Based on the interest and comments that these articles have been receiving it seems prudent to offer up more in depth content. The focus here is the “how to”… the raw data will come later.
How do you sprue? Well, to quote a friend and mentor ” You are a little silver car… that can only down shift… with no brakes… and you are running out of gas. Ready? Pick the route to your destination during rush hour traffic.” Now, imagine you are every car in traffic, that sums up how metal flow behaves. So, you build highways and roads to handle the traffic. Six lane highways with smooth merge lanes, soft lefts and rights for off ramps, no U-turns, wide intersections, and roomy shoulders for nervous drivers to pull over. You want to build clean effective roads for your frantic drivers on a hectic rush hour day.
Note: the size of flask can change the recommended burnout. Ranging from a 5-12 hour burnout depending on size and number of flasks.
At this point photos get hard to take. Below there are links to video of the process (it is 30+minutes of video). It was kept in realtime so people will know what to expect.
First video is the casting of Wades Stack from the Rapid Manufacturing MK1 article. The metal ~1400F which is excessively hot, but it seemed prudent to show a workable temperature range.
1st video Wades Stack (Video Length 10:00 minutes)
Second video is the casting of the Gyro Ornament in the sprueing example above. The metal is cast at the ideal temperature, this is more important for thin feature parts, and heavy parts, both are more drastically affected by linear contraction from high temperature cooling.
2nd video Gyro Ornament (Video Length 9:12 minutes)
Third video is the quenching process. Remember, aluminum and plaster hold a lot of thermal mass, and erupt violently in the water. When it is done correctly it is safe and quite anticlimactic.
3rd video Quenching (Video Length 6:47 minutes)
Fourth video is temperature data for the proper tempering and quenching for the aluminum. Any surface defects are pointed out in the castings. And, there is a quick demonstration on de-sprueing the wades stack.
4th video Tempering/De-sprueing (Video Length 8:02 minutes)
Fifth video is of the working Gyro Ornament… After de-vesting, de-sprueing, some clean up, and tweaking.
5th video functioning Gyro Ornament (Video Length 20 seconds)
Troubleshooting and Diagnostics:
Symptom: Partial plaster embedded in the part.
Possible Causes: Plaster shift, Porous print, Flashing, Checking, Hollow voids
Hole diameters in the part are either too small, or too long to withstand the force of the metal flow [TestFeaturesCast.stl].
Hexagon formation, small hexagonal recessed portions indicate that the surface of the 3D print was not water tight, and plaster leaked into the interior geometry.
Air bubbles commonly form on interior surfaces or convex surfaces relative to the parts orientation, allowing fragments of plaster to shift easily at the meniscus’ edges.
Solutions: Check investment mixing instructions, make sure printed part is water tight, do not vacuum part, redesign sprue systems, minimize thin features under 1/16″ or [1.4mm].
Possible Causes: Premature quenching, large volumetric contraction, or both.
Diagnostics: If the part is heavy it is most likely due to volumetric contraction, this is most common in aluminum.
Solutions: Fillets and chamfers help diffuse these internal stresses. Redesign with gussets, ribs, piercings, through holes, or webs instead of solid mass parts.
Cause: Premature quenching
Diagnostics: Bulging is the precursor to blebbing. It occurs when the molten metal comes into contact with water. The energy transfer of water turning to steam forces the steam to expand into the molten metal pushing it out through the hottest remaining contours.
Solutions: Wait longer before quenching, use a thermocouple if necessary to measure the temperature. Aluminum remains viscous ~900F. You can temper the aluminum by quenching between 500-750F. Remember the heavier areas of a part will take significantly longer to cool, the thermocouple will only give you a vague average of the button temperature. Bronze similarly will stay viscous ~1500-1600F …same rules apply.
Possible Causes: Failure to print a continuous layer, bad flow in mold, or crack in the plaster, firing the kiln too quickly can cause the PLA to expanded and crack the plaster in one continuous plane.
Diagnostics: Reprint part and look for layers of delamination, make sure the extruder can run continuously. For flow issues, test the edge cases with TestFeaturesCast.stl the pitch example can ensure that the metal is flowing properly through the mold.
Solution: Minimize the thin features under 1/16″ or [1.4mm].
Tags: 3d print to casting, 3d printed parts pre-sprued, cast gyro ornament, Casting 3D printed parts, casting 3D prints, Casting Walkthrough, Investing, lost PLA, lost PLA casting, Lost PLA casting walkthrough, Lost PLA diagnostics, Lost PLA Troubleshooting, Lost PLA walkthrough, PLA burnout, print to cast, rapid manufacture, rapid manufacturing, Sprueing, Wades Gear Dream, wades gear stack