Hammer versus press forming, kinetic energy vs pressure
Hammer versus press forming, kinetic energy vs pressure
(OP)
Hello,
I am trying to work out the difference in force exerted by either a press or a power hammer, for a sheet metal forming application.
I worked out that the kinetic energy of a hammer is calculated as E = ½mv².
Example of power hammer: 0.5 * 30 kg * (15m/sec)sq = 3.375 KJ
How does this relate to the force exerted by a 20 ton press, where the momentum/velocity doesn't really matter that much, or does it, if it is only 0.01 m/s ?
20 ton Press : 0.5 * 20000 kg * (0.01m/sec)sq = 1 KJ
That doesn't make sense, does it ?
There must be another force comparison between pressure and kinetic energy.
What about this relation :
1 tonne-force = 9806.65 N = 9806.65 joule/meter?
So the 20 ton press would exert a force of 196.13 KJ/meter ?
Still doesn't seem enough in comparison with the hammer blow.
Can anyone help me with this ?
Thanks, Benjamin
I am trying to work out the difference in force exerted by either a press or a power hammer, for a sheet metal forming application.
I worked out that the kinetic energy of a hammer is calculated as E = ½mv².
Example of power hammer: 0.5 * 30 kg * (15m/sec)sq = 3.375 KJ
How does this relate to the force exerted by a 20 ton press, where the momentum/velocity doesn't really matter that much, or does it, if it is only 0.01 m/s ?
20 ton Press : 0.5 * 20000 kg * (0.01m/sec)sq = 1 KJ
That doesn't make sense, does it ?
There must be another force comparison between pressure and kinetic energy.
What about this relation :
1 tonne-force = 9806.65 N = 9806.65 joule/meter?
So the 20 ton press would exert a force of 196.13 KJ/meter ?
Still doesn't seem enough in comparison with the hammer blow.
Can anyone help me with this ?
Thanks, Benjamin





RE: Hammer versus press forming, kinetic energy vs pressure
Pressure and energy are two diffent things units for energy are Joules =(kgm^2/s^2) or (Nm), pressure on the other hand is measured in N/m^2.
Now a constant force acting over a travelled distance ie:- Force * Distance = Energy, so if you consider dropping a mass of 10kg through a vertical height of say 5m we can say:-
mass*g*h= 10*9.81*5= 490.5 Nm or joules
Now assuming no losses you can say that the energy used in dropping the stone from 5m is converted into kinetic energy
therefore:-
mass*g*h=0.5*mass*V^2
[490.5/(0.5*10)]^0.5 = V = 9.9 m/s
Hope this helps
regards
desertfox
RE: Hammer versus press forming, kinetic energy vs pressure
Simply stated, you cannot directly compare the force used in metal forming operation of presses. For hammer and screw presses, their main capacity is work (energy). A hammer's work capacity is determined from the ram mass and drop height. For a screw press, the work capacity is stored in the rotating masses.
For a hydraulic press, the deformation force is directly controlled through adjusting pressure.
Source; Metal Forming Practise
by Heinz Tschaetsch
RE: Hammer versus press forming, kinetic energy vs pressure
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Forging http://mech.e.tripod.com
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Ddraig Breuddwydia....www.tailofthedragon.com
RE: Hammer versus press forming, kinetic energy vs pressure
RE: Hammer versus press forming, kinetic energy vs pressure
it is interesting to see how many perspectives there are on the subject.
So it seems there is no straightforward equation to relate the two types of forces/loads applied in the two forming processes.
I guess the difference in time, between the impulsive hammer force and the steady pressure of a press, is what makes the comparison difficult.
As CoryPad suggested, maybe it's worth setting up an experiment, where identical pieces of metal are subjected to either process and the resulting deformation is compared.
As to the application - I create negative, saddle-shaped curvature in sheet metal for sculpture, and after some experimentation am wondering which direction - to develop my tooling in - whether press or power hammer, or a heavy duty rolling press, like a pressurised, motorised English wheel.
Many thanks again - Benjamin
RE: Hammer versus press forming, kinetic energy vs pressure
You can ballpark the press requirements, but if the press or metal forming parameters are operated at the edge of capability the best way to determine formability is at the press. What is the ballpark? Depends on the product and the presses, things you learn about your plant over-time.
You could compare the (force)*(time) area under the press curve, but that numerical data isn't really captured by any press; which leads back to variables of quality and accuracy in measuring. This would require the synchronized numerical measurement of the ram force, and duration of forming; throughout the entire forming operation to draw the area and make a comparison or estimation to the next press.
After that, you might have to add a formation timer to the hydraulic press to compare to the estimate and have an efficient stroke. These ideas require instrumentation and/or control which most companies don't have on their presses.
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Forging http://mech.e.tripod.com
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Ddraig Breuddwydia....www.tailofthedragon.com
RE: Hammer versus press forming, kinetic energy vs pressure
RE: Hammer versus press forming, kinetic energy vs pressure
And thanks Robertmet, can you tell me what kind of press you are using for forging the tool steel?
That sounds promising.
Cheers, Benjamin
RE: Hammer versus press forming, kinetic energy vs pressure