Forming method for controlling deformation of injection-molded luggage shell

Abstract

The invention discloses a forming method for controlling deformation of an injection-molded luggage shell in the technical field of injection molding, which comprises the following steps: S1, presetting the position of a needle valve hot runner inlet gate according to the size and shape of a product; s2, the injection mold is adjusted, and the wall thickness of the product close to a pouring gate is increased; s3, injection molding is conducted; s4, after injection molding, the multi-section pressure maintaining process is conducted, and in the tail-section pressure maintaining process, the adopted pressure is set to be 0; a hot runner needle valve pouring mode is used for a bag shell product, the shrinkage amount of a near-pouring-gate part is increased by increasing the local wall thickness of a near-pouring gate of the product, meanwhile, the curing time of a material core layer near the pouring gate is prolonged by increasing the local wall thickness, and a time opportunity is provided for material backflow in the pressure maintaining process; in the injection molding pressure maintaining process, a material backflow method is utilized, local pressure distribution and shrinkage distribution of the product are changed, and adjustment of the deformation trend and the deformation amount of the product is achieved.

Description

Technical Field

[0001] This invention relates to the field of injection molding technology, and in particular to a molding method for controlling the deformation of injection-molded bag shells. Background Technology

[0002] In the production of bag shells (especially deep-cavity shells), due to the characteristics of the product filling process, there is a significant molding pressure difference between the area near the gate and the area far from the gate. Existing control methods resulted in higher local pressure and lower molding shrinkage near the gate, while lower local pressure and higher molding shrinkage occurred at the area far from the gate, leading to large-area outward deformation of the product. Traditional control methods typically involved pre-deformation design during product and mold design to compensate for deformation during molding. However, because the amount of deformation is affected by factors such as material type, batch performance, product wall thickness distribution, molding conditions, and mold temperature distribution, it is usually difficult to accurately determine the pre-deformation amount. This often requires multiple modifications to the mold structure, and the deformation may not meet the requirements after changing materials. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to improve the deformation problem after injection molding of bag shell and the difficulty in controlling deformation.

[0004] The technical solution adopted by this invention to solve its technical problem is: A molding method for controlling the deformation of injection-molded luggage shells includes the following steps: S1: Pre-set the position of the needle valve hot runner inlet according to the product size and shape; S2: Adjust the injection mold to increase the wall thickness of the product near the gate; S3: Perform injection molding; S4: After injection molding, a multi-stage pressure holding process is performed. During the final stage of pressure holding, the pressure is set to 0.

[0005] Furthermore, in step S1, the pouring position is set to multiple, including a main pouring point and multiple auxiliary pouring points, and the multiple auxiliary pouring points are arranged around the main pouring point.

[0006] Furthermore, the product is configured to cover multiple pouring locations within a wall thickness zone.

[0007] Furthermore, in step S2, the wall thickness is increased by 0.2mm to 0.3mm from the original wall thickness.

[0008] Furthermore, a transition section is provided at the junction of the position where the wall thickness is increased and the position where the wall thickness is not increased, and the width of the transition section ranges from 30mm to 50mm.

[0009] Furthermore, step S4 includes a three-stage pressure holding process: the first stage pressure holding time is no more than 0.5s, the middle stage pressure holding time is 1s-4s, and the final stage pressure holding time is 5s-8s.

[0010] Furthermore, the pressure range for the first stage of pressure holding is 20MPa-40MPa.

[0011] Furthermore, the pressure range for the intermediate pressure holding section is 70MPa-80MPa.

[0012] Furthermore, the holding speed in the middle stage and the holding speed in the final stage are both greater than 40% of the maximum holding speed.

[0013] The beneficial effects of this invention are: For bag shell products, a hot runner needle valve injection mode is used. By increasing the local wall thickness near the gate, the shrinkage near the gate is increased. At the same time, the increased local wall thickness extends the curing time of the core layer of the material near the gate, providing time for material backflow during the holding pressure process. During the injection holding pressure process, the "material backflow method" is used to change the local pressure distribution and shrinkage distribution of the product, thereby adjusting the product deformation trend and deformation amount. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the gate location design of the present invention; Figure 3 This is a PVT curve of the plastic material of this invention; The diagram is marked as follows: 1 - main pouring point, 2 - auxiliary pouring point, 3 - area with increased wall thickness. Detailed Implementation

[0015] The invention will be further described below with reference to the accompanying drawings.

[0016] like Figure 1 As shown in the embodiment of this application, a molding method for controlling the deformation of injection-molded bag shells is proposed, characterized by comprising the following steps: S1: The position of the needle valve hot runner inlet is preset according to the product size and shape; the inlet position is set to multiple, including one main inlet point 1 and multiple auxiliary inlet points 2, and the multiple auxiliary inlet points 2 are arranged around the main inlet point 1; for example Figure 2 As shown in this embodiment, a main injection point 1 is set at the center of the front or back of the main body of the box, and four auxiliary injection points 2 are set. The four auxiliary injection points 2 form a rectangle or trapezoid, and the four auxiliary injection points 2 correspond to the four corners of the box, so as to ensure multi-point injection, improve injection efficiency, ensure effective filling of the product and form a better surface appearance effect.

[0017] S2: Adjust the injection mold to increase the wall thickness of the product near the gate; the wall thickness increase range is 0.2mm-0.3mm from the original wall thickness, which can reduce deformation by 3-8mm while ensuring small shrinkage at the gate position; the area where the wall thickness is set covers multiple gate positions, and the area with increased wall thickness 3 is the area near the gate, such as... Figure 2 The elliptical region is shown in the diagram. When there is a main gate 1 and multiple auxiliary gates 2, the wall thickness region 3 is increased to connect the main gate 1 and the multiple auxiliary gates 2 into a sheet. This improves the problem of large-area outward deformation of the product caused by high local pressure and corresponding small molding shrinkage near the gate, and low local pressure and corresponding large molding shrinkage at the far end of the gate.

[0018] A transition section is provided at the junction of the increased wall thickness location and the non-increased wall thickness location. The width of the transition section ranges from 30mm to 50mm to avoid poor appearance caused by abrupt changes in wall thickness.

[0019] S3: Perform injection molding; adopt high-speed injection, which means increasing the injection speed of the corresponding injection molding machine to more than 80% to shorten the product filling time as much as possible and ensure injection molding efficiency.

[0020] S4: After injection molding, a multi-stage holding pressure process is performed. During the final holding pressure process, the pressure is set to 0. Injection molding is a rapid solidification process where the surface layer contacts the mold surface. Subsequently, the solidified layer thickens over time until it is completely solidified. The solidification time in the middle is proportional to the square of the product wall thickness. In other words, the aforementioned increase in wall thickness can delay the solidification time of the product near the gate. The local increase in wall thickness extends the solidification time of the core layer of the material near the gate, providing an opportunity for material backflow during the holding pressure process.

[0021] The holding speed in the middle stage and the holding speed in the final stage are both greater than 40% of the maximum holding speed.

[0022] The multi-stage pressure holding process includes three stages: the first stage pressure holding time is no more than 0.5s, the middle stage pressure holding time is 1s-4s, and the final stage pressure holding time is 5s-8s. By holding pressure for different durations, the best molding effect of the product can be achieved.

[0023] The pressure range for the first stage of pressure holding is 20MPa-40MPa. Using such a medium-low pressure can effectively avoid flash caused by impact filling.

[0024] The pressure range for holding pressure in the middle section is 70MPa-80MPa. The pressure setting should be based on not generating flash or burrs. The holding time is 1-4 seconds, which varies depending on the product wall thickness, mold temperature, and material. Generally, the thinner the wall thickness, the greater the influence of temperature on the material's flowability. The lower the mold temperature, the shorter the holding time, but the greater the corresponding pressure requirement, to ensure that the pressure is effectively transmitted to the far end of the product filling, i.e., the far gate position. At this time, due to the flow resistance, a pressure distribution from high to low is formed from the near gate position to the far gate position.

[0025] In the final stage of pressure holding, zero pressure is used, with a holding rate (>40%) and a holding time of 5-8 seconds. At this point, because the pressure inside the mold cavity is greater than the pressure in the injection molding cylinder, the material inside the mold cavity is forced back into the sprue and hot runner through the gate, thus forming material backflow (backflow is a description of normal material flow, where material flows from the gate to the far gate of the product; backflow refers to material flowing from the product back to the gate). During material backflow, due to flow resistance, a reverse pressure distribution from low to high is formed from the near gate position to the far gate position. The third stage of zero pressure holding to form material backflow can also be enhanced by using the linkage of machine tool and hot runner needle valve to form negative pressure holding.

[0026] In summary, this invention proposes a molding method for controlling the deformation of injection-molded bag shells, from... Figure 3 The PVT curves of plastic materials show that the molding shrinkage is less in the high-pressure areas than in the low-pressure areas. During normal production of bag shell products, due to pressure distribution, the shrinkage is small near the gate (bottom or top surface) and large in the areas far from the gate (side of the shell), especially for thin-walled bags, with some products deforming by more than 10mm. Increasing the wall thickness near the gate by 0.2-0.3mm can reduce the deformation by 3-8mm (the effect varies depending on the initial wall thickness and side height). Using the material reflow method can further reduce the deformation by 3-8mm. At the same time, the material reflow method reduces the pressure near the gate, and the increased shrinkage can reduce the increase in product thickness and weight caused by the increase in mold cavity wall thickness. The degree of product deformation can be adjusted according to the material reflow time and the second-stage holding pressure. For products with particularly high deformation risk, the structure and deformation methods of this invention can be implemented together, which can solve the problem of inaccurate pre-deformation by customers and reduce the difficulty of debugging.

Claims

1. A molding method for controlling the deformation of injection-molded bag shells, characterized in that, Includes the following steps, S1: Pre-set the position of the needle valve hot runner inlet according to the product size and shape; S2: Adjust the injection mold to increase the wall thickness of the product near the gate; S3: Perform injection molding; S4: After injection molding, a multi-stage pressure holding process is performed. During the final stage of pressure holding, the pressure is set to 0.

2. The molding method for controlling the deformation of injection-molded bag shells according to claim 1, characterized in that, In step S1, the pouring position is set to multiple, including a main pouring point (1) and multiple auxiliary pouring points (2), and the multiple auxiliary pouring points (2) are arranged around the main pouring point (1).

3. The molding method for controlling the deformation of injection-molded bag shells according to claim 2, characterized in that, The product settings add a wall thickness area (3) to cover multiple of the aforementioned pouring positions.

4. The molding method for controlling the deformation of injection-molded bag shells according to any one of claims 1-3, characterized in that, In step S2, the wall thickness of the increased wall thickness area (3) is increased by 0.2mm to 0.3mm based on the original wall thickness size.

5. The molding method for controlling the deformation of injection-molded bag shells according to claim 4, characterized in that, A transition section is provided at the junction of the area with increased wall thickness (3) and the area without increased wall thickness. The width of the transition section ranges from 30mm to 50mm.

6. The molding method for controlling the deformation of injection-molded bag shells according to claim 1, characterized in that, Step S4 includes three pressure holding processes: the first pressure holding time is no more than 0.5s, the middle pressure holding time is 1s-4s, and the last pressure holding time is 5s-8s.

7. The molding method for controlling the deformation of injection-molded bag shells according to claim 6, characterized in that, The pressure range for the first stage of pressure holding is 20MPa-40MPa.

8. The molding method for controlling the deformation of injection-molded bag shells according to claim 6, characterized in that, The pressure range for intermediate pressure holding is 70MPa-80MPa.

9. The molding method for controlling the deformation of injection-molded bag shells according to claim 6, characterized in that, The holding speed in the middle stage and the holding speed in the final stage are both greater than 40% of the maximum holding speed.

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