Basic concept
Precision casting refers to the general term for the process of obtaining precise size castings. Compared with the traditional sand casting process, the castings obtained by precision casting are more accurate in size and have a better surface finish. Precision casting is also called lost wax casting. Its products are precise, complex and close to the final shape of the part. It can be used directly without processing or with little processing.
It includes investment casting, ceramic casting, metal casting, pressure casting, and lost foam casting. Among them, investment casting is more commonly used, also known as lost wax casting: choose suitable investment materials (such as paraffin) to invest in. Repeat the process of dipping refractory paint and spreading refractory sand on the investment, hardening the shell and drying. Melt the internal investment mold to obtain the cavity. Bake the shell to obtain sufficient strength and burn off the remaining investment material. Pour the required metal materials. Solidify and cool, and clean the sand after shelling, to obtain high precision the finished product. Heat or cold work and surface treatment as required by the product.
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Process flow
Wax pressing (wax injection to make a wax mold) — wax repair — wax inspection — tree group (wax module tree) — shell making (first dip, sand, then dip, and finally Mold shell air-drying)—Dewaxing (steam dewaxing)—mold shell roasting–Chemical analysis–Pouring (casting molten steel in the mold shell)—Vibration shelling— Casting and casting rod cutting and separation—grinding gate—initial inspection (raw embryo inspection)—shot blasting cleaning—machining—polishing—finished product inspection— warehousing
The casting production process is generally like this. Generally speaking, it can be divided into wax pressing, shell making, pouring, post-processing, and inspection.
Press wax includes (press wax, trim wax, tree group)
Wax pressing—use the wax pressing machine to make a wax mold
Repair wax—correct wax mold
Group tree — group wax mold into a tree
Shell making includes (sand hanging, pulp hanging, air-drying)
Pouring includes (roasting, the chemical analysis also called a spectrum, pouring, shell shock, gate cutting, gate grinding)
Post-processing includes (sandblasting, shot blasting, correction, pickling)
Inspection includes (wax inspection, initial inspection, intermediate inspection, finished product inspection)
Advantages
1) Perfect surface treatment
The investment casting process provides a very good surface finish compared to forgings and sand castings. Sometimes this is important and machining or other finishing operations can be avoided.
2) Closer to finished part design
Investment casting provides a near-net shape to the manufactured part, thereby eliminating or reducing tooling costs. Holes, undercuts, grooves, and other difficult-to-handle details are often available that other processes cannot. Another benefit of near net shape is material savings, especially expensive alloys such as nickel and cobalt alloys.
3) Tighter tolerances
Due to the nature of the process, investment castings can hold tighter tolerances than sand castings or forgings.
4) Competitive mold cost
The initial cost of investment casting tools is generally less expensive than sand castings.
5) Thin-walled castings
The investment casting process produces reliable castings with much thinner walls than sand castings. Advantages include significantly lower scrap rates and lower weight castings due to thin walls.
6) Fewer casting defects
As a cleaner process than sand casting, investment casting generally provides a higher percentage of defect-free castings.
Broad prospects for development
Investment casting refers to a fusible model made of fusible materials, coated with several layers of special refractory coatings, dried and hardened to form an integral shell, and then steam or hot water is used to remove the mold from the shell. Melt out the model, then place the mold shell in a sandbox, fill it with dry sand for modeling, and finally, put the mold into a roasting furnace for high-temperature roasting. After the mold or shell is roasted, molten metal is poured into it to Get castings.
The products obtained by investment casting are precise and complex, close to the final shape of the parts, and can be used directly without processing or with little processing. The application is very wide. It is not only suitable for casting of various types and alloys, but also produces castings with higher dimensional accuracy and surface quality than other casting methods, and even complex, high temperature resistant, and difficult to process castings that are difficult to be cast by other casting methods. All can be cast by investment casting.
The world’s investment casting forming process has developed rapidly and is widely used. The future development trend of this process is that casting products are getting closer and closer to component products. Traditional investment castings are only used as blanks, which are no longer suitable for rapid market changes. The complexity and quality of parts and components products are getting higher and higher, the research and development methods are getting stronger and stronger, and professional cooperation has begun to appear. The application of CAD, CAM, and CAE has become the main technology for the development of parts and components products.
From the analysis of the development situation, the application of investment casting technology is very extensive, and its future development prospects are expected to be broad.
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