Molding and casting is a process that is widely used in different industries with various materials. It is especially used in production lines that have components that would not differ from one another and therefore mass produced. In our case, we will use Silicone to mold and cast it with Resin. This would help understanding the process and its potential use in upcoming projects. So again we had two assignments this week, a group and individual assignment and they are as follows:
Individual Assignment
Design a 3D mold around the stock and tooling that you'll be using,
machine it, and use it to cast parts
Group Assignment
Review the safety data sheets for each of your molding and casting materials,
then make and compare test casts with each of them
Testing Various Molding Material
In order to perform this week's assignment, we tried two differnt Molding Material and we compared the technical specification and the results. The following material were available in the lab and were used during this week's assignment:
Alumilite - Amazing Mold Rubber
Alumilite - High Strength 2
Concerning safety usage, both material had the same safety descriptions:
Always use safety products when working with silicone and resin. Always wear gloves, apron, coveralls, boots, chemical goggles. Mixed High Strength rubber will absorb into porous materials and may stain! Avoid clothing, carpet, upholstery, and any other porous materials which will stain and will not come out. Mold making and casting is best done in a designated area such as a basement, garage, or hobby room with adequate air movement or ventilation. Cover any surfaces including floors with plastic sheeting, or plywood to prevent damage from spilled resin. To clean up unmixed or still liquid material, use rubbing alcohol on a rag or paper towel to quickly clean and remove. In some instances, such as spills on non-porous surfaces, it's easier to clean up silicone after it's allowed to cure. Then simply peel away and discard.
The following are the safety warning for both material:
Keep out of reach of children
Avoid eye and skin contact
In case of skin contact, wash with soap and water
Use with ventilation. In case of ill effects, remove to fresh air
Keep container closed
Do not take internally
Do not use for food
A detailed discription of the technical data sheet for both materials is described below. You can download the data sheet for the material from the following links:
The following is a summary Amazing Mold Rubber datasheet:
Color: Pink
Mix Ratio: 10:1 by WEIGHT
Open Time: 20-30 mins
Demold Time: 2-4 hours
Mixed Viscosity (cps.): 15,000
Specific Gravity: 1.15
Shore A Hardness: 25
Linear Shrink (%): 0.3
Tensile Strength (psi): 550
Elongation: 500%
Temperature Range (F): -67 to 395
Vacuum Required: No
High Strength 2 datasheet summary:
Color: Pink
Mix Ratio: 10:1 by WEIGHT
Open Time: 45 mins
Demold Time: 12-18 hours
Mixed Viscosity (cps.): 18,000
Specific Gravity: 1.15
Shore A Hardness: 25
Linear Shrink (%): 0.3
Tensile Strength (psi): 550
Elongation: 500%
Temperature Range (F): -67 to 395
Vacuum Required: No
The latter has a longer cure time but they both share the same rigidity as high tear strength rubber material.
Casting Materials
The following material was used during this week's assignment:
Resin Material: Alumilite Casting Resin - White
Alumilite Coloring Dyes (multiple colors)
The technical specs of the Alumilite White Casting Resin are as follows:
Color: White
Mix Ratio: 1:1 by Volume
Pot Life: 2.5 to 3 minutes (100g mass at 75 Degrees F)
Demold time: 5 to 15 minutes (100g mass at 75 Degrees F)
Mixed Viscosity (cps.): 90
Specific Gravity: 1.05
Shore Hardness (ASTM D-2240): 72 D
Shrinkage (in./in.): 0.006
Tensile Strength (ASTM D-638) (psi): 4500
Elongation: 10%
Temperature Resistance: 185 Degrees F.
You can download the datasheet for the material from the following link: Amazing Casting Resin
Testing Casting Material
We had only one type of resin material that we used in this week's assignment. However, we had a variety of coloring dyes. So what we did is test pouring resin using various colors. Some parts were poured all in one color. Other parts were poured in phases, thus having a combination of different colors in the same end product.
For this assignment, we had to design, machine, mold and cast a certain object. In my case, I couldnt think of something that might be used for my final project, so I went with a simple logo with my initials just to test it out. In order to achieve this I will have to go through the following steps:
Design
The software I used for my design was Fusion360
I first started a sketch and drew my 2D design, My design is circular so I started with the outter perimeter and worked on the inner details. Also before the design, take into consideration the dimensions and limitations of your machinable wax. The one we could get our hands on limited the diameter of my design to 5cm, taking into consideration the wall that is 1cm thick and having some distance between the wall and the extruded design.
For the final design I added two counter pivot points that could both serve as a guiding point/precision and an element of stability/rigidity for the casting process. It is a circle extruded and an opposing circle with the same diameter but extruded cut this time where the circle would go in.
Once the 2D design is done, we now have to generate the Gcode to transfer onto the CNC. In order to do so, go to CAM on the upper left corner of Fusion360 and set the settings for the CNC. As in setting the starting point and the Z axis orientation.
For the roughing we first have to choose 3D adaptive clearing and adjust the settings. First Thing is selecting the geometry as in the area where the roughing will take place.
Select the Spindle RPM
The Spindle speed (RPM) is calculated in the following formula:
N = VC / (d x pi)
N = Spindle speed
Vc = Cutting speed in mm / min
D = Tool diameter in mm
Pi = 3.14
Then again with the settings, under passes, select the proper stepdown, in this case it was 0.3 mm .
Once the initial CAM setup is configured, it is time to add the tools that would be used and set their settings. I used a Flatend mill for the Roughcut and a Ball end mill for the smoothing. The set-up and settings are as shown below.
Select the spindle RPM Speed
Once the setup is done for the tools, as in two different passes, the roughing then the smoothing it is time to run a simulation of the CNC to check for any errors and make sure it is what you want because that will eventually become the Gcode.
Roughing post process (select proper CNC)
Smoothing post process
Now that everything is set, you can proceed by generating the Gcode, tool titled postprocessing on Fusion360
Machining
The CNC we used to machine the wax was the Roland MDX-40, first I set aside the tool bits that would be used for this project
Then I ran the roughing process first
The Result of the Roughing
Then swithched the tool bits and started the Smoothing process which is the second Gcode generated
Mold setup
To set the mold, first make sure your freshly carved machinable wax slab has been properly cleaned and smooth ou any obvious imperfections to have a better mold.
The first step is to get out your Silicone and its catalyst. Read the instructions and follow accordingly. For this process make sure you are wearing protective gloves, and fairly good space to work in.
Now that we have the instructions for ratio of silicone and catalyst, I preferred to measure the volume of each open in my machinable wax first, by putting the slab on the scale, TARE and add water to ine of the areas, it turned out to be 50g so I needed 100g of silicone to work with. I mixed in a bit more than that just to be on the safe side. So the ration is 10 parts silicone and 1 part catalyst. I added 105g of silicone and 15 grams catalyst. Then stir the mixture slowly to prevent any bubbles in the mold.
Once the mixture is fairly mixed, pour it carfully into the openings in the machinable wax slab. You will notice a few bubbles showing up from the mixing or pouring process, a good way to get rid of them with limitied tools is to set them on the case of a grinder to produce vibrations and help the air bubbles surface and escape. Then let it rest for the instructed time which was 2 to 4 hours in this case. (We left it for more than 2 days since we had national holidays and the lab was closed.)
And finally coming to see the results
Casting
Now that we have the silicone ready, it is time to mix the resin and pour it into the mold.
Resin comes is a combination of 2 parts, A and B. They have to be mixed equally and then poured into the mold. First wear safety gloves and wear a gas mask as this is a strong chemical reaction and toxic fumes are best avoided.For my first cast I poured it while having the mold open just to test it out.
Once properly mixed, pour into the mold carefully
Let it set for about 15 mins and get it out check the results, the image below my first cast.
After testing a couple of casts with the open mold, it was time to close it and test the full cast. So I cut a small opening at the top of the mold on both sides, and a smaller opening close to it to act as an release valve, so it helps the air stuck inside a way out. The result however was not what I expected, an area inside my designed had trapped air and didnt allow the resin the flow in. I tried making two other openings inside the mold but same result. The rules of physics always win. I could have tried other ways but I would ruin the mold. So I will take that into consideration for my next molds and designs.
Final Results
These are my final results
Even though that one was poured the open mold, they are the best cast, I still have to glue them together.
