Technical Crash course in metallurgy,,,

I’m needing to modify a standard air hammer bit by welding something to it.
To hold a piece of Delrin tooling.

I’ve got no idea what the bit shank is made of, or treated to but the holder is just mild steel. Everything I’ve tried has failed within an hour of use time. But 3500 bpm x 60 is about 210,000 cycles before it breaks.

The tooling concept works perfectly, just need it to last longer. Thanks

 

Have you tried welding to a smoothing hammer head instead of shank?

 

Have you tried heating the whole part up to almost a glow and then slow cooling it in something like sand? I am assuming it is breaking just beyond the heat affected zone (HAZ). Heating and slow cooling will draw out the molecules. This should make the part softer and could "mushroom" possibly but you said holder is just mild steel.

 

Without photos of how it is failing, I can't provide you a reasonable suggestion of how to fix your metallurgy problem (metallurgist here).

 

Are you getting a full penetration weld between the two parts. If your just welding a fillet on the surface of the two parts. It's never going to hold up against that type of repetitive impact.

Is the AH shank welding like its a weldable steel ?

 

When you say fail what’s happening ? And a picture of before and after would be great. I know I make a bunch of tooling out of O-1. It’s user friendly and can harden it to many different rockwells.

 

It’s failed in several ways.

Tig welded with er70s6
The welds break or the shaft will break off above the weld.

Im thinking I need to anneal the shank first, then weld it up then re harden it. maybe im FOS too. And not sure of the process for doing that either.
Im also remembering/ dreaming that those shanks have different range of hardness from end to end.

 

you are always going to have a tough time trying to weld any lower carbon steel to extremely hard high carbon steel like that. you could try torch annealing the welded area after welding. i have turned down air hammer shanks and pressed them into a hole in the low carbon steel heads for some of my tooling, such as doming and soft faced dies and have had zero failures.

 

Some pics,
This first pics had broken several times and rewelded/ repaired at least 5 times.
The last attempt was added gussets, then they broke at the shaft, re welded again and then shaft broke.




This is the thinking for my next attempt.

 

Maybe a pick or two?

 

i'll try to remember when i hit the shop in a bit. what i would do based on your pics, and assuming no lathe with carbide tooling, is cut off the head of the air hammer tool so you have a smaller diameter straight shank, drill a hole in the new head a few thousands smaller than the shank, ideally with at least as much axial engagement as the shank diameter, and a flat or drill point bottom to the hole that the hardened shank can bottom out against when pressed in. without machining equipment, you could grind a very slight taper on the shank and you should be able to press the shank in and have it stay in place without any welding.

 

Can you carve your pattern in this?

 

I have those, got the whole kit
the nylon head gets all buggered up quickly.
Also have the steck kit and the heads melt.

I’ve got some plastic type of material it’s hard and works but gets deformed and goofy. I got some Delrin and you’d be hard pressed to tell it’s been used at all. Incredible stuff

 

I’ve got a small lathe

 

This is how I did mine on my hand planishing hammer. Made a holder with a quick release spring loaded ball bearing. I can change tooling by just snapping it off.

 

I’m guessing that the air hammer bit is made of S series steel which you should preheat and then temper at 400 f for an hour after welding. There is a tig rod for S series rod but since you are welding to mild steel I don’t know if it would help. I use the wife’s oven for tempering just make sure to degrease first.
Dan

 

@05snopro440 does the above procedure look like it might work? I’m no metallurgist but I experiment a little.
Dan

 

A bunch of the other guys have touched on some of these, but what I see is:

1. You've created a stress concentration in your design going from the round shaft to the flat plate.
2. That stress concentration is right at the weld area, where you're joining a hardened likely tool steel shaft to mild steel. You therefore made the weld and surrounding heat affected zone the likely area of failure.
3. You need to appropriately pre-heat and post-heat your parts, and use appropriate filler and parameters for the materials being joined. As I don't know what you're joining exactly, I can't tell you the parameters to use.
   
4. You may be best off with a mechanical joining method as mentioned by someone else, to alleviate the failures you're experiencing.

As the fracture surface isn't in focus in your photos I can't say more than that.

 

It is definitely a good starting point and in the ballpark. Whether it will alleviate all his issues is tricky to say.

Unfortunately the initial heat treat parameters for the tool steel are important, and we won't know what those are, so some experimentation is necessary. You're on the right track, though.

https://www.diehlsteel.com/technical-information/welding-of-tool-steel/

 

I'm betting the original air hammer bit is only case hardened mild steel to start with. When ever I have reshaped a cutting edge on one of those tools, it mushrooms out pretty fast afterwards. Water cooling the reshaped edge increases its edge life a bit, but not much.

You will notice that all the air hammer tooling is of a one piece design. Making it from two pieces is a failure waiting to happen. The blows per minute will turn the welded area into the failure zone. Two pieces of metal welded together by any means, when placed under the pounding effect of the air hammer, will return to two pieces. Feel free to continue on your path, my experiences may be wrong, maybe I have missed something along the way.

 

Yeah, I would find a air hammer bit with a flat or convex face, make a mating cup for the delrin holder, and operated them as two separate pieces if that is at all possible.

 

How about making a round cup that fits the hammer head snugly, drill and pin, weld to the delrin holder.

 

Whenever I have to weld on hardened or higher alloy steels I use ER309 Tig welding filler rod. I'm no expert, but this is what I use to weld dissimilar metals like mild steel to stainless.
I had to shorten and reweld a hardened hood latch plate on my 55 and the ER309 filler rod worked real good.
Might be worth a try.

 

I used to use a tig rod 6800 or arc rod 680, by Eutectic, don't know modern day equivalent. When an issue with holding/separating/cracking would occur I would put a layer of weld on each item, assemble and then weld the welds. Be surprised how well it works/holds up.

 

Try TIG welding using silicone bronze filler rod

 

You know 210,000 cycles ain’t too bad, I’d be interested in the solution if you find one. I’m also interested in what you’re hammering on, pics? I’m thinking about hammering some grooves in floor pan but not sure how to accomplish with out a mess.
Thanks
Dan

 

As a former manufacturer building tooling for others we didn’t weld stuff together. It was built out of one piece or engineered for replacement. Welding bits together is a learning process and inconsistent and not good for commercial use.

 

I agree with building out of one piece of material being superior, but most of us don’t have the equipment in our home shop to perform that type of fabrication. So we have to weld, bolt or press together our contraptions.
Dan

 

Trial and error solution ordered .
I’ll weld a post to the holder that fits inside this cavity.


wheel arch openings



It’s relatively easy to knock some beads into a floor pan.

 

Impressive
Dan