Mold clamping force setting method for pull rod stress balance of plastic injection molding machine

Abstract

The invention discloses a mold locking force setting method for pull rod stress balance of a plastic injection molding machine, which is used for solving the problem that the set mold locking force is not uniformly distributed on four pull rods or the set value exceeds the actually required mold locking force due to the fact that the geometric center of a mold cavity does not coincide with the mold locking center of a machine. The mold clamping force setting method comprises the following steps: (1) reading the projection area of a mold cavity including a runner system on a parting surface; and (2) calculating the mold expanding force of the melt on the mold cavity. And (3) calculating the calculated mold clamping force when mold expansion does not occur and a qualified product is formed. And (4) judging whether the projection pattern of the mold cavity on the parting surface is centrosymmetric about the center of the main runner of the gating system or not. And (5) calculating the set clamping force when the central positions coincide. And (6) calculating the set clamping force when the central positions are not overlapped. According to the invention, two conditions that the center of the clamping force coincides with or does not coincide with the centers of the four pull rods are considered, and the clamping force can be set as required, so that the four pull rods are uniformly stressed, the service lives of equipment and a mold are prolonged, and particularly, the stable operation of the main force-bearing component pull rods for the clamping force of the injection molding machine is protected; and the stability of the production process and the product quality are ensured, so that the method has wide application space.

Description

Technical Field

[0001] The invention relates to the field of injection molding machines, and in particular to a method for setting a clamping force of a plastic injection molding machine with balanced force on a tie rod. Background Art

[0002] When the injection molding machine is operating, for the clamping part, the tie rod is an important bearing component for the injection molding machine to implement reliable clamping force on the mold. The opening and closing actions of the injection molding machine are completed by driving the crosshead of the clamping part through the cooperation of the hydraulic motor and the hydraulic cylinder piston (for hydraulic type) or through the cooperation of the servo motor and the ball screw (for all-electric type). The crosshead cooperates with the toggle mechanism of the part to drive the injection molding mobile template to make reciprocating linear motion along the machine tool guide rails on the four tie rods fixed to the front and rear fixed templates of the injection molding machine. The tie rods are subjected to high-frequency tensile and compressive stresses in this process. At the same time, during the high pressure of the clamping during the molding process, the mold is locked by the high pressure of the clamping force provided by the injection molding machine. In the injection and holding stages, the high-temperature plastic melt is injected into the mold cavity under the injection pressure applied by the screw. In order to resist the reverse expansion force generated by the plastic melt filling the cavity under higher injection pressure, the clamping part of the injection molding machine must apply sufficient clamping force to the mold to prevent defects such as mold separation, expansion flash, and overflow due to insufficient clamping force. On the other hand, if the clamping force applied is too large, it will not only make it difficult to vent the mold, but also increase the resistance of the melt filling the cavity. In order to improve the ability of the melt to fill the cavity, the injection pressure must be increased in the process, which will have many adverse effects on product quality, and the mold and machine will also be overly deformed, shortening their service life and increasing unnecessary energy consumption. Therefore, after the mold is closed, the clamping force applied to the mold must be set reasonably.

[0003] Secondly, from the mechanical analysis, it can be known that the clamping force applied to the mold is ultimately borne by four tie rods fixed to the tie rod mounting holes of the dynamic and fixed mold base plates of the injection molding machine (four on each of the dynamic and fixed mold base plates). Generally speaking, the four tie rods of the injection molding machine require that the load size be evenly distributed and in a state of force balance, which is beneficial to the production process, product quality, and the service life of the mold and the machine. In the actual production process, due to the rich variety of plastic products and the ever-changing mold structure, there is a situation where the geometric center of the mold cavity does not coincide with the clamping center of the machine. The setting of the traditional clamping force depends on the experience of the operator, and does not take into account that due to the non-coincidence of the above two centers, the set clamping force may be unevenly distributed among the four tie rods or the set value may exceed the actual required clamping force, thereby damaging the tie rods, causing the service life of the injection molding machine to be seriously shortened, affecting the stability of the production process and product quality. Summary of the invention

[0004] In order to overcome the shortcomings of the above existing technologies, the present invention provides a method for setting the clamping force of a plastic injection molding machine tie rod with balanced force. The method is implemented by the following technical solution, which is characterized by comprising the following steps:

[0005] Step (1): Read the projection area A of the cavity including the runner system on the parting surface. Import the mold 3D modeling file into the 3D design software (such as UG, Cero, CATIA), extract the position of the coordinate system, the size and position of the projection figure of the mold cavity on the parting surface, and the coordinate data of the center point of the main flow channel of the pouring system on the parting surface; and read the projection area A of the cavity including the runner system on the parting surface (unit: cm 2 ).

[0006] Step (2): Calculate the expansion force P of the melt on the mold cavity 胀 .P 胀 (Unit: tf) Calculated according to formula (1).

[0007] P 胀 =K×S×P×A (1)

[0008] In step (2), K, S, and P respectively represent the plastic multiplication constant (value range is 1 to 2), the pressure loss coefficient (value range is 30% to 60%), and the cavity pressure value (unit: bar); K, S, P, and A are determined by step (2.1), step (2.2), step (2.3), and step (1), respectively. Step (2.1), step (2.2), and step (2.3) are specifically as follows:

[0009] Step (2.1): Determine the multiplication constant K of the plastic. According to the plastic multiplication constant K corresponding to the plastic type, organize the data on the relationship between the plastic type and the plastic multiplication constant, and the organizational structure of the data is: (plastic type, plastic multiplication constant K). The plastic multiplication constant K takes the average value of its value range. According to the type of plastic raw material used, retrieve the corresponding plastic multiplication constant.

[0010] Step (2.2): Determine the pressure loss coefficient S. The pressure loss coefficient S is 30%, 45%, and 60%, wherein the plastic with high flowability or low viscosity takes the small value of 30%, the plastic with low flowability or high viscosity takes the large value of 60%, and the plastic with moderate flowability or moderate viscosity takes the middle value of 45%.

[0011] Step (2.3): Calculate the cavity pressure P value. It includes step (2.3.1), step (2.3.2), and step (2.3.3), as follows.

[0012] Step (2.3.1): Calculate the ratio of flow length to wall thickness. In 3D design software (such as UG, Cero, CATIA), starting from the front center of the main channel of the pouring system (i.e., the position in contact with the front end of the injection molding machine nozzle), read and calculate the maximum flow length (unit: mm) and minimum wall thickness (unit: mm) of the flow channel and the product along the flow direction. Define the ratio of flow length to wall thickness δ as the ratio of the maximum flow length to the minimum wall thickness, and calculate the value of the ratio of flow length to wall thickness δ.

[0013] Step (2.3.2): Establish cavity pressure data on wall thickness, process length and wall thickness ratio δ. According to the relationship between cavity pressure, wall thickness, process length and wall thickness ratio, establish cavity pressure curve data for conventional injection molded parts with a minimum wall thickness of 0.4 to 2.0 mm and a process length to wall thickness ratio of 50:1, 100:1, 150:1, 200:1, 250:1, 275:1, and 300:1, respectively. The data is organized in the form of: (minimum wall thickness value, process length to wall thickness ratio δ, cavity pressure value), and the minimum wall thickness step of the injection molded parts is set to 0.1 mm.

[0014] Step (2.3.3): Calculate the cavity pressure value. The minimum wall thickness value and the process length to wall thickness ratio δ obtained in step (2.3.1) are used as the basis for the minimum wall thickness value and the process length to wall thickness ratio of the actual product, and the cavity pressure value corresponding to the actual product molding is calculated through the cavity pressure data established in step (2.3.2). The calculation method is: if the minimum wall thickness value and the process length to wall thickness ratio match one of the seven process length to wall thickness ratios pre-stored in step (2.3.2), the cavity pressure value P is directly retrieved by using the corresponding minimum wall thickness value and the process length to wall thickness ratio; if the minimum wall thickness value and the process length to wall thickness ratio are within the above range but not equal to the above value, the minimum wall thickness value is first rounded to one significant figure after the decimal point according to the rounding method, and then it is retrieved to retrieve two ratios of adjacent process length to wall thickness ratios. Then, the cavity pressure value P is calculated according to the linear interpolation method with reference to the values ​​of the two adjacent process length to wall thickness ratios. If the ratio of process length to wall thickness is not within the range pre-stored in step (2.3.2), exit the program and terminate the calculation.

[0015] The linear interpolation method in step (2.3.3) calculates the cavity pressure according to formula (2).

[0016] (PP i ) / (P i+1 -P i )=(δ-δ i ) / (δ i+1 -δ i ) (2)

[0017] In the linear interpolation method in step (2.3.3), P and P in formula (2) are i , P i+1 They represent the ratios of process length to wall thickness as δ and δ respectively. i , δ i+1 The cavity pressure value, where δ i , δ i+1 It represents the ratio of two adjacent values ​​of the seven process length to wall thickness ratios described in step (2.3.3), i = 1, 2, 3, ... 6. δ is the process length to wall thickness ratio of the actual product for which the cavity pressure is to be determined.

[0018] Step (3): Calculate the clamping force F that does not cause mold expansion and produces qualified products 计 . Calculate the clamping force F according to formula (3): 锁 .

[0019] F 计 ≥P 胀 (3)

[0020] Step (4): Determine whether the projection of the mold cavity on the parting surface is centrally symmetrical about the center of the main channel of the pouring system (i.e., the geometric center of the clamping force of the machine). If it is centrally symmetrical, go to step (5); otherwise, go to step (6).

[0021] Step (5): When the geometric center of the cavity coincides with the geometric center of the machine clamping force, set the clamping force F on the machine. 设 If the center is symmetrical, it means that the geometric center of the mold cavity coincides with the geometric center of the machine's clamping force, that is, the projection of the mold cavity on the parting surface is symmetrical about the geometric center, and has two symmetry axes that pass through the geometric center, are orthogonal to each other, and are parallel to the horizontal plane and the vertical plane respectively. Then set the clamping force F 设 =F 计 At this time, due to the symmetry of the geometric center, the load carried by each tie rod is equal to F 设 / 4.

[0022] Step (6): When the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, set the clamping force F on the machine. 设 The geometric center of the cavity does not coincide with the clamping center of the machine. If the clamping force F is set according to step (5) 设 The action of closing the mold and applying high pressure to the mold may cause the load distribution of the four tie rods of the injection molding machine to be unbalanced, causing potential damage to the tie rods. Therefore, for this working condition, the clamping force F is set 设 The calculation should be based on providing sufficient clamping force and not causing mold expansion flash (i.e. F 设 ≥P 胀) under the condition of ensuring that the load on each tie rod is balanced. Therefore, the load P on each tie rod can be calculated using the moment balance method. 杆i , find the maximum load P on the four tie rods 杆max At this time, the clamping force F set on the machine is applied to the mold. 设 Equal to the maximum load P 杆max 4 times, the load on each tie rod is equal to P 杆max , thereby ensuring that the load on each tie rod is balanced. It includes steps (6.1), (6.2), and (6.3). The specific calculation process is as follows:

[0023] Step (6.1): Solve for the centroid coordinates of the projection area of ​​the cavity on the parting surface. Import the machine dimension parameters such as the diameter of the injection molding machine tie rod, the position of the tie rod center on the fixed platen, the tie rod spacing and the diameter of the center hole of the fixed platen, and establish a coordinate system XOY on the mold parting surface with the center of the main flow channel as the coordinate origin. The horizontal direction is the X axis and the vertical direction is the Y axis. Its positive direction conforms to the right-hand rule. Use the area centroid method to apply the resultant moment theorem to each coordinate axis to obtain the moment and list the equilibrium equation. Use the first group of formulas (4) and (5) or the second group of formulas (6) and (7) to solve the centroid coordinates x of the projection area of ​​the product including the flow channel on the parting surface. c ,y c .

[0024] The first set of formulas:

[0025]

[0026] The second set of formulas:

[0027]

[0028] Step (6.1) Formulas (4) and (5) are used to solve the centroid coordinates x of the projection area by integration. c ,y c Strictly defined formula; Step (6.1) Formulas (6) and (7) are based on the actual working conditions of the irregular shape of the mold cavity or the layout of multiple cavities in one mold. In actual solution, the projection figure of the cavity on the parting surface can be divided into simple and regular unit figures to calculate the centroid coordinates x of the projection area. c ,y c Discretization formula of . Assume that it is divided into n unit graphics, i = 1, 2, 3, ... n. x i ,y i are the x- and y-direction coordinates of the projection area of ​​the i-th unit figure, A i is the projected area of ​​the i-th unit figure.

[0029] Step (6.2): ​​Solve the loads on the four tie rods of the injection molding machine separately, compare the loads, and find the maximum load P among the four tie rods. 杆max Assume that the loads on the four tie rods of the injection molding machine corresponding to the first, second, third and fourth quadrants of the XOY coordinate system are P1, P2, P3 and P4 respectively. Since the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, it will inevitably lead to the resultant force of the cavity expansion force P 胀 The resultant force of the expansion force P is offset from the origin O of the XOY coordinate system, and must be in a certain quadrant. 胀 It occurs in the second quadrant and is y and x lengths away from the X and Y axes respectively. The loads P1, P2, P3, and P4 acting on the four rods are calculated by the resultant moment theorem, which can be calculated by the third group of formulas (8), (9), (10), (11) or the fourth group of formulas (12), (13), (14), (15) (choose 1 from 2).

[0030] The third set of formulas:

[0031] P 胀 =P1+P2+P3+P4 (8)

[0032] P1×(L1 / 2+x)=P4×(L1 / 2-x) (9)

[0033] P1×(L2 / 2-y)=P2×(L2 / 2+y) (10)

[0034] P2×(L1 / 2+x)=P3×(L1 / 2-x) (11)

[0035] The fourth set of formulas:

[0036] P 胀 =P1+P2+P3+P4 (12)

[0037] (P1+P4)×L1=P 胀 ×(L1 / 2+x) (13)

[0038] (P1+P2)×L2=P 胀 ×(L2 / 2+y) (14)

[0039] P1+P3=P2+P4 (15)

[0040] Among them, L1 and L2 are respectively the center distances of two horizontal and two vertical tie rods among the four tie rods arranged in the clamping part of the injection molding machine (they are machine parameters of the injection molding machine, which become known conditions after the injection molding machine is selected).

[0041] Then the maximum force P among the four tie rods is 杆max Calculated by formula (16):

[0042] P 杆max =max{P1, P2, P3, P4} (16)

[0043] From this, we can solve the maximum force P in the four rods. 杆max The center of expansion force in other quadrants can be calculated in the same way.

[0044] Step (6.3): Calculate the set clamping force F applied to the mold 设 The clamping force F applied to the mold 设 Equal to the load P on the tie rod with the maximum load 杆max 4 times, that is, F 设 Calculated by formula (17):

[0045] F 设 =4×P 杆max (17)

[0046] At this time, it can be ensured that the load on each tie rod is equal to P 杆max , the mold and the machine are in a state of force balance.

[0047] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0048] 1. The calculation of the product, mold and runner by the present invention makes the clamping force set on the machine more accurate and effective; the torque balance calculation method is adopted to achieve the force balance of the tie rod, minimize the damage of the tie rod caused by uneven force, and protect the machine and extend its service life.

[0049] 2. The present invention analyzes the mold cavity into two situations: symmetrical distribution and asymmetrical distribution, and proposes a complete set of calculation methods for clamping force setting to help technicians determine the appropriate clamping force, which is beneficial to reducing damage to the mold, protecting the mold and extending its service life.

[0050] 3. The method of the present invention has strong adaptability and is particularly suitable for the production of products with complex shapes and has a broad application space. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a calculation flow chart of setting clamping force of the present invention.

[0052] Figure 2 It is a grouping table of flow characteristics of thermoplastics of the present invention.

[0053] Figure 3 It is a proportional relationship diagram of the mold cavity pressure, wall thickness, flow distance and wall thickness of the present invention.

[0054] Figure 4It is a schematic diagram of the position and dimensions when the center of the expansion die force of the present invention is located in the second quadrant. DETAILED DESCRIPTION

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0056] An embodiment of the present invention provides a method for setting the clamping force so that the force of the tie rods of a plastic injection molding machine is balanced during the molding process. This method can prevent the injection molding machine from being improperly set up, resulting in the clamping force not being set as required when the geometric center of the mold cavity does not coincide with the clamping center of the machine, so that the clamping force may be unevenly distributed on the four tie rods or the set value may exceed the actual required clamping force. This is beneficial to extending the service life of the equipment and the mold, and is particularly beneficial to protecting the smooth operation of the tie rods, the main load-bearing components of the clamping force of the injection molding machine, to ensure the stability of the production process and product quality.

[0057] Figure 1 To set the calculation process of clamping force. Import the mold 3D modeling file into the 3D design software as the initial condition; obtain the projected area A of the product and runner on the parting surface, and calculate the cavity pressure value P in the order of determining the plastic multiplication constant K, pressure loss coefficient S, calculating the process length-to-wall thickness ratio, and establishing the cavity pressure data; solve and calculate the clamping force F 计 ; Determine whether the mold center and the cavity center coincide with each other, and calculate the clamping force F set on the machine according to the two situations of coincidence and non-coincidence. 设 This method mainly highlights the situation where the mold center and the cavity center do not coincide. By synthesizing and decomposing the parallel force system, the moment of the four tie rods is taken to calculate the load P of the tie rod with the largest load among the four tie rods. 杆max , according to the setting clamping force F that is expected to be applied to the mold on the machine 设 Equal to the load P on the tie rod with the maximum load 杆max 4 times, so that the load distributed on each tie rod is equal to P 杆max , thus ensuring that the load on each tie rod is balanced. Figure 1 , the above process includes the following steps:

[0058] Step (1): Read the projection area A of the cavity including the runner system on the parting surface. Import the mold 3D modeling file into the 3D design software (such as UG, Cero, CATIA), extract the position of the coordinate system, the size and position of the projection figure of the mold cavity on the parting surface, and the coordinate data of the center point of the main flow channel of the pouring system on the parting surface; and read the projection area A of the cavity including the runner system on the parting surface (unit: cm 2 ).

[0059] Step (2): Calculate the expansion force P of the melt on the mold cavity胀 .P 胀 (Unit: tf) Calculated according to formula (1).

[0060] P 胀 =K×S×P×A (1)

[0061] In step (2), K, S, and P respectively represent the plastic multiplication constant (value range is 1 to 2), the pressure loss coefficient (value range is 30% to 60%), and the cavity pressure value (unit: bar); K, S, P, and A are determined by step (2.1), step (2.2), step (2.3), and step (1), respectively. Step (2.1), step (2.2), and step (2.3) are specifically as follows:

[0062] Step (2.1): Determine the multiplication constant K of the plastic. Figure 2 The plastic multiplication constant K provided organizes the data on the relationship between plastic types and plastic multiplication constants. The data is organized in the form of (plastic type, plastic multiplication constant K). Figure 2 Provides the average value of the data range. According to the type of plastic raw material used, retrieve the corresponding plastic multiplication constant.

[0063] Step (2.2): Determine the pressure loss coefficient S. The pressure loss coefficient S is 30%, 45%, and 60%, where the plastic with high flowability or low viscosity takes the small value of 30%, the plastic with low flowability or high viscosity takes the large value of 60%, and the plastic with moderate flowability or moderate viscosity takes the middle value of 45%. The relationship between plastic types and corresponding pressure loss coefficients can be found in Figure 2 .

[0064] Step (2.3): Calculate the cavity pressure P value. It includes step (2.3.1), step (2.3.2), and step (2.3.3), as follows.

[0065] Step (2.3.1): Calculate the process length to wall thickness ratio of the process length to the wall thickness. In the 3D design software (such as UG, Cero, CATIA), starting from the front end center position of the main channel of the pouring system (i.e., the position in contact with the front end of the injection molding machine nozzle), read and calculate the maximum process length (unit: mm) and minimum wall thickness value (unit: mm) of the flow channel and the product along the flow direction. Define the process length to wall thickness ratio δ as the ratio of the maximum process length to the minimum wall thickness, and calculate the value of the process length to wall thickness ratio δ.

[0066] Step (2.3.2): Establish cavity pressure data related to wall thickness, process length and wall thickness ratio δ. Figure 3The provided cavity pressure, wall thickness, process length and wall thickness ratio relationship are used to establish cavity pressure curve data for conventional injection molded parts with a minimum wall thickness range of 0.4 to 2.0 mm, with process length and wall thickness ratios of 50:1, 100:1, 150:1, 200:1, 250:1, 275:1 and 300:1 respectively. The data is organized in the form of: (minimum wall thickness value, process length and wall thickness ratio δ, cavity pressure value), where the minimum wall thickness step of injection molded parts is set to 0.1 mm.

[0067] Step (2.3.3): Calculate the cavity pressure value. The minimum wall thickness value and the process length to wall thickness ratio δ obtained in step (2.3.1) are used as the basis for the minimum wall thickness value and the process length to wall thickness ratio of the actual product, and the cavity pressure value corresponding to the actual product molding is calculated through the cavity pressure data established in step (2.3.2). The calculation method is: if the minimum wall thickness value and the process length to wall thickness ratio match one of the seven process length to wall thickness ratios pre-stored in step (2.3.2), the cavity pressure value P is directly retrieved by using the corresponding minimum wall thickness value and the process length to wall thickness ratio; if the minimum wall thickness value and the process length to wall thickness ratio are within the above range but not equal to the above value, the minimum wall thickness value is first rounded to one significant figure after the decimal point according to the rounding method, and then it is retrieved to retrieve two ratios of adjacent process length to wall thickness ratios. Then, the cavity pressure value P is calculated according to the linear interpolation method with reference to the values ​​of the two adjacent process length to wall thickness ratios. If the ratio of process length to wall thickness is not within the range pre-stored in step (2.3.2), exit the program and terminate the calculation.

[0068] The linear interpolation method in step (2.3.3) calculates the cavity pressure according to formula (2).

[0069] (PP i ) / (P i+1 -P i )=(δ-δ i ) / (δ i+1 -δ i ) (2)

[0070] In the linear interpolation method in step (2.3.3), P and P in formula (2) are i , P i+1 They represent the ratios of process length to wall thickness as δ and δ respectively. i , δ i+1 The cavity pressure value, where δ i , δ i+1 express Figure 3 Two adjacent ratios of the seven process length to wall thickness ratios provided in , i = 1, 2, 3, ... 6. δ is the process length to wall thickness ratio of the actual product for which the cavity pressure is to be determined.

[0071] Step (3): Calculate the clamping force F that does not cause mold expansion and produces qualified products 计 . Calculate the clamping force F according to formula (3): 锁 .

[0072] F 计 ≥P 胀 (3)

[0073] Step (4): Determine whether the projection of the mold cavity on the parting surface is centrally symmetrical about the center of the main channel of the pouring system (i.e., the geometric center of the clamping force of the machine). If it is centrally symmetrical, go to step (5); otherwise, go to step (6).

[0074] Step (5): When the geometric center of the cavity coincides with the geometric center of the machine clamping force, set the clamping force F on the machine. 设 If the center is symmetrical, it means that the geometric center of the mold cavity coincides with the geometric center of the machine's clamping force, that is, the projection of the mold cavity on the parting surface is symmetrical about the geometric center, and has two symmetry axes that pass through the geometric center, are orthogonal to each other, and are parallel to the horizontal plane and the vertical plane respectively. Then set the clamping force F 设 =F 计 At this time, due to the symmetry of the geometric center, the load carried by each tie rod is equal to F 设 / 4.

[0075] Step (6): When the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, set the clamping force F on the machine. 设 The geometric center of the cavity does not coincide with the clamping center of the machine. If the clamping force F is set according to step (5) 设 The action of closing the mold and applying high pressure to the mold may cause the load distribution of the four tie rods of the injection molding machine to be unbalanced, causing potential damage to the tie rods. Therefore, for this working condition, the clamping force F is set 设 The calculation should be based on providing sufficient clamping force and not causing mold expansion flash (i.e. F 设 ≥P 胀 ) under the condition of ensuring that the load on each tie rod is balanced. Therefore, the load P on each tie rod can be calculated using the moment balance method. 杆i , find the maximum load P on the four tie rods 杆max At this time, the clamping force F set on the machine is applied to the mold. 设 Equal to the maximum load P 杆max 4 times, the load on each tie rod is equal to P 杆max , thereby ensuring that the load on each tie rod is balanced. It includes steps (6.1), (6.2), and (6.3). The specific calculation process is as follows:

[0076] Step (6.1): Solve for the centroid coordinates of the projection area of ​​the cavity on the parting surface. Import the machine dimension parameters such as the diameter of the injection molding machine tie rod, the position of the tie rod center on the fixed platen, the tie rod spacing and the diameter of the center hole of the fixed platen, and establish a coordinate system XOY on the mold parting surface with the center of the main flow channel as the coordinate origin. The horizontal direction is the X axis and the vertical direction is the Y axis. Its positive direction conforms to the right-hand rule. Use the area centroid method to apply the resultant moment theorem to each coordinate axis to obtain the moment and list the equilibrium equation. Use the first group of formulas (4) and (5) or the second group of formulas (6) and (7) to solve the centroid coordinates x of the projection area of ​​the product including the flow channel on the parting surface. c ,y c .

[0077] The first set of formulas:

[0078]

[0079] The second set of formulas:

[0080]

[0081] Step (6.1) Formulas (4) and (5) are used to solve the centroid coordinates x of the projection area by integration. c ,y c Strictly defined formula; Step (6.1) Formulas (6) and (7) are based on the actual working conditions of the irregular shape of the mold cavity or the layout of multiple cavities in one mold. In actual solution, the projection figure of the cavity on the parting surface can be divided into simple and regular unit figures to calculate the centroid coordinates x of the projection area. c ,y c Discretization formula of . Assume that it is divided into n unit graphics, i = 1, 2, 3, ... n. x i ,y i are the x- and y-direction coordinates of the projection area of ​​the i-th unit figure, A i is the projected area of ​​the i-th unit figure.

[0082] Step (6.2): ​​Solve the loads on the four tie rods of the injection molding machine separately, compare the loads, and find the maximum load P among the four tie rods. 杆max Assume that the loads on the four tie rods of the injection molding machine corresponding to the first, second, third and fourth quadrants of the XOY coordinate system are P1, P2, P3 and P4 respectively. Since the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, it will inevitably lead to the resultant force of the cavity expansion force P 胀 If the XOY coordinate system is offset from its origin O, its resultant force must be in a certain quadrant. Figure 4 , assuming that the resultant force of the expansion force P 胀It occurs in the second quadrant and is y and x lengths away from the X and Y axes respectively. The loads P1, P2, P3, and P4 acting on the four rods are calculated by the resultant moment theorem, which can be calculated by the third group of formulas (8), (9), (10), (11) or the fourth group of formulas (12), (13), (14), (15) (choose 1 from 2).

[0083] The third set of formulas:

[0084] P 胀 =P1+P2+P3+P4 (8)

[0085] P1×(L1 / 2+x)=P4×(L1 / 2-x) (9)

[0086] P1×(L2 / 2-y)=P2×(L2 / 2+y) (10)

[0087] P2×(L1 / 2+x)=P3×(L1 / 2-x) (11)

[0088] The fourth set of formulas:

[0089] P 胀 =P1+P2+P3+P4 (12)

[0090] (P1+P4)×L1=P 胀 ×(L1 / 2+x) (13)

[0091] (P1+P2)×L2=P 胀 ×(L2 / 2+y) (14)

[0092] P1+P3=P2+P4 (15)

[0093] Among them, L1 and L2 are respectively the center distances of two horizontal and two vertical tie rods among the four tie rods arranged in the clamping part of the injection molding machine (they are machine parameters of the injection molding machine, which become known conditions after the injection molding machine is selected).

[0094] Then the maximum force P among the four tie rods is 杆max Calculated by formula (16):

[0095] P 杆max =max{P1,P2,P3,P4} (16)

[0096] From this, we can solve the maximum force P in the four rods. 杆max The center of expansion force in other quadrants can be calculated in the same way.

[0097] Step (6.3): Calculate the set clamping force F applied to the mold 设 The clamping force F applied to the mold 设Equal to the load P on the tie rod with the maximum load 杆max 4 times, that is, F 设 Calculated by formula (17):

[0098] F 设 =4P 杆max (17)

[0099] At this time, it can be ensured that the load on each tie rod is equal to P 杆max , the mold and the machine are in a state of force balance.

[0100] From the above calculation, we can know that when the mold cavity projection area does not have two symmetry axes, it cannot be understood that the forces of the four tie rods will be the same, and the maximum clamping force cannot be equal to the expansion force, which should not be ignored. For this reason, the maximum clamping force should be checked using the moment balance method, and the rated clamping force of the injection molding machine should be selected to be greater than the maximum clamping force required by the mold.

[0101] The specific implementation methods described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for setting the clamping force of a plastic injection molding machine tie rod with balanced force, characterized in that The main steps include: Step (1): Read the projection area A of the cavity including the runner system on the parting surface. Import the mold 3D modeling file into the 3D design software, extract the position of the coordinate system, the size and position of the projection figure of the mold cavity on the parting surface, and the coordinate data of the center point of the main flow channel of the pouring system on the parting surface; and read the projection area A of the cavity including the runner system on the parting surface (unit: cm 2 ). Step (2): Calculate the expansion force P of the melt on the mold cavity 胀 .P 胀 (Unit: tf) Calculated according to formula (1). P 胀 =K×S×P×A (1) Step (3): Calculate the clamping force F that does not cause mold expansion and produces qualified products 计 . Calculate the clamping force F according to formula (2): 锁 . F 计 ≥P 胀 (2) Step (4): Determine whether the projection of the mold cavity on the parting surface is symmetrical about the center of the main channel of the pouring system (i.e., the geometric center of the machine's clamping force). If it is symmetrical, go to step (5); otherwise, go to step (6). Step (5): When the geometric center of the mold cavity coincides with the geometric center of the machine's clamping force, set the clamping force F 设 If the center is symmetrical, it means that the geometric center of the mold cavity coincides with the geometric center of the machine's clamping force, that is, the projection of the mold cavity on the parting surface is symmetrical about the geometric center, and has two symmetry axes that pass through the geometric center, are orthogonal to each other, and are parallel to the horizontal plane and the vertical plane respectively. Then set the clamping force F 设 =F 计 At this time, due to the symmetry of the geometric center, the load carried by each tie rod is equal to F 设 / 4. Step (6): When the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, set the clamping force F on the machine. 设 The geometric center of the cavity does not coincide with the clamping center of the machine. If the clamping force F is set according to step (5) 设 The action of closing the mold and applying high pressure to the mold may cause the load distribution of the four tie rods of the injection molding machine to be unbalanced, causing potential damage to the tie rods. Therefore, for this working condition, the clamping force F is set 设 The calculation should be based on providing sufficient clamping force and not causing mold expansion flash (i.e. F 设 ≥P 胀 ) under the condition of ensuring that the load on each tie rod is balanced. Therefore, the load P on each tie rod can be calculated using the moment balance method. 杆i , find the maximum load P on the four tie rods 杆max At this time, the clamping force F set on the machine is applied to the mold. 设 Equal to the maximum load P 杆max 4 times, the load on each tie rod is equal to P 杆max , thereby ensuring that the load on each tie rod is balanced.

2. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 1, characterized in that: In step (2), K, S, and P respectively represent the plastic multiplication constant (value range is 1 to 2), the pressure loss coefficient (value range is 30% to 60%), and the cavity pressure value (unit: bar). K, S, P, and A are determined by step (2.1), step (2.2), step (2.3), and step (1), respectively. Step (2.1), step (2.2), and step (2.3) are specifically as follows: Step (2.1): Determine the multiplication constant K of the plastic. According to the plastic multiplication constant K corresponding to the plastic type, organize the data on the relationship between the plastic type and the plastic multiplication constant, and the organizational structure of the data is: (plastic type, plastic multiplication constant K). The plastic multiplication constant K takes the average value of its value range. According to the type of plastic raw material used, retrieve the corresponding plastic multiplication constant. Step (2.2): Determine the pressure loss coefficient S. The pressure loss coefficient S is 30%, 45%, and 60%, wherein the plastic with high flowability or low viscosity takes the small value of 30%, the plastic with low flowability or high viscosity takes the large value of 60%, and the plastic with moderate flowability or moderate viscosity takes the middle value of 45%. Step (2.3): Calculate the cavity pressure P value.

3. A method for setting clamping force of a tie rod of a plastic injection molding machine with balanced force as claimed in claim 2, characterized in that: In step (2.3), calculating the cavity pressure P value includes step (2.3.1), step (2.3.2), and step (2.3.3), as follows. Step (2.3.1): Calculate the ratio of flow length to wall thickness. In the 3D design software, starting from the front center of the main channel of the pouring system (i.e., the position in contact with the front end of the injection molding machine nozzle), read and calculate the maximum flow length (unit: mm) and minimum wall thickness (unit: mm) of the flow channel and the product along the flow direction. Define the ratio of flow length to wall thickness δ as the ratio of the maximum flow length to the minimum wall thickness, and calculate the value of the ratio of flow length to wall thickness δ. Step (2.3.2): Establish cavity pressure data on wall thickness, process length and wall thickness ratio δ. According to the relationship between cavity pressure, wall thickness, process length and wall thickness ratio, establish cavity pressure curve data for conventional injection molded parts with a minimum wall thickness of 0.4 to 2.0 mm and a process length to wall thickness ratio of 50:1, 100:1, 150:1, 200:1, 250:1, 275:1, and 300:1, respectively. The data is organized in the form of: (minimum wall thickness value, process length to wall thickness ratio δ, cavity pressure value), and the minimum wall thickness step of the injection molded parts is set to 0.1 mm. Step (2.3.3): Calculate the cavity pressure value. The minimum wall thickness value and the process length to wall thickness ratio δ obtained in step (2.3.1) are used as the basis for the minimum wall thickness value and the process length to wall thickness ratio of the actual product, and the cavity pressure value corresponding to the actual product molding is calculated through the cavity pressure data established in step (2.3.2). The calculation method is: if the minimum wall thickness value and the process length to wall thickness ratio match one of the seven process length to wall thickness ratios pre-stored in step (2.3.2), the cavity pressure value P is directly retrieved by using the corresponding minimum wall thickness value and the process length to wall thickness ratio; if the minimum wall thickness value and the process length to wall thickness ratio are within the above range but not equal to the above value, the minimum wall thickness value is first rounded to one significant digit after the decimal point according to the rounding method, and then it is retrieved to retrieve two ratios of adjacent process length to wall thickness ratios. Then, the values ​​of the two adjacent process length to wall thickness ratios are used as references, and the cavity pressure value P is calculated according to the linear interpolation method. If the ratio of process length to wall thickness is not within the range pre-stored in step (2.3.2), exit the program and terminate the calculation.

4. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 3, characterized in that: In step (2.3.3), the linear interpolation method calculates the cavity pressure according to formula (3). (PP i ) / (P i+1 -P i )=(d-d i ) / (d i+1 -d i ) (3) 5. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 4, characterized in that: In formula (2), P and P i , P i+1 They represent the ratios of process length to wall thickness as δ and δ respectively. i ,δ i+1 The cavity pressure value, where δ i ,δ i+1 It represents the ratio of two adjacent values ​​of the seven process length to wall thickness ratios described in step (2.3.3), i = 1, 2, 3, ...

6. δ is the process length to wall thickness ratio of the actual product for which the cavity pressure is to be determined.

6. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 1, characterized in that: In step (6), when the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, the calculation of the clamping force F set on the machine includes step (6.1), step (6.2), and step (6.3). The specific calculation process is as follows: Step (6.1): Solve for the centroid coordinates of the projection area of ​​the cavity on the parting surface. Import the machine dimension parameters such as the diameter of the injection molding machine tie rod, the position of the tie rod center on the fixed platen, the tie rod spacing and the diameter of the center hole of the fixed platen, and establish a coordinate system XOY on the mold parting surface with the center of the main flow channel as the coordinate origin. The horizontal direction is the X axis and the vertical direction is the Y axis. Its positive direction conforms to the right-hand rule. Use the area centroid method to apply the resultant moment theorem to each coordinate axis to obtain the moment and list the equilibrium equation. Use the first group of formulas (4) and (5) or the second group of formulas (6) and (7) to solve the centroid coordinates x of the projection area of ​​the product including the flow channel on the parting surface. c ,y c . The first set of formulas: The second set of formulas: Step (6.2): ​​Solve the loads on the four tie rods of the injection molding machine separately, compare the loads, and find the maximum load P among the four tie rods. 杆max Assume that the loads on the four tie rods of the injection molding machine corresponding to the first, second, third and fourth quadrants of the XOY coordinate system are P1, P2, P3 and P4 respectively. Since the geometric center of the cavity does not coincide with the geometric center of the machine clamping force, it will inevitably lead to the resultant force of the cavity expansion force P 胀 The resultant force of the expansion force P is offset from the origin O of the XOY coordinate system, and must be in a certain quadrant. 胀 It occurs in the second quadrant and is y and x lengths away from the X and Y axes respectively. The loads P1, P2, P3, and P4 acting on the four rods are calculated by the resultant moment theorem, which can be calculated by the third group of formulas (8), (9), (10), (11) or the fourth group of formulas (12), (13), (14), (15) (choose 1 from 2). The third set of formulas: P 胀 =P1+P2+P3+P4 (8) P1×(L1 / 2+x)=P4×(L1 / 2-x) (9) P1×(L2 / 2-y)=P2×(L2 / 2+y) (10) P2×(L1 / 2+x)=P3×(L1 / 2-x) (11) The fourth set of formulas: P 胀 =P1+P2+P3+P4 (12) (P1+P4)×L1=P 胀 ×(L1 / 2+x) (13) (P1+P2)×L2=P 胀 ×(L2 / 2+y) (14) P1+P3=P2+P4 (15) Among them, L1 and L2 are respectively the center distances of two horizontal and two vertical tie rods among the four tie rods arranged in the clamping part of the injection molding machine (they are machine parameters of the injection molding machine, which become known conditions after the injection molding machine is selected). Then the maximum force P among the four tie rods is 杆max Calculated by formula (16): P 杆max =max{P1, P2, P3, P4} (16) From this, we can solve the maximum force P in the four rods. 杆max The center of expansion force in other quadrants can be calculated in the same way. Step (6.3): Calculate the set clamping force F applied to the mold 设 The clamping force F applied to the mold 设 Equal to the load P on the tie rod with the maximum load 杆max 4 times, that is, F 设 Calculated by formula (17): F 设 =4×P 杆max (17) 7. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 6, characterized in that: In step (6.1), the formulas (4) and (5) are used to solve the centroid coordinates x of the projection area by integration. c ,y c The formula (6) and (7) are formulas that take into account the irregular shape of the mold cavity or the actual working conditions of a mold with multiple cavities. When solving the problem, the projection figure of the cavity on the parting surface can be divided into simple and regular unit figures to calculate the centroid coordinate x of the projection area. c ,y c Discretization formula of . Assume that it is divided into n unit graphics, i = 1, 2, 3, ... n. x i ,y i are the x- and y-direction coordinates of the projection area of ​​the i-th unit figure, A i is the projected area of ​​the i-th unit figure.

8. A method for setting clamping force of a tie rod of a plastic injection molding machine with force balance as claimed in claim 6, characterized in that: In step (6.2), L1 and L2 involved in equations (9), (10), (11) of the first set of formulas and equations (13) and (14) of the second set of formulas are respectively the center distances of two horizontal and two vertical tie rods among the four tie rods arranged in the clamping part of the injection molding machine.

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