CN104608351B

CN104608351B - Method and molding machine for determining a setpoint value for a control variable

Info

Publication number: CN104608351B
Application number: CN201410756238.7A
Authority: CN
Inventors: J·吉绍夫; G·皮尔韦恩
Original assignee: Engel Austria GmbH
Current assignee: Engel Austria GmbH
Priority date: 2013-09-30
Filing date: 2014-09-29
Publication date: 2020-10-16
Anticipated expiration: 2034-09-29
Also published as: DE102014014231A1; AT514847A1; AT514847B1; CN104608351A

Abstract

The invention relates to a method for determining a target value for a control parameter in a casting process, wherein a casting material in liquid phase is introduced at least once under pressure into a mold cavity (4) formed by two mold halves, a clamping force is exerted on the mold halves during the filling of the mold cavity (4), wherein at least one profile of a variable which characterizes the clamping force is measured, a relationship between the measured profile or a variable derived from the measured profile on the one hand and a parameter of an injection molding process on the other hand is determined, and the target value for the control parameter is determined from the relationship.

Description

Method and molding machine for determining a setpoint value for a control variable

Technical Field

The invention relates to a method for determining a target value for a control variable in a casting process and to a molding machine.

A molding machine is understood here to be any machine which is suitable for filling a mold cavity with a casting material in the liquid phase under pressure. This is in particular the case with injection molding machines, injection presses, injection compressors and the like.

Background

The prior art of injection molding processes will be described below, wherein the problems arising can also be transferred to other casting processes.

During the injection of the casting compound into the mold cavity, for example, a worm or piston is moved in the direction of the mold cavity. The setpoint value default information for this movement can be a speed characteristic for displacement or time, a pressure characteristic for displacement or time, or a displacement characteristic for time. In practice, combinations of different phases with different preset information are often used in sequence.

In particular, the injection phase is first of all speed-regulated and then the pressure-regulated phase (pressurization phase). After the pressurization phase, a cooling phase (cooling time) is carried out, in which the molded part is cooled to a temperature suitable for demolding.

The properties of the injection molded part produced are substantially determined in these three stages of the injection molding process. The control parameters which are effective in these phases and the duration of these phases are of great significance in terms of process technology. The main parameters for these three phases are for example:

an injection stage: jetting velocity profile and switching point

A pressurization stage: supercharging characteristic curve and supercharging time

And (3) a cooling stage: mold temperature and cooling time

The transition from the injection phase to the pressurization phase can take place when a specific position is reached, a specific pressure is reached, or after a specific time has elapsed. This transition is also referred to as a switching point in the following. The transition from the charging phase to the cooling phase and the end of the cooling phase are typically controlled in dependence on time.

The transition (switching) from the injection process with controlled speed to the pressurization phase with controlled pressure is generally carried out in that a certain variable exceeds or falls below a threshold value. In practice, for example, the worm position, the injection pressure, the injection time or the mold internal pressure are often used as switching criteria. Ideally, the switching point is selected such that the volume of the filling chamber is substantially guaranteed at the switching time. The speed-controlled injection process is mainly used for filling the mould, while the following pressure-controlled pressurization phase is mainly used for shrinkage compensation. If the switching is done too early, the chamber is only completely filled in the following pressure build-up phase, in which the pressure is controlled, whereby this process is very susceptible to material viscosity fluctuations. Furthermore, a significant drop in the injection pressure can also result after switching when the mold is not yet completely filled. If, conversely, the switching is done too late, it may result in overfilling of the cavity, leading to a violent pressure rise, overspray, burr generation, increased die wear, and other adverse consequences. The adjustment of the switching point is not optimal and therefore has many negative consequences which hamper a stable production.

But optimal adjustment of the switching point is not easy to achieve in practical situations. It is often necessary to resort to so-called filling studies in which the injection process is interrupted early at different times in the injection phase, the speed of which is controlled, and the degree of filling of the manufactured component is assessed. A hypothetical optimum switching point is then obtained based on the partially filled component. This is not only time consuming but does not always guarantee the desired result. Even if the injection process is terminated at the switching point, a certain time is required until the injection pressure completely disappears. Additional material is delivered into the cavity during this time period. It is not easy to read the exact filling level at the switching moment on the manufactured component.

Similar problems exist with respect to injection speed. The injection pressure rises sharply due to the increase in the volume flow when the injection speed is high, and rises due to the cooling of the melt during the injection process when the injection speed is low.

Boost height and boost time are also important. The shrinkage caused by cooling the profile is compensated for in this phase and the dimensions of the produced profile are determined substantially simultaneously. The pressurization time should be as large as possible than the so-called sealing time. The sealing time is the time at which the gate of the molded part is frozen in such a way that material can no longer be transported into the mold cavity. If the pressurization pressure is too low or the pressurization time is too short, shrinkage cavities or shrinkage depressions in the molded part may result due to the lack of compensation for shrinkage. If the boost pressure and/or boost time is adjusted to too large a value, the process is no longer optimal from an economic and energy point of view. Conventional methods for determining the minimum or optimal pressurization time include symmetrically varying the pressurization time and measuring the weight of the manufactured part, which is relatively time consuming.

The cooling phase determines both the profile accuracy and the deformation of the shaped part. Too short a cooling time reduces the profile accuracy of the surface of the shaped part or may lead to increased deformation. If the cooling time is longer than necessary, productivity is reduced and energy consumption is increased. Ideally, the pressure in the mold should be reduced to at least near ambient pressure at the end of the cooling time.

Furthermore, if the pressurization time and/or the pressurization height are/is set too low, this can lead to the moulded part no longer coming into contact with the mould wall during the cooling time due to shrinkage (shrinkage), as a result of which heat can no longer be transferred well. This reduces the efficiency of cooling while unnecessarily extending the required cooling time.

Finding the appropriate values for adjusting the parameters in the casting process is often difficult and time consuming.

Disclosure of Invention

The object of the present invention is therefore to provide a method which allows simple determination of the setpoint values of the control variables for the casting process. Furthermore, a molding machine for carrying out such a method should be provided.

To this end, the invention proposes a method for determining a target value for a control parameter in a casting process, the control parameter relating to melting of a casting compound, filling of a mold cavity with the casting compound and/or cooling of the casting compound filled into the mold cavity, wherein a liquid-phase casting compound is filled under pressure at least once into the mold cavity formed by two mold halves, a clamping force being exerted on the mold halves during filling of the mold cavity, characterized in that at least one profile of a variable for characterizing the clamping force is measured, a relationship between the measured profile or a variable derived from the measured profile on the one hand and a parameter of the casting process on the other hand is determined, and the target value for the control parameter is determined from the relationship.

The present invention also proposes a molding machine having: a mold clamping unit for applying a mold clamping force to two mold halves constituting a mold cavity; an injection unit for filling the mold cavity with a casting material; a measuring device for measuring at least one variation curve of a variable for characterizing a clamping force, characterized in that a control or regulating device is provided, which is connected to the measuring device and is designed to determine a relationship between the measured variation curve or a variable derived from the measured variation curve on the one hand and a parameter of a casting process on the other hand, and to determine a setpoint value for a regulating parameter from the relationship, the regulating parameter relating to melting of a casting compound, filling of a mold cavity with the casting compound and/or cooling of the casting compound filled into the mold cavity.

This is achieved by measuring at least one variation curve of the variable for characterizing the clamping force, determining a relationship between the measured variation curve or a variable derived from the measured variation curve on the one hand and a parameter of the injection process on the other hand, and determining a setpoint value for the control parameter from the relationship.

In most cases the clamping force is measured relatively directly as the hydraulic pressure of the clamping cylinder or as the force that is applied to the mold clamping plate by the electric clamping drive. However, it is also conceivable: for example, deformations in the clamping unit or the molding tool are measured, which characterize the clamping force. The resulting curve of the variable which characterizes the clamping force does not have to be converted into the clamping force itself for the purposes of the present invention, but can be used directly for determining the relationship.

However, for the sake of simplicity and accuracy, the measurement of the clamping force and the clamping force profile is referred to in the following, wherein it is always known to the skilled person that the same objective can be achieved by measuring a variable, for example, having a known functional relationship with the clamping force, which variable is used to characterize the clamping force.

As parameters of the casting process, variables (e.g., the position of the worm screw) can be used which are each characteristic of the casting process (e.g., the clamping force) or which occur during the casting process.

Based on the measured values and sensor signals (in particular the clamping force) present on the machine, it is possible with the method according to the invention to obtain optimum values for important control parameters in the different phases of the casting process (in particular the injection, pressurization and cooling phases), or to detect the present control and, if necessary, to provide the operator with appropriate instructions for improving the control.

Not essential to the invention here is: whether the movement is controlled or regulated during the injection or pressurization phase. Also of no importance is: for introducing the melt into the mold cavity and distributing it therein, a worm, a piston or another movable element, for example a punch element in an injection molding tool, is used. In the simplest case, the so-called characteristic curve may also comprise only constant values.

The setpoint values determined according to the invention for the control variables can be used further in various ways. On the one hand, it can be automatically used by the machine as a setpoint value for the controlled or regulated movement. On the other hand, it can also be displayed simply as a recommendation to the operator, or it can display a warning signal if the set setpoint value to be set deviates significantly from the setpoint value determined according to the invention.

It should be noted that it is not necessary to establish a relationship between the clamping force profile and the corresponding control variable. It may be advantageous in many cases: a relationship is established between a variable derived from the mold clamping force curve and a control variable. Examples for these variables are the mold breathing (Werkzeugatmung), the derivative of the mold clamping force curve with respect to time, the position or another independent variable or the like. Furthermore, for example, fourier transformation for filtering oscillations can be carried out, or individual points (e.g., extreme values) can be extracted from the clamping force profile.

A preferred embodiment of the invention may be: the correspondence of the time parameter to the mold clamping force profile or a variable derived from the mold clamping force profile and the correspondence of the time parameter to a parameter of the casting process are used as the relationship. This may show a particularly simple implementation of the invention, since many parameters on the molding machine are measured in a time-dependent manner.

Another preferred embodiment of the present invention may be: the relationship is used as a correspondence of the manipulated variable to the mold clamping force profile or a variable derived from the mold clamping force profile. In many cases, the relationship can be shown particularly simply in this way.

The so-called correspondence can preferably be shown as a curve or graph (for this purpose see the figures). However, this need not be the case, in particular, when the determination of the setpoint values for the control variables is carried out automatically. This is sufficient if there is a correspondence within the machine control.

In a further preferred embodiment of the invention, it can be provided that: a threshold value or target value is predetermined for the measured change curve or a variable derived from the measured change curve, and a value of a parameter of the casting process corresponding to the threshold value or target value is determined from the relationship and is determined as a setpoint value for the control parameter. When a target value is used, it is not necessary to achieve exact agreement with the target value. In general, a range around the target value is reached as a condition.

However, it is also possible to set: the value of the parameter of the casting process is determined from the relationship, which corresponds to the measured profile or an extreme value of a variable derived from the measured profile, and is determined as a setpoint value for the control parameter. Depending on which control parameter is to be optimized and whether the clamping force or a variable derived therefrom is used, a suitable criterion can be selected, wherein the general form of the relationship to be investigated is preferably taken into account.

In order to optimize the adjustment parameters particularly quickly, it can be provided that: exactly one casting cycle takes place, in which the casting material is filled into the mold cavity.

When the relationship is complex or when particularly precise adjustment of the setpoint value is required, it can be provided that: a plurality of casting cycles are carried out, in which the casting material is filled into the mold cavity, wherein the control parameters are varied in the different casting cycles.

Depending on which regulating parameter a setpoint value should be found for, appropriate casting process parameters must be used, which are subject to variation during a casting cycle or a plurality of casting cycles.

The adjustment parameter itself may be used as the parameter in some cases. Examples of this are:

-an injection speed of the injection movement,

-a pressure build-up level,

-the cylinder temperature of the injection cylinder,

-the temperature of the mould,

-a dynamic head of a fluid-dynamic type,

-the worm speed, and

-hot runner temperature.

Examples of tuning parameters for optimization by varying other parameters are:

a switching point of the injection movement between a phase in which the speed is regulated and a phase in which the pressure is regulated, wherein the worm position can be used as a parameter,

a sealing point and/or a termination point of the injection movement, wherein the pressurization time can be used as a parameter,

a boost time, wherein a time parameter is used as a parameter,

mold clamping force, wherein the current mold clamping force is used as a parameter,

a cooling time, wherein a time parameter is used as a parameter, an

-an injection pressure limit, wherein injection pressure is used as a parameter.

Of course, it is also possible in the regulating parameters which can be determined by changing other parameters: the setpoint value is determined by changing the control variable itself. However, it is also possible to determine the setpoint value by means of other parameters, so that only a single cycle needs to be carried out, which can decisively shorten the regulation of the casting cycle.

In a preferred embodiment, it can be provided that: the set value for the control parameter is used in the control or regulation of the molding machine, wherein it is particularly preferred if the set value is automatically received by a control or regulation device of the molding machine which carries out the pouring process.

Drawings

Further advantages and details of the invention can be taken from the drawings and the accompanying description. In the drawings:

fig. 1a and 1b show assumed relationships with respect to control variables for the purpose of illustrating the basic principle of the invention;

FIG. 2 illustrates different relationships for deriving a switching point;

FIG. 3 shows a relationship for obtaining jetting velocity;

fig. 4a, 4b and 5 show different mold clamping force or mold clamping force difference variation curves for varying pressurization times;

FIG. 6 shows the relationship for determining the sealing point derived from FIGS. 4 and 5;

FIG. 7 shows an injection molding machine having an electric clamp actuator according to the present invention;

fig. 8 shows an injection molding machine according to the invention with a hydraulic closing drive.

Detailed Description

Fig. 1a shows an assumed relationship between a variable S, which is derived from a mold clamping force curve, and a variable P, both variables being shown in relation to time t. In this case, the target value E is used as the control variable E^*The criterion of (1) determines the time at which the variable S derived from the clamping force curve has a minimum value as a limit value. This time is denoted t^*. The desired setpoint value E for the control variable E is thus obtained^*＝P^*。

Fig. 1b shows an assumed relationship between a variable S derived from a mold clamping force curve and a parameter P, which in this case is the manipulated variable E itself. As a reference value E for selecting a control variable^*The criterion of (2) here being a preset minimum value S^*. Setpoint value E for a control variable^*＝P^*Then it follows from this relationship.

Fig. 2a shows the results of a test series in which the force increase at the switching time is observed at different switching times (parametrized by the worm antechamber volume). The worm antechamber volume can be automatically defined by a predetermined threshold value (indicated by a horizontal dashed line), which can be used as a setpoint value for the switching time. (in this case the fourth measurement point accidentally falls exactly on the border.)

One of the advantages of the invention is that at least the threshold values for a plurality of casting processes can be selected solely on the basis of the forming machine (not the forming mould), so that a reliable regulation of the casting process can be achieved without the operator having to experience many years in this respect.

Fig. 2b shows a further alternative determination of the setpoint value. The upper graph shows the mold clamping force over time. The worm position with respect to time is shown in the second diagram of fig. 2 b. By determining the threshold value for the clamping force, the corresponding setpoint value for the worm position can be found.

The embodiments of fig. 2a and 2b differ in that in the first embodiment a plurality of cycles have to be performed, whereas for the second embodiment only one cycle has to be performed. (because the worm position can be converted into the volume of the worm antechamber due to the known geometry of the worm and the injection cylinder, the nominal values determined by the two different methods according to the invention are of the same size.)

Fig. 3 shows the variable derived from the clamping force curve. The set value v is shown as an respiration value (Atmungswert) which is dependent on the injection speed (which means that the clamping unit or the mold is deformed by the injection pressure)^*The minimum value of the curve is preset here.

Calculation of the mold breathing from the clamping force is achieved at a predetermined effective spring constant that describes the deformation of the clamping unit of the molding machine under the clamping force and the injection pressure.

Fig. 4, 5 and 6 relate to a method for determining a sealing point. In order to illustrate the formation of fig. 5, fig. 4a and 4b show, on the one hand, two mold clamping force curves and, on the other hand, the difference between the two mold clamping force curves. The mold clamping force curves differ in that different pressurization times are used during the generation. Clearly in fig. 4 b: how the differences in the mold clamping curves are eliminated. Additional casting compound can be fed into the cavity by a slightly longer pressurization time, as a result of which the pressure in the cavity and thus the mold clamping force are increased. Naturally, a slight time difference between the maxima of the two clamping force profiles can also be easily seen, which is likewise a result of the different length of the charging times.

Fig. 5 shows a plurality of mold clamping force difference variation curves as in fig. 4 b. The casting cycle is carried out with a pressurization time of between 0.2 and 2.6 seconds, a time step of 0.2 seconds being used. The curves are the difference curves between the mold clamping force curves, which are characterized by a pressurization time difference of 0.2 seconds.

As can be seen, a uniform difference curve is shown starting from a certain charging time, only the maximum value of the difference curve being offset by the charging time difference. It can be concluded from this that the sealing point is reached starting from the moment when the difference curve starts to be drawn. This is shown more clearly in fig. 6, where the difference of the maximum values is shown with respect to the increase in time, respectively, which in this case indicates the rate of pressure change. As used herein, the criteria is that the rate of pressure change falls below a threshold or substantially disappears.

As can be seen from the relationship shown in fig. 6, a simple and precise determination of the sealing point can be achieved by the method according to the invention. In a further embodiment of the invention: a variable pressure characteristic curve is superimposed on the supercharging pressure characteristic curve by the plasticizing worm. This pressure characteristic curve can be clearly seen in the profile of the closing pressure profile before the sealing point is reached. This is no longer the case after the sealing point is reached, since the casting material has solidified in the runner. In this way the sealing point can be determined.

Fig. 7 and 8 each show an injection molding machine 1 according to the invention having a clamping unit 2 and an injection unit 3, wherein in the first case an electric clamping drive and in the second case a hydraulic clamping drive are provided.

The injection unit 3 has in this embodiment a plasticizing worm 5, by means of which it can fill the mold cavity 4 with a casting compound, for example plasticized plastic. The thinnest point near the mold cavity 4, where solidification of the casting material first occurs at the time of filling, is referred to as the gate 9. The injection drive 6 serves to drive the plasticizing worm 5.

The so-called sensor and the injector drive are each connected to a control or regulating device 7.

The worm position sensor may be implemented by a rotary encoder within the jetting drive 6.

Other sensors that may be used to measure parameters on the injection molding machine 1 include a hydraulic pressure sensor 12 (fig. 8), a force sensor 13 (fig. 7) for measuring the mold clamping force applied by an electric mold clamp actuator, an in-mold pressure sensor 10, a pressure sensor 11 near the gate 9, and an injection pressure sensor 8.

The force sensor 13 may be designed as a strain gauge or a torque sensor in the drive.

Claims

1. Method for determining a target value for a control parameter in a casting process, which control parameter relates to melting of a casting compound, filling of a mold cavity (4) with the casting compound and/or cooling of the casting compound filled into the mold cavity (4), wherein the casting compound in liquid phase is filled under pressure at least once into the mold cavity (4) formed by two mold halves, a clamping force being exerted on the mold halves during filling of the mold cavity (4), characterized in that,

at least one curve of a variable for characterizing the clamping force is measured,

determining a relationship between the measured profile or a variable derived from the measured profile on the one hand and a parameter of the casting process on the other hand, and

from this relationship, a setpoint value for the control variable is determined.

2. Method according to claim 1, characterized in that the correspondence of a time parameter to the measured variation curve or a quantity derived from the measured variation curve and the correspondence of a time parameter to a parameter of the pouring process are used as the relation.

3. Method according to claim 1, characterized in that the correspondence of a parameter of the pouring process to the measured variation curve or a quantity derived from the measured variation curve is used as the relation.

4. Method according to any one of claims 1 to 3, characterized in that a threshold value or a target value is preset for the measured change curve or a quantity derived from the measured change curve, and a value of a parameter of the casting process corresponding to the threshold value or target value is obtained by the relation and determined as a nominal value for the regulating parameter.

5. Method according to any one of claims 1 to 3, characterized in that values of parameters of the casting process are obtained from the relationship, which values correspond to limit values of the measured profile or of a variable derived from the measured profile and are determined as nominal values for the control parameters.

6. Method according to any one of claims 1 to 3, characterized in that exactly one casting cycle is carried out, in which casting cycle the casting material is filled into the mould cavity (4).

7. Method according to any one of claims 1 to 3, characterized in that a plurality of casting cycles are carried out in which the casting material is filled into the mould cavity (4), wherein the parameters of the casting process are changed in different casting cycles.

8. Method according to one of claims 1 to 3, characterized in that a setpoint value for the switching point of the injection movement between the phase in which the speed is regulated and the phase in which the pressure is regulated is determined as a regulating parameter, wherein the worm position is used as a parameter.

9. Method according to one of claims 1 to 3, characterized in that a setpoint value for the sealing point and/or the end time of the injection movement is determined as a control variable, wherein a pressurization time is used as a parameter.

10. Method according to one of claims 1 to 3, characterized in that a setpoint value for the charging time is determined as a control variable, wherein a time variable is used as a parameter.

11. Method according to one of claims 1 to 3, characterized in that a setpoint value for the cooling time is determined as a control variable, wherein a time variable is used as a parameter.

12. Method according to one of claims 1 to 3, characterized in that a setpoint value for the injection pressure limit is determined as a control variable, wherein the injection pressure is used as a parameter.

13. Method according to any of claims 1 to 3, characterized in that the injection speed of the injection movement is used as a regulating parameter and parameter.

14. Method according to any one of claims 1 to 3, characterized in that the cooling time for the shaped part to be produced is used as regulating parameter and parameter.

15. Method according to any of claims 1 to 3, characterized in that the cylinder temperature of the injection cylinder is used as a regulating parameter and parameter.

16. A method according to any one of claims 1 to 3, characterized in that the mould temperature is used as a regulating parameter and parameter.

17. A method according to any one of claims 1 to 3, characterized in that a dynamic head is used as the adjustment parameter and parameter.

18. Method according to any one of claims 1 to 3, characterized in that the worm speed is used as a regulating parameter and parameter.

19. A method according to any one of claims 1 to 3, characterized in that at least one hot runner temperature is used as regulating parameter and parameter.

20. Method according to one of claims 1 to 3, characterized in that a switching point of the injection movement between a phase in which the speed is regulated and a phase in which the pressure is regulated is used as regulating parameter and parameter.

21. A method according to any one of claims 1 to 3, characterized in that a boost height is used as a regulating parameter and parameter.

22. A method according to any one of claims 1 to 3, characterized in that a supercharging time is used as a regulating parameter and parameter.

23. A method according to any of claims 1 to 3, characterized in that the injection pressure limit is used as a regulating parameter and parameter.

24. A method according to any one of claims 1 to 3, characterised in that the nominal values for the regulating parameters are used in regulating or controlling the moulding machine.

25. A molding machine is provided with:

a clamping unit (2) for applying a clamping force to the two mold halves forming the mold cavity (4),

an injection unit (3) for filling the mold cavity (4) with a casting compound,

measuring means (8, 10, 11, 12, 13) for measuring at least one curve of a variable for characterizing the clamping force,

characterized in that a control or regulating device (7) is provided, which is connected to the measuring device and is designed to determine a relationship between the measured profile or a variable derived therefrom on the one hand and a parameter of the casting process on the other hand and to determine a target value for a regulating parameter from the relationship, the regulating parameter relating to the melting of the casting compound, the filling of the mold cavity (4) with the casting compound and/or the cooling of the casting compound filled into the mold cavity (4).