Assignments Goals

• Design and make a 3D mould (~ft2 /300mm²), and produce a fibre composite part in it

Week's Lectures

3D Mold Design

For this week assignment I decided to create an almost full size Iron Man Helmet. So I started searching for a 3D model of the mask and ended up on this site, that has a lot of free 3d models.

After a bit of browsing I downloaded a model that seemed good enough for my purpose, with little overhangs and without high definition details. This is the model I choose. Then I imported the design in Rhino and started to modify it to obtain only the front face of the helmet.

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The zip package has a lot of formats (Iges, Step, Dxf, Dwg) but the only usable one is the Iges. Unfortunately the model has a lot of errors, open surfaces and missing edges, so I spent a lot of time correcting the most of them. Then I trimmed the model to obtain only the front, using an intersecting plane, and the function TRIM, to cut the model in 2 parts.

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The other problem that arose, is that the maximum Z depth of the Roland MDX-40A, and the length of the mills we have in the fablab are too small to machine the whole helmet in one shot, so I had to split the model in 2 parts: the upper face and the lower base.

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Now I was ready to machine my two parts using the Roland Modela MDX-40A and Vectric Aspire CAM.

Work files links

3D Mold Machining

To create the 3D mold, I used once again the software Vectric Aspire (for more info about it, check Week 12 Assignment). I started making the top part of the helmet, using a high-density foam block.

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As I learned in previous assignment, I choose the right mills to do the roughing job and the finishing job, using the speed and depth parameters shown in the pictures below. Because the foam is a really soft material, I used the same parameters for both jobs, and the result was very satisfactory.

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After a couple of hours I had my first part ready, and after another 3 hours the base part was ready too.

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Finally I glued togheter the parts to obtain the full helmet. Very nice!

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Work files links

Using composites

Once the mold was firmly glued together, it was ready to be covered with resin and flax bandages. So to approximate the material usage quantity, I created a number of pre-cut bandages and tried to put them on the mold, without resin, just to verify the process. When I was happy with the result, I sprayed the mold with a detaching spray solution, wax based.

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Then I started to spread a layer of epoxy resin [60% catalyzer solution] and lay a bandage, trying to soak it evenly across the surface. Then the second layer and so on. The result was quite difficult to obtain, mainly because the flax loses a lot of strands, that end up making a mess in the already layed resin. Moreover, the resin is really sticky and dense, so I often ended resorting to using my fingers or a small squegee instead of the brush.

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Anyway, after a bit hassling, the result was quite good, but I had the sensation that there was too much resin compared to the bandages used.

To overcome this sensation (I was worried that too much resin would give poor results) and to make a more detailed mask, I wanted to try to use the vacuum technique to squeeze out the excess resin, but the Fab Academy kit for vacuum bags never arrived, so it was time to come up with a bright idea!

After talking with Stefano and Marco, We thought that we could easily use a trash plastic bag, some mastic strips, the air compressor and a Venturi's vacuum valve. The process was quite funny to perform, because the first step was to cover the piece with a layer of "DomoPak" (I don't know what's the equivalent in english, but essentially it's a really thin plastic transparent film) and to puncture a bunch of small holes in it with a pin. Then cover it with a layer of absorbent material, and finally cover again with another layer of DomoPak. In this way, the sandwich will retain the excess resin, when vacuum is applied.

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Finally I used my trash vacuum bag that worked flawlessly!

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After a couple of days, the resin was completely cured, and the result was quite good, but the DomoPak left a lot of signs on the surface, so that it seems the mask is still in a film enclosure. Moreover despite I used a lot of detaching wax spray, I had a lot of trouble dividing the mask from the mold, and I ended destroying the foam mold.

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Assignments Outcomes

• Recognise the benefits and limitations of 3 axis machining
• Demonstrate workflows used in mould design and construction
• Select and apply suitable materials and processes to create a composite part

Have you:

shown how you made your mould and created the composite
described problems and how you fixed them
included your design files and hero shot photos of the mould and the final part