JP7595866B2 - Injection molding mold and injection molding method using the same - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Name of the meeting: Japan's first "Modeling of manufacturing processes using 3D additive manufacturing" results presentation (2nd edition) (held online) Date held: May 17, 2021 Date posted: May 20, 2021 Posting address: https://dempa-digital. com/article/192729

The present invention relates to an injection molding die used in injection molding, in which heated and molten material is injected into a mold and cooled and solidified, and an injection molding method using the same, and in particular to an injection molding die suitable for molding eyeglass frame components and an injection molding method using the same.

The injection molding method has been widely used to produce molded products by injecting molten resin material into a mold and allowing it to cool and solidify. By forming highly accurate molding voids in the mold, it is possible to produce molded products with high precision and complex shapes.

In such injection molding methods, a mold that is precisely shaped to correspond to the complex shape of the molded product is used, and a cooling passage for circulating a cooling fluid is formed in the mold to solidify the filled molten resin in a short time. For example, Patent Document 1 describes an injection molding mold that is molded by rapid prototyping and has a cooling passage formed with a uniform thickness from the cavity surface. Patent Document 2 describes that a temperature control circuit is simultaneously formed inside the mold when the mold is molded by sintering metal powder using laser light. Patent Document 3 describes that a mold that includes a fixed side mold and a movable side mold, in which resin is injected into a cavity formed in the contact area between the mold and the movable side mold, is provided with a temperature control section in at least one of the fixed side mold or the movable side mold, which includes a flow channel through which a temperature control medium flows and a plurality of channel support columns that support a load in the flow channel.

Patent No. 4544398 Japanese Patent Application Publication No. 11-348045 Patent No. 6191356

In Patent Document 1, a cooling passage is formed with a uniform thickness from the cavity surface of the injection molding die, but a single cooling passage is formed to surround the side surface of the three-dimensional shape formed by the cavity surface. Therefore, the temperature of the cooling fluid flowing through the cooling passage changes as it flows, and uneven cooling is unavoidable.

In Patent Document 2, it is possible to form a desired temperature control circuit within the molded die, but the temperature control circuit is formed in a spiral shape around the cavity, which creates the problem of uneven cooling caused by temperature changes in the cooling medium flowing through the temperature control circuit. In Patent Document 3, flow channels through which the temperature control medium flows are formed in the fixed side die and the movable side die, but this creates the problem of uneven cooling caused by temperature changes while the temperature control medium flows through the flow channels.

When making eyeglass frame components by injection molding using resin material, the molding process is carried out with temperature control circuits placed on both sides of the molding gap formed in the injection mold, but uneven cooling of the eyeglass frame components can cause deformation, leading to an unavoidable loss of precision, and making it necessary to make fine adjustments when attaching eyeglass lenses.

Therefore, the present invention aims to provide an injection molding mold and an injection molding method using the same that can perform efficient and stable molding processing by forming a frame-shaped temperature control flow path in the frame-shaped region of the molding gap portion formed in the injection molding mold corresponding to the eyeglass frame member.

The injection molding mold according to the present invention is an injection molding mold that includes a cavity mold and a core mold formed by stacking and sintering metal powder material, and in which molten resin is injected into a molding gap portion formed in the abutment area of the cavity mold and the core mold, the molding directions of which are set to coincide and abut, and inside the cavity mold, frame-shaped cavity side temperature control flow paths are formed so as to overlap with the frame-shaped area of the molding gap portion at a predetermined interval in the molding direction, and inside the core mold, frame-shaped core side temperature control flow paths are formed so as to overlap with the frame-shaped area at a predetermined interval in the molding direction. Furthermore, the cavity-side temperature control flow path has a pair of cavity-side connection paths through which the temperature control fluid flows in and out on the side opposite the frame-shaped region, formed along the molding direction, and the core-side temperature control flow path has a pair of core-side connection paths through which the temperature control fluid flows in and out on the side opposite the frame-shaped region, formed along the molding direction, and the cavity-side connection paths and the core-side connection paths are arranged to face each other. Furthermore, an injection path that communicates with the molding gap is formed between the pair of frame-shaped regions, and a gas vent that communicates with the molding gap is formed on the side opposite the injection path of the frame-shaped region. Furthermore, the gas vent is formed of a porous material through which gas can flow.

The injection molding method according to the present invention is an injection molding method in which molten resin is injected into the molding cavity portion formed in the injection mold, and a temperature control fluid is caused to flow in opposite directions through the cavity-side temperature control flow path and the core-side temperature control flow path.

By having the above-mentioned configuration, the present invention forms temperature control flow paths inside the cavity mold and the core mold so that they overlap with the frame-shaped region corresponding to the frame portion of the eyeglass frame member, making it possible to efficiently control the temperature of the entire frame-shaped region from both sides and produce molded products of stable quality.

The frame portion of the eyeglass frame member is where the eyeglass lens is fitted, so it needs to be molded with high precision to match the three-dimensional shape of the peripheral portion of the eyeglass lens. However, as described above, by adjusting the temperature of the frame-shaped area corresponding to the frame portion from both sides, it is possible to carry out the preheating and cooling processes around the frame-shaped area in a stable temperature state, and the molding process can be carried out accurately and efficiently.

In addition, a pair of connection paths through which the temperature control fluid flows in and out are formed on the opposite side of the frame-shaped region, so that the effect of the temperature control fluid flowing through the connection paths on the temperature state of the frame-shaped region can be suppressed, and the temperature state caused by the temperature control fluid flowing through the temperature control flow path can be stably maintained.

In addition, the gas vent is made of a porous material that allows gas to flow through, so gas generated during processing can be smoothly exhausted, preventing the molding process from being affected by gas generation.

In addition, the temperature control fluid flows in opposite directions through the temperature control flow paths formed on both sides of the frame-shaped region, allowing the entire frame-shaped region to be set to a more uniform and stable temperature state.

FIG. 1 is an explanatory view showing a schematic configuration of an injection molding die according to the present invention, illustrating the internal structure in a see-through manner. FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, and is an explanatory diagram showing the internal structure in a see-through manner. FIG. 5 is a cross-sectional view taken along the line BB in FIG. 4, and is an explanatory diagram showing the internal structure in a see-through manner.

The following is a detailed description of the embodiments of the present invention. Note that the embodiments described below are preferred examples of the present invention, and therefore various technical limitations are imposed on them. However, the present invention is not limited to these forms unless otherwise specified in the following description to limit the invention.

Figure 1 shows a schematic configuration of an injection molding die according to the present invention, and is an explanatory diagram drawn to give a see-through view of the internal structure. The injection molding die for molding eyeglass frame members includes a cavity die 1 and a core die 2 (each shown by a dashed line), and in this example, the front portion of the eyeglass frame member that holds the eyeglass lens is molded from a resin material. Therefore, when the cavity die 1 and the core die 2 are in contact with each other, a molding gap portion C (shown by a thin line) corresponding to the front portion is formed in the contact area, and a pair of frame-shaped regions C1 and C2 are formed in the molding gap portion C corresponding to the rim portion into which the eyeglass lens is fitted.

Between the pair of frame-shaped regions C1 and C2, an injection path 40 communicating with the molding gap portion C is connected, and on the opposite side of the injection path 40 of the frame-shaped regions C1 and C2, gas venting sections 30a and 30b communicating with the molding gap portion C are formed. The injection path 40 is connected to an area corresponding to the bridge of the front portion, and molten resin material is injected from a supply device (not shown). The gas venting section 30a is extended from the end corresponding to the end piece of the frame-shaped region C1 toward the side of the injection mold, and is formed porous so that gas can flow through it. Therefore, gas generated when molten resin is injected into the molding gap portion C to perform injection molding is discharged to the outside, and the molten resin filled in the molding gap portion C is prevented from leaking. The gas venting section 30b is extended from the end corresponding to the end piece of the frame-shaped region C2 toward the side of the injection mold, and is formed porous so that gas can flow through it, similar to the frame-shaped region C1. This allows the generated gas to be discharged without leaking the molten resin filled in the molding cavity C.

The cavity mold 1 is integrally formed with the base plate 10 as shown by the dashed line, and frame-shaped cavity-side temperature control flow paths 11 and 12 (shown by thin lines) are formed inside. The cavity-side temperature control flow paths 11 and 12 are composed of pipes for circulating a temperature control fluid such as water adjusted to a predetermined temperature. The cavity-side temperature control flow path 11 is formed at a predetermined interval so as to overlap with the frame-shaped region C1 in a plan view, and the cavity-side temperature control flow path 12 is formed at a predetermined interval so as to overlap with the frame-shaped region C2 in a plan view.

A pair of cavity-side connection paths 13a and 13b through which the temperature control fluid flows in and out are formed on the cavity-side temperature control flow path 11 on the side opposite the frame-shaped region C1, and the cavity-side connection paths 13a and 13b are each connected to a pair of flow paths 15a and 15b formed in the base plate 10.

A pair of cavity-side connection paths 14a and 14b through which the temperature control fluid flows in and out are formed on the cavity-side temperature control flow path 12 on the side opposite the frame-shaped region C2, and the cavity-side connection paths 14a and 14b are each connected to a pair of flow paths 16a and 16b formed in the base plate 10.

The core mold 2 is integrally formed with the base plate 20 as shown by the dashed line, and frame-shaped core-side temperature control flow paths 21 and 22 (shown by thin lines) are formed inside. The core-side temperature control flow paths 21 and 22 are composed of pipes for circulating a temperature control fluid such as water adjusted to a predetermined temperature. The core-side temperature control flow path 21 is formed at a predetermined interval so as to overlap with the frame-shaped region C1 in a plan view, and the core-side temperature control flow path 22 is formed at a predetermined interval so as to overlap with the frame-shaped region C2 in a plan view.

A pair of core side connection paths 23a and 23b through which the temperature control fluid flows in and out are formed on the core side temperature control flow path 21 on the side opposite the frame region C1, and the core side connection paths 23a and 23b are each connected to a pair of flow paths 25a and 25b formed in the base plate 20.

A pair of core side connection paths 24a and 24b through which the temperature control fluid flows in and out are formed on the core side temperature control flow path 22 on the side opposite the frame region C2, and the core side connection paths 24a and 24b are each connected to a pair of flow paths 26a and 26b formed in the base plate 20.

In the above example, the frame-shaped cavity-side temperature control flow path 11 and the core-side temperature control flow path 21 are arranged so as to overlap on both the top and bottom of the frame-shaped region C1, and the frame-shaped cavity-side temperature control flow path 12 and the core-side temperature control flow path 22 are arranged so as to overlap on both sides of the frame-shaped region C2. Therefore, by circulating the temperature control fluid through the temperature control flow paths arranged on both the top and bottom of the frame-shaped region, the frame-shaped region can be efficiently adjusted to a stable temperature state.

The temperature control fluid is caused to flow in the cavity-side temperature control flow path and the core-side temperature control flow path arranged above and below the frame-shaped region in opposite directions to each other, thereby making the temperature state of the entire frame-shaped region more uniform. As shown by the arrows in FIG. 1, in the frame-shaped region C1, the temperature control fluid flows in the cavity-side temperature control flow path 11 from the flow path 15a to the cavity-side connection path 13a to the cavity-side temperature control flow path 11 to the cavity-side connection path 13b to the flow path 15b, and in the core-side temperature control flow path 21, the temperature control fluid flows in the flow path 25b to the core-side connection path 23b to the core-side temperature control flow path 21 to the core-side connection path 23a to the flow path 25a, and the flow directions are set in opposite directions to each other. Similarly, in the frame-shaped region C2, the flow directions are set in opposite directions to each other in the cavity-side temperature control flow path 12 and the core-type temperature control flow path 22.

The temperature of the temperature control fluid changes while flowing through the pipeline. For example, when the injection mold is preheated before the injection of the molten resin, the temperature of the temperature control fluid decreases while flowing through the pipeline, and when the injection mold is cooled after the injection of the molten resin, the temperature of the temperature control fluid increases while flowing through the pipeline. Therefore, the temperature of the temperature control fluid changes between the inlet side connecting path and the outlet side connecting path of the temperature control flow path, causing unevenness in the temperature state of the frame-shaped region. Therefore, by setting the inlet side and outlet side of the cavity side temperature control flow path and the core mold temperature control flow path to be in opposite directions, the temperature state of the frame-shaped region can be made more uniform, and the temperature states of both frame-shaped regions can be made almost the same. In addition, by performing such temperature adjustment, it is also easy to adjust the mold temperature by changing the temperature of the temperature control fluid.

The cavity and core dies used in such injection molding can be manufactured by a known metal powder sintering method. In the metal powder sintering method, first, slice data of a three-dimensional shape is created based on three-dimensional CAD data of the mold. Then, metal powder laid out at a specified thickness on a flat surface is irradiated with high-energy laser light based on the slice data to melt and solidify the metal powder, forming a cross-sectional shape. Such cross-sectional shapes can be stacked to form a three-dimensional shape. By manufacturing the mold in this way, it is possible to increase the degree of freedom of the piping through which the temperature-controlling fluid flows inside the mold, and it is possible to efficiently form piping that can adjust the temperature state inside the mold with high precision.

Figure 2 is a perspective view of the cavity mold, and Figure 3 is a cross-sectional view taken along line A-A in Figure 2, which is an explanatory diagram drawn to give a see-through view of the internal structure. The contact surface of the cavity mold 1 is formed in a convex curved shape to match the shape of the front portion, and the contact surface has a three-dimensional stepped portion formed in correspondence with the molding gap portion C. Inside the cavity mold 1, a frame-shaped cavity-side temperature control flow path 11 is formed at a predetermined distance from the frame-shaped region C1, and a frame-shaped cavity-side temperature control flow path 12 is formed at a predetermined distance from the frame-shaped region C2.

When the cavity mold 1 is manufactured by the metal powder sintering method, metal powder is laid to a predetermined thickness on the upper surface of the base plate 10, and laser light is irradiated to stack the powder in the vertical direction to form the mold. Therefore, each cavity side temperature control flow path can be accurately formed at a predetermined interval in the molding direction for each frame-shaped region, and can be accurately formed so as to overlap when viewed from the molding direction. Furthermore, when forming a frame-shaped temperature control flow path that intersects with the molding direction, the cross-sectional shapes 11a and 12a of the temperature control flow paths 11 and 12 can be formed into a stable shape by forming them into an approximately hexagonal shape with both sides along the molding direction and both ends of the upper side cut out diagonally.

A pair of cavity-side connection paths 13a and 13b are formed facing downward in the cavity-side temperature control flow path 11, and a pair of cavity-side connection paths 14a and 14b are formed facing downward in the cavity-side temperature control flow path 12. A pair of flow paths 15a and 15b and a pair of flow paths 16a and 16b are formed in the base plate 10 from both sides by drilling or the like, and the flow paths 15a and 15b are connected to the cavity-side connection paths 13a and 13b, respectively, and the flow paths 16a and 16b are connected to the cavity-side connection paths 14a and 14b, respectively.

When constructing such pipelines, each flow passage is formed in the base plate 10, and each cavity-side connection passage is then shaped to match the top opening of each flow passage, allowing the interconnected pipelines to be formed accurately.

Figure 4 is a perspective view of the core mold, and Figure 5 is a cross-sectional view taken along line B-B of Figure 4, which is an explanatory diagram drawn to give a perspective view of the internal structure. The contact surface of the core mold 2 is formed in a concave curved shape to match the three-dimensional shape of the front portion, and the contact surface has a step portion formed in a three-dimensional shape corresponding to the molding gap portion C. A pair of frame-shaped regions C1 and C2 of the molding gap portion C are formed with band-shaped gas vent portions 30a and 30b extending outward, respectively. Inside the core mold 2, a frame-shaped core-side temperature control flow path 21 is formed at a predetermined interval from the frame-shaped region C1, and a frame-shaped core-side temperature control flow path 22 is formed at a predetermined interval from the frame-shaped region C2.

When the core mold 2 is manufactured by the metal powder sintering method, similar to the cavity mold 1, metal powder is laid in a predetermined thickness on the upper surface of the base plate 20 and laser light is irradiated to stack and shape in the vertical direction. Therefore, each core side temperature control flow passage can be accurately formed at a predetermined interval in the molding direction for each frame-shaped region, and it is possible to accurately form them so that they overlap when viewed from the molding direction. Since the core mold 2 is stacked and shaped in the vertical direction like the cavity mold 1, when the two are abutted, the molding directions match.

When forming a frame-shaped temperature control flow path that intersects with the forming direction, the cross-sectional shapes 21a and 22a of the temperature control flow paths 21 and 22 can be formed into a stable shape by forming them into an approximately hexagonal shape with both sides along the forming direction and both ends of the upper side cut out diagonally.

For the gas venting sections 30a and 30b, a porous member is formed by layering and sintering metal powder at a low density separately from the core mold to match the shape of the gas venting section. The formed core mold is then partially cut by cutting to match the position of the gas venting section, and the gas venting section is then formed by fitting and embedding a porous member at the cut position. By forming the gas venting section in a porous form, it is possible to ensure air permeability between the molding gap portion C and the outside. In addition, for the connection portions between each gas venting section and each frame-shaped region, the molding density is increased to a level that prevents the molten resin filled in the molding gap portion C from leaking out, making it possible to perform injection molding reliably.

In the core-side temperature control flow path 21, a pair of core-side connection paths 23a and 23b are formed facing downward, and in the core-side temperature control flow path 22, a pair of core-side connection paths 24a and 24b are formed facing downward. In the base plate 20, a pair of flow paths 25a and 25b and a pair of flow paths 26a and 26b are formed from both sides by drilling or the like, and the flow paths 25a and 25b are connected to the core-side connection paths 23a and 23b, respectively, and the flow paths 26a and 26b are connected to the core-side connection paths 24a and 24b, respectively.

When constructing such pipelines, each flow passage is formed in the base plate 20, and each core-side connection passage is then shaped to match the top opening of each flow passage, allowing the interconnected pipelines to be formed accurately.

The cavity mold shown in Figure 2 was molded on a steel base plate (175 mm long x 225 mm wide x 30 mm thick) using a metal powder sintering molding device (LUMEX Avance-25, manufactured by Matsuura Machine Works, Ltd.). Maraging steel (average particle size 45 μm, Matsuura Maraging II, manufactured by Matsuura Machine Works, Ltd.) was used as the metal powder. The molded cavity mold was formed to a size of 100.3 mm long x 200.3 mm wide x 19.4 mm thick, and the contact surface including the molding gap portion C was then precisely machined by cutting.

The core mold shown in Figure 4 was molded on a base plate (175 mm long x 225 mm wide x 20 mm thick) made of steel using the same metal powder sintering molding device as the cavity mold. The same maraging steel as the cavity mold was used as the metal powder. The molded core mold was formed to a size of 100.3 mm long x 200.3 mm wide x 20 mm thick, and the contact surface including the molding gap portion C was then precisely machined by cutting. For the gas vent portion, a porous member was prepared that was molded from the same metal powder as the cavity mold, and fine grooves corresponding to the gas vent portion were formed in the core mold by cutting, and the porous member was fitted into the fine grooves that were formed and fixed.

The resulting cavity mold and core mold were fixed together with their contact surfaces in close contact, and a preheating treatment was performed by circulating a temperature control fluid (water, 82°C) through the temperature control flow path. After 10 minutes of preheating, the mold surface temperatures in both frame-shaped regions were stable at around 47°C with an almost uniform temperature distribution. The temperature control fluid circulated in the same direction through the temperature control flow paths arranged in parallel in each mold, while the temperature control fluid circulated in opposite directions in the cavity mold and core mold, resulting in an almost uniform temperature distribution in both frame-shaped regions.

Next, polyamide resin (manufactured by Daicel-Evonik) was molten at a high temperature (260°C to 280°C) and injected through an injection port provided in the cavity mold to fill the molding gap. A temperature-control fluid was continuously circulated through the temperature-control flow path to perform a cooling process for 20 seconds. 60 seconds after the mold was opened, the mold surface temperature had dropped to 46°C to 48°C, and the cooling process was able to be performed almost uniformly over the entire frame-shaped area.

The eyeglass frame components obtained after demolding after opening the mold had been precisely molded with an almost uniform shrinkage rate in the rim area, and no defects such as gas pockets were found. This enabled us to consistently produce high-quality molded products.

It was also confirmed that preheating and cooling processes can be carried out efficiently, which is effective in shortening processing time and improving productivity.

Comparative Example
The cavity mold and the core mold were formed by cutting steel material. The contact surfaces of the cavity mold and the core mold were cut to form a molding gap portion similar to that of the examples, and a pair of temperature control flow paths were formed by drilling a straight pipe line through the lower side of the molding gap portion. The pipe line was configured so that the temperature control fluid was circulated through one temperature control flow path and then flowed into the other temperature control flow path.

The cavity mold and core mold were fixed together with their contact surfaces in close contact, and a preheating process was performed by circulating a temperature control fluid (water, 82°C) through the temperature control flow path. During the preheating process, even after 20 minutes, the mold surface temperature in the frame-shaped region was 43°C to 54°C, and there were unevenness in the temperature distribution, and the temperature was not uniform. This unevenness in the temperature distribution occurs because the temperature control fluid is circulated, so the temperature of the frame-shaped region closer to the inlet tends to be higher and the temperature of the frame-shaped region further away tends to be lower, resulting in temperature unevenness.

Next, similar to the example, polyamide resin was molten at high temperature and injected through an injection port provided in the cavity mold to fill the molding gap. A temperature control fluid was continuously circulated through the temperature control flow path to perform a cooling process for 35 seconds. 60 seconds after the mold was opened, the mold surface temperature was 50°C to 55°C, and the cooling process for the entire frame-shaped area was performed in an uneven state.

The eyeglass frame parts obtained after demolding after opening the mold were found to have been molded with uneven shrinkage in the rim area, low precision, and defective areas such as gas pockets.

C: Molding gap portion, C1, C2: Frame-shaped region, 1: Cavity mold, 10: Base plate, 11, 12: Cavity side temperature control flow path, 13a, 13b, 14a, 14b: Cavity side connection path, 15a, 15b, 16a, 16b: Flow path, 2: Core mold, 20: Base plate, 21, 22: Cavity side temperature control flow path, 23a, 23b, 24a, 24b: Cavity side connection path, 25a, 25b, 26a, 26b: Flow path, 30a, 30b: Gas vent, 40: Injection port

Claims (5)

An injection molding mold that includes a cavity mold and a core mold formed by stacking and sintering metal powder material, and in which molten resin is injected into a molding gap portion formed in the abutment area of the cavity mold and the core mold corresponding to an eyeglass frame member, the cavity mold and the core mold are set so that they abut with the same molding direction, and inside the cavity mold, frame-shaped cavity side temperature control flow paths are formed so as to overlap with the frame-shaped area of the molding gap portion at a predetermined interval in the molding direction, and inside the core mold, frame-shaped core side temperature control flow paths are formed so as to overlap with the frame-shaped area at a predetermined interval in the molding direction. The injection molding die according to claim 1, wherein the cavity-side temperature control flow passage has a pair of cavity-side connection passages along the molding direction through which the temperature control fluid flows in and out on the side opposite the frame-shaped region, and the core-side temperature control flow passage has a pair of core-side connection passages along the molding direction through which the temperature control fluid flows in and out on the side opposite the frame-shaped region, and the cavity-side connection passages and the core-side connection passages are arranged to face each other. The injection molding die according to claim 1 or 2, wherein an injection passage that communicates with the molding gap is formed between the pair of frame-shaped regions, and a gas vent that communicates with the molding gap is formed on the opposite side of the frame-shaped region from the injection passage. The injection molding die according to claim 3, wherein the gas vent is formed of a porous material through which gas can flow. An injection molding method for injecting molten resin into the molding cavity portion formed in the injection mold according to any one of claims 1 to 4, in which a temperature control fluid is caused to flow in the cavity-side temperature control flow path and the core-side temperature control flow path in opposite directions.

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