This document discusses several advanced metal forming processes that use energy sources other than conventional machines to deform metals at high rates. It describes high energy rate forming processes that apply energy over a short time period to produce high particle velocities. Explosive forming and electrohydraulic forming are covered, which use explosives or electrical discharge to generate shockwaves. Magnetic pulse forming and electromagnetic forming are also summarized, which use intense magnetic fields to deform conductive materials. Finally, hydroforming is introduced, using water pressure to form sheet or tubular metals into complex shapes.

1. 05 ADVANCED
FORMING PROCESSES

2. Introduction
 Advanced forming processes:-
 In conventional forming, conventional machines are used for deformation of
metals.
 In advanced forming process, we use energy or combination of energies
(Explosive, Electric energy, magnetic energy, hydraulic energy, ) to deform the
metal. Rate of forming is more in advanced forming process.
 The metals which can not be worked by conventional forming can be worked by
this process.

3. High Energy Rate Forming (HERF) Processes
 Larger energy is applied for a very short interval of time.
 High particle velocities are produced in contrast with conventional forming process.
 The velocity of deformation is also very large and hence these are also called High Velocity
Forming (HVF) processes.
 Many metals tend to deform more readily under extra fast application of force.
 Large parts can be easily formed by this technique.

4. Advantages of HERF Processes
Production rates are higher, as parts are made at a rapid rate.
Die costs are relatively lower.
Tolerances can be easily maintained.
Versatility of the process – it is possible to form most metals including difficult to form metals.
No or minimum spring back effect on the material after the process.
Production cost is low as power hammer (or press) is eliminated in the process. Hence it is
economically justifiable.
Complex shapes / profiles can be made much easily, as compared to conventional forming.
The required final shape/ dimensions is obtained in one stroke (or step), thus eliminating
intermediate forming steps and pre forming dies.
Suitable for a range of production volume such as small numbers, batches or mass production.

5. Limitations:
Highly skilled personnel are required from design to execution.
Not suitable to highly brittle materials
Source of energy (chemical explosive or electrical) must be handled carefully.
Governmental regulations/ procedures / safety norms must be followed.
Dies need to be much bigger to withstand high energy rates and shocks and to prevent
cracking.
Controlling the application of energy is critical as it may crack the die or work.

6. Applications
 In ship building – to form large plates / parts (up to 25 mm thick).
 Bending thick tubes/ pipes (up to 25 mm thick)
 Radar dishes
 Elliptical domes used in space applications.

7. Explosive Forming
 Introduction
 A punch in conventional forming is replaced by an explosive charge.
 Explosives used can be:
 High energy chemicals like TNT, trinitrotoluene (TNT)RDX, Royal Demolition eXplosive
and Dynamite.
 Gaseous mixtures
 Propellants.

8. Types of explosive forming:
1) Unconfined type or Standoff technique
2) Confined type or Contact technique

9. 1) Unconfined type (or Standoff technique)
Principle:
 The work is firmly supported on the die and the die cavity is evacuated.
 A definite quantity of explosive is placed suitably in water medium at a definite stand off distance
from the work.
 On detonation of the explosive charge, a pressure pulse (or a shock wave) of very high intensity is
produced.

10. 1) Unconfined type (or Standoff technique)
When the pressure pulse impinges against
the work (plate or sheet, the metal is deformed
into the die with a high velocity of around 120
m/s (430km/h).
The vacuum is necessary in the die to
prevent adiabatic heating of the work which may
lead to oxidation or melting.
Role of water:
i) Acts as energy transfer medium
ii) Ensures uniform transmission of energy
iii) Smooth application of energy on the work
without direct contact.

11. Process Variables
Process Variables
i) Type and amount of explosive: wide range of explosive is available.
ii) Stand off distance – SOD- (Distance between work piece and explosive): Optimum SOD must be
maintained.
iii) The medium used to transmit energy: water is most widely used.
iv) Work material properties (Ductile)
v) Vacuum in the die

12. 1) Unconfined type (or Standoff technique)
 Advantages:-
Shock wave is efficiently transmitted through
water and energy is transmitted effectively on
the work
Less noise
Less probability of damage to work.
Large and thick parts can be easily formed
Economical, when compared to a hydraulic press
Limitations:
 Optimum SOD (Stand off distance ) is essential for
proper forming operation.
 Vacuum is essential and hence it adds to the cost.
 Dies must be larger and thicker to withstand shocks.
 Not suitable for small and thin works.
 Explosives must be carefully handled according to the
regulations of the government.

13. Applications:
Ship building
Radar dish
Elliptical domes in space applications

14. 2) Confined System (or Contact Technique)
 Principle:
 The pressure pulse or shock wave
produced is in direct contact with the
work piece (usually tubular) and hence
the energy is directly applied on the work
without any water medium.
 The tube collapses into the die cavity and
is formed.

15. 2) Confined System (or Contact Technique)
Advantages:
Entire shock wave front is utilized as there is no loss in water.
More efficient as compared to unconfined type.
Disadvantages:
More hazard of die failure
Vacuum is required in the die
Air present in the work piece (tube) is compressed leading to heating.
Not suitable for large and thick plates.
Applications:
Bulging and flaring of tubes.

16. Electro hydraulic Forming
Principle:-
A sudden electrical discharge in the form of
sparks is produced between electrodes and this
discharge produces a shock wave in the water
medium. This shock wave deforms the work plate
and collapses it into the die.
The characteristics of this process are similar to
those of explosive forming. The major difference,
however, is that a chemical explosive is replaced by a
capacitor bank, which stores the electrical energy.
The capacitor is charged through a charging
circuit. When the switch is closed, a spark is
produced between electrodes and a shock wave or
pressure pulse is created. The energy released is
much lesser than that released in explosive forming.

17. Electro hydraulic Forming
Process Characteristics:
i) Stand off distance: It must be optimum.
ii) Capacitor used: The energy of the
pressure pulse depends on the size of
capacitor.
iii) Transfer medium: Usually water is used.
iv) Vacuum: the die cavity must be evacuated
to prevent adiabatic heating of the work due
to a sudden compression of air.
v) Material properties with regard to the
application of high rates of strain.
Advantages:
i) Better control of the pressure pulse as source of energy is electrical-
which can be easily controlled.
ii) Safer in handling than the explosive materials.
iii) More suitable if the work size is small to medium.
iv) Thin plates can be formed with smaller amounts of energy.
Limitations:
i) Suitable only for smaller works
ii) Need for vacuum makes the equipment more complicated.
iii) Proper SOD is necessary for effective process.
Applications:
They include smaller radar dish, cone and other shapes in thinner and
small works.

18. Magnetic pulse forming (MPF) or Electromagnetic Forming
 Magnetic pulse forming (MPF) is a forming technique for the plastic deformation of a plate with a rate of 15 to 300 m/s
using a high intensity magnetic field.
 The EMF process uses a capacitor bank, a forming coil , a field shaper , and
an electrically conductive workpiece to create intense magnetic fields that are
used to do the useful work.
 This very intense magnetic field, produced by the
discharge of a bank of capacitors into a forming coil, lasts only a few
microseconds.
 The resulting eddy currents that are induced in a conductive
workpiece that is placed close to the coil then interact with the magnetic field
to cause mutual repulsion between the workpiece and the forming coil.
 The force of this repulsion is sufficient to stress the work metal beyond its yield
strength, resulting in a permanent deformation.

19. Magnetic pulse forming (MPF) Electromagnetic Forming

20. Advantages and Limitations MPF:
Applications
 This process is primarily applied in
the forming of good conducting
Materials such as: copper, aluminum,
silver and low carbon steel. It can also
be used to form a poor conductor like
stainless steel.
 Electromagnetic forming is chiefly
used to expand, compress, or form
tubular shapes.
Advantages
 It gives a high rate of production
 Non contact forming
 Strength: joints made by this process are typically
stronger than the parent material.
 Tooling: the tooling for process is relatively inexpensive .
Limitations:
 The process is also limited to those materials that are
electrically conductive
 As forming time is very less, the material does not lend
itself to deep drawing of materials.

21. Forming with hydrostatic pressure- Hydro Forming
INTRODUCTION:-
Hydro Forming uses water pressure to form complex shapes from sheet or tube material.
The pressure may go up about 60,000 psi depending on the component.
As the automobile industry strives to make car lighter, stronger and more fuel efficient, it will
continue to drive hydro forming applications.
Some automobile parts such as structural chassis, instrument panel beam, engine cradles and
radiator closures are becoming standard hydro formed parts.

22. 22
METHODS OF HYDRO FORMING
There are two types of Hydro forming:-
1. Sheet Hydro forming
2. Tube Hydro forming
 Sheet hydro forming converts the irregular shaped material into a finished and uniform
thickness sheet.
 The tube hydro forming process is used to form parts in materials such as steel tubes and
aluminum extrusions by applying hydraulic pressure.

23. 23
SHEET HYDRO FORMING
 Sheet hydro forming involves forming of sheet with application of fluid pressure.
 A sheet metal blank informed by hydraulic counter pressure generated by punch drawing
sheet into pressurized water chambers.
 The water pressure effectively punches the sheet firmly against punch to form required shape.
 The major advantage of fluid forming is increased drawing ratio.
 The process take place in two stages performed during one press stroke.
 The sheet in preformed by applying low fluid pressure while it is in clamped firmly by a blank
holder pressure.
 Preforming achieves on evenly distributed strengthening in the component center.
 In next step fluid pressure in gradually increased and blank holder pressure in controlled
relative to sheet reformation.

24. 24
Fig. Sheet hydro forming