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12. Molding and Casting

This week’s individual assignment is to 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.

Individual Assignment

Mold Design

I thought about what type of part would be useful for my final project. I landed on silicone feet for the frame of the machine with a M5 bolt molded in to the conical foot I will design.

Based on the testing we did for the group project and the materials that we have in our lab, I settle on making four feet with the Smooth On Silicone material OOMOO 30.

I chose this material because of its potential vibration dampening effects for the machine.

It’s a two part mold with a should in the bottom piece to hold the M5 bolt above the bottom plane of the foot to isolate it from the table the machine will sit on.

Here is my design for the molds.

To give myself an idea of what the machined molds would look like, I went ahead and printed them on the Bambu X1C in the lab using PLA. I used the “ironing” feature for “Top surfaces” in the Avanced Process menu of Bambu Studio to improve the surface finish on mold. Here is a picture of the finished print.

Here is a link to the tutorial I used to create the toolpaths in Fusion 360 using the model above.

I realized that I needed to add the Bantam Tool Library to my computer and used the instructions at this link.

Mold redesign

Given this year’s option of using the Formlabs 3B Resin printer for the mold instead of using a wax mold, I decided to try that instead. I redesigned the mold to be printed on the resin printer to minimize the amount of resin required to produce the mold. Indexing tabs were also added to assist in lining up the two parts of the mold.

After this was completed, the part was loaded into the Formalabs Pre-Form software for slicing. It came back with “Cup Detected” error (see link for description). The “Cup” will prevent the resin printer frmo being able to properly make the part, so I needed to add a vent hold on the half of the mold with the orange highlight

  1. PreFormCupError

I added a vent hole to the design and resliced the part in PreForm and the “Cup” error was resolved.

  1. AddedVent
  2. PreFormMoldingandCasting

Part Design

I actually designed this backwards and made the mold from the design in my head, so I went back and used the Combine Tool in Fusion 360 to make the part as it will come out of the mold.

To accomplish this, I aligned the two halves of the mold together to have an “as molded” view of the molds. From there, I made another box that fit just inside the mold to allow me to use the “Combine” feature to “cut” the overlapping parts of the mold and “material” leaving the molded part below. The missing piece is that I will be adding an M5Bolt to the mold as it cures to allow for assembly on the machine frame.

Here is a link to the Kevin Kennedy Tutorial on Mold Making that allowed me to figure out the Combine and Cut process I used to make the model below from the mold models.

CombineTool

Material Selection

It turns out we’re out of the OOMOO 30, so I went through the options available and settled on Sorta Clear 37 for the feet instead. Sorta Clear 37 is a silicone rubber material that will dampen vibration from the machine as well. An added advantage is that it and will blend in with aluminum extrusion well due to its clear/translucent color.

As part of this assignment, I printed the mold on both the Bambu X1C printer with PLA filament and the Formlabs Form 3B with Durable resin.

Molding Process

  1. Taped the two parts of the mold together with blue painters tape making sure the pouring hold and vent hole were facing the correct direction (up).

    1. MoldingProcess-1
    2. MoldingProcess-2
    3. I followed the mixing and pouring instructions for Sorta Clear 37
    4. Poured equal parts A & B (2 oz each) in a clear container
    5. Carefully mixed the parts for three minutes making sure to fold the material from the walls on bottom of the cup into the mixture. I did not use the vacuum degasser to remove all the bubbles that were trapped in the mixture.
    6. Slowly poured the mixture in to the mold while holding it an angle to allow the as much air as possible to escape from the two part mold through both the pouring hole and the vent hole.
    7. Shook and tapped the mold a bit to see if I could get some trapped air to escape so the Sorta Clear could better cling to the walls of the mold.
    8. These molded pieces are going to be attached to the aluminum extrusion frame for my final project with an M5 bolt and t-slot nut, so I added an M5 bolt to the mold while it was curing using popsicle sticks and tape to keep it in place. See photos below.
    9. This process was used for both the PLA and Resin molds.
    10. PLA MoldMoldingProcess3
    11. Resin MoldMoldingProcess4

    12. Once the parts had cured overnight, I took them out of the mold and trimmed the M5 bolts with a reciprocating saw.

    13. PLA Mold Removal MoldingProcess5

    14. Resin Mold Removal MoldProcess6
    15. The material isn’t stiff enough to easily trim the excess length off the bolt, so it was put back in the PLA Mold and put in the vice to hold steady while cur with the reciprocating saw. MoldingProcess7
    16. Bolt Trimming MoldingProcess7-2
    17. Finished Trimming MoldProcess8

Finished Pieces and Analysis

  1. The excess material was trimmed and here are the results from the two molds
    1. PLA Mold FinishedPiece-1
    2. Resin Mold FinishedPiec-2
    3. Bottom of PLA mold (Left) and Resin (Right). Note the faint filament line on the left with the PLA mold. It’s very minor and only seen at certain angles. There is not a distinguishable difference when feeling the two samples Finished Piece
    4. Given the material is “Sorta Clear 37” it meant that all the trapped bubbles are visible that normally would be unseen with opaque material. That could be prevented by using a vacuum degasser before pouring in the future. However the parts are functional and will dampen/absorb vibration when installed on the bottom of the machine, so it’s a win.
    5. Note in the picture below that it’s virtually impossible to distinguish which mold produced which piece. FinishedPieces4

Files

Link to my files for the week.

Group Assignment

Link to our group assignment.