Molding and Casting:
What is molding and Casting and how it works.
What is molding and Casting and how it works.
Some references about the "Rubber Foot" I want to create for my project.
Thing to keep on mind at the moment of creating the first mold.
Here is the process to create the wax block and to mill it.
Specifications for my 3D printed version.
Here you will find the process of mixing the silicone and pouring it.
This is how my object looks after unmolding it. and some reflections on the process.
Molding and Casting is the process of creating a mold from a 3D model or a physical object, and then casting it with certain material to make copies of it, or to reply the model. I found this definition from the guys of Smooth-On that defines it pretty well:
Molding or Moldmaking is the act of creating the cavity / form that carries a negative or reverse impression of an original model. Molds can be made of a rigid material, such as plaster or plastic resin or more commonly, a flexible material such as rubber. The material to use should be chosen considering the material of the model, the material to be used to make castings, and whether there are any undercuts.
Casting is the act of pouring liquid material into the cavity of a mold. After a period of time, this liquid will cure via chemical reaction or cooling. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay.
First you will need to cast a wax block that has at least the dimensions of the 3D mold you´ve just created or bigger. I did this by melting wax in a pot, and then pouring it in a 5mm acrylic mold they already had in the FabLab and let it cool down until the next day and un-mold it.
You could then create the files for the SRM in fabmodules, mods or in the SRM native software. I created mine in fabmodules and is the process I documented.
NOTE: In my first try to mill the file I created, I tested it in the air (with the Z set 20mm in the air) to check where it was going to cut and it was cutting outside of the mold. I checked everything again and realized that the problem was that the ORIGIN of my STL file was not in a corner, but it was in the middle instead, so I had to adjust the file by setting the origin to a corner and do the fabmodules process again.
In Fab modules you first select the input file to read, and select your STL mesh file.
NOTE: If you don´t see your mesh loading in the screen, it could be because of the view the file was created with. So you might need to adjust the view angle in fabmodules, but to know if you have the right view, since the top and bottom view look the same in the mesh, you will need to calculate it. If you only see a flat image, you might be looking at the mold from under.
You select Roland Mill in as the Output Format. For the process, we are going to do first a Rough Cut in which the machine does a first pass removing material from the outside to the inside, layer by layer with a 50% overlaps.
ROUGH CUT FILE:
Patas_de_caucho_origen_ROUGH_CUT.rml
We will need to create another file for a Finish Cut, that is a two pass more detailed horizontal and vertical removal, with a 90% overlaps.
FINISH CUT FILE:
Patas_de_caucho_origen_FINISH_CUT.rml
The drill we use for this is a 1/8 inch drill (3.175mm), and you could also change the drill between this to do the rough cut with a flat one and the finish cut with a round one if you want more detail.
In my case, since my object didn't needed that much detail, I did it all with a flat one.
INPUT SETTINGS:
- Set units to 25.4 (relation between mm and inch).
- Change the view angle if needed.
- Scale the mesh to 1.
- Set the resolution to 400dpi if your mold does not need much detail.
OUTPUT SETTINGS:
- Select SRM-20 as the machine.
- Set speed to 20.
- Set the Z axis move to home to high above the border of your mold, instead you have done a leveling of the mold first.
NOTE: Molds are higher in the outer walls than in the middle, you could do a leveling by sending a flat file to mill to correct this, or mill in the middle, checking carefully that no wall is going to hit the drill while it moves.
PROCESS SETTINGS:
- Set tool diameter to 3.17mm (1/8 inch).
- Change tool overlap depending of the quality wanted. This setting changes from 50% in rough cut to 90% in finish cut.
For the Silicon Mold I used the Easyl 940-FDA -Silicona Alimentaria which comes in two different pots that you have to mix in equal parts of 1-1. You should always check for the datasheet to see the specifications of the mix, because it could be in a proportion of volume or weight. In the datasheet you can also see the whole process of preparation and the indications you should have in mind.
To measure the amount of silicon needed, a good tip was to fill the mold with water, and pour it into a measuring container to check the volume. That will be the volume needed of silicon (half of the volume of each one of the mixes).
Then you should clean and dry the mold very well, and add some Release Agent in spray. You should do this outside since it is a hard chemical, from a distance of 20 centimeters from the mold, and try not to inhale the spray.
Poor the two parts of the silicon and mix it very well. In the datasheet is specifies the time you have to work with the silicon, which in my case was 30 minutes, and the time it will take to dry and get hard. You could also put it into an oven, but in my case I let it dry for 5 hours and it un-molded pretty well.
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