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10. Molding and casting

Tasks for this week

  • Explaine how you design your 3D mold and created your rough and finish tool paths for machining. Done.
  • Show how you made your mold and cast the parts. Done.
  • Describe problems and how you fixed them. Done.
  • Include your design files and ‘hero shot’ photos of the mold and the final object. Done.
  • Review the safety data sheets for each of your molding and casting materials, then made and compared test casts with each of them. Done.

Group assignment

The most interesting part for me was that this week included the usage of bigger CNC machine Roland MDX-40A, as it is required for my final project. We have learned how to use it to create the object out of modeling wax. Therefore, it was necessary to learn the procedures to create proper G-code and use proper tools.

For example, it is important to remember the length of the endmill to avoid the collet hit the model. It can cause damage to the model and ruin all the milling process.

Also, we have learned different purposes of the endmills. For example, the endmills with the flat head are more suitable to cut flat surfaces, and the ball head endmills are better for finishing curvy surfaces.

Also, we compared some different ways of molding and materials. The comparison of some material can be found in the individual assignment part. Comparing different molding methods was interesting to me. I realized that it is possible to create even very complex structures with this process. However, there are also some basic methods like vacuum mold creation. It does not allow to make very detailed molds, but it is cheap, fast, and easy to apply.

There are more information about group assignment of the page of my classmate Pamela.

Individual assignment

I have decided to cast the part of the device of my final project. This part should be made out of ceramic. I did not have a ceramic to do it. But I decided to try other materials and see, how the process will go. I have selected low temperature melting metal and two components resin.

3d Model

The part that I want to cast is just a piece of the bigger part that will be used as a heating chamber.

It is an interesting part because it has an inner structure. It is necessary to use a two-sided mold to make it. Therefore, I have created a 3D model to be milled in the wax block.

One side of this model is the outer part, and another side is the inner part. Because the part itself has the hole in the center, it was necessary to close it at a certain point. The trick was that the hole should be closed in the same place both in the outer and inner part. In this case, two molds connected will touch each other in this place, and the material will not go through.

Another trick that I have used is that instead of fixing pins and holes, I used channel around the model of the part for better fixation of the molds. After the model was created, it was saved as an STL file and transferred to another software to create a toolpath for the CNC machine.

Creating toolpath

To create toolpath, I have used SRP player.

I have decided to use 4 mm flat up-cut endmill for roughing. 3 mm flat up-cut endmill for finishing vertical and horizontal surfaces and 3 mm ball-shaped endmill for sloping surfaces.

Also, I separately prepared toolpath for both sides as I wanted to avoid the machine goes from one side to another side after each layer. This program sometimes creates this strange tool path.

Cutting

I used Vpanel for machine control.

Before cutting the modeling wax, I have decided to test the process on the piece of Styrofoam.

I did not go through the whole process. I just wanted to confirm that the tool path and the orientation overall are ok.

I have noticed that only 4 mm endmill is not enough for roughing as there still will be quite deep spaces that will not be cut through. Therefore, I have decided to add roughing with 3 mm endmill.

Then I continued with modeling wax.

The resulted model is here.

Molding

For molding, I have used OOMOO 25 silicon.

I measured both components by weight, mixed them and applied liquid silicon to the model.

The resulted molds.

Casting

I have used two materials for casting: low temperature melting metal and resin.

Low temperature melting metal

I used Bismuth-Tin Alloy as it does not produce hazardous gases, and it has a low-temperature melting point. The properties of the material:

  • Melting point 95 to 100 Celsius degrees
  • It can be produced in various form such as wire, bar, powder, paste
  • Density 8.12-8.56 gram per cm^3

Usage:

  • In some cases, it can be used for soldering, where lower temperatures are required
  • It can be used for casting
  • It can be mixed with other metals to change their properties

Raisin

The second material is Xencast P6 Toughened Polyurethane Casting Resin. The information was taken from the product description page

This material usually used to create different structures with the molding process. Polyurethane resin can be used to produce all manner of cast parts, but it is best suited to making parts where high mechanical strength, increased resilience or reduced brittleness are required such as product prototypes, engineering components, and low-volume manufactured components, making it an ideal casting resin for structural parts.

Suggested Uses:

  • Detailed figurines
  • Models
  • Patterns
  • Product prototypes
  • Sculpture/artwork reproductions
  • Fishing Lures
  • Ornaments
  • Architectural Features

The raisin consigns of two parts that should be mixed and applied to the mold. The process should be not more than 2 minutes, as the material stating to get hard quickly.

Key Processing Information:

  • Mix ‘Part A’ and ‘Part B’ 1:1 by weight. Use digital scales.
  • A resin will heat-up while it cures. Large moldings will require a filler. Once mixed, pour resin immediately.
  • Suitable for fine detail. Minimum section thickness is 0.5mm.
  • For large castings with a thickness above 50mm (2”) aluminum trihydroxide (ATH) filler should be added to reduce overheating and during cure.
  • Larger/thicker castings will heat up more and cure quicker (around 30mins). Small castings or thin sections will take longer (around 60mins).
  • A wide range of pigments and fillers (including metal powders) can be added to change the properties and appearance.

Before applying any material, I have created the holes. One hole should let the air go outside and the second hole for the material. Also, as hot metal easily sticks to silicon, I covered both molds with talk.

The resulted product was very precise and smooth.

Unfurtunately, I do not have pictures with the process of pouring the metall and reisin. However, you can see that Bismuth-Tin Alloy can be meleted on ordinary owen.

Also, I used resin for casting. The result was also very good. However, the part made of resin required some post-production process. For example, I have to cut some traces in the place of connection of two molds.

Files

STL model for creating a tool path. Link. Link