Week 10 Assignment:Molding & Casting



This week, what we are asked to do is that design a 3D mould, machine it, and cast parts from it.

Introduction to molding and casting

Molding is a manufacturing process in which we are creating our own shapes using materials such as wood and wax ,followled by casting with plastics, metals and even with rubber. molding is usually preferred process for manufacturing plastic parts.

Casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods

3D Modelling

So here I planned to do a comic character face, later I switched to batman mask.
So first I selected a suitable pic and took its bitmap in inkscape. The file is saved as .dxf format and imported into Rhinoceros software.
Then what I did was that, developed its 3D

The next step is to make its mold. So I decided to make it in the Shopbot. I decided to use V-Carve software. So I then converted my 3D file to .stl .

Next we have to set the origin

Next is where we can set the parameters needed for the cut. Also we can claculate the time estimate.
Next is to set the bit needed
And finally in V-carve we can see the preview machining, where we can see the way in which the machine cuts the material which we provided.
Here what is that fixing the wax in the bed. For that I used a double sided tape and pasted the material firmly on another sheet. Then I fixed that over the bed.
Then set the origin and started to cut.
So here is how I otained my mould.

Casting

Next is the casting process.

I used Liquid silicone rubber (LSR1) for preparing the mold.two parts are there which has to be mixed with 100:10 mixing ratio.This process als require 24 hours.

LSR’s specific properties are a result of its unique chemical structure. Its backbone is formed by a series of siloxane bonds which, compared to carbon bonds, are stronger and more stable. This provides liquid silicone rubber products with:

  • Superior temperature range performance. Liquid silicone products won’t elongate at high temperatures. They also remain flexible at temperatures as low as -40˚C. High thermal stability makes LSR parts suitable for heavy-duty applications.
  • Chemical stability. Liquid silicone rubber parts are chemically inert, hypoallergenic and resistant to bacteria growth. They also feature high biocompatibility, which makes them suitable for healthcare applications. However, they can degrade when exposed to certain organic compounds, or to highly acidic or basic environments.
  • Electrical resistance. On its own, LSR offers high resistance to corona discharge, making it a good choice for use as an insulator in high-voltage applications. However, it is also possible to add conductive materials without compromising the other properties of an LSR component, so that it can be used to make keyboard contact points and other electrical parts.
  • Liquid silicone rubber molded parts are odorless and tasteless. Unique colors and visual effects can be achieved through the use of pigments and master-batches. Parts are also ozone and UV safe. Other notable features of liquid silicone rubber parts include:
  • Resistance to steam and humidity
  • Flame retardancy
  • Low creep and compression set
  • Weatherability
  • Vibration absorption
  • Corrosion resistance
  • Resistance to mold, mildew, and bacteria growth
  • UL component recognition

I mixed the solution hardly so as to get it in a correct proportion and poured the solution into the mould.
Then after 24 hours I tested my casting. It was set and I got it perfect. The projections for eyes also was perfect.

Plastic Casting

Next i tried Plastic casting, Used high glossy epoxy resin we procured locally, the technical document is shown below. It is also a two part system with a mixing ratio of 100:60, having agel time of 10min and setting time of 30minutes.
Here I took the two materials in appropriate proportion added one drop of black color sampler to it and mixed it well. After that the gel was poured into my mold. this time i carefully done the pouring and after few hours i got my plastic part of batman.
So the next day it came pretty good.
In whole, I feel that the final cast which I obtained was well finished and it was stronger. But the side was not so good as I milled the material in shopbot. The bit path was clearly seen. So all else its ok..
The mould would be much smoother if the stepover percent is around the range of 5 to 20%. Depending on the features of the design, the bit size could be set, i.e., if there are small features, it would be best to go for smaller bit size.

Based on the reviews I got, the design is technically 3D with a filleting done on the edges of the mould. But I went to try out chamfering the edges of batman itself.

Design files batman

Design files batman with chamfered edges

Design files batman mould

Design files Shopbot PartWork file

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