Method For Controlling An Injection Molding System

Abstract

A method is provided for controlling an injection molding system, which includes a mold having an inner surface defining at least two groups of cavities, each group of cavities defining precisely one cavity with one pressure sensor at the inner surface. Each group of cavities is at least partially surrounded by a tempering unit that provides an energy flow to the surrounded cavities. According to the method, a pressure is determined in each group of cavities of the at least two groups of cavities. A reference pressure is determined for each group of cavities. A difference between the reference pressure and the pressure in at least one group of cavities is determined and controlled to become minimum by manipulating the energy flow of the tempering unit.

Claims

1. Method for controlling an injection molding system with a mold having an inner surface and at least two groups of cavities, each group of cavities comprising at least one cavity, being confined by the inner surface, and each group of cavities further having precisely one pressure sensor being arranged at the inner surface in a region of a cavity of each group of cavities, and each group of cavities being at least partially surrounded by a respective tempering unit that provides an energy flow to or from the respective at least partially surrounded group of cavities, the method comprising the steps of: a) determining a pressure in each group of cavities of the at least two groups of cavities, b) determining a reference pressure for each group of cavities, c) determining a difference between the reference pressure and the pressure of at least one group of cavities, and d) controlling the difference to become minimum, e) wherein step d) is performed by regulating the energy flow of the respective tempering unit.

2. Method according to claim 1, wherein step c) includes determining a difference between the reference pressure and the pressure of each group of at least two groups of cavities, and wherein step d) includes controlling each difference of each group of at least two groups of cavities to become minimum, and wherein step e) is performed by regulating the energy flow of each tempering unit of each group of at least two groups of cavities.

3. Method according to claim 1, wherein step d) includes controlling the difference to become minimum at a predetermined time.

4. Method according to claim 1, wherein step d) includes controlling the difference to become minimum over a predetermined period of time.

5. Method according to claim 1, wherein step b) includes determining a reference pressure by averaging the pressures of each group of cavities.

6. Method according to claim 1, further comprising the step: f) Storing the reference pressure in a memory.

7. Method according to claim 1, wherein step e) includes regulating a tempering energy flow of the tempering unit.

8. Method according to claim 1, wherein step e) includes regulating a flow rate of a tempering medium through the tempering unit.

9. Method according to claim 8, wherein step e) includes regulating a valve of the tempering unit.

10. Method according to claim 1, further comprising the step: f) Determining temperature of a material in a cavity of each group of cavities or of the tempering medium of the tempering unit of a group of cavities or of the inner surface of a group of cavities of the at least two groups of cavities.

11. Controller for performing the method according to claim 1, the controller comprising: a) an input for receiving a pressure of each group of cavities of at least two groups of cavities of a mold of an injection molding system, each group of cavities comprising at least one cavity, b) an input and/or a calculator for receiving and/or calculating, respectively, a reference pressure for each group of cavities, c) a subtracter for calculating a difference between the reference pressure and the pressure of at least one group of cavities, and d) a control function for controlling the difference to become minimum, and e) an output for manipulating an energy flow of a tempering unit.

12. Use of a controller according to claim 11 in an injection molding system.

13. Injection molding system comprising: a controller according to claim 11 and a mold having a) an inner surface, b) at least two groups of cavities, each being confined by the inner surface, each group of cavities comprising at least one cavity, c) precisely one pressure sensor being arranged at the inner surface in a region of each group of cavities, and d) at least two tempering units, wherein each group of cavities is at least partially surrounded by one tempering unit, and wherein each tempering unit is arranged to provide a tempering power.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The drawings used to explain the embodiments show:

[0078] FIG. 1 an injection molding system,

[0079] FIG. 2 a mold with two groups of cavities, pressure sensors and tempering units,

[0080] FIG. 3 a typical pressure distribution for different groups of cavities of a mold over the time according to the prior art,

[0081] FIG. 4 a method for controlling the pressures in the different groups of cavities of a mold according to the invention,

[0082] FIG. 5 a pressure distribution for different cavities of a mold over the time according the invention.

[0083] In the figures, the same components are given the same reference symbols.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0084] FIG. 1 shows an injection molding system 1 comprising a mold 2 and a controller 30. The controller 30 controls the injection molding system 1 and is arranged outside the mold 2.

[0085] FIG. 2 shows a mold 2 in a closed configuration. The mold may comprise two halves which are arranged together at an inner surface 4 of the mold 2. The inner surface 4 confines two groups of cavities 3, each comprising at least one cavity 8, which cavities 8 are separated and spaced from each other. Each group of cavities 3 is surrounded by a tempering unit 5 for individually tempering the group of cavities 3 with its respective cavities 8. At the inner surface 4 in an area of each group of cavities 3, or in other words at the inner surface 4 of one cavity 8 of each group of cavities 3, a pressure sensor 6 and an optional temperature sensor 7 are arranged for measuring the pressure and the temperature of a material in each group of cavities 3, respectively. A processible material can be pressed via runners (not shown) and nozzles (not shown) into each cavity 8 of each group of cavities 3 to form at least two articles (not shown) simultaneously. In an open configuration of the mold 2 (not shown), the two halves of the mold 2 are separated from each other for ejecting the two articles.

[0086] FIG. 3 shows a typical pressure 10 distribution for different groups of cavities 3 of a mold 2 over the time 20 during a conventional injection molding process according to the prior art. A pressure 11 of a first group of cavities of the mold 2, a pressure 12 of a second group of cavities of the same mold 2, and a pressure 13 of a third group of cavities of the same mold 2 start to rise at the same initial rising time 21, when material is being pressed into a cavity that includes the pressure sensor of each group of cavities. However, each of pressures 11, 12, 13 reaches its peak value at slightly different peak times 22. Also, at the predefined time 23, the pressures 11, 12, 13 have different values.

[0087] FIG. 4 schematically shows a method for controlling the pressures 11, 12, 13 in the different groups of cavities 3 of the mold 2, and an implementation of the method in the form of a controller 30. From a reference pressure 31, the actually measured pressures 11, 12, 13 are subtracted by subtracter 32 to determine a difference pressure 33 between the actually measured pressures 11, 12, 13 and the reference pressure 31. It is possible to have a bundle of difference pressures 33, that is to say one difference pressure 33 for each measured pressure 11, 12, 13. Difference pressure 33 is the input of the control function 34 like for example a PID function. Control function 34 outputs an intended flow rate 35 of a tempering medium. The intended flow rate 35 forms an input of valve 36 which is adapted to establish an actual flow rate of the tempering medium corresponding to the outputted intended flow rate 35. A pressure sensor (not shown in FIG. 4, but shown in FIG. 2) arranged in a cavity 8 of each of the group of cavities (not shown in FIG. 4, but shown in FIG. 2) measures the actual pressures 11, 12, 13 in each group of cavities. Said actually measured pressures 11, 12, 13 are, as already mentioned, an input of subtracter 32.

[0088] FIG. 5 shows a pressure 11, 12, 13 distribution for different groups of cavities 3 (not shown) over the time 20 according to the invention. As the difference pressure 33 (see FIG. 4) is controlled to become minimum, the pattern of the reference pressure 31 and the patterns of the measured pressures 11, 12, 13 are essentially identical.

[0089] In summary, it is to be noted that the different aspects of the invention and the different embodiments thereof solve the object of the invention well.

LIST OF REFERENCE SYMBOLS

[0090] 1 injection molding system

[0091] 2 mold

[0092] 3 group of cavities

[0093] 4 inner surface

[0094] 5 tempering unit

[0095] 6 pressure sensor

[0096] 7 temperature sensor

[0097] 8 cavity

[0098] 1 pressure

[0099] 11 pressure in a first cavity

[0100] 12 pressure in a second cavity

[0101] 13 pressure in a third cavity

[0102] 20 time

[0103] 21 initial rising time

[0104] 22 peak time

[0105] 23 predetermined time

[0106] 24 predefined period of time

[0107] 30 controller

[0108] 31 reference pressure

[0109] 32 subtracter

[0110] 33 difference

[0111] 34 control function

[0112] 35 flow rate of a tempering medium

[0113] 36 valve