Chop, Chop, Chop!

Big Picture Learning Objective

The goal of project 4- Molding and Casting- is to take the finalized design of our handle from the exploration stages using clay and wood to the mass production stage. When we design things, we have to think about how we can scale up production of our physical product. In many cases, this can include methods such as injection molding, casting and extrusions.

The other reason we are exploring resin casting is because many handles have organic shapes that are not easily replicable with geometrically contrained production methods. Making designs out of very malleable mediums like clay, and then casting them out of harder, more durable materials like resin, help us make consumer-ready products that still retain unique design features with high fidelity.

Recap of Design

I’m making a kitchen knife handle. 

Key Design Considerations

I thought about the post processing and preparation required to create molds and cast my knife handle design. Based off of my design, I determined a two part mold was best, with the seam close to the middle of the handle, and the pour spout for the casting resin to be at the flat top of the handle. This would allow the seam to be easily sanded and not obstructive. The pour spout was placed on a flat portion of the handle, so it can easily be sanded down as well.

Process Overview

We took the clay model and embedded it in a different kind of clay. This clay did not dry or harden, making it a great medium to hold the place of the second half of the mold while the first part of the mold was poured. The silicon used to make the molds was Mold Max 29NV from the brand Smooth-On.

A foam core box was made with about .75 inches of spaces in all directions away from the handle. This box will hold the silicon as it cures to create both parts of the mold. 

  After mixing the silicon according to the included instructions by weight, the mix was put into a vacuum chamber to remove gas. Relief cuts were made with a pen in the clay layer so when the two resulting silicon halves are joined, they have unique shapes that securely fit in order to align them. This entire clay and original model (Project 3 deliverable as the positive for the mold) layer was covered in mold release spray prior to pouring the silicon.   

The below image is the first silicon half removed from the clay layer.

  After the two halves of the mold are made, the foam core was reused as plates that press the silicon halves together and evenly distribute the pressure from the rubber bands keeping them together. The approximate amount of resin needed was determined by estimating the volume of a bounding box around the handle. A pink dye was used in the first cast. However, I did not realized that the ratio for the two parts of resin by weight was different from the ratio by volume. The first cast was weaker than expected (fractured two ways when I was trying to clean it) and has a slimy, shiny film on one half. It was cured in the pressurized paint sprayer, and positioned upright because the pour spout was on the face of a vertical end of the handle.   

  Subsequent casts used the correct 10A:9B ratio for the resin used, with much more durable resulting casts. Of the 4 casts done, the yellow handle was sanded and processed with sandpaper and a deburrer. The blue handle, the final deliverable, featured a black acrylic blade that helped the user visualize the intended use of the handle. The pour spout was modified to accommodate the hilt of the blade, and the acrylic was cast into the handle.   

Future Considerations

The improve the handle in the future, I would try to add texture to the handle to improve grip and feel. A silicon

mat that has textures such as these can be used: