The first step in the investment casting process is to make an investment pattern, which is the key to forming the shape of the casting inside the refractory shell.
Therefore, in order to obtain a casting with high dimensional accuracy and good surface finish, the investment pattern itself must have extremely high dimensional accuracy and surface finish. The quality of the investment pattern directly affects the quality of the final casting.
Investment casting process steps:
Principle: Use sand (usually mixed with a binder) to make a mold, pour molten metal and cool it to form.
Steps:
Molding: Make a master mold corresponding to the shape of the part with wood, metal or plastic.
Molding: Put the master mold into the sand box, fill it with molding sand and compact it to form the upper and lower sand molds.
Combining the box: Combine the upper and lower sand molds to form a complete mold cavity.
Pouring: Pour the molten metal into the mold cavity.
Cooling and sand removal: After cooling, destroy the sand mold and take out the casting.
Cleaning: Remove the pouring riser and flash, and perform surface treatment.
In the sand casting process, the sand mold needs to be made first. Sand molds are models made of refractory materials that are used to form the shape of castings. The key to sand casting is to ensure the dimensional accuracy and surface finish of the sand mold to ensure the quality of the casting. The quality of the sand mold directly affects the dimensional accuracy and surface finish of the casting.
Sand casting process steps:
Principle: Make a ceramic shell through a melted wax mold, and pour metal after melting the lost wax mold.
Steps:
Making wax molds: Make a model consistent with the part with wax.
Tree assembly: Weld multiple wax molds on the wax pouring system to form a “wax tree”.
Coating and hanging shells: Repeatedly dip refractory slurry (such as silica sol and zircon sand) to form a multi-layer ceramic shell.
Dewaxing: Heat the shell to melt the wax and flow out to obtain a hollow cavity.
Firing: Firing the shell at high temperature to enhance strength and remove residual impurities.
Pouring and cleaning: Pour metal, break the shell after cooling to take out the casting, cut the pouring system and polish.
Investment casting and sand casting are similar in some aspects, such as both need to ensure high precision of the model. However, there are also obvious differences between the two. Investment casting uses a mold made of fusible material, while sand casting uses a sand mold made of refractory material. The main advantage of investment casting is that it can produce castings with complex shapes, while sand casting is more suitable for mass production of simple castings.
Investment casting is usually used to produce small batches of castings with complex shapes, especially for castings with high surface finish requirements. Sand casting is more suitable for mass production, which can save costs and improve production efficiency. The main advantage of sand casting is its cost-effectiveness and can meet the needs of mass production.
| Comparison Items | Sand Casting | Investment Casting |
| Materials and molds | Sand mold (reusable or disposable) | Ceramic shell (disposable) |
| Mold costs | Low (wooden or metal mold) | High (wax model + multi-layer shell) |
| Production cycle | Short (suitable for rapid production) | Long (shell production and drying time-consuming) |
| Surface roughness | Rough (Ra 12.5~25 μm) | Smooth (Ra 1.6~6.3 μm) |
| Dimensional accuracy | Low (CT10~13 grade) | High (CT4~6 level) |
| Minimum wall thickness | Thick (usually ≥3mm) | Extremely thin (up to 0.5mm) |
| Applicable metals | Cast iron, cast steel, aluminum alloy, etc. | High melting point alloys (such as stainless steel, titanium alloy) |
| Suitable for batches | Suitable for single piece, small batch to large batch | Suitable for small to medium batches (especially complex parts) |
| Typical applications | Engine cylinder block, machine tool base, large valve | Turbine blades, jewelry, medical equipment, precision parts |
| Advantages | Low cost, adaptable to large size, simple process | High precision, good surface quality, complex structure molding |
| Disadvantages | Rough surface, need subsequent processing, limited precision | High cost, long production cycle, easy cracking of shell |
Investment casting and sand casting also differ in production processes. Investment casting requires heating the mold to dissolve it, and then cooling and solidifying it in the mold shell to form a casting. Sand casting requires placing the sand mold in a sand box, then injecting molten metal, cooling and solidifying it to form a casting. The production cycle of investment casting is relatively long, but it can ensure the dimensional accuracy and surface finish of the casting.
Sand casting has a shorter production cycle, but the dimensional accuracy and surface finish of the casting may not be as good as investment casting. Investment casting and sand casting each have their own advantages and limitations.
Of course, which process to choose depends on the specific application requirements and economic conditions. In actual applications, customers need to comprehensively consider factors such as production scale and cost budget to choose the appropriate casting process.
If you have large-scale metal casting customization needs, you can choose Mulan Metal to cooperate. Mulan Metal is a professional custom metal casting processor in China with 12 years of processing experience and serving customers in more than 30 countries. With complete certificates, it can meet the custom casting needs of customers from different countries.
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