Lamination Production
by: John Roberts / Sko‐Die, Inc
Presentation Mission
• Understand the construction for magnetic cores
• Chose the best methods for producing
Magnetic cores are constructed
• From soft magnetic materials
• Consist of stacking thin laminated sheets
• Completed stack must represent a nearly unified structure…
Stator lamination & stator core
Lamination production requires both Accuracy and Precision
Two basic concepts for production exist
• Laminations may be cut ( machined ) from steel sheet materials
• Laminations may be stamped from sheet, or coil materials…
The following processes exhibit these two concepts
• Laser cutting
• Water jet cutting
• Electrical Discharge Machining ( EDM )
• Other
• Metal stamping methods
•Progressive dies
•Steel rule dies
•Fine blanking….
The typical stator lamination
• All of the cutting methods involve tracing the perimeter of the part until all scrap material is removed from the part contour…
• There is approx 54”
total perimeter in this stator lam..
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Laser cutting video
There are some disadvantages with the laser cutting process
• Production rates are not extremely fast
• There is minimal likelihood for improvements in production rate…as throughput is determined by part geometry…particularly total perimeter inches.
• Cost reductions from process improvements are minimal…
• Precision parts are not as good as one would like
for core stacking
Large & small
Stator cores
Note : the surface
condition on the
OD contour for
each of these
cores….
Large core exhibits
condition we call a
“saw tooth”
surface
There exists some significant advantages to this type of processing
• Usually there is minimal “set‐up”
requirements to start production…
• Little, or no capital expense for tools, or fixtures..
• Changes with part features are easily…and economically made… usually with simple program modifications…
Stamping laminations as production alternative..
The basic concept for stamping production…is Pushing a hardened steel punch through material…and into a matching die cavity…
This is a high impact process…
• The punch penetrates the material to a certain depth of thickness…shearing contour to match the geometry of the punch…
• The die cavity has matching contour to the punch…but is a bit larger…
• As the force of impact reaches tensile strength of material…a break will occur in the die block releasing the sheared material…
Die on die block…matching punch in punch holder
Two important stamping references
• Piercing operations…typically produce features in parts
• Blanking operations…typically remove parts from the sheet…
Piercing operations in laminations
• Typically would put ID contours in stators….shaft holes in rotor lams
• Slots in both stator and rotors
• Vent holes in rotors
• Bolt holes for assembly
High Speed Piercing Operations
• Pictured is a high speed indexing press…
• Blank is inserted on the driver…
• Press indexes a programmed number of times piercing equal number of rotor slots
Typical slot die for high speed notching
• This die produces one slot with each press stroke..
• High speed notching presses can run up to 1500 SPM
• slotting operations may produce 24 to 110 slots per lam
The Blanking Operation
• The blanking operation removes parts from the sheet…
• The blanks pass through the die block
• Dimensions are formed by the contour of the die…
A section lam produced from a blanking operation
• At right is a stamped lamination that is produced solely from a blanking operation…
• This part is entirely produced in the die cavity…
• There are no pierced features in this part
Compound Stamping Operations
• Compound stamping dies perform both the blanking & piercing operations with one stroke…
• At the right…is a “donut” produced from a compound die process… ID is pierce, OD is blanked…
Compound die construction Compound stamping OP
with automated parts unloading
• Compound stamping with parts unloader…
• video There are some real advantages
with stamping production of
lams
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Improved process rates
Better production throughput
Lower piece part costs
Better accuracy on part features
Higher level of precision……. There is a downside to this production method
• There will be some capital expense involved for tools
• Separation of parts from scrap can be difficult
• Finished parts need to be collected, sorted, oriented…
• Without automation, process can be labor intensive…
Pick and place automation
• Robotic video….
The Progressive Die
• The progressive die performs multiple operations with each stroke
• Operations are performed within incremental sections…called progressions, or multiples
Progressive Die
Progressive Die Stripper Plate
• The stripper plate mirrors the punch configuration
• Stripper plate makes first contact with the stock strip
• Stripper plate is last to release before strip progresses
The strip layout
• The strip layout shows the operations being performed in each progression.
• This strip shows five stations, plus a cut‐off…
• Pilot holes assist with positioning of the multiple…
Progressive Die with Strip Layout
Advantages with progressive die stamping ops
• High speed processing rates….
• Better throughput capabilities…provides for lower labor costs
• Parts are removed in an organized, orderly fashion…little, or no sorting is required
• Multiple operational options can be built into the stamping die….
Progressive die in action
• Video clip…progressive die stamping..
Disadvantages to prog die production
• There can be considerable upfront capital expense for tooling
• Tools can be extremely complex, require complicated monitoring, and significant maintenance…
• Lower volume production requirements can be more costly than with simpler processes…
• Changes in part features can be nearly impossible, and/or costly to achieve…
Estimating budgetary costs
• Raw materials
• Presented in sheet form…
• Presented in coil form…
• Ready for production…
Frame the part into squares/rectangles
• Assume 4.5” stator lamination…
• Frame by square sheet…
• Square to be 4.75” x 4.75”
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Calculate volume of material…
Assume lamination thickness to be 0.025”
Assume typical electrical grade silicon steel
Calculate 4.75 x 4.75 x 0.025 x 0.284 = 0.160#
Estimated cost for material
• Each lam will required 0.160# of raw material to make…
• Alternate thinking would be that 1000 laminations would require 160# of material…
• One can expect to pay $ 1.00 to $ 1.20 for ranges of fully processed steel grades M15‐
M47
• Lower M grades reflect better mag properties.
Review and dollarize our processes
• The laser cutting process must trace the part perimeter each time a lam is produced…
• Assume average cutting speed to be 40 ipm
• Our 18 slot stator lam of 54” is expected to take 1.35 min to cut…
• Without interruptions to process… we should produce approx 44 lams per hour…
• We can usually expect 10 mins interrupted process time… reducing out yield to 36 / hr Estimated cost to produce
• Boss says that the laser work center must return capital at the rate of $ 65 / hr…
• This rate will compensate labor…overhead…engineering program/set up…i.e. all costs to produce these parts
• Very simply… $ 65 / 36 = $ 1.81 / lam
• Addition of material cost $ 0.18 / lam
• Total cost to produce: $ 1.81 + 0.18= $1.99/ea
Now reviewing our laser cut video
• After we have completed the laser cut blank…we will pierce the slots on our indexing notching press…
• Load/unload/ pierce 36 slots…200 pc / hr yld
• Workcenter cost is $ 110 /hr… stamping cost is $ 0.55 / ea…
• Material cost for 25 “ blank is $ 4.85
• Laser cut cost for 32 / hr is $ 1.85
• Together with stamping… lam price is $ 7.25
Laser cutting this part completely
• Would have added 400” to laser program…i.e. 36 slots plus ID of lam…
• Part yield would decrease to approx 5 /hr…and cost $13 / ea..
• With material… added total lam price would be $ 17.85… instead of the $ 7.25 from last analysis…
Capital cost for tools
• Piercing die for this operation costs around $ 5,000 to be “production ready”
• 475 lams completely laser cut would be around $ 8,475
• 475 lams @ $ 7.25 /ea + $ 5,000 for tools gives total costs of $ 8,450…
• Merely from the economies of this situation…can you determine which course for action may be decided….?
Taking it up a level…
• Review our laser cut and pierced stator lam @ $ 7.25 / ea
• The first op of laser cutting blank contributed approx $ 1.85 of cost to this production…
• Consider construction of compound blanking die to produce this lam….
This die to cost some $ 30,000 !!!
• This tool would provide throughput at a rate around 800 pcs per hour…
• Workcenter costs to run this production would be at $ 200 / hr…
• Cost to produce this blank is $200 / 800 pcs • Compare this cost… $ 0.25 / ea with that of laser cutting… $ 1.85 / ea…
Payback period….
• Cost reduction of $ 1.60 /lam..
• Break even quantity is 30,000 / 1.60 • Tooling amortized at apporx 19,000 pcs…
The ultimate…progressive die
• Production rates for progressive tools can range from 3,000 pc / hr… up to 30,000 pcs / hr
• Workcenters capable of stamping with progressive tooling typically generate $200 / hr upwards to $ 500 / hr…
• Costs to produce lams under this format can be as low as pennies per each…
• Complex progressive dies can cost hundreds of thousands of dollars to construct
Brief summary……
• Material costs are driven by size and shape of laminations…generally processing is not a factor affecting material requirements…
• Processing costs are dependent on process throughput…
• Consideration for demand should be analyzed to determine compatible process…
Tooling costs….
• In general…tooling costs will be driven by size of tools…
• Costs will be driven by complexity of tools….
• Costs will be driven by capability demands at the workcenter….( i.e. The press machinery )
• Avoiding “over engineering” will control capital costs for tooling...