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Extruding


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I am in the process of making the tools to forge a large, French pattern sledge hammer. One of those tools is a pair of 2.25" fullers. I have the bottom one already, but need to make its mate so tonight after work I started on that. Since I'll be hand forging the hammer, I wanted to get a feel for doing work of similar size so in this case, I chose to use a 2x2x6 inch piece of alloy steel. I sectioned off 1.5" of that to make the striking end and then upset the balance (2x2x4.5) to a block 2.25 x about 2.5 x 3. When I was done it was T shaped with a rough radius forged in. I did this in the anvil as if I were going to make a hardy tool. At 1.5" square the shank will be plenty big enough for the striking end of the tool. What I found surprising was that the shank grew in length from 2.625" to 4" during the upsetting process. Has anyone else observed this and do you have any rules of thumb for how to estimate the amount of extrusion you'll get on a job? 

 

I've seen this extrusion effect many times at work where we are press forging, but I didn't think that I would have sufficient power to do that by hand. I expected all the metal that started above the anvil surface to flare out. That did happen, but apparently not as much as I'd anticipated.

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Thomas- There is a very slight bevel on the hardy hole. I think the reason I got the result I did was because the hammer I was using for the upset was a 14# sledge and the anvil was the one a made a couple of years ago that weighs a bit over 1000#. I'm sure this let me transfer the vast majority of the hammer's energy to the work piece, I just didn't anticipate that happening because my past experience with upsetting has  tended to only affect the metal very near the struck surface.

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Patrick: Which way the stock moves and how far is simply a matter of volume/external dimension. For example, draw 2" of 1"sq. to 1/2" sq and it will be 8" long.

 

Factoring in how much you will lose to scale depends on how much scale if made, I see 10% used frequently but I believe that's darned pessimistic. I know if I lost 10% on every heat there are things I've made that would've been nothing but a memory before I finished.

 

The only way I've come up with to properly make close approximations of volume is by weight.

 

Frosty The Lucky.

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Frosty- I think maybe you mis understood what I did. I drew out a shank with a length of 2 5/8" inches leaving a 1/4" shoulder all the way around . This shank went in the hardy hole leaving a block of metal 2x2x4.5 above this anvil face. This was upset, but during the upsetting process, the shank grew an additional 1.375" in length. I never hammered on the shank during any of the work after initially drawing out the 2.625" length noted earlier. The question I have is how to predict how much to allow for extrusion of the shank if I do something similar again.

 

I'm sure I lost some metal to scale but not 10%. At work we us a factor of 3% and since this forging is relatively small compared to that and the heat up time relatively short I think it was probably less than 3%, but scale losses are not related to the extrusion issue I'm describing

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Patrick; I think that the amount of extrusion you got surprised you because of the heavier hammer that you used... mostly.  Remember that when you hit harder the metal is deformed (moved) more deeply.  Since you only had a 1/4" shoulder to begin with and a 1 1/2" Hardy it makes sense that much of the force from your early strikes pushed metal into the hardy hole!  Now that you KNOW you could cool the starter shank just a bit and/or use a smaller hammer to hit more softly and oftener until you get more material upset beyond the hardy hole to get a smaller extrusion.  Using a peened sledge to push more metal to the sides (rather than straight down) could also help some!  You could use a bolster of the depth that you want the struck shank to be to strictly limit the extrusion that you would get.  I hope these thoughts help you... I cannot give you any kind of rule of thumb that would be helpful... but hopefully you will now see more clearly what is happening and how you can manage it to suit you! 

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I think this is one of those situations where there are too many variables to have a simple formula or standard percentage allowance.  As mentioned likely part of your problem was the small shoulder.  So as variables you have radius/taper on top of hole, size of stock in relation to hammer size, size  of hole, size of shoulder and finally the heat. 

 

I have some jobs I do where I notice some extrusion into the  bolster but all of these jobs are repeat jobs so I have established stock lengths that work with trial and error.    I suspect I get variation in amount extruded even on semi production items but have never done an analysis on it as i get more variation during the drawing down stage as the drawing down has a multiplying effect on length.   As an  example drawing  an extra 1/32 when drawing  2.75 " to 1"  I end up with almost 1/4" extra length.   On one off jobs if it is possible to easily cut off extra material or the job can be left heavier than the drawing calls for I almost always add extra to my volume calculations to allow for unexpected issues like your extrusion problem.  Steel is cheap compared to labour.  

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You're right Patrick I did misunderstand your question. The only advice I can offer is to keep notes of what you've done and with enough results, hopefully you'll be able to estimate accurately enough for your purposes. That's what I'd have to do if someone here couldn't give me a good idea how to make the correction estimate.

 

It might be a good case for localized heating with a torch or quenching. Even so, the region you want to form the shoulder is exactly what's going to be driven into the shank so I'm thinking just leave the shank shorter or trim it afterwards. I think trim it's what Occam is whispering in my ear.

 

Frosty The Lucky.

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Hey Patrick, I would have thought that out of anyone you would have know a formula for the amount of extrusion, I have no idea of a rule of thumb for it either for that matter.  We do a job of a small gear blank here (pinion) that is 140 dia (17kg) starting stock that when jumped up on the press will extrude a spigot 60mm dia 45mm into the bottom bolster/tool (the pinion end up with a head on it 240 dia x 40mm thick.  So armed with this knowledge we tried another job (bit bigger) 32KG 140 dia again, same kind of bottom tool, we needed to get 85 dia x 96mm long, I figured that as we only 27.5mm either side for the stock to sit on it should extrude no problems, no such luck, we only got about 75mm of 85 dia come down into the bolster, so much for my theory!  That was also with a big radius on ID on the bolster and heaps of forge die lube on it too.  I think the shape of the shoulder has a bit to do with it too, sharper seems to allow more extrusion, it seems to actually cut into the stock, a radius seems to not allow that to happen so much.  There has to be a relation too with how much force is directed at the stock and how much the extrusion pushes in, I'd love to be able to try the same job on a hammer the equivalent of our press, to see how much difference there is over static push compared to a hammer blow or series of.

 

Phil

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Wouldn't the angle of the hammer strike and the profile of the hammer face also influence the extrusion?

 

Could a larger version the type of block Hofi uses for foring rivets be employed so that no extrusion is possible? Bassically a bottom swage with the same size hole as the hardy the tool is to be used in that could be fixed on top of the anvil or other surface for striking. It would be a header of sorts, no opportunity for the shank to grow.

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Phil: Your experience is good info, thank you. It also makes sense to me that a radius in the pin part of the die would indeed impede the extrusion. A square/sharp edge will sheer while the radius will force the steel to TRY to compress when forced in. Steel sheers much easier than it compresses.

 

That's just my intuitive reasoning and is worth what supposition often is.

 

A short while ago a video was posted, "History of the Forging Industry." In the first video the example of closed die upsetting pretty well covers exactly this subject/project. A closed die hardy upsetting die should produce a product needing only final sharpening and factory/brand finish.

 

The  section of the dies forming the shaft on the parts had sharp edges at the transition from large diameter (cluster gear?) to shaft.

 

Frosty The Lucky.

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Thanks for all you input guys. I don't think we have a formula at work for this either. We do much like what forgemaster does only with larger parts. We will often use two ring tools to make pinion type forgings. The first has a hole the diameter of the shank and the second is taller than the first with an ID that will just fit over the OD of the short tool. We forge a round bar and drop in in the short tool. We upset one end to fill the larger tool and then flip the whole thing over and put 1/2" flat bar between the smaller tool (now bottom up) and the top die. The bars are on either side of the hole in the tool and with this arrangement we can get just enough extrusion to fill in the corners of the hole. Too much extrusion and you will rivet the two tools together.

 

For purposes of this particular tool the shank length was not critical, I just didn't expect to get that result and if I did need to control the shank length I'd use a bolster block sitting on the anvil.

 

Here are some pictures of the hammer I want make. The plan is to start with 3" round. I'll forge the middle section down to about 2.25" square, then punch and drift the eye. It is at this point that the fullers would be used to refine the profile of the hammer.

post-474-0-99860400-1407208354_thumb.jpg

post-474-0-77904400-1407208375_thumb.jpg

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Patrick, had the same thing happen to me a few years ago.  The only thing I could figure I was doing, was bringing the sledge down overtop of the hardy hole instead of half-hammer blows around the perimeter.  This directed all of the energy into driving the metal down the hole, extruding it unintentionally.  Rounded edges on the hardy hole only helped the process.

 

You obviously need to hit directly over the hardy hole, but I've found that judicious use of a straight peen to move the metal sideways, as well as half-hammer blows, makes for a big difference in the amount of extrusion.

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Thankyou Patrick for that little gem of info, (the 2 bars of 1/2 flat) we too use the 2 ring method, (I seem to remember seeing it on the internet somewhere years ago, something to do with a forge in Scotland or something like that ;-0 ) I just copy the good ideas and discard the bad.

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