Method for online characterization of injection molding mold deformation and temperature fluctuations

Abstract

The application provides an online characterization method for injection molding mold deformation and temperature fluctuation, which comprises six steps. Step one is to set the temperature of the mold temperature machine. Step two is to set the injection molding parameters for trial molding. Step three is to establish a safe identification area of the peak current of the mold closing motor. Step four is to record the mold temperature. Step five is to record the peak current of the mold closing motor corresponding to 10 groups of mold temperatures. Step six is data fitting. The 10 groups of mold temperature and mold closing motor peak current data obtained are linearly fitted, so as to characterize the relationship between the mold temperature, mold deformation and motor current. Compared with the traditional method of measuring the mold deformation by attaching strain gauges, the online characterization method can greatly eliminate the influence of environmental factors on the test results in the previous stop test of the mold deformation, and can more truly reflect the deformation of the mold in the working process.

Description

Technical Field

[0001] This invention relates to the field of injection molding technology, and more specifically, to an online characterization method for the deformation and temperature fluctuation of injection molds. Background Technology

[0002] Injection molding, as one of the most important plastic processing methods, is widely used in the production of products in aerospace, military, automotive, high-speed rail, and medical and health fields. The processing principle of injection molding is as follows: plastic granules are melted by heating the barrel and shearing action of the screw, and then injected into the mold cavity under the action of the screw. After cooling and solidification within the mold, the mold is opened and the product is removed. The mold is a key element determining the appearance and shape of the molded product. According to the PVT (Polymer Transformer-Temperature Transformer) properties of polymers, even small fluctuations in mold deformation and temperature directly affect the precision of the injection-molded product. Therefore, certain methods are needed to accurately monitor the mold condition during the injection molding process.

[0003] Ultra-precision injection molded products generally require dimensional accuracy within 0.01mm-0.001mm. All-electric injection molding machines are used for molding these products due to their high response accuracy and stable operation. During the injection molding process, fluctuations in ambient temperature and cycle time affect the mold's heat exchange balance, leading to temperature fluctuations and consequently changes in mold deformation, impacting the stability and consistency of the molded product's quality. However, the mold temperature distribution exhibits a gradient during injection molding, making traditional single-point mold temperature monitoring inaccurate. Furthermore, mold deformation caused by temperature changes cannot be accurately detected using effective methods. Current methods for characterizing injection mold deformation often employ external strain gauges, which cannot accurately detect and analyze the overall mold deformation during actual production.

[0004] Therefore, in order to solve the problem of online monitoring of mold temperature fluctuations and mold deformation during injection molding, this invention proposes a method for online monitoring of mold status using built-in sensors in injection molding machines, specifically for the field of all-electric injection molding machines. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of online detection of deformation and temperature fluctuations in injection molds, and to provide an online characterization method for deformation and temperature fluctuations in injection molds, which can accurately monitor changes in mold state during the injection molding process.

[0006] This invention provides an online characterization method for deformation and temperature fluctuation of injection molding dies, the main contents of which are as follows:

[0007] 1) During the operation of the all-electric injection molding machine, the working temperature of the mold temperature controller is set according to the requirements of the molding material and the product, so that the mold temperature controller maintains the mold temperature within the required molding range. When the mold temperature reaches the set temperature, the mold temperature at this time can be considered as the set temperature of the mold temperature controller.

[0008] 2) After the continuous production process begins, the heat transfer from the plastic melt to the mold, the heat transfer from the mold to the template and the air, and the heat exchange between the water channels and the mold may be disrupted due to fluctuations in the production cycle and changes in ambient temperature and humidity. This will cause the mold temperature to change (denoted as ΔT), and the change in mold temperature will cause the mold deformation to change under the action of thermal expansion and contraction (denoted as ΔL).

[0009] Preferably, the relationship between mold thickness variation and mold temperature can be expressed by the following formula:

[0010] ΔL=α×L×ΔT

[0011] Where ΔL is the linear expansion of the mold, L is the original thickness of the mold, and α is the coefficient of linear expansion of the mold.

[0012] 3) Temperature fluctuations in the mold cause deformation that is directly reflected in the thickness direction of the mold. Changes in mold thickness lead to changes in the deformation of the elbow or tie rod in the mold clamping mechanism during mold locking. That is, the peak clamping force required when passing the dead point of the elbow mechanism during mold closing changes, denoted as ΔF, and its formula is as follows:

[0013] ΔF=CΔL

[0014]

[0015] In the formula, C is the total stiffness of the mold clamping system. P Z represents the stiffness of the tie rod, m1 and m2 represent the number of elbows in the clamping system's elbow mechanism, C1 and C2 represent the stiffness of the connecting rod, and ΔL represents the total deformation of the clamping system.

[0016] 4) The clamping mechanism of the all-electric injection molding machine is driven by a clamping motor that drives a ball screw to achieve reciprocating motion. Therefore, the change in peak clamping force during the clamping process will be directly displayed in the motor output torque value, which is denoted as T. s ;

[0017] Preferably, the torque T of the mold clamping motor s It can be obtained from the following formula:

[0018]

[0019] It can be concluded that

[0020]

[0021] In the formula, P is the motor power, N is the motor speed, F1 is the axial force of the lead screw (force on the crosshead), h is the lead screw lead, and n1 is the positive efficiency of the feed lead screw.

[0022] 5) Mold clamping motor torque T s The magnitude of the voltage is related to the motor power P, which can be obtained from the motor current I and voltage U. The voltage is the rated operating voltage, and the current varies with the power output.

[0023] Preferably, the motor power P can be obtained by the following formula:

[0024] P = UI

[0025] It can be concluded that

[0026]

[0027] From ΔF=CΔL=CαLΔT, we can obtain that

[0028]

[0029] make

[0030]

[0031] but

[0032] K1ΔI=K2K2ΔT

[0033] ΔT=(K1 / (K2K3))ΔI

[0034] ΔL=α×L×ΔT

[0035] The specific implementation steps of the online characterization method for deformation and temperature fluctuation of injection molding molds are as follows:

[0036] Step 1: Set the mold temperature controller. Connect the inlet and outlet water pipes of the mold temperature controller to the mold, start the mold temperature controller and water pump, and set the mold temperature controller temperature to T, with a range of 25~99℃. After a period of preheating, the default mold temperature is the set temperature T.

[0037] Step 2: Set injection molding parameters and conduct trial molding. Start the injection molding machine, add PP material, and set the injection molding parameters as follows: barrel temperature 180℃, injection speed 70mm / s, holding pressure 30MPa, back pressure 3MPa, material storage position 80mm, V / P switching position 30mm, and then conduct trial molding.

[0038] Step 3: Establish a safe identification zone for the peak current of the mold clamping motor. When monitoring the reciprocating mold opening and closing action, and there is no heat exchange in the mold (considered as isothermal conditions), the peak clamping force motor current will drift slightly. Therefore, data normalization processing and the establishment of a safe identification zone are required.

[0039] Step 4: Record mold temperature. After the trial molding, the formal experiment begins. The injection molding machine is in fully automatic mode (to reduce heat loss during part removal, which could affect the temperature results). The mold temperature is recorded every 5 mold runs, for a total of 10 sets of mold temperature records. The mold temperature is measured on the surface of the cavity after mold opening using a temperature gun. The average value is taken after measuring the temperature at 5 locations on the surface of the cavity.

[0040] Step 5: Record the peak current of the mold clamping motor corresponding to 10 sets of mold temperatures. The current value detected by the current sensor built into the mold clamping motor can be obtained by connecting to the Changfeiya injection molding machine controller via a computer.

[0041] Step Six: Data Fitting. The 10 sets of acquired mold temperature and peak current data of the mold clamping motor are linearly fitted to characterize the relationship between mold temperature, mold deformation, and motor current. The mold temperature and motor current have a linear relationship, and the mold deformation and mold temperature have a linear relationship. After obtaining the fitted curves of mold temperature and motor current, the relationship curve between mold deformation and mold temperature is obtained using ΔL = α × L × ΔT.

[0042] Compared with the prior art, the advantages and positive effects of the method of the present invention are as follows: Compared with the traditional method of measuring mold deformation by attaching strain gauges, the method of the present invention characterizes mold deformation by detecting the change of peak current of the mold closing motor during the operation of the injection molding machine. This can largely eliminate the influence of environmental factors on the test results in the previous test of mold deformation during shutdown, and can more realistically reflect the deformation of the mold during the operation process. Attached Figure Description

[0043] Figure 1 This is a flowchart of the online characterization method for deformation and temperature fluctuation of injection molding molds according to the present invention;

[0044] Figure 2 This is a mathematical derivation diagram of the peak clamping force, mold thermal expansion deformation, and mold temperature in the online characterization method of injection molding mold deformation and temperature fluctuation of the present invention.

[0045] Figure 3 It is a rectangular spline plot;

[0046] Figure 4 This is a graph showing the relationship between mold temperature and motor current, which verifies the feasibility of the online characterization method for deformation and temperature fluctuation of injection molding molds according to the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the method of the present invention clearer, the technical solutions of the method of the present invention will be clearly and completely described below in conjunction with specific examples and accompanying drawings. The injection molding machine used in the experiment was a Changfeiya all-electric injection molding machine, model ZE1200 / 300, with an injection capacity of 116 cm³. 3 The material is PP, grade SABIC 579S; the mold temperature controller is STW; the mold is made of 45# steel; the injection molded sample is a rectangular template, such as... Figure 1-3 As shown.

[0048] refer to Figure 1 This invention provides an online characterization method for deformation and temperature fluctuation of injection molding dies, the main contents of which are as follows:

[0049] 1. During the operation of the all-electric injection molding machine, the working temperature of the mold temperature controller is set according to the requirements of the molding material and the product. The mold temperature controller maintains the mold temperature within the required molding range. When the mold temperature reaches the set temperature, the mold temperature can be considered to be the set temperature of the mold temperature controller. In this embodiment, the set temperature T of the mold temperature controller is 40℃, that is, the mold temperature is 40℃.

[0050] 2: After the continuous production process begins, the heat transfer from the plastic melt to the mold, the heat transfer from the mold to the template and the air, and the heat exchange between the water channels and the mold may be disrupted due to fluctuations in the production cycle and changes in ambient temperature and humidity. This will cause the mold temperature to change (denoted as ΔT), and the change in mold temperature will cause the mold deformation to change under the action of thermal expansion and contraction (denoted as ΔL).

[0051] refer to Figure 2 The relationship between mold thickness variation and mold temperature can be expressed by the following formula:

[0052] ΔL=α×L×ΔT

[0053] Where ΔL is the linear expansion of the mold, L is the original thickness of the mold, and α is the coefficient of linear expansion of the mold.

[0054] In this embodiment, the mold thickness is 300mm, and the mold is made of No. 45 steel, whose coefficient of linear expansion is 11.6×10⁻⁶. -6 (mm℃ -1 We can obtain:

[0055] ΔL=α×L×ΔT=11.6×10 -6 ×300×ΔT=0.00348ΔT

[0056] 3. Temperature fluctuations in the mold cause deformation that is directly reflected in the thickness direction of the mold. Changes in mold thickness lead to changes in the deformation of the elbow or tie rod in the mold clamping mechanism during mold locking. That is, the peak clamping force required when passing the dead point of the elbow mechanism during mold closing changes, denoted as ΔF, and its formula is as follows:

[0057] ΔF=CΔL

[0058]

[0059] In the formula, C is the total stiffness of the mold clamping system. p Z represents the stiffness of the tie rod, m1 and m2 represent the number of elbows in the clamping system's elbow mechanism, C1 and C2 represent the stiffness of the connecting rod, and ΔS represents the total deformation of the clamping system.

[0060] In this embodiment, the stiffness C of the tie rod is... p Given a tie rod stiffness of 15000 N / mm, a tie rod number Z of 4, a toggle mechanism with m1 = m2 = 2 toggles, and a connecting rod stiffness C1 = C2 = 5000 N / mm, we can obtain:

[0061]

[0062] ΔF=CΔL=4615.38×0.00348ΔT=16.06ΔT

[0063] 4. The clamping mechanism of a fully electric injection molding machine is driven by a clamping motor that uses a ball screw to achieve reciprocating motion. Therefore, the change in peak clamping force during the clamping process will be directly displayed in the motor output torque value, denoted as T. s ;

[0064] refer to Figure 2 Mold clamping motor torque T s It can be obtained from the following formula:

[0065]

[0066] It can be concluded that

[0067]

[0068] In the formula, P is the motor power, N is the motor speed, F1 is the axial force of the lead screw (force on the crosshead), h is the lead screw lead, and n1 is the positive efficiency of the feed lead screw.

[0069] In this embodiment, the lead screw pitch h is 40mm, and the positive efficiency of the feed screw n1 is 0.8, therefore:

[0070]

[0071] 5: Mold clamping motor torque T sThe magnitude of the voltage is related to the motor power P, which can be obtained from the motor current I and voltage U. The voltage is the rated operating voltage, and the current varies with the power output.

[0072] refer to Figure 2 The motor power P can be obtained by the following formula:

[0073] P = UI

[0074] It can be concluded that

[0075]

[0076] In this embodiment, the voltage U is 220V and the motor speed N is 200r / min, therefore:

[0077]

[0078] ΔI = 12.17ΔT

[0079] Figure 4 This is a fitting curve of mold temperature and peak current of mold clamping motor recorded every 5 molds in an all-electric injection molding machine. As can be seen from the figure, as the mold temperature increases, the peak current of mold clamping motor also increases, showing a clear correlation. This is consistent with the derived mathematical relationship between mold clamping motor current ΔI and mold temperature change ΔT.

[0080] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0081] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. The implementation schemes in the above embodiments can also be further combined or replaced. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for online characterization of deformation and temperature fluctuation of injection molding molds, characterized in that: Step 1: Set the mold temperature controller temperature. Connect the inlet and outlet water pipes of the mold temperature controller to the mold. Start the mold temperature controller and water pump, and set the mold temperature controller temperature to [temperature value missing]. T After a period of preheating, the mold temperature is set by default. T Step 2: Set injection molding parameters and conduct trial molding; Step 3: Establish a safe identification zone for the peak current of the mold clamping motor, monitor the reciprocating mold opening and closing action. When there is no heat exchange in the mold, the peak clamping force motor current will drift slightly. Perform data normalization and establish a safe identification zone; Step 4: Record mold temperature. After the trial molding, start the formal experiment. The injection molding machine adopts fully automatic mode and records the mold temperature every 5 molds, continuously recording 10 sets of mold temperatures; Step 5: Record the peak current of the mold clamping motor corresponding to the 10 sets of mold temperatures; Step 6: Data fitting. Perform linear fitting on the 10 sets of mold temperature and peak current data of the mold clamping motor to characterize the relationship between mold temperature, mold deformation and motor current. The change of peak clamping force during mold closing is directly displayed in the motor output torque value. The voltage is the rated working voltage, and the change of mold temperature is indirectly reflected by the change of motor current.

2. The online characterization method for deformation and temperature fluctuation of injection molding molds according to claim 1, characterized in that: In step one, the temperature range of the mold temperature controller is set to 25-99℃.

3. The online characterization method for deformation and temperature fluctuation of injection molding molds according to claim 1, characterized in that: Step 4: The temperature of the mold cavity surface is measured using a temperature gun after the mold is opened. The average value is taken after measuring the temperature at 5 locations on the mold cavity surface.

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