_Week12_MOLDING AND CASTING

_Introduction

Molding and casting week was a good assignment to see how something (again) from a 3Dmodel become physical, we go through a variety of tools that we already know like 3d modeling, milling and now work with new materials for doing even the mold and the cast of the form that we want.

_Background

Casting is a manufacturing process in which a molten material is introduced into a solid mold and allowed to solidify. The solid material takes the shape of the mold. Molding as a process might also use a mold to shape the soft material, but doesn't necessarily require one.

Vendors

  • FormX
  • Smooth-On

    • _Week Assignments

  • Design a 3D mold, machine it, and use it to cast parts.

    • _Workflow /Step by Step

    _Design 3D mold

    For designing the 3D mold I worked with the 3Dmodel that I've done in Computer aided-design that is an approach of my final project so it was a good idea to start to work on it. This piece is kind of complex for doing it in milling because of the sinuous forms but anyway I tried; the idea of the mold is to build the wall of the piece because this one is gonna be empty (for having inside the electronics) trying first with 0.03mm of thickness.

    Thus, I made an offset of the piece having and empty space between the two forms that this will be the wall of the pieces.

    So after build the two molds, I verified that the two molds fit well for casting one part of the pieces.

    At the end, I will need 4 molds for casting the two parts of the one piece.

    _3D Milling

    So in order of having the 3Dmold, we recycle wax from already milled blocks and works from previous years, this wax has a melting point of 100 ° so with due protection by releasing toxic gases in the process, we melt and create the wax blocks from some molds of wood.The wax have to me moving all the time while is getting melted to disappear all the large pieces and to have a homogeneous mixture.

    Afterwards, put them in an oven that is maintained at 100 ° and is lowering the temperature to solidify the wax.

    Once having the wax block, I continued the milling process using the Monofab SRM20 but this time creating the .prn file, which is based in two processes the roughing and the finishing, in the software of the machine as follows:

  • Load the model in .stl into the software.
  • Select the machine, in this case the Monofab SRM20
  • Set the size and orientation of the model
  • Configurate the general settings of each process at it follows in the image (first the roughing and then the finishing).
  • Later, as in the others assignment I continued with the normal way of milling using the 3.175mm drill bit for both process.
  • NOTE: As seen in the last image I have an error measure the block and the dimension that I put in the software that's why I've lost two walls of the mold.

    • _Molding process.

    For create the mold from silicon, I made a box of wood (because i lost two walls) and put inside the wax mold for later empty the silicon inside. The silicon that i used was the FormSil 25 and follow these next steps for create the silicon mold from the wax mold:

  • Have ready your workspace with all the things that I will need like gloves, glases, scales, sticks, the vacuum pump, etc.
  • Combine the two components of the silicon in proportion 5% of the B for all the A, mixed until you have a very good mix and then put it in the mold (you only have less than 5 minutes to get hard the silicon).
  • Put the mix inside the mold high getting a thin line of silicon dropping inside. Then I shake it up because it was too big for the vacuum pump.
  • After 48hrs I could have the 4 molds ready to cast!

    • _Casting process.

    For casting the parts I wanted to use the clear resins (for later put inside a board with a LED towards my final project) so I worked with Smooth-On 326 that is a fast-cast plastic resin that also comes in two components but the proportion is 50-50 in this case.

    To create the cast I filled the molds with a syringe until it was full inside through two holes made into the silicon mold, in the first try (because I was guessing the amount of material inside) it was not enough material to cast all the part.

    One hole to fill the mold with resin and the other one to get out the air inside.

    Therefore, I remove the first cast and clean the mold for cast again but this time i filled with water and close the "sandwich" mold for measure the amount of material that I need. Then I prepared the mix and fill again the mold. This time I got better results and the two pieces were ready!.

    _Final review.

    Things to correct after this exercise:

  • Be more careful about the proportion in the resin cast.
  • Use sprues next time designed from the start in the 3D mold.
  • Make more holes for filling resin into the mold and for pushing out the air (this time I only made 2 one for filling and one for getting the air out) this would help for having less bubbles.

    • _FILES

    All the files for this assignment are available to download here