The foundry business has been under siege for the last 10 years, maybe more. In fact, here in Philadelphia, during the 60′s there were at least 30 major foundries. Now there is only one major producer. But the casting process is growing on a global basis. It is the backbone of manufacturing the majority of our metal products. Let’s take a look at the advantages and disadvantages of 5 casting processes.
1) Sand Casting
Sand casting is one of the oldest processes. As the name implies. a fine form of sand is used as the
mold. Metal is poured(gravity feed) into the mold. After the material has cooled, the frame is released and the sand falls away. Leaving the parts to be ground and cleaned.
This type of casting is the most rudimentary of all. But it has a tremendous advantage. This is the least expensive and maybe the only way to make large castings. Castings that weigh 50 lbs., up to thousand of pounds are made using this method.
2) Investment Casting
Compared to sand casting, this process yields a more precise, complex component. IC process has been used for hundreds of years to make jewelry.
To make an investment casting, a tool is machined out of aluminum. Then wax is injected into the tool. The tool then produces a wax model that is an exact replica(with some allowances for shrinkage) of the part to be made.
The wax is then assembled with other waxes on a tree. Depending on the size of the part, each tree becomes 10 – 200 pieces. After the tree is totally assembled, it is dipped in 5 coats of ceramic slurry.
After the ceramic hardens, the wax is melted out of the tree.
Now you have a tree which is ready for alloy to be poured in. This is a gravity fed process which is suitable for a wide variety of alloys – ferrous and non-ferrous. Investment casting gives you a very precise casting with a very smooth finish. It is excellent for making parts that weigh less than 10 lbs.
3) Graphite Mold Casting
This is also a gravity feed process with graphite being used to make the molds for this process.
A cavity(negative model of the part) is machined into two large blocks of graphite. These two halves
are aligned to one another and placed in a semi-automatic press.
The process yields precision castings which are excellent for large thin covers and bases for instrumentation. Thus saving the cost of extensive machining.
5) Metal Injection Molding
This is a relatively new process( 30 years old) used for making small parts. The tooling for this process is almost exactly like tooling for plastic injection molding. Once the green part has been molded, they are debound and sintered.
This process is gaining ground in the medical device field. It’s major disadvantage is that tooling is very expensive, $25,000 and up. But it does give you great precision and a relatively low piece price for high volume components.
5) Pressure Die Casting
Steel hardened tools are also used for this process. $25,000 and more is a typical price for a die cast tooling. But it is by far the most cost effective way to cast aluminum, zinc and magnesium components. Die casting is a highly automated process and therefore very capital intensive. But similar machines are found throughout the world. Making the die casting process a global business.
If you have any further question about developing a casting, there are many great resources on the internet. One site that explains these processes in more detail is [http://www.diecastingtechnologies.com]
Post time: 04-01-2017