Using a silicone mold with the injection machine
I want to make a mold with silicone because it’s much cheaper than metal, but I’m worried about the compression. I talked with a silicone expert, and he has a silicone which can withstand high temperatures. I tested it by extruding plastic onto a piece, and it held up. This guy says he can make a mold of the object I want to create which is a roughly 12 cm diameter ball. He can make the mold for about 50 USD. Has anyone tried using silicone molds? If so, how did you ensure a proper seal and connection to the injection nozzle, and how did you reinforce the silicone so it wouldn’t warp or move when pressure was applied from the plastic filling the mold? Any ideas are welcome, thanks
If you are going to use an injection machine, there is a lot of pressure. Even if you encase the mold in something rigid, I’m not sure you can hold shape or detail.
Also, a 12 cm sphere is about 900 cc. That is a lot for an injection machine.
Hi s2019, thanks for your thoughts. If injecting doesn’t work for this, we might try just putting the mold in an oven and adding shredded flakes until it’s full. I’m worried about air bubbles with that method but it’s worth a shot. If you have any ideas for how to make this sphere, would be interested to hear. Cheers
If it is a smooth sphere, for a low cost mold you could try one of these, Carefully cut it in half and encase each half in something strong like mesh reinforced concrete and a steel box.
I’m not sure how you avoid bubbles or voids. I think the compression approach would do several flat melt/press/fold cycles and then compress in the mold. Probably depends on how efficient the process needs to be and how many you want to make.
As an update, we were successful using silicone molds with our injection machine. We had previously cut molds to make flat objects like coasters using a laser cutter, and we just used the flat top and bottom pieces from those molds with the silicone inside to do this. To make a climbing hold, we first molded it in a box so the result was a cube shaped silicone mold with a big empty cavity. The mold we used was sold in two containers, one with the majority of silicone inside and one smaller one that gets mixed in before molding. It cost about 8 USD for the 0.5 kilogram of silicone in Vietnam. Then we put that finished mold between our lasercut pieces (the top one has a hole and welded nut to interface with the injection machine and the bottom one is just a flat piece. We were able to hold the 3 objects together by using the holes which we already cut for bolts in our lasercut piecese. During injection, we were careful to not overinject because there wasn’t so much pressure holding the 3 objects together. The result was acceptable, and we think that silicone molds inside lasercut pieces can be an alternative to expensive CNC cut aluminum molds while still having great detail.
The pink one is the original climbing hold and the two others were made inside the silicone mold from HDPE plastic flakes in the injection machine as in the above stated method
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