Now that I decided to make an aluminum mold I needed to take what I learned from the silicone molds and make it better. Method I was using to make a silicone mold was quite easy. 3D print a master part and cast silicone around it. I 3d printed my part already cut at my parting line of the mold. This made it easy to cast the first half of the mold. Then 3d printed the full part (including inserts, sprues, gates, etc) put it in the first half of the mold and cast the second half.
This worked better than I expected and parts were a lot stronger than I expected as well. But it was not perfect. A few things I didn't like
- Silicone will pick up every detail. So if the 3d print's dimensions are off, so will your molded parts. You will even get the surface finish of the 3d printer. Not good or bad. Just something to be aware of.
- The silicone mold is not very tough and can wear out fairly easily if you are rough with it. So be gentle.
- You can not inject the resin under pressure. The silicone is flexible and will deform and stretch. It will probably get back to the right shape after time if you left it alone, but the resin can squeeze between the mold halves and then your parts are deformed.
- I had trouble keeping the mold halves together. Rubber bands worked okay. But were a pain to put on and take off. They also
I thought about machining aluminum masters. This would improve my tolerances, and if I made a nice set up I could make many silicone molds quickly. But I wanted to have the heater built into the mold for increased production.
I started designing my aluminum mold. I did quite a bit of research into mold design and there is a ton of information out there. I am by no means an expert. I also have limited machining abilities. I taught myself to use a manual mill and lathe. Over the past 5 years I have been pushing myself to machine better parts. I taught myself how to use a cnc mill and I am lucky that I have access to a Tormach PCNC mill. It is a entry level cnc mill, but for this project was good enough. I really tried to design the mold to make machining it as easy as possible.
I made sure that all the critical features could be done at the same time without removing the block of aluminum from the vice. I also designed the mold around the tools I had access to. Some parts of the mold are quite deep and in order to get into the tight corners I needed a small end mill bit. I decided to limit myself to 1/16" end mill bits. So I had to design the mold around that. I also added in a relief in one section of the mold. I put in dowel pins to help align the mold halves and thumb screws to clamp the molds together.