Machining 3D printed metal parts, is that actually possible?

[joanlluch]

As some may have read on my lsfornells thread I made the experiment of 3D printing some simple parts directly in metal in order to test whether they would be machineable. The purpose was getting confidence on the technique in order to hopefully replace complex machined parts with 3D printed ones, then just take the minimal machining steps to bring important surfaces to size.

This should allow for making complex parts by directly 3D printing them in metal followed by minimal machining. A good candidate for this would be crossheads, for instance the ones Roger has built for his locomotive.

As I described here modeleng.proboards.com/post/126178 my experiment on this can be considered a failure. My 3D printed S.S. parts are so hard that they can not be even drilled a hole!  The result is that metal 3D printed parts can not be machined.

Does anyone have any experience or attempts at this ?

[jasonb]

Seems this cap was able to do final machining of his printed stainless parts

modelengineeringwebsite.com/Bucyrus_4.html

[fostergp6nhp]

Maybe print in a different metal, e.g. Bronze, or heat treat to reduce the hardness?

[Cro]

I think I mentioned this somewhere else when we spoke about 3D printing and metal came up, it was certainly discussed on the facebook page but you found the same issue that someone else found for some buckeye style couplings that he struggled to machined them after as they are stainless steel infused with bronze I think and the combination made it so so hard you couldn't get anywhere with it.

You'd do better to follow the currently proven routes at the moment of wax printing and casting with small machining allowances

[Doug]

Sintered laser deposition is fairly early in its development it will get better with time in fact at my company we drill a 3d printed titanium assembly for aerospace that is so close to size it does not require machining on its profile however this technology is very expensive and time consuming.
Joan have you considered EDMing the holes there is always another way to machine it if it's hard.

[Roger]

Can you file the cast parts or does the file just slip over the surface without making any marks? If you can mark it with a file then you ought to be able to machine them, even if they are tough. Tapping a hole in something really tough can be a challenge though, even if you don't go for a full depth thread.
The biggest issue with parts like buffers is how to hold them securely and accurately without damaging the buffer head. It may be cheap to get then to the cast state but overall it may work out more expensive than CNC machining them because of the finishing operations that need to be done.

[vulcanbomber]

Sintered Stainless I'd an absolute bloody nightmare when it comes to machining which sounds like what you've got.... However there's no reason why Sandvik H13A inserts won't cut it.... Tapping it will be a right barrel of laughs and carbide drills should manage if used properly. It is however an abrasive.

[joanlluch]

The point is not making this particular part but experimenting with it in order to possibly make others that would be very expensive or not possible to make by only subtractive machining.

A M4 thread in the part was attempted by a true professional, not me. What he found is that the tap gets stuck in the hole and it doesn't want to turn. He had also a lot of difficulty to just resize a blind hole from 3mm to a slightly greater diameter. Also he could not make the drill to advance beyond the bottom of the blind hole. That was like a barrier for the drill.

This material is very strange. It is made from 60% 420 SS + 40 % Bronze, and yes it can be marked with a file, but machining tools get stuck so hard on it. You may recall that one the parts had a 3D printed M12 screw in one side. The screw was finished with a die on a lathe, but the required torque was extremely high and the part got burned in the process. It is really a tough material.

[fostergp6nhp]

For tapped holes if they are thro holes how about this for an idea due to the already mentioned difficulties.
Print the item with the 'threaded' hole to take a press fit flanged bush with the thread in it, that can be made normally on a lathe.

[44767]

From what people are saying about this material I think the material is work hardening very quickly. I think it is made worse by the nature of the sintered material which is possibly a slightly open structure. This allows the material to push away from the cutter rather than being cut. The only way to avoid it is to have very sharp cutters but I suspect even this won't help much. Carbide cutters would handle the job better in that they should be hard enough to cut even the work hardened metal but you'll need rigid set ups akin to milling rather than using a drill press. Normally stainless steel itself is easy enough to cut as long as one doesn't allow the surface to work harden by not feeding hard enough and keeping to an appropriate surface cutting speed. I use a speed of 8 m per minute for stainless steel. Also, if what I suspect is true about the material pushing away from the cut, then I'd consider using roll taps rather than cutting ones.

Cheers, Mike

[arch1947]

I have had the same issue with so-called stainless, it looks more like a combination of bronze and something else. Anyway I could not drill it or machine it and gave up. Fortunately I had the same part 3D printed in "steel" and it machines very nicely. The apperance is grey but when you cut it it looks like bronze but the swarf is magnetic so it is clearly a combination of metals. Good luck.
Arch

[joanlluch]

Jun 26, 2015 7:25:59 GMT 44767 said:

From what people are saying about this material I think the material is work hardening very quickly. I think it is made worse by the nature of the sintered material which is possibly a slightly open structure. This allows the material to push away from the cutter rather than being cut. The only way to avoid it is to have very sharp cutters but I suspect even this won't help much. Carbide cutters would handle the job better in that they should be hard enough to cut even the work hardened metal but you'll need rigid set ups akin to milling rather than using a drill press. Normally stainless steel itself is easy enough to cut as long as one doesn't allow the surface to work harden by not feeding hard enough and keeping to an appropriate surface cutting speed. I use a speed of 8 m per minute for stainless steel. Also, if what I suspect is true about the material pushing away from the cut, then I'd consider using roll taps rather than cutting ones.

Cheers, Mike

Hi Mike, Your observation is quite interesting, and it may explain why the material is so difficult. This material is particular. It does not behave neither as bronze or stainless, as it is a different beast. I will have a try on what you suggest though.

[joanlluch]

Jun 26, 2015 23:56:46 GMT arch1947 said:

I have had the same issue with so-called stainless, it looks more like a combination of bronze and something else. Anyway I could not drill it or machine it and gave up. Fortunately I had the same part 3D printed in "steel" and it machines very nicely. The apperance is grey but when you cut it it looks like bronze but the swarf is magnetic so it is clearly a combination of metals. Good luck.
Arch

Hi Arch. Thank you for your input. But I am confused about the materials. This was printed by ShapeWays in what they call "Steel" of "Stainless Steel" depending on where you look at.

In the "Steel" or "Stainless Steel" generic category you find the following subcategories (finishes):

"Stainless Steel" (a)
"Mate Bronze Steel" (a)
"Polished Bronze Steel" (a)
"Mate Gold Steel" (b)
"Polished Gold Steel" (b)
"Polished Nickel Steel" (b)
"Mate Black Steel" (c)
"Polished Grey Steel" (c)

My understanding is that /some/ of the above finishes are made by depositing a layer of another material on the surface. Particularly the ones marked (b).  The ones marked with (a) are cheapest.

All these materials are printed from Stainless Steel powder and subjected to an infusion process with bronze. They are not castings. Other materials such as bronze are available but they are much more expensive because they are made through a longer process involving actual moulding and casting.

So What is the material you refer to by "Steel" that machines nicely?  Did you get it printed from one of the global 3D printing services?

Thanks !

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