brookhaven science associates manufacturing and quality assurance magnet production workshop frank...

BROOKHAVEN SCIENCE ASSOCIATES

Manufacturing and Quality Assurance

Magnet Production WorkshopFrank DePaola

April 11-12, 2012


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


Magnet Production Workshop – April 11-12, 20123

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



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



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



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



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




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





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





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


Manufacturing Process Comparison


11




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




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




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





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





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)




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




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




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




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



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




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




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




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



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.



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


Manufacturing Process Comparison


27


Lessons Learned Workshop, April 11-13, 201228

Acknowledgements

THANKS TO THE BNL MAGNET TEAM

AND

OUR INDUSTRIAL CONTRACTORS

AROUND THE WORLD

brookhaven science associates manufacturing and quality assurance magnet production workshop frank...

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