JPS58122150A - Production of wax pattern for precision casting - Google Patents

Abstract

PURPOSE:To produce a wax pattern for precision casting which decreases surface shrinkage and torsional deformation by heating the powdery wax packed in the cavity of a metal mold and melting the same near the inside surface of the mold then cooling the wax to solidify. CONSTITUTION:Powdery wax 3 is packed into the cavity of a metal mold 1 through a wax packing port 2. A heating medium such as an aq. soln. of ethylene glycol is admitted into the fluid passages 5 formed in the thick walled part of the mold 1 to heat the mold 1 and to melt the wax 3 near the inside surface of the mold 1, whereby a liquid layer 4 is formed. The thickness of the layer 4 is preferably about 2-5mm.. After the layer 4 is solidified by cooling the mold 1, the mold is opened and the wax pattern is removed. It is preferable for tight adhesion of the layer 4 to the inside surface of the mold to apply gaseous pressure of 0.2-10kg/cm<2> or the like upon the cavity inside in the stage of cooling the mold 1 and it is also possible to form a hollow pattern by removing the unmolten wax.

Description

Detailed Description of the Invention The present invention is a wax model IJ1 for lost wax precision casting.
Relating to a manufacturing method.

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 inside of a mold, 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 are due to the setting of molding conditions.
Mold design can eliminate pressure problems.

However, the model failure due to surface shrinkage and torsional deformation
t is difficult to eliminate. These defects are caused by cooling and solidification shrinkage of the molten wax. That is, after the gate portion for pressure-injecting molten wax into the metal cavity solidifies, internal contraction progresses, resulting in a decrease in internal pressure, and when the outer shell strength is weak, a dent occurs, or so-called surface shrinkage.

Surface shrinkage is large in thick parts and small in thin parts, so
In molded products with large wall thickness changes, 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 tension and torsional deformation.

In the present invention, 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 and the wax for precision casting is placed horizontally. It manufactures.

Hereinafter, the present invention will be explained in more detail based on the drawings.

In FIG. 1, powdered wax 3 is filled into a cavity of a mold 1 through a wax filling port 2. As shown in FIG. Here, it is desirable that the particle diameter 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 melted to form a liquid phase 4. The mold 1 can be heated by providing a flow passage in the thick wall part Kftft 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.

The thickness of the liquid phase 4 produced by melting the powdered wax 3 is preferably 2 to 5 m. 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, the thickness of the solidified layer after melting the wax can be kept almost constant to mold the chess, so even if there are sudden changes in the thickness of the model, the cooling rate of each part can be made almost uniform. can. 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 be destroyed when the metal welding device is removed. When the liquid phase 4 becomes 5s1 or more, internal shrinkage caused by cooling and solidification shrinkage increases. As a result, the internal pressure decreases significantly and surface shrinkage occurs. Since the thickness of the liquid phase 4 becomes non-uniform and the cooling rate of each part is not constant, residual stress is generated inside the model and twisting deformation occurs.

After melting the powdered wax to form the liquid phase 4, the mold l can be cooled while applying fluid pressure. In the case of normal wax, the wax O liquid phase surface is brought into close contact with the inner surface of the mold, and the liquid phase 4 is also cooled by fluid from the inner surface side, so that a strong shell corresponding to the cavity shape can be formed. 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 gold Ill to the inside 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, it is preferable that the gas blowing pressure be 0.2 to 10 kg/cttt.

When the gas blowing pressure is less than 0.2 Kg/cm, 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 swells from the inner surface of the mold, especially in the upper mold. Due to the mold cavity shape, 9
It is not possible to mold the model. Gas pressure 10Kg/1
M! Although it is possible to mold a model using the above, it is necessary to create a durable mold that can withstand 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.
/m" or more, the unmelted solid particles are forced 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, and the solid particles are exposed from 9 places. , it is not possible to create a model with a smooth surface.In the liquid injection method, any liquid such as water that does not dissolve the wax can be used as the liquid.

If 4G is a liquid, it will serve to increase the cavity internal pressure and at the same time cool the liquid phase 4 of wax from the inside.

Next, the mold 1 is cooled with a uniform cooling medium to lower the Venusian temperature to below the melting point of the wax. Any type of cooling medium may be used as long as it can maintain the temperature of the mold at a temperature low enough to lower the temperature of the mold to 11 degrees below the melting point of the wax. Examples of the cooling medium include dry ice, liquid nitrogen, water, ice, and oil.

The position where fluid is blown or injected into the cavity is 5.
A part of the mold having a thickness of 2 or more is desirable, and it is more desirable that this part corresponds to the riser part when the mold is used to manufacture a casting. In the parts of the mold having a thickness of less than 5 mm, it is not possible to blow or inject fluid through the threshold of powdered wax because the filled powdered wax is almost melted. Furthermore, the injection or injection position of the fluid will be repaired with wax after the structure is formed, but it will be difficult to inject the fluid into the casting. If the repaired portion is left intact, the target dimensional accuracy cannot be achieved and 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 the fluid injection or injection position.

Next, open the gold ml and take out the wax model, which can be used as a solid wax model as it is, or remove the unmelted powdered wax from the gas inlet of the removed wax model and use it as a hollow model. You can also. When a hollow model is used, the material cost of the model can be saved, and since the weight of the model is light, it is easy to handle when assembling the horizontal wrinkles and making the lid.

Example: Commercially available wax sheath for models) (0.1 to 0.2 mm thick)
was cut into 0.5 to LO+w angles to obtain powdered wax. Next, the metal lid vibrates with an amplitude of 2 1.5 mV and a frequency of 300.
The powdered wax was filled into the cavity of the mold while giving 0 (VPM). Next, an 80C ethylene glycol aqueous solution is poured into the liquid circulation path provided in the thick wall of the metal lid to heat the mold, and after 5 minutes have passed, the mold is placed at a position corresponding to the riser part when manufacturing castings. Blow in compressed air at a rate of 3 Kf/cut into the wax filling port provided in the wax filling port, and when the internal pressure of the metal lid cavity reaches 3 Kf/m, stop the circulation of the liquid and maintain the internal pressure. A model was formed by cooling the gold with dry ice and solidifying the molten wax layer near the inner surface of the mold. The mold was removed and a model having the shape shown in FIGS. 2 to 5 was molded. In FIGS. 2 and 3, 6 corresponds to a wax filling port and gas inlet. Next, the model ta degree is 25c±2c.

It was left standing in a room controlled at a humidity of 50%±5%, and after 3 hours, surface shrinkage and torsional deformation were measured.

The surface shrinkage was measured on the ventral side 5A (thickness: 20 cm) in FIG. 5 using an electric micrometer (precision: 1/1000). 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 scale).

Table 1 shows the size of the surface shrinkage on the ventral side 5A in Figure 5,
Table 2 shows the degree of torsional deformation at the wing radius section 4A in Figure 4.
- is shown by the distance moved inward.

Table 1 Table 2 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 a horizontal molding method for precision casting that is currently popular. It is. The molding conditions are injection temperature 60C and injection pressure 20 to 4/cm.
” is.

The same thing as in the above example was carried out using N8 at an original pressure of 150 kg/cm.
Using gas, spraying was carried out at pressures α2 Kg/cm and 10 Kg/cm, 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 structure with little surface shrinkage or torsional deformation even in the case of a complex shape with a large change in wall thickness. Therefore, it is extremely effective for molding a gas turbine member, etc., which has a complicated shape with a three-dimensional curved surface and requires strict dimensional accuracy.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the principle of the present invention, Figure 2 is a front view showing the shape of a wax model obtained by the present invention,
I, Figure 3 is a side view of Figure 2, Figure 4 is A-Ai of Figure 1.
5 is a sectional view taken along line BB@ in FIG. 1.

Claims (1)

[Claims] 1. After filling the cavity of the mold with powdered wax,
A method for manufacturing a wax model for precision casting, characterized by heating a mold to melt powdered wax near the inner surface of the mold, and then cooling the mold. z A method for manufacturing a wax pattern for precision casting according to claim 8, wherein fluid pressure is applied within the cavity during cooling of the mold. 3. The method for manufacturing a wax model for precision casting according to claim 1, wherein the fluid pressure is gas pressure. 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 method for manufacturing a wax model for precision casting according to claim 1, wherein the filling port for powdered wax and the fluid inlet port are at the model-○ position corresponding to a feeder during casting manufacturing. a Gas pressure 25E 0.2 Kg/cm” ~10
K17cm""? 'A method for manufacturing a wax model for precision casting according to claim 3.