Electrohydraulic Forming of Sheet Metal Rachel Sharp Corinne Packard Isaac Feitler Hao Hu Third Update March 6, 2003

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

High-Velocity Metalworking Includes electrohydraulic, electromagnetic, explosive, and pneumatic-mechanical processes Deformation velocities fps Hydraulic press- 0.2 fps Mechanical press- up to 5 fps Drop hammer fps

Strain rate and fracture initiation Low ε-rate Necking in a small area Little plastic deformation in bulk Localized thinning leads to fracture

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

Advantages of Electrohydraulic Forming Over low ε-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

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

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

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

Calculations Thick-walled sphere For deforming a workpiece: Aluminum=72.5ksi

Considerations Viton rubber sheet chosen to seal between pressure vessel, workpiece, and die Cast metal for dies—easier and less expensive than machining entire parts Copper electrodes—high conductivity and availability Steel plate—strength and resistance to bending

Die progress CAD drawings of hemispherical, conical, and automobile mirror shapes

Capacitor bank update Magnaform electromagnetic former found in Watertown over 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

Progress Week Break Pressure VesselCapacitor BankMoldElectrohydraulic formingFinal Presentation 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 Electrohydraulic test Funnel formation Final part formation Presentation preparation

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

Revised Gantt Chart Week Break Pressure VesselCapacitor BankMoldElectrohydraulic formingFinal Presentation Vessel design and parts acquisition Capacitor bank acquisition Pressure Vessel assembly CAD Casting of mold Electrohydraulic test Funnel formation Final part formation Presentation preparation

Despite setbacks… Design changes increase safety— pressure 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

Next Steps Finish calculations for clamping safety Max. force~170,000lbs. Investigating bolts, clamps, and hydraulic presses Investigate casting and cast dies Transport Magnaform Assemble apparatus