Fab Academy 2015
How to make almost anything

Luis Peña Mendoza

    Assignment 9 - week 9 - Mar 25

    Design a 3D mold, machine it, and cast parts from it

    Molding and Casting

    This week assignment is to design a 3D mold, machine it, and cast parts from it.


    A. Designing the mold:

    For the process of molding and casting I was decided to make a plate 400 x 112 mm in the front have forms in high relief, for which it was designed in AutoCAD as some commercial samples. The high relief that would have a thickness of 4 mm. I generated a DXF file extension to worked with the ShopBot CNC, as follows:
    1. The material served us as a basis for generating the negative rubber was High Density Polyethylene (HDPE) 16 mm thick
    2. A rectangular recess of dimensions 400 x 112 mm to 3 mm in depth, there was another recess according to the form with a depth of 7 mm was made.
    3 Was generated with these steps the mold for emptying the rubber molding.




    Downloading link for my archives:
    Archives

    B. Molding

    Before starting the molding process, we ensure that we have all the supplies and tools. We must also endeavor to review the MSDS of chemical components before opening. Moreover, we use personal protective equipment such as gloves, goggles and optional mask.

    Materials Molding:
    -molding pack, which contains: URETHANE and RUBBER MOLD COMPOUND
    -plastic cups to sample each component, and then mix
    -release agent, To apply the positive mold
    -wooden pallets
    -cloth rags

    Molding Equipment:
    -Scale: To have the same weight of both components.

    PPE for Molding:
    -MSDS of chemicals
    -gloves
    -safety glasses
    -masks

    Molding Test
    After obtaining the base HDPE proceeded to flush out the components for generating the rubber mold. We used the materials respecting the mixing ratio and the process according to the technical specifications. A separator as a release which is smeared, until fully spread it on the base was used. We proceeded to pour the mixture proceeding quickly to prevent product it heals.

    Once emptied the product of the base stand at rest for over 10 hours before demolding process gum. Gum was demolded easily, and the mold with the desired shape as negative of the final shape is obtained. Even the rubber mold replica small errors in the process of working with CNC or texture resulting from the resolution of the CNC or type of drill bit used. Real Molding Step 1: Identify molded package which contains the URETHANE COMPOUND MOLD and RUBBER COMPOUND. We also checked the percentage of mixture, in this case, MIX RATIO is 1A: 1B BY VOLUME OR WEIGTH. Step 2: The following process must be fast, because otherwise the components may lose their possessions and harden, but considering security measures. Proceed to open the URETHANE (dark brown liquid) and the vessel emptied 74g (about half the vessel) is in balance. Then close the container and repeat the process with the other RUBBER component (transparent color, and more biscoso than the first), in another vessel. The amount of weight should be very close to the first component or exactly equal. Step 3: Mesclamos the content of the two components into one, and with the aid of a wooden pallet. The mix until there is none of the first two components, then will turn light brown, and continue mixing a little more. Before pouring the mixture, apply release agent to the positive to make it easy to remove the mold when it solidifies. Step 4: Apply the mixture on the positive, spreading to cover the positive integrally. If missing more mixed for mold positive, repeat the steps above mixture of components. We help spread the mixture with a wooden paddle, and once this full, leave a few paddles on the surface so that the solidifying help us remove the mold. Step 5: We let it dry environment until it solidifies. It can be left to dry in the sun to accelerate the process.



    C. Casting

    A wooden frame so that it fits exactly the rubber mold ie the inner frame dimension is 400 x 112 mm was used first. Was placed in the bottom part within the rubber mold. Separator spread across the surface of the rubber mold and the inner edges of the wooden frame and proceeded to perform the mixing of the components of Smooth-Cast 305 liquid plastic is estimated that by the size of the piece would be used throughout product content so all the contents of the flask A with the entire contents of the bottle B. mescló rapidly and the corresponding recess was performed mixed. In this process details not take as:
    1. The level of the table where the emptying process was implemented was not optimal which caused it to make emptying gap which will cause the thickness of the final product is not even noticed.
    2. Due to its porosity wood absorbed the release agent which caused the plastic adheres slightly to the wooden frame
    3. The tolerances between the extent of the wooden frame and the dimensions of the mold caused a certain amount of plastic liquid seep into certain spaces between the mold and wood frame.
    After 8 hours of rest proceeded to demolding the plastic. Finding the difficulties arising from the detailed comments, the plate with the desired high relief was obtained.



    As second experience I decided to do a dump of the same plate but with white cement. I proceeded to make a frame with L profile 1 "so that we achieve a size that fits inside the rubber mold. Based on past experience I decided to discount the original measures 1mm rubber mold, so that the inside measurement of the metal frame is 398mm x 110mm. The rubber mold inside the metal frame was placed and proceeded to spread the release agent. It was noted that the rubber mold accurate fit under and there was room for leaks. Liquid mass was prepared with white cement and water and dispensed into the mold on standing.




    Enjoy!