Forging and the physics of plasticity

[Tai Google]

Here?s something that seems hard to find good applicable information on.
http://en.wikipedia.org/wiki/Plasticity_%28physics%29

If we take into account the geometry of the metal, the effects of heat, the amount of force applied, the placement of the force, chilling effect of the anvil or die, the shape or geometry of the hammer or die face, etc? it gets really complicated!

Is forging strictly intuitive or are there some helpful rules and guidelines that it will always follow?

Strictly based on my own experience, I can come up with a few basic principals, but still desire to know more about it.

Check me on this?

#1. For every action there is a reaction.
For example, when you apply force to the surface of a flat bar of metal it becomes thinner, AND wider. Whenever possible use both the action and reaction to your advantage.

#2. The path of least resistance.
The flow of the metal always follows the path of least resistance. The path of least resistance can be manipulated or altered, by heat placement, and to some degree by the geometry of the hammer face or applied force.

#3. The effects of the amount of force applied.
In other words, with a light blow the force may not penetrate the metal clean through, and mushrooming on the side of the hammer blow or force will result. With a medium blow or ?efficient? applied force the metal does not mushroom but reacts the same clean through. With a heavy or hard blow, the metal swells in the middle, due to reverberation of the applied force. Not that any of these are right or wrong, but each can be used in certain instances to our advantage.

#4. Centered and symmetrical force and mass.
If the metal is centered or symmetrical the applied force can travel through the center and effect both sides equally or symmetrically, if the blow is efficient. If the metal form is asymmetrical, the flow will follow the path of least resistance.

[Martin Brandt]

Yup, dat's it I tink. But I tink da metal do it better if it know ya like wackin it. An if ya really do like wackin it, it's cause ya like what da metal do when ya wack it. And da more ya wack it, if ya like wackin it, da better da metal do what "you" said. An da more da metal do what "you" said, cause ya like wackin it, da better ya wack it da right way. An da more ya wack it da right way to get what ya want da metal ta do, ya get it ta do it even better. An da more ya get it ta do it even better, ya jes keep liken it more. Am I right on dis? I hope so cause I really like to be wackin on dat metal an gettin it ta do what I want it to do, at least most of da time. But even when it don't do it da way I want it ta do it, I learns sumpin new about it. It's a wonerful ting.

[Tai Google]

LOL

Here's a little exercise we call all try. Take a piece of clay, pinch it, squeeze it, twist it, poke it, pound on it and smear it around for 5 minutes. Then sit back and try to wrap our noodles around everything that just happened.

[Tai Google]

There's probably a lot we could say about dents... Any thoughts?

[Tai Google]

I know this topic of plasticity seems kind of funny, which is probably why folks don?t talk about it much,... but isn?t forging basically taking advantage of the plasticity of metals? So, to understand the principals of forging we need to have a basic understanding of plasticity. Does that make sense?

[azmike]

Dents are one of those things that i'm still working on -- eliminating not producing them. azmike

[Tai Google]

Mike, producing dents is very important, but in the end you usually want to eliminate them. The dents are an indication of how much material is being moved and the direction of the movement.

[Tai Google]

Another thing I?ve noticed about metals (and plasticity) that I like is that,? all they ever do is ?react?. They have their properties, but don?t do anything on their own. They don?t corkscrew, bend, stretch, or slide etc... or become blades on their own. They don?t do anything,? unless acted on by an outside force. They only react to what the smith does?

[Fox Creek]

I have always been intrigued by the two terms "Mallable" and "Ductile" which seem to have different compartmentalized meaningings to the material engineers. "Plasticity" seems a more useful concept for bladesmithing.

[azmike]

Tai, i know that making dents is important in working the metal, and that eliminating them as i get closer to finishing is the goal for me. I just got to work on not making the dents so deep and pronounced that they affect the end results-- get the dents out and end up with a blade too thin ( ask me about my first bowie attempt--soon to hopefully transformed into a filet knife for a friend that is going to retire soon and go fishin). no failures-just design changes. azmike

[Martin Brandt]

The plasticity of hot steel is what drew me back to forging after a small amount of it when I was in junior high. I attended a Northwest Blacksnith Association conference and watched a 5th generation Dutch smith turn steel into incredible objects of beauty and form. What little forging I had done was never more than putting a bevel on a knife blade already profiled at a grinder. I had had little concousness that you could do so much with metal. That you could transform your mental pictures into reality at the forge started me down the road to a lifes work of learning and creating. Every year the skill level gets a little better. It's a very reluctant plasticity when hand hammering, but with patience and careful thought you can move the metal to the form you want. I used to get blades formed into long blobs somewhat blade shaped, then draw around them on paper and then see what blade shape I could fit into that outline, then grind away everything else. With time , practice, and watching other smiths work I learned how to forge much closer to the shape I want the blade to be, so very little grinding away needs to be done, and the as forged blade is a close mirror of what I drew on paper before I started forging. It's all about building the skills and knowledge of what can be done to take advantage of the plasticity that is there. This forum, hammerins, visiting other shops, and experimenting in your own shop is the way to build those skills of hand and mind to take that plasticity to new levels.

[prizzim]

Whenever I describe the smithing process to someone, I tell them to think of hot metal as clay. The hotter, the squishier. That mental image gets a lot of people over the hump of understanding what's going on with hammer and anvil.

[TexasJack]

When you get the steel just at the right heat and it's moving - almost like clay - under the hammer, it's a very satisfying feeling.

[Tai Google]

Here's one I just finished "squeezing" out. It's 16-1/2 inches from 7/8ths round W2.


I'm going to try something different with the construction,... a "hidden full tang". I'm going to cut the tang off a little short, slot the wood and rivet it on, so the tang doesn't run all the way back. Then, I'm going to wrap over the joinery with Turk?s head knots, so none of it shows, and do a washer and stud on the back end.

[BlueSkyJaunte]

Tai, that is awesome! But you knew I'd say that, didn't you?