JPS6333144A - Pattern forming method for lost wax casting - Google Patents

Abstract

PURPOSE:To prevent the flow of a wax and to prevent the generation of a shrinkage cavity by having the external shape to form the recessed part for connecting a sprue stick, installing the fitting forming the aperture which communicates with an injection port and the cavity of the inside of a die inside the die and taking off the fitting after the wax injection. CONSTITUTION:A melted wax is fed from the injection port Ri of the whole body in the state of descending the upper die. This wax is injected into the die cavity from each injection port a, b, c, d. The wax of the die cavity inside is held under uniform pressure by the injection pressure acting on each injection port a-d and the solidification is progressed gradually in the state of the flow of the wax being restrained. At the stage of the whole body being solidified the upper die is ascended together with the fitting 1 for forming the recessed part, then the recessed part for connecting a sprue stick is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming a wax model used in lost wax casting.

[Prior Art] It is well known that the lost wax casting method is advantageous for casting products having complex internal shapes and thin-walled castings. This lost wax casting method involves injecting wax into a cavity in a mold to form a wax model.
Similarly, after forming a tree assembly by joining the sprue connecting recesses of each wax model to each sprue rod provided in a runner made of wax, coating by dipping and sanding is repeated to form a kind of shell mold. After drying this shell mold, the wax in the shell mold is melted by steam heating and dewaxed (autoclaved), then the shell mold is fired in a furnace to form a ceramic shell mold, and the mold is The process consists of casting through the runner while maintaining the temperature at a high temperature, breaking the mold after solidification, and finally separating each product from the runner and finishing it.

An example of a cast product for which such a lost wax casting method is most suitable is a rotor for a rotary piston engine.

Conventionally, when injection molding a wax model of a rotor, injection molding was performed at a position close to each vertex equidistant from the axial center of a triangular rotor, as shown in Figures 4 and 5 with the mold removed. By setting outlets a, b, and c and injecting the wax under pressure from the injection outlet R4 of the runner R that connects these injection outlets a, b, and c in series, wax as shown in the cross section in Fig. 5 is produced. I was trying to mold a model WM.

In conventional molding of this type of wax model WM, the fourth
As shown by the hatched area a l + bl + CI in the figure, there was a problem in that a "sink mark" (see FIG. 5a) occurred in a portion corresponding to the boss portion of the rotor.

Note that the recess shown by B in FIG. 5 is the recess for connecting the sprue rod described above.

Area a l + bl + where such “sink” occurs
CI is not only farthest from the mold, but also the farthest distance from each of the opposing injection ports a, b, and c, making it difficult for injection pressure to act on it, making it difficult to suppress the fluidity of the wax, and solidifying it last. It is thought that the above-mentioned sink marks occur due to the following reasons:

[Object of the Invention] An object of the present invention is to effectively utilize the molding of the sprue rod connection recess to reliably prevent "sink marks" that may occur during wax model molding as described above.

[Structure of the Invention] Therefore, the present invention provides a metal fitting having an external shape forming a concave portion for connecting a sprue rod, and having a tapered hole formed in the axial direction to communicate the injection port and the cavity in the mold. The wax is installed in the mold, and the wax is injected from this metal fitting into the cavity in the mold, and the injection pressure is evenly applied around the recess for connecting the sprue rod to prevent the formation of whiskers. In some embodiments, the metal fitting can be removed from the mold without leaving any traces of the injection hole.

[Effects of the Invention] According to the present invention, wax injection pressure can also be applied from the molding fitting of the sprue rod connection recess, so the injection pressure can be applied uniformly to each part of the cavity. This reliably prevents the internal wax from flowing and prevents the formation of whiskers, and since the injection hole of the metal fitting is tapered toward the cavity, the metal fitting can be taken out without leaving traces of the injection hole. be able to.

[Example] Examples of the present invention will be specifically described below.

2 and 3 show a method of molding a wax model of the rotor, excluding the mold, in order to contrast with FIGS. 4 and 5 showing the conventional structure.

As is clear from the comparison with FIGS. 4 and 5, in this embodiment, a recess forming metal fitting 1 for forming a recess for connecting a sprue rod is provided in a portion corresponding to the axial center of the rotor l, This recess molding fitting 1 has an injection hole 3 having a tapered shape (towards the cavity) whose upper end communicates with the injection port d newly provided in the center of the runner R, and whose lower end opens into the cavity in the mold. is installed through the shaft in the axial direction.

Therefore, in addition to the conventional three injection ports a, b, and c corresponding to each top of the rotor, another injection port d is formed in the narrow part of the rotor. Wax is injected into the mold cavity from a total of four injection ports a, b, c, and d. Therefore, the injection pressure acts almost uniformly within the cavity, and flow that may cause sink marks can be completely suppressed, and a perfect wax model WM can be molded.

Furthermore, by making the injection hole 3 tapered toward the lower end, when the recess molding metal fitting l is later taken out, it can be taken out without leaving traces of the injection hole 3.

FIG. 1 shows a specific example of an injection mold for a wax model of a rotor to which the basic structure shown in FIGS. 2 and 3 is applied.

As shown in Figure 1, an injection mold basically consists of:
Lower mold 12 positioned and held by lower mold holder 11
and an upper mold 14 positioned and held by an upper mold holder 13.

The lower mold 12 supports a divided mold 15 (actually divided into three parts) for forming each flank surface of the rotor, and has an internal cavity in the center for forming the internal cavity of the rotor. The forming molds 16 are respectively positioned and attached.

On the other hand, the upper mold 14 can be separated from the lower mold 12 by raising the upper mold holder 13, and as described above, the injection ports a, b, c, d (in FIG. (only a and d are shown) are formed, and the recess forming metal fitting 1 is fixedly held by a retaining ring 17 so that the injection hole 3 matches the newly installed injection hole d in the center.

Further, the upper mold holder 13 is formed with a runner R that communicates with each injection port a, b, c, and d, and an injection nozzle fitting 18 is attached to the starting end of the runner R. An injection port Ri is formed.

In the above configuration, as shown in FIG. 1, when the upper mold 14 is lowered and molten wax is supplied from all injection ports Rib), this wax is distributed to each injection port a, b.
, c, d, and is injected into the mold cavity 19.

When the mold cavity 19 is filled with wax, the wax in the mold cavity 19 is maintained under uniform pressure by the injection pressure acting on each injection port a, b, c, and d, so that the wax does not flow. Solidification progresses gradually while the solidification is suppressed, and when the entire mold is solidified, the upper mold 14 is raised together with the recess forming metal fitting l. After the four-part molding fitting l is pulled out, a recess B for connecting the sprue rod is formed. In this case, since the injection hole 3 of the concave molding fitting l is formed in a tapered shape, the solidified wax in the injection hole 3 will be separated from the root without leaving any traces.

In the above embodiments, a model for molding a rotor of a rotary piston engine was described, but it goes without saying that the method of the present invention is not limited to this.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a wax model forming mold used in an embodiment of the method of the present invention, and FIGS. 2 and 3 are a plan view and a cross-sectional view showing a model molding method showing the features of the method of the present invention, respectively. 4 and 5 are a plan view and a cross-sectional view, respectively, showing a conventional model forming method. B... Recess for sprue rod connection, 1... Metal fitting for forming the recess, End... Injection hole.

Claims (1)

[Claims] (1) When molding a concave part for joining a sprue rod in a model molded with wax, the above-mentioned external shape part for molding the concave part and a tapered hole communicating with the cavity in the mold and the wax injection port are provided. A model forming method for lost wax casting, characterized in that a metal fitting for forming a concave portion is installed in a mold, and the metal fitting is taken out from the mold after wax injection.