Engineering Division 1

Integration and Pixel MechanicsProgress

27-April 2011HFT Mechanics Meeting

E Anderssen, LBNL

Engineering Division

Pixel Carriage

• Test Stand for Carriage Insertion ‘F’-shaped supports part of ‘Box’ in which detector will be delivered

• Compliance added to bottom rail bearings—allowing for rail misalignment—here about 300microns. 2

Engineering Division

Parts are Symmetric (common)• Carriage is rotationally

symmetric about STAR Coordinates

• Same component parts can be used for the North or South Detector halves

• Same 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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Engineering Division

Hinge Assembly Installed

• Hinge provides DOF allowing PXL to articulate around Large Beampipe and close in around Be Beampipe

• Swings thru motion nicely—no rattle or slop in motion

• Left 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 4

Engineering Division

D-Tube Mounted on Hinge

• D-Tube not bonded together yet (happens today)• Held together with tape to check dimensions• Service burden similar in volume to detector—will

look at handling as part of this effort5

Engineering Division

PXL Sectors Mounted on D-Tube

• Only mounted 2-sectors as D-Tube is only *taped* together

• Will pull out 5-sectors after D-Tube is bonded• General comment is they seem to line up well with

rails, even for something taped together… (parts fit well) 6

Engineering Division

Other Side

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Engineering Division

D-Tube Assembly

• Ready for Bonding—shown in bond fixture; just need to get to it

• T-Slots for locating Kinematic Mounts, again symmetric, but ‘Top’ remains reference between North/South

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Engineering Division

Sector Mount Plate• Dovetail mounts on ends of

sectors slide into these positions

• Central one used to locate sectors relative to Kinematic Mounts in same fixture

• Fixture 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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Engineering Division

WSC Mandrel

• Mandrel and Cart delivered late March just before review

• QC 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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Engineering Division

Autoclave Thermal Tests

• The WSC mandrel was run alone with several thermocouples to assess thermal performance

• Autoclave 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 1st run) 11

Engineering Division

Fabrication Process Overview• Composite materials in our application come pre-impregnated

with a tightly controlled resin content• Layers 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

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

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Engineering Division

Test Shell Production—Ply Cutting

• Test laminates are required to verify the fabrication procedure and tooling--3-4 test laminates are required

• Approx 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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Engineering Division

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 required

Engineering Division

Pre-Compacted Ply Stacks

• Using mechanical (window) templates registered to pins (black buttons in picture), plies are stacked and compacted

• Fiber orientation per-layer is important; using precision cut plies and mechanically registered placement assures quality 15

Engineering Division

Ply-Stack Application to Tool (Mandrel)• Pre-Compacted (flat) ply-stacks

allow for more rapid and accurate deposition of material

• A 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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Engineering Division

Base-Stack on Mandrel

• Previous slide showed application of outer stack on this one

• Base Stack sequence most important—plies in Hoop direction most prone to buckling

• Circular constraint susceptible to external pressure… 17

Engineering Division

First Prototype Shell

• Generally successful, but inner hoop plies fail (buckle/wrinkle) during pre-cure compaction on mandrel

• Uncomfortable with hoop ply failures, but likely acceptable

• On the plus side Outside Diameter is 400.1mm* (400mm Nom)

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Engineering Division

Shell Prototype Efforts• First Prototype was ‘acceptable’ but looking for

methods to avoid fiber buckling during mandrel application/compaction

• Second 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– Inclusion 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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Engineering Division

Hoop Layers• ‘Hoop’ plies have fibers

oriented in phi-direction—most susceptible to buckling under external pressure

• Chose to apply ‘Hoop’ plies independent from Base Stack

• Allows 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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Engineering Division

IDS Cone Prototype

• Paper templates of ply shapes were generated to study the formability of the shapes

• These 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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Engineering Division

Cone Ply Shapes Verified

• Paper is a conservative analog for non-formable surfaces

• Cone is fabricated from cloth-prepreg—forgiving in shear

• Program for ~250 unique plies programmed into ply-cutter for 24 layers plus pad-up at flanges

• Will cut ~12m^2 of fiber today22