welding 4140 bolt on dies

[will52100]

After 5+ years the top die on my tire hammer came loose.  I bought it from a fellow that was upgrading to an air hammer, so didn't do the initial welding myself.  I did have to fix a lot of the welds the first few months of owning it.  It was built in a class with Clay Spencer.

Anyway, the dies are supposed to be 4140, I know to preheat to 400 deg.F., but what about post welding heat treat?  The welds that broke loose were not what I'd consider good welds, very light penetration and not much material build up.  In other words I'm amazed the welds lasted this long, especially after wailing flat out on some of the high alloy steels I forge.

Anybody know how Clay did the dies at the classes?  I'm planning on using 1/8" 7018 rods, with a good V grove around it for good build up and penetration.

Thanks

[BIGGUNDOCTOR]

Sounds good. I always did a post heat to anneal the heat affected zone from the weld. I would get it really hot with a torch then toss the item in my ash barrel to cool slowly if it was bigger. Smaller items I would just torch it for awhile, never had any breaks with these methods. If you dress the welds leave a good radius, as sharp corners create stress risers that can induce a crack.

 

What about just drilling and tapping for a stud?

Edited May 27, 2015 by BIGGUNDOCTOR

[will52100]

Thanks, I think I'll throw it in the oven and heat to 400, then weld and let it slow cool in the oven.  Shouldn't affect the temper, and would stress relieve the welds.

[Matthew Paul]

It wouldn't be a bad idea to clean the die faces and sides really well with scotchbrite or some light sand paper so that you can see if the welding actually effected the temper or not. I use 1045 for mine so the heat treat is a bit different. But, if you have the time it may not be a bad idea to remove the entire die block from the plate, Put a nice 1/2" chamfer on the bottom of the die block (like you said), and then rebuild it with several passes. The problem with re welding the whole block, especially with 1/8" 7018 is the heat build up. I'd bet that you would soften them right up. I'm not sure what heat range you use welding 1/8 7018 but I tend to run in the 145 AC range, give or take, and that imparts some serious heat on a small piece like that. Best thing you could do is go for it and see what happens.

The temper temperature called for on 4140, for around 50rc is only 400deg.

If you don't have access to a kiln, I'd probably just weld it and call it good. If you do have access to a kiln, I'd probably just re heat treat the dies.

[arftist]

145 is a little high for 1/8" 7018. On DC 110 amps is usually sufficient, with a recommended max of around 125.

That aside, welding need not be a continuous operation. Some templesticks would serve well to monitor the heat of the dies. Weld, pause, allow a little cooling, weld some more. 

[will52100]

Thanks, I weld 1/8" 7018 rite at 100 amps DC on my machine.  Your rite about heat build up, but weld a pass and let it cool down, weld some more, ect. until finished.  Also the die came completely off, so no issues about grinding a chamfer and clean up.

 

I was mainly wondering if anybody knew how they did them in the course, because in spite of have poor welds the die held up very well for a number of years.

[ironwolfforgeca]

if you have some 110-18 I would use that its a better rod & will last longer before cracking again

7018 will last for years BUT it will crack in time

[will52100]

Got it welded, will see how well it holds up.  The bottom die shows no signs of cracking, yet.  In the daylight the welds appear a lot better than they did in the dark, they were actually pretty decent welds on the dies.

I pre heated the whole thing to 400 deg.F., then welded, after grinding the old weld off and V ing it, then back in the oven for an hour at 400.  Hopefully it'll last another 5-6 years.  If it last that long it may be time for new dies anyway.

The only real downside I see to the tire hammer design is the bolted dies, sure be nice to have dove tailed ones to make die changes easier and to be able to use factory dies.

[Matthew Paul]

yeah, I agree. The bolt on dies are ok, and cheep to make. But, If I make another one I'd spend the extra time and coin on making it so that it took normal style dies. Good to hear that ya got it all fixed up.

[will52100]

Thanks, got it bolted on and tested today.  The dies were a success, the wrought iron hawk was a failure, got a few cold shuts while stacking it up from small pieces to make a larger one.  You'd think I'd know better by now.