
Researchers uncover the art of printing extremely hard steels flawlessly - pseudolus
https://phys.org/news/2020-04-uncover-art-extremely-hard-steels.html
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abakker
For those who may be unaware: martensitic steels encompass all standard tool
steels, e.g the ones used for knives, springs, dies, files etc. martensitic
means hardenable.

Being able to 3D print these into arbitrary shapes vs machining them will
likely be of the most value for parts that need to be light.

I’m curious that they mention wanting to print low alloy steels, since low
alloy steels tend to be relatively easy to machine. I’d have expected more
interest in higher performance steels. Can anyone comment why people would
want to print in low-alloy martensitic steel?

The article doesn’t address this, but, the martensitic transformation
typically changes a part’s volume by ~4%. that can make it difficult to make
precision parts unless final finishing happens at full hardness. I wonder if
this process results in direct production of martensite, or if the parts still
need heat treatment.

To me, this is a very interesting process, but doubly so given the
possibilities of generative design. For those who want to visualize why you
might want to 3D print steels vs machining them, think more about brackets and
support structures than turbines, and take a look at some generative design
parts.

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econcon
Turbine blades, impellers, valves are good candidate for printing.

Machining creates chips and I think you need to have variety of metal stock to
spin on lathe, with different dimensions.

So if you've simply a bucket of metal to form any shape you want, it might be
favourable to avoid uncessary wastage, cleaning, or stocking.

For example, in 3d printing plastic you just need a roll of plastic or
pellets.

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abakker
Actually, I’d be surprised if any of those were good candidates. Turbine
blades in jet engines aren’t even machined now - they are grown out of
inconel. Valves are highly dependent on surface finish and frequently multi-
material setups - e.g. o rings.

Not to make light of matching costs, but in the scheme of getting a part made,
even of tool steel, the overall contribution of the materials is usually not
super high. Machine time, tool bits, and design work are all MUCH more costly.

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c22
Huh, from the hangout and hack stuff all day at the maker space perspective
this is flipped completely on its head. I have plenty of time to design things
and operate machines, and even the cost of the machines (bits included) is
shared to the point that it's almost free as an individual. It's waiting on
those gosh darn materials budgets to appear that holds up all my projects.

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abakker
I should clarify, in production projects, materials may end up being a much
greater overall part of the process, especially if the production is heavily
automated. However, 3D printing of tool steels seems like it is aimed at lower
volume parts where the automation will be lower, so paying a machinist to
load/unload, finish, debur etc might be a relatively larger portion of the
time.

For us hobbyists, the CAD time is free, so it tends to cost less :)

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bradknowles
It seems to me that the ideal pattern is to 3D print the rough form, but it is
likely to take some machining to get it finished to the final shape and
surface treatment you want.

Or am I missing something?

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JoeAltmaier
They discovered the science, not the art? Haven't actually executed on the
science: they don't have a 3D printer that works this way?

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rsfern
I don’t understand your second question — they printed a bunch of martensitic
steel tensile specimens with a pretty common laser melting technique, then ran
a bunch of mechanical testing. Where’s the lack of execution?

I think the art/science thing is just a bit of editorializing, it’s sort of
accepted that a lot of the fundamental science behind metal additive
manufacturing is just not established. I.e. it’s far from trivial to just set
up shop and print an alloy that hasn’t been printed before.

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JoeAltmaier
I read it again. They 'developed a framework'. I'm thinking they 'printed' a
few microscopic samples in a lab? A real printer could print a car hood, or at
least a gear. If they didn't get that far (with all the associated problems of
delamination, gaps, vibration defects etc) then they don't have a real 3D
printer. The 'art' is in the delivery.

