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Metal Extruder and Syringe Pump

by mattmoses, published

Metal Extruder and Syringe Pump by mattmoses Aug 22, 2009
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License

GNU - GPL
Metal Extruder and Syringe Pump by mattmoses is licensed under the GNU - GPL license.

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Summary

This is the final episode of a three-part mini-series on making things with low-melting-temperature-alloy. The collection of things here form a hot material transfer system that can be used to extrude (sort of) molten metal or wax. This is inspired by earlier work done by Dr. Sells and Prof. Bowyer http://reprap.org/bin/view/Main/AutomaticDepositionOfMoltenAlloyIntoACastingChannelToCreateAVerySimpleElectro-mechanicalComponent .

As usual, remember that low-melt alloys are toxic and hot enough to cause burns and fires, so only use this material if you are experienced in a lab environment. On the plus side, this system can also be used to make things out of wax, which is much safer to use, although you still have to watch out for burns and fires! Possible uses for a wax-handling system include: 1) automated wax casting; 2) use of wax as a support material.

If you omit the heaters, you can probably use the nozzle and syringe pump to deposit slurries or liquids.

The idea of operation is that a standard RepRap prints a layer of plastic (HDPE, ABS, etc). Then the toolheads are switched, and the metal/wax toolhead deposits molten material in the channels or cavities formed by the plastic. If necessary, the process can be repeated for constructing thicker and more complex parts.

We have had good success using the nozzle as a hand-held tool for transferring metal. For example, we used it to make this thing: http://www.thingiverse.com/thing:802 .

We have had somewhat less success using it when mounted to a RepRap, as seen in the pictures. The main problem is poor control of flow-rate (see photo of pattern on hot plate). With some modification (such as a smaller nozzle hole diameter) and tuning of parameters (feed rate, height of nozzle above plate, etc) it might work much better. We RepRapped a simple test piece, manually filled it with metal while it was still on the hotplate, then let it cool (see photo of widget with 25-cent piece). This yielded fairly good results, indicating that an automated system may be able to produce usable parts.

The main components of the system are

1) Heated cup - this is a heated reservoir that contains the molten work material.

2) Heated copper nozzle - the nozzle slurps up material from the cup, then moves to a desired location and deposits the material.

3) Syringe pump - a motor-driven syringe controls air flow in and out of the nozzle, which in turn causes the nozzle to slurp or deposit material.

4) Heated plate - this keeps the work hot to improve the flow of the heated material. It also melts the base of the deposited part, creating a good seal between part and plate, so that molten material does not leak under the part. In general, the heated plate seems to help avoid warping, but the downside is that the bottom of the part starts to ooze outwards after a while.

Instructions

The standard safety warnings apply. Low-melt alloys are toxic and hot enough to cause burns and fires. Use them only if you are experienced in a lab environment.

In addition: the nozzle, cup, and plate get dangerously hot. These can cause fires and burns. Operate with good ventilation, never operate the system unattended, and know where your fire extinguishers and escape routes are.

  1. Heated Cup ----------------------------------

The cup heaters were purchased from American Science and Surplus ( http://www.sciplus.com ) which seems to no longer have them in stock. They were intended for coffee makers or something. By chance, the cups were the right size and resistance (8 ohms) for what we needed. You can probably find something similar at one of the many surplus outfits. For temperature control, a thermistor was JB-welded to the bottom of the cup.

  1. Heated Nozzle -----------------------------------

This is a derivative of the old RepRap Thermoplast Extruder V1.1. The copper part of the nozzle is treated with JB-weld, wound with nichrome wire, and equipped with a thermistor as described on the RepRap website here: http://reprap.org/bin/view/Main/ExtruderMechanicalParts .

The copper nozzle and PTFE adapter have to be machined using a lathe. A drill press or small milling machine, in addition to simple hand tools (files, etc) will come in handy. A standard disposable syringe is cut up and glued to the PTFE adapter with silicone caulk. The syringe top is used as a plumbing fitting to connect to the syringe in the pump.

The little safety pin is important. Without the pin, if the nozzle were to get blocked during use, the syringe pump could generate enough pressure to pop the copper nozzle out of the PTFE adapter, spraying molten metal everywhere. The pin prevents this. It can be tricky to get a good seal between the PTFE and copper nozzle. If needed, you can leak-check the whole assembly underwater using another syringe to provide pressure.

The nozzle mount is made from laser-cut parts and is intended to fit the old-school carriage of an early BitsFromBytes ( http://bitsfrombytes.com/ ) kit. It is a good idea to make a little stand that will safely hold the hot nozzle while it is not in use.

  1. Syringe Pump --------------------------------------

The syringe pump uses a standard disposable 12cc plastic syringe (0.7 inch outside diameter). It is made mostly from laser-cut parts, except for the motor coupling. The motor coupling design could certainly be improved, but we made it with bits we had sitting around and so that is what's uploaded.

You will need assorted nuts and bolts to put the thing together, in addition to 2 microswitches, a Solarbotics gear motor, a 6-32 threaded rod (3.5 inches long), and a 6-32 nut. The syringes have a standard Luer-lock fitting, which allows quick connect/disconnect of the hose that goes from pump to nozzle.

If you bypass each limit switch with a diode, you can create a 2-wire device that acts like a DC motor, but has the limit function built-in.

  1. Heated Plate ----------------------------------------

This is a 6 by 6 by 1/4 inch aluminum plate with five 40 ohm, 25 watt power resistors (wired in parallel) JB-welded underneath. The plate has some tapped holes at the corners so you can clamp stuff down to it. In the photo you can see some heat damage to the wiring underneath, indicating that this thing gets HOT when running. Be careful...

  1. Electrical Interface to RepRap -----------------------

This system is designed for the older single-Arduino setup. The heated plate and heated cup are controlled by a separate Arduino with PWM Driver running off a 24V supply. The nozzle is a pin-for-pin replacement for the old RepRap Thermoplast extruder. The interface is: 3 leads for thermistor board (+5, ground, signal), 2 leads for motor, and 2 leads for nichrome heater. We use a big rotary switch to select between different toolheads.

  1. Parts and Materials -------------------------------------

copper bar stock (0.5 inch diameter)
PTFE bar stock (0.75 inch diameter)
cable ties
hose clamp

JB weld
silicone caulk
superglue (for syringe pump parts)
5-minute epoxy (for microswitches)

3 RRRF thermistor boards (nozzle, plate, cup)

syringes - 12cc disposable plastic syringes (0.7 inch outside diameter)

0.2 inch thick acrylic (syringe pump and nozzle mount)

6-32 threaded rod, 3.5 inches long
Solarbotics gear motor

2 microswitches
assorted nuts and bolts
wire and connectors

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This is an incredible idea. Only one question. Any idea where one might find one of those heater cups? It seems they are sold out on American Science and Surplus.

Short answer: No.

Long answer: There are several other options. Best is probably to put metal cups or laboratory glassware in a hot water bath. This is safest and it is easy to control. Many low-melt metals and waxes will melt below water's boiling temp. I use an appliance (not even sure what it is) I got at a
thrift store as a hot water bath. You can see it here http://www.thingiverse.com/thing:9608http://www.thingiverse.com/thi...

You could also put lab glassware on a hotplate.

You could find off-the-shelf metal cups (or crucibles) that are about right and bolt or jbweld power resistors to them.

Or if you wanted to go crazy you c
ould machine something out of a block of metal and bolt your power resistors to that :)

Electromagnet 2

This is great.

But I have a silly question, is the nicrhome wire attached to the outside of the copper nozzle?

First the copper nozzle was coated with a thin layer of JBweld to electrically insulate it. Then bare, uninsulated nichrome was wound on top of that. Then another layer of JBweld went over the nichrome. The thick white wires are twisted and soldered to the nichrome (even though nichrome does not solder well this provides an acceptable conncection).

This setup works ok for lower temperatures, but the JBweld degrades over time. Newer designs for hot ends use high temperature cement instead of jbweld, and sometimes power resistors instead of nichrome. The newer designs work much better.

thanks for your response Matt,

Im really interested in the nozzle design, and specifically what you mentioned about newer designs. Would you happen to have any links to this?

I want to try developing something that doesnt have to slurp up material, but instead melts it within a nozzle chamber and then deposits it, similar to a glue gun

The nozzles I was thinking of are usually intended for plastic extrusion, but they should work for metals under the right circumstances. Two examples are

heater block for glass nozzle
http://reprap.org/wiki/Heater_Block_For_Glass_Nozzlehttp://reprap.org/wiki/Heater_...

one of nophead's designs
http://hydraraptor.blogspot.com/2009/01/yet-another-quick-heater-hack.htmlhttp://hydraraptor.blogspot.co...

you can also search for "hot end" on thingiverse or the reprap wiki
http://www.thingiverse.com/tag:hot_endhttp://www.thingiverse.com/tag...
http:/
/http://reprap.org/wiki/Category:Hot_Endreprap.org/wiki/Category:Hot_E...

Some of the work on depositing metal can be found at these links:

A new approach to printing metals
http://blog.reprap.org/2011_06_01_archive.htmlhttp://blog.reprap.org/2011_06...

reprap solder extruder
http://www.youtube.com/watch?v=Wnu4lmOnX00http://www.youtube.com/watch?v...

Simple hot metal valve
http://blog.reprap.org/200http://blog.reprap.org/200
8/04/simple-hot-metal-valve.html

Thanks for this! A couple of questions about the syringe pump, though: Which gear motor should I use with it ('solarbotics gear motor' is a bit vague, since they sell more than one), and how is the motor coupled to the rod? I presume the motor housing was designed with one particular motor and gearing arrangement in mind, but you don't specify.

The motor in the pictures is GM2

http://www.solarbotics.com/products/gm2/http://www.solarbotics.com/pro...

but it would probably work as well or better with GM8

http://www.solarbotics.com/products/gm8/http://www.solarbotics.com/pro...

The parts in motorCoupler-mm.stl and threadedRodCoupler-mm.stl need to be
glued together with the rod. The flat motor shaft then fits into the coupler without the
need for glue. See attached pictures.

Hm, I see the GM8 is still only 40RPM, which seems like it will take an awfully long time to depress the syringe. It looks like I may have to get a faster motor and modify the housing.

Scaling up the lasercut parts would probably work for a larger syringe. The printed parts were from another project, and we used them for the motor mount and coupler just because we had them. So that part is not optimal. We also wanted a slow feed rate - not the best for a drink-bot :)

You could probably use a motor like this: http://www.solarbotics.com/products/22044/http://www.solarbotics.com/pro...

and a coupler like this: http://www.thingiverse.com/thing:7678http://www.thingiverse.com/thi...

It should be pretty easy to mount the tamiya motor to a lasercut pump assembly.

Spider Coupling with rubber insert: 4.75mm stepper motor to 8mm threaded shaft

Awesome - thanks! This ought to work perfectly for a syringe pump for the drink-bot I'm planning. Any tips on adapting to a larger (30cc) syringe? Should I just be able to scale up most of the parts?

Very nice! if this is conductive, then it can be used to print circuits instead of having to etch copper. Or perhaps the soldering alloy could be used to do that?

cheers

Potassium + Sodium alloy is runny at low temperatures. Could be a candidate =-X

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