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Designing a 3D Metal Printer

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LAN_403

Conundrum

Sat Jun 08 2013, 09:42AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

The trick is to use plastics whose MP is matched to that of the alloy.
While this may seem counterintuitive, it isn't as the shrinking of the plastic when cooling is matched by the metal shrinkage seen with low melt alloys.
I have confirmed this experimentally and in fact the common BiSnIn alloy if mixed with a small amount of copper will behave differently.
This method is also used in Sn99Cu1 solder...
Try 57.2%Bi, 24.8%In and 18%Sn as this is a known formula with predictable properties.
See

NB: If using commercial bismuth you may discover that it is contaminated with tin, please adjust the formula accordingly.
Typical lead free shot is Bi97Sn3 with smaller amounts of lead, cadmium and other s**t mixed in to make it heavier and possibly also the odd bit of tungsten in high performance shells to make the pellets disintegrate when it hits something and cause more damage.

As an aside, has anyone tried "MGEIM" ie metal glass epoxy in mould as a 3D printing technique?
The method here is to print out a layer of porous metal, a layer of glass beads or fibres then a layer of epoxy resin.
The "spikes" of metal help bond the whole thing together and the glass acts as a weight reduction agent and reinforcement.
Also when depositing resin you could use UV curable epoxy as this prints nicely and tends not to shrink when cured.

Laser sintering could also be used with a lower power laser and workpiece in a static induction field or HV bias on the tip; the object is to raise the workpiece temperature at the point of fusing so the laser gets it past this point.
A simple current limiter would work here, as would a physical connection via low impedance baseplate to the workpiece so that the HV goes through the work not the powder.

-A
-A

Dr. Slack

Sat Jun 08 2013, 10:10AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Carbon_Rod wrote ...

My results were not that great, as the material was more like a useless spongy mess.

Stop giving the guy a hard time. For any new technology, there's a huge amount of 'YMMV' until the methods get sorted out. For instance, there's a helluva difference between sticking a copper anode in CuSO4 and trying to electroplate something and getting a cr@p deposit, and using cyanides and all sorts of nasty additives, controlling the current density, preparing the surface etc. A lot of trial and error will be needed to find a process that works adequately. Probably two processes, one for amateur levels of expenditure, and one for industry.

The potential for an additive computer controlled method is enormous. Of course the subtractive methods (like milling from solid) give better strength, finish etc at the moment. Even given that laser sintering is not likely to ever achieve parity for ultimate strength and finish, improving the technology will increase the proportion of applications where those are good enough to enable the flexibility of the process to be used.

I'm all for seeing the experiments done by more people. For instance, do you need 10W, or 100W? Can you coat metal grains so they absorb more heat, or stick together? Zinc, bismuth, fluxes, gas blankets?

Conundrum

Sat Jun 08 2013, 02:43PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

I agree.
Perhaps what we need is a dedicated "3D printer hacking" page on 4hv's server, like the home pages.
People can add to it but any large scale editing remains under the control of the site admins.

-A
#include "bad_Ram_Sucks.h"

johnf

Sat Jun 08 2013, 08:00PM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

The other technique that is used for additive metal fab is electron beam melting which should easily be in the amateur endevour. Again a good vacuum is required and an oxygen getter to keep oxides at bay

Thomas W

Sat Jun 08 2013, 09:20PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

what about printing a thin metal compound layer then jetting a reactive gas over it, breaking high energy bonds enough to cause the atoms of metal to heat up enough to bond to eachother to form a solid layer, the impure gas/compound is then blown away and next layer is printed?

Metalbot

Sun Jun 09 2013, 04:41PM

Registered Member #15261 Joined: Fri Apr 26 2013, 07:57AM
Location:
Posts: 5

My results were not that great, as the material was more like a useless spongy mess.

Why did it fail, what can you do to improve your results? In any case the MIM process is very different to "Selective laser sintering" which uses a laser on an X-Y plotter. MIM needs binders, a lot of post processing and a mold to begin with.

@ Conundrum...

Laser sintering could also be used with a lower power laser and work piece in a static induction field or HV bias on the tip; the object is to raise the work piece temperature at the point of fusing so the laser gets it past this point.

This is a very good and important point! If we could bring a local area of powder to near melting point through any means then a lower wattage laser is required to push the powder over the sintering threshold.

Your idea of using an induction field is particularly good! if implemented I will make sure you get credit

.

A 'pancake' induction could would be very interesting!!

In effect taking the donkey work of putting the energy into the powder away from the laser...

The laser would have to scan a small section at a time very fast, perhaps following behind in an forwards backwards motion while the induction coil preheats the powder! This is a very interesting idea, this is why I come to places like this

So... the biggest challenge facing the project is finding an affordable laser that a) can deliver the power and b) has the optical qulity we are looking for... a resolution of 100um or better. By using an energy source that may not deliver the resolution we need, perhaps heating up a 0.5mm^2 of powder, you could simply beam the laser in the middle of the heated powder and have fine control over the resolution of the printed part.

You can take the concept further and improve the printing speed by having a variable focus laser. Printing with a focus of say 50um for the outline of the cross section and then expanding the focus and increasing the power of the laser to 200um to sinter the inside of the outline fast.

I'm all for seeing the experiments done by more people. For instance, do you need 10W, or 100W? Can you coat metal grains so they absorb more heat, or stick together? Zinc, bismuth, fluxes, gas blankets?

These are all open questions... regarding the lasers, there are some very interesting up and coming experiments using all sorts of lasers, diode lasers, Nd:Yag, CO2 etc... it is all about the energy density or W/mm^2 , a 25W IR laser diode will sinter metals quite will if you have a good focus, that is a laser on it's own taking metal powder with a melting point of 1500C from cold to melted in milliseconds.

@johnf, check out the Metalicarap project, they are working on EBM (electron beam melting). We have decided to go the route of the laser because the difficulty of making a high vacuum big enough for printing in is very much out of reach for most hobbyists! Electron beams can deliver much more power and therefore are ideal for printing large volumes.

Conundrum

Sun Jun 09 2013, 07:05PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Metalbot, thanks for your kind words.
I am more of a "theory guy", often coming up with good ideas but lacking the resources, money and time to complete them.

Re. lasers, an interesting point to note is that blue ie 445nm and NUV ie 405nm are a LOT better for precise etching than red or infrared for a given power level.
Yes they are finicky to control but many people use them due to properly matched optics being present in the drive itself and G1 coated lenses being readily available if not.

I priced up a basic etcher the other day and it was under Â£100 if an Arduino Uno was used as the brain and A3928 boards *3 as the servo controllers with all the other parts except the diode and heatsinks salvaged from broken drives.

See

USE SAFETY GOGGLES IDEALLY WITH GLOVES!!!!!!!

-A

Metalbot

Tue Oct 22 2013, 12:49PM

Registered Member #15261 Joined: Fri Apr 26 2013, 07:57AM
Location:
Posts: 5

Hi everyone!

A qick update: It has been a few months and the Metalbot project is slowly coming together!

Check out what is going on:

We have had loads of great ideas and there are quite a few very interesting projects unfolding at the moment (take a look at the projects section).

We are slowly working towards a preliminary design and there are a lot of options now so if you guys have any ideas, please send them our way!

All the best,

Jethro.

Chris Cristini

Tue Oct 22 2013, 06:29PM

Registered Member #1749 Joined: Fri Oct 10 2008, 02:04AM
Location: Claremont New Hampshire
Posts: 497

That is awesome good work.

Conundrum

Tue Oct 22 2013, 09:33PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Also worth mentioning, using a 12W or two phlatlight LEDs to spot heat the material then the bluray to superheat and fuse.
These are a lot easier to obtain and can do surface modification of plastics with a simple pair of red blocking OD6+ goggles for eye protection.
As the source is incoherent the spot size will be limited to the size of the emitter though.

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