A method and device for laser-assisted molding of injection molded parts with uneven wall thickness

Abstract

The present invention relates to a processing device, and specifically to a method and device for laser-assisted molding of injection molded parts with uneven wall thickness. The present invention sets a light guide path in a traditional injection mold to introduce laser energy into the thin-wall cavity area of ​​the injection molded part with uneven wall thickness, and regulates the temperature of this area; a temperature sensor is used for feedback, and then the laser parameters are adjusted through PLC control to form a certain temperature difference between the thin-wall cavity and the thick-wall cavity, so that the plastic flow can fill the thin-wall area more smoothly during final injection molding, and the thick and thin walls can be relatively evenly molded during cooling. The present invention can effectively reduce defects such as weld marks and shrinkage warping caused by uneven wall thickness of plastic parts during injection molding, reduce the trial and error time of injection molding process parameters and the adjustment of injection molds, and improve molding efficiency and quality.

Description

Technical Field

[0001] The invention relates to a processing device, in particular to a method and a device for laser-assisted molding of injection molded parts with uneven wall thickness. Background Art

[0002] Laser processing uses the energy of light to reach a high energy density at the focal point after being focused by a lens, and relies on the photothermal effect for processing. Laser processing does not require tools, has a fast processing speed, and has small surface deformation, and can process various materials. As a special processing technology, laser processing has the advantages of strong controllability, high processing efficiency and wide applicability. Based on the thermal effect of laser, by adjusting the power density range of laser, the laser beam is widely used in various processing of materials, such as punching, cutting, scribing, welding, additive manufacturing, heat treatment, etc. The composite processing technology combining traditional processing methods with lasers shows its new advantages. The two technologies complement each other and interact with each other to improve the precision of the product. For example, in laser-electrochemical composite processing, the addition of laser solves the problem of electrochemical processing producing a recast layer on the processing surface.

[0003] Injection molded products are increasingly used in life, and improving their precision has always been an important research direction for scholars and a goal that manufacturers have been pursuing. Filling balance is one of the important research contents of precision injection molding technology. The problem of unbalanced filling will cause differences in weight, shrinkage, warping, mechanical properties and optical properties of the products. This requires people to improve the balance of filling of multiple or single cavities as much as possible when designing molds and setting process parameters. The design of product thickness is an important aspect of structural design. In order to make the product have a certain structure, function, strength and rigidity, different thickness dimensions are often set at different positions of the product, but uneven wall thickness will bring many defects to the product, such as stress concentration, warping deformation and weld marks.

[0004] Due to factors such as temperature difference effect, uneven wall thickness injection molded parts are prone to uneven volume shrinkage after molding, resulting in defects such as warping, deformation and shrinkage, resulting in poor product appearance and precision. Under the existing technology, the above defects are solved by modifying the product structure, switching materials and process parameters through trial and error, or setting cooling water channels on traditional molds to adjust temperature differences. However, these two methods cannot accurately control temperature differences, have long development time, low efficiency and high cost. Summary of the invention

[0005] In view of the above problems, the present invention proposes a method and device for laser-assisted molding of uneven wall thickness injection molded parts. The present invention uses the thermal effect of laser to accurately control the temperature difference of the molding cavity, solves the problems of warping, shrinkage, and weld marks after molding of uneven wall thickness injection molded parts, and solves the problem of long development cycle for such parts, thereby improving efficiency and reducing costs.

[0006] The specific technical solution adopted by the present invention is as follows:

[0007] A laser-assisted device for molding uneven wall thickness injection molded parts includes a laser control device, an injection mold with an optical path, and a horizontal injection molding machine. The laser control device is composed of a PLC control cabinet, a PLC control display screen, a laser generator, and an XYZ three-coordinate slide rail to achieve laser parameter and position control. In the injection mold with an optical path, the fixed mold plate is fixedly connected to the fixed mold base plate located above the fixed mold plate, and there are four guide pillars between the fixed mold plate and the movable mold plate located below the fixed mold plate, which can form relative movement; the movable mold pad located below the movable mold plate is fixedly connected to the movable mold plate and fixedly installed on the bracket; the bracket is fixedly connected to the movable mold base plate located below the bracket, and a movable push plate is installed in the hollow structure of the bracket, and a push rod fixing plate is fixedly connected to the push plate, and three push rods are installed on the push rod fixing plate; the optical path is set in the fixed mold plate, a reflector is bonded to the fixed block, and fixed in the fixed mold plate with hexagon socket screws, a convex lens is set directly below the reflector, and the convex lens is bonded to the shoulder in the vertical step groove in the fixed mold plate, there is a piece of quartz glass below the lens, and an absorption layer is provided on the bottom surface of the step groove below the quartz glass; a horizontal through groove is also opened on the right side of the fixed mold plate.

[0008] Furthermore, the fixing block has a 45-degree inclined wedge surface for bonding the reflector; the through groove on the right side of the fixed template is a rectangular through groove, the center plane of which is perpendicular to the center plane of the fixing block and intersects with the center of the inclined wedge surface.

[0009] The laser control device can control the position of the laser generator in three directions of XYZ, and can adapt to injection molds of plastic parts with different thickness and uneven shapes.

[0010] Furthermore, a temperature sensor is installed below each of the thick-walled cavity and the thin-walled cavity in the movable mold plate to detect the temperature difference between the two locations and feed it back to the control system to achieve laser temperature regulation.

[0011] Furthermore, the absorption layer can absorb laser energy and transfer heat to the wall below relatively evenly.

[0012] A method for laser-assisted injection molding of uneven wall thickness parts, characterized in that the molding temperature in the thin-wall cavity is regulated by using the thermal effect of the laser to control the uniform molding of the uneven wall thickness parts and reduce defects such as weld marks and thin-wall warping during such molding process. The specific steps are as follows:

[0013] A. Based on the original injection molding parameters, an external heat source is applied locally in the thin-wall area, and CAE software is used for analysis and simulation to obtain the optimal heat source parameters.

[0014] B. Assemble a special mold with a light path and install it on a horizontal injection molding machine.

[0015] C. According to the simulation parameters, input the initial laser parameters on the laser machine and input the previous molding parameters on the injection molding machine.

[0016] D. The laser starts scanning the thin-wall cavity for preheating, and then injection molding begins after a period of time.

[0017] E. Injection molding is completed, pressure is maintained, cooling is performed, parts are removed, and inspection is performed.

[0018] Furthermore, in step A, the original injection molding parameters refer to the parameters previously used for injection molding the plastic part with uneven wall thickness, including injection pressure, injection temperature, injection time and holding time parameters; the applied external heat source is a reciprocating scanning heat source, and the heat source parameters mainly include scanning speed and power density; the simulation results should also detect the temperature gradient of thick-walled and thin-walled areas, and establish the relationship between the temperature gradient and the heat source parameters.

[0019] Furthermore, in the step B, the light path in the mold with the light path is composed of a light path channel, a reflector, a convex lens, quartz glass and an absorption layer; during the mold assembly process, the assembly accuracy of the mold should be ensured.

[0020] Furthermore, in the step D, the specific preheating time is determined according to the material properties of the plastic raw material and the size of the wall thickness difference. The thinner the thin-walled cavity is, the longer the preheating time is, and the preheating time ranges from 1 to 25 seconds. After the injection molding starts, the temperature in the cavity is monitored in real time using the temperature sensors under the thick-walled cavity and the thin-walled cavity in the mold, and the temperature difference is fed back through the feedback system. The laser parameters and position are continuously and automatically adjusted using PLC control, so that the temperature of the thin-walled cavity is higher than that of the thick-walled cavity, ranging from 20°C to 100°C.

[0021] Furthermore, in step E, during the cooling process, the laser continues to regulate the temperature of the thin wall so that the temperature of the thick-wall cavity and the thin-wall cavity are consistent, thereby making the cooling rate at the thin wall consistent with that at the thick wall, and the volume shrinkage at each location relatively consistent, thereby reducing the degree of warping deformation caused by excessive shrinkage of the thick-wall area.

[0022] The beneficial effects of the present invention are:

[0023] The injection mold with its own optical path can effectively guide the laser into the cavity through the reflector and lens, and the laser energy can be effectively utilized and evenly act on the thin-walled cavity by using the laser scanning and absorption layer; the setting of quartz glass can guide the laser on the one hand, and reduce the weakening of the injection mold on the other hand.

[0024] Based on the thermal effect of laser, the role of laser is added to the injection molding process to regulate the temperature in the thin-wall cavity. The temperature sensor is used for feedback, and then the laser parameters are controlled by PLC to form a certain temperature difference between the thin-wall cavity and the thick-wall cavity. Finally, during injection molding, the plastic flow can fill the thin-wall area more smoothly. During pressure holding and cooling, the thick and thin walls can be formed relatively evenly, avoiding defects such as warping, deformation and weld marks. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the examples or descriptions of the prior art.

[0026] Figure 1 This is the front view of the laser-assisted plastic part with uneven wall thickness.

[0027] Figure 2 This is the left view of the laser-assisted plastic part with uneven wall thickness.

[0028] Figure 3 A cross-sectional view of an injection mold with light paths.

[0029] Figure 4 This is an enlarged view of the light path of the injection mold.

[0030] Figure 5 The figure is a flow chart of the laser-assisted molding method for injection molding parts with uneven wall thickness.

[0031] Figure 6 This is a simulation diagram of the volume shrinkage results of the injection molded parts in the embodiment.

[0032] Among them, 1. barrel, 2. fixed mold base plate, 3. cavity, 4. fixed block, 5. hexagon socket screw, 6. reflector, 7. convex lens, 8. quartz glass, 9. first temperature sensor, 10. push rod, 11. push plate, 12. stop nail, 13. movable mold base plate, 14. bracket, 15. second temperature sensor, 16. movable mold pad, 17. movable mold plate, 18. fixed mold plate, 19. guide column, 20. laser generator, 21. PLC control display screen, 22. PLC control cabinet, 23. push rod fixing plate, 24. absorption layer, M, injection mold, ZSJ, horizontal injection molding machine. DETAILED DESCRIPTION

[0033] The specific implementation modes of the present invention are described below to facilitate those skilled in the art to understand the present invention. Detailed implementation modes and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0034] like Figure 1 , 2As shown, a laser-assisted device for forming uneven wall thickness injection molded parts includes a laser control device, an injection mold M with an optical path, and a horizontal injection molding machine ZSJ. The laser control device is composed of a PLC control cabinet 22, a PLC control display screen 21, a laser generator 20, and an XYZ three-coordinate slide rail to achieve laser parameter and position control. Figure 3 and Figure 4 As shown, in the injection mold M with an optical path, the fixed mold plate 18 is fixedly connected to the fixed mold base plate 2 located above the fixed mold plate, and there are four guide pillars 19 between the fixed mold plate 18 and the movable mold plate 17, which can form relative movement; the movable mold pad 16 located below the movable mold plate is fixedly connected to the movable mold plate 17 and fixedly mounted on the bracket 14; the bracket 14 is fixedly connected to the movable mold base plate 13, and a movable push plate 11 is installed in the hollow structure of the bracket, and a push rod fixing plate 23 is fixedly connected to the push plate, and three push rods 10 are installed on the push rod fixing plate 23; the optical path is set in the fixed mold plate 18, a reflector 6 is bonded to the fixed block 4, and is fixed in the fixed mold plate 18 with a hexagon socket screw 5, a convex lens 7 is set directly below the reflector 6, and the convex lens 7 is bonded to the shoulder in the stepped groove in the vertical direction of the fixed mold plate, and a quartz glass 8 is provided below the convex lens 7, and an absorption layer 24 is provided on the bottom surface of the stepped groove below the quartz glass 8; a horizontal through groove is also opened on the right side of the fixed mold plate 18.

[0035] The fixing block 4 has a 45-degree inclined wedge surface for bonding the reflector 6; the through slot on the right side of the fixed template 18 is a rectangular through slot, the center plane of which is perpendicular to the center plane of the fixing block 4 and intersects with the center of the inclined wedge surface.

[0036] The laser control device can control the position of the laser generator in three directions and can adapt to injection molds of plastic parts with different wall thickness and uneven shapes.

[0037] In the movable mold plate, a first temperature sensor 9 and a second temperature sensor 15 are respectively installed below the thin-wall cavity and the thick-wall cavity to detect the temperature difference between the two locations and feed it back to the control system to achieve laser temperature control.

[0038] The absorption layer 24 can absorb laser energy and transfer heat to the wall surface below relatively evenly. Black paint or aluminum foil can be used as the absorption layer 24.

[0039] Example

[0040] Processing Figure 6 Taking the injection molded part shown in the figure as an example, the height of the thick wall area of ​​the injection molded part is 3mm, the height of the thin wall area is 1mm, the plastic raw material is PPA, the filling time is 0.1s, the melt temperature is 320℃, the mold temperature is 120℃, the maximum injection pressure is 150Mpa, and the gate position is located above the thick wall.

[0041] Initially set the laser power density to 2*10^4W / m 2, the spot diameter is 8mm, the thin-wall cavity is preheated for 2s, and then injection molding and filling the cavity are started; during the injection molding process, the laser continuously scans above the thin-wall cavity, and the power density of laser heating is controlled by temperature sensor feedback to make the temperature of the thin-wall cavity 60℃ higher than that of the thick-wall cavity. During pressure-holding cooling, the laser heat source only needs to ensure that the temperature of the thin-wall cavity and the thick-wall cavity are consistent when cooling with the cooling pipeline.

[0042] In this embodiment, Figure 5 The simulation results show that under the same molding process parameters and gate position, after the thin-walled cavity is regulated by an external laser heat source, the overall volume shrinkage of the molded product is relatively uniform except for the gate position. The shrinkage of the thin-walled part is roughly the same as that of the thick-walled part, thereby reducing the risk of shrinkage and warping due to uneven shrinkage.

[0043] The injection mold with its own optical path can effectively guide the laser into the cavity through the reflector and lens, and the laser energy can be effectively utilized and evenly act on the thin-walled cavity by using the laser scanning and absorption layer; the setting of quartz glass can guide the laser on the one hand, and reduce the weakening of the injection mold on the other hand.

[0044] Based on the thermal effect of laser, the role of laser is added to the injection molding process to regulate the temperature in the thin-wall cavity. The temperature sensor is used for feedback, and then the laser parameters are controlled by PLC to form a certain temperature difference between the thin-wall cavity and the thick-wall cavity. Finally, during injection molding, the plastic flow can fill the thin-wall area more smoothly. During pressure holding and cooling, the thick and thin walls can be formed relatively evenly, avoiding defects such as warping, deformation and weld marks.

Claims

1. A laser-assisted device for molding injection molded parts with uneven wall thickness, the device comprising a laser control device and a horizontal injection molding machine, characterized in that: An injection mold with an optical path is also provided. In the injection mold with an optical path, a fixed mold plate is fixedly connected to a fixed mold bottom plate located above the fixed mold plate, and four guide pillars are provided between the fixed mold plate and a movable mold plate located below the fixed mold plate, so that relative movement can be formed. The movable die pad located below the movable die plate is fixedly connected to the movable die plate and is fixedly mounted on the bracket; The bracket is fixedly connected to the movable mold bottom plate located below the bracket, and a movable push plate is installed in the hollow structure of the bracket. A push rod fixing plate is fixedly connected to the push plate, and three push rods are installed on the push rod fixing plate; The optical path is set in the fixed template, a reflector is glued on the fixed block and fixed in the fixed template with a hexagon socket screw, a convex lens is set directly below the reflector, the convex lens is glued to the shoulder in the vertical step groove in the fixed template, there is a piece of quartz glass below the lens, and an absorption layer is provided on the bottom surface of the step groove below the quartz glass; a horizontal through groove is also opened on the right side of the fixed template.

2. The laser-assisted device for molding uneven wall thickness injection molded parts according to claim 1, characterized in that: The laser control device consists of a PLC control cabinet, a PLC control display screen, a laser generator and an XYZ three-coordinate slide rail to achieve laser parameter and position control.

3. The laser-assisted device for molding uneven wall thickness injection molded parts according to claim 1, characterized in that: The fixing block is provided with a 45-degree inclined wedge surface for bonding the reflector; the through slot on the right side of the fixed template is a rectangular through slot, the center plane of which is perpendicular to the center plane of the fixing block and intersects with the center of the inclined wedge surface.

4. The laser-assisted device for molding uneven wall thickness injection molded parts according to claim 1, characterized in that: A temperature sensor is installed under each of the thick-wall cavity and the thin-wall cavity in the movable mold plate to detect the temperature difference between the two locations and feed it back to the control system to achieve laser temperature regulation.

5. The laser-assisted device for molding uneven wall thickness injection molded parts according to claim 1, characterized in that: The absorption layer can absorb laser energy and evenly transfer heat to the wall below.

6. A method for laser-assisted injection molding of uneven wall thickness parts, using the device as claimed in any one of claims 1 to 5, characterized in that the molding temperature in the thin-walled cavity is regulated by the thermal effect of the laser to control the uniform molding of the uneven wall thickness parts, and the specific steps are as follows: A. Based on the original injection molding parameters, an external heat source is applied locally in the thin-wall area, and the CAE software is used for analysis and simulation to obtain the optimal heat source parameters; B. Assembling the mold with the light path and installing it on a horizontal injection molding machine; C. According to the simulation parameters, input the initial laser parameters on the laser machine and the original injection molding parameters on the injection molding machine; D. The laser starts scanning the thin-wall cavity for preheating, and then starts injection molding; E. Injection molding is completed, pressure is maintained, cooling is performed, parts are removed, and inspection is performed.

7. The method according to claim 6, characterized in that In step A, the original injection molding parameters refer to the parameters previously used for the injection molding of the plastic part with uneven wall thickness, including injection pressure, injection temperature, injection time and holding time parameters; the applied external heat source is a reciprocating scanning heat source, and the heat source parameters include scanning speed and power density.

8. The method according to claim 6, characterized in that In the step D, the preheating time ranges from 1 to 25 seconds. After the injection molding starts, the temperature in the cavity is monitored in real time using temperature sensors under the thick-walled cavity and the thin-walled cavity in the mold, the temperature difference is fed back through the feedback system, and the laser parameters and position are adjusted using PLC control so that the temperature of the thin-walled cavity is higher than that of the thick-walled cavity, and the temperature difference ranges from 20°C to 100°C.

9. The method according to claim 6, characterized in that In the step E, during the cooling process, the laser continues to regulate the temperature of the thin wall so that the temperature of the thick wall cavity and the thin wall cavity are consistent.

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