9.Molding and Casting¶
## Group assignment:
- Review the safety data sheets for each of your molding and casting materials.
- Make and compare test casts with each of them.
- Extra credit: try other molding and casting processes.
link to group assignment
## Individual assignment:
- 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.
- Extra credit: use more then two mold parts.
What is molding and casting?¶
Molding is a technique through which a material, often plastic, but also metal, rubber, or powder mixtures is shaped on the outline of a die or mold. There are many different techniques for molding materials, just as there are many different applications for each process.
Casting is a manufacturing process in which a liquid material is usually poured into amold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process.
For this week’s assignment we were given 180mm by 80mm wax for making the positive mold of our design. So to start the designing I had first measured the wax so as to make a design which will fit in the given wax. I opened fusion 360 and drew a rectangle and gave the dimension of 141mm by 59mm so as to have the mold inside with 4 sided wall cover through which I will be able to make the negative mold using silicon rubber.
The 180mm by 80 mm wax
Next up I extruded the rectangular shape by 20mm since the wax was 40mm in thickness.
Next I created another sketch to insert the name text in our nathional language that is Dzongkha. Go to create sketch>> text to add the text on top of the rectangular shape.
Now the text has been inserted, I extruded the text up top by 5mm.
Now to make smooth curves around the edges I used the fillet function to make them smooth.
The designing is now complete, so I export the .stl files from fusion 360 and will be milling it with the help of SRM-20 milling machine. For that I firstly uploaded the .stl file in the Modela player software to create the toolpath for the mold. Once it’s opened, select ‘top cut’ and the material as ‘modeling wax’ as we are using wax for the mold as shown below;
After choosing the material and the ‘top cut’ function, you have to open the modeling form to define the thickness of the side borders. I set them to 5mm on each side as 5mm will be enough for my mould.
Now you start a new process and do some settings which best fulfills your requirements. Some of the settings I did are as follows.
While milling you have to mill twice that is, roughing process(initial process) and the finishing process where the milling will smoothen your mold. So I firstly choose the roughing process.
No choose ‘partial’ and set the start height to 5mm and end height to -25mm.
Press next and choose the type of tool path as ‘contour lines’ for roughing.
Press next and set the cutting parameters as shown below;
Next up you name your roughing process and then click on finish and in a few seconds your toolpath will be created.
The toolpath for the roughing process looks something like this;
Next you have to start a new process for generating finishing tool path. The process of making it is as same as the roughing process, the only difference is selection of the cutting tool and selection of the tool path as ‘scan lines’.
Now that the toolpath generation process has been done, you have to do the cutting position setup as per your requirement. As for me I did the following setup.
Once the toolpaths have been generated, you have to upload the file in the Vpanel for SRM20 for cutting. First you have to upload the roughing file and once its done then proceed with the finishing file. After the rooughing and the finishing prorcess my mold came out nice and smooth as shown in the following image;
To make the negative mold I used platinum silicon rubber which has part A and part B which needs to be mixed together in equal proportions. For mixing I used two small plastic cups and poured part A in one plastic cup and the poured part B in another plastic cup in the same proportions and poured in a big plastic cup for mixing. You can see the procedures to be followed given below and me mixing the part A and part B materials.
Once the part A and part B are poured in the plastic cup I used a small stick and mixed it for several minutes till I was satisfied with the mixing. After that I started pouring the mixture on the postive mold wax. While cutting the wax through the SRM20 machine, one of the side walls was cut so thin that I accidentallly broke some parts of it, it was caused by my settings where I kept 5mm width for the side walls but somehow it came out thin attached another block wax to the broken walls side for making the negative mold.
After pouring the mixture, in order to eliminate any air bubbles I had to tap on the mixture for several minutes.
So after keeping the silicon rubber mixture to cure for about 24 hours, my negative mold came out nice and smooth as shown below.
For casting I used hydrostone, and to prepare the stone first I took 33 grams of hydrostone and 20.5 gram of water and mixed the hydrostone with the water and poured it on the negative mold.
Now after keeping the cast for 48 hours I took out the cast and it came out nice and smooth as shown below;
Its my name in our nathional language that is ‘Dzongkha’.