CN114407314A - Micro injection mold with in-mold rheology online measurement function and measurement and control method - Google Patents
Micro injection mold with in-mold rheology online measurement function and measurement and control method Download PDFInfo
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- 238000005259 measurement Methods 0.000 title claims abstract description 42
- 238000000518 rheometry Methods 0.000 title claims abstract description 31
- 238000000520 microinjection Methods 0.000 title claims abstract description 25
- 238000000034 method Methods 0.000 title claims abstract description 23
- 229920000642 polymer Polymers 0.000 claims abstract description 79
- 238000001746 injection moulding Methods 0.000 claims abstract description 25
- 238000010438 heat treatment Methods 0.000 claims abstract description 8
- 239000012530 fluid Substances 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 4
- 238000010094 polymer processing Methods 0.000 claims description 4
- 238000012545 processing Methods 0.000 claims description 4
- 238000011144 upstream manufacturing Methods 0.000 claims description 3
- 230000008569 process Effects 0.000 abstract description 9
- 238000000465 moulding Methods 0.000 abstract description 6
- 230000001105 regulatory effect Effects 0.000 abstract description 6
- 239000000463 material Substances 0.000 abstract description 3
- 238000005516 engineering process Methods 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 230000007547 defect Effects 0.000 description 5
- 239000004033 plastic Substances 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 239000002861 polymer material Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005489 elastic deformation Effects 0.000 description 1
- 230000009477 glass transition Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 239000012815 thermoplastic material Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/76—Measuring, controlling or regulating
- B29C45/78—Measuring, controlling or regulating of temperature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/26—Moulds
- B29C45/27—Sprue channels ; Runner channels or runner nozzles
- B29C45/2701—Details not specific to hot or cold runner channels
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/76—Measuring, controlling or regulating
- B29C45/77—Measuring, controlling or regulating of velocity or pressure of moulding material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/76006—Pressure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/7604—Temperature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76003—Measured parameter
- B29C2945/7605—Viscosity
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76177—Location of measurement
- B29C2945/76254—Mould
- B29C2945/76274—Mould runners, nozzles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76494—Controlled parameter
- B29C2945/76531—Temperature
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76655—Location of control
- B29C2945/76658—Injection unit
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2945/00—Indexing scheme relating to injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould
- B29C2945/76—Measuring, controlling or regulating
- B29C2945/76822—Phase or stage of control
- B29C2945/76859—Injection
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/76—Measuring, controlling or regulating
- B29C45/7646—Measuring, controlling or regulating viscosity
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- Engineering & Computer Science (AREA)
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- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
The invention relates to a micro injection mold with an in-mold rheology online measurement function and a measurement and control method, wherein in the molding process, materials flow into a mold cavity through a flow channel through a nozzle in a molten state, wherein a section of a measurement channel far away from a sprue is taken as a rheology measurement channel by utilizing the characteristic of narrow cross section and long length of the flow channel in the micro injection mold so as to ensure that a polymer is fully developed in the flow channel, pressure sensors and temperature sensors are arranged at two ends of the measurement channel, and a controller analyzes and calculates the rheology state of the polymer by utilizing data to realize online measurement of the rheology state of the polymer in the mold; the heating power of the plasticizing unit is dynamically controlled by utilizing the difference between the obtained real-time viscosity and the set viscosity of the polymer, the plasticizing process of the polymer is dynamically regulated and controlled by means of the rheological state, the online control of the polymer rheology in the mold is realized, and the high-quality and rapid molding of the injection molding product with the fine structure is ensured.
Description
Technical Field
The invention relates to the field of microstructure injection molding, in particular to a micro injection mold with an in-mold rheology online measurement function and a measurement and control method.
Background
During the production process of injection-molded products, the changes of the state parameters (temperature, pressure, viscosity, etc.) of the polymer can affect the defects of surface roughness, flash, warping, profile precision, surface profile corrugation, etc. of the final products, and the quality of the products. In the polymer processing process, the online characterization technology can characterize the state of the polymer, and the processed data can be used for regulating and controlling process parameters, so that the online characterization technology is more and more important for flexible production processes.
In the prior art, the rheological measurement in the injection molding process of the microstructure polymer is mainly based on an off-line rheological measurement technology, and the rheological property of the material can be measured only under the condition of departing from the real production process of the polymer material. The rheological properties of the polymer material during the injection molding of microstructures are not clear and are different from the state of the polymer during the conventional injection molding process. The rheological state of the polymer in the traditional injection molding process cannot be accurately obtained by utilizing an offline rheological measurement technology, and the rheological representation of the polymer in the microstructure injection molding process cannot be further performed.
With the continuous progress of the micro injection molding machine technology, the injection rate of the screw or piston system can reach 750mm/s at present, conditions are created for rheological measurement of a micro-structure injection molding product, an online detection method of the rheological state of a polymer in the micro-structure injection molding process is integrated, reference can be provided for adjustment of the state parameters of the polymer, and the method has a very important effect on detection, regulation and control of the micro-structure polymer injection molding process. Related scientific research personnel adopt the advantages to measure the rheological property of the polymer with the fine structure at the nozzle of the microstructure injection molding machine, and the development of the polymer on-line rheological characterization technology is promoted. However, the rheological state of the polymer in the mold is still different from that of the polymer at the nozzle, the prior art cannot directly measure and control the rheological property of the polymer with a fine structure in the mold in the actual production process, and the online accurate measurement and control of the rheological state of the polymer in the injection molding process of the fine structure still have great challenges.
Disclosure of Invention
Aiming at the quality defects in the injection molding process of the existing fine microstructure plastic product and the defect that the online accurate measurement and control of the rheological state of the polymer in the injection molding process of the fine microstructure can not be realized, the invention provides the micro injection mold with the in-mold rheological online measurement function and the measurement and control method.
The purpose of the invention is realized by the following technical scheme:
a micro injection mold with an in-mold rheology online measurement function comprises a mold assembly and a rheology measurement assembly;
the die assembly comprises a feeding hole, a fixed die base plate, a fixed die plate, a movable die plate, a cushion block and a movable die base plate which are arranged in sequence from top to bottom; cooling pipelines are arranged inside the fixed template and the movable template; at least two runners with circular cross sections and a product cavity connected with the end parts of the runners are formed when the fixed die plate and the movable die plate are locked; the flow channels are arranged along the feed inlet in a mirror image mode, and the length-diameter ratio L/D of the flow channels is larger than 15;
the rheological measurement assembly comprises an outlet temperature sensor, an inlet temperature sensor, an outlet pressure sensor, an inlet pressure sensor, an amplifier and a controller; the outlet temperature sensor and the outlet pressure sensor are both arranged near the outlet of the flow channel, and the inlet temperature sensor and the inlet pressure sensor are arranged near the inlet of the flow channel; the outlet temperature sensor, the inlet temperature sensor, the outlet pressure sensor and the inlet pressure sensor are all connected with the amplifier, and the amplifier is connected with the controller;
the amplifier is used for receiving the signal detected by the sensor, amplifying the signal and transmitting the amplified signal to the controller;
the controller is used for processing and calculating the signal of the amplifier to obtain the real-time viscosity of the polymer in the mould; analyzing the real-time viscosity as a reference for adjusting the temperature of the polymer in the plasticizing unit of the injection molding machine;
further, the outlet pressure sensor and the inlet pressure sensor are both arranged on the inner wall surface of the flow channel; the outlet temperature sensor and the inlet temperature sensor are both arranged at positions close to the wall surface of the flow channel;
further, the outlet temperature sensor and the outlet pressure sensor are temperature and pressure integrated sensors, and the inlet pressure sensor and the inlet temperature sensor are also temperature and pressure integrated sensors;
another object of the present invention is to provide a measurement and control method using any of the above solutions, which includes the following steps:
(1) selecting a section of the flow channel with the length-diameter ratio larger than 10 as a measuring flow channel, arranging an outlet temperature sensor and an outlet pressure sensor at the downstream end of the measuring flow channel, and arranging an inlet temperature sensor and an inlet pressure sensor at the upstream end of the measuring flow channel;
(2) injecting polymer melt from a feed inlet, and filling a product cavity through the runner; the outlet temperature sensor, the outlet pressure sensor, the inlet temperature sensor and the inlet pressure sensor measure the inlet and outlet pressure and temperature of the polymer melt in real time, signals are amplified by the amplifier and then transmitted to the controller, and the controller calculates the real-time viscosity difference delta eta of the polymer melt in the following mode:
wherein eta isaIs polymerized intoThe real-time viscosity of the compound melt is expressed in Pa.s; eta is the polymer processing set viscosity obtained based on a Cross-WLF equation, and the unit is Pa & s; tau iswIs wall shear stress in MPa;
is the wall shear rate in units of s-1(ii) a Δ p is the pressure drop between the inlet and outlet of the measurement channel in Pa; r is the radius of the measurement channel in m; l is the length of the measuring channel and is in m;
the apparent shear rate is the shear rate of the Newtonian fluid at the wall of the tube in units of s-1；TnThe temperature of the polymer melt in the plasticizing unit during the nth die closing is measured in units of temperature; t is the temperature of the current polymer melt, and the unit is; delta T is the adjusting temperature of a plasticizing unit of the injection molding machine, and the unit is; the power of the plasticizing heating sleeve can be used for adjustment; delta is a set viscosity threshold in Pa · s; eta0Zero shear viscosity in Pa · s units,
is shear rate, in units of s-1，τ*The critical shear stress at the transition to shear thinning is given in MPa.
(4) And controlling the temperature of a plasticizing unit of the injection molding machine by utilizing the real-time viscosity difference so as to control the real-time viscosity of the polymer melt in the mold.
The invention has the beneficial effects that:
(1) according to the micro injection mold with the in-mold rheology online measurement function and the measurement and control method, the rheology measurement component is integrated in the micro injection mold, the viscosity of a polymer passing through a flow channel of the micro injection mold is detected in real time, and the micro injection mold is convenient, efficient, compact in structure, small in size and capable of saving the installation space;
(2) a section of the flow channel is selected as a measuring channel, the change of viscoelasticity of the polymer in the circular measuring channel is considered, the polymer is ensured to be fully developed in the flow channel, and the measuring precision is high.
(3) The online rheological state of the polymer melt is used as an index, the rheological state of the polymer melt in the micro injection mold is regulated and detected by utilizing the temperature of the plasticizing unit during repeated mold closing, the heating power of the plasticizing heating sleeve is dynamically regulated, the state of the polymer is further regulated, and the defects in the injection molding process of the plastic product with the fine structure are reduced.
(4) Compared with the traditional production process of plastic products, the method can realize the monitoring and control of the rheology of the polymer melt and realize the high-quality and rapid production of the plastic injection molding products.
Drawings
FIG. 1 is a perspective view of a micro injection mold according to the present invention;
FIG. 2 is a schematic view of an inner runner of a micro injection mold according to the present invention;
FIG. 3 is a block diagram of a digital circuit process to which the present invention relates;
in the figure: the mold comprises a mold component 1, a rheological measurement component 2, a heating jacket 3, a feeding hole 101, a fixed mold base plate 102, a fixed mold plate 103, a cooling pipeline 104, a movable mold plate 105, a cushion block 106, a movable mold base plate 107, an outlet temperature sensor 201, an inlet temperature sensor 202, an outlet pressure sensor 203, an inlet pressure sensor 204, a flow channel 205, a measurement flow channel 2051, an amplifier 206 and a controller 207.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments, and the objects and effects of the present invention will become more apparent, it being understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
As shown in fig. 1, in the present embodiment, a micro injection mold with an in-mold rheology online measurement function includes a mold assembly 1 and a rheology measurement assembly 2.
The die assembly comprises a feed inlet 101, a fixed die base plate 102, a fixed die plate 103, a movable die plate 105, a cushion block 106 and a movable die base plate 107 which are arranged from top to bottom in sequence. Cooling pipelines 104 are arranged inside the fixed die plate 103 and the movable die plate 105; when the fixed die plate 103 and the movable die plate 105 are locked, less than two runners 205 with circular cross sections and product cavities connected with the end parts of the runners are formed; the flow channels are arranged in mirror image along the feed port 101 and the length to diameter ratio L/D of the flow channel 207 is greater than 15. The number of the flow passages 205 is set as required, and not less than two.
The rheological measurement assembly includes an outlet temperature sensor 201, an inlet temperature sensor 202, an outlet pressure sensor 203, an inlet pressure sensor 204, an amplifier 206, and a controller 207. Both the outlet temperature sensor 201 and the outlet pressure sensor 203 are arranged near the outlet of the flow channel 205, and the inlet temperature sensor 202 and the inlet pressure sensor 204 are arranged near the inlet of the flow channel 207. The outlet temperature sensor 201, the inlet temperature sensor 202, the outlet pressure sensor 203 and the inlet pressure sensor 204 are all connected with an amplifier 206, and the amplifier 206 is connected with a controller 207. The amplifier 206 is used for receiving the signal detected by the sensor, amplifying the signal and transmitting the amplified signal to the controller; the controller 207 is used for processing and calculating the signal of the amplifier 206 to obtain the real-time viscosity of the polymer in the mold; and the real-time viscosity is analyzed as a reference for adjusting the temperature of the polymer in the plasticizing unit of the injection molding machine.
Preferably, the outlet temperature sensor 201 and the outlet pressure sensor 203 are temperature and pressure integrated sensors capable of measuring temperature and pressure simultaneously. The inlet pressure sensor 204 and the inlet temperature sensor 202 are also temperature and pressure integrated sensors.
The on-line monitoring method for the rheological property of the polymer in the injection molding process of the microstructure realizes the viscosity measurement of the polymer in a micro injection mold in the molding process through a plurality of sensors. As shown in FIG. 2, after entering the runner 205 through the gate, the polymer melt fills the product cavity, and a section of the runner 205 where the fluid flows stably is selected as a measuring channel 2051, wherein the measuring channel 2051 has a structural form with a circular cross section, and the length-diameter ratio L/D of the channel is strictly controlled to be more than 10. In order to ensure the accuracy of the rheological measurement and prevent the elastic deformation of the polymer fluid from causing measurement errors, the temperature sensor 202 and the pressure sensor 204 which are arranged on the side wall of the measuring channel 2051 are positioned at the upstream of the runner 205, and the outlet temperature sensor 201 and the outlet pressure sensor 203 which are arranged on the side wall of the measuring channel 2051 are positioned at the outlet of the runner 205And (3) downstream. The pressure p of the polymer melt on the pipe wall at the inlet of the measuring channel 2051 is detected by an inlet pressure sensor 2041The pressure p of the polymer melt on the pipe wall at the outlet of the measuring channel 2051 is detected by the outlet pressure sensor 2032The inlet and outlet pressure difference Δ p is calculated from the inlet and outlet pressure.
As shown in fig. 3, the detected signals are amplified by the inlet temperature sensor 202, the inlet pressure sensor 204, the outlet temperature sensor 201, and the outlet pressure sensor 203 through the amplifier 206, and the amplified signals are a/D converted and then sent to the controller 207. The controller 207 receives signals from the inlet temperature sensor 202, the inlet pressure sensor 204, the outlet temperature sensor 201 and the outlet pressure sensor 203, processes and calculates the signals and displays the real-time viscosity. The controller 207 analyzes the calculated real-time viscosity, combines a Cross-WLF equation, utilizes algorithm processing to analyze the state of the polymer melt, regulates and detects the rheological state of the polymer melt in the micro injection mold by utilizing the temperature of the plasticizing unit during repeated mold closing, calculates the real-time viscosity of the polymer melt in the mold, considers that the viscosity of the polymer melt reaches a reasonable range when the difference value between the real-time viscosity and the set viscosity is not greater than a set threshold value, realizes the online control of the rheological state in the polymer mold, ensures that the polymer reaches an optimal flowing state, reduces the defects of products in the micro injection molding process, and realizes the rapid and efficient molding of injection molded products with fine structures.
In this embodiment, the online measurement and control method for the intramode rheology of the polymer may include the following measurement and control steps:
the rheological state of the polymer in the micro injection mould is calculated by mainly utilizing a calculation formula of circular tube shear stress and a Weissenberg-Rabinowtich shear rate formula.
Shear stress tauwThe calculation formula is as follows:
shear rate
The calculation formula is as follows:
in the formula: Δ p is the pressure drop between the measurement channels in Pa; r is the radius of the measurement channel in m; l is the length of the measuring channel and is in m;
the apparent shear rate is the shear rate of the Newtonian fluid at the wall of the tube in units of s-1。
Firstly, any polymer melt flowing through a measuring channel is regarded as Newtonian fluid, and the shear stress tau borne by the material at the pipe wall is calculated through the pressure drop measured by a pressure sensorwAfter the volume flow or the average flow velocity of the melt is measured, the apparent shear rate at the pipe wall can be obtained
According to the nature of the particular polymer, i.e. the shear stress τ at the tube wallwAnd apparent shear rate
Constitutive relation between or measured
The true shear rate at the pipe wall of the polymer melt flowing through the measuring channel can be determined
From shear stress τ of the pipe wallwAnd shear rate
Obtaining a polymer material inViscosity in the mold
The regulation and control of the viscosity state of the polymer are based on a Cross-WLF equation, and the correlation of the temperature, the shear rate and the pressure of the viscosity of the thermoplastic material is established, and the specific expression formula is as follows:
wherein:
A2＝A3+D3+P
wherein η is the viscosity of the polymer melt in Pa · s; eta0Zero shear viscosity in Pa · s;
is shear rate, in units of s-1；τ*The critical shear stress when changing to shear thinning is expressed in MPa; t is temperature in units of; t is*Glass transition temperature in units of; p is pressure in Pa; d1、A1、A3And D3Are fitted data coefficients.
The rheological state of the polymer in the mould is adjusted by adjusting the heating power of the plasticizing unit, namely, the real-time viscosity of the polymer melt in the mould is controlled:
wherein: Δ η is the current measured viscosity ηaWith polymer processing meansDetermining the difference between the viscosities eta, wherein the unit is Pa & s; t isnThe temperature of the polymer melt in the plasticizing unit in the previous n times of die assembly is measured in units of ℃; t is the temperature of the current polymer melt, and the unit is; delta T is the adjusting temperature, and can be adjusted by the power of a plasticizing heating sleeve, and the unit is; Δ is the set viscosity threshold in Pa · s.
Considering the delay generated in the regulation and control process, the current temperature is approximate by using the melt temperature of the plasticizing unit during n times of mold closing, so that the rheological state of the polymer melt in the micro injection mold is regulated and detected, the real-time viscosity of the polymer melt in the mold is calculated, and when the difference value between the real-time viscosity and the set viscosity is not greater than the set threshold value, the viscosity of the polymer melt is considered to reach a reasonable range.
According to the method for calculating the viscosity, a part of the flow channel with stable fluid flow in the flow channel is selected as the measuring channel, so that errors brought by the change of the viscoelasticity of the polymer to the measurement are avoided, the polymer is ensured to be fully developed in the flow channel, and therefore the measuring result has higher accuracy. By the measuring method, a complex and expensive capillary rheometer is not needed, the rheological property of the polymer in the die in the injection molding process of the fine structure can be represented, and the influence of the viscosity of the polymer in the die cavity on the product is detected.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and although the invention has been described in detail with reference to the foregoing examples, it will be apparent to those skilled in the art that various changes in the form and details of the embodiments may be made and equivalents may be substituted for elements thereof. All modifications, equivalents and the like which come within the spirit and principle of the invention are intended to be included within the scope of the invention.
Claims (4)
1. The micro injection mold with the in-mold rheology online measurement function is characterized by comprising a mold component and a rheology measurement component;
the die assembly comprises a feeding hole, a fixed die base plate, a fixed die plate, a movable die plate, a cushion block and a movable die base plate which are arranged in sequence from top to bottom; cooling pipelines are arranged inside the fixed template and the movable template; at least two runners with circular cross sections and a product cavity connected with the end parts of the runners are formed when the fixed die plate and the movable die plate are locked; the flow channels are arranged along the feed inlet in a mirror image mode, and the length-diameter ratio L/D of the flow channels is larger than 15;
the rheological measurement assembly comprises an outlet temperature sensor, an inlet temperature sensor, an outlet pressure sensor, an inlet pressure sensor, an amplifier and a controller, wherein both the outlet temperature sensor and the outlet pressure sensor are arranged near the outlet of the flow channel, and the inlet temperature sensor and the inlet pressure sensor are arranged near the inlet of the flow channel; the outlet temperature sensor, the inlet temperature sensor, the outlet pressure sensor and the inlet pressure sensor are all connected with the amplifier, and the amplifier is connected with the controller;
the amplifier is used for receiving the signal detected by the sensor, amplifying the signal and transmitting the amplified signal to the controller;
the controller is used for processing and calculating the signal of the amplifier to obtain the real-time viscosity of the polymer in the mould; and the real-time viscosity is analyzed as a reference for adjusting the temperature of the polymer in the plasticizing unit of the injection molding machine.
2. The micro injection mold with the on-line intramode rheology measurement function according to claim 1, wherein the outlet pressure sensor and the inlet pressure sensor are both arranged on the inner wall surface of the runner; the outlet temperature sensor and the inlet temperature sensor are both arranged at positions close to the wall surface of the flow channel.
3. The micro injection mold with the on-line measurement function of the intramode rheology according to claim 1, wherein the outlet temperature sensor and the outlet pressure sensor are temperature and pressure integrated sensors, and the inlet pressure sensor and the inlet temperature sensor are also temperature and pressure integrated sensors.
4. An on-line measurement and control method for the in-mold rheology of a polymer, which is realized based on the micro injection mold with the in-mold rheology on-line measurement function of claim 1, is characterized by comprising the following steps:
(1) selecting a section of the flow channel with the length-diameter ratio larger than 10 as a measuring flow channel, arranging an outlet temperature sensor and an outlet pressure sensor at the downstream end of the measuring flow channel, and arranging an inlet temperature sensor and an inlet pressure sensor at the upstream end of the measuring flow channel;
(2) injecting polymer melt from a feed inlet, and filling a product cavity through the runner; the outlet temperature sensor, the outlet pressure sensor, the inlet temperature sensor and the inlet pressure sensor measure the inlet and outlet pressure and temperature of the polymer melt in real time, signals are amplified by the amplifier and then transmitted to the controller, and the controller calculates the real-time viscosity difference delta eta of the polymer melt in the following mode:
wherein eta isaIs the real-time viscosity of the polymer melt in Pa · s; eta is the polymer processing set viscosity obtained based on a Cross-WLF equation, and the unit is Pa & s; tau iswIs wall shear stress in MPa;
is the wall shear rate in units of s-1(ii) a Δ p is the pressure drop between the inlet and outlet of the measurement channel in Pa; r is the radius of the measurement channel in m; l is the length of the measuring channel and is in m;
the apparent shear rate is the shear rate of the Newtonian fluid at the wall of the tube in units of s-1；TnThe temperature of the polymer melt in the plasticizing unit during the nth die closing is measured in units of temperature; t is the temperature of the current polymer melt, and the unit is; delta T is the adjusting temperature of a plasticizing unit of the injection molding machine, and can be adjusted by the power of a plasticizing heating sleeve, and the unit is; delta is a set viscosity threshold in Pa · s; eta0Zero shear viscosity in Pa · s units,
is shear rate, in units of s-1，τ*The critical shear stress when changing to shear thinning is expressed in MPa;
(4) and controlling the temperature of a plasticizing unit of the injection molding machine by utilizing the real-time viscosity difference so as to control the real-time viscosity of the polymer melt in the mold.
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