Method for determining at least one parameter during an injection moulding process, and injection moulding apparatus

Abstract

In a method for determining at least one parameter during an injection moulding process, the injection moulding process is carried out using an injection moulding apparatus (1) which comprises at least one channel (4), which is in the form of a hot channel or cold channel, and at least one needle valve nozzle (5), which adjoins the channel(s) and via which a moulding compound (F) is injected into a cavity (3) of a moulding tool (2). A shut-off needle (7) of the needle valve nozzle (5) is positioned using an electric motor (6), as a result of which an internal geometry of the needle valve nozzle (5) is set. The volume flow with which the moulding compound (F) flows through the needle valve nozzle (5) is set. During the injection moulding process, a measuring device (10) is used to ascertain the mechanical stress occurring on the shut-off needle (7) as a result of the moulding compound (F) flowing past and / or pressing against the shut-off needle (7). A calculation logic is used to determine the parameter on the basis of the ascertained mechanical stress, the known internal geometry of the needle valve nozzle (5) and the known volume flow of the moulding compound (F).

Description

[0001] METHOD FOR DETERMINING AT LEAST ONE PARAMETER DURING

[0002] AN INJECTION MOLDING PROCESS AND INJECTION MOLDING DEVICE

[0003] The invention relates to a method for determining at least one parameter during an injection molding process, wherein an injection molding device is used for the injection molding process, which has at least one channel, which is designed as a hot runner or cold runner, and at least one adjoining needle shut-off nozzle, via which a molding compound is injected into a cavity of a mold, wherein a shut-off needle of the needle shut-off nozzle is positioned with the aid of an electric motor, whereby an internal geometry of the needle shut-off nozzle is set, and wherein the volume flow with which the molding compound flows through the needle shut-off nozzle is set.

[0004] Furthermore, the invention relates to an injection molding device, as well as a method for balancing an injection molding device and a method for detecting the achievement of an isothermal state in an injection molding device during a heating process.

[0005] It is known that parameters occurring during an injection molding process, for example those relating to the molding compound, influence both the effectiveness of the injection molding process and the mechanical properties of the molded parts produced by the injection molding process.

[0006] Many of these parameters, such as the volume flow with which the molding compound is introduced or injected into a mold during the injection molding process, can be directly specified or adjusted. Other parameters, however, result from the presettings made and the boundary conditions occurring during the injection molding process. In conventional processes, these parameters, which cannot be directly adjusted or controlled, are usually assumed on the basis of known empirical values, which generally requires prior, complex series of tests and only provides a (more or less accurate) approximation, or are calculated with the help of complex, computer-generated models, which is resource-intensive, error-prone and often limited to very specific applications.

[0007] The invention is therefore based on the object of providing a method that does not have the disadvantages of the prior art. In particular, a method is to be provided with which parameters occurring during an injection molding process can be determined in a simple and as accurate a manner as possible. Likewise, a device is to be provided that makes it possible to determine parameters occurring during an injection molding process in a simple and as accurate a manner as possible.

[0008] This object is achieved according to the invention with a method having the features of claim 1 and with a device having the features of claim 5.

[0009] Furthermore, the invention is based on the object of providing a method for balancing an injection molding device with which it can be ensured that, in an injection molding device which has a mold with several cavities, all cavities are filled at approximately the same speed or are completely filled at approximately the same time.

[0010] This object is achieved according to the invention with a method having the features of claim 7. The invention is also based on the object of providing a method with which the attainment of an isothermal state in an injection molding device during a heating process can be detected.

[0011] This object is achieved according to the invention with a method having the features of claim 10.

[0012] Preferred and advantageous embodiments of the invention are the subject of the subclaims.

[0013] According to the invention, during the injection molding process, the mechanical stress occurring on the shut-off needle due to the flow past and / or pressure of the molding compound on the shut-off needle is determined with the aid of a measuring device.

[0014] In particular, while the cavity is being filled, a tension-induced stress (i.e., a tensile stress) occurs on the valve pin, which is caused by the molding compound flowing past the valve pin and out of a nozzle opening of the valve pin nozzle into the cavity.

[0015] As soon as the cavity is completely filled, the molding compound exerts pressure on the needle (particularly opposite to the tensile stress) due to the back pressure in the cavity, which changes the stress acting on the needle. In particular, the mechanical stress acting on the valve pin changes (from tensile stress to compressive stress).

[0016] Likewise, during the flow-by or when the cavity is completely filled, the molding compound can be transferred to the

[0017] A shear stress is exerted on the valve needle. In the course of the method according to the invention, the parameter is determined with the aid of a calculation logic and on the basis of the determined mechanical stress (or stresses), as well as the known internal geometry of the needle valve nozzle and the known volume flow of the molding compound.

[0018] Preferably, the method according to the invention determines a parameter relating to the molding compound, namely the viscosity of the molding compound flowing through the needle valve nozzle. The tensile stress exerted on the valve needle is particularly important for determining the viscosity, so that, knowing the volume flow of the molding compound and the internal geometry of the nozzle, the viscosity can be determined continuously as long as the cavity is filled, without having to resort to complex calculation or simulation models.

[0019] Particularly preferably, the method according to the invention can also be used to determine whether the molding compound is flowing into the cavity or not, i.e. whether the cavity or the region of the cavity into which the molding compound is injected with the aid of the needle shut-off nozzle is completely filled or filled or not yet. Achieving complete filling can be regarded as a parameter relating to the molding compound in that the molding compound has a flow velocity of > 0 m / s while the cavity is not yet completely filled, and a flow velocity of 0 m / s as soon as the cavity is completely filled. The method according to the invention is therefore preferably used to determine whether the molding compound is (currently) flowing through the needle shut-off nozzle or not. When the molding compound flows into the cavity, tensile stress acts on the shut-off needle, and as soon as the cavity is completely filled or filled, tensile stress acts on the shut-off needle.When the injection molding process is complete, the molding compound flowing into and out of the cavity exerts compressive stress on the valve pin (particularly on its tip). The cavity is thus either completely filled or not completely filled during the injection molding process.

[0020] How the viscosity and / or the achievement of maximum filling of the cavity can be determined or calculated based on the known stress occurring on the shut-off needle, in particular the tensile, compressive and / or shear stress occurring on the shaft of the shut-off needle, and the known volume flow of the molding compound with a known internal geometry of the needle shut-off nozzle, is within the knowledge of a specialist in the field of injection molding technology who has sufficient knowledge of rheology, fluid mechanics and materials science, and does not need to be explained further here.

[0021] The parameter(s) of the injection molding process are preferably determined continuously over the duration of the injection molding process so that, for example, the viscosity of the molding compound can be monitored and / or it can be determined at what point in time the cavity is completely filled.

[0022] In one embodiment of the method using an injection molding apparatus with multiple needle-gate nozzles, these multiple needle-gate nozzles can, for example, each open into different regions of a single cavity. If one of the regions is filled and the molding compound from this region penetrates into other regions, this can be noticeable, for example, by an increasing compressive stress on the valve pin of the needle-gate nozzle opening into the filled region.

[0023] The method according to the invention can also be used in a cascade injection molding process in that the needle valve nozzles downstream in the cascade are only opened when maximum filling of the cavity or the associated area of ​​the cavity is detected at the upstream needle valve nozzles (i.e. when the backflow of the molding compound in the area adjacent to the upstream needle valve nozzle causes the stress occurring at the valve needle to change from tensile stress to compressive stress).

[0024] Particularly preferably, in the method according to the invention, the measuring device detects the electrical current and / or the electrical voltage (or its change over time) used to drive the electric motor. The electric motor is in particular a servo motor or a stepper motor. By measuring the electrical current required to hold the shut-off needle in a predetermined position (or by measuring changes in the power consumption of the electric motor), direct conclusions can be drawn about the mechanical stress(s) occurring on the shut-off needle.

[0025] In an alternative embodiment, it can be provided that a sensor suitable for voltage measurements (in particular for measuring changes in length) is arranged on the closure needle and the measuring device detects a signal from the sensor and uses this to determine the voltage occurring at the closure needle. The sensor is arranged in particular at the beginning of the shaft of the closure needle. The sensor can, for example, be a strain gauge sensor which has one or more strain gauges (strain gauges). In this case, the measuring device would detect a change in resistance of the strain gauge sensor when there is a change in the voltage occurring at the shaft of the closure needle (actually when the shaft is stretched or compressed). However, the sensor can also be a piezoelectric sensor in which a change in charge and / or capacitance is detected, or any other sensor suitable for measuring a change in voltage (i.e.a change in the length of the valve pin with known valve pin geometry and known material properties of the valve pin ) be a suitable sensor .

[0026] The invention also relates to an injection molding device comprising:

[0027] A molding tool with at least one cavity, at least one channel which is designed as a hot runner or cold runner, at least one needle valve nozzle adjoining the channel for injecting a molding compound into the cavity, and at least one electric motor for positioning a valve pin inside the needle valve nozzle. The internal geometry of the needle valve nozzle can be adjusted by positioning, in particular pushing in and pulling out, the valve pin into the interior of the needle valve nozzle. In particular, both the internal volume of the needle valve nozzle through which flow can pass and a cross-sectional area of ​​a gap formed between a valve pin tip and an inner wall of the needle valve nozzle in the region of a nozzle opening can be adjusted.

[0028] Furthermore, the injection molding machine comprises a plasticizing unit with which a volume flow of the molding compound introduced into the mold can be adjusted, as well as a logic unit with a calculation logic.

[0029] The injection molding apparatus further comprises a measuring device which is designed to determine the mechanical stress occurring on the shut-off needle as a result of the molding compound flowing past and / or being pressed against the shut-off needle. For this purpose, the measuring device can record the motor current (or the motor voltage) of the electric motor in order to use this to determine the stress acting on the shut-off needle (in particular on its shaft). The measuring device can also comprise a sensor which is arranged on the shut-off needle and detects, for example, a change in the length of the shut-off needle, so that, with knowledge of the shut-off needle geometry and the material properties of the shut-off needle, the stress occurring on the shut-off needle can be recorded.

[0030] According to the invention, the calculation logic is designed to determine a parameter during an injection molding process (in particular the viscosity of the molding compound flowing through the needle shut-off nozzle and / or the achievement of complete filling of the cavity or of the region of the cavity into which the molding compound is injected using the needle shut-off nozzle) on the basis of the determined mechanical stress as well as the known internal geometry of the needle shut-off nozzle and the known (set) volume flow of the molding compound.

[0031] The injection molding device according to the invention and its logic unit are particularly suitable or intended for use in the method according to the invention. In particular, the injection molding device and its logic unit are configured to carry out the method according to the invention. It is therefore understood that features described only for the injection molding device can also be adequately implemented in the method, and vice versa.

[0032] The invention also relates to a method for balancing an injection molding device.

[0033] In injection molding machines that have a mold with multiple, independent cavities that are filled within a single injection molding process, it is desirable for the cavities to be completely filled at approximately the same time. On the one hand, this offers a logistical advantage, as the injection molding process is not finished until all cavities are completely filled. On the other hand, it also ensures that the material properties of the molded parts produced by the injection molding process are largely the same, since the material properties of injection-molded parts are influenced by how long the molding compound remains in the cavity at certain temperatures or pressures during the injection molding process.

[0034] The balancing method according to the invention comprises a plurality of injection molding processes, for which an injection molding apparatus is used, which has at least one channel, designed as a hot runner or cold runner, and at least two adjoining needle valves. Each of the needle valves is assigned its own cavity. The cavities are independent of one another, i.e., essentially not connected to one another, but are all located in a common mold.

[0035] Preferably, the molding tool has more than two, in particular four, six, eight or more than eight (e.g. ten or twenty) cavities, each of the cavities being assigned its own needle valve nozzle.

[0036] A molding compound is injected into the corresponding cavity of the mold via each of the needle valve nozzles. The molding compound is injected through an opening in the needle valve nozzle. The valve needle can be positioned closer to or further away from the opening by the electric motor.

[0037] For each of the needle-gate nozzles, a valve pin is positioned using an associated electric motor. This adjusts the internal geometry of the needle-gate nozzle. Essentially, this increases or decreases the outlet cross-section of the nozzle opening. The volumetric flow rate at which the molding compound flows through the channel is adjusted on the injection molding device used.

[0038] During each injection molding process, the mechanical stress occurring on each valve pin due to the molding compound flowing past and / or being pressed against the valve pin is determined with the aid of an assigned measuring device. The mechanical stress occurring on the valve pin can be determined as described in the method for determining at least one parameter. In particular, the measuring device records the electrical current and / or the electrical voltage used to drive the electric motor (with which the position of the valve pin is adjusted) and uses this to determine the mechanical stress occurring on the valve pin. Each valve pin can be assigned its own measuring device, but one measuring device can also be assigned to several valve pins, or a single measuring device can be assigned to all valve pins.During the injection molding process, the current curve of each of the electric motors assigned to the valve pins changes, as the electric motor requires different amounts of current to hold the valve pin in the preset position depending on the level or orientation of the mechanical tension acting on the valve pin. For example, the electric motor consumes more power when a greater tensile stress is applied to the valve pin.

[0039] With the help of a calculation logic, the mechanical stress measured during each injection molding process is used to determine when each cavity is completely filled. At the same time, the times at which the cavities are completely filled are determined (or recorded). This calculation logic can also serve as a measuring device that records the current or voltage driving the electric motor and uses this to determine the mechanical stress.

[0040] As already described, the molding compound flowing past the valve pin exerts a tensile stress on the valve pin during cavity filling, which is measured using the measuring device. As soon as the cavity is completely filled, no more molding compound flows past the valve pin, so the tensile stress drops. At the same time, with the cavity completely filled, a compressive stress is built up on the valve pin (particularly on its tip) due to the molding compound backing into and out of the cavity.

[0041] If, for example, the measuring device records the electrical current used to drive the electric motor in order to hold the valve pin in the set position, the current curve essentially has a plateau or a section with a slight gradient before the cavity is fully filled. When full filling is reached, a section of the current curve begins with a steep gradient because, when the cavity is fully filled, the mechanical stress acting on the valve pin reverses (compressive stress instead of tensile stress). The point in time at which the section of the current curve with the steep gradient begins can be recorded by the calculation logic, for example by smoothing the current curve and determining a local maximum or minimum (i.e. an inflection point with a gradient = 0) of the 2nd derivative of the current curve in the relevant time range.

[0042] After each injection molding process (or between injection molding processes), the last determined times of complete filling of the cavities are compared with a specified reference time. This comparison is preferably also performed by the calculation logic or by another logic or control system configured for this purpose.

[0043] Based on this comparison, the needle valve nozzles are:

[0044] • the valve pin is positioned closer to the opening of the valve pin nozzle if the last determined time of complete filling of the associated cavity is at least a predefined tolerance time before the reference time,

[0045] • the valve pin is positioned further away from the opening of the valve pin nozzle if the last determined time of complete filling of the associated cavity is at least the predefined tolerance time period after the reference time, or

[0046] • maintain the position of the valve pin if the last determined time of complete filling of the assigned cavity does not reach the predefined

[0047] Tolerance time span deviates from the reference time.

[0048] The valve pin is repositioned for each of the needle valve nozzles via the assigned electric motor. After each comparison in which a deviation is detected, the valve pin can be moved a predefined distance towards or away from the opening. However, it is also possible for the distance the valve pin is moved towards or away from the opening to be selected depending on the extent of the actual deviation between the last determined time and the reference time, and to be greater or smaller depending on the extent of the actual deviation (i.e. depending on how much the actual deviation exceeds the tolerance period).By means of the method according to the invention for balancing an injection molding device which comprises a molding tool with a plurality of cavities, the needle valve nozzles of the injection molding device can be adjusted during a plurality of injection molding processes in such a way that all cavities are filled at approximately the same speed or are completely filled at approximately the same time.

[0049] Particularly preferred in the balancing process is the last determined time of complete filling of one of the cavities, which is defined as the reference cavity. This reference cavity can be determined manually or by the calculation logic based on predefined selection criteria.

[0050] Particularly for molds with four or more cavities, it may be provided that an average of the most recently determined times of complete filling of some or all cavities is set as the reference time. This time is set manually, but preferably with the aid of the calculation logic.

[0051] In the method according to the invention for balancing an injection molding device, injection molding processes of the method (i.e. the injection molding processes during which the mechanical tension on the shut-off needles is detected) can take place directly one after the other, but further injection molding processes can also take place between two consecutive injection molding processes of the method, in which no detection and / or comparison of the times of complete filling and possibly no repositioning of the shut-off needles is carried out.

[0052] The balancing method used in the invention

[0053] An injection molding machine may have a mold whose cavities are of equal size. Here, the differences between the times at which the cavities are fully filled arise, for example, from the position of the cavity in the mold.

[0054] However, the injection molding device can also have a mold in which at least some of the cavities have different internal volumes. In such molds, also referred to as family molds, the differences between the times at which the cavities are fully filled are primarily due to the different internal volumes of the cavities.

[0055] In an injection molding process that involves a large number of consecutive injection molding operations, the balancing process can only be carried out at the beginning, i.e., over a predefined number of injection molding operations that take place at the beginning of the process. Preferably, however, the balancing process is carried out over the entire injection molding process.

[0056] The balancing process can compare the last determined time of complete filling of the cavities with a specified reference time after each injection molding process. This ensures particularly consistent production quality throughout the entire injection molding process.

[0057] However, it is also possible for the balancing process to be distributed over a large number of injection molding processes which do not follow one another directly, but between which other injection molding processes of the injection molding process take place. The large number of injection molding processes in the process can, in particular, be regularly distributed over all injection molding processes of the injection molding process. In order to be able to carry out more intensive balancing, particularly at the beginning of the injection molding process, i.e. in the first injection molding processes of the injection molding process, which is simply maintained in the later injection molding process, no further injection molding processes can be carried out at the beginning between the injection molding processes of the balancing process and further injection molding processes can only be carried out between the injection molding processes of the balancing process once a predetermined number of injection molding processes has been carried out.At the beginning, fewer additional injection molding processes may be carried out between the injection molding processes of the balancing process than after the specified number of injection molding processes has been reached.

[0058] The reference point in time can remain the same throughout the balancing process or can be varied or adjusted (manually or via the calculation logic according to predefined criteria).

[0059] The method for balancing an injection molding device can be carried out using an injection molding device according to the invention, in which the mold has more than one cavity, in particular two or more than two cavities. Likewise, an injection molding device according to the invention configured in this way and its logic unit can be configured to carry out the method according to the invention for balancing an injection molding device as described above.

[0060] The method for balancing an injection molding device can essentially comprise, for each injection molding process, a method according to the invention for determining at least one parameter, wherein the achievement of complete filling of the cavity is determined as the parameter. The achievement of complete filling of the cavity can essentially be determined only on the basis of the determined mechanical stress, wherein the internal geometry of the needle valve nozzle and the volume flow of the molding compound can be known for determining the achievement of complete filling of the cavity, but do not have to be, or do not have to be included in the determination.

[0061] The invention further relates to a method for detecting the reaching of an isothermal state in an injection molding device during a heating process.

[0062] Before and during injection molding processes, injection molding equipment is heated up to minimize undesirable cooling of the molding compound used in the injection molding process. When the injection molding equipment is heated up from a cooled state, components of the injection molding equipment expand, so that parameters important for an injection molding process can change undesirably during the heating-up phase. Injection molding processes can therefore only begin once the injection molding equipment has reached an isothermal state in which the heat input is equal to the heat output and there is no further change in the size of the components of the injection molding equipment and therefore no further undesirable change in parameters important for the injection molding process.

[0063] The injection molding device used during the process for detecting the achievement of an isothermal state has at least one channel, which is designed as a hot runner or cold runner, and at least one adjoining needle valve nozzle, via which the molding compound can be injected into a cavity of a mold. In particular, two or more than two needle valve nozzles can be connected to the channel, each of which has its own cavity of the

[0064] molding tool. The needle valve nozzle (or each of the needle valve nozzles) has a valve pin that can be positioned by means of an electric motor.

[0065] During the heating process, a measuring device is used to continuously or discontinuously measure the mechanical stress on the valve pin, which occurs due to the pin pressing against a valve seat of the needle valve. The valve seat is located in the area of ​​the opening of the needle valve, through which the molding compound can be injected into an adjacent cavity. When the valve pin is pressed against the valve seat, the opening of the needle valve is closed.

[0066] The determination of the mechanical stress occurring on the valve pin takes place in particular as in one of the methods described above, namely via a measuring device.

[0067] As soon as the determined mechanical stress value deviates from a specified stress reference value over a predefined high tolerance period, the position of the valve pin is changed in order to bring the mechanical stress occurring on the valve pin closer to the stress reference value. The stress reference value is set in particular by pressing the valve pin against the valve seat with a predefined pressure before the heating process. If the determined mechanical stress value is higher than the reference stress value over the tolerance period, the valve pin is moved away from the valve seat. Or the valve pin is moved towards the valve seat if the determined mechanical stress value is lower than the reference stress value over the tolerance period.The valve pin can be repositioned using predefined strokes, with the mechanical stress occurring on the valve pin being re-measured after each stroke. The valve pin can also be repositioned using continuous adjustment, which is aborted as soon as the mechanical stress occurring on the valve pin, which is also constantly determined, returns to within the tolerance period around the stress reference value.

[0068] In the method according to the invention, the isothermal state is detected in the injection molding device as soon as the determined mechanical stress value does not deviate from the stress reference value beyond the tolerance time period over a predefined period of time.

[0069] To carry out the method, a control system is preferably provided which automatically determines the mechanical stress occurring on the shut-off needle at predefined intervals or continuously, compares it with the reference stress value and, if necessary (i.e. in the event of a deviation that is greater than the tolerance time period), changes or adjusts the position of the shut-off needle. This control system can also detect and store or communicate the time at which the isothermal state is reached in the injection molding device. Alternatively, although not preferred, some or all of the method steps can also be carried out manually by an operator.

[0070] Using this method for detecting the attainment of an isothermal state, it is possible to determine precisely when the injection molding machine is ready to begin the injection molding process, i.e., consecutive injection molding operations. This can save considerable time compared to conventional methods, in which the injection molding machine is heated up and the injection molding process only begins after a predetermined, unnecessarily long period of time for safety reasons.

[0071] It is understood that features which are described only for one of the methods or devices can also be implemented adequately in the other methods and vice versa.

[0072] Further details, features, and advantages of the invention will become apparent from the following description with reference to the accompanying drawings. It shows:

[0073] Fig. 1 is a highly simplified representation of an injection molding device according to the invention,

[0074] Fig. 2 is a schematic representation of the sequence of a method according to the invention for determining a parameter,

[0075] Fig. 3 is a schematic representation of the sequence of a method according to the invention for balancing an injection molding device, and

[0076] Fig. 4 is a schematic representation of the sequence of a method according to the invention for detecting the achievement of an isothermal state in an injection molding device.

[0077] Fig. 1 shows an injection molding device 1 according to the invention in a highly simplified, schematic representation.

[0078] The injection molding device 1 according to the invention has a mold 2 in which at least one cavity 3 is formed for receiving molding compound F.

[0079] Furthermore, the mold 2 comprises at least one channel 4, which can be designed as a hot runner or a cold runner. Connected to the channel 4 is at least one needle valve nozzle 5, which serves to inject the molding compound F into the cavity 3.

[0080] The needle valve nozzle 5 is assigned an electric motor 6, by means of which a valve pin 7 is positioned within the needle valve nozzle 5. By positioning the valve pin 7 (in particular by pushing the valve pin 7 back and forth in the direction of the longitudinal extension of its shaft), an internal geometry of the needle valve nozzle 5 can be adjusted.

[0081] The injection molding device 1 further comprises a plasticizing unit 8 for introducing the liquefied molding compound F into the mold 2. The volume flow of the introduced molding compound F can be adjusted using a control 9 of the plasticizing unit 8.

[0082] A measuring device 10 of the injection molding device 1 is designed to determine the mechanical stress or stresses occurring on the shut-off needle 7 (in particular on the shaft of the shut-off needle 7). This stress or stresses occurs due to

[0083] • the flow of the molding compound F past the shut-off needle 7 (tensile stress),

[0084] • the lateral pressure of the molding compound F on the shut-off needle 7 (shear stress), and / or

[0085] • the back pressure of the molding compound F when the cavity 3 is completely filled and the pressure (compressive stress) exerted by the molding compound F on the tip of the shut-off needle 7.

[0086] The measuring device 10 can, for example, measure the motor current of the

[0087] Electric motor 6 or the change in the motor current over time and use this to determine which voltage(s) acts on the shut-off needle 7, which is held in position within the needle shut-off valve 5 by the electric motor 6.

[0088] Not only information concerning the mechanical stress(s) determined by the measuring device 10 is transmitted to a logic unit 11 of the injection molding device 1 according to the invention, but also the position of the shut-off needle 7 and thus information concerning the internal geometry of the needle shut-off valve 5. Furthermore, the logic unit 11 receives from the controller 9 of the plasticizing unit 8 the information regarding the volume flow at which the molding compound F is fed to the mold 2.

[0089] With the aid of calculation logic implemented in the logic unit 11, a parameter of the injection molding process can be determined based on this information. In particular, a viscosity of the molding compound F flowing through the needle valve nozzle 5 can be determined. Likewise, it can preferably be determined whether the molding compound F is flowing through the needle valve nozzle 5 (as a result of which a tensile stress acts on the valve needle 7) or whether it is no longer flowing, which means that the cavity 3 is completely filled (as a result of which the tensile stress acting on the valve needle 7 changes into a compressive stress).

[0090] Fig. 2 shows the sequence of the method according to the invention for determining a parameter in a highly simplified form.

[0091] During the injection molding process, the following steps are carried out (preferably essentially simultaneously): a) Determining the tension(s) occurring at the valve pin 7 using the measuring device 10, b) Providing information concerning the internal geometry of the valve pin 5, wherein the

[0092] Internal geometry is adjustable by positioning the shut-off needle 7 with the aid of the electric motor 6 in the needle shut-off valve 5, and c) providing information regarding the volume flow with which the plasticizing unit 8 introduces the molding compound F into the molding tool 2, wherein the volume flow is adjustable via the control 9 of the plasticizing unit 8.

[0093] In a further (particularly chronologically subsequent) step d), information determined or provided in steps a) to c) is transmitted to the logic unit 11. In step e), the logic unit 11 determines at least one parameter of the injection molding process with the aid of the integrated calculation logic and based on the information transmitted in step d).

[0094] The steps a) to e) indicated above can essentially be carried out continuously during the entire injection molding process or at specific times during the injection molding process, so that the parameter(s) can be monitored continuously or selectively.

[0095] Fig. 3 shows the schematic sequence of a method for balancing an injection molding device 1. The method takes place during an injection molding process that includes a plurality of successive injection molding operations.

[0096] For the injection molding processes of the method, an injection molding device 1 is used which has at least one channel 4, which is designed as a hot runner or cold runner, and at least two needle valve nozzles 5 connected thereto.

[0097] The molding compound F is injected via each of the needle valve nozzles 5 into a separate cavity 3 of the molding tool 2 assigned to the needle valve nozzle 5. The cavities 3 of the molding tool 2 are independent of one another or separate. The molding compound F exits from an opening of the needle valve nozzle.

[0098] Each of the needle valve nozzles 5 has a valve pin 7, which can be positioned by means of an associated electric motor 6, whereby an internal geometry of the needle valve nozzle 5 can be adjusted. In particular, by repositioning the valve pin 7 toward the opening of the needle valve nozzle 5, an exit cross-sectional area from the needle valve nozzle 5 can be reduced, and by repositioning the valve pin 7 away from the opening of the needle valve nozzle 5, an exit cross-sectional area from the needle valve nozzle 5 can be increased.

[0099] The balancing method comprises a plurality of injection molding processes. During each of these injection molding processes, the mechanical stress occurring at each valve pin 7 due to the flow past and / or pressure of the molding compound F on the valve pin 7 is determined with the aid of an associated measuring device 10. A calculation logic determines when, i.e., at what point in time, each of the cavities 3 is completely filled based on the determined mechanical stress values ​​at the valve pins 7.

[0100] After each of the injection molding processes, the calculation logic compares for each of the needle valve nozzles 5 how much the last determined time ZB of reaching the complete filling of the associated cavity 3 deviates from a reference time ZR.

[0101] If the deviation is within a tolerance time period ZT, the position of the shut-off needle 7 is not adjusted, so that the outlet cross-sectional area of ​​the needle valve nozzle 5 remains unchanged. If, on the other hand, the deviation exceeds the tolerance time period ZT, the position of the shut-off needle 7 is changed. The shut-off needle 7 is moved closer to the opening of the needle valve nozzle 5 if the last determined time ZB is more than the tolerance time period ZT before the reference time value ZR (as a result of which the needle valve nozzle 5 is closed further). If the last determined time ZB is more than the tolerance time period ZT after the reference time value ZR, the shut-off needle 7 is moved away from the opening of the needle valve nozzle 5 (as a result of which the needle valve nozzle 5 is opened further).

[0102] This comparison process is carried out for each of the needle valve nozzles 5 or associated cavities 3.

[0103] Between and after the injection molding processes of the balancing procedure, further injection molding processes can take place in which no parameters are determined.

[0104] Fig. 4 shows methods for detecting the achievement of an isothermal state in an injection molding device 1 during a heating process.

[0105] The injection molding device 1 used here has at least one channel 4 , which is designed as a hot runner or cold runner , and at least one adjoining needle valve nozzle 5 , via which a molding compound F can be injected into a cavity 3 of a molding tool 2 .

[0106] The shut-off needle 7 of the needle-type shut-off nozzle 5 can be positioned with the aid of an associated electric motor 6. When the heating process of the injection molding device 1 starts, the shut-off needle 7 of the needle-type shut-off nozzle 5 is pressed against a valve seat of the needle-type shut-off nozzle 5 with a predetermined voltage reference value SR. The valve seat is located in the region of the opening of the needle-type shut-off nozzle 5, with an opening of the needle-type shut-off nozzle 5 being closed when the shut-off needle 7 is pressed against the valve seat.

[0107] During the heating process, the mechanical stress occurring on the valve pin 7, which occurs due to the pressing of the valve pin 7 against the valve seat, is continuously or discontinuously determined with the aid of a measuring device 10. Thus, a mechanical stress value SE is determined.

[0108] If the determined mechanical stress value SE deviates from the stress reference value SR by more than a predefined high tolerance stress value ST over a predefined period of time, the position of the shut-off needle 7 is changed so that the mechanical stress occurring at the shut-off needle 7 (i.e. the determined mechanical stress value SE) is again closer to the stress reference value SR.

[0109] The process is then continued by again determining whether the determined mechanical stress value SE deviates from the stress reference value SR by more than a predefined high tolerance stress value ST over a predefined period of time.

[0110] As soon as the determined mechanical stress value SE deviates from the stress reference value SR by no more than the predefined high tolerance stress value ST over the predefined period of time, it is recognized that the isothermal state has been reached. The process is then terminated.

[0111] 1 injection molding device

[0112] 2 mold tool

[0113] 3 Cavity

[0114] 4 channel

[0115] 5 Needle valve nozzle

[0116] 6 Electric motor

[0117] 7 locking needle

[0118] 8 Plasticizing unit

[0119] 9 Control of plasticizing unit

[0120] 10 Measuring device

[0121] 11 Logic unit

[0122] F molding compound

[0123] E.g. specific time of complete filling

[0124] ZR Reference Time

[0125] ZT tolerance time span

[0126] SE determined mechanical stress value

[0127] SR reference voltage value

[0128] ST tolerance voltage value

Claims

Claims:

1. Method for determining at least one parameter during an injection molding process, wherein an injection molding device (1) is used for the injection molding process, which has at least one channel (4) designed as a hot runner or cold runner, and at least one adjoining needle valve nozzle (5) via which a molding compound (F) is injected into a cavity (3) of a molding tool (2), wherein a valve needle (7) of the needle valve nozzle (5) is driven by an electric motor (6) is positioned, whereby an internal geometry of the needle valve nozzle (5) is adjusted, and wherein the volume flow with which the molding compound (F) flows through the needle valve nozzle (5) is adjusted, characterized in that during the injection molding process, with the aid of a measuring device (10), the volume flow at the valve needle (7) occurring, mechanical stress, which occurs due to the flow past and / or pressing of the molding compound (F) on the shut-off needle (7), is determined, and that with the aid of a calculation logic on the basis of the determined mechanical stress, as well as the known internal geometry of the needle shut-off nozzle (5) and the known volume flow of the molding compound (F), the parameter is determined.

2. Method according to claim 1, characterized in that the viscosity of the molding compound (F) flowing through the needle valve nozzle (5) and / or the achievement of complete filling of the cavity (3) or of the region of the cavity (3) into which the molding compound (5) is injected with the aid of the needle valve nozzle (5) is determined as a parameter.

3. Method according to claim 1 or 2, characterized in that the measuring device (10) measures the electric current and / or the electric voltage required for the drive of the electric motor (6) is recorded and from this the mechanical stress occurring on the shut-off needle (7) is determined.

4. Method according to one of claims 1 to 3, characterized in that the measuring device (10) receives a signal from at least one sensor arranged on the closure needle (7), in particular a change in charge and / or a change in capacitance of at least one piezoelectric sensor arranged on the closure needle (7) and / or a change in resistance of at least one sensor arranged on the closure needle (7) arranged strain gauge sensor, and from this the mechanical stress occurring on the shut-off needle (7) is determined.

5. Injection molding device (1) comprising • a mold (2) with at least one cavity (3), at least one channel (4) which is designed as a hot runner or cold runner, at least one needle valve nozzle (5) adjoining the channel (4) for injecting a molding compound (F) into the cavity (3), and at least one electric motor (6) for positioning a valve needle (7) within the needle valve nozzle (5), whereby an internal geometry of the needle valve nozzle (5) can be adjusted, • a plasticising unit (8) with which a volume flow of the moulding compound (8) which can be introduced into the moulding tool (2) can be adjusted, and • a logic unit (11) with a calculation logic, • characterized in that the injection molding device (1) further comprises a measuring device (10) which is designed to determine the mechanical stress occurring on the shut-off needle (7) due to the flow past and / or pressing of the molding compound (F) on the shut-off needle (7), and that the calculation logic is set up to determine a parameter based on the determined mechanical stress as well as the known internal geometry of the needle valve nozzle (5) and the known volume flow of the molding compound (F).

6. Injection molding device according to claim 5, characterized in that the injection molding device (1) and its logic unit (11) with the integrated calculation logic are set up to carry out a method according to one of claims 1 to 4.

7. A method for balancing an injection molding device (1), wherein the method comprises a plurality of injection molding processes, wherein an injection molding device (1) is used for the injection molding processes, which has at least one channel (4) designed as a hot runner or cold runner, and at least two, preferably more than two, adjoining needle valve nozzles (5), each with its own, associated cavity (3) of a common mold (2), wherein a molding compound (F) is injected into the associated cavity (3) via each of the needle valve nozzles (5), wherein a shut-off needle (7) of each needle valve nozzle (5) is positioned with the aid of an associated electric motor (6), whereby an internal geometry of each needle valve nozzle (5) is adjusted, and wherein the volume flow with which the molding compound (F) flows through the channel (4) is adjusted, characterized in that • that during each injection molding process, the mechanical stress occurring on each shut-off needle (7) due to the flow past and / or pressure of the molding compound (F) on the shut-off needle (7) is determined with the aid of an associated measuring device (10), that during each injection moulding process, with the aid of a calculation logic based on the determined mechanical stress, the achievement of complete filling of each of the cavities (3) is detected and the time (ZB) at which this occurs is determined, • that after each injection moulding process of the method, the last determined times (ZB) of complete filling of the cavities (3) are compared with a fixed reference time (ZR), and • that for the needle valve nozzles (5): - the shut-off needle (7) is positioned closer to the opening of the needle valve nozzle (5) when the last determined time (ZB) of complete filling of the associated cavity (3) is at least one predefined tolerance time period (ZT) before the reference time (ZR), - the shut-off needle (7) is positioned further away from the opening of the needle valve nozzle (5) if the last determined time (ZB) of complete filling of the associated cavity (3) is at least the predefined tolerance time period (ZT) after the reference time (ZR), or - the position of the closure needle (7) is maintained if the last determined time (ZB) of complete filling of the associated cavity (3) does not deviate from the reference time (ZR) by the predefined tolerance time period (ZT). Method according to claim 7, characterized in that the reference time (ZR) is the last determined time (ZB) of complete filling of one of the cavities (3), the is defined as the reference cavity, or that an average value of the last determined times (ZB) of the complete filling of some or all cavities (3) is defined as the reference time (ZR).

9. Method according to claim 7 or 8, characterized in that the cavities (3) of the mold (2) of the injection molding device (1) are of the same size, or that at least some of the cavities (3) have different internal volumes.

10. Method for detecting the achievement of an isothermal state in an injection molding device (1) during a heating process, wherein the injection molding device (1) has at least one channel (4) which is designed as a hot runner or cold runner, and at least one adjoining needle valve nozzle (5) via which a molding compound (F) can be injected into a cavity (3) of a molding tool (2), wherein a valve needle (7) of the needle valve nozzle (5) can be positioned by means of an electric motor (6), characterized in that • that during the heating process, the mechanical stress occurring on the shut-off needle (7) due to the pressing of the shut-off needle (7) against a valve seat of the needle shut-off nozzle (5) is determined continuously or discontinuously with the aid of a measuring device (10), • that the position of the locking pin (7) is changed as soon as the determined mechanical stress value (SE) deviates from a specified stress reference value (SR) by more than a predefined high tolerance stress value (ST) in order to to bring the mechanical stress occurring in the valve pin (7) back to the reference value, and that the achievement of the isothermal state in the injection molding device (1) is recognized as soon as the determined mechanical stress value (SE) does not deviate from the stress reference value (SR) by more than the tolerance stress value (ST) over a predefined period of time.

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