Molding and Casting
In this assignment we are to create a mold using the CNC, which will be used to cast a design out of resin.
1. Designing the mold.
First I design the end product that is to be casted out of resin.
I then sketch and extrude out a box that completely covers the design.
I then used combine cut to cut out the design from the block. The imprint will appear on the underside.
I then extruded a larger box with an offset of 5mm.
Then I combine cut the smaller box out. The end product is a container with the design in its base.
2. Generating g-code.
To generate the file needed we will use the MANUFACTURE feature of FUSION 360.
Under Setup tab, select New setup, click ok.
Here I will be using Adaptive Clearing. It will first do a rough mill to remove majority of the material, following by a finishing mill to smoothen the mould.
Under Sample tools - Metric, select the 3mm Flat endmill and click select.
Once finishig setup, you can move on to post process to export the NC file.
To create the mould, I first use bluefoam to cut out the design. As my design dimensions are 70x70x25mm, I used a 25mm thick foam and cut out a 70x70mm square.
I mark the centre of the block to set the tool's zero position. Similar to cutting PCB make sure the foam does not move in place and clear the cutting space from items. Then turn on the drill and start.
The end result is quite smooth, but the surface can be made smoother if a toolbit of smaller when doing the finishing cut, for this the rough cut and finish cut uses the same toolbit.
2. Mold and casting.
Once fresh from the CNC cutter, clean the interior. You can use water, but make sure the foam is dry before creating the mold.
When preparing to create the mold, I covered the workplace with paper towels. I will require a plastic cup (styrofoam cup can react with the chemicals), measuring scale, vacuum chamber, stirring sticks. I'll be using Smooth On's Mold Cast 30 to create the rubber mold.
The pot life of Mold star is 45 minutes, giving me alot of time to ensure the chemicals are mixed thoroughly. Its curing time is 6 hours at room temperature, hence I left it to set overnight.
The mixing ratio of A:B is 1:1, I using the weighing scale I measured and mixed 20g of A and 20g of B.
Next I placed the mixture into the vacuum chamber to remove the trapped air. You can see the mixture bubbling and foaming up.
Once the mixture settles and no bubbles are rising out, I turn off the vacuum pump and slowly let the air in.
I then slowly poured it into the styrofoam mould and left it at a corner to set.
The next day I ripped the mold out of the styrofoam.
Next is casting with Resin. Its pot life is around 10 minutes with curing time 2 hours. The mix ratio of resin to harderner is 3:1, so I mixed 40g resin and 13g harderner, placed it in the vacuum chamber, poured into the mould and left it to cure.
For some reason bubbles started appearing on the top, but the shape was there.
Several attempts the resin casting failed due to reaction occuring while it was setting, causing the resin to bubble and rise up, but on the third attempt, I left the resin in the vaccuum chamber longer and the cast came out nice.
Download: Mold.f3d, nc program