Basics of Investment Casting – How to Do Investment Casting | CNCLATHING

2021.4.26

Investment casting, also known as lost wax casting or precision casting, the investment castings are sometimes referred to as near-net-shape castings because they can often be used with little or no subsequent finishing operations. How to do investment casting and what is investment casting process? Let’s learn about the basics of investment castings now.

Basics of Investment Casting - How to Do Investment Casting

The investment casting process is an economical manufacturing method that offers many benefits and advantages over other processes. Precision investment casting services at Junying can offer you high volume consistent casting parts with low cost and expected quality. The defining characteristics of an investment casting including its smooth surfaces, dimensional accuracy, and high degree of detail attainable. The degree of internal detail possible with an investment casting is one of its most versatile characteristics, this detail is formed using either simple poles in the tooling or by using soluble wax or ceramic coring techniques for more complex internal detail for prototyping or very short runs, purchasing of production-oriented tooling is not always economical, so there is the option of special printed patterns produced using Stereolithography from 3D CAD data. How to make investment castings? Based on the YouTube video, check out how to explain the investment casting process. 

1. The entire manufacturing process begins with the production of wax patterns from injection dies. To create the wax patterns, the dies are loaded into a wax press and filled through injection ports with a special wax melted into a paste to shape the wax pattern which solidifies in the die. The die is opened and the wax pattern is removed; this process is repeated for each required component. For high-volume work, multiple cavity tools are used to reduce costs and improve efficiency. 

2. Once the wax patterns have been formed, they must be assembled into a feed system known as a sprue. The sprue is made of recycled wax and is built to not only hold the wax patterns but also to form an adequate pathway metal flows through, the mold in casting provides a sound or defect-free part during solidification with the waxes. 

3. The tree is finished when it is assembled to the sprue. To pass the exact detail of the wax pattern to the casting, the trees are encased in a seamless ceramic shell mold, which is created by robots dipping or investing the wax into a slurry, drying the wood, and repeating this process to build up 3/8 to 1/2 inch of ceramic around the tree; this ceramic shell or mould will receive the molten metal during the casting process. 

4. The first coat is called the primary coat, and it forms the innermost surface of the mold, so it must be carefully applied under very regulated conditions to ensure quality. Progressively, additional layers of increasingly coarser secondary ceramic layers are added, and the completed shell takes shape. 

5. The next step is to remove the wax patterns and sprue, you can do this by inverting the shell into either a steam autoclave or flash fire dewaxing furnace, the wax melts and runs out and the shell is now complete and fully self-supporting, when the shells are scheduled to be poured they are reheated to approximately 1700 degrees to further condition and strengthen the ceramic shell, they are now able to withstand the thermal stress they must endure during the next stage. 

6. While the shells preheat, prepare, and melt the metal to be cast when at the proper pouring temperature, the chemistry of the alloy is checked and the molds are filled with the molten metal, the metal completely fills the cavities of the mold taking on the geometric shape which will form the outer detail of the cast component inside the cavity, the molten metal also surrounds any cores which will impart the same detail to the internal geometry of the casting, the metal is allowed to cool into its solid form and the ceramic shell is now ready to be removed from the castings using a variety of cleaning methods including blasting vibration or chemical cleaning.

7. The castings are cut from the sprue and the gate is removed by grinding, finally, the individual investment castings are given a final cleaning to expose the smooth and detailed surface, if heat number traceability is requested, this identification is directly engraved onto each of the castings, the castings are now ready for final processing to the customer’s requirements including heat treatment, CNC machining, surface treatment or other value-added processes.