Best way to repair sintered metal parts?

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On this one, if it fails, it doesn't look like there is much chance of a major catastrophe. The weapon may become inoperable, but shouldn't explode, or set off a round by accident. But that's just from looking at the parts drawing.
With that caveat, the owner decides....
Personally, I'd order a new one.
Reply to
Richard
Fella brought over a gun part for a Marlin lever action..he was
missing a pin..so I made one up for him and installed it..and as I was
inspecting it..I noticed a rather serious crack starting to develop at
one end of the sintered metal part. I fixed it by using my tig torch
and silver bearing flux..I packed the crack full of the heavy green
flux and zapped it with the tig..sealed it up well enough and I put a
slight layer over the area of the crack. After polishing it up with a
fine wire wheel, it looked good. But...is it?
How well does this sort of thing work with sintered metal parts?
Should I warn the guy to buy a new Widget? (Marlin just closed their
doors...so parts may become hard to find)
Any suggestions for other similar fixs with sintered metal parts?
Gunner
Reply to
Gunner Asch
Get an expert involved. High-strength ferrous sintered parts often are copper-infiltrated.
Don't weld that stuff unless you know what you're doing, especially if it's a safety-related part.
Reply to
Ed Huntress
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Part #8, 9, and 10 (and 11)
He was missing the #10 pin..and I turned, annealed, replaced it and peened it into place gently.
Gunner
Reply to
Gunner Asch
Oh..its not..not a safety critical piece. Not in the slightest. Which is why I silver soldered it..and then asked here.
I notice that Midway sells a later version of it for $50 or so.
So Ill warn the end user, but had been courious about the idea of soldering sintered metal.
Gunner
Reply to
Gunner Asch
Its a lever action 357 Mag...I dought it could be overstressed very much.
Sintered metal parts...dont have a sterling track record.....in some cases. Particularly those that take "impact"/high loading
They work well enough for static loads...the Buck folder in my pocket..the brass frame..is powdered metal sintering..but it never has a sudden high stress loading.
A lot of motorcycle brake disks are sintered. But they dont get hit.
Gunner
Reply to
Gunner Asch
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Sintered metal parts start out with a bazillion "cracks" (voids) when they go into the furnace (or hot isostatic press) and hopefully come out with none. Everything is controlled (temperature, pressure, atmosphere) to get near net shape and avoid having to machine the part. Not to say that it can't be repaired, but I'd rather go to the dentist.
Reply to
Denis G.
Dollars to donuts, though, they ain't HIPping those gun parts. At most, they're post-pressed and copper-infiltrated.
This part, though, looks like it wouldn't be practical to post-press. And it's probably not infiltrated.
Reply to
Ed Huntress
I was guessing that it was HIPped with the holes and final features drilled and machined. (Certainly you can't pull apart the mold with those sideways holes. The HIPped parts I've seen have copper powder mixed in and with 30-50 ksi pressing you get pretty good part strength and compaction and it's more state-of-the-art. On the other hand, my experience is more with R&D and I don't know how much throughput you'd get from HIPping vs. more conventional belt- driven open air sintering furnaces, so maybe you're right.
Reply to
Denis G.
Unless there's some advance in HIPping since I was covering PM, it's done in strippable metal cans -- one for each part. That drives costs 'way up. It's used mostly in aerospace, or it was.
HIPping of cast parts doesn't require cans, but PM does, or it did.
Ferrous parts that require some toughness and a bit of ductility often are pressed, sintered, possibly hot post-pressed, and then infiltrated, usually with copper. As an example, that's how they make the bevel driven gears on DeWalt angle-head grinders. It's not cheap compared to plain press-and-sinter, but it's a heck of a lot cheapter than HIP. You get 100% density with infiltration, as you can with HIP.
Reply to
Ed Huntress
You're right about the cans. They're crushed and disposable and the HIPped material had to undergo final machining. It is more expensive. I've been away from that business for a while and don't remember everything. I pulled out one of my PM books and saw the process that you describe. The PM that I'm familiar with had the all powders premixed before pressing.
Reply to
Denis G.
I mispoke there. They're EITHER post-pressed or infiltrated. I never heard of doing both on the same part.
Either one can get you to 100% density, but infiltration usually results in more impact resistance and ductility, but with slightly less tensile strength.
> As an example, that's how they make >the bevel driven gears on DeWalt angle-head grinders. It's not cheap >compared to plain press-and-sinter, but it's a heck of a lot cheapter >than HIP. You get 100% density with infiltration, as you can with HIP.
Reply to
Ed Huntress
What you're describing is by far the most common way it's done.
PM can be fascinating. By mixing powders and sintering at full diffusion temperatures, you can produce alloys that are not possible any other way.
For example, the most exotic of the high-speed-steels: Crucible CPM REX 121. You can't make it by melting. That stuff is HIPped, BTW.
Regarding memory, I can empathize with that. d8-)
Reply to
Ed Huntress
PM is a neat subject. Although it get a lot of bad press for cheap parts, I wonder how many people would sleep at night knowing that most jet turbine blades are made with it.
Reply to
Denis G.
I have a book called "The Component Contribution Engine Progress Through the Specialist Manufacturers" by Alan Baker ISBN 0 09 136290 3 and it mentions the use of what they call powder forging being used by GKN to produce conrods for the Porsche 928. The book dates from 1979 and the 928 1978 so looks like some high performance applications have been around for a while. I presume this would be an application of what you're referring to as HIPed. IIRC the hot initially powder form is placed in dies and struck to produce a 100% part with high dimensional and weight accuracy compared to standard forging processes.
BTW the book is a fascinating read if you haven't read it already and it looks like it's available cheaply on Amazon. Maybe a little dated in the last 34 years but still a good read.
Reply to
David Billington
Richard
Right. And the connecting rods in a lot of automobile engines. PM is all over the place, and it's often hard to identify, particularly when it's been post-pressed. It looks like a high-quality forging. And it often performs as well or even better than one.
It's come a long way from the days when it was used for cheap parts that often were brittle and weak.
Reply to
Ed Huntress
Yes, I remember that. The 928 engine used a lot of advanced technologies. Porsche was trying all their new tricks, including running the pistons in aluminum cylinders. Unlike the Chevy Vega, they got it right.
They may have sleeved the 928 later, but it started as a hypereutectic aluminum block with the pistons running directly in the block.
I doubt if they were HIPped. I saw Chevy con rods made of PM in the mid-'90s, and they were being made with conventional sintering and then post-pressing to increase the density.
Reply to
Ed Huntress

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