HIGH ENERGY RATE FORMING
HIGH ENERGY RATE FORMING
PROBLEM-1(Explosive Forming)SOLUTION
(a) Standoff Distance-This is the distance between workpiece and
explosive
Given Diameter, D=1.2 mso Stand off Distance=0.51.2=0.6m(b)
Hydrostatic pressure
Hydrostatic head, H=2S (where S is the standoff distance)
H=20.6=1.2m
Hydrostatic Pressure, P=gH =10009.811.2 =11760 N/m2(c) Solid
Angle
The expression for solid angle is
=tan-1( ) =45
= (1-cos45)=0.14644180=26.36
(d) Central height of the formed partGiven
data:Efficiency,=0.4Yield Strength of mild strength,y=350 Mpa
Q. Calculate the efficiency of a explosive forming process under
water. Assume 3 kg for the weight of moving water front(w) and an
impact velocity(v) of 200 m/sec. Specific energy content of
explosive is 3103 KJ/kg. Mass of average charge 0.1 kg
PROBLEM-2(Explosive Forming)Solution:-Given Data:Weight of the
moving water front,(w)=3 kgImpact Velocity,(v)=200 m/secSpecific
energy content of explosive,=3103 KJ/kgMass of an average charge
=0.1 kg
Actual Energy Generated by the Explosion, Ec=es m
Q. A charge of TNT weighing 10 N is used in an unconfined
explosive forming operation. Plot the peak pressure over the work
surface with stand off distance.Ans.With water as the transmitting
medium, the peak pressure p obtained is given by
p=CWn/3D-n N/mm2PROBLEM-3(Explosive Forming)Peak Pressure vs
Stand off DistancePeak pressureStand Off DistanceQ. Calculate the
quantity of the explosiverequired for forming of an ultra-thin wall
steel decorating spherehaving diameter 2000mm and thickness 3mm.The
material is Q235 steel sheet.Take KN,the coefficient related to
shell structure and material property=4.51910-6PROBLEM-4(Explosive
Forming)Q. Calculate the deformation energy of the shellof metallic
decorating sphere having 10 number of multiple sections during
explosive forming where strain energy of each tapered section is
300 KJ and the strain energy of top and bottom end sheet is
250KJ.PROBLEM-5(Explosive Forming)solutionELECTROMAGNETIC
FORMING
Q. A brass tube(=300MPa) of 150mm outer diameter and 2.5mm
thickness is to be formed using EMF. Calculate the magnetic
pressure required to deform it, using a multiplying factor of 8 for
high strain rates.
PROBLEM-6(Electromagnetic Forming)Given data:Yield strength of
brass, =300MPa,Outer diameter Do=150mm,Thickness of tube
t=2.5mm,Multiplying factor, N=8
SOLUTIONQ. The charging voltage of an EHF machine is 16kV and
the bank of capacitors is 120 F. Calculate the machine capacity,
given that process efficiency is 20%.
PROBLEM-7(Electrohydraulic Forming)Given data:Charge
voltage(vc)=16kv,Capacitance(cap.)=120F
a)Energy stored in charged capacitor(or machine capacity) E=0.5
cap.(Vc )2 =0.512010-6 (16103)2 =15360 J =15.36 KJ SOLUTIONQ.
Calculate the peak pressure in water for 0.1 kg of TMT at a stand
of 0.5m & comment if this pressure is sufficiently high for
forming sheet metal.Solution:PROBLEM-8(Explosive Forming)
Where,p = peek pressure in MpaK = A constant dependent on the
explosive = for TNT
W = weight of the explosive in kgR = stand off distance of the
explosive from the work piece in meter.a = 1.5(usual)Therefore,
Q.A Thin-walled spherical shell is under internal pressure, p.
The shell is 0.5m in diameter and 2.5 mm thick. It is made of a
perfectly plastic material with a yield stress of 140 Mpa.
Calculate the pressure required to cause yielding of the shell
according to both yield criteria. Solution given, shell
diameter=0.5m shell thickness=2.5mm yield stress =140 Mpa
PROBLEM-9For a shell under internal pressure, the
membraneStresses are given by
Where r=254mm and t=2.54mm. The stresses in the thickness
direction, ,is negligible because of the high r/t ration of the
shell. Thus, according in the maximum shear stress criterion,
or
And
HenceThe pressure required is then According to the
direction-energy criterion
Or
Hence Therefore, the answer is the same, or p=2.8MPa
