assignments

Assignments

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.

All the important links are Here

Learning outcomes

Design appropriate objects within the limitations of your process

Demonstrate workflows used in mold design, construction and casting

Group Assignment

For further information, please check our Group Assignment

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

What is Molding and Casting

Molding:

Molding involves creating a hollow cavity (a mold) that matches the shape of the desired object. This mold is then filled with a material that can take its shape, such as liquid plastic or molten metal. Once the material inside the mold hardens or sets, it takes on the shape of the mold.

Casting:

Casting is the process of pouring a material, usually a liquid or molten substance, into a mold to create a copy of the original object. The material fills the mold and takes its shape, then solidifies or cools down to form the final product. This technique allows for the creation of multiple identical copies of the same object.

Molding creates the shape of the object's cavity (negative space), while casting fills that shape to create the final object (positive space).

Vocabulary

Positive Mold A positive mold is a mold that replicates the shape and details of the original object. It's used to create exact copies of the object.
Negative Mold A negative mold is a mold created as the inverse of the original object. It represents the space the original object occupied and can be used to create replicas.
Pot lifePot life, also known as working time, is a term often used in the context of casting, molding, and other fabrication processes. It refers to the period during which a mixed material, such as resin or plaster, remains in a liquid state and is workable. After this time, the material begins to harden or cure, making it difficult or impossible to manipulate. The length of the pot life can vary depending on the specific material and environmental conditions such as temperature and humidity.
Cure timeCure time refers to the period required for a material, such as resin or plaster, to fully harden or set after it has been mixed and applied. The length of the cure time can vary widely depending on the specific material, its formulation, the volume used, and environmental conditions such as temperature and humidity.
Injection Molding: Heating up material until it's liquid, then shooting it into a mold at high pressure to shape it into things like plastic toys or parts for machines.

Insert Molding: Placing metal or other materials into the mold before injecting the plastic, so they become part of the finished product.

Overmolding: Adding another layer of material onto an existing part to give it extra features or protection.

Blow Molding: Inflating a heated plastic tube inside a mold, like blowing up a balloon, to create hollow objects such as bottles or containers.

Rotational Molding: Rotating the mold while heating it, allowing the material to evenly coat the inside and form hollow or large parts with consistent thickness.

Slip Casting: Pouring a slurry of liquid material (like clay) into a porous mold, where water is absorbed, leaving behind a solid object.

Die Casting: Forcing molten metal into a mold cavity under high pressure, producing precise metal parts with fine details.

Flexible Molds: Making molds from materials that can bend or stretch, allowing for easier removal of the casted object without damaging it.

Materials: Various substances like foam, rubber, plastic, metal, or clay used as raw materials for casting different objects.

Additives: Substances added to the base material to alter its properties, such as making it stronger, more flexible, or resistant to heat.
Safety: Ensuring proper handling of materials, ventilation to avoid inhaling fumes, using protective gear, and disposing of waste responsibly.
Machining: Using tools and machines to shape, cut, or smooth materials to achieve desired shapes and surface finishes.
Software: Computer programs used for designing molds, simulating casting processes, and generating toolpaths for CNC machining, aiding in the manufacturing process.

Group Assignment

Smooth On OOMOO 25 SILICONE RUBBER COMPOUND:

Pot Life: 15 minutes
Cure Time: 75 minutes
Mixing Time: 3 minutes
Outcome: When used for 3D printing molds, OOMOO 25 leaves filament marks on both the negative and positive molds, resulting in a textured finish. However, milling molds with OOMOO 25 produces smoother outcomes with faint lines from the drilling bit.

SORTA CLEAR 37 TRANSLUCENT SILICONE RUBBER:

Pot Life: 25 minutes
Cure Time: 4 hours
Mixing Time: 3 minutes
Outcome: 3D printing molds with SORTA CLEAR 37 captures intricate and detailed patterns effectively due to its translucent properties. Conversely, milling molds with SORTA CLEAR 37 yields smoother outcomes but may exhibit slight textures from the milling process.

Smooth-Cast™ 305:

Pot Life: 7 minutes
Cure Time: 30 minutes
Mixing Time: 3 minutes
Outcome: Both 3D printing and milling molds with Smooth-Cast™ 305 produce bright white castings with minimal bubble formation. However, milling molds may offer slightly smoother finishes compared to 3D printing.

When comparing 3D printing versus milling molds, it's essential to consider the specific characteristics of each material and method. While 3D printing excels in capturing intricate details, milling may offer smoother finishes but is limited by the size of the drill bit. Ultimately, the choice depends on the project's requirements and desired level of detail in the final product.

In our lab, we have a comprehensive array of molding materials, each tailored to specific applications. Among these are Smooth On OOMOO 25 SILICONE RUBBER COMPOUND, SORTA CLEAR 37 TRANSLUCENT SILICONE RUBBER, BLUE WAX BLOCK, and AMACO FLEXWAX

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.

The design I chose for my mold is a dog paw (I wanted a paw shaped chocolate mold)

I looked at Mr.Anith's documentation for a basic knowledge when designing the mold Mr.Anith Ghalley

Firstly the paw design

As simple as it sounds, Use inkscape to trace the bitmap of the design and export it in .svg file.

Now, the mold design itself with the paw print in the middle. You will have to first create a square sketch with the sizes 150mm by 150mm. And then use the "Offset" tool to create two offset sketches. Offset 1 for the Outer edge for the mold wall. And Offset 2 for the Inner edge for the mold wall.

For the Offset tool

Then extrude the innermost square by 39mm which is a little but smaller than the thickness of the material I am using to mill/

Now after extruding since the drilling bits are circular it is not advised to make 90 degree anges in your design. So, I used the fillet tool to make the outer square with smooth edges.

Next you would want to create another offset for the outer side of your mold so that your paw design is in the middle to pour the cast over it.

Now insert the .svg file you created earlier of the traced bitmap of the paw design

Adjust the file accordingly

Extrude the design after adjusting your design but not till the edge of the mold, leave a bit of space

Lastly use the fillet for the inner edges

3D printed Result

And then generate the g-Code

Making the mold

For the mold I used the Smooth-On Sorta Clear 37

Remember to Pre-mix both the parts before mixing measuring them and mixing them

Measure the part A and part B equally.(I used more than whats shown in the image, I used 110gof both parts for my mold )

Then mix it thoroughly for 3 minutes.

Then pour the mixture in your mold and let it set.

Result

Making the cast

I used the Smooth-Cast 305

Remember to Pre-mix both the parts before mixing measuring them and mixing them

Just like for the Mold, measure equal amounts of part A and B

Then combine the parts and mix it thoroughly for 3 minutes

Then add color if you like and then pour it in your positive mold.

Then let it set

I kept it overnight

Now comes the flaw in my design

Since I didn't have anything that was connecting the paws together, though the result was very good, it came out as separate pieces.

All the coutcomes of "the Paw Design"

The other design I chose is a mold of a Bhutan Map outline(For milling)

I traced the bitmap of the bhutan map outline like I did for the paw design.

So firstly I took the dimensions of the molding wax I was planning on milling on and created this sketch. One sketch of the exact dimensions and the other a offset of 3mm.

Then I extruded the inner rectangle that is the offset of the actual dimensions to 1cm since I needed it to be smaller than the actual block and the overall height of the design came to 2.2cm and the actual height of the mold wax is 3.9cm.

Then I added the traced bitmap of the Bhutan Map to my design by going to insert-insert svg-insert from my computer

Then you extrude the inserted svg file

And you are done.

I printed the mold and the output was evident that my design was too big.

Redesigning

This time I started by creating 1cm smaller than the original block I am going to mill on. And set anf offset of 5mm.

I extruded the base only to 5mm since in the last design when the output came, that part of the block I extruded to 1cm was a complete waste and unnecessary.