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5-Axis Test-Piece:Influence of Machining Position

Michael Gebhardt, Wolfgang Knapp, Konrad Wegener

Institute for Machine Tools and Manufacturing (IWF), Swiss Federal Institute of Technology (ETH), Zurich, Switzerland

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1 Introduction2 Test pieces for 5-axis machine tools3 Simulation of axes motion4 Machining of test-pieces5 Interpretation of machined test-pieces6 Conclusions7 Education, Future Steps

Overview

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IWF/inspire research on 5-axis machine tools geometric testing dynamic testing thermal testing compensation

since begin of 2010 new5-axis machining center with swiveling rotary

table vertical machining center

t-(C)-Z-X-Y-b-B-C-w

strong integration into student’seducation

Introduction

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5-Axis Test-Pieces

Introduction

Truncated square pyramid test-pieceCone frustum test-piece

Two 5-Axis test-pieces were presented in ISO/CD 10791-7: 2010-10-06

Current version of ISO/DIS 10791-7:2012-02-14 only includes the conefrustum test-piece

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Alternative test-piece: truncated square pyramid

Milling is possible with just two axes in motion,but tool path can be reconstructed optically

Contact length of the tool is not constant,this results in a not constant process force

CMM is necessary for evaluation(Parallelism / Squareness)

Reversal movement in air(No start- / stop – marks)

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Influence of machining position on accuracy of conical test-piece

Four positions were considered for simulations and machining experiments:

- Basis location:BM (Bottom, Middle)

- Radial offset to C:BO (Bottom, Outside)

- Radial offset to B:TM (Top, Middle)

- Combination of two offsets:TO (Top, Outside)

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Realization of different heights

Reference cornerfor probing Test-piece

Different tube elementsrealize a variable heigth

Fixture in slots of machine tool (variable radial offset)

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Measurements were carried out with capacitive sensors FEM simulation and measurements

show a displacement within 1.5 mat top of the fixture due to gravityat B=90°

Process forces Only radial comp. to test-piece Constant except start / stop Small (~3 µm) change of circularity

of cone

Bending of fixture (FEM calculation and measurement)

-0.50

0.00

0.50

1.00

1.50

2.00

0 50 100

Ben

ding

in

m

B-Rotation in °FEM simulation of bending due to gravity

Measurements withcapacitive sensors(1 measuring point per 5°)

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Different locations lead to different axis motions – example: X-axis

Simulation of axis motion

For all positions: B-Axis: 60°- motion C-Axis: 360°- motion

Position BM: just 4-axis motion!

X-axis motions

Axes ranges for different locations of theconical test-piece

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Simulations – Position TO (Top, Outside),Different inclination angles (1)

Inclination angle = -30°Offset to B-axis: 220 mmOffset to C-Axis: 160 mm

Inclination angle: = 30°Offset to B-axis: 220 mmOffset to C-Axis: 160 mm

Ranges:

84 mm

360 mm

16 mm

60°

360°360°

60°

410 mm

280 mm

410 mm

= REVERSAL POINTS

C-A

xis

C-A

xis

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Simulations – Position TO (Top, Outside),Different inclination angles (2)

Inclination angle = -30°Offset to B-axis: 220 mmOffset to C-Axis: 160 mm

Inclination angle: = 30°Offset to B-axis: 220 mmOffset to C-Axis: 160 mmC

-Axi

s

C-A

xis

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Machining test-pieces

NC-programming and simulation in ESPRIT®

Following machining sequence wasrealized:

(1) Face milling of upper surface(2) Milling of groove in upper surface(3) Flank milling of cylinder (4) Flank milling of cone

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Analysis of milled test-pieces (1)

Measurement on a Talyrond 265 roundnessmeasuring machine

Radial probing for cylinder and cone

machine axis X

machine axis Y

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Analysis of cylinder (circularity):Comparison of four different positions

Positioning error, EXX = EYY

Squareness XY,C0Y = 0

X-Reversal < 5 m

Y-Reversal < 1 m

X-Reversal < 5 m

Y-Reversal < 1 m

EYY > EXX, pitchof Y EAY

X-Reversal < 7 m

Y-Reversal < 1 m

Positioning error, EXX = EYY

Squareness XY,C0Y = 0

X backlash and pitch of X, EBX atreversal point

EYY > EXX, pitchof Y EAY

X-Reversal < 7 m

Y-Reversal < 1 m

X backlash and pitch of X, EBX atreversal point

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Analysis of cone (circularity):Comparison of four different positions (=-30°)

From Cylinder:EXX = EYY, COY ~ 0From Simulation:Z=0

Form errorcaused by B and/or C Axis reversalcaused by X and/or B

From Cylinder:EXX = EYY, COY ~ 0 Form errorcaused by Z, B and/or C Axis reversalcaused by X, Zand/or B

From Cylinder:EXX, EYY, COY ~ 0

From Cylinder:EXX, EYY, COY ~ 0 Additional formerror caused by Z, Band/or C Axis reversalcaused by X, Z and/or B

Additional formerror caused by Z, Band/or C Axis reversalcaused by X, Z and/or B

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Analysis:Special phenomena (1)

Peaks at position BM which do not appear at position BO (tagged red)Possible reason: reversal points of Y-axis

Amplitude of «noise» in roundness measurement at position BO larger thanat position BMPossible reason: influence of angular positioning of C-Axis(Resolution C-Axis: 0.001°, 2x resolution * offset ~1.2 m)

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Analysis: correlation between measurements and Monte Carlo Simulation

Monte Carlo Simulation:Mean values and twice the standard deviation

Measurements:Mean values and twice the standard deviation

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Conclusions

investigation of influence of machining position- a variable setup to realize different machining positions was built.- for every position, several cone frustum test-pieces were milled. - axis movement and form deviation were simulated.

analysis of test-pieces- cylinder and cone were analyzed on a roundness measuring machine.- machine tool characteristics as axis reversal, pitch or squareness could be

identified.

special phenomena- “amplitude of noise” increases with increasing offset of milling position to C-axis.- sporadic occurrence of peaks looking like lubrication impulses. further measurements required

comparison of measurements and simulation- large circular form errors come along with large axis motion - Monte Carlo simulations of form deviation and measurements of milled test-pieces

show form deviations of similar range

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machine tool used for demonstrations and practical exercises in the following lectures:

practical course ‘from the idea to the workpiece’machining examples, machining of landscape topographie

machine tool metrologymeasurement of positioning accuracy with laser interferometer on NMV5000DCGmeasurement of straightness with straightedge on NMV5000DCGmeasurement of tool spindle with spindle analyzer on NMV5000DCG

manufacturing processes 1 and 2NC programming, milling

production machines 1 and 2design of machine tools, components of machine tools, machine tool performance (DCG), modeling of machine tools

Use of machine tool for education

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machine tool used for following thesis / student projects:

semester thesis ‘Measuring on machine tool’measurements and manufacture on NMV5000DCG

student focus project ‘sun car’manufacturing of key parts on NMV5000DCG

Use of machine tool for education

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Thermal testing including rotary axescompensation for thermal distortion of rotary axes

Future Activities

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Acknowledgement

IWF/inspire thanks MTTRF and MoriSeikifor generous support of research for 5-axis machining centers.