JPS6225063B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a wax model for lost wax precision casting. The models used in lost wax precision casting are generally in the form of liquid, semi-solid, or solid, which is pressure-injected into the cavity of a mold, and then cooled and solidified to form the mold. An injection molding machine is used for the pressure injection method. Many of the model defects that occur with this method can be eliminated by setting molding conditions, mold design, etc. However, it is difficult to eliminate model defects caused by surface shrinkage and torsional deformation. The cause of these defects is the cooling and solidification shrinkage of the molten wax. In other words, after the gate part that pressure-injects molten wax into the mold cavity solidifies,
As internal shrinkage progresses, internal pressure decreases, and when the outer grain strength is weak, dents occur, so-called surface shrinkage. Surface shrinkage is large in thick parts and small in thin parts, so in molded products with large changes in wall thickness, twisting changes are likely to occur because the solidification rate between thick and thin parts is not constant. An object of the present invention is to provide a method for manufacturing a wax model for precision casting with less surface shrinkage and torsional deformation. In the present invention, after filling the cavity of a mold with powdered wax, the mold is heated to melt the powdered wax near the inner surface of the mold, and then the mold is cooled to form a wax model for precision casting. It is manufactured. Hereinafter, the present invention will be explained in more detail based on the drawings. In FIG. 1, powdered wax 3 is filled into the cavity of a mold 1 through a wax filling port 2. As shown in FIG. Here, it is desirable that the particle size of the powdered wax 3 is smaller. This is because if the particle size is large, the melting rate will be slow and the model forming time will be long. After filling the entire cavity with powdered wax 3, the mold 1 is heated to melt the powdered wax near the inner surface of the mold 1 and turn it into a liquid phase 4. The mold 1 can be heated by providing a fluid flow passage 5 in the thick part of the mold 1 and flowing a heating medium into the fluid flow passage 5. As the heating medium, ethylene glycol aqueous solution, divalent or trivalent alcohol aqueous solution, and turbine oils having a relatively high boiling point can be used. Liquid phase 4 produced by melting powdered wax 3
The thickness is preferably 2 to 5 mm. When the thickness of the liquid phase 4 is 2 to 5 mm, when the liquid phase portion is cooled and solidified and shrunk, the solidified layer portion has a small internal shrinkage and there is almost no decrease in internal pressure, so that no surface shrinkage occurs. Furthermore, since the model can be molded with a substantially constant thickness of the solidified layer after melting the wax, even if there is a sudden change in wall thickness of the model, the cooling rate of each part can be made substantially uniform. Therefore, no residual stress is generated inside the model, so no torsional deformation occurs. However, if the thickness of the liquid phase 4, that is, the thickness of the solidified layer, is less than 2 mm, the strength of the model will be weak, and there is a risk that the model will break when taken out from the mold. When the liquid phase 4 exceeds 5 mm, internal shrinkage caused by cooling and solidification shrinkage increases. As a result, the internal pressure decreases significantly and surface shrinkage occurs. Further, the thickness of the liquid phase 4 becomes non-uniform, and the cooling rate of each part becomes non-uniform, so that residual stress is generated inside the model, causing torsional deformation. After melting the powdered wax to form the liquid phase 4, the mold 1 can be cooled while applying fluid pressure. In the case of normal wax, a strong shell corresponding to the cavity shape is formed by bringing the liquid phase surface of the wax into close contact with the inner surface of the mold and cooling the liquid phase 4 from the inner surface side with fluid as well. Therefore, it is desirable to apply fluid pressure when cooling the mold 1. However, by selecting the composition of the wax, the shell is gradually formed from the inner surface of the mold 1 to the inner side of the cavity, so it is not necessarily necessary to apply fluid pressure. Methods of applying fluid pressure into the cavity include a gas injection method and a liquid injection method. As the gas, air or an inert gas such as nitrogen or argon gas can be used. When increasing the cavity internal pressure with such a gas, the gas blowing pressure is preferably 0.2 to 10 kg/cm ² . If the gas blowing pressure is less than 0.2 kg/cm ² , the force that presses the solidified layer of wax formed near the inner surface of the mold against the inner surface of the mold is weak, and the molten wax layer will drip from the inner surface of the mold, especially in the upper mold. The model cannot be molded according to the shape of the mold cavity. Although it is possible to mold a model with a gas pressure of 10 kg/cm ² or more, it is necessary to create a strong mold that can withstand the high internal pressure. If the internal pressure is high, a special press device is required to fix the mold, which has the disadvantage of increasing the manufacturing cost of the model. Moreover, at 10 kg/cm ² or more, unmelted solid particles are pressed toward the inner surface of the mold. This force destroys the solidified layer of soft wax that has formed near the inner surface of the mold, exposing solid particles from the destroyed area, making it impossible to create a model with a smooth surface. In the liquid injection method, any liquid such as water that does not dissolve wax can be used. Particularly in the case of liquid, the liquid phase 4 of the wax is increased at the same time as increasing the cavity internal pressure.
It also plays a role in cooling the body from the inside. Next, the mold 1 is cooled with a suitable cooling medium to lower the mold temperature to below the melting point of the wax. Any type of cooling medium may be used as long as it can maintain a temperature low enough to lower the mold temperature below the melting point of the wax. Specific examples of the cooling medium include dry ice, liquid nitrogen, water, permanent coolant, and oil. The position where fluid is blown or injected into the cavity is preferably a part of the mold with a thickness of 5 mm or more, and furthermore, this part is the part that corresponds to the riser part when producing castings using the mold. It is more desirable to do so. In the parts of the mold having a thickness of 5 mm or less, the filled powdered wax is mostly melted, so that it is not possible to blow or inject fluid through the gaps in the powdered wax. Furthermore, the position where the fluid is blown or injected is repaired with wax after the model is formed, but the repaired portion cannot achieve the target dimensional accuracy when the casting is manufactured, so machining is required. However, machining is often not allowed at positions other than the feeder section.
Therefore, it is preferable to use a location corresponding to the feeder portion as a fluid injection or injection position. Next, the mold 1 is opened and the wax model is taken out, which can be used as a solid wax model as it is, or the unmelted powdered wax can be removed from the gas inlet of the taken out wax model and used as a hollow model. be able to. When using a hollow model, the material cost of the model can be saved,
Furthermore, since the model is light in weight, it is easy to handle during model assembly and molding. Example A commercially available wax sheet for modeling (0.1 to 0.2 mm thick) was cut into 0.5 to 1.0 mm squares to obtain powdered wax. Next, the powdered wax was filled into the cavity of the mold while applying vibration (vibration: 1.5 mm, frequency: 3000 (VPM)) to the mold.Next, the liquid circulation provided in the thick part of the mold was applied. The mold is heated by pouring an 80℃ ethylene glycol aqueous solution into the flow path, and after 5 minutes have elapsed, the wax is compressed to 3 kg/cm ² from the wax filling port, which is located at a position corresponding to the riser part when manufacturing castings. After air is blown into the mold cavity and the internal pressure reaches 3 kg/cm ² , the liquid circulation is stopped and the mold is immediately cooled with dry ice while maintaining the internal pressure to remove the molten wax layer near the inner surface of the mold. The model was formed by solidification.The model was removed from the mold and the second
A model having the shape shown in FIGS. 5 to 5 was molded. In FIGS. 2 and 3, 6 corresponds to a wax filling port and a gas blowing port. Next, the model was placed at a temperature of 25℃±2℃ and humidity.
It was left standing in a room controlled at 50% ± 5%, and after 3 hours, surface shrinkage and torsional deformation were measured. Surface shrinkage was measured on the ventral side 5A (thickness: 20 mm) in Figure 5 using an electric micrometer (accuracy: 1/1000 mm). Torsional deformation was measured using a three-dimensional guillotine gauge, and the gap between the guillotine gauge and the model was measured using a dedicated gap gauge (accuracy: 1/100 mm). Table 1 shows the magnitude of surface shrinkage on the ventral side 5A in Figure 5, and Table 2 shows the magnitude of torsional deformation in terms of the distance moved inward of the wing radius portion 4A in Figure 4. .

【table】

[Table] The conventional examples in Tables 1 and 2 are the results of measurements made using the same method as the invention on models molded by injection molding, which is currently the most popular molding method for precision casting models. The molding conditions are injection temperature 60℃,
Injection pressure is 20Kg/ ^cm2 . The surface shrinkage of the embodiment is 1/3 of that of the conventional example, and the magnitude of torsional deformation is less than 1/4 of that of the conventional example. In addition, the same thing as in the above example was carried out using N ₂ at an original pressure of 150 kg/cm ^2.
Using gas, blowing pressure 0.2Kg/ ^cm2 and 10Kg/ ^cm2
The experiment was carried out for the case of , and almost the same results as in the above example were obtained. As described above, according to the present invention, it is possible to mold a wax model with little surface shrinkage or torsional deformation even in the case of a complex shape with large wall thickness changes. Therefore, it is extremely effective for molding models of gas turbine blades, etc., which have complex shapes with three-dimensional curved surfaces and require strict dimensional accuracy.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the principle of the present invention, FIG. 2 is a front view showing the shape of a wax model obtained by the present invention, FIG. 3 is a side view of FIG. 2, and FIG. 5 is a sectional view taken along line AA in the figure, and FIG. 5 is a sectional view taken along line BB in FIG. 1... Mold, 2... Wax filling port, 3... Powdered wax, 4... Liquid phase (wax molten layer),
5...Fluid flow path.

Claims (1)

[Claims] 1. After filling the cavity of the mold with powdered wax, the mold is heated to melt the powdered wax near the inner surface of the mold, and then the mold is cooled. A method for manufacturing wax models for precision casting. 2. A method for manufacturing a wax model for precision casting according to claim 1, wherein fluid pressure is applied within the cavity during cooling of the mold. 3 Claim 1 in which the fluid pressure is gas pressure
A method for manufacturing a wax model for precision casting as described in . 4. The method for manufacturing a wax model for precision casting according to claim 1, wherein after melting the powdered wax near the inner surface of the mold, unmelted wax is taken out of the cavity. 5 The powder wax filling port and fluid inlet port are
The method for manufacturing a wax model for precision casting according to claim 1, wherein the position of the model corresponds to a feeder during casting production. 6. The method for manufacturing a wax model for precision casting according to claim 3, wherein the gas pressure is 0.2 Kg/cm ² to 10 Kg/cm ² .