The manufacturing process of large precision castings

The manufacturing process of large precision castings

Investment casting, also known as wax loss 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 batch production of small and medium-sized parts (weighing 0.05-30kg). Generally, precision castings weighing 0.3-5kg are conventional products. Today, we will introduce the process of making large precision castings weighing over 50kg.

1、The die is made of forged aluminum 6061 and is integrally formed. The upper core is taken by pneumatic method.

2、The module was tested: the 20 ton single station wax ejector was used for wax injection, the wax injection temperature was 52 ℃, the wax injection pressure was 3.5MPa, the wax injection time was 20 minutes, and the pressure was maintained for 3 minutes. The electric hoist attached to the wax ejector was used to assist the mold opening, and the wax mold was water-cooled. Under these data, wax molds are more suitable for forming wax parts. The wax turnover process, as well as the number of types and groups, are all carried out by using a sponge to stand on the bottom. When assembling the tree, it is supported by a tree assembly bracket and bonded with adhesive wax. The upper part of the mold head is reinforced with four auxiliary lifting platforms to increase the lifting strength of the entire module.

3、Shell making, the shell is made of 8 layers, including the surface layer of zircon sand, the transition layer of mullite sand with a mesh size of 50-100, the back layer of mullite sand with a mesh size of 30-60 (one layer), and the layer of mullite sand with a mesh size of 16-30 (repeated for five layers). The drying time for each layer is 24 hours. Steel wire mesh is used to reinforce the shell after the 5 layers of shell making. In addition, the blind chamber inside the shell is filled with dry sand after 4 layers to avoid poor drying of the inner cavity and solve the difficulty of shell cleaning in the cleaning process. The drying method is a directional drying chamber hanging drying to facilitate the drying of the inner cavity of the mold shell.

4、Dewaxing, using an electric steam dewaxing kettle, one piece per furnace, with a dewaxing time of 15 minutes.

5、Shell roasting, using a gas roasting furnace with a roasting temperature of 1120 ℃ and a roasting time of 1.5 hours. Due to the heavy weight of the shell, it is difficult to achieve traditional fork shell loading and pouring. Therefore, we use a shell baking fixture (welded from 50 * 50mm steel plates) to load together with the shell in the furnace to facilitate the removal and placement of the shell. Both shell loading and shell unloading are carried out using manual forklifts (the teeth of the forklifts are pre wrapped with fire-resistant cotton to avoid high-temperature deformation).

6、Pouring, the pouring process adopts subcontracting pouring. Due to the overall wall thickness of the product being only 8mm, in order to ensure that the metal is completely filled with the mold, the pouring temperature is 1680 ℃ for rapid pouring.

Precision machining