I recently had a project where I needed to create a couple dozen identical foam ear shapes.  Casting from a mold is the clear solution here.  However, the ears needed to fit onto an existing product, so I knew some tweaking of the design would be necessary to get it right before I could make the dozens.  I was able to use Instructables' Objet Connex printers to make my molds, based on CAD drawings I made, and after a couple tweaks I got the design right and was able to make the full run.

In this Instructable I'll share what I learned about how to draw a CAD for a mold and 3D printing it out.  I will assume you have access to and moderate proficiency with a CAD system (it doesn't matter what kind).  For the printing, if you want to make your own but don't have access to a 3D printer, there are many services which print for a fee, or Instructables may be able to do that for you.  The actual casting I will leave out as I was using an expanding polyurethane foam, which is not a generally applicable material.

Unfortunately my print picture set and my mold CAD picture set do not show the same mold.  The pictures of the print, in the second half of the instructable, are of a slightly more complex mold, with a two-plane parting line.  The process I outline is the same for both, however.

Step 1: CAD Prep

For the purposes of this instructable, which is about 3-d printing a mold, I am going to assume you have an original object already drawn, or can obtain one from (for example) Thingiverse or another source.

First, ensure you have a "solid" object, rather than abutting surfaces.  The object must be theoretically water-tight.  Save it as a new file (I just call mine 'originalname-MOLD.3dm').  Next, consider the orientation of the mold.  It doesn't have to be printed such that the object is in its expected upright position, it can be at any angle that is suitable for casting.  Do you have a flat bottom, such that you can make a one-piece mold, or  do you need a parting line, the join where the mold will come apart to extract the casting?  If so, where is the best place for it?  In general this should be at the widest part of the object, and it is often easier to extract the casting if the parting line runs more or less along the length, rather than width or height, of the object.  If you have undercuts in the object, significant concave areas, consider placing the parting line through or near these.  Good parting line placement is a bit of an art.

If the parting line has to be highly shaped, the technique becomes more difficult; for this simple tutorial I am assuming a straight parting line, either in one plane or only on a few intersecting planes.  If you are planning cast with a flexible material such as silicone or foam, you can get away with fudging some of these guidelines a small amount as I did in the example.
<p>How did you get access to the Object Connex printer? Does Instructables run a print service? Note that the ABS created by a PolyJet printer like that is not quite the same as the ABS filament most people are using on their own desktop printers. I got some turtle wax to see if it works on regular ABS.</p>
<p>Instructables' Pier 9 facility has several Objet Connex printers. Currently the only way to use them is through the Artist in Residence program, which is expanding rapidly. There's a link about it at the bottom of every page.</p><p>Did the turtle wax work on regular ABS? I haven't tried that as the desktop FDM printers haven't got quite the resolution needed for this kind of thing and a lot of surface prep would be needed - my thinking on that is Bondo but I haven't tested it yet. I'd be interested in your results!</p>
<p>The turtle wax did work as a mold release on regular ABS, but I was using Great Stuff window insulation as the foam and that did not work. The problem with that kind of foam is that it shrinks as it dries so you get a wrinkly and deformed surface.</p>
<p>Check out Smooth On for foam products. </p><p>http://www.smooth-on.com/Rigid-and-Flexible/c10/index.html</p><p>Ive not had good luck with Great Stuff foam products for builds. </p>
<p>rachel can i get your direct number? i have a furniture(antique reproduction) project, know very little about cad and all the keying for mold can you help?</p>
Nice job! What CAD software are you using in this instructable? Thanks
I use a program called Moment of Inspiration (http://moi3d.com) for most of my projects.
At first I thought, what's the point, how useful could this be? But then I remembered how hard it is to find really good molded insoles for my feet. Then I thought, I could even make insoles and sandles that perfectly fit anyone's feet! This is most impressive. <br>Thanks, and Merry Christmas!!
What mold release compound did you use? I am also trying to make expanding foam parts on a 3d printed mold.
I ended up using Turtle Wax, yeah the car stuff. It worked fine, not great but not bad. The silicone spray I tried was noticeably worse, which surprised me. I'd be interested if you find something better, as the wax needed to be spread in just the right thickness in order to keep the foam from sticking, but also not impede its expansion. I'm almost done with a foam casting Instructable which I should be able to publish in the next few days, with more information. If you come up with a better release agent I'd love to hear about it!
APW wax is what you need, http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__APW_Soft_Release_Wax_426.html here's an example. Don't know where you from but you should look for it ;) Looks great but small question; Why didn't you 3D print the part en Cast the mould? would have been cheaper no?
And what kind of expanding foam did you use? was it the two-part A B foam, or was it great stuff/ spray foam?
Awesome tutorial, thanks for sharing. <br> <br>I have posted a link to this on the Shapeways blog <br> <br>http://www.shapeways.com/blog/archives/1707-Instructable-How-to-Make-a-3D-Printed-Mold.html <br> <br>Cheers
Resolution is quite a bit finer than my RepRap. I want one of those.
excited to see the final product!
Nice molds!

About This Instructable




Bio: I run Neal's CNC in Hayward, CA, an expert CNC cutting and fabrication service. Check out what we do at http://www.nealscnc.com ... More »
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