Injection mold capable of eliminating weld lines on surface of plastic part

Abstract

The invention discloses an injection mold capable of eliminating weld lines on the surface of a plastic part. The injection mold comprises a fixed mold fixing plate, a hot runner plate, a fixed mold, a movable mold, mold feet and a movable mold fixing plate. In a mold closing state, a mold cavity is formed between the fixed mold and the movable mold; a hot runner assembly is mounted on the hot runner plate; the hot runner assembly comprises a pouring runner; the pouring runner is communicated with the mold cavity through a pouring gate; a blind runner is arranged on the injection molding surface of the movable mold; and the blind runner extends to the weld line position from the sprue. In the injection molding process, when molten plastic flows in the mold cavity, the flowing direction and the flowing speed can be changed under the action of the blind runner, so that the molten plastic is firstly filled at the position where weld lines can be generated, and meanwhile, gas in the mold cavity can be sequentially pushed to the exhaust channel of the sealed edge until the gas is exhausted; therefore, weld lines on the surface of the plastic part can be eliminated, the influence of the weld lines on the appearance and performance of the plastic part is reduced, and the product percent of pass is improved.

Description

Technical Field

[0001] The invention relates to the technical field of injection molds, and in particular to an injection mold capable of eliminating weld lines on the surface of a plastic part. Background Art

[0002] Injection molding has the advantages of fast production speed and high efficiency. It can realize automated operation, has a wide variety of patterns and colors, and can be shaped from simple to complex, and from large to small. In addition, the product size is precise, the product is easy to update, and it can form parts with complex shapes. It has been widely used in many molding and processing fields.

[0003] During the injection molding of plastic products, the mold is closed and the molten plastic is injected into the mold cavity through the gate; after the plastic fills the mold cavity, the desired product is formed. Some plastic product structures are usually provided with multiple holes or concave inside, which makes the molten plastic flow to various places in the fixed mold in different directions when entering the mold cavity, and finally converge; and in the convergence process, due to the different flow directions of the two molten plastics, the injection molded products are prone to produce weld lines at the confluence, which has appearance defects and leads to rejection during product delivery, resulting in economic losses; and the weld line is the trace formed after the two melts meet and cool. Usually, the mechanical properties and surface quality of the product are not good where the weld line appears. When the product is at high temperature for a long time, there will be a risk of cracking at the weld line. This requires the design of a special mechanism to solve it. The conventional solution to the weld line is to add exhaust inserts for exhaust. However, the effect is not good. In case of severe air entrapment, even if the exhaust insert is added, the problem of the weld line cannot be completely solved. It can only be improved, but it also increases the mold cost and production cycle. Summary of the invention

[0004] The present application provides an injection mold that can eliminate weld lines on the surface of plastic parts, so as to overcome the above-mentioned problems existing in the prior art. The injection mold that can eliminate weld lines on the surface of plastic parts of the present application is provided with a dark runner on the injection molding surface of the movable mold, and the dark runner is designed in combination with the gate layout. During the injection molding process, when the molten plastic flows in the mold cavity, it will change the flow direction and flow speed under the action of the dark runner, so that the molten plastic will first fill the position where the weld line will be generated, and at the same time, the gas in the mold cavity will be pushed to the exhaust channel at the edge of the sealing mold in an orderly manner until the gas is discharged, thereby eliminating the weld line on the surface of the plastic part, reducing the influence of the weld line on the appearance and performance of the plastic part, and improving the product qualification rate; and the present application can be realized only by optimizing the movable mold structure, without the need to set up additional accessories, and the production cost is low.

[0005] The technical solution of the present application is: an injection mold capable of eliminating weld lines on the surface of a plastic part, comprising a fixed mold assembly and a movable mold assembly; the fixed mold assembly comprises a fixed mold fixing plate, a hot runner plate and a fixed mold arranged in sequence; the movable mold assembly comprises a movable mold, a mold foot and a movable mold fixing plate arranged in sequence; in a mold closing state, a mold cavity is formed between the fixed mold and the movable mold; an ejector plate is provided between the movable mold and the movable mold fixing plate, and an ejector mechanism is provided on the ejector plate for ejecting the injection molded part from the injection mold; a hot runner assembly is installed on the hot runner plate, and a pouring runner is provided in the hot runner assembly; the pouring runner is connected to the mold cavity through a gate; a dark runner for diversion is provided on the injection molding surface of the movable mold; the dark runner extends from the gate to the weld line position, so that the molten plastic can flow rapidly along the dark runner and fill the weld line position before the two streams merge.

[0006] Compared with the prior art, the injection mold of the present application which can eliminate the weld lines on the surface of plastic parts is provided with a dark runner on the injection molding surface of the movable mold, and the dark runner is designed in combination with the gate layout, which can guide the flow direction of the molten plastic and improve its flow state; during the injection molding process, when the molten plastic flows in the mold cavity, it will change the flow direction and flow speed under the action of the dark runner, so that the molten plastic will first fill the position where the weld line will be generated, so that the merged plastics can be better integrated, and at the same time, the gas in the mold cavity will be pushed orderly to the exhaust channel at the sealing edge until the gas is discharged, thereby eliminating the weld lines on the surface of the plastic parts, reducing the impact of the weld lines on the appearance and performance of the plastic parts, and improving the product qualification rate; and the present application can be achieved only by optimizing the movable mold structure, without the need to set up additional accessories, reducing the auxiliary equipment for machine adjustment, and having a low production cost.

[0007] As an optimization, in the aforementioned injection mold capable of eliminating weld lines on the surface of plastic parts, the dark runner is in a straight line shape. Thus, after the molten plastic enters the mold cavity, it can fill the weld line position more evenly and quickly. Furthermore, the dark runner is an arc-shaped groove, which is easy to process.

[0008] As an optimization, in the aforementioned injection mold that can eliminate the weld line on the surface of the plastic part, the ejection mechanism includes an inclined ejector rod; the lower end of the inclined ejector rod is slidably arranged on the ejector plate, and the upper end is provided with an inclined ejector block; the upper end surface of the inclined ejector block is flush with the injection molding surface of the movable mold, and part of the dark flow channel is located on the upper end surface of the inclined ejector block. As a result, exhaust can be directly carried out through the assembly gap between the inclined ejector block and the movable mold without the need to open an additional exhaust channel, which reduces the difficulty of mold processing and only requires the conventional inclined ejector rod assembly method. Furthermore, an exhaust groove is provided between the lower end surface of the inclined ejector block and the movable mold. As a result, during the injection molding process, the gas inside the mold cavity can flow to the exhaust groove for storage. When the plastic part is ejected by the inclined ejector rod, the gas is discharged from the exhaust groove into the air, avoiding the problem of trapped air.

[0009] As an optimization, in the aforementioned injection mold capable of eliminating weld lines on the surface of plastic parts, a plurality of cooling pipes are provided in the fixed mold. Thus, the heat dissipation efficiency of the fixed mold can be improved, and uneven shrinkage of the plastic parts during the cooling process due to excessive heat can be avoided, causing warping and deformation, and the cooling time of the plastic parts can be shortened, thereby improving production efficiency. Furthermore, a plurality of cooling pipes are arranged at intervals around the gate.

[0010] As an optimization, in the aforementioned injection mold capable of eliminating weld lines on the surface of plastic parts, a positioning ring is provided on the upper part of the hot runner assembly, and the positioning ring is fixedly connected to the fixed mold fixing plate. Therefore, when installing the injection mold, the positioning ring can be first inserted into the positioning hole on the injection molding machine, and then the position of the mold can be adjusted so that the pouring channel in the hot runner assembly is consistent with the nozzle of the injection molding machine, so that the molten plastic can smoothly enter the mold cavity, which is convenient and easy to operate.

[0011] As an optimization, in the aforementioned injection mold that can eliminate the weld line on the surface of the plastic part, the design process of the dark runner is as follows: first, determine the weld line position; then, in combination with the gate layout, open a dark runner on the injection molding surface of the movable mold, extending from the gate to the weld line position; the dark runner exceeds the weld line by 2-5mm. The weld line position can be determined by the following two methods: ① Through mold flow analysis, find the flow direction and welding shape of the plastic on the mold flow to determine the weld line position. ② Find the position of the trapped air weld line by hitting the part on the machine and making a short shot. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic structural diagram of an injection mold capable of eliminating weld lines on the surface of a plastic part in an embodiment of the present application;

[0013] Figure 2 yes Figure 1 A cross-sectional view of the injection mold in FIG.

[0014] Figure 3 It is a structural schematic diagram of the movable mold assembly in an embodiment of the present application;

[0015] Figure 4 yes Figure 3 An enlarged schematic diagram of part A in FIG.

[0016] Figure 5 It is a schematic diagram of the assembly of the inclined ejector block and the movable mold in the embodiment of the present application;

[0017] Figure 6 It is a structural schematic diagram of the movable mold in the embodiment of the present application;

[0018] Figure 7 It is a schematic structural diagram of the inclined top block in the embodiment of the present application;

[0019] Figure 8 is a distribution state diagram of the cooling pipeline and the hot runner assembly in the embodiment of the present application;

[0020] Fig. 9 It is a structural schematic diagram of the drawer door side panel in the implementation case of this application.

[0021] The markings in the accompanying drawings are: 1-fixed mold fixing plate; 2-hot runner plate; 3-fixed mold; 4-movable mold, 401-mold cavity, 402-injection molding surface, 403-dark runner, 404-exhaust groove; 5-mold foot; 6-movable mold fixing plate; 7-ejector plate; 8-hot runner assembly, 801-pouring runner, 802-gate; 9-elevator rod; 10-elevator block; 11-cooling pipeline, 111-first cooling pipeline, 112-second cooling pipeline, 113-third cooling pipeline; 12-positioning ring. DETAILED DESCRIPTION

[0022] The present application is further described below in conjunction with the accompanying drawings and embodiments. The described embodiments are exemplary and are intended to be used to illustrate the present invention, but are not intended to be a basis for limiting the present invention.

[0023] In the injection molding of plastic parts, when the molten plastic flows and converges in the mold, a weld line is easily formed at the convergence due to structural influences or various other factors, such as mold temperature, plastic fluidity, etc. The conventional solution to weld lines is to add exhaust inserts for exhaust; however, if the air is seriously trapped, even if exhaust inserts are added, the weld line problem cannot be completely solved, but can only be improved, which will increase the mold cost and production cycle.

[0024] In view of this, the applicant improved the structure of the injection mold. First, find the position where the weld line will be generated. There are two methods: 1. Through mold flow analysis, find the plastic flow direction and weld shape on the mold flow to determine the weld line position (not all conditions can be reflected by mold flow analysis, it can only be used as a reference, and the actual state of the machine-made parts shall prevail); 2. Machine-made parts, and make short shots to find the position of the trapped gas weld line. After finding the weld line position, combined with the gate layout, a dark runner starts on the injection molding surface of the movable mold, extending from the gate to the weld line position. The dark runner should be opened 2-5mm beyond the weld line to guide the flow direction of the plastic, so that the molten plastic can fill the weld line position more evenly and quickly first, so that the two converging streams can be better integrated. Moreover, when the molten plastic flows on the dark runner, it will also push the gas in the mold cavity to the sealing edge of the mold in an orderly manner, and then the gas is discharged from the exhaust channel until the product is full; after the gas is discharged, there will be no weld line on the product, thereby improving the quality and performance of the plastic parts and the product qualification rate. In addition, the injection mold is designed according to the above structure, which can also save manufacturing time, reduce development costs, and shorten the production cycle. The specific structure of the injection mold is as follows.

[0025] Example:

[0026] See also Figure 1 and Figure 2 The injection mold capable of eliminating the weld line on the surface of the plastic part in this embodiment comprises a fixed mold assembly and a movable mold assembly; the fixed mold assembly comprises a fixed mold fixing plate 1, a hot runner plate 2 and a fixed mold 3 arranged in sequence; the movable mold assembly comprises a movable mold 4, a mold foot 5 and a movable mold fixing plate 6 arranged in sequence; in the mold closing state, a mold cavity 401 is formed between the fixed mold 3 and the movable mold 4; an ejector plate 7 is arranged between the movable mold 4 and the movable mold fixing plate 6, and an ejector mechanism is arranged on the ejector plate 7 for ejecting the plastic part out of the injection mold; the hot runner plate 2 is provided with The hot runner assembly 8 includes a pouring runner 801; the pouring runner 801 passes through the fixed mold plate 1, the hot runner plate 2 and the fixed mold 3, and is connected to the mold cavity 401 through the gate 802 (in this embodiment, the number of the gate 802 is one); a dark runner 403 for diversion is provided on the injection molding surface 402 of the movable mold 4; the dark runner 403 extends from the gate 802 to the weld line position, so that the molten plastic can flow quickly along the dark runner 403, and fill the weld line position before the two streams merge.

[0027] See also Figure 3 and Figure 4 In this embodiment, the dark runner 403 is in a straight line shape. Therefore, after the molten plastic enters the mold cavity 401, it can fill the weld line position more evenly and quickly. Furthermore, the dark runner 403 is an arc-shaped groove. In this case, the mold is easy to process, which is conducive to shortening the production cycle of the mold.

[0028] See also Figures 5 to 7 In this embodiment, the ejection mechanism includes an inclined ejector rod 9; the lower end of the inclined ejector rod 9 is slidably arranged on the ejector plate 7, and an inclined ejector block 10 is arranged on the upper end; the upper end surface of the inclined ejector block 10 is flush with the injection molding surface 402 of the movable mold 4, and part of the dark flow channel 403 is located on the upper end surface of the inclined ejector block 10. Therefore, exhaust can be directly carried out through the assembly gap between the inclined ejector block 10 and the movable mold 4 without opening another exhaust channel, which reduces the difficulty of mold processing and only requires the conventional inclined ejector rod assembly method. Furthermore, an exhaust groove 404 is arranged between the lower end surface of the inclined ejector block 10 and the movable mold 4. Therefore, during the injection molding process, the gas inside the mold cavity 401 can flow to the exhaust groove 404 for storage. When the plastic part is ejected by the inclined ejector rod 9, the gas is discharged from the exhaust groove 404 into the air, thereby avoiding the problem of trapped air.

[0029] See also Figure 8In this embodiment, three cooling pipelines 11 are arranged in the fixed mold 3 and are arranged at intervals around the gate 802. In this way, the heat dissipation efficiency of the fixed mold 3 can be improved, and uneven shrinkage of the plastic parts during the cooling process due to excessive heat can be avoided, causing warping and deformation, and the cooling time of the plastic parts can be shortened, thereby improving production efficiency. Specifically, along the direction close to the gate 802, the first cooling pipeline 111, the second cooling pipeline 112 and the third cooling pipeline 113 are arranged in sequence, and finally the third cooling pipeline 113 is opened for cooling. Each cooling pipeline includes an input pipe and an output pipe.

[0030] In this embodiment, a positioning ring 12 is provided on the upper part of the hot runner assembly 8, and the positioning ring 12 is fixedly connected to the fixed mold fixing plate 1. Therefore, when installing the injection mold, the positioning ring 12 can be inserted into the positioning hole on the injection molding machine first, and then the position of the mold can be adjusted to make the pouring flow channel 801 in the hot runner assembly 8 coincide with the nozzle of the injection molding machine, so that the molten plastic can smoothly enter the mold cavity 401, which is convenient and easy to implement.

[0031] In this case, the injection mold that can eliminate the weld line on the surface of the plastic part is used to produce the drawer door side panel of the car interior plastic part (see Fig. 9 ). First, the injection mold is installed on the injection molding machine, and the injection material is PC+ABS; then, the injection mold is closed, the injection molding machine and the hot runner assembly 8 are started, and the molten plastic is injected into the mold cavity 401 through the pouring channel 801. The molten plastic flows in the mold cavity 401. When passing through the dark runner 403, the flow direction and flow speed will change, so that the molten plastic will first fill the position where the weld line will be generated originally; after the pouring is completed, the cooling pipeline 11 is started to cool the product; after the plastic part is cooled, the injection mold is opened, and the ejection mechanism is started to eject the product.

[0032] Testing of the injection-molded drawer door side panels revealed no weld lines on the product surface, and that the product’s strength and appearance quality met the quality standards for automotive interior plastic parts.

[0033] Of course, the injection mold capable of eliminating weld lines on the surface of plastic parts of the present application is not limited to the above-mentioned practical applications, and can be used for the production of plastic parts in the fields of automobiles, medical treatment, daily necessities, etc.

[0034] The above general description of the invention involved in this application and the description of its specific implementation methods should not be understood as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art can, without violating the constituent elements of the invention involved, add, reduce or combine the disclosed technical features in the above general description or / and specific implementation methods (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. An injection mold capable of eliminating weld lines on the surface of a plastic part, comprising a fixed mold assembly and a movable mold assembly; the fixed mold assembly comprises a fixed mold fixing plate (1), a hot runner plate (2) and a fixed mold (3) arranged in sequence; the movable mold assembly comprises a movable mold (4), a mold foot (5) and a movable mold fixing plate (6) arranged in sequence; in a mold closing state, a mold cavity (401) is formed between the fixed mold (3) and the movable mold (4); an ejector plate (7) is arranged between the movable mold (4) and the movable mold fixing plate (6), and an ejector mechanism is arranged on the ejector plate (7) for ejecting the plastic part out of the injection mold; the characteristics are as follows: A hot runner assembly (8) is mounted on the hot runner plate (2), and the hot runner assembly (8) comprises a pouring runner (801); the pouring runner (801) is connected to the mold cavity (401) via a gate (802); a dark runner (403) for guiding flow is provided on the injection molding surface (402) of the movable mold (4); the dark runner (403) extends from the gate (802) to the weld line position, so that molten plastic can flow quickly along the dark runner (403) and fill the weld line position before the two streams of material merge.

2. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: The underflow channel (403) is in a straight line shape.

3. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 2, characterized in that: The dark flow channel (403) is an arc-shaped groove.

4. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: The ejection mechanism comprises an inclined ejector rod (9); the lower end of the inclined ejector rod (9) is slidably disposed on the ejector plate (7), and the upper end is provided with an inclined ejector block (10); the upper end surface of the inclined ejector block (10) is flush with the injection molding surface (402) of the movable mold (4), and part of the dark flow channel (403) is located on the upper end surface of the inclined ejector block (10).

5. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 4, characterized in that: An exhaust groove is provided between the lower end surface of the inclined ejector block (10) and the movable mold (4).

6. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: A plurality of cooling pipelines (11) are arranged in the fixed mold (3).

7. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 6, characterized in that: A plurality of cooling pipelines (11) are arranged at intervals in the circumferential direction around the gate (802).

8. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: A positioning ring (12) is provided on the upper portion of the hot runner assembly (8), and the positioning ring (12) is fixedly connected to the fixed mold fixing plate (1).

9. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: The design process of the dark runner (403) is as follows: first, through mold flow analysis, the flow direction and welding shape of the molten plastic are found on the mold flow to determine the weld line position; then, combined with the gate layout, a dark runner (403) is opened on the injection molding surface (402) of the movable mold (4), extending from the gate (802) to the weld line position; the dark runner (403) exceeds the weld line by 2-5 mm.

10. The injection mold capable of eliminating weld lines on the surface of plastic parts according to claim 1, characterized in that: The design process of the dark runner (403) is as follows: first, the position of the trapped air weld line is found by machine punching and short shots; then, in combination with the gate layout, a dark runner (403) is opened on the injection molding surface (402) of the movable mold (4), extending from the gate (802) to the weld line; the dark runner (403) exceeds the weld line by 2-5 mm.

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