Mold clamping device, injection molding machine, and mold clamping method

Abstract

To provide a mold clamping device capable of preventing deterioration due to excess mold clamp force.SOLUTION: A mold clamping device (2) includes: two mold platens (13, 14); a ball screw mechanism (18) connecting the mold platens (13, 14) to each other; a servomotor (22) for driving the ball screw mechanism (18); and a control apparatus (5). The ball screw mechanism (18) is provided with axial force detection means (24) for detecting an axial force applied to the ball screw mechanism (18). The control apparatus (5) is constituted so as to execute axial force increase control for increasing an axial force of the ball screw mechanism (18) by driving the servomotor (22) when an increase of an axial force is detected by the axial force detection means (24) when performing injection.SELECTED DRAWING: Figure 4

Description

Technical Field

[0004] , ,

[0001] The present invention relates to a mold clamping device including two mold plates and a ball screw mechanism for connecting these mold plates, an injection molding machine, and a mold clamping method in the mold clamping device.

Background Art

[0002] An injection molding machine or a press machine is provided with a mold clamping device for clamping a mold. There are various types of mold clamping devices, and Patent Document 1 describes a mold clamping device composed of two mold plates. That is, the mold clamping device includes a fixed plate and a movable plate. The fixed plate and the movable plate are connected by four tie bars. Threaded portions are formed on each of the four tie bars, and a half nut that meshes with these threaded portions is provided on the movable plate. Therefore, the movable plate is slid by an opening / closing mechanism to close the molds provided on the fixed plate and the movable plate. When the half nut is driven, the tie bar and the half nut mesh. That is, the movable plate is fixed to the tie bar. By the way, a hydraulic mold clamping mechanism is provided in the fixed plate and is connected to the tie bar. When pressure oil is supplied to the hydraulic mold clamping mechanism, the tie bar is slightly slid with respect to the fixed plate, and thereby a mold clamping force is generated. That is, clamping is performed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a mold clamping device, the mold is clamped, and then the injection material is injected into the mold to produce a molded product. However, if the clamping force is insufficient, the mold will open due to the injection pressure, resulting in molding defects. Therefore, sufficient clamping force is generated to prevent the mold from opening due to the injection pressure. However, if the clamping force is excessively large, it can degrade the mold clamping device.

[0005] This disclosure provides a clamping device that prevents deterioration due to excessive clamping force.

[0006] Other challenges and novel features will become apparent from the description and accompanying drawings in this specification. [Means for solving the problem]

[0007] This disclosure relates to a mold clamping device comprising two mold plates, a ball screw mechanism connecting the mold plates, a servo motor provided in the ball screw mechanism for driving the ball screw mechanism, and a control device. The ball screw mechanism is provided with an axial force detection means for detecting the axial force acting on the ball screw mechanism. The control device is configured to perform axial force increase control by driving the servo motor to increase the axial force of the ball screw mechanism when an increase in axial force is detected by the axial force detection means during injection. In axial force increase control, the amount of rotation of the servo motor being driven is the amount obtained by multiplying the increase in axial force detected by the axial force detection means, the effective length of the ball screw of the ball screw mechanism which is the distance between the two mold plates, and a coefficient. [Effects of the Invention]

[0008] This disclosure makes it possible to generate sufficient clamping force and prevent deterioration of the clamping device. [Brief explanation of the drawing]

[0009] [Figure 1] This is a front view showing an injection molding machine relating to the first embodiment of this implementation. [Figure 2] This is a perspective view showing the clamping device relating to the first embodiment of this implementation. [Figure 3A] This is a front view showing a part of an injection molding machine relating to the first embodiment of this invention during injection molding. [Figure 3B]This is a front view showing a part of an injection molding machine relating to the first embodiment of this invention during injection molding. [Figure 4] This is a flowchart showing the clamping method according to this embodiment. [Figure 5] This is a front view showing an injection molding machine relating to the second embodiment of this implementation. [Modes for carrying out the invention]

[0010] The following describes specific embodiments in detail with reference to the drawings. However, the embodiments are not limited to those described below. For clarity, the following descriptions and drawings have been simplified as appropriate. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations have been omitted where necessary. Also, hatching has been omitted in some parts of the drawings to avoid clutter.

[0011] [First Embodiment] <Injection molding machine related to the first form of this implementation> The injection molding machine 1 according to the first embodiment of this implementation consists of a clamping device 2 provided on the bed B, an injection device 4, and a control device 5 that controls these, as shown in Figure 1.

[0012] <Injection device> The injection device 4 consists of a heating cylinder 6, a screw 7 placed inside the heating cylinder 6, and a screw drive device 8 that drives the screw 7. The heating cylinder 6 is equipped with a hopper 10, and an injection nozzle 11 is provided at its tip. Injection material is fed from the hopper 10, and when the screw 7 is rotated and the injection material is melted, it is metered at the tip of the screw 7. When the screw 7 is driven in the axial direction, the injection material is injected.

[0013] <Mold clamping device> The clamping device 2 according to the first embodiment of this implementation consists of a so-called two-platen clamping device. That is, as shown in Figure 2, the clamping device 2 comprises two platens 13 and 14, i.e., a fixed platen 13 and a movable platen 14. The fixed platen 13 is fixed on the bed B, and the movable platen 14 is mounted on linear guides 15, 15 provided on the bed B. That is, the movable platen 14 is slidable in the direction of approaching and moving away from the fixed platen 13. As shown in Figure 1, a fixed-side mold 16 is attached to the fixed platen 13, and a movable-side mold 17 is attached to the movable platen 14.

[0014] The clamping device 2 according to the first embodiment of this implementation has two mold plates 13, 14, that is, a fixed plate 13 and a movable plate 14, connected by four ball screw mechanisms 18, 18, ... Each ball screw mechanism 18, 18, ... comprises a ball screw 19, 19, ... and ball nuts 20, 20, ... attached to the ball screws 19, 19, ...

[0015] Although not shown in Figure 2, the movable platen 14 has through holes, and ball nuts 20, 20, ... are fixed to these through holes. In other words, one end of each ball screw 19, 19, ... is connected to the movable platen 14 via the ball nuts 20, 20, ... The other end of each ball screw 19, 19, ... passes through the fixed platen 13 and is rotatably supported relative to the fixed platen 13. The fixed platen 13 is equipped with servo motors 22, 22, ... which are connected to the ball screws 19, 19, ... Therefore, when the servo motors 22, 22, ... are driven, the ball screws 19, 19, ... rotate, causing the movable platen 14 to slide. That is, the molds 16, 17 (see Figure 1) are opened and closed.

[0016] <Axial force detection means> In the mold clamping device 2 according to the first embodiment, axial force detecting means for detecting the axial force acting on each of the ball screw mechanisms 18, 18,... is provided. Specifically, load cells 24, 24,... are provided between the movable platen 14 and the ball nuts 20, 20,.... During mold clamping, axial force acts on the ball screw mechanisms 18, 18,.... It can also be said that the axial force detecting means is means for detecting the mold clamping force.

[0017] The servo motors 22, 22,... and the load cells 24, 24,... are connected to the control device 5 (see FIG. 1). In the mold clamping method according to the present embodiment, which will be described later, in the injection process, the control device 5 monitors the change in axial force by the load cells 24, 24,... that is, the axial force detecting means, and drives the servo motors 22, 22,....

[0018] <Behavior of the mold clamping device in the injection process> The behavior of the mold clamping device 2 when carrying out the injection process of injecting the injection material will be described with reference to FIGS. 3A and 3B. As shown in FIG. 3A, recesses 26, 27 are formed in the parting lines of the molds 16, 17 respectively, and a cavity 28 is formed when the molds are clamped. In the clamped state, when the injection material is injected from the injection device 4, the cavity 28 is filled with the resin 30. Due to the pressure of the resin 30 injected into the cavity 28, that is, the injection pressure, a force in the opening direction acts on the molds 16, 17. This force is given by the product of the pressure receiving area, which is the projected area of the cavity 28, and the injection pressure. When the mold clamping force in the mold clamping device 2 is sufficiently large, the molds 16, 17 do not open in the injection process. Then, the ball screws 19, 19,... do not elongate in the injection process. That is, the axial force detected by the load cells 24, 24,... does not change.

[0019] On the contrary, when the mold clamping force is relatively small, as shown in FIG. 3B, the molds 16, 17 open slightly due to the injection pressure of the resin 30. Then, the ball screws 19, 19,... elongate slightly. Due to this elongation, an increase in axial force is detected by the load cells 24, 24,....

[0020] <Method for clamping according to this embodiment> The clamping method according to this embodiment will now be described. The control device 5 (see Figure 1) performs initial clamping in step S01 as shown in Figure 4. That is, the clamping device 2 (see Figures 1 and 2) drives the servo motors 22, 22, ... to rotate the ball screws 19, 19, .... This causes the molds 16 and 17 to come into contact, generating a predetermined clamping force. In this embodiment, the clamping force generated in this initial clamping is made to be slightly smaller than the product of the pressure-receiving area, which is the projected area of ​​the cavity 28 (see Figure 3A), and the injection pressure in the injection process.

[0021] The control device 5 starts the injection process in step S02, as shown in Figure 4. That is, it drives the screw 7 in the axial direction in the injection device 4 (see Figure 1). The control device 5 then executes step S03 to start monitoring the axial force detected by each load cell 24, 24, ... The control device 5 has pre-set thresholds necessary for monitoring the axial force. From this point onward, it monitors changes in the axial force.

[0022] If it is determined in step S04 that the axial force has increased beyond a threshold (YES), then step S05 is executed. That is, the axial force increase step is executed. Specifically, the corresponding servo motors 22, 22, ... are driven for the ball screw mechanisms 18, 18, ... in which an increase in axial force has been detected. In other words, the ball screw mechanisms 18, 18, ... are tightened. This prevents the molds 16, 17 (see Figures 3A and 3B) from opening. The preferred drive amount for the servo motors 22, 22, ... driven at this time will be explained in detail later. After step S05 is performed, the process returns to step S04. That is, it is monitored again to see if an increase in axial force occurs.

[0023] In step S04, if it is determined that the axial force has not increased beyond the threshold (NO), the control device 5 (see Figure 1) proceeds to step S06. In step S06, it checks whether the injection process has been completed. If the injection process has not been completed (NO), it returns to step S04. If the injection process has been completed (YES), it terminates the process.

[0024] <Preferred drive amount of the servo motor in step S05> When driving the servo motors 22, 22, ... in step S05, it is preferable to tighten the ball screw mechanisms 18, 18, ... by the same length as the amount of elongation generated in the ball screws 19, 19, ... during injection, as shown in Figure 3B. This is because it is the minimum drive required to prevent the molds 16, 17 from opening. The amount of elongation ΔL generated in the ball screws 19, 19, ... during injection can be calculated from the increase in axial force ΔF, the effective length L of the ball screws 19, 19, ... (see Figures 3A and 3B), the cross-sectional area S of the ball screws 19, 19, ... and the Young's modulus E of the ball screws 19, 19, ... as follows. ΔL = ΔF·L / (S·E) (Equation 1)

[0025] In other words, the servo motors 22, 22, ... only need to be driven to tighten the ball screw mechanisms 18, 18, ... by the amount of extension ΔL. Since 1 / (S·E) is a constant value in equation 1, the amount driven by the servo motors 22, 22, ... can be the product of the increase in axial force ΔF, the effective length L of the ball screws 19, 19, ... and a coefficient.

[0026] [Second Embodiment] <Injection molding machine related to the second form of this implementation> The injection molding machine 1A according to the second embodiment of this invention includes a clamping device 2A and an injection device 4, which are provided on the bed B, as shown in Figure 5. Although not shown in Figure 5, the injection molding machine 1A according to this second embodiment also includes a control device 5, similar to the first embodiment shown in Figure 1. The injection device 4 of the injection molding machine 1A according to the second embodiment is configured in the same way as the injection device 4 of the injection molding machine 1 according to the first embodiment described in Figure 1, so its description is omitted.

[0027] <Mold clamping device> In the mold clamping device 2A according to the second embodiment, the fixed platen 13 and the movable platen 14 are slidably connected by three guide bars 35, 35, ... and linked by a single ball screw mechanism 18. The single ball screw mechanism 18 consists of a ball screw 19 and a ball nut 20, and is equipped with a servo motor 22. As in the first embodiment, a load cell 24 is provided between the ball nut 20 and the movable platen 14. In other words, the mold clamping device 2A according to the second embodiment has only one ball screw mechanism 18 for opening / closing and clamping the mold, and only one load cell 24 as the means for detecting axial force.

[0028] When performing the injection process in the clamping device 2A according to the second embodiment, the load cell 24 monitors whether or not the axial force increases, similar to the first embodiment. If the axial force increases, the servo motor 22 is driven to increase the axial force, similar to the first embodiment.

[0029] <Variation> This embodiment can be modified in various ways. For example, the clamping method according to this embodiment can be modified. In the clamping method according to this embodiment, initial clamping is performed as step S01 (see Figure 4) to generate clamping force. However, in step S01, the molds 16 and 17 (see Figure 1) may simply be closed so that virtually no clamping force is generated. If the clamping force is virtually zero during initial clamping, when the injection process is started in step S02, an increase in axial force will be detected by the load cell 24 immediately thereafter. Once this increase in axial force is detected, the axial force increase step S04 is performed promptly, so injection can be performed without opening the molds 16 and 17.

[0030] The present invention has been described in detail above based on embodiments, but it goes without saying that the present invention is not limited to the embodiments already described, and various modifications are possible without departing from the spirit of the invention. The multiple examples described above can also be implemented in combination as appropriate. [Explanation of symbols]

[0031] 1 Injection molding machine 2 Mold clamping device 4. Injection device 5. Control unit 6 Heating cylinder 7 Screw 8 Screw drive mechanism 10 Hopper 11 Injection nozzle 13 Fixing plate 14. Movable plate 15. Linear guide 16 Fixed mold 17 Movable mold 18 Ball screw mechanism 19 Ball screw 20 Ball nuts 22 Servo motors 24 Load cell 26 Recess 27 Recess 28 Cavity 30 resin B Bed C center

Claims

1. Two molds, A ball screw mechanism connecting the aforementioned panel plates, A servo motor provided in the ball screw mechanism for driving the ball screw mechanism, A control device is provided, The ball screw mechanism is provided with axial force detection means for detecting the axial force acting on the ball screw mechanism. The control device monitors the axial force detected by the axial force detection means during injection, and when it detects an increase in axial force, it drives the servo motor to perform axial force increase control, thereby increasing the axial force of the ball screw mechanism. A mold clamping device in which the amount of rotation of the servo motor driven in the axial force increase control is the amount obtained by multiplying the amount of increase in axial force detected by the axial force detection means, the effective length of the ball screw of the ball screw mechanism which is the distance between the two mold plates, and a coefficient.

2. The clamping device according to claim 1, wherein a plurality of ball screw mechanisms are provided to connect the mold plates, a plurality of servo motors are provided to each of the ball screw mechanisms, the axial force detection means is provided to each of the plurality of ball screw mechanisms, the axial force increase control is performed independently for each of the plurality of ball screw mechanisms, and the servo motor corresponding to the ball screw mechanism in which an increase in axial force is detected during injection is driven.

3. The clamping device according to claim 1 or 2, wherein the control device is set to a clamping force setting value which is the sum of the axial forces generated in a plurality of ball screw mechanisms, and the clamping force setting value is set to a value smaller than the product of the injection pressure at the time of injection and the pressure receiving area which is the projected area of ​​the cavity in the mold provided in the clamping device.

4. The clamping device according to claim 1 or 2, wherein the detection of the increase in axial force is determined by whether or not the axial force has increased beyond a threshold set in the control device.

5. A mold clamping device for clamping the mold, An injection device for injecting injection material, It consists of a control device and, The clamping device comprises two mold plates, A ball screw mechanism connecting the aforementioned panel plates, A servo motor provided in the ball screw mechanism for driving the ball screw mechanism, A control device is provided, The ball screw mechanism is provided with axial force detection means for detecting the axial force acting on the ball screw mechanism. The control device monitors the axial force detected by the axial force detection means during injection, and when it detects an increase in axial force, it drives the servo motor to perform axial force increase control, thereby increasing the axial force of the ball screw mechanism. In the axial force increase control described above, the amount of rotation of the servo motor driven is the amount obtained by multiplying the increase in axial force detected by the axial force detection means by the effective length of the ball screw of the ball screw mechanism, which is the distance between the two mold plates, and a coefficient, in an injection molding machine.

6. The injection molding machine according to claim 5, wherein a plurality of ball screw mechanisms are provided to connect the mold plates, a plurality of servo motors are provided to each of the ball screw mechanisms, the axial force detection means is provided to each of the plurality of ball screw mechanisms, the axial force increase control is performed independently for each of the plurality of ball screw mechanisms, and the servo motor corresponding to the ball screw mechanism in which an axial force increase is detected during injection is driven.

7. The injection molding machine according to claim 5 or 6, wherein the control device is set to a clamping force setting value which is the sum of the axial forces generated in a plurality of ball screw mechanisms, and the clamping force setting value is set to a value smaller than the product of the injection pressure at the time of injection and the pressure receiving area which is the projected area of ​​the cavity in the mold provided in the clamping device.

8. The injection molding machine according to claim 5 or 6, wherein the detection of the increase in axial force is determined by whether or not the axial force has increased beyond a threshold set in the control device.

9. Two molds, A ball screw mechanism connecting the aforementioned panel plates, A clamping method to be implemented in a clamping device comprising a servo motor provided in the ball screw mechanism for driving the ball screw mechanism, The ball screw mechanism is provided with an axial force detection means for detecting the axial force acting on the ball screw mechanism. The clamping method includes an initial clamping step of clamping a mold provided in the clamping device to generate a clamping force, An axial force monitoring step involves monitoring the change in axial force from the axial force detection means during injection, The axial force monitoring step includes an axial force increase step in which, upon detecting an increase in axial force, the servo motor is driven to increase the axial force of the ball screw mechanism, A mold clamping method in which the amount of rotation of the servo motor driven in the axial force increase step is the amount obtained by multiplying the increase in axial force detected by the axial force detection means by the effective length of the ball screw of the ball screw mechanism, which is the distance between the two mold plates, and a coefficient.

10. In the mold clamping device, a plurality of ball screw mechanisms are provided to connect the mold plates, a plurality of servo motors are provided in each of the ball screw mechanisms, and the axial force detection means is provided in each of the plurality of ball screw mechanisms. The clamping method according to claim 9, wherein the axial force monitoring step is performed for each of the multiple ball screw mechanisms, and the axial force increasing step drives the corresponding servo motor to the ball screw mechanism in which an increase in axial force is detected during injection.

11. The clamping method according to claim 9 or 10, wherein in the axial force monitoring step, the detection of an increase in axial force is determined by whether or not the axial force has increased beyond a predetermined threshold.

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