13. Moulding and Casting

Goals

Group assignment:

-[x] review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them -[x] compare mold making processes

Individual assignment:

-[x] design a mold around the process you’ll be using, -[x] produce it with a smooth surface finish that -[x] does not show the production process toolpath, and use it to cast parts -[x] extra credit: use more then two mold parts

Tools Used

Pureref - An amazing program for gathering images into a big moodboard
Concepts - My goto sketching app on the ipad
Fusion 360 - 3D CAD/CAM software from autodesk
Bambu Lab P1S - The printer I use in my farm, I don’t do much multi colour printing but I have one with and AMS that I used for this project.
Orca Slicer - My main slicer for Bambu Lab 3D printers, Open source and has the ability to store “k-values” along with your material
Modela MDX-50 Tool changing precision milling machine

TLDR; Nice images

Group Project

For the group project we are looking at that safety data sheets and testing each ouf our casting and moulding materials

For my part I will be looking at:

Casting: Jesmonite AC100
Moulding: Duroflex 30 PU casting rubber from MBFibreglass

link to group page

Summary

Jesmonite was a fantastic material to work with and i will be bringing it forward to the next project.

Individual Project

1. Case for Adafruit MacroPad

For this weeks project I made a Jesmonite case for my Adafruit MacroPad

It started of as a simple idea but as it went on i had to be a bit more ambitious to include features like the side holes.

1.0 Sketching

I try to start all my ideas even with a very simple sketch. I feel like this grounds the design and helps get past the initial feeling of not knowing how to tackle a problem in CAD

I was lucky in that Adafruit provide a full CAD model for most of there products. i was able to use this to take critical measurements

1.1 CAD

The design is a simple block raising the pad to a sightly more comfortable height and adding a 5% angle.

I also tried to include add design features that would aid in getting the part out of the mould like the large angled facets on the top half of the part.

As i advanced the CAD model i realized how much of a pain the side holes were going to be. Each one was going to have to be its own separate insert.

To help this as much as possible i tried to keep the bottom of the hole flat and aligned with the natural seam between the faceted top and the flat sides.

I then sliced the file and 3D printed it, not to use as part of the model but just to verify my design and the fastener locations.

1.2 3D printed Prototype

Supports removed and happy with my choices.

To create the two mould halves i extruded a box around the part as a new body

I can then split this in half ant my desiered seam line and use split body and combine to create each half of the mould

I then take another box and subtract each half of the mould from it, creating a mould for the mould.

The stock was set up with the size of wax block we had available.

1.3 CAM

I added some spheres to the rim of the design to help with the registration. They were combined with union on one side difference and difference on the other side.

The milling setup I used was the following:

6mm flat endmill - 3D adaptive - 0.15 mm feed per tooth
3mm flat endmill - 3d adaptive - 0.05 mm feed per tooth
3mm flat endmill - Drill screw locations - 0.05 mm feed per tooth
3mm flat endmill - 3D contour vertical walls - 0.05 mm feed per tooth
3mm flat endmill - 3d Flat on top surfaces - 0.05 mm feed per tooth
3mm ball endmill - Morphed Spiral - 0.05 mm feed per tooth
3mm ball endmill - Blend - 0.05 mm feed per tooth

1.4 Milling

For setting up the MDX 50 there is a jig for making sure that your tools have the correct stickout.

I used my 3D printed prototype mould to insure that the stickout was correct.

1.5 Making the mould to make the mould

The first step was stock preparation. I ran a 6mm flat endmill to do a facing toolpath on the surface of the wax. I then flipped the tool and ran it again to ensure that my double sided tape and good contact with the bed and that the two surfaces were parallel.

I setup for the main operation with double sided tape.

The begining for the roughing with the 6mm flat endmill.

Roughing complete

The finished surface after using a morphed spiral to do a finish pass at 0.3 step over and then using the blend toolpath to go back and touch up the corner radius.

I attempted a bit of hand finishing as i had made a mistake and gouged the surface in a few places.

This was due to mixing up the flat endmill with the the ball endmill.

1.6 Making the actual mould

I used water to estimate the amount of rubber needed

For the mould I used 30 durometer polyurethane.

It is a slow cure, 24 hour to de-mould, but this tends to make a for a very tough mould, and i do plan to eventually use this for concrete so that should help.

once mixed as per the instructions, 1:1 ratio by weight, i degassed the mixture in a vacuum chamber.

I poured from the lowest point on the mould and let it fill to try and reduce air pockets.

I also used a stick to poke the small m3 screw holes to ensure they were filled.

1.7 Making parts with the mould.

Fast forward about 36 hours it was time to de-mould the mould.

Finished parts.

This details shows the inserts that are used for the side holes.

Laser cut a few quick plates to hold the half.

The polyurethane should release ok but i still used some mould release for safety.

Jesomnite uses a 2.5 Powder to 1 Liquid ratio by weight.

Started the pour but needed this is where i realised that i should have made a larger pour hole.

This became a bit of a mess …

In the end this was just a lot of slow of pouring and tapping on the mould to fill the part.

Jesomnite take about 45min to get to the point where you can de-mould.

Just opening the mould as carfully as possible trying to wiggle out the part.

The floors are looking great!

The first attempt is under filled.

So tried again with a lager volume of Jesmonite.

After this i did some wet sanding to smooth the surface of the part

Parts drying in the sun.

All the parts laid out.

1.8 Results

The housing is assembled with the adafruit macro-pad and all the holes for mounting lined up.

Including the side holes for the power port.

And the side hole for the reset button.

In Summary

I feel like by and large this week was a success but there was definitely a few notes for if I was doing this again.

Things I would do differently next time

Never buy cheap elastic bands, most frustrating experience ever
Make pouring spouts and vent holes larger than you think you need.
After having some issues the the cnc im not sure that it was worth it over 3D printing the master mould.

See below link to to files created this week:

Week 13 Files