Integrated forming method of light-weight high-strength automobile exterior trimming part

Abstract

The invention discloses an integrated forming method of a light-weight high-strength automobile exterior trimming part, which comprises the following steps: selecting long glass fiber reinforced polypropylene as a base material, adding a modifier, an antioxidant and a lubricant, mixing, extruding and granulating to obtain light-weight high-strength composite granules; an integrated forming mold is adopted, a mold cavity is subjected to polishing treatment, then a release agent is sprayed, preheating is conducted, and mold locking is completed; drying the prepared composite granules, adding into an injection molding machine, heating and melting, injecting into a mold cavity, maintaining the pressure, and cooling to obtain an exterior trimming part framework; keeping the mold slightly open, and performing flame treatment on the surface of the framework through a flame spray gun; rotating the mold to a coating station, closing the mold, and injecting the bi-component polyester paint to form a functional layer on the surface of the skeleton; and opening the mold and taking out to obtain a light-weight high-strength automobile exterior trimming part finished product. One-time forming of the exterior trimming part is achieved, framework preparation and surface functional layer forming are completed, the process is simplified, the cost is reduced, and the lightweight level and the structural strength of a product are improved.

Description

Integrated molding method for lightweight high-strength automotive exterior parts Technical Field

[0001] This invention relates to the field of automotive parts manufacturing technology, specifically to an integrated molding method for lightweight, high-strength automotive exterior parts. Background Technology

[0002] As the automotive industry moves towards low-carbon and lightweight designs, the design and manufacturing of automotive exterior components face the dual challenge of reducing weight to improve energy efficiency while ensuring structural strength to meet safety requirements. Currently, the manufacturing of automotive exterior components (such as front and rear bumpers, mudguards, and front-end modules) mostly adopts traditional segmented processes. This involves first preparing the basic framework through injection molding and stamping, followed by subsequent splicing, painting, assembly, and other processes to complete the finished product.

[0003] The existing technology has the following significant drawbacks: First, the cumbersome process leads to low production efficiency. Traditional processes involve multiple processing steps and transfer steps, which not only prolongs the production cycle but also increases labor and logistics costs, making it difficult to meet the high-speed mass production needs of the automotive industry. Second, it is difficult to balance lightweight and high-strength performance. In the selection of traditional materials, ordinary plastics are lightweight but lack strength, while metal materials meet the strength requirements but are too heavy. Even when using modified materials such as glass fiber reinforcement, the material performance is often not fully realized due to limitations in the molding process. Third, it has poor environmental performance and low material utilization. The energy consumption of traditional painting processes accounts for about 70% of the total energy consumption of automobile production, resulting in high carbon emissions. At the same time, the segmented processing process easily generates waste of scrap materials, and the material utilization rate is usually less than 60%. Fourth, the overall structural integrity is poor. The connection points formed by segmented splicing are prone to becoming weak points, affecting the impact resistance and service life of the exterior parts, and the splicing gaps are prone to causing insufficient assembly precision.

[0004] Existing integrated molding technologies still have many shortcomings. For example, some in-mold painting processes require extremely high precision in mold micro-opening, which easily leads to flash defects; some injection molding-painting integrated solutions still require secondary spraying and flash trimming, failing to truly simplify the process. Therefore, developing an integrated molding method for automotive exterior parts that can balance lightweight, high-strength performance, simplified processes, and environmental efficiency has become a pressing technical problem for the industry. Summary of the Invention

[0005] To address the technical shortcomings of existing automotive exterior parts manufacturing processes, such as cumbersome procedures, difficulty in achieving both lightweight and high strength, poor environmental performance, and insufficient structural integrity, this invention provides an integrated molding method for lightweight, high-strength automotive exterior parts. This method enables the one-time molding of the exterior parts to complete the skeleton preparation and surface functional layer molding, simplifying the process, reducing costs, and significantly improving the product's lightweight level and structural strength. The specific technical solution is as follows: An integrated molding method for lightweight high-strength automotive exterior parts includes the following steps: S1, Preparation of lightweight high-strength composite material: Long glass fiber reinforced polypropylene (LGFPP) is selected as the substrate, wherein the glass fiber length is 10-25mm and the glass fiber content is 20-40%. 5-10% modifier, 1-3% antioxidant, and 1-2% lubricant are added. The mixture is then put into a high-speed mixer and mixed at 80-100℃ for 10-15 minutes. Subsequently, it is extruded and granulated using a twin-screw extruder to obtain lightweight high-strength composite granules; S2, Mold pretreatment: An integrated molding mold with rotary positioning function is used. After polishing the mold cavity, a release agent is sprayed and preheated to [temperature missing]. S3. In-mold injection molding of the skeleton: After drying the composite granules prepared in step S1, add them to the injection molding machine, heat and melt them, and inject them into the mold cavity. Hold the pressure and cool to 40-50℃ to obtain the skeleton of the exterior part; S4. In-mold surface modification treatment: Keep the mold slightly open and perform flame treatment on the surface of the skeleton using a flame gun; S5. In-mold coating to form the functional layer: Rotate the mold to the coating station, close the mold, inject the two-component polyester paint, hold the pressure and cool to 30-40℃ to form a functional layer on the surface of the skeleton; S6. Finished product removal and post-processing: Open the mold and remove the molded part. After visual inspection and removal of small burrs, obtain the lightweight high-strength automotive exterior part finished product.

[0006] Preferably, the modifier is maleic anhydride-grafted polypropylene, the antioxidant is a hindered phenolic antioxidant, and the lubricant is calcium stearate; the density of the composite granules is 1.05-1.15 g / cm³, the tensile strength is ≥120 MPa, and the flexural modulus is ≥6000 MPa.

[0007] Preferably, in step S1, the screw speed of the twin-screw extruder is 200-300 r / min, and the extrusion temperature is 220-240℃.

[0008] Preferably, in step S2, the surface roughness Ra of the mold cavity is ≤0.8μm; the locking mechanism includes a bidirectional lead screw, a threaded plate and a limiting block, and locking is achieved by driving the bidirectional lead screw to rotate and causing the limiting block to be tightly attached to the limiting post.

[0009] Preferably, in step S3, the drying conditions for the composite granules are drying at 90-100℃ for 2-3 hours; the temperatures of each section of the injection molding machine barrel are 180-200℃ for the feeding section, 220-240℃ for the compression section, and 230-250℃ for the homogenization section; the injection pressure is 80-100MPa, the holding pressure is 30-50MPa, and the holding time is 10-20s.

[0010] Preferably, in step S4, the mold micro-opening gap is 2-5mm; the flame is a mixture of methane and air with an equivalent ratio of 0.9-1.2, a total flow rate of 100-150L / min, the distance between the spray gun and the skeleton surface is 75-85mm, and the processing time is 20-30ms.

[0011] Preferably, in step S5, the two-component polyester paint is composed of component A (isocyanate) and component B (polyester polyol + color paste + catalyst) mixed in a mass ratio of 1:1.2-1:1.5; the paint injection pressure is 20-30MPa, the injection speed is 80-120g / s, and the functional layer thickness is 300-500μm; after mold closing, the mold temperature is maintained at 50-60℃, and the holding time is 5-10s.

[0012] Compared with the prior art, the present invention has the following significant creative and beneficial effects: 1. Excellent lightweight and high strength performance: The present invention uses long glass fiber reinforced polypropylene composite material. Through reasonable glass fiber content and modifier ratio, the density of the finished exterior parts is only 1.05-1.15g / cm³, which is 40-50% lighter than traditional metal exterior parts. Compared with ordinary plastic exterior parts, the tensile strength is increased by more than 60% and the flexural modulus is increased by more than 50%, achieving a perfect balance between lightweight and high strength, which can effectively improve the energy utilization efficiency and driving range of vehicles.

[0013] Simplified process and significantly improved production efficiency: This invention uses an integrated molding process to complete the skeleton preparation and surface functional layer molding in one step, eliminating multiple processes such as splicing, secondary spraying, and trimming of flash in traditional processes, shortening the production cycle by more than 60%; at the same time, the use of automated molds and robotic arms reduces labor costs by 40%, enabling high-speed batch production and meeting the needs of large-scale manufacturing in the automotive industry.

[0014] Environmentally friendly and reduces production costs: This invention eliminates the traditional independent coating process, avoiding waste gas and wastewater pollution generated during the coating process, and reducing the carbon footprint of the manufacturing process by 30-35%; at the same time, the material utilization rate of composite granules is increased to over 90%, and waste of scrap materials is significantly reduced. Combined with the energy consumption reduction brought about by process simplification, the overall production cost is reduced by 30-40%.

[0015] Strong structural integrity and stable product quality: Through in-mold integrated molding, the weak links formed by segment splicing are avoided, the overall torsional stiffness of the finished exterior parts is increased by 20-30%, and the impact resistance is significantly enhanced. Detailed Implementation

[0016] A method for integral molding of lightweight, high-strength automotive exterior parts includes the following steps: S1. Preparation of lightweight, high-strength composite material: Long glass fiber reinforced polypropylene (LGFPP) is selected as the base material, wherein the glass fiber length is 10-25 mm and the glass fiber content is 20-40%. 5-10% of a modifier (maleic anhydride-grafted polypropylene), 1-3% of an antioxidant (hindered phenolic antioxidant), and 1-2% of a lubricant (calcium stearate) are added. The mixture is then added to a high-speed mixer and mixed at 80-100℃ for 10-15 min. Subsequently, it is extruded and granulated using a twin-screw extruder to obtain lightweight, high-strength composite granules. The density of the composite granules is 1.05-1.15 g / cm³, the tensile strength is ≥120 MPa, and the flexural modulus is ≥6000 MPa. The screw speed of the twin-screw extruder is 200-300 r / min, and the extrusion temperature is 220-240℃.

[0017] S2. Mold Pre-treatment: An integrated molding mold with rotary positioning function is adopted. The mold includes a fixed mold, a moving mold and an in-mold coating mechanism. The mold cavity corresponds to the shape design of the automotive exterior parts. The mold cavity is polished to ensure that the surface roughness Ra≤0.8μm. Then, a release agent is sprayed on the surface of the cavity and preheated to 50-70℃. The fixed mold and the moving mold are locked and fixed by the mold locking mechanism to achieve precise locking of the mold and avoid shaking during the molding process.

[0018] S3. In-mold injection molding of the skeleton: The composite granules prepared in step S1 are placed in a drying oven and dried at 90-100℃ for 2-3 hours to remove moisture, then added to the hopper of the injection molding machine; the composite granules are heated and melted by the injection molding machine, with the temperatures of each section of the barrel set as follows: feeding section 180-200℃, compression section 220-240℃, homogenization section 230-250℃; the molten composite material is injected into the mold cavity at an injection pressure of 80-100MPa, and after injection, a holding pressure of 30-50MPa is maintained for 10-20 seconds, followed by cooling to 40-50℃ to obtain the automotive exterior skeleton. The injection speed is 50-80mm / s, and the cooling method is internal cooling water circulation cooling with a cooling water flow rate of 2-3m / s.

[0019] S4. In-mold surface modification treatment: Keep the mold in a slightly open state (mold opening gap of 2-5mm), and use a robotic arm to operate a flame gun to flame treat the surface of the skeleton inside the cavity; the flame uses a mixture of methane and air, with an equivalent ratio of 0.9-1.2 and a total flow rate of 100-150L / min. The distance between the flame gun and the skeleton surface is controlled at 75-85mm, and the flame treatment time is 20-30ms. This increases the content of active groups on the skeleton surface by more than 30%, enhancing the bonding force between the skeleton and subsequent functional layers.

[0020] S5. In-mold coating forming functional layer: Rotate the mold 90° to the coating station, close the mold, and maintain the mold temperature at 50-60℃; use a two-component polyester paint as the functional layer material. The paint is composed of component A (isocyanate) and component B (polyester polyol + color paste + catalyst) mixed at a mass ratio of 1:1.2-1:1.5; place components A and B in vacuum storage tanks respectively, and stir evenly at 500-800 r / min at 40-60℃. Then, inject the mixed paint into the mold cavity at a pressure of 20-30 MPa using a high-pressure pump to form a functional layer with a thickness of 300-500 μm on the skeleton surface; after injection, hold the pressure for 5-10 seconds, and then cool to 30-40℃. The paint injection rate is 80-120 g / s. The functional layer has weather resistance (color difference ΔE ≤ 2.0 after 1000h of UV aging) and scratch resistance (scratch resistance grade ≥ 4).

[0021] S6. Finished Product Removal and Post-processing: Open the mold, eject the molded part through the ejector mechanism, and remove it using a robotic arm; perform an appearance inspection on the removed molded part to remove any possible small burrs (if any), and obtain a lightweight, high-strength automotive exterior part.

[0022] This invention overcomes the limitations of empirical formulation in traditional glass fiber reinforced materials. By precisely controlling the length (10-25mm) and content (20-40%) of long glass fibers and compounding them with a specific proportion of maleic anhydride-grafted polypropylene modifier, a composite material system with synergistic effects of "matrix-reinforcing phase-interface modifier" is constructed. This system solves the problems of uneven glass fiber dispersion and weak interfacial bonding in traditional composite materials, enabling the composite granules to achieve a tensile strength ≥120MPa and a flexural modulus ≥6000MPa while maintaining a lightweight structure with a density of only 1.05-1.15g / cm³, thus achieving a synergistic optimization of lightweight and high strength.

[0023] This invention employs a continuous, integrated process of "in-mold injection molding - in-mold flame modification - in-mold rotary coating," eliminating the independent steps of traditional processes such as post-frame transfer, secondary surface treatment, and offline coating. Through the rotational positioning function of the mold and the coordinated control of a robotic arm, seamless integration of different processes within the same mold is achieved. This solves the defects of existing integrated technologies, such as poor process integration, secondary contamination, or dimensional deviations, significantly improving production efficiency and product consistency.

[0024] To address the industry pain point of weak bonding between the skeleton and functional layer, an in-mold flame modification technology with precise and controllable parameters has been developed. By optimizing key parameters such as the equivalent ratio of mixed gas (0.9-1.2), the spray gun distance (75-85mm), and the processing time (20-30ms), the content of active groups on the skeleton surface is increased by more than 30%, significantly enhancing the interfacial bonding between the skeleton and the subsequent polyester functional layer. This effectively avoids quality problems such as functional layer detachment and cracking, while also avoiding the pollution and increased energy consumption caused by offline surface treatment.

[0025] Example 1: An integrated molding method for a lightweight, high-strength automotive front bumper, comprising the following steps: S1: Preparation of lightweight, high-strength composite material: Long glass fiber reinforced polypropylene (LGFPP) is selected as the substrate, wherein the glass fiber length is 15 mm and the glass fiber content is 30%. 8% maleic anhydride-grafted polypropylene, 2% hindered phenolic antioxidant, and 1.5% calcium stearate are added and mixed in a high-speed mixer at 90°C for 12 min. Subsequently, the mixture is extruded and granulated using a twin-screw extruder (screw speed 250 r / min, extrusion temperature 230°C) to obtain composite granules. The density of the composite granules is 1.10 g / cm³, the tensile strength is 135 MPa, and the flexural modulus is 6500 MPa.

[0026] S2. Mold pretreatment: An integrated molding mold with rotation positioning function is adopted, and the mold cavity corresponds to the shape of the front bumper of the car. The cavity is polished to Ra=0.6μm, and after spraying release agent, it is preheated to 60℃. The mold is precisely locked by a locking mechanism.

[0027] S3. In-mold injection molding skeleton: The composite granules are dried at 95℃ for 2.5h and added to the hopper of the injection molding machine; the temperature of each section of the barrel is set to 190℃ for the feeding section, 230℃ for the compression section, and 240℃ for the homogenization section; the molten composite material is injected into the mold cavity at an injection pressure of 90MPa and an injection speed of 65mm / s, the holding pressure is 40MPa, the holding time is 15s, and the temperature is cooled to 45℃ through the cooling water circulation system (water flow rate 2.5m / s) to obtain the front bumper skeleton.

[0028] S4. In-mold surface modification treatment: Maintain a mold opening gap of 3mm, and use a robotic arm to control a flame gun to flame treat the surface of the skeleton; the equivalent ratio of the mixed gas (methane + air) is 1.0, the total flow rate is 120L / min, the distance between the flame gun and the skeleton is 80mm, and the treatment time is 25ms.

[0029] S5. In-mold coating forming functional layer: Rotate the mold 90° to the coating station, close the mold and maintain the mold temperature at 55°C; mix the two-component polyester paint component A (isocyanate) and component B (polyester polyol + color paste + catalyst) at a mass ratio of 1:1.3, place them in a vacuum storage tank and stir evenly at 650 r / min at 50°C; inject the mixed paint into the cavity through a high-pressure pump at a pressure of 25 MPa and a speed of 100 g / s to form a 400 μm thick functional layer on the surface of the skeleton; hold the pressure for 8 seconds and then cool to 35°C.

[0030] S6. Finished Product Removal and Post-processing: Open the mold, eject the molded part and remove it through a robotic arm. After visual inspection, remove minor burrs to obtain the finished car front bumper.

[0031] The front bumper prepared in this embodiment has a density of 1.12 g / cm³, which is 45% lighter than the traditional steel front bumper. It has a tensile strength of 132 MPa, a bending modulus of 6400 MPa, a color difference ΔE=1.5 after 1000 hours of UV aging of the surface functional layer, a scratch resistance level of 5, a dimensional accuracy error of ±0.15 mm, and a product qualification rate of 98.5%.

[0032] Example 2: An integrated molding method for a lightweight, high-strength automotive mudguard, comprising the following steps: S1: Preparation of lightweight, high-strength composite material: Long glass fiber reinforced polypropylene (LGFPP) is selected as the substrate, wherein the glass fiber length is 10 mm and the glass fiber content is 25%. 6% maleic anhydride-grafted polypropylene, 1.5% hindered phenolic antioxidant, and 1% calcium stearate are added and mixed in a high-speed mixer at 85°C for 10 min. Subsequently, the mixture is extruded and granulated using a twin-screw extruder (screw speed 220 r / min, extrusion temperature 225°C) to obtain composite granules. The density of the composite granules is 1.08 g / cm³, the tensile strength is 125 MPa, and the flexural modulus is 6200 MPa.

[0033] S2. Mold pretreatment: An integrated molding mold with rotation positioning function is adopted, and the mold cavity corresponds to the shape of the car mudguard; the cavity is polished to Ra=0.7μm, and after spraying release agent, it is preheated to 55℃; the mold is precisely locked by the locking mechanism.

[0034] S3. In-mold injection molding skeleton: The composite granules are dried at 90℃ for 2 hours and added to the hopper of the injection molding machine; the temperature of each section of the barrel is set to 185℃ for the feeding section, 225℃ for the compression section, and 235℃ for the homogenization section; the molten composite material is injected at an injection pressure of 85MPa and an injection speed of 55mm / s, the holding pressure is 35MPa, the holding time is 12s, and the material is cooled to 42℃ through a cooling water circulation system (water flow rate 2m / s) to obtain the mudguard skeleton.

[0035] S4. In-mold surface modification treatment: Maintain a mold opening gap of 2mm. Flame treatment parameters: equivalent ratio of mixed gas 0.95, total flow rate 110L / min, spray gun distance 78mm, treatment time 22ms.

[0036] S5. In-mold coating forming functional layer: The mold is rotated 90° to close, and the mold temperature is 52℃; the two-component polyester paint A:B=1:1.2 is stirred evenly at 550r / min at 45℃; the paint is injected at a pressure of 22MPa and a speed of 90g / s to form a 350μm thick functional layer; after holding the pressure for 6s, it is cooled to 32℃.

[0037] S6. Finished product removal and post-processing: Remove the molded part, inspect its appearance, and remove any small burrs to obtain the finished car mudguard.

[0038] The mudguard prepared in this embodiment has a density of 1.10 g / cm³, which is 15% lighter than traditional plastic mudguards. It has a tensile strength of 123 MPa, a flexural modulus of 6100 MPa, a color difference ΔE=1.8 after 1000 hours of UV aging of the surface functional layer, a scratch resistance level of 4, a dimensional accuracy error of ±0.18 mm, and a product qualification rate of 98.2%.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Any adjustments and optimizations made by those skilled in the art to material selection, process parameters, etc., without departing from the principles and innovative concepts of the present invention, should be considered within the scope of protection of the present invention.

Claims

1. A method for integral molding of lightweight, high-strength automotive exterior parts, characterized in that, Includes the following steps: S1. Preparation of lightweight high-strength composite material: Long glass fiber reinforced polypropylene (LGFPP) is selected as the base material, with a glass fiber length of 10-25 mm and a glass fiber content of 20-40%. 5-10% modifier, 1-3% antioxidant, and 1-2% lubricant are added. The mixture is then added to a high-speed mixer and mixed at 80-100℃ for 10-15 minutes. Subsequently, it is extruded and granulated using a twin-screw extruder to obtain lightweight high-strength composite granules. S2. Mold pretreatment: An integrated molding mold with rotary positioning function is used. After polishing the mold cavity, a release agent is sprayed and preheated to 50-70℃. The mold is then locked using a locking mechanism. S3. In-mold injection molding of the skeleton: After drying the composite granules prepared in step S1, add them to the injection molding machine, heat and melt them, and inject them into the mold cavity. Hold the pressure and cool to 40-50℃ to obtain the skeleton of the exterior part; S4. In-mold surface modification treatment: Keep the mold slightly open and perform flame treatment on the surface of the skeleton using a flame gun; S5. In-mold coating to form the functional layer: Rotate the mold to the coating station, close the mold, inject the two-component polyester paint, hold the pressure and cool to 30-40℃ to form a functional layer on the surface of the skeleton; S6. Finished product removal and post-processing: Open the mold and remove the molded part. After visual inspection and removal of minor burrs, obtain the finished lightweight high-strength automotive exterior part.

2. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S1, the modifier is maleic anhydride-grafted polypropylene, the antioxidant is a hindered phenolic antioxidant, and the lubricant is calcium stearate; the density of the composite granules is 1.05-1.15 g / cm³, the tensile strength is ≥120 MPa, and the flexural modulus is ≥6000 MPa.

3. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S1, the screw speed of the twin-screw extruder is 200-300 r / min, and the extrusion temperature is 220-240℃.

4. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S2, the surface roughness Ra of the mold cavity is ≤0.8μm; the locking mechanism includes a bidirectional lead screw, a threaded plate and a limiting block, and locking is achieved by driving the bidirectional lead screw to rotate and causing the limiting block to be tightly attached to the limiting post.

5. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S3, the drying conditions for the composite granules are 90-100℃ for 2-3 hours; the temperatures of each section of the injection molding machine barrel are 180-200℃ for the feeding section, 220-240℃ for the compression section, and 230-250℃ for the homogenization section; the injection pressure is 80-100MPa, the holding pressure is 30-50MPa, and the holding time is 10-20s.

6. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S4, the mold micro-opening gap is 2-5mm; the flame uses a mixture of methane and air with an equivalent ratio of 0.9-1.2, a total flow rate of 100-150L / min, a distance of 75-85mm between the spray gun and the skeleton surface, and a processing time of 20-30ms.

7. The integrated molding method for lightweight high-strength automotive exterior parts according to claim 1, characterized in that: In step S5, the two-component polyester paint is made by mixing component A (isocyanate) and component B (polyester polyol + color paste + catalyst) in a mass ratio of 1:1.2-1:1.5; the paint injection pressure is 20-30MPa, the injection speed is 80-120g / s, and the functional layer thickness is 300-500μm; after mold closing, the mold temperature is maintained at 50-60℃, and the holding pressure time is 5-10s.