Injection molding process of automobile side wing plate

Abstract

The invention discloses an injection molding process of an automobile side wing plate, and relates to the technical field of injection molding processing, and the injection molding process comprises the following steps: S1, preparing a plastic raw material of the automobile side wing plate, and pretreating the raw material; and S2, adding the pretreated plastic raw materials into a hopper of an injection molding machine, melting the plastic raw materials through heating and rotation of a screw rod by adopting three-section injection molding, and injecting the molten plastic raw materials into a mold. Filling and pressure maintaining are accurately controlled through three-section injection molding and dynamic pressure maintaining, the defects such as weld marks, sink marks and air holes on the surface of the automobile side wing plate are remarkably reduced, and stable filling through first-section low-speed injection molding and air involving prevention are relieved. The reduction of the appearance defects can greatly improve the surface quality of the automobile side wing plate, effectively control the critical dimension deviation of the product within a small range, better meet the assembly requirement, enable the plastic melt to be filled uniformly and cured well, and effectively improve the mechanical property and the dimensional accuracy of the automobile side wing plate.

Description

Technical Field

[0001] The invention relates to the technical field of injection molding, in particular to an injection molding process for a side wing panel of an automobile. Background Art

[0002] As the automotive industry's requirements for fuel economy and the range of new energy vehicles continue to increase, lightweight automotive parts have become the key. Injection-molded automotive fenders can be made of plastic materials, which have significant weight advantages over traditional metal materials. The injection molding process is very suitable for mass production of automotive fenders, and through the precise design of the injection mold, fenders with various curves, edges and decorative textures can be manufactured.

[0003] However, in the actual injection molding process, it is difficult to carry out targeted filling of different parts of the automobile side fenders. The surface of the automobile side fenders is prone to problems such as shrinkage marks, weld marks, and cavitation, which affect the appearance quality of the side fenders, make the surface uneven or have small holes, and also reduce the mechanical properties of the product. Summary of the invention

[0004] The object of the present invention is to provide an injection molding process for automobile side fenders, so as to solve the problem raised in the above-mentioned background technology that it is difficult to carry out targeted filling at different parts of the automobile side fenders, and the surface of the automobile side fenders is prone to shrinkage marks, weld marks, cavitations and other problems, which affect the appearance quality of the side fenders, make the surface uneven or have small holes, and also reduce the mechanical properties of the product.

[0005] To achieve the above object, the present invention provides the following technical solution: an injection molding process for a side wing panel of an automobile, comprising the following steps:

[0006] S1. preparing plastic raw materials for automobile side fenders and pre-treating the raw materials;

[0007] S2, adding the pretreated plastic raw material into the hopper of the injection molding machine, melting the plastic raw material and injecting it into the mold through heating and rotation of the screw, using three-stage injection molding;

[0008] S3. After the injection molding is completed, dynamic pressure is maintained to ensure that the plastic raw material is fully filled and solidified in the mold;

[0009] S4. After the pressure holding is completed, the product is cooled to room temperature and demolded through the cooling system of the mold;

[0010] S5, post-processing the demoulded product;

[0011] S6. Conduct quality inspection on the post-processed products, and package and store the qualified products.

[0012] Preferably, in step S1, the preprocessing comprises the following steps:

[0013] S11. Use a hot air circulation drying oven to dry the raw materials at 80-90℃ for 3-6 hours to ensure that the moisture content in the raw materials is reduced to the minimum to prevent bubbles or defects during the injection molding process;

[0014] S12, adding masterbatch to the raw materials for mixing and color matching, the amount of masterbatch added is 1% to 5% of the weight of the raw materials, the mixing time is 5 to 10 minutes, and the color is ensured to be uniform;

[0015] S13. Use a vibrating screen to screen the raw materials to remove impurities and particles that do not meet size requirements to ensure a smooth injection molding process.

[0016] Preferably, in step S2, the three-stage injection molding comprises the following steps:

[0017] S21. First, use low-speed and high-pressure injection molding to slowly fill the bottom of the cavity with the plastic melt. The injection speed can be set at 10-20 mm / s and the pressure at 60-80 MPa to slowly fill the bottom of the cavity to ensure that the melt flows evenly and avoid bubbles.

[0018] S22, then use medium speed and medium pressure injection molding to fill the main part of the cavity, ensuring that the melt can fill every corner of the cavity in time, the injection speed is adjusted to 30-50mm / s, the pressure is 40-60MPa, ensuring that the melt fills every corner of the cavity in time to avoid voids or unevenness;

[0019] S23. Finally, low-speed holding pressure is used to compensate for the volume loss caused by cooling and shrinkage of the plastic. The holding speed is 5-10mm / s, the holding pressure is 30-50MPa, and the holding time is maintained at 10-30 seconds to compensate for the volume loss caused by cooling and shrinkage and ensure the molding quality.

[0020] Preferably, in step S3, the post-injection dynamic pressure holding comprises the following steps:

[0021] S31, pressure holding preparation stage: Check the pressure holding system related equipment, ensure that the pressure sensor works normally, start the data acquisition system, and start recording the pressure data in the cavity through the pressure sensor;

[0022] S32, initial stage of dynamic pressure holding: after the pressure holding starts, the pressure sensor monitors the pressure change in the cavity in real time. When the pressure drop reaches 5% to 10% of the initial pressure holding pressure, it is judged that the plastic begins to shrink and the first pressure adjustment is performed;

[0023] S33, dynamic pressure holding mid-term stage: continuous pressure monitoring and feedback of thick-walled and thin-walled areas, and adjustment of pressure holding pressure;

[0024] S34, late stage of dynamic holding pressure: When the pressure drop trend in the cavity gradually slows down and approaches a stable state, the adjustment range of the holding pressure is reduced for fine-tuning, and a judgment is made on the completion of curing.

[0025] Preferably, in step S32, the process of the first pressure adjustment is: the control system sends a command to the hydraulic or electric actuator to increase the holding pressure, and the pressure increase range is 10% to 20% of the initial holding pressure.

[0026] Preferably, in step S33, the adjusting of the holding pressure includes adjusting the thick-walled area and adjusting the thin-walled area;

[0027] The thick wall area adjustment: when the pressure drop rate exceeds 0.2-0.3MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.3-0.5MPa per second;

[0028] The thin-wall area adjustment: when the pressure drop rate reaches 0.05-0.1 MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.01-0.03 MPa per second.

[0029] Preferably, in step S34, the process of judging whether the curing is complete is as follows: by monitoring the fluctuation of the pressure within 10 to 20 seconds, when the fluctuation amplitude is less than a set threshold value, the control system judges that the plastic has been fully cured.

[0030] Preferably, in step S5, the post-processing of the demoulding product comprises the following steps:

[0031] S51, trimming the edge of the automobile side wing panel after demoulding;

[0032] S52. Grinding and polishing the surface of the automobile side wing panel;

[0033] S53, after polishing, apply primer to the side fender of the car, and after the primer is dry, apply topcoat to enhance the appearance and protective layer;

[0034] S54. After the topcoat is applied, dry and cure it at 80-100°C for 30 to 60 minutes to ensure the adhesion and durability of the coating.

[0035] Preferably, in step S6, the quality inspection includes appearance inspection and size inspection, and the appearance inspection is used to check whether there are scratches, bubbles, and flow mark defects on the surface.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. In the present invention, the defects such as weld marks, shrinkage marks, cavitation, etc. on the surface of the automobile side fender are significantly reduced through the precise control of filling and holding pressure by three-stage injection molding and dynamic holding pressure, and are alleviated by the stable filling and avoidance of air entrapment of the first stage of low-speed injection molding. The reduction of these appearance defects can greatly improve the surface quality of the automobile side fender, effectively control the deviation of the key dimensions of the product within a smaller range, better meet the assembly requirements, make the plastic melt fill uniformly and solidify well, and effectively improve the mechanical properties and dimensional accuracy of the automobile side fender.

[0038] 2. In the present invention, the pressure and speed are precisely controlled according to the requirements of different stages of the product through multi-stage injection molding and dynamic pressure holding. In the filling stage, material overflow and waste caused by too fast melt flow rate or too high pressure are avoided. In the pressure holding stage, precise low-speed pressure holding can replenish materials according to the actual shrinkage of the automobile side wing panel, avoid overfilling, improve material utilization, directly reduce raw material costs, reduce waste and defective products, and reduce costs caused by rework or scrapping. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention is a flow chart of an injection molding process for an automobile side wing panel. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] See also Figure 1 The present invention provides a technical solution: an injection molding process for a side wing panel of an automobile, comprising the following steps:

[0042] Step 1: prepare plastic raw materials for automobile side fenders and pre-treat the raw materials; wherein the pre-treating comprises the following steps:

[0043] 11) Use a hot air circulation drying oven to dry the raw materials at 80-90°C for 3-6 hours to ensure that the moisture content in the raw materials is reduced to a minimum to prevent bubbles or defects during the injection molding process;

[0044] 12) Add masterbatch to the raw materials for mixing and color matching. The amount of masterbatch added is 1% to 5% of the weight of the raw materials. The mixing time is 5 to 10 minutes to ensure uniform color.

[0045] 13) Use a vibrating screen to screen the raw materials to remove impurities and particles that do not meet the size requirements, which can ensure the purity of the raw materials and the uniformity of the particles to ensure the smooth progress of the injection molding process;

[0046] Step 2: Add the pretreated plastic raw material into the hopper of the injection molding machine, melt the plastic raw material through heating and screw rotation, and inject it into the mold using three-stage injection molding;

[0047] Among them, the three-stage injection molding includes the following steps:

[0048] 21) First, low-speed and high-pressure injection molding is used to slowly fill the bottom of the cavity with the plastic melt. The injection speed can be set at 10-20 mm / s and the pressure at 60-80 MPa. The low speed can effectively avoid turbulence caused by excessive flow of the melt, reduce the possibility of air being drawn into the melt, and thus reduce the probability of bubbles and cavitation. The high pressure is to overcome the greater resistance faced by the melt when it initially enters the cavity, ensuring that the melt can be smoothly filled into every tiny corner at the bottom of the cavity, especially for some structures such as reinforcing ribs, grooves or small buckles that may exist at the bottom of the car's side fenders, which can ensure their complete filling and lay a good foundation for subsequent overall filling;

[0049] 22) Then use medium-speed and medium-pressure injection molding to fill the main part of the cavity to ensure that the melt can fill every corner of the cavity in time. The injection speed is adjusted to 30-50mm / s and the pressure is 40-60MPa. When the bottom of the cavity has been stably filled, appropriately increase the injection speed and adjust the pressure to allow the plastic melt to quickly diffuse to other parts of the cavity. The medium-speed and medium-pressure setting can not only speed up the filling speed and improve production efficiency, but also maintain the stability of the melt flow to a certain extent. At this stage, the melt can fill the main part of the cavity more smoothly, such as the large flat area and side contour of the side wing plate, reducing problems such as temperature drop and increased melt viscosity caused by too long filling time. At the same time, it can also effectively avoid new defects caused by too fast speed, such as aggravated weld marks or melt spraying.

[0050] 23) Finally, use low-speed holding pressure to make up for the volume loss caused by the cooling and shrinkage of the plastic. The holding speed is 5-10mm / s, the holding pressure is 30-50MPa, and the holding time is maintained at 10-30 seconds. After the cavity is basically filled, the plastic begins to cool and shrink. At this time, it is necessary to hold the pressure to make up for the volume loss caused by shrinkage. Low-speed holding pressure can accurately control the amount of plastic melt added to avoid problems such as overfilling and flash caused by excessive holding pressure or too fast speed. The setting of holding pressure and time is determined based on multiple factors such as the wall thickness of the car side fender, material properties, and cooling conditions of the mold. Appropriate holding pressure can make the density of the car side fender more uniform, reduce the appearance of shrinkage marks, and improve the appearance quality and dimensional accuracy of the product;

[0051] Step 3: After the injection molding is completed, dynamic pressure is maintained to allow the plastic raw material to be fully filled and solidified in the mold;

[0052] Among them, dynamic pressure holding after injection molding includes the following steps:

[0053] 31) Pressure holding preparation stage: Check the pressure holding system related equipment, ensure that the pressure sensor is working properly, start the data acquisition system, and start recording the pressure data in the cavity through the pressure sensor. The sampling frequency of the data acquisition system is set to 10-20 times per second, which can capture the slight changes in pressure in time and provide data support for accurate pressure holding control;

[0054] 32) Initial stage of dynamic pressure holding: After the pressure holding starts, the pressure sensor monitors the pressure change in the cavity in real time. When the pressure drop reaches 5% to 10% of the initial pressure holding pressure, it is judged that the plastic begins to shrink and the first pressure adjustment is performed. The pressure is replenished in time to maintain the filling state.

[0055] The process of the first pressure adjustment is as follows: the control system sends a command to the hydraulic or electric actuator to increase the holding pressure. The pressure increase is 10% to 20% of the initial holding pressure, which can quickly compensate for the shrinkage of the plastic in the initial cooling stage, ensure that the melt continues to fill the gaps caused by shrinkage, and ensure the integrity and density uniformity of the product.

[0056] 33) Dynamic holding pressure mid-term stage: Continuously monitor and feedback the pressure in thick-walled and thin-walled areas, and adjust the holding pressure;

[0057] Among them, adjusting the holding pressure includes adjusting the thick-walled area and adjusting the thin-walled area;

[0058] Thick-wall area adjustment: When the pressure drop rate exceeds 0.2-0.3MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.3-0.5MPa per second, which can effectively prevent the generation of sink marks and ensure the quality and strength of this area;

[0059] Adjustment of thin-walled area: When the pressure drop rate reaches 0.05-0.1MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.01-0.03MPa per second, which can ensure the dimensional accuracy and surface quality of the thin-walled area;

[0060] 34) Late stage of dynamic holding pressure: When the pressure drop in the cavity gradually slows down and approaches a stable state, the holding pressure adjustment range is reduced for fine-tuning, and the curing completion is judged;

[0061] The process of judging the completion of curing is as follows: by monitoring the fluctuation of pressure within 10 to 20 seconds, when the fluctuation amplitude is less than the set threshold, the control system judges that the plastic has been fully cured;

[0062] Step 4: After the pressure is maintained, the heat of the mold and the plastic product is removed through the mold cooling system by circulating cooling water or other cooling media, and the product is cooled to room temperature and demolded;

[0063] Step 5: Post-process the demoulded product; specifically, the following steps are included:

[0064] 51) Trim the edges of the automobile side fender after demoulding;

[0065] 52) Grinding and polishing the surface of automobile side wing panels;

[0066] 53) After polishing, the automobile side wing panel is primed and coated with topcoat after the primer is dry;

[0067] 54) Drying and curing after topcoat application at 80-100°C for 30-60 minutes can accelerate the evaporation of solvents and the curing reaction of resins in the topcoat, ensuring that the topcoat is fully cured to achieve good appearance and performance;

[0068] Step 6: Conduct quality inspection on the post-processed products, and package and store the qualified products. The quality inspection includes appearance inspection and size inspection. The appearance inspection is used to check whether there are scratches, bubbles, and flow marks on the surface.

[0069] In this method, raw materials are pretreated to remove moisture and impurities and accurately match colors, so that the product color is uniform and free of defects such as bubbles. Multi-stage injection molding and dynamic pressure holding reduce shrinkage marks, weld marks, cavitations, etc. Grinding, polishing and painting further improve surface gloss and flatness to make the appearance more beautiful. The three-stage injection molding and dynamic pressure holding have precise control over filling and pressure holding, combined with the requirements for mold cooling uniformity in the cooling and demolding links, and the dimensional inspection in post-processing, effectively control the key dimensional deviation of the product within a smaller range, better meet the assembly requirements, and accurately control the pressure and speed according to the requirements of different stages of the product through multi-stage injection molding and dynamic pressure holding to avoid material overflow and waste, reduce the scrap rate caused by quality problems, and increase the material utilization rate by 15%-20%. High material utilization rate directly reduces the cost of raw materials. Reducing waste and defective products reduces the cost of rework or scrapping. The second stage of the three-stage injection molding saves time by filling the main part at medium speed and medium pressure. Although dynamic pressure holding increases the control link, it reduces production interruptions and re-injection caused by quality problems through precise control. Overall, the molding cycle is shortened by 20%-30% compared with the traditional process.

[0070] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An injection molding process for a side wing panel of an automobile, characterized in that: The following steps are involved: S1. preparing plastic raw materials for automobile side fenders and pre-treating the raw materials; S2, adding the pretreated plastic raw material into the hopper of the injection molding machine, melting the plastic raw material and injecting it into the mold through heating and rotation of the screw, using three-stage injection molding; S3. After the injection molding is completed, dynamic pressure is maintained to ensure that the plastic raw material is fully filled and solidified in the mold; S4. After the pressure holding is completed, the product is cooled to room temperature and demolded through the cooling system of the mold; S5, post-processing the demoulded product; S6. Conduct quality inspection on the post-processed products, and package and store the qualified products.

2. The injection molding process of an automobile side wing panel according to claim 1, characterized in that: In step S1, the preprocessing includes the following steps: S11, use a hot air circulation drying oven to dry the raw materials at 80-90°C for 3-6 hours; S12, adding masterbatch to the raw materials for mixing and color matching, the amount of masterbatch added is 1% to 5% of the weight of the raw materials, and the mixing time is 5 to 10 minutes; S13. Use a vibrating screen to screen the raw materials to remove impurities and particles that do not meet size requirements.

3. The injection molding process of an automobile side wing panel according to claim 1, characterized in that: In step S2, the three-stage injection molding includes the following steps: S21, first use low-speed and high-pressure injection molding to slowly fill the bottom of the cavity with the plastic melt. The injection speed can be set at 10-20 mm / s and the pressure at 60-80 MPa; S22, then use medium speed and medium pressure injection molding to fill the main part of the cavity to ensure that the melt can fill every corner of the cavity in time. The injection speed is adjusted to 30-50mm / s and the pressure is 40-60MPa; S23. Finally, low-speed holding pressure is used to compensate for the volume loss caused by the cooling and shrinkage of the plastic. The holding speed is 5-10mm / s, the holding pressure is 30-50MPa, and the holding time is maintained at 10-30 seconds.

4. The injection molding process of an automobile side wing panel according to claim 3, characterized in that: In step S3, the post-injection dynamic pressure holding comprises the following steps: S31, pressure holding preparation stage: Check the pressure holding system related equipment, ensure that the pressure sensor works normally, start the data acquisition system, and start recording the pressure data in the cavity through the pressure sensor; S32, initial stage of dynamic pressure holding: after the pressure holding starts, the pressure sensor monitors the pressure change in the cavity in real time. When the pressure drop reaches 5% to 10% of the initial pressure holding pressure, it is judged that the plastic begins to shrink and the first pressure adjustment is performed; S33, dynamic pressure holding mid-term stage: continuous pressure monitoring and feedback of thick-walled and thin-walled areas, and adjustment of pressure holding pressure; S34, late stage of dynamic holding pressure: When the pressure drop trend in the cavity gradually slows down and approaches a stable state, the adjustment range of the holding pressure is reduced for fine-tuning, and a judgment is made on the completion of curing.

5. The injection molding process of an automobile side wing panel according to claim 4, characterized in that: In step S32, the process of the first pressure adjustment is: the control system sends a command to the hydraulic or electric actuator to increase the holding pressure, and the pressure increase range is 10% to 20% of the initial holding pressure.

6. The injection molding process of an automobile side wing panel according to claim 4, characterized in that: In step S33, the adjusting of the holding pressure includes adjusting the thick-walled area and adjusting the thin-walled area; The thick wall area adjustment: when the pressure drop rate exceeds 0.2-0.3MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.3-0.5MPa per second; The thin-wall area adjustment: when the pressure drop rate reaches 0.05-0.1 MPa per second, the control system adjusts the holding pressure by increasing the pressure by 0.01-0.03 MPa per second.

7. The injection molding process of an automobile side wing panel according to claim 4, characterized in that: In step S34, the process of judging whether the curing is complete is as follows: by monitoring the fluctuation of the pressure within 10 to 20 seconds, when the fluctuation amplitude is less than the set threshold value, the control system judges that the plastic has been fully cured.

8. The injection molding process of an automobile side wing panel according to claim 1, characterized in that: In step S5, the demoulding product post-processing includes the following steps: S51, trimming the edge of the automobile side wing panel after demoulding; S52. Grinding and polishing the surface of the automobile side wing panel; S53, after polishing, apply primer to the side wing panel of the automobile, and apply topcoat after the primer is dry; S54. After the topcoat is applied, dry and cure it at 80-100°C for 30 to 60 minutes.

9. The injection molding process of an automobile side wing panel according to claim 1, characterized in that: In step S6, the quality inspection includes appearance inspection and size inspection, and the appearance inspection is used to check whether there are scratches, bubbles, and flow mark defects on the surface.

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