MOLDING & CASTINGSAVERIO SILLI

MAKING A MOLD WITH MACHINABLE WAXMY FIRST ATTEMPT AT

AND ALL THE ERRORS I MADE

fabacademy.org/archives/2015/eu/students/silli.saverio/exercise09.html

DESIGNING A MOLDYour 3D model resembles what your final product will be, but in order to make it machinable as a mold, and for the mold to be working, you need to modify it.

DESIGNING A MOLDBy splitting the model or rotating parts you can achieve a shape that has no undercuts or that is symmetrical (meaning you can make only one rubber mold and cast twice).

DESIGNING A MOLDIn the same block of wax you can carve more than one mold. In this case we’ll have a one-valve mold on the left and a two valve mold on the right (notice registration keys are symmetrical).

CARVING THE MOLD IN WAXThe wax block is secured to your CNC milling machine (in this case, a Shopbot) with wooden sticks and double-sided tape underneath.

CARVING THE MOLD IN WAXRough-cut path (6mm end-mill) and cutting results. As you can see on the right, the mill was too large to pass between the part and the mold walls, resulting in a lot of material not being removed in the rough-cut step…

CARVING THE MOLD IN WAX - TROUBLESHaving all that wax not being removed during roughing-cut resulted in the 3mm ball-nose mill used for finishing, to crack just at the beginning of the finishing-cut. TIP: Design your mold having in mind what size your mills are going to be.

CARVING THE MOLD IN WAX - RESULTSThe final result shows a misalignment due to the incident with the milling bit. Also the registration keys didn’t came out good. A lot of manual work was needed to adjust this mold. An attempt at using a flame to smooth the surface resulted in melting one wall tath was too thin (on the left).

MAKING THE MOLD WITH SILICONE RUBBERThe two valves side of the mold was made with a “brush on” technique, in which you only apply a layer of rubber of a couple of mm on the mold. When the rubber hardens you pour some stiff material like gypsum to make an armor that holds the soft rubber. The other side of the mold is just poured silicon rubber (notice the walls had to be risen with tape).

CASTING WITH URETHANE RESINThe two valves were framed in two wooden boxes to make the mold easier to close (it was used for rotational casting). The one valve part came out pretty good. Despite all the problems I had on the mold all the copies came out good.