CN106827389B - External gas-assisted injection molding method and molding equipment based on ultrasonic measurement - Google Patents

External gas-assisted injection molding method and molding equipment based on ultrasonic measurement Download PDF

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Publication number
CN106827389B
CN106827389B CN201710107543.7A CN201710107543A CN106827389B CN 106827389 B CN106827389 B CN 106827389B CN 201710107543 A CN201710107543 A CN 201710107543A CN 106827389 B CN106827389 B CN 106827389B
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gas
time
assisted
ultrasonic
control device
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CN106827389A (en
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李吉泉
贾亚东
鲁聪达
赵朋
姜少飞
赵佳伟
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Zhejiang University of Technology ZJUT
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Zhejiang University of Technology ZJUT
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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
    • B29C45/1703—Introducing an auxiliary fluid into the mould
    • B29C45/174—Applying a pressurised fluid to the outer surface of the injected material inside the mould cavity, e.g. for preventing 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
    • B29C45/76—Measuring, controlling or regulating
    • 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
    • B29C2945/76551—Time
    • 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
    • B29C2945/76775—Fluids
    • B29C2945/76779—Fluids auxiliary fluids introduced into the cavity
    • 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
    • B29C2945/76829—Feeding
    • B29C2945/76839—Feeding auxiliary fluids, e.g. gas, liquid
    • 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
    • B29C2945/76929—Controlling method
    • B29C2945/76973—By counting

Abstract

The invention discloses an external gas-assisted injection molding method and molding equipment based on ultrasonic measurement. The equipment comprises an injection mold, wherein the injection mold is provided with a pouring gate, a cavity, a gas needle, a gas inlet channel, a material pulling rod and an ultrasonic probe, the ultrasonic probe is connected with a signal processing device, the signal processing device is sequentially connected with a control device and a gas auxiliary control device, the gas auxiliary control device is connected with the gas needle through the gas inlet channel, and compressed gas in the gas auxiliary control device enters the cavity through the gas needle. The invention reasonably applies the ultrasonic detection technology to the external auxiliary forming equipment, thereby not only simply and rapidly judging the appropriate gas injection time and improving the production efficiency, but also effectively removing the surface sink marks of the plastic parts and improving the product quality.

Description

External gas-assisted injection molding method and molding equipment based on ultrasonic measurement
Technical Field
The invention belongs to the technical field of external gas-assisted injection molding, and particularly relates to an external gas-assisted injection molding method and molding equipment based on ultrasonic measurement.
Background
With the rapid development of the plastic industry and the injection molding technology, plastic products are gradually developed in the directions of being lighter, thinner, more personalized and more complicated, so that the injection molding products are required to have higher surface quality and precision while meeting certain requirements on strength and rigidity. However, the molding surface quality and precision of the product are seriously affected by defects such as surface sink marks and overall shape warping caused by the shrinkage of the plastic part. In the traditional process, a method for increasing the pressure holding pressure and the pressure holding time is adopted, so that the shrinkage condition of a product can be reduced to a certain extent, but the mold locking force in the injection molding process is increased while the pressure holding pressure and the pressure holding time are increased, the production period is prolonged, and further the production cost is increased. Further, the increased holding pressure causes the product to have a flash phenomenon, and the higher the pressure, the more severe the flash. For products with rib-shaped structures and convex columns and large and flat thin-wall plastic parts, the pressurization compensation method in the traditional process is still useless. The traditional internal gas-assisted injection molding technology can reduce the defects of shrinkage marks and warping deformation of the plastic part and improve the surface quality of the plastic part. It is only suitable for articles that are hollow or that allow the creation of air channels inside, but is not advisable for articles that are not hollow and do not allow air channels inside. Therefore, the external gas-assisted injection molding can be carried out.
The external gas auxiliary injection moulding technology (called external auxiliary for short) is an advanced plastic processing technology, after the melt is completely filled into the cavity, the inert gas with a certain pressure is uniformly injected between the surface of the cavity of the mould and the plastic condensation layer formed in the filling stage from the external auxiliary equipment, and the melt is continuously pushed to the mould wall by using the pressure of the gas, so that the melt is tightly attached to the cavity wall to counteract the shrinkage generated in the moulding process, and the purpose of reducing the defects generated by the shrinkage of the plastic part to the maximum extent is achieved. Compared with the traditional pressure maintaining method, the mold clamping force required by the mold during production can be reduced by adopting an external auxiliary process, and meanwhile, a part of heat can be taken away by gas, so that the cooling time is reduced, and the production period is shortened. Compared with the traditional internal gas-assisted injection molding technology, the novel gas-assisted injection molding technology has the advantages that the structure of the gas channel does not need to be large in size, the structure of a product is not changed, the wall thickness of each part of the product can be further improved to improve strength and save materials, and the technical application range is wider. Is especially suitable for large and flat thin-wall products with rib-shaped structures and convex columns.
The injection molding process can be generally described as: the glassy state granules are heated in a charging barrel of an injection molding machine at room temperature, plasticized from a glassy state through a high elastic state and then converted into a viscous state, and then enter a mold cavity through a pouring system of the mold. Cooling gradually in the die cavity, returning from viscous state to high elastic state, and converting to glass state to obtain the product with the shape identical to that of the die cavity. In the process of cooling the plastic from a viscous state to a glassy state, each aggregation state is divided into a plurality of layers in the thickness direction, and the molten plastic firstly contacts a mold cavity with a lower temperature to form a condensation layer on the surface. As the forming process progresses, the condensation layer gradually advances inward, and the plastic also gradually cools from a molten state to a solid state. Since the thickness of the layers changes over time during the cooling of the melt, the thickness of the condensation layer also changes over time.
The main difference between the external auxiliary injection molding and the traditional injection molding is represented in the pressure maintaining stage, the gas pressure maintaining replaces the traditional screw to push the melt for pressure maintaining, wherein the delay time is an important parameter influencing the gas pressure maintaining effect and is matched with the thickness of a cooling solidification layer. In the earlier stage of pressure maintaining and cooling, the temperature of the cooling solidified layer is higher, the thickness is relatively thinner, the strength is lower, and if gas is injected between the surface of the mold cavity and the cooling solidified layer at the moment, the gas with pressure can cause the surface of the plastic part to be uneven and even break through the plastic part, so that the requirement of the high-quality surface plastic part cannot be met. And as the pressure maintaining cooling is carried out, the temperature is gradually reduced, the condensation layer is gradually thickened, and the strength is continuously increased. If the external gas injection time is too late, the gas with pressure injected from the outside basically has no pushing effect on the cooled solidified layer because most of melt is cooled to be below the glass state temperature of the plastic, and the gas pressure maintaining effect required by external auxiliary injection molding cannot be achieved.
Disclosure of Invention
In view of the above problems in the prior art, the present invention provides an external air assisted injection molding method and a molding apparatus based on ultrasonic measurement. The method can solve the problems that the existing equipment can not prepare and judge reasonable gas injection time and has too complex judging method and the problem that the external auxiliary forming equipment is easy to cause gas breakdown to a plastic part or can not obviously eliminate sink marks.
The external gas-assisted injection molding method based on ultrasonic measurement is characterized by comprising the following steps of:
1) acquiring ultrasound signals
Installing an ultrasonic probe in a mold cavity of a mold, transmitting n groups of ultrasonic waves to a flow direction vertical to a melt in a molding process according to a transmitting frequency (f), and acquiring reflection echoes LB1, LB2, LB3, LB5 and … … LBn of each group of ultrasonic waves; LBn is a reflection echo of the nth group of ultrasonic waves generated at a condensation layer interface, wherein the condensation layer interface is an interface between the inner surface of the mold and the condensation layer;
2) calculating the thickness of the condensation layer
a. Calculating the thickness h of the condensation layer
The time interval Δ t between the incident wave and the reflected wave LBn is calculated by a signal processing device connected with the ultrasonic probe, and the thickness h of the condensation layer is as follows: h =1/2 Xv Δ t;
wherein v is the propagation velocity of the ultrasonic wave in a condensation layer, and the condensation layer is formed on the surface of a mold cavity with a lower temperature which is firstly contacted with the molten plastic in the injection molding process;
b. calculating the velocity v of the ultrasonic waves in the condensation layer
Cutting the prepared plastic product at the position corresponding to the ultrasonic wave to obtain the thickness h0 of the plastic product at the position corresponding to the ultrasonic wave, then transmitting the ultrasonic wave at one side of the plastic product to the other side of the plastic product for receiving, thereby obtaining the time t when the ultrasonic wave passes through the plastic product, and further calculating the propagation speed v = h0/t of the ultrasonic wave in a condensation layer;
c. calculating the time interval of ultrasonic wave emission
Obtaining the emission period T =1/f by the known ultrasonic emission frequency f, namely the number of times of ultrasonic emission in unit time, further obtaining the time interval T of ultrasonic emission, and substituting the speed v and the time interval T in the steps b and c into the step a to obtain the thickness h of the condensation layer;
3) establishing a time-condensing layer thickness reference standard
The establishment of the time-condensation layer thickness reference coordinate mainly comprises the following steps:
a, connecting the ultrasonic probe to a signal processing device, converting a received waveform signal into an electric signal by the signal processing device, transmitting the electric signal to a control device for processing, and processing the received signal into a group of ultrasonic wave transmitting time and a time interval between each group of incident wave and the group of reflected wave, namely (at 1 Δ t 1) (at 2 t 2) (t 3 Δ t 3) … … (tn) according to the received electric signal and the transmitting frequency of the ultrasonic wave;
b, inputting the calculation formula in the step 2) into the control device to obtain corresponding data of each group of ultrasonic emission time t and the condensation layer thickness h, namely (t 1h 1) (t 2h 2) (t 3h 3) … … (tnhn), and then carrying out second-order polynomial fitting on the obtained data by the control device to obtain a time-condensation layer thickness coordinate curve;
c, dividing a time horizontal axis in the coordinate curve according to the same time interval, finding the corresponding condensation layer thickness, and setting each time-condensation layer thickness as an ideal gas injection time-condensation layer thickness area as a reference standard;
4) selecting a suitable insufflation time region
Selecting a group of plastic parts in injection molding, feeding back signals of each area in the reference standard obtained in the step 3) to the input end of the gas-assisted pressure regulating device of each corresponding gas-assisted control device by the control device in the injection molding process of the plastic parts, sending the obtained signals to a gas compressor through the output end by the gas-assisted pressure regulating device, controlling the gas compressor to convey gas with corresponding pressure to enter a gas storage tank for storage, opening a gas-assisted switching device, injecting the gas in the gas storage tank into the plastic through a gas inlet channel and a gas guide, taking out a demolding part after the gas injection is finished, measuring the depth value of a sink mark of the plastic part corresponding to each time-distance area by a measuring device, and taking the time with the minimum sink mark depth value as a proper gas injection time area;
5) and when the plastic parts are subjected to batch injection molding, taking the time of the gas injection time region obtained in the step 4) as the gas injection time, namely after the injection molding is finished and the time of cooling to the gas injection time region, performing gas injection auxiliary molding.
The external gas-assisted injection molding method based on ultrasonic measurement is characterized in that the time interval is divided according to the following steps: and selecting the pressure maintaining and cooling early stage for division.
The external gas-assisted injection molding method based on ultrasonic measurement is characterized in that an ultrasonic probe monitors the thickness change of a condensation layer in real time, each waveform signal is transmitted to a signal processing device, and the waveform signals are transmitted to a control device through electric signal conversion by the signal processing device.
The ultrasonic measurement-based external gas-assisted injection molding method is characterized in that a control device comprises a signal receiving device, a data processing device and a signal transmission device, the signal receiving device receives waveform signals from the signal processing device, the data processing device establishes a statistical model of the change of the thickness of a condensation layer along with time in the molding process, data are drawn into a time-condensation layer thickness coordinate curve graph, a time horizontal axis is divided according to the same time interval to find corresponding condensation layer thickness areas, each time-condensation layer thickness area is set as an ideal gas injection area, the set ideal gas injection area signals are transmitted to a gas-assisted control device through the signal transmission device in sequence, and external gas injection is performed through parameters of the gas-assisted control device.
The external air-assisted injection molding method based on ultrasonic measurement is characterized in that a data processing device in a control device processes received signals into each group of ultrasonic wave emission time and a time interval between each group of incident waves and each group of reflected waves, namely (t 1 Δ t 1) (t 2 t 2) (t 3 t 3) … … (tn Δ tn), converts the received signals into corresponding data of each group of ultrasonic wave emission time t and corresponding data of the condensation layer thickness h at the time, namely (t 1h 1) (t 2h 2) (t 3h 3) … … (tnhn), and carries out second-order polynomial fitting on the obtained data to obtain a time-condensation layer thickness coordinate curve.
The external gas auxiliary injection molding method based on ultrasonic measurement is characterized in that a gas auxiliary control device receives signals transmitted by a control device to control a gas compressor to output high-pressure gas with corresponding pressure so as to complete the external gas injection process; the gas-assisted pressure adjusting device is used for adjusting parameters of the gas compressor to generate gas with different pressures, and the gas-assisted switching device controls whether gas is injected or not.
The utility model provides an outside gas assists injection moulding equipment based on ultrasonic measurement, including injection mold, injection mold is equipped with runner, die cavity, gas needle, inlet channel, draws material pole, push rod and ultrasonic transducer, its characterized in that ultrasonic transducer and signal processing device connect, and control device and gas assist control device are connected gradually to signal processing device, and gas assist control device passes through inlet channel and connects the gas needle, and the compressed gas in the gas assist control device passes through inside the gas needle gets into the die cavity.
The utility model provides an injection moulding equipment is assisted to outside gas based on ultrasonic measurement, its characterized in that gas is assisted controlling means and is included gas and assist pressure regulating device, gas compressor, gas holder and gas and assist switching device, gas is assisted pressure regulating device input and controlling means signal connection, and gas compressor is connected to gas assistance pressure regulating device output, and gas compressor passes through inlet channel with gas holder, gas needle and is connected, and gas is assisted switching device and is set up on the inlet channel between gas holder and gas needle for the control gas needle is given vent to anger.
The external gas-assisted injection molding equipment based on ultrasonic measurement is characterized in that a gas needle is fixedly connected inside an injection mold body through threads, and the end head of the gas needle is located on the surface of a cavity.
The external gas-assisted injection molding equipment based on ultrasonic measurement is characterized in that an ultrasonic probe is provided with threads, is fixedly arranged in an injection mold body through the threads and is used for measuring the change of the distance between a condensation layer and the inside of a cavity in real time.
By adopting the technology, compared with the prior art, the invention has the following beneficial effects:
1) the invention relates to an external gas auxiliary injection molding device based on ultrasonic measurement, which comprises an injection mold, wherein the injection mold is provided with a pouring gate, a cavity, a gas needle, a gas inlet channel, a material pulling rod and an ultrasonic probe;
2) according to the invention, the thickness of the condensing layer is measured in real time, the relation of the change of the thickness of the condensing layer along with time in the forming process is established, the gas injection time for ensuring the reasonable thickness of the condensing layer is determined by combining with the analysis of the forming process, and the obtained gas injection time is applied to external auxiliary forming equipment to finish good gas pressure maintaining; the method not only simply and quickly judges the appropriate gas injection time, improves the production efficiency, but also can effectively remove the surface sink marks of the plastic parts and improve the product quality.
Drawings
FIG. 1 is a schematic diagram of ultrasonic testing;
FIG. 2 is a graph of distance between a condensation layer and an inner wall of a mold cavity versus time obtained without intervention of external gas;
FIG. 3 is a schematic diagram of the structure of the apparatus of the present invention.
In the figure: the method comprises the following steps of 1-pouring gate, 2-mould cavity, 3-gas needle, 4-gas inlet channel, 5-material pulling rod, 6-push rod, 7-ultrasonic probe, 8-signal processing device, 9-control device, 10-gas auxiliary pressure adjusting device, 11-gas compressor, 12-gas storage tank, 13-gas auxiliary switch device, 14-gas auxiliary control device, 15-melt, 16-condensation layer and 17-mould.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings, but the scope of the invention is not limited thereto:
as shown in figure 1, the external gas auxiliary injection molding device based on ultrasonic measurement comprises a pouring gate 1, a mold cavity 2, a gas needle 3, a gas inlet channel 4, a material pulling rod 5, a push rod 6 and an ultrasonic probe 7 which are arranged on a mold 17, wherein the gas needle 3 is arranged in the mold cavity 2 through threads, the end of the gas needle 3 is positioned on the surface of the mold cavity 2, the ultrasonic probe 7 is provided with threads and is arranged on the surface of the mold cavity 2 through threaded connection and used for monitoring the change of the distance between the inner wall of the mold cavity and a condensation layer 16, the ultrasonic probe 7 is connected with a signal processing device 8, the signal processing device 8 is used for controlling the ultrasonic probe to emit ultrasonic waves and also used for receiving and collecting ultrasonic reflected waves and transmitting the received and collected reflected waves to a connection control device 9 through signal conversion, and the control device 9 is connected with a gas auxiliary control device 14, control device 14 is assisted to gas includes that pressure regulating device 10, gas compressor 11, gas holder 12 and gas are assisted switching device 13, pressure regulating device 10, gas compressor 11, gas holder 12 and gas are assisted to gas, pressure regulating device 10 input and controlling means 9 signal connection are assisted to gas, and gas compressor 11 is connected to 10 output of gas-assisted pressure regulating device, and gas compressor 11 passes through inlet channel 4 in gas holder 12, gas needle 3 and connects, and switching device 13 is assisted to gas sets up on inlet channel 4 between gas holder 12 and gas needle 3 for control gas needle 3 gives vent to anger.
The ultrasonic probe 7 measures the change of the thickness of the condensation layer in real time, transmits a waveform signal to the signal processing device 8, processes the signal by the signal processing device 8 and then transmits the signal to the control device 9. The control device 9 comprises a signal receiving device, a data processing device and a signal transmission device, wherein the signal receiving device receives an electric signal from the signal processing device 8, the data processing device establishes a statistical model of the change of the thickness of the condensation layer along with time in the forming process, data is drawn into a time-condensation layer thickness coordinate curve, a time cross shaft is divided according to the time interval of ultrasonic emission, a corresponding condensation layer thickness area is found, each time-condensation layer thickness area is set as an ideal gas injection area, the set ideal gas injection area signal is transmitted to the gas auxiliary control device 1 through the signal transmission device in sequence, and the gas auxiliary control device performs external auxiliary gas injection through parameters.
The gas auxiliary control device 14 receives the signal transmitted by the control device 9 to control the gas compressor 11 to output high-pressure gas with corresponding pressure so as to complete the external gas injection process; the gas-assisted pressure regulating device 10 is used for regulating parameters of the gas compressor 11 to generate gas with different pressures, and the gas-assisted switching device 13 controls whether gas is injected or not.
As shown in the figure, the working process of the invention is as follows; after the injection molding is finished, the ultrasonic probe 7 detects the change of the distance between the mold cavity 2 and the condensation layer 16 and feeds the change back to the signal processing device 8, the signal processing device 8 processes a waveform signal, namely, a reflected wave signal received by the ultrasonic probe on the inner surface of the mold cavity 2 is subjected to electric signal conversion and then is sent to the control device 9, the control device 9 processes the received waveform signal from the ultrasonic probe, a statistical model of the change of the distance and the time between the mold cavity and the condensation layer in the molding process of an injection molding product is established, the time is used as an abscissa and the distance is used as an ordinate, the corresponding distance and the time are drawn into a time-condensation layer thickness coordinate graph, the time of the abscissa is divided according to the same time interval, a corresponding distance area is found, and each time-condensation layer thickness area is set as an ideal gas injection area, selecting a plastic part in injection molding which is the same as an ideal gas injection area, performing a parallel test, and selecting the optimal gas injection time from the plastic part, wherein the specific process is as follows:
in the injection molding process of the plastic part, each ideal area signal in the reference datum is fed back to the input end of the gas-assisted pressure adjusting device of each corresponding gas-assisted control device by the control device, the obtained signal is sent to the gas compressor through the output end by the gas-assisted pressure adjusting device, the gas compressor 11 is controlled to send gas with corresponding pressure to enter the gas storage tank 12 for storage, the gas-assisted switch device 13 is opened, the gas in the gas storage tank 12 is injected into the plastic through the gas channel 4 and the gas needle 3, after the injection is finished, each part is taken out of the mold, the depth value of the sink of the plastic part corresponding to each distance-time area is measured by the measuring device, and the time with the minimum depth value of the sink is taken as a proper gas injection area.
In the process of batch injection molding, the obtained proper gas injection time region is taken as an actual gas injection time period, namely after injection molding is finished, the gas is cooled to the actual gas injection time period, then the gas auxiliary pressure adjusting device 10 of the gas auxiliary control device 14 controls the pressure of compressed gas of the gas compressor 11 through the gas auxiliary pressure adjusting device 10, so that the compressed gas with corresponding pressure input by the gas compressor 11 is stored in the gas storage tank 12, the gas auxiliary switch device 13 is opened, the gas with corresponding pressure in the gas storage tank 12 is injected through the gas inlet channel 4 and the gas needle 3, namely, the gas auxiliary pressure adjusting device 10 flexibly adjusts the pressure parameter of the gas compressor 11 to generate gas with different pressures, and the gas auxiliary switch device 13 is used for controlling whether to inject gas to the outside, the reaction is sensitive and rapid, the ultrasonic testing technology is reasonably used in an external auxiliary molding device, the method can judge the appropriate gas injection time, improve the production efficiency, effectively remove the surface sink marks of the plastic parts and improve the product quality.
When the mold is opened, the main runner congeals materials and is pulled out from the sprue bush under the action of the material pulling rod 5, and then the plastic part and the congeal materials are pushed out of the mold by the push rod 6, so that a product is taken out.
The time-condensation layer thickness coordinate curve is obtained by fitting a plurality of groups of data, and the higher the ultrasonic emission frequency is, the more accurate the fitted coordinate curve is. In addition, the time interval area of the invention selects the pressure maintaining cooling early stage as the partition area, and the more the number of the sections divided by the time horizontal axis of the obtained coordinate curve is, the closer the ideal time value is.
Example 1;
as shown in fig. 2, the diagram is a graph of the thickness of the condensing layer in the pressure-maintaining cooling phase without the intervention of external gas as a function of time. At the moment, the injection molding of the melt 15 in the cavity is completed, the melt in the cavity begins to cool and contract, a condensation layer begins to form, and meanwhile, the distance between the inner wall of the cavity of the mold and the condensation layer begins to be increased gradually. In the figure, t0-t5 represent the pressure maintaining cooling early stage, and the control device divides the pressure maintaining cooling early stage according to the time interval of ultrasonic wave emission, namely t0-t 1; t1-t 2; t2-t 3; t3-t 4; t4-t 5; in total, 5 time intervals, t6 shows that the melt is basically solidified and not contracted after the pressure maintaining cooling, and the distance between the mold cavity and the condensation layer reaches the maximum and is kept constant. Then starting injection molding, wherein the injection molding is performed for the time, gas is injected outside the plastic part under a certain pressure in t0-t1, pressure maintaining and cooling are performed, then demolding is performed to take the plastic part, the surface sink mark value is measured and recorded after the plastic part is cooled to room temperature, and the same method is adopted for sequentially performing t1-t 2; t2-t 3; t3-t 4; t4-t 5; and carrying out external gas auxiliary forming inside the plastic part, and recording the surface sink mark value of each plastic part. And finally, determining the final gas injection time by comparing the size of the sink mark value. And the gas injection time corresponding to the minimum indentation value is taken as the gas injection time corresponding to the final mass production. When the time interval is smaller, the divided time periods are more, the corresponding gas injection time is more ideal, the generated sink mark value is smaller, and the product quality is improved to the maximum extent.
The invention described is only an enumeration of implementations of the inventive concept. The scope of the invention should not be construed as being limited to the particular forms set forth in the examples, but rather as being limited to the equivalents thereof which may occur to those skilled in the art upon consideration of the teachings herein.

Claims (10)

1. The external gas-assisted injection molding method based on ultrasonic measurement is characterized by comprising the following steps of:
1) acquiring ultrasound signals
An ultrasonic probe (7) is arranged in a mold cavity (2) of a mold (17), n groups of ultrasonic waves are transmitted to the flow direction which is vertical to a melt (15) in the molding process according to the transmitting frequency (f), and reflection echoes LB1, LB2, LB3, LB5 and LB … … LBn of each group of ultrasonic waves are collected; wherein LBn is the reflection echo of the nth group of ultrasonic waves at the interface of a condensation layer (16), wherein the interface of the condensation layer is the contact interface of the condensation layer on the inner surface of the mould and the melt (15) adjacent to the condensation layer;
2) calculating the thickness of the condensation layer
a. Calculating the thickness h of the condensation layer
The time interval Δ t between the incident wave and the reflected wave LBn is calculated by a signal processing device (8) connected with the ultrasonic probe (7), and the thickness h of the condensing layer is as follows: h =1/2 Xv Δ t;
wherein v is the propagation velocity of the ultrasonic wave in the condensation layer;
b. calculating the velocity v of the ultrasonic waves in the condensation layer
Cutting the prepared plastic product at the position corresponding to the ultrasonic wave to obtain the thickness h0 of the plastic product at the position corresponding to the ultrasonic wave, then transmitting the ultrasonic wave at one side of the plastic product to the other side of the plastic product for receiving, thereby obtaining the time t when the ultrasonic wave passes through the plastic product, and further calculating the propagation speed v = h0/t of the ultrasonic wave in a condensation layer;
c. calculating the time interval of ultrasonic emission
Obtaining the transmission period T =1/f by the known ultrasonic transmission frequency f, namely the number of times of ultrasonic transmission in unit time, further obtaining the time interval of ultrasonic transmission, and then obtaining the interval (Δ T) between the time of ultrasonic transmission of each group and the reflection echo of the group of ultrasonic1、∆t2……∆tn) Substituting the speed v and the time interval t in the steps b and c into the step a to obtain the thickness h of the condensation layer;
3) establishing a time-condensing layer thickness reference standard
The establishment of the time-condensation layer thickness reference coordinate mainly comprises the following steps:
a, the ultrasonic probe (7) is connected to a signal processing device (8), the signal processing device (8) converts the received waveform signal into an electric signal and transmits the electric signal to a control device (9) for processing, the control device (9) processes the received signal into each group of ultrasonic wave transmitting time and the time interval between each group of incident wave and the group of reflected wave, namely (t 1, Δ t 1) (t 2, Δ t 2) (t 3, Δ t 3) … … (tn, Δ tn);
b, inputting the calculation formula in the step 2) into a control device (9) to obtain corresponding data of each group of ultrasonic emission time t and the condensation layer thickness h, namely (t 1, h 1) (t 2, h 2) (t 3, h 3) … … (tn, hn), and then carrying out second-order polynomial fitting on the obtained data by the control device (9) to obtain a time-condensation layer thickness coordinate curve;
c, dividing a time horizontal axis in the coordinate curve according to the same time interval, finding the corresponding condensation layer thickness, and setting each time-condensation layer thickness as an ideal gas injection time-condensation layer thickness area as a reference standard;
4) selecting a suitable insufflation time region
Selecting a group of plastic parts in injection molding, feeding back each area signal in the reference standard obtained in the step 3) to the input end of the gas-assisted pressure regulating device (10) of each corresponding gas-assisted control device (14) by the control device in the injection molding process of the plastic parts, sending the obtained signal to the gas compressor (11) by the gas-assisted pressure regulating device (10) through the output end, controlling the gas compressor (101) to convey the gas with corresponding pressure into the gas storage tank (12) for storage, opening the gas-assisted switching device (13), injecting the gas in the gas storage tank (12) into the plastic through the gas inlet channel (4) and the gas needle (3), demoulding and taking the plastic parts after the gas injection is finished, measuring the depth value of the sink mark of the plastic part corresponding to each time-distance area through a measuring device, and taking the time with the minimum sink mark depth value as a proper gas injection time area;
5) and when the plastic parts are subjected to batch injection molding, taking the time of the gas injection time region obtained in the step 4) as the gas injection time, namely after the injection molding is finished and the time of cooling to the gas injection time region, performing gas injection auxiliary molding.
2. External gas-assisted injection moulding method based on ultrasonic measurements according to claim 1, characterised in that the time intervals are divided according to: and selecting the pressure maintaining and cooling early stage for division.
3. The external gas-assisted injection molding method based on ultrasonic measurement according to claim 1, wherein the ultrasonic probe (7) monitors the thickness change of the condensation layer in real time, transmits each waveform signal to the signal processing device (8), and transmits the waveform signal to the control device (9) through electrical signal conversion through the signal processing device (8).
4. The ultrasonic measurement-based external gas-assisted injection molding method according to claim 1, wherein the control device (9) comprises a signal receiving device, a data processing device and a signal transmission device, the signal receiving device receives the waveform signal from the signal processing device, the data processing device establishes a statistical model of the change of the thickness of the condensation layer along with the time in the molding process, and draws the data into a time-condensation layer thickness coordinate curve graph, and divides the time horizontal axis according to the same time interval to find corresponding condensation layer thickness areas, each time-condensation layer thickness area is set as an ideal gas injection area, and then the signal transmission device sequentially transmits the set ideal gas injection area signal to the gas-assisted control device (14), and the gas-assisted injection is performed by the parameters of the gas-assisted control device.
5. The external gas-assisted injection molding method based on ultrasonic measurement as claimed in claim 1, wherein the data processing device in the control device (9) processes the received signals into time intervals of each set of ultrasonic emission time and each set of incident wave and the set of reflected wave, i.e., (t 1, Δ t 1) (t 2, Δ t 2) (t 3, Δ t 3) … … (tn, Δ tn), and converts the time intervals into a time-condensing layer thickness coordinate curve obtained by performing a second order polynomial fit on the corresponding data of each set of ultrasonic emission time t and the corresponding data of the condensing layer thickness h, i.e., (t 1h 1) (t 2h 2) (t 3h 3) … … (tnhn).
6. The external gas-assisted injection molding method based on ultrasonic measurement according to claim 1, wherein the gas-assisted control device (14) receives the signal transmitted by the control device (9) to control the gas compressor (11) to output high-pressure gas with corresponding pressure to complete the external gas injection process; the gas-assisted pressure regulating device (10) is used for regulating parameters of the gas compressor (11) to generate gas with different pressures, and the gas-assisted switching device (13) controls whether gas is injected or not.
7. An external gas-assisted injection molding device based on ultrasonic measurement for the method according to claim 1, which comprises an injection mold, wherein the injection mold is provided with a pouring gate (1), a mold cavity (2), a gas needle (3), an air inlet channel (4), a material pulling rod (5), a push rod (6) and an ultrasonic probe (7), the injection molding device is characterized in that the ultrasonic probe (7) is connected with a signal processing device (8), the signal processing device (8) is sequentially connected with a control device (9) and a gas-assisted control device (14), the gas-assisted control device (14) is connected with the gas needle (3) through the air inlet channel (4), and compressed gas in the gas-assisted control device (14) enters the mold cavity (2) through the gas needle (3).
8. The external gas-assisted injection molding equipment based on ultrasonic measurement according to claim 7, wherein the gas-assisted control device (14) comprises a gas-assisted pressure adjusting device (10), a gas compressor (11), a gas storage tank (12) and a gas-assisted switch device (13), the input end of the gas-assisted pressure adjusting device (10) is in signal connection with the control device (9), the output end of the gas-assisted pressure adjusting device (10) is connected with the gas compressor (11), the gas compressor (11) is connected with the gas storage tank (12) and the gas needle (3) through the gas inlet channel (4), and the gas-assisted switch device (13) is arranged on the gas inlet channel (4) between the gas storage tank (12) and the gas needle (3) and used for controlling the gas needle (3) to discharge gas.
9. The external gas-assisted injection molding equipment based on ultrasonic measurement of claim 7, characterized in that the gas needle (3) is fixedly connected inside the injection mold body through threads, and the end of the gas needle (3) is located on the surface of the cavity.
10. The external gas-assisted injection molding equipment based on ultrasonic measurement according to claim 7, wherein the ultrasonic probe (7) is provided with threads, and is fixed in the injection mold body through the threads for measuring the distance change between the condensation layer and the inside of the cavity in real time.
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