Methods, apparatus and systems for molding articles

Abstract

The invention relates to a method for controlling a molding phase (100) of an injection molding process and to an injection molding apparatus (1) for carrying out the method. The method involves monitoring a mold breathing signal (104) indicative of a separation between a first mold part (31) and a second mold part (32) during the molding phase (100). The method also involves switching between at least two stages (105, 106, 107, 108, 109, 205, 206, 207, 208, 209) of the injection molding process based at least in part on the mold breathing signal (104).

Description

[0001] METHODS, APPARATUS AND SYSTEMS FOR MOLDING ARTICLES

[0002] FIELD OF THE INVENTION

[0003] This invention relates generally to methods, apparatus and systems for molding articles. More specifically, although not exclusively, this invention relates to apparatus, systems and methods for controlling dynamically the molding phase of an injection molding process for making articles.

[0004] BACKGROUND OF THE INVENTION

[0005] Molding is a process by virtue of which a molded article can be formed from molding material, such as a plastics material, by using a molding system, such as an injection molding system or a compression molding system.

[0006] As an illustration, injection molding of articles can involve heating a polymeric material to a homogeneous molten state and injecting, under pressure, the so-melted material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece. Typically, the female cavity piece is mounted to a cavity plate and the male core piece is mounted to a core plate of a mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient to keep the cavity and the core pieces together against the pressure of the injected material.

[0007] The molding cavity has a shape that corresponds substantially to a final cold-state shape of the molded article to be molded. The so-injected material is then cooled to a temperature sufficient to enable removal of the so-formed molded article from the molding cavity. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be subsequently de-molded by ejecting it off the core piece.

[0008] The mold typically includes cooling channels, which are designed to maintain the cavity and core pieces within a predetermined temperature range throughout the molding cycle. This temperature range is selected to cool of the molten material injected into the cavity. This cooling begins as soon H-8303 as the molding phase starts, with the material being injected into the cavity and continues throughout the molding phase until the parts are de-molded. Injection rates and pressures must be sufficient during the molding phase to ensure the entire cavity is filled completely, without causing excessive shear in the material or premature wear of mold components.

[0009] As such, the molding phase generally involves different stages, including an injection stage, at least one holding stage and a cooling stage. The molding phase is followed by a demolding phase or stage, which includes several sub-stages in which the clamp force is removed, the mold parts are separated and the molded articles are ejected. After the demolding stage, or as part thereof, the mold is closed and clamp force is applied once more to recommence the molding cycle.

[0010] During the injection stage, injection of the molten material is typically governed by the speed of the injector. During the holding stage, injection is typically governed by a holding pressure and that pressure is reduced drastically or removed during the cooling stage. The speeds, pressures and time periods for each of these stages is selected to fill the cavity with the appropriate amount of material to avoid defects resulting from underfilling, such as sink marks, and from overfilling, such as flash and / or wear.

[0011] Traditionally, these parameters are normally selected by the operator when setting up a production run and adjusted as and when any quality issues are observed. This approach requires regular quality checks and intervention as required, which adds to the complexity, risks and cost of manufacture.

[0012] SUMMARY OF THE INVENTION

[0013] The present invention seeks to provide an alternative means of mitigating at least some of the aforementioned issues of the prior art.

[0014] A first broad aspect provides a method for controlling a molding phase of an injection molding process by varying one or more parameters of the inj ection process based at least in part on movement between parts of a mold.

[0015] The inventors have observed that a small separation between mold parts is indicative of the degree to which a cavity of the mold is filled. As such, the molding phase can be adapted based on direct feedback of when the cavity is filled. The inventors have also observed that a reduction in this separation is indicative of the material shrinking during cooling, which can be used to adapt the cooling stage.

[0016] The method may comprise monitoring a mold breathing signal, which may be indicative of a separation between a first mold part relative to a second mold part, e.g. during the molding phase. The method may comprise switching between at least two stages of the injection molding process, for example based at least in part on the mold breathing signal.

[0017] Another broad aspect provides a method for controlling a molding phase of an injection molding process, the method comprising: monitoring a mold breathing signal indicative of a separation between a first mold part and a second mold part during the molding phase; and switching between at least two stages of the injection molding process based at least in part on the mold breathing signal.

[0018] The mold may comprise a cavity. The cavity may be described between the first and second mold parts.

[0019] Another broad aspect provides an injection molding apparatus, e.g. for carrying out the aforementioned method.

[0020] The apparatus may comprise a clamp unit. The clamp unit may comprise first and second platens. The first and second platens may be movable relative to one another. The apparatus may comprise a mold. The mold may include a first mold part and / or a second mold part. The mold may comprise a cavity. The cavity may be described between the first and second mold parts. The first mold part may be mounted to the first platen. The second mold part may be mounted to the second platen.

[0021] The apparatus may comprise an injection unit, e.g. for injecting material into the cavity. The apparatus may comprise one or more sensors, e.g. for generating a mold breathing signal. The mold breathing signal may be indicative of a separation between the first and second mold parts. The apparatus may comprise control means. The control means may be operatively connected to one or more or each of the clamp unit, the injection unit and the sensor(s). The control means may be configured to monitor a mold breathing signal, which may be generated by the sensor(s). The control means may be configured to monitor the mold breathing signal during a molding phase of an injection molding process.

[0022] The control means may be configured to switch between at least two stages of the injection molding process, e.g. based at least in part on the mold breathing signal.

[0023] The control means may comprise one or more control units or controllers. Hereinafter, use of the term controller may be replaced with any of these terms.

[0024] Another broad aspect provides an injection molding apparatus comprising: a clamp unit with first and second platens movable relative to one another; a mold including a first mold part mounted to the first platen and a second mold part mounted to the second platen, a cavity being described between the first and second mold parts; an injection unit for injecting material into the cavity; one or more sensors for generating a mold breathing signal indicative of a separation between the first and second mold parts; and a controller operatively connected to the clamp unit, the injection unit and the sensor(s); wherein the controller is configured to: monitor a mold breathing signal generated by the sensor(s) during a molding phase of an injection molding process; and switching between at least two stages of the injection molding process based at least in part on the mold breathing signal.

[0025] Another broad aspect provides a method for controlling a molding phase of an injection molding process by varying one or more parameters of the injection process based at least in part on a signal received from at least one sensor, which may comprise the or a mold breathing sensor.

[0026] Any aspect, feature or step of the method described above or below applies equally to the apparatus described above or below.

[0027] The method may comprise switching between at least two of the stages when the mold breathing signal exceeds a threshold, e.g. a predetermined threshold. The threshold may comprise a mold breathing signal value, e.g. a predetermined mold breathing signal value. Additionally, or alternatively, the threshold comprises a rate of change. The rate of change may comprise a rate of change in a mold breathing signal value, which may be predetermined rate of change in a mold breathing signal value. H-8303

[0028] The controller may be operable, configured or programmed to switch between at least two of the stages when the mold breathing signal exceeds a threshold, e.g. a predetermined threshold. The threshold may comprise a mold breathing signal value, e.g. a predetermined mold breathing signal value. Additionally, or alternatively, the threshold comprises a rate of change. The rate of change may comprise a rate of change in a mold breathing signal value, which may be predetermined rate of change in a mold breathing signal value. The controller may be configured to enable a user to adjust the threshold, for example via input means, such as an input device.

[0029] The stages may comprise one or more filling stages. The stages may comprise one or more holding stages, for example two or more holding stages such as first and second molding stages and / or one or more further holding stages. The stages may comprise one or more cooling stages. The stages may comprise a demolding stage. The demolding stage may comprise one or more of an unclamping stage, a mold opening stage, an ejection stage, a mold closing stage and a clamping stage. Further stages or sub-stages are also envisaged without departing from the scope of the invention.

[0030] Molten material may be supplied to the mold at a first holding pressure, e.g. in or during the or a first holding stage. Molten material may be supplied to the mold at a second holding pressure, e.g. in or during the or a second holding stage. The second holding pressure may be lower than the first holding pressure. Molten material may be supplied to the mold at an injection speed, e.g. in or during the or a filling stage.

[0031] The method may comprise switching from the first holding stage to the second holding stage based at least in part on the mold breathing signal. The controller may be operable, configured or programmed to switch from the first holding stage to the second holding stage based at least in part on the mold breathing signal.

[0032] The method may comprise storing, e.g. on a memory, the mold breathing signal. The method may comprise storing the mold breathing signal from one or more injection cycles. The method may comprise comparing the mold breathing signal from at least part of one or more injection cycles with the mold breathing signal of at least part of one or more other, e.g. earlier or later, injection cycles. The method may comprise identifying one or more deviations or trends in the mold breathing signal H-8303 of a plurality of different injection cycles. The method may comprise adapting the injection molding process based on the comparison, e.g. a deviation or trend identified.

[0033] The controller may comprise a memory means or memory, hereinafter memory but this term may be replaced with memory means. The controller may be operable, configured or programmed to store, e.g. on the memory, the mold breathing signal of or for at least part of at least one injection cycle. The controller may be operable, configured or programmed to compare the mold breathing signal from at least part of one or more injection cycles with the mold breathing signal of at least part of one or more other, e.g. earlier or later, injection cycles. The controller may be operable, configured or programmed to identify one or more deviations or trends in the mold breathing signal of a plurality of different injection cycles. The controller may be operable, configured or programmed to adapt the injection molding process based on the comparison, e.g. a deviation or trend identified.

[0034] The method may comprises switching between at least two stages based at least in part on the mold breathing signal of one or more prior injection cycles. The method may comprises switching from the filling stage to the first holding stage, for example based at least in part on the mold breathing signal of one or more prior injection cycles.

[0035] The controller may be operable, configured or programmed to switch between at least two stages based at least in part on the mold breathing signal of one or more prior injection cycles. The controller may be operable, configured or programmed to switch from the filling stage to the first holding stage, for example based at least in part on the mold breathing signal of one or more prior injection cycles. The controller may be operable, configured or programmed to switch from the first holding stage to the second holding stage based at least in part on the mold breathing signal of one or more prior injection cycles. The controller may be operable, configured or programmed to switch from a holding stage, e.g. the second or a subsequent holding stage, to the cooling stage based at least in part on the mold breathing signal of one or more prior injection cycles. The controller may be operable, configured or programmed to switch from the cooling stage to the demolding stage based at least in part on the mold breathing signal of one or more prior injection cycles.

[0036] The method may comprise switching from the filling stage to the first holding stage later than the previous cycle, for example if the first holding stage of that previous cycle was longer than a predetermined threshold. The method may comprise switching from the filling stage to the first H-8303 holding stage earlier than the previous cycle, for example if the first holding stage of that previous cycle was shorter than a predetermined threshold.

[0037] The controller may be operable, configured or programmed to switch from the filling stage to the first holding stage later than the previous cycle, for example if the first holding stage of that previous cycle was longer than a predetermined threshold. The controller may be operable, configured or programmed to switch from the filling stage to the first holding stage earlier than the previous cycle, for example if the first holding stage of that previous cycle was shorter than a predetermined threshold.

[0038] The method may comprise generating a warning if the first holding stage exceeds or falls below the or a predetermined threshold. The controller may be operable, configured or programmed to generate a warning if the first holding stage exceeds or falls below the or a predetermined threshold. The controller may comprise a display, which may display the warning. Alternatively, the controller may be configured to transmit the warning, or a warning signal indicative of the warning, to a further device or server.

[0039] Molten material may cool within the mold, e.g. in or during the cooling stage or at least one of the cooling stages. The mold parts may be separated, e.g. for ejecting a molded article formed by the mold or cavity, in or during the demolding stage.

[0040] The method may comprise switching from the cooling stage to the demolding stage, e.g. based at least in part on the mold breathing signal. The controller may be operable, configured or programmed to switch from the cooling stage to the demolding stage, e.g. based at least in part on the mold breathing signal.

[0041] The method may comprise switching from the cooling stage to the demolding stage based in part on a signal indicative of a temperature of one or more articles, which may have been molded in one or more prior injection cycles. The controller may be operable, configured or programmed to switch from the cooling stage to the demolding stage based in part on a signal indicative of a temperature of one or more articles, which may have been molded in one or more prior injection cycles.

[0042] The method may comprise switching from the or a first holding stage, e.g. in which molten material is supplied to the mold at the a first holding pressure, to the cooling stage. The controller may be operable, configured or programmed to switch from the or a first holding stage, e.g. in which molten material is supplied to the mold at the a first holding pressure, to the cooling stage. Switching from the first holding stage to the cooling stage may be based in part on a signal indicative of a weight of one or more articles, which may have been molded in one or more prior injection cycles.

[0043] The method may comprise adjusting a clamp force exerted on the first and second mold parts during the injection process, for example based at least in part on the mold breathing signal. The controller may be operable, configured or programmed to adjust a clamp force exerted on the first and second mold parts during the injection process, for example based at least in part on the mold breathing signal.

[0044] The one or more sensors for generating a mold breathing signal may be mounted to or otherwise associated with one or each mold part. The sensor(s) comprise position sensor(s), e.g. for determining the position of one of the mold parts relative to the other mold part. The sensor(s) may comprise distance sensor(s), e.g. for determining a distance between the mold parts. At least one of the sensor(s) may comprise an optical sensor, a capacitive sensor, an inductive sensor, an ultrasonic sensor or any other suitable type of position or distance sensor. Additionally, or alternatively, at least one of the sensors may be suitable for measuring a stress or strain in a component of the apparatus, for example one or more tie bars or one or more platens of the machine. In such a case, at least one of the sensors may comprise a strain gauge or any other suitable type of sensor.

[0045] The apparatus or sensors may comprise one or more temperature sensors, e.g. for generating the or a signal indicative of a temperature of one or more molded articles. The temperature sensor(s) may be mounted to or associated with the mold, e.g. one of the mold parts. Alternatively, the temperature sensor(s) may be mounted to or associated with a downstream feature, component or device, such as a take off device or a conveyor. The or at least one temperature sensor may comprise a non-contact temperature sensor. The or at least one temperature sensor may comprise a thermal sensor, an infrared sensor or thermometer, a pyrometer or an optical sensor, for example a thermographic optical sensor or camera.

[0046] The apparatus or controller may comprise a human-machine interface (HMI), which may comprise or provide the input means or device and / or the display. The apparatus or controller may comprise a processor. The apparatus or controller may comprise a memory. The processor may be operatively connected to the memory. The memory may comprise a program means, e.g. a program element or a program stored thereon. The program means may be arranged to make a computer execute a procedure to implement the aforementioned method or at least one or more steps of the aforementioned method.

[0047] A further aspect of the invention provides a computer program element comprising computer readable program code means for causing a processor to execute a procedure to implement one or more steps of the aforementioned method.

[0048] A yet further aspect of the invention provides the computer program element embodied on a computer readable medium.

[0049] A yet further aspect of the invention provides a computer readable medium having a program stored thereon, where the program is arranged to make a computer execute a procedure to implement one or more steps of the aforementioned method.

[0050] A yet further aspect of the invention provides a control means or control system or controller comprising the aforementioned computer program element or computer readable medium.

[0051] For purposes of this disclosure, and notwithstanding the above, it is to be understood that any controller(s), control units and / or control modules described herein may each comprise a control unit or computational device having one or more processors, e.g. electronic processors. The controller may comprise a single control unit or electronic controller or alternatively different functions of the control of the system or apparatus may be embodied in, or hosted in, different control units or controllers or control modules. As used herein, the terms “control unit” and “controller” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) or control module(s) to implement the control techniques described herein (including the method(s) described herein). The set of instructions may be embedded in one or more electronic processors, or alternatively, may be provided as software to be executed by one or more electronic processor(s).

[0052] For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on one or more electronic processors, optionally the same one or more processors as the first controller. It will H-8303 be appreciated, however, that other arrangements are also useful, and therefore, the present invention is not intended to be limited to any particular arrangement. In any event, the set of instructions described herein may be embedded in a computer-readable storage medium (e.g., a non-transitory storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational device, including, without limitation: a magnetic storage medium; optical storage medium; magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions.

[0053] For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible.

[0054] For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0055] BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0057] FIG. 1 depicts an injection molding apparatus for carrying out an injection molding process; H-8303

[0058] FIG. 2 depicts a graph showing an injection pressure profile and a mold breathing profile during a molding phase of an injection molding process; and

[0059] FIG. 3 depicts a graph showing an injection pressure profile and a mold breathing profile during a variation of the molding phase of FIG. 2.

[0060] DETAILED DESCRIPTION OF THE INVENTION

[0061] With reference to FIG. 1, there is depicted a non-limiting embodiment of an injection molding apparatus 1, which includes a clamp unit 2, a mold 3, an injection unit 4, sensors 5 and a controller 6. The clamp unit 2 has a first, stationary platen 21 and a second, moving platen 22 which is movable relative to the first platen 21. The mold 3 includes a first, stationary mold part 31 mounted to the first platen 21 and a second, moving mold part 32 mounted to the second platen 22. A plurality of cavities 33 are described between the first and second mold parts 31, 32. The injection unit 4 is configured to inject material into the cavities 33 when the mold parts 31, 32 are clamped together by the platens 21, 22. The clamp unit 2 is operable to move the second platen 22 relative to the first platen 21 to separate the mold parts 31, 32, thereby exposing the cavities 33 for demolding articles molded within the cavities 33.

[0062] In this example, the sensors 5 include a plurality of sensor pairs 51, 52 and a plurality of temperature sensors 53. Each sensor pair 51, 52 includes a first sensor 51 mounted to a respective side of the first mold part 31 and a second sensor 52 mounted to a corresponding side of the second mold part 32. The sensor pairs 51, 52 are configured to generate a mold breathing signal 104, depicted in FIG. 2, which is indicative of a separation between the first and second mold parts 31, 32 during a molding phase 100. Whilst a single sensor pair 51, 52 is also envisaged, the provision of multiple sensors 5 can provide a more accurate measure of mold breathing, for example in the case of slight misalignment between the mold parts 31, 32.

[0063] Indeed, it is envisaged that the mold breathing signal 104 may be provided by means intended for detecting mold alignment or misalignment, for example the sensors 5 may comprise mold alignment sensors. In such examples, the apparatus 1 may have a sensor 5 at each of the four corners of the mold 3 for providing feedback to the controller 6 relating to the alignment of the mold, with this feedback being used to determine or calculate the mold breathing signal 104. Additionally, or alternatively, the H-8303 mold breathing signal 104 could be provided by (or determined using) strain sensors configured to measure a stretch in tie bars 23 of the clamp unit 2 of the apparatus 1. In some examples, a mold breathing signal may be determined or calculated based on feedback from different types of sensors, for example sensors 5 of the kind described above and strain sensors configured to measure a stretch in the tie bars 23. Other arrangements are also envisaged.

[0064] Each temperature sensor 53 is mounted to the second mold part 32 above a respective one of the cavities 33. The temperature sensors 53 in this example are infrared sensors configured to measure the temperature of a molded article retained with the second mold part 32 when the mold parts 31, 32 are separated. In other examples, the temperature sensors 53 are provided downstream of the mold 3, e.g. on or around a conveyor or take off apparatus. The temperature sensors 53 may comprise any type of temperature sensor. Preferably, however, the temperature sensors 53 are non-contact temperature sensor, such as a thermal sensor, an infrared sensor or thermometer, a pyrometer or an optical sensor, for example a thermographic optical sensor or camera.

[0065] The controller 6 includes a human-machine interface (HMI) 60, a processor 61 and a memory 62. The controller 6 is operatively connected to the clamp unit 2, the injection unit 4 and the sensors 5. The controller 6 includes computer program means stored on the memory 62, which is executable via the processor 61 to monitor a mold breathing signal 104 generated by the sensor pairs 51, 52 during a molding phase 100 of the injection molding process. The controller 6 is configured to switch between at least two stages of the injection molding process based at least in part on the mold breathing signal 104.

[0066] FIG. 2 illustrates various profiles during the molding phase 100 of an injection molding process using the apparatus 1 of FIG. 1. These profiles include an injection speed setpoint profile 101, a holding pressure setpoint profile 102, an injection pressure profile 103 and a mold breathing signal profile 104. The molding phase 100 includes a filling stage 105, a first holding stage 106, a second holding stage 107 and a cooling stage 108. The end of the cooling stage 108 coincides with the beginning of the demolding phase or stage 109, which follows the molding phase 100 and includes a various substages, such as unclamp, mold open, ejection, mold close and clamp-up.

[0067] During the filling stage 105, molten material is supplied to the mold at an injection speed according to the injection speed setpoint profile 101. The injection speed setpoint profile 101 includes a steep H-8303 slope 110 up to a first speed setpoint 111, followed by a more gradual slope 112 down to the transition from the filling stage 105 to the first holding phase 106. This results in a steep increase in the injection pressure up to a peak 130, which coincides with the end of the first speed setpoint 111, followed by a decline to the transition from the filling stage 105 to the first holding stage 106, as illustrated by the injection pressure profile 103.

[0068] At this transition, control of the injection unit 4 changes from the injection speed setpoint profile 101 to the holding pressure setpoint profile 102. In this example, the holding pressure setpoint profile 102 includes a first holding pressure setpoint value 121 for the duration of the first holding stage 106 and a second holding pressure setpoint value 122 for the duration of the second holding stage 107, although further holding stages are also envisaged.

[0069] During the first holding stage 106, the cavities 33 are packed out, which results in a continuation of the decline in injection pressure until they are nearly full, when the injection pressure increases to the transition from the first holding stage 106 to the second holding stage 107, as also illustrated by the injection pressure profile 103.

[0070] The injection pressure profile 103 matches substantially the second hold pressure setpoint value 122 throughout most of the second holding stage 107 until the hold pressure is removed, at the transition from the second holding stage 107 to the cooling stage 108. The skilled person will appreciate that, at this stage, the cavities 33 may be sealed off, for example using valve stems (not shown). When the hold pressure is removed, there is a sharp decline in the injection pressure to a negligible value through the rest of the cooling stage 108, as illustrated by the injection pressure profile 103.

[0071] Referring now to the mold breathing signal profile 104, it can be seen that the mold breathing signal remains constant until shortly before the transition from the filling stage 105 to the first holding stage 106, where it starts to increase as the cavities 33 are filled. The mold breathing signal continues to increase into the second holding stage 106 until the cavities 33 are fully packed, where it levels off for the rest of the second holding stage 106. When the hold pressure is removed, the mold breathing signal declines gradually throughout the cooling stage 108.

[0072] In accordance with an embodiment of the invention, the controller 6 is configured to trigger the transition 140 from the first holding stage 106 to the second holding stage 107 when the mold H-8303 breathing signal reaches a first predetermined threshold value 141. As a result of this closed loop approach to controlling the switching from the first holding stage 106 to the second holding stage 107, overfilling of the cavities 33 is less likely, thereby inhibiting flashing of the mold 3 and the risk of premature wear to its components.

[0073] Furthermore, the controller 6 in this example is also configured to trigger the end of the cooling stage 108, namely the transition 142 from the cooling stage 108 to the demolding stage 109, when the mold breathing signal reaches a second predetermined threshold value 143. This ensures that the mold parts 31, 32 separate at the appropriate time, when the material has solidified to the extent appropriate for demolding. The skilled person will appreciate that opening the mold 3 before the molded articles have cooled sufficiently could result in preform defects, whilst excessive cooling can result in excessive forces being exerted on the stack components of the mold 3 during demolding, which can result in premature wear.

[0074] The skilled person will appreciate that numerous conditions are subject to variation that would affect the molding conditions and therefore change the parameters required to fill the cavities 33 to the appropriate level. For example, in the case of hygroscopic materials a small increase or decrease in the moisture content can change the viscosity of the material. Similarly, variations in environmental conditions within manufacturing facilities that do not have tightly controlled environments (e.g. temperature, humidity and the like) can also affect the molding conditions.

[0075] The invention therefore provides a convenient means of adjusting the timing of switching between the various stages of the molding process to compensate for such variations. This improves the consistency of molded articles and reduces the resource burden associated with the traditional approach described above.

[0076] FIG. 3 illustrates various profiles during a further molding phase 200 of an injection molding profile using the apparatus 1 of FIG. 1. The molding phase 200 illustrated in FIG. 3 is similar to the molding phase 100 shown in FIG. 2, wherein like references depict like features incremented by 100. The molding phase 200 illustrated in FIG. 3 differs from that of FIG. 2 in that the transition 240 from the first holding stage 206 to the second holding stage 207 is triggered when the mold breathing signal reaches a first predetermined rate of change threshold 241, or slope, instead of a threshold value 141. The transition 242 from the cooling stage 208 to the demolding stage 209 still occurs when the mold H-8303 breathing signal reaches a second predetermined threshold value 243 in this example, but this can also be determined based on a different threshold parameter.

[0077] In both of the aforementioned molding phase examples 100, 200, the controller 6 may be configured to generate and display on the HMI 60 a warning if the length of the first holding stage 106 exceeds or falls below the or a predetermined threshold. This could be indicative of a change in one or more environmental conditions or a condition of the molding material, which could have an impact on cycle time or on the quality of molded articles. Such an alarm could alert a user to perform a quality check and / or investigate the performance of the apparatus 1.

[0078] The controller 6 may also be configured to enable the operator to adjust the first predetermined threshold value 141, 241 and / or the second predetermined threshold value 143, 243, for example if preform defects are observed, such as flashing or sink marks, or if excessive ejection force is observed, which may be indicative of excessive cooling. Such adjustment may be carried out via the HMI 60.

[0079] Furthermore, the molding phase 100, 200 of each example may involve switching between any of the aforementioned stages 105, 106, 107, 108, 109, 205, 206, 207, 208, 209 based at least in part on the mold breathing signal and / or based at least in part on a signal received from the temperature sensors 53 of one or more prior injection cycles.

[0080] For example, the controller 6 may switch from the filling stage 105, 205 to the first holding stage 106, 206 later than in the previous cycle, if the first holding stage 106, 206 of that previous cycle was longer than a predetermined threshold value or based on a predetermined threshold deviation from a yet previous cycle. A longer than expected first holding stage 106, 206 could be indicative of an increase in viscosity of the material, which could be due to a change in environmental conditions or moisture content in a hygroscopic material. In such a case, extending the filling stage 105, 205 may improve the filling of the cavities 33 and reduce the overall cycle time.

[0081] Alternatively, the controller 6 may switch from the filling stage 105, 205 to the first holding stage 106, 206 earlier than the previous cycle if the first holding stage 106, 206 of that previous cycle was shorter than a predetermined threshold value or based on a predetermined threshold deviation from a yet previous cycle. A shorter than expected first holding stage 106, 206 could be indicative of a decrease in viscosity of the material, which could also be due to a change in environmental conditions H-8303 or moisture content in a hygroscopic material. In such a case, shortening the filling stage 105, 205 may reduce the likelihood of flashing.

[0082] Additionally, or alternatively, the controller 6 may be configured to switch from the cooling stage 108 to the demolding stage 109 based at least in part on a signal received from the temperature sensors 53 indicative of a temperature of one or more articles molded by the apparatus in one or more prior injection cycles. More specifically, if the temperature of the molded articles is too high, the second predetermined threshold value 143, 243 may be reduced and / or the cooling stage 108 may be extended. Alternatively, if the temperature of the molded articles is too low, the second predetermined threshold value 143, 243 may be increased and / or the cooling stage 108 may be shortened.

[0083] It is also envisaged that other molding parameters may be modified based at least in part on the mold breathing signal and / or the temperatures measured by the temperature sensors 53 during one or more prior injection cycles. For example, the injection speed setpoint profile 101, 201 and / or the holding pressure setpoint profile 102 may be adjusted. More specifically, at least one of the slopes 110, 112, 210, 212 up and the first speed setpoint 111 of the injection speed setpoint profile 101, 201 may be adjusted. Additionally, or alternatively, the first and / or second holding pressure setpoint values 121, 122, 221, 222 and / or the duration of the second holding stage 107 may be adjusted. The skilled person will appreciate the various other molding parameters could also be modified, such as a clamp force exerted on the mold parts 31, 32 and / or any other appropriate parameter.

[0084] In some examples, a weight sensor or scale (not shown) may be included, e.g. for generating a signal indicative of a weight of one or more molded articles. In such examples, the controller 6 may be operatively connected to the weight sensor and configured to switch between any of the aforementioned stages 105, 106, 107, 108, 109, 205, 206, 207, 208, 209 based at least in part on a signal received from the weight sensor, which is indicative of a weight of one or more articles molded by the apparatus in one or more prior injection cycles.

[0085] For example, if a weight of the one or more articles exceeds a threshold value or deviates by a predetermined amount from the weight of a previous cycle, the filling stage 105, 205 and / or at least one of the holding stages 106, 107, 206, 207 may be shortened. Similarly, if a weight of the one or more articles falls below a threshold value or deviates by a predetermined amount from the weight of H-8303 a previous cycle, the filling stage 105, 205 and / or at least one of the holding stages 106, 107, 206, 207 may be extended.

[0086] It will be appreciated by those skilled in the art that several variations to the construction and / or use of aforementioned examples are envisaged without departing from the scope of the invention. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1. A method for controlling a molding phase of an injection molding process, the method comprising: monitoring a mold breathing signal indicative of a separation between a first mold part and a second mold part during the molding phase; and switching between at least two stages of the injection molding process based at least in part on the mold breathing signal.

2. The method of claim 1 comprising switching between at least two of the stages when the mold breathing signal exceeds a predetermined threshold.

3. The method of claim 2, wherein the predetermined threshold comprises a predetermined mold breathing signal value.

4. The method of claim 2, wherein the predetermined threshold comprises a predetermined rate of change in a mold breathing signal value.

5. The method of any preceding claim, wherein the stages comprise a first holding stage, in which molten material is supplied to the mold at a first holding pressure, and a second holding stage, in which molten material is supplied to the mold at a second holding pressure which is lower than the first holding pressure, the method comprising switching from the first holding stage to the second holding stage based at least in part on the mold breathing signal.

6. The method of claim 5 comprising generating a warning if the first holding stage exceeds or falls below the or a predetermined threshold.

7. The method of any preceding claim, wherein the stages comprise a cooling stage, in which molten material cools within the mold, and a demolding stage, in which the mold parts are separated for ejecting a molded article formed by the cavity, the method comprising switching from the cooling stage to the demolding stage based at least in part on the mold breathing signal.H-83038. The method of claim 7 comprising switching from the cooling stage to the demolding stage based in part on a signal indicative of a temperature of one or more articles molded in one or more prior injection cycles.

9. The method of any preceding claim, comprising switching from a holding stage, in which molten material is supplied to the mold at a holding pressure, to the cooling stage based in part on a signal indicative of a weight of one or more articles molded in one or more prior injection cycles.

10. The method of any preceding claim, wherein the stages comprise a filling stage, in which molten material is supplied to the mold at an injection speed, and the or a first holding stage, in which molten material is supplied to the mold at the or a first holding pressure, the method comprising switching from the filling stage to the first holding stage based at least in part on the mold breathing signal of one or more prior injection cycles.

11. The method of claim 10 comprising switching from the filling stage to the first holding stage later than the previous cycle if the first holding stage of that previous cycle was longer than a predetermined threshold.

12. The method of claim 10 or claim 11 comprising switching from the filling stage to the first holding stage earlier than the previous cycle if the first holding stage of that previous cycle was shorter than a predetermined threshold.

13. The method of any preceding claim comprising adjusting a clamp force exerted on the first and second mold parts during the injection process based at least in part on the mold breathing signal.

14. A computer program element comprising computer readable program code means for causing a processor to execute a procedure to implement the method of any preceding claim.

15. A computer readable medium having a program stored thereon, where the program is arranged to make a computer execute a procedure to implement the method of any one of claims 1 to 13.

16. A controller comprising the computer program element of claim 14 or the computer readable medium of claim 15.

17. A kit of parts for an inj ection molding apparatus, the kit comprising one or more mold breathing sensors and a computer readable medium according to claim 15 or a controller according to claim 16.

18. An injection molding apparatus comprising: a clamp unit with first and second platens movable relative to one another; a mold including a first mold part mounted to the first platen and a second mold part mounted to the second platen, a cavity being described between the first and second mold parts; an injection unit for injecting material into the cavity; one or more sensors for generating a mold breathing signal indicative of a separation between the first and second mold parts; and a controller operatively connected to the clamp unit, the injection unit and the sensor(s); wherein the controller is configured to: monitor a mold breathing signal generated by the sensor(s) during a molding phase of an injection molding process; and switching between at least two stages of the injection molding process based at least in part on the mold breathing signal.

19. The apparatus of claim 18, wherein the controller is configured to switch between at least two of the stages when the mold breathing signal exceeds a predetermined threshold.

20. The apparatus of claim 19, wherein the predetermined threshold comprises a predetermined mold breathing signal value.

21. The apparatus of claim 19, wherein the predetermined threshold comprises a predetermined rate of change in a mold breathing signal value.

22. The apparatus of any one of claims 18 to 21, wherein the stages comprise a first holding stage, in which molten material is supplied to the mold at a first holding pressure, and a second holding stage, in which molten material is supplied to the mold at a second holding pressure which is lower than the first holding pressure, the controller being configured to switch from the first holding stage to the second holding stage based at least in part on the mold breathing signal.

23. The apparatus of claim 22, wherein the controller is configured to generate a warning if the length of the first holding stage exceeds or falls below the or a predetermined threshold.

24. The apparatus of any one of claims 18 to 23, wherein the stages comprise a cooling stage, in which molten material cools within the mold, and a demolding stage, in which the mold parts are separated for ejecting a molded article formed by the mold, the controller being configured to switch from the cooling stage to the demolding stage based at least in part on the mold breathing signal.

25. The apparatus of claim 24 comprising a temperature sensor for generating a signal indicative of a temperature of one or more molded articles, wherein the controller is operatively connected to the temperature sensor and configured to switch from the cooling stage to the demolding stage based at least in part on a signal received from the temperature sensor indicative of a temperature of one or more articles molded by the apparatus in one or more prior injection cycles.

26. The apparatus of claim 24 or claim 25 comprising a weight sensor for generating a signal indicative of a weight of one or more molded articles, wherein the controller is operatively connected to the weight sensor and configured to switch from the or a first holding stage, in which molten material is supplied to the mold at the or a first holding pressure, to the cooling stage based at least in part on a signal received from the weight sensor indicative of a weight of one or more articles molded by the apparatus in one or more prior injection cycles.

27. The apparatus of any one of claims 18 to 26, wherein the stages comprise a filling stage, in which molten material is supplied to the mold at an injection speed, and the or a first holding stage, in which molten material is supplied to the mold at the or a first holding pressure, the controller being configured to switch from the filling stage to the first holding stage based at least in part on the mold breathing signal of one or more prior injection cycles.

28. The apparatus of claim 27, wherein the controller is configured to switch from the filling stage to the first holding stage later than the previous cycle if the first holding stage of that previous cycle was longer than a predetermined threshold.H-830329. The apparatus of claim 27 or claim 28, wherein the controller is configured to switch from the filling stage to the first holding stage earlier than the previous cycle if the first holding stage of that previous cycle was shorter than a predetermined threshold.

30. The apparatus of any one of claims 18 to 29, wherein the controller is configured to adjust a clamp force exerted on the first and second mold parts by the clamp unit during the injection process based at least in part on the mold breathing signal.

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