Week 12

For this week we have molding and casting, and I have to say that is one of my favorite things to do. As a designer this subject is familiar to me, when I was studying design I loved it.

Even though is not the first time I do molding and casting, it is the first time I'll try some of the materials that we have available for practicing.

Objectives

  • Design a mold in a CAD program.

  • Machine the mold in a milling machine.

  • Cast parts from the resulting mold.


  • Weekly Progress >

    First, we had our weekly lecture with Neil Gershenfeld, you can watch it here.





    Beno Juarez gave this week’s lecture, he talked about the Amazon Floating Fab Lab.

    This is a great project, if you want to follow it or become part of it, check out here.

    The Floating Fab Lab in the Amazon is a project started by the Latin American Fab Lab Network (Fab Lat) that aims to bring digital fabrication to the Amazon region in South America. This is an effort on articulating people and efforts to make a sustainable and accesible lab through the Amazon river.




    Assingment >

    As I said before, I love like Molding and Casting, but to be honest I had no idea of what to do, so following Ferdi and Santi's (our tutors) advice I decided to go for something small, later I found out why the advise us. The wax milling times are too slow, so when you do yours, do it small, it will save you time that you can use to experiment with different casting materials.

    So I designed my model in Rhino. My idea was to make a small tile that can be used to cover small surfaces, like furniture for example.

    Then after having my model I used it to make the negative mold. Pretty straight forward. Just keep in mind two things, be careful with the deepness, the angle of the walls and distance between geometries, remember, the milling machine and the milling bit have a maximum reach point, they have a fixed size, so for example if you try to go deeper than the actual reach of the machine it will stop and you won't be able to continue, or if the distance you left between the external wall an the actual model is to small the bit will mill where you don't want to, be careful.

    Key factors to remember:

  • For the roughing we use the 1/8 drill bit (3.175mm / 0.125"). Be careful with the distance between the bottom of the drill bit and your machine's drill bit holder.

  • For the finishing we use the 1/32 drill bit (0.7938mm / 0.03125"). You can't mill straight walls higher than 3 mm.





  • You can download the model here.




    Milling Process

    I followed the following process. An observation: If the surface of your wax block is un-even you can first make a flattening pass.

    First set up:

  • Select the machine: File > Select machine (SRM-20)

  • Set the dimensions of the piece.

  • Set origin: top left, front corner of the piece

  • Add tools (milling bits)

  • Roughing:

  • Generate G-code (new process) for roughing 1/8 (3.175mm) tool:Select the tool > Select the material > We used this values: XY speed: 24 / Z speed: 15 / Spindle: 6500-7000 / Cutting-in amount: 1.5 > Ok > Create tool path

  • Finishing:

  • Generate G-code (new process) for finishing 1/32 (0.79mm) tool:Select the tool > Select the tool path: Contour lines Up Cut > Select the material > We used this values: XY speed: 15 / Z speed: 10 / Spindle: 6500-7000 / Cutting-in amount: 0.2 > Path Interval: 0.2 > Ok > Create tool path

  • Set coordinates and send to mill.




  • Casting Process

    For casting the mold I chose a white silicon rubber, which is perfect for the type of object I want to cast. You can also use a food grade silicon if you want to make a chocolate mold for example.

    The process of making it is really easy, but you have to be accurate: First put gloves > Set your weighing scale to 0 > Pour the silicon and the catalyzer into a mixing cup (follow the mix parameters) > Mix for 3 min approx. > Pour the mix into your mold (with a brush apply a the first layer) > Put the mold into the vacuum to get rid of the bubbles > Let your mold cure.

    This are the parameters that the producer (FormX) gives:

    Formsil 25 Pro Silicon Rubber

  • Mixing Ratio: Formsil: 100/ Catalyzer: 3

  • Working time:30 min

  • Setting time: 4 hrs

  • Strength: 25A

  • You can apply it with a brush or by pouring.





  • For casting I used a material called Marble Cast. Is a great material, I love it, and is perfect for my pieces, it gives you a ceramic texture. This material is an alpha-crystalline gypsum and is used in the production of statues , decorative objects and works of architecture and interior design.

    When you se that the mixture is homogeneous (more or less 2 min of mixing), you can start pouring into the mold, my suggestion is to first give a small layer to all the surface so you cover any hard spot, and then, pour all the material.

    My pieces where touchable in more or less 20 min. For full cured pieces wait an hour or more. Mind that my pieces where really small, so times depend on your model.

    This are the parameters that the producer (FormX) gives:

    MarbleCast standard

  • Mixing Ratio: MarbleCast 100/ Water 25 to MarbleCast 100/ Water 30

  • Soaking time: 30 sec

  • Mechanical mixing time: 1 min

  • Work start: 10 min

  • Work end: 13 min

  • Setting time: 30 min


  • And this is the final model! Im extremely happy with the result. If you make some my only advise is to be aware of the bubble, make a good mix and if you want us the vacuum just to be sure you get rid of possible bubbles, usually there's no need for this.

    Next steps are to apply different types of finishings, try coloring the marble cast, and also trying to make a bigger model.