Formaplode:
Electrohydraulic
Forming of Sheet Metal
Second Report
February 20, 2003
Rachel Sharp
Corinne Packard
Isaac Feitler
Hao Hu
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.
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.
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.
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.
Pressure Vessel
and Die Assembly
Image by Hao Hu
2D VIEWS
Images by Hao Hu
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
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.
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
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.
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 (at MIT, outside of MIT if needed)
Pressure Vessel assembly
CAD & 3D printing of mold
Break
Casting of mold
Electrohydraulic test
Funnel formation
Final part formation
Presentation preparation
Pressure Vessel
Capacitor Bank
Mold
Electrohydraulic forming
Final Presentation
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.