Process

The process flow of dewaxing casting is: mold design - mold opening - wax injection (mold) - trimming wax mold (welding wax mold) - wax tree planting (- weighing) - making shell mold ——Shell mold roasting——casting——vibration shell——cleaning sand treatment

Each process is described below.

Making product molds

Generally, the molds are aluminum molds and steel molds. However, it is inconvenient to use. The factory gets the drawings and the engineering department designs the corresponding molds and gates according to the drawings. Then, the aluminum material is processed by a series of CNC machine tools to manufacture the mold.

Waxing

After the mold is opened, the wax injection operation can be performed. The wax injection operation should pay attention to factors such as wax temperature, pressure and compression of the plastic mold.

The wax used to make the wax model is generally blue model paraffin, its melting temperature is about 60℃, and the wax injection temperature is about 65℃. There are also some other colors of paraffin with slightly different properties. The wax temperature and injection pressure are determined by the wax injection machine. There are usually two types of wax injection machines: air pressure type and vacuum type. The wax injection principle of these two types of wax injection machines is basically similar, that is, the molten wax is injected into the plastic mold by air pressure. The difference between the two is that the vacuum wax injection machine can first vacuum the plastic mold and inject wax into the plastic mold; while the air pressure wax injection machine can only directly inject wax into the plastic mold. Therefore, it is usually easier to master the vacuum type wax injection machine, while the air pressure type wax injection machine requires certain experience.

The heater and temperature sensor in the wax injection machine can make the wax liquid reach and maintain a certain temperature. Usually, the temperature of the wax in the wax injection machine should be kept between 70 and 75 °C, which can ensure the fluidity of the wax liquid. If the temperature is too low, the wax liquid is not easy to fill the wax mold, resulting in incomplete wax mold; on the contrary, the wax liquid temperature is too high, which will cause the wax liquid to overflow from the gap of the plastic mold or from the wax injection port, which is easy to form flash or burn. finger.

The pressure in the wax cylinder of the wax injection machine is provided by an external air pump, which should generally be maintained between 0.5~0.7at (or kgf/cm2), that is, 0.051~0.071Bar, or according to the volume and complexity of the wax model. Make appropriate adjustments.

Before injecting wax, the plastic mold should be opened first to check the integrity and cleanliness of the plastic mold. If it is a used plastic mold, you should spray dewaxing agent (you can also sprinkle a small amount of talc powder) on the plastic mold, especially the small and complex shapes, to facilitate the removal of the wax mold; secondly, the wax injection machine should be preheated, Turn on the air pump and adjust the pressure and temperature.

When injecting wax, you should clamp the plastic mold in the splint (which can be plexiglass, wood, aluminum, etc.) with both hands. Pay attention to the distribution of your fingers so that the plastic mold is evenly pressed; The wax nozzle is advanced in parallel. After the wax nozzle is firmly injected, the hands do not move. Gently step on the wax injection switch with your feet and release it immediately. The mold has a bottom, the bottom of the mold should be pulled out first), and the wax mold is taken out. After the wax mold is taken out, check it carefully. If there are serious problems such as missing edges and broken feet, such a wax mold is a waste product. If it is some relatively small defects, the wax model should be trimmed.