Electrohydraulic%20Forming%20of%20Sheet%20Metal

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Electrohydraulic Formingof Sheet Metal

• Rachel Sharp
• Corinne Packard
• Isaac Feitler
• Hao Hu

Third Update March 6, 2003
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Today

• Effects of high-velocity metalworking
• Update on progress
• Design alterations
• Next steps

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High-Velocity Metalworking

• Includes electrohydraulic, electromagnetic,
  explosive, and pneumatic-mechanical processes
• Deformation velocities 100-1000 fps
• Hydraulic press- 0.2 fps
• Mechanical press- up to 5 fps
• Drop hammer- 1-20 fps

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Strain rate and fracture initiation

• Low e-rate
• Necking in a small area
• Little plastic deformation in bulk

Localized thinning leads to fracture
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High strain rate

• Necking initiates and area strain-hardens before
  localized thinning occurs
• Velocity varies linearly, until necking
• Velocity gradient forms
• Non-uniform inertial forces produce tensile
  stresses in material outside of neck

Energy is distributed over more of the sample,
increasing ductility
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Advantages of Electrohydraulic Forming

• Over low e-rate pressing-
• Some metals can only be formed at high rates
• Only one die needed
• Tubular designs possible
• Closer thickness tolerances can be achieved
• Over explosive forming-
• Much slower production rates with explosives

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Design Decisions
Cast Metal Dies
Rubber flanges
Copper electrodes
Epoxy encased in steel pipe
Steel plate
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Pressure Vessel Design

• Hemisphere chosen over cylinder to reduce stress
  concentrations

To form a hemisphere, embed a spherical glass
ornament in epoxy halfway -Glass can be broken
out after cure -Low cost readily
available -Temperature not a concern
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Considerations

• Epoxy was chosen for ease of casting, electrical
  insulation, fracture resistance
• 2-3 of high-strength epoxy needed for safety
• Curing issues limited suppliers
• Cast into steel pipe with 10 inside diameter to
  convert from tension to compression on the epoxy
• Pipe scrap needed, found in Southampton

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Calculations
Thick-walled sphere
For deforming a workpiece
Aluminum72.5ksi
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Considerations

• Viton rubber sheet chosen to seal between
  pressure vessel, workpiece, and die
• Cast metal for dieseasier and less expensive
  than machining entire parts
• Copper electrodeshigh conductivity and
  availability
• Steel platestrength and resistance to bending

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Die progress

• CAD drawings of hemispherical, conical, and
  automobile mirror shapes

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Capacitor bank update

• Magnaform electromagnetic former found in
  Watertown over reuse_at_mit.edu
• Contains a 6kJ capacitor bank that will
  interface easily with our system
• Working out transportation to borrow the 1 ton
  machine for the remainder of our project
• Contingency remains 1kJ Boomer from Edgerton
  Center

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Progress
Week
1 2 3 4 5 6 7 8 9 10 11 12 13 14

Vessel design and parts acquisition
Capacitor bank acquisition (at MIT, outside of
MIT if needed)
Pressure Vessel assembly
CAD 3D printing of mold
Casting of mold
Break
Electrohydraulic test
Funnel formation
Final part formation
Presentation preparation
Pressure Vessel
Capacitor Bank
Mold
Electrohydraulic forming
Final Presentation
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Obstacles

• Epoxy is a special formulation and will take 6wks
  ? not feasible
• Other options investigated and debated
• Plaster compounds or cast metal
• Bored steel
• Central Machine Shop can have a steel billet
  bored by the end of next week
• They have stock on hand, but a donation from Ohio
  may be possible

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Revised Gantt Chart
Week
1 2 3 4 5 6 7 8 9 10 11 12 13 14

Vessel design and parts acquisition
Capacitor bank acquisition
Pressure Vessel assembly
CAD
Break
Casting of mold
Electrohydraulic test
Funnel formation
Final part formation
Presentation preparation
Pressure Vessel
Capacitor Bank
Mold
Electrohydraulic forming
Final Presentation
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Despite setbacks

• Design changes increase safetypressure vessel
  will now withstand 18,800psi !
• Outsourcing pressure vessel frees up laboratory
  group to focus on die fabrication and other
  assembly
• Decreased time with an apparatus will limit
  experimental work, but excess time was included
  in original timeline

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Next Steps

• Finish calculations for clamping safety
• Max. force170,000lbs. Investigating bolts,
  clamps, and hydraulic presses
• Investigate casting and cast dies
• Transport Magnaform
• Assemble apparatus

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