Method and apparatus to regulate heating of a hot runner in a multicavity mould

The invention relates to a method according to the preamble of claim 1. Such a method is known from the article "Computerized Mold Diagnostics and closed loop Molds" in the magazine "Injection Moulding", March 1997 pages 87/88. There will described that to maintain a desired pressure range in the individual cavities, the temperatures in the individual Hot runners in dependency of the measured mold internal pressures be adjusted in the individual cavities.

For the quality of plastic injection molded parts, it is known inter alia essential that the achievement of the switching point recognized at the end of the filling phase as accurately as possible at the time is when the mold cavity just filled volumetrically is. For multi-cavity tools can be a good and uniform only achieve quality, therefore, if all wells to same time are just filled volumetrically. object of The invention is a uniform filling in all cavities a multi-cavity tool reach. This object is achieved using the characterizing features of claim 1. Requirement is for the application of the inventive method however, that all cavities of a tool in the shape and size are equal.

The measurement of the times for the achievement of an arbitrary reference pressure, the only higher than the pressure at the end of the filling and below the lowest maximum pressure in a cavity must give accurate and reliable knowledge of the time, when the volumetric filling cavities einzelenen has been errreicht. In addition, it shows which wells in filling "run ahead" and that this "lag". Such detailed statements can with a pressure range control as in the mentioned prior art, not be recovered, as for example at a maximum pressure control may Pressures in cavities are measured, in which the melt already has solidified; this has been shown in tests.

A very simple, but relatively time-consuming control of the Mold filling can be carried out with the new procedure, if gradually each the hot runner temperature of the first filled, ie lowers the leading in their pressure profile cavities and / or that of the last filled, that is the trailing, Cavity is increased.

To errors in the regulation of fillings in the individual cavities - For example due to pressure fluctuations or other Disorders - exclude possible, can in the regulation of individual hot runner temperatures in a predetermined, for all cavities at the same time the area formed for each well Pressure / time integrals are considered. The time range must start no later than at the switching of the first cavity filled and between the switching time and the date of Reaching the maximum pressure of the last filled cavity forming. The determined pressure / time integrals can be added in a similar manner be used in a successive approximation as above described for the time measurements.

Another additional optimization of the process is possible, when beyond the maximum cavity pressure in each cavity recognized and considered in the hot runner temperature control will.

As mentioned, the indicated iterative approximations to a simultaneous filling of all cavities relatively lengthy and require possibly a greater number of approximate steps. Fast can be a simultaneous filling of all cavities achieved if from the obtained time, integral and / or Maximum pressure values ​​of all wells each on a hypothetical average and the differences of the values ​​obtained to the fictitious mean value are formed, wherein the control of the individual hot runner temperatures takes place, that the differences formed against go to zero. Very practical in this procedure is when doing the methods of fuzzy logic be applied. By detecting the sizes of the respective difference values, it is so simple Manner possible, the intervention in the individual heating systems of individual hot runners targeted different dosing.

For the determination of the required switching points, the use an automatic changeover point proved how for example, in EP-A-0707.936 or in the Swiss Patent Application described 1997 0939/97 from 23.04.1997.

Furthermore, it may be useful to the material dependent adjustable mean set temperature of the melt not only in a known manner to measure the distribution and regulate, but also as a mean the measured in the individual hot runners to record temperatures and to comply with the prescribed by the melting material ago Temperature range to be used. This causes that also whenever acting on individual hot runners as a result of the inventive Method of the predetermined material from the area of not "leave" average melting temperature. Is it a tendency, so, due to the averaging, the Temperatures in the individual hot runners overall in the same be increased or decreased mass.

In the following, the inventive method is of an exemplary embodiment explained in more detail in connection with the drawing.<sl><li>Fig. 1 shows schematically a plant for carrying out the new process;</li><li>Fig. 2a-c and Fig. 3a-c give the courses of the cavity pressure in the various cavities in function of time again, FIG. 2 the entire pressure curve during a Injection molding process, and FIG. 3 relevant to the new procedure Section in the area of ​​the switching points and the maximum pressures with respect to FIG. 2 fourfold stretched timeline represent.</li><li>Fig. 4 schematically shows an example of how the tool internal pressures in the evaluation unit by means of fuzzy logic to the information required Target temperatures can be processed in the hot runners.</li></sl>

The injection molding apparatus of FIG. 1, a tool 10 from Metal on which surrounds a hollow interior space 11; the two-piece Tool 10 is of an, eg hydraulic clamping unit 12 opened and closed. The inner space 11 in which the Injection molded parts are formed, is formed by four in the form and Size 1 to 4 same cavities, each through a hot runner 5 are connected to a manifold. 6 stands over the sprue 7 the distributor 6 to the outlet nozzle of an injection device 8 in connection.

includes preparation for and for injecting the molding compound the device 8 an injection cylinder 9, one on the upper side Hopper 13 for the introduction of the granular molding material opens, and in which a screw 14 axially movable and is rotatably arranged. The movement of the screw 14 is, as usual controlled by a control device 15th

The distributor 6 is not shown in a conventional manner by a Heater heated, of a commercial Heisskanalregelgerät 17 is operated. A not shown temperature sensor thereby controls the distributor 6, the manifold heater so, that a predetermined by the melting material, adjustable Temperature range is maintained.

Each hot runner 5 has a separate heater which symbolically is indicated as a heating coil 16th These separate heaters 16 are also "served" by Heisskanaregelgerät 17th furthermore each hot channel 5 equipped with its own temperature sensor, which is not shown expressly. From the measured Absolute temperatures in the individual hot runners 5, a formed mean and material-dependent with the set, Temperature range compared. If the average of the temperatures in the hot runners 5 the tendency of the set temperature range "Emigrate", this value is through a uniform Throttling or increasing the heating power of all heating coils 16 17 so controlled by the device that it is in the range adjusted average temperature remains. A schematically illustrated connection 18 between the Heisskanalregelgerät 17 and the mold cavity 11 is the exchange of the control the heating necessary signals indicated.

For carrying out the inventive method, each cavity 1-4 equipped with a pressure sensor 19th As sensors most known types of pressure sensors are used, wherein piezoelectric sensors have proved to be particularly suitable. Via a connection 20 pass the measured values ​​of the pressure sensors 19 to one for each cavity 1-4 own charge amplifier 21, of the made them as electrical voltages via a connection 22 a Computer 23 as signal processing and evaluation unit will. In addition, the computer 23 is equipped with an automatic Changeover point 24. The computer is 23 after evaluation and processing of its inputs control commands via a schematically illustrated connection 25, via which it the actual temperatures of the individual cavities 1-4 as an additional Input signals are supplied from the control device 17, for individual Regulation of the temperatures in the hot runners 5 to the Heisskanalregelgerät 17. This throttles or increases the heating power the individual heating elements 16 accordingly.

In the embodiment of FIGS. 2 and 3 underlying Injection molded parts are molded from styrene-butadiene. For this Material is the average processing temperature 250 ° C, so that the temperature range to be maintained somewhere between 240 ° C and 260 ° C lies.

In the diagrams of Figs. 2 and 3, respectively, the course of Cavity pressure p in cash for each cavity Kl to K4 function from the time t recorded in seconds. The two graphs a quote the pressure curves of an unregulated injection cycle again, after reaching the average processing temperature has been "driven".

The diagrams show the pressure curves b a - only for trial and demonstration purposes recorded - intermediate state in the substantially by increasing the temperature in the hot channel 5 for cavity K2 whose filling time with those of the rest Wells has been approximated.

In the diagrams, a cycle c is recorded, in which the effect the complete process carried out is reproduced.

While Fig. 2 only an overall impression of the measured pressure gradients intended to convey, the procedure is again with reference to FIG. 3 described.

In all graphs ac the same reference pressure pR is entered, the inventively einerseit on the discharge pressures of the filling phases at switching U1-U4 (Fig. 3a) is, for example, determined by the automatic changeover point 24 will. On the other hand, the reference pressure is smaller than the lowest maximum pressure pMK2 (Fig. 3a) in a cavity of here Cavity K2.

From Fig. 3a of the first recorded molding cycle it will be seen that the cavity K1 is filled as the first and at time t1 the reference pressure pR achieved; as next the cavity K4 is filled, wherein the reference pressure PR is achieved at the time t2. The pressure curve in the cavity K3 exceeds the reference pressure pR in Time t3, while in the much-delayed filling of K2 Pressure pR is reached until the time t4.

Before the recording of the diagram 3b is the novel Method in the computer 23 by means of the difference between the time t4 and the fictitious time mean tM incomplete been applied so far, that the heating power of the cavity K2 has been increased by a certain amount. In the thereafter carried out and shown in Fig. 3b cycle reach the Pressures in the Ka activities K1 and K4 to almost unchanged times t1 and t2 the reference pressure pR. The reinforced heater for the cavity K2 has however causes in this cavity the pressure pR at time t3 is exceeded just before the time t4, the now belongs to cavity K3.

A - turn on the difference between actual value and t1 fictitious time mean tM triggered - throttling of the heating for the Cavity K1 is reduced, the anticipation of the filling of this cavity, as Fig. 3c illustrates. As final effect of the new procedure thus the filling times for the individual cavities very strongly matched to one another, wherein the pressure curves for the cavities K2 and K4 practically coincide.

Since interventions in the individual heating powers of the individual Cavities influences the temperatures in adjacent Hot runners 5 or cavities K1 to K4 not completely prevented can be, move the "fill time" t until reaching the reference pressure pR for cavities slightly whose Heating over previous cycles remained unchanged are.

In the computer 23, in addition to the pressure curves and their time integrals or the maximum pressure values, similar example, using Subtractions against fictitious averages addition are used for evaluation to disorders such Example strong pressure fluctuations, which in the described series of test cycles have not occurred, to recognize and Computer 23 to protect them from false conclusions. For the purposes the thus extended the process to have the methods fuzzy logic (fuzzy logic) proved useful.

In the example of a processing of the input signals shown in Fig. 4 the evaluation unit 23, with the aid of fuzzy logic, get the reshaped to electrical voltages metrics the cavity pressure in each cavity 1 to 4 on the compound 22, for each cavity 1 to 4 separately, in a first processing stage 26 of the evaluation unit or the computer 23rd

The processing of these input signals in the computer 23 is now for a first cavity K1 described in detail; it is carried out for the other cavities K2 to K4 in the same way.

In stage 26 is firstly, triggered by the automatic Changeover point 24 in connection with the lowest measured Peak or maximum pressure pM, automatically a reference pressure pR determined, as indicated in the 27th The reference pressure pR is advantageously selected so that it better in the lower half, still in the lower third of the pressure difference between the pressure at Switching point and the lowest peak pressure pM, pMK2 in execution recordable FIGS. 3a, lies.

Further, in step 26, first for each cavity K1 to K4, the times t1 to t4 detected in which in each cavity K1 to K4 of the reference pressure pR is reached. From the measured times then be a fictitious time mean value and for each cavity K1 K4 to the difference .DELTA.t of the determined time for them to the fictional Mean formed. For the cavity K1, this difference is assigned via a link 28 ΔtK1 one of these cavity Processing element 29K1 supplied.

In the same way further in the first stage 26, the Pressure / time integral I of the cavity K1 via an all cavities K1 to K4 formed at the same time range, the latest in Switching point of the first filled cavity K1 (Fig. 3a) starts and between the changeover of the last filled cavity K2 (Fig. 3a) and the time of reaching of the maximum pressure pMK2 ends. For this I integrals for all cavities K1 to K4 are a fictitious mean value and the differences between .DELTA.I the individual values ​​and the mean value formed over a second connection 28ΔIK1 also the processing element is 29K1 fed.

Finally, we proceed with the consideration of the cavity K1 determined maximum or peak pressure pM in the same way and to the member 29K1 again the difference ApMK1 the appropriate Compound 28 to.

In the elements 29, 30 and 31 carried out the fuzzification which Fuzzy inference and defuzzification of the supplied difference values by the known methods and rules of fuzzy logic.

As outputs of the fuzzy logic is a connection 32 in the final processing stage 33 of the computer 23 - if a "Mismatch" of temperature in the cavity K1 or the hot runner temperature exists for this cavity - a temperature difference entered, the magnitude and sign of the mismatch reproduces.

Further input signals of stage 33, the material dependent adjustable, medium target temperature for the melt as well as the actual values ​​of the temperatures in the individual cavities K1 to K4 or in its hot runners 5 through the in Fig. 1 schematically reproduced Signal connection 25 supplied.

From the input signals described above are in the Level 33, taking into account the material-dependent middle Target temperature of the melt new setpoints for the temperatures T (K1) to T (K4) in each cavity K1 to K4 respectively in the associated Hot Runner 5 is calculated and also via the connection 25, the Heisskanalregelgerät 17 received; of this then the for maintaining or reaching the new temperature in the cavities necessary cutbacks or gains of the individual Hot runner heaters triggered. Here the level of the mean value is the new temperatures of all cavities of the adjustable average set temperature of the melt equalized. However, permanent To avoid fluctuations in the hot runner temperatures The new target values ​​for the temperatures in the various Wells initially with the measured actual values ​​and the compared old setpoints and only after this comparison in the Level 33 of the computer decides whether a command for setting the new setpoint for a cavity to the Heisskanalregelgerät is passed on 17th

Of course, the invention is not limited to the embodiment shown with only four cavities and / or to the described Evaluation and processing of the measured cavity pressure limited. Rather, it is and especially in injection molds applicable with a plurality of cavities, wherein also other evaluation methods for determining the desired values ​​for the temperatures can be used in the individual cavities.

Refernzliste

<dl tsize="5" compact="compact"><dt>1-4</dt><dd>wells</dd><dt>K1-K4</dt><dd>wells</dd><dt>5</dt><dd>Heisskanaltechnik</dd><dt>6</dt><dd>distributor</dd><dt>7</dt><dd>sprue</dd><dt>8th</dt><dd>injection molding device</dd><dt>9</dt><dd>injection cylinder</dd><dt>10</dt><dd>Tool</dd><dt>11</dt><dd>mold cavity</dd><dt>12</dt><dd>hydraulic closure device</dd><dt>13</dt><dd>funnel</dd><dt>14</dt><dd>slug</dd><dt>15</dt><dd>controller</dd><dt>16</dt><dd>heating coil</dd><dt>17</dt><dd>Heisskanlaregelgerät</dd><dt>18</dt><dd>signal connection</dd><dt>19</dt><dd>pressure sensor</dd><dt>20</dt><dd>signal connection</dd><dt>21</dt><dd>charge amplifier</dd><dt>22</dt><dd>signal connection</dd><dt>23</dt><dd>Evaluation unit (computer)</dd><dt>24</dt><dd>changeover point</dd><dt>25</dt><dd>signal connection</dd><dt>26</dt><dd>first-stage processing in the computer 23</dd><dt>27</dt><dd>automatic reference pressure setting</dd><dt>28</dt><dd>signal connection</dd><dt>29</dt><dd>fuzzyfication</dd><dt>30</dt><dd>Fuzzy inference</dd><dt>31</dt><dd>defuzzification</dd><dt>32</dt><dd>signal connection</dd><dt>33</dt><dd>last stage of processing in the computer 23</dd></dl>