3D printing case vs block molds for ceramics

Left are case molds, they are made by 3D printing the positive profile on a backplate (with holes for natches). These are secured into slotted rails. Right is a block mold, it is made by 3D printing the profile of a working mold with integrated rails. This one is printed vertically in four pieces. It is held together and straight with printed brackets. We pour rubber into these to make case molds. Each method has advantages and issues.
-Case: Faster to print. Easier to draw. Joins cast as easily removed bumps on the working molds. This is only suitable for prototyping, making one working mold.
-Block: Much more attention is needed in printing, there are more issues with orientation of print, infill, printed support, multi-piecing, fit and seam-filling. 3D drawing of these is more difficult. And block molds are bigger because they are molds of molds. They also need to be more precise to merit the cost of the rubber.

Related Pictures

Poor plaster release from 3D printed mug handle case molds

My objective was to continue skipping the making of a rubber case mold and 3D print them directly. Since 3D printed surfaces naturally part well from plaster and the artifacts, although visible, do not show on the final fired pieces, I even wanted to do this whole process without any sanding or oiling. However, despite printing a dozen or more variations, carefully controlling plaster/water ratios and waiting/mixing the recommended time periods, few good plaster molds were extracted without corner-breaking. Even painting the inner surface, oiling over it and beveling corners did resolve this issues. It seems that a combination of the printing artifacts, sharp corners, the handle perpendicular (because of the oval cross-section) and the inside negative shape all enabled the plaster to get a very firm grip on the PLA print. Although I could have resorted to a heat gun to soften the PLA material enough to pull it away I relented and decided to switch to making a block mold (for rubber) rather than a case mold (for plaster).

Assorted problems with 3D printing PLA molds

I am 3D printing a block mold - rubber will be poured into it to make a case mold for beer.bottles. It is an amazing process but there are still issues to deal with:
-Stringing (top left). This usually happens when the nozzle is running too hot. This new batch of filament needs a slightly lower temperature, so I adjusted from 215 to 207.
-Size constraints: This is too big to print as one mold so it has to be done in multiple sections (two mains, two end-caps). Pieces fit precisely and can be glued or taped.
-Experience shows where glue, tape or special brackets (e.g. corners lower left) are needed.
-Special tools must be made (lower left is a clip-insertion tool).
-Corner lifting: Happens mid-print (the large thin pads on the lower right are to prevent that).
-Pressure bowing: The stabilizer bars spanning the two mid-pieces (lower left) and the triangular lip (upper right) keep that edge straight despite pressure from the liquid rubber inside.

Pouring the v4 plaster beer bottle mold

This project is a testament to my wife's patience with me using her kitchen as a mold making shop. Most of the tools I need are there. A nice stable table to run two 3D printers, lots of room and plugins, electrical appliances, utensils and supplies of every type, good lighting. And pleasant company!

I have already poured PMC-746 rubber into 3D printed block molds and have printed and put in place stabilizers to hold the rubber in place. Embeds are in place on both the bottle base and bottom mold (upper right). The flexibility of this rubber is amazing, it makes possible extraction of the plaster base, although with difficulty. It also preserves the embossed logo on the foot. This is version 4 (version 5 will have a shallow base piece and modified sliding natches).

The $5 garage sale mixer does not pull bubbles to the surface so I just pull them up by counter-stirring with a serving spoon. A common sense workflow (never pouring any down the sink, cleaning everything in a settling bucket) makes this no problem in the kitchen.

Links

Glossary	Infill and Support Infill and support are structural elements that 3D slicer software uses (e.g. to fill the interior of solid parts or support contours over empty space)
Glossary	3D-Printing Standard 3D printing technology (not printing with clay itself) is very useful to potters and ceramic industry in making objects that assist and enable production.

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