Systems and approaches for manufacturing components

Abstract

A system and approach are provided for controlling a molding machine having a mold that forms 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 mold cycle. The approach includes injecting a molten polymer into the mold cavity and obtaining a first measurement of a variable during an injection cycle using a first sensor positioned on or near the screw. A second sensor positioned on or near the nozzle is used to obtain a second measured variable during the injection cycle. A measured compressibility ratio value is determined in the form of 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.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Application No. 63 / 352,518, filed Jun. 15, 2022, and U.S. Provisional Application No. 63 / 417,913, filed Oct. 20, 2022, the entire contents of each of which are hereby expressly incorporated by reference herein.

[0002] Field of Disclosure The present disclosure generally relates to molding, and more particularly to an approach for controlling injection and / or extrusion molding machines using sensor - based measurements.

Background Art

[0003] Molding, particularly injection and extrusion molding, is a technique commonly used for the mass production of parts made of thermoplastic materials. In both repeated injection molding processes and continuous extrusion molding processes, the thermoplastic resin is typically introduced in the form of small pellets or beads into an injection molding machine that melts the pellets under heat and pressure. In the injection cycle, the molten material is forced into a mold cavity having a specific desired cavity shape. The injected plastic is held under pressure within the mold cavity and subsequently cooled, and is removed as a solidified part having a shape closely resembling the shape of the mold cavity. One mold may have any number of individual cavities, which can be connected to the flow path by gates that direct the flow of the molten resin into the cavities. A typical injection molding procedure generally includes four basic operations: (1) heating the plastic in an injection molding machine to enable the plastic to flow under pressure; (2) injecting the molten plastic into one or more mold cavities defined between two closed mold halves; (3) cooling the plastic under pressure within one or more cavities to enable it to harden; and (4) opening the mold halves and removing the part from the mold. After removing the part from the mold, the device (e.g., a screw or auger) that injects the molten plastic into one or more mold cavities enters a recovery phase in which it 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 subsequently cooled and removed as a solidified part having a shape closely resembling the shape of the die orifice. The molded part is provided in an elongated shape, a tube, or other shapes, and is subsequently cut to the desired length. A typical extrusion molding process generally includes three basic operations: (1) heating the plastic in an extrusion molding machine to enable the plastic to flow under pressure, (2) extruding the molten plastic through or into a die; and (3) enabling the plastic to cool and harden. Each of these operations is typically performed simultaneously or nearly so.

[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, the injection cycle or other molding operations can be driven by fixed and / or variable melt pressure and / or screw speed profiles (or screw rotation speed profiles), and the control device uses, as input for determining the driving force applied to the material, the sensed pressure at a specified position (e.g., the nozzle) and / or the properties of the material or the extrudate such as, for example, the screw speed.

[0005] Due to the increasing awareness of the environment, the use of sustainable manufacturing processes is increasing. For example, post-consumer recycled plastic materials or recycled plastic materials are increasingly being used as materials for forming molded parts. Sometimes, this material may be supplied from different product lots that have not been properly sorted, and therefore, subsequent batches of plastic may have different material properties. Further, even if the products are properly sorted before being reused in manufacturing, the individual containers within a particular lot may have different viscosity and / or density characteristics. As a result, the molten polymer material obtained from the reused containers used to form the parts may not have material properties such as a uniform viscosity and / or density.

[0006] Furthermore, when molding with a re-ground material, material properties such as viscosity and / or density may change during a single injection cycle and / or extrusion operation. Existing systems may be able to determine and address changes in the viscosity of the molten polymer material, but such systems often cannot distinguish between changes in material viscosity and density, and when either a viscosity change or a density change is detected, the same adjustment may be applied to the operation of the molding process. As a result, these molding machines may produce low-quality parts, which must be removed during quality control inspections, leading to a decrease in operational efficiency. Additionally, since the molding operation may involve hundreds or thousands of pounds of material, the properties of the molten plastic material are not constant from one operation to the next. Thus, even if the mold cycle takes into account changes in material properties at the start of the operation, the changes in properties may still result in the production of low-quality parts and parts with varying properties later in the operation.

Summary of the Invention

[0007] Embodiments within the scope of the present invention are directed to controlling a molding machine for producing repetitive, consistent parts. A system and approach are provided for controlling a molding machine having a mold that forms 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 mold cycle. The approach includes injecting a molten polymer into the mold cavity and obtaining a first measured variable during the injection cycle using a first sensor positioned on or near the screw. A second sensor positioned on or near the nozzle is used to obtain a second measured variable during the injection cycle. A measured compressibility ratio value is determined in the form of the 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 approaches, the measurement variable is in the form of the compressibility of the molten plastic material. In some forms, the compressibility of the molten plastic material may be used to determine its density value.

[0009] 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 path 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 approach may include measuring the shear rate of the molten plastic material to determine a change in the viscosity value of the molten plastic material, and adjusting at least one control parameter based on the 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 the previous injection cycle. The previous injection cycle may be in the form of a verification cycle or a projection cycle.

[0012] According to a second aspect, the molding machine includes a molding unit, a control device, a first sensor, and a second sensor. The injection unit includes a mold that forms a mold cavity and a screw that moves from a first position to a second position toward the nozzle. The injection unit receives a molten plastic material and injects it into the mold cavity through the screw and the nozzle to form a molded part. The control device controls the operation of the injection molding machine according to a molding cycle. The first sensor is positioned on or near the screw and is communicably connected to the control device to measure variables during the injection cycle. The second sensor is positioned on or near the nozzle and is communicably connected to the control device to measure variables at a second time during the injection cycle. The control device starts the injection of the molten polymer into the mold cavity and determines a measured compressibility ratio value in the form of the difference between the measured variables obtained by the first sensor and the measured variables obtained by the second sensor. The control device 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, a system and approach are provided for controlling a molding machine having a die that forms a profile and a screw that is rotatable at a variable speed and is controlled according to set molding parameters, including extruding a molten polymer through the die and obtaining a first variable measurement 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 measured variable. The measured compressibility ratio value is determined in the form of the 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 with 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 approaches, the measured variable is in the form of the compressibility of the molten plastic material. In some aspects, the compressibility of the molten plastic material may be used to determine its density value.

[0015] In some of these examples, the first sensor may be positioned behind the proximal end portion 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 path of the unit upstream of the die. In other examples, the second sensor may be positioned outside the flow path of the molding unit. In some embodiments, the third sensor is positioned within the flow path of the molding unit upstream of the die. In still other examples, the third sensor is positioned outside the flow path 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 embodiments, the approach may include measuring the shear rate of the molten plastic material to determine a change in the viscosity value of the molten plastic material and adjusting at least one control parameter based on the 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 verification run or a predictive run.

[0018] According to a fourth aspect, the molding machine includes a molding unit, a control device, a first sensor, and a second sensor. The molding unit includes a die that forms a profile and a screw that is rotatable at a variable speed. The molding unit receives a molten plastic material and extrudes it through the profile via the screw to form a molded part. The control device controls the operation of the molding machine according to set parameters. The first sensor is positioned on or near the screw and is communicably connected to the control device to measure variables during operation. The second sensor is positioned on or near the die and is communicably connected to the control device to measure variables at a second time during operation. The control device starts the extrusion of the molten polymer through the die and determines a measured compressibility ratio value in the form of the difference between the measured variables obtained by the first sensor and the measured variables obtained by the second sensor. The control device 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] This specification particularly points out and distinctly claims the subject matter regarded as the invention, which is concluded in the claims, but the invention is considered to be more fully understood from the following description taken in conjunction with the accompanying drawings. Some of the figures may be simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some of the figures do not necessarily indicate the presence or absence of a particular element in any of the exemplary embodiments, except as explicitly defined in the corresponding written description. None of the drawings are necessarily to scale. For example, the dimensions and / or relative positions of some of the elements in the figures may be exaggerated relative to other elements to improve the understanding of the various embodiments of the invention.

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

[0021] Detailed Description Generally speaking, aspects of the present disclosure include systems and approaches for controlling a molding machine (e.g., an injection molding machine and / or an extrusion molding machine), where a number of sensors are positioned inline and upstream from a mold cavity or orifice to sense changes in the compressibility of a molten polymer. The sensors calculate the relative change in the compressibility of the molten polymer during the injection process and are arranged to compare the relative change to a reference value to determine whether corrective adjustments should be made to produce stable and consistent parts. This information may be used to make real-time adjustments to the melt pressure setpoint and / or driving force of the molten polymer.

[0022] The systems and approaches described herein may use a molding machine (e.g., an injection molding machine or other molding machine) that may operate at a substantially constant melt pressure value compared to conventional systems that include a steep ramp-up of melt pressure until a peak pressure value is obtained and then a decrease in pressure until the injection cycle is complete. Such operation at a substantially constant pressure value advantageously eliminates the need to dynamically perform calculations based on sensor measurements due to changes in the pressure value.

[0023] In some examples (and as described herein), the molding machine may incorporate a single sensor, two sensors, or more than two sensors used to calculate changes in density in real time.

[0024] Turning to the drawings, various molding processes are described. The approaches described herein may be suitable for electric presses, servo-hydraulic presses, hydraulic presses, and other known machines. Referring to FIGS. 1 and 2, an injection molding process is described, and referring to FIGS. 3 and 4, an extrusion molding process is described. As shown in FIG. 1, an injection molding machine 100 includes an injection unit 102 and a clamping system 104. The injection unit 102 includes a hopper 106 adapted to receive pellets 108 or any other suitable form of material. In many of these examples, the pellets 108 may be a polymer or polymer-based material, such as, for example, post-consumer regrind (PCR). Other examples are possible.

[0025] The hopper 106 supplies the pellets 108 to the heating barrel 110 of the injection unit 102. Once supplied to the heating barrel 110, the pellets 108 may be driven by a reciprocating screw 112 movable from a first, original position 112a to a number of subsequent positions for injecting the first, second, third, and / or any subsequent shots, toward the end of the heating barrel 110 toward the barrel end cap 110a. The heating of the heating barrel 110 and the compression of the pellets 108 by the reciprocating screw 112 cause the pellets 108 to melt, thereby forming a molten plastic material or polymer 114. The molten plastic material 114 is typically processed at a temperature selected within the range of about 130°C to about 410°C (manufacturers of specific polymers typically provide injection molders with the recommended temperature range for a given material).

[0026] The reciprocating screw 112 includes a proximal end portion 113, advances from a first position 112a to a second position 112b, biases the molten plastic material 114 toward the nozzle 116 to form a shot of plastic material, which is ultimately injected into the mold cavity 122 of the mold 118 through one or more gates 120 that direct the flow of the molten plastic material 114 into the mold cavity 122. In other words, the reciprocating screw 112 is driven to exert a force on the molten plastic material 114. In other embodiments, the nozzle 116 may be separated from one or more gates 120 by a supply system (not shown). The mold cavity 122 is formed between 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.

[0027] The press or clamp unit 124 applies a predetermined clamping force greater than the force exerted by the injection pressure acting to separate the two mold halves 125, 127 during the molding process, thereby holding the first and second mold sides 125, 127 together while the molten plastic material 114 is injected into the mold cavity 122. To support these clamping forces, the clamping system 104 may include a mold frame and a mold base in addition to any other number of components such as tie bars.

[0028] In some examples, when a shot of molten plastic material 114 is injected into mold cavity 122, the reciprocating screw 112 stops its forward movement. The molten plastic material 114 assumes the shape of the mold cavity 122 and cools inside the mold 118 until the plastic material 114 solidifies. Once solidified, the press 124 releases the first and second mold sides 115, 117, which then separate from each other. The finished product may then be ejected from the mold 118. The mold 118 may include any number of mold cavities 122 to increase the overall production rate. The shape and / or design of the cavities may be identical, similar, and / or different from each other. For example, a family mold may include cavities for related components intended to fit together or otherwise operate with each other. In some forms, an "injection cycle" is defined as those steps and functions performed between the start of injection and ejection. When the injection cycle is complete, a recovery profile is initiated, during which the reciprocating screw 112 returns to the first position 112a.

[0029] The injection molding machine 100 also includes a control device 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 adapted to transmit and / or receive electronic signals. In these examples, the control device 140 signal communicates with at least one sensor, such as sensors 128, 130, which are disposed, for example, within the machine 100 or otherwise associated with the machine 100 and the control device 140. In some examples, the first sensor 128 is disposed at or near the proximal end 113 of the nozzle 112, and the second sensor 130 is disposed within, at, or near the nozzle 116 in a location near the mold cavity 122. It is understood 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 installed in a desired arrangement of the machine 100.

[0030] The control device 140 can be arranged at a number of positions with respect to the injection molding machine 100. By way of example, the control device 140 can be integral with the machine 100, can be included in a housing placed on the machine, can be included in a separate housing positioned adjacent or close to the machine, or can be positioned away from the machine. In some embodiments, the control device 140 can partially or fully control the functions of the machine via wired and / or wireless signal communication, as known and / or commonly used in the art.

[0031] The sensors 128, 130 can be any type of sensor adapted to (directly or indirectly) measure one or more properties of the molten plastic material 114 and / or parts of the machine 100. The sensors 128, 130 can measure any property of the molten plastic material 114 known and used in the art, such as, for example, compressibility, pressure value, temperature, flow rate, hardness, strain, viscoelasticity, or any one or more of any number of additional properties indicative thereof. 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 can be in the form of force sensors and / or transducers. In some examples, the sensors 128, 130 can be adapted to measure not only properties related to the molten plastic material 114, but also any number of properties of the injection molding machine 100. As an example, the sensors 128, 130 can be pressure transducers that measure the melt pressure (during the injection cycle) and / or the back pressure (during the extrusion profile and / or the recovery profile) of the molten plastic material 114 at the nozzle 116.

[0032] Each of the sensors 128, 130 generates a signal that is transmitted to the input section of the control device 140. The control device 140 may receive the measured values and convert them into other properties of the molten plastic material 114, such as viscosity values.

[0033] As described above, in various embodiments, the first sensor 128 may be disposed at or near the distal end 113 of the screw 112. The second sensor 130 may be disposed at or near the nozzle 116, or may be disposed anywhere in the flow path before the material reaches the mold cavity 122, without being positioned inside (resulting in a pressure loss where the measured compressibility becomes a zero value). Other suitable locations for placing the sensors 128, 130 are possible anywhere, for example, before the check ring of the screw 112.

[0034] The control device 140 also communicates with the screw control device 126 in signal communication. In some embodiments, the control device 140 generates a signal transmitted from the output of the control device 140 to the screw control device 126. The control device 140 can control any number of characteristics of the machine, such as injection pressure (by advancing the screw 112 at a rate that controls the screw control device 126 to maintain a desired value corresponding to the molten plastic material 114 in the nozzle 116), barrel temperature, clamp closing speed and / or opening speed, cooling time, injection advance time, overall cycle time, pressure set point, injection time, screw recovery speed, back pressure value exerted on the screw 112, and screw speed.

[0035] Signals from the control device 140, or signals, are generally used to control the operation of the molding process so that variations in material density, viscosity, mold temperature, melt temperature, and other variations that affect the filling rate can be taken into account by the control device 140. Alternatively or additionally, the control device 140 may make adjustments necessary to control other material properties. The adjustments may be made by the control device 140 in real time or near real time (i.e., with minimal delay between when the sensors 128, 130 sense a value and when a change is made to the process), or the corrections may be made in a subsequent cycle. Further, a plurality of signals obtained from any number of individual cycles may be used as a basis for making adjustments to the molding process. The control device 140 may be connected to the sensors 128, 130, the screw control device 126, and any other components within the machine 100 via any type of signal communication approach.

[0036] The control device 140 includes software 141 adapted to control its operation, any number of hardware elements 142 (such as non-transitory memory modules and / or processors, etc.), any number of input portions 143, any number of output portions 144, and any number of connection portions 145. The software 141 may be directly loaded into the non-transitory memory module of the control device 140 in the form of a non-transitory computer-readable medium, or alternatively may be located remotely from the control device 140 and communicate with the control device 140 via any number of control approaches. The software 141 includes logic, commands, and / or executable program instructions, which may include logic and / or commands for controlling the injection molding machine 100 according to a mold cycle. The software 141 may or may not include an operating system, an operating environment, an application environment, and / or a user interface.

[0037] Hardware 142 receives signals, data, and information from an injection molding machine controlled by control device 140 using input section 143. Hardware 142 transmits signals, data, and / or other information to the injection molding machine using output section 144. Connection section 145 represents a path through which signals, data, and information can be transmitted between control device 140 and its injection molding machine 100. In various embodiments, this path may be a direct or indirect physical connection or a non-physical communication link that operates similarly to a physical connection configured in any manner described herein or known in the art. In various embodiments, control device 140 may be configured in any additional or alternative manner known in the art.

[0038] Connection section 145 represents a path through which signals, data, and information can be transmitted between control device 140 and injection molding machine 100. In various embodiments, these paths may be physical connections or non-physical communication links that function similarly to either direct or indirect physical connections configured in any manner described herein or known in the art. In various embodiments, control device 140 may be configured in any additional or alternative manner known in the art.

[0039] As shown previously, the second sensor 130 is positioned downstream from 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 portion 113 of the screw 112 (i.e., where the first sensor 128 is generally positioned) compared to the location at or near the mold cavity 122 (i.e., where the second sensor 130 is generally positioned). The sensors 128, 130 may measure variables such as material compressibility (e.g., by a method of measuring the force exerted thereon by the molten plastic material 114) at their respective locations, which may in turn be used to determine the measured density of the molten plastic material 114 at their respective locations. The control device 140 may receive these sensed values and determine a measured compressibility ratio value, which in some examples may be the difference and / or average between the measured variables obtained by the first and second sensors 128, 130.

[0040] This measured compressibility ratio value may then be compared to a previously obtained reference compressibility ratio value. In some examples, during a validation phase, a number of change injection cycles are performed until a molded part having ideal and / or desirable characteristics is obtained. The measured values obtained from the first and second sensors 128, 130 may be compared to each other during this ideal injection cycle to generate a reference compressibility ratio value. In other examples, the reference compressibility ratio value may be obtained during a previous injection cycle of the machine or during a production run. More specifically, when the user identifies a preferred molded part or parts, they may instruct the control device 140 to flag a particular injection cycle for use in subsequent injection cycles for the purpose of using the values sensed and measured therein. Other examples are possible.

[0041] Depending on the environment, the measured compressibility ratio value may differ from the reference compressibility ratio value. For example, in some examples where PCR is used, the molten polymer material 114 may be heterogeneous and thus may have different material properties throughout the product operation. As a result, in subsequent injection cycles, the density of the molten plastic material 114 may increase or decrease. Existing systems may be able to determine whether material properties such as viscosity and density have changed, but such systems cannot distinguish between changes in the viscosity of the material and changes in the density of the material. Instead, regardless of what actual changes occur, the same adjustment or adjustment may be made to the injection cycle.

[0042] Based on the relationship change and comparison between the measured compressibility ratio value and the reference compressibility ratio value, the control device 140 may adjust at least one control parameter for the purpose of making the subsequently obtained sensed measured value equal to the reference compressibility ratio value (or, in some examples, within a specified threshold of about ±5% of the reference compressibility ratio value). Some existing systems that can adjust changes in the viscosity of the material may adjust operating parameters such as injection pressure in an attempt to account for changes in the material during the molding cycle, but such adjustments are generally performed at different stages of the injection process than when variations in material density are addressed. More specifically, viscosity-based variations are generally accounted for and adjusted in the range of about 10% to 60% of the completion time of the injection molding cycle (i.e., during the filling stage of the cycle). However, the approach in the present disclosure advantageously measures and determines the material density and thus may cause the control device 140 to adjust the operating parameters to compensate for changes in compressibility within the range of the first about 10% by shot time and the last about 40% by shot time, and as such, may more accurately account for these changes.

[0043] In some examples, the operating parameters may be in the form of other corrective actions such as driving force of the screw, target injection pressure, screw recovery profile, end-of-fill response, and / or sending the molten plastic material 114 for further processing or blending. Such operating parameters may be performed on-the-fly during each injection cycle 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 make corrections using process factor A and / or other similar techniques. In some examples, the end-of-fill and / or transfer positions may also be adjusted. In some examples, these adjustments and other adjustments may be made on a shot-in or shot-to-shot basis by incorporating a dynamic shot process.

[0044] It is understood 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 change in the viscosity of the molten polymer material 114 and adjust the 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 rate at which the molten polymer material 114 moves relative to the amount of pressure applied). Such measurements may be made via the use of screw movement (e.g., speed) measurements coupled to sensors positioned at or near the nozzle. Other suitable approaches are possible. The measured shear rate may be compared to a reference shear rate, and the difference between these values may be used to adjust the operating or control parameters such that the subsequently measured shear rate becomes equal to (or falls within an acceptable threshold of) the reference shear rate.

[0045] Turning to FIG. 2, an approach 200 is provided for controlling a molding machine having a mold that forms 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 mold cycle. First, at step 202, molten polymer is injected into the mold cavity. At step 204, a first measurement variable during the injection cycle is obtained using a first sensor positioned on or near the screw. At step 206, a second measurement variable is obtained during the injection cycle. As described above, the second sensor is positioned on or near the nozzle. At step 208, a measured compressibility ratio value is determined in the form of the difference between the measurement variable obtained by the first sensor and the measurement 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 operating or control parameter is adjusted based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0046] Furthermore, it will be understood that the systems and approaches described herein may be applied to an extrusion apparatus. Generally, in such an apparatus, a mold cavity is not provided; rather, extrusion components may be incorporated into the system. Referring to FIGS. 3 and 4, an extrusion machine 300 includes an extrusion unit 302. The extrusion unit 302 includes a hopper 306 adapted to receive pellets 308 or any other suitable form of material. In many of these examples, the pellets 308 may be a polymer or polymer-based material such as, for example, post-consumer regrind (PCR). Other examples are possible. The extrusion unit 302 further includes a heating barrel 310, a rotating screw 312, and a die 316.

[0047] Similar to the examples described in FIGS. 1 and 2, hopper 306 supplies pellets 308 to the heating barrel 310 of the extrusion unit 302. Once supplied to the heating barrel 310, the pellets 308 may be driven by the rotating screw 312 towards the end of the heating barrel 310 towards the barrel end cap 310a. The rotating screw 312 remains stationary relative to the heating barrel 310. Heating of the heating barrel 310 and compression of the pellets 308 by the reciprocating screw 312 cause the pellets 308 to melt, thereby forming a molten plastic material or polymer 314. The molten plastic material 314 is typically processed at a temperature selected within the range of about 130°C to about 410°C (manufacturers of specific polymers typically provide the extrusion machine with the recommended temperature range for a given material).

[0048] The rotating screw 312 biases the molten plastic material 314 towards the die 316, ultimately forming an extruded plastic material that becomes the molded part.

[0049] An activation unit 322 is provided that is operatively coupled to the rotating screw 312 to facilitate its powered rotation. In some examples, the activation device 322 may be in the form of a hydraulic motor. In other examples, the activation unit 322 may be in the form of an electric motor. In these and other examples, the activation unit 322 may additionally or alternatively include any of a valve, a flow control device, an amplifier, or various other suitable control devices for an extrusion or non-extrusion forming device.

[0050] Die 316 may be associated with a mold post-treatment device 325. The molten plastic material 314 is extruded to form an extrudate 331, which becomes the final product 334 after passing through any desired mold post-treatment device 325. The extrudate 331 may take an intermediate form 332 during the operation of the mold post-treatment device 325. The molten thermoplastic material 314 cools significantly as it flows through the die 316, although the mold post-treatment device 325 may supply additional cooling. In some embodiments, the mold post-treatment device 325 may include a plurality of options for producing various molded parts (e.g., tubes, rods, films, blown films, bags, pellets, bottles, etc.). The mold post-treatment device 325 may also include electronic components that can generate an output signal 336 that transmits the state and / or characteristics of the extrudate 331, such as thickness, temperature, line speed, etc., to a control system (e.g., remote controller 46 and / or native controller 40) via a signal line 352.

[0051] As described above, the extruder 300 also includes a native control device 340 communicatively coupled to the extruder 300 via a connection portion 345. The connection portion 345 may be any type of wired and / or wireless communication protocol adapted to transmit and / or receive electronic signals. In these examples, the native control device 340 signals communicate with the screw control unit 326 via the connection portion 345. The native control device 340 instructs the screw control unit 326 to rotate the rotating screw 312 at a speed that maintains the desired forming process, such that other variations that can affect the material viscosity, die temperature, melt temperature, and extrusion speed are taken into account by the native control device 340. Such adjustments may be made in real time by the native control device 340. In one embodiment, when the actuator 322 is a hydraulic motor, the screw control unit 326 may include a hydraulic valve associated with the rotating screw 312. In another embodiment, when the actuator unit 322 is an electric motor, the screw control unit 326 can include an electric control device associated with the rotating screw 312. In the embodiment of FIG. 3, the native control device 340 can control the rotational speed of the rotating screw 312, for example, by generating a signal transmitted from the output portion of the native control device 340 to the screw control unit 326.

[0052] The native control device 340 can be an on-board control device originally provided in the extrusion unit 302 and constructed together with the extrusion unit 302. The native control device 340 can be arranged at a number of positions relative to the extrusion machine 300. By way of example, the control device 340 can be integral with the extrusion machine 300, can be included in a housing mounted on the machine, can be included in a separate housing positioned adjacent to or in proximity to the machine, or can be positioned remotely from the machine. In some embodiments, the native control device 340 can partially or fully control the functions of the machine via wired and / or wireless signal communication, as is known and / or commonly used in the art. Thus, in some instances, changing the control architecture of the native control device 340 or removing the native control device 340 can be time-consuming, costly, and in some cases impossible.

[0053] The native control device 340 can be any of various suitable control devices for controlling the molding process. In some arrangements, the native control device 340 may be a PID control device that is natively configured to implement a PID control algorithm. In addition to the native control device 340 controlling the screw rotation of the activation unit 322 using the melt pressure sensor 329, the control variable may be, for example, the temperature or pressure associated with the molten thermoplastic material 314 at a specific location within the extrusion unit 302. The molten thermoplastic resin pressure to be controlled may correspond to, for example, (1) the extrusion pressure detected via the extrusion pressure sensor 328 disposed in or near the activation unit 322, (2) the melt pressure detected via the melt pressure sensor 329 disposed in or near the die 316, or (3) the pressure detected via the die pressure sensor 330 disposed proximate to the end of the die 316. The native control device 340 is generally configured to provide a control signal for controlling the operation of the extrusion unit 302 (e.g., a signal to the screw control unit 326 for controlling the rotating screw 312 based on a sensed control variable provided as an input to the control algorithm of the native control device 340 (e.g., based on a comparison of the sensed control variable with a set value defined by the native control device 340)).

[0054] The extrusion pressure sensor 328 can facilitate the detection (directly or indirectly) of the extrusion pressure inside the heating barrel 310 (i.e., the pressure of the heating barrel 310 at the start of the rotating screw 312) by providing a feedback signal to the native control device 340 via the signal line 344. In some embodiments, the native control device 340 can detect the extrusion pressure from the feedback signal and control the pressure within the extruder 300 (e.g., feedback control) by controlling the screw control unit 326 that controls the extrusion speed by the extrusion unit 302.

[0055] The melt pressure sensor 329 can facilitate the detection (either directly or indirectly) of the actual melt pressure (e.g., the 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 the input of the native control device 340 via the signal line 341 in response to the melt pressure at the die 316. In some embodiments, the melt pressure sensor 329 can facilitate the monitoring of any of various additional or alternative characteristics of the molten thermoplastic material 314 at the die 316 that can indicate the melt pressure, such as, for example, temperature, viscosity, and / or flow rate. When the melt pressure sensor 329 is not disposed within the die 316, the native control device 340 can be set, configured, and / or programmed with logic, commands, and / or executable program instructions to provide an appropriate correction factor for estimating or calculating the value of the measured characteristic within, at, or near the die 316. It will be understood that sensors other than the melt pressure sensor can be employed to measure one or more of other characteristics such as temperature, viscosity, flow rate, strain, velocity, etc., or any of these, of the molten thermoplastic material 314, the screw 312, the barrel 310, etc.

[0056] The die pressure sensor 330 may facilitate the detection (either directly or indirectly) 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 die pressure sensor 330 can be a pressure transducer that transmits an electrical signal to the input of the native control device 340 or the input of the remote control device 346 via the signal line 351 in response to the die pressure within the die 316. In other embodiments, the die pressure sensor 330 can facilitate the monitoring of any of various additional or alternative characteristics of the thermoplastic material 314.

[0057] Referring also to FIG. 3, the remote controller 346 (e.g., a PID controller) can communicate with the native controller 340, the extrusion pressure sensor 328, the melt pressure sensor 329, and / or the die pressure sensor 330 in a signal communication. Before the remote controller 346 is retrofitted to the extruder 300, the native controller 340 can communicate with any one or more of the extrusion pressure sensor 328, the melt pressure sensor 329, and the die pressure sensor 330 in the above-described manner. To retrofit (e.g., associate) the remote controller 346 to the extruder 300, the output from one or more of the extrusion pressure sensor 328, the melt pressure sensor 329, and / or the die pressure sensor 330 is connected to the remote controller 346 (optionally disconnected from the native controller 340), whereby the sensor output from the sensor(s) can be diverted to the remote controller 346 instead of the native controller 340. When the retrofit is completed, the native controller 340 may no longer directly receive the feedback signal from one or more sensors that have been disconnected from the native controller 340. Instead, the remote controller 346 receives these feedback signals and generates a modified feedback signal that enhances the operation of the native controller 340 by affecting the way the native controller 340 controls the operation of the extruder 300, and transmits the modified feedback signal to the native controller 340. In this way, the native controller 340 and the remote controller 346 operate in a closed-loop type of control arrangement that mimics the arrangement that existed prior to the addition of the remote controller 346.

[0058] In some of the above embodiments, the extrusion pressure sensor 328, the melt pressure sensor 329, and the die pressure sensor 330 are already present on the extrusion unit 302 prior to the additional introduction and are in signal communication with the native controller 340. In such embodiments, the additional introduction of the remote controller 346 to the extrusion apparatus 300 involves disconnecting the sensors from the native controller 340 and reconnecting the sensors 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 not already be present on the extrusion unit 302 prior to the additional introduction. In these examples, the additional introduction of the remote controller 346 to the extrusion machine 300 may include installing one or more sensors on the extrusion unit 302 and connecting the installed sensors to the remote controller 346.

[0059] In some embodiments, the additional introduction of the remote controller 346 to the extrusion machine 300 may include diverting (or installing and connecting) other sensor outputs to the remote controller 346 in a manner similar to that described above, instead of the native controller 340, where the other sensor(s) is configured to measure control variables (e.g., temperature sensor, flow rate sensor, etc.) related to the control strategy of the native controller 340 and / or the remote controller 346.

[0060] Furthermore, the step of additionally introducing the remote control device 346 into the extrusion molding device 300 may include connecting the output of the set value of the native control device 340 to the remote control device 346. That is, the native control device 340 before the additional introduction may provide the native control device set value to the control algorithm of the native control device 340, while the native control device 340 after the additional introduction may additionally provide the set value to the remote control device 346 via signal communication. Considering the fact that the set value defined by the native control device may change over the course of the extrusion molding cycle (e.g., as a product of ramp-up or step-up of the control variable set value during control iteration), it should be understood that the provision of the native control device set value to the remote control device 346 may include providing the set value each time the native control device 340 defines a control variable set value (e.g., for each iteration of the control loop). Therefore, the remote control device 346 maintains the recognition of the current value of the native control device set value so as to correctly provide the modified feedback signal provided to the native control device 340 as described herein.

[0061] The native control device 340 includes software (not shown) adapted to control its operation, any number of hardware elements (not shown; e.g., non-transitory memory modules and / or processors, etc.), any number of input parts, any number of output parts, and any number of connection parts. The software may be directly loaded into the non-transitory memory module of the native control device 340 in the form of a non-transitory computer-readable medium, or alternatively, may be arranged in the remote control device 346 and communicate with the native control device 340 via any number of control approaches. The software may include logic, commands, and / or executable program instructions including commands for controlling the extrusion molding machine 300 according to the mold cycle. The software may or may not include an operating system, an operating environment, an application environment, and / or a user interface.

[0062] Hardware receives signals, data, and information from extruder 300 controlled by native controller 340 using an input section. Hardware transmits signals, data, and / or other information to extruder 300 using an output section. In various embodiments, the path between native controller 340 and extruder 300 may be a physical connection or a non-physical communication link that operates similarly to a direct or indirect physical connection configured in any manner described herein or known in the art. In various embodiments, native controller 340 may be configured in any additional or alternative manner known in the art.

[0063] As shown previously, second sensors 329, 330 are positioned downstream from first sensor 328. Due to the inherent material properties of molten plastic material 314, the material will exhibit lower compressibility at the end of rotating screw 312 closest to screw control section 326 or in its vicinity (i.e., the location where first sensor 328 is generally positioned) compared to the location at or near die 316 (i.e., the location where second and third sensors 329, 330 are generally positioned). Sensors 328, 329, 330 may measure variables such as material compressibility (e.g., by a method of measuring the force exerted thereon by molten plastic material 314) at their respective locations, which may be used to determine the measured density of molten plastic material 314 at each location. Native controller 340 receives these sensed values and determines a measured compressibility ratio value, which in some examples may be the difference and / or average between the measured variables obtained by sensors 328, 329, 330.

[0064] The measured compressibility ratio value may then be compared to the previously obtained reference compressibility ratio value. In some examples, during the validation stage, a number of variable extrusion sample runs are performed until a molded product having ideal and / or desirable characteristics is obtained. The measured values obtained from sensors 328, 329, 330 may be compared to each other during this ideal extrusion operation to generate a reference compressibility ratio value. In other examples, the reference compressibility ratio value may be obtained during a previous extrusion operation or during a production operation of the machine. More specifically, when a user identifies a preferred molded product or part, the user may instruct the control device 340 to flag a specific extrusion operation for the purpose of using the values sensed and measured in subsequent extrusion operations. Other examples are possible.

[0065] Depending on the environment, the measured compressibility ratio value may differ from the reference compressibility ratio value. For example, in some examples where PCR is used, the molten polymer material 314 may be non-uniform and thus may have different material properties throughout the product run. As a result, the density of the molten plastic material 314 may increase or decrease throughout the run. Existing systems may be able to determine whether material properties such as viscosity and density have changed, but such systems may not be able to distinguish between a change in material viscosity and a change in material density and instead may make the same adjustment or adjustments to the extrusion process regardless of what actual changes have occurred.

[0066] Based on the relationship change and comparison between the measured compressibility ratio value and the reference compressibility ratio value, the native control device 340 may adjust at least one control parameter for the purpose of causing the subsequently obtained sensed measurement value to be equal to the reference compressibility ratio value (or, in some examples, fall within a specified threshold of, for example, about ±5% of the reference compressibility ratio value).

[0067] In some examples, the operating parameters may be in the form of other corrective actions such as driving force of the screw, target extrusion pressure, and / or sending for further processing or blending of the molten plastic material 314. Such operating parameters may be performed on-the-fly during the extrusion operation by controlling the machine 300 to maintain the relative compressibility ratio between the first and second sensors 328, 329, 330.

[0068] 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 may additionally sense any change in the viscosity of the molten polymer material 314 and adjust the operating parameters in response to these changes. It is understood that, as a non-limiting example, the machine 300 may measure the shear rate of the molten polymer material 314 (e.g., the rate at which the molten polymer material 314 moves relative to the amount of pressure applied). Such measurement may be performed via the use of measurements of the movement (e.g., rotational speed) of the screw coupled to a sensor located in or near the die. Other suitable approaches are possible. The measured shear rate may be compared to a reference shear rate, and the difference between these values may be used to adjust the operating or control parameters such that the subsequently measured shear rate equals (or falls within an acceptable threshold of) the reference shear rate.

[0069] Turning to FIG. 4, an approach 400 is provided for controlling a molding machine having a die that forms a profile and a screw that rotates at a variable speed and is controlled according to a continuous extrusion process. First, at step 402, molten polymer is extruded through the die. At step 404, a first measurement variable during extrusion is obtained using a first sensor positioned on or near the screw. At step 406, a second measurement variable is obtained during extrusion. As described above, the second sensor is positioned on or near the die. At step 408, a measured compressibility ratio value is determined in the form of the difference between the measurement variable obtained by the first sensor and the measurement variable obtained by the second sensor. At step 410, the measured compressibility ratio value is compared with a reference compressibility ratio value. At step 410, at least one operating or control parameter is adjusted based on the difference between the reference compressibility ratio value and the measured compressibility ratio value.

[0070] Also, it is understood that the molding machines and approaches 100, 200, 300 and / or approach 400 described herein may measure compressibility and / or density using any number of alternative suitable approaches. For example, in some arrangements, a flow meter (not shown) may be disposed at the feed throat of the machine. Further, the use of two or three sensors may advantageously provide redundancy, but in some arrangements, an existing melt pressure transducer may be used in combination with additional sensors to approximate changes in material density. Similarly, in some examples, a load cell or hydraulic press may be used in combination with additional sensors to measure density. However, in other examples, the use of two or three separate sensors may advantageously eliminate the load cell and thus result in reduced equipment costs. In still other arrangements, a plunger advance system may be incorporated into the molding machine as an alternative to the screw that pushes the molten polymer material into the mold cavity. Compared to conventional systems that use upstream sensors, the system of the present invention may easily incorporate sensors downstream while allowing adjustment for changes in the density of the material.

[0071] Furthermore, in some arrangements, changes in material density may be used to determine scaling values for correction. For example, instead of starting the production of appropriate parts using a system that first determines initial setting values, it may be determined that this system should be used as a correction factor to correct for detected density changes in the initial parameters.

[0072] The molding machines 100 and 300 arranged in this way can make information-based decisions about process adjustments while accurately identifying the nature of changes in the material properties of the molten polymer material by distinguishing between density changes and viscosity changes, and unnecessary process adjustments may be eliminated. For example, although melt density and viscosity are independent properties of the molten polymer material, they can be affected by the same changes to the extrusion process. Therefore, adjustments to viscosity (e.g., pressure and other adjustments made during the molding process) may inadvertently affect the melt density during a cycle or process. Such adjustments may be eliminated in this system and approach because the system instead makes separately calculated pressure adjustments (e.g., at the end of the filling stage of an injection cycle). This decision may result in achieving the same stress distribution, shrinkage rate, and / or dimensional specifications as other processes that can adjust for viscosity variations, while also resulting in maintaining consistent part quality throughout the product run.

[0073] Such a system may allow an operator and / or machine to calculate in real time the true density (and / or viscosity) changes of the molten plastic and use this information in a feedback loop to appropriately adjust the system. Further, the material data may be saved in real time for the purpose of transmitting material quality data points to the processing equipment to assist in maintaining appropriate PCR regrind quality. Also, past data may be collected and saved for process quality control.

[0074] By incorporating the approach described herein, the molding machines 100, 300 can operate safely in an efficient manner by ensuring the production of parts with minimal defects and / or flaws while adjusting to keep the density and / or viscosity of the material constant. The processes described herein may be advantageously incorporated into conventional injection molding systems, injection molding systems incorporating a substantially constant pressure approach at low pressure, injection molding systems incorporating special controls based on real-time density measurements, extrusion molding systems, and other systems.

[0075] Furthermore, depending on the environment, the real-time density measurements described herein may result in time savings while consistently producing high-quality parts. The processes described herein may be advantageously incorporated into various extrusion molding systems for manufacturing tubes, rods, films, blown films, bags, pellets, bottles, and the like.

[0076] Furthermore, it will be understood that the systems and approaches described herein may be applied to the formation of any number of different molded parts composed of various materials such as, for example, silicone parts and metal parts.

[0077] The approach described above may be used in combination with any injection process in which the pattern specified above is used to drive at least a portion of the injection cycle. These approaches may be used in the formation of any number of different molded parts composed of various materials such as, for example, silicone parts and metal parts.

[0078] Those skilled in the art will recognize that various modifications, changes, and combinations can be made to the embodiments described above without departing from the scope of the invention, and such modifications, changes, and combinations are considered to be within the scope of the concept of the invention.

[0079] The appended claims of this patent application are not intended to be construed under 35 U.S.C. § 112(f) unless express recitation of conventional means-plus-function language such as "means for" or "steps for" is expressly recited in the claim(s). The systems and methods described herein are directed to improving computer functionality and are improvements over conventional computers.

Claims

1. A method for controlling a molding machine having a mold for forming a mold cavity, a nozzle, and a screw that moves from a first position to a second position toward the nozzle, wherein the injection molding machine is controlled by a control device according to a mold cycle, and the method is Injecting the molten polymer into the mold cavity, Using a first sensor positioned on or near the screw, a first measurement variable during the injection cycle is obtained. Using a second sensor positioned in or near the nozzle, a second measurement variable during the injection cycle is obtained. The method involves determining a measureable compressibility ratio value, wherein the measureable compressibility ratio value is the difference between the measureable variable obtained by the first sensor and the measureable variable obtained by the second sensor. The measured compressibility ratio value is compared with the reference compressibility ratio value. Adjusting at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value. Methods that include...

2. The method according to claim 1, wherein the measurement variable includes the compressibility of the molten plastic material.

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

4. The method according to claim 1, wherein the first sensor is positioned behind the base end of the screw.

5. The method according to claim 4, wherein the first sensor comprises a force sensor.

6. The method according to claim 1, wherein the second sensor is located in the flow path of the injection unit upstream of the mold cavity.

7. The method according to claim 1, wherein the step of adjusting the at least one control parameter includes adjusting the target injection pressure value.

8. A step of measuring the shear rate of the molten plastic material and determining the change in the viscosity value of the molten plastic material, and The method according to claim 1, further comprising the step of adjusting at least one control parameter based on the difference between the measured shear rate and the reference shear rate.

9. The method according to claim 1, wherein the reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during the previous injection cycle.

10. The method according to claim 9, wherein the preceding injection cycle includes a verification cycle or a projection cycle.

11. The molding machine, A molding unit having a mold for forming a mold cavity and a screw that moves from a first position to a second position toward a nozzle, wherein the injection unit is adapted to receive and inject molten plastic material into the mold cavity via the screw and the nozzle to form a molded part. A control device adapted to control the operation of the injection molding machine according to the molding cycle, A first sensor positioned on or near the screw and connected to the control device in a manner that allows communication, wherein the sensor is adapted to measure a variable during the injection cycle, A second sensor positioned on or near the nozzle and connected to the control device in a manner that enables communication with the control device, wherein the second sensor is adapted to measure the variable at a second time during the injection cycle. Equipped with, The control device is Initiating the injection of the molten polymer into the mold cavity, The method involves determining a measureable compressibility ratio value, wherein the measureable compressibility ratio value is the difference between the measureable variable obtained by the first sensor and the measureable variable obtained by the second sensor. The measured compressibility ratio value is compared with the reference compressibility ratio value, and Adjusting at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value. A molding machine that conforms to the requirements.

12. The molding machine according to claim 11, wherein the measurement variable includes the compressibility of the molten plastic material.

13. The molding machine according to claim 12, wherein the compressibility of the molten plastic material is used to determine its density value.

14. The molding machine according to claim 11, wherein the first sensor is positioned behind the base end of the screw.

15. The molding machine according to claim 11, wherein the first sensor comprises a force sensor.

16. The molding machine according to claim 11, wherein the second sensor is located in the flow path of the injection unit upstream of the mold cavity.

17. The molding machine according to claim 11, wherein the at least one control parameter includes a target injection pressure value.

18. The molding machine according to claim 11, wherein the control device is further adapted to measure the shear rate of the molten plastic material and determine a change in the viscosity value of the molten plastic material, and the control device is further adapted to adjust at least one control parameter based on the difference between the measured shear rate and a reference shear rate.

19. A method for controlling a molding machine having a die for forming a profile and a screw that can rotate at a variable speed, wherein the molding machine is controlled by a control device according to at least one molding parameter, and the method is Extruding the molten polymer through the die, A first measurement variable is obtained using a first sensor positioned on or near the screw. A second measurement variable is obtained using a second sensor positioned on or near the die. The method involves determining a measureable compressibility ratio value, wherein the measureable compressibility ratio value is the difference between the measureable variable obtained by the first sensor and the measureable variable obtained by the second sensor. The measured compressibility ratio value is compared with the reference compressibility ratio value, and Adjusting at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value. Methods that include...

20. The method according to claim 19, wherein the measurement variable includes the compressibility of the molten plastic material.

21. The method according to claim 20, wherein the compressibility of the molten plastic material is used to determine its density value.

22. The method according to claim 19, wherein the first sensor is positioned behind the base end of the screw.

23. The method according to claim 22, wherein the first sensor comprises a force sensor.

24. The method according to claim 19, wherein the second sensor is located in the flow path of the molding unit upstream of the die.

25. The method according to claim 19, wherein the second sensor is located outside the flow path of the molding unit.

26. The method according to claim 19, wherein the third sensor is located in the flow path of the molding unit upstream of the die.

27. The method according to claim 19, wherein the third sensor is located outside the flow path of the molding unit.

28. The method according to claim 19, wherein the step of adjusting the at least one control parameter includes a target molding pressure value.

29. A step of measuring the shear rate of the molten plastic material and determining the change in the viscosity value of the molten plastic material, and A step of adjusting at least one control parameter based on the difference between the measured shear rate and the reference shear rate. The method according to claim 19, further comprising:

30. The method according to claim 19, wherein the reference compressibility ratio value is obtained by measuring the reference compressibility ratio value during the previous operating period.

31. The molding machine, A molding unit having a die for forming a profile and a screw that can rotate at a variable speed, wherein the molding unit is adapted to receive and extrude molten plastic material through the profile via the screw to form a part. A control device adapted to control the operation of the molding machine according to at least one set parameter, A first sensor positioned on or near the screw and connected to the control device in a manner that enables communication, wherein the first sensor is adapted to measure a variable during operation, A second sensor positioned on or near the die and connected to the control device in a manner that enables communication with the control device, wherein the second sensor is adapted to measure the variable during a second period of time during the operation. Equipped with, The control device, To initiate the extrusion of the molten polymer through the die, The method involves determining a measureable compressibility ratio value, wherein the measureable compressibility ratio value is the difference between the measureable variable obtained by the first sensor and the measureable variable obtained by the second sensor. The measured compressibility ratio value is compared with the reference compressibility ratio value, and Adjusting at least one control parameter based on the difference between the reference compressibility ratio value and the measured compressibility ratio value. A molding machine that conforms to the requirements.

32. The molding machine according to claim 31, wherein the measurement variable includes the compressibility of the molten plastic material.

33. The molding machine according to claim 32, wherein the compressibility of the molten plastic material is used to determine its density value.

34. The molding machine according to claim 31, wherein the first sensor is positioned behind the base end of the screw.

35. The molding machine according to claim 34, wherein the first sensor comprises a force sensor.

36. The molding machine according to claim 31, wherein the second sensor is located in the flow path of the molding unit upstream of the die.

37. The molding machine according to claim 31, wherein the second sensor is located outside the flow path of the molding unit.

38. The molding machine according to claim 31, wherein the third sensor is located in the flow path of the molding unit upstream of the die.

39. The molding machine according to claim 31, wherein the third sensor is located outside the flow path of the molding unit.

40. The molding machine according to claim 31, wherein the at least one control parameter includes a target pressure value.

41. The molding machine according to claim 31, wherein the control device is further adapted to measure the shear rate of the molten plastic material and determine a change in the viscosity value of the molten plastic material, and the control device is further adapted to adjust at least one control parameter based on the difference between the measured shear rate and a reference shear rate.

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