Injection-molding mold

Abstract

To suppress mold wear to the utmost even when injection molding a resin containing a fiber reinforcing material and by this, to enable continuous implementation of production of injection molded works at low cost.SOLUTION: This injection-molding mold 11 includes a mold cavity 13 becoming a molding space of an injection molded work W, a runner 15 connected to the mold cavity 13, and a gate 16 positioned at the tip of the runner 15 and open to the mold cavity 13. Cross sections of the runner 15 and the gate 16 both have flat shapes, and a longitudinal dimension L1 of the gate 16 is larger than a cross section longitudinal dimension W2 of the runner 15.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an injection mold.

Background Art

[0002] As is well known, injection-molded resin products are applied not only to small parts but also to large and strength-required parts such as panel-shaped members that form part of an automobile body.

[0003] In addition, in this type of molded product, for the purpose of improving strength or dimensional stability, resin blended with fibrous reinforcing materials such as carbon fiber and glass fiber is also injection-molded (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in this type of injection molding, there is a problem that the molding surface of the injection mold is worn by the fibrous reinforcing material contained in the injection material. That is, since the fibrous reinforcing material such as glass fiber contained in the injection material exhibits high rigidity, with injection, the fibrous reinforcing material in the injection material collides with the inner surface of the runner part, the inner surface of the gate part, or the inner surface of the mold (molding surface) near the gate part, so that the above-mentioned inner surface and molding surface tend to be worn easily. Therefore, by continuing injection molding, the wear of the runner part and the gate part progresses, and the shape of the gate part changes, which may change the flow pattern of the injection material. Depending on the change in the flow pattern, the occurrence of weld lines, which may cause problems, and ultimately molding defects may occur. Alternatively, the wear of the molding surface near the gate part may transfer the wear marks to the surface of the injection molded product, which may also lead to a deterioration in the appearance quality.

[0006] When the mold is worn out as described above, it is necessary to repair the worn part. Naturally, this repair requires a great deal of time. In addition, in order to avoid a situation where production stops during the repair, it is necessary to separately prepare a spare mold, which is a factor in cost increase.

[0007] In view of the above circumstances, in this specification, even when injecting a resin containing a fibrous reinforcing material, it is an object to be solved to suppress mold wear as much as possible and thereby enable continuous production of injection-molded products at low cost.

Means for Solving the Problems

[0008] The solution to the above problems is achieved by an injection mold according to the present invention. That is, this mold is an injection mold including a cavity that serves as a molding space for an injection-molded product, a runner connected to the cavity, and a gate located at the tip of the runner and opening into the cavity. The cross-section of the runner and the gate are both flat, and the longitudinal dimension of the gate is characterized in that it is larger than the longitudinal dimension of the cross-section of the runner.

[0009] Conventionally, regarding the flow mechanism of the injection material (resin) in injection molding, since a skin layer of resin solidified on the inner surface of the mold is formed immediately after the start of injection, it has been considered that the inner surface of the mold is protected from the fibrous reinforcing material by the skin layer when injecting a resin containing a fibrous reinforcing material. Regarding this point, the present inventor has conducted intensive studies through flow analysis and actual machine verification. As a result, a skin layer is not formed on the entire inner surface of the mold immediately after the start of injection. Depending on the flow rate of the injection material, the higher the flow rate, the less likely a skin layer is to be formed, and the more likely wear of the inner surface of the mold by the fibrous reinforcing material occurs at locations where a skin layer is less likely to be formed. In other words, the present inventor has obtained the finding that there is a certain correlation between the degree of wear by the fibrous reinforcing material and the flow rate of the injection material at the worn location.

[0010] The present invention has been made based on the above findings. Aiming to reduce the flow velocity of the injection material in the vicinity of the gate, which is likely to exhibit a relatively high flow velocity distribution, the longitudinal dimension of the flat gate is made larger than the cross-sectional longitudinal dimension of the corresponding runner. By configuring in this way, it is possible to relatively reduce the flow velocity immediately after injection from the gate among the inner surfaces of the mold. Therefore, it becomes possible to actively form a skin layer on the inner surface of the mold located in the vicinity of the gate and effectively protect the inner surface of the mold from the fibrous reinforcing material. Further, even when the skin layer is not formed, since the velocity of the fibrous reinforcing material is also reduced due to the decrease in the flow velocity, the collision with the inner surface of the mold is also alleviated. Due to the above actions, the wear of the inner surface of the mold is suppressed, so the frequency of repair can be reduced. Also, if the wear of the inner surface of the mold is suppressed, the time required for repair can be shortened, so the repair can be completed within the operating period, and thus a spare mold is not required. From the above, according to the injection mold according to the present invention, it is possible to suppress the total cost related to the continuous implementation of injection molding. Further, since the gate has a flat shape, even when the cross-sectional area of the gate increases by increasing its longitudinal dimension, it is possible to relatively easily cut the solidified part in the runner and the injection molded product at their boundary (gate). Therefore, it is possible to avoid a situation where a part of the solidified part in the runner remains in the injection molded product and ensure productivity.

[0011] Further, in the injection mold according to the present invention, the runner may have a shape in which its cross-sectional longitudinal dimension increases as it approaches the gate on the tip side of the runner.

[0012] By making the tip side of the runner have the above-described shape, the injection material can be diffused over a wider range. Therefore, it becomes possible to further reduce the flow velocity. Also, by adopting the above shape, the fibrous reinforcing material also diffuses over a wide range, so it becomes possible to more effectively suppress the wear of the inner surface due to the collision with the inner surface of the mold.

[0013] Further, in the injection mold according to the present invention, the cavity has a shape corresponding to the panel-shaped member, and the gate may open at a portion corresponding to a region on the non-design surface side of the edge of the panel-shaped member among the molding surfaces constituting the cavity. Further, in this case, the portion corresponding to the corner formed between the edge and the panel-shaped member body by bending the edge to the non-design surface side may be formed into an R shape.

[0014] In the case of a panel-shaped member in which the injection-molded product has a design surface, the portion where the gate can be provided may be limited to the region on the non-design surface side as described above. In this case, the distance from the gate to the inner surface of the mold facing the gate (the portion of the molding surface that molds the design surface) becomes very close to the thickness dimension of the panel-shaped member, so there is concern about wear of the molding surface due to the fibrous reinforcing material. In this regard, for example, if the edge is bent to the non-design surface side as described above to increase the distance from the gate to the molding surface facing the gate, wear of the molding surface due to the fibrous reinforcing material can be suppressed. On the other hand, however, a corner is inevitably formed between the edge and the panel-shaped member body by bending the edge. This corner becomes a corner portion on the molding surface of the injection mold and is located at a position visible from the gate. Therefore, for example, when the fibrous reinforcing material in the resin is injected linearly toward the corner portion, the risk of severe wear of the corner portion due to the collision with the fibrous reinforcing material increases. In contrast, by previously forming the corner portion of the molding surface corresponding to the corner portion of the injection-molded product described above into an R shape, the frequency of collision between the fibrous reinforcing material and the corner portion is reduced, or the collision is mitigated. Therefore, according to this configuration, it is possible to suppress wear of the molding surface during injection.

Advantages of the Invention

[0015] As described above, according to the injection mold according to the present invention, even when injecting a resin containing a fibrous reinforcing material, it is possible to suppress the wear of the mold as much as possible, so that it is possible to continuously produce injection-molded products at low cost.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

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Figure 5

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Figure 8

Mode for Carrying Out the Invention

[0017] Hereinafter, the content of an injection mold according to an embodiment of the present invention and an injection molding apparatus including this mold will be described based on the drawings.

[0018] FIG. 1 shows a cross-sectional view of an injection molding apparatus 10 according to an embodiment of the present invention. This injection molding apparatus 10 mainly includes an injection mold 11 for obtaining an injection molded product of a predetermined shape, and an injection machine 12 for injecting and supplying a predetermined injection material to the injection mold 11.

[0019] As the material to be injected by the injection machine 12, a resin having an arbitrary and known composition can be used. For example, in the case of a relatively large panel-shaped member in the form of a thin plate as in the present embodiment and when high strength is required, a resin obtained by blending a predetermined amount of fibrous reinforcing materials such as glass fibers and carbon fibers with a known base resin such as a thermoplastic resin can be suitably used as the injection material. Note that the dimensions (longitudinal dimension, aspect ratio) of the fibrous reinforcing material can be set within an arbitrary range as long as it functions as a reinforcing material for the resin to be injected.

[0020] The injection mold 11 for injection molding includes a main body of the injection mold 11 for injection molding, a cavity 13 formed inside the main body and serving as a molding space for the injection molded product, a sprue 14 connected to the nozzle of the injection machine 12, a runner 15 connecting the sprue 14 and the cavity 13, and a gate 16 located at the tip of the runner 15 and opening into the cavity 13. In the present embodiment, the injection mold 11 for injection molding is a mold for injection molding a panel-shaped member, and the cavity 13 has a shape corresponding to the panel-shaped member that becomes the injection molded product (see FIG. 2). In this illustrated example, an injection mold 11 for injection molding a back door inner as the panel-shaped member is exemplified.

[0021] Also, in this case, a plurality of runners 15 are disposed at predetermined positions of the cavity 13 via the gate 16. In the present embodiment, as shown in FIG. 2, a plurality of runners 15 and gates 16 are provided in a portion of the cavity 13 corresponding to the region on the non-design surface W1 side of the edge Wa of the panel-shaped member W. In this illustrated example, one or more runners 15 and gates 16 are also provided in a portion corresponding to the central portion Wb on the non-design surface W1 side of the panel-shaped member W.

[0022] FIG. 3 shows a cross-sectional view (A-A cross-sectional view in FIG. 2) of the periphery of the gate 16 of the injection mold 11 shown in FIG. 2. FIG. 5 conceptually shows the three-dimensional shapes of the periphery of the gate 16 shown in FIG. 3, that is, the runner 15 and the cavity 13 in the vicinity of the gate 16. Further, FIG. 6 is a view of the gate shown in FIG. 3 as seen from the opening direction thereof (a view as seen from the direction of arrow B in FIG. 3). As shown in these figures (particularly FIG. 6), the gate 16 has a flat shape. In the present embodiment, the gate 16 opens at a portion corresponding to the edge Wa of the cavity 13 such that the direction along the edge Wa of the panel-shaped member W to be an injection-molded product coincides with the longitudinal direction of the gate 16 (see FIGS. 2 and 3).

[0023] At least the tip portion 15a of the runner 15 has a flat shape similar to that of the gate 16 (see FIG. 5). Further, the longitudinal direction of the flat tip portion 15a coincides with the longitudinal direction of the gate 16.

[0024] At this time, the aspect ratio, that is, the ratio L1 / S1 of the longitudinal dimension L1 to the lateral dimension S1 of the gate 16 is set to, for example, 10 or more, preferably 20 or more.

[0025] Here, the longitudinal dimension d1 of the cross section of the tip portion 15a of the runner 15 is set to a value larger than the longitudinal dimension d2 of the cross section of the runner 15 main body (see FIG. 5). In the present embodiment, the tip portion 15a of the runner 15 has a shape such that the longitudinal dimension d1 of its cross section increases as it approaches the gate 16. In this case, the longitudinal dimension d1 of the portion of the tip portion 15a of the runner 15 that connects to the gate 16 coincides with the longitudinal dimension L1 of the gate 16.

[0026] Regarding the shape of the cavity 13, in the present embodiment, at least a portion of the edge Wa of the panel-shaped member W where the runner 15 (gate 16) is provided is bent toward the non-design surface W1 side (see FIG. 3). In this way, when the edge Wa of the panel-shaped member W formed by the cavity 13 is bent toward the non-design surface W1 side, a corner portion Wc is formed between the edge Wa and the main body of the panel-shaped member W (see FIG. 4). This corner portion Wc becomes a corner portion 17a on the molding surface 17 of the corresponding cavity 13. This corner portion 17a is disposed at a position visible from the gate 16 (see FIG. 3 in each case).

[0027] In the present embodiment, the corner portion 17a of the molding surface 17 disposed at the above-described position has an R shape (see FIG. 3).

[0028] Next, the operation and effect of the injection mold 11 having the above-described configuration will be described based on a comparison with a conventional injection mold 21 (see FIGS. 7 and 8).

[0029] For example, as shown in FIGS. 7 and 8, when resin mixed with a fibrous reinforcing material is injected by an injection machine 12 at an injection pressure and injection amount (flow rate) that are considered to be required for normal injection molding using an injection mold 21 having a runner 22 having a conventional shape with a constant cross-sectional longitudinal dimension, the resin passes through the gate 23 at the same speed as when flowing through the inside of the runner 22 and is injected into the cavity 24. In this case, a skin layer R formed by solidification of the resin is formed on the inner surface (molding surface 25, inner surfaces of the runner 22 and the gate 23) of the injection mold 21 immediately after the start of injection. However, the higher the flow velocity of the injection material, the more difficult it is to form the skin layer R. In FIG. 7, for example, it is difficult to form the skin layer R in a region near the gate 23 or a region facing the gate 23 on the molding surface 25. Since regions where it is difficult to form the skin layer R are more likely to be attacked by the fibrous reinforcing material, there is a tendency that the inner surface of the mold is more likely to be worn by the fibrous reinforcing material in regions where it is difficult to form the skin layer R as described above.

[0030] In contrast, in the injection mold 11 according to the present embodiment, aiming to reduce the flow velocity of the injection material in the vicinity of the gate 16, which is likely to exhibit a relatively high flow velocity distribution, the longitudinal dimension L1 of the flat gate 16 is made larger than the cross-sectional longitudinal dimension d2 of the corresponding runner 15 (runner 15 main body). By configuring in this way, it is possible to relatively reduce the flow velocity particularly in the vicinity of the gate 16 on the inner surface of the mold 11. Therefore, it becomes possible to actively form the skin layer R in the said area | region and to protect the inner surface of the mold 11 from a fibrous reinforcement effectively. Moreover, even when the skin layer R is not formed, since the speed of the fibrous reinforcement is also reduced due to the reduction of the flow velocity, the collision with the inner surface of the mold 11 is also alleviated. From the above actions, the wear of the inner surface of the mold 11 is suppressed, so that the frequency of repair can be reduced. Further, if the wear of the inner surface of the mold 11 is suppressed, the time required for repair can be shortened, so that the repair can be completed within the operating period, and thus a spare mold is not required. From the above, according to the injection mold 11 according to the present embodiment, it is possible to suppress the total cost related to the continuous implementation of injection molding. Further, since the gate 16 has a flat shape, even when the cross-sectional area of the gate 16 increases by increasing its longitudinal dimension L1, it is possible to relatively easily cut the solidified part by the runner 15 and the injection molded product (here, the panel-shaped member W) at its boundary (the part of the gate 16). Therefore, it is possible to avoid a situation where a part of the solidified part by the runner 15 remains in the injection molded product and ensure productivity.

[0031] Further, in the present embodiment, since the tip portion 15a of the runner 15 has a shape in which the cross-sectional longitudinal dimension d1 increases as it approaches the gate 16 on the tip side of the runner 15, the injection material can be diffused over a wider range. Therefore, it is possible to further reduce the flow velocity. Further, by adopting the above shape, the fibrous reinforcement is also diffused over a wide range, so that it is possible to more effectively suppress the wear of the inner surface due to the collision with the inner surface of the mold 11.

[0032] In the present embodiment, the cavity 13 is formed in a shape corresponding to the panel-shaped member W, and the gate 16 is opened in a portion corresponding to the region on the non-design surface W1 side of the edge Wa of the panel-shaped member W among the molding surfaces 17 constituting the cavity 13 (see FIGS. 2 to 4). Further, in this case, the corner portion 17a corresponding to the corner portion Wc generated between the edge portion Wa and the main body of the panel-shaped member W by bending the edge portion Wa toward the non-design surface W1 side is formed in an R shape (see FIG. 3).

[0033] As described above, when the corner portion Wc is generated between the edge portion Wa and the main body of the panel-shaped member W by bending the edge portion Wa of the panel-shaped member W toward the non-design surface W1 side, the corner portion 25a corresponding to this corner portion Wc is provided on the molding surface 25 of the mold 21 (see FIG. 7). Since this corner portion 25a is located at a position visible from the gate 23 due to its structure, for example, when the fibrous reinforcing material in the resin is injected linearly from the gate 23 toward the corner portion 25a, the risk of severe wear of the corner portion 25a due to the collision with the fibrous reinforcing material increases. On the other hand, in the present embodiment, since the corner portion 17a of the molding surface 17 is formed in an R shape (see FIG. 3), the collision frequency between the fibrous reinforcing material and the corner portion 17a decreases, or the collision is mitigated. Therefore, according to this configuration, it is possible to suppress the wear of the molding surface 17 during injection.

[0034] As described above, although one embodiment of the present invention has been described, the injection mold according to the present invention can adopt configurations other than the above as long as it does not deviate from the gist thereof.

[0035] For example, in the above embodiment, the case where the shape of the tip side (tip portion 15a) of the runner 15 is such that the cross-sectional longitudinal dimension d1 increases as it approaches the gate 16 is illustrated, but of course, it is not limited to this. As long as the longitudinal dimension L1 of the gate 16 is larger than the cross-sectional longitudinal dimension d2 of the runner 15 main body and the inside of the cavity 13 can be filled with the injection material (resin containing a fibrous reinforcing material) by injection, the tip side of the runner 15 can take any form.

[0036] Also, there are no particular restrictions on the short-side dimension S1 of the gate 16. For example, as long as the operator can manually separate the solidified portion of the runner 15 and the injection molded product at the gate 16 after molding, the short-side dimension S1 can be set to any size.

[0037] Also, the positional relationship between the gate 16 and the corner 17a is arbitrary. For example, from the perspective of minimizing the collision of the fibrous reinforcing material with the corner 17a, a surplus portion Wd may be provided on the corner 17a side of the edge Wa having a shape bent toward the non-design surface W1 side with respect to the gate 16, more precisely, between the gate 16 and the corner 17a (see FIG. 4). By providing the surplus portion Wd at a position adjacent to the gate 16 of the injection molded product (panel-shaped member W) in this way, a space 18 corresponding to this surplus portion Wd is formed between the gate 16 and the corner 17a. As a result, the corner 17a can be moved away from the gate 16 by the amount of the space 18, and thus, with this configuration, it is also possible to reduce the collision of the fibrous reinforcing material with the corner 17a.

[0038] In the above description, the case of injection molding the panel-shaped member W as an injection molded product has been exemplified, but it goes without saying that the injection mold according to the present invention can be applied to injection molded products having forms other than the panel-shaped member W.

Explanation of Reference Numerals

[0039] 10 Injection molding apparatus 11 Injection mold 12 Injection machine 13 Cavity 14 Sprue 15 Runner 15a Tip 16 Gate 17 Molding surface 17a Corner 18 Space 21 Injection mold 22 Runner 23 Gate 24 Cavity 25 Molding surface 25a Corner L1 Dimension in the longitudinal direction R Skin layer S1 Dimension in the short transverse direction d1, d2 Cross-sectional dimension in the longitudinal direction (runner) W Panel-shaped member W1 Non-design surface W2 Design surface Wa Edge Wb Central part Wc Corner Wd Excess material part

Claims

Claim 1 In an injection mold comprising a cavity serving as a molding space for an injection molded product, a runner connected to the cavity, and a gate located at the tip of the runner and opening into the cavity, both the cross-section of the runner and the gate have a flat shape, an injection mold, characterized in that the longitudinal dimension of the gate is larger than the longitudinal dimension of the cross-section of the runner.

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