[Kelly Coffield] makes intake manifolds for old Ford throttle bodies for fun, demonstrating an excellent technique for making such things in the small shop. The mould patterns are CNC machined from a solid polystyrene block, with all the necessary gates to feed the aluminium into the mould. The principle is to introduce aluminium from a large central runner into the mould structure, which feeds the gates into the mould parts. The various foam mould components are then glued with an extra brace bar at the bottom to strengthen it.

The complete structure is then sprayed with surfactant (just plain old soapy water) and dip-coated in a refractory slurry. The surfactant adjusts the coating’s surface tension, preventing bubbles from forming and ruining the surface quality produced by this critical coating step.

Once a satisfactory coating has been applied and hardened, the structure is placed inside a moulding pan fitted with a pneumatic turbine vibrator, to allow sand to be introduced. The vibrations ease the flow of sand into all the nooks and crannies, fully supporting the delicate mould structure against the weight of the metal, and gases produced as the foam burns away. A neat offset pouring cup is then added to the top of the structure and packed in with more sand to stabilise it. It’s a simple setup that can easily be replicated in any hackerspace or backyard for those motivated enough. [Kelly] is using A356 aluminium alloy, but there’s no reason this technique won’t work for other metals.

It was amusing to see [Kelly] demould by just dumping out the whole stack onto the drive and throwing the extracted casting into a snow bank after quenching. We might as well use all that free Midwest winter cooling capacity! After returning to the shop, [Kelly] would typically perform any needed adjustments, such as improving flatness in the press, while the part was in the ‘as cast temper’ condition. We’ll gloss over the admission of cutting the gates off on the table saw! After these adjustments, the part is artificially aged to a T5-like specification, to give it its final strength and machinability properties. There are plenty more videos on this process on the channel, which is well worth a look.

Aluminium casting is nothing new here, here’s a simple way to cast using a 3D printed pattern. But beware, casting aluminum can be hazardous, it does like to burn.

Continue reading “Lost Foam Aluminium Alloy Casting” →