Investment Casting is an age old process that is over 6,000 years old.
The process involves creating a mold in which a liquid material is poured into and then dried or cooled to create the desired shape/object. The most common use of this process is to produce steel casting parts.
This process is flexible enough that complicated shapes and designs can be used to create products that are ultimately cast in one piece. Where other processes may demand that the product be created in multiple pieces which then need to be assembled post process. Since Investment Casting is so flexible, it allows for the parts to have a much nicer aesthetic appearance and perform as well or better than a part with multiple pieces.
So your may ask, how does investment casting work? Well, you start off with a CAD design model. Ensure that your data is correct and then move onto creating an aluminum wax mold. The mold will be used to create a wax version of the part represented in the CAD model. During this process you will make determinations as to where you want to gate the part both as a wax model and ultimately as a casting. This will then get designed into the aluminum mold. When designing the mold, you should also consider the investment casting material and it’s shrink rate.
When the mold is finished and all cuts are verified, the mold is mounted on a machine that injects hot wax into the open cavity. This creates a wax version of the object you are seeking to cast. The actual part in wax.
Several of these wax parts are initially molded. It mainly depends on how many parts you need per cycle and how many will fit on the tree based on the size and shape of the part. You may need to create multiple trees.
Once all of the parts are connected to the tree, they are then put through a ceramic shell building process. This process creates a hardened ceramic shell around the entire part tree.
After the drying process is complete, the tree is placed into an oven to complete the process. First to harden the ceramic material that makes up the shell. Second to melt out the wax from the inside of the new mold. The wax is reusable, but may need to to have an additive mixed back into it as it’s chemical structure does change after exposure to the extreme heat. Virgin wax should always be used in the molding of the actual parts. This ensures part stability and detail.
The tree is removed from the oven and set aside to cool and harden.
Now, we are ready to make our castings. Re-heat the tree to a specific temperature to ensure that there is not a shock experienced by the mold when the liquid hot metal is poured into it. Take the tree out of the oven and place it in the area where the metal can be poured into it. Pour your hot metal into the mold and fill it up. Now quickly take the filled tree and place it in an air tight chamber to kill off the oxygen and allow for the part to cool .
Once cool and solid, the ceramic shell can be removed from the solid metal tree encased inside. This can be done several ways, one way is to use a machine that vibrates the ceramic material to break off the shell. After the shell is removed it’s time to separate the parts from the core of the tree. This is done by the preferred cutting method. Some techniques used are: water jet, laser, rotary cutting disk.
After the part has been separated from the core of the tree, it’s now time to smooth out any parting lines and finish off the outside surface of the part. Once finished, you can use your part.
The goal of Investment Casting is to create an accurate representation of a part at a low cost in as little steps possible with the desired material. Investment casting can eliminate many post operations that would be required by other processes. Click why choose investment casting to learn more…