Automobile roof low-pressure injection molding system and injection molding process

Abstract

The application provides a kind of automobile roof low-pressure injection molding system and injection molding process, including movable mould, fixed mould and hot runner assembly, movable mould and fixed mould are equipped with cavity, hot runner assembly includes hot runner plate, hot runner plate is equipped with glue inlet and multiple glue outlets, hot runner plate is equipped with multiple glue injection barrels that are passed in movable mould on the side close to cavity, both ends of each glue injection barrel are communicated with glue outlet and cavity respectively;Valve stem that can slide along its axial direction is passed in each glue injection barrel, one end of valve stem in glue injection barrel cavity is connected with valve core, the outer peripheral wall of valve core and the inner peripheral wall of glue injection barrel form glue inlet channel, and the opening size of glue inlet channel can change with the movement of valve core, the other end of valve stem is passed out of glue injection barrel;Driving mechanism for driving valve stem to move respectively is equipped on movable mould and / or hot runner plate.The automobile roof low-pressure injection molding system and injection molding process disclosed by the application can accurately control injection molding pressure and temperature, and protect PU foam cushion layer from heat damage.

Description

Technical Field

[0001] This invention relates to the field of injection molding system technology, and more specifically, to a low-pressure injection molding system and injection molding process for automotive headliners. Background Technology

[0002] A car headliner is an interior component installed beneath the sheet metal of a car's roof, serving multiple functions including heat insulation, sound insulation, sound absorption, and decoration. Currently, car headliners commonly employ low-pressure injection molding, a one-piece molding process. This process involves embedding non-woven fabric or other decorative materials into the mold cavity before injecting molten plastic. The molten plastic then contacts and firmly adheres to the decorative material during the molding process. This process offers advantages such as high molding efficiency, high interlayer adhesion strength, and one-piece molding without the need for secondary overlays. For example, producing headliner interior parts using low-pressure injection molding takes only about 87 seconds. Furthermore, low-pressure injection molding eliminates the need for adhesives, allowing for one-time molding and effectively avoiding odor pollution from glue, making it more low-carbon and environmentally friendly.

[0003] However, the existing mass-produced low-pressure injection molded headliner fabrics are basically double-layer composite structures, consisting of a surface knitted / suede fabric and a bottom non-woven fabric, with no cushioning foam layer in between. The finished headliner made from this double-layer fabric has high overall rigidity, no cushioning rebound when pressed, and poor interior tactile comfort, failing to meet the requirements of high-end passenger vehicle interiors for a softer, more refined appearance and feel.

[0004] To improve the tactile feel of interior materials, the industry has experimented with adding a PU foam cushioning layer to the fabric, designing a three-layer composite material consisting of fabric, PU foam, and non-woven fabric. However, this three-layer composite material cannot be directly adapted to traditional low-pressure injection molding processes. The reason for this is that traditional low-pressure injection molding systems have the following technical defects: Firstly, traditional low-pressure injection molding systems use hydraulic systems for pressure control, which suffers from poor pressure control accuracy and lag, making it impossible to match the cavity filling status in real time. Secondly, the temperature control method is a general, coarse-grained approach, resulting in large temperature fluctuations and an inability to accurately adapt to the heat resistance threshold of the PU foam. Under these conditions, the molten plastic flows directly into the fabric layer through the gate and cavity, easily causing the PU foam in the fabric layer to be burned by high temperatures. After being burned by heat, the internal foaming structure of the PU foam breaks down, leading to a significant decrease in the fabric's resilience after demolding and poor uniformity of rebound across different areas. Simultaneously, the thermal damage to the PU foam results in internal stress differences, causing large areas of uneven, orange-peel-like defects on the outer surface of the top layer, resulting in a persistently high rate of appearance defects and making it completely unsuitable for mass production.

[0005] In summary, existing low-pressure injection molding systems have inherent shortcomings in terms of pressure and temperature control precision, failing to balance melt flowability with the heat protection requirements of high-density PU foam. Consequently, stable mass production of low-pressure injection molding with thick, high-density PU foam profiles has been impossible for a long time. Therefore, there is an urgent need to develop a low-pressure injection molding system and method for automotive headliners that can precisely control injection pressure and temperature and effectively protect the PU foam cushioning layer from heat damage. Summary of the Invention

[0006] The present invention aims to provide a low-pressure injection molding system and injection molding process for automotive headliners, which can precisely control injection pressure and temperature and effectively protect the PU foam buffer layer from heat damage.

[0007] This invention provides a low-pressure injection molding system for automotive headliners: comprising a moving mold, a fixed mold, and a hot runner assembly. When the molds are closed, a cavity for molding the automotive headliner is formed between the moving mold and the fixed mold. The hot runner assembly includes a hot runner plate disposed on the side of the moving mold facing away from the fixed mold. The hot runner plate has an inlet and multiple outlets. Multiple injection cylinders are disposed on the side of the hot runner plate near the cavity. The injection cylinders are respectively inserted into the moving mold, with the inlet end of each injection cylinder communicating with the outlet and the outlet end communicating with the cavity. Each valve stem is slidable along its axial direction. One end of the valve stem, located inside the cavity of the injection cylinder, is connected to a valve core. A glue inlet channel is formed between the outer peripheral wall of the valve core and the inner peripheral wall of the injection cylinder. The opening size of the glue inlet channel can change with the movement of the valve core. The other end of the valve stem extends out of the injection cylinder. A driving mechanism is provided on the moving mold and / or hot runner plate. The driving mechanism is used to drive each valve stem to move along its axial direction to move the valve core in the cavity, thereby adjusting the opening size of the glue inlet channel.

[0008] Furthermore, the plurality of injection cylinders include a plurality of first injection cylinders and a plurality of second injection cylinders. The plurality of first injection cylinders are arranged circumferentially along the radially outer side of the cavity, and the plurality of second injection cylinders are arranged circumferentially along the radially inner side of the cavity. Both the first injection cylinders and the second injection cylinders are perpendicular to the hot runner plate.

[0009] Furthermore, the driving mechanism includes a first driving component and a second driving component. The first driving component is used to drive the valve stem in the first dispensing cylinder to move, and the second driving component is used to drive the valve stem in the second dispensing cylinder to move.

[0010] Furthermore, the first drive assembly includes a first servo electric cylinder, a horizontal connecting rod, and an actuator. The first servo electric cylinder is fixed to the outer wall of the moving mold, and the actuator is connected to the hot runner plate. One end of the horizontal connecting rod is connected to the drive end of the first servo electric cylinder, and the other end is connected to one end of the actuator. The other end of the actuator is connected to the end of the valve stem in the first injection cylinder away from the valve core. The actuator is used to convert the horizontal movement of the horizontal connecting rod into the vertical movement of the valve stem.

[0011] Furthermore, the actuator includes a fixed base and a flipping component. The fixed base is connected to the hot runner plate, and the flipping component is rotatably connected to the fixed base in a vertical plane. One end of the flipping component is connected to one end of the horizontal connecting rod, and the other end is connected to one end of the valve stem. The horizontal movement of the horizontal connecting rod is used to drive the flipping component to rotate vertically, thereby driving the valve stem to move vertically.

[0012] Furthermore, the second drive assembly includes a second servo electric cylinder, which is connected to the hot runner plate, and the drive rod of the second servo electric cylinder is used to directly drive the valve rod in the second dispensing cylinder to move vertically.

[0013] Furthermore, the first and second glue injection cylinders have the same structure, both including an inner tube and an outer tube. One end of the inner tube is connected to the glue outlet, and the outer tube is fitted over the inner tube. A mounting cavity for installing a heating element is formed between the inner tube and the outer tube. A nozzle is detachably connected to one end of the inner tube near the cavity. The nozzle has a glue spraying channel for connecting the cavity of the inner tube and the cavity. The valve core is located in the glue spraying channel.

[0014] Furthermore, the adhesive spraying channel includes a plurality of tapered holes spaced apart along its axial direction, and the end of each tapered hole near the cavity is the small diameter end. In any two adjacent tapered holes, the large end diameter of one tapered hole near the cavity is the same as the small end diameter of the other tapered hole. The valve core has a tapered surface that matches at least the tapered hole with the smallest diameter.

[0015] On the other hand, the present invention also provides an injection molding process for a low-pressure injection molding system for an automotive headliner, comprising the following steps: S1: Mold preparation: Heat the injection mold to 60-70℃ and maintain a constant temperature. Spray a special release agent evenly on the surface of the mold cavity to ensure that the parts can be demolded smoothly after molding and avoid damage to the fabric by pulling. S2: Fabric positioning: The pre-made three-layer composite fabric is laid flat inside the mold cavity and fits against the inner wall of the cavity in the bottom mold. The fabric is precisely fixed by the positioning structure preset around the mold. S3: Injection Molding: Molten rubber is injected into each injection cylinder through the inlet. The servo closed-loop control system of the gate electric cylinder is activated to control the drive mechanism, which drives the valve rod in each injection cylinder to move and continuously push the rubber into the cavity to form the roof skeleton on the back of the three-layer composite fabric. During the material pushing process, the melt is injected according to the segmented pressure and speed parameters appropriate to the corresponding fabric specifications. The overall temperature control range of the injection cylinder is controlled at 230-265℃, and the temperature control range of the nozzle is controlled at 265-275℃. The pushing pressure of each servo electric cylinder is controlled at 30-100 bar. After the rubber is pushed, it is held at a low pressure of 30-40 bar for 5-10 seconds to ensure that the melt fully adheres to the fabric without gaps or stress concentration. S4: Cooling and Demolding: After injection molding is completed, the mold is continuously cooled at a constant temperature. Once the overall temperature of the mold has dropped to 30-40℃, the mold is opened and demolded smoothly.

[0016] Furthermore, in step S3, the temperature control of the dispensing cylinder is 260-265℃ for the front section, 245-260℃ for the middle section, and 230-245℃ for the rear section; the control parameters of each servo electric cylinder are: initial filling pressure 30-40 bar, speed 28-35 mm / s; middle filling pressure 85-100 bar, speed 70-80 mm / s; final filling speed 15-20 mm / s, holding pressure 35 bar, and holding time 8 s.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: 1. High pressure control precision. This invention uses a servo electric cylinder in conjunction with a closed-loop control system to drive the valve stem and valve core, allowing for independent and precise adjustment of the opening size of the glue inlet channel for each injection cylinder, thus achieving precise control of the melt pressure and flow rate in the injection cavity. Compared to the uniform pressure adjustment method of traditional hydraulic systems, this invention offers higher pressure control precision and faster response speed, enabling real-time matching of changes in the cavity filling state.

[0018] 2. High temperature control accuracy. This invention adopts a segmented and independent precise temperature control method for the hot runner plate, dispensing cylinder (front / middle / rear section), and nozzle, with a temperature control accuracy of ±1℃. This ensures that the melt maintains a suitable temperature throughout the entire flow path, avoiding the defects of large temperature fluctuations under traditional coarse temperature control methods.

[0019] 3. Effectively protects the PU foam layer. Through precise pressure and temperature control, the temperature and impact force of the molten plastic when it comes into contact with the fabric layer are controlled within the range that the PU foam can withstand, avoiding the PU foam from being burned by high temperature or damaged by high pressure impact, and ensuring the resilience and uniformity of the fabric after the finished product is demolded.

[0020] 4. The finished product has a good appearance quality. Because the PU foam layer is not damaged by heat during the injection molding process and there is no internal stress difference, the outer surface of the finished product is free of orange peel defects, resulting in a high yield rate and fully meeting the requirements for mass production.

[0021] 5. Wide process versatility: The molding process of the fabric and the frame can be adapted to all low-pressure injection molded interior parts of automobiles, such as door panels, pillars, and dashboards, making it widely applicable.

[0022] The aforementioned advantages and improvements of the present invention will be set forth in detail in the following specific embodiments, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained through the structures particularly pointed out in the description and drawings. Attached Figure Description

[0023] Figure 1 This is a top view of the hot runner assembly structure of the low-pressure injection molding system for automotive headliners according to the present invention. Figure 2 This is a bottom view of the hot runner assembly structure of the low-pressure injection molding system for automotive roofs according to the present invention. Figure 3 This is a partial structural diagram of the hot runner assembly in this invention; Figure 4 for Figure 3 Another perspective view of the structure; Figure 5 for Figure 3 A structural diagram of a first driving component and a second driving component; Figure 6 This is a partial cross-sectional view of the first drive component and the first dispensing cylinder drive connection structure in the present invention, excluding the first servo electric cylinder; Figure 7 for Figure 6 Enlarged structural diagram at point X in the image.

[0024] Explanation of reference numerals in the attached figures: 1. Hot runner plate; 2. Dispensing cylinder; 201. Inner tube; 202. Outer tube; 203. Mounting cavity; 204. Nozzle; 205. Dispensing channel; 2051. Tapered hole; 206. First heating element; 2061. Heating section one; 2062. Heating section two; 207. Third heating element; 21. First dispensing cylinder; 22. Second dispensing cylinder; 3. Valve stem; 4. Valve core; 5. Dispensing channel; 6. First drive assembly; 601. First servo electric cylinder; 602. Horizontal connecting rod; 603. Fixed base; 604. Tilting component; 7. Second drive assembly; 701. Second servo electric cylinder. Detailed Implementation

[0025] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0026] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "fixed" and "connected" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0027] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1: like Figures 1 to 7 As shown in the figure, this application provides a low-pressure injection molding system for an automotive headliner, including a moving mold, a fixed mold, and a hot runner assembly. The moving mold and the fixed mold are arranged opposite to each other, and a cavity for molding the automotive headliner is formed between the moving mold and the fixed mold when the mold is closed. The side of the fixed mold facing the moving mold is the cavity surface, which is used to place the three-layer composite fabric to be injected (i.e., surface knitted / suede fabric + middle PU foam cushioning layer + bottom non-woven fabric). The side of the moving mold facing the fixed mold is provided with a molding surface that matches the shape of the headliner frame. In this structure, the moving mold and the fixed mold are not shown in the structural diagram; only the hot runner assembly is described in detail (related to the inventive point).

[0029] In a preferred embodiment, a guiding mechanism (such as guide pillars and guide sleeves) is provided between the moving mold and the fixed mold to ensure mold closing accuracy. Cooling channels are provided in the moving mold and / or the fixed mold, and the cooling channels are connected to an external cooling water source for rapid cooling of the mold after injection molding.

[0030] The hot runner assembly includes a hot runner plate 1 disposed on the side of the moving mold away from the fixed mold. The hot runner plate 1 is provided with a sprue and multiple outlets. The sprue is used to connect with the nozzle of the injection molding machine to receive molten plastic from the injection molding machine. The hot runner plate 1 is provided with a main runner and branch runners. One end of the main runner is connected to the sprue, and the other end is connected to each branch runner. Each branch runner is connected to its corresponding outlet.

[0031] The hot runner plate 1 is provided with multiple injection cylinders 2 on the side near the cavity. The multiple injection cylinders 2 are respectively inserted into the moving mold. The inlet end of each injection cylinder 2 is connected to the outlet and the outlet end is connected to the cavity. Molten plastic enters the hot runner plate 1 from the inlet, flows into each injection cylinder 2 from each outlet through the main runner and the branch runner, and then is injected into the cavity through the injection cylinder 2.

[0032] like Figure 6 As shown, each injection cylinder 2 is equipped with a valve stem 3 that can slide along its axial direction. One end of the valve stem 3, located inside the cavity of the injection cylinder 2, is connected to a valve core 4. A glue inlet channel 5 is formed between the outer peripheral wall of the valve core 4 and the inner peripheral wall of the injection cylinder 2, and the opening size of the glue inlet channel 5 can change with the movement of the valve core 4. The other end of the valve stem 3 protrudes from the injection cylinder 2. A drive mechanism is provided on the moving mold and / or the hot runner plate 1. The drive mechanism is used to drive each valve stem 3 to move along its axial direction, thereby moving the valve core 4 in the cavity and adjusting the opening size of the glue inlet channel 5.

[0033] In a preferred embodiment, the valve core 4 is integrally molded at one end of the valve stem 3 located inside the injection cylinder 2. This integral molding structure avoids gaps at the connection between the valve core 4 and the valve stem 3, preventing melt leakage or residue. It also improves the overall structural strength of the valve core 4 and valve stem 3, ensuring the positional accuracy and reliability of the valve core 4 during reciprocating motion.

[0034] like Figure 6 and Figure 7 As shown, the glue injection cylinder 2 specifically includes an inner tube 201 and an outer tube 202. One end of the inner tube 201 is connected to the glue outlet, and the outer tube 202 is fitted over the inner tube 201, forming a mounting cavity 203 between the inner tube 201 and the outer tube 202 for mounting the first heating element 206. The heating element is preferably an electric heating rod or an electric heating coil, distributed along the axial direction of the inner tube 201. A nozzle 204 is detachably connected to one end of the inner tube 201 near the cavity. The nozzle 204 has a glue spraying channel 205 for connecting the cavity of the inner tube 201 with the cavity, and the valve core 4 is located within the glue spraying channel 205.

[0035] As a more preferred implementation method, such as Figure 7 As shown, the glue spraying channel 205 includes multiple tapered holes 2051 spaced apart along its axial direction, with the end of each tapered hole 2051 near the cavity being the smaller diameter end. The larger diameter of one tapered hole 2051 near the cavity in any two adjacent tapered holes 2051 is the same as the smaller diameter of the other tapered hole 2051. That is, the inner wall of the glue spraying channel 205 has a multi-stage stepped tapered surface structure. The valve core 4 has a tapered surface that matches at least the smallest diameter tapered hole 2051. When the valve stem 3 drives the valve core 4 to move axially within the glue spraying channel 205, the tapered surface engages with tapered holes 2051 at different positions, enabling precise adjustment of the opening size of the glue inlet channel 5—when the tapered surface moves towards the cavity, the opening of the glue inlet channel 5 decreases; when the tapered surface moves away from the cavity, the opening of the glue inlet channel 5 increases.

[0036] In this embodiment, the dispensing cylinder 2 adopts a double-layer structure of inner tube 201 and outer tube 202. A heating element is installed between the inner tube 201 and outer tube 202 to precisely heat and maintain the temperature of the molten plastic flowing through the dispensing cylinder 2, preventing the melt from cooling down and solidifying during the flow process. The dispensing channel 205 adopts a multi-stage conical orifice 2051 structure, which, together with the valve core 4 with a conical surface, allows for stepless precise adjustment of the opening size of the dispensing channel 5, thereby enabling fine control of the melt flow rate and velocity injected into the cavity. The valve core 4 and valve stem 3 are integrally formed, eliminating connection gaps and improving motion accuracy and sealing reliability.

[0037] Understandably, in order to adapt to the injection molding of the roof structure with a skylight, while also considering the rationality of the mold space, in this embodiment, the multiple injection cylinders 2 include multiple first injection cylinders 21 and multiple second injection cylinders 22. The multiple first injection cylinders 21 are arranged circumferentially along the radially outer side of the cavity, and the multiple second injection cylinders 22 are arranged circumferentially along the radially inner side of the cavity. Both the first injection cylinders 21 and the second injection cylinders 22 are perpendicular to the hot runner plate 1. The structures of the first injection cylinders 21 and the second injection cylinders 22 are identical, and their specific structures have been described above and will not be repeated here. Similarly, in this embodiment, the driving mechanism includes a first driving assembly 6 and a second driving assembly 7. The first driving assembly 6 is used to drive the valve stems 3 within the multiple first injection cylinders 21 to move, and the second driving assembly 7 is used to drive the valve stems 3 within the multiple second injection cylinders 22 to move.

[0038] The injection cylinder 2 is arranged circumferentially along the inner and outer sides of the cavity, allowing the melt to be poured simultaneously from multiple positions within the cavity. This ensures uniform filling of large ceiling cavities and avoids insufficient filling or uneven pressure caused by excessively long flow paths. The independent drive design on both the inner and outer sides allows the injection volume and timing in different areas of the cavity to be adjusted independently according to the actual filling status.

[0039] like Figure 6 and 7As shown, the first drive assembly 6 includes a first servo cylinder 601, a horizontal connecting rod 602, and an actuator. The first servo cylinder 601 is fixed to the outer wall of the moving mold. The actuator is connected to the hot runner plate 1. One end of the horizontal connecting rod 602 is connected to the drive end of the first servo cylinder 601, and the other end is connected to one end of the actuator. The other end of the actuator is connected to the end of the valve stem 3 in the first injection cylinder 21 away from the valve core 4. The actuator is mainly used to convert the horizontal movement of the horizontal connecting rod 602 into the vertical movement of the valve stem 3. Specifically, the actuator includes a fixed base 603 and a flipping member 604. The fixed base 603 is connected to the hot runner plate 1, and a vertically penetrating mounting slot is provided on the fixed base 603. The flipping member 604 is rotatably connected to the mounting slot in the vertical plane. One end of the flipper 604 is connected to one end of the horizontal connecting rod 602, and the other end is connected to one end of the valve stem 3. The horizontal movement of the horizontal connecting rod 602 drives the flipper 604 to rotate vertically, thereby driving the valve stem 3 to move vertically. In this structure, the flipper 604 is a lever-like component, which is connected between the two side walls of the mounting slot through a rotating shaft. Through the cooperation of the horizontal connecting rod 602 and the flipper 604, the horizontal driving force of the first servo electric cylinder 601 is converted into the vertical movement of the valve stem 3, cleverly solving the spatial layout contradiction of limited space on the outer wall of the moving mold and the hot runner plate 1 located above the moving mold.

[0040] Similarly, the second drive assembly 7 includes a second servo cylinder 701, which is connected to the hot runner plate 1. The drive rod of the second servo cylinder 701 directly drives the valve rod 3 inside the second injection cylinder 22 to move vertically. This structure differs from the first drive assembly 6. Due to space constraints, the second servo cylinder 701 is directly installed inside the mold, specifically fixed to the hot runner plate 1, and drives the valve rod 3 inside the second injection cylinder 22 to move by direct drive of the drive rod.

[0041] In this embodiment, the first servo cylinder 601 and the second servo cylinder 701 are controlled by a gate electric cylinder servo closed-loop control system. This system monitors the position and driving force of the valve stem 3 in real time using position sensors and / or pressure sensors installed within the first servo cylinder 601 and the second servo cylinder 701, compares these values ​​with preset target values, and adjusts the output of the first servo cylinder 601 and the second servo cylinder 701 in real time using a closed-loop control algorithm (such as PID control) to achieve precise control of the valve stem 3 position. The two servo cylinder systems, working in conjunction with the closed-loop control system, enable precise control of the valve stem 3 position with fast response and high control accuracy.

[0042] It is understood that the injection molding system of this embodiment also includes a temperature control system. Accordingly, a second heating element and a first temperature sensor can be further provided in the hot runner plate 1. The second heating element is used to heat the hot runner plate 1, and the first temperature sensor is used to detect the temperature of the hot runner plate 1 in real time. The temperature control system controls the heating power of the second heating element according to the feedback signal of the first temperature sensor, so that the temperature of the hot runner plate 1 is maintained within a preset range.

[0043] Within the mounting cavity 203 of each dispensing cartridge 2, the second heating element comprises two independent structures, specifically a heating section 2061 and a heating section 2062 spaced apart along the axial direction. A second temperature sensor and a third temperature sensor are respectively positioned at corresponding locations on each heating section. The second heating element heats the dispensing cartridge 2, while the second and third temperature sensors detect the temperature at different locations on the dispensing cartridge 2 in real time. Based on the feedback signals from each temperature sensor, the temperature control system controls the heating power of each heating section, ensuring that the temperature of each dispensing cartridge 2 is independently maintained within a preset range.

[0044] Each nozzle 204 is equipped with a third heating element 207 and a fourth temperature sensor. The third heating element 207 is used to heat the nozzle 204, and the fourth temperature sensor is used to detect the temperature of the nozzle 204 in real time. The temperature control system controls the heating power of the third heating element 207 according to the feedback signal of the fourth temperature sensor, so that the temperature of the nozzle 204 is maintained within a preset range.

[0045] The temperature control system employs a multi-segment independent temperature control method, allowing independent temperature control for the hot runner plate 1, injection cylinder 2, and nozzle 204. Temperature control accuracy reaches ±1℃. This segmented, independent, and precise temperature control of the hot runner plate 1, injection cylinder 2, and nozzle 204 ensures that the molten plastic maintains a suitable temperature throughout its flow path from the inlet to the mold cavity, preventing the melt from solidifying and clogging due to excessively low temperatures or from being burned by excessively high temperatures in the PU foam layer of the material. Each segment's temperature can be independently adjusted, allowing for flexible configuration of temperature gradients according to actual process needs. For example, different temperature settings can be used for the front, middle, and rear sections of injection cylinder 2 to accommodate varying heat losses during melt flow. Precise temperature control is a crucial prerequisite for protecting the PU foam buffer layer from heat damage.

[0046] Example 2: The present invention also provides an injection molding process using the above-mentioned low-pressure injection molding system for automotive roofs, the process comprising the following steps.

[0047] Step S1: Mold Preparation The injection mold is heated to 60-70℃ and kept at a constant temperature. The mold heating can be achieved through heating channels or heating plates set inside the mold, and the constant temperature control is achieved through a temperature control system in conjunction with a temperature sensor for closed-loop adjustment.

[0048] Apply a specialized release agent evenly to the surface of the mold cavity. The purpose of the release agent is to ensure that the molded parts can be easily demolded, avoiding damage to the fabric due to difficult demolding. The release agent can be applied manually or using an automatic spraying device. The application should be even, without omissions or accumulation. The preferred mold temperature for this step is 65℃.

[0049] Step S2: Fabric Positioning The pre-fabricated three-layer composite fabric is laid flat inside the mold cavity and fitted against the inner wall of the moving mold. The three-layer composite fabric consists of a knitted / suede outer layer, a PU foam cushioning layer, and a non-woven fabric bottom layer. During fabric placement, the fabric is precisely fixed by pre-set positioning structures around the mold. These positioning structures can be in the form of hanging pins, pressure blocks, or positioning pins. The fabric should be placed flat and wrinkle-free, with appropriate allowance around the edges to ensure that the fabric is evenly compressed by the molten material during injection molding. After the fabric is placed, the mold is closed, causing the moving and fixed molds to shut down and form a closed cavity.

[0050] Step S3: Injection Molding Molten rubber (preferably polypropylene PP material) is injected into each injection cylinder 2 through the inlet. After being heated and melted in the injection molding machine, the rubber enters the inlet of the hot runner plate 1 through the injection molding machine nozzle, and then enters each injection cylinder 2 from each outlet through the main runner and branch runner.

[0051] The servo closed-loop control system of the gate electric cylinder is activated to control the drive mechanism, which in turn moves the valve rod 3 in each injection cylinder 2, continuously pushing the adhesive material into the cavity to form the roof skeleton on the back of the three-layer composite fabric. During the material pushing process, melt injection is performed according to the segmented pressure and speed parameters adapted to the corresponding fabric specifications. The overall temperature control range of the injection cylinder 2 is maintained between 230-265℃, and the temperature control range of the nozzle 204 is maintained between 265-275℃. The pushing pressure of each servo electric cylinder (including the first servo electric cylinder 601 and the second servo electric cylinder 701) is controlled between 30-100 bar.

[0052] After the adhesive is pushed in, maintain a low pressure of 30-40 bar for 5-10 seconds to ensure that the melt fully adheres to the fabric without gaps or stress concentration.

[0053] The temperature control range of 30-265℃ for the dispensing cylinder 22 and 265-275℃ for the nozzle 204 in this step ensures that the polypropylene melt has sufficient fluidity to smoothly fill the cavity, while controlling the melt temperature within the temperature range that the PU foam can withstand (PU foam can withstand temperatures of approximately 200℃), preventing the PU foam layer from being burned when the high-temperature melt directly contacts the fabric. The servo closed-loop control system precisely controls the pushing pressure (30-100 bar), which, compared to the coarse pressure adjustment of traditional hydraulic systems, can control pressure fluctuations within a very small range, avoiding sudden pressure changes that could cause the melt to impact the fabric at high speed. Low-pressure holding (30-40 bar) allows the melt to fully adhere to the fabric at a lower pressure, ensuring interlayer bonding strength while avoiding compression damage and stress concentration to the fabric caused by excessive pressure.

[0054] Step S4: Cooling and demolding After injection molding, the mold is continuously cooled at a constant temperature. Cooling is achieved by introducing cooling water through cooling channels in the moving mold and / or stationary mold. Once the entire mold has cooled to 30-40℃, the mold is smoothly opened and demolded. The preferred demolding temperature is 35℃.

[0055] During demolding, an ejector mechanism can be used to eject the molded canopy product from the moving mold. Since a release agent has been sprayed in step S1, the demolding resistance is low, which can prevent the fabric layer from being pulled and damaged.

[0056] In this embodiment, as a further explanation of step S3, the temperature control of the dispensing cylinder 2 adopts a segmented temperature control strategy: the front section (the end near the nozzle 204) is 260-265℃, the middle section is 245-260℃, and the rear section is 230-245℃.

[0057] The preferred control parameters for each servo electric cylinder are: initial filling pressure 30-40 bar, speed 28-35 mm / s; mid-filling pressure 85-100 bar, speed 70-80 mm / s; final filling speed 15-20 mm / s, holding pressure 35 bar, and holding time 8 s.

[0058] Specifically, in the initial stage of injection molding, as the melt begins to enter the cavity, a lower pressure (30-40 bar) and speed (28-35 mm / s) are used to ensure a smooth entry of the melt and prevent high-speed impact on the fabric, which could cause fabric displacement or damage to the PU foam layer. As filling progresses, the cavity gradually becomes filled with melt, increasing flow resistance. At this point, a higher pressure (85-100 bar) and speed (70-80 mm / s) are used to ensure the melt quickly fills all corners of the cavity, preventing incomplete filling. Towards the end of the filling process, as the cavity is about to be filled, the speed is reduced (15-20 mm / s) to prevent the melt from impacting the end of the cavity, which could cause fabric wrinkles or melt flash. After filling is complete, a pressure of 35 bar is maintained for 8 seconds to allow the melt to fully compact and adhere to the fabric under continuous pressure, compensating for volume shrinkage caused by melt cooling.

[0059] Preferably, the barrel temperature is controlled in segments: 240℃ for the rear segment, 255℃ for the middle segment, 260℃ for the front segment, and 68℃ for the nozzle; the mold temperature is kept constant at 65℃; the temperature fluctuation of each temperature zone is ≤±1℃; the electric cylinder pressure is controlled in segments: 35 bar for the initial filling stage, 90 bar for the middle filling stage, and 35 bar for the holding pressure stage; the injection speed is controlled in segments: 30 mm / s for the initial stage, 75 mm / s for the middle stage, and 18 mm / s for the final stage; the holding pressure time is 8s; the servo system response time is ≤50ms, and the pressure parameters are precisely controlled in a closed loop throughout the process.

[0060] In this preferred embodiment, the segmented temperature control strategy of the front, middle, and rear sections of the injection cylinder 2 can precisely match the temperature requirements of the melt at different positions within the injection cylinder 2—the front section has the highest temperature to ensure the melt is fully melted, the middle section is appropriately lowered to avoid overheating, and the rear section is further lowered to meet the protection requirements of the PU foam when approaching the cavity. The segmented pressure and speed control strategy ensures that the melt is in an optimal flow state at each stage of cavity filling: low pressure and low speed in the initial stage of filling to avoid impact on the fabric; high pressure and high speed in the middle stage of filling to ensure the cavity is filled; and low speed in the final stage of filling to avoid impact and flash. The holding pressure stage uses moderate pressure (35 bar) and sufficient holding time (8 s), which ensures sufficient adhesion and bonding strength between the melt and the fabric, while avoiding excessive internal stress and warping deformation of the finished product caused by excessive holding pressure. The comprehensive optimization of the above parameters enables the three-layer composite fabric with a PU foam buffer layer to achieve stable mass production in low-pressure injection molding process, ensuring the molding quality of the roof frame and effectively protecting the integrity and resilience of the PU foam layer.

[0061] Working principle: Before injection molding (in the open mold state), the three-layer composite fabric (outer fabric + middle PU foam + bottom non-woven fabric) is precisely fixed to the cavity surface of the moving mold using a positioning structure, and the mold is closed to form a closed cavity. During injection molding, the molten plastic enters the hot runner plate 1 through the sprue, and then enters each injection cylinder 2 through the branch channels. The servo closed-loop control system of the gate electric cylinder controls the movement of the valve rod 3 of each servo electric cylinder according to the preset segmented pressure and speed parameters, which drives the valve core 4 to move within the injection cylinder 2, precisely adjusting the opening size of each injection channel 5, so that the melt is injected into the cavity simultaneously from each injection cylinder 2 at the set pressure and speed, forming the top frame on the back of the fabric. During the injection molding process, the temperature control system performs segmented and precise temperature control on the hot runner plate 1, the front / middle / rear sections of the injection cylinder 2, and the nozzle 204. After injection molding, pressure is held, cooling is performed, and demolding is carried out to obtain the finished product.

[0062] In the description of this application, the references to terms such as "this embodiment," "some embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0063] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A low-pressure injection molding system for an automotive headliner, comprising a moving mold, a fixed mold, and a hot runner assembly, wherein, during mold closing, a cavity for molding the automotive headliner is formed between the moving mold and the fixed mold, characterized in that: The hot runner assembly includes a hot runner plate disposed on the side of the moving mold opposite to the fixed mold. The hot runner plate has an inlet and multiple outlets. Multiple injection cylinders are disposed on the side of the hot runner plate near the cavity. Each injection cylinder passes through the moving mold, with its inlet end connected to the outlet and its outlet end connected to the cavity. Each injection cylinder has a valve stem that can slide axially within it. One end of the valve stem, located within the cavity of the injection cylinder, is connected to a valve core. An injection channel is formed between the outer peripheral wall of the valve core and the inner peripheral wall of the injection cylinder, and the opening size of the injection channel can change with the movement of the valve core. The other end of the valve stem extends out of the injection cylinder. The moving mold and / or the hot runner plate is provided with a driving mechanism. The driving mechanism drives each valve stem to move axially, thereby moving the valve core within the cavity and adjusting the opening size of the injection channel.

2. The low-pressure injection molding system for automotive headliners according to claim 1, characterized in that: The plurality of injection cylinders include a plurality of first injection cylinders and a plurality of second injection cylinders. The plurality of first injection cylinders are arranged circumferentially along the radially outer side of the cavity, and the plurality of second injection cylinders are arranged circumferentially along the radially inner side of the cavity. The first injection cylinders and the second injection cylinders are both perpendicular to the hot runner plate.

3. The low-pressure injection molding system for automotive headliners according to claim 2, characterized in that: The driving mechanism includes a first driving component and a second driving component. The first driving component is used to drive the valve stems in a plurality of first dispensing cylinders to move, and the second driving component is used to drive the valve stems in a plurality of second dispensing cylinders to move.

4. The low-pressure injection molding system for automotive headliners according to claim 3, characterized in that: The first drive assembly includes a first servo electric cylinder, a horizontal connecting rod, and an actuator. The first servo electric cylinder is fixed to the outer wall of the moving mold. The actuator is connected to the hot runner plate. One end of the horizontal connecting rod is connected to the drive end of the first servo electric cylinder, and the other end is connected to one end of the actuator. The other end of the actuator is connected to the end of the valve stem in the first injection cylinder away from the valve core. The actuator is used to convert the horizontal movement of the horizontal connecting rod into the vertical movement of the valve stem.

5. The low-pressure injection molding system for automotive headliners according to claim 4, characterized in that: The actuator includes a fixed base and a flipping component. The fixed base is connected to the hot runner plate. The flipping component is rotatably connected to the fixed base in a vertical plane. One end of the flipping component is connected to one end of the horizontal connecting rod, and the other end is connected to one end of the pressure rod. The horizontal movement of the horizontal connecting rod is used to drive the flipping component to rotate vertically, thereby driving the valve stem to move vertically.

6. The low-pressure injection molding system for automotive headliners according to claim 4, characterized in that: The second drive assembly includes a second servo electric cylinder, which is connected to the hot runner plate, and the drive rod of the second servo electric cylinder is used to directly drive the valve rod in the second dispensing cylinder to move vertically.

7. The low-pressure injection molding system for automotive headliners according to claim 2, characterized in that: The first and second glue injection cylinders have the same structure, both including an inner tube and an outer tube. One end of the inner tube is connected to the glue outlet, and the outer tube is fitted outside the inner tube. An installation cavity for installing the first heating element is formed between the inner tube and the outer tube. A nozzle is detachably connected to one end of the inner tube near the cavity. The nozzle has a glue spraying channel for connecting the cavity of the inner tube and the cavity. The valve core is located in the glue spraying channel.

8. The low-pressure injection molding system for automotive headliners according to claim 7, characterized in that: The adhesive spraying channel includes a plurality of tapered holes spaced apart along its axial direction, and the end of each tapered hole near the cavity is the small diameter end. In any two adjacent tapered holes, the large end diameter of one tapered hole near the cavity is the same as the small end diameter of the other tapered hole. The valve core has a tapered surface that matches at least the tapered hole with the smallest diameter.

9. An injection molding process based on the low-pressure injection molding system for automotive roofs as described in claim 6, characterized in that, Includes the following steps: S1: Mold preparation: Heat the injection mold to 60-70℃ and maintain a constant temperature. Spray a special release agent evenly on the surface of the mold cavity to ensure that the parts can be demolded smoothly after molding and avoid damage to the fabric by pulling. S2: Fabric positioning: The pre-made three-layer composite fabric is laid flat inside the mold cavity and fits against the inner wall of the cavity in the bottom mold. The fabric is precisely fixed by the positioning structure preset around the mold. S3: Injection Molding: Molten rubber is injected into each injection cylinder through the inlet. The servo closed-loop control system of the gate electric cylinder is activated to control the drive mechanism, which drives the valve rod in each injection cylinder to move and continuously push the rubber into the cavity to form the roof frame on the back of the three-layer composite fabric. During the material pushing process, the melt is injected according to the segmented pressure and speed parameters appropriate to the corresponding fabric specifications. The overall temperature control range of the injection cylinder is controlled at 230-265℃, and the temperature control range of the nozzle is controlled at 265-275℃. The pushing pressure of each servo electric cylinder is controlled at 30-100 bar. After the rubber is pushed, it is held at a low pressure of 30-40 bar for 5-10 seconds to ensure that the melt fully adheres to the fabric without gaps or stress concentration. S4: Cooling and Demolding: After injection molding, the mold is continuously cooled at a constant temperature. Once the overall temperature of the mold has dropped to 30-40℃, the mold is opened and demolded smoothly.

10. The injection molding process of the low-pressure injection molding system for an automotive roof as described in claim 9, characterized in that: In step S3, the temperature of the dispensing cylinder is controlled as follows: 260-265℃ for the front section, 245-260℃ for the middle section, and 230-245℃ for the rear section. The control parameters of each servo electric cylinder are: initial filling pressure 30-40 bar, speed 28-35 mm / s; middle filling pressure 85-100 bar, speed 70-80 mm / s; final filling speed 15-20 mm / s, holding pressure 35 bar, and holding time 8 seconds.

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