Molding & Casting

For this week’s assignment we had to design a mold for 3D object, mill it, and use it to cast parts.

Mold Making

I decided to design a mold for a fish I designed several weeks ago using the forming tool in fusion 360. forming tool is a useful tool helps you creat form and edit it as a mesh to creat curved, non uniform, and smooth objects. its a sculpting tool,you just have to create the form ( circular or rectangular), and then start pull (edges or vertices or faces) in or out to achieve the desired shape.

starting with fusion I made the negative of the fish, by just adding a solid block and subtract the fish from it using combine tool.

Then I split the block into two parts and added a pouring cup and riser opening to allow the air to leave the mold cavity.

The last step in the fusion is the draft analysis, to make sure that the positive will be removed from the mold.

During the quarantine period, I made a cam simulation for this mold using manufacturing tool in fusion 360, I created using 3 toolpath, one for the face cleaning, one for the roughing and one for finishing. Video

now since we are in the lab, I made the mold using Roland, to learn different cam tool I decided to use SRP player software to create the toolpaths.

For the roughing I used 1/8 flat end mill, and for the finishing I used 1/8 ball end mill. I wanted to use 1/16 ball end for the finishing, but since there is no long 1/16 ball mill and I needed it to be long, I couldn’t use it, so I used 1/8.

This image below shows the part after the roughing toolpath only without finishing job.

After I reached this point, I discovered my mistake, since I am trying to make a rubber mold, I should’ve made the positive part of the fish using milling, and then pouring the silicon rubber inside it to make the required mold which should then poured resin or liquid plastic or whatever I want. So I repeated the hole process using a new design for the positive portion of the fish.

Below is the new design, I made it smaller and combined them in one part to mill them in one job (multiple toolpaths).

In SRP player I created the toolpath again and started milling it.

 
 
 
 
        1.Import the STL model into the working space and select the exact dimensions of your model, you can also rotate your model depending on the orientation you need.
 



       2.The second step to select the type of milling, if your model contains curvatures or straight edges.
       



       3.Create toolpath step, here you have to select the material you want to mill, the size of your stock, and the toolpath settings. 
       







       4.Preview step, here you just simulate your milling process to make sure that all the areas will be milled properly and the estimated time. 
       




       
  
       5.Then the last step is perform cutting. Here you have to select whether you want your cutting output to the Rolland directly of as .rlm file, and the most important thing in this stage is the origin position , you have to make sure that you selected the origin point that you used when you set the zero for the X,Y.

and this is the final result.

Pouring

For the mold I decided to use Mold Star 30 silicon rubber, because it has a medium curing time, and cures to soft and strong rubber.

For the pouring process, I followed the instruction in the datasheet. First of all, I made sure that the wax mold is clean and doesn’t contain any contaminants (in the datasheet the warned us from using it with and material that contains “Latex, sulfur clays, certain wood surfaces, newly cast polyester, epoxy or urethane rubber may cause inhibition”).

Also, I didn’t use a release agent because it mentioned the datasheet that it’s not necessary with this product of silicone rubber.

I used the volume the ratio (1A:1B by volume), I measured the volume of the wax mold by water, and divided the volume of water into two parts each equals the amount of each part from A & B.

In the video below, you can see the exact steps of measuring and mixing. Video1

After mixing them very well, I started pouring the material exactly as the instructions. I didn’t use the vacuum degassing because it’s not necessary with this product type. Video2

I left it overnight, though it needs only 6 hrs. to cure. it removed easily and smoothly.

Then I sealed it to pour the smooth-cast 305 bright white liquid plastic in it. Its pot life is 7min, so I had to be fast and accurate. After Stirring each part alone, I mixed them together very well. Then I added a yellow pigment for it, but unfortunately it didn’t melt properly and I couldn’t spend long time stirring to melt it because I had only 7 min before it starts curing. So I poured them to the silicon mold through the pouring opening.

The final result was very good, especially because most of the non-melted pigment particles raised up to the riser and the pouring cup and the cast seamed spotted. Video

Group work

I tested different types of materials as a group assignment for this week.

Mold Star 30 silicon rubber

This is the material I used for my fish mold, it cures soft but strong material, it was very flexible also.

Mixing ratio	1A:1B by volume
Pot time	20 min
Curing Time	6 hrs
Shore A hardness	30
color	Blue

mold max 60 silicone rubber compound

I decided to use this material to test the difference in the hardness between it and the mold star 30. So, I used a 3d printed mold one of the students in the lab made and poured the mold max 60 in it after mixing the hardener very well. The result was very good but it really feels harder, it still flexible but much less than the mold star. I think it’s good to be used for molding purposes but not for soft robotics or anything that needs flexibility.

Mixing ratio	100A:3B by Weight
Pot time	40 min
Curing Time	24 hrs
Shore A hardness	60
color	Red

Dragon Skin 10 MEDIUM

I used it with my Colleague Karam, he wanted to learn how to make molds. So, I helped him.

He did all the steps as I made my assignment , and when ha reached the pouring step I helped him since he never did something like it. The first step as always we read the datasheet to know the ratio and the pot life and the curing time, then we started mixing.

Mixing ratio	1A:1B by Weight or Volume
Pot time	20 min
Curing Time	6 hrs
Shore A hardness	10
color	white

Fish STL files
Wax Mold STL files
SRP player Files