Molding & Casting

Task

I have this week worked with molding and casting and completed the following:

• Created a parametric 3D design considering stock and tool
• Created toolpath in Fusion 360
• Machine the mold on the ShopBot
• Casted a negative and then the final model

Computer Assisted Machining in Fusion 360

I created a 'Tool Library' (available at the bottom of the page) with the tools - that we most likely were going to use to create our molds. Setting up a tool library based on actual tools available enables Fusion 360 to give warnings for errornous settings and run really useful simulations - which both can assist in avoiding possible cut-depth errors.

I followed the following steps to produce the Tool Library:

• Select Tool library.
• Right click on local folder to create a new local library.
• Browse samples to find generic tools similar to your actual tools.
• Copy and past generic tools to your newly created library.
• Modify parameters to reflect the actual tool.
• Setup speed and feedrates - and check the chip load.

Creating CAM Toolpath in Fusion 360

1: Select '3D' > 'Pocket Clearing'

2. Select 'New Setup'

3. Select 'Tool'

4. 6mm Flat End Mill for roughing

5. Restricting tool to stay inside boundary

6. Checking various heights
look for possible collisions

7. Setting roughing step down
(equal to or less than tool diameter)

8. Setting ramp to (just) plunge

9. Observing the calculated toolpath

• Yellow = transit
• Red ramping
• Blue machining

10. Finding best smoothing technique:

• Radial
• Contour
• Spiral (my final choice)

11. Setting up 'Drilling'

12. Select 'Post Process' to export

13. Set 'Post processor' to 'ShopBot OpenSBP'

14. Save the .sbp-file (ShopBot-toolpath)

Using Shopbot to Machine the Mold

1. Adding a smooth surface

2. Fixing with double sided adhesive

3. Extra fixture using pieces of wood

4. Zeroing Z-axis to the top of the material

5. Roughing complete

6. Mold after first roughing
Seems like chips melted together because of incorrect settings - because we were borrowing the Shopbot at our neighbour FabLab for a limited time and other where waiting in line to finish their job - I decided to accept the slightly imperfect result.

7. Mold after second roughing
This time completed with:

• 8000 RPM instead of 14000RPM
• 50% reduction of feedrate

8. Mold after finishing

Casting with Silicone Rubber

1. Preparing, testing and greasing

• Reading SDS - read how to
• Covering table with plastic
• Lining up materials & equipment
• Wearing safety gear
• Ensuring ventilation

2. Opening both OOMOO components

3. Stirring the A & B component

4. Mixing A & B component

5. Pouring silicone into the mold

6. Adding tabs for easier removal

7. Removing the 'negative' silicone mold

8. Error:
Silicone didn't make it to the bottom

9. Error:
Large air bubble in the center

Hacking, Molding & Casting

I decided to drill a hole in order to let the air out of the mold.

The hack worked and I had now created a negative mold.

I then casted a plastic prototype of my design. - the result is a foot for my fin.

I am now waiting for the delivery of a softer urethane plastic which is more suitable material for a foot for my final design.

I have created a revision of the original design (and added it to the list of design files below), which includes the manual hack.

I molded the feet with Smooth-Cast® 305 with a pot life on 7 min and a cure time of 30 min. Mixing, pouring into the mold and releasing the casted feet were uneventful.

Integration with Final Project

4 casted feet are included in my final project.

Design Files

• Fusion 360 Tool Library (2kb)
• Tool Library w. wax settings (2kb)
• Mold (.stl 137kb)
• Revised Mold (.stl 137kb)
• Roughing Toolpath (.sbp 37kb)
• Finishing Toolpath (.sbp 53kb)
• Drilling Toolpath (.sbp 356b)

Noticable Work from other FabAcademists

• Sigridur Helga Hauksdottir portfolio
• Ari Vuokila portfolio - Using SRM-20