Forging, calculating what counts

[JTknives]

I have often wondered what makes a power hammer move material so much faster then hand forging. Is it how fast it is able to strike or how much the head weighs. I thought I would crunch some numbers just to see what I come up with. Also does steel respond better to slower striking speed with more weight or faster striking speed with lighter weight? So let’s do some math.

Say a man/woman can swing a hammer 50 miles/hr and this hammer weighs say 3 pounds. How much contact energy is imparted into the steel?

50-mile/hr X 5280-ft/mile = 264000-ft/hr
264000-ft/ht / 60-min/hr = 4400-ft/min
4400-ft/min / 60-sec/min = 72.33-ft/sec

So the hammer is travailing at a speed of 72.33 feet per second
Now how much force is the hammer hitting with?

First we need to convert pounds to grains as that is the formula I know. There is 7000 grains in a pound.

3-pounds x 7000-grains/pound = 21000 grains
Now to convert that to foot pounds of force.

21000-grains x 72.33^2-ft/sec = 109864206.9
Now divide that by 450400
109864206.9 / 450400 = 243.9 ft/lbs

So that means that when the hammer comes in contact with the steel it is carrying 243.9 ft/lbs of energy. Does that mean that if you gently placed a 243.9 pound weight on the steel and let it sit there it would have the same affect as the hammer?

Now I will calculate that for a 50lb power hammer as well, I will save you the math.

That means that a 50 pound head moving at the same speed as the hammer 50 mile/hr would produces 4180.11 ft/lbs of force to the steel. Now does that really mean that the hammer can move steel at least 17.13 times faster then a human arm can?

Now what about Hydraulic presses?
Does that mean to get the same amount of material deformation as a 50lb power hammers one strike you would only need a 2.09 ton press. Could that also mean that a 20 ton press will do the work of 9.56 strikes of the power hammer? But the amount of time the weight is in contact with the material has to affect the amount of material deformation.

Do you remember silly putty; let’s use that as an example. You can stretch it quite easily if you pull it slow but if you pull it fast it does not want to stretch and it brakes. Does that mean that it is more efficient to forge with more weight at a slower speed then it is to forge with faster speed and less weight?

I don’t think I have answered any of my questions but I sure have created more

 

[NickWheeler]

Hey, I've often wondered why it's faster to drive 100 miles in the car than to walk. I think you should crunch those numbers.



If I hadn't already spent 5 hours on homework tonight, I'd try to figure out why a 100# ram moving 200+ times per minute on the 'ol Little Giant seems to move steel faster than me swinging a 3.5 lb. cross pein. Hmmmmmmm...... *scratching head*

Don't forget to calculate Ray Richard in your equation.

 

[JTknives]

are you making fun of me.

I mean i know why its faster with a power hammer but I'm trying to figure out is does steel like high speed whacks or low speed whacks. I mean i know ft/lbs are ft/lbs but how does the steel prefer to take it. whats the most efficient way to apply it. Say i make a treadle hammer that has a 300LB head. that head is connected to a 9 pulley block and tackle above it. then the rope goes down to a foot control then i push down to lift up the head. 300 pounds run through a 9 pulley block and tackle would require 33 pounds of force to lift. and if the foot control had a movement of 24" that would give the head a travel of 2.66 inches. would dropping a 300 pound weight 2 inches really do anything at all. I'm just trying to wrap my head around the property's of steel.

 

[galadduin]

We call it Momentum. The power hammer as far as I know gets its ability to move steel from the momentum / the area of the hammer edge, it is pressure I guess. So three variables for that: speed, weight and area. But Hydrolic press uses the pressure X time. Power hammer transfers energy to the piece at a little bit of time with its momentum, Press transfers the pressure (hammer size always matters) multiplied by time I guess.

Finally steel moves because of the energy transferred as pressure to the workpiece. So you have to convert all your equations to Energy base to compare because the two machines work by different principles. That means a bomb placed on the steel would move the steel also, but where I don' know .

 

[Dan Zawacki]

I would not underestimate the entropic forces at work. With a hammer and an anvil, you are losing a massive amount of energy which is being transferred to the anvil, through it, into the standm and then the ground. Any energy that makes the hammer rebound is also wasted (wasted, in this case means not moving the steel).

Moving steel is work, by the most basic definition of the word. Work requires energy. The more energy you put into the steel, the more it will move (the more work you can accomplish). The more of that energy you allow to chaotically dissipate into other places the less work can be accomplished, thus, the less the steel will move. This is why a good anvil, with a hard face, which reflects the energy (has a good rebound) well helps a smith, as more of the energy stays in the work peice.

Placing dead weight oto the steel is a more efficient way to transfer energy, as you are letting that transfer of potential happen at the speed of gravity. By striking more quickly, we, being able to hit with only a much lighter hammer, are able to cause much more energy (than out little hammer just falling) to strike the workpeice, but the speed is a diminishing return investment, in that the energy loss (not destruction, but chaotic dissipation as vibration, heat, and movement of all three, the workpeice [lateral and vertical motion] the hammer and the anvil) increases as the speed does.

 

[DrThunder88]

I could be wrong (it's been a long time since I flunked out of MatSci), but I think gladduin is right about the pressure, or "stress," being key to deformation. Increasing stress could mean decreasing the contact area, or increasing the force being applied. Decreasing the area is simple, that's how knives cut, after all. Now, to figure out the impulse of force of the impact, as I recall, take the mass of the hammer multiplied by the quantity difference in velocity divided by elapsed time.

My physics is almost as rusty as my materials, though.

 

[Karl B. Andersen]

It's all in the configuration of the dies and how the blow/press is transfered to the steel.
Unless of course, you're Ray Richard.

 

[birdog4]

Are you forgetting about ambient temperature, steel type, full moon, etc.
You guys have too much free time on yer hands.
Go make some cable hawks, all these questions will be answered, one way or another.

 

[Stacy E. Apelt - Bladesmith]

Jarod, You have probably gotten some sleep by now and this has all passed.

I=Fdt
There are many more things in this equation besides weight and speed. The mass of the anvil, and mass of the hammer are the two that make the most difference in forging. Hammer speed increases impulse, but at little gain in forging control. The reason a hydraulic press does so much is that it applies a greater force (20+tons) in a manageable time period of about one or two seconds. A 5 pound hammer traveling at the speed of sound could do about the same job....but would be much harder to control. A power hammer is a trade-off. It has a heavier hammer (25-500#) and a speed greater than a hand hammer. This allows for a controlled use of more force. But, as anyone who uses a power hammer knows, the faster the beat -the harder it is to control. Effectively a single heat with a hydraulic press delivers about ten blows with a 40,000# hammer...a power hammer delivers 50 blows with a 50# hammer, and your arm delivers 20-30 blows with a 4# hammer. Doesn't take higher math to see which delivers the most work. Your arm makes up for some of the shortfall by increasing the distance of the swing, thus increasing the impulse. A power hammer or hydraulic press doesn't need to worry about the distance...it is a disadvantage, actually, to them.

The thing I tell all new smiths is....It is not how hard you swing the hammer....or how heavy the hammer is.....but how accurately you strike the blow. If the steel is at the right temperature, and the blow allows all the impulse to be transferred to the steel the steel will move.

 

[Tai Goo]

Slow heavy blows are better for some stuff and light rapid blows are better for others. The force and cadence of the blow is something to consider in most forging operations.

Slow heavy blows are great when working large thick pieces or "hogging", and when you want to avoid mushrooming, etc...

Light rapid blows are great for forge welding, working thin stock, and when you want mushrooming or upsetting, etc...

... just a few examples.

Of course there are other things to consider,... placement of the blow, size and shape of the hammer face or dies, angle of the blow, etc... all have an effect on how the steel moves and what's most efficient for any given operation.

 

[JTknives]

I think stacy is right, it is now morning and I'm thinking clearly now. some times i get a wield hair when I'm up late and go off on something.

 

[ginshun]

I don't know anything about forging, but it is more complicated that just saying either speed of the hammer or the weight of the hammer matters more.

this is assuming that the energy imparted on the steel is what matters, that may or may not be true.

The formula for kinetic energy is 1/2mv^2 where m is the mass and v is the velocity, so you are squaring your velocity.

For simplicity sake, lets use SI units. Then we don't have to worry about lbs force and lbs mass and all that jazz.

The SI unit for energy is a joule.
1 joule = 1 kg (m/s)^2

Lets say to start with a guys can swing a 2 kg hammer at 10 meters per second (this is roughly a 5 lb hammer at 22 mph, a pretty hefty swing really, but anyway...) ...
the energy produced is (0.5)*(2)*10^2 = 100 J

If he can swing a 3kg hammer at the same speed the energy is:
(0.5)*(3)*10^2 = 150J

If he can swing the original 2kg hammer at 11m/s the energy is:
(0.5)*(2)*11^2 = 121J

So in this specific case, increasing the weight by 1 unit makes more of a difference. In the real world though, what is a bigger change? The change from a 2 to 3 kg hammer or the change from 10-11 m/s? I would say that in the scheme of things that is a bigger weight change than velocity change.

I think in real world terms, its the weight of the hammer that is making more difference. A person swinging a hammer, the weight of that hammer will never approach the weights of a power hammer, where I don't think the speeds are really all that different.

So for a 5lb hammer to impart the same energy as a 500lb hammer, it would have to increase a whole lot in speed. If I am doing my math and conversions correctly, in order to get the same energy as a 500lb hammer moving at 25mph, the 5 lb hammer would have to be moving at about 250mph. I don't think that a 5lb hammer moving at that speed is really practical.

I might be doing stuff all wrong though too, this is all off the top of my head.
(feel free to point out that I basically just babbled and didn't really help the issue)

 

[butchesforge]

3 1/2#hand hammer versus 50 or 60#s=no contest,but if you need to finese different story,but I wouldn't take anything for my homemade tirehammer,can hit hard or light:thumbup:Butch PS:age and experience matters to-----

 

[Tai Goo]

You're better off grinding them out!... just get some air hardening precision ground steel, a controlled electric heat treating furnace and a belt grinder... save yourself the trouble!

... besides,... doing the math is boring...

 

[sharpeknives]

I do it by hand just because I like the way it sounds. The hammer striking the steel is music to my ears. Also I can't afford a power hammer.