high emergy rate

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SEMINAR ON HIGH ENERGY RATE FORMING
THAPAR UNIVERSITY, PATIALA Delivered
to Delivered by ER. VINOD KUMAR
SINGLA RUPESH KAUSHIK (Sr. Lecturer) M.E.
(P IE) 1st Year (Mechanical Engg. Deptt.
) 800882007
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INTRODUCTION

• High-energy rate forming (HERF) refers to process
  that form parts at very high velocities and
  extremely high pressure. A more accurate name for
  process might be high velocity forming because
  the most distinguishing feature is the high
  forming velocity rather than the expenditure of
  large quantities of energy. All the HERF
  processes involve a short, sharp, forming energy
  input usually microsecond duration.
• The energy level employed in HERF very widely
  depending upon the requirement of application.
  Generally speaking, HERF process makes use of
  short burst of energy that is transmitted to the
  part surface through a medium such as water or
  air. The resulting force or shockwave acts to
  force the part into a die cavity that has the
  desired shape of finished part. Forcing the part
  into a die in this manner drastically reduces die
  cost because the need for a male die is
  completely eliminated.

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INTRODUCTION

• Materials being formed at a very high velocity
  behave almost like a fluid they can be formed
  beyond their usual limits and maintain excellent
  dimensional control. HERF will typically improve
  material proprieties by improving the ultimate
  tensile strength and producing a more uniform
  strain throughout the part.
• Three processes are prominent in the HERF family
  they are
• Electromagnetic forming
• Explosive forming
• Electrohydraulic forming

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Why need this type of system
Process Velocity m/sec
Hydraulic press 0.03
Brake press 0.03
Mechanical press 0.03-0.73
Drop hammer 0.24-4.2
Gas-actuated ram 2.4-82
Explosive (HERF) 9-228
Magnetic (HERF) 27-228
Electrohydraulic (HERF) 27-228

• Approximate deformation velocity

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1) Electromagnetic forming

• Electromagnetic forming (EM forming or
  Magneforming) is a high energy rate metal forming
  process that uses pulsed power techniques to
  create ultrastrong pulsed magnetic fields to
  rapidly reshape metal parts.
• In practice the metal "work piece" to be
  fabricated is placed in close proximity to a
  heavily constructed coil of wire (called the work
  coil). A huge pulse of current is forced through
  the work coil by rapidly discharging a high
  voltage capacitor bank using an ignitron or a
  spark gap as a switch. This creates a rapidly
  oscillating, ultrastrong electromagnetic field
  around the work coil.
• The rapidly changing magnetic field induces a
  circulating electrical current within the work
  piece through electromagnetic induction, and the
  induced current creates a corresponding magnetic
  field around the metal work piece. Because of
  Lenz's Law, the magnetic fields created within
  the metal work piece and work coil strongly repel
  each another.

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1) ELECTROMAGNETIC FORMING

• The high work coil current (typically tens or
  hundreds of thousands of amperes) creates
  ultrastrong magnetic forces that easily overcome
  the yield strength of the metal work piece,
  causing permanent deformation. The metal forming
  process occurs extremely quickly (typically tens
  of microseconds). The forming process is most
  often used to shrink or expand cylindrical
  tubing, but it can also form sheet metal by
  repelling the work piece onto a shaped die at a
  high velocity.
• Since the forming operation involves high
  acceleration and decelleration, inertia of the
  work piece plays a critical role during the
  forming process. The process works best with good
  electrical conductors such as copper or aluminum,
  but it can be adapted to work with poorer
  conductors such as steel.

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Working of electromagnetic forming

• Electromagnetic forming is based on something
  called the Lorentz force. Basically whenever an
  electrical current is rapidly imposed within an
  electrical conductor, it will develop a magnetic
  field. This change in magnetic field will induce
  eddy currents in any nearby conductor that
  generally run in a direction opposite to the
  primary current (like in a transformer). These
  eddy currents develop their own magnetic field
  and cause a mutual repulsion between the
  workpiece and actuator. This technique is quite
  general and is suitable for any workpiece made
  from a good conductor provided the current pulse
  is of a sufficiently high frequency.

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Working of electromagnetic forming
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Arrangement in electromagnetic forming
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Manufacturing part with the help of
electromagnetic forming
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Design with the help of electromagnetic forming
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Manufacturing of rings
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Application

• Used by automotive industries to form and
  simultaneously swage copper rings around rubber
  seal in ball joint assembly
• Retaining band into oil filter
• Repair dents
• Making aircraft part.

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Advantages

• Only one die require
• No requirement of part lubrication
• Easily automated with high rates
• Applicable to high volume production

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Disadvantages

• Coil placement sometime limits configuration
• Electromagnetic forming can be used to form
  light-gauge metal into shapes up to 300mm.
• Capital cost is potentially very high

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2) Explosive forming

• Explosive forming was used in the 1960s for
  aerospace applications, such as the chine plates
  reconnaissance plane and various Soviet rocket
  parts it continued to be developed in Russia.
  Explosive forming was also applied in the 1960's
  in the USA for aerospace and space applications.
• It is a metalworking technique in which an
  explosive charge is used instead of a punch or
  press. It can be used on materials for which a
  press setup would be prohibitively large or
  require an unreasonably high pressure, and is
  generally much cheaper than building a large
  enough and sufficiently high-pressure press on
  the other hand, it is unavoidably a batch
  process, producing one product at a time.

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2) Explosive forming

• There are various approaches one is to place
  metal plate over a die, with the intervening
  space evacuated by a vacuum pump, place the whole
  assembly underwater and detonate a charge at an
  appropriate height above the plate. For
  complicated shapes, a segmented die can be used
  to produce in a single operation a shape that
  would require many manufacturing steps, or to be
  manufactured in parts. There is often some degree
  of work hardening from the explosive-forming
  process, particularly in mild steel.
• Explosive forming has evolved as one of the most
  dramatic of the new metalworking techniques.
  Explosive forming is employed in Aerospace and
  aircraft industries and has been successfully
  employed in the production of automotive-related
  components. Explosive Forming or HERF (High
  Energy Rate Forming) can be utilised to form a
  wide variety of metals, from Aluminium to high
  strength alloys. In this process the punch is
  replaced by an explosive charge.

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2) Explosive forming

• The process derives its name from the fact that
  the energy liberated due to the detonation of an
  explosive is used to form the desired
  configuration. The charge used is very small, but
  is capable of exerting tremendous forces on the
  workpiece. In Explosive Forming chemical energy
  from the explosives is used to generate shock
  waves through a medium  (mostly water), which are
  directed to deform the workpiece at very high
  velocities.

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Methods of Explosive Forming

• Explosive Forming Operations can be divided into
  two groups, depending on the position of the
  explosive charge relative to the workpiece.
• Standoff Method
• In this method, the explosive charge is located
  at some predetermined distance from the workpiece
  and the energy is transmitted through an
  intervening medium like air, oil, or water. Peak
  pressure at the workpiece may range from a few
  thousand psi (pounds/inch2) to several hundred
  thousand psi depending on the parameters of the
  operation.
• Contact Method
• In this method, the explosive charge is held in
  direct contact with the workpiece while the
  detonation is initiated. The detonation produces
  interface pressures on the surface of the metal
  up to several million psi (35000 MPa).

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Explosive Forming Set Up
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Explosive Forming Set Up
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Working of explosive Forming

• The die assembly is put together on the bottom of
  the tank. Workpiece is placed on the die and
  blankholder placed above. A vacuum is then
  created in the die cavity. The explosive charge
  is placed in position over the centre of the
  workpiece. The explosive charge is suspended over
  the blank at a predetermined distance. The
  complete assembly is immersed in a tank of water.
  
• After the detonation of explosive, a pressure
  pulse of high intensity is produced. A gas bubble
  is also produced which expands spherically and
  then collapses until it vents at the surface of
  the water. When the pressure pulse impinges
  against the workpiece, the metal is displaced
  into the die cavity.

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Explosives

• Explosives are substances that undergo rapid
  chemical reaction during which heat and large
  quantities of gaseous products are evolved.
  Explosives can be solid (TNT-trinitro toluene),
  liquid (Nitroglycerine), or Gaseous (oxygen and
  acetylene mixtures). Explosives are divide into
  two classes Low Explosives in which the burns
  rapidly rather than exploding, hence pressure
  build up is not large, and High Explosive which
  have a high rate of reaction with a large
  pressure build up. Low explosives are generally
  used as propellants in guns and in rockets for
  the propelling of missiles.

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Features of Low and High Explosives
Property High Explosives Low Explosives
Method of initiation Primary HE-ignition, spark, flame, or impact Ignition
Conversion time Microseconds Milliseconds
Pressure up to about 4,000,000psi up to about 40,000psi

• Time required to convert a working amount of
  high explosive into high-pressure gaseous products

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Advantages of Explosion Forming

• Maintains precise tolerances.
• Eliminates costly welds.
• Controls smoothness of contours.
• Reduces tooling costs.
• Less expensive alternative to super-plastic
  forming.

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Die Materials
Material of Die Application Area
Kirksite Low pressure and few parts
Fiberglass and Kirksite Low pressure and few parts
Fiberglass and Concrete Low pressure and large parts
Epoxy and Concrete Low pressure and large parts
Ductile Iron High pressure and many parts
Concrete Medium pressure and large parts
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Transmission Medium

• Energy released by the explosive is transmitted
  through medium like air, water, oil, gelatin,
  liquid salts. Water is one of the best media for
  explosive forming since it is available readily,
  inexpensive and produces excellent results. The
  transmission medium is important regarding
  pressure magnitude at the workpiece. Water is
  more desirable medium than air for producing high
  peak pressures to the workpiece.

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Explosive forming making complicated shape
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Advantages

• Explosive forming offers unique solutions because
  explosives can be applied in any shape and mass.
  We have no restrictions in product size, shape,
  material and thickness.Sizes range currently up
  to 10x2 meters, thicknesses from 0,3 mm aluminium
  to 60 mm stainless steel and many types of
  aluminium, titanium, stainless steel and nickel
  have been successfully formed by explosive
  forming. These ranges are not limits.
• The shape of the blank material can be optimized
  for any product shape. Sheets can be formed from
  flat or bent condition, or from a conical or
  cylindrical shape.An extreme example of applying
  an optimized blank shape is an explosive formed
  lobe mixer. A disk is folded and explosive formed
  in a segmented die. The result is a seamless
  shape while the conventional method is to weld
  the shape from many pressed segments.

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Advantages

• The tooling for explosive forming is relatively
  simple. One die half is needed without a mating
  part. Low cost tooling concepts decrease costs
  further.
• Prototypes can be delivered quickly. The tooling
  is relatively simple and can normally be
  manufactured quickly. The tooling does not need
  to be installed in a machine so that production
  can be started immediately.
• Explosive-forming has many benefits. It employs
  lower tooling costs and uses stamping type
  applications which only require a one-sided
  tooling die. Explosive energy can be transmitted
  differently across the part, in order to
  concentrate force onto specific forming features.
  It has a large size capability and is suited to
  difficult configurations.

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3) Electrohydraulic forming

• Electrohydraulic forming is a type of metal
  forming in which an electric arc discharge is
  used to convert electrical energy to mechanical
  energy and change the shape of the workpiece. A
  capacitor bank delivers a pulse of high current
  across two electrodes, which are positioned a
  short distance apart while submerged in a fluid
  (water or oil). The electric arc discharge
  rapidly vaporizes the surrounding fluid creating
  a shock wave. The workpiece, which is kept in
  contact with the fluid, is deformed into an die.
• Electrohydraulic forming is a variation of the
  older, more general, explosive forming method.
  The only fundamental difference between these two
  techniques is the energy source, and
  subsequently, the practical size of the forming
  event.

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3) Electrohydraulic forming

• Very large capacitor banks are needed to produce
  the same amount of energy as a modest mass of
  high explosives. This makes electrohydraulic
  forming very capital intensive for large parts.
  On the other hand, the electrohydraulic method
  was seen as better suited to automation because
  of the fine control of multiple, sequential
  energy discharges and the relative compactness of
  the electrode-media containment system.

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Electrohydraulic forming set up
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Electrohydraulic forming set up
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Application

• With proper design, electrohydraulic forming is
  capable of same performance described in
  electromagnetic forming. Used by automotive
  industries to form and simultaneously swage
  copper rings around rubber seal in ball joint
  assembly, retaining band into oil filter, for
  repair dents, for making aircraft part. However
  unlike electromagnetic forming, electrohydraulic
  forming can be performed on poor conductor and is
  typically cheaper because expensive coils do not
  have to be designed and build.

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• Thanks