1 Integration and Pixel Mechanics - PowerPoint Presentation

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Integration and Pixel MechanicsProgress

27-April 2011

HFT Mechanics Meeting

E Anderssen, LBNLSlide2

Pixel Carriage

Test Stand for Carriage Insertion ‘F’-shaped supports part of ‘Box’ in which detector will be deliveredCompliance added to bottom rail bearings—allowing for rail misalignment—here about 300microns.

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Parts are Symmetric (common)

Carriage is rotationally symmetric about STAR CoordinatesSame component parts can be used for the North or South Detector halvesSame is true for ‘F’ Stands

Only difference is how parts are assembled, i.e. the ‘Top’ Rail on both sides remains the ‘Top’

Compliance mentioned on previous slide only for ‘Bottom’ rail

Means there are no ‘mirror’ parts between Pixel Halves, only assembly variations

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Hinge Assembly Installed

Hinge provides DOF allowing PXL to articulate around Large Beampipe and close in around Be BeampipeSwings thru motion nicely—no rattle or slop in motionLeft Picture shows outer-most position to clear BP flanges

Right shows full range of motion inward—not this much is required, exaggerated to show DOF

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D-Tube Mounted on Hinge

D-Tube not bonded together yet (happens today)Held together with tape to check dimensionsService burden similar in volume to detector—will look at handling as part of this effort

5Slide6

PXL Sectors Mounted on D-Tube

Only mounted 2-sectors as D-Tube is only *taped* togetherWill pull out 5-sectors after D-Tube is bondedGeneral comment is they seem to line up well with rails, even for something taped together… (parts fit well)

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Other Side

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D-Tube Assembly

Ready for Bonding—shown in bond fixture; just need to get to itT-Slots for locating Kinematic Mounts, again symmetric, but ‘Top’ remains reference between North/South

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Sector Mount Plate

Dovetail mounts on ends of sectors slide into these positionsCentral one used to locate sectors relative to Kinematic Mounts in same fixtureFixture Machined by UTA, parts fit nicely

Small problem with machining of Dovetail plate in bond area—complicated transition area

Rectified with a rat-bastard on prototypes—will be programmed in for production CNC

Still need to bond—just need to get to it…

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WSC Mandrel

Mandrel and Cart delivered late March just before reviewQC indicates the mandrel is 125microns oversize on Dia.*Varies less than 25microns along length which is about our repeatability with a Pi-Tape…

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Autoclave Thermal Tests

The WSC mandrel was run alone with several thermocouples to assess thermal performanceAutoclave has a ducted internal flow of about 2000cfm recirculated

via the bottom

chordal

duct and distributed by baffles in the door and back

Studies with tool position and some internal added baffles lead to an optimal performance (all TC’s within 10F during temp-ramps) (not shown in plot above which was 1

st

run)

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Fabrication Process Overview

Composite materials in our application come pre-impregnated with a tightly controlled resin contentLayers of this material, with specific fiber orientation, are laminated together under pressure and heat which cures the resin system, and yields a composite laminate

A ‘Layer’ is composed of ‘Plies’ which are discrete shapes of the pre-

preg

material with specific fiber orientation

A ‘Lay-up’ is the physical deposition of the plies with accurate positions and orientations to build-up the component laminate (also a noun referring to the pre-cured part amid-fabrication)

The impregnated fibers have ‘tack’ (tackiness) which allows a ply to ‘stick’ in position when placed (depends on resin content/temp)

Pressure (compaction) is required at various stages of fabrication, generally applied by vacuum bag after manual pressure (squeegee)

Compaction is required first to adhere a ply to plies in previous layers via ‘tack’, then to remove entrained air in the ply-stack

D

uring cure Compaction is required to exceed the vapor pressure of water and other entrained volatiles to avoid void nucleation

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Test Shell Production—Ply Cutting

Test laminates are required to verify the fabrication procedure and tooling--3-4 test laminates are requiredApprox 50 linear meters of material is used in each test

Plies are cut using an automated ply cutter with auto-feed

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Ply Stack wrapping on Mandrels

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Example from ATLAS—ignore fiber orientations

Ply stacks are ‘bricked’ to provide overlaps in plies between layers, so gaps are bridged by continuous fibers

Staggers and Offsets in Z and phi are requiredSlide15

Pre-Compacted Ply Stacks

Using mechanical (window) templates registered to pins (black buttons in picture), plies are stacked and compactedFiber orientation per-layer is important; using precision cut plies and mechanically registered placement assures quality

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Ply-Stack Application to Tool (Mandrel)

Pre-Compacted (flat) ply-stacks allow for more rapid and accurate deposition of materialA mechanical guide, registered to the Mandrel axis and pre-aligned allows accurate placement

No overlaps are allowed, gaps up to 1mm are tolerable

Flat pre-compaction can lead to some problems

Inner-plies when bent around mandrel go into compression

Careful attention to tension and order is required to prevent fiber buckling on vacuum compaction

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Base-Stack on Mandrel

Previous slide showed application of outer stack on this oneBase Stack sequence most important—plies in Hoop direction most prone to bucklingCircular constraint susceptible to external pressure…

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First Prototype Shell

Generally successful, but inner hoop plies fail (buckle/wrinkle) during pre-cure compaction on mandrelUncomfortable with hoop ply failures, but likely acceptableOn the plus side Outside Diameter is 400.1mm* (400mm Nom)

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Shell Prototype Efforts

First Prototype was ‘acceptable’ but looking for methods to avoid fiber buckling during mandrel application/compactionSecond Prototype planned independent application of first Hoop ply (there are 2)

Second Prototype effort spanned weekend—flat stack with second hoop ply pre-compacted on Friday

‘Flat’ compacted stacks exhibited fiber buckling in hoop ply

‘Bubbles’ coalesce to high curvature regions under a compliant vacuum bag

I

nclusion of ‘caul plate’ under vacuum bag distributes pressure allowing relaxation of high curvature regions

Current plan is independent application of each hoop layer separately, only pre-compacting oriented plies

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Hoop Layers

‘Hoop’ plies have fibers oriented in phi-direction—most susceptible to buckling under external pressureChose to apply ‘Hoop’ plies independent from Base StackAllows greater tension and compaction on tool surface

Removes concern about compression from bending of flat stack onto mandrel

Note that Mandrel expands 1.8mm during cure, ~6mm circumference

Wrinkles/Buckling on finished product unlikely—only occurs during Lay-up—difficult to avoid

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IDS Cone Prototype

Paper templates of ply shapes were generated to study the formability of the shapesThese have been iterated and the final trial lay-up on the cone tool tested to verify gaps and assure no-overlaps

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Cone Ply Shapes Verified

Paper is a conservative analog for non-formable surfacesCone is fabricated from cloth-prepreg—forgiving in shearProgram for ~250 unique plies programmed into ply-cutter for 24 layers plus pad-up at flanges

Will cut ~12m^2 of fiber today

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