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DESIGN AND DEVELOPMENT OF A PRECISION

MACHINE TOOL

Submitted by

Arjyajyoti Goswami

02/PRD/10

Submitted to.

Prof. SHAMSHER

Department of MECHANICAL ENGINEERING

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EMERGING TRENDS

Continued accuracy

Surface finish of 1 m or less

Motion accuracy of 1 nm

Allowable temperature deviation upto 0.1C

All of above at a productive material removal rate

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DESIGN OBJECTIVE

To design a machining center

To design a high precision machining center

To achieve the desired precision at high speedso as to achieve a sustainable productive rate

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DESIGN OF STRUCTURE OF THEMACHINE TOOL

Independent axes to avoid accumulation oferror

Movement along Z axis is achieved by moving theworktable instead of the spindle

Use ofpair of linear motors to improve accuracy

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Control of thermal deformation

Materials with good stiffness-to-weight ratio need to beconsidered to achieve high static and dynamic stiffness

Use of radiation shields and high thermal resistance mountingsare made to form a thermal break and then cool them down.

All moving parts are of ceramic, to have low mass, highstiffness and lesser thermal deflection owing to their smallthermal expansion co-efficient

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The highlycompressed air is

subjected to thesudden expansionafter going throughthe air turbineblades, and this

sudden expansionprovides the coolingeffect

Heat is generated within the bearing due to the shear effect

between the static air and rotating high-speed spindle

Both the cooling effect and the generated heat, cancels out eachother and stable state is achieved within a very short time

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SYMMETRICAL DESIGN

Symmetrical designs are simpler to analyze

Require less information to build

Allow more accurate measuring and manufacturing methods

The loads on the symmetric structure can be self-cancelingthus resulting in greater dynamic balancing

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Vibration suppression

Vibration control can be

achieved through PASSIVE orACTIVE DAMPINGMETHODS

Working conditions are

continuously changing, so activevibration control is necessary forhigh-speed precision systems

The basic idea is to use two

moving counter balance massesalong X and Y axes to suppressthe vibration caused by spindleand worktable respectively

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The total mass of two damping masses is equal to the mass ofthe X-axis slider, the resultant reactive forces exactly match the

active force.

The two fixed supports are very close to each other, torsion loadson the fixed supports are greatly reduced

X, Y and Z axes are equipped with 2 linear motors such that theresultant feed is always acting at the center of gravity

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Tool Holding System

Compared to other tool holding devices, this tool holder providesstronger tool holding capability in high load operations

This also provides high speed and high accuracy tool change

without deflection

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LASER detection of Workpiece and Tool Position

LASER detectionsystem are installed in

the machine toautomatically determinethe positions of thecutting tool.

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The repeatibility of the two LASER detection system is around0.2-0.5m.

Once the positions of the workpiece and the tool are found, the

offset between the cutting tool and the workpiece is obtainedautomatically

The position of workpiece can be measured with a touchprobe, using the LASER measurement device as referencepoint

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Performance Evaluation

The run out of the spindle is less than 0.5 m

The deviation ofmeasured tool diameter is around1.5 m , in

70 observations

The thermal displacement for most cases is less than 0.5 m

The maximummeasured temperature change is less than 0.5Cin the machine area

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Z.G.Wang, X.Cheng, K.Nakamoto, S.Kobayashi, K.Yamazaki,

Design and development of a Precision machining tool usingcounter motion mechanisms, International Journal ofMachineTools and Manufacture 50 (2010) 357-365

M. Weck, J. Hennig, R. Hilbing, Precision cutting processes for

manufacturing of optical components, lithographic andmicromachining techniques for optical component fabrication,Proceedings of SPIE 4440 (2001) 145151

J.A. Wickert, C.D. Mote Jr., Current research on the vibration and

stability of axially moving materials, Shock and Vibration Digest 20(1) (1988) 313

E. Shamoto, C.H. Park, T. Moriwaki, Analysis and improvement ofmotion accuracy of hydrostatic feed table, CIRP Annals 50 (1)

(2001) 285288

REFERENCES