Molding and casting

This week we are going to get started molding and casting. I don't wanna make something big this week because Im still super busy with university and needing to finish my final project.

Designing a mold

We first had a local lecture on thursday about molding with Saco where we got explained the basics and some examples where shown. When designing a mould you need a negative of the object you wanna mould.

Here are a lot of design guides to follow when making a mould

• Parting line - The line where the mould seperates in 2 pieces
• Draft angle - The angle how the mould is split
• Vent locations - Locations of the vents where the air bubbles can escape when pouring the materials
• Riser locations - ???
• Wall thickness - ???
• big and small volumes - With high volumes of exothermic moulds watch out with the temperature.
• Required details or resolution - How detailed you want your mould, because it will directly influence the end product.
• Material choice - When making a hard final product you can't make the mould of a hard material, otherwise you aren't able to remove the product without destroying the mould.

Reading the material sheets.

When using a material it is super beforehand to read the datasheets. Saco showed us a nice website where you can easily find any datasheet

https://www.smooth-on.com/documents/

When looking at the data sheet and safety sheet make sure to set the region to Europe.

Safety sheet

Make sure to read this carefully so you know what you're working with and what safety precautions to take.

Make sure to read the Hazards identification. Luckily the Dragon Skin 10 MEDIUM doesn't have many hazards.

And also important is the First aid measures

Data sheet

Once you've read through that you can read the data sheet on how to use the material and what properties it has.

Here you can find the Pot Time which is the time you have to mix and to pour the material. For this material it is 20 minutes which is quite some time. Some have over an hour of pot time and some have 4 minutes depending on how fast the Cure time is.

Pouring the material

When pouring the material we first need to ratios which can be found in the data sheets. (Last image at the bottom right) For this one I needed a 1:1 ratio. But I accidentally poured too much of one and then I also needed to do that for the other to keep the ratio.

After I poured I cleaned the top of the lids because it leaves a big mess. So the next person has a clean bottle to work with.

After that stir it gently so no air bubbles can be formed. What also helps is smacking the cup against the table with the bottom to get the bubbles out.

I've also searched online and there they recommended using a heat gun or pre-heating the resin a bit to get the bubbles out. source

After I was done mixing I put it in the vacuum chamber to let it cure.

The vacuum chamber helps by pulling out the air of the resin.

My first one didn't go so well because I eye balled the ratio. So I still had a lot unmixed fluid.

The bottom half cured well while the top half didn't cure so much.

This was my second attempt which has gone a lot better. This is the Mold Star 16 Fast

Making our own moulds

To create our own moulds we first need to create a block where we can cut in.

To create this block we needed a lot of of this material. The nice part about these moulds is that you can recycle the mould into a new mould. So you can melt them into new ones.

Making the mould material soft takes some time with the pan. We had a separate pan and spoon we didn't use anywhere else to keep things sanitary.

After it all was molten we could pour it in the mould to make the mould itself.

Henk told us to do it at an angle and gently to avoid bubbles in the mould. After that it needs to rest for a while. It is going to shrink a little bit.

Designing something for the assignment

I wanna make something small for this assignment because I wanna continue on my final project and University papers. So after brainstorming for a bit wanting something easy and functional I came up with a component/screw mat. This is the end result of me modeling it. I wanted to machine the components out negatively on the cnc machine so I could cast this in a mould.

Now that I have measured the moulding block the design maximum are 15x10 CM. So I am going to change my design to that.

So my longest side is 20cm's if I scale that down by a bit more than 1/4 it fits within the mould.

So I scaled it down to 70%.

When creating toolpaths I had a bit of trouble of making a negative cut. So I am going to make a smaller block than the wax block and combine it.

Then I asked Henk how big the milling bit is. It is 5 mm's.

My design has holes less than 5mm's wide So I will need to fix that.

Here is the fixed design with 5mm thick walls.

Milling the moulds

Milling the moulds didn't go that straight forward for me. Henk thought us how to mill the moulds and it was a bit different than milling wood. For example the residu of the milling we where going to use to melt into a new block.

To mill a wax block it first needs to be fastened. We did that using 4 pieces of wood.

While fastening the wood push it into the wax block. Otherwise it may get loose during milling and this can happen.

What happened here is that the mill went into the block and the block wasn't fastened properly. What also didn't help is that the bottom of the wax block was un-even on the bottom.

So after that I made a file to flatten out the wax block. But there was some damage that was going to be visible in the final product. After flattening it out I milled it again and this time it went well.

Because the mould didn't have any edges because my design was too big so I made some ducktape edges and poured the mould in.

Henk also gave me the tip to measure with water how much space I needed to fill in. So I first filled it with water and poured it into a cup. After that I knew how much moulding fluid I needed.

One day after I removed the silicone from the wax.

Here you can see the part that broke off during the milling accident. Then I used a stanley knife to cut all the excess off and then this is my final product of the week.

For next time: I should've poured slower and more gentle because there are a lot of air bubbles and be more careful when milling and better inspect the block and if its mounted well.

Another thing is the placement of the milling bit job home. Because the milling bit is dead centre on the corner in the software it should also be placed half on the corner and half off. When working with super tight tolerances and smaller things it is super important to place the job home perfectly. I learned that the hard way by almost cutting into the wood.