Preferred Principal Axis of Inertia Spheres for John Conklin · Preferred Principal Axis of Inertia...

Daniel Clark | Mike Dolphin | Marlo Dreissigacker | Martin Trittler | John Ulmen

ME324: Precision Engineering David Beach, Dan DeBra Spring 2007

Preferred Principal Axis of Inertia Spheres for John Conklin



Overview • Background of LISA program and customer requirements

• Sphere manufacturing

– Three parts

– Two parts

• Sphere joining

• Iterative lapping

• Iterative metrology



Sphere Manufacturing Approaches

Two

Piece

Method

Three

Piece

Method

Geometry Requirements: ~ 50mm diameter

k1 > 0.1

Density loss < 20%



Manufacturing Times

Three Piece Two PieceFixture manufacturing time 12 hours 1 hour

Fixtures made 1 4

Cap (2 per sphere) 5 hours

Core (1 per sphere) 9 hours

Hemisphere (2 per sphere) 2.5 hours

Total manufacturing time per sphere 19 hours 5 hours

Total spheres made 2 10



Design for 3-piece Method



Manufacturing



From Hex to Round



Cap Manufacture



Cap Fixturing



Core Manufacture



Core Fixturing



Completed 3-part Sphere



Design for 2-piece Method



Internal Geometry Modification

Sharp internal features

Filleted internal features



Critical Internal Features

– Tapped hole for 6-32

machine screw

– Fixture alignment surfaces

– Sphere alignment post and

hole

– Well for silver braze wire

preform



Internal Geometry Machining



Fixturing for Second Operation

Internal fixture alignment geometry

machined in, and seen through,

a cast acrylic block.



Hemispherical Surface Machining

• Spherical surface cutting

– Roughing

– Surfacing

• Face tolerance set to +0.005” and +0.0005”

(0.127 mm and 0.0127 mm)



Joining Operations for Sphere Halves

Process Selection and Joining Procedure



Joining Operations • Adhesive

• Interference fit

• Mechanical fastening



Joining Operations

• Heat Operations

– Solder

– Braze

– Weld



Laser Welding

• Brass alloys are

not good

candidates



E-Beam Welding

• Fixturing

• Waitlist



Brazing



Joint clearances of .001" and .005" (0.076 to 0.126mm)

25 ksi (172 MPa) typical shear strength



Brazing Possibilities



Brazing Process

Method Braze Material Braze Object Results

Oven Soft solder paste Blocks

Oven Silver solder paste Blocks

Rosebud Silver solder paste Blocks

Mapp Torch Soft solder Blocks

Rosebud Silver solder preform Blocks

Rosebud Silver solder preform Extra halves

Rosebud Silver solder preform Spheres



Spheres Joined



Lapping and Polishing

• Flat lap and spherical lap

• Lubricants may improve

performance

• Wet vs. dry method

• Dry lapping: Lap must be soft

relative to part



Spherical Lap • Self aligning geometry

• Naturally removes high points on sphere

• Two phases

– Phenolic lap rough cutting brass parts

– Cast iron lap final cutting and polishing brass parts



Practice Lapping



Lapping Glass Marbles • Paint removal is easy!

• Large scale material removal is slow.

• Approximately 24 hours of total lapping time:

– Removal rate ≈0.03mm (0.0012”) per hour on diameter

– Highly dependent on grit quality and water content

• 60 grit aluminum oxide

• 2-3 hour grit life-span



Marble Results • Slow but measurable convergence to sphericity

• No “eggs” or ellipsoids

• Valuable lessons about grit and lubricant



Track Wear



Lapping Brass Parts



The Phenolic Lap

2.5 Hours



6 Hours



Brass Lapping Process • 30 hours in phenolic lap with 60 grit

• 10 hours in cast iron lap with 150 grit

6 Hours



Brass Lapping Status • A work in progress

• Rough cutting works well

• Next steps:

– Fine grits

– Polishing

• Stay tuned for current metrology data



Metrology

spheres or eggs?

keeping track of diameter and roundness

• Kinematic 3 point mount for repeatable and stable positioning

• Gage 2000 CMM (Coordinate Measuring Machine)

- Repeatable accuracy ~5 micrometer

- About 18 hits per (hemi-) sphere measurement

- Internal software algorithm and backtalk + external MATLAB algorithm for

data analysis



Measurement Principle

• Measurement results dependant on orientation of the sphere on

mounting bracket

– Brazing joint

– Difference in single parts of sphere

• Each sphere measured in 3 orientations for meaningful information



Tuesday Wednesday Thursday Friday

Brass Lapping History

Phenolic Lap,

60 Grit, 12

Hours

Cast Iron Lap,

150 Grit, 6

Hours

Phenolic Lap,

60 Grit, 5

Hours

Phenolic Lap,

1000 Grit, 1.5

Hours

Cast Iron Lap,

150 Grit, 7

hoursPhenolic Lap,

60 Grit, 9

Hours



Evolution of a 2 Part Sphere

Orientation Diameter [mm]

I 50.774 50.722 50.635 50.677

III 50.407 50.324 50.109 50.123

Deviation of roundness [mm]

I 0.055 0.023 0.036 0.033

III 0.255 0.153 0.215 0.192



Orientation Diameter [mm]

I 50.897 50.673 50.782 50.610

III 51.058 50.889 50.810 50.669

Deviation of roundness [mm]

I 0.136 0.0525 0.084 0.055

III 0.207 0.0681 0.100 0.089

Evolution of a 3 Part Sphere



Results / Summary

• Average reduction of diameter : ~ 0.195 mm / 0.39 %

• Average of material removed : ~ 781 mm3 / 1.15 %

• Best reduction of roundness deviation : ~ 47.3%

• Avg. reduction of roundness deviation : ~ 25.7 %

• Best achieved roundness dev. : 0.031 mm



Future

• Iterative process to final LISA test mass

– Measurement of mass center offset and moment of inertia

distribution

– Iteration of fabrication process based on the gained experience

– Adapt the experiences to final material of test mass

Detect Gravitational Waves!



Thanks and Acknowledgments

• John Conklin

• Richard Peattie at Surface Engineering

• Craig Milroy of the Product Realization Lab

• Karlheinz Merkle of the Varian Machine Shop

• PRL Shop TAs

• Materials Science Shop

• Dave Beach and Dan DeBra



Questions?

Please join us up front to look at some of our parts.



References • http://www.aladdin3in1.com/solder.htm

• //www.silvaloy.com/brazing_table.php

• http://laser-industrial.com/laser_welding4.html

• http://hussle.harvard.edu/~gabrielse/gabrielse/papers/2001/TheRoadtoAntihydrogen.pdf

• http://www-group.slac.stanford.edu/mfd/ebeam.html

• http://www-group.slac.stanford.edu/mfd/lightms.html

http://laser-industrial.com/laser_welding4.html



http://hussle.harvard.edu/~gabrielse/gabrielse/papers/2001/TheRoadtoAntihydrogen.pdf

http://hussle.harvard.edu/~gabrielse/gabrielse/papers/2001/TheRoadtoAntihydrogen.pdf

http://www-group.slac.stanford.edu/mfd/ebeam.html



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