1. Formaplode: Electrohydraulic Forming of Sheet Metal Second Report February 20, 2003 Rachel Sharp Corinne Packard Isaac Feitler Hao Hu

2. Review High velocity metal forming techniques have advantages in forming complex parts with close tolerances, from alloys that might not be formable by stamping. Electrohydraulic forming uses the explosive force generated by a high energy underwater discharge to deform a workpiece into a die.

3. Review, Continued A basic apparatus for Electrohydraulic forming includes a pressure vessel, a matching die, a capacitor bank, and an electronic control system to trigger the discharge.

4. What’s New? Pressure vessel design Reconsidered workpiece material; we’ll use Aluminum first, then possibly Titanium. Better understanding of failure-postponing phenomena in high-velocity deformation. Ready to begin ordering some parts. Some lower-power capacitor banks are available.

5. Pressure Vessel Design Considerations The weakest part of the system is the workpiece. The workpiece is strongest when it has been bulged out to a hemisphere. A smaller workpiece requires more pressure to strain. The pressure it takes to strain a small (3”) workpiece when it is hemispherical should be the upper bound for the pressure the vessel must withstand.

6. Pressure Vessel and Die Assembly Image by Hao Hu

7. 2D VIEWS Images by Hao Hu

8. Basic Properties of Aluminum High strength to weight ratio Corrosion Resistance Surface reacts with oxygen to form aluminum oxide Protects against corrosion by oxygen, water, and chemicals Electrical Conduction Heat Conduction Heats up quickly and evenly, also cools quickly Light and Heat Reflection Reflects about 80% of incoming light, as well as heat Shaping Properties Shaped by most metal working process Can also be bolted, glued, riveted, soldered, and welded

9. Why High Velocity? Metals normally fail in quasi-static (low velocity) tension when a phenomenon called ‘necking’ occurs. In necking, cross-sectional area decreases and stress increases, to the point of failure. At high velocities, inertia plays a role in the deformation, and can offset the loss of cross sectional area, reducing stress, and allowing greater strains before failure. Metals in tension may also form internal voids, which contribute to a loss in area and failure.

10. Parts for the Pressure Vessel 6” lawn ornament sphere for vessel casting High tensile strength epoxy Gasket material 10” steel drain pipe to cast in Copper rod for electrodes Valves and tubing for water and vacuum Nuts and bolts for clamping

11. Capacitor Bank Search 5kJ or greater discharge energy desired So far, 1kJ bank may be available on campus via Edgerton Center A hobbyist’s 3kJ bank may be another option, but it is off-campus. 1kJ – 3kJ of discharge energy should certainly create measurable results, but would probably not be sufficient for demonstrating the forming of a useful part.

12. Gantt Chart 1234567891011121314 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

13. Risks and Contingencies Relying on outside sources for key components such as capacitor bank. We may be constrained to a low energy explosion. Large turnaround time for experiment setup. Mirror casing shape potentially too complicated.