Method for Controlling a Rate or Force of a Clamp in a Molding System Using One or More Strain Gauges

Abstract

A method of monitoring and controlling a molding clamping apparatus in an injection molding or other molding process is disclosed. The method includes creating a target strain profile, receiving a deviation limit, receiving a change in strain relating to a mold while it is closing from a first strain gauge, identifying a deviation from a target strain profile based on the output from the first strain gauge, determining that the deviation exceeds the deviation limit, and adjusting the rate or force of clamp movement. The target strain profile may have a first portion relating to a clamp closing process, a second portion relating to a filling process, and a third portion relating to a clamp opening process. The first portion relating to the clamp closing process may include an intermediate portion relating to a coining process having an intermediate clamp force setpoint.

Claims

1. A method of monitoring and controlling a molding clamping apparatus comprising: creating, by one or more processors, a target strain profile for a clamping and unclamping process of a molding apparatus; receiving, via an interface, an upper deviation limit and a lower deviation limit for the target strain profile; receiving, as an output from a first strain gauge, a change in strain in a mold; identifying, by the one or more processors, a deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge; comparing, by the one or more processors, the deviation to the upper deviation limit or the lower deviation limit; determining, by the one or more processors, that the deviation exceeds the upper deviation limit or the lower deviation limit and adjusting a rate or a force of clamp movement.

2. The method of monitoring and controlling a molding clamping apparatus of claim 1, wherein the first strain gauge is located on an outside surface of the mold and is configured to be portable between multiple locations on the outside surface of the mold or to a second mold or to a strain gauge bracket.

3. The method of monitoring and controlling a molding clamping apparatus of claim 1, wherein the first strain gauge is a strain pin installed on a cavity block outside the molding surface.

4. The method of monitoring and controlling a molding clamping apparatus of claim 1, and: receiving, as an output from a supplemental strain gauge, a supplemental change in strain; and identifying, by the one or more processors, the deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge and the supplemental sensed change in strain provided as the output from the supplemental strain gauge.

5. The method of monitoring and controlling a molding clamping apparatus of claim 1, wherein adjusting the rate or the force of clamp movement includes adjusting a flow of oil to at least one hydraulic valve.

6. The method of monitoring and controlling a molding clamping apparatus of claim 1, wherein adjusting the rate or the force of clamp movement includes adjusting an electric current or voltage to an electric motor.

7. The method of monitoring and controlling a molding clamping apparatus of claim 1, wherein the target strain profile has a first portion relating to a clamp closing process, a second portion relating to a filling process, and a third portion relating to a clamp opening process.

8. The method of monitoring and controlling a molding clamping apparatus of claim 7, wherein the first portion relating to the clamp closing process includes an intermediate portion relating to a coining process having an intermediate clamp force setpoint.

9. A non-transitory computer-readable storage medium storing processor-executable instructions that, when executed, cause one or more processors to: create, by one or more processors, a target strain profile for a clamping and unclamping process of a molding apparatus; receive, via an interface, an upper deviation limit and a lower deviation limit for the target strain profile; receive, as an output from a first strain gauge, a change in strain in a mold; identify, by the one or more processors, a deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge; compare, by the one or more processors, the deviation to the upper deviation limit or the lower deviation limit; determine, by the one or more processors, that the deviation exceeds the upper deviation limit or the lower deviation limit and adjust a rate or a force of clamp movement.

10. The non-transitory computer-readable storage medium storing processor-executable instructions of claim 9, wherein the processor-executable instructions, when executed, cause the one or more processors to: receive, as an output from a supplemental strain gauge, a supplemental change in strain; and identify, by the one or more processors, the deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge and the supplemental sensed change in strain provided as the output from the supplemental strain gauge.

11. The non-transitory computer-readable storage medium storing processor-executable instructions of claim 9, wherein the processor-executable instructions, when executed, cause the one or more processors to: adjust the rate or the force of clamp movement by adjusting a flow of oil to at least one hydraulic valve.

12. The non-transitory computer-readable storage medium storing processor-executable instructions of claim 9, wherein the processor-executable instructions, when executed, cause the one or more processors to: adjust the rate or the force of clamp movement by adjusting an electric current or voltage to an electric motor.

13. The non-transitory computer-readable storage medium storing processor-executable instructions of claim 9, wherein the processor-executable instructions, when executed, cause the one or more processors to: create, by one or more processors, a first portion of the target strain profile relating to a clamp closing process, a second portion of the target strain profile relating to a filling process, and a third portion of the target strain profile relating to a clamp opening process.

14. The non-transitory computer-readable storage medium storing processor-executable instructions of claim 13, wherein the processor-executable instructions, when executed, cause the one or more processors to: create, by one or more processors, an intermediate portion relating to a coining process having an intermediate clamp force setpoint, the intermediate portion included in the first portion of the target strain profile relating to a clamp closing process.

15. A client device comprising one or more processors, one or more interfaces, and a non-transitory computer-readable memory storing thereon instructions that, when executed by the one or more processors, cause the client device to: create, by one or more processors, a target strain profile for a clamping and unclamping process of a molding apparatus; receive, via an interface, an upper deviation limit and a lower deviation limit for the target strain profile; receive, as an output from a first strain gauge, a change in strain in a mold; identify, by the one or more processors, a deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge; compare, by the one or more processors, the deviation to the upper deviation limit or the lower deviation limit; determine, by the one or more processors, that the deviation exceeds the upper deviation limit or the lower deviation limit and adjust a rate or a force of clamp movement.

16. The client device of claim 15, wherein the instructions, when executed by the one or more processors, cause the client device to: receive, as an output from a supplemental strain gauge, a supplemental change in strain; and identify, by the one or more processors, the deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge and the supplemental sensed change in strain provided as the output from the supplemental strain gauge.

17. The client device of claim 15, wherein the instructions, when executed by the one or more processors, cause the client device to: adjust the rate or the force of clamp movement by adjusting a flow of oil to at least one hydraulic valve.

18. The client device of claim 15, wherein the instructions, when executed by the one or more processors, cause the client device to: adjust the rate or the force of clamp movement by adjusting an electric current or voltage to an electric motor.

19. The client device of claim 15, wherein the instructions, when executed by the one or more processors, cause the client device to: create, by one or more processors, a first portion of the target strain profile relating to a clamp closing process, a second portion of the target strain profile relating to a filling process, and a third portion of the target strain profile relating to a clamp opening process.

20. The client device of claim 19, wherein the instructions, when executed by the one or more processors, cause the client device to: create, by one or more processors, an intermediate portion relating to a coining process having an intermediate clamp force setpoint, the intermediate portion included in the first portion of the target strain profile relating to a clamp closing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 illustrates, semi-schematically, a conventional injection molding apparatus, wherein a first portion of strain gauge sensor assembly containing a strain gauge is placed adjacent to a first mold side in the vicinity of the nozzle to the mold cavity and a second portion of the strain gauge sensor assembly is placed on a second mold side downstream of the nozzle and is configured to contact the first portion of the strain gauge sensor assembly when the mold is in a closed position.

[0021] FIG. 1A illustrates an enlarged perspective view of the first and second portions of the strain gauge sensor assembly depicted in FIG. 1.

[0022] FIG. 2 illustrates schematically clamp force control of a hydraulic clamping mechanism.

[0023] FIG. 3 illustrates schematically clamp force control of an electric clamping mechanism.

[0024] FIG. 4 is an exemplary target strain profile during clamp closing.

[0025] FIG. 4A is an exemplary target strain profile during clamp closing with an intermediate step.

[0026] FIG. 5 is an exemplary target strain profile for clamping force during injection of plastic and filling of the mold.

[0027] FIG. 6 is an exemplary target strain profile during clamp opening.

[0028] FIG. 7 is an exemplary target strain profile for clamping forces application throughout the entire molding process.

[0029] FIG. 8 is a flow diagram of an example method of monitoring and controlling a rate or a force of clamp movement.

[0030] FIG. 9A illustrates a conventional injection molding apparatus having a first mold installed with portable strain gauges sensor assemblies provided on the first mold.

[0031] FIG. 9B illustrates the conventional injection molding apparatus of FIG. 9A where the portable strain gauge sensor assemblies have been removed from the first mold and stored in a strain gauge bracket provided on the molding apparatus.

[0032] FIG. 9C illustrates the conventional injection molding apparatus of FIGS. 9A and 9B where the first mold has been removed, a second mold has been installed, and the portable strain gauge sensor assemblies have been removed from the strain gauge bracket and provided on the second mold.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Referring to the figures in detail, FIG. 1 illustrates an exemplary injection molding apparatus 10 for producing thermoplastic parts in high volumes (e.g., a class 101 injection mold, or an ultra-high productivity mold, a class 102 (medium-to-high productivity mold), or class 103 (a medium productivity mold)). The injection molding apparatus 10 generally includes an injection system 12 and a clamping system 14. A thermoplastic material may be introduced to the injection system 12 in the form of thermoplastic pellets 16. The thermoplastic pellets 16 may be placed into a hopper 18, which feeds the thermoplastic pellets 16 into a heated barrel 20 of the injection system 12. The thermoplastic pellets 16, after being fed into the heated barrel 20, may be driven to the end of the heated barrel 20 by a ram, such as a reciprocating screw 22. The heating of the heated barrel 20 and the compression of the thermoplastic pellets 16 by the reciprocating screw 22 causes the thermoplastic pellets 16 to melt, forming a molten thermoplastic material 24. The molten thermoplastic material is typically processed at a temperature of about 130 C. to about 410 C.

[0034] The reciprocating screw 22 forces the molten thermoplastic material 24 toward a nozzle 26 to form a shot of thermoplastic material, which will be injected into a mold cavity 32 of a mold 28 via one or more gates. The molten thermoplastic material 24 may be injected through a gate 30, which directs the flow of the molten thermoplastic material 24 to the mold cavity 32. In some instances, more than one gate 30 may be provided per mold cavity 32. The mold cavity 32 is formed between first and second mold sides 25, 27 of the mold 28 and the first and second mold sides 25, 27 are held together under pressure by a press or clamping unit 34. The press or clamping unit 34 applies a clamping force during the molding process that is greater than the force exerted by the injection pressure acting to separate the two mold halves 25, 27, thereby holding the first and second mold sides 25, 27 together while the molten thermoplastic material 24 is injected into the mold cavity 32. In a typical high variable pressure injection molding machine, the press typically exerts 30,000 psi or more because the clamping force is directly related to injection pressure. To support these clamping forces, the clamping system 34 may include a mold frame and a mold base.

[0035] Once the shot of molten thermoplastic material 24 is injected into the mold cavity 32, the reciprocating screw 22 stops traveling forward. The molten thermoplastic material 24 takes the form of the mold cavity 32 and the molten thermoplastic material 24 cools inside the mold 28 until the thermoplastic material 24 solidifies. Once the thermoplastic material 24 has solidified, the press 34 releases the first and second mold sides 25, 27, the first and second mold sides 25, 27 are separated from one another, and the finished part may be ejected from the mold 28. The mold 28 may include a plurality of mold cavities 32 to increase overall production rates. The shapes of the cavities of the plurality of mold cavities may be identical, similar or different from each other. (The latter may be considered a family of mold cavities).

[0036] A controller 50 is communicatively connected with a strain gauge sensor 52, a screw control 36, and a temperature sensor 70. The strain gauge 52 may be located on a first portion of a strain gauge assembly 58, which is secured to the exterior surface of a first mold side 25 near the parting line between the first mold side 25 and the second mold side 27 and in the vicinity of the nozzle 26. In other embodiments within the scope of the present disclosure, the strain gauge 52 may be located directly on the mold 28 or in another location in the injection molding apparatus 10 altogether. The temperature sensor 70 is located near the strain gauge 52. The controller 50 may include a microprocessor (or another suitable processing unit, or several such units), a non-transitory memory, and one or more communication links.

[0037] In some embodiments, as shown in FIG. 1A, the first mold side 25 has holes drilled therein. A first portion of a strain gauge sensor assembly 58 is secured to the first mold side 25 by bolts 82 that are inserted through the first portion of the strain gauge sensor assembly and into the first mold side 25 and by a peg 84 which is inserted partially into the first portion of a strain gauge sensor assembly 58 and partially into a hole in the first mold side 25. The second mold side 27 has holes drilled into it, and second portion of the strain gauge sensor assembly 62 is secured to the second mold side 27 by a bolt 88 that is inserted through the second portion of the strain gauge sensor assembly 62 into the second mold side 27 and by a peg 90 which is inserted partially into the second portion of the strain gauge sensor assembly 62 and partially into a hole in the second mold side 27. A side of the second portion of the strain gauge sensor assembly 62 is aligned with the parting line of the mold 28 along an edge of second mold side 27 and is configured to contact the first portion of the strain gauge sensor assembly 58 when the mold 28 is closed.

[0038] Data from the strain gauge sensor 52 and the temperature sensor 70 may be communicated to a processor that calculates a change in strain. Electric signals from the strain gauge sensor 52 and temperature sensor 70 may travel along one or more electrical paths, such as wires 54, depicted in FIG. 1 in solid lines, ranging in strength from 10 to 10 Volts. The controller 50 may be connected to the screw control 36 via wired connection 56. In other embodiments, the controller 50 may be connected to the screw control 36 via a wireless connection, a mechanical connection, a hydraulic connection, a pneumatic connection, or any other type of communication connection known to those having ordinary skill in the art that will allow the controller 50 to communicate with the screw control 36.

[0039] Additionally, the controller 50 is in communication with a virtual cavity sensor 51, which is implemented as a program, or a set of software instructions. In this disclosure, the term virtual cavity sensor can refer to a module that determines the value of a process variable, such as pressure or a rate or force exerted by clamping unit 34, without directly measuring this process variable. The virtual cavity sensor 51 strives to achieve a target strain profile in the injection molding apparatus 10 over time. The target strain profile may relate, for example, to a rate or a force of movement of the clamping unit 34. In some instances, the virtual cavity sensor 51 in conjunction with the controller 50 is able to achieve the target strain profile on its own. In some instances, problems may arise that cannot be corrected by the virtual cavity sensor 51 in conjunction with the controller 50. In such an instance, the virtual cavity sensor 51 activates an alarm 104. The alarm 104 may be a visual alarm, such as a flashing light or a pop-up window on a computer screen, or may be an audible alert such as a beeping sound or siren, or may be both visual and audible.

[0040] FIG. 2 illustrates a side view of a hydraulic clamping system apparatus 200, which could be used in a system similar to that depicted in FIGS. 1 and 1A. Alternatively, the mold 208, 210 could be used in other molding processes, such as a substantially constant pressure injection molding process, an injection-blow molding process, a metal injection molding (MIM) process, a reaction injection molding (RIM) process, a liquid injection molding (LIM) process, a structural foam molding process, a liquid crystal polymer (LCP) molding process and an injection-stretch blow molding process. One or more sensors 202 are located on the mold 208, 210 to measure the amount of strain exhibited by the mold during the molding process. The sensors 202 may be strain gauges or strain pins. One of the sensors 202 may be considered a first or primary strain gauge, while the other may be considered a supplemental strain gauge. A controller 212, optionally in conjunction with a virtual cavity sensor (not depicted), compares the strain value to a target strain profile and increases or decreases the flow of hydraulic oil to piston valves 206 and/or lock nut valves 204 to increase or decrease the amount of clamping force or the rate of clamping accordingly.

[0041] FIG. 3 illustrates a side view of an electric clamping system apparatus 300, which could be used in a system similar to that depicted in FIGS. 1 and 1A. Alternatively, the mold 304, 306 could be used in other molding processes, such as a substantially constant pressure injection molding process, an injection-blow molding process, a metal injection molding (MIM) process, a reaction injection molding (RIM) process, a liquid injection molding (LIM) process, a structural foam molding process, a liquid crystal polymer (LCP) molding process and an injection-stretch blow molding process. One or more sensors 302 are located on the mold 304, 306 to measure the amount of strain exhibited by the mold during the molding process. The sensors 202 may be strain gauges or strain pins. One of the sensors 202 may be considered a first or primary strain gauge, while the other may be considered a supplemental strain gauge. A controller 310, optionally in conjunction with a virtual cavity sensor (not depicted), compares the strain value to a target strain profile and increases or decreases the electric current and/or voltage to electric motor 308 to increase or decrease the amount of clamping force or rate of clamping accordingly.

[0042] FIG. 4 is an exemplary target strain profile 400 during clamp closing. During initial mold closing 402 there is no mold contact and no strain change. Once mold contact occurs 404, there is an increase in strain until clamp force setpoint is reached 406.

[0043] FIG. 4A is an exemplary target strain profile during clamp closing with an intermediate step, otherwise known as coining. During initial mold closing 402 there is no mold contact and no strain change. Once mold contact occurs 404, there is an increase in strain until intermediate clamp force setpoint is reached 408. A further increase in strain is experienced during injection 404 until final clamp force setpoint is reached 406.

[0044] FIG. 5 is an exemplary strain profile 500 for clamping force during injection of plastic. Once the mold has been closed 502 and plastic starts to fill the mold 504, the clamping force varies during fill based on the target strain profile.

[0045] FIG. 6 is an exemplary strain profile 600 during clamp opening. Once the part has been cooling and starts to shrink away from the molding surfaces a decrease in strain will start to occur 602. Based on the target strain profile, the clamp will reduce force to zero 604 and start to open.

[0046] FIG. 7 is an exemplary strain profile 700 for clamping forces application throughout the entire molding process. The mold closes and starts to apply force 702 followed by the filling of the mold with plastic 704. As the part cools 706, the clamping force is decreased and the mold opens 708.

[0047] FIG. 8 is a flow diagram of an example method 800 of monitoring and controlling a rate or a force of clamp movement. Box 802 illustrates creating, by one or more processors, a target strain profile for a clamping and unclamping process of a molding apparatus. Box 804 illustrates receiving, via an interface, an upper deviation limit and a lower deviation limit for the target strain profile. Box 806 illustrates receiving, as an output from a first strain gauge, a change in strain in a mold. Box 808 illustrates identifying, by the one or more processors, a deviation from the target strain profile based on the sensed change in strain provided as the output from the first strain gauge. Box 810 illustrates comparing, by the one or more processors, the deviation to the upper deviation limit or the lower deviation limit. Box 812 illustrates determining that the deviation exceeds the upper deviation limit or the lower deviation limit and adjusting a rate or a force of clamp movement.

[0048] FIGS. 9A-9C illustrate the use of strain gauge sensor assemblies 58 in different molds 28 interchangeable in the same injection molding apparatus 10. In FIG. 9A, a first mold 28a is used in injection molding apparatus 10. Strain gauge sensor assemblies 58 are provided on first and second mold sides 25a and 27a of the first mold 28a. As shown in FIG. 9B, the strain gauge sensor assemblies 58 are removed from the first mold 28a and placed in a strain gauge bracket 99 on the injection molding apparatus 10. First mold 28a is then removed from the injection molding apparatus 10 and a second mold 28b is installed. As shown in FIG. 9C, after installation of second mold 28b, the strain gauge sensor assemblies 58 are removed from the strain gauge bracket 99 and provided on first and second mold sides 25b and 27b of the second mold 28b. Although FIGS. 9A-9C depict the portability of strain gauge sensor assemblies 58 from a first mold 28a to a second mold 28b, the strain gauge sensor assemblies 58 could likewise be moved from a first location on a mold 28 to a second location on a mold 28. Further, a single strain gauge assembly 58 or more than two strain gauge assemblies 58 could be portable between various locations and molds 28.

[0049] While specific embodiments have been described herein, variations may be made to the described embodiments that are still considered within the scope of the appended claims.