brookhaven science associates manufacturing and quality assurance magnet production workshop frank...
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BROOKHAVEN SCIENCE ASSOCIATES
Manufacturing and Quality Assurance
Magnet Production WorkshopFrank DePaola
April 11-12, 2012
BROOKHAVEN SCIENCE ASSOCIATES
Abstract
Manufacturing and Quality Assurance
Frank DePaola, NSLS-II Project Building Quality into the Magnets necessitates that the quality requirements for the performance specifications are incorporated into the production process and methods used to produce the magnets. This is accomplished through manufacturing travelers, documented procedures, early QA involvement that takes a proactive approach for preventing defects, and the use of established best practices for manufacturing the coils and yokes. *Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886
DOE Review of the NSLS II Project, November 15 - 17, 20102
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OUTLINE
• Manufacturing and Quality Assurance Interface
• Build Quality into the Product
• Manufacturing Travelers
• Role of Quality Assurance in Manufacturing
• Magnet Production
• Magnet Yoke Fabrication
• Magnet Coil Fabrication
• Magnet Assembly
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Build Quality Into The Product
Successful manufacturers build quality into their products
• The quality necessary to achieve the required specification is designed
and planned into the product upfront – it than becomes integrated into
the manufacturing methods used to produce the product
• This is accomplished through the use of manufacturing travelers,
documented procedures, inspection and test plans, engineered tooling
and fixtures, and continuous improvement
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Manufacturing Travelers
The single most important item is the manufacturing traveler
• Sequential listing of required tasks
• References special work instructions and procedures
• Incorporates in-process inspection and test requirements
• Captures individual part data (actual measurements & test results)
• Provides hold points that require approval prior to proceeding
• Historical record for each individual item produced
• Provides consistency from part to part throughout the production run
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Role of Quality Assurance in Manufacturing
• Provide a systematic and proactive approach for preventing defects
• Implement procedures that ensure manufactured products consistently
meet the required quality specifications
• Incorporate the QA requirements into the manufacturing traveler
• Perform audits to ensure:
• Established procedures are being followed
• Personnel performing the work are adequately trained
• Equipment is calibrated and in good repair
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Magnet Yoke Fabrication
MATERIAL
• Ideally all magnets from the same family are manufactured from a
single batch of steel (same heat)
• Shuffling systematically distributes the steel properties among all the
yoke segments and ensures that all the magnets in a single family
have reproducible and uniform magnetic properties
• Sorting ensures that variations in the sheet thickness (caused by
crowning during the rolling process) are systematically distributed – If
the laminations are symmetrical they can be flipped during the stacking
process
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Magnet Yoke Fabrication
Solid Steel Yokes or Steel Laminated Yokes
Solid Steel Yokes
• Machined from a solid block of material
• Cannot be cycled or pulsed rapidly (eddy currents)
• Acceptable for use in storage ring accelerator applications
• Should be considered if a small number of magnets are required
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Magnet Yoke Fabrication
Solid Steel Yokes or Steel Laminated Yokes
Laminated Steel Yokes
• Joining Methods – Glued / Welded / Combination of gluing and welding
• Gluing is generally used for magnets that are < 0.5 meter in length
• Longer dipole magnets are more suited to a welded construction
• Trying to glue dipole magnets that have a long length to yoke cross
section ratio is very difficult to accomplish – and stacking curved
dipole magnets adds yet another level of complexity
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Magnet Yoke Fabrication
Solid Steel Yokes or Steel Laminated Yokes
Cost Comparison
“ Typical undocumented studies have shown that the cost of fabricating a few (≤ 4)
laminated magnet yokes is dominated by the tooling costs and exceeds the cost of
machining the same number of yokes from solid blocks. However, these same
studies have shown that the cost of machining exceeds the cost of fabricating
laminated cores for the typical accelerator application where the tooling costs can
be shared by the larger number of core segments.” (J. T. Tanabe)
If secondary machining is required to achieve high mechanical precision
the cost advantage offered by laminated yokes is lost
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Manufacturing Process Comparison
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Magnet Yoke Fabrication
Preparing Laminations for Stacking and Bonding
• Unclean laminations will result in poorly bonded yokes
• Laminations contaminated with stamping lubricants or cutting oils and
handling laminations with bare hands that can leave dirt and oily finger
prints on the surface
• Important to handle the laminations wearing clean lint free gloves and
cleaning the laminations prior to stacking using a recommended or
proven cleaning method
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Magnet Yoke Fabrication
Preparing Laminations for Stacking and Bonding
• Burrs on lamination cut edges and other defects (bent or creased
laminations) will result in poorly bonded yokes with low and inconsistent
packing densities
• Indications of these defects can generally be observed on the outer
surface of the yoke at the un-bonded area
• Incorporate a visual inspection of laminations – a deburring process –
and a sorting procedure to ensure that defective laminations do not end
up in the stacked yoke
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Magnet Yoke Fabrication
Yoke Stacking / Bonding Fixture
• Stacking fixtures that do not apply an evenly distributed pressure
across the entire yoke and a constant pressure throughout the bonding
cycle will result in poorly bonded yokes
• Some stacking fixtures had to be modified to incorporate the following
standard practices and features
A) Engineered to be sufficiently rigid so that it will not deflect or deform
under the applied forces
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Magnet Yoke Fabrication
Yoke Stacking / Bonding Fixture
B) The clamping arrangement must apply a uniform pressure
across the entire yoke
• Provide as many clamping positions as possible
• Ideally located directly over the laminations or at least as close
as possible to the laminations
• Positioned in a symmetrical arrangement
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Magnet Yoke Fabrication
Yoke Stacking / Bonding Fixture
C) Belleville washers are used to apply a constant pressure throughout
the bonding cycle
D) If top and bottom yoke halves are stacked at the same time using the
same fixture – Stacking the laminations in series generally has better
results than stacking them side by side
E) Registration surfaces must be smooth and coated with a molybdenum
based lubricant to minimize frictional forces (Molykote leaves no trace
of contamination)
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Magnet Yoke Fabrication
Yoke Bonding
• Optimized bonding conditions (pressure , time and temperature) are
paramount in producing strongly bonded yokes
• Material manufacturers generally give a broad range for the bonding
conditions – The optimized conditions are dependent on the actual yoke
size and geometry as well as the method of heating
• Optimized conditions are best developed through the use of engineering
analysis that take into account the following considerations
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Magnet Yoke Fabrication
Yoke Bonding
Applied Pressure
• Stay within the material manufacturer’s recommended range for
applied pressure if possible
• Pressure measurement film is an accurate and visual representation of
the pressure distribution that is being applied to the yoke by the
stacking fixture under actual conditions at room temperature
• Applied pressure should be maintained for as long as possible during
the yoke cool down period
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Magnet Yoke Fabrication
Yoke Bonding
Time and Temperature
• Analysis should be performed to determine the heating profile
(ramp-up rate, maximum temperature, soak time, and cool-down
rate) using the actual geometry and mass of both the yoke plus
the stacking fixture
• For the most accurate readings – Thermal couples used to
monitor the yoke temperature are attached as close as possible to
the center of the yoke
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Magnet Yoke Fabrication
Packing Density
• A packing density greater than 98% with less than a 0.2%
variation between the top and bottom yokes is required for high
precision quality magnets
• Magnet asymmetries caused by a variation in packing density
between the top & bottom yokes can often cause disturbance to
the field as a result of a displacement between the mechanical
and magnetic centers
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Magnet Coil Fabrication
• Vacuum impregnation of the coils and the use of a potting mold was
specified in order to accurately produce the coil’s final shape and close
mechanical tolerance requirements for
• Coil installation onto the poles
• Providing the clearance necessary for installation of the vacuum
chamber and other components
• Solutions to production issues that were encountered during coil
fabrication are shown on the next three slides
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Magnet Coil Fabrication
Coil Preparation Prior to Potting
• Preformed G10 reinforcement blocks are used to provide the structural
support necessary to strain relieve the conductor leads as they exit the
encapsulated coil assembly – The conductor and reinforcement block
must be secured to the coil assembly using fiberglass tape
• A ground wrap of fiberglass tape is wound around the completed coil
assembly securing its shape during potting
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Magnet Coil Fabrication
Coil Potting Mold
• Coat the inside surfaces of the mold cavity with a mold releasing agent
to facilitate the removal of the cured coil
• G10 strips are used to center the wound coil within the mold allowing
the epoxy to flow uniformly around the entire coil assembly
• Large molds containing cavities for multiple coils to be potted
simultaneously can potentially cause problems trying to fill all of the
cavities in the allotted time before the epoxy starts to cure
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Magnet Coil Fabrication
Coil Potting (Encapsulation) Process
Vacuum impregnation of the coils
• In order to completely evacuate air from the mold cavity – The vacuum
pump draws the mixed epoxy into the cavity from the bottom of the
mold – completely fills the cavity – and exists through the top of the
mold
• Alumina filled epoxy resin prolongs the life of the coils by providing
added radiation resistance – Getting the mixture to flow uniformly
through the mold cavity proved to be a challenging task for most until
the exact recipe (alumina particle size, mixing time and temperature)
was established
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Magnet Assembly
Secondary Processing
Small variations during fabrication and assembly have
an adverse effect on magnet performance and
repeatability.
Reducing these variations to an acceptable level
requires secondary processing of the magnet after
bonding and assembly.
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Magnet Assembly
Secondary Processing
To achieve the high precision quality requirements of the magnetic
field and to ensure repeatable magnetic performance after
disassembly and reassembly of the magnet
• Machine the mating registration surfaces of each yoke half and each
mid-plane spacer
• Assemble yoke halves using a documented bolt tightening sequence
and torque procedure
• Best magnetic field quality results are achieved when the pole profile is
machined in the assembled magnet
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Manufacturing Process Comparison
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Lessons Learned Workshop, April 11-13, 201228
Acknowledgements
THANKS TO THE BNL MAGNET TEAM
AND
OUR INDUSTRIAL CONTRACTORS
AROUND THE WORLD