WO2014062281A1 - Surveillance de moule capacitive - Google Patents

Surveillance de moule capacitive Download PDF

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Publication number
WO2014062281A1
WO2014062281A1 PCT/US2013/054076 US2013054076W WO2014062281A1 WO 2014062281 A1 WO2014062281 A1 WO 2014062281A1 US 2013054076 W US2013054076 W US 2013054076W WO 2014062281 A1 WO2014062281 A1 WO 2014062281A1
Authority
WO
WIPO (PCT)
Prior art keywords
mold
mold cavity
molding machine
changing capacitance
capacitance
Prior art date
Application number
PCT/US2013/054076
Other languages
English (en)
Inventor
Brian Esser
Original Assignee
Husky Injection Molding Systems Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Husky Injection Molding Systems Ltd. filed Critical Husky Injection Molding Systems Ltd.
Publication of WO2014062281A1 publication Critical patent/WO2014062281A1/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/76—Measuring, controlling or regulating
    • B29C45/768—Detecting defective moulding conditions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C37/00—Component parts, details, accessories or auxiliary operations, not covered by group B29C33/00 or B29C35/00
    • B29C2037/90—Measuring, controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
    • B29C2945/76—Measuring, controlling or regulating
    • B29C2945/76003—Measured parameter
    • B29C2945/7615—Electrical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
    • B29C2945/76—Measuring, controlling or regulating
    • B29C2945/76003—Measured parameter
    • B29C2945/76163—Errors, malfunctioning
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0003—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds having particular electrical or magnetic properties, e.g. piezoelectric
    • B29K2995/0006—Dielectric

Definitions

  • This relates to the use of capacitive sensing in a mold.
  • transducers have also been positioned behind mold ejector pins to measure the force on these pins during mold operation.
  • the capacitance within a mold cavity is measured for a period of time while material is introduced into the mold cavity. As material is introduced, the effective dielectric constant of the cavity changes such that the measured capacitance changes. If the changing capacitance falls outside pre-defined bounds, a fault condition is determined.
  • a method of operating a molding machine comprising: sensing a changing capacitance within a mold cavity over a time period while a material is introduced into said mold cavity; and determining a fault condition if said changing capacitance over said time period falls outside one or more pre-defined bounds.
  • a molding machine comprising: a mold having a first mold portion and a second mold portion which, when said mold is closed define, at least in part, a mold cavity with at least a first wall section of said first mold portion opposite at least a second wall section of said second mold portion across said mold cavity; an electric isolator, the electric isolator configured to electrically isolate said first mold portion from said second mold portion other than at at least a portion of said mold cavity; and a controller connected for sensing capacitance between said first mold portion and said second mold portion.
  • a molding machine comprising: a mold, the mold defining a mold cavity; electrically isolated components arranged so that application of a voltage to said electrically isolated components provide an electric field in said mold cavity; a controller connected between said electrically isolated components and configured for: sensing a changing capacitance within said mold cavity of said mold over a time period while material is introduced into said mold cavity; and determining a fault condition if said changing capacitance over said time period falls outside pre-defined bounds.
  • a controller for a molding machine comprising: means for sensing a changing capacitance within said mold cavity over a time period while a material is introduced into said mold cavity; and means for determining a fault condition if said changing capacitance over said time period falls outside pre-defined bounds.
  • FIG. 1 is a schematic view of an injection molding machine
  • FIG. 2 is a schematic detail of a portion of the injection molding machine of FIG. 1 ;
  • FIG. 3 is a graph of time versus measured capacitance from several different cycles of the injection molding machine of FIG. 1 ;
  • FIG. 4 is a flow diagram illustrating operation of a controller associated with the injection molding machine; and FIG. 5 is a schematic view of another injection molding machine.
  • FIG. 1 a non-limiting embodiment of an injection molding machine 10 is depicted.
  • the injection molding machine 10 has a stationary platen 12 and a moving platen 14.
  • a stationary clamp block 16 is located behind the moving platen 14, and the moving platen 14 rides on a tie bar 18 that is supported at its ends by the stationary clamp block 16 and the stationary platen 12.
  • tie bar 18 typically there are four such ties bars, one extending between each of the four corners of the moving platen 14, the stationary platen 12, and the stationary clamp block 16.
  • a mold 24 has a first mold portion 26 attached to the stationary platen 12 and a second mold portion 28 attached to the moving platen 14.
  • the first mold portion 26 has a first mold core piece 30 and the second mold portion 28 has a second mold core piece 32.
  • the front walls of the first and second mold core pieces 30, 32 are configured such that when they are brought together they form a mold cavity 34.
  • a platen moving actuator 35 is connected between the moving platen 14 and the stationary clamp block 16 for moving the moving platen 14 with respect to the stationary platen 12 and thus the first mold portion 26 with respect to the second mold portion 28.
  • a clamp actuator 36 and a clamp shutter 38 are associated with the stationary clamp block 16. The clamp shutter 38 selectively connects the clamp actuator 36 with the moving platen 14 to clamp the first and second mold portions 26, 28 together.
  • An ejector actuator 40 functions to eject a molded part from the mold 24.
  • a screw injector 42 has a screw 44 rotated by a screw drive 46.
  • a hopper 48 supplies the material 50, such as granulated resin, to the screw 44.
  • a heater assembly 52 is coupled to the mold 24.
  • An outlet (not separately numbered) of the screw injector 42 communicates with a sprue 54 that, in turn, communicates with a runner 56 providing a passageway into the mold cavity 34 through a valved gate 58.
  • FIG. 2 is a schematic detail of a non-limiting embodiment of a portion of the injection molding machine 10.
  • an electric isolator 60 can be applied to second mold core piece 32 of second mold portion 28.
  • the electric isolator 60 is configured to electrically isolate the second mold core piece 32.
  • the electric isolator 60 is a dielectric coating.
  • the dielectric coating can cover sections 62a, 62b of the front wall of second mold core piece 32 such that when the first and second mold core pieces 30, 32 are brought together to form mold cavity 34, the dielectric coating electrically isolates the second mold core piece 32 from first mold core piece 30 other than at the mold cavity 34.
  • second wall section 62c of second mold core piece 32 bounding the mold cavity 34 is opposite first wall section 64c of first mold core piece 30 across the mold cavity 34.
  • the dielectric coating could be applied to the first mold core piece 30 of the first mold portion 26.
  • the coating could be applied to both mold core pieces 30, 32.
  • a voltage generator and capacitance measurement circuitry 66 can be connected across first and second mold core pieces 30, 32 by electrical wires 72, 74.
  • the voltage generator may be a direct current (DC) or an alternating current (AC) generator. Where the voltage generator is an AC generator, it may have a high frequency to allow accurate measurement of small capacitances.
  • the capacitance measurement circuitry may be a bridge circuit or any other suitable circuitry (for example, in simple embodiments, the capacitance measurement circuitry could be merely a resistor or capacitor connected in series with an AC voltage generator).
  • a controller 70 is operatively connected to the capacitance measurement circuitry.
  • the controller 70 receives input signals on lines 76 from various sensors (not shown) including, for example, a rotation sensor (not shown), when screw injector 42 is activated during a mold cycle.
  • the controller 70 outputs, on lines 78, control signals to, for example, the platen moving actuator 35, clamp actuator 36, clamp shutter 38, ejector actuator 40, screw drive 46, heater assembly 52, and valved gate 58.
  • controller 70 activates the platen moving actuator 35 to push the moving platen 14 to close first and second mold portions 26, 28 to form mold cavity 34.
  • controller 70 controls the clamp actuator 36 and clamp shutter 38 to lock moving platen 14 in this position.
  • the controller 70 activates the screw drive 46 of screw injector 42 and receives a feedback signal on lines 76 that the screw 44 of the screw injector 42 is rotating. This signals the controller 70 to output a valved gate opening signal on lines 76 and to begin to monitor the capacitance between first and second core pieces 30, 32 across mold cavity 34.
  • material 50 With the screw 44 operating, material 50 will be conveyed from hopper 48 by the screw injector 42.
  • the material is injected through sprue 54 and runner 56 past valved gate 58 into the mold cavity 34.
  • the screw injector 42 can be de-energized and the valved gate 58 closed.
  • the material in the mold cavity 34 cools, the mold 24 is then opened and the ejector actuator 40 operates to eject the finished product from the mold 24, all under control of controller 70.
  • the heater assembly 52 maintains the material at a desired temperature.
  • an electric field can be set up across mold cavity 34.
  • the resulting capacitance is inversely proportional to the strength of this electric field.
  • An increase in the effective dielectric constant of the mold cavity 34 will reduce the effective electric field.
  • the capacitance between first and second mold core pieces 30, 32 also increases.
  • the effective dielectric constant of the mold cavity 34 Prior to material being introduced into mold cavity 34, the effective dielectric constant of the mold cavity 34 is relatively low (as the dielectric constant of the air filling the mold cavity 34 is approximately equal to 1 ) and so the capacitance between first and second mold core pieces 30, 32 is relatively low.
  • the effective dielectric constant of the mold cavity 34 will progressively increase and the capacitance will therefore
  • the effective dielectric constant of the mold cavity 34 at any moment will result from the unique combination of air (unfilled portion of the mold cavity 34) and material 50 (filled portion of the mold cavity 34) in the mold cavity 34, giving a unique value of capacitance directly related to the amount of material 50 inside the mold cavity 34.
  • the controller 70 continuously measures this changing capacitance.
  • the changing capacitance measured by controller 70 may follow curve 80.
  • the time, T at which capacitance begins to increase indicates when valved gate 58 opens and material 50 begins to flow into mold cavity 34.
  • the maximum rate of change of capacitance occurs between about times T 2 and T 4 as the mold cavity 34 fills and this rate of increase in capacitance slows.
  • the capacitance reaches a maximum value, CM, at about T 5 once the mold cavity 34 is full.
  • Curve 80 may represent the expected curve when the injection molding machine 10 is operating normally.
  • valved gate 58 opened late, then the measured capacitance would not begin to increase until a time after T-i . This result is shown by curve 82 where capacitance does not begin to increase until time T 3 .
  • the controller 70 may start monitoring capacitance at the nominal time when material 50 begins to be injected into the mold cavity 34 (S100). Monitoring could begin, for example, the time at which the controller 70 signals the screw injector 42 to begin operating, or the time when the controller 70 signals the valved gate 58 to open.
  • the controller 70 may store an upper bound for the initial capacitance, C
  • the controller 70 may also store a lower bound for the time when capacitance begins to increase such that if capacitance does not begin to increase by this time (as illustrated by curve 82) (S106), the controller 70 can determine a fault condition and may output a signal indicative of a faulty gate and/or change the timing or initial position of the gate so that it opens earlier in the mold cycle (S108). Where, on the other hand, the lower bound is within specification, the controller may report this (S109).
  • the controller 70 may store a threshold value (lower bound) for the maximum rate of change of capacitance during a mold cycle.
  • the controller 70 can determine a fault condition. Given this circumstance, the controller 70 could simply signal the fault or could take corrective action, specifically, increase the current to the heater assembly 52 in order to increase the temperature of the material 50 (S112) or increase the speed of the screw drive 46. With a low rate of change of capacitance, the controller could also increase the temperature of other heaters (not shown) of the injection molding machine, such as manifold zone heaters (not shown). If the maximum rate of change of capacitance is within specification, the controller may report this
  • the controller may store a threshold value (lower bound) for the final value of the capacitance such that if the final value is below this threshold value (as illustrated by curve 84) (S114), it can determine a fault condition. Given this circumstance, the controller could simply signal the fault, or could eject the resultant molded project to a reject bin (not shown) (S116). Where the final value of the capacitance meets the threshold value, the controller may report that this parameter is within specification (S118).
  • the controller 70 may cease measuring capacitance (S120).
  • fault conditions reported by the controller may be used to prescribe maintenance requirements for the injection molding machine 10.
  • controller 70 could, for example, store a curve of the expected varying capacitance in an ideal mold cycle and compare this curve to actual curves measured during a mold cycle, basing action taken on variances between the ideal curve and the measured curve.
  • molds for products of intricate shape may have, in addition to two main mold core pieces, additional mold core pieces, with all of these pieces coming together to form the mold cavity 34.
  • each of these mold core pieces could be electrically isolated from each other and a voltage applied between several different pairs of these mold core pieces in order to form different capacitors having electric fields centered across different portions of the mold cavity 34.
  • each mold core piece could be manufactured with one or more dielectric inserts which electrically partition the mold core piece into two or more capacitive elements. This would allow the mold core pieces to form multiple capacitors for measuring changing capacitance with precision at different portions of the mold cavity 34.
  • Injection molding machine 10 is shown with one mold cavity 34.
  • a molding machine 200 may have a mold 224 with mold portions 226 and 228 having mold core pieces 230, 232 that define multiple, typically identical, mold cavities 234a, 234b, 234c that are electrically isolated by electrical isolators 260' and 260".
  • voltage generator and capacitance measurement circuitry 266a, 266b, 266c may be connected across each of electrically isolated areas to a controller 270 which independently measure capacitance(s) across each mold cavity 234a, 234b, and 234c and takes appropriate action based on the capacitance curve(s) for each mold cavity 234a, 234b, and 234c.
  • the controller can use the capacitance measurements at each cavity to determine in real time whether the fill rates of the cavities are balanced. On sensing an imbalance, the controller may indicate a fault condition and/or take corrective action, such as adjusting a zone heater. With this operation, the need for short-shot balance testing is avoided.
  • first and second mold core pieces 30, 32 as the capacitive elements allows for the capacitive surfaces to extend on opposite sides of the mold cavity 34 which allows capacitance to be measured more globally in the mold cavity 34 than would be the case with a separate capacitor at the mold cavity 34 surface.
  • first and second mold core pieces 30, 32 as the capacitive elements avoids the risk of a witness mark that could result from positioning a separate capacitor at the mold cavity 34 surface. Nevertheless, useful
  • measurements of changing capacitance over the mold cycle could, at least for some molding machines, still be obtained by a separate capacitor at the mold cavity 34 surface, and so this is contemplated as an option for such machines.
  • valved gate 58 is shown as a valved gate, it will be appreciated by those skilled in the art that the gate may not have a valve.
  • controller 70 has been described as the master controller for the injection molding machine, in alternative non-limiting embodiments, controller 70 could be a sub-controller that monitors changing capacitance and communicates with a separate master controller to signal a fault condition. Controller 70 will typically be a digital controller (operating with digital to analog and analog to digital converters where required). However, the controller 70 could also be an analog controller 70. Furthermore, as will be apparent to those skilled in the art, controller 70 could be replaced with electromechanical controls that perform the same functions as controller 70.
  • voltage generator 66 has been described as a separate element, the voltage generator 66 could be part of the controller.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Mechanical Engineering (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)

Abstract

Selon la présente invention, une tension est appliquée entre des composants isolés électriquement pour créer un champ électrique dans une cavité du moule (24) d'une machine de moulage. La capacitance résultante est mesurée pendant la durée pendant laquelle le matériau est introduit dans la cavité de moule (34). Au fur et à mesure que le matériau est introduit, la constante diélectrique effective de la cavité change de telle sorte que la capacitance mesurée change. Si le changement de la capacitance se situe en dehors de limites prédéfinies, une situation de défaut est déterminée.
PCT/US2013/054076 2012-10-17 2013-08-08 Surveillance de moule capacitive WO2014062281A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201261714770P 2012-10-17 2012-10-17
US61/714,770 2012-10-17

Publications (1)

Publication Number Publication Date
WO2014062281A1 true WO2014062281A1 (fr) 2014-04-24

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107589154A (zh) * 2016-07-08 2018-01-16 群达模具(深圳)有限公司 一种模内熔体传感器和模内熔体传感系统
US20220365144A1 (en) * 2020-09-16 2022-11-17 Landis+Gyr Innovations, Inc. In-situ testing of electric double layer capacitors in electric meters

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5595693A (en) * 1993-12-27 1997-01-21 Toshiba Machine Co., Ltd. Method for automatically setting injection molding speed condition in injection molding machine
US5919492A (en) * 1997-06-13 1999-07-06 Tarr; John Injection molding system with sequential gate control
US20050194705A1 (en) * 2004-03-03 2005-09-08 Smith Roger P. Plastic forming process monitoring and control
US20070185611A1 (en) * 2001-03-21 2007-08-09 Signature Control Systems, Inc. Controlling the Curing of a Rubber Compound
US20090243131A1 (en) * 2006-09-19 2009-10-01 Sumitomo Heavy Industries, Ltd. Injection Molding Machine and Control Method of the Injection Molding Machine
US20120123583A1 (en) * 2010-11-16 2012-05-17 Mks Instruments, Inc. Controlling a Discrete-Type Manufacturing Process with a Multivariate Model

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5595693A (en) * 1993-12-27 1997-01-21 Toshiba Machine Co., Ltd. Method for automatically setting injection molding speed condition in injection molding machine
US5919492A (en) * 1997-06-13 1999-07-06 Tarr; John Injection molding system with sequential gate control
US20070185611A1 (en) * 2001-03-21 2007-08-09 Signature Control Systems, Inc. Controlling the Curing of a Rubber Compound
US20050194705A1 (en) * 2004-03-03 2005-09-08 Smith Roger P. Plastic forming process monitoring and control
US20090243131A1 (en) * 2006-09-19 2009-10-01 Sumitomo Heavy Industries, Ltd. Injection Molding Machine and Control Method of the Injection Molding Machine
US20120123583A1 (en) * 2010-11-16 2012-05-17 Mks Instruments, Inc. Controlling a Discrete-Type Manufacturing Process with a Multivariate Model

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107589154A (zh) * 2016-07-08 2018-01-16 群达模具(深圳)有限公司 一种模内熔体传感器和模内熔体传感系统
US20220365144A1 (en) * 2020-09-16 2022-11-17 Landis+Gyr Innovations, Inc. In-situ testing of electric double layer capacitors in electric meters
US11680995B2 (en) * 2020-09-16 2023-06-20 Landis+Gyr Innovations, Inc. In-situ testing of electric double layer capacitors in electric meters

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