Challenges in creating a 3D printer

[hazel1919]

Hi everyone!

I would like to discuss the pros/cons and engineering challenges one would face in order to create a 3D printer capable of printing in metal.

I have created an open source initiative (linked to below) that deals with this subject, there is quite a bit of information I have amassed on the subject, so it is worth checking out...

http://www.metalbot.orgI am sure most people here have heard of 3D Printers/printing, perhaps some of you've had the opportunity to use them.

From what I have learned, the two limiting factors with 3D printing have always been a - strength of the printed parts and b - part resolution. Hopefully it is possible to solve both of these problems by designing printer that works through a process called 'laser sintering' (although a few other avenues are being pursued).

I would be more than happy to answer any questions to the best of my knowledge!



Jethro.

 

[Danger]

Boy, am I glad to see this!
I've bookmarked the site and will check it frequently. Unfortunately, I can't be of any assistance to you. I also probably won't be able to afford to build one after it's designed; I'm just now getting to the point where I'll soon have enough saved for a RepRap kit.
Best of luck with the project.

 

[hazel1919]

I am not sure if you saw the thread over on Reprap.org that started this project?

http://forums.reprap.org/read.php?1,190528

Currently the only commercial systems are being manufactured by Arcam (using electron beams) and EOS (Fiber lasers). These systems start at a base price of $680k. So clearly our work is cut out!

There are loads of ways to help out if you like...

Thanks again for the feedback :)

 

[bigaggie]

I would think you have three major challenges

1)Temperature- you have to literally melt whatever metal you're trying to work with to the other particles of metal...without sticking to your baseboard, and without melting everything else around it. Could be difficult.

2) Cost- sounds like you're wanting to use a laser for this. To generate the kind of power to melt metal in relatively short order (to where this would be practical) is usually not cheap.

3) Metal Strength- I can't speak for all metals, but I know that laser cladding is used to apply overlays on wear parts, and usually the clad material (that has been hit with the laser) is very hard, on the order of 45-50 HRC, sometimes higher sometimes lower. You may have to incorporate a post-process heat treatment to anneal your part, or it could become too brittle.

 

[Danger]

With reference to Bigaggie's first sentence, I would definitely recommend that your build table be composed of some ceramic material. That's because I think that something like Nomex might stick to the build material.

 

[hazel1919]

Hi bigaggie,

You bring up good points. So regarding temperature. When we aim the <10um laser beam onto the powder we want the powder to melt and fuse to the layer below.

This ties in with your second point because the higher wattage the laser, the more expensive it costs (and that is no small cost). So the simplest solution is to use smaller powder layers (30um for example).

We need to document and graph the sintering threshold of different materials and a whole bunch of variables (laser wattage - spot area - layer thickness - powder granule size etc...).

As for the strength of materials. EOS -one of the main companies specializing the metal printing - have reported that their sintered titanium parts have strength that surpasses forged parts.

Since we will print in thinner layers the parts will be as dense and hopefully as strong too.

@ Danger - very interesting suggestion... another idea is to spread down a few layerrs of un sintered powder before the first cross section of the part is sintered, but ceramic is certainly a good idea - thank you!

Putting down a precision powder layer is quite a challenge. Also there are concerns that after many runs the titanium powder will sand down the powder bed and abrasion will occur.

Jethro.

 

[Danger]

ceramic is certainly a good idea - thank you!

Putting down a precision powder layer is quite a challenge. Also there are concerns that after many runs the titanium powder will sand down the powder bed and abrasion will occur.

Oh, wow... I have trouble believing that I actually contributed something potentially useful. Way cool...
I have a question about your last sentence that I quoted here. Does this thing use the same sort of spreading mechanism as non-metallic printers, with some sort of "squeegie" pulling a layer of material over the build table? I'm asking because I don't know what you mean by "the powder bed" or where the suspected abrasion will occur. If it is an issue of excess build-up of powder, would there be any advantage to building a vibrator system into the build table to just sift the unwanted crap off to the side? (But how could you gauge that?)
My head is starting to hurt; I need more beer.

 

[hazel1919]

It is an interesting suggestion. The biggest requirement would be for the surface of the 'build table' to be extremely flat - imagine spreading a layer of powder only 30 microns thick, over a 200mm surface area. That table needs to be FLAT, so I suppose this is a question for the machining forums...

Does this thing use the same sort of spreading mechanism as non-metallic printers, with some sort of "squeegee" pulling a layer of material over the build table?

Sorry for not being clear... the powder bed is the build table and there is a squeegee action going on.

The titanium is a very hard material and after many runs abrasion could occur.

If it is an issue of excess build-up of powder, would there be any advantage to building a vibrator system into the build table to just sift the unwanted crap off to the side? (But how could you gauge that?)
My head is starting to hurt; I need more beer.

A vibration system was considered, the trouble is that it could upset the printed parts and offset the layers...

I think I need the same medicine :)

 

[Danger]

A vibration system was considered, the trouble is that it could upset the printed parts and offset the layers...

Good point. Hmm...
Curse you—now I'm hooked! I'll be up all night thinking about this. :grumpy:

 

[OldBill]

Perhaps a carbonmide-impregnated thermoset polymer feed may get you close to achieving metallic-like properties and comparable structural integrity. But that's out of my field, so I dunno.

 

[Danger]

I've got a bunch of things sneaking around in my head, none of which I can imagine being useful...
sprinkling the powder on rather than squeegeeing it... leveling it with air pressure... using a liquid carrier for the powder, so it will self-level until hardened... elves...
I actually kind of liked the liquid one for a minute or two, until I realized that the entire neigbourhood would evaporate once sintering begins...

 

[SteamKing]

There used to be a machine that printed in metal: it was called a Linotype and the metal it used was lead.

 

[Danger]

There used to be a machine that printed in metal: it was called a Linotype and the metal it used was lead.

That doesn't actually print in metal; it's a pour-moulding process.

 

[hazel1919]

Hi Danger! The sprinkling system was originally considered. We were even going to have ultrasonic transducers underneath a curved sheet of metal that would gently drop the powder in place. The trouble with this is that it needs to be very precisely tuned... where as when using a spreader you don't have to calculate precise amounts. Any excess powder gets pushed over the edge into the recycling bin! Evaporating your neighbors is considered bad etiquette ;)

There is some interesting discussion going on at the practical machinist, maybe it will give you a few ideas.

http://www.practicalmachinist.com/v...-metal-printer-264901/index3.html#post2030059

Jethro.

 

[Danger]

Evaporating your neighbors is considered bad etiquette

I know; I have a criminal record to prove it. :grumpy:

I'll check out that machining site in a while. It sounds like someplace that I'd like to visit.

 

[hazel1919]

Here is a very interesting project which is along the lines of where we need to go... for your perusal http://focussls.blogspot.nl/ .

There are some interesting discussions going on!

 

[hazel1919]

Hi Danger!

Check out some preliminary designs for the Metalbot printer... http://www.metalbot.org/forum/viewtopic.php?f=4&t=111

If you have google sketchup you can download the model here... http://sketchup.google.com/3dwarehouse/details?mid=154316e5f0930d093ff7a6479db06f74&prevstart=0

Best!

Jethro.

 

[Danger]

Hi, Jethro;
I've been absent for a while due to health reasons, and even now I'm barely capable of participating here. I have not, therefore, examined your links yet. I will when I'm able. Meanwhile, I got another of my whacko thoughts; is there some way, perhaps by using an alloy rather than pure titanium, that the powder could be distributed and constrained by having the table heavily magnetized?
(I really do want to get into this, but my life is a bit messed up right now.)

 

[hazel1919]

I am very sad to hear this. First port of call: rest and recover.

As usual... that is certainly an interesting suggestion . The viability strongly depends on the usefulness of the alloys, but it is an out the box thought for sure!

Again, I hope you get well soon. Just take one day at a time...

 

[Danger]

Thanks. I'm still thinking to the best of my ability, but that varies hourly according to oxygen absorbtion.

 

[hazel1919]

Hi Danger,

I hope you are well, I don't know if you frequent here any more... I thought you might like to see how the project has taken off: http://www.metalbot.org/

I am truly sorry to hear about your circumstances.