wiki:LostPLA
Last modified 13 days ago Last modified on 10/18/14 17:17:25

Lost PLA Processes

Our Microwave-Only Procedures

Overview

Our system uses a consumer microwave unit to perform the burn-out of PLA from molds, followed by a second microwave to liquefy the aluminum, so that it can be poured into the mold.

Future Vision

Under human control, 3D printer-inspired mechanics can move the aluminum from the microwave into the target mold. This can be done by a human operator across the network, so that there is minimal risk to the person operating the machine. In order to automate this process, we plan to use two or three simple machines powered by arduinos with minimum axes. One machine will be a forklift to pickup the kiln and deposit it safely onto a pair of fire bricks. A second machine serves as a crane to pickup the top from the kiln, and a third operates as a kind of combination forklift and (x,y) table. This will pickup a cup full of aluminium, place over target, and pour through a heated steel funnel into the mold.

Ideally, we see an operator walking to the machine, starting the microwave on the mold, and starting another microwave on the aluminium. When notified via the network that the machine is done, the operator can use gloves to pickup and bury the mold and sprue extenders in sand, then walk back to their workstation, and pour the aluminum. This will reduce the risk of injury to the operator, and not require any dangerous gases to perform the melt.

Kiln Creation

First, here are some videos so you know what you are doing:

Materials

Find the following list of materials:

Safety equipment
  • Face masks (for when mixing)
  • Gloves (for when mixing)
  • Eye protection (for when mixing)
  • Welders gloves (for removing kiln from oven)
Tools
  • Potato masher (for mixing)
  • Measuring cups
  • A well vented microwave with the rotating tray removed, and a microwave emitter in the top. Make sure the microwave is as large as possible.
  • 1 stainless steel cup with handle. As short as possible. This will serve to hold liquid aluminium.
  • 1 trowel (for spreading fire cement)
  • 1 large steel bowl (for mixing fire cement)
  • 1 sheet of tempered glass the size of the bottom of the microwave (for seal creation)
  • 1 paintbrush
Consumables
  • Several (6+) containers of High Heat Furnace Cement -- Available at Home Depot
  • 1 bag of perlite -- at Home Depot, $17 for two cubic feet.
  • 1 Pound of silicon carbide grinding powder, 1200 grit -- at Amazon, $30 for 1 Lb.
  • Water
  • Cardboard
  • Newspaper
  • Painter's tape
  • Large static bags

Chamber

Inside Layer
  • Create a box out of cardboard and painters tape. This is going to serve as our 'Chamber Mold', or the inside of our chamber.
    • Make the box long on one side (but short enough to fit in your oven vertically), and just large enough on the other sides to fit your stainless steel cup inside of the box.
  • Cover the outsides of the 'Chamber Mold' tightly with a layer of cut up static bag material, then a layer of newspaper. Use the painters tape to ensure the static bag and newspaper are as tight as possible.
  • Mix fire cement, water, and perlite in the large steel bowl. The directions for this step will vary wildly depending on the water content of your fire cement.
    • Generally, throw some fire cement into the bowl, add some water to make it easy to mix with the masher, then add perlite until it stops being easy to mix.
    • Add water and perlite until the mixture looks like oatmeal, and mushes like peanut butter.
  • Coat 5 sides of the 'Chamber Mold' from the first step in a 30mm+ layer of our perlite/fire_cement/water mix. This is going to be the 'inside layer' of our kiln.
    • Use the trowel to make flat sides.
    • Make sure not to coat more than the height of the cup on the chamber mold. not deep enough can be fixed later, but too deep of a box will require starting over.
  • Stand the inside layer and chamber mold on end in the oven, and Heat to 100C for 2 hours.
  • Remove the inside layer from oven, and remove chamber mold from the chamber. The box and plastic should tear away easily, while the newspaper will stick, and can be burned out later.
  • Place the inside layer into the oven, and Heat to 200C for 2 hours.
  • Finally, heat the inside layer to 250/230C in an oven for an hour, to ensure it has hardened properly.
Outside Layer(s)
  • Mix fire cement, water, and perlite in the large steel bowl. The directions for this step will vary wildly depending on the water content of your fire cement.
    • Generally, throw some fire cement into the bowl, add some water to make it easy to mix with the masher, then add perlite until it stops being easy to mix.
    • Add water and perlite until the mixture looks like oatmeal, and mushes like peanut butter.
  • Coat 5 sides of the 'Inside Layer' in a THICK layer of our perlite/fire_cement/water mix.
    • Use the trowel to make flat sides.
    • Make sure not to coat more than the height of the cup on the chamber mold. not deep enough can be fixed later, but too deep of a box will require starting over.
    • Make sure not to make the chamber too big for the microwave.
  • Place the chamber in the oven, and Heat to 100C for 2 hours.
  • Heat the chamber to 200C for 2 hours.
  • Finally, heat the chamber to 250/230C in an oven for an hour, to ensure it has hardened properly.
  • Wash, Rinse, Repeat.
Top Seal
  • Mix fire cement, water, and perlite in the large steel bowl. The directions for this step will vary wildly depending on the water content of your fire cement.
    • Generally, throw some fire cement into the bowl, add some water to make it easy to mix with the masher, then add perlite until it stops being easy to mix.
    • Add water and perlite until the mixture looks like oatmeal, and mushes like peanut butter.
  • Spread mixture on the top layer of the chamber. use the trowel to get a flat surface.
  • Place news paper on top of chamber, and place tempered glass on top of the newspaper to serve as a weight.
  • Place the chamber in the oven, and Heat to 100C for 1 hour.
  • Flip the chamber so that its weight is pressing down on the tempered glass.
  • Heat the chamber to 200C for 2 hours.
  • Finally, heat the chamber to 250/230C in an oven for an hour, to ensure it has hardened properly.

Lid

To create the lid to the chamber:

  • Mix fire cement, water, and perlite in the large steel bowl. The directions for this step will vary wildly depending on the water content of your fire cement.
    • Generally, throw some fire cement into the bowl, add some water to make it easy to mix with the masher, then add perlite until it stops being easy to mix.
    • Add water and perlite until the mixture looks like oatmeal, and mushes like peanut butter.
  • Place a sheet of newspaper on the tempered glass, then the lid, then another sheet of newspaper.
  • Place the chamber on top of the lid seal downward, to force the lid to be flat, and to mate up with the chamber.
  • Place the chamber and lid in the oven, and Heat to 100C for 2 hours.
  • Heat the chamber and lid to 200C for 2 hours.
  • Finally, heat the chamber and lid to 250/230C in an oven for an hour, to ensure it has hardened properly.

Suceptor Coating

A coating of suceptor goes on the inside of our chamber. to apply:

  • Make a paste using 5 parts powdered sugar, 3 parts suceptor, and 2 parts water.
  • Paint this suceptor paste on the inside of the chamber, and the part of the lid that will face the inside of the chamber.
    • Do not paint suceptor onto the part of the lid that contacts the chamber seal.
  • Bake the chamber and lid in an oven at 100C for an hour. After the first layer is cooked on, you can switch to using the microwave to cook on additional layers.
  • Microwave the chamber and lid. You should smell caramel as the sugar burns off.

Mold Creation

First, find the following lists of materials:

Safety Equipment

  • Face masks (for mixing powders)
  • Eye protection (for mixing wet glop)
  • Gloves (for mixing, otherwise the materials can dry out your skin over time)

Tools

  • Something to vibrate out air bubbles with (Tell what you use!!!!!)
  • A large spoon (mixing tool)
  • A hair Drier (for blowing out ash)
  • A very well vented, adjustable power microwave with the rotating tray in bottom.
  • A Squirt bottle, with a 'fine mist' setting (we used a 'glossing spray' bottle)
  • Measuring tools (What measuring???? Liquid Volume? Length? Weight? etc....)

Consumables

Have at least the following amounts on hand, to start this process:

  • Styrofoam in 1" and .5" thicknesses, 2 square feet of each.
  • Plaster of Paris, 25lbs -- Home Depot $16 for 25 Lbs.
  • Perlite, 2 cubic ft -- Home Depot, $17 for two cubic feet.
  • Silicon carbide grinding powder 1200 grit, 1lb. -- Amazon, $30 for 1 Lb.
  • Disposable mixing containers, 2. For mixing plaster of paris, perlite, and water. Should be made of flexible plastic, so it can be banged on to remove residue for the next batch.
  • Water, on tap.
  • Powdered sugar, 1lb.
  • 70% isopropyl alcohol, 700ml.
  • Some thin, very flexible, cheap plastic containers, for containing molds. Size & number determined by your needs. Each needs to be at least an inch taller than the parts you are making.
  • A disposable piece of metal, for cooling and applying hot glue, a dull knife is good.

Process

  • Choose the object/part you want to cast in Aluminium.
  • Print the object/part in PLA at 103% of desired final size, to account for aluminium shrinkage during cooling.
  • Attach gates and downsprues, made of at least 0.5" styrofoam, by using slightly cold hot glue.
    • Attach gates near opposing outside corners of the object, on surfaces that do not require high precision.
      • Apply hot glue to the plastic part, wait a for the glue to cool (~15 seconds), and press the styrofoam into place.
    • Attach one of the gates at the bottom of the object, to collect the defects from the PLA burning off.
    • Attach downsprues made of at least 1" styrofoam to the in and out gates, ensuring that they are wider at the top than the bottom, and that the bottoms of the downsprues are lower than the bottom of the gate to allow for defects to collect in the extra space.
    • Attach a runner between one of the downsprues, and the bottom mounted gate.
      • When attaching styrofoam to styrofoam with hot glue, apply the hot glue to the disposable piece of metal, and use the metal to smear the glue into place after letting it cool a bit.
  • Mix 50 mL water, 10 mL alcohol, 1 tbs powdered sugar, and 1 tbs susceptor [silicon carbide].
    • Place this mixture in the spray bottle. This is our suceptor spray.
  • Spray the suceptor spray on the PLA object, the downsprues, runners, and gates. We found that 2 layers with about 3-4 coatings each did the trick. Wait 15 minutes between each coat and careful not to spray too close or you will have undesirable dripping.
  • Allow the suceptor spray to dry, and create a grey/green tacky surface.
  • Locate an appropriately sized thin plastic container for the mold.
  • Mix the "investment", made of perlite, plaster of paris, and water. Use equal parts plaster and perlite. Mix the dry ingredients before adding one part water (equal to the perlite or the plaster).
    • Always make 'too much' goo as 'too little' is a disaster.
    • The Investment should have the consistency of thick soup (think: pancake batter).
    • Do not stop stirring for more than 15 seconds after water is added, or the investment will harden. Stir until you're ready to pour, then pour quickly!
  • Pour a little investment into the container to serve as a 'floor' for the object to rest on.
  • Place the object on top of the investment.
  • Cover the object with the remainder of your investment, until the object is no longer visible.
    • Make sure the downsprues are still sticking out of the mold.
  • Vibrate the container to remove air bubbles.
  • Wait for the investment to completely set. This should take about 1 hour.
  • Remove the mold from the plastic container.
  • Microwave the mold in short bursts at half power until all the water has left it. DO NOT USE INDOORS!
    • It will sweat water, and try to create puddles in the bottom of the microwave. You may want to use a towel to remove freestanding water.
  • Once the mold stops steaming, microwave it burn away the PLA object, and all styrofoam. DO NOT USE INDOORS!
  • When the smoke starts to get really thin, use the hair drier to blow out ash. Do not use too much air pressure, or you might blow away parts of the mold, losing the fine detail.

Pouring Aluminium

Tools

Consumables

  • Sand
  • A cardboard box
  • Sprue extenders (aluminium cans without top/bottom)

Procedure

  • Place the sprue extenders over the aluminium entry channels. Duct tape them into place like crazy, to prevent the entry of sand where they join with the mold.
  • Cover the top of the sprue extenders in foil to prevent the accidental entry of sand when covering it in sand.
  • Place the cooked out mold and sprue extenders in a large cardboard box, on top of a bed of sand.
  • Surround the mold in sand, excepting the sprue extenders.
  • Surround sprue extenders in sand. Make sure to cover all the way to the top of the sprue extenders, without accidentally pouring in sand.
  • Remove the aluminium foil from the top of the sprue extenders.
  • Pour in liquid aluminium.

Online Documentation of Standard lost PLA Processes

Manufacturing a propane/fired forge

  • Large box.
  • Small Coffee Can (4 inch)
  • Hack Saw (or any metal cutting tool)
  • Drill (or metal punch or improvised hole making tool)
  • Scrap steel bar like from a printer, about a foot long (you can buy 5/8 steel bar at lowes)
  • A sharpie (or any marking tool)
  • Tape
  • Cardboard
  • Short (about 2 or 3 inches) iron or steel tube that the torch head fits in. long enough to penetrate between box side, and chamber (optional)
  • A ball peen hammer (any hammer will suffice)
  • Some propane gas (i buy the ones for camping stoves because their $4.38 for a 2 pack of 16.4 oz tanks.)
  • An oven (optional)
  • A vice. ( kinda optional. you could find another way but i find the vice necessary)
  • A mini muffin tin (optional. you just need something to pour the aluminum into.)
  • Some cheap thin steel wire (1/8 diameter max. but strong enough to hold some weight)

new model:

  • oh. and a small handtruck that can handle ~100lbs

You'll get quite a bit of slag, but if you can find some bailing wire (needs to have carbon in it) some where around you, you can just dip a piece in and the slag will attach itself to the wire.

How to Make a Crucible

Verify Bottle Is Empty And Able To Cut

  • Burner (5000 btu propane 10000 Map gas)
  • install burner on the bottle (RIght tight Left Loose)
  • Gas only has to be hand tightened
  • turn on as Bottle
  • Has an electronic ignition. Test no Ignition from bottle
  • Verify the Electronic Ignition is working after removing bottle.
  • Shake Can to see if you can feel something shaking.
  • Turn all the way off Before you connect to the bottle
  • Reinstall the valve (to verify the gas discharge)
  • After you verify everything else, press the safety valve and check for an audible sound.

Using the Forge

  • Our forge uses 2 flame sources:
    • Small output direction flame For controlling airflow
    • High BTU output unit for raising the temperature. this also has our electronic ignition, for relighting the system when the hardware is too hot to handle.
  • Check each nozzle to verify it is rated for the gas you are using.
  • Install the equipment onto the canisters:
    • Make sure nozzle is fully off
    • Tighten nozzle flow control to the right as tight as possible
    • Install
    • If applicable, check the electric start to make sure it works.
  • Aim flame from small output to one side to create heat vortex
  • Place crucible in the forge, and wait at least
  • Do not exceed Steel melting temps
  • TO speed up process use oxygen and cutting torch

An oxygen canister can be used to accelerate the flames

  • Hunter is turning up a canister and notices its dead

*All canisters are made of steal

Shows failure

  • The steal crucible became to hot and burned a hole
  • Some canisters have reverse threading
  • Always shut the oxygen off when not in use.
  • It is an accelerant and CAN and WILL BLOW UP
  • Always wear a mask and gloves when using cutting torch
  • with oxy/map and oxy/acc the torch is hard to tune up on start
  • When you see smoke, there is not enough oxygen in the gas
  • again very hard to tune
  • Use a striker, not al lighter
  • Use mask because of the infrared emissions from the cut.
  • Map gas
  • if you want to use dual gas, you must have to regularulators that are in
  • make sure you turn them off before you turn off the gas.
  • Hunter is Burning the crucible to fail.
  • Dont try this at home,
  • You don't take the molten pieces out, you shake em off

PLAExperiments

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