A control method and device for back pressure exhaust of an injection molding machine

Abstract

The application discloses a control method and device for back pressure exhaust of an injection molding machine, and relates to the field of injection molding machines, mainly comprising the following steps: a top pin is used to press and slide a slidable side plate to an initial position; the top pin is used to press the slidable side plate through a top pin proportional back pressure valve, and under the combined pressure of back pressure and material pressure, gas in injection melt is discharged through a safety gap under the action of pressure difference; the cavity pressure in a mold cavity is controlled to be within a safe cavity pressure range before the slidable side plate is returned to the maximum displacement through the control of the size of the back pressure. The application controls the speed of the return of the ejector rod through the regulation and control of the size of the back pressure, so that the pressure in the cavity is higher than the cavity pressure during normal injection molding without the need of increasing the injection pressure, so that the gas in the injection melt is discharged through the safety gap under high pressure by means of the better fluid performance of the injection melt compared with the injection melt, and the injection molding and molding are realized simultaneously.

Description

Technical Field

[0001] This invention relates to the field of injection molding machines, and more specifically to a control method and device for back pressure venting in injection molding machines. Background Technology

[0002] During the injection molding process, gases are generated inside the barrel, mold cavity, or after the raw material is heated. If these air cannot be effectively expelled, they can seep into the raw material, resulting in incomplete injection molding or compressed air seeping into the product, causing quality defects such as porosity and silver streaks. Venting within the mold cavity can usually be addressed by adding venting grooves or using inserts. However, for some highly viscous, poorly flowing materials, especially those used to produce long, cylindrical hydraulic seals, the deep mold cavities and the need for excellent sealing performance place even greater demands on venting. Traditional venting methods cannot effectively compress the air within the raw material, and poor venting can easily lead to defects such as porosity, significantly reducing the product's yield.

[0003] To address the lack of corresponding injection molding processes for such hydraulic sealing products, and in order to ensure sufficient venting and uniform compaction of the plastic raw material, eliminate internal stress, and guarantee uniform product wall thickness and no air bubbles, it is urgent to optimize and improve the venting methods during the injection molding process. Summary of the Invention

[0004] To better expel gases from the melt during high-viscosity injection molding and avoid affecting the quality of the finished product, this invention proposes a back pressure venting control method for injection molding machines. This method includes a slidable side plate on the ejector pin, which slides with the ejector pin. The slidable side plate can be controlled to slide within the mold cavity under the pressure of the ejector pin. A safety clearance is maintained between the slidable side plate and the mold contact surface. The specific steps include:

[0005] S1: After receiving the confirmation signal that the injection molding machine has closed the mold to the bottom, the ejector pin presses the sliding side plate and slides it to the initial position, and records the screw position in the initial state;

[0006] S2: Control the injection melt to be injected into the mold cavity at a uniform speed through the injection port, and obtain the ejector pin retraction amount caused by the sliding side plate being pressed back under the action of material pressure;

[0007] S3: The ejector pin is controlled by the proportional back pressure valve to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference.

[0008] S4: By controlling the back pressure, the cavity pressure in the mold cavity is kept within a safe range before the sliding side plate retracts to the maximum displacement, and the screw position at the maximum displacement is recorded.

[0009] S5: Controls the injection melt to be injected into the mold cavity through the injection port at a preset holding pressure.

[0010] Furthermore, in step S3, when the cavity pressure is at a safe cavity pressure, the injection molten metal cannot be discharged through the safe gap due to the viscosity of the molten metal.

[0011] Furthermore, in step S4, the screw position at the point of maximum displacement is the pressure holding switching point.

[0012] Furthermore, in step S4, during the uniform injection stage, the retraction speed of the sliding side plate is adjusted by decreasing the back pressure in several stages, and the arrival of each stage is determined based on the retraction amount of the push rod.

[0013] Furthermore, step S5 is followed by the following step:

[0014] S51: Obtain the screw position after the pressure holding period ends and the actual screw stroke of the current injection mold cycle;

[0015] S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value. If yes, proceed to step S53. If no, adjust according to the decrease of the current back pressure, proceed to the next injection molding cycle after mold opening, and return to step S1.

[0016] S53: Adjust the ejector pin retraction speed by adjusting the back pressure of each stage in the next injection molding cycle and adjusting the retraction distance ratio of each stage. After mold opening, proceed to the next injection molding cycle and return to step S1.

[0017] Furthermore, in step S52, the actual screw stroke is expressed by the following formula:

[0018] s = s1 - s0

[0019] In the formula, s is the actual screw stroke, s0 is the screw position in the initial state, and s1 is the screw position after the pressure holding period ends;

[0020] The ideal screw stroke is expressed by the following formula:

[0021] s ′ =(4000M) / (kρπd) 2 )

[0022] In the formula, s' is the ideal screw stroke, M is the total mass of the target injection molded part, k is a coefficient, ρ is the room temperature density of the injection plastic, and d is the screw diameter.

[0023] Furthermore, in step S53, the adjustment of the back pressure magnitude at each stage is expressed by the following formula:

[0024] Pnm =(A n -A n+1 ) / (A0-A N )*(s / s ′ )*Pn m-1

[0025] In the formula, n is a constant from 0 to N, m is the module count, N is the total number of stages, and Pn m Let A be the back pressure value in the nth stage of the mth module. n Let A be the screw position in the nth stage. n+1 Let A0 be the screw position in the (n+1)th stage, and A0 be the screw position when the sliding side plate begins to displace under material pressure. N Pn represents the screw position in the last stage of the current module. m-1 This represents the back pressure value of the nth stage in the (m-1)th module.

[0026] The present invention also proposes a control device for back pressure venting in injection molding machines, comprising:

[0027] The sliding side plate is mounted on the ejector pin and can slide with the ejector pin. Under the pressure of the ejector pin, the sliding position is controlled in the mold cavity.

[0028] A safety gap is provided between the sliding side plate and the mold contact surface;

[0029] The main control chip is used to control the ejector pin to press against the sliding side plate and slide it to the initial position after receiving the confirmation signal that the injection molding machine has closed the mold to the bottom.

[0030] The injection module is used to control the injection melt to be injected into the mold cavity at a uniform speed through the injection port when the sliding side plate slides to the initial position, and to control the injection melt to be injected into the mold cavity at a preset holding pressure through the injection port after entering the holding pressure stage.

[0031] The ejector pin proportional back pressure valve is used to control the ejector pin to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference, and the cavity pressure in the mold cavity is controlled within the safe cavity pressure range before the sliding side plate retracts to the maximum displacement.

[0032] A displacement sensor is used to obtain the amount of retraction of the ejector pin during the injection molding process.

[0033] Furthermore, in the ejector pin proportional back pressure valve, when the cavity pressure is under the safe cavity pressure, the injection molten metal cannot be discharged through the safe gap due to the viscosity of the molten metal.

[0034] Furthermore, during the process of the ejector pin proportional valve controlling the ejector pin, the screw position at the maximum displacement of the sliding side plate is the pressure holding switching point.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] (1) The method and device for controlling back pressure exhaust of injection molding machine described in this invention controls the speed of ejector retraction by adjusting the back pressure, thereby making the pressure in the cavity higher than the cavity pressure during normal injection without increasing the injection pressure, so that the gas in the injection melt can be discharged through the safety gap under high pressure by taking advantage of the better fluid properties of the injection melt, thus realizing simultaneous injection molding and forming.

[0037] (2) By adjusting the retraction speed, the actual stroke of the screw can be adjusted, thereby better controlling the quality of the finished product and reducing the scrap rate caused by unstable weight. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating the steps of a control method for back pressure venting in an injection molding machine.

[0039] Figure 2 This is a module diagram of a control device for back pressure venting in an injection molding machine;

[0040] Figure 3 This is a schematic diagram showing the location of the sliding side panel structure.

[0041] Explanation of reference numerals in the attached drawings: 1-Ejector rod, 2-Sliding side plate, 3-Ejector pin, 4-Cavity. Detailed Implementation

[0042] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0043] Example 1

[0044] To address the problem of air bubbles causing defects in finished products when injection molding long cylindrical parts from highly viscous, poorly flowing raw materials, this invention proposes a method for controlling back pressure venting in injection molding machines, such as... Figure 3 As shown, within the cavity 4, a slidable side plate 2 is first installed on the ejector pin 1, which can extend and slide with the ejector pin 1. One side of this slidable side plate is the mold cavity, and the other side contacts the ejector pin 3, thus allowing the slidable side plate to be controlled (or constrained) in its sliding position within the mold cavity under the pressure of the ejector pin. Simultaneously, a safety clearance is maintained between the slidable side plate and the mold. The ejector pin's role here is primarily to fix the slidable side plate, ensuring that the safety clearance remains constant across all contact surfaces between the slidable side plate and the mold during injection molding. This invention controls the sliding position of the slidable side plate during injection molding and utilizes the safety clearance to allow gas to escape from the highly viscous injection molten metal. Specifically, as shown... Figure 1 As shown, the steps include:

[0045] S1: After receiving the confirmation signal that the injection molding machine has closed the mold to the bottom, the sliding side plate is pressed by the ejector pin and slid to the initial position, and the screw position (s0) in the initial state is recorded.

[0046] S2: Control the injection melt to be injected into the mold cavity at a uniform speed through the injection port, and obtain the ejector pin retraction amount caused by the sliding side plate being pressed back under the action of material pressure;

[0047] S3: The ejector pin is controlled by the proportional back pressure valve to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference.

[0048] S4: By controlling the back pressure, the cavity pressure in the mold cavity is kept within a safe range before the sliding side plate retracts to the maximum displacement, and the screw position at the maximum displacement is recorded.

[0049] S5: Controls the injection melt to be injected into the mold cavity through the injection port at a preset holding pressure.

[0050] After the moving and fixed mold plates of the injection molding machine are fully closed, they are tightly sealed together, ensuring the stability of the mold during the injection process. Furthermore, unlike traditional injection molding processes that leave a complete cavity unformed during injection, this invention uses ejector pins to push the sliding side plate towards the injection port at the start of injection until it reaches its initial position (set according to the thickness of the injection port end of the actual molded part or the allowance for redundancy), effectively compressing the cavity first. Additionally, the screw position at this initial state needs to be recorded as a reference for subsequent injection molding cost and quality.

[0051] Then, the injection molding machine is started, and the molten injection is injected into the mold cavity at a uniform speed through the injection port. At this time, due to the material pressure in the mold cavity, the ejector pin and the sliding side plate are pushed back. During the pushing back process, in order to better expel the gas in the molten injection, this invention controls the speed of ejector pin retraction by adjusting the back pressure of the ejector pin proportional back pressure valve. In this way, in addition to the material pressure, the cavity is also subjected to pressure from the sliding side plate. At this time, the molten injection will compress the air in the material due to the high pressure in the cavity, while the gas in the molten injection will be discharged through the safety gap or the existing venting channel under the action of pressure difference. The reason why gas can be discharged but not molten injection is that the high viscosity and poor fluidity of molten injection mean that it requires a higher pressure to be discharged from these small gaps compared to gas. Therefore, when setting the safety gap, it is necessary to consider whether it can ensure that the molten injection cannot be discharged from the gap under the safety cavity pressure. Furthermore, this injection molding process enables simultaneous injection molding and forming (partial injection molding), unlike traditional processes where the entire injection melt must be filled before overall shaping can be performed.

[0052] Furthermore, to better control the quality of the injection-molded product, during the ejector pin retraction process (the injection port is uniformly pressed into the molten metal), this invention divides it into multiple stages (the arrival of each stage is determined based on the ejector pin's retraction amount) and adjusts the back pressure by decreasing accordingly. This achieves control over the retraction speed of the sliding side plate at its maximum displacement. The screw position corresponding to this maximum displacement is the pressure holding switching point, also known as the V / P switching point. Therefore, after step S5, the following step is also included:

[0053] S51: Obtain the screw position (s1) after the pressure holding period ends and the actual screw stroke of the current injection mold cycle;

[0054] S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value. If yes, proceed to step S53. If no, adjust according to the decrease of the current back pressure, proceed to the next injection molding cycle after mold opening, and return to step S1.

[0055] S53: Adjust the ejector pin retraction speed by adjusting the back pressure of each stage in the next injection molding cycle and adjusting the retraction distance ratio of each stage. After mold opening, proceed to the next injection molding cycle and return to step S1.

[0056] Considering control costs and program stability, this embodiment takes three-stage back pressure (N = 3) as an example for illustration. After the melt is injected into the cavity and reaches a certain pressure, the ejector rod starts to be pushed back. Record the screw position A0 at this time. Then, perform a first-stage retraction according to the first preset back pressure value. When retracting to the starting position of the second stage, perform a retraction according to the second preset back pressure value. Record the screw position A1 at this time. When retracting to the starting position of the third stage, perform a retraction according to the third preset back pressure value and record the screw position A2 at this time. When retracting to the maximum displacement of the ejector rod, record the screw position A3 at this time. This also represents the end of the uniform melt injection stage, and it is necessary to enter the holding pressure stage.

[0057] After the holding pressure stage is also completed, obtain the screw position s1. Then, the actual stroke s of the screw in the current mold cycle is s = s1 - s0. In order to control the weight of the injection molded product, generally, an ideal injection screw stroke s' of the qualified plastic product is preset in advance. Since the ideal injection screw stroke in the first trial mold cannot be accurately determined, it can be obtained from the density calculation formula:

[0058] ρ = M / V

[0059] V = πd 2 / (400*s ′ / 10)

[0060] It can be obtained that

[0061] s ′ =(4000M) / (kρπd 2 )

[0062] In the formula, M is the total mass of the target injection molded part, k is a coefficient, ρ is the room temperature density of the injection molding material, and d is the screw diameter.

[0063] By comparing the ratio of the actual screw stroke to the ideal screw stroke compared to the ideal screw stroke, when it exceeds the preset value, it is considered that adjustment is required. At this time, if s > s', the back pressure value of each stage is appropriately increased according to the preset formula to slow down the final retraction speed of the ejector rod. If s < s', the back pressure value of each stage is appropriately decreased according to the preset formula to increase the final retraction speed of the ejector rod. The preset formula is as follows:

[0064] Pn m =(A n -A n+1 ) / (A0 - A N )*(s / s ′ )*Pn m-1

[0065] In the formula, n is a constant from 0 to N, m is the mold cycle count, N is the total number of stages, Pn m is the back pressure value of the nth stage in the mth mold cycle, A nLet A be the screw position in the nth stage. n+1 Let A0 be the screw position in the (n+1)th stage, and A0 be the screw position when the sliding side plate begins to displace under material pressure. N Pn represents the screw position in the last stage of the current module. m-1 This represents the back pressure value of the nth stage in the (m-1)th module.

[0066] The preset formula automatically adjusts the ejector pin back pressure value at each stage of the injection molding process until the weight of the finished product meets the requirements. Then, the actual screw stroke of the qualified injection molded product is officially replaced as the fixed ideal injection screw stroke. Afterward, the actual screw stroke of each mold continues to be compared with the fixed ideal screw stroke, and the ejector pin back pressure value is continuously fine-tuned to ensure sufficient venting of the plastic product and to make the quality more stable.

[0067] Example 2

[0068] To better understand the technical content of this invention, this embodiment describes the invention through a system structure, such as... Figure 2 As shown, a control device for back pressure venting in an injection molding machine includes:

[0069] The sliding side plate is mounted on the ejector pin and can slide with the ejector pin. Under the pressure of the ejector pin, the sliding position is controlled in the mold cavity.

[0070] A safety gap is provided between the sliding side plate and the mold contact surface;

[0071] The main control chip is used to control the ejector pin to press against the sliding side plate and slide it to the initial position after receiving the confirmation signal that the injection molding machine has closed the mold to the bottom.

[0072] The injection module is used to control the injection melt to be injected into the mold cavity at a uniform speed through the injection port when the sliding side plate slides to the initial position, and to control the injection melt to be injected into the mold cavity at a preset holding pressure through the injection port after entering the holding pressure stage.

[0073] The ejector pin proportional back pressure valve is used to control the ejector pin to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference, and the cavity pressure in the mold cavity is controlled within the safe cavity pressure range before the sliding side plate retracts to the maximum displacement.

[0074] A displacement sensor is used to obtain the amount of retraction of the ejector pin during the injection molding process.

[0075] Furthermore, with the ejector pin proportional back pressure valve, when the cavity pressure is under the safe cavity pressure, the injection molten metal cannot be discharged through the safe gap due to the viscosity of the molten metal.

[0076] Furthermore, during the process of the ejector proportional valve controlling the ejector pin, the screw position at the maximum displacement of the sliding side plate is the pressure holding switching point.

[0077] In summary, the back pressure venting control method and device for injection molding machines described in this invention controls the speed of ejector pin retraction by adjusting the back pressure, thereby making the pressure inside the cavity higher than the cavity pressure during normal injection without increasing the injection pressure. This allows the gas in the injection melt to be discharged under high pressure through a safe gap by taking advantage of the better fluid properties of the injection melt, thus achieving simultaneous injection and molding.

[0078] By adjusting the retraction speed, the actual stroke of the screw can be adjusted, thereby better controlling the quality of the finished product and reducing the scrap rate caused by unstable weight.

[0079] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0080] Furthermore, in this invention, descriptions involving terms such as "first," "second," and "a" are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0081] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0082] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A method for controlling back pressure venting in an injection molding machine, characterized in that, The ejector pin is equipped with a slidable side plate that slides with the ejector pin. The slidable side plate can be controlled to slide within the mold cavity under the pressure of the ejector pin. A safety clearance is provided between the slidable side plate and the mold contact surface. The specific steps include: S1: After receiving the confirmation signal that the injection molding machine has closed the mold to the bottom, the ejector pin presses the sliding side plate and slides it to the initial position, and records the screw position in the initial state; S2: Control the injection melt to be injected into the mold cavity at a uniform speed through the injection port, and obtain the ejector pin retraction amount caused by the sliding side plate being pressed back under the action of material pressure; S3: The ejector pin is controlled by the proportional back pressure valve to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference. S4: By controlling the back pressure, the cavity pressure in the mold cavity is kept within a safe range before the sliding side plate retracts to the maximum displacement, and the screw position at the maximum displacement is recorded. S5: Controls the injection melt to be injected into the mold cavity through the injection port at a preset holding pressure; In step S3, when the cavity pressure is under the safe cavity pressure, the injection molten material cannot be discharged through the safe gap due to the action of the melt viscosity. The step S5 is followed by the following step: S51: Obtain the screw position after the pressure holding period ends and the actual screw stroke of the current injection mold cycle; S52: Determine whether the deviation ratio between the actual screw stroke and the ideal screw stroke is less than the preset value. If yes, proceed to step S53. If no, adjust according to the decrease of the current back pressure, proceed to the next injection molding cycle after mold opening, and return to step S1. S53: Adjust the ejector pin retraction speed by adjusting the back pressure of each stage in the next injection molding cycle and adjusting the retraction distance ratio of each stage. After mold opening, proceed to the next injection molding cycle and return to step S1. In step S53, the adjustment of the back pressure at each stage is expressed by the following formula: In the formula, n is a constant from 0 to N, m is the number of modules, and N is the total number of stages. This represents the back pressure value in the nth stage of the mth module. The screw position in the nth stage. This represents the screw position in the (n+1)th stage. This refers to the screw position when the sliding side plate begins to displace under material pressure. This refers to the screw position in the last stage of the current module. This is the back pressure value in the nth stage of the (m-1)th module.

2. The method for controlling back pressure venting in an injection molding machine as described in claim 1, characterized in that, In step S4, the screw position at the point of maximum displacement is the pressure holding switching point.

3. The method for controlling back pressure venting in an injection molding machine as described in claim 1, characterized in that, In step S4, during the uniform injection stage, the retraction speed of the sliding side plate is adjusted by decreasing the back pressure in several stages, and the arrival of each stage is determined based on the retraction amount of the push rod.

4. The method for controlling back pressure venting in an injection molding machine as described in claim 1, characterized in that, In step S52, the actual screw stroke is expressed by the following formula: In the formula, s is the actual screw stroke, s0 is the screw position in the initial state, and s1 is the screw position after the pressure holding period ends; The ideal screw stroke is expressed by the following formula: In the formula, s' is the ideal screw stroke, M is the total mass of the target injection molded part, and k is a coefficient. d is the room temperature density of the injection molding compound, and d is the screw diameter.

5. A control device for back pressure venting in an injection molding machine, employing the control method described in claim 1, characterized in that, include: The sliding side plate is mounted on the ejector pin and can slide with the ejector pin. Under the pressure of the ejector pin, the sliding position is controlled in the mold cavity. A safety gap is provided between the sliding side plate and the mold contact surface; The main control chip is used to control the ejector pin to press against the sliding side plate and slide it to the initial position after receiving the confirmation signal that the injection molding machine has closed the mold to the bottom. The injection module is used to control the injection melt to be injected into the mold cavity at a uniform speed through the injection port when the sliding side plate slides to the initial position, and to control the injection melt to be injected into the mold cavity at a preset holding pressure through the injection port after entering the holding pressure stage. The ejector pin proportional back pressure valve is used to control the ejector pin to press against the sliding side plate. Under the combined pressure of back pressure and material pressure, the gas in the injection melt is discharged through the safety gap under the action of pressure difference, and the cavity pressure in the mold cavity is controlled within the safe cavity pressure range before the sliding side plate retracts to the maximum displacement. A displacement sensor is used to obtain the amount of retraction of the ejector pin during the injection molding process.

6. The control device for back pressure venting of an injection molding machine as described in claim 5, characterized in that, When the ejector pin proportional back pressure valve is under the safe chamber pressure, the injection molten metal cannot be discharged through the safe gap due to the viscosity of the molten metal.

7. A control device for back pressure venting in an injection molding machine as described in claim 5, characterized in that, During the process of the ejector pin proportional valve controlling the ejector pin, the screw position at the maximum displacement of the sliding side plate is the pressure holding switching point.

Images