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HERF is a nonconventional forming process.Different types of HERF are explosive forming,hydraulic forming and magnetic 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,



HenceThe pressure required is then According to the direction-energy criterion


Hence Therefore, the answer is the same, or p=2.8MPa