Molding

For this week I made three pieces, a well plate that failed and I use it for documenting the process of making the wax mold. A jewel, since my wellplate failed I had to come up with something quickly to get the week completed. Finally probes, as the nice final touch for my final project, and to cover their making I am using them to explain the final stage of casting plastic into the silicone mold.

This week's assignment was to design a piece to be molded and cast. Since I was inspired by our group project. I chose to design a well plate, of 92 wells that should take about 0.5ml of liquid. Purpose of it, is that I can then program the handler to pick from a source different colors of fluids and program it to mix out a rainbow, into well plates. Problem was that the silicone was too thick, and didnt reach every nook and cranny of the mold.

I figure it would take a syringe or some silicone spreader meant for construction work to ram it down the wells, so for the purpose of this assignment I had to come up with something simpler. A Jewel like thing, that would look like a massive ruby if done with transparent red.

I just randomly chose a geometric design from the net, an 8 sided thing called Rhombicuboctahedron, that I then designed as a 8 sided block in Inventor and then just made cuts to it to get the sides I wanted. This gave me a half piece I would then by using the 123D Design add 2 of them to design the model I would then mill from wax as the mold for silicone.

I got the wax mold for the jewel done, altough it was removed from the roland mill before I had a chance to run its finishing run, but the model is adequate for the purpose of making a silicon mold.

In the end making the silicone mold is not that difficult, measure the materials in the right amounts, at 100A:90B ratio, and then mix them well to ensure proper curing. You will want to use a vacuum chamer to suck out the airbubbles that got made during the mixing. Then just pour the stuff into the wax mold you made and let it sit in a well ventilated space for a day.

Since I did the silicone mold on my own, it was impossible to document the process properly. Might want to look into developing a documentation drone... Now I am ready to make the plastic casting, thinking of using dark red plastic for it, to amplify the jewel look of it.

In the end I chose to use dark green, to make it look like an emerald, but I used way too much color. The "stone " ended up looking almost black.

In thermoplastic molding, like injection molds it is necessary to use draft angles to make the parts easier to detach. Usually a draft angle of 1-2 degrees is enough, and the point is to make the mold open up instead of it closing in. This is necessary because when you are working with molten plastic, when it cools down it contracts a bit, and with the draft angles you can take its shrinkage into consideration.

Using darft angles wasnt necessary with this week's work, because neither the silicone or the liquid plastic we used had thermoplastic issues of contracting, and as such didnt need any help extracting them.

In a group of my own

During this week I used three different products for my casting and molding projects.

• OOMOO 25 Silicone

This is the silicone we used to make the mold for the plastic, it is relatively safe stuff to use, better to use it in a well ventilated room. Needed a vacuum to force all the bubbles out. In general there is nothing really dangerous in the material, one should use protective or expendable clothing, the silicone could settle in between the fibers and will never wash out.

• Smooth-Cast 310, plastic

The nastiest stuff of the three. Well ventilated area is critical, and one needs to wear protective gear, like gloves, protective glasses and protective clothing. While you dont want it on your skin, breathing the fumes in is the more dangerous part and it is not a bad idea to have a respitory protection handy. From your skin you can just rinse it off with plenty of water, just monitor the area for possible irritation, because that means a doctor needs to take a look.

If you get any on your clothes, they need to be throughly washed before using again.

• So-Strong colours

The different colours I used for my casting, very potent and the smallest jars of them will last for a long time. Will probably never be used in such excessive amounts that warrant any special precautions, other materials used in the process dont already demand. Gloves and such are useful, while the stuff isnt toxic, your skin would probably be colored for a good while if some gets on your skin. Rinsing with water and soap is recommended.