Overview: Investment casting of large precision castings, also known as dewaxing casting, is an advanced process of near net forming that can produce precision and complex parts that are close to the final shape of the parts, with small machining allowances. The silica sol process precision casting is suitable for large-scale production of small and medium-sized parts (weighing between 0.05-30kg). Our company adopts the silica sol precision casting process. The conventional product is precision casting, weighing 0.3-5kg, with a maximum production capacity of 35kg. The company attempted to use specialized production auxiliary tools for trial production of products weighing over 50kg and achieved good results.

1 Product Introduction: Large precision castings are used as seals for marine heat exchangers, made of CF8M material, weighing 57.2kg, with a total wall thickness of 8mm. The original process was to form a steel plate tube and weld it with the steel plate before stamping it. Low production efficiency, complex manufacturing process, high cost, and high cost of inspection. In addition, surface treatment is required for the appearance to achieve good roughness, so the dimensional accuracy cannot meet the usage requirements. The overall use of precision casting saves expensive welding costs, meets the requirements of Ra6.3 and above dimensional accuracy and surface roughness, and meets customer requirements.

II Experimental production process

1. Mold making: The mold is made of integral molding and forged aluminum 6061 material. The mold size is approximately: long × wide × Height=650mm × 650mm × 420mm. The upper core adopts pneumatic coring

2. Module: 20 ton single position waxing machine, temperature 52 ℃, pressure 3.5mpa. The waxing time is 20 minutes, and the pressure is maintained for 3 minutes. Start the mold with an electric hoist equipped with a waxing machine and cool the wax mold with water. During the wax flipping process, stand on the bottom wax piece with a sponge toe and change the shape and number of components. The mold head is reinforced with four auxiliary lifting platforms to increase the lifting strength of the entire module. The group tree flowchart and process simulation are shown in the following figure:

3. Shell making: The shell is composed of 8 layers of zirconium sand. The transition layer of mullite sand is 30-60 mesh (1 layer), and the transition layer is mullite sand 30-60 mesh (1 layer) and 16-30 mesh mullite sand (5 layers repeated). The drying time for each layer is 24 hours. After the shell is made into 5 layers, it is reinforced with steel wire mesh. The traditional shell making operation involves directly hand pasting, sprinkling, or boiling sand, but due to the large volume of the product, manual direct operation is more difficult. To solve this problem, our company has developed a movable slurry hanging shell auxiliary vehicle, which can adjust the height and rotate 360 degrees in both directions, greatly reducing the labor intensity of workers. In addition, the blind chamber inside the shell adopts 4 layers of dry sand, avoiding poor drying of the inner chamber and solving the difficulties of shell cleaning during the cleaning process. The drying method is directional drying chamber hanging drying, which facilitates the drying of the inner cavity of the shell.