Investment casting is widely used as a method for manufacturing products. It can cast metallic very precisely. Investment casting has a ceramic, plaster, or plastic shell formed around a wax object. Then remove the wax, pour the metal into the shell for finishing the casting.
Nowadays, investment casting has become very popular in manufacturing, because of its precise casting, lower production cost, and waste. It has been used in many industries manufacturing, such as power generation, automotive, oil and gas, space exploration, medical, agriculture, construction, commercial, and consumer products.
What Is Investment Casting Process?
Investment casting mainly include 8 process steps:
- Creating a wax pattern
- Wax tree assembly
- Shell building (slurry coating and stucco coating )
- Wax removing
- Metal pouring
- Shell knock off
- Cut off
- Individual castings
More detail in the investment casting process flow chart.
Investment casting process animation:
4 Advantages of investment casting
- Superior surface finish: the ceramic shell was made according the smooth-surfaced wax pattern. Coat the wax pattern with the ceramic, and when you remove the wax, you will get a superior finished surface.
- Complex, near net geometries: the wax pattern inside the ceramic is nearly the final shape, and the feature of liquid ceramic can round the wax pattern and any details of it. When the wax was removed, the shape still retaining. Therefore, pour the melted metal into the shell and wait for it cool. You will get the final geometries.
- Wide range of alloys: the ceramic shell is very hard that can tolerant the extreme heat temperatures of melted metal. The melting point of the most metal is lower than the tolerant point of the shell. Therefore the investing casting can be used in a wide range of alloys.
- Fine detail: the liquid ceramic shell will warp all the details that the wax pattern has, so the final product will have the fine detail.
8 Processes of Investment Casting
The investment casting process, also called the investment moulding process, has 8 main investment casting process steps. The primary step is creating a wax pattern for its basic function of shaping ceramic shell which will cast the final metal parts.
Creating Wax Pattern
Crating wax pattern is the first step of investment casting and also the basis of the precision investment casting process.
The wax pattern is made by injecting the wax into a metal mold.
When you create a wax pattern, you should consider the whole detail of the products because all the casting is based on the shape which the wax pattern created.
Wax Tree Assembly
The finished wax pattern will assemble at a wax sprue for mass production because make small parts at one time is not economical. With this wax sprue, manufacturers will have a combination of many wax patterns, which will later provide voids for molten alloy, and the sprue also creates a flow path for the liquid molten alloy into the void.
The “Gates” indicates the wax connect the pattern and the sprue, and they control the direction and flow of the molten alloy into the void created by the wax patterns.
After creating a wax tree you need to build a ceramic shell around the tree, and later, the molten alloy will be poured into the shell.
There are two steps to build a shell: slurry coating and stucco coating.
- Slurry coating: Dip the wax tree into a ceramic bath or slurry.
- Stucco coating: apply the sand or stucco on to the wet surface.
Waiting for the mold becomes dry and repeated the processing time by time until the shell can tolerant the stresses of the casting process, and the shell was built.
Removing the wax which inside the shell relates to the quality your investment casting has. So it is very important that explain the lost wax investment casting process.
There are two methods to finish the lost wax investment casting process:
Steam-dewax autoclave: this kind of dewax machine remove the majority of the wax, these wax can be reused.
Flashfire oven: burns off the rest wax and make the shell hard. Make a clear and tough shell for casting.
Most of manufacturers use both methods in concert.
You should ensure that the shell is preheated to a specific temperature to avoid the solidification or freezing off during the injection process. The shell should keep the temperature until the shell is filled.
Induction melting means manufacturers use a ceramic cup which also called a crucible to melt alloy. And when the alloy reaches its melting point, it can be poured into the shell.
Shell knock off
When you finish the metal pouring process, you should remove the shell material next. There are three common mechanical methods to remove the shell.
Hammer, High Pressure Water Blast, Vibratory Table
Though the shell also can be removed chemically, while it will take the problem of health and the environment.
When you remove the shell from the tree, you should cut the part from the sprue, and ground of the gates. Manufacturers always cut off parts with a chop saw, torch or laser, while laser has limited applications.
The last investment casting process step can be finished by vibratory, belting, or hand grinding or polishing. Deal with the automated process is efficient.
Application of investment casting process
The investment casting process is nearly used at all manufacturing industries, such as power generation, firearm, automotive, aerospace, military, gas and oil, food service, and energy industries.
The investment casting process can produce nearly every kind of metal parts like triggers, hammers firearm in the firearms industry. Every industry which applies metal parts can use the investment casting process to produce its parts.
Investment casting process can also devided as water galss investment casting process and aluminium investment casting process.
As one kind of manufacturing method, investment casting products by pouring molten metal into a shell. With a lower cost and friendly environment, investment casting has become popular in the manufacturing industry. And it can be seen in many situations, such as automotive, aerospace, food service, etc.
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