Lost wax casting process
Lost wax casting (also known as investment casting or precision casting) is a casting process, which is to inject liquid wax into a metal mold to make a wax model consistent with the casting, and then wrap several layers of refractory ceramic materials such as clay on its exterior, heating the wax to melt out, so as to obtain a hardened shell formed by refractory materials. The hardened ceramic shell is roasted, and the molten metal is poured into the mold shell. After the metal is cooled, the mold shell is vibrated to get the metal casting.
The term investment casting comes from the process of melting wax inside a mold shell by heating it. Investment casting is often more popular than other casting processes, because investment casting castings have high dimensional accuracy and good surface roughness, can be thin-walled parts or parts with complex internal and external structures, and unlike sand casting, it has no draw slope.
Investment casting materials are wide, carbon steel, alloy steel, stainless steel, etc., can also be non-ferrous materials, such as aluminum or copper alloys. In the field of hot processing, it can be applied to investment casting for difficult parts or parts that are not easy to form and some forging parts with high processing costs; In the field of casting, some products can be used to replace other forms of casting, reduce machining and cutting margins, reduce costs, improve dimensional accuracy and surface roughness as well as the mechanical properties of materials, so as to achieve the purpose of upgrading product grades.
Investment casting process
The investment casting process includes several steps: metal mold making, wax mold production and pattern tree, Shell Moulding, pouring, sand cleaning and cutting, grinding gate and finishing.
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1.Metal Mold Making
According to customer drawings and product requirements, through the casting simulation system to design the casting process, gate location, and design product mold, making metal mold. It is necessary to calculate the shrinkage rate of the product in the production process according to the production process.
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2.Wax Mold Production
The production of product wax mold is carried out in the constant temperature wax mold workshop, and the liquid wax is transported to the paste making machine by the liquid wax conveying pipe, and the wax paste is made by cooling and stirring, and is sent to each production station through the wax paste conveying pipe. The wax paste is injected into the metal mold through a certain pressure to make the wax mold.
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3.Wax Pattern Tree
After the wax mold is cooled, it is polished and inspected. According to the production process card of the product, the wax mold is welded to the wax rod one by one according to the requirements to form a product casting system, which is the group tree of the wax mold.
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4.Shell Moulding
The wax mold after the formation of the tree is sent to the shell making robot by the automatic production line, By a four-to-eight-armed robot, wax molds are sequentially immersed in a slurry made of silica sol and mullite powder.and then the various specifications of Molay sand are sprayed to the surface of the product by the sand machine, and then into the drying chamber of constant temperature and humidity for drying. After seven operations, a hard shell is formed on the surface of the wax mold. After being naturally placed for 24 hours, the mold shell is placed in a wax loss tank, and the wax in the mold shell is melted by high-temperature steam to make a shell mold with a hollow inner cavity.
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5.Pouring
The mold shell is heated to 880-1000°C by high-temperature roasting. During the heating process, the water, residual wax and other debris in the mold shell are removed, and the silica sol is fully reacted to further enhance the strength of the mold shell.
The medium frequency induction furnace is used to melt raw materials (low-carbon scrap steel), and alloying elements are added according to different materials of each furnace. When the temperature of molten steel reaches 1580-1640℃, it can be poured. According to the requirements of the melting operation instructions, the molten steel is smoothly poured into the shell mold, and the molten steel in the shell mold can be moved after 20-40 minutes of full condensation.
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6.Cleaning And Cutting
After the pouring is fully solidified and cooled, the shell mold is put into a special shelf and suspended into a large shell stripping machine. The sand shell on the surface of the product is removed by high-speed jetting steel pellets. The product is then cut with flame from the process gate bar of the tree assembly.
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7.Grinding Gate And Finishing
Remove the remaining sprue roots on the rough casting , mainly grinding by grinding wheel or machining,This process is divided into initial grinding and precision grinding , grinding can not damage the part body. The subsequent finishing is mainly to repair some surface defects that may exist on the surface of the casting, such as sand holes, slag holes, burrs, bulges, deformations, etc. The main way is grinding, welding repair, shaping and shot blasting.
After passing the appearance inspection, the castings are transferred to the heat treatment production line for heat treatment in different processes.
Production process
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1. Mould
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2. Radiowax
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3. Wax parts assembly welding
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4. Wax string
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5. Automatic shell making
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6. Dewaxing
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7. Calcination
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8. Casting
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9. Casting
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10. Checkout
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11. Shot blasting
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12. Polish
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