CH702154A1 - Method for controlling injection process during manufacturing molded part, involves controlling velocity of injection unit, temperature of mass, termination of injection or starting of subsequent process based on state change of detector - Google Patents

Abstract

The method involves coupling a measuring location (13) of a cavity (3) to a binary detector (14) that changes from a defined state to another defined state at a time, where melt mass (6) arrives at the measuring location at the time. Injection velocity of an injection unit (5) in an open-loop or closed-loop manner, temperature of the melt mass before injection, termination of the injection at a nozzle (8) or starting of a subsequent process are controlled by an open-loop or closed-loop control unit (10) based on a state change of the detector.

Description

Technical area

The invention relates to a method for controlling or regulating an injection process in the manufacture of a molded part, is injected in the melt of at least one injection unit via at least one nozzle in at least one of a tool surrounded cavity.

State of the art

Controls and controls in injection molding processes usually include the injection phase, in which a cavity is filled in a tool with a liquid mass, the holding pressure phase, which is intended to compensate for material loss, and a subsequent cooling phase, in which the mass finally to the desired Form part solidifies until the tool finally opened and the finished molding can be removed. In all these phases, process controls and controls are necessary to ensure that the finished molded parts are of consistent, reproducible quality.

In another manufacturing process, injection-compression molding, an embossing process follows the injection process. In the case of fluid injection technology or projectile technology, on the other hand, molded parts with cavities are produced. In these manufacturing processes, the injection process is followed by a further process step in which the hot plastic melt is displaced by a fluid.

In all these and other processes in the injection phase, the control and control must in particular ensure that the cavity is filled optimally. In injection molding, for example, it should be completely filled but not overcrowded. If several cavities are present, this of course applies to all cavities simultaneously.

The filling quantity in the cavity in turn depends on the injection speed of the injection screw and on the temperature of the nozzle before injection into the cavity. This decisively determines the viscosity of the plastic melt, which has an effect on the flow behavior. Finally, at the right time, the filling process must be stopped.

In DE 2 358 911 a method is described, which describes a control device of injection molding machines on the basis of pressure and temperature measurements. Due to temperature measurements at various points, the flow front speed is determined, on the basis of which finally a control valve for the next cycle is set.

From EP 897 786 a method for controlling an injection molding is also known. It also regulates various control parameters for the next cycle based on pressure measurements.

All of these methods are very complex and require sensors that continuously record readings that need to be evaluated and processed.

Presentation of the invention

The object of the present invention is to provide a method described above, which manages without extensive data acquisition and appropriate evaluation and in particular without expensive and technologically advanced and fault-prone Meßwerterfassungssysteme. As a result, the instrumentation necessary for the control should, on the one hand, be more cost-effective and, on the other hand, more process-reliable.

The object is solved by the characteristics of the independent claim.

The idea underlying the invention is that at least one cavity has a measuring point, which is coupled to a binary switch which detects the time t of arrival of the melt at this measuring point and transmits a characteristic time signal to an evaluation unit. On the basis of this time signal alone, the method controls or regulates the injection speed V of at least one injection unit, the termination of the injection at at least one nozzle, the temperature T of the melt prior to injection and / or starts a follow-up process. Such a follow-up process may, for example, be the starting of a further injection unit and / or the opening of a further nozzle.

Characterized in that in the inventive method, only the time t of the arrival of the melt must be detected, cheap components can be used as a binary switch. In contrast to the prior art, no time-dependent measurement curves are recorded and evaluated here.

Brief description of the drawings

In the following the invention will be explained in detail with reference to the drawings. Show it <Tb> FIG. 1 <sep> is a schematic representation of a system according to the invention with a cavity and a nozzle; <Tb> FIG. 2 <sep> Diagram of a signal output of a switch before and after an event t; <Tb> FIG. 3 <sep> is a schematic representation of a system according to the invention with a nozzle to a cavity which is subjected to a later embossing, in the (a) open and (b) closed state; <Tb> FIG. 4 is a schematic representation of a system according to the invention with a cavity and two injection units which can fill the cavity with different materials; <Tb> FIG. 5 is a schematic representation of a system according to the invention with a cavity and an injection nozzle and with a liquid injection device for fluid injection processes, (a) before and (b) after liquid injection. <Tb> FIG. 6 is a schematic representation of a system according to the invention with a hot runner and a plurality of nozzles for each cavity, in which a molded part with a weld line is produced, with a measuring point at the weld line, (a) in the unfinished state and (b) in the finished state of FIG molding; <Tb> FIG. 7 is a schematic representation according to FIG. 6, with two measuring points in the weld line, (a) in the unfinished state and (b) in the finished state of the molded article; <Tb> FIG. 8 is a schematic representation of a system according to the invention with two injection units with different masses to form a cavity, with a molded part with a weld line; <Tb> FIG. 9 is a schematic representation of a system according to the invention with a hot runner and a plurality of nozzles for the same cavity; <Tb> FIG. 10 <sep> a part of a tool with a measuring point for detecting the arrival of the melt front, wherein the arrival of the melt front (a) directly on the Kavitätsoberfläche, (b) in the mold wall near the Kavitätsoberflache, (c) behind a Auswerfestift or measuring pin detected becomes.

Ways to carry out the invention

The reference numerals have been retained in both drawings.

FIG. 1 shows a process installation 1 according to the invention for producing a molded part 2 in a cavity 3, which is surrounded by a tool 4. An injection unit 5 is supplied with melt 6 during production and transports it, for example by a screw feed, to a nozzle 8, which is connected by a channel 9 to the cavity 3. The melt 6 penetrates into the cavity 3 until it is completely filled. A controller 10 now switches the process to repressurization.

A heating module 11 in the region of the nozzle 8 can influence the temperature of the melt in the nozzle 8 and thus change the viscosity thereof. A warmer melt has a higher viscosity and thus flows faster into the cavity 3 than a cooler melt. Thus, the flow rate can be controlled by the temperature at the nozzle 8. On the other hand, the screw feed rate is responsible for the flow rate. Finally, the system can also have a slide 12 between the nozzle 8 and the cavity 3, which can stop the injection by being closed.

According to the invention, the process plant 1 has at least one measuring point 13, which is coupled to a binary switch 14. This switch 14 is designed such that it changes its state at the time t of arrival of the melt front 15 at this measuring point 13. An evaluation unit controls or controls the injection on the basis of such a state change. This may relate, in particular, to the change in the injection speed of the injection unit, the regulation of the temperature of the molten mass 6 before the injection, and / or the termination of the injection after a nozzle 8, for example by a slide 12.

In the present example, the measuring point 13 is preferably located near the point at which the flow path of the melt 6 is completed, ie at the end of the cavity 3. Thus, upon detection of the arrival of the melt front 15 on the complete filling of the cavity 3 is closed whereupon, for example, the process of the filling phase can be completed and the holding pressure phase can be initiated.

The arrival of the melt front 15 at the measuring point 13 can be detected by the binary switch 14 at various points. In particular, this can be detected by a measuring element adjacent to the cavity 3 or in the cavity wall near the cavity 3. On the other hand, a suitable measuring element can also be mounted behind an ejector pin 18 or behind a measuring pin 18. Even if the measuring element is arranged far away from the cavity 3, then the measuring point 13, that is to say the determining location, at which the melt front 15 must be passed in order to put the switch 14 into another state, is always directly at the cavity wall.

A measuring element can detect the time t of the arrival of the melt front 15, for example mechanically, optically, thermally electrically or chemically. The switch 14 can change the state when exceeding a certain pressure, a certain temperature, a certain voltage, when falling below a certain distance measurement to a counterpart, which can be performed optically, for example, or in a chemical change of the measuring element. Behind a Auswerfestift 18 especially pressure-sensitive sensors are suitable.

Crucial for the switch 14 mentioned here is that not a measured value has to be determined and recorded over a certain period of time, but only the change of the switch 14 must be detected. This means, first, that the change of state, for example, by a temperature switch, also called bimetal switch, as they are known from thermostatic switches, can be achieved. In contrast to thermocouple temperature measurements, where special thermocouple materials such as nickel-chom / nickel and / or corresponding equalizing leads must be used as leads and connections to obtain accurate readings, conventional copper leads are sufficient in the present case. The same applies to pressure measurements: For piezoelectric pressure measurements, highly insulated cables and connections with insulation sheaths of at least 10A12 ohms are required to prevent the interference signals. For the purpose of a switch 14, however, basically only two states must be distinguished. Therefore, no special requirements for the lines and connections to the pressure measuring elements are necessary for this, simply insulated copper cables and commercially available connections are sufficient. The use of a binary switch 14 is therefore generally cheaper and easier than an evaluation of time-dependent measurement data.

Fig. 2 shows the change of the signal at time t as an example. Here, the output of the switch 14 changes from 0 to 1.

In Fig. 3, the method of injection molding is shown. In such a method, in a first stage as in injection molding melt 6 is injected into a cavity 3, but this is not completely filled. Fig. 3a shows an example of a filling state at the end of this first stage. In a second stage, finally, the two tool halves 4, which surround the cavity 3, are moved together for an embossing process. The molten mass 6 is now distributed in the entire cavity 3, as shown in Fig. 3 b. It is important that the filling level after the first stage is probably sufficient to fill the mold in the second stage, but on the other hand is not overcrowded. For this purpose, according to the invention a binary switch 14 can be coupled to a suitable measuring point 13, which recognizes the optimum filling state. An evaluation unit interrupts the filling of the cavity 3 at this time t and initiates the closing of the mold halves 4.

Another example is given in Fig. 4, the production of multi-component moldings 2. Again, the injection process is stopped and then started another process step. This process step is the starting of a further injection unit using, for example, another material or another property (e.g., color) of the same material as the melt 6. Again, by determining the melt front 15 by means of a binary switch 14, the optimum filling state and thus the correct time t for stopping the first injection unit 5 and for starting the following process can be initiated.

In Fig. 5, an example of a fluid injection process is shown. In this, in turn, a certain amount of molten mass 6 is injected into a cavity 3, as shown in FIG. 5a. In a subsequent phase, liquid is finally injected through a device for liquid injection 19 into the molten mass 6, as a result of which this molten mass 6 is forced to the edge of the cavity 3. Again, the level is determined by the binary switch 14.

In FIGS. 6-8, in each case one cavity 3 is filled simultaneously by at least two nozzles 8. This creates a conjunctiva at the point where two flow fronts meet. Firstly, such places are less resilient mechanically and secondly optically recognizable. In addition, if a plurality of injection units 5 are used, different enamel masses 6 can also be used, as shown in FIG. 8. In all these cases, the location of the weld line 17 should be placed at a predetermined location.

For this purpose, as shown in Fig. 6, according to the invention, a first measuring point 13 are equipped with a switch 14. When switching the switch 14, for example, the supply of molten mass 6 is stopped at the first switch 14, so that the rest of the cavity 3 is filled solely by the second nozzle 8.

In FIG. 7, two measuring points 13 are equipped with switches 14. By the second switch 14 can now be determined when the cavity 3 is now completely filled by the second nozzle 8. On the other hand, it can be achieved by the temperature control of the nozzles 9 and thus by the adaptation of the viscosities of the enamels 6 in the nozzles 8 that both enamel fronts 15 pass through the measuring points 13 at the same time. Even then it is ensured that the weld line 17 is located between the two measuring points 13. Both examples of Figs. 6 and 7 may, of course, be made with the same or different melt masses 6, i. be performed with an injection unit 5 and a hot runner 20 or with two injection units 5. In the case of a plurality of injection units 5, as shown in Fig. 8, the injection speeds can be controlled independently of each other by the binary switch 14. to be controlled.

In Fig. 9, another example of a multi-cavity tool 4 is given. Here injects an injection unit 5 via a hot runner 20 with a plurality of nozzles 8 melt 6 in as many cavities 3, wherein at the end of each cavity 3, a measuring point 13 with a switch 14 corresponds. By controlling the temperature at the nozzles 8, the various viscosities can be adjusted so that all cavities 3 are filled simultaneously.

LIST OF REFERENCE NUMBERS

[0030] <Tb> 1 <sep> Process plant <tb> 2 <sep> Molding, multi-component molding <Tb> 3 <sep> cavity <tb> 4 <sep> Tool, tool half, multi-cavity tool <Tb> 5 <sep> injection unit <Tb> 6 <sep> melting mass <Tb> 7 <sep> snail <Tb> 8 <sep> Nozzle <Tb> 9 <sep> Channel <tb> 10 <sep> control <Tb> 11 <sep> heating module <Tb> 12 <sep> slide <Tb> 13 <sep> measuring point <tb> 14 <sep> binary switch, switch <Tb> 15 <sep> melt front <Tb> 16 <sep> evaluation <Tb> 17 <sep> weld <tb> 18 <sep> ejector pin or gauge pin <tb> 19 <sep> Liquid injection device <Tb> 20 <sep> Heisskanaltechnik <tb> T <sep> melt temperature <Tb> V <sep> Snails feed rate <tb> t <sep> time of arrival of the melt

Claims (13)

1. A method for controlling or regulating an injection process in the production of a molded part (2), wherein the molten mass (6) of at least one injection unit (5) via at least one nozzle (8) in at least one of a tool (4) surrounded cavity (3 ) is sprayed, characterized in that the at least one cavity (3) has at least one measuring point (13) which is coupled to a binary switch (14), wherein the binary switch (14) at the time t of the arrival of the molten mass (6 ) at the measuring point (13) changes its state, and due to the state change an evaluation unit (16) the injection speed V of the at least one injection unit (5), the temperature T of the molten mass (6) before the injection, canceling the injection at the controls or regulates at least one nozzle (8) and / or starting a follow-up process. 2. The method according to claim 1, characterized in that the evaluation unit (16) on the basis of the change in state of the switch (14) stops stopping the injection process and the start of a subsequent process step, in particular the holding pressure phase, in the case of an injection-compression process embossing, in the case the production of multi-component molded parts starting another injection unit or in the case of a fluid injection process, the start of the liquid injection. 3. The method according to any one of the preceding claims, characterized in that the molten mass (6) via two or more nozzles (8) is simultaneously injected into the same cavity (3), whereby a weld line (17) in each case two melting fronts (15) is formed wherein the evaluation unit (16) controls the starting and / or canceling of the injection of at least one nozzle (8) due to the state change of the switch (14) to reach a predetermined position of the weld line (17). 4. The method according to claim 1 or 2, characterized in that the melt (6) via two or more nozzles (8) is simultaneously injected into the same cavity (3), whereby a weld line (17) in each case two melting fronts (15) is formed , and wherein two or more binary switches (14) are mounted coupled to two or more measuring points (13), which change their states when passing the melt fronts (15) at the measuring points (13), wherein the evaluation unit (16) due to this Changes in state, the temperatures T of the melt masses (6) before injection controls to achieve a predetermined position of the weld line (17). 5. The method according to claim 4, characterized in that the temperatures T of the enamel masses (6) are controlled prior to injection such that the enamel fronts (15) reach the measuring points (13) simultaneously. 6. The method according to any one of the preceding claims, characterized in that two or more injection units (5) the same or different enamel masses (6) in each inject at least one nozzle (8). 7. The method according to claim 6, characterized in that the evaluation unit (16) controls the injection speeds V of the injection units (5). 8. The method according to any one of the preceding claims, characterized in that the molten mass (6) via two or more nozzles (8) is simultaneously injected into two or more cavities (3), each cavity (3) has at least one measuring point (13) in each case with a binary switch (14) coupled thereto, the binary switches (14) changing their states at the times of arrival of the enamel fronts (15) at the respective measuring points (13), and whereupon the evaluation unit (16) initiates the injection at least breaks off a nozzle (8) and / or controls the temperatures T of the melt masses (6) prior to injection. 9. The method according to claim 8, characterized in that the temperatures T of the enamel masses (6) are controlled such that the enamel fronts (15) reach all measuring points (13) simultaneously. 10. The method according to any one of the preceding claims, characterized in that the binary switch (14) comprises a measuring element which detects the time t mechanically, optically, thermally, electrically or chemically. 11. The method according to any one of the preceding claims, characterized in that the binary switch (14) the arrival of the melt front (15) at the measuring point (13) in the tool (4) directly adjacent to the cavity (3), in the tool wall ( 4) near the cavity (3), behind a Auswerfestift or behind a measuring pin (18) detected. 12. The method according to any one of the preceding claims, characterized in that at least one measuring point (13) is arranged near a point at which a flow path of the molten mass (6) to be terminated. 13. The method according to any one of the preceding claims, characterized in that the switch (14) transmits a signal via a single insulated copper wire to the evaluation unit (16).