In modern high-end manufacturing, there are not many casting processes that can simultaneously balance complex structures, high surface precision, and multi alloy compatibility, and gypsum mold precision casting is one of them. This precision casting technology, developed since the 1970s, has become one of the core technologies for manufacturing high-precision metal castings due to its unique process advantages. 

1 Gypsum precision casting: the core process of high-precision metal castings

Gypsum casting is a precision forming method that uses gypsum as the main material for casting molds. Unlike ordinary casting, it can balance complex structures, fine patterns, and high surface quality in a single forming process, and is widely used in precision component manufacturing fields that require high precision. The entire process is interdependent, from wax mold assembly to final metal castings, each step directly affects the quality of the finished castings. Understanding this process helps the purchaser determine whether it is suitable for their product structure, material, and precision requirements.

2  Detailed explanation of gypsum casting process flow

The complete process of gypsum type precision casting can be summarized into five core steps, each of which plays a crucial role in the quality of the final casting.

（1） Assemble and fix wax molds. Assemble the wax mold components according to the product structure and fix them in the grouting steel cup to prevent the wax mold from shifting during grouting, laying a stable foundation for subsequent forming.

（2） Gypsum slurry is poured and solidified. Prepare gypsum slurry, pour it into a steel cup under vacuum environment, eliminate slurry bubbles and ensure complete filling; Then wait for the slurry to solidify and preliminarily dry, forming a gypsum mold with basic strength. Vacuum infusion is the key to ensuring the compactness and fine surface of the mold.

（3） Mold removal. Melt and discharge the internal wax mold through heating or chemical means, forming a casting cavity in the gypsum mold that is completely consistent with the product structure.

（4） Drying and roasting. First, let it dry naturally to remove moisture, and then send it to the roasting furnace for high-temperature roasting according to the set curve to remove residual moisture and organic matter, significantly improving the strength and high-temperature resistance of the mold, ensuring that it can withstand subsequent pouring of molten metal.

（5） Vacuum casting. Place the qualified gypsum mold into the vacuum casting equipment and inject molten metal liquid in a vacuum environment to avoid metal liquid suction, effectively reduce porosity defects, and ultimately obtain metal castings with dense structure and stable quality.

3 Technological advantages and application scope

The reason why gypsum type precision casting occupies an important position in the field of high-end precision components is due to its distinct technological advantages.

High surface accuracy: Gypsum slurry has good fluidity, and vacuum infusion can fully replicate the fine patterns of wax molds. The surface smoothness of castings can reach Ra1.6-Ra3.2 μ m, which can meet the surface requirements of most precision parts.

Can produce large and complex integral castings: Compared to traditional investment casting, gypsum molds are not limited by coating thickness and can achieve one-time forming of large and complex structures, reducing welding and assembly processes.

Suitable for the production of thin-walled parts: Gypsum has low thermal conductivity and slow cooling of alloy liquid, making it very suitable for producing thin-walled parts of 0.5-3mm.

At the same time, the process itself also has characteristics that need to be taken seriously: The thick parts of the gypsum mold solidify slowly, which is prone to shrinkage and looseness; And the mold has poor breathability. If the pouring system and exhaust structure are not designed properly, defects such as porosity, insufficient pouring, and cold insulation are prone to occur. This is also a higher requirement for the process design and control capabilities of casting enterprises.

Application scope:

This process is suitable for aluminum alloys, zinc alloys, copper alloys, and precious metals such as gold and silver. The maximum size of castings can reach 1000 × 2000mm, with a single piece weight range of 0.03kg-908kg and a local wall thickness of up to 0.5mm. With this wide adaptability, gypsum type precision casting is widely used in aerospace, weapons, electronics, ships, instruments, jewelry, watches, dental precision components and other fields, serving as a reliable bridge connecting design creativity and high-quality products.

4 Gypsum mold powder opening: a key link in mold quality

In the process of preparing gypsum molds, powder opening is the core process that determines the molding effect and casting yield of the mold. The accuracy of ingredient calculation, uniformity of mixing, and control of vacuum parameters all directly affect the quality of the slurry and the strength of the mold.

Calculation of gypsum powder dosage: Basic ratio is 1000g gypsum powder mixed with 400cc water, which can be adjusted according to the gypsum powder model. The calculation formula is: gypsum powder amount (g)=steel cup radius (mm) ² × steel cup height (mm) × 3.14 ÷ 785. Taking a steel cup with a diameter of 90mm and a height of 125mm (radius 45mm) as an example, the amount of gypsum powder used is 45 × 45 × 125 × 3.14 ÷ 785 ≈ 1012.5g, corresponding to a water volume of approximately 405cc.

Standard Operating Procedure

The main steps include: opening the lower barrel cover of the equipment, placing the steel cup containing wax trees steadily and aligning it with the injection hole; Connect the power supply and confirm that the injection hole handle is in the open horizontal position; According to the calculated amount, add half of the water first, add all the gypsum powder, and then add the remaining half of the water; Control the water temperature at 24 ℃± 2 ℃ and start stirring for 3-5 minutes until the slurry is fine and free of particles; Cover the barrel and vacuum for 3 minutes, maintaining a vacuum degree of -0.09-0.95MPa; Close the vacuum valve of the upper barrel while maintaining a vacuum state, open the injection hole for grouting, and exhaust after filling; Remove the steel cup and let it stand for 60-120 minutes until it hardens; Finally, cut off the power, disassemble the parts, rinse the remaining gypsum with clean water, and dry the assembled equipment.

Strictly implementing standardized powder opening operations can effectively improve production efficiency, reduce defect rates, and achieve stable mass production of gypsum mold precision casting.

Gypsum precision casting has high precision, multiple types of compatible alloys, and controllable costs, making it an important process for the production of high-end precision components. Gypsum mold powder opening is a key process, and the ratio, mixing uniformity, and vacuum parameters all affect the quality of the mold and the yield of castings. Strictly implementing standardized operations can improve production efficiency, reduce defect rates, and achieve stable mass production processes.

Yihui Casting Technology Co., Ltd. was established in 2003. After more than 20 years of accumulation, Yihui has now developed into a national high-tech enterprise that integrates research and development, production, sales, consulting, installation, and training of lost wax casting equipment, and provides one-stop solutions for metal casting. Yihui Casting Technology products include metal casting equipment, casting wax, graphite products, quartz products, etc., which are exported to Southeast Asia, the Middle East, Europe, America and other regions. The company has its own R&D team, which independently develops and produces automated vacuum die-casting machines, G20 vacuum bead scattering machines, and intelligent system D3 vacuum pressure casting machines, breaking the industry's long-standing dependence on imported high-performance jewelry equipment.

For more information about Yihui Casting Technology Co., Ltd., please visit our official website or contact our team.website: www.yihuicasting.com      email : [email protected]     whatsapp : +86-13802830498