The gap that i am trying to fill is the need to melt and cast aluminium.
This will allow for a more effective manner for making prototypes. It will also help grow the range of tools that we can make for our own use. This increases the range of things we can bootstrap.
The range of tools needed include:
- a furnace that can reach the temperature of 660 degrees C safely.
- a crucible for holding molten aluminium at 660 degrees C, that can be moved around and used to pour safely.
- a casting bed, that can be used to hold the forms for the moulds, and that can deal with spills safely, ie. it can hold the mould, the crucible and have molten aluminium spilled onto it safely.
- the cope and drag, which are the top and bottom frames, for holding the foundry sand. The sand, itself, is the mould.
I’ve started this task by prototyping the crucible.
Initial design notes
As it is going to be dealing with high temperatures, the material used will reflect this requirement. For the functionality to properly tested, it will have to be capable of dealing with those high temperatures.
Prototyping with plastic, and moving water around with them would be a safe way of testing the design, but would not give the functionality which is necessary for a full test.
Making them out of the stock materials that we would finally be using, will give a better test of our ability to do rapid-prototyping.
This in turn will aid the transition from one-off prototypes, to production runs. The size of the production run being from 1 to 1000′s.,
The use of stock materials, and pre-made sections, will reduce the costs, and increase the speed of manufacturing.
The choice of 3mm steel box section was made because it’s the thickest steel i could find. Steel of 8mm and 12mm thickness, is available, and will be used in versions 2 and 3. Initial cost considerations meant prototyping with the 3mm steel was a cheaper option.
Care will have to be taken to test the initial prototypes properly, due to safety concerns, but that’s why i made them out of the thinner materials. It’s going to be an interesting test of how long the 3mm steel will last before weakening to the point where it’s no longer safe to use. Further testing of the thicker materials will give a good range of data, so i can get the optimum design for the best cost.
This is necessary, as crucibles are consumables. It doesn’t matter whether you are building them out of concrete and ceramics for pouring steel, or the smaller graphite-carbon materials, that are used for precious metals. The constant exposure to wide changes in temperature WILL weaken the component materials, to the point where it will be unsafe to use them.
The use of steel manufactured to an existing standard will also help ensure reliability, and give a consistent lifespan. This is necessary as they are going to hold approximately a pint of molten metal.
Three prototypes were made initially, using arc welding.
One of them suffered from inclusions during the welding process, which left leaks through pin-hole-sized holes. Grinding back to the original material to test where the fault lies, will help improve my skill in welding. However careful testing caught this flaw.
The other two were fully functional, and give a good base templates for the rest of the design testing.
The maximum volume that will fit into each one is nearly a litre of liquid.
This will not be a safe working quantity. Around half to two-thirds of that will be safer for the initial tests.
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