electrohydraulic forming of sheet metal rachel sharp corinne packard isaac feitler hao hu third...
Post on 22-Dec-2015
239 views
TRANSCRIPT
Electrohydraulic Formingof Sheet Metal
Rachel SharpCorinne Packard
Isaac FeitlerHao 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 100-1000 fpsHydraulic press- 0.2 fpsMechanical press- up to 5 fpsDrop hammer- 1-20 fps
Strain rate and fracture initiation
Low ε-rateNecking in a small areaLittle 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 ratesOnly one die neededTubular designs possibleCloser 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
ConsiderationsEpoxy was chosen for ease of casting, electrical insulation, fracture resistance2-3” of high-strength epoxy needed for
safetyCuring issues —limited suppliers
Cast into steel pipe with 10” inside diameter to convert from tension to compression on the epoxyPipe scrap needed, found in Southampton
Calculations
32
31
31
32
max 2
)(2
rr
rrP y
r
tP y2
Thick-walled sphere
For deforming a workpiece:
y 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 [email protected]• 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
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Week
Bre
ak
Pressure Vessel Capacitor Bank Mold Electrohydraulic forming Final 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
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Week
Bre
ak
Pressure Vessel Capacitor Bank Mold Electrohydraulic forming Final 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 assemblyDecreased time with an apparatus will limit experimental work, but excess time was included in original timeline
Next Steps
Finish calculations for clamping safetyMax. force~170,000lbs. Investigating
bolts, clamps, and hydraulic presses
Investigate casting and cast dies
Transport Magnaform
Assemble apparatus