System and method for manufacturing part

Abstract

Systems and methods are provided for controlling a molding machine having a mold forming a mold cavity, a nozzle, and a screw that moves toward the nozzle from a first position to a second position and is controlled according to a molding cycle. In one embodiment, a method includes injecting a molten polymer into a mold cavity and acquiring a first measurement of a variable during an injection cycle using a first sensor positioned at or near a screw. A second sensor positioned at or near the nozzle is used to acquire a second measurement of the variable during the injection cycle. The measured compressibility ratio is determined in the form of a difference between the measured variable acquired by the first sensor and the measured variable acquired by the second sensor. The measured compressibility ratio is compared to a reference compressibility ratio and at least one control parameter is adjusted based on a difference between the reference compressibility ratio and the measured compressibility ratio.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 352,518, filed on June 15, 2022, and U.S. Provisional Application No. 63 / 417,913, filed on October 20, 2022, the entire contents of each of which are expressly incorporated by reference. Technical Field

[0002] The present disclosure relates generally to molding, and more particularly, to methods for controlling injection and / or extrusion molding machines using sensor-based measurements. Background Art

[0003] Molding, and specifically injection and extrusion molding, are techniques commonly used to mass-produce parts made of thermoplastic materials. During a repeated injection molding process and a continuous extrusion molding process, thermoplastic resins are typically introduced into an injection molding machine in the form of small pellets or beads, which melt the small pellets under heat and pressure. During the injection cycle, the molten material is forcibly injected into a mold cavity having a specific desired cavity shape. The injected plastic is maintained under pressure within the mold cavity and is subsequently cooled and removed as a solidified part having a shape that is very similar to the cavity shape of the mold. A single mold can have any number of independent cavities, which can be connected to flow channels through gates that can direct the molten resin into the cavity. The typical injection molding process generally includes four basic operations: (1) heating the plastic in an injection molding machine to allow the plastic to flow under pressure; (2) injecting the molten plastic into one or more mold cavities, which are defined between two closed mold halves; (3) allowing the plastic to cool and harden under pressure in the one or more cavities; and (4) opening the mold halves and ejecting the part from the mold. After the part is ejected from the mold, the device (e.g., a screw or auger) that injects the molten plastic into the one or more mold cavities enters a recovery phase during which the device returns to its original position. In the extrusion process, the molten material is continuously and forcibly extruded through a die having a specific desired shape. The extruded plastic is then cooled and removed as a solidified part having a shape that is very similar to the shape of the die orifice. The molded part is provided in an elongated shape, tube, or other form and is then cut to the desired length. The typical extrusion process generally includes three basic operations: (1) heating the plastic in the extruder to allow the plastic to flow under pressure; (2) extruding the molten plastic through one or more dies; and (3) allowing the plastic to cool and harden. Each of these operations usually occurs simultaneously or nearly simultaneously.

[0004] In these systems, a control system controls the molding process according to an injection cycle that defines a series of control values ​​for various components of the molding machine. For example, an injection cycle or other molding operation can be driven by a fixed and / or variable melt pressure and / or screw rate profile (or screw rotation rate profile), where the controller uses, for example, pressure sensed at a particular location (e.g., a nozzle) and / or material or extrudate properties (such as, for example, screw rate as an input to determine the driving force applied to the material).

[0005] Increasing environmental awareness can lead to an increased use of sustainable manufacturing processes. For example, post-consumer regrind or recycled plastic materials are increasingly being used as materials for forming molded parts. Sometimes, these materials can come from different product batches that may not have been properly sorted, and therefore, subsequent batches of plastics may have different material properties. In addition, even if the products are properly sorted before being reused in manufacturing, each individual container in a particular batch may have different viscosity and / or density characteristics. Therefore, the molten polymer material obtained from the reused container for forming the part may not have uniform material properties, such as viscosity and / or density.

[0006] Furthermore, when molding with regrind material, material properties, such as viscosity and / or density, are likely to change within a single injection cycle and / or extrusion run. While existing systems are capable of determining and accounting for changes in viscosity of molten polymeric materials, such systems often fail to account for the distinction between changes in viscosity and density of a material, and may apply the same adjustments to the operation of the molding process if a change in either viscosity or density is sensed. As a result, these molding machines may produce lower quality parts, resulting in inefficient operations, and these lower quality parts must be removed during quality control inspections. Furthermore, because a molding run can include hundreds or even thousands of pounds of material, the properties of the molten plastic material are not constant from run to run. Therefore, even if the molding cycle is adapted to account for changes in material properties at the beginning of a run, the changed properties may still result in the production of lower quality parts and / or parts with different properties later in the run. Summary of the invention

[0007] Embodiments within the scope of the present invention relate to controlling a molding machine to produce repetitive and consistent parts. A system and method for controlling a molding machine is provided, the molding machine having a mold forming a mold cavity, a nozzle, and a screw that moves from a first position to a second position toward the nozzle and is controlled according to a molding cycle. The method includes injecting a molten polymer into the mold cavity and obtaining a first measurement of a variable using a first sensor positioned at or near the screw during the injection cycle. A second sensor positioned at or near the nozzle is used to obtain a second measurement of the variable during the injection cycle. A measured compressibility ratio value is determined as a difference between the measured variable obtained by the first sensor and the measured variable obtained by the second sensor. The measured compressibility ratio value is compared to a reference compressibility ratio value and at least one control parameter is adjusted based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0008] In some methods, the variable measured is in the form of the compressibility of the molten plastic material. In some forms, the compressibility of the molten plastic material can be used to determine its density value.

[0009] In some of these examples, the first sensor can be positioned behind the proximal end of the screw. The first sensor can be in the form of a force sensor. In some examples, the second sensor can be positioned in a flow channel of the injection unit upstream of the mold cavity.

[0010] In some forms, the step of adjusting at least one control parameter includes adjusting a target injection pressure value. In other forms, the method may include the steps of measuring a shear rate of the molten plastic material to determine a change in a viscosity value of the molten plastic material and adjusting at least one control parameter based on a difference between the measured shear rate and a reference shear rate.

[0011] In these and other examples, the reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during a previous injection cycle. The previous injection cycle may be in the form of a verification cycle or a prediction cycle.

[0012] According to a second aspect, a molding machine includes a molding unit, a controller, a first sensor, and a second sensor. The injection unit includes a mold forming a mold cavity and a screw, the screw moving from a first position to a second position toward a nozzle. The injection unit receives molten plastic material via the screw and the nozzle and injects it into the mold cavity to form a molded part. The controller controls the operation of the injection molding machine according to a molding cycle. The first sensor is positioned at or near the screw and is communicatively coupled to the controller and measures a variable during the injection cycle. The second sensor is positioned at or near the nozzle and is communicatively coupled to the controller and measures a variable at a second time during the injection cycle. The controller starts injecting the molten polymer into the mold cavity and determines a measured compressibility ratio value, the measured compressibility ratio value being in the form of a difference between a measured variable obtained by the first sensor and a measured variable obtained by the second sensor. The controller further compares the measured compressibility ratio value with a reference compressibility ratio value and adjusts at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0013] According to a third aspect, there is provided a system and method for controlling a molding machine having a die that forms a profile and a screw that rotates at a variable rate and the molding machine is controlled according to configured molding parameters, and includes extruding a molten polymer through a die and obtaining a first measurement of a variable using a first sensor positioned at or near the rear of the screw. A second sensor positioned at or near the die is used to obtain a second measurement of the variable. A measured compressibility ratio value is determined, the measured compressibility ratio value being in the form of a difference between a measured variable obtained by the first sensor and a measured variable obtained by the second sensor. The measured compressibility ratio value is compared to a reference compressibility ratio value and at least one control parameter is adjusted based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0014] In some methods, the variable measured is in the form of the compressibility of the molten plastic material. In some forms, the compressibility of the molten plastic material can be used to determine its density value.

[0015] In some of these examples, the first sensor may be positioned behind the proximal end of the screw. The first sensor may be in the form of a force sensor. In some examples, the second sensor may be positioned within the flow channel of the injection unit upstream of the die. In other examples, the second sensor may be positioned outside the flow channel of the molding unit. In some forms, the third sensor is positioned within the flow channel of the molding unit upstream of the die. In yet other examples, the third sensor is positioned outside the flow channel of the molding unit.

[0016] In some forms, the step of adjusting at least one control parameter includes adjusting a target molding pressure value. In other forms, the method may include the steps of measuring a shear rate of the molten plastic material to determine a change in a viscosity value of the molten plastic material and adjusting at least one control parameter based on a difference between the measured shear rate and a reference shear rate.

[0017] In these and other examples, the reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during a previous operating period. The previous operating period may be in the form of a validation run or a predictive run.

[0018] According to a fourth aspect, a molding machine includes a molding unit, a controller, a first sensor, and a second sensor. The molding unit includes a die that forms a profile and a screw that rotates at a variable rate. The molding unit receives extruded molten plastic material and extrudes the molten plastic material through the profile via the screw to form a molded part. The controller controls the operation of the molding machine according to configured parameters. The first sensor is positioned at or near the screw and is communicatively coupled to the controller, and measures a variable during operation. The second sensor is positioned at or near the die and is communicatively coupled to the controller, and measures a variable in a second time during operation. The controller starts extruding the molten polymer through the die and determines a measured compressibility ratio value, the measured compressibility ratio value being in the form of a difference between a measured variable obtained by the first sensor and a measured variable obtained by the second sensor. The controller further compares the measured compressibility ratio value with a reference compressibility ratio value and adjusts at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Although this specification is summarized with claims that specifically point out and explicitly require to be considered as the subject matter of the present invention, it is believed that the present invention will be better understood by the following description in conjunction with the drawings. In order to more clearly show other elements, some of the drawings in the drawings can be simplified by omitting selected elements. Such omission of elements in some drawings does not necessarily indicate the presence or absence of specific elements in any exemplary embodiment, and the difference can be clearly described in the corresponding written description. All drawings are not necessarily drawn to scale. For example, the size and / or relative position of some elements in the drawings can be exaggerated relative to other elements to help promote the understanding of various embodiments of the present invention.

[0020] Figure 1 shows a schematic view of an example injection molding machine having a controller coupled thereto according to various embodiments of the present disclosure;

[0021] Figure 2An example flow chart of an example injection cycle having a density based control method according to various embodiments of the present disclosure is shown;

[0022] Figure 3 shows a schematic view of an example extrusion apparatus having a controller coupled thereto according to various embodiments of the present disclosure; and

[0023] Figure 4 An example flow chart of an example molding cycle having a density-based control method according to various embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0024] In general, aspects of the present disclosure include systems and methods for controlling a molding machine (e.g., an injection molding machine and / or an extrusion molding machine) in which a plurality of sensors are positioned inline and upstream of a mold cavity or orifice to sense changes in the compressibility of a molten polymer. The sensors are arranged to calculate relative changes in the compressibility of the molten polymer during the injection process, and compare any relative changes to a reference value to determine whether corrective adjustments should be made to produce stable and consistent parts. This information can be used to adjust the melt pressure set point and / or the driving force on the molten polymer in real time.

[0025] The systems and methods described herein use a molding machine (e.g., an injection molding machine or other molding machine) that can operate at a substantially constant melt pressure value, as compared to conventional systems that include a steep ramp up of melt pressure until a peak pressure value is obtained, followed by a pressure drop until the injection cycle is completed. Such operation at a substantially constant pressure value advantageously eliminates the need to dynamically perform calculations based on sensor measurements due to changes in pressure values.

[0026] In some examples (and as will be described herein), a molding machine may incorporate a single sensor, two sensors, or more than two sensors for calculating density changes in real time.

[0027] Turning to the drawings, various forming processes are described. The methods described herein can be adapted to electric presses, servo hydraulic presses, hydraulic presses, and other known machines. Figure 1 and Figure 2 , describes the injection molding process; ref. Figure 3 and Figure 4 , describes the extrusion process. Figure 1As shown, the injection molding machine 100 includes an injection unit 102 and a clamp system 104. The injection unit 102 includes a hopper 106 that is adapted to receive a material in the form of pellets 108 or any other suitable form. In many of these examples, the pellets 108 may be a polymer or polymer-based material, such as post-consumer regrind (PCR). Other examples are possible.

[0028] The hopper 106 feeds the pellets 108 into the heating barrel 110 of the injection unit 102. After being fed into the heating barrel 110, the pellets 108 can be driven to the end of the heating barrel 110 toward the barrel end cap 110a by the reciprocating screw 112, which can be moved from a first, original position 112a to a plurality of subsequent positions to inject the first, second, third and / or any subsequent injections. The heating of the heating barrel 110 and the compression of the pellets 108 by the reciprocating screw 112 melt the pellets 108, thereby forming a molten plastic material or polymer 114. The molten plastic material 114 is typically processed within a selected temperature range of about 130°C to about 410°C (where the manufacturer of a particular polymer typically provides a recommended temperature range for a given material for an injection molding machine).

[0029] The reciprocating screw 112 includes a proximal end 113 and is advanced from a first position 112a to a second position 112b and forces the molten plastic material 114 to move toward the nozzle 116 to form an injection of the plastic material, which will eventually be injected into a mold cavity 122 of the mold 118 via one or more gates 120, which guide the molten plastic material 114 to flow toward the mold cavity 122. In other words, the reciprocating screw 112 is driven to apply force to the molten plastic material 114. In other embodiments, the nozzle 116 can be separated from the one or more gates 120 by a feeding system (not shown). The mold cavity 122 is formed between the first and second mold sides 125, 127 of the mold 118, and the first and second mold sides 125, 127 are held together under pressure via a press or clamp unit 124.

[0030] The press or clamp unit 124 applies a predetermined clamping force during the molding process that is greater than the force applied by the injection pressure acting to separate the two mold halves 125, 127, thereby holding the first and second mold sides 125, 127 together as the molten plastic material 114 is injected into the mold cavity 122. To support these clamping forces, the clamp system 104 may include a mold frame and a mold base, in addition to any number of other components, such as tie rods.

[0031] In some examples, once the injection of molten plastic material 114 is injected into mold cavity 122, reciprocating screw 112 stops moving forward. The molten plastic material 114 takes the form of mold cavity 122 and cools within mold 118 until plastic material 114 solidifies. After solidification, press 124 releases first and second mold sides 115, 117, and then separates the first and second mold sides 115, 117 from each other. Then, the finished part can be ejected from mold 118. Mold 118 can include any number of mold cavities 122 to improve overall productivity. The shape and / or design of the cavities can be the same, similar and / or different from each other. For example, a family mold can include cavities of related component parts that are intended to cooperate with each other or operate in other ways. In some forms, an "injection cycle" is defined as the steps and functions performed from the start of injection to ejection. After the injection cycle is completed, the recovery profile begins, during which the reciprocating screw 112 returns to the first position 112a.

[0032] The injection molding machine 100 also includes a controller 140 communicatively coupled to the machine 100 via a connection 145. The connection 145 may be any type of wired and / or wireless communication protocol suitable for transmitting and / or receiving electronic signals. In these examples, the controller 140 is in signal communication with at least one sensor, such as, for example, sensors 128, 130 disposed within or otherwise coupled to the machine 100 and the controller 140. In some examples, the first sensor 128 is located at or near the proximal end 113 of the nozzle 112, and the second sensor 130 is located within, at, or near the nozzle 116 at a location proximate to the mold cavity 122. It will be appreciated that any number of additional real and / or virtual sensors capable of sensing any number of characteristics of the mold 118 and / or the machine 100 may be used and may be placed at desired locations on the machine 100.

[0033] The controller 140 may be disposed at a variety of locations relative to the injection molding machine 100. As examples, the controller 140 may be integrated with the machine 100, contained in a housing mounted on the machine, contained in a separate housing positioned adjacent or proximate to the machine, or may be positioned remote from the machine. In some embodiments, the controller 140 may partially or fully control the functions of the machine via wired and / or wireless signal communications, as is known and / or commonly used in the art.

[0034] The sensors 128, 130 may be any type of sensor suitable for measuring (directly or indirectly) one or more properties of the molten plastic material 114 and / or parts of the machine 100. The sensors 128, 130 may measure any property of the molten plastic material 114 that is known and used in the art, such as, for example, compressibility, pressure value, temperature, flow rate, hardness, strain, viscoelasticity, or one or more of any number of or additional properties indicative of these properties. The sensors 128, 130 may or may not be in direct contact with the molten plastic material 114. In some examples, the sensors 128, 130 may be in the form of force sensors and / or transducers. In some examples, the sensors 128, 130 may be suitable for measuring any number of properties of the injection molding machine 100 and properties that are not only related to the molten plastic material 114. As an example, the sensors 128 , 130 may be pressure transducers that measure melt pressure (during an injection cycle) and / or back pressure (during an extrusion profile and / or a recovery profile) of the molten plastic material 114 at the nozzle 116 .

[0035] Each of the sensors 128, 130 generates a signal that is transmitted to an input of the controller 140. The controller 140 may receive the measurements and convert them into other properties of the molten plastic material 114, such as a viscosity value.

[0036] As previously described, in various embodiments, the first sensor 128 can be located at or near the distal end 113 of the screw 112. The second sensor 130 can be located at or near the nozzle 116, or at any location in the flow path before the material reaches the mold cavity 122 without being positioned inside (because the resulting pressure drop will result in a measured compressibility of zero value). Other suitable locations for the sensors 128, 130 are possible, such as, for example, anywhere in front of the stop ring of the screw 112.

[0037] The controller 140 is also in signal communication with the screw control 126. In some embodiments, the controller 140 generates a signal that is transmitted from an output of the controller 140 to the screw control 126. The controller 140 can control any number of characteristics of the machine, such as injection pressure (advancing the screw 112 at a rate that maintains a desired value corresponding to the molten plastic material 114 in the nozzle 116 by controlling the screw control 126), barrel temperature, clamp closing and / or opening speed, cooling time, injection advance time, overall cycle time, pressure set point, ejection time, screw recovery speed, the amount of back pressure applied to the screw 112, and screw speed.

[0038] One or more signals from the controller 140 can generally be used to control the operation of the molding process so that the controller 140 takes into account changes in material density, viscosity, mold temperature, melt temperature and other factors that affect the filling rate. Alternatively or additionally, the controller 140 can make necessary adjustments to control other material properties. Adjustments can be made by the controller 140 in real time or near real time (i.e., the minimum delay between the sensor 128, 130 sensing value and the change made to the process), or corrections can be made in subsequent cycles. In addition, several signals from any number of separate cycles can be used as the basis for adjusting the molding process. The controller 140 can be connected to the sensors 128, 130, the screw control 126 or any other component in the machine 100 via any type of signal communication method.

[0039] The controller 140 includes software 141 suitable for controlling its operation, any number of hardware elements 142 (such as, for example, a non-transitory memory module and / or a processor), any number of inputs 143, any number of outputs 144, and any number of connections 145. The software 141 may be loaded directly onto the non-transitory memory module of the controller 140 in the form of a non-transitory computer readable medium, or may alternatively be remote from the controller 140 and communicate with the controller 140 via any number of control methods. The software 141 includes logic, commands, and / or executable program instructions, which may include logic and / or commands to control the injection molding machine 100 according to a molding cycle. The software 141 may or may not include an operating system, an operating environment, an application environment, and / or a user interface.

[0040] The hardware 142 uses input 143 to receive signals, data, and information from an injection molding machine controlled by the controller 140. The hardware 142 uses output 144 to send signals, data, and / or other information to the injection molding machine. Connection 145 represents a path through which signals, data, and information are transmitted between the controller 140 and the injection molding machine 100 of the controller 140. In various embodiments, the path can be a physical connection or a non-physical communication link that works in a manner similar to a direct or indirect physical connection configured in any manner described herein or known in the art. In various embodiments, the controller 140 can be configured in any additional or alternative manner known in the art.

[0041] Connections 145 represent pathways through which signals, data, and information are transmitted between the controller 140 and the injection molding machine 100 of the controller 140. In various embodiments, these pathways may be physical connections or non-physical communication links that operate in a manner similar to direct or indirect physical connections configured in any manner described herein or known in the art. In various embodiments, the controller 140 may be configured in any additional or alternative manner known in the art.

[0042] As previously described, the second sensor 130 is positioned downstream of the first sensor 128. Due to the inherent material properties of the molten plastic material 114, the material will exhibit greater compressibility at or near the proximal end 113 of the screw 112 (i.e., where the first sensor 128 is typically positioned) than at or near the mold cavity 122 (i.e., where the second sensor 130 is typically positioned). The sensors 128, 130 can measure a variable (such as the compressibility of the material) at each respective location (e.g., by measuring the force exerted thereon by the molten plastic material 114), which in turn can be used to determine a measured density of the molten plastic material 114 at each location. The controller 140 can receive these sensed values ​​to determine a measured compressibility ratio value, which in some examples can be a difference and / or an average between the measured variables acquired by the first and second sensors 128, 130.

[0043] The measured compressibility ratio value may then be compared to a previously acquired reference compressibility ratio value. In some examples, during the validation phase, a plurality of different injection cycles are performed until a molded part having ideal and / or desired characteristics is obtained. The measurements acquired from the first and second sensors 128, 130 may be compared to each other during the ideal injection cycle to generate a reference compressibility ratio value. In other examples, the reference compressibility ratio value may be acquired during a previous injection cycle or production run of the machine. More specifically, after the user identifies one or more preferred molded parts, they may instruct the controller 140 to mark a particular injection cycle so that the sensed and measured values ​​may be used in subsequent injection cycles. Other examples are possible.

[0044] In some circumstances, the measured compressibility ratio value may be different from the reference compressibility ratio value. For example, in some examples using PCR, the molten polymer material 114 may be non-uniform and therefore may possess different material properties throughout a product run. As a result, in subsequent injection cycles, the density of the molten plastic material 114 may increase or decrease. While existing systems are able to determine whether material properties (such as viscosity and density) have changed, such systems are unable to distinguish between a change in material viscosity and a change in material density, and may instead make the same one or more adjustments to the injection cycle regardless of what changes actually occurred.

[0045] Based on the change in relationship and comparison between the measured compressibility ratio value and the reference compressibility ratio value, the controller 140 may adjust at least one control parameter so that a subsequently acquired sensed measurement is equal to the reference compressibility ratio value (or, in some examples, for example, within a specified threshold of approximately ±5%). While some existing systems that are capable of responding to changes in material viscosity may attempt to adjust operating parameters (such as injection pressure) to account for such material changes during the molding cycle, these adjustments are typically performed at different stages in the injection process, rather than where changes in material density can be addressed. More specifically, changes based on viscosity are typically accounted for and adjusted within a range between approximately 10% and 60% of the completion time of the injection molding cycle (i.e., during the filling phase of the cycle). However, the method of the present disclosure advantageously measures and determines material density, and therefore may cause the controller 140 to adjust operating parameters to compensate for changes in compressibility within approximately the first 10% of the time of injection and approximately the last 40% of the time of injection, and thereby may more accurately account for these changes.

[0046] In some examples, the operating parameters may be in the form of a driving force on the screw, a target injection pressure, a screw recovery profile, a fill end response, and / or other corrective actions, such as sending the molten plastic material 114 for further processing or mixing. During each injection cycle, such operating parameters may be set in real time by controlling the machine 100 to maintain the relative compressibility ratio between the first and second sensors 128, 130. In some examples, the system may use Process Factor A and / or other similar techniques for correction. In some examples, the fill end and / or transfer position may also be adjusted. In some examples, any of these and other adjustments may be made on an intra-injection or inter-injection basis in conjunction with a dynamic injection process.

[0047] It will be appreciated that in some examples, in addition to sensing and adjusting parameters in response to changes in the density of the molten polymer material 114, the machine 100 may additionally sense any changes in the viscosity of the molten polymer material 114 and adjust operating parameters in response to these changes. As a non-limiting example, the machine 100 may measure the shear rate of the molten polymer material 114 (e.g., the speed at which the molten polymer material 114 moves relative to the amount of applied pressure). Such a measurement may occur via the use of a screw movement (e.g., speed) to measure coupled to a sensor positioned at or near the nozzle. Other suitable methods are possible. The measured shear rate may be compared to a reference shear rate, and any difference between these values ​​may be used to adjust operating or control parameters to cause a subsequently measured shear rate to be equal to the reference shear rate (or within an allowed threshold thereof).

[0048] Go to Figure 2, a method 200 for controlling a molding machine is provided, the molding machine having a mold forming a mold cavity, a nozzle, and a screw, the screw moving from a first position to a second position toward the nozzle and being controlled according to a molding cycle. First, at step 202, a molten polymer is injected into the mold cavity. At step 204, a first measurement of a variable is obtained during the injection cycle using a first sensor positioned at or near the screw. At step 206, a second measurement of the variable is obtained during the injection cycle. As previously described, the second sensor is positioned at or near the nozzle. At step 208, a measured compressibility ratio value is determined, the measured compressibility ratio value being in the form of a difference between a measured variable obtained by the first sensor and a measured variable obtained by the second sensor. At step 210, the measured compressibility ratio value is compared with a reference compressibility ratio value. At step 210, at least one of the operating or control parameters is adjusted based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0049] Furthermore, it will be appreciated that the systems and methods described herein may be applied to extrusion molding devices. Typically, in such devices, a die cavity is not provided, but rather an extrusion molding component may be incorporated into the system. Figure 3 and Figure 4 , the extruder 300 includes an extrusion unit 302. The injection unit 302 includes a hopper 306 adapted to receive a material in the form of pellets 308 or any other suitable form. In many of these examples, the pellets 308 may be a polymer or a polymer-based material, such as post-consumer regrind (PCR). Other examples are possible. The extrusion unit 302 further includes a heating cartridge 310, a rotating screw 312, and a die head 316.

[0050] like Figure 1 and Figure 2 In the example described in , the hopper 306 feeds the pellets 308 into the heating barrel 310 of the extrusion unit 302. After being fed into the heating barrel 310, the pellets 308 can be driven to the end of the heating barrel 310 toward the barrel end cap 310a by the rotating screw 312. The rotating screw 312 remains stationary relative to the heating barrel 310. The heating of the heating barrel 310 and the compression of the pellets 308 by the reciprocating screw 312 melt the pellets 308, thereby forming a molten plastic material or polymer 314. The molten plastic material 314 is typically processed within a selected temperature range of about 130° C. to about 410° C. (where the manufacturer of a particular polymer typically provides a recommended temperature range for a given material to the extruder).

[0051] Rotating the screw 312 forces the molten plastic material 314 toward the die 316 to form an extruded plastic material which will ultimately be a molded part.

[0052] An actuation unit 322 is provided that is operatively coupled to the rotation screw 312 to facilitate its powered rotation. In some examples, the actuation unit 322 may be in the form of a hydraulic motor. In other examples, the actuation unit 322 may be in the form of an electric motor. In these and other examples, the actuation unit 322 may additionally or alternatively include any of a variety of other suitable control devices for control devices of an extrusion molding device or a non-extrusion molding device.

[0053] The die 316 may be associated with a post-mold processing device 325. After the molten plastic material 314 is extruded to form an extrudate 331 and undergoes any desired post-mold processing equipment 325, a final product 334 is produced. During the operation of the post-mold processing equipment 325, the extrudate 331 may take an intermediate form 332. The molten thermoplastic material 314 cools significantly when flowing through the die 316, but the post-mold processing equipment 325 may provide additional cooling. In certain embodiments, the post-mold processing equipment 325 may include multiple options to generate various molded parts (e.g., tubes, rods, films, blown films, bags, pellets, bottles, etc.). The post-mold processing equipment 325 may also include electronic components that are capable of generating output signals 336, which transmit the state and / or characteristics (such as thickness, temperature, line speed, etc.) of the extrudate 331 to a control system (e.g., a remote controller 46 and / or a native controller 40) via a signal line 352.

[0054] As previously described, the extruder 300 also includes a native controller 340 that is communicatively coupled to the extruder 300 via a connection 345. The connection 345 can be any type of wired and / or wireless communication protocol suitable for transmitting and / or receiving electronic signals. In these examples, the native controller 340 communicates signals with the screw control 326 via the connection 345. The native controller 340 can command the screw control 326 to turn the rotating screw 312 at a rate to maintain the desired molding process, so that the native controller 340 takes into account material viscosity, die temperature, melt temperature and other changes that can affect the extrusion rate. Such adjustments can be made in real time by the native controller 340. In one embodiment, when the actuation unit 322 is a hydraulic motor, the screw control 326 may include a hydraulic valve associated with the rotating screw 312. In another embodiment, when the actuation unit 322 is an electric motor, the screw control 326 may include a hydraulic valve associated with the rotating screw 312. In Figure 3 In an embodiment of the present invention, the native controller 340 can, for example, generate a signal that is transmitted from an output of the native controller 340 to the screw control 326 to control the rotation rate of the rotating screw 312.

[0055] The native controller 340 can be an onboard controller and built with the extrusion molding unit 302, which is an original part of the extrusion molding unit 302. The native controller 340 can be set at multiple positions relative to the extrusion molding machine 300. As an example, the controller 340 can be integrated with the extrusion molding machine 300, contained in a housing mounted on the machine, contained in a separate housing adjacent to or close to the machine, or can be located at a location away from the machine. In some embodiments, as known in the art and / or commonly used, the native controller 340 can partially or completely control the functions of the machine via wired and / or wireless signal communication. Therefore, in some examples, modifying the control architecture of the native controller 340 or removing the native controller 340 may be time-consuming, expensive, and in some examples impossible.

[0056] The native controller 340 can be any of a variety of suitable controllers for controlling the molding process. In some arrangements, the native controller 340 can be a PID controller that is locally configured to implement a PID control algorithm. In addition to the native controller 340 controlling the screw rotation of the actuation unit 322 using the melt pressure sensor 329, the control variable can be, for example, a temperature or pressure associated with the molten thermoplastic material 314 at a specific location in the extrusion molding unit 302. For example, the controlled molten thermoplastic pressure can correspond to (1) an extrusion pressure detected via an extrusion pressure sensor 328 located at or near the actuation unit 322, (2) a melt pressure detected via a melt pressure sensor 329 located at or near the die 316, or (3) a pressure detected via a die pressure sensor 330 located near the end of the die 316. The native controller 340 is typically configured to provide control signals to control the operation of the extrusion molding unit 302 (e.g., sending a signal to the screw control 326 to control the rotation of the screw 312 based on a sensed control variable (e.g., based on a comparison of the sensed control variable and a set point defined by the native controller 340), the sensed control variable being provided as an input to a control algorithm of the native controller 340).

[0057] The extrusion pressure sensor 328 can facilitate (directly or indirectly) detection of the extrusion pressure inside the heating cylinder 310 (i.e., the pressure of the heating cylinder 310 when the screw 312 is started to rotate) by providing a feedback signal to the native controller 340 via the signal line 344. In some embodiments, the native controller 340 can detect the extrusion pressure from the feedback signal and control (e.g., feedback control) the pressure inside the extruder 300 by controlling the screw controller 326, which controls the extrusion rate of the extrusion unit 302.

[0058] The melt pressure sensor 329 can facilitate detection (direct or indirect) of an actual melt pressure (e.g., measured melt pressure) of the molten thermoplastic material 314 at or near the die 316. The melt pressure sensor 329 may or may not be in direct contact with the molten thermoplastic material 314. In some embodiments, the melt pressure sensor 329 can be a pressure transducer that transmits an electrical signal to an input of the native controller 340 via a signal line 341 in response to the melt pressure at the die 316. In some embodiments, the melt pressure sensor 329 can facilitate monitoring any of a variety of additional or alternative characteristics of the molten thermoplastic material 314 at the die 316 that may be indicative of melt pressure, such as temperature, viscosity, and / or flow rate. If the melt pressure sensor 329 is not located within the die 316, the native controller 340 may be configured, configured, and / or programmed using logic, commands, and / or executable program instructions to provide appropriate correction factors to estimate or calculate the measured characteristic value within, at, or near the die 316. It is understood that in addition to the melt pressure sensor, other sensors may be used to measure any other characteristics of the molten thermoplastic material 314, the screw 312, the barrel 310, etc., which are known in the art, such as temperature, viscosity, flow rate, strain, speed, etc., or any other characteristic that is indicative of one or more.

[0059] The die pressure sensor 330 may facilitate detection (direct or indirect) of the melt pressure of the molten thermoplastic material 314 within, at, or near the die 316. The die pressure sensor 330 may or may not be in direct contact with the molten thermoplastic material 314. In some examples, the melt pressure sensor 330 may be a pressure transducer that transmits an electrical signal to an input of the native controller 340 or an input of the remote controller 346 via a signal line 351 in response to the die pressure at the die 316. In other embodiments, the die pressure sensor 330 may facilitate monitoring any of a variety of additional or alternative characteristics of the thermoplastic material 314.

[0060] Still refer to Figure 3, the remote controller 346 (e.g., a PID controller) can communicate signals with the native controller 340, the extrusion pressure sensor 328, the melt pressure sensor 329, and / or the die pressure sensor 330. Before retrofitting the remote controller 346 to the extruder 300, the native controller 340 can communicate signals with one or more of the extrusion pressure sensor 328, the melt pressure sensor 329, and the die pressure sensor 330 in the manner described above. To retrofit (e.g., associate) the remote controller 346 to the extruder 300, the output of one or more of the extrusion pressure sensor 328, the melt pressure sensor 329, and / or the die pressure sensor 330 may be connected to the remote controller 346 (and optionally disconnected from the native controller 340), thereby transferring the sensor output of the sensor(s) to the remote controller 346 in place of the native controller 340. Once the retrofit is complete, the native controller 340 may no longer directly receive feedback signals from the one or more sensors disconnected from the native controller 340. Instead, the remote controller 346 receives these feedback signals and generates and transmits modified feedback signals to the native controller 340 that enhance the operation of the native controller 340 by affecting the manner in which the native controller 340 controls the operation of the extruder 300. Thus, the native controller 340 and the remote controller 346 operate in a closed-loop control arrangement that mimics the existing arrangement prior to the addition of the remote controller 346.

[0061] In some embodiments as described above, the extrusion pressure sensor 328, the melt pressure sensor 329, and the die pressure sensor 330 are already present on the extrusion molding device 302 before modification and are in signal communication with the native controller 340. In such embodiments, retrofitting the remote controller 346 to the extrusion molding device 300 involves disconnecting the sensor from the native controller 340 and reconnecting the sensor to the remote controller 346. Alternatively, in some arrangements, one or more of the extrusion pressure sensor 328, the melt pressure sensor 329, and the die pressure sensor 330 may be present in the extrusion molding device 302 before modification. In these examples, retrofitting the remote controller 346 to the extrusion molding machine 300 may include installing one or more sensors to the extrusion molding unit 302 and connecting the installed (multiple) sensors to the remote controller 346.

[0062] In some embodiments, retrofitting the remote controller 346 to the extruder 300 may include transferring (or installing and connecting) the outputs of other sensors to the remote controller 346 rather than the native controller 340 in a manner similar to that described above, wherein the other (multiple) sensors (e.g., temperature sensors, flow sensors, etc.) are still configured to measure control variables involved in the control strategies of the native controller 340 and / or the remote controller 346.

[0063] In addition, the process of retrofitting the remote controller 346 to the extrusion molding apparatus 300 can include connecting the output of the set point of the native controller 340 to the remote controller 346. That is, the native controller 340 before modification can provide the native controller set point to the control algorithm of the native controller 340, and the native controller 340 after modification can additionally provide its set point to the remote controller 346 via signal communication. It should be understood that, given that the set point defined by the native controller may change during the extrusion molding cycle (e.g., as a product of the ramping or stepping up of the control variable set point during the control iteration), providing the set point of the native controller to the remote controller 346 can include providing the set point each time the native controller 340 defines the set point of the control variable (e.g., in each iteration of the control loop). Therefore, as described herein, the remote controller 346 maintains awareness of the current value of the native controller set point in order to correctly provide a modified feedback signal to the native controller 340.

[0064] The native controller 340 includes software (not shown) suitable for controlling its operation, any number of hardware elements (not shown; such as, for example, a non-volatile memory module and / or a processor), any number of inputs, any number of outputs, and any number of connections. The software may be loaded directly onto the non-volatile memory module of the native controller 340 in the form of a non-volatile computer readable medium, or may alternatively be located on a remote controller 346 and communicate with the native controller 340 via any number of control methods. The software includes logic, commands, and / or executable program instructions, which may include logic and / or commands for controlling the extruder 300 according to the molding cycle. The software may or may not include an operating system, an operating environment, an application environment, and / or a user interface.

[0065] The hardware uses inputs to receive signals, data, and information from the extruder controlled by the native controller 340. The hardware uses outputs to send signals, data, and / or other information to the extruder 300. In various embodiments, the path can be a physical connection between the native controller 340 and the extruder 300 or a non-physical communication link that works in a manner similar to a direct or indirect physical connection configured in any manner described herein or known in the art. In various embodiments, the native controller 340 can be configured in any additional or alternative manner known in the art.

[0066] As previously described, the second sensors 329, 330 are positioned downstream of the first sensor 328. Due to the inherent material properties of the molten plastic material 314, the material will exhibit lower compressibility at or near the end of the rotating screw 312 closest to the screw control 326 (i.e., where the first sensor 328 is typically positioned) than at or near the mold cavity 316 (i.e., where the second and third sensors 329, 339 are typically positioned). The sensors 328, 329, 330 can measure a variable (such as the compressibility of the material) at each respective location (e.g., by measuring the force exerted thereon by the molten plastic material 314), which in turn can be used to determine a measured density of the molten plastic material 314 at each location. The native controller 340 can receive these sensed values ​​to determine a measured compressibility ratio value, which in some examples can be a difference and / or an average between the measured variables acquired by the sensors 328, 329, 330.

[0067] The measured compressibility ratio value can then be compared to a previously acquired reference compressibility ratio value. In some examples, during the validation phase, multiple different extrusion sample runs are performed until a molded part having ideal and / or desired properties is obtained. The measurements acquired from sensors 328, 329, 330 can be compared to each other during the ideal extrusion run to generate a reference compressibility ratio value. In other examples, the reference compressibility ratio value can be acquired during a previous extrusion run or production run of the machine. More specifically, after the user identifies one or more preferred molded parts, they can instruct the controller 340 to identify a specific extrusion run so that the sensed values ​​and the measured values ​​can be used in subsequent extrusion processes. Other examples are possible.

[0068] In some circumstances, the measured compressibility ratio value may be different from the reference compressibility ratio value. For example, in some examples using PCR, the molten polymer material 314 may be non-uniform and therefore may possess different material properties throughout a product run. Thus, the density of the molten plastic material 314 may increase or decrease throughout a run. While existing systems are able to determine whether material properties (such as viscosity and density) have changed, such systems are unable to distinguish between a change in material viscosity and a change in material density, and may instead make the same one or more adjustments to the extrusion process regardless of what changes actually occurred.

[0069] Based on the change in relationship and comparison between the measured compressibility ratio value and the reference compressibility ratio value, the native controller 340 can adjust at least one control parameter so that a subsequently acquired sensed measurement is equal to the reference compressibility ratio value (or, in some examples, for example, within a particular threshold of approximately ±5%).

[0070] In some examples, the operating parameters may be in the form of a driving force on a screw, a target extrusion pressure, and / or other corrective actions such as sending the molten plastic material 314 for further processing or mixing. Such operating parameters may be set on the fly by the controller 300 to maintain the relative compressibility ratio between the first and second sensors 328, 329 during each extrusion run.

[0071] It will be appreciated that in some examples, in addition to sensing and adjusting parameters in response to changes in the density of the molten polymer material 314, the extruder 300 can additionally sense any changes in the viscosity of the molten polymer material 314 and adjust operating parameters in response to these changes. As a non-limiting example, the machine 300 can measure the shear rate of the molten polymer material 314 (e.g., the speed at which the molten polymer material 314 moves relative to the amount of applied pressure). Such a measurement can occur via the use of screw movement (e.g., rotational speed) to measure the coupling with a sensor positioned at or near the die head. Other suitable methods are possible. The measured shear rate can be compared to a reference shear rate, and any difference between these values ​​can be used to adjust operating or control parameters to make the subsequently measured shear rate equal to the reference shear rate (or within its allowed threshold).

[0072] Go to Figure 4, a method 200 for controlling a molding machine is provided, the molding machine having a die head and a screw that forms a profile, the screw rotating at a variable rate and being controlled according to a continuous extrusion molding process. First, at step 402, a molten polymer is extruded through the die head. At step 404, a first sensor positioned at or near the screw is used to obtain a first measurement of a variable during extrusion. At step 406, a second measurement of the variable is obtained during extrusion. As previously described, the second sensor is positioned at or near the die head. At step 408, a measured compressibility ratio is determined, the measured compressibility ratio being in the form of a difference between a measured variable obtained by the first sensor and a measured variable obtained by the second sensor. At step 410, the measured compressibility ratio is compared with a reference compressibility ratio. At step 410, at least one of the operating or control parameters is adjusted based on the difference between the reference compressibility ratio and the measured compressibility ratio.

[0073] It is also understood that the molding machine and method 100, 200, 300 and / or method 400 described herein can use any number of alternative suitable methods to measure compressibility and / or density. For example, in some arrangements, a flow meter (not shown) can be arranged in the feed throat of the machine. In addition, although redundancy can be advantageously provided using two or three sensors, in some arrangements, an existing melt pressure transducer can be used in combination with an additional sensor to simulate the change in material density. Similarly, in some examples, a load cell or hydraulic pressure can be used in combination with an additional sensor to measure density. However, in other examples, the use of two or three independent sensors can advantageously lead to the elimination of load cells, thereby reducing equipment costs. In yet other arrangements, a plunger propulsion system can be incorporated into the molding machine as a replacement for a screw to push the molten polymer material into the mold cavity. Compared with the conventional system using an upstream sensor, the present system can be easily incorporated into a downstream sensor while still being able to adjust for changes in the density of the material.

[0074] Additionally, in some arrangements, changes in material density can be used to determine scaling values ​​for correction. For example, instead of using a system that first determines an initial set point to begin manufacturing a suitable part, the present system can be used to determine what initial parameters to use as correction factors to correct for detected changes in density.

[0075] As arranged, the present molding machine 100, 300 can make intelligent decisions in process adjustments while accurately identifying changes in properties in the material characteristics of the molten polymer material by distinguishing between changes in density and changes in viscosity, and unnecessary process adjustments can be eliminated. For example, although melt density and viscosity are independent properties of the molten polymer material, they are also affected by the same changes in the extrusion process. Therefore, during a cycle or process, adjustments to viscosity (e.g., pressure and other adjustments made during the molding process) can inadvertently affect the melt density. These adjustments can be eliminated in the present system and method because the system will instead make a separately calculated pressure adjustment (e.g., at the end of the filling phase of the injection cycle). This determination can result in parts that achieve the same stress distribution, shrinkage and / or dimensional specifications as other processes, which are able to adjust for changes in viscosity while additionally maintaining consistent part quality throughout the product run.

[0076] Such a system can allow an operator and / or machine to calculate in real time the change in the true density (and / or viscosity) of the molten plastic, and can use this information in a feedback loop to adjust the system appropriately. Additionally, in order to send data points of material quality to processing equipment, material data can be stored in real time to assist in maintaining proper PCR regrind quality. Historical data can also be collected and stored for process quality control.

[0077] By incorporating the methods described herein, the molding machines 100, 300 can be safely operated in an efficient manner while ensuring that parts with minimal defects and / or flaws are produced by making adjustments to ensure that the density and / or viscosity of the material remains constant. The processes described herein can be advantageously incorporated into conventional injection molding systems, injection molding systems incorporating low pressure, injection molding systems incorporating substantially constant pressure methods, injection molding systems incorporating specific controls based on real-time density measurements, extrusion molding systems, and any other system.

[0078] Furthermore, in some circumstances, real-time density measurements as described herein can result in time savings while consistently producing high quality parts. The processes described herein can be advantageously incorporated into various extrusion systems for making tubes, rods, films, blown film, bags, pellets, bottles, and the like.

[0079] Furthermore, it will be appreciated that the systems and methods described herein may be applied to form any number of different molded parts constructed from a variety of materials, such as, for example, silicone and metal parts.

[0080] The methods described above can be used in conjunction with any injection process in which the previously identified patterns are used to drive at least a portion of the injection cycle. These methods can be used to form any number of different molded parts made of a variety of materials, such as, for example, silicone and metal parts.

[0081] Those skilled in the art will appreciate that various modifications, changes and combinations may be made with respect to the embodiments described above without departing from the scope of the present invention, and such modifications, changes and combinations will be deemed to be within the scope of the inventive concept.

[0082] The patent claims at the end of this patent application are not intended to be interpreted under 35 U.S.C. §112(f) unless conventional means-plus-function language is expressly recited, such as "means for" or "step for" language is expressly recited in the claim(s). The systems and methods described herein relate to improving computer functionality, as well as improving the functionality of conventional computers.

Claims

1. A method for controlling a molding machine, the molding machine having a mold forming a mold cavity, a nozzle and a screw, the screw moving from a first position to a second position toward the nozzle injection molding machine is controlled according to a molding cycle controller, the method comprising: injecting molten polymer into the mold cavity; obtaining a first measurement of a variable during an implantation cycle using a first sensor positioned at or near the screw; obtaining a second measurement of the variable during the injection cycle using a second sensor positioned at or near the nozzle; determining a measured compressibility ratio value, the compressibility ratio value being a difference between a measured variable acquired by the first sensor and a measured variable acquired by the second sensor; comparing the measured compressibility ratio value with a reference compressibility ratio value; as well as At least one control parameter is adjusted based on a difference between the reference compressibility ratio value and the measured compressibility ratio value.

2. The method according to claim 1, characterized in that The measured variables include the compressibility of the molten plastic material.

3. The method according to claim 2, characterized in that The compressibility of the molten plastic material is used to determine its density value.

4. The method according to any one of claims 1 to 3, characterized in that The first sensor is positioned behind the proximal end of the screw.

5. The method according to claim 4, characterized in that The first sensor includes a force sensor.

6. The method according to any one of claims 1 to 5, characterized in that The second sensor is positioned in a flow channel of the injection unit upstream of the mold cavity.

7. The method according to any one of claims 1 to 6, characterized in that The step of adjusting the at least one control parameter comprises adjusting a target injection pressure value.

8. The method according to any one of claims 1 to 7, further comprising the following steps: Measuring the shear rate of the molten plastic material to determine a change in the viscosity value of the molten plastic material; as well as At least one control parameter is adjusted based on a difference between the measured shear rate and a reference shear rate.

9. The method according to any one of claims 1 to 8, characterized in that The reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during a previous injection cycle.

10. The method as claimed in claim 9, characterized in that The previous injection cycle includes a verification cycle or a prediction cycle.

11. A molding machine comprising: a molding unit and a screw, the molding unit having a mold forming a mold cavity, the screw moving from a first position to a second position toward a nozzle, an injection unit adapted to receive molten plastic material and inject the molten plastic material into the mold cavity via the screw and the nozzle to form a molded part; a controller adapted to control the operation of the injection molding machine according to a molding cycle; a first sensor positioned at or near the screw and communicatively coupled to the controller, the sensor adapted to measure a variable during the injection cycle; a second sensor positioned at or near the nozzle and communicatively coupled to the controller, the sensor adapted to measure a variable at a second time during the injection cycle; Characterized in that the controller is suitable for: Begin injecting molten polymer into the mold cavity, determining a measured compressibility ratio value, the compressibility ratio value being a difference between a measured variable acquired by the first sensor and a measured variable acquired by the second sensor, comparing the measured compressibility ratio value with a reference compressibility ratio value, and At least one control parameter is adjusted based on a difference between the reference compressibility ratio value and the measured compressibility ratio value.

12. The molding machine according to claim 11, characterized in that The measured variable includes the compressibility of the molten plastic material.

13. The molding machine according to claim 11 or claim 12, characterized in that: The compressibility of the molten plastic material is used to determine its density value.

14. The molding machine according to any one of claims 1 to 13, characterized in that: The first sensor is positioned behind the proximal end of the screw.

15. The molding machine according to claim 14, characterized in that The first sensor includes a force sensor.

16. The molding machine according to any one of claims 11 to 15, characterized in that: The second sensor is positioned in a flow channel of the injection unit upstream of the mold cavity.

17. The molding machine according to any one of claims 11 to 16, characterized in that: The at least one control parameter includes a target injection pressure value.

18. The molding machine according to any one of claims 11 to 17, characterized in that: The controller is further adapted to measure a shear rate of the molten plastic material to determine a change in a viscosity value of the molten plastic material, and the controller is further adapted to adjust the at least one control parameter based on a difference between the measured shear rate and a reference shear rate.

19. A method for controlling a molding machine having a die head for forming a profile and a screw rotating at a variable rate, the molding machine being controlled by a controller according to at least one molding parameter, the method comprising: extruding a molten polymer through the die; obtaining a first measurement of a variable using a first sensor positioned at or near the screw; obtaining a second measurement of the variable using a second sensor positioned at or near the die; determining a measured compressibility ratio value, the compressibility ratio value being a difference between a measured variable acquired by the first sensor and a measured variable acquired by the second sensor; comparing the measured compressibility ratio value with a reference compressibility ratio value; as well as At least one control parameter is adjusted based on a difference between the reference compressibility ratio value and the measured compressibility ratio value.

20. The method of claim 19, wherein: The measured variables include the compressibility of the molten plastic material.

21. The method of claim 19, wherein: The compressibility of a molten plastic material is used to determine its density value.

22. The method according to any one of claims 19 to 21, characterized in that The first sensor is positioned behind the proximal end of the screw.

23. The method of claim 22, wherein: The first sensor includes a force sensor.

24. The method according to any one of claims 19 to 23, characterized in that The second sensor is positioned within a flow channel of the molding unit upstream of the die.

25. The method according to any one of claims 19 to 23, characterized in that The second sensor is positioned outside the flow channel of the molding unit.

26. The method according to any one of claims 19 to 25, characterized in that A third sensor is positioned within the flow channel of the molding unit upstream of the die.

27. The method according to any one of claims 19 to 25, characterized in that The third sensor is positioned outside the flow channel of the molding unit.

28. The method according to any one of claims 19 to 27, characterized in that The step of adjusting the at least one control parameter includes a target molding pressure value.

29. The method of any one of claims 19-28, further comprising the steps of: Measuring the shear rate of the molten plastic material to determine the change in the viscosity value of the molten plastic material; as well as At least one control parameter is adjusted based on a difference between the measured shear rate and a reference shear rate.

30. The method according to any one of claims 19 to 29, characterized in that The reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during a previous operating period.

31. A molding machine comprising: a molding unit having a die forming a profile and a screw rotating at a variable rate, the injection unit being adapted to receive molten plastic material and to extrude the molten plastic material through the profile via the screw to form a molded part; a controller adapted to control operation of the molding machine based on at least one configuration parameter; a first sensor positioned at or near the screw and communicatively coupled to the controller, the first sensor being adapted to measure a variable during the operation; a second sensor positioned at or near the die and communicatively coupled to the controller, the sensor adapted to measure a variable at a second time during the run; Characterized in that the controller is suitable for: Begin extruding the molten polymer through the die, Determine the ratio of the measured compressibility, the measured compressibility The ratio is the difference between the measured variable acquired by the first sensor and the measured variable acquired by the second sensor, The measured compressibility ratio is compared with the reference The compressibility ratios are compared, and At least one control parameter is adjusted based on a difference between the reference compressibility ratio value and the measured compressibility ratio value.

32. The molding machine according to claim 31, characterized in that The measured variable includes the compressibility of the molten plastic material.

33. A forming machine according to claim 31 or claim 32, characterized in that The compressibility of the molten plastic material is used to determine its density value.

34. A molding machine according to any one of claims 31 to 33, characterized in that The first sensor is positioned behind the proximal end of the screw.

35. The molding machine according to claim 34, characterized in that The first sensor includes a force sensor.

36. A molding machine according to any one of claims 31 to 35, characterized in that The second sensor is positioned within a flow channel of the molding unit upstream of the die.

37. A molding machine as claimed in any one of claims 31 to 35, characterized in that The second sensor is positioned outside the flow channel of the molding unit.

38. A molding machine according to any one of claims 31 to 37, characterized in that A third sensor is positioned within the flow channel of the molding unit upstream of the die.

39. A molding machine according to any one of claims 31 to 37, characterized in that The third sensor is positioned outside the flow channel of the molding unit.

40. A molding machine according to any one of claims 31 to 39, characterized in that The at least one control parameter includes a target pressure value.

41. A molding machine according to any one of claims 31 to 40, characterized in that The controller is further adapted to measure a shear rate of the molten plastic material to determine a change in a viscosity value of the molten plastic material, and the controller is further adapted to adjust the at least one control parameter based on a difference between the measured shear rate and a reference shear rate.

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