27-06-2014, 03:06 PM
Analysis of Water Hammer Forming on the Sheet Metal
Analysis of Water Hammer Forming on the Sheet Metal.pdf (Size: 727.99 KB / Downloads: 27)
Abstract
The most important item in the analysis of a metal forming processes is the determination of the magnitude
of the applied energy, since it is a parameter necessary for the design of processing equipment. Another
important factor is to know the extent of deformation to which a work piece can be subjected before it fails.
So, we ought to know the relationship between the energy and the deformation that it produces. The present
paper considers relationship between the energy applied and extent of deformation as well as the variations
of the radial strains, hoop strains along the radius under different hydraulic mediums is studied
Introduction
It can be defined as the process in which the desired shape and size are obtained through plastic
deformation of the material. This is a very economical process as the desired shape, size and finish can be
obtained without significant loss of material and also improves the strength of the product through strain
hardening. Both computational and experimental results are analyzed on the phenomena of condensation
induced water hammer in steam systems. This work clearly illustrates the potential damage that could occur
within a steam system, should a slug of liquid water be allowed to accumulate in the main. Water hammer
can be eliminated by a commercial water hammer eliminator, or by a cheap, homemade variety. Eliminators
work by using some elastic substance to relieve the instantaneous shock caused by the sudden stoppage of
water under pressure. An eliminator as close to each faucet as possible or valve is needed if system does not
have a low pressure system. During the 20th century there was considerable research conducted into water
hammer with column separation. Bergant et al, report attempts to span all of the significant research that
has been carried out and the occurrence of low pressures and associated column separation during water
hammer events has been a concern for much of the 20th century in the design of pipe systems for
distribution and cooling. The closure of a valve or shutdown of a pump may cause pressures so low that the
liquid will cavitate. The collapse of vapor cavities and rejoinder of water columns can generate nearly
instantaneously extremely large pressure that may cause significant damage or ultimately failure of the pipe
system. Water hammer forming of 50.8-mrn-dia low-carbon-steel sheet specimens using a water column as
the energy transmitting medium, presented that allows an estimation of the pressure variation, within the
water column, with time to be made. The energy is supplied from a falling weight that impacts a punch
resting on the top surface of the water column. The large mass of the falling weight relative to the mass of
the water column allows an energy balance to be made between the kinetic energy of the weight and the
strain energy absorbed by the column. Experimental results are presented that show the theory to be capable
of providing a reasonable estimation of pressure variation. In spite of the complexity of the situation and
the assumptions that have been made, the analysis of water hammer free forming of small diameter sheets,
assuming a simple spring mass system with a high mass ratio, does allow an estimate of the pressure time
profile to be made and an estimate of the polar deflection of the sheet
Experimentation
The working temperature is lower than the recrystallization temperature of the material and then the
process is called cold forming. According to the speed of (Energy Rate) forming, the processes can be
divided into the following categories. Explosive forming, Magnetic pulse forming and Electro Hydraulic
forming come under (High Energy Rate) High Speed Forming processes. This present work comes under
high speed forming. The speed of deformation in water hammer forming is less than that in explosive and
Electro hydraulic forming but greater than that of conventional forming processes and the Experimental
setup of the water hammer forming is shown in Figure
Water hammer forming theory
Water hammer forming process is similar to Explosive forming process in producing the shapes like
conical, convex and cup shaped. This is somewhat slower than the explosive forming process, similar to
explosive forming in which an enormous amount of energy is applied to the work piece, which deforms
into required shape within fraction of the second. In this process large amount of kinetic energy of a falling
weight is converted into pressure energy with the help of water hammer forming equipment. The pressure
energy is directed to the blank, which will deform the blank into the die shape. The central deflection of
blank depends on the amount of pressure developed in the cylinder, which indirectly depends on the height
of fall and weight of the fall. Also the thickness and size of the blank affects the central deflection and
energy required i.e. height and weight. The water hammer effect is explained below in the case of sudden
closure of cylinder, in which fluid in motion can be taken as the basis for analyzing the pressures developed
in the cylinder of the water hammer forming equipment. There is a sudden repeated knocking in the
pipeline when the pressure is released suddenly from the tap in a toilet. This mini version is known as
“water hammer”. Its magnified level is dangerous for irrigation and hydroelectric projects, but it has great
application in sheet forming process. The pressure waves that are created in the column of water by impact
of plunger; These created pressure waves are transmitted and exert the force on work piece, which is
plastically deformed by straining in an arrangement of die.
Conclusion
From the experimental data and graphs for radial strains it is observed that the radial strains and hoop
strains are almost negligible in the flange region of cup compared to the region near to the center. This
shows stretch forming of the material in the center of the cup. This is understandable, since in the
present experimental setup the cylinder is directly seated on the blank and the swing bolt force is
restraining the movement of the blank in the flange area. To avoid this it is suggested that a step should
be machined in the die holder. The cylinder should rest directly only on the step machined on the die
holder and the sheet metal gets effective sealing and contact only through the rubber “O”rings arranged
at the bottom of the pressure cylinder. In case of the data obtained for the deflection of the metal piece
it was observed that as the potential energy is increased there is an increase in deflection of the metal.
With accessories like motor driven positing device for drop weight, we can adopt water hammer
forming process very efficiently for low volume production in small industries. Suitable dies can also
be designed to achieve deep drawing with multiple blows and impact bulging for tubes etc.