A process for integrally injection molding an automobile air conditioner housing

Abstract

The application relates to the technical field of automobile air conditioner shells, and discloses an automobile air conditioner shell integrated injection molding process method, which comprises the following steps: S1, raw material modification mixing: mixing glass fiber, a toughening agent and a plastic matrix resin at a high speed according to proportions to obtain modified composite injection raw material; S2, sectional gradient drying and dehumidifying: the modified composite injection raw material is subjected to sectional temperature rising drying and dehumidifying, and the water content of the raw material is controlled to be lower than 0.02%; and S3, screw multi-stage plasticizing and melting. According to the scheme, a resin, glass fiber and a toughening agent are compounded to form a modification system, the toughness and structural uniformity of the material are significantly improved, the defects of insufficient rigidity and easy deformation of single PP material are improved, a three-section gradient temperature rising and dehumidifying mode is adopted, absorbed water and combined water in the raw material can be completely removed step by step, the problems of raw material caking and incomplete water removal caused by traditional single high-temperature drying are avoided, appearance defects such as injection molding bubbles, silver lines and pinholes are eliminated from the source of the raw material, and the shell forming yield is greatly improved.

Description

Technical Field

[0001] This application relates to the field of automotive air conditioning housing technology, and in particular to a method for integral injection molding of automotive air conditioning housing. Background Technology

[0002] The automotive air conditioning housing is a core load-bearing and protective structural component of the vehicle's air conditioning system. It primarily houses the evaporator, air ducts, dampers, and electronic control components. Its molding precision, structural strength, and dimensional stability directly affect the assembly precision, operating noise, and overall vehicle durability. Currently, automotive air conditioning housings are commonly injection molded from glass fiber reinforced polypropylene. This material offers advantages such as light weight, low cost, high rigidity, and temperature and corrosion resistance, making it widely used in the production of air conditioning structural components for passenger cars, new energy commercial vehicles, and other models.

[0003] In existing technologies, automotive air conditioning housings mostly employ traditional one-piece injection molding processes. These processes are relatively fixed, generally using a molding mode of fixed-temperature plasticizing, constant screw back pressure, uniform-speed injection, single-pressure holding, and constant-temperature cooling. This approach has several inherent technical defects in actual mass production. Firstly, traditional injection molding raw material pretreatment often uses a single high-temperature drying mode. This rapid heating rate and limited dehumidification zone easily lead to problems such as surface melting and clumping of the raw material, and incomplete removal of internal moisture. The accuracy of raw material moisture content control is poor, resulting in defects such as bubbles, pinholes, and silver streaks inside the molded housing, leading to a low product yield. Simultaneously, conventional simple mixing processes easily cause uneven dispersion of glass fiber and additives, resulting in large differences in local mechanical properties and poor structural uniformity within the housing.

[0004] Secondly, traditional injection molding processes lack precise control over melt rheological properties, relying solely on fixed process parameters for plasticizing and molding. This prevents dynamic adjustment of melt viscosity based on plasticizing temperature, screw operating conditions, and batch-to-batch variations in raw materials. Significant fluctuations in melt flow index occur between different production batches and under varying ambient temperatures, easily leading to issues such as incomplete mold filling due to excessively high melt viscosity or flash overflow due to excessively low melt viscosity. Poor melt plasticizing uniformity and weak batch consistency severely impact the molding precision and assembly interchangeability of air conditioner housings, failing to meet the production requirements of high-precision automotive components. Summary of the Invention

[0005] To address the problem that the aforementioned process flow is relatively rigid, and the molding mode of fixed temperature plasticizing, constant screw back pressure, uniform speed injection, single pressure holding and constant temperature cooling has many inherent technical defects in actual mass production, this application provides a one-piece injection molding process for automotive air conditioning housings.

[0006] The technical solution provided in this application for an integrated injection molding process for automotive air conditioning housings is as follows:

[0007] A method for integral injection molding of automotive air conditioning housing, comprising the following steps:

[0008] S1. Raw material modification and mixing: Glass fiber, toughening agent and plastic matrix resin are blended at high speed in proportion to obtain modified composite injection molding raw material;

[0009] S2. Segmented gradient drying and dehumidification: Modified composite injection molding raw materials are dried and dehumidified in segments with increasing temperature to control the moisture content of the raw materials to below 0.02%;

[0010] S3, Multi-stage plasticizing and melting with screw: The raw material is sheared and plasticized by screw in a four-stage temperature range to obtain a uniform melt.

[0011] S4. Adaptive control of melt viscosity: The melt flow index is calculated based on the real-time temperature of the melt, and the melt viscosity is dynamically adjusted by the screw back pressure.

[0012] S5. High-speed integrated injection filling: The melt is filled into the mold cavity of the air conditioner housing in one go by the variable speed segmented injection method to achieve integrated molding and filling of the housing.

[0013] S6. Multi-stage pressure holding and stabilizing molding: The melt in the mold cavity is stabilized and fed by a segmented decreasing pressure holding method;

[0014] S7. Gradient Cooling and Shaping: The mold is cooled in stages using a gradient temperature reduction method to obtain a low-internal-stress, one-piece molded air conditioner housing; wherein, the melt flow index (MFI) satisfies the calculation formula:

[0015] In the formula, K is the melt material constant, T is the plasticizing temperature, P is the screw back pressure, and t is the plasticizing holding time.

[0016] Preferably, in step S1, the modified composite injection molding raw material comprises, by weight: 70-85 parts PP resin, 10-20 parts alkali-free glass fiber, 3-8 parts POE toughening agent, 0.2-0.6 parts antioxidant, and 0.1-0.3 parts lubricant; the high-speed blending speed is 800-1200 r / min, the mixing time is 8-15 min, and the mixing temperature is 40-60℃.

[0017] Preferably, the S2 segmented gradient drying and dehumidification is as follows: the first stage temperature is 60-70℃ and the drying time is 20-30 minutes; the second stage temperature is 80-90℃ and the drying time is 40-60 minutes; the third stage temperature is 95-105℃ and the drying time is 30-40 minutes; and the hot air circulation speed throughout the process is 1.2-1.8 m / s.

[0018] Preferably, the four-stage plasticizing temperatures of the S3 are as follows: feeding stage 180-190℃, compression stage 195-205℃, homogenization stage 210-220℃, and nozzle stage 215-225℃; the screw speed is 40-80 r / min.

[0019] Preferably, in step S4, the screw back pressure adjustment range is 0.4 to 1.2 MPa. When the melt flow index (MFI) is lower than the standard range, the screw back pressure is increased; when the melt flow index (MFI) is higher than the standard range, the screw back pressure is decreased to stabilize the melt flow index at 18 to 25 g / 10 min.

[0020] Preferably, the S5 variable speed segmented injection specifically comprises: a first stage of low-speed injection, with an injection speed of 20-35 mm / s, filling 1 / 3 of the cavity volume; a second stage of medium-speed injection, with an injection speed of 40-60 mm / s, filling 1 / 3 to 2 / 3 of the cavity volume; and a third stage of high-speed injection, with an injection speed of 65-85 mm / s, completing the overall cavity filling, with an injection pressure of 80-110 MPa.

[0021] Preferably, the S6 multi-stage pressure holding and stabilization specifically comprises: a first-stage pressure holding pressure of 75-85 MPa and a holding time of 3-5 s; a second-stage pressure holding pressure of 55-65 MPa and a holding time of 6-10 s; and a third-stage pressure holding pressure of 35-45 MPa and a holding time of 10-15 s.

[0022] Preferably, the S7 gradient cooling specifically involves: an initial mold temperature of 55–65°C, a first stage of uniform cooling to 40–45°C at a cooling rate of 1.5–2.5°C / min, a second stage of uniform cooling to 25–30°C at a cooling rate of 0.5–1.2°C / min, and an overall cooling time of 40–70 seconds.

[0023] In summary, this application includes the following beneficial technical effects:

[0024] 1. This invention significantly improves the toughness and structural uniformity of materials through a compound modification system of resin, glass fiber, and toughening agent, and improves the defects of insufficient rigidity and easy deformation of single PP materials. At the same time, it adopts a three-stage gradient heating and dehumidification method, which can thoroughly remove adsorbed water and bound water inside the raw materials step by step, avoiding the problems of raw material clumping and incomplete moisture removal caused by traditional single high-temperature drying. It eliminates appearance defects such as injection molding bubbles, silver lines, and pinholes from the source of raw materials, and greatly improves the yield of shell molding.

[0025] 2. This invention establishes a dedicated MFI rheological calculation formula and combines it with multi-parameter linkage control of plasticizing temperature, screw back pressure, and plasticizing time to dynamically correct the melt rheological properties. It stably controls the melt flow index within the optimal molding range of 18-25 g / 10 min. Compared with traditional fixed parameter injection molding, it effectively solves the problems of melt overflow due to temperature fluctuations and raw material differences, and incomplete mold filling due to excessively thick melt. Combined with four-segment zoned precise plasticizing, it makes the melt plasticizing more uniform and the rheological stability stronger, significantly improving the shell density and mechanical uniformity.

[0026] 3. This invention avoids the problems of high-speed injection air marks and low-speed incomplete filling by using a segmented injection method that combines fast and slow injection. It achieves precise molding through progressively decreasing holding pressure, first compensating for shrinkage, then shaping, and finally releasing pressure, stabilizing the shell's dimensions. Combined with a gradient cooling mode that starts fast and then slows, it ensures rapid shell shaping while mitigating internal residual stress. The final molded air conditioner shell has a wall thickness error of ≤±0.15mm, warpage deformation of ≤0.3mm, and is free of weld lines, shrinkage cavities, and cracks. Its dimensional accuracy, structural stability, and assembly adaptability are far superior to traditional one-piece injection molding processes, meeting the high-precision assembly requirements of automotive air conditioning systems and demonstrating strong industrial applicability. Attached Figure Description

[0027] Figure 1 This is a flowchart of the overall process for the one-piece injection molding of the automotive air conditioning housing according to the present invention. Detailed Implementation

[0028] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0029] This invention discloses a one-piece injection molding process for automotive air conditioning housings. The overall process includes seven core steps: raw material modification and mixing, segmented gradient drying and dehumidification, multi-stage screw plasticizing and melting, adaptive melt viscosity control, high-speed one-piece segmented injection filling, multi-stage holding and stabilizing molding, and gradient cooling molding. This invention innovatively introduces a melt flow index calculation formula. By real-time acquisition of plasticizing temperature, screw back pressure, and plasticizing time parameters, it dynamically corrects melt viscosity and flow uniformity, ensuring consistency of melt state under different batches of raw materials and different environmental conditions. Combined with a segmented variable-speed injection and gradient cooling system, it significantly reduces residual internal stress and molding defects in the one-piece molded housing, improving product dimensional stability and structural strength.

[0030] The specific formula for calculating the melt flow index is as follows:

[0031]

[0032] Wherein, K is the melt material constant, with a value range of 0.85 to 0.95 suitable for glass fiber reinforced PP systems; T is the plasticizing temperature of the screw homogenization section, in °C; P is the screw back pressure, in MPa; and t is the screw plasticizing holding time, in min. This invention uses this formula to close-loop control of the melt flow index, stably controlling the melt MFI within the optimal molding range of 18–25 g / 10 min, ensuring a balance between melt filling fluidity and molding density.

[0033] In a preferred embodiment, PP resin is used as the matrix resin in the raw material modification and mixing stage, combined with alkali-free glass fiber to improve structural rigidity and dimensional stability. POE toughening agent improves the brittleness and cracking problem of the glass fiber system, while antioxidants and lubricants enhance melt processing stability and demolding performance. By limiting the high-speed blending speed, temperature, and duration, uniform dispersion of glass fiber, additives, and matrix resin is ensured, avoiding glass fiber agglomeration and stratification, thus providing a raw material basis for subsequent uniform plasticization.

[0034] In a preferred embodiment, the segmented gradient drying and dehumidification adopts a three-stage heating and drying mode. Compared with the traditional single high-temperature drying, it can avoid the problems of the raw material surface overheating and melting, clumping, and internal moisture not being able to be discharged. The low-temperature stage initially removes surface adsorbed moisture, the medium-temperature stage deeply removes the bound water inside the resin, and the high-temperature stage thoroughly dehumidifies and sets the shape, gradually reducing the moisture content of the raw material to below 0.02%, thus eliminating defects such as bubbles, silver streaks, and pores during injection molding.

[0035] In a preferred embodiment, the screw multi-stage plasticizing and melting adopts a four-section zoned independent temperature control structure to match the rheological characteristics of plastic melt. The feeding section preheats and softens the resin at a low temperature to avoid local overheating and decomposition; the compression section heats up and shears to melt, achieving preliminary plasticization of the resin; the homogenization section precisely controls the temperature to ensure uniform melt temperature; and the nozzle section moderately heats up to reduce melt outlet viscosity and improve mold filling smoothness, which, together with a constant screw speed, achieves uniform shearing and plasticizing of the melt.

[0036] In a preferred embodiment, adaptive melt viscosity control relies on the melt flow index formula to achieve closed-loop control. The current melt MFI value is calculated based on real-time plasticizing parameters, and the screw back pressure is dynamically adjusted. When the MFI is low and the melt flowability is poor, the back pressure is appropriately increased to enhance screw shearing and improve plasticizing uniformity. When the MFI is high and the melt viscosity is too low and prone to overflow, the back pressure is decreased to reduce shear heat and ensure the melt is always within the optimal molding viscosity range.

[0037] In a preferred embodiment, the variable-speed segmented injection filling is set with three injection speeds according to the differentiating logic of the mold cavity filling. The initial low-speed slow filling avoids jetting and air marks caused by high-speed injection; the middle section is medium-speed and smooth, ensuring uniform filling of the cavity; the final high-speed rapid filling of the cavity ensures the integrity of the shell outline, and the matching injection pressure achieves a full and integrated filling.

[0038] In a preferred embodiment, the multi-stage pressure holding and stabilizing molding adopts a progressively decreasing pressure holding mode. In the early stage of molding, high pressure holding is used for rapid shrinkage compensation to offset the volume shrinkage of the melt during cooling. In the middle stage, medium pressure is used for stabilizing and molding to stabilize the basic dimensions of the shell. In the later stage, low pressure holding is used for relaxation to release surface stress and avoid stress concentration and demolding warping problems caused by single high pressure holding.

[0039] In a preferred embodiment, gradient cooling and shaping adopts a segmented cooling strategy of fast cooling followed by slow cooling. The rapid cooling in the early stage enables the shell to be quickly shaped and prevents deformation; the slow cooling in the later stage releases the internal residual stress, solves the shell warping, deformation, and internal micro-crack defects caused by traditional quenching process, and ensures shell wall thickness uniformity and dimensional accuracy.

[0040] To further illustrate the feasibility and stability of the process parameters of this invention in a complete and clear manner, three sets of specific embodiments covering the entire numerical range of the claims are provided below.

[0041] Example 1

[0042] This embodiment provides a method for integral injection molding of automotive air conditioning housings, the specific steps of which are as follows:

[0043] S1. Raw material modification and mixing: Take 85 parts by weight of PP resin, 10 parts of alkali-free glass fiber, 3 parts of POE toughening agent, 0.2 parts of antioxidant, and 0.1 parts of lubricant; mix at 40℃ and 800r / min for 15min to obtain a uniformly modified composite injection molding raw material.

[0044] S2. Segmented gradient drying and dehumidification: the first stage is drying at 60℃ for 30 minutes, the second stage is drying at 80℃ for 60 minutes, and the third stage is drying at 95℃ for 40 minutes. The hot air circulation speed is 1.2 m / s, and the moisture content of the raw material after dehumidification is ≤0.02%.

[0045] S3, Multi-stage plasticizing and melting of screw: Four-stage temperature control is adopted, with the feeding section at 180℃, the compression section at 195℃, the homogenization section at 210℃, and the nozzle section at 215℃. The screw speed is 40r / min to complete uniform plasticizing and melting.

[0046] S4. Adaptive control of melt viscosity: Based on the melt flow index formula, the material constant K is taken as 0.85, and the screw back pressure is adjusted to 0.4MPa to stabilize the melt flow index at 18g / 10min.

[0047] S5, High-speed integrated injection filling: The first stage fills the cavity to 1 / 3 at a low speed of 20mm / s, the second stage fills the cavity to 2 / 3 at a medium speed of 40mm / s, and the third stage fills the cavity to the full speed of 65mm / s, with an injection pressure of 80MPa.

[0048] S6, Multi-stage pressure holding and stabilization: Level 1 pressure holding 75MPa, holding for 5s; Level 2 pressure holding 55MPa, holding for 10s; Level 3 pressure holding 35MPa, holding for 15s.

[0049] S7. Gradient cooling and shaping: The initial mold temperature is 55℃. The first stage cools down to 40℃ at 1.5℃ / min, and the second stage cools down to 25℃ at 0.5℃ / min. The total cooling time is 70s. After demolding, an integrated automotive air conditioning housing is obtained.

[0050] Example 2

[0051] The specific steps in this embodiment are as follows:

[0052] S1. Raw material modification and mixing: 78 parts PP resin, 16 parts alkali-free glass fiber, 5 parts POE toughening agent, 0.4 parts antioxidant, and 0.2 parts lubricant; mix at 50℃ and 1000r / min for 12min.

[0053] S2. Segmented gradient drying and dehumidification: the first stage is drying at 65℃ for 25 minutes, the second stage is drying at 85℃ for 50 minutes, and the third stage is drying at 100℃ for 35 minutes, with a hot air velocity of 1.5 m / s.

[0054] S3, multi-stage plasticizing and melting of the screw: feeding section 185℃, compression section 200℃, homogenization section 215℃, nozzle section 220℃, screw speed 60r / min.

[0055] S4. Adaptive control of melt viscosity: material constant K is set to 0.90, screw back pressure is 0.8MPa, and melt flow index is controlled at 22g / 10min.

[0056] S5, High-speed integrated injection filling: The first stage fills 1 / 3 of the cavity at 30mm / s, the second stage fills 2 / 3 of the cavity at 50mm / s, and the third stage fills the cavity completely at 75mm / s, with an injection pressure of 95MPa.

[0057] S6, Multi-stage pressure holding and stabilization: Level 1 pressure holding 80MPa, 4s; Level 2 pressure holding 60MPa, 8s; Level 3 pressure holding 40MPa, 12s.

[0058] S7. Gradient cooling and shaping: Initial mold temperature 60℃, first stage cooling at 2.0℃ / min to 42℃, second stage cooling at 0.8℃ / min to 28℃, total cooling time 55s.

[0059] Example 3

[0060] The specific steps in this embodiment are as follows:

[0061] S1. Raw material modification and mixing: 70 parts PP resin, 20 parts alkali-free glass fiber, 8 parts POE toughening agent, 0.6 parts antioxidant, 0.3 parts lubricant; mix at 60℃ and 1200r / min for 8min.

[0062] S2. Segmented gradient drying and dehumidification: the first stage is drying at 70℃ for 20 minutes, the second stage is drying at 90℃ for 40 minutes, and the third stage is drying at 105℃ for 30 minutes, with a hot air velocity of 1.8 m / s.

[0063] S3, multi-stage plasticizing and melting of the screw: feeding section 190℃, compression section 205℃, homogenization section 220℃, nozzle section 225℃, screw speed 80r / min.

[0064] S4. Adaptive control of melt viscosity: material constant K is set to 0.95, screw back pressure is 1.2MPa, and melt flow index is controlled at 25g / 10min.

[0065] S5, High-speed integrated injection filling: The first stage fills 1 / 3 of the cavity at 35mm / s, the second stage fills 2 / 3 of the cavity at 60mm / s, and the third stage fills the cavity completely at 85mm / s, with an injection pressure of 110MPa.

[0066] S6, Multi-stage pressure holding and stabilization: Level 1 pressure holding 85MPa, 3s, Level 2 pressure holding 65MPa, 6s, Level 3 pressure holding 45MPa, 10s.

[0067] S7. Gradient cooling and shaping: Initial mold temperature 65℃, first stage cooling to 45℃ at 2.5℃ / min, second stage cooling to 30℃ at 1.2℃ / min, total cooling time 40s.

[0068] The foregoing description, with reference to preferred embodiments, illustrates an exemplary implementation of the integral injection molding process for an automotive air conditioning housing provided by this disclosure. However, those skilled in the art will understand that various modifications and alterations can be made to the above specific embodiments without departing from the spirit of this disclosure, and various combinations can be made to the various technical features and structures proposed in this disclosure without exceeding the protection scope of this disclosure, the protection scope of which is determined by the appended claims.

Claims

1. A method for integral injection molding of an automotive air conditioning housing, characterized in that, Includes the following steps: S1. Raw material modification and mixing: Glass fiber, toughening agent and plastic matrix resin are blended at high speed in proportion to obtain modified composite injection molding raw material; S2. Segmented gradient drying and dehumidification: Modified composite injection molding raw materials are dried and dehumidified in segments with increasing temperature to control the moisture content of the raw materials to below 0.02%; S3, Multi-stage plasticizing and melting with screw: The raw material is sheared and plasticized by screw in a four-stage temperature range to obtain a uniform melt. S4. Adaptive control of melt viscosity: The melt flow index is calculated based on the real-time temperature of the melt, and the melt viscosity is dynamically adjusted by the screw back pressure. S5. High-speed integrated injection filling: The melt is filled into the mold cavity of the air conditioner housing in one go by the variable speed segmented injection method to achieve integrated molding and filling of the housing. S6. Multi-stage pressure holding and stabilizing molding: The melt in the mold cavity is stabilized and fed by a segmented decreasing pressure holding method; S7. Gradient Cooling and Shaping: The mold is cooled in stages using a gradient temperature reduction method to obtain a low-internal-stress, one-piece molded air conditioner housing; wherein, the melt flow index (MFI) satisfies the calculation formula: In the formula, K is the melt material constant, T is the plasticizing temperature, P is the screw back pressure, and t is the plasticizing holding time.

2. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, In S1, the modified composite injection molding raw material includes, by weight: 70-85 parts PP resin, 10-20 parts alkali-free glass fiber, 3-8 parts POE toughening agent, 0.2-0.6 parts antioxidant, and 0.1-0.3 parts lubricant; the high-speed blending speed is 800-1200 r / min, the mixing time is 8-15 min, and the mixing temperature is 40-60℃.

3. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, The S2 segmented gradient drying and dehumidification process is as follows: the first stage temperature is 60-70℃ and the drying time is 20-30 minutes; the second stage temperature is 80-90℃ and the drying time is 40-60 minutes; the third stage temperature is 95-105℃ and the drying time is 30-40 minutes; and the hot air circulation speed throughout the process is 1.2-1.8 m / s.

4. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, The S3 four-stage graded plasticizing temperatures are as follows: feeding section 180~190℃, compression section 195~205℃, homogenization section 210~220℃, nozzle section 215~225℃; screw speed 40~80r / min.

5. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, In S4, the screw back pressure adjustment range is 0.4 to 1.2 MPa. When the melt flow index (MFI) is lower than the standard range, the screw back pressure is increased; when the melt flow index (MFI) is higher than the standard range, the screw back pressure is decreased to stabilize the melt flow index at 18 to 25 g / 10 min.

6. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, The S5 variable speed segmented injection is specifically as follows: the first stage is low-speed injection, with an injection speed of 20-35 mm / s, filling 1 / 3 of the cavity volume; the second stage is medium-speed injection, with an injection speed of 40-60 mm / s, filling 1 / 3 to 2 / 3 of the cavity volume; the third stage is high-speed injection, with an injection speed of 65-85 mm / s, completing the overall cavity filling, with an injection pressure of 80-110 MPa.

7. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, The S6 multi-stage pressure holding and stabilization is as follows: Level 1 pressure holding pressure 75-85MPa, pressure holding time 3-5s; Level 2 pressure holding pressure 55-65MPa, pressure holding time 6-10s; Level 3 pressure holding pressure 35-45MPa, pressure holding time 10-15s.

8. The integral injection molding process for automotive air conditioning housing according to claim 1, characterized in that, The S7 gradient cooling process is as follows: the initial mold temperature is 55-65℃, the first stage cools down to 40-45℃ at a constant rate of 1.5-2.5℃ / min, the second stage cools down to 25-30℃ at a constant rate of 0.5-1.2℃ / min, and the overall cooling time is 40-70s.

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