Electrohydraulic Forming and Electromagnetic Forming Topics covered 1) Introduction 2) Process Principle 3) Constructional details 4) Advantages and Disadvantages 5) Application

1. ELECTROHYDRAULIC FORMING AND
ELECTROMAGNETIC FORMING
Submitted by –
Sandeep Kashyap(2015PR21)
M.Tech. (Prod. Engg.)
Submitted to –
Dr. Avanish Kumar
Dubey
Mechanical Engg. Deptt.
MNNIT Allahabad

2. Overview
 Electrohydraulic Forming and
Electromagnetic Forming
 Introduction
 Process Principle
 Constructional details
 Advantages and Disadvantages
 Application

3. Introduction :
 In these forming processes large amount of energy is applied
for a very short interval of time.
 These processes are useful to deform materials like Titanium
and Tungsten alloys, under high strain rates
 The parts are formed at a rapid rate, and thus these
processes are also called High Velocity Forming (HVF)
Processes.
 There are several advantages of using these forming
processes, like die costs are low, easy maintenance of
tolerances, possibility of forming most metals, and material
does not show springback effect.
 The production cost of components by such processes is low.
 The limitation of these processes is the need for skilled
personnel.

4. ELECTROHYDRAULIC
FORMING
(Also Known as Electrodischarge
or Electroshape or Electrospark
Forming)

5. Process Principle :
 Electro-hydraulic forming tools and processes,
produce a shockwave by creating a high voltage
discharge in a liquid that is in contact with the sheet
metal blank to be formed.
 The shockwave in the liquid is propagated towards
the blank and causes the blank to be deformed into
an open die that has a forming surface.
 The shockwave forces the blank into engagement
with the forming surface to form the metal blank into
the desired shape.

6. Constructional Details and
Working:
 A typical configuration of EHF includes a discharge chamber,
electrodes, forming die, and a pulse generator which consists of a
high-voltage low-inductive bank of capacitors C, a high-voltage/high-
current discharge switch D, and a charging/amplifying/rectifying circuit
is illustrated in Fig 1.
 The capacitor bank is capable of producing discharges of 5–25 kV and
can store energies up to 100 kJ.
 A sheet metal blank is placed on top of the discharge chamber.
 A one-sided die is positioned above the blank.
 After the air is evacuated from both sides of the blank, the chamber is
filled with water, fully immersing the electrodes.

7.  After the voltage is applied to the electrodes, an electrical breakdown
occurs between the exposed tips of the electrodes which leads to the
formation of a stable plasma channel.
 The channel expands quickly resulting in shock waves of pressure
which then continuously transform into flow of liquid. The pressure
pulse propagates through the water and applies pressure to the
surface of the blank forming it into the die cavity.

8.  The deformation can be controlled by applying external
restraints in the form of die or by varying the amount of
energy released, Fig 2.

9. Process Parameters:
 Stand off distance : It must be optimum.
 Capacitor used : The energy of the pressure
pulse depends on the size of capacitor.
 Transfer medium : Usually water is used.
 Vacuum : The die cavity must be evacuated to
prevent adiabatic heating of the work due to a
sudden compression of air.
 Materials formed : Materials having low ductility
or having critical impact velocity less than 30 m/s
are generally not considered to be good
candidate for EHF. All materials that can be
formed by conventional forming processes can
be formed by EHF also. These materials are
aluminum alloys, nickel alloys, stainless steels,
titanium, and Inconel 718.

10. Advantages and
Disadvantages :
Advantages :
 EHF can form hollow shapes with much ease and at
less cost compared to other forming techniques.
 A single step process (rather than progressive
stamping)
 Extremely fast
 Enables extremely deep forming (much more than is
possible with conventional stamping)
 Fine details and sharp lines can be easily formed
 Forming of male and female shapes (negative and
positive)
 The process does not depend on the electrical
properties of the work material.
 Safer in handling than the explosive materials.

11. Disadvantages :
 Suitable only for smaller works.
 Need for vacuum makes the equipment more complicated.
 Proper SOD is necessary for effective process.
 Each discharge of the electrodes to create the high voltage
discharge in the fluid results in the formation of impurities in the
water that results in vaporization of the electrodes and may
create surface defects in the surface of the part formed in the
process.
 The fluid in the vessel generally must be drained and replaced
for each tool cycle. The volume of fluid in the vessel for a larger
part tends to be fairly substantial and a considerable portion of
the cycle time of the tool is dedicated to draining and refilling the
vessel.
Advantages and
Disadvantages :

12.  It include smaller radar dish, cone and other
shapes in thinner and small works,
 Reduction of capital investment for low volume
aerospace applications,
 In Automobile sector such as inside components of
a passenger car door,
 Miniature and fancy equipments having
complicated profile for electronic industry, etc.
Applications :

13. ELECTROMAGNETIC
FORMING
(Also Known as Magnetic Pulse
Forming)

14.  This process is based on the principle stated by lorentz
force law that the electromagnetic field of an induced
current always opposes the electromagnetic field of the
inducing current.
 In this method a large capacitor bank is discharged
producing a current charge through a coiled conductor.
 If the coil has been placed within a conductive cylinder,
around a cylinder or adjacent to a flat sheet of metal, then
the discharge induces a secondary current in the
workpiece.
 This secondary current further causes it to be repelled
from the coil and conformed to a die or mating work
piece.
 The process is very rapid and is used primarily to expand
or contract tubing or to permanently assemble component
Process Principle :

15. Constructional Details and
Working:
 The setup of EMF consists of the pulsed power generator, the inductor
including a fieldshaper, if applicable, the workpiece and application-
dependent further tool components such as form-defining dies etc.
 The process is started by charging and subsequently discharging the
capacitor of the pulsed power generator.
 A sinusoidal current flows through the inductor. This current induces a
corresponding magnetic field.
 If there is an electrically conductive workpiece in direct proximity to
inductor, a second opposedly directed current is induced.
 The energy density stored in the magnetic field between workpiece
and inductor acts as magnetic pressure which can reach several
hundreds of megapascal and causes the acceleration and deformation
of the workpiece.
 The direction of the movement is always targeted away from the
inductor

16.  Depending on the geometry and the alignment of tool and workpiece,
three process variants can be distinguished. These are :
(i) electromagnetic compression of tubes and hollow profiles by means
of an inductor enclosing the workpiece,
(ii) electromagnetic expansion of tubes and hollow profiles by means
of an inductor positioned within the workpiece,

17. (iii) electromagnetic sheet forming, for which an inductor is positioned in
close proximity of a flat semi-finished part or a preformed component.

18.  Workpiece thickness – A higher thickness means that the
magnetic field diffuses slower through the workpiece wall.
 Electrical conductivity – The higher the electrical conductivity
of the workpiece, the better the shielding of the magnetic
field, the pressure difference in higher.
 Frequency – A higher frequency of the discharged current can
balance a low conductivity or a small wall thickness.
 Size of the capacitor bank
 The strength of the current, which decides the strength of the
magnetic field and the force applied.
 Gap between workpiece and tool coil – The smaller the air
gap, higher is magnetic field and pressure.
 Winding of the tool coil – For each pulse generator and each
forming task exists an optimum of number of turns.
Process Parameters:

19. Advantages and
Disadvantages :
Advantages :
 Suitable for small tubes
 Operations like collapsing, bending and crimping can be
easily done.
 Electrical energy applied can be precisely controlled
and hence the process is accurately controlled.
 The process is safer compared to explosive forming.
 Wide range of applications.

20. Disadvantages :
 Applicable only for electrically conducting materials.
 Not suitable for large work pieces.
 Rigid clamping of primary coil is critical.
 Shorter life of the coil due to large forces acting on it.
Advantages and
Disadvantages :

21.  Electromagnetic forming process is capable of a wide
variety of forming and assembly operations.
 Crimping of coils, tubes, wires
 Bending of tubes into complex shapes
 Bulging of thin tubes.
 It has found extensive applications in the fabrication of
hollow, non – circular, or asymmetrical shapes from
tubular stock.
 Flat coils have been used on flat sheets to produce
stretch (internal) and shrink (external) flanges on ring
and disc – shaped work pieces.
 Electromagnetic forming has also been used to perform
shearing, piercing, and rivettting.
Applications :

22. References :
 R.K.Rajawat, “Electromagnetic Forming – A Technique with
Potential Applications in Accelerator” Proceedings of APAC
2004, Gyeongju, Korea.
 Dhiraj Gayakwad, “A Review on Electromagnetic Forming
Process” 3rd International Conference on Materials
Processing and Characterisation (ICMPC 2014)
 Sergey Golovashchenko, Beverly Hills, MI (US), “Electro-
Hydraulic Forming tool having Two Liquid Volumes Separated
by a Membrane” Patent Application Publication, Pub. No.: US
2008/0134741 A1
 J. Varis, H. Martikka, “Prototyping of 3D sheet metal parts
using electro hydraulic forming” ISSN 1392 - 1207.
MECHANIKA. 2005. Nr.3(53)
 NPTEL
“http://nptel.ac.in/courses/112107144/Metal%20Forming%20
&%20Powder%20metallurgy/lecture9/lecture9.htm”