tool side turning, therequired characteristics from spindle,as shown inTable 2, are classif ied by two such as (1) How toshorten the overall spindle length. (2) Reliabili tyof bearing lubrication structure that is able torespond to the position change. The shorteningneeds of item (1) was come from that byshortening the spindle, the oscil lation space ofturning is reduced, the effect on the linear motionshaft is controlled, and to avoid uselessovergrown of the machine, and by downsizing thespindle, the capacity of turning motor isdecreased. For the position change of item (2), isit designed that the reliabil ity of bearinglubrication is not damaged by the positionchange?3.3.23.3.23.3.23.3.2 ShorteningShorteningShorteningShortening ofofofof overalloveralloveralloverall spindlespindlespindlespindle lengthlengthlengthlengthTo increase the load capacity of spindle, by increasing thenumber of bearing row and reducing the load per abearing row is common practice, but the spindle islengthened and it is difficult to use for 5-axis machine ofturning spindle type. As far as the angular contact ballbearing, the matched back-to-back arrangement (DB) isshorter than the four-row back-to-back arrangement(DBB), and for the cylindrical roller bearing, the single-rowis shorter than the double-row, but the load capacity issmaller in each case. Especially in case of multitaskinglathe in comparison to 5-axis machining center, the casethat it is forced to make compromise this point is foundhere and there. In case of the machining center, if 2-axisturning are equipped at work side, this point does notbecome something of a problem. And though the machineadopting turning spindle system in such composition,since the machine itself is large mostly, the problem ishard to become obvious. However, when it is consideredthat the deployment and expansibility of 5-axis machine tovarious processes in the future, it is necessary to takemeasures to shorten the overall length as much aspossible by composing compact bearing system includinglubrication mechanism and by optimizing bearingarrangement inside the spindle.

And recently since the built-in motor is used in thespindle, and the spindle itself becomes compact, forturning spindle system 5-axis machine, the built-in motorspindle is optimum. In such case, since the motor is thefactor determining the overall length of spindle in manycases, the commercialization of smaller size and higheroutput motor is desired.3.3.33.3.33.3.33.3.3 MeasuresMeasuresMeasuresMeasures forforforfor positionpositionpositionposition changechangechangechangeFor the oil-air lubrication which is now perfectlyestablished as the lubrication system of high-speedspindle, the smooth drainage of lubrication oil which is fedcontinuously is an important point to realize the stability inthe aspect of lubrication. In case of the composition ofturning spindle, it is necessary to pay full attention for thedesign of drain channel in response to the turning angle.Also, for the units performing turning motion, it should befree from wiring and piping as much as possible. Ifpossible, to adopt grease lubrication is the one ofsolutions. However, in such case, there is a concernabout the deterioration of life due to dropping out ofgrease in comparison with the spindle without positionchange. In addition, as the big challenge which thespindle has, there is the problem that how to prevent theingress of coolant inside the spindle. In this point, the riskof ingress increases from the vertical type, the horizontaltype, and the turning type in order.

3.43.43.43.4 MeasuresMeasuresMeasuresMeasures forforforfor greasegreasegreasegrease lubricationlubricationlubricationlubrication3.4.13.4.13.4.13.4.1 SealedSealedSealedSealed angularangularangularangular contactcontactcontactcontact ballballballball bearingbearingbearingbearingFor the machine tool spindle bearing, the environmentfriendly clean technology attracts a lot of attention, as thebearing in response to such requirement, the precisionsealed angular contact ball bearing (refer to Figure 12) iscome into use. In this bearing, compact non-contact sealsare adopted, while it is holding the interchangeabilitywith conventional bearing, and the workabilityimprovement by prelubricated grease, splash preventionof grease, and improvement of high-speed rotation arestriven. Also, by using this bearing, it is not only theextension of grease life is able to be striven but also it is

Figure 12: Sealed angular contact ball bearing

Table 2: Required characteristics from turning spindle and problem area


possible to prevent the drop of grease in case of thevertical type spindle.3.4.23.4.23.4.23.4.2 GreaseGreaseGreaseGrease replenishingreplenishingreplenishingreplenishing lubricationlubricationlubricationlubrication bearingbearingbearingbearingSince the grease lubrication can be used for a long timeonly to be filled the specified amount of grease when thebearing is mounted, it is very easy and it is widely used asthe most common lubrication method. However, in caseof the built-in motor spindle, the continuous running athigh speed with urgent acceleration and deceleration isincreasing, though it is possible to rotate for a short timewith conventional grease lubrication, the failure case thatthe grease is deteriorated or depleted by high-speedcontinuous running and it causes the occurrence ofseizure begins to increase.Consequently, when the grease life is considered, forexisting grease lubrication the maximum rotating speed islimited. As well as the oil lubrication, the greasereplenishing lubrication is that by supplying the lubricantexternally, the grease life was improved spectacularly,and it attained the maximum rotating speed 20000min-1

though it is grease lubrication.Figure 13 illustrates the structure of new greasereplenishing lubrication system developed by NSK Ltd.For the application except the area of machine toolspindle, until recently, there were the methods to greaseinto bearings with use of grease replenishing piping orgrease nipple etc. However, in this new system, there arethe biggest features such as the quantity of suppliedlubricant is extremely small amount, in addition thegrease is fed directly into the bearing which is rotatingathigh speed. In case of the oil-air lubrication, as theoiling quantity, the lubrication oil of about 1-3cm3 is

Spindle end taper NT40/HSK-A63(Op)

Maximum rotating speed 20000min-1

Maximum output 22/18.5kW(15Minutes/Continuous)

Maximum torque 118N･m(25%ED)

Bearing bore diameter Ф70mm

Preload type Position preload(DBB arrangement)

consumed by single row of bearing for 24 hours. In themeantime, the grease quantity of grease replenishinglubrication is extremely small such as less than 0.1cm3,and it is not necessary to drain the lubricant to outside.In addition, since the consumption of air to supply thelubrication oil is not necessary; as a result, it is free fromsplashing the oil to atmosphere, as ecological point ofview, the grease replenishing lubrication is superior to theoil-air lubrication or the oil mist lubrication. Figure 14shows the grease replenishing unit “Fine-Lub II” used forthe grease replenishing lubrication system.NSK Ltd. Has developed “High-speed built-in motorspindle”4) as the standard spindle of NT40 Class adoptedgrease replenishing lubrication (Refer to Figure 15). Thisspindle adopted the world’s first new lubrication systemsaying that grease replenishing lubrication, it attained themaximum rotating speed 20000min-1 though it is greaselubrication. The main specifications of this spindle arelisted in Table 34).

3.53.53.53.5 MeasuresMeasuresMeasuresMeasures forforforfor intelligentintelligentintelligentintelligent spindlespindlespindlespindleAs the direction of machine tool spindle in the future, thedemand of intelligent spindle is increasing, but there is notyet the intelligent spindle which comes into practical usein the market. NSK Ltd. has developed the spindle5) inwhich the load displacement sensor and the encoderwere integrated to detect the axial displacement duringcutting process in addition to MEMS sensor describedabove. The rotation of this spindle was demonstrated inJIMTOF2010.The purposes of development of this spindle were thecontrol of tool life by detecting the load change at cuttingprocess, the automatic process shutoff by detectingabnormal load, the review of process conditions, and thepreventive measures of bearing failure by detecting thepreload of bearing etc. Figure 16 illustrates the image of

Figure 13: Grease replenishing lubrication system

Figure 14: Grease replenishing unit Fine-Lub II

Figure15 : High-speed built-in motor spindle

Table 3: B1 Spindle specification (L type)

Flow of greaseFlow of greaseFlow of greaseFlow of grease

Discharged greaseDischarged greaseDischarged greaseDischarged grease Flow of greaseFlow of greaseFlow of greaseFlow of greaseGrease storage grooveGrease storage grooveGrease storage grooveGrease storage groove

Discharging Discharging Discharging Discharging spacerspacerspacerspacer

ShaftShaftShaftShaft

HousingHousingHousingHousing

Flow of greaseFlow of greaseFlow of greaseFlow of grease

Discharged greaseDischarged greaseDischarged greaseDischarged grease Flow of greaseFlow of greaseFlow of greaseFlow of greaseGrease storage grooveGrease storage grooveGrease storage grooveGrease storage groove

Discharging Discharging Discharging Discharging spacerspacerspacerspacer

ShaftShaftShaftShaft

HousingHousingHousingHousing

Flood coolantFlood coolantFlood coolantFlood coolant

BuiltBuiltBuiltBuilt----in motorin motorin motorin motor

Tool clamping unitTool clamping unitTool clamping unitTool clamping unit

Rotary unionRotary unionRotary unionRotary union

Tool unclamping cylinderTool unclamping cylinderTool unclamping cylinderTool unclamping cylinder

BearingBearingBearingBearing

Flood coolantFlood coolantFlood coolantFlood coolant

BuiltBuiltBuiltBuilt----in motorin motorin motorin motor

Tool clamping unitTool clamping unitTool clamping unitTool clamping unit

Rotary unionRotary unionRotary unionRotary union

Tool unclamping cylinderTool unclamping cylinderTool unclamping cylinderTool unclamping cylinder

BearingBearingBearingBearing


load change at cutting process. It is possible to detect theincrease of cutting load or emergent cutting defect. Figure17 shows the mounting arrangement of the loaddisplacement sensor in the spindle. The shape of sensoris like nozzle top of oil-air lubrication, and the encoder isthe inner ring spacer of bearing.This spindle was mounted on the actual machiningcenter; a work (cast iron) was put on the Kistlerdynamometer, and when the drilling process wasoperated as shown in Figure18, the cutting process testwas conducted by comparing the output of displacementsensor and the input load. The comparison result of thetest is shown in Figure 19. Including other end mill cuttingetc., the almost same values are obtained between theinput load and the output of displacement sensor.

4444 CONCLUSIONSCONCLUSIONSCONCLUSIONSCONCLUSIONSWith a focus on the speeding up of machine tool spindle,the technology development of spindle for about 35 yearswas explained but the speeding up is standstill in recentyears, the market requirement is changing from highspeed and high accuracy to high stiffness andimprovement of reliability, and nowadays environmentalresponsiveness, saving energy, and intelligent spindle. Inthis year, JIMTOF2012 is scheduled to be held, it isconsidered that Japanese machine tool industry aimssaving energy and ecology-conscious directivity in thefuture, and the high value-added machine tools areincreasing by adopting new material such as CFRP andby performing curved surface processing of 3 dimension.Above all, it is considered that the technology aimingfurther speeding up of spindle along with the lifeenhancing and improvement of reliability of greaselubrication will be revived newly. Continuously I will leadthe world from the aspect of spindle technology andintend to advance new research and development aimingthe improvement of unique machine tool technology ofJapan.

REFERENCESREFERENCESREFERENCESREFERENCES[1] S.Sugita, Y.Katsuno, Y.Oura, Ultrahigh-speed

angular contact ball bearings for machinetool spindle, Technical Journal673:(2003)54-56 (in Japanese)

[2] M.Aoki, S.Nakamura, Technology trend andnew technology of machine tool bearings,Journal of The Japan Society for PrecisionEngineering Vol.74 No.9 (2008)913-916 (inJapanese)

[3] M.Aoki, Latest trend of spindle and ultrahigh-speed spindle technology, Text of 39thMachine tool associated engineers’conference (2009) (in Japanese)

[4] M.Aoki, Y.Morita, Development of greasereplenishing lubrication built- in motor spindle

NSK Technical Journal 676 (2003) 16-25 (inJapanese)

[5] Y.Inagaki, Technological trend of spindle andintell igent technology Text of 40 th Machinetool associated engineers’ conference (2011)(in Japanese)

Figure 16: Image of cutting load

Figure 17: Spindle integrated load displacement sensor

Figure 18: Cutting process test by actual machine

Figure 19: Comparison of cutting process test results

Cut

ting

load

Cut

ting

load

Cut

ting

load

Cut

ting

load

（NN N N）

Sudden cutting defectSudden cutting defectSudden cutting defectSudden cutting defect(Built(Built(Built(Built----up edge etc.)up edge etc.)up edge etc.)up edge etc.)

Increase of cutting loadIncrease of cutting loadIncrease of cutting loadIncrease of cutting load

Cut

ting

load

Cut

ting

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Cut

ting

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Cut

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（NN N N）



Cut

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Cut

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Cut

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SensorSensorSensorSensor

Bearing unit integrated Bearing unit integrated Bearing unit integrated Bearing unit integrated special shape encoderspecial shape encoderspecial shape encoderspecial shape encoder

Placement in the middle of bearingsPlacement in the middle of bearingsPlacement in the middle of bearingsPlacement in the middle of bearings

Assumption of cooling oil pathAssumption of cooling oil pathAssumption of cooling oil pathAssumption of cooling oil path Handling of wiringHandling of wiringHandling of wiringHandling of wiring

Investigation of groove pair numberInvestigation of groove pair numberInvestigation of groove pair numberInvestigation of groove pair numberPosition where is less subject to Position where is less subject to Position where is less subject to Position where is less subject to thermalthermalthermalthermaldisplacement displacement displacement displacement

Number of cutting tooth Number of cutting tooth Number of cutting tooth Number of cutting tooth ≠ Number of groove pairNumber of groove pairNumber of groove pairNumber of groove pair

Oil resistanceOil resistanceOil resistanceOil resistance

Spindle unitSpindle unitSpindle unitSpindle unit

Replacement easiness Replacement easiness Replacement easiness Replacement easiness Measures for noise Measures for noise Measures for noise Measures for noise

SensorSensorSensorSensor

Bearing unit integrated Bearing unit integrated Bearing unit integrated Bearing unit integrated special shape encoderspecial shape encoderspecial shape encoderspecial shape encoder

Placement in the middle of bearingsPlacement in the middle of bearingsPlacement in the middle of bearingsPlacement in the middle of bearings

Assumption of cooling oil pathAssumption of cooling oil pathAssumption of cooling oil pathAssumption of cooling oil path Handling of wiringHandling of wiringHandling of wiringHandling of wiring

Investigation of groove pair numberInvestigation of groove pair numberInvestigation of groove pair numberInvestigation of groove pair numberPosition where is less subject to Position where is less subject to Position where is less subject to Position where is less subject to thermalthermalthermalthermaldisplacement displacement displacement displacement

Number of cutting tooth Number of cutting tooth Number of cutting tooth Number of cutting tooth ≠ Number of groove pairNumber of groove pairNumber of groove pairNumber of groove pair

Oil resistanceOil resistanceOil resistanceOil resistance

Spindle unitSpindle unitSpindle unitSpindle unit

Replacement easiness Replacement easiness Replacement easiness Replacement easiness Measures for noise Measures for noise Measures for noise Measures for noise

Work (Cast iron) Work (Cast iron) Work (Cast iron) Work (Cast iron)

DrillDrillDrillDrill

Main spindleMain spindleMain spindleMain spindle

Load cellLoad cellLoad cellLoad cell Work (Cast iron) Work (Cast iron) Work (Cast iron) Work (Cast iron)

DrillDrillDrillDrill

Main spindleMain spindleMain spindleMain spindle

Load cellLoad cellLoad cellLoad cell

Testing conditionsTesting conditionsTesting conditionsTesting conditions・Drill diameterDrill diameterDrill diameterDrill diameter ：Φ5mm5mm5mm5mm・Rotating speedRotating speedRotating speedRotating speed ：1500min1500min1500min1500min----1111

・Feed speedFeed speedFeed speedFeed speed ：200mm/min200mm/min200mm/min200mm/min・Work materialWork materialWork materialWork material ： Cast ironCast ironCast ironCast iron

-0.005

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　　　Displacement sensor outputDisplacement sensor outputDisplacement sensor outputDisplacement sensor output　　　 Input loadInput loadInput loadInput load

Time(sec)Time(sec)Time(sec)Time(sec)

machine tool spindle Technology development and future ...sme-japan.org/journal1-nakamura-eng.pdf · case of multitasking lathe, the trend toward speeding up Figure 1:Transition of

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