CN107310092B - Precision injection molding method and device for optical device with polymer complex surface - Google Patents

Precision injection molding method and device for optical device with polymer complex surface Download PDF

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CN107310092B
CN107310092B CN201710384687.7A CN201710384687A CN107310092B CN 107310092 B CN107310092 B CN 107310092B CN 201710384687 A CN201710384687 A CN 201710384687A CN 107310092 B CN107310092 B CN 107310092B
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temperature
micro
mold
motion
injection molding
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CN107310092A (en
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张楠
张皓洋
房丰洲
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Tianjin University
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Tianjin University
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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
    • B29C45/0025—Preventing defects on the moulded article, e.g. weld lines, shrinkage marks
    • 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
    • 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
    • B29C45/72—Heating or cooling
    • B29C45/73—Heating or cooling of the mould
    • 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
    • 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
    • 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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2011/00—Optical elements, e.g. lenses, prisms

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

Abstract

The invention belongs to the field of precise optical injection molding in advanced manufacturing and optical manufacturing, aims at solving the problems of large volume shrinkage, low surface shape precision, obvious residual stress and the like caused by factors such as thickness, surface shape and the like, and aims to realize injection molding of a polymer optical device with high surface shape precision and low residual stress. The invention relates to a precise injection molding method and a device for an optical device with a polymer complex surface, which consists of an injection molding machine, a mold, a multi-section variable mold temperature auxiliary molding system based on the surface shape and an in-mold micro-motion correction auxiliary molding system. The multi-section variable mold temperature auxiliary forming system based on the surface shape is realized by a variable mold temperature power supply module, a variable mold temperature control module, a heating element, a heat insulation element, a cooling water path and a variable mold temperature sensing module, and is used for enabling the temperature of a mold surface to be higher than the glass transition temperature of a material or to be close to the melting temperature of the material in the filling and pressure maintaining stages; and then gradually reducing the temperature of the mold to the viscoelastic state temperature of the material to realize feature replication. The invention is mainly applied to optical injection occasions.

Description

Precision injection molding method and device for optical device with polymer complex surface
Technical Field
The invention belongs to the field of precise optical injection molding in advanced manufacturing and optical manufacturing, and is particularly suitable for injection molding processing of complex-shaped and thick-wall polymer optical devices.
Background
Typical optical devices such as f-theta scanning lenses in laser printers, optical lenses with complex surfaces with thick walls such as projection prisms in virtual reality glasses, and micro-lens arrays in light field cameras are all key imaging components of photoelectric products. The micro lens array has wide application in the fields of robot detection, micro aircraft systems, light uniformization, uniform imaging and the like. In recent years, aspheric surfaces, free-form surface optics, and the like have attracted attention from researchers. Although the design of optical devices varies from application to application, they have essentially in common that they are complex in shape and uneven in wall thickness.
For complex-faced optics, non-uniform thickness tends to result in non-uniform cooling during processing. Uneven cooling can lead to uneven shrinkage, which in turn results in greater residual stress, lower profile accuracy and limits the effective imaging area. In order to overcome the problem, scholars at home and abroad carry out a great deal of experimental and theoretical researches on surface shape precision, residual stress, imaging quality and the like. At present, the main control methods for ensuring the surface shape precision include precision mold core compensation and adjustment, injection molding process optimization, injection compression molding process and the like. The common methods for controlling the residual stress include a variable mold temperature technology, annealing and the like. Although the precision mold core compensation can reduce the surface shape error to a certain extent, the reconstruction and fitting are difficult, the process stability is not high, and the compensation effect is not obvious. The process optimization can improve the surface shape precision and reduce the residual stress, but the influence factors are numerous, and the improvement is difficult when the surface shape precision reaches a certain degree. The injection compression process is beneficial to forming a thin-wall optical device with low internal stress and high dimensional accuracy, but the condition of uneven pressure transmission in the compression process can exist, so that the uniformity of the density and the refractive index of the optical device is influenced, and the phenomena of larger residual stress and birefringence are caused. In addition, the motion control precision of the traditional injection molding compression process is low, and the requirement of thickness tolerance of a precision optical device cannot be met. The variable mold temperature auxiliary forming and annealing post-treatment are beneficial to removing residual stress and birefringence. At present, the same set of cooling and heating water channels are generally adopted for cooling and heating of the traditional variable-mold-temperature system, the temperature uniformity of the mold surface and the cooling uniformity of a sample cannot be well controlled, and the residual stress cannot be remarkably reduced or even eliminated under the condition of ensuring the surface shape. Although the annealing can eliminate the stress, the treatment time is long, and the release of residual stress can obviously influence the surface shape precision. It can be found from the literature that the precision injection molding of the optical device mainly aims at the plano-convex spherical lens, and the study on complex surfaces such as aspheric surfaces and free-form surfaces is less. With the wide application of the complex surface in the fields of imaging, lighting, light gathering and the like, the precise and ultra-precise forming technology of the complex surface becomes the leading edge of research. Therefore, the precise and ultra-precise injection molding technology of the optical device with the complex surface, even the optical device with the free-form surface, has great challenge, and the method and the basic research thereof have important significance and application value for the development of the optical industry.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a precise and ultra-precise injection molding method for a polymer optical device with a complex surface, aiming at the problems of large volume shrinkage, low surface precision, obvious residual stress and the like caused by factors such as thickness, surface shape and the like, and realizing the injection molding of the polymer optical device with high surface precision and low residual stress. The invention adopts the technical scheme that the precise injection molding device for the optical device with the complicated polymer surface consists of an injection molding machine, a mold, a variable mold temperature auxiliary molding system based on the surface shape and an in-mold micro-motion shape correction auxiliary molding system. The surface shape-based variable mold temperature auxiliary forming system is realized by a variable mold temperature power supply module, a variable mold temperature control module, a heating element, a heat insulation element, a cooling water path and a variable mold temperature sensing module, and is used for enabling the mold surface temperature to be higher than the glass transition temperature of a material or to be close to the melting temperature of the material in the filling and pressure maintaining stages, reducing the molecular chain orientation caused by wall surface shearing when a polymer is injected into a mold, and further reducing the residual stress caused by flowing; then gradually reducing the temperature of the mold to the viscoelastic state temperature of the material, and matching with micro-motion compression to realize feature replication;
the in-mold micro-motion shape correction auxiliary forming system is composed of a micro-motion power supply module, a micro-motion control module, a micro-motion compression driver, a forming heat insulation element and a micro-motion sensing module, and has two operation modes: firstly, in the cooling process, micro-motion compression is carried out on the material in a viscoelastic state temperature range to precisely regulate and control the surface shape and the micro-nano structure replication precision of a sample, thermal residual stress is further released, and then the temperature of a die is reduced to be lower than the thermal deformation temperature of the material in a micro-motion compression state; secondly, cooling the sample to the thermal deformation temperature to form the prefabricated part, then raising the temperature of the mold to the viscoelastic state temperature, realizing surface shape correction through material creep under micro-motion compression, further releasing residual stress, and then lowering the temperature of the mold to be below the thermal deformation temperature of the material in the micro-motion compression state.
The stroke of the micro-motion compression is measured through a resistance strain gauge integrated in the micro-motion compression driver, and one-way in-mold micro-motion correction or multidirectional in-mold micro-motion correction can be performed.
The precise injection molding method of the optical device with the complicated polymer surface comprises an injection molding process, a temperature changing process and a shape correcting process, wherein the temperature changing process corresponds to a variable mold temperature auxiliary molding system based on the surface shape, and the shape correcting process corresponds to a micromotion shape correcting auxiliary molding system in a mold; the injection molding process comprises plasticizing, injecting, pressure maintaining, cooling, mold opening, ejecting and mold closing, wherein the plasticizing, cooling, mold opening and ejecting process links are parallel; meanwhile, in an injection molding cycle, the temperature changing process consists of a coil heating link, a water channel cooling link and a coil heating link, and the shape correcting process consists of a micro-motion compression/execution link and a micro-motion compression/release link; the injection molding process, the temperature changing process and the shape correcting process are carried out in parallel;
the variable mold temperature auxiliary forming based on the surface shape in the mold is realized by designing a heating and cooling system, wherein the heating and cooling system comprises a heating element, a heat insulation element and a cooling water path, the heating mode can be selected from electromagnetic induction heating, ceramic heating and liquid heating, and the cooling mode can be selected from liquid cooling and gas cooling; for the condition that the surface shape change of the free curved surface is large, a heating and cooling system and the package thereof need to be designed into a three-dimensional structure according to the surface shape change of the optical element; the integral heating and cooling system is integrated on the fixed die core and the movable die core, and a ceramic heat insulation sleeve is arranged outside the die core to realize the rapid temperature rise and cooling of the die core; the variable mold temperature sensing module can be selected from a temperature sensor, a pressure sensor and a temperature and pressure sensor so as to measure the temperature and the pressure in the mold; the variable-temperature auxiliary forming system based on the surface shape adopts a time sequence control method similar to an injection molding process, is triggered by an injection signal of an injection molding machine, is powered by a variable-mold-temperature power module, drives a heating and cooling system to work by a variable-mold-temperature control module, and acquires temperature data in a mold by a variable-mold-temperature sensing module; and ensuring that the pressure in the die cavity does not exceed the maximum output pressure of the micro-motion correction system according to the measured data of the temperature and the pressure in the die cavity.
Starting micro-motion compression through an execution device of a precise micro-motion compression system, wherein a micro-motion shape correction system in the die consists of a micro-motion compression driver and a heat insulation element and is matched with a movable die core to perform micro-motion shape correction; the micro-motion sensing module is selected from a resistance type sensor, a capacitance type sensor and an inductance type sensor, so that the micro-motion compression stroke is measured, and the micro-motion compression driver is matched to correct the shape of the sample within the thickness tolerance range.
For an optical device, the glass state temperature of the material is high, and when the material is actually used, the micro-motion compression driver and the micro-motion sensing module can work within the range of room temperature to 140 ℃. The micro-motion sizing process needs a certain pressure, and the sizing pressure is set to 1000N within the range of ensuring the extension and contraction of the piezoelectric ceramics. The whole shape correcting process is powered by a micro-motion power module, triggered by an injection molding signal of an injection molding machine, drives a micro-motion compression driver to work by a micro-motion control module, and collects micro-motion compression displacement data by a micro-motion sensing module; the start of the micro-motion shape correction is determined according to the temperature and pressure value change of the die cavity, and the start is carried out through time sequence delay, wherein shape correction parameters comprise shape correction pressure, shape correction time and shape correction temperature; the micro-motion compression auxiliary shape correction has two operation modes: firstly, in the cooling process, micro-motion compression is carried out on the material in a viscoelastic state temperature range to precisely regulate and control the surface shape and the micro-nano structure replication precision of a sample, thermal residual stress is further released, and then the temperature of a die is reduced to be lower than the thermal deformation temperature of the material in a micro-motion compression state; secondly, cooling the sample to the thermal deformation temperature to form a prefabricated part, then raising the temperature of the mold to the viscoelastic state temperature, realizing surface shape correction through material creep under micro-motion compression, further releasing residual stress, and then lowering the temperature of the mold to be below the thermal deformation temperature of the material in the micro-motion compression state; on one hand, the close contact between the die surface and the die core in the cooling process is ensured, and the surface shape correction or the precise copying of a fine structure is realized; on the other hand, in order to further eliminate the residual stress generated by uneven cooling, after the sample is cooled, the temperature is raised, a certain die cavity pressure is kept, and further surface shape correction and tempering are carried out, so that the surface shape error and the residual stress generated by cooling shrinkage are further eliminated.
The temperature changing process and the shape correcting process are matched with the whole injection molding process and are independent working units which can be respectively used for molding different ultra-precise lenses or copying micro-nano characteristics; in addition, the temperature-changing process and the micro-motion correction process based on the surface shape can be flexibly used for optical elements in different forms.
The invention has the characteristics and beneficial effects that:
(1) according to the invention, according to the shape characteristics of different optical devices, a variable mold temperature auxiliary molding system based on the shape of the surface is adopted in a targeted manner, the oriented molecule relaxation process can be actively adjusted by controlling the mold temperature, the heat preservation time and the like in the injection and pressure maintaining processes, the residual stress caused by flow is reduced, the residual stress generated by uneven cooling is reduced in the cooling stage, and the birefringence phenomenon is further effectively improved.
(2) According to the invention, according to the optical surface settings of different optical devices, the in-mold micro-motion shape correction system can perform micro-motion compression in a micron and submicron scale mold on a polymer material in one direction or multiple directions, compensate micron and submicron scale surface shape errors while the material is in viscoelastic deformation, or correct the copying precision of a micro-nano structure.
(3) In the invention, the in-mold micro-motion correction system has the characteristic of high upper limit of working temperature (150 ℃), can process various levels of optical-grade polymer resin, obtains micro-motion compression displacement and injection molding pressure parameters in situ in the injection molding process, does not need extra cooling, and reduces the cost of the system.
(4) According to the invention, the temperature and pressure of the polymer in the molding process in the mold cavity can be actively controlled based on the variable mold temperature auxiliary molding and the micro-motion in the mold auxiliary molding of the surface shape, and the mold surface and the polymer are ensured to be tightly attached in the phase change process, so that the precise copying of the surface shape, the copying of a micro-nano structure and the controllable manufacturing of an optical device are realized.
Description of the drawings:
FIG. 1 is a process flow diagram.
FIG. 2 is a schematic view of a mold based on surface shape variable temperature auxiliary molding and micro-motion compression sizing.
FIG. 3 is a schematic diagram of the variation curve of the temperature and pressure in the mold under the process conditions of the surface shape temperature-changing auxiliary forming and the micro-motion correction.
FIG. 4 is a schematic view of variable mold temperature assisted molding based on surface shape.
FIG. 5 is a schematic diagram of one-way in-mold jogging correction.
FIG. 6 is a schematic view of multi-directional in-mold jogging correction.
FIG. 7 is a schematic diagram of micro-nano structure in-mold micro-motion compression auxiliary filling.
The reference numeral 1 is a micro-nano structure of a heating structure 26 based on a surface shape of a moving die base, 2 is a push plate, 3 is a push rod fixing plate, 4 is a cushion block, 5 is a push rod, 6 is a micro-motion compression driver, 7 is a moving die supporting plate, 8 is a moving die template, 9 is a fixed die template, 10 is a fixed die supporting plate, 11 is a positioning ring, 12 is a sprue bush, 13 is a heating element, 14 is a temperature sensor, 15 is a flow channel, 16 is a fixed die core, 17 is a device, I18 is a heating element, 19 is a cooling water channel, 20 is a moving die core, 21 is a heat insulation element, 22 is
Detailed Description
According to the invention, the injection molding of the polymer optical device with low residual stress or no residual stress and high surface shape precision is realized by combining the variable mold temperature auxiliary molding based on the surface shape and the micromotion correction auxiliary molding in the mold according to the heat deformation history of the polymer material in the injection molding process and the basic theory of material cooling phase change. The invention can also be used for high-precision replication of micro and nano structures with high depth-to-depth ratio.
The invention provides a rapid heating and cooling system based on surface shape aiming at the characteristics of complex surface shapes such as a free-form surface and the like, and realizes uniform cooling of the complex surface, thereby reducing the residual stress caused by cooling. In addition, the temperature of the die surface is finely regulated and controlled, the surface shape is regulated and controlled by combining with micro-motion compression in the die, and further release of residual stress under the surface shape condition is guaranteed. In the filling and pressure maintaining stage, the temperature of the mold surface is higher than the glass transition temperature of the material or close to the melting temperature of the material, so that the molecular chain orientation caused by wall shearing when the polymer is injected into the mold is reduced, and the residual stress caused by flowing is further reduced; and then gradually reducing the temperature of the die to the viscoelastic state temperature of the material, and matching with micro-motion compression to realize high-precision characteristic replication. The in-mold micro-motion compression is combined with a variable mold temperature auxiliary forming system based on the surface shape aiming at the extreme requirements of surface shape errors, size tolerance, micro-nano structures and the like of complex surfaces on micron and submicron reproduction precision, and the correction of the surface shape and the reproduction precision of the optical free-form surface element is carried out within a tolerance range.
The invention relates to a precise and ultra-precise injection molding system of a polymer optical device, which consists of an injection molding machine, a mold, a variable mold temperature auxiliary molding system based on surface shape and an in-mold micro-motion correction auxiliary molding system. The surface-shape-based variable-mold-temperature auxiliary forming system is composed of a variable-mold-temperature power supply module, a variable-mold-temperature control module, a heating element, a heat insulation element, a cooling water path and a variable-mold-temperature sensing module. The in-mold micro-motion shape correction auxiliary forming system is composed of a micro-motion power supply module, a micro-motion control module, a micro-motion compression driver, a heat insulation element and a micro-motion sensing module.
The invention is further described below with reference to the accompanying drawings.
The method comprises the following specific operation steps:
(1) designing and manufacturing a heating and cooling system based on surface shape variable mold temperature auxiliary forming and an in-mold precise micro-motion shape correction auxiliary forming system. According to the surface shape characteristics of the optical device, the shapes and the distribution of the heating system and the cooling system are designed and optimized; and selecting a reasonable micro-motion correction execution device according to parameters such as optical element design, tolerance range and the like.
(2) And a mold temperature control system, a precise micro-motion shape correcting system and an injection molding system are integrated through the visual operation interface of an upper computer and the communication with an injection molding machine.
(3) After the entire system is ready, injection molding is started. As shown in fig. 1, the whole precision injection molding process consists of an injection molding process, a temperature changing process and a shape correcting process, wherein the temperature changing process corresponds to a surface shape-based variable mold temperature auxiliary molding system, and the shape correcting process corresponds to an in-mold micro-motion shape correcting auxiliary molding system. The injection molding process comprises plasticizing, injecting, pressure maintaining, cooling, mold opening, ejecting and mold closing, wherein the plasticizing can be performed in parallel with the cooling, mold opening, ejecting and other process links. Meanwhile, in an injection molding cycle, the temperature changing process consists of a coil heating link, a water channel cooling link and a coil heating link, and the shape correcting process consists of a micro-motion compression (execution) link and a micro-motion compression (release) link. The injection molding process, the temperature changing process and the shape correcting process are performed in parallel according to the time sequence shown in fig. 1. FIG. 2 is a schematic view of a mold based on surface shape variable temperature auxiliary molding and micro-motion compression sizing. The auxiliary molding based on the surface deformation mold temperature in the mold is realized by designing a heating and cooling system. The heating and cooling system comprises a heating element 18, a heat insulating element 21 and a cooling water circuit 19. The heating mode can be selected from electromagnetic induction heating, ceramic heating and liquid heating, the cooling mode can be selected from liquid cooling and gas cooling under the condition that the surface shape change of the free-form surface is large, and the heating system, the cooling system and the package thereof need to be designed into a three-dimensional structure according to the surface shape change of the optical element so as to ensure the uniformity of cooling and reduce the residual stress caused by cooling, as shown in fig. 4. The design of the whole coil and the cooling water channel needs to be optimized through numerical calculation. The integral heating and cooling system is integrated on the fixed die core 16 and the movable die core 20, and a ceramic heat insulation sleeve is arranged outside the die cores to realize the rapid temperature rise and cooling of the die cores. The variable mold temperature sensing module may be selected from a temperature sensor, a pressure sensor, and a temperature and pressure sensor. In the present invention, the die face temperature is measured using an integrated in-die temperature and pressure sensor 14. The surface-shaped variable-temperature-based auxiliary forming system adopts a time sequence control method similar to an injection molding process, is triggered by signals such as injection of an injection molding machine and the like, is powered by a variable mold temperature power module, drives a heating and cooling system to work by a variable mold temperature control module, and acquires temperature data in a mold by a variable mold temperature sensing module. The process parameters include mold temperature, duration, etc. In the injection and pressure maintaining stage, the mold is heated to the glass state temperature of the polymer material or higher, so that the molecular orientation and residual stress caused by mold filling flow of the polymer melt are reduced, a rapid condensation layer of the polymer on the surface of the mold is prevented, and the filling of the micro-nano structure is improved. According to the measured data of the temperature and the pressure in the die cavity, ensuring that the pressure in the die cavity does not exceed the maximum output pressure of the micro-motion correction system; ensures that the temperature is above the glass state temperature of the material and has better fluidity.
And under the condition that the conditions are met, starting the micro-motion compression by an executing device of the precise micro-motion compression system. The micro-motion shape correcting system in the die consists of a micro-motion compression driver 6 and a heat insulation element 21 which are matched with each otherThe mold core 20 is subjected to fine motion correction. The micro-motion sensing module may be selected from a resistive sensor, a capacitive sensor, and an inductive sensor. In the present invention, the stroke of the micro-motion compression is measured by a resistive strain gauge integrated in the micro-motion compression driver 6. Because the surface shape error range is generally within ten microns and does not exceed the thickness tolerance range of the sample, the sample is generally corrected within the thickness tolerance range to realize the submicron-level surface shape precision. For optical devices, the glass transition temperature T of materials is relatively high, such as cyclic polyolefins (COC E48R)gIs-139 ℃. In actual use, the micro-motion compression system can work at a higher temperature. The micro-motion sizing process needs a certain pressure, and the sizing pressure is set to 1000N within the range of ensuring the extension and contraction of the piezoelectric ceramics. The whole shape correcting process is powered by the micro-motion power supply module, triggered by an injection molding signal of the injection molding machine, drives the micro-motion compression driver to work through the micro-motion control module, and collects micro-motion compression displacement data through the micro-motion sensing module. The start of the micro-motion correction can be determined according to the change of the temperature and pressure values of the die cavity, and the start is carried out through time sequence delay. The shape correction parameters comprise shape correction pressure, shape correction time, shape correction temperature and the like. The micro-motion compression auxiliary shape correction has two operation modes: firstly, in the cooling process, micro-motion compression is carried out on the material in a viscoelastic state temperature range to precisely regulate and control the surface shape and the micro-nano structure replication precision of a sample, thermal residual stress is further released, and then the temperature of a die is reduced to be lower than the thermal deformation temperature of the material in a micro-motion compression state; secondly, cooling the sample to the thermal deformation temperature to form the prefabricated part, then raising the temperature of the mold to the viscoelastic state temperature, realizing surface shape correction through material creep under micro-motion compression, further releasing residual stress, and then lowering the temperature of the mold to be below the thermal deformation temperature of the material in the micro-motion compression state. On one hand, the close contact between the die surface and the die core in the cooling process is ensured, and the surface shape correction or the precise copying of a fine structure is realized; on the other hand, in order to further eliminate the residual stress generated by uneven cooling, after the sample is cooled, the temperature is raised, certain die cavity pressure is kept, further surface shape correction and tempering are carried out, and therefore surface shape errors generated by cooling shrinkage are further eliminatedAnd residual stress. The variation of the temperature and pressure in the mold cavity during the complete process is shown in fig. 3, and is matched with the injection molding process, the temperature changing process and the shape correcting process.
The starting time of the micro-motion compression, the temperature of the mold cavity and the time for maintaining the pressure are determined according to the material, the surface shape, the residual stress or the copying condition of the micro-nano structure of the optical device, which is a process for optimizing the process.
The temperature changing process and the shape correcting process are matched with the whole injection molding process, are independent working units and can be respectively used for molding different ultra-precise lenses or copying micro-nano characteristics. In addition, the temperature-changing process and the micro-motion correction process based on the surface shape can be flexibly used for optical elements in different forms. As shown in FIG. 5, for a device III 28 with a single side such as the surface II 29 having higher precision and surface shape requirement, the unidirectional in-mold micro-motion correction as shown by the arrow direction can be carried out on the side of the single side surface II 29; as shown in fig. 6, for a device iv 30 with higher precision and surface shape requirements such as a multi-sided surface iii 31, a surface iv 32, a surface v 33, etc., multi-directional in-mold micro-motion correction as shown by arrow direction can be performed on the sides of the multi-sided surface iii 31, the surface iv 32, and the surface v 33; as shown in fig. 3, for a device v 34 having a precision requirement as the micro-nano structure 35, in-mold micro-motion correction as shown by an arrow direction can be performed on the micro-nano structure 35 side.
The process is suitable for injection molding of typical optical devices, such as free-form optical lenses of microlens arrays, Fresnel lenses, cubic phase plates and the like, and is also suitable for copying of micro-nano structures with high depth-depth ratio. While the present invention has been described in terms of its functions and operations with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise functions and operations described above, and that the above-described embodiments are illustrative rather than restrictive, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined by the appended claims.

Claims (6)

1. A precise injection molding device for an optical device with a polymer complex surface is characterized by comprising an injection molding machine, a mold, a multi-section variable mold temperature auxiliary molding system based on the surface shape and an in-mold micro-motion correction auxiliary molding system, wherein the multi-section variable mold temperature auxiliary molding system based on the surface shape is realized by a variable mold temperature power module, a variable mold temperature control module, a heating element, a heat insulation element, a cooling water path and a variable mold temperature sensing module, and is used for enabling the mold surface temperature to be higher than the glass transition temperature of a material or to be close to the melting temperature of the material in the filling and pressure maintaining stages, reducing the molecular chain orientation caused by wall surface shearing when the polymer is injected into the mold, and further reducing the residual stress caused by flowing; then gradually reducing the temperature of the mold to the viscoelastic state temperature of the material, and matching with micro-motion compression to realize feature replication;
the in-mold micro-motion shape correction auxiliary forming system is composed of a micro-motion power supply module, a micro-motion control module, a micro-motion compression driver, a forming heat insulation element and a micro-motion sensing module, and has two operation modes: firstly, in the cooling process, micro-motion compression is carried out on the material in a viscoelastic state temperature range to precisely regulate and control the surface shape and the micro-nano structure replication precision of a sample, thermal residual stress is further released, and then the temperature of a die is reduced to be lower than the thermal deformation temperature of the material in a micro-motion compression state; secondly, cooling the sample to the thermal deformation temperature to form the prefabricated part, then raising the temperature of the mold to the viscoelastic state temperature, realizing surface shape correction through material creep under micro-motion compression, further releasing residual stress, and then lowering the temperature of the mold to be below the thermal deformation temperature of the material in the micro-motion compression state.
2. The precision injection molding apparatus for polymer complex-shaped surface optics according to claim 1, wherein the stroke of the micro-motion compression is measured by a resistance strain gauge integrated in a micro-motion compression driver, and one-way in-mold micro-motion correction or multi-way in-mold micro-motion correction can be performed.
3. A precise injection molding method of an optical device with a polymer complex surface is characterized by comprising an injection molding process, a temperature changing process and a shape correcting process, wherein the temperature changing process corresponds to a multi-section variable-mold temperature auxiliary molding system based on the surface shape, and the shape correcting process corresponds to an in-mold micro-motion shape correcting auxiliary molding system; the injection molding process comprises plasticizing, injecting, pressure maintaining, cooling, mold opening, ejecting and mold closing, wherein the plasticizing, cooling, mold opening and ejecting process links are parallel; meanwhile, in an injection molding cycle, the temperature changing process consists of a coil heating link, a water channel cooling link and a coil heating link, and the shape correcting process consists of a micro-motion compression/execution link and a micro-motion compression/release link; the injection molding process, the temperature changing process and the shape correcting process are carried out in parallel;
the variable mold temperature auxiliary forming based on the surface shape in the mold is realized by designing a heating and cooling system, wherein the heating and cooling system comprises a heating element, a heat insulation element and a cooling water path, the heating mode can be selected from electromagnetic induction heating, ceramic heating and liquid heating, and the cooling mode can be selected from liquid cooling and gas cooling; for the condition that the surface shape change of the free curved surface is large, a heating and cooling system and the package thereof need to be designed into a three-dimensional structure according to the surface shape change of the optical element; the integral heating and cooling system is integrated on the fixed die core and the movable die core, and a ceramic heat insulation sleeve is arranged outside the die core to realize the rapid temperature rise and cooling of the die core; the variable mold temperature sensing module can be selected from a temperature sensor, a pressure sensor and a temperature and pressure sensor so as to measure the temperature and the pressure in the mold; the surface shape variable temperature-based auxiliary forming system adopts a time sequence control method similar to an injection molding process, is triggered by an injection signal of an injection molding machine, is powered by a variable mold temperature power module, drives a heating and cooling system to work by a variable mold temperature control module, and acquires temperature data in a mold by a variable mold temperature sensing module; according to the measured data of the temperature and the pressure in the die cavity, ensuring that the pressure in the die cavity does not exceed the maximum output pressure of the micro-motion correction system;
the micro-motion compression auxiliary shape correction has two operation modes: firstly, in the cooling process, micro-motion compression is carried out on the material in a viscoelastic state temperature range to precisely regulate and control the surface shape and the micro-nano structure replication precision of a sample, thermal residual stress is further released, and then the temperature of a die is reduced to be lower than the thermal deformation temperature of the material in a micro-motion compression state; secondly, cooling the sample to the thermal deformation temperature to form the prefabricated part, then raising the temperature of the mold to the viscoelastic state temperature, realizing surface shape correction through material creep under micro-motion compression, further releasing residual stress, and then lowering the temperature of the mold to be below the thermal deformation temperature of the material in the micro-motion compression state.
4. The method for precision injection molding of an optical device with a polymer complex surface as claimed in claim 3, wherein the micro-motion compression is started by an execution device of a precision micro-motion compression system, and the micro-motion shape correction system in the mold is composed of a micro-motion compression driver and a heat insulation element and is matched with a movable mold core to perform micro-motion shape correction; the micro-motion sensing module is selected from a resistance type sensor, a capacitance type sensor and an inductance type sensor, so that the micro-motion compression stroke is measured, and the micro-motion compression driver is matched to correct the shape of the sample within the thickness tolerance range.
5. The method of claim 3, wherein the optical device has a high glass temperature, and the micro-motion compression driver and the micro-motion sensing module can operate at room temperature to 140 ℃ during actual use; the micro-motion sizing process needs a certain pressure, and the sizing pressure is set to be 1000N within the range of ensuring the extension and contraction of the piezoelectric ceramics; the whole shape correcting process is powered by a micro-motion power module, triggered by an injection molding signal of an injection molding machine, drives a micro-motion compression driver to work by a micro-motion control module, and collects micro-motion compression displacement data by a micro-motion sensing module; the start of the micro-motion correction is determined according to the temperature and pressure value change of the mold cavity, and the start is carried out through time sequence delay, and correction parameters comprise correction pressure, correction time and correction temperature, so that on one hand, the close contact between the mold surface and the mold core in the cooling process is ensured, and the surface shape correction or the precise copying of a fine structure is realized; on the other hand, in order to further eliminate the residual stress generated by uneven cooling, after the sample is cooled, the temperature is raised, a certain die cavity pressure is kept, and further surface shape correction and tempering are carried out, so that the surface shape error and the residual stress generated by cooling shrinkage are further eliminated.
6. The method for precision injection molding of an optical device with a polymer complex surface as claimed in claim 3, wherein the temperature changing process and the shape correcting process are matched with the whole injection molding process, and are independent working units which can be respectively used for molding different ultra-precision lenses or copying micro-nano features; in addition, the temperature-changing process and the micro-motion correction process based on the surface shape can be flexibly used for optical elements in different forms.
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