JPH0653375B2 - Molding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molding method.

[Background technology]

FIG. 7 shows one of the injection molding apparatuses mainly intended for resin molding, aluminum die cast molding and the like. The apparatus includes a fixed-side mold member 1 and movable-side mold members 2 and 3, and the movable-side mold members 2 and 3 include a receiving plate 5 provided on the front side of the mounting plate 4. A recess 8 into which the tip of a cylinder 7 having a piston 6 is fitted, and an injection port 9 communicating with the recess 8 are provided in the center of the fixed-side mold material 1. Two passages 10 and 11 communicate with the injection port 9. In addition to the cavities 12 and 13 being formed in the movable mold members 2 and 3, cooling holes 14 and 15 are provided. Each cavity 12 of the same mold material 2, 3
Ejector pins 16 and 17 arranged on the front surface of the mounting plate 4 face the surface 13.

By the way, in the conventional molding method, the mold materials 2 and 3 are cooled to a temperature below the temperature at which the injected material 20 is solidified, and the molten material 20 in the cylinder 7 is placed in the cavities 12 and 13 of the piston. 1 by injecting at 6 and solidifying
A molding cycle was constructed. In the thick-walled cavity 13 shown in FIG. 8 (a), the material 21 is deprived of heat from the cavity 13, and solidification proceeds from the surface layer portion 21a to the central portion 21b. The surface layer portion 21a that is first solidified during the solidification process is pulled by the central portion 21b that subsequently solidifies and shrinks, so that sink marks 22 occur as shown in FIG. 8 (b). It was supposed to be taken out as a part. in this way,
A warped molded product is not preferable as a product. In the conventional molding method, the mold materials 2 and 3 are cooled in advance and the material is injected later. Therefore, as shown in FIG. 9, the material is injected from the gate 18 into the cavity 12. Material 24 begins to solidify near gate 18
In the final filling portion 24a separated from 8, the solidification is delayed, and a difference in filling pressure occurs between the two, resulting in variations in the mechanical and electrical characteristics of the obtained molded product,
This has been a factor of quality deterioration.

[Object of the Invention]

In view of the above circumstances, the present invention provides a molding method capable of obtaining a molded product of good quality that is free from warpage and variations in characteristics.

[Disclosure of Invention]

In order to achieve the above object, the present invention includes at least a step of injecting a molten material into a cavity of a mold material heated to a softening temperature of an injected material or higher, and cooling the mold material to solidify the injected material. A step of heating the mold material above the softening temperature of the material while holding the solidified material in the cavity and filling the same molten material in the cavity, and cooling the mold material after the filling. The gist of the molding method is to provide a step of cooling the material in the mold material in one molding cycle.

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof.

1 to 6 show an embodiment of a molding method according to the present invention. As shown in these drawings, the molding apparatus for carrying out this molding method is substantially the same as that described in the above-mentioned conventional art, and therefore, the same components are designated by the same reference numerals and will not be described. A high-boiling-point medium is made to flow into the cooling holes 14 and 15 provided in the movable mold members 2 and 3, and high frequency induction coils 27 are wound around the peripheral members of the mold members 2 and 3, respectively. By heating and cooling only the mold body, the cycle time can be shortened.

By the way, in the molding method according to the present invention, first, the mold materials 2 and 3 are rapidly heated by the high-frequency induction coils 27 and 27 so that the temperature becomes equal to or higher than the softening temperature of the injected material 30. This corresponds to the section A in Fig. 6, in which the mold members 2 and 3 are heated from t ₁ ° C (solidification temperature of the material) to t ₂ ° C (softening or melting temperature of the material).

Next, the material 30 that is molten in the cylinder 7 is pushed out by the piston 6 and passes through the inlet 9 to the two gates 1.
It is injected into the cavities 12 and 13 from 8 and 19. Since the material 20 is heated to the softening temperature of the material 30 or higher, the material 20 does not solidify immediately after entering the cavities 12 and 13 from the vicinity of the gates 18 and 19,
While maintaining the molten state in the cavities 12 and 13, a uniform pressure state is obtained as a whole. As a result, the packing density of the material 30 in the cavities 12 and 13 is made uniform at any point, and by the cooling in the next step, the mechanical and electrical characteristics are consistent. To be The state where the mold material temperature is kept at a constant t ₂ ° C during the injection is shown in section B of Fig. 6.

The cooling step corresponds to section C in FIG. In this section, the mold materials 2, 3 are cooled from t ₂ ° C to t ₁ ° C, which is due to the high boiling medium passed through the cooling holes 14,15. When the cooling process ends, the section D in FIG. 6, that is, the solidification section starts. In the solidification section D, the mold material temperature is maintained at t ₁ ° C. FIG. 2 shows an outline of the solidification, and FIG. 3 shows an enlarged view of the inside of the cavities 12 and 13 after solidification. In the thick-walled cavity 13 shown in FIG. 3, sink marks 31a are generated in the solidified material 31, which is similar to the conventional case. By the way, in the molding method according to the present invention, instead of taking out the molded product as it is,
By combining the next molding cycle as the latter half cycle, it is possible to obtain a good product without the warp.

That is, the latter half cycle is a combination of the steps of heating the mold material E, melting the surface of the molding material and injecting F, cooling G, and solidifying H as shown in FIG. The mold material heating E
In the section, the mold members 2 and 3 are heated from t ₁ ° C to t ₂ ° C. In the next section F, the solidified material 33 in each of the cavities 12 and 13 is melted only at the surface layer portion 33a while being maintained at t ₂ ° C. Since only the surface layer portion 33a of the material 33 is melted, a volume shrinkage 35 is left between the cavities 12 and 13 and the material 33, and the same molten material 37 is filled in the void of the shrinkage 35. It is injected from the cylinder 7 and the insides of the cavities 12 and 13 are filled. As a result of this filling, the molten material 37 is transferred to each surface layer portion 3
3a and 3a are melt-mixed with each other, and if the solidified material has been removed, it will be in a disappeared form. When the filling is completed, the process proceeds to the next cooling step G, in which the mold materials 2 and 3 are cooled from t ₂ ° C to t ₁ ° C, and then to the solidification step H that maintains t ₁ ° C. . In this solidifying step H, as shown in FIG. 5, since the central portion having a slow solidifying rate has already solidified and only the surface portion is melted and the solidifying rate becomes uniform,
It solidifies without sink marks or warpage. As a result, it is possible to obtain a high-quality molded product which is free from warpage and has no characteristic variation as described above. The surface melting and pouring step F is shorter than the step B in terms of time. This is because in Step F, only the surface layer needs to be melted, not the entire material.

〔The invention's effect〕

Since the molding method according to the present invention is configured as described above, it is possible to obtain a molded product of good quality that is free from warpage and variation in characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view showing a molding apparatus for carrying out the molding method according to the present invention in a material injection step, and FIG.
The figure shows a cross-sectional view of the same device during the solidification process,
The figure is a cross-sectional view showing the state of the solidified material in the cavity, and Fig. 4 is a cross-sectional view showing the relationship between the material whose surface layer is solidified in the cavity and the material supplemented to it, and Fig. 5 is the final figure. Sectional view showing the state of the solidified material, FIG. 6 is a graph showing the state of time and temperature change in each step, and FIG. 7 is a forming apparatus for carrying out the conventional forming method. The cross-sectional view and Fig. 8 show the appearance of sink marks in thick materials,
Figure (a) is a cross-sectional view showing how the central part of the material pulls the outer peripheral part during solidification, (b) is a cross-sectional view showing the appearance of sink marks, and Figure 9 is the cavity gate. FIG. 6 is a cross-sectional view showing a state of solidifying nearby and remaining molten at the final filling portion. 1, 2, 3 ... Mold material, 12, 13 ... Cavity

Claims (2)

[Claims] 1. At least a step of injecting a molten material into a cavity of a mold material heated to a softening temperature of the material to be injected, a step of cooling the mold material to solidify the injected material, and the solidified material. Heating the mold material above the softening temperature of the material while holding the mold in the cavity to fill the same molten material in the cavity, and cooling the mold material after the filling to fill the material in the mold material. A molding method comprising the step of cooling the mixture in one molding cycle. 2. The molding method according to claim 1, wherein the mold material is provided with heating / cooling means near the cavity.