Fab Academy 2018 - Assignment 9

Molding and Casting

This week the topic was molding & casting. I was really looking forward to getting to know techniques of casting & molding as I have never done it before and I like the idea of being able to reproduce an usual object with different materials than wood or PLA. We used two ways for creating molds:
1. Use the CNC milling machine to create a mole
2. Use the three way process to produce a mole

Again, we were asked to do a group assignment: review the safety data sheets for each of your molding and casting materials and make compare test casts. You can find the documentation on the Group project page.

Design with Fusion360

For the CNC milled mole I first created a 3D model with Fusion 360.

1. Create a basic star shape in 2D.

2. Duplicate the 2D start shape and create different stars by varying their dimensions.
3. Use the tool 'Extrude' to form 3D objects.

4. Stack the different 3D stars on top of each other. On the lowest level is the biggest star.

5. I decided five stars on top of each other are enough. The star on the top level was modified with the tool 'Rule Fillet'. This way the top of the star was made round.

6. Create a box by using the tool 'Create -> Box'.

7. Use the tool 'Modify -> Combine' to subtract the star from the box and form the mold this way.

CAM processor of Fusion360

The steps in the CAM processor to prepare the model are the same as in the CNC milling week. Except this time I did not define a 2D Contour. I defined 'Adaptive Clearing' in 3D by clicking on this

button and choosing 'Adaptive Clearing' there. Please have a look there to see the exact procedure you need to follow. The two provided pictures underneath show the model in the CAM processor and simulation mode.

Using the Cam processor to prepare the model for the milling process.

Simulation mode to check if milling is done properly.

UCCNC software Stepcraft

The steps in the UCCNC software to mill the model are the same as in the CNC milling week. Please have a look there to see the exact procedure you need to follow. The two provided pictures underneath show the star in the UCCNC software during the mill process.

Milling process in the UCCNC software.

Milling the Molds

For the milling process I took care of the same steps as in the CNC milling week. The pictures underneath give a better impression of how milling worked. I milled two molds, one with sharp edges and one with rounded edges. For the sharp edges I used a nut mill head. For the rounded mold I made use of a radius mill head that has the effect of smooth edges.

Milling the rounded edges mold.

Taking out the sharp edges mold after the milling process.

Finished rounded edges mold.

Finished sharp edges mold.

Creating the Casts

I decided to use concrete to fabricate casts with my milled molds. Depending on how the molds can be dissolved from the concrete material I plan to test silicone for the cast as well.

1. Molds before the casting process.

2. All needed material for the casting process: concrete, bucket, mold release agent, breathing mask and glasses (for safety).

3. Mixing up the concrete material with water, mixing proportion: 10:1 (concrete:water).

4. Agitating the material to assure everything is mixed properly.

5. Mold filled with the mold release agent.

6. Both molds filled with casting material.

Dissolving the Casts

After both molds have been filled with the concrete I put the molds aside and had to wait for 3 days until it was dry enough to be dissolved.

The mold release agent did not work as much as I intended it too. Therefore, I had to use a cutter to be able to dissolve the mold from the cast.

Trash =P.

Finished sharp edges star cast.

Finished rounded edges star cast.

Attached files:

Fusion 360 file Star

Three Step Mold

As a second process to fabricate a cast and mold I made use of the 'three step mold' technique. I.e. using a real object to produce a mold. This mold can later be used make the cast. This way you are able to replicate a real object and you do not need to use and design software.

Important: To create the mold I had to build a simple box that was used as the housing during the molding process. You need a housing, in which you can put the real object and then lavish the silicone on it. I simply laser cut a box out of acrylic glass. I used this box generator to get a box with the correct dimensions. Additionally, during the fabrication of the mold I used rubber bands to keep the box together tightly.

Mold with Silicon

1. Mixing up the two different silicons, mixing proportion: 1:1.

2. The horse is put into the box. With putty I filled those parts of the box that should not be filled with silicone in the first round. I decided to have a three-part-mold as otherwise I could not make the head of the horse be produced properly. I might not be able to get the horse out of the silicon anymore.

3. Fill in silicone for first part of three-part-mold.

4. Waiting for the silicon to be dry (about 90 minutes).

5. Getting out the first part of the mold.

6. Preparing for second part of three-part-mold which will be the head of the horse.

7. Waiting for the silicon to be dry (about 90 minutes).

8. Getting out the second part of the mold.

9. First and second finished part of the mold.

10. Preparing for third part of three-part-mold which will be the lower part of the horse. To be able to fill in cast material later on I needed to form 'material-fill-in tubes'. Additionally, these tubes are needed for the air to be able to get out during the filling with material. You need two tubes minimum (one for the material, one for the air to escape). I choose all four legs of my horse and put putty there, so no silicon would come there.

11. All parts of three-part-mold are dry.

12. Starting to dissolve the mold from the original, starting with the head part.

13. Dissolving upper part.

14. Dissolving lower part.

15 All parts of the three-part-mold and the original next to them.

Casting with Three Step Mold

I decided to use wax as casting material. An advantage of wax is that it is a material for really fast cast production. It only takes about 45 minutes to be dry and ready to take out of the mold. So perfect for testing if my mold works properly and forms the original again.

1. I heated the wax until it was liquid and then filled it into the mold using the formed tubes at the legs. The mold was kept together tightly using rubber bands again. In two of the legs I put candlewicks to produce a working candle.

2. One problem occurred while filling in. If the wax touched the rubber bands they would break as they could not stand the heat. For future I suggest to use the box that I used to form the silicon mold as well with the wax material as the box can keep distance between the heat of the wax and the rubber bands.

3. Broken rubber bands.

4. Waiting for 45 minutes to let the wax get dry.

5. Starting to get out the wax cast. I started with the bottom part.

6. Getting out the upper part of the cast.

7. Comparing final wax cast and original next to each other. As you can see the cast misses some parts. The head e.g. did not fill up with wax material properly. I think adding a tube at the lower side of the head (i.e. the jaw) will assure that the head is formed correctly.

8. Those parts of the cast that worked fine also show the details as the original. Here e.g. you can see the details of the horse tail.

10. Hero shot of the final cast.

Additional tip: I had the feeling that 45 minutes were a little to less to wait as some parts of the wax cast were still a little warm when I got it out of the mold, especially the body part. That is the reason why I deformed the body a little when I got it out. Next time I will give the wax cast a little more time to assure the body will not be deformed and the result of the cast will be even better.

Mold of a Mold

Using Fusion360 I also designed model that is the mold of a mold. This way I can produce e.g. a silicone mold using this model and then using the fabricated mold to produce a cast of the inside of this model's box. I designed a spare part for a friend's bike as his original part was broken.