presented by Leo pauly Jithin A.S Dinu jose
The explosive forming of metals has been known for about 100 years. years. Explosive forming was first proposed at the Kharkov Aviation Institute in the 1940 ’s and was widely used in the mid-1950’s in the production of oversize parts for rockets and airplanes. Some suggestions to apply explosives were made at end of the 18th century, but they were not implemented as industrial applications.
The metal forming involves the detonation of an explosive charge, causing a shock wave and a large momentum in the water, the expansion of detonation gases, and the subsequent interaction with the metal plate. A metal plate is clamped into a mould, and then immersed in a water basin. The energy releasing upon explosion of high explosive substance acts directly or through a conductive medium on a metal plate and deform it to fit the die profile. Usually, explosive forming is done with the explosive charge in water
The charge used is very small, but is capable of exerting tremendous forces on the work piece. 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 work piece at very high velocities. The shock waves act as a punch. Explosive Forming is also known as HERF (High Energy Rate Forming)
Explosive Forming Operations can be divided into two groups, depending on the position of the explosive charge relative to the work piece.
There are two methods used when forming with explosives, are the standoff method and the contact method
Standoff Method
In this method, the explosive charge is located at some predetermined distance from the work piece and the energy is transmitted through an intervening medium like air, oil, or water. Peak pressure at the work piece may range from a few thousand psi (pounds/inch2) to several hundred thousand psi depending on the parameters of the operation.
Schematic Diagram of Stand off Method
Figure 1 shows an arrangement of Standoff Explosive forming operation. The die assembly is put together on the bottom of the tank. Work piece is placed on the die and blank holder placed above. A vacuum is then created in the die cavity. The explosive charge is placed in position over the centre of the work piece. The explosive charge is suspended over the blank at a predetermined distance (known as standoff 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 work piece, the metal is displaced into the die cavity.
The system used for Standoff operation consists of following parts: -
1)
An explosive charge
2)
An energy transmitted medium
3)
A die assembly
4)
The work piece.
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).
•
Few parts ---
concrete
•
Small explosive forces - glass fiber reinforced epoxy resins
high pressure intensities --- ductile cast iron and frequent use
•
high quality surface finish --- machined tool steel and long production runs
•
Gaseous, liquid, elastic and loose medium is used in practice as a conductive medium. The use of water as a universal conductive medium of good characteristics for transmission of energy impulse has gained most spread.
Contact
Method
In
this method, the explosive charge is held in direct contact with the work piece while the detonation is initiated.
The
detonation produces interface pressures on the surface of the metal up to several million psi (35000 MPa).
• It can simulate a variety of other conventional metal forming techniques such as stamp- or press-forming and spin-forming in a single operation • It can offer significant cost savings on short -run parts because it employs lower tooling cost • Explosive hydro-forming can efficiently form large parts
• improved quality of parts (by high-strength materials), • perfecting the installation through adapting active media to different shapes of part, • simply adapting to production process, • reduction of production stages, • flexibility of the process due to quick and simple transformation of the tool elements, • low production costs. Maintains precise tolerances. Eliminates costly welds. Controls smoothness of contours. Reduces tooling costs. Less expensive alternative to super-plastic forming.
Explosive forming is mainly applied for nuclear installations, gas turbine components, architectural buildings and art. Some examples are: ·Exhaust collectors for the Rolls-Royce MT30 gas turbine. Cover plates for a nuclear water basin. Many types of combustor liners from nickel alloys Many types of manifolds for both gas turbines with a very uniform thickness.
PROCESS ECONOMY The capital cost of an explosive forming facility are reported as being less than that of a conventional facility of equal capability by a factor ranging from 10:1 to 50:1. On the other hand, labour costs per part can be appreciably higher for explosive forming.
STRENGTHS -explosive forming is versatile (complex shapes possible) -requires low capital investment -increased ductility that may be obtained at certain deformation velocities WEAKNESS -requirement of specialist process knowledge -the need to handle explosives. -adverse effect on work piece surface due to shock waves
Boiler Products
Missile Components
Aircraft Radar Shields
