Week 13. Molding and Casting¶
Group Assignment
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This week, we learned how to make molds and cast different materials like metal, plaster, plastic, and silicone. We used both milling and 3D printing to create the molds.
We also learned about safety rules, especially for casting metal and using silicone. It is important to wear protection and use dry materials, because wet plaster or mold can cause accidents.
Our first metal casting failed because the plaster was not dry and not heat resistant. But after a few tries, we got better results. We also tested casting with different plastic materials and used tools to remove air bubbles.
I learned how different materials react during casting and how important it is to prepare well. Now I understand that mold quality, drying time, and safety all affect the final result.
Individual Assignment¶
This week for Molding and Casting, I used my brother’s machines and decided to make an injection molding project.
Short about Injection Molding.¶
Injection molding is a manufacturing process where melted material is forced into a mold cavity. Once inside the mold, the material cools down and hardens into the desired shape. After hardening, the mold opens and the finished part is removed. This method is commonly used to make plastic products of various shapes and sizes.
Design Part¶
Because there wasn’t much time, I downloaded a model from GrabCAD.com and started designing the mold.
I placed the model inside a box. Then, in the Combine menu, I chose the Cut option and used Subtract to cut the model shape from the box.
Then I made holes for bolts to fix the mold, and I also added guide shafts so that after casting, the mold would be as symmetrical as possible.
At the end, I added holes for the sprue so that the plastic can be injected from this place inside the mold.
As you can see, I made 4 holes to fix the two parts, 2 holes for guide shafts, and 1 hole for injecting the plastic.
Machining Part¶
For Machining I used several milling tools:
- For Roughing 8mm , 6mm, 4mm End Mills.
- For Finishing 6mm, 2.5mm Ball Nose Mills.
- For Making Holes 4mm Drill Bit.
Here is the Parameters that I used for our machine.
Toolpaths¶
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The first operation was face milling to get the correct overall dimensions of the material.
Result:
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The next operation was roughing. Here I used two different diameter end mills — 6 mm and 4 mm — because after roughing with the 6 mm mill, there were areas where the tool couldn’t reach because of its large diameter.
Result:
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After roughing, I did the finishing. Here I used two different operations with two different mills. One operation is called Parallel, and the other is Contour. Both are 3D operations and here are differences:
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Parallel Operation: This operation moves the tool in parallel lines across the surface. It is good for finishing smooth, flat, or gently curved areas. The tool moves side to side, layer by layer, to make the surface smooth.
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Contour Operation (sometimes called 3D Contour): This operation follows the shape (contours) of the 3D model. It moves the tool up and down along the surface. It is good for vertical or angled walls and gives a more accurate shape in those areas.
Result:
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After finishing the inside of the mold, I did a center drilling operation. Then, I made the holes using a drilling machine.
Result:
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The last operation was cutting the mold out along the contour. Here I used an 8 mm end mill with a 0.5 mm stepdown.
Result:
After cutting the contours, I drilled all the holes, put in the guide shafts, and used a vise to hold them tight. Then I started boring the hole for the sprue, where the plastic will be injected.
The result was perfect.
Injection Molding¶
About Our Machine¶
We used a homemade injection molding machine, and here is how it looks.
Basically, it is a piston with a sleeve. Inside the sleeve, there are plastic pellets. The sleeve is heated using a band heater. At the bottom, there is a hydraulic rod that pushes the mold toward the nozzle.
The machine has 5 heaters that heat 3 different parts of the sleeve. Each part has a temperature sensor that sends signals to turn the heater on or off. This 3-zone heating system gives better plastic quality and produces very few defective parts, even when injecting 1000 or more of the same item.
Injecting !!¶
Here is the video of the injection process.
After injecting, we let the mold cool down and then opened it. Here is the final result.
Conclusion¶
This week’s project helped me learn the full process of injection molding — from designing and milling the mold to injecting heated plastic with a homemade machine. I understood that good machining, correct temperature, and good mold alignment are very important for high-quality results. This project showed me that industrial processes can be done at a small level with the right tools and skills.