METHOD OF MULTI-CAVITY INJECTION MOLDING AND MOLD

Abstract

Disclosed is a technology for eliminating the need for the adjustment of imbalance in an injection molded product and also enabling multi-cavity molding, a method of multi-cavity injection molding including: a dividing step of dividing a molten resin material into a plurality of portions; a resin density adjustment step of adjusting a resin density distribution; and a filling step of filling the molten resin material into a region where the molten resin material is formed into a molded product. The method of multi-cavity injection molding has a configuration containing a combined-use step which includes both a hot runner step and a cold runner step. The combined-use step is dividing the molten resin material from the hot runner to the plurality of cold runners through a spool and a branch runner. A plurality of series of steps from the dividing step to the filling step is concurrently performed in one mold.

Claims

1. A method of multi-cavity injection molding for enabling multi-cavity molding of injection molded products required to have sophisticated resin density distribution, comprising: a dividing step of dividing a molten resin material from an injection apparatus into a plurality of portions through a plurality of equal-length runners; a resin density adjustment step of adjusting a resin density distribution of the molten resin material divided into each portion in the dividing step; and a filling step of filling the molten resin material having a resin density which has been adjusted in the resin density adjustment step into a region where the molten resin material is formed into a molded product, wherein the resin density adjustment step includes a combined-use step in which both a hot runner step of readjusting a temperature of the molten resin material to adjust fluidity and a cold runner step of adjusting pressure and speed are used in combination, the combined-use step is dividing the molten resin material from a hot runner to a plurality of cold runners through a spool and a branch runner, and a plurality of series of steps from the dividing step to the filling step is performed concurrently in one mold.

2. The method of multi-cavity injection molding according to claim 1, wherein a pin gate format in which a plurality of fillings of the molten resin material from the plurality of cold runners into filling regions is arranged to be dispersed in a regular and evenly spaced manner is employed.

3. A mold for multi-cavity injection molding, the mold being for injection molding used in the method of multi-cavity injection molding according to claim 1, comprising: a dividing structure dividing a molten resin material from an injection apparatus into a plurality of portions through a plurality of equal-length runners; a resin density adjustment structure adjusting a resin density distribution of the molten resin material of each portion by division by the dividing structure; and a filling structure filling the molten resin material having a resin density which has been adjusted by the resin density adjustment structure into a region where the molten resin material is formed into a molded product, wherein the resin density adjustment structure comprises a combined-use runner structure in which both a hot runner readjusting a temperature of the molten resin material to adjust fluidity and cold runners adjusting pressure and speed are used in combination, the combined-use runner structure divides the molten resin material from the hot runner to the cold runners through a spool and a branch runner, and a plurality of series of structures from the dividing structure to the filling structure is provided in one mold, and the plurality of series of structures is concurrently operated.

4. The mold for multi-cavity injection molding according to claim 3, wherein a pin gate structure in which a plurality of fillings of the molten resin material from the cold runners into filling regions is arranged to be dispersed in a regular and evenly spaced manner is employed.

5. A mold for multi-cavity injection molding, the mold being for injection molding used in the method of multi-cavity injection molding according to claim 2, comprising: a dividing structure dividing a molten resin material from an injection apparatus into a plurality of portions through a plurality of equal-length runners; a resin density adjustment structure adjusting a resin density distribution of the molten resin material of each portion by division by the dividing structure; and a filling structure filling the molten resin material having a resin density which has been adjusted by the resin density adjustment structure into a region where the molten resin material is formed into a molded product, wherein the resin density adjustment structure comprises a combined-use runner structure in which both a hot runner for readjusting a temperature of the molten resin material to adjust fluidity and cold runners for adjusting pressure and speed are used in combination, the combined-use structure divides the molten resin material from the hot runner to the cold runners through a spool and a branch runner, and a plurality of series of structures from the dividing structure to the filling structure is provided in one mold, and the plurality of series of structures is concurrently operated.

6. The mold for multi-cavity injection molding according to claim 5, wherein a pin gate structure in which a plurality of fillings of the molten resin material from the cold runners into filling regions is arranged to be dispersed in a regular and evenly spaced manner is employed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a flowchart illustrating steps of a method of multi-cavity injection molding according to the invention of the present application.

[0025] FIG. 2 is a front view illustrating a configuration for two-cavity molding according to the invention of the present application.

[0026] FIG. 3 is an enlarged front view for explaining the combined use of a hot runner and a cold runner.

[0027] FIG. 4 is a movable-side front view for two-cavity molding according to the invention of the present application.

[0028] FIG. 5 is a fixed-side bottom view for two-cavity molding according to the invention of the present application.

DETAILED DESCRIPTION

[0029] The present invention includes both a hot runner 150 and a cold runner 160. Furthermore, the major feature of the present invention is that a plurality of runners having the same lengths is connected so that multi-cavity molding is possible while the accuracy is high.

[0030] Hereinafter, examples will be described based on the drawings. It is noted that the invention of the present application is not limited to the shape and dimension illustrated in the drawings. Modification is possible within the technical scope that can be said to be the main part of the creation of the technical idea indicated herein.

[0031] FIG. 1 is a flowchart illustrating steps used in the method of multi-cavity injection molding according to the present invention. The invention of the present application is an injection molding method that enables multi-cavity molding of a molded product required to have a uniform density distribution. Specifically, resin is needed to be filled in such a manner as to have uniform density for a molded product which rotates at high speed, such as a blast fan which rotates at several thousand revolutions per minute, such as a sirocco fan and a turbofan.

[0032] In a dividing step 10, a molten resin material from a spool 120 of an injection apparatus is divided into a plurality of portions through a plurality of equal-length runners. The molten resin material supplied from the dividing step 10 is supplied to a hot runner system. It is noted that FIGS. 2 to 5 illustrate an example of two-cavity molding. Therefore, the runners with equal lengths centered at the spool 120 are a straight line. However, for example, the runners are in three directions at intervals of 120 degrees for three-cavity molding, and in four directions at intervals of 90 degrees for four-cavity molding.

[0033] A resin density adjustment step 20 is a step of adjusting the distribution of the resin density of the molten resin material. The resin density adjustment step 20 includes both a hot runner step 22 and a cold runner step 24. The hot runner 150 and the cold runner 160 are connected via a branch runner 154. It is noted that the branch runner 154 is a runner radially extending with a hot runner nozzle 140 located in the center thereof. The branch runner 154 illustrated in FIGS. 2 and 3 is an example in which the cold runner 160 is regularly arranged at six locations on the same pitch circle having its center at the axial center of a fan which becomes a molded product. It is noted that the leading end of the runner is desirably disposed with a slug well 152.

[0034] In the hot runner step 22, the resin which has been heated in an injection apparatus to become in a molten state is heated again immediately before being filled into a cavity 180. The hot runner step 22 is used as the first method for achieving good fluidity thereby to obtain uniform resin density. Also, it is desirable to use a common heater or the like for heating by a manifold 190 so that a stable molten state is retained. It is noted that the hot runner nozzle 140 is either an open gate type in which the leading end of the nozzle is opened and recovered or a valve gate type in which an open-close mechanism is provided, and is not limited to either. However, the cutting of the gate is better by the valve gate type which has the open-close mechanism of the gate. The valve gate-type mold is somewhat expensive, but the temperature of the gate portion can be set more easily than the open gate-type mold. Therefore, the valve gate type as illustrated in FIG. 2 is desirable for a rotation fan or the like which is involved in the problem of the invention of the present application.

[0035] The cold runner step 24 is carried out for adjusting the flow rate and pressure of the molten resin material having been heated to high temperature by the hot runner nozzle 140 when the resin material is filled into the cavity 180. Especially, for example, when a molded product includes an extraordinarily thin flow portion like a blade portion of a sirocco fan, excessively increased fluidity causes the filling speed into such a narrow channel to increase. Then, molecules constituting the resin are stretched in the flow direction, causing a phenomenon of flow orientation or molecular orientation in which the molecules are arranged in the flow direction.

[0036] This leads to problems such as residual stress. Therefore, taking advantages of the hot runner 150 in the previous step, there is adopted a configuration in which the cold runner 160 is used in combination such that the flow properties of the molten resin is adjusted by physical interaction between the temperature difference in the flow channel from the high-temperature region to the low-temperature region and the pressure difference due to the throttle in the cold runner 160.

[0037] A filling step 30 is the step of filling the molten resin material having been subjected to resin density adjustment by the resin density adjustment step 20, from a predetermined position of each cavity 180 from an isometric position. It is noted that various arrangement configurations were reviewed by experiment. As a result, when such an arrangement is six equal parts, particularly favorable uniform resin density was obtained.

[0038] It is noted that a subsequent cooling step is commonly-practiced air cooling by air, water cooling by cooling water, or the like. A mold releasing step is a similar to a typical step, such as extrusion with an extruding pin 230, extruding plates 240 and 250, and the like. Therefore, a subsequent cooling step is omitted.

[0039] FIG. 2 is a front view of an example of two-cavity molding when a molded product is a sirocco fan. The feature of this example is that the hot runner 150 and the cold runner 160 are used in combination. The hot runner 150 and the cold runner 160 are arranged in series as illustrated in the drawing. The molten resin having been adjusted in temperature is adjusted in pressure by a predetermined throttle. This causes the resin to be filled into the shape of a substantially cylindrical fan with uniform speed and properties. It is noted that when the molten resin supplied from the injection apparatus is excessively heated to high temperature, thermal degradation is generally caused. This thermal degradation causes distortion and residual stress to be generated. Therefore, typically, when the runner which flows out from a set upper limit of the temperature is long, the temperature significantly changes, thereby causing such harmful effects in some cases. Also, when the hot runner 150 is used, a waste runner does not remain. Therefore, the use of the hot runner 150 is economical. However, in the invention of the present application, the adjustment of filling speed and pressure by the cold runner 160 has priority over the advantage of the hot runner 150. Therefore, the configuration the cold runner 160 in which the runner remains is used in combination on purpose. More specifically, the molten resin material which has been heated by the injection apparatus to obtain fluidity is heated again by the hot runner nozzle 140 upstream from the cavity. When this further increases the fluidity of the molten resin material, the flow rate of the molten resin material increases in a thin channel of a blade portion. As a result, the above-described harmful effects are caused. To address these harmful effects, the nozzle portion of the cold runner 160 and the flow channel of the cold runner 160 are throttled to adjust the pressure and also to achieve uniform flow rates. Furthermore, it is desirable that a plurality of pin gates is provided so that the flow rates are further adjusted to ensure favorable flow states.

[0040] FIG. 2 is a side view illustrating a configuration of two-cavity molding for a sirocco fan. FIG. 3 is an enlarged view illustrating flow channels of a molten resin material. FIG. 4 is a movable-side plan view in the case of two-cavity molding which corresponds to FIG. 2, and FIG. 5 is a fixed-side bottom view in the case of two-cavity molding which corresponds to FIG. 2. Each drawing illustrates an example for a sirocco fan. This sirocco fan is used for air conditioning of an automobile. The blade of the molded product is thin, and the number of blades is as many as 30 to 60. Therefore, this molded product is required to have a uniform resin density distribution.

[0041] The present inventor has also conducted experiments with various types such as a propeller fan, a turbofan, and a blower fan, other than the sirocco fan. The temperature control of the hot runner 150, the channel diameter, throttle, nozzle shape, or presence or absence of the gate of the cold runner 160, and the like are prepared in such a manner as to be selectable for any type. Thus, it has been found that a favorable result can be obtained when any fan type is subjected to multi-cavity molding.

[0042] It is noted that a mold 1 does not have a particular structure. The mold 1 may be a typically used two-plate or three-plate mold as illustrated in FIGS. 2 to 5. A movable-side mold includes a male mold 220, and a fixed-side mold 100 includes a female mold 170. Also, FIG. 5 illustrates that the leading end of the cold runner 160 is disposed at six locations isotropically from the axial center of the cavity 180. However, the number of leading ends and the positions of the leading ends are not limited. In principle, the number of leading ends can be changed according to the adjustment of pressure and flow rates. It is noted that in the case of the sirocco fan illustrated in the drawing, a sirocco fan supplied from the six locations was physically excellent. Therefore, this is indicated as an example.

[0043] The hot runner 150 system is a system which heats a molten resin material supplied from a spool through equal-length runners again to increase fluidity, as illustrated in FIGS. 2 and 3. The hot runner nozzle 140 and the manifold 190 are disposed to the fixed-side mold 100. The hot runner nozzle 140 may be any typically-used nozzle as long as it electrically controls and heats a heater disposed therein. As described above, the hot runner nozzle 140 is either an open gate type in which the leading end of the nozzle is opened and recovered or a valve gate type in which an open-close mechanism is provided, and is not limited to either. However, in the valve gate type which has the open-close mechanism, the cutting of the gate is better, and therefore, the setting of the temperature in the gate portion is easier. For this reason, the valve gate type is desirable for a rotation fan or the like which is involved in the problem of the invention of the present application.