Moulding and Casting

April 21, 2024

Challenge

• Group assignment:

  • Review the safety data sheets for each of your molding and casting materials.🤥
  • 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. 🫠

This week is one of the exiting weeks for me as I have no previous backgrounds about molding neither casting, I was very eager to learn how to design and build my first mold but then after I started I realized that I need to wait until I see the result which was frustrated to me.

However I enjoyed every single moment during the preparation and making the mold specially when I finished my design and started to machine it.

I will explain below some of the new Information I learned about molding and casting. In addition to this please have a look at my first testing for the molding and casting material in the following LINK

Molding: is a container with a specific shape where we pour a liquid into it, while this liquid will hardness and take the shape of the mold.

Casting: Is the final product cones out from the mold.

Baking or Pot time: is the time we have after mixing the two material together before it start to be hard.

Cure Time: Is the time needed for the material to hardness after it being poured in the mold.

Individual Assignment:

I will design a mold and machine it then I will create a Silicon mold (Permanent) from it.

Design:

I will be using (Onshape) to design my mold.

I have nothing in mind to create but I will try to create something that can be used for different things so It can be a (Soap mold or even a candle mold) but at this moment I have no clear visual about what im about to create.

After 4 hours of thinking and going back and forth I had an Idea of creating a flower with a base that might be used for all the purposes above.

Let’s Go Ahead

• I will start by creating a sketch and then I will extrude it. for more Information About how to create sketches and more please refer to this LINK

• I will Draw Hexagon, and then I will extrude it by 5mm.

• Then I will create my flower.

• I will create it at the top surface of the hexagon.

• Then I will extrude it by 5mm.

• Then I will extrude the butterfly shape inside the flower.

• Then I will add some letters at the top surface of the flower and I will engrave them inside it so I can have them bumped out when I have the final product (Silicon mold).

• I will use the extrude remove by 2mm to engrave them inside the flower.

• Then I will Extrude the inside of the flower by 3mm to have the butterfly bumped out also when it comes to the final product.

• Then I will fillet all the edges and chamfer the internal circle.

Here we go the final look

For this design I have not included any overhanging and any complex drawing, I also tried to keep my path clearance wide enough so my 1 mm bit can go through the path and later on the material can go through easily and I can take it out when it dried off without loosing any details, as per the overhanging I will be using subtractive manufacturing (Milling) so these are one of machining limitation so I have to avoid it.

Raw Files

Design

STL
IGES

Machining:

Here I will machine the mold using the SRM20.

The bit I’m going to use are (1 mm Ballnose).

I will start the machining using the foam then I will move on to wax.

1 mm Bit

• The settings used with this bit for every type of material.

Foam

• For roughing :

• For finishing :

Wax

• For roughing :

• For finishing :

SRP Player

• Cam Software from Roland for rapid prototyping.

Useful LINK.

• I will Import my file to SRP player.

You can import STL, DXf, 3DM or IGES files.

• In My case I have exported my module from Onshape as STL file.

• Then I will start the flow for creating the toolpath.

• In this step I can re-scale my module and rotate it to meet my needs.

• Then I will move on to the type of milling as I can choose the type of surface finish I want in addition to how it should be cut.

• Then I will move on the toolpath creation.

• Here I can set the material type and the dimension of my material block in addition to the placement of my model within the material block (top, center, and bottom) finally I can edit the cutting parameters and other useful options in regards to the material.

• Moving to the Edit of the toolpath –> I can change the settings for both the roughing part and the finish part, I can also change the bit size and type.

• Then I will press on create tooplpath after exiting from the edit window to check the estimation time and preview if needed.

Foam Estimated time

Wax Estimated time

As seen the wax will take 6 hours almost to finish which is a very long time machining.

So having it done on foam before is a great option as we can see the result and check for errors and things to be modified much faster.

• Now I will move on to perform cutting.

• Here I can whether run it immediately to the machine or exported as a file then run each part alone (Rough and finish)

Important Note : beside the tool there is a number 21 under L which is the length needed for the bit so the spindle wont hit the sides of the block.

Models After Machining

Foam:

• Here I have the Foam Master Done.

Wax:

• Here I have the Wax Master Done.

These steps was the easiest steps for me as I’m used to them, the next which is mixing the material together is new thing to me I was a bit confident at the beginning but after couple of times it appears to be easier than designing and machining.

However the process was amazing for me as trying the foam at the beginning to check the design as it fast to mill compared to wax was a great approach I would recommend it to do.

Also, I could make the process faster if I have a tool changer because I have to leave it for overnight (I would not be able to change the tool in the middle by my self) where I could use a bigger bit to rough then the 1 mm to finish, I would think it will make a big difference in time, But I’m so proud of the result specially the wax is so clean and the details are great.

Note for the SRP we can use two different bits one for the roughing process and another for the finishing process and then even without ATC, SRP will give a notification to change the tool when the roughing process ends to change the tool.

Molding:

In this process I will be using silicon rubber to create my mold out of the master mold previously created.

I will use both the foam master mold and the wax master mold and I will compare both results together.

As for the mixing its the same for both master molds.

Mixing the material:

I’ll be using Mold Star 15 Slow from Smooth-ON

• This product is Silicon Rubber have 1:1 Mixing Ratio with 1-hour pot time and 4-hours cure time.

• Now I will mix the volume I need which is almost 55 to 60 ml –> I calculated this by calculating the volume of my master mold which has a dimension (70 mm X 60 mm X 20 = 84000 mm) - the module dimension (55 mm X 62 mm X 10 mm = 34100 mm ) –> (49900 mm) So I need around 50 ml to 55 ml but if I want to add the loss which is the excess that would stick to the walls of the cup I will go for 70 ml of material so (A= 35 ml and B = 35 ml).

• I will use a very sensitive scale to make sure the mixing ratio is accurate.

• I will put the cup and zero the scale.

• Then I will start pouring both and mixing them.

• Mixing them well.

• Then Pouring them on the foam master mold.

• After 4 Hours the mold is now ready.

• Now I will Do it again to have it from the wax master mold.

• After mixing I will Pour the silicon to my wax mold.

• Before I poured the mixture I added WD40 to the master mold to make it easier later when removing the silicon mold from the master.

I used WD40 as we don’t have mold release substance.

• After pouring the silicon I will shack the master mold to make sure the air bubbles will go out.

Unfortunately We don’t have vacuum chamber so I had to do this way by hitting the master mold to shake it.

• After 4 Hours the silicon mold is ready.

Here we Go

Reflection

The process was great and exciting to me I liked the result as it looks so clean and without defects which satisfy me the most. but there is a quite clear different between the silicon mold out from the foam and the wax and this is due to the foam texture so the wax absorbed and reflected the foam texture so this is why it appears not clean and full of small pimples unlike the silicon out from the wax which is very clean. However each of them has its advantage as foam is very fast to machine and to prototype unlike the wax which takes time in addition to the foam is a very cheap material unlike the wax, But on the other hand the wax gives the clean details needed and the rigidity which allows the user to make many molds from one master mold unlike the foam which might git damaged during the process of pulling out the mold.

Casting:

Now this is the final stage in the process where I will see the product of My Silicon mold.

For me I will use Resin epoxy to pour it inside the silicon mold.

Resin: is a two-part synthetic polymer material that, when mixed together, undergoes a chemical reaction resulting in a durable, high-strength, and adhesive substance.

• The resin I’m Gonna use is not from a known company but it does what is needed.

• The mixing ratio is 1:1 and this resin has 1-hour pot time and 24-hour cure time.

• I will use again the sensitive scale to add the needed amounts.

• In my case the Module is (55 mm X 62 mm X 10 mm = 34100 mm ) –> converting this to milliliters = 34.1 ml but I will add excess to avoid any shortage. So I will make between 40 and 45.

• After pouring it I made 44 grams.

• Then I will mix and pour the mixture in the foam silicon Mold.

As seen the resin is full of air bubbles and we don’t have vacuum chamber to remove the air bubbles.

So I will use the heat gun to do so.

• Then I will use the heat gun to get rid of the air bubbles.

• After some minutes the air bubbles will start to move out of the mixture leaving it clear.

• And Here we go the mixture has now less air bubbles and it looks more clear.

–

• Now I will do the other silicon mold as I will pour the same mixture but this time I will add color to the mixture.

• This Time we will use the thin high pouring technique which is used to reduce the amount of air bubbles in the mixture after it being poured.

• However the technique was good but not perfect as also air bubbles are their.

• So I used the heat gun to remove the air bubbles also.

• And Here we go this is also ready.

• After Waiting 24 hours the castings are now ready.

The cast has some air bubbles inside this due to not shake it well and also we don’t have vacuum chamber.

The process of using the heat gun reduced the amount of air bubbles but not eliminate them.

I loved the texture of the foam on the Resin its really nice.

But unfortunately this resin is not solid as a stone if I apply good force i can bend it.