WEEK12 Molding and casting
WEEK12 Molding and casting
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 compare printing vs milling molds
Individual Assignment
design a mold around the process you’ll be using, produce it with a smooth surface finish, and use it to cast parts extra credit: use more then two mold parts
For this assignment, I have decided to take on the challenge of making a chess piece. The general process is as follows:
1.Design parts using 3D CAD.
2.Mill wax using a milling machine to create a mold.
3.Pour liquid Silicone Rubber to create negative parts.
4.Pour Urethane resin into the negative parts.
Design parts using 3D CAD
The chess piece I chose was the Knight, but that's where the mistake began.
Create a 3D model based on the above image
Create MOLD data based on the 3D data I created above
Export the .stl file to generate g-code
Download: Stl file
Generate 2 g-code files for the rough cut and the final cut @ mods CE.
Rough Cut
Select "mill 2.5D stl" from the pulldown menu. The tool diameter is 3.175mm and the offset number is 0. Then press the caluculate button.
Final Cut
Select "mill 3D stl" from the pulldown menu. The tool diameter is 1.587mm. The mesh units is 1mm.
Then press the caluculate button.
Process
Start milling the WAX using the two generated G-codes.
WAX
Using the glue gun to fix the wax.
I was about to start the initial setup of the milling machine, but encountered an issue where the connection with the PC could not be enabled. I tried rebooting the PC, upgrading the G-code sender, and installing other applications, but the connection still failed. Therefore, I decided to borrow the instructor's laptop to proceed with the work. (Thank you, Tamiya-san.) Once the zero positions for X, Y, and Z are set, I will press the start button to begin milling.
After finishing the milling, I tried connecting with my own PC again and this time, the connection was successfully established. The cause remains unknown.
Milling
Making the negative mold
I use MOLD STAR 31T for the production of the negative mold.
Safety precautions
・Work in a well-ventilated area to avoid inhaling toxic fumes.
・Wear protective gear like gloves, goggles, and a work apron, as silicone rubber can cause skin and eye irritation.
・Properly dispose of used silicone rubber separately from regular trash, following recommended disposal methods.
・Read and follow the instructions and safety guidelines.
Cover the table with a vinyl sheet and prepare trash bags for safety.
Start
Mold Star™ 31T is a two-part product, requiring you to mix Part A and Part B in a 1:1 ratio by volume or weight. It's vital to mix the components accurately. Mix thoroughly using a stir stick until you achieve a uniform color.
Slowly pour the mixed silicone into the mold to facilitate air bubble escape.
Once the silicone has fully cured, carefully remove it from the mold.
Casting
Smooth-Cast320 is used for casting.
Safety precautions
Wear safety glasses, long sleeves and rubber gloves to minimize contamination risk. Use only in a well-ventilated area.
1st attempt
Align the surfaces of the negative mold, sandwich them between boards, and secure them in a vice to prevent slipping.
Smooth-Cast™ 320 is a two-part resin. Before use, thoroughly stir Part A and Part B separately. The correct mixing ratio is 100% of Part A to 90% of Part B by weight. After mixing the components together, pour the mixture into the mold promptly and wait for it to cure.
The manual states that "Smooth-Cast™ 320 begins to harden about 10 minutes after mixing and takes approximately 30 minutes to fully cure." However, in reality, it starts to harden in about one minute, which does not leave enough time to adequately pour the mixture into the mold. I widened the path for the cast with a cutter, but the condition shown in the following image was the limit.
It is already 8:00pm. Let's go home and try again!
2nd Attempt
Because the resin started to harden before it could fill the mold using the natural drop method, I decided to try using a syringe. I used the following syringe.
Even with this method, I was unable to sufficiently fill the mold. I think the reason is that the syringe I bought was too small.
Since it looked good when partially filled, I decided to top it up by injecting resin through the air hole of the mold.
Finally, it worked well.I found that using the syringe and injecting the resin in two separate stages was successful.
Next, I will try creating a colored piece using black paint.
Mixing Part A and Part B is done as usual, but before mixing them, I dissolve the paint in Part A. The subsequent process is exactly the same.
Splitting the injection into two stages also worked well this time.
They are the the work for this assignment.
The pieces on both ends were made with a low melting point alloy. I would heat the alloy up with water at 80 degrees Celsius, draw it into a syringe, and quickly pour it into the mold while it was still melted. Since the alloy solidifies within a very short time while transferring it from the syringe to the mold, it took several tries to succeed. I learned that it's important to keep the syringe in hot water until just before injecting it into the mold to prevent the alloy from solidifying.
The metal that melts in hot water is quite unique, and I forgot to take pictures during the process.