wiki:LostPLA
Last modified 4 days ago Last modified on 09/15/14 01:50:03

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 will use two or three 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 one on the aluminium. When notified the machine is done, the operator can use gloves to pickup and bury the mold in sand, then walk back to their workstation, and pour the aluminum remotely. This will reduce the risk of injury to an 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

Next, 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.
  • 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.
  • 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

Chamber

  • Create a box out of the 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 box 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.
    • 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 our chamber and chamber mold on end in the oven, and Heat to 100C for 2 hours.
  • Remove the chamber 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 chamber into the oven, and Heat 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 a batch of the same perlite and fire cement mix as above.
  • 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, to force the lid to be flat, and to mate up with the chamber.
  • Bake all of this the same way as the chamber.

suceptor coating

A coating of succeptor goes on the inside of our chamber.

  • Make a paste using 5 parts powdered sugar, 3 parts suceptor, and 2 parts water.
  • Paint this succeptor paste on to inside of chamber, and the lid.
  • 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 when mixing powders)
  • Regular gloves (for use when mixing)
  • Eye protection (for use when mixing)

Tools

  • Something to vibrate out air bubbles with
  • A large spoon (for use as a mixing tool)
  • A Hair Drier (for blowing out ash)
  • A Well vented microwave with the rotating tray in bottom. Make sure the power level is adjustable
  • A Squirt bottle, with a 'fine mist' setting (we used a 'glossing spray' bottle)
  • Handheld infrared temperature sensor
  • Measuring tools

Consumables

  • Styrofoam in 1" and .5" thicknesses
  • 1 bag of Plaster of Paris -- at Home Depot $16 for 25 Lbs.
  • 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.
  • Disposable mixing containers, 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
  • Powdered sugar
  • 140 proof isopropyl alcohol
  • thin cheap tupperware, for containing molds. Needs to be very flexible.

Process

  • Select your part to print.
  • Print the part at 103%, to account for the aluminium shrinking while it is 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.
  • Mix the water, alcohol, powdered sugar, and grinding powder.
  • Spray this mixture on our PLA object, the downsprues, runners, and gates.
  • Allow mixture to dry, and create grey/green tacky surface.
  • Locate an appropriately sized tupperware 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).
    • 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.
  • Vibrate the container to remove air bubbles.
  • Wait for investment to completely set. should take ~1 hour.
  • Microwave in short bursts until all water has left the investment.
  • Microwave in well vented microwave to burn away 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, or you might blow away fine detail.

Pouring Aluminium

Consumables

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

Procedure

  • Place sprue extenders over the aluminium entry channels. Duct tape them in 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.
  • Place the cooked out mold in 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 up to the top, without accidentally pouring in sand.
  • 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)

PLAExperiments

Attachments