Precision Casting is also commonly known as Investment Casting. It is a manufacturing process based on the lost-wax casting process, which is an old metal casting techniques that have been used since ancient times. At that time it was mainly used to create a duplicate metal sculpture from an original sculpture. We are still using this method for metal casting, but the process is much more efficient than before as we have access to better technology and materials.
Precision Casting is used for manufacturing complex metal parts with intricate details. It is preferred by manufacturers for its excellent precision, quality, repeatability, and wide range of material support.
There are a lot of preparations required for Precision Casting. The process of Precision Casting is discussed in detail below.
Creating Molds
A master pattern is needed for large scale production. It could be made from wax, wood, clay, plastic, etc. The master pattern is usually made using machining or a 3d printing technology. It can be used to produce a large number of molds cost-effectively.
Creating Wax Patterns
Once molds are ready, Wax is poured into it to create wax patterns. The wax pattern can be a solid fill or just a coating. Some manufacturers may use alternative materials such as plastic for this process. For batch production, the wax patterns are usually joined together to create a larger pattern. This allows multiple parts to be cast at once.
Applying Refractory Material
The wax pattern is coated with a refractory material such as Ceramic. The ceramic coating applied is known as investment. The wax pattern is repeatedly dipped inside a slurry of ceramic until a thick and uniform layer is formed. The layer is usually made 5 to 15 mm thick. They are then dried and hardened. The drying usually takes 16 to 48 hours, but it can be accelerated by keeping them in a controlled environment.
Dewaxing
Once the ceramic coating is hardened the molds are placed into a furnace to melt the wax. This stage needs to be done rapidly because wax expands when it is heated. Wax has a thermal expansion coefficient that is much higher than the ceramic coating. So, the wax would put too much stress on the ceramic mold thus causing it to crack. That’s why the dewaxing is done rapidly so that some wax starts melting before it can put excess stress on the mold. Sometimes holes are drilled on the mold to help the wax drain out.
Preheating and Pouring
After dewaxing the mold, it is again preheated at a very high temperature before pouring metal. This is to make sure that no moisture or wax is present. This also helps keep the molten metal stay liquid for longer so that it gets enough time to reach all recesses. Then the molds are placed inside a tub full of sand. The metal alloy is molten in a furnace and carefully poured inside the mold using a ladle. This step is often assisted by creating a vacuum or applying pressure when molds have thin walls.
Retrieving the Casting
Once the molten metal cools down and solidifies the ceramic mold is destroyed to retrieve the finished casting. When castings are done in a batch they are separated and trimmed down to remove any excess metal attached.
Then surface treatment may be provided on the completed casting. This will improve its corrosion resistance and appearance.
ADVANGATES OF PRECISION CASTING
Precision Casting has some drawbacks compared to die casting. But, it has some advantage as well that makes it an ideal choice for some situation.
Can cast almost any metal
This is the biggest advantage of Precision Casting. You are not tied to a specific type of metal with this process. Precision Casting can cast almost any metal including ferrous metals such as Iron. When you have an extremely high strength requirement that can’t be met by any other common metal alloys, you will need Precision Casting for that.
Good Surface Finish
The finished casting has a good finish with no flash or parting lines present. So, you get a near-net-shape casting that reduces some additional post-processing operations. This can save some costs in case of parts with intricate details.
High level of Precision
Precision Casting yields parts with higher dimensional accuracy. Certain parts with complex geometry and intricate details can be cast using Precision Casting that is often impossible using other methods.
PRECISION CASTING VS DIE CASTING , WHICH ONE IS BETTER?
In terms of economy and production time, Die casting is the clear winner here. But these two processes cannot substitute one another in some cases. And each of the processes has its pros and cons.
The biggest advantage of Precision Casting over Die Casting is that it can cast both ferrous and non-ferrous metal. But Die casting is limited to non-ferrous metals only. So, if you need Iron castings, then you have to go with Precision Casting. But, Precision Casting is very expensive and not a viable choice for small volume projects. The mold creation takes an awful lot of time, labor, and specialized equipment. Also, this process is limited to smaller castings and it is difficult to cast parts with a core.
All of these results in a longer casting cycle and production difficulties. Considering all these facts Aluminum Die Casting is a much better choice. The castings have excellent physical and mechanical strength, and it is one of the most cost-effective metal casting methods.
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