Method and apparatus for injection molding of plastic material

Abstract

A method for injection molding plastic material into the cavity (4) of a mold (1) by means of at least one injector (6), the opening and closing of which is operated by an electronic control unit (8), wherein an undesired opening of the mold (1), caused by any overpressure of the plastic material injected into the cavity (4), is detected and corrected by the electronic unit (8) of the at least one injector (6), wherein the detection of the opening of the mold (1) is carried out by sensor means (9) provided outside the cavity (4) of the mold (1), and the detected opening of the mold (1) is corrected by adjusting the stroke and / or the speed and / or the closing / opening acceleration of the at least one injector (6) during the injection step and / or during the subsequent compression step of the injected plastic material, characterized in that a maximum opening value of the mold (1) is set.at which point the opening of at least one injector (6) is interrupted or reduced.

Description

Field of invention

[0001] The present invention relates to the injection molding of plastic materials into the cavity of a mold by means of at least one injector, the opening and closing of which is carried out by means of an electronic servo control. State of the art

[0002] Over the years, the applicant has designed and developed an electronic injector control system, called Flexflow®, which ensures precise control of the flow of injected material during the molding process. Specifically, the actuator of the injector(s), which typically, but not necessarily, consists of a rotating electric motor, is electronically controlled to programmatically adjust one or more of the functions of the needle valve's position, speed, and acceleration in order to control the pressure and flow rate of the injected plastic, as described and illustrated, for example, in document US 9,102,085 B2 on behalf of the applicant.

[0003] During the molding process, the problem of unwanted mold opening due to overpressure from the injected plastic material can occur. Even a slight opening can lead to damage, if not mold breakage, and the formation of clearly visible defects on the molded parts.

[0004] To solve this problem, it was proposed to detect and correct, reduce, or eliminate any overpressure of the plastic material injected into the cavity through the electronic control of the injector(s). For example, US document 5,556,582 proposes detecting any overpressure of the injected plastic material using sensors placed within the cavity of the mold. During injection molding, the opening degree of the injector(s) is adjusted based on the pressure reading from the sensor(s) within the cavity.

[0005] While this solution is efficient in terms of detecting and correcting potential overpressures, it has the disadvantage that the presence of the pressure sensor or multiple pressure sensors inside the cavity results in more or less obvious defects in the molded parts when dealing with large objects.

[0006] Document EP1 990 603 A1 describes a laser device used outside of a mold to detect any separation between the moving part and the fixed part of the mold.

[0007] Although the technical problem of detecting potential mold opening is solved, this solution is relatively complex and expensive, as it requires precise alignment between the laser transmitter, reflector, and receiver, which are mounted on the two mold parts. Furthermore, the potential opening detected by the laser device is simply displayed on a screen or, at most, signaled by an audible alarm. The reclosure is then corrected by adjusting the moving part of the mold, leading to further technological complexities.

[0008] WO 2018 / 094186 A1 describes an injection molding machine and a method for controlling the stroke position of the valve needles of injectors for opening and closing the injectors using measurements from strain sensors.

[0009] JP 2002-103401 A refers to a process for injection compression molding. In this process, the movement speed of a mold core out of a cavity during the filling process is monitored by sensors for position determination. Based on this, a flow rate of the material injected into the cavity is controlled, and the point in time at which the mold core is moved towards the cavity is determined in order to form the molded part by means of the closing pressure.

[0010] WO 2015 / 066004 A1 describes an injection molding process in which one or more sensors detect the pressure of the plastic melt. Based on the measurement signal, a control device controls a valve needle to follow a predefined, desired pressure profile during the process by adjusting the melt flow rate.

[0011] FR 2527976 A1 describes an injection molding device that includes, among other things, sensors for measuring the opening of a mold. Depending on a comparison of the measured opening with a target value, a transition from an injection phase to a holding phase is triggered when this target value is reached. During the injection phase, the feed of a screw is controlled according to a predefined program by acting on a flow-limiting valve, allowing the mold to open freely. During the holding phase, the controller actuates a pressure-limiting valve to maintain the mold opening at the set value until the sprue solidifies.

[0012] DE 2302175 A discloses an injection molding machine comprising measuring elements for determining the gap size of a mold parting line between two mold halves. Based on the mold parting line, the injection volume during operation of the injection molding machine is regulated by an injection pressure acting on a plasticizing screw or its metering stroke in order to maintain the mold parting line at a specific dimension.

[0013] CN 103358501 A relates to an injection molding machine that includes a clamping force sensor for measuring the clamping force of a mold. A clamping force monitoring unit uses this measurement to calculate one or more mold opening distances. Summary of the invention

[0014] The object of the present invention is to overcome the technical problem defined above, and this object is achieved in the injection molding process according to the invention by means of sensors located outside the mold cavity to detect the opening of the mold by means of an overpressure of the plastic material injected into the mold cavity, and by correcting the detected opening of the mold by adjusting the stroke and / or the speed and / or the opening / closing acceleration of the at least one injector during the injection step and / or during the subsequent compression step of the injected plastic material. According to the invention, a maximum opening value of the mold is further defined, at the point at which the opening of the at least one injector is interrupted or reduced.

[0015] The receiving means can be located outside or inside the mold, but in any case outside its cavity. For example, the receiving means can be positioned on the fixed part of the mold, on the molding machine plate, or on the sliding columns of the moving part of the mold.

[0016] The sensor type can be selected from deformation sensors, flexion sensors, torsion sensors, or pressure sensors. Such sensors can be of the contact type or the magnetic induction type.

[0017] If the injection is to be actuated by a plurality of autonomously controlled injectors, the method according to the invention further provides an autotuning method in which, when defining the tolerable maximum opening value of the mold, the opening of an injector is controlled successively, and the influence of each injector is checked by the aforementioned sensor means as a function of this maximum value. The influence of each injector during the subsequent mold cycle is taken into account in the electronic control system.

[0018] The invention also relates to an injection molding device for implementing the process. Brief description of the drawings

[0019] The invention will now be described in detail with reference to the accompanying drawings, which serve only as a non-limiting example, wherein: - Fig. 1 is a schematic perspective view which - in a transparent manner - shows a first example of an injection molding device for implementing the method according to the invention, - Fig. 2 a side view of height Fig. 1 is, - Fig. 3 a top view of Fig. 2 is, and - the Fig. 4, Fig. 5 and Fig. 6 each to the Fig. 1, Fig. 2 and Fig. Three analogous views are shown, which represent a second example of the device for implementing the injection molding process according to the invention. Detailed description of the invention

[0020] Firstly, with reference to the Fig. 1, Fig. 2 and Fig. Figure 3, a first example of an apparatus for injection molding plastic materials for implementing the method according to the invention, comprises a mold 1 consisting of a fixed part or matrix 2, which is applied to a molding machine plate in a known manner (not shown), and a movable part or punch 3, which is displaceable along the slide columns relative to the fixed part 2 (also known and not shown in detail). In the closed position of the mold 1, as shown in the drawings, the fixed and movable parts 2 and 3 together define a mold cavity 4. In the illustrated example, the cavity 4 is designed for forming a large spoiler for use in the automotive industry.

[0021] The mold 1 is equipped with an injection system that conventionally comprises a manifold or hot runner 5, supplied by a mold press and connected to a series of injectors 6, which are also of the conventional type. It should be noted that the number and arrangement of the injectors 6 are shown only as examples.

[0022] Each injector 6 comprises – in a manner known per se and therefore not shown in detail – a nozzle in which a needle valve is axially movable. This needle valve is displaceable between a fully closed position and a maximum opening position for injecting the pressurized plastic material into the cavity 4. The displacement of the needle valve of each injector 6 is controlled by a corresponding actuator 7, of a fluid type or, more practically, of an electrical type, for example, a rotary type, which is controlled by an electronic unit shown with 8.

[0023] The electronic control unit 8 is programmed to control each actuator 7, and thus each needle valve 6, to adjust the pressure and flow rate of the plastic material injected into the cavity 4 during the molding cycle. In particular, the control unit can adjust the position, speed, acceleration, and stroke of the injector 6's needle valve during the cavity 4 filling step.

[0024] The molding device according to the invention is also provided with sensor means for detecting an unwanted opening of the mold 1 caused by excessive pressure of the plastic material injected into the cavity 4, and are functionally connected to the electronic unit 8, which, as explained below, is programmed to limit or even prevent the opening of the mold 1.

[0025] According to the characteristic feature of the invention, these receiving means are positioned outside the cavity 4 and arranged inside or even outside the shape 1.

[0026] In the Fig. 1, Fig. 2 and Fig. In the embodiment shown in Figure 3, the sensor means consist of a series of four sensors 9, which are positioned in the fixed part 2 of the form 1 such that they face the movable part 3 in its closed position. The sensors 9 can be selected from deformation sensors, flexion sensors, torsion sensors, or pressure sensors, and they can be of the contact type or of the magnetic induction type.

[0027] If, during operation, mold 1 is closed and the plastic material coming from the hot runner 5 is injected into the cavity 4 by means of the injectors 6, the sensors 9 detect any possible opening movement of the moving part 3 relative to the fixed part 2 due to excessive pressure of the plastic material injected into the cavity 4 and send corresponding signals to the electronic unit 8. The electronic unit 8 identifies the injector(s) 6 that caused the detected overpressure and corrects this by adjusting the opening stroke and / or the speed and / or acceleration of the respective needle valve, thereby restoring the optimal pressure. A maximum opening value of mold 1 is predefined; when this value is reached, the opening of the injector(s) 6 that triggered this maximum value is interrupted or reduced.

[0028] It should be noted that the aforementioned correction step can be activated not only when introducing the plastic material into the mold, but also during the subsequent compaction step of the injected plastic material.

[0029] In the case of the in the Fig. 4, Fig. 5 and Fig. In the variant shown in Figure 6, in which parts that are identical or similar to those already described are marked with the same reference numbers, the sensors 9 are placed outside the fixed part 2 and the movable part 3 of form 1, such that they are opposite each other.

[0030] It should be noted that the sensors for detecting the unwanted opening of mold 1 can also be arranged in positions other than those shown in the examples and even outside of mold 1, such as on the molding machine plate or along the slide columns of the moving part 3 relative to the fixed part 2. In any case, these sensors are always arranged outside the cavity 4 of mold 1, so that their presence does not in any way affect the aesthetic and structural properties of the parts formed in the cavity 4.

[0031] As already mentioned, the invention provides for a first autotuning step at the beginning of the molding cycle. In this step, when defining a tolerated maximum opening value of the mold 1, the opening of an injector 6 is controlled sequentially, and the influence of each injector is displayed by the sensors 9 as a function of the tolerated maximum opening value. This makes it possible to determine which areas of the mold 1 are most stressed by each individual injector 6, regardless of the opening sequence of the injectors 6 during the molding cycle. This enables the monitoring of the influence of each injector 6, and the electronic unit 8 is able to calibrate the injectors that influence a specific area of ​​the mold 1.

[0032] Naturally, the design details and embodiments may differ greatly from what has been described and illustrated, without deviating from the scope of protection of the present invention as defined in the following patent claims.

Claims

[1] A method for injection molding plastic material into the cavity (4) of a mold (1) by means of at least one injector (6) whose opening and closing is operated by an electronic control (8) and wherein an undesired opening of the mold (1) caused by any overpressure of the plastic material injected into the cavity (4) is detected and corrected by the electronic unit (8) of the at least one injector (6), wherein the detection of the opening of the mold (1) is carried out by sensor means (9) provided outside the cavity (4) of the mold (1) and the detected opening of the mold (1) is corrected by adjusting the stroke and / or the speed and / or the closing / opening acceleration of the at least one injector (6) during the injection step and / or during the subsequent compression step of the injected plastic material, characterized by, that a maximum opening value of the form (1) is specified, upon reaching which the opening of the at least one injector (6) is interrupted or reduced. [2] Method according to claim 1, wherein the form (1) comprises a fixed part (2) and a movable part (3), characterized by , that the receiving means (9) are positioned on the fixed part (2) of the mold (1). [3] Method according to claim 1, wherein the fixed part (2) of the mold is applied to a molding machine plate, characterized by , that the receiving means (9) are positioned on the forming machine plate. [4] Method according to claim 1, wherein the form (1) comprises a fixed part (2) and a movable part (3) which is displaceable relative to the fixed part (2) along slide columns, characterized by that the receiving means (9) are positioned on the columns. [5] Method according to any one of the preceding claims, characterized by, that the sensor means (9) are selected from deformation sensors, flexion sensors, torsion sensors, pressure sensors. [6] Method according to claim 5, characterized by that the sensors are of the contact type. [7] Method according to claim 5, characterized by that the sensors are of the magnetic induction type. [8] Method according to one or more of the preceding claims, wherein the injection is actuated by a plurality of autonomously controlled injectors (6), characterized by , that it provides an initial autotuning step in which, when defining the maximum opening value of the mold (1), the opening of an injector (6) is controlled at a given time, and the influence of each injector (6) relative to this maximum value is detected by the sensor means (9), and this influence is monitored during the electronic control of each injector (6) during the subsequent mold cycle. [9] Device for injection molding plastic material into the cavity (4) of a mold (1) formed between a fixed part (2) and a movable part (3), comprising at least one injector (6) whose opening and closing is effected by means of an electronic control (8), and sensor means (9) suitable for detecting the unwanted opening of the mold (1) caused by the pressure of the plastic material injected into the cavity (4), wherein the sensor means (9) are functionally connected to the electronic control (8), wherein the sensor means (9) are arranged outside the cavity (4) of the mold (1) and the electronic control (8) is designed to reduce the pressure inside the mold (1),to limit this opening by adjusting the stroke and / or the speed and / or the opening / closing acceleration of the at least one injector (6) during the injection step and / or during the subsequent compression step of the injected plastic material, characterized by , that a maximum opening value of the form (1) is specified, upon reaching which the opening of the at least one injector (6) is interrupted or reduced. [10] Device according to claim 9, characterized by , that the receiving means (9) are positioned on the fixed part (2) of the mold (1). [11] Device according to claim 9, wherein the fixed part (2) is applied to a forming machine plate, characterized by , that the receiving means (9) are positioned on the forming machine plate. [12] Device according to claim 9, wherein the movable part (3) is displaceable relative to the fixed part (2) along slide columns, characterized bythat the receiving means (9) are positioned on the columns. [13] Device according to any one of claims 9 to 12, characterized by , that the sensor means (9) are selected from deformation sensors, flexion sensors, torsion sensors, pressure sensors and they are of the contact type or of the magnetic induction type.

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