Computer-implemented injection molding process, injection molding machine, computer and computer program

Abstract

The invention relates to an injection molding process for the production of plastic molded parts, in particular for the production of plastic molded parts from material mixtures with unknown and / or fluctuating composition. The invention further relates to an injection molding device designed for carrying out this process.

Description

Field of invention The invention relates to an injection molding process for the production of plastic molded parts, in particular for the production of plastic molded parts from material mixtures with unknown and / or fluctuating composition. The invention further relates to an injection molding device designed for carrying out this process. State of the art In the injection molding process, an injection-moldable material is transferred from a feed chamber A into one or more individual part chambers Cl, ..., Cn of a closed injection mold of an injection molding machine. The individual part chambers C1, ..., Cn can have the same or different geometries. The injection-moldable material is a plastic, e.g., an organic polymer. The individual part chambers Cl, ..., Cn are arranged in the vicinity of the feed chamber A, with the number n of individual part chambers C1, ..., Cn being freely selectable. Feed chamber A is connected to the individual molded part chambers C1, ..., Cn via a system of distribution channels that are always filled with melt. This system may also integrate intermediate connections, volume reservoirs, or pistons. For the sake of simplicity, all these components that are always filled with melt—i.e., intermediate connections, volume reservoirs, pistons, or distribution channels—which are also filled with melt immediately after demolding, are assigned to feed chamber A during volume transfer. The entirety of the cavities that become molten-free when the molded part is ejected is assigned to the individual molded part chambers C1, ..., Cn and together with these form a molded part chamber B. The molding chamber B, comprising one or more individual molding chambers C1, ..., Cn, has a total volume VB. The total volume VB is the sum of the volumes of the individual molding chambers VC1, ..., VCn. The injection molding process is cyclical, with each cycle, also referred to as a shot, comprising an injection phase. The subsequent phases are a filling phase preceding the injection phase (for completely filling the feed chamber A), and three phases following the injection phase: a holding pressure phase (to compensate for shrinkage of the molded parts during cooling), a curing phase (to cure the molded parts in the individual part chambers C1, ..., Cn), and an ejection phase (to eject the finished individual parts from the individual part chambers C1, ..., Cn of the opened injection mold). The present invention involves an optimization of the injection phase and the holding pressure phase. During the injection phase, a user-selectable target volume ZV of the molten, injection-moldable material is transferred from the feed chamber A into the part chamber B.The feed chamber A must therefore always have a larger volume than the target volume ZV, which is to be transferred from feed chamber A to part chamber B during the injection phase. The target volume ZV must always be less than or equal to the volume VB of part chamber B. To avoid over-molding of the molded parts, the target volume ZV is generally chosen to be slightly smaller than the volume VB of part chamber B, e.g., in the range 0.95 VB < ZV < 0.99 VB. The remaining unfilled area is filled in a holding pressure phase, during which shrinkage compensation also takes place. In this application, over-molding is understood to mean that the target volume ZV transferred into part chamber B exceeds the volume VB of part chamber B, so that part chamber B is "overfilled," leading to uncontrolled opening of the injection mold. DE 10 2004 051 109 A1 discloses a method for operating an injection molding machine in which the machine switches to pressure control depending on the achievement of a transition criterion. For this purpose, an extrapolated value is determined from a measured value and compared with the transition criterion. If the extrapolated value equals or exceeds the transition criterion, the machine switches to pressure control. Furthermore, EP 0 887 171 A1 discloses a method for determining the switchover point, in which the mold cavity pressure is measured at at least two points located one after the other in the flow direction. A differential pressure is calculated from the measured values, the sudden drop of which signals that the switchover point has been reached. German patent DE 39 27 995 A1 discloses a method for controlling an injection molding process for the production of molded parts, in particular a holding pressure phase, in which the isobaric holding pressure duration (tNiso) and / or the isobaric holding pressure (pN) are controlled. This control is based on characteristic data fields that were determined in at least one previous learning cycle. In this learning cycle, process parameters are varied and the resulting target parameters for the molded part are measured in order to determine their dependency and store them as a characteristic map. In the industrial application of injection molding, the challenge lies in producing identical molded parts, i.e., parts with constant geometric dimensions. This dimensional consistency must be guaranteed both for parts from the same batch and for parts from multiple batches, i.e., across batches. This challenge has already been fully addressed in cases 1 and 2, which are described below. Case 1: The injection-moldable material used is virgin material, i.e., material obtained directly from a manufacturer, of consistent quality, meaning with known constant physical properties, in particular constant compressibility and constant viscosity. The following solution 1 is known from the prior art for producing identical molded parts from this material. Solution 1: When using a material with constant properties, the volume VA displaced from feed chamber A during the injection phase is measured in a series of trial cycles (trial-and-error tests) and corrected until the resulting molded parts meet the user's requirements, i.e., exhibit the desired fill level in chamber B. The molded parts can be subjected to automated inspection, e.g., optical inspection, or visual inspection by an operator. If the molded parts produced in a trial cycle meet the requirements, this means that the volume VA of the injection-moldable material displaced from feed chamber A during the injection phase has been transferred to the required target volume ZV, i.e., that the volume VA has the optimal size VA,opt. Such a successful trial cycle is called a reference cycle.The optimal volume of injection-moldable material VA,opt displaced from feed chamber A in this reference cycle is maintained in the subsequent production process, so that (in the absence of external disturbances) molded parts with the desired properties are produced reproducibly. Such molded parts are referred to as good parts. It should be noted that the injection-moldable material is a plastic which, unlike liquids and solid materials, has a non-negligible compressibility. When the injection-moldable material is pressurized, its volume decreases and its density increases. Therefore, the volume VAin displaced from the feed chamber A during the injection phase of a cycle is generally larger than the target volume ZV. However, it can also be smaller than the target volume ZV if foamed parts are produced by adding a blowing agent additive to the injection-moldable material. In industrial injection molding processes, using injection-moldable materials with constant material properties, a one-time determination of the optimal process parameters, i.e., the compressibility of the injection-moldable material, is sufficient to transfer the target volume ZV and produce good parts with consistent properties by maintaining the determined optimal process parameters over a batch or across batches. Case 2: In the industrial manufacturing process, a change occurs from a first injection-moldable material with known material properties to a second injection-moldable material with modified, but also known, material properties. To determine the optimal process parameters for injection molding with the second injection-moldable material, the following solutions 2 and 3 are known from the prior art. Solution 2: Analogous to the previously described Solution 1 for an injection-moldable material with constant material properties, the optimal process conditions, in particular the optimal volume VA,opt, are determined using a learning phase comprising several trial cycles. As soon as a trial cycle yields a good part, it is selected as the reference cycle. The process parameters selected in this reference cycle, especially the optimal volume VA,opt, are then adopted in the subsequent production process. The number of required trial cycles can be reduced by reading the compressibility of the second injection-moldable material from a material data card provided by the manufacturer and using this approximate optimal volume VA,opt in the first trial cycle.As a rule, the volume calculated in this way corresponds very well to the optimal volume VA,opt, so that the first trial cycle can already be chosen as the reference cycle. Such solutions are known, for example, from EP 3 359 365 B1, US 11 883 986 B2, EP 3 055 116 B1 and DE 10 2007 030 637 B4. These established solutions always rely on a reference cycle or a learning phase. A reference cycle perfectly tailored to the material composition of an injection-moldable material is required. These solutions are therefore very well suited for industrial injection molding processes where the material properties of the injection-moldable material are known and remain constant. However, these solutions fail completely when recycled materials are used as the injection-moldable material. Recycled materials are in the form of granules produced by shredding or grinding collected waste plastics. The granules consist of particles with unknown material properties (composition, density, compressibility, viscosity) that vary from particle to particle. Solution 3: Analogous to the previously described Solution 2, adjustments are made at the switchover point between the injection and holding pressure phases for an injection-moldable material with variable material properties. These adjustments are based on the previously described material data cards and the pressure resulting from the process. The aim is to compensate for the associated change in the compression ratio. However, this change originates from the specific compressibility of the current material composition for the material being transferred. Consequently, the compressibility is corrected using material data cards, even though the actual composition of the material being transferred deviates from this, for example, due to incorrectly sorted material batches, i.e., foreign material content. Solution 1 has the following disadvantages, which complicate or even preclude its use with recycled materials: Ensuring minimal property variations always involves increased effort for the manufacturer of recycled materials, such as fine sorting or multiple compounding processes to homogenize the batch. Despite this effort, material sources from recycled materials or comparable processing routes with material deviations or consisting of material mixtures generate transfer errors in the actual volume transferred in the mold chamber B after the end of the injection phase for each shot. The volume VA displaced from the feed chamber A is not transferred to the required target volume ZV; rather, it is either underfilled or exceeded. Consequently, poorly filled, unfilled, or even overmolded molded parts are demolded from the mold cavity of the injection mold, i.e., the mold chamber B, after the injection molding cycle.The operator attempts to adjust the volume misdosing in the subsequent cycle, but does not know the material composition of the material prepared for volume transfer, only, at best, that of the already produced molded part. If the composition of the injection-moldable material prepared in feed chamber A deviates even slightly from the composition of the produced molded part, the operator cannot specifically correct the deviation. Consequently, changes within the batch cannot be addressed, and the required target volume (ZV) will be either undershot or exceeded in subsequent cycles as well. Furthermore, this procedure ties the operator to the machine. Solution 2, as will be shown below, also cannot overcome the disadvantages of Solution 1, thus making its use with recycled materials difficult or even impossible. Unlike Solution 1, Solution 2 already includes compensation for the compressibility of the injection-moldable material, but only based on predefined material data cards or generalized estimation curves, via good part curves, or learning cycles before the production of the molded parts. Solution 3 also corrects the compressibility using material data cards, even though the actual composition of the material to be transferred differs from these.The actual material present in chamber A for each individual shot, which may also be a mixture of materials, cannot be described using these solutions, especially when there are variations in properties and their causes change, as in heterogeneous post-consumer recycled (PCR) materials, in which materials of the same type but with different molecular chain lengths are mixed. The material properties, especially the compressibility, of the injection-moldable material transferred from feed chamber A to part-molding chamber B generally change from shot to shot. Its material properties can therefore only be estimated inadequately. Despite the efforts described above to compensate for the compression effects, the volume VA from feed chamber A cannot be reliably transferred to the target volume ZV in part-molding chamber B due to the consistently inadequate estimation of the material behavior. None of the solutions known from the prior art can guarantee the processability and reproducible mold filling of plastics with fluctuating compression behavior due to fluctuating composition and fluctuating viscosities of an injection-moldable material in any batch and across batches. Object of the invention The object of the invention is to provide an injection molding process and an injection molding device that allows plastics, in particular recycled plastics, with unknown and / or fluctuating material parameters to be used as an injection moldable material and to produce molded parts with reproducible volumes from them. Specifically, the task is to determine, for each cycle of an injection molding process, an optimal volume VA,opt of the injection-moldable material, whose material properties are unknown at the start of the cycle, which is transferred during an injection phase from a feed chamber A into a molding chamber B and there into the required target volume ZV, defined by the geometry of the molded parts to be produced. This must be guaranteed even if no information about the injection-moldable material to be transferred, which is present as a melt or as a melt mixture, is available at the start of the cycle. The volume transfer of the injection-molded material from the feed chamber A to the target volume ZV of the molding chamber B can only occur within the system boundaries of the specific injection molding device. If these system boundaries, in particular the volume VB of the molding chamber B, are not known before the start of the injection molding process, then the experimental determination of this volume VB becomes an additional objective of the invention. Solution to the task The object of the invention is solved by a computer-implemented injection molding process for use in an injection molding device, which allows a decoupling of the influences of compressibility and viscosity of an injection-moldable material, so that the specific compression tendency of the injection-moldable material during an injection phase is determined in real time from a pressure profile, i.e. a pressure-time function, p(t), and the time of switching from the injection phase to a holding pressure phase tfinalumschaltwithin the running time of this injection phase is controlled by means of the determined compression tendency and the current pressure at each time during the flow of the melt, so that an optimal volumeVA,optn of the injection-moldable material is transferred from a feed chamber A into a predetermined target volume ZV of a molding chamber B of the injection molding device. The injection molding process can be carried out once (in a single cycle) or cyclically (in any number of cycles). In cyclical execution, the previously described procedure is repeated in each cycle, so that the optimal volume VA,opt of the injection-moldable material is determined separately in each cycle, taking into account its material properties (especially its compressibility), which can change between successive cycles. If the volume VB of the molded part chamber B of an injection molding device is not known before the start of the injection molding process, it is determined in a trial cycle in which an injection phase is extended in time until an extreme pressure increase is registered in the injection-moldable material, which indicates a complete filling of the volume VB and a transition to over-molding. Thus, the injection molding process according to the invention ensures the production of molded parts with reproducible properties from injection-moldable materials with properties unknown at the beginning of the cycle over any number of cycles. The object of the invention is further achieved by providing an injection molding device adapted for the inventive method, which is equipped with a pressure sensor for continuously detecting a pressure profile p(t) with which the injection-moldable material is subjected and which has a computer designed to control the injection molding process. Description of the drawings Fig. 1: Schematic representation of a typical pressure profile p(t) during a complete injection phase. Fig. 2: Schematic representation of a measured pressure profile p(t) up to time t1 of an injection phase, the real-time evaluation of this pressure profile p(t) at time t1, the determination of a first idealized time for the transition from volume compression to volume transfer t1,ideal, and the setting of a future time t1,switch, at which the injection phase is to be terminated according to the information available at time t1.Fig. 3: Schematic representation of a measured pressure profile p(t) beyond time t1 up to time t2 of an injection phase, the real-time evaluation of the pressure profile p(t) at time t2, the determination of a second idealized time for the transition from volume compression to volume transfer t2,ideal, and the control of the future time t1,switch to a corrected time t2,switch, at which the injection phase is to be terminated according to the information available at time t2. Fig. 4: Schematic representation of a measured pressure profile p(t) beyond time t2 up to the end of the injection phase, wherein, through the real-time evaluation of the pressure profile p(t), a correction is continuously made as the previously determined time t2,switch for the end of the injection phase is approached, down to a final time t3,switch = tfinal,switch for the end of the injection phase.Figure 5: Schematic representation of a measured pressure profile p(t) during an injection phase and a subsequent holding pressure phase. Figures 6, 7, 8, 9, 10 to 11 serve to illustrate embodiment 1. They show the time course of a hyperbolic fit, i.e., the fitting of a hyperbolic function (hyperbolic sine) to the measured pressure-time function p(t) and the ongoing iterative adjustment of the switchover time from the injection phase to the holding pressure phase until the final switchover time tfinal,switch is determined. For quantitative values, a decimal point is used instead of a decimal comma in the figures. Fig. 6 : Course of the measured pressure-time function p(t) between a time tStart, at which a lower pressure threshold of 15 bar is exceeded, and a time tE, at which an upper pressure threshold of 115 bar is exceeded.Curve-fit of a hyperbolic function (hyperbolic sine) to the measured pressure-time function p(t) in the time interval tStart to tE. (Due to the excellent agreement of the hyperbolic function with the pressure-time function p(t), the hyperbolic function is hidden.) Fig. 7: Extrapolation of the hyperbolic function to higher pressures, with c = 6.3. The extrapolation serves only for illustration, as the hyperbolic function can be rearranged to calculate the idealized times for the transition from volume compression to volume transfer t1,ideal, t2,ideal, ... Fig. 8 : First iteration step: From the pressure-time function p(t) measured up to a time t1, a first idealized time for the transition from volume compression to volume transfer t1,ideal is determined and a first time for the switch from the injection phase to the holding pressure phase t1,switch is calculated for the current pressure value p(t1) at time t1.The time difference t1,switching- t1 is approximately 3 s. Fig. 9: Second iteration step: From the pressure-time function p(t) measured up to a time t2, a second idealized time for the transition from volume compression to volume transfer t2,ideal is determined, and a second time for the switch from the injection phase to the holding pressure phase t2,switching is calculated for the current pressure value p(t2) at time t2. The time difference t2,switching- t2 is only about 2 s (Fig. 10: Third iteration step: From the pressure-time function p(t) measured up to time t3, a third idealized time point for the transition from volume compression to volume transfer t3,ideal is determined, and a third time point for the switchover from the injection phase to the holding pressure phase t3,switching is calculated for the current pressure value p(t3) at time t3. The time difference t3,switching- t3 approaches zero.Time t3,switch coincides with time t3, at which point the iteration is complete, and time t3,switch is the final time tfinal,switch for switching from the injection phase to the holding pressure phase. Fig. 11: Course of the measured pressure-time function p(t) over an entire cycle, comprising an injection phase and a holding pressure phase. Figs. 12, 13, 14, 15 to 16 serve to illustrate embodiment 2 and correspond in content to Figs. 1, 2, 3, 4 to 5. They have been supplemented with quantitative, experimentally measured data, with Fig. 12 showing the fitting of a hyperbolic sine to the measured pressure-time function p(t) in the pressure range of 15 bar to 45 bar. Fig. 17 : Schematic representation of an injection molding device adapted for the process according to the invention. Detailed description of the solution Any commercial or experimental injection molding device V can be adapted for the method according to the invention by equipping it with the following additional components: - a pressure sensor S for detecting the pressure p acting on an injection-moldable material located in a feed chamber A, as a function of time t: p = p(t), - a computer C, preferably a microcontroller, which controls the process steps described below for detecting and evaluating the pressure profile p(t) and for real-time correction of the volume of an injection-moldable material transferred from the feed chamber A to a part chamber B within an ongoing injection molding cycle (hereinafter referred to as cycle). The computer has communication channels to the pressure sensor S and to a machine control system of the injection molding device, which can be wireless or wired. A detailed description of the adapted injection molding device follows the process description. Inventive method The method according to the invention is based on the idea described below. In order to determine the volume VAopt of the injection-moldable material to be displaced from the feed chamber A during the injection phase of a cycle, which is to be transferred into a known, application-specific target volume ZV of the molded part chamber B, the specific compression tendency of the injection-moldable material to be transferred in this cycle must be known. The specific compression tendency m = Δp / Δt is defined as the difference quotient of the pressure difference Δp that builds up during pure compression of a melt and the time difference required for this pressure build-up. Pure compression of a melt means that the melt is compressed without flowing. This pure compression is equivalent to volume compression in a closed system, e.g., if the transition between chamber A and chamber B were sealed, preventing any melt from flowing into chamber B. If the screw piston reduces the volume of chamber A, the injection-moldable material in chamber A is subjected to pure compression. The specific compression tendency depends on both the material properties, especially the compressibility of the melt, and the volume VA of the feed chamber A of the injection molding machine. In contrast to the compressibility ĸ, which is well known to those skilled in the art, the specific compression tendency m = Δp / Δt is therefore not a material constant. The compressibility x can be calculated from the specific compression tendency and the plant geometry, however, knowledge of it is not required for the implementation of the present invention. During the injection phase, the injection-moldable material is present as a melt, which flows from the feed chamber A into the molding chamber B under the influence of a pressure p(t). A typical pressure-time function p(t) during the injection phase of a real melt is shown in Fig. 1. The injection phase begins at a pressure build-up point tstart and ends at a final switchover point tfinalswitch, at which it switches to a holding pressure phase by pressure release. At the beginning of the injection phase, no information is available about the compression behavior of the melt, so the final switchover point tfinalswitch cannot yet be determined at the beginning of the injection phase. Therefore, the information about the compression behavior of the melt must be acquired during the injection phase. The flow of the melt from feed chamber A into molding chamber B is determined by the specific compression tendency and the viscosity η of the melt, where the viscosity η depends on the temperature T of the melt: η(T). During volumetric flow control, the effects of compression and viscosity overlap, so that the specific compression tendency and the viscosity η of the melt cannot be measured separately. Therefore, it is necessary to decouple the influences of compression and viscosity in order to measure the specific compression tendency of the melt independently of its viscosity η. According to the invention, this decoupling is achieved by a method in which, at the beginning of the injection phase, when the melt is at rest, a pressure build-up occurs, compressing the melt but preventing it from flowing due to its inertia and static friction on the walls of the feed chamber A. This pressure build-up is achieved by continuously reducing the volume VA of the feed chamber A, which is completely filled with an injection-moldable material, with this volume reduction occurring linearly over time. During this time interval before the melt begins to flow, the compression of the melt can be investigated separately from its viscosity. The method according to the invention comprises a control loop for the injection phase of an injection molding cycle and proceeds according to the following steps, wherein the pressure as a function of time p(t) is to be measured and evaluated in a time interval before the injection phase (optional), during the entire injection phase, in order to continuously estimate the time for switching from the injection phase to a holding pressure phase (estimated values ​​t1,switch, t2,switch, ...) and to control it in real time to a final value tfinal,switch. Step 1: Measurement of a pressure p(tStart) by a pressure sensor and verification of the constancy of this pressure in a time interval before the injection phase (optional step) The pressure p(t) in the melt as a function of time t is measured quasi-continuously, i.e., at a high sampling rate, using the pressure sensor. Commercially available pressure sensors offer sampling rates from 2 kHz to 20 kHz, with the lower value of 2 kHz already fully meeting the requirements presented here. The pressure p(t) measurement can be started in a time interval before the compression of the injection-moldable material begins. This is particularly useful for the first injection molding cycle of a batch to verify the correct function of the pressure sensor. Since compression has not yet started, the measured pressure p(t) must remain constant at a starting pressure p(tStart) during this time interval, which extends until the pressure build-up point tStart, the point at which compression is initiated and thus the injection phase begins. A change in the measured pressure would indicate a malfunction of the pressure sensor, such as drift. The time interval should be sufficiently long to detect such a change in the measured value. Therefore, this time interval should have a duration of at least 1 second.Since the melt is not yet compressed, i.e., not yet pressurized, the measured pressure should be a constant p(tStart) = 0 bar. If the measured starting pressure p(tStart) deviates from 0 bar, an offset correction can be made, in which the pressure p(tStart) is set to 0 bar. This simplifies the evaluation described in the following steps. The invention requires the precise measurement of pressure differences; therefore, the measured absolute pressure values ​​may exhibit a consistent systematic error within the investigated pressure range. It is therefore also possible to work with a non-zero pressure p(tStart), which is documented in the measured pressure-time function p(t). If it is ensured that the pressure sensor is functioning correctly, the measurement of the start pressure p(tStart) prior to the injection phase can be omitted. If the correct function of the pressure sensor has been confirmed in an initial injection molding cycle, this omission is permissible for subsequent injection molding cycles. The time interval for measuring the pressure p(t) before the start of compression of the injection-moldable material can therefore be reduced to zero; this measurement is thus an optional step. Step 2: Determination of a factor f from an initial volume VStart, which is the volume in chamber A at the start of the injection phase. Initiation of an injection phase at a pressure build-up start point tStart by pressurizing a melted injection-moldable material above a defined threshold and measuring a pressure-time function p(t) of the pressure acting on the melt during a time interval of pure melt compression and a subsequent time interval of superimposed compression and melt flow. Transmission of the pressure-time function p(t) measured by the pressure sensor to the computer. The factor f is determined based on the starting position of the screw piston at the beginning of injection. This starting position also defines the output volume in chamber A of the respective process. Therefore, the factor f is known at the latest at the beginning of injection. The factor f is formed via the following power function using the initial volume VStartin of the unit cm3. At time tStart, the pressure build-up point corresponding to the start of the injection phase, the melt is pressurized by a linear reduction in its volume over time, thus initiating a period of pure melt compression. At time tStart, the melt is under the starting pressure p(tStart), which may have already been measured in optional step 1. Starting from the pressure build-up point tStart, the subsequent pressure profile p(t) is measured and recorded. Instead of the starting pressure p(tStart) = 0 bar, a lower pressure threshold defined by the operator can also be used. The time tStart is then determined in real time using the pressure sensor. The pressure sensor records the pressure-time function p(t) and determines the time at which the pressure p exceeds the defined lower pressure threshold. This time is the pressure build-up point tStart.The starting pressure p(tStart) is then given by the defined lower pressure threshold. The lower pressure threshold is preferably chosen in the interval from 0 bar to 30 bar; a lower pressure threshold of 15 bar is particularly preferred. To achieve compression, the feed chamber A is typically designed as a cylinder, limited at one end by a movable piston. The piston can be a screw piston with a non-return valve. Such a screw piston is rotatable, but during the injection phase it is not rotated; instead, it is merely moved along the axis of the cylinder, thus performing a translational movement. The screw piston and cylinder are referred to as a screw piston unit. The piston is set in motion at time tStart and pushed into the feed chamber A, which is designed as a cylinder with a cross-section Q, at a constant velocity v. This process is controlled by the machine control of the injection molding device. Over a period Δt, the volume VA of the feed chamber, completely filled with the injection-moldable material present as melt, decreases by ΔVA = Q · v · Δt.As long as the melt is not yet flowing, a pressure p builds up in volume VA, starting from the initial pressure ptStart, thus compressing this volume. During this time interval of pure compression, the pressure profile p(t) exhibits a linearly increasing section for low-viscosity injection-moldable materials (melt flow index MFI ≥ 400 g / 10 min), the slope of which m determines the specific compression tendency m = Δp / Δt. As soon as the melt begins to flow into the molded part volume B, this linear pressure increase flattens out, thus assuming a non-linear profile. This flattening of the pressure increase indicates that compression and flow of the melt are superimposed, i.e., occur simultaneously. The pressure-time function p(t) can take a different course after leaving the linearly increasing section of pure compression. As Fig. 2 shows, the pressure can settle at a plateau pressure p(t1) at time t1, which remains constant over time, thus forming a pressure plateau. Reaching such a plateau pressure p(t1) indicates that the melt flows with a constant volume flow rate Q · v without further compression. This constant volume flow rate Q · v results from the constant velocity v of the piston and the cross-sectional area Q of the cylinder. The pressure-time function p(t) can also, as shown in Fig. 3, exhibit an increasing profile, indicating a superposition of flow and further compression, and / or, as shown in Fig. 4, form further pressure plateaus. However, the pressure-time function p(t) no longer reaches the increase m measured in the time interval of pure compression, provided the system boundaries of the specific injection molding device are not exceeded. The profile of the pressure-time function p(t) is determined by the geometry of the molding chamber B with the individual molding chambers C1, ..., Cn. The method according to the invention is applicable to any desired profile of the pressure-time function p(t), regardless of the geometry of the molding chamber B. Therefore, the geometry of the molding chamber B does not need to be known for the implementation of the method according to the invention. Step 3: The core of the invention is to use the increasing section of the pressure-time function p(t) continuously measured by the pressure sensor during the time interval of pure compression for determining and continuously controlling a time for the transition from the injection phase to a holding pressure phase. The rising portion of the pressure-time function p(t) measured by the pressure sensor, used to determine this time, extends from time tStart, at which the lower pressure threshold p(tStart) is exceeded, to time tE, at which an upper pressure threshold p(tE) is exceeded. It has been experimentally determined that an upper pressure threshold p(tE) = 115 bar is suitable for all injection-moldable compounds with an MFI < 400 g / 10 min, which are subsequently classified as higher-viscosity injection-moldable compounds. The time tE of exceeding the upper pressure threshold is recorded by the pressure sensor. The behavior of the pressure-time function p(t) in the interval tStart to tE can be reliably described by a curve fit (fitting a function to the curve of the pressure-time function p(t)) using hyperbolic, exponential, and / or parabolic functions. Experimentally, it was found that the pressure-time function p(t) in the time interval between tStart and tE can be described particularly accurately by curve fitting the following function, which is based on the hyperbolic sine function: c is the fitting parameter to be determined by the curve fit. Once the fitting parameter c has been determined, the resulting fit function can return the compression component of the injection process based on the current pressure at the pressure sensor. With currently available computing technology, fitting the function and its subsequent extrapolation in step 4 take, on average, less than 20 milliseconds. It should be emphasized again that, in addition to curve fits based on hyperbolic functions, curve fits based on exponential and / or parabolic functions, as well as polynomials, can also be used as fit functions. These fit functions can also be combined. A suitable fit function would be, for example, a parabolic function of the form p(t) = (k+t)r- Kr, where k and r are fitting parameters. A person skilled in the art can easily devise other fit functions suitable for curve fits. Step 3a (special case for low-viscosity injection-moldable materials (MFI ≥ 400 g / 10 min)): Calculation of the specific compression tendency of the melt m from a linearly increasing section of the pressure-time function p(t) by the computer In the special case of low-viscosity melts, i.e., melts with MFI ≥ 400 g / 10 min, a simplification can also be achieved by linearizing the specific compression tendency, equivalent to adapting it to the pressure-time function, via the pressure measured at the sensor during the injection process. This is a simplifying approach because the described function is also linear at a lower pressure threshold p(tE) (in the example from Fig. 13, 45 bar instead of 115 bar) within the correspondingly adjusted fitting interval. The simplification is thus based on the fact that, for low-viscosity melts, the pressure-time function p(t) can be considered linear when suitable pressure thresholds are selected (in embodiment 2, the lower pressure threshold remains 15 bar, but the upper pressure threshold is 45 bar instead of 115 bar for higher-viscosity melts).A hyperbolic sine function adapted to the pressure-time function p(t) in the section between these two threshold values ​​also runs linearly, as shown in Fig. 12. In this special case, it is possible to determine the specific compression tendency of the melt m = Δp / Δt from the linearly increasing portion of the pressure-time function p(t) during the time interval of pure compression, and to use this for determining and continuously controlling the point in time for the transition from the injection phase to a holding pressure phase. The volume fraction of the compression, which describes the difference between the optimal volume VAopt to be transferred from the feed chamber A to the molding chamber B and the target volume ZV in the molding chamber, can also be calculated from the specific compression tendency of the melt m = Δp / Δt. To determine the specific compression tendency, defined as the slope m = Δp / Δt of the linearly increasing portion of the pressure-time function p(t), the measured pressure profile p(t) is transmitted to a computer, preferably a microcontroller. This computer extracts the start and end times of the linearly increasing portion tStart and the corresponding pressure values ​​p(tE) from the pressure profile p(t). Thus, the pairs of values ​​for two points that define the linearly increasing portion of the pressure profile p(t) are known. These are represented in Fig. 2 by a circle (value pair [p(tStart), EStart]) and a square (value pair [p(tE), tE]). The computer now calculates the equation of the straight line passing through these two points, i.e., through the linearly increasing region of the pressure-time function p(t). The specific compression tendency of the injection-moldable material in the feed chamber A is given by the slope m of this line: Step 4: Extrapolation of the fit function and determination of the time t1, ideal for the idealized transition between volume compression and volume transfer by the computer The current pressure during the further course of injection is tracked / monitored; that is, the pressure-time function p(t) continues to be continuously recorded. Using predefined iteration steps (depending on the hardware used), the current pressure of the first iteration step, here p(t1) as an example, is applied to the curve of the previously fitted and extrapolated function to determine the idealized time component of compression for the current filling progress. For this purpose, equation (3) is rearranged to solve for t, and t is subsequently denoted as ti,ideal with indices i=1, 2, ... for the respective iteration step. The preferred value of 15 bar is used for p(tStart). This results in the following equation: For each value p(t) present at the pressure sensor, an ideal time ti,ideal can be calculated using this equation. For time t1, the idealized time t1,ideal is calculated. If the time required for simply filling the target volume is added to the idealized time t1,ideal, the switch-over time is averaged. Due to the constantly changing actual pressure during the injection process, the determination of the switch-over point is adjusted iteratively. For simplicity, only three iteration intervals are described in the examples until the final switch-over point is reached; however, more are practical and can be easily implemented with current computing technology. Step 4a (special case for low-viscosity injection-moldable materials (MFI ≥ 400 g / 10 min)): Extrapolation of the linearly increasing section of the pressure-time function p(t) and determination of the time t1, ideal for the idealized transition between volume compression and volume transfer by the computer From the measured pressure profile p(t), when the first pressure plateau is reached at time t1, a time t1, ideal for the idealized transition between volume compression (pure compression of the melt without flow) and volume transfer (pure flow of the compressed melt into the molding chamber B without further compression) is calculated. If the measured pressure profile does not form a plateau, but rather a flat ramp, as schematically shown in Fig. 3, then time t1 can be chosen arbitrarily within this ramp and the pressure p(t1) at this time t1 can be used as the plateau pressure. As shown in Fig. 2, t1,ideal is determined by extrapolating the range of the linear pressure increase up to the plateau pressure p(t1) and recording the corresponding time t1,ideal. For the time interval in which pure compression occurs, this results in a duration ΔtK = t1,ideal - tStart. During this time interval, the volume of the injection-moldable material in chamber A is compressed from VA to V4 - Q · v · ΔtK. Step 5: Calculation of the time t1, switching for the transition from volume transfer, i.e. from the injection phase, to a holding pressure phase during the ongoing volume transfer by the computer, transmission of this time to the machine control of the injection molding device, which sets this time. The compressed volume VA-Q · v · ΔtK is now transferred into the known target volume ZV of the molding chamber B, which is specified by the user. The prerequisite is that the compressed volume VA-Q · v · ΔtK is greater than or equal to the target volume ZV. This requirement is easily met by appropriately dimensioning the injection molding machine with a sufficiently large volume VA in chamber A. The time interval ΔtF for the volume transfer (flow), i.e., the required duration of the volume transfer, results from Thus, the time for the end of the volume transfer, i.e., the injection phase, and the transition to a holding pressure phase is: t1,switching= t1,ideal+ ΔtF. This point in time is calculated immediately after reaching a (first) pressure plateau or ramp in the pressure profile p(t), i.e., at the beginning of the volume transfer. Fig. 2 shows the time t1,switch, which can already be calculated at time t1. Step 6: Measurement of the pressure-time function p(t) during the further course of the volume transfer by the pressure sensor and, in the case of pressure changes, one or more corrections to the time for switching from the injection phase to the holding pressure phase t1,switch to a final switchover time tfinal,switch by the computer, transmission of the final switchover time tfinal,switch to the machine control of the injection molding device, which sets this time. If, as schematically depicted in Figs. 3 and 4, pressure changes are observed during the further course of the volume transfer, e.g., a pressure increase to a higher plateau at time t2, as schematically depicted in Fig. 3, or a pressure increase to a third plateau at time t3, a correction of the time t1,switchover is required for the switchover from the injection phase to the holding pressure phase. For this purpose, the current pressure, i.e., the pressure p(t2) or p(t3) at time t2 or t3, is recorded, and the range of the linear pressure increase up to this current pressure p(t2) or p(t3) is extrapolated, and a corrected time t2,ideal or t3,ideal is recorded for the idealized transition between volume compression and volume transfer. The time difference between the corrected time t2,ideal or t3,ideal is then calculated. t3,ideal and the previous, earlier determined time t1,ideal.The switching point from the injection phase to the holding pressure phase, t1,switching, is corrected by the same time difference and thus, if necessary via several corrections, set to the (intermediate) times t2,switching, t3,switching, and finally to the final switching point tfinal,switching. In the situation shown in Fig. 4, time t3,switching corresponds to the final switching point tfinal,switching. In the event of a further pressure change immediately before reaching the last estimated switching point, a correction for this would also have been possible. Such corrections are possible at any time when approaching the switching point, whereby the current, last measured pressure must always be used for extrapolation during the correction. Step 7: Continuation of the volume transfer until the final switchover point tfinal,switch and switchover to a holding pressure phase by the machine control of the injection molding device By continuing the injection phase until the final switchover time tfinal,switching, the target volume ZV is completely filled. However, since the target volume ZV was chosen to be slightly smaller than the volume VB of the molded part chamber B, namely in the range 0.95 VB < ZV < 0.99 VB, a pressure-controlled holding pressure phase is required to fill the remaining volume. At the final switchover time tfinal,switching, the system switches from the injection phase to this holding pressure phase by reducing the pressure p to 0.5 to 0.7 times the pressure at the end of the injection phase pfinal. Preferably, the pressure pND in the holding pressure phase is set to 2 / 3 of the pressure at the end of the injection phase, i.e., the pressure a few milliseconds before or at the time of switching to the holding pressure phase (see Fig. 5).The duration of the holding pressure phase tND can be specified by the user or determined by a temperature sensor that detects when a predefined temperature level is undershot, indicating that the molded parts have cooled sufficiently. Preferably, the duration of the holding pressure phase tND is determined by the piston coming to a standstill (v=0 m / s) despite the applied holding pressure. Preferably, the duration of the holding pressure phase is 0.1 s. <tND<10 s vorzugsweise 1 s. The injection molding cycle is then completed by carrying out a residual cooling phase after the holding pressure phase, a filling phase to refill the feed chamber A superimposed on the residual cooling phase, and finally a demolding phase. The present invention thus makes it possible to calculate, set, and continuously correct the duration of the volume transfer ΔtFund and the time for the end of the volume transfer tfinal,switch, which is equal to the time for the end of the injection phase, in real time from experimental data, in particular the pressure profile p(t), which are only obtained during an already running injection phase, using a computer, preferably implemented as a microcontroller. Thus, during the injection phase of each injection molding cycle, the optimal volume to be transferred can be determined and, by defining the required volume transfer duration ΔtF and setting the end time of the volume transfer tfinal, transferred to the required target volume ZV using a constant volume flow rate Q · v, without having prior information about the material properties of the injection-moldable material present in that cycle. The injection phase is volume flow-controlled, meaning the volume flow rate is kept constant. It is also possible to vary the volume flow rate in a defined manner. The invention allows the solution of another practically relevant problem, namely the experimental determination of the volume of the molded part chamber B of an injection molding device. The volume VB of the molding chamber B of the specific injection molding machine is usually known. If it is unknown, e.g., if a used injection molding machine with an incomplete technical description is used, it must be determined experimentally before the regular injection molding process begins. According to the invention, a further optional step (step 0) is placed before the steps described above. Step 0: Experimental determination of the volume VB of a molding chamber B of an injection molding machine A single test cycle with quasi-continuous measurement of the pressure profile p(t) is performed. First, the linear portion of the pressure-time function (the region of pure compression with slope m) is recorded, followed by the volume transfer region into chamber B. Several pressure plateaus and / or ramps with a slope < m may occur during this phase; these need not be considered. The volume transfer continues until the pressure-time function p(t) again exhibits a significant increase with a slope corresponding to the slope m in the previously traversed linear portion of the pressure-time function p(t). This marked pressure increase indicates that the volume VB of the molded part chamber B has been completely filled. This marks the point in time when chamber B is completely filled under a predetermined injection volume flow rate or volume flow profile, which is kept constant by the system. Analogous to the procedure in step 4, a time tideal is determined for the idealized transition between volume compression and volume transfer. For this purpose, the linear segment of the pressure-time function p(t) is extrapolated up to a pressure value pfull. The pressure pfull used for extrapolation is the pressure present at time tfull, the beginning of the marked pressure increase, because the onset of the pressure increase indicates that the molded part chamber B is already completely filled. From the known injection volume flow rate Q · v and the time difference tfull - tideal, the volume VB of the molded part chamber B is calculated: VB = Q · v · (tfull - tideal).The target volume ZV is then selected, as described above, in the range 0.95 VB < ZV < 0.99 VB. Device according to the invention Fig. 17 shows a schematic representation of an injection molding device V adapted for the method according to the invention. It comprises a reservoir for injection-moldable material VB, a screw piston unit SK, a feed chamber A, an injection mold W consisting of two mold halves W1, W2, the inner contour of which defines a molded part chamber B, and a mechanism M for opening and closing the injection mold W. For the sake of simplicity, other components such as intermediate connections, volume reservoirs, and distribution channels are not shown. For the purpose of adaptation to the method according to the invention, the injection molding device V is equipped with the following additional components: - A pressure sensor S for detecting the pressure p acting on an injection-moldable material located in a feed chamber A, as a pressure-time function p(t). The pressure sensor can be positioned in various ways.It can, for example, also be in the form of a load cell on the screw piston. The pressure sensor is a digital pressure sensor that measures the pressure with a sampling rate of 2 kHz to 20 kHz. A computer C, preferably a microcontroller, is connected to the pressure sensor S via a communication channel K1. The computer C receives the pressure profile measured by the pressure sensor S and controls the process steps described above for acquiring and evaluating the pressure profile p(t) and for real-time correction of the volume of an injection-moldable material transferred from the feed chamber A to a molding chamber B within an ongoing injection molding cycle (hereinafter referred to as cycle). The computer C performs the calculations described above, in particular...It determines the compression tendency m, the volume flow rate Q · v, calculates the time for switching from the injection phase to the holding pressure phase, and corrects this time in response to pressure changes during the injection phase until the final time tfinal,switch for switching from the injection phase to the holding pressure phase is reached. Computer C is connected via a communication channel K2 to the (not shown) machine control of the injection molding device V, enabling it to control the pressure build-up at the beginning of the injection phase, the volume flow rate, and the switch from the injection phase to the holding pressure phase. The communication channels K1 and K2 of computer C can be wireless or wired. As a data processing system, the computer provides the functions of data input (data reception), data processing, data storage, and data output.A computer program that can be executed on a computer is designed to perform the necessary calculations. Further advantages of the invention: The invention is applicable not only to constant but also to variable volume flows. Variations in the volume flow or related parameters (e.g., screw feed movement, speed, acceleration, etc.) during the injection phase are possible and can be taken into account by a volume-proportional conversion for the correct timing adjustment of the switchover point between the injection and holding pressure phases, ensuring that the target volume ZV is reliably filled by this switchover point. The invention is arbitrarily scalable, i.e., it is applicable in a large pressure range and can therefore be used for any commercially available or experimental injection molding device. Typical usable parameter ranges are: Pressure: 4 bar to 3000 bar; Target volume: Depends on the screw piston diameter. The plasticizing units are usually designed with the maximum volume VA of the feed chamber A based on the calculation: four times the screw diameter multiplied by the cross-sectional area Q. Cylinder cross-section: Diameter 20 mm to 120 mm → The cross-sectional area Q results from a cylinder cross-sectional area calculation. Here, the crucial factor is how well the speed can be controlled in relation to the volume to be transferred. Injection phase duration: 0.2 s to 15 s, primarily dependent on the mold wall temperature in combination with the solidification behavior (solidification temperature) of the melt. Duration of a complete cycle: 2 s to 10 min, depending on the volume to be transferred and the wall thickness of the molded part to be produced. Example 1 The invention will now be explained in more detail by means of an embodiment based on a real experiment. The experiment also served to validate the method according to the invention. Therefore, a reference material with known material properties was used as an injection-moldable material, but the experiment was carried out without access to these material properties. Borealis PP BC612WG with an MFI of 5 g / 10 min at 230°C and a weight of 2.16 kg was chosen as the reference material. The experiment is explained using the measured pressure-time functions p(t) presented in Fig. 6-11. It was carried out on an injection molding machine KM160CX-750 (manufacturer: KraussMaffei), using a molding chamber B with a target volume ZV = 46 cm³. The plasticization process was automated until the required initial volume of VStArt = 223.5 cm³ was reached. Using the power function (2) given above, the factor f is derived solely from the initial volume of chamber A and can therefore always be calculated and used before the start of injection. For the initial volume VStarter described here, f = 14.4 cm3 is obtained. Fig. 6 shows the situation at time t1 = 0.30 s. The injection phase was initiated at time tStart = 0.0 s, the pressure build-up point, starting from a pressure p(tStart) = 15 bar. A constant flow rate of 14.4 cm³ / s was set via the screw piston speed. The computer calculates the time ΔtF required to fill the target volume at the given flow rate: ΔtF = 46.0 cm³ / 14.4 cm³ / s = 3.23 s. The pressure-time function p(t) is in the pure compression range, and at most a negligible amount of melt transfer is superimposed on the compression applied here. The computer documented the pressure-time function and, using the fitting function, calculated the value c with the best possible match. Once the value c is determined, the volume fraction of compression can be calculated for any measured pressure within this injection process. For clarity, the function from the curve-fit was extrapolated over the display range (see Fig. 7). This is based on the knowledge of the time required for a part filling without compression (ΔtF) and the result of the pure compression fraction from the curve-fit equation, in combination with the most recent pressure p(t). This iterative procedure is outlined in Fig. 8 at t1 = 1.0 s, in Fig. 9 at t2 = 2.75 s, and in Fig. 10 at t3 = 4.7 s, as the actual iteration rate can be significantly higher if necessary. In Fig. 10, the time summation of t3,ideal+ ΔtF is achieved at time t3.The switchover process occurs when the target volume for the holding pressure phase is reached. The most recent pressure value in the injection phase is then multiplied by 2 and divided by 3, thus defining the holding pressure level (see Fig. 11). The holding pressure phase is pressure-controlled, meaning a constant pressure is applied. The injection molding cycle is then completed by finishing the holding pressure phase, followed by a residual cooling phase, which overlaps with the filling phase to refill the feed chamber A (plasticizing process), and finally a demolding phase (ejecting the molded part / emptying chamber B). The demolded plastic molded parts meet the requirements. Example 2 The invention will now be explained in more detail by means of a further embodiment based on a real experiment. The experiment also served to validate the method according to the invention. Therefore, a reference material with known material properties was used as an injection-moldable material, but the experiment was carried out without access to these material properties. Borealis HL508FB (MFI = 800 g / 10 min, at 230°C and 2.16 kg) was chosen as the reference material. The experiment is explained using the measured pressure-time functions p(t) presented in Figs. 12-16. It was performed on an injection molding machine KM160CX-750 (manufacturer: KraussMaffei), using a molding chamber B with a target volume ZV = 36.9 cm³. Plasticization was carried out until an initial volume of VStart = 108.5 cm³ was reached. Using the power function (2), the factor f can be determined as f = 8.0 cm³. Due to the MFI = 800 g / 10 min, the pressure interval p(tStart) = 15 bar and p(tE) = 115 bar was reduced to p(tE) = 45 bar. This adjusted the time interval for the curve fit. Figure 12 shows the result of the curve fit and, for comparison, the injection profile. Due to the linearizable behavior of the function adapted here (see Fig. 13) in the required pressure range, a simplified / accelerated and alternative procedure for the reliable dosing of a target volume with injection-moldable materials MFI>400 g / 10 min is described below: For recording reasons, the time scale starts at 0.8 s. Since only time differences are important, this is not significant. Fig. 13 shows the situation at time t1 = 1.00 s. The injection phase was initiated at time tStart = 0.84 s, the pressure build-up start point, starting from a starting pressure p(tStart) = 0. A constant volume flow rate of 46.8 cm³ / s was set via the screw piston speed. The computer calculates the time for volume transfer ΔtF required to fill the target volume at the given volume flow rate: ΔtF = 36.9 cm³ / 46.8 cm³ / s = 0.79 s. The pressure-time function p(t) has passed through the linear region of pure compression, flattened out, and transitioned into a pressure plateau with a plateau pressure p(t1) = 88 bar at time t1 = 1.00 s. The computer continuously determined the instantaneous increase of the pressure-time function and registered that the linear range, characterized by a constant increase, was left at time tE=0.87 s, at which a pressure p(tE)=44 bar was present.From the measured values, he calculated the compression tendency m = 44 bar / 0.03 s = 1467 bar / s. At the current time t1 = 1.00 s, at which a constant plateau pressure p(t1) = 88 bar has been established, the computer extrapolates the linear range up to the plateau pressure and obtains the time for the idealized transition between volume compression and volume transfer t1,ideal = 0.91 s. The computer adds the time for the volume transfer ΔtF = 0.79 s and already obtains a first estimate for the time of the switch from the injection phase to the holding pressure phase t1,switch = 1.70 s. Fig. 14 shows the situation at time t2 = 1.25 s. The pressure-time function p(t) has left the previous pressure plateau and transitioned to a second pressure plateau with a plateau pressure p(t2) = 140 bar. The computer extrapolates the linear range of pure compression up to this second plateau pressure p(t2) = 140 bar and obtains a time for the idealized transition between volume compression and volume transfer, corrected by 0.03 s: t2,ideal = 0.94 s. The computer applies the same correction to the time of the switch from the injection phase to the holding pressure phase and obtains a corrected estimate: t2,switch = 1.73 s. Fig. 15 shows the situation at time t3 = 1.70 s. The pressure-time function p(t) has again transitioned to a higher pressure plateau with a plateau pressure p(t3) = 157 bar. The computer extrapolates the linear range of pure compression up to this higher plateau pressure p(t3) = 157 bar and obtains a time for the idealized transition between volume compression and volume transfer, corrected by a further 0.01 s: t3,ideal = 0.95 s. The computer applies the same correction to the time of the switch from the injection phase to the holding pressure phase, obtaining a corrected estimate t3,switch = 1.74 s. Since no further pressure increase is observed, no further correction is necessary, and t3,switch is equal to the final time tfinal,switch for the switch from the injection phase to the holding pressure phase.In the event of a further pressure change immediately before reaching the last estimated switching time, a correction would still have been possible. Such corrections are possible at any time as the switching time approaches, whereby the current, last measured pressure must always be used for extrapolation during the correction. Fig. 16 shows the situation at time 1.90 s. At the final time for switching from the injection phase to the holding pressure phase (tfinal,switch = 1.74 s), the computer commanded the machine control of the injection molding machine to reduce the current pressure of 157 bar by one-third, thus switching from the injection phase to the holding pressure phase. The machine control executed this command. The injection molding cycle is currently in the holding pressure phase at time 1.90 s. The holding pressure phase is pressure-controlled, meaning a constant pressure is applied. The injection molding cycle is then completed by finishing the holding pressure phase, followed by a residual cooling phase, a filling phase to refill the feed chamber A (superimposed on the residual cooling phase), and finally a demolding phase. The demolded plastic molded parts meet the requirements. Reference symbol list A Feed chamber B Molding chamber C Computer K1, K2 Communication channels M Mechanism for opening and closing the injection mold S Pressure sensor SK Screw piston unit V Injection molding device VB Reservoir for injection-moldable material W Injection mold W1, W2 Mold halves of the injection mold

Claims

A computer-implemented injection molding process for producing molded parts with reproducible properties from injection-moldable material with unknown and / or fluctuating material parameters using an injection molding device, comprising the following steps: Step 1 - Measurement of a pressure p(tStart) by a pressure sensor and verification of the constancy of this pressure in a time interval before an injection phase (optional step), Step 2 - Determination of a factor f from an initial volume VStart and initiation of an injection phase at a pressure build-up start point tStart by pressurizing an injection-moldable material transferred into a melt and measuring a pressure-time function p(t) of the pressure acting on the melt in a time interval of pure compression of the melt and a subsequent time interval of superimposed compression and flow of the melt, transmission of the measured pressure-time function p(t) from the pressure sensor to a computer.Step 3 - Fitting a function to the pressure-time function p(t) in a time interval from a time tStart, at which a lower pressure threshold p(tStart) is exceeded, to a time tE, at which an upper pressure threshold p(tE) is exceeded. Step 4 - Extrapolation of the function and determination of a time t1, ideal for the idealized transition between volume compression and volume transfer by the computer. Step 5 - Calculation and setting of a time t1, switching point for the transition from volume transfer, i.e., from the injection phase, to a holding pressure phase during the ongoing volume transfer by the computer. Transmission of this time point to the machine control of the injection molding device, which sets this time point. Step 6 - Measurement of the pressure-time function p(t) during the further course of the volume transfer by the pressure sensor and, in the case of pressure changes,One or more corrections to the switching point from the injection phase to the holding pressure phase t1,switch to a final switching point tfinal,switch by the computer; transmission of the final switching point tfinal,switch to the machine control of the injection molding device, which sets this point; Step 7 - continuation of the volume transfer until the final switching point tfinal,switch and switching to a holding pressure phase by the machine control of the injection molding device, so that at the final switching point tfinal,switch a target volume ZV of a mold chamber (B) of an injection molding device (V) is filled with the injection-moldable material. Computer-implemented injection molding method according to claim 1, characterized in that the fitting function is a hyperbolic function, exponential function, parabolic function, power function or a polynomial or a combination of these functions. Computer-implemented injection molding process according to claim 1, wherein, in the special case that the injection-moldable material is a low-viscosity injection-moldable material, steps 3 and 4 are replaced by step 3a - calculation of the specific compression tendency of the melt m from a linearly increasing section of the pressure-time function p(t) by the computer, step 4a - extrapolation of the linearly increasing section of the pressure-time function p(t) and determination of the time t1, ideal for the idealized transition between volume compression and volume transfer by the computer. Computer-implemented injection molding process according to claim 1, 2 or 3, characterized in that further phases of an injection molding cycle are added following steps 1 to 7, wherein these phases comprise the holding pressure phase, a residual cooling phase, a filling phase for refilling the feed chamber A superimposed on the residual cooling phase and finally a demolding phase. Computer-implemented injection molding process according to claim 4, characterized in that it is carried out cyclically by repeating steps 1 to 7 and the further phases of the injection molding cycle as often as desired. Computer-implemented injection molding process according to one of claims 1, 2, 3 or 4, comprising as a further optional step 0 an experimental determination of the volume VBeiner molded part chamber (B) of an injection molding device (V). Computer-implemented injection molding process according to one of claims 1 to 6, characterized in that the injection-moldable material is formed from a plastic, preferably from a plastic recyclate. Injection molding device (V) for carrying out the method according to one of claims 1 to 7, comprising a storage container for injection-moldable material (VB), a screw piston unit (SK), a feed chamber (A), an injection mold (W) consisting of two mold halves (W1, W2) whose inner contour defines a molded part chamber (B), a mechanism (M) for opening and closing the injection mold (W), a machine control, characterized in that it is equipped with a pressure sensor (S) for measuring a pressure-time function p(t) and a computer (C) for carrying out the tasks according to claim 1, which is connected to the pressure sensor (S) and the machine control via communication channels (K1, K2). Injection molding device (V) according to claim 8, characterized in that the computer (C) is designed as a microcontroller. Computer (C) configured to control an injection molding device (V) according to one of claims 8 or 9 such that the method according to one of claims 1 to 7 is carried out on the injection molding device (V). Computer program that is executable on the computer (C) and is designed to perform the calculations according to claims 1, 2 or 3.

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