Jan 14, 2019
Factors affect the accuracy of the castings produced by investment casting
The size accuracy of the investment has a great influence on the accuracy of the casting. The size deviation of the investment mold is mainly caused by the instability of the molding process, such as the size of the combined force, the temperature of the wax, the pressure of the injection, the pressure holding time, the molding temperature, the opening time, the cooling method, the room temperature and the like. Investment size deviation.
When the wax is hand pressed, the above process parameters fluctuate within a relatively large range. In terms of the type of screw locking, the operator has different forces, and the injection pressure is inconsistent, which causes the dimensional deviation of the passing part to be more than 0.3 mm. The pressure of the wax, the pressure of the injection, the pressure holding time and the molding temperature affect the shrinkage rate of the investment line during the injection, and the higher the temperature of the wax, the larger the shrinkage rate of the investment line.
1. Pressure wax temperature: For mold materials with different line shrinkage ratios, the mold temperature of the mold with large line shrinkage has a greater influence on the temperature of the wax.
2. Injection pressure: The injection pressure has a great influence on the shrinkage of the investment line. For most mold materials, the line shrinkage varies with the pressure of the injection. The larger the injection pressure, the smaller the shrinkage rate of the investment line. When the injection pressure changes within the range of 0.1~0.4Mpa, the change of the shrinkage rate of the investment line is the most sensitive.
3. Holding time and molding temperature: The longer the holding pressure is, the smaller the shrinkage is. The higher the molding temperature, the larger the shrinkage of the investment line.
The use of automatic waxing machine to control the temperature of injection molding, pressure of injection pressure, holding time and other factors is beneficial to stabilize the molding process factors and improve the accuracy of the investment size. In addition, the use of a mold with a small line shrinkage is also advantageous in reducing the influence of process factors on the dimensional deviation of the investment.
In actual production, in order to improve productivity, the time for the investment mold to be placed in the press type should not be too long, generally 2 to 5 minutes. After the mold is taken, the shrinkage still needs to be continued, and the mold of most of the mold materials needs to be stabilized after 24 hours. For investment molds with high dimensional accuracy requirements, care must be taken to prevent shrinkage and deformation during storage after modulo. For this purpose, the mold and storage should be kept at a constant temperature. For the mold with special requirements, it should be placed in the tire mold after the mold is taken, parked for a certain period of time, and then taken out after the size is stable.