The injection molding tools used in an injection molding machine are frequently kept at a constant temperature so as to enable fast cooling of the molded part. However, there is an increasing demand initially to briefly heat the injection molding tool before injection, for example to the temperature of the plastic melt, and to cool down to the de-molding temperature only after injection. This situation is referred to as dynamic or vario-thermal temperature control. This technique of the dynamic temperature control of injection molding tools is known since several years (Menges/Michaeli/Mohren: “Anleitung zum Bau von Spritzgieβwerkzeugen” (Manual for the construction of injection molding tools), 5 edition, Hanser-Verlag, 1999, Chapter 8.7.4 “Dynamische Werkzeugtemperierung” (Dynamic tool temperature control)). In the article “Variotherme Temperierung—Methoden und Einsatzmöglichkeiten” (Vario-thermal temperature control—Methods and Applications) by J. Giesslauf, ENGEL Austria GmbH, VDI Technical Meeting “Injection Molding 2008—Innovation and Productivity” of 29.-30. January 2008 in Baden-Baden, Germany, several different methods for vario-thermal temperature control of injection molding tools and their potential applications are presented.
The documents DE 10 2007 019 389 A1, WO 97/16274 A1 and U.S. Pat. No. 5,376,317 A disclose temperature control devices for dynamic and vario-thermal temperature control of injection molding tools operating with two separate temperature control circuits, namely a first temperature control circuit with a fluid at a first temperature (for example relatively hot water or oil) and a second temperature control circuit with a fluid at a second temperature (for example relatively cold water or oil). A control device switches back and forth between the two temperature control circuits at predetermined times. These times can be defined by certain events or states that occur during the injection molding cycle, for example by the event “mold open” or the state “maximum pressure in cavity reached” (see, for example, U.S. Pat. No. 5,376,317 A, column 11, lines 18-52). An injection molding tool can thus be first heated and subsequently cooled down with this temperature control device in each injection molding cycle. The injection molding tool can hereby attained a temperature profile, such as illustrated for example in FIG. 2a of the U.S. Pat. No. 5,376,317 A. A programmable logic controller (PLC) for temperature control is disclosed in DE 10 2007 019 389 A1, wherein data acquired from sensors, for example temperature sensors, are processed by these SPS and control signals are outputted to certain parts of the temperature control device. Signals for the switchover times between the colder and warmer medium depending on the process can be provided by the machine control via programmable inputs and/or outputs.
The times where the temperatures in the injection molding tool are supposed to change, for example when a switchover occurs from heating to cooling and vice versa, are fixedly defined or fixedly programmed in the conventional injection molding machines and temperature control devices, typically in a programmable logic controller (PLC). This is the case even if these times are defined by certain events or states determined during the injection molding cycle, as disclosed for example in the aforementioned U.S. Pat. No. 5,376,317 A. Only actual temperature values, which should be approached with the temperature control device by heating and/or cooling (desired temperatures), can be inputted into a control device by an operator. Accordingly, a desired temperature profile can only be determined or adjusted by an operator in a limited way. A user or operator of an injection molding machine has therefore limited possibilities to affect the course of temperature in the injection molding tool. To change the time dependence of the desired temperature profile, the PLC must be reprogrammed, which a user or operator of an injection molding machine is typically unable to do. This means that appropriately trained personnel must be called, which is associated with a certain time and cost factor.
Based on the aforementioned state-of-the-art, it is the object of the invention to provide a control device for an injection molding machine, whereby an operator of the injection molding machine can easily set up a certain desired value temperature profile (cycle-synchronous desired value temperature profile) which is, in particular, temporally exactly matched to each injection molding cycle.
The object is attained by a control device having the features of claim 1. Advantageous improvements and embodiments are recited in the dependent claims.
In that the control device is constructed such
An operator can therefore easily set up or freely program a desired temperature profile which does not adhere to exact fixed absolute times, but instead follows cycle-synchronous the events and/or states that occur during an injection molding cycle. It is therefore unimportant during the operation of the injection molding machine at which time these events and/or states occur, i.e., any time delays caused by interfering events do not negatively affect the desired value temperature profile to be followed.
In addition, certain desired temperature values to be approached by the temperature control device may be associated with the start conditions. The temperature control device is operated in a manner so that the temperature in the region to be temperature-controlled changed towards the desired temperature value predetermined for this region. If the desired temperature values cannot be reached or not be reached reliably commensurate with the time dependence of the desired temperature profile during the operation of the injection molding machine, then the temperature control device may be reconfigured or a different temperature control device may be employed. The operator may also change “his/her” desired temperature profile and adapt the profile to the respective situation defined in particular by the existing injection molding machine, the existing injection molding tool and the temperature control devices connected thereto.
The flexibility of the free programmability of the temperature is enhanced by a possible time-delayed control of the temperature control device. An operator may simply define times defining a delay for controlling the temperature control device for a start condition and enter these times in the control device. This means that after an event and/or state occurs, the entered time should elapse commensurate with the formed desired temperature profile before the temperature control device is controlled.
As needed, different types of temperature changes can be or are stored in the control device.
The following exemplary types of temperature changes should be mentioned:
Other types of temperature changes are feasible and can optionally be stored in the control device or read in from a data carrier.
The control device preferably includes a control console with a display, with a number of windows provided when a certain program is called, for displaying and entering information. A first window may be provided or opened, in which available events and/states are displayed, and from which the operator can select desired or predefined events and/or states as a start condition for controlling the temperature control device. A second window can be provided or opened, in which the available types of selectable temperature changes are displayed, from which the operator can select desired or defined types of temperature changes and associate these with a start condition. By repeated selection of certain events and/or states, on one hand, and certain types of temperature changes, on the other hand, and their mutual association, a series of associated events/states and types of temperature changes can be formed. In addition, additional windows can be provided for selecting or entering numerical values for one or more additional parameters.
An injection molding machine with a control device according to the invention and with a temperature control device that can be controlled by the control device is particularly suited for the production of molded plastic parts by the aforementioned vario-thermal temperature control of injection molding tools. Advantageously, depending on the plastic molded parts, several regions that can be annealed independent from each other may be arranged in the injection molding tools for manufacturing this plastic molded part. Accordingly, different desired temperature values, in particular different desired temperature profiles, may be set up for these different regions of an injection molding tool. To this end, a number of selectable regions to be temperature-controlled may be stored in the control device for selection by an operator. For each of these regions, an associated desired temperature profile may be freely programmed by a user or operator of the injection molding machine. Advantageously, a dedicated temperature control device for separate temperature control of each region and thus for each temperature channel of the control device may be provided. Depending on the design of a temperature control system, several temperature control devices may be “combined” or housed together in a single temperature control system.
The invention will now be described in more detail with reference to an exemplary embodiment. The injection molding machine may be any type of conventional injection molding machine with a plasticizing and injection unit and with a closure unit with one or several injection molding tools. The control device of the injection molding machine has a program for setting up and following a desired temperature profile.
In a window 2, the temperature channel to which the following temperature values to be entered and the later desired temperature profile should relate can be selected. A temperature channel may be associated with, for example, a certain zone in an injection molding tool. For example, a first temperature channel may be provided for the one mold half and a second temperature channel may be provided for the other mold half so that the temperatures for the two mold halves of the injection molding tool can be adjusted to be different and independent from each other. However, two temperature channels may also be provided in a single mold half, for example, if different zones are to have different temperatures. The temperature channel may be, for example, a channel in a certain region of the injection molding tool through which a liquid heat transfer medium flows. However, different types of temperature controls for the zone or region and thus for this temperature channel may be contemplated, for example with an electric resistance heater, an infrared radiator, a Peltier heater or other temperature control means. In the present example, this is the temperature channel 1. One or several temperature control devices may also be provided, wherein preferably a dedicated temperature control is provided for each temperature channel. In practical applications, this may only be a single temperature controller, as long as the controller is capable of controlling the temperature of different temperature channels independent from each other.
Furthermore, different adjustment possibilities may be provided depending on the type of the injection molding tool. When using injection molding tools for a multi-component injection molding process employing a so-called rotary platen technique, the position of, for example, the rotary platen where the mold temperature should be dynamically controlled may predetermined, in the present example in the position 180°.
In another window 3, a display screen for the actual value in the selected temperature channel is provided as well as the option to enter a minimum and a maximum release temperature. The release temperature refers to the temperature which must be reached before the next injection molding process can start, i.e., before this start is “released.” In the present example, the temperature in the temperature channel 1 must therefore have a value between 100° C. and 150° C. before the start for injection can be released. In practical applications, an actual value between 100° C. and 150° C. would be displayed during standard operation of the injection molding machine as “Actual Temperature—Temperature Channel” shortly before the injection. Conversely, if a temperature value outside this range were measured and indicated in the temperature channel 1, then the start for the injection would not yet be released. The minimum and maximum release temperatures depend, inter alia, on the plastic material to be processed. Preferred processing temperatures for each plastic material are specified by the manufacturer of the plastic material.
The window 4 at the bottom in the FIG. is composed of several windows or columns 4.1 to 4.7, the significance of which will now be described:
The column 4.1 shows the running number “No.” which is associated with a specific segment of an injection molding cycle. Depending on the injection molding cycle, the entire injection molding cycle may be subdivided more or less finely into individual consecutively numbered segments. For example, in the present example, an injection molding cycle may be divided into eight segments.
In column 4.2, the operator can select a certain type for each consecutive number of the available types of temperature changes and thus specify a certain type of temperature change for this number. To this end, different types for a temperature change are stored in the controller of the injection molding machine and can be read into the controller from a data carrier and stored. The stored types of temperature changes represent a selection which are available to the operator during the free programming of the desired temperature profile and from which the operator can select the presently desired or specified type. In the present example, three types of temperature changes are available to the operator for a change in temperature, which are listed in the rows No. 1 to No. 3, namely a temperature jump, a standby and a temperature ramp. However, other types of changes in temperature for a temperature change are also feasible.
In this column, the operator can select for each running number a certain start condition from predetermined or predeterminable start conditions. For this purpose, several events and/or states specific for the injection molding cycle and occurring during the injection molding cycle are stored or storable in the control device. The stored events and/or states are available to the operator for selection. These may, for example, include the specific events and states occurring during the injection molding cycle listed below, from which the operator can make a selection:
Selectable Events:
Selectable States:
This allows for a time-delayed control of the temperature control. In other words, the temperature change according to the associated type of change in temperature is not immediately started when the start condition occurs, but instead with a predetermined time delay. The operator can enter, for example, that a temperature change should start only after a certain time following the start of the mold closure, i.e., a predetermined time after the occurrence of the event “Close Mold.” In the present example, this delay time is 1 second. Moreover, as in the present example, it would be possible to wait for a certain time after the event “Closure Force Reached”—in the present example 2 seconds—until the temperature changes to 100° C. commensurate with the type “Standby”. The type “Standby” is characterized in that the temperature control is simply switched off, for example by turning the control device for temperature control off, and a cooldown to the desired temperature of 100° C. is achieved by simply dissipating the existing heat into the environment. When using a temperature control device with a liquid heat transfer medium, the flow of the heat transfer medium could be stopped, for example. The temperature control is activated again and the control device is again turned on only when the predetermined temperature of presently 100° C. has been reached. When using a temperature control device with a liquid heat transfer medium, the flow of the heat transfer medium and control of the desired temperature could then again be started.
In this column, those temperatures can be entered which should be reached at the temperature change according to the running number in column 4.1. These temperatures are therefore desired temperature values which produce the desired temperature curve in a cycle.
In this column, an upper limit can be assigned to the time-on duration ED of the control path computed by the temperature controller of the control device. The heating power in this phase can thereby be limited to a desired maximum.
The operator has here the option to limit the time for the respective segment (i.e., the number from column 4.1) of the injection molding cycle. A cycle segment is terminated if either the desired temperature in column 4.5 has been reached or if the next start condition in 4.3, i.e. the next event or the next state, has been reached. A premature termination may also occur when a preselected time duration entered in column 4.7 has been reached. The last criterion is advantageous in particular at the end of an injection molding cycle if the present desired temperature is not to be maintained until the next start condition occurs, but if instead, for example, the temperature control device is to be turned off and a switchover to a supervisory control circuit for a standard operating temperature is to occur. This can also be beneficial in the event of a fault.
Overall, in the present example, a sequence of eight associated events and/or states, on one hand, and types of temperature changes, on the other hand, can be displayed. Accordingly, eight pairs of events/states and types of temperature changes can be formed by an operator. Depending on the programming of the control device, more or less such associated pairs of events, states and types of temperature changes may be formed.
Instead of one or more of the aforedescribed windows, suitable regions within a single window may also be provided to display data and/or to enter data. Likewise, separate display screen pages may be used for displaying and/or entering data. Display screen pages may be used as replacement for windows and/or regions; these can also be combined with windows and/or regions. The desired visualization for displaying and/or entering data depends on the respective circumstances and is not a limitation of the invention.
The following process flow is therefore obtained for the example illustrated in
In the same way, the further process flow of the injection molding cycle and the associated parameters for temperature control (type, start condition, delay, . . . ) can be entered, until finally a certain injection molding cycle with a certain desired value temperature profile is completely adjusted.
The user is thus able to set up, i.e. to program and optionally optimize “his/her” desired value temperature profile without programming knowledge. By defining the start conditions by the events and/or states that occur during the injection molding cycle, deviations that occur during the operation are automatically “transferred” to the temperature profile, i.e., it is for example unimportant that the state “Closure Force Reached” is always reached at the same time or if this time is subject to variations.
It can be ensured by suitable measures that unworkable or detrimental parameters cannot be entered into the controller. For example, only temperature values within predetermined limits may be entered and temperature values outside these limits would not be accepted by the program. In addition, a monitoring mechanism could be provided which intervenes and makes corrections when the predetermined desired temperature values during an injection molding cycle are still absent when the next start condition is reached. In the simplest situation, the injection molding machine would simply wait and stop the injection molding cycle.
Which temperature is monitored, i.e., measured, and is entered into the control circuit for the desired temperature value entered in column 4.5 as a controlled valuable depends on the particular circumstances. For example, this could be a temperature in the tool wall in the proximity of the cavity surface. However, it could also be a temperature of a heat transfer medium at a certain location in the temperature control loop of the liquid temperature control medium.
Number | Date | Country | Kind |
---|---|---|---|
10 2009 020 193.9 | May 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP10/55818 | 4/29/2010 | WO | 00 | 11/4/2011 |