The Material Science of Metal 3D Printing


This episode of Real Engineering is brought
to you by Brilliant, a problem solving website that teaches you to think like an engineer. One of the first things you learn in Mechanical
Engineering is how to design your inventions in a way that is possible to manufacture and
assemble. This is a skill that takes time to learn, primarily by working with machinists
that look at your design and laugh at the imcompetitance of this young college kid.
From placing fastener holes in inaccessible locations to placing a sharp inner corners
that no milling machine can achieve. So much of our engineering capabilities are
dictated by what we can manufacture and every time a new method of manufacturing is invented,
it ushers in new technologies once deemed impossible. Just as the simple cylinder boring
machine facilitated the industrial revolution, 3D printing may now be opening doors to new
designs. Complicated hollow structures are now possible.
Allowing designers to integrate cooling ducts directly into parts, an incredible useful
tool for high temperature parts like turbine blades and rocket nozzles. We can perform
something called topology optimization, where we use finite element analysis, a type of
stress simulation, to tell us exactly where material is needed. Allowing us to generate
the perfect structure for our application, similar to how our hollow bones are formed,
and thus allowing us to save on weight. Helping our lightweight vehicles to gain even more
performance. Often parts are machined down from giant blocks
of raw material to their final form. In aviation we measure this waste with the buy to fly
ratio. Which divides the weight of the final part by the weight of the raw material it
was manufactured from. Imagine taking a material like a titanium alloy which can cost upwards
of 30 dollars per kilo, and then throwing away 90% of it in the manufacturing process.
Needless to say this is a massive source of increased costs, that 3D printing could help
reduce. All of these benefits can come together to
unshackle engineers to form the perfectly shaped objects and perhaps one of the most
interesting applications of this is this incredible 3D printed aerospike rocket engine, that has
incorporated liquid cooling channels directly into the rocket nozzles interior and shaped
everything optimally to provide a highly efficient rocket nozzle that can operate efficiently
at many different altitudes.[1] But, even with all these amazing applications.
We rarely see 3D printed parts outside of prototyping applications like this. It’s
clear that 3D printing can be take human manufacturing to it’s next evolution, but what’s holding
it back? As usual the first problem is cost. If we
plot the price of a 3D printed part as a function of the number of parts created. It would look
something like this. [2] It’s price will be dominated by initial machine cost, and
that line will only marginally trend downwards as we print more parts, due to the insane
time it takes to print a single part, after all we are essentially welding hundreds of
kilometres of metal powder together. To scale up our manufacturing we need to buy
additional machines, which will not lower our cost. This turns our traditional economies
of scale on its head. Take an injection molded part. Early on the
cost will be dominated by the cost of creating an expensive mold needed to form the part,
but once that is finalised this machine can churn out piece after piece in rapid succession,
we mostly just have to wait for the plastic to cool down before we can eject it from the
mould and restart the process. This results in a graph that looks something
like this where our cost per part rapidly decreases as we build more, soon becoming
dominated by the material costs. This means that it only makes economic sense to use 3D
printing for parts that fall behind this break even point. Which is why it is used so frequently
for rapid prototyping. If we can reduce the raw material cost, with better supply, and
decrease 3D printer machine costs we can lower this line and open up more parts to being
replaced by 3D printing. That is gradually happening as the cost of these machines lowers,
in large part due to patents expiring in the last 5 years. However it’s not just cost
preventing 3D printed parts from entering the market. This month I spoke with Professor Roger Reed,
the founder of OXMET, a company taking on the challenge of developing metal alloys and
printing techniques to improve the material properties of these additive manufactured
parts. To get a better idea of the material science that prevents 3D printed parts from
being approved for even specialized small batch applications. We have thousands of years of experience mostly
through trial and error of learning how manufacturing techniques affect the material properties
of the metals we use. From learning how to tailor carbon content during iron ore smelting,
to learning hour each hammer blow can affect the crystalline structure of the metal. In
particular, we have learned how the exact way we heat and cool a metal effects it’s
material properties, as a result of it’s internal crystalline structure. But additive manufacturing throws away much
of the techniques we have developed. Forcing us to build much of our understanding up from
scratch and develop completely novel techniques for studying and optimizing our material properties. One of the key areas of research in this regard
is improving 3D printed metal fatigue life.[3] Fatigue life is a measure of how many cycles
of stress a part can sustain before breaking. Because materials CAN fracture even below
their ultimate strength, if you cycle them at a lower stress for extended periods. This
affects every metal and is the reason continually maintenance is always needed for machinery. We can visualise a materials fatigue strength
by plotting on a S-N curve, which places the magnitude of the alternating stress on the
Y-axis and the number of cycles it survived on the y-axis. For traditional machined titanium
it looks something like this, [3][4] whereas for 3D printed parts it looks more like this.
Put simply, 3D printed parts fail much sooner. Stopping many of the parts from being approved
for the applications they are best suited for, like aviation. So why does this happen? First we need to
understand what causes fatigue fractures. The primary cause of these fractures is crack
growth, [5] where small voids and imperfections within the part can force stress to divert
and pile up in sharp corners and thus exceed the metals strength locally and cause the
crack to grow. The more imperfections present, the more likely your fatigue life is going
to suffer. And 3D printed material tend to have a lot
of imperfections. We got a clearer look at why this happens when researchers used high-speed
synchrotron X-ray imaging to get this phenomenal footage of the laser melting process, which
revealed many of the phenomenon resulting in imperfections. [6] Here we have a powder bed of iron-nickel alloy
called Invar 36, which has been turned into a powder by blasting a stream of molten metal
with a high pressure gas. This process is called atomization. As the laser moves across the powder bed it
melts it, essentially forming a weld line. You can see that this layer tended to dig
into the powder bed. Creating a track that varies in height. These sort of imperfection
means the final product needs a surface machining to create a quality part. Although it’s important to note that this
study was specifically studying something called an overhang condition where the part
has no structure below it and has to build on the loose bed of powder instead. As the laser marches on, the powder in front
of it gets blown away, meaning the laser no longer has metal powder to melt in that region
and instead forms a new beads of molten metal ahead of the original track, which eventually
coalesce with the original. Finally we can see some worrisome behaviour as the laser
reaches the end of this track as the molten metal begins to cool, we see pores begin to
form in the upper surface of the track. The exact kind of imperfections that could allow
crack growth to occur in the future. This study also varied several factors like
laser speed and laser power to study their effects on the melt tracks properties. Here
they increased the speed of the laser to a point that the metal particles did not have
enough time to heat up and coalesce. In another experiment they investigated the
interaction of two melt tracks. Here we can see more pores forming as a result of overhangs
trapping gas, and yet more pores form in the same manner as before as we reach the end
of our track. Clearly, this process is much more complicated
than just melting some metal powder together and in the end the final products that come
directly out of a 3D printer are far from finished and need a significant amount of
post processing. For example, we can help close these pores
by using a method called hot isostatic pressing, where we apply heat and a very high isostatic
pressure, which just means the pressure is the same in all directions. [7] This maintains
the overall part shape, but compresses and heats the part up enough to close those pores
to improve our fatigue strength, but not enough to compete with traditionally machined parts. This of course pushes this cost bar higher,
making 3D printing again less attractive for applications outside of rapid prototyping,
and we have yet more material property issues to address. We explored the science of forging with my
friend Alex Steele in a previous video. We learned how the internal crystal grain structures
is one of the most influential factors in determining a materials final material properties.
We can control the materials hardness and ductility by simple heating and cooling it
in a particular way. Typically when a piece of molten metal is
cooled, crystals grow at random from individual nucleation points and form crystal grains.
The size and structure of these grains dictates so many of the metals final material properties
and we have learned over thousands of years of metal forging how to get the best out of
our materials. Once again, additive manufacturing throws much of this knowledge out the window.
Leaving us to start from scratch. We have learned that 3D printed materials
tend to form these columnar grains that rise up in the direction of the print and that
the grains tend to follow the direction of the laser. [8] Forming directional grain structures
that can almost be thought of like the grains in a piece of wood. This means that how the laser moves has a
massive effect on the material properties of the material and thus we can use this to
our advantage by tailoring our laser scan strategy. [9] One of the most common laser scan strategies
is the islands scan strategy where a pattern like this is formed created 5 mm islands of
laser track paths oriented perpendicularly to each other, these islands are formed in
a random sequence. This scan strategy developed by Concept Laser was created to alleviate
residual stresses that form as a result of uneven heating a cooling within the metal,
which can decrease the parts overall strength. Just another factor designers have to consider
and often requires the part to be placed in an oven after printing to help alleviate residual
stresses However, one study found that this scan strategy
has some unique effects on the grain structure. Creating those aforementioned vertical grain
structures with fine grain boundaries between each island, and these fine grain boundaries
had a high density of cracks, which again can grow a cause fatigue failure. [8] There
are of-course alternative laser scan strategies like this helical one. [10] Other researchers
are attempting to use thermal and other specialised cameras inside the build chamber to observe
the phenomenon like pore formation and inform the laser exactly how to operate with machine
learning to maximise material properties. While I don’t see this manufacturing technique
ever being used for low cost high volume parts where other manufacturing techniques are much
better suited, if we can improve the fatigue life of these metals we could start seeing
them appear in more applications. Like that incredible 3D printed aerospike engine we
saw earlier. This is a VERY new area of research, that
could use more eyes. Just as I learned how to design to get the best out of carbon fibre
composites and moulded plastics over the course of my university life and industry experience.
We are now seeing young engineers beginning their education with this form of design in
mind, allowing them to create designs that were once deemed impossible. I believe there is going to be a fascinating
meeting of material science and machine learning in this space to customise laser scanning
patterns for particular parts and allow the machines to spot and fix defects as they happen,
and I would imagine the overlap of material scientists and machine learning coders is
a small pool of people at the moment. So perhaps this could be a career path for you, and you
could start working towards it right now by taking this course on Machine Learning on
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100 thoughts on “The Material Science of Metal 3D Printing”

  1. I do not have enough time to make a teamtrees video for Real Engineering, but we did make a video about methods to conserve rainforest habitats over on Real Science. I planted 1000 trees yesterday over on teamtrees.org. Every tree gets us closer to our 20 million target. https://www.youtube.com/watch?v=mV6GL7RrXz8&t=1s

  2. I noticed this was all about 3D printing using Laser technology. Do you have a perspective on blasting technique … kinetic fusion …. such as used by Melbourne company Titomic? www.titomic.com

  3. What if they heated the powder up to just under melting before the laser hits it?I know in Aluminum extrusion, you heat the metal billet up to just under melting before forcing it thru the die.Too cold & you get problems like they are talking about here.

  4. I hope someday they can recreate organic material that could possibly be a food source for interstellar exploring. To have an edible and nutritious food made completely from atoms and molecules that are not very different from that made naturally or otherwise on Earth would be a great leap and also a relief in the planning of space exploration

  5. Heat the powder, use an ambient temp that makes it easy to melt and lengthens the crystal formation time treat it like glass.

  6. @6:46 As a fan of Alec Steel I'm very upset you didn't include him in your Credits. https://www.youtube.com/user/alectheblacksmith NVM you mention him later @9:50 Yay

  7. This really only covers SLM, or selective laser melting, a type of powder bed fusion. Metal 3d printing covers a lot more than just this. Powdered bed fusion also includes Electron Beam Melting, but is less precise but faster for larger parts in comparison to SLM machines, but are also more commonly used in aerospace and medical applications. There's also Bound Powder Extrusion, Binder Jetting and Direct Energy Deposition, which includes Powder and Wire DED.
    If you're going to title your videos with a broad subject, like you have with this one, cover all relevant manufacturing methods, or just use a title that names the relevant manufacturing method. It's just as bad as clickbait, honestly, and I'm pretty disappointed in this channel's video titling decisions.

    As for the future of 'metal 3D printing', which should honestly just be referred to as additive manufacturing, as '3D printing' is nothing more than a buzzword (hello, clickbait), Powder DED is the future, as it allows for a larger range of alloys, and with 5-axis machines, can produce a true 3D part, and not a 2.5D part. Each manufacturing method has it's place, and has it's relevant time period, but the future of any kind of additive and subtractive manufacturing lies within automation and multi-axis machines that can produce true 3D parts within a set of operations with no stops within the process.

  8. What about 3D printing with Hemp plastics? Hemp plastics can be much stronger than steel. Can you make a video on cost comparisons for Hemp plastics being 3D printed? I feel like it'll be much less expensive than 3D printing metals.

  9. I work at an aerospace company that 3d prints a lot of production parts, both sls and slm. This is the first "mainstream" video i've seen that doesn't treat printing as a way to magically appear every structure. It's an exiting newish technique to make thinks, with it's own strengths and weaknesses. For instance thermal conductivity has a large correlation with print quality, so while titanium and croco and stainless steel print very well, aluminium is limited to weak casting alloys and crap surface quality (but finer grains than castings). Exeption being scalmaloy, great stuff, approacing 7xxx series in strength, but it's patented so about 5x the price of regular slm alloys.
    Annoying thing is that most printers are being ran by companies in subtractive machining, who don't know what they can do and seem unwilling to learn, and want to write off the machine in 5 years, leading to astronomical pricing

  10. Perhaps it’s being approached wrong with all those powders and expensive lasers melting in small locations all over the parts causing irregularities throughout the entirety of the part. What if you had a large Cauldron with molten metal in it. A large hook dips into it a slowly begins to rise out but as it’s rising a Computer numerically controlled robotic arm is blasting sub freezing gasses at the hook in such a way that it forms parts out of the hot liquid metal being cooled in a controlled manner. Simply pulling the part out of the liquid metal as the hook mentioned previously slowly rises up and out of that cauldron of hot molten metal.

  11. If you live in the developed west don't bother learning this. They are just going to outsource it to Asia anyway. They'll have your create the tech and then you will end up training your replacement. Think I'm kidding? I'm a software developer of +10 years with a Masters. My brother is a diesel mechanic. He makes more money than I do with no education. Why? #treasonVisas and #traitorSourcing. His job cannot easily be sent to Asia. …so far.

  12. Very good and informative video! Another issue these days additive manufacture facing is the metrology, especially in-situ metrology with powerder bed.

  13. any small up to large metal milling operation have a waste recycling program or partner,
    no metal filings are accounted as financial loss, but partial loss, only 9% to 16% of the total weight of shavings translates to actual material waste.

  14. Interestingly, I am intending to start my PhD next year approaching some of these exact problems with additive manufacturing.

  15. Ive learnt that metal 3d printers get used on warships like aircraft carriers to make replacement parts because storage is quite a problem there.

  16. Just stop. It is NOT 'printing'. '3D printing' is just about one of the stupidest terms. 'Additive fabrication' and 'additive manufacturing' are much more appropriate and descriptive.

  17. Boeing Aircraft company prints large sections of their wings in their Seattle area plant. Boeing bought the printing company, who is right down the street from them. The printers are big, costing at least 20 million a piece.

  18. Personally speaking I think the 15min format is a few mins too long especially considering how long you make the ad at the end.

  19. Has nobody bothered trying the old-fashioned heat treating techniques? Part of the point of heat treating, and cryo treating, is to change the crystalline structure. Surely somebody could find a heat/cryo schedule that smoothed out the cracks and voids left by the laser. It wouldn't help make parts more cost-effective but it might allow inherently expensive parts to be redesigned for printing.

  20. Doesnt it seem the main reason is we dont 3d print metal the same way as we do plastic. In theory a correctly printed 3d metal would be molten liquid coming out of a nozzle..building up on to the previous layer…

  21. How high do you think you could build a brick wall until it collapses, assuming the brick wall was on top of cement, 1 brick thick and just using mortar as the glue I just randomly thought of this while sleeping this has nothing to do with the video clearly

  22. could we not use perlin noise to generate the laser path, creating randomised 3D islands that are interlocked to mimic the random grain of traditional manufacturing?

  23. Thanks for the video, very informative, as usual.

    First, a very naive question: what about using lower-intensity lasers, which would presumably take longer to melt the powder, before reducing the intensity gradually, in order to produce bigger crystals? Obviously, this would take longer, and likely lead to higher cost, but might it make sufficiently better parts to justify the extra cost?

    Second, a question that's a bit out of the box, and possibly very silly: would using some sort of magnetic confinement in combination with the laser make any sense? It might be helpful in confining the powder to prevent it from being sprayed everywhere, and it could also be used to control the temperature.

  24. Use metal 3d printer to make more metal 3d printers… 😂. The parts likely need annealing with an induction coil.

  25. The best experience I have ever gained as a mechanical engineer is working in the machine shop with the machinists who had to make my parts.

  26. We can use 3D printers to create molding parts that are more advanced than before.
    This improves everything in manufacturing 🙂

  27. During my days as an electronics engineering student, we had to learn the "reality" how to fabricate our own electronics circuit design. We never outsourced them and have to do the manual way. We did not just have to make them work, the grading starts by thump testing or basically lifting our projects and dropping it at a height while plugged in and see if it still works. Planned obsolescence are not taught in school, greedy manufacturers did that btw.

  28. The crucial point is, that most pioneers do not have a title, but in order to get a job where that level of experience matters, a title is required. So in the end, companies have to reinvent the wheel, where instead they could drill down requirements and gain people who matter.

  29. I don't believe it… I worked on the topology optimization module (TOSCA in reality) in SolidWorks, and you just showed it !

  30. with 3d printing we should of been printing homes by now, witch means quantum crafting should liberate every human being from ever having to work ever again. with have going thru the industreal revolution, by passing the gold barter trade system printing paper money, and now quantum crafting all combined this should free every men from having to be a slave no more from any task choire action or any monotness jobs. BUT THATS IF OUR WORLD LEADERS LEAD US RIGHTIOUSLY. IF THIS HPPENS THE WORLD ELITES WOULDNT HAVE TO PAY OR ASK ANYONE TO DO THIS BECAUSE PPL WOULD BE THE ONES APPROACHING THEM TRYNA RETURN EVERY FAVOR IN GRATITUDE. IT JUS SEEMS POINTLESS TO HAVE A HUMAN BEING DO ANYMORE TASK OR JOB IN ACTION WEN HAVE MACHINES THAT CAN DO IT FOR US. PLUS MACHINES WOULD NEVER NEED BREAKS N WOULD BE MUCH EFFEICENTLY FASTER EFFECTIVELY. PEACE N MCH LUV 2ALL 4WE ARE ALL ONE. 1LUV I.N.R.I.

  31. so as someone who has worked with concept and eos machines, I find the two biggest problems that i feel this guy didnt cover is layer height and your gas. If you have too thick of a start layer, nothing will bond well, thats why you need to build supports for overhangs. you need to have next to no oxygen in your chamber as well, as that will make your weld pop instead of lay nice. metal 3d printing in my work experience has been mostly prototype, however the items that have been made are actually being used. I can think of two companies that mass produce with metal printers, the big one being ge and the second is daniel defense. Good video, I look forward to seeing 3d printing gain popularity with mainstream.

  32. Nice. I’m not an engineer but I did wonder about the properties of the metal in the product after being ‘printed’ in this manner. Thanks.

  33. For how new this technology is, you have to admit it has made some pretty rapid strides in just the last few years. It will only continue to get better from there as people work out the kinks. Promising stuff.

  34. 3:00 "welding hundreds of kilometers of metal powder together" Don't you mean hundreds of KILOGRAMS of metal powder?

  35. 9:50 "We explore the science of forging with my friend Alex Steel(e)". For real? No joke? Just coincidence?

  36. Another good one. I was hoping for a bit more insight into the various ways metal additive manufacturing/printing works but this was still fascinating.

  37. Meh. I don’t like this guy anymore. Sounds like Connor mcgreggor too much. …

    Jks jks. Just popped popcorn every time he makes a new video.

  38. I feel like it's important to point out that overhang conditions are not, say, some unavoidable subset of the 3D printing process but rather something you strictly avoid when printing. If possible you'll try to design the part with no overhangs steeper than your machine can handle, or when absolutely necessary print additional material to support the structure. Trying to blind print an overhang is an example of a design/processing mistake when it comes to printing, akin to the example you gave of impossible-to-access fastener holes.

  39. “A important part of engineering is to design your inventions in a way manufacturable by machines”
    That’s what exactly I do with 3D printing lol. Hangout structures will collapse during printing… and 3D printers are vulnerable to faults. A slight tweak during printing process could let your print in the recycle bin…

  40. Ok, I have an out there scifi idea that I've wanted to know when it comes to metal 3D printing . What would it take to be able to recycle already 3D printed into the material needed to 3D print? Would it be possible to some day make it where when some 3D printed engine breaks down it can be tossed into a machine that turns it back into the powder used in the printing process. I know metal changes when worked/heated. But I'm curious if it's possible, even at a loss of a few % of the over all, would it be possible/worth it?

  41. I always considered 3d printing as an alternative to casting. I've done a lot of work for oil and gas (machining extremely low volume cast impellers mostly), and the sheer number of jobs that had top go back for welding due to porosity or were scrapped outright because porosity appeared on finishing cuts is phenomenal. Add to that the setup cost of producing the patterns for casting i think 3d printing is a very viable alternative. I'd regularly get jobs where unimportant faces and diameters (the shrouds, o/d and the hub face used for the sprue) were cast with 20mm, 50mm and 150mm of metal on them (respectively) for absolutely no reason. being able to print the part leaving 1mm on the tolerance'd diameters and faces would have been a godsend.

    The money doesn't stop being saved there – the parts would require minimal balancing and fettling after machining.. I can't believe no one has jumped on this area.

  42. With due respect, this video is very informative, but I am not okay the opening line "One of the first things that you learn in mechanical engineering…."
    I really respect this channel and the content creator a lot….

    I should seriously stop typing before the channel mob attacks me….I should stop typing….

    STOP!

  43. couldn't printing in an evacuated chamber help alleviate the gassing issue? and using a sonic inducer (at least on non-magnetic metals) between layers to pre-settle the grains help with the laser post-settling them?

  44. Once we learn how to control the crystallization of the metal ,we'll be able to grow it like you would a mushroom

  45. What do you mean the 90% of the titanium is thrown away. It's bought back and recycled. What the hell, are you a democrat?

  46. Haaas been tried to metal 3D print in a vacuum chamber?

    It could solve some of the problem of gas enclosure and oxidation, some titanium-nikel alloys are worked in vacuum so it's not a complete new thing

    No one ever tried it?

  47. would magnetizing the powder beds help with the powder blast that occurs in front of the laser during welding? Has magnetic technology been implemented into any aspect of this technology?

  48. They are now adding high metal content into plastic filament. Which can be printed on a cheap desktop fdm printer now. Still need to be sintered but its huge change in cost, since the machines cost is way down. Lookup virtual foundry, Metalum and basf

  49. Why aren't the metal 3d printing process show here done under a a shield gas atmosphere similar to what we see in welding?

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