In-mold cut gate device and injection mold having the same

Abstract

The application discloses an in-mold gate cutting device and an injection mold with the same. The injection mold comprises a fixed mold assembly, a movable mold assembly, a cutting member with a working end, and a driving mechanism. The working end comprises a shearing part opposite to a section of a gating runner close to a molding cavity, and an extruding part with a larger cross-sectional area on the side of the shearing part away from the fixed mold assembly. The driving mechanism drives the cutting member to perform continuous variable-speed pushing processes in the direction close to the fixed mold assembly: in the first stage, the shearing part cuts off the melt in the section at a first speed and traps part of the melt; in the second stage, the extruding part extrudes the trapped melt at a second speed smaller than the first speed and pushes the trapped melt into the molding cavity to compensate for the volume shrinkage of the melt inside the molding cavity during the cooling and solidification process. The application effectively eliminates the surface shrinkage defects of the injection molded product by integrating the cutting and extruding compensation functions, and improves the molding quality.

Description

Technical Field

[0001] This invention relates to the field of injection mold technology, and more specifically, to an in-mold gate cutting device and an injection mold. Background Technology

[0002] In precision injection molding, especially for thick-walled parts or products with high requirements for internal residual stress, the melt shrinks during the cooling and solidification process. Traditional injection molding press pressure holding methods often fail to transmit the holding pressure to the mold cavity for compensation of shrinkage because the melt at the interface between the gating system and the molding cavity solidifies prematurely. This results in products prone to shrinkage depressions or internal stress defects.

[0003] To improve production efficiency, the industry has introduced in-mold gate technology. Existing in-mold gate technology typically uses a drive mechanism to push a straight cutting element, directly cutting off the material at the connection between the gating system and the molding cavity during the later stages of injection molding and holding pressure, thus eliminating the need for manual trimming. However, this traditional in-mold gate technology has limitations: the straight cutting element only cuts the melt; after the cutting action is completed, the melt inside the molding cavity is completely physically isolated from the gating system. At this time, the melt inside the molding cavity continues to cool and shrink, and the existing cutting element cannot provide further volume compensation within the molding cavity, resulting in the molded product still being prone to shrinkage. Adding an independent extrusion pusher or lateral holding pressure structure within the mold to solve the shrinkage problem would complicate the internal structure of the mold, occupy more layout space, and increase the risk of mechanical interference and malfunction. Summary of the Invention

[0004] The main objective of this invention is to provide an in-mold gate cutting device and an injection mold to solve the technical problem that existing in-mold gate cutting technology can only cut off the material. After cutting off the material at the connection between the gating channel and the molding cavity, it cannot compensate for the volume of the continuously shrinking melt inside the molding cavity, which leads to shrinkage depressions and internal stress defects in the injection molded products.

[0005] The in-mold gate cutting device provided by the present invention includes: Fixed mold assembly; The moving mold assembly is closed and docked with the fixed mold assembly to define the molding cavity and the gating channel connecting the molding cavity; A cutting element is movably disposed within the moving mold assembly and has a working end; the working end includes a shearing portion facing the section of the gating channel near the molding cavity, and an extrusion portion located on the side of the shearing portion away from the fixed mold assembly; the cross-sectional area of ​​the extrusion portion is larger than the cross-sectional area of ​​the shearing portion. A drive mechanism, connected to the cutting element, is configured to drive the cutting element to move closer to the fixed mold assembly when the mold is closed and the melt is not completely solidified. The movement of the cutting element includes a continuous variable-speed propulsion stroke. In the first stage, the drive mechanism drives the cutting member to move at a first speed, thereby causing the shearing part to cut the melt in the section, so as to retain a portion of the melt between the cutting member and the forming cavity; In the second stage, the driving mechanism drives the cutting member to continue moving at a second speed less than the first speed, which in turn drives the extrusion section to extrude the trapped melt and push the trapped melt into the molding cavity to compensate for the volume shrinkage of the melt inside the molding cavity during the cooling and solidification process.

[0006] Preferably, the surface of the extrusion section facing the molding cavity is an inclined surface; The inclined surface extends inclinedly toward the side closer to the molding cavity in a direction away from the shearing part; In the second stage, the intercepted melt is pushed into the molding cavity using the inclined surface.

[0007] Preferably, the driving mechanism includes a servo power source, which is connected to the cutting element in a transmission manner; The servo power source is configured to perform segmented pulse output to drive the cutting member to move at a first rotational speed within a first preset duration, and to drive the cutting member to move at a second rotational speed within a subsequent second preset duration, thereby enabling the cutting member to perform the variable speed propulsion stroke.

[0008] Preferably, the in-mold gate cutting device further includes a base plate movably disposed within the moving mold assembly, and the cutting member is fixedly disposed on the base plate; The driving mechanism is connected to the substrate to drive the substrate and the cutting member to move synchronously.

[0009] Preferably, the substrate has a clearance hole, and the wall of the clearance hole has a stepped surface facing the fixed mold assembly. The reset rod passes through the clearance hole and is configured such that when the mold is in the closed state, the front end of the reset rod abuts against the fixed mold assembly; The reset rod is provided with a limiting head, which is located on the side of the stepped surface near the fixed mold assembly; Before the cutting member performs the variable speed advance stroke, the stepped surface and the limiting head are spaced apart to form a gap; At the end of the second stage, the substrate drives the step surface to move towards the fixed mold assembly until the step surface abuts against the limiting head to limit the maximum displacement of the cutting member.

[0010] Preferably, the moving mold assembly further includes a base plate located on the side of the substrate away from the fixed mold assembly; A pad is disposed at the end of the reset rod away from the fixed mold assembly. When the mold is in the closed state, the pad abuts against the base plate to restrict the reset rod from moving away from the fixed mold assembly, thereby supporting the reset rod to maintain the gap between the limiting head and the step surface.

[0011] Preferably, the servo power source is electrically connected to the control system of the injection molding machine and is configured to start the variable speed propulsion stroke after the pressure holding action of the injection molding machine is completed.

[0012] The present invention also provides an injection mold, including the in-mold gate cutting device described in any of the above claims.

[0013] One or more technical solutions provided in this invention have at least the following technical effects or advantages: The cutting component of this invention integrates a shearing section facing the section of the gating channel near the molding cavity at its working end, and an extrusion section located behind the shearing section, with the cross-sectional area of ​​the extrusion section being larger than that of the shearing section. A drive mechanism executes a continuous variable-speed propulsion stroke. In the first stage, the shearing section moves at a first speed to cut the melt within that section, thereby trapping a portion of incompletely solidified melt between the cutting component and the molding cavity. In the second stage, the extrusion section continues to move at a second speed, less than the first speed. The extrusion section, with its larger cross-sectional area, squeezes the trapped melt, forcibly pushing this trapped melt into the molding cavity as a shrinkage compensation source. This allows the invention to simultaneously cut the gating channel and trap and squeeze a portion of the melt, effectively compensating for the volume shrinkage of the melt inside the molding cavity during cooling and solidification, thereby improving the surface shrinkage problem of injection molded products, reducing molding stress, and improving product molding quality.

[0014] Furthermore, this invention integrates the melt cutting function and the extrusion and compensation function of the molding cavity into the continuous unidirectional movement of the same cutting component, which can be achieved simply by executing the variable speed propulsion stroke through the drive mechanism. Compared with the solution of adding an independent lateral extrusion structure in the injection mold, this invention effectively simplifies the mechanical structure of the mold, saves internal space of the mold, and helps to improve the stability and reliability of the in-mold gate cutting device during operation. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the overall cross-sectional structure of the in-mold gate cutting device of the present invention in the initial state (i.e., when the mold is closed and the injection pressure holding has just ended).

[0016] Figure 2 yes Figure 1 A magnified view of a portion of point A in the middle.

[0017] Figure 3 This is a schematic diagram of the cross-sectional structure of an in-mold gate cutting device of the present invention at the end of the first stage of operation (i.e., when the melt in the section is cut off and part of the melt is retained).

[0018] Figure 4 yes Figure 3 A magnified view of a portion of point B in the middle.

[0019] Explanation of reference numerals in the attached drawings: 10, fixed mold assembly; 11, clearance groove; 20, moving mold assembly; 21, molding cavity; 22, gating runner; 30, cutting part; 31, working end; 311, shearing part; 312, extrusion part; 3121, inclined surface; 40, base plate; 41, clearance hole; 411, stepped surface; 50, reset rod; 51, limit head; 52, pad block; 60, base plate; 70, ejector roller. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Reference Figure 1 and Figure 2 This embodiment provides an in-mold gate cutting device, which is integrated into a precision injection mold. The injection mold mainly consists of a fixed mold assembly 10 and a moving mold assembly 20 that open and close relative to each other. When they are closed and joined, they jointly define a molding cavity 21 for molding the target product on the parting surface, and a gating channel 22 that communicates with the nozzle of an external injection molding machine to deliver high-temperature molten plastic. Those skilled in the art will understand that the cutting and patching device of this invention is particularly suitable for injection molded products such as thick-walled transparent structural parts and large-size optical lenses, which have extremely high requirements for local shrinkage compensation accuracy and internal residual stress.

[0022] A guide channel perpendicular to the parting surface is provided inside the moving mold assembly 20, and the cutting component 30 can slide axially through the guide channel. Considering the high temperature, high pressure and frequent shearing conditions during the injection molding process, the cutting component 30 is usually made of high-hardness and wear-resistant materials such as powder metallurgy high-speed steel or cemented carbide, and its surface is treated with titanium plating or carbonitriding to further improve its self-lubricating performance and service life. The end of the cutting component 30 facing the parting surface is formed as a working end 31. The left side wall of the working end 31 maintains a precise sliding fit with the inner wall of the guide channel, and its foremost end is formed as a shearing part 311 with a sharp and straight cutting edge. The lower solid part of the shearing part 311 on the side away from the fixed mold assembly 10 is formed as an extrusion part 312. The surface of the extrusion part 312 facing the molding cavity 21 is constructed as an inclined surface 3121. The inclined surface 3121 extends obliquely towards the side closer to the molding cavity 21 in a direction away from the shearing portion 311 (i.e., from top to bottom), such that the overall cross-sectional area of ​​the extrusion portion 312 is larger than that of the shearing portion 311 at the top. In other alternative embodiments, the side of the extrusion portion 312 facing the molding cavity may also be a stepped boss or a smooth arc-shaped expansion surface, as long as it can achieve the effect of increasing the cross-sectional area and generating radial displacement volume. To accommodate the upward cutting overrun of the cutting element 30, the fixed mold assembly 10 has a pre-machined clearance groove 11 at the corresponding position opposite to the working end 31.

[0023] Reference Figure 1 and Figure 3 The cutting component 30 is driven and precisely positioned using a bottom linkage and dead-point structure. A base plate 40 and a bottom plate 60 are arranged parallel to each other behind the moving mold assembly 20, away from the fixed mold assembly 10. The bottom end of the cutting component 30 is fixedly anchored to the base plate 40 to achieve synchronous axial linkage. An ejector roller 70, passing through the bottom plate 60, abuts against the bottom of the base plate 40. The drive mechanism of the device typically uses a servo power source to achieve precise displacement and speed control. In specific implementation scenarios, this servo power source can be selected as a servo ejector shaft integrated into a fully electric injection molding machine, or a transmission assembly consisting of an external independent servo motor and a high-precision ball screw, or a servo hydraulic cylinder equipped with a high-sensitivity linear displacement sensor. The power output of the servo power source acts on the ejector roller 70, providing continuous and variable-speed linear thrust to the base plate 40 and the cutting component 30 through the ejector roller 70.

[0024] This embodiment cleverly utilizes the existing reset rod structure of the mold to construct a high-rigidity mechanical dead-point limiting system. A stepped clearance hole 41 is formed through the substrate 40, with an upward-facing stepped surface 411 at the abrupt change in hole diameter. The reset rod 50 slides through the clearance hole 41 of the substrate 40 and the corresponding through hole of the moving mold assembly 20, with its bottom end integrally formed or securely connected to a limiting head 51 with an enlarged cross-section. The pad 52 is fixedly disposed on the upper surface of the base plate 60 and rigidly supported on the bottom surface of the limiting head 51. Figure 1 In the fully closed state of the mold, the front end of the reset rod 50 is pressed against the lower surface of the fixed mold assembly 10, and its rear end is stably supported on the base plate 60 by the pad 52. At this time, the reset rod 50 is completely clamped and constrained in the axial direction, which essentially constitutes a fixed guide shaft when the base plate 40 slides upward. In this initial state, the limiting head 51 is suspended directly above the step surface 411, and an axial gap of a preset height is formed between the two. In actual mold debugging and production maintenance, the operator only needs to replace the hard metal pads 52 of different standard thicknesses, or add or remove them using open U-shaped shims, to precisely adjust the value of the initial gap without disassembling the mold body, thereby achieving flexible quantitative adjustment of the subsequent extrusion and shrinkage volume.

[0025] Combination Figures 1 to 4 This paper elaborates on the dynamic working principle of the continuously variable propulsion stroke of the present invention and its associated beneficial effects.

[0026] Near the end of the holding pressure stage in the injection molding process, the surface layer of the main melt in the gating channel 22 begins to solidify, but the interior is not yet fully cured. The servo power source starts according to the instructions of the injection molding machine control system, driving the substrate 40 via the ejector roller 70 and causing the cutting element 30 to move upwards. In the first stage, the servo power source drives the cutting element 30 upwards at a relatively high initial speed, and the shearing part 311 quickly penetrates and cuts the melt in the section of the gating channel 22 near the molding cavity 21. Relying on the tight shearing fit between the vertical left side wall of the working end 31 and the mold steel, the feed channel is instantly physically cut off. Simultaneously, because the cutting action occurs at the end section of the runner, a portion of the incompletely solidified high-temperature melt is successfully retained between the cutting element 30 and the molding cavity 21. This high-speed cutting process effectively prevents the melt from producing stringing or dust defects at the separation point.

[0027] At the instant the first stage of the cutting action is completed, the servo power source executes a pulse switch to enter the state as follows: Figure 4In the second stage shown, the cutting element 30 continues to move slowly upward at a second speed, less than the first speed. During this process, the shearing part 311 first extends into the clearance groove 11 of the fixed mold assembly 10. Since the shearing part 311 and the clearance groove 11 are precisely fitted and maintain a very small sealing gap, the shearing part 311, after entering the clearance groove 11, essentially forms a physical blockage of the entrance of the clearance groove 11, thereby cutting off the channel for the melt to overflow upward. Subsequently, the extrusion part 312 with a larger cross-sectional area forcibly weds into the space where the intercepted melt is located. Under the gentle pushing guidance of the inclined surface 3121, the intercepted melt, in an environment where it is blocked above and closed on the left by the side wall of the cutting element, is subjected to a continuous and gentle volumetric extrusion force, and is unidirectionally forced into the molding cavity 21 as if being pushed by a miniature plunger. This low-speed extrusion and shrinkage compensation action effectively compensates for the volume shrinkage of the product inside the molding cavity 21 during the cooling and solidification process, fundamentally eliminating surface shrinkage depressions in thick-walled areas, and significantly reducing the internal residual stress caused by the instantaneous injection of high-pressure melt.

[0028] At the end of the second stage of the operation, the stepped surface 411 inside the substrate 40 rises along with the entire substrate 40 until it rigidly abuts against the stationary limiting head 51 above. At this time, the rigid mechanical dead point closes, the cutting member 30 reaches its set maximum absolute displacement and immediately stops rising. This limiting structure not only ensures the absolute consistency of the extrusion and compensation volume in each molding cycle, but also effectively avoids serious accidents caused by the overtravel error that may exist in the servo system, which could lead to a destructive impact between the working end 31 and the bottom wall of the clearance groove 11. This greatly improves the operational stability and safe lifespan of the mold during long-term mass production.

[0029] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural modifications made based on the description and drawings of the present invention are similarly included within the patent protection scope of the present invention.

Claims

1. An in-mold gate cutting device, characterized in that, include: Fixed mold assembly (10); The moving mold assembly (20) is closed and docked with the fixed mold assembly (10) to define the molding cavity (21) and the gating channel (22) connecting the molding cavity (21). A cutting element (30) is movably disposed within the moving mold assembly (20) and has a working end (31); the working end (31) includes a shearing portion (311) facing the section of the gating channel (22) near the molding cavity (21), and an extrusion portion (312) located on the side of the shearing portion (311) away from the fixed mold assembly (10); the cross-sectional area of ​​the extrusion portion (312) is larger than the cross-sectional area of ​​the shearing portion (311); A drive mechanism, connected to the cutting element (30), is configured to drive the cutting element (30) to move closer to the fixed mold assembly (10) when the mold is closed and the melt is not completely solidified. The movement of the cutting element (30) includes a continuous variable-speed propulsion stroke. In the first stage, the drive mechanism drives the cutting member (30) to move at a first speed, thereby causing the shearing part (311) to cut the melt in the section, so as to retain a portion of the melt between the cutting member (30) and the molding cavity (21); In the second stage, the driving mechanism drives the cutting member (30) to continue moving at a second speed less than the first speed, which drives the extrusion part (312) to extrude the trapped melt, so as to push the trapped melt into the molding cavity (21) to compensate for the volume shrinkage of the melt inside the molding cavity (21) during the cooling and solidification process.

2. The in-mold gate cutting device according to claim 1, characterized in that, The surface of the extrusion section (312) facing the molding cavity (21) is an inclined surface (3121). The inclined surface (3121) extends inclinedly toward the side closer to the molding cavity (21) in a direction away from the shearing part (311); In the second stage, the intercepted melt is pushed into the molding cavity (21) using the inclined surface (3121).

3. The in-mold gate cutting device according to claim 1, characterized in that, The driving mechanism includes a servo power source, which is connected to the cutting member (30) in a transmission manner; The servo power source is configured to perform segmented pulse output to drive the cutting member (30) to move at a first rotational speed within a first preset duration, and to drive the cutting member (30) to move at a second rotational speed within a subsequent second preset duration, thereby enabling the cutting member (30) to perform the variable speed propulsion stroke.

4. The in-mold gate cutting device according to claim 1, characterized in that, It also includes a base plate (40) movably disposed within the moving mold assembly (20), and the cutting member (30) is fixedly disposed on the base plate (40); The driving mechanism is connected to the substrate (40) to drive the substrate (40) and the cutting member (30) to move synchronously.

5. The in-mold gate cutting device according to claim 4, characterized in that, The substrate (40) has a clearance hole (41), and the wall of the clearance hole (41) has a stepped surface (411) facing the fixed mold assembly (10). The reset rod (50) passes through the relief hole (41) and is configured such that when the mold is in the closed state, the front end of the reset rod (50) abuts against the fixed mold assembly (10). The reset rod (50) is provided with a limiting head (51), and the limiting head (51) is located on the side of the step surface (411) close to the fixed mold assembly (10); Before the cutting member (30) performs the variable speed propulsion stroke, the stepped surface (411) and the limiting head (51) are spaced apart to form a gap; At the end of the second stage, the substrate (40) drives the step surface (411) to move closer to the fixed mold assembly (10) until the step surface (411) abuts against the limiting head (51) to limit the maximum displacement of the cutting member (30).

6. The in-mold gate cutting device according to claim 5, characterized in that, The moving mold assembly (20) also includes a base plate (60) located on the side of the substrate (40) away from the fixed mold assembly (10). A pad (52) is disposed at one end of the reset rod (50) away from the fixed mold assembly (10), and is configured such that when the mold is in the closed state, the pad (52) abuts against the base plate (60) to restrict the reset rod (50) from moving away from the fixed mold assembly (10), thereby supporting the reset rod (50) so that the gap is maintained between the limiting head (51) and the step surface (411).

7. The in-mold gate cutting device according to claim 3, characterized in that, The servo power source is electrically connected to the control system of the injection molding machine and is configured to start the variable speed propulsion stroke after the pressure holding action of the injection molding machine is completed.

8. An injection mold, characterized in that, Includes the in-mold gate cutting device as described in any one of claims 1 to 7.

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