Forge Welding contact pressure?

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
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I have been thinking and wondering for a while about the amount of force needed to complete a forge weld. how much force is required between hot peaces of steel to get them to weld. do you just need to over come the modulus of elasticity of the steel at that temperature.
 
I took a damascus class with J.D. Smith. Once the billet was stacked, heated and fluxed to where it was at uniform welding temp we did the first weld in a vise. Basically just gave it a good squeeze to set the initial weld. From there we went to the press.

So to answer your question you can weld in a vise or with a hand hammer. The vise is more uniform and does not splatter hot flux everywhere.
 
I have a forging press with some large flattening dies.
 
Not much. I've set welds on 19 layer stacks that were over 3" thick with an 800 gram hammer and a medium-light blow.

-d
 
Details are important .You don't want any more oxide than you can avoid.Get the pieces hot, wire brush the oxide ,add flux and hammer. Initial blows are light ,followed by heavier blows after it's set.Blows should be from one end to another or from center out to help squeeze out slag. If the steel is hot enough and fluxed properly things should go together easily.
 
I think a lot of people my self included at one time thing that you really have to beat the steel to get it to weld. but i am thinking of my press in that the flat dies are 3" x 5" and that just sprieds out the 20 tons total i have to work with. so realy i would be doing a weld section about 1.5" wide by 3" long and maybe 2" thick per press. and i just was wondering if thats to much surface area for a 20 ton press.
 
JTknives said:
I think a lot of people my self included at one time thing that you really have to beat the steel to get it to weld.
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You'll find that you will REALLY frustrate yourself trying that,

you'll tend to blow the molten bits out of the joint and it will just about never weld.


the pictures you see of guys setting a weld where there's a HUGE halo of sparks around is more of a gimick than good shop technique. It DOES look cool though eh.


more heat, lighter blows..... you'll be glad you did
 
stephanfowler said:
You'll find that you will REALLY frustrate yourself trying that,

you'll tend to blow the molten bits out of the joint and it will just about never weld.


the pictures you see of guys setting a weld where there's a HUGE halo of sparks around is more of a gimick than good shop technique. It DOES look cool though eh.


more heat, lighter blows..... you'll be glad you did
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I know what you mean, the first time i did some damascus i just way over coated the blade with flux and beat the hell out of it. now like you say it does look cool but not very effective. then you look down and see the burnt line across your shirt. maybe that's what fanny packs are for, just fill them with cold water and if you catch fire thy burst and put you out.
 
I'm sure there are a ton of variations, but I was shown to make the whole weld in one press rather than sections. See if you can make your stack 5" or shorter (lengthwise to fit your flat die) and it may work out.

Good luck with it, Craig
 
cdent said:
I'm sure there are a ton of variations, but I was shown to make the whole weld in one press rather than sections. See if you can make your stack 5" or shorter (lengthwise to fit your flat die) and it may work out.

Good luck with it, Craig
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I might just make some special welding dies that are longer because mine are 4 or 5" wide and 3" long. but if i was to make a special set that was 3" wide and say 7" long and make them thick as thy will be sticking out a bit then it should work good. i just wonder how much force i can create on that large of a surface area. so as I'm a man that likes math lets see if i can solve this mathematically. so first off lets compute a hammer swing. So just guessing and a little timing it seams that a fast hammer swing is around 20 fps and at say 3 pounds that would equal. using this formula
8ac4afe868ab54cec61fddfa35a87bdb.png

E= (3lb x 20fps^2)/2 which is 600ft/lbs of energy in a hammer swing. now if i pressed a 2" wide by 7" long billet in a 20 ton press that would be 40,000 total pounds on an area of 14 square inches which would be 2857 pounds per square inch. and assuming the hammer is say 1.5 in diameter that would mean that the hammer was only applying 400 foot/pounds per square inch. so i would have to say that the press would more then be able to weld a long billet. i could even do a longer billet, so for fun lets see how long i could go to get to the same force as a hammer blow. it seams that the press could press a billet that is 2" wide by 50" long and still press with 400 pounds per square inch. now this is absurd and would be impossible but that just shows that my press can do longer billets. but now i am not claiming my math is right and if i have made a mistake please correct me. its just what i have picked up from the net doing some research.
 
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J, I'm not real good with this stuff, but watch your overhangs and keep the work centered where you think your press is the strongest. You could always turn down your psi (tons) a bit if you don't need it all.

Have safe fun with it, Craig
 
JTknives said:
I might just make some special welding dies that are longer because mine are 4 or 5" wide and 3" long. but if i was to make a special set that was 3" wide and say 7" long and make them thick as thy will be sticking out a bit then it should work good. i just wonder how much force i can create on that large of a surface area. so as I'm a man that likes math lets see if i can solve this mathematically. so first off lets compute a hammer swing. So just guessing and a little timing it seams that a fast hammer swing is around 20 fps and at say 3 pounds that would equal. using this formula
8ac4afe868ab54cec61fddfa35a87bdb.png

E= (3lb x 20fps^2)/2 which is 600ft/lbs of energy in a hammer swing. now if i pressed a 2" wide by 7" long billet in a 20 ton press that would be 40,000 total pounds on an area of 14 square inches which would be 2857 pounds per square inch. and assuming the hammer is say 1.5 in diameter that would mean that the hammer was only applying 400 foot/pounds per square inch. so i would have to say that the press would more then be able to weld a long billet. i could even do a longer billet, so for fun lets see how long i could go to get to the same force as a hammer blow. it seams that the press could press a billet that is 2" wide by 50" long and still press with 400 pounds per square inch. now this is absurd and would be impossible but that just shows that my press can do longer billets. but now i am not claiming my math is right and if i have made a mistake please correct me. its just what i have picked up from the net doing some research.
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Sorry I'm late to this. You have made a mistake, although you are correct at 600ft/lb of available kinetic energy, but you haven't calculated the pressure/force generated when the hammer decelerates on contact with the workpiece. This acceleration can be huge as the hammer decelerates in a very short distance from 20ft/s to 0. Newtons laws of motion can give you the force generated over this distance (usually for hammer/dynamic impacts this can be a fraction of a millimetre and result in many tons of force, and very high psi). There is no definite answer to the initial query as a lot depends on the temperature of the workpieces at the time of working and several other factors; but it is tons not just pounds per square inch.
Check out the 'hydraulic press channel' and you can see demonstrations of force/area needed to deform things such as metals. From that you should be able to get a feel for the answer to the original question.
Also see 'Shurap' (Dmitry Shevchenko) his videos offer lots of pointers to hammer vs press.
And Walter Sorrels site, he also covers the practical side of hammers vs press.
 
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