CN100443890C - Real-time monitoring method of DC resistance method in LCM process - Google Patents

Abstract

The real-time monitoring method of the LCM process direct current resistance method, according to the size of the component, the excitation wire and the induction wire are cross-arranged on the upper and lower surfaces of the preform to determine the monitoring point; DC voltage is applied on both sides of the monitoring point, and the preform for the measured monitoring point Resistors are connected in series with reference resistors to form a voltage divider circuit, and the voltage at both ends of the reference resistor is measured. The voltage is collected and displayed on the PC in real time through the op amp and AD conversion, and the resistance of the preformed body to be tested can be obtained through calculation; resin filling When filling the mold, scan all the monitoring points cyclically to monitor the sudden change of the voltage value to judge the arrival of the resin flow front; after the mold filling is completed, the resistance of the preform at each monitoring point is increasing, and the resistance of these preforms is measured Changes, that is, through monitoring, the curing situation of the resin can be understood in real time. The invention can accurately reflect the arrival of the resin flow front at the monitoring point and the subsequent curing process, thereby providing a basis for reducing defects such as incomplete filling or dry spots, reducing the reject rate, improving product quality, and effectively solving resin-based compounding problems. The problem of unstable product quality exists in the production of materials.

Description

Real-time monitoring method of DC resistance method in LCM process

technical field

The invention relates to a real-time monitoring method of composite material liquid molding process LCM.

Background technique

Composite material liquid molding process LCM (Liquid Composites Molding) refers to injecting a special liquid low-viscosity resin under a certain pressure into a closed cavity pre-laid with fiber reinforced materials or heating and melting the resin film in the cavity, and the resin flows and infiltrates. It is an advanced composite material process method that strengthens materials and solidifies them. It is widely used in aerospace, automobile, shipbuilding, construction and other industries. The LCM process is a one-step molding process, which has the advantages of flexible operation, strong designability, low equipment and process costs, and basically no pollution to the environment. Since the quality of components produced by this process largely depends on the flow filling process of resin and its chemical curing reaction, the LCM process itself has obvious disadvantages: such as long resin flow time, improper mold and process design are easy to produce defective products, Typical defects such as dry spots and air bubbles are formed, which seriously affect the appearance and component quality.

The current method to solve the problems in the LCM process is to optimize the process by computer simulation, but the simulation cannot completely and accurately reflect the process situation, and the most effective method is to monitor the resin flow and curing process in real time. Process monitoring can accurately reflect process conditions in real time, facilitate timely adjustment of process conditions, minimize scrap rate, improve product quality, and provide reliable data for research on resin-infiltrated preforms. The existing LCM process monitoring technology can be divided into two types: non-embedded and embedded. Non-embedded monitoring methods include ultrasonic monitoring, thermal spectroscopy, and imaging, etc., which generally do not affect the process, but require quite expensive monitoring equipment; embedded monitoring technologies include: thermal monitoring with thermocouples as monitoring components, and The pressure sensor is the pressure monitoring of the medium, the optical fiber monitoring technology, the direct current monitoring and the dielectric monitoring technology and so on. Embedded components affect resin flow and part quality more or less, but they have the advantage of accurately transmitting information within the part.

In 1993, the American ARL (Army Research Laboratory) and the University of Delaware successfully developed the SMART weave flow monitoring sensor system and obtained a patent, Walsh Shawn M.In-situsensor method and device.US5210499, 1993. This technology is to pre-embed a network of perpendicular wires in the mold cavity. Each node of the network is a sensing point, and a dielectric field is used to introduce movable ions. When the resin bridges the transverse "yarn" wires, a closed current is formed. These nodes will feed back the flow state in the mold cavity, and the thermal gradient and curing state can be deduced according to the change of electrical conductivity, so as to achieve the purpose of real-time monitoring. The SMART weave system has been used to monitor the advancement of resin flow fronts on large components and provide process control information. However, there are two major defects in this system. One is that the pre-embedding of the wires in the preform is quite time-consuming; the other is that it can only provide information on the flow front and solidification at the junction. Its data processing software also has certain limitations. For example, it cannot describe the change of the output voltage during the mold filling process, so that the DC monitoring output information cannot be compared effectively with the LCM analog information. Therefore, the technique is generally only used for large, high-cost components.

Based on this direct current measurement technology, a linear direct current (LDC) monitoring system has been developed. It is similar to the SMART weave monitoring system, and both use resin to bridge the gap between two conductive elements to form a closed circuit. However, the conductive element of the LDC monitoring system is composed of two parallel wires. After the wires are covered with resin, the position of the flow front can be detected by detecting the change of the output impedance or capacitance between the two wires. The LDC monitoring system can monitor the flow front along the entire length of the wire, reduce the number of wires, and obtain continuous flow information, especially suitable for monitoring processes with simple flow patterns. The main disadvantage of LDC sensing technology is the calibration of resistivity. The resistivity of the resin is a function of the mutual parallelism of the two wires, the type of resin and the time. It must be ensured that the two wires are parallel to each other during installation to keep the resistivity constant. Especially with vertical flow fronts and slanted wires, it is difficult to accurately determine the sensor response. The development of this type of technology has not yet raised issues such as the best method of use and how to arrange it in the mold, and it is still in research and development.

Domestic research on real-time monitoring of LCM process mostly uses optical fiber sensing technology, such as light intensity modulation type and fiber grating sensor. Li Chensha, Liang Ji, Zhang Boming, Wang Dianfu, Optical fiber sensor monitors the curing and molding process of composite materials, Journal of Tsinghua University (Natural Science Edition), 2002, 42(2): 161-164.; Wu Zhanjun, Zhang Boming, etc., based on the refractive index Research on online monitoring of changing composite material solidification, Journal of Composite Materials, 2002, 19(6): 87-91 The research is to use optical fiber sensing technology for real-time monitoring of LCM process.

The basic principle of light intensity modulation optical fiber sensor is to change the light intensity in the optical fiber by the disturbance of the external signal, and then realize the measurement of the external signal by measuring the change of the output light intensity. This type of sensor is easy to use, durable, low in cost and accurate in demodulation. Light intensity modulation technologies such as variable refractive index type, fluorescent effect type, transparency type, and microbending loss type have been used to measure the viscosity and void of liquids. The basic principle of the fiber grating sensor is that when the physical quantity of the fiber grating environment changes, the grating period or the refractive index of the fiber core will change, so that the wavelength of the reflected light will change. By measuring the change of the reflected light wavelength before and after the change, the measured changes in physical quantities. There are many types of fiber gratings, which are mainly divided into short period gratings (FBG) and long period gratings (LPG). When the two transmission modes in the fiber grating are coupled, the FBG couples the energy of the forward-transmitted guided mode to the reverse guided mode, and the LPG couples the energy from the forward-transmitted guided mode to the cladding mode. There are multiple absorption peaks.

Optical fiber sensing technology has a series of unique advantages that are difficult to compare with other sensing technologies, such as a variety of monitoring and measurement of various physical quantities, light weight, small size, easy to embed in structures, high sensitivity, and is not immune to electromagnetic waves. , radio frequency interference, etc., but it also has some inevitable defects. For composite materials, the embedded optical fiber sensor affects the integrity of the main component of the composite material due to interference with the local strain field of the fiber-matrix interface, causing stress concentration. degrades the performance of the structure. Most experiments show that optical fibers with a diameter of 125 μm or less have no obvious effect on the damage behavior, tensile strength, Poisson's ratio, etc. of the composite material, but have a significant effect on the compressive strength of the composite material, and the strength drops by about 24 to 60%. , also has a significant impact on the fatigue life. Therefore, real-time monitoring of LCMs using fiber optic sensing technology is limited.

Contents of the invention

The technical problem of the present invention is to overcome the deficiencies of the prior art, and provide a real-time monitoring method of the direct current resistance method of the LCM process, which is capable of real-time monitoring, accurate monitoring, simple operation and low cost

Technical solution of the present invention: the real-time monitoring method of LCM process direct current resistance method, it is characterized in that realize by following steps:

(1) According to the size of the component, the excitation wires and induction wires are cross-arranged on the upper and lower surfaces of the preform to determine the monitoring points, and these monitoring points constitute the resistance of the measured preform;

(2) Apply a DC voltage on both sides of the resistance of the preformed body to be tested, and connect a reference resistor whose size matches each other in series for the resistance of the preformed body to be tested to form a voltage divider circuit, and measure the voltage at both ends of the reference resistance. After the operational amplifier and AD conversion, it is collected and displayed on the PC in real time, and the resistance of the measured preform can be obtained through calculation;

(3) Carry out resin mold filling, scan all monitoring points cyclically during mold filling, and judge the arrival of the resin flow front by monitoring the sudden change of voltage value; after the mold filling is completed, the resistance of the preform at each monitoring point is increasing, Measuring the changes in the resistance of these preforms, that is, the curing of the resin can be understood in real time through monitoring.

Compared with the prior art, the present invention has the advantages that: the present invention can accurately reflect the arrival of the resin flow front at the monitoring point and the subsequent curing process, thereby guiding process optimization, reducing defects such as incomplete mold filling or dry spots, and reducing Reduce the scrap rate, improve product quality, and effectively solve the problem of unstable product quality in the production of resin-based composite materials.

Description of drawings

Fig. 1 is the schematic diagram of the principle of the inventive method;

Fig. 2 is a schematic diagram of the wiring of the preform of the present invention;

Fig. 3 is a block diagram of a monitoring system for realizing the method of the present invention.

Detailed ways

As shown in Figures 1 and 2, the concrete steps of the present invention are as follows:

(1) According to the size of the component, criss-cross wiring on the upper and lower surfaces, the upper surface discharges the excitation wire, and the lower surface discharges the induction wire. The intersection of each excitation wire and induction wire is the monitoring point, and its resistance value R _x is the preset The resistance at the monitoring point of the molded body, the monitoring points should be evenly distributed on the entire surface of the component, so as to monitor the filling process as a whole; also find out the points that may have process defects through process simulation, and use them as monitoring points.

(2) A reference resistor R _c is connected in series with the monitoring point of the preform. The value selection method of R _c is as follows: firstly, the value of the resistance R _x of the preform is roughly measured through repeated tests, and then the resistance R x at the same value as R _x is selected. order of magnitude or matching reference resistance R _c , the value of R _c in the present invention is on the order of 10 ¹⁰ -10 ¹¹ ohms, and then a DC voltage U _d is applied to both ends of the two series resistances R _c and R _x . Experiments must be carried out to determine that the value of the added DC voltage U _d can make the value of the electrical signal of the preform infiltrated with resin around 200. U _in is the DC voltage obtained by the reference resistor R _c , U After _in is output by the operational amplifier, it becomes U _out , and U _out is transmitted to the PC for real-time display and storage after A/D conversion.

According to the basic principle of the voltage divider circuit, as shown in Figure 1,

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

U _out = n · U _in (2)

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; out</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 5</span>}\mathrm{<span\; class="notranslate">\; V</span>}}{{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 8</span>}}}\mathrm{<span\; class="notranslate">\; DATA</span>}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; DATA</span>}}{\mathrm{<span\; class="notranslate">\; 51</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, n is the magnification factor, DATA is the real-time data collected on the PC after U _out is converted by AD, 5V is the reference voltage of the A/D conversion chip, and 2 ⁸ means that the chip used is 8-bit A/D conversion.

Combining formulas (1), (2) and (3), we get:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; DATA</span>}}{\mathrm{<span\; class="notranslate">\; 51</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

From the collected electrical signal DATA, the resistance value of the preform at any monitoring point can be solved according to the following formula

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 51</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}{\mathrm{<span\; class="notranslate">\; DATA</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

(3) Carry out resin mold filling, scan all monitoring points cyclically during mold filling, and judge the arrival of the resin flow front by monitoring the sudden change of voltage value; after the mold filling is completed, the resistance R _x of the preform at each monitoring point is all increasing Large, measure the change of the resistance _Rx of these preforms, that is, the curing situation of the resin can be known in real time through monitoring.

As shown in Figure 3, the monitoring system that realizes the method of the present invention consists of the arrangement of preforms, reference resistance _Rc , output voltage controller, amplifier and A/D converter, control circuit CPU and PC, etc., the present invention 1-16 excitation wires and induction wires can be set up and down, so 1-256 monitoring points can be formed. The control circuit CPU makes the output voltage controller select one or more of the 1-256 points through the control signal. After the reference resistor R _c is connected in series, a DC voltage is applied. After the voltage is amplified by the amplifier and A/D converted, the control circuit CPU scans and collects the monitoring signals of 1-256 monitoring points. The A/D conversion module is set, the data conversion and transmission speed is very high, and it only takes 1 second to scan all 256 monitoring points once.

The control circuit CPU has a control cycle scanning function. When monitoring, it performs cycle scanning on 256 monitoring routes. For routes that are not connected, the monitoring signal will be displayed as zero.

Claims (3)

1. The real-time monitoring method of the direct current resistance method of the composite material liquid forming LCM process, which is characterized in that it is realized through the following steps: (1) According to the size of the component, the excitation wires and induction wires are cross-arranged on the upper and lower surfaces of the preform to determine the monitoring points, and these monitoring points constitute the resistance of the measured preform; (2) Apply a DC voltage on both sides of the resistance of the preformed body to be tested, and connect a reference resistor whose size matches each other in series for the resistance of the preformed body to be tested to form a voltage divider circuit, and measure the voltage at both ends of the reference resistance. After the operational amplifier and AD conversion, it is collected and displayed on the PC in real time, and the resistance of the measured preform can be obtained through calculation; (3) Carry out resin mold filling, scan all monitoring points cyclically during mold filling, and judge the arrival of the resin flow front by monitoring the sudden change of voltage value; after the mold filling is completed, the resistance of the preform at each monitoring point is increasing, Measuring the changes in the resistance of these preforms, that is, the curing of the resin can be understood in real time through monitoring. 2. The real-time monitoring method of LCM process DC resistance method according to claim 1, characterized in that: the value of the reference resistance R _c is 10 ¹⁰ -10 ¹¹ ohms. 3. The real-time monitoring method of DC resistance method for LCM process according to claim 1, characterized in that: the number of monitoring points is 1-256.

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