Patricia Samudio :: Fab Academy 2023 ::

Molding and Casting

In this week, we explore the field of molds and castings to obtain different parts. In the laboratory we have materials and tools necessary to produce the molds and later, supplies to perform the laundry.

As for the preparation of the molds, we first determine the size and thickness required for the objects to be molded and then we make some boxes to pour the preparation of kerosene (250 g) and the high density plastic pellet (180 g), mixed in a container that is exposed to heat to first melt the kerosene and then incorporate the plastic until it melts, and the mixture is as homogeneous as possible, and to a point of consistency such that it can be easily poured into a wooden structure of the dimensions of the desired object. In my case, the mold obtained had dimensions of 100 x 100 x 36 mm. I also tested with polyphoam, obtaining these results:

📍 Note: in the initial preparation we worked with the basic color of the plastic. In a second preparation, pieces of red and yellow wax crayon were added to the mixture, which made it possible to tint the base mixture and obtain an orange-colored block during mixing and a pale yellow color when curing was completed.

Task

Link to the group assignment page.

Reviewed the safety data sheets for each of your molding and casting materials, then made and compared test casts with each of them.

Documented how you designed your 3D mold and created your rough and finish toolpaths for machining, including machine settings.

Shown how you made your mold and cast the parts.

Described problems and how you fixed them.

Included your design files and ‘hero shot’ of the mold and the final object.

Challenges

Grupal:

Review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them.

Individual

Design a mold around the stock and tooling that you'll be using, mill it (rough cut + three-axis finish cut), and use it to cast parts.

As long as the mold was ready for machining, we experimented the process of casting in silicone to obtain molds: one of a heart 💛, of a duckling 🦆 (molds made by FabLab interns) and some ears (mold made by Dr. Royg, of the FabAcademy 2022 generation). Using the two-component silicone (A-B), mixed in the 1:1 ratio, we pour the mixture into the three molds. The curing process lasted approximately 6-9 hours.

The next day, already with the silicone molds, we proceeded to use the epoxy resin also of two components. Mixed in 1:1 ratios, for about 15 minutes. Then, it is dumped into the silicone molds. The curing process lasted approximately 24 hours.

Molding

Capitalizing on the topic of week 12: molding and casting, this week my goal is to explore in the production of an important component for the MoliNito 😎: the grinder. First, we analyze together with Abdon the possibilities to produce the conical model of the grinder: a priori answer NO 😞 due to the fact that the machines we have cannot produce the conical part ☹️. Although I will continue to explore this week the alternatives in terms of design and materials, which in principle I would like to realize it with ceramic. For the moment, I focused on the design of the flat grinder.

First, I review some tutorials on YouTube to understand the process of modeling and preparation of the file for the manufacture of the mold.

STL to 3D Printed Injection Mold

Then, more tutorials on coffee grinder models ☕️:

Coffee Mill Fusion360 Study

Now, following part of this tutorial, I make the model:

Machining

To prepare the file, I use the Fusion 360 functionality for mold manufacturing, with the following parameters. I recommend this series of videos that explain the process that will be applied to the model, until the NC or RML file is obtained.

Fusion360 Help - AP Mastercam Manufacturing Setups

Then, the .nc file is generated in my case, since the .rml file type produced an error at the time of generation.

The mistake was in setting the Z from the starting face of the machining, which caused the milling to be done across the entire width of the part, and not just on the surface. This was solved by machining the wax block.