The Manufacturing Process Mechanism and Development Trend of Load Cell

The Manufacturing Process Mechanism and Development Trend of Load Cell

【Summary】Strain gauge load cell is a technological product based on the manufacturing process and developed depending on the manufacturing process. Manufacturing process is not only a common basic technology, but also a key professional technology. The concept of "seeing the level from the technology and the quality from the equipment" has become the consensus of domestic and foreign load cell manufacturers. This article starts from the position and role of manufacturing process in the development and production of strain gauge load cells; the mechanism of supporting process, basic process, core process and special process composing the manufacturing process; facing the in-depth integration of information technology and manufacturing technology to achieve digitization and networking , The new requirements of intelligent design and manufacturing, as well as the innovative development trend of manufacturing process, etc. expound the above concepts.

[Keywords] load cell; manufacturing process mechanism; supporting process; basic process; core process; special process;

I:Overview

At the beginning of human civilization and society, they recognized the status and role of manufacturing technology and manufacturing technology. Labor creates the world, manufacturing technology, and manufacturing process have always been the connotation of active productivity, the most active factor in the materialization of engineering technology, and the bridge for the transformation of scientific research results into commodities. The technology and products of strain gauge load cells (hereinafter referred to as load cells) are no exception. Since their introduction in the early 1940s, they have been developed entirely on the basis of manufacturing processes and relying on continuous improvements in manufacturing processes. The structural principle and production process of the load cell determine that there are more manual operation procedures, and human factors have a greater impact on product quality, which restricts the development of load cell technology.With the advancement of science and technology and the improvement of industrial production automation, digitization and intelligence, the general consensus of foreign weighing sensor manufacturers in the position of leader in the electronic weighing instrument market is: the manufacturing process of weighing sensors is definitely not what some people think. "Workshop craftsmanship", manufacturing process is not only a common basic technology in the development and production process, but also a professional technology that plays a key role. It is a comprehensive technology integrating machinery, electronics, information, materials and management. The concept and connotation of manufacturing process continue to expand, from narrow to broad, from part to whole, from single item to system, combining traditional load cell manufacturing technology with modern manufacturing technology, and deep integration of information technology and manufacturing technology to achieve digitalization. Networked and intelligent design and manufacturing form a new modern design and manufacturing process system. These concepts are more and more accepted by domestic weighing sensor manufacturers, and the development and innovation of manufacturing processes are increasingly concerned and valued by domestic technicians. The competition of weighing sensors in the international electronic weighing market is mainly the competition of manufacturing processes, the application of high-tech research and development of new products and the competition of independent intellectual property rights products, which is finally reflected in the competition of accuracy, stability and reliability of the weighing sensor.The common pursuit of load cell manufacturers in a leading position in the international market is: the structure of the load cell is more reasonable; the material of the elastic element is more sophisticated; the environmental stress screening of the components is more stringent; the support process, basic process, core process, special The application and integration of the process are more scientific, reasonable and repeatable; the circuit compensation and adjustment equipment and compensation process are more complete; the application of high-accuracy load cells is more extensive to enhance the core competitiveness of the enterprise. This should also become the common pursuit of my country's load cell manufacturing enterprises, and special attention should be paid to improving and enhancing the manufacturing processes and process equipment that are far from foreign companies; understanding the supporting processes, basic processes, core processes, and special processes that make up the manufacturing process Mechanism and innovation development trend.

II.Position and role of manufacturing process in the development and production of load cells. Analysis of the structural principle and manufacturing process of load cells shows that there are four key issues in the development and production process, namely, elastic element structure and elastic element metal material. , The whole process manufacturing process and testing equipment and methods. Among them, the scientificity, rationality and repeatability of the manufacturing process are the fundamental guarantee to ensure that every load cell produced meets the requirements of national standards. Therefore, the manufacturing process is the core professional technology that plays a key role in the development and production process. The manufacturing process and the load cell technology are complementary to each other to promote and drive the relationship. The rationality, stability and repeatability of the manufacturing process have promoted the development of the load cell technology. In turn, the increase in the measurement level of the load cell requires the manufacturing process. Towards automation, intelligence, and high stability. It can be said that the manufacturing process is an important means for the load cell manufacturing enterprises to strengthen their competitiveness and improve economic benefits. Which company attaches importance to the research and application of manufacturing technology, which company will benefit more and make rapid progress. In order to survive, develop and obtain economic benefits in today's fierce and almost cruel market competition, load cell manufacturers must rely on diverse product varieties, superior quality, low cost and timely delivery to occupy the market.The main means to obtain these comprehensive advantages is to rely on product development, scientific and reasonable selection of manufacturing processes, and continuous improvement and innovation. The German weighing instrument industry is well-known in the world weighing instrument market for manufacturing high, precise and cutting-edge technology products, and has a high level of expertise in the field of weighing technology. Especially in the research, manufacture and application of load cells, there are a group of manufacturing experts in load cells such as HBM Electronic Measurement Technology Co., Ltd., Balluff Sensor Co., Ltd., etc., which can produce high stability and reliability. Accuracy products are based on advanced manufacturing technology. Manfred Manfred, senior consultant of the German Institute of Engineering Physics Dr. Kochschko believes that this is mainly due to the growing technological and technological innovation capabilities and insatiable spirit of innovation in the German weighing instrument manufacturing industry. The load cell is a knowledge-intensive, technology-intensive and skill-intensive high-tech product, which requires the coordination and integration of multiple disciplines, multiple technologies and multiple manufacturing processes. The so-called high-tech products, "high" is high in terms of the technical content and the difficulty of the manufacturing process, especially in the middle and large-scale production, it is strict to the scientificity, rationality and stability of the manufacturing process and its process flow. test.Just as the evaluation of international manufacturing experts: "If product development takes ten times more effort, then mass production technology development will take a hundred times more effort." The load cell manufacturing companies in some industrially developed countries in the United States and Europe are theirs. Hundreds of efforts have been used in the development of mass production technology to become the leader in the international load cell technology and market competition, and it has remained so. The important role of the load cell manufacturing process in the development and production is often not recognized by people and has not been given enough attention. Some companies in our country adapt to the manufacturing process during the design stage of the load cell product, and adapt to the process equipment during the manufacturing process design. This is the root cause of the long-term lag in the weighing sensor technology and manufacturing process, and it is also the consequence of not paying attention to technological transformation. The reason is that the research work of the manufacturing process itself is relatively difficult, and certain test equipment is required, and the practice of the manufacturing process needs to be repeated. It needs to accumulate many years of practical experience. After several years of hard research and testing, certain technologies and Process difficulties. Therefore, it is difficult to produce results, talents, and benefits in the short period of 2020.09 of the 19th Weighing Technology Symposium.However, the quality and cost of the load cell are closely related to the manufacturing process, and companies must pay attention to it. The development practice of load cell products has proved that optimizing the structure design and manufacturing process is the main link to ensure that each product in mass production meets the national standards. As far as load cell products are concerned, to underestimate the manufacturing process is to relax the product quality. Only by paying attention to and grasping the manufacturing process can a large number of hidden dangers in the production process be eliminated in the bud. There is nothing wrong with focusing on product quality, and there will be no peace if you do not grasp the manufacturing process. This also reflects the status and importance of the manufacturing process in the development and production of load cells from another side. How to implement the "Made in China 2025" development strategy in the current load cell industry and how to deeply integrate information technology and manufacturing technology to achieve digital, networked, and intelligent design and manufacturing are issues that larger companies in the industry must face.

In recent years, three-dimensional digital design and manufacturing capabilities have become the core of competition between domestic and foreign companies, and are the fulcrum and breakthrough point for the transformation of corporate research and development capabilities. This change with the nature of a weather vane should cause load cell companies to attach great importance to it. Although the principle and manufacturing process of the load cell determine that it cannot be mass-produced on an automated, intelligent, seamless production line like machine parts, the structural design and manufacturing process of the load cell should also be upgraded with Internet thinking. It is as close as possible to digital, intelligent or partially digitalized, intelligent production, to keep up with the pace of development of international weighing sensor manufacturers.

III. Key manufacturing process and mechanism analysis of load cell

The structure and working principle of the load cell determine that its production process is a technical product based on the manufacturing process. The scientificity, rationality and repeatability of the manufacturing process, the advanced nature of the manufacturing process equipment and the level of automation and intelligence are the fundamental guarantee for producing products that meet the requirements of national standards. According to the structural principle of the load cell and the characteristics of the manufacturing process, the manufacturing process can be divided into support process, basic process, core process and special process.

1:Support process and mechanism analysis

The supporting processes of the load cell production process are mainly forging, machining, heat treatment, and surface treatment of the elastic element blanks. Among them, the quality of forging processing, machining size and shape tolerance, comprehensive performance of heat treatment, and surface treatment quality directly affect the accuracy, stability, reliability and appearance quality of the load cell.

(1) The forging process should make the elastic element have the best mechanical properties. The purpose of forging of the elastic element blank is to smash the coarse grains to make them uniform and compact. At the same time, the direction of the flow line of the metal material and the load cell are required. The force direction is the same, and no crossover, overlap, etc. are allowed. Therefore, only the elastic element blanks are allowed to stretch during the forging process, and the piers are not allowed to be thick, so that the elastic element has the best mechanical properties, which is very important to improve the measurement performance of the load cell, especially the long-term stability.For 40 CrNiMoA medium-carbon alloy steel materials commonly used in China, the forging heating temperature is 1180℃, the heating time is 3 to 4 hours, the holding time is≥30 minutes, the opening forging temperature is 1140～1160℃, the final forging temperature is≥850℃, air cooling. The annealing process is: heating temperature 860℃, heat preservation for 1.5 hours, furnace cooling. If it is slowly cooled after forging, annealing treatment is not necessary, and the elastic element can be processed directly. After forging, the metallographic structure of the elastic element blank belongs to sorbite and tempered α phase (10% HNO3 alcohol solution corrosion), and the hardness of the 19th Weighing Technology Conference Proceedings 2020.9 Nanjing 4HRC30. In recent years, large-scale load cells ranging from several hundred tons to thousands of tons have been applied. The size of the elastic element blanks is relatively large, and the slow cooling should be paid attention to after forging.

(2)The hot and cold processing technology should make the elastic components produce as little residual stress as possible

Since the most important mechanical part of the load cell is the elastic element, its function is to counteract the applied load and at the same time concentrate the effect of the load in a uniform strain field. Therefore, it is required that the blank of the elastic element can only be stretched during the forging process. The direction of the metal flow line should be consistent with the direction of the elastic element's force; in the process of machining, heat treatment, and surface treatment, ensure that the manufacturing process is as small as possible Of the resulting residual stress. The main sources of residual stress in the elastic element are: the residual stress generated during the forming process of the material in rolling or drawing; the residual stress generated by the uneven cooling temperature and phase change during the heat treatment process; in the machining process In, the residual stress generated by the cutting force. The latter forms a metamorphic layer on the surface of the elastic element, which makes the tissue in an unstable state, and the internal stress relaxes over time, resulting in dimensional changes. Machining such as planing, milling, turning, and grinding makes the surface of the elastic element deform unevenly, resulting in greater residual stress. The greater the amount of cutting, the greater the residual stress on the surface.

During turning, the axial and circumferential residual stresses are different for different feed rates. The maximum residual tensile stress is on the surface of the elastic element, and the maximum residual compressive stress is 40-80μm from the surface. During grinding, the residual stress generated is the largest. The greater the grinding depth, the greater the residual stress generated. The maximum residual stress is located at a distance of 20 to 40μm from the surface. The residual stresses generated by the four mechanical processing methods of planing, milling, turning and grinding can be summarized as follows:

① The maximum residual stress is between the surface of the elastic element and the depth of 100μm, the value is relatively large;

② The residual stress decays quickly, and it is very small at a depth of 200μm;

③ The greater the cutting amount, the greater the residual stress;

④ When the elastic element is finished by grinding, the residual stress is the largest, and its value can reach 900N/mm2. Therefore, it is required that the finish machining of the elastic element after heat treatment does not use grinding as much as possible, and the cutting amount is as small as possible when the size of the strain zone is close.

(3) Stability treatment process to eliminate residual stress in cold and hot processing The stability treatment to eliminate residual stress in cold and hot processing of elastic elements mainly includes cold and heat cycle process, secondary vacuum tempering process, and high temperature oil boiling process.

Heat and cold cycle process-the elastic element after heat treatment, the core part is tensile stress, and the surface layer is compressive stress. In the heat and cold cycle treatment, due to the difference of cold and heat temperatures, the thermal stress and residual stress in the opposite direction are offset each other. The process specification is:-196℃×4h /+190℃×4h, cycle three times. Secondary vacuum tempering process-to transform the retained austenite in the elastic element into martensite. For medium-carbon alloy steel 40CrNiMoA elastic elements, after 480℃ tempering, vacuum tempering is performed again to eliminate the residual stress of cold and hot processing. The process specification is: 460℃×2h, vacuum degree 10-5 Support. High-temperature oil boiling process-for steel elastic elements that are qualified for cold and hot processing and have been surface treated, in order to eliminate their cold and hot processing, the residual stress of the 19th Weighing Technology Symposium 2020.9 Nanjing 5 can also be implemented in High temperature oil boiling process for 2-4 hours in a high temperature oil tank of 250℃.

2. Basic technology and mechanism analysis

The core component of the load cell, the resistance strain gauge and its strain adhesive, the raw materials and components used in the circuit compensation and adjustment process, and the various protective and sealing materials used in the package all belong to the basic process category. They are the basis of the load cell manufacturing process. The preconditions for producing products that consistently meet the accuracy and stability requirements of the national standards for load cells. In order to save space, this article only analyzes the core component of the load cell resistance strain gauge manufacturing process and its strain transmission principle.

Resistance strain gauges for load cells should have the best working characteristics and compatibility with elastic components. The magnitude of the strain transmitted by the resistance strain gauge is very small. Take the resistance strain gauge with a sensitive grid length of L=5mm and a deformation of 1000με at full scale as an example. If the resolution is 10-5, then △L=5×10-8mm. That is to say, the elastic element must reflect the distance of one atom in the length of 5mm. This requirement is indeed very high. The working characteristics, stability and reliability of the resistance strain gauge determine the accuracy, stability and reliability of the load cell to a large extent. Since the strain gauge cannot be used twice after the test, it can only measure the working characteristics and fatigue life under laboratory environmental conditions, which brings great difficulties to research and selection. At present, resistance strain gauges are mostly selected around sensitive gate materials and structural forms, substrate and cover layer materials, manufacturing processes and process equipment levels.

In order to select a resistance strain gauge that meets the measurement performance requirements of the elastic element of the load cell, it is necessary to understand the strain transmission principle of the resistance strain gauge attached to the elastic element. Under the action of external load, the elastic element deforms extremely small and is transferred to the sensitive grid through the strain adhesive and the resistance strain gauge substrate. Because the transferred deformation is very small, the working characteristics of the resistance strain gauge and the strain adhesive are very demanding. In summary, the main points are: good strain transmission linearity; small hysteresis and creep; small temperature and time drift; good electrical insulation performance and no moisture absorption. Production practice has proved that for the load cell of the same structure, the resistance strain gauges of different structures are pasted, and the creep index, the pass rate and the fatigue life of the same accuracy level are significantly different. This is because the structure of the sensitive grid, Caused by improper selection of base length and base width. The schematic diagram of the resistance strain gauge pasted on the elastic element of the load cell is shown in Figure 1.

The surface of the strain area of the elastic element of the load cell, the base of the resistance strain gauge, and the strain adhesive are all in surface contact, so the deformation can be effectively transmitted. The deformation of the elastic element is sequentially transferred to the resistance strain gauge base and the sensitive grid in the form of shear. During deformation, the displacement at both ends of the base of the resistance strain gauge is the largest, so the shear stress is the largest, and the displacement at the middle section is zero, so the shear stress is zero, and the signs of the shear stress at both ends are opposite, and L0 is the equivalent length.

The axial force on the sensitive grid of the resistance strain gauge is distributed along the X axis, the force at both ends is zero, and rises to a certain value in an exponential curve. The strain is uniformly distributed in the equivalent length L0, but the length participating in the deformation is reduced by 2a, resulting in a decrease in △R, while R does not change, so △R/R becomes smaller, which reduces the sensitivity to the strain of the elastic element. It is the end effect of the resistance strain gauge. Analyzing the transmission of strain, we can get.

① Through the transfer of shear stress, the tensile and compression resistance strain gauge sensitive grid realizes strain transmission, that is, the central shear stress of the sensitive grid is zero, and the two ends rise to the maximum in an exponential curve, which is called the shear stress transmission zone.

② The strain of the elastic element is transferred to the sensitive grid through the resistance strain gauge substrate, most of its area is in a unidirectional stress state, and the transmitted strain is basically equal to the strain of the elastic element, so it is called the normal strain transfer area.

③ Corresponding to the sensitive grid part of the resistance strain gauge in the shear stress transfer area, the strain ε decreases with the increase of x,  and the end is zero, and the strain transfer lags in this area.

In order to reduce the influence of end effect, the selection principle of resistance strain gauge and adhesive is:

① Try to choose resistance strain gauges with frame-shaped ends;

②There must be enough distance from the edge of the base to the end to increase the area of the shear stress transfer zone;

③When selecting the sensitive grid or sensitive wire, the thinner or finer the better, the substrate thickness is required to be 25μm to ensure effective strain transmission;

④The thinner the adhesive layer is, the better, and the larger the adhesive elastic modulus and shear elastic modulus, the better, which is beneficial to reduce the hysteresis and creep errors of the load cell.

3. Core process and mechanism analysis

The core manufacturing process of the load cell is the whole production process flow from the preparation of resistance strain gauges, elastic components, circuit compensation materials, and components to the completion of all the manufacturing processes of the load cell. Among them, the key processes in the core process are the pasting and curing of resistance strain gauges, welding of Wheatstone bridge circuits, circuit compensation and adjustment, and protection and sealing.

(1) Pasting process mechanism of resistance strain gauge

Pasting the resistance strain gauge on the surface of the strain zone of the elastic element is a physical bond. It uses the adhesion force on the surface of the metal material and the gravitational force between the molecules. It is not very strong because it is polymerized by molecular bonds like a chemical bond. Therefore, in order to make the resistance strain gauge stick to the elastic element densely and firmly, very good bonding conditions must be created, which is to polish or sandblast the surface of the elastic element. Its role is:

①Remove the oxide layer on the surface of the elastic element patch, purify the surface, activate surface molecules, and create conditions for increasing the adhesion of the surface;

②Increase the effective bonding area and improve the bonding strength, especially the shear strength;

Proceedings of the Nineteenth Weighing Technology Symposium 2020.9 Nanjing 7

③The strained adhesive can better infiltrate and penetrate the surface of the elastic element to ensure the quality of the paste.

Pasting resistance strain gauges is a key process in the manufacturing process of load cells, and should be operated in strict accordance with process technical requirements. In order to keep the position of the resistance strain gage pasted on the elastic element accurate, it should be isolated from the high temperature rubber sheet that applies pressure. That is, a layer of polytetrafluoroethylene film is placed between the resistance strain gauge and the high temperature rubber plate to ensure that the resistance strain gauge will not move or rotate when pressure is applied. The thickness of the PTFE film used in the process of pasting resistance strain gauges in my country is about 0.07mm, the thickness of the American process is 0.003 inches (0.0762mm), and the Japanese process is 0.025mm ~ 0.075mm. Due to the low coefficient of friction of the PTFE film, it is used as a sliding film between the resistance strain gauge and the high-temperature rubber plate, allowing the high-temperature rubber plate and the pressure block or pressure plate on it to have room for free movement without affecting the resistance The accuracy of the strain gauge sticking position. In fact, a non-adsorbent interface is provided between the pasted resistance strain gauge and the high-temperature rubber sheet, which creates conditions for the correct installation of the pressurized fixture and the accurate position of the resistance strain gauge.

(1)The positioning error of the resistance strain gauge pasted on the elastic element

Choose any type of resistance strain gauge according to the elastic element structure of the load cell, which has a certain sensitive grid and base size, and paste (position) it at the set position of the elastic element strain zone, such as the midpoint of the strain beam, strain The center of the regional blind hole web is just an assumption. Because no matter how strict the pasting process is required, a certain amount of positioning error will occur. The main effect of this error is that the amount of strain felt by the resistance strain gauges is not exactly the same, or even larger differences. This difference in the perceived strain is reflected in the load cell bridge circuit, that is, the change in the resistance of a bridge arm in the bridge does not match the reverse change of the resistance of the adjacent bridge arm, which causes the non-linearity of the bridge output error. Especially for load cells with double-hole parallel beam structure, the positioning tolerance requirements of resistance strain gauges are very strict. If the resistance strain gauge deflects or translates along the center line of the parallel beam, or both, it will not only produce nonlinear errors but also It also produces a large eccentric load error, so the positioning error of the resistance strain gauge must be strictly controlled. According to the experimental research, if the positioning deviation of the resistance strain gage pasted on the elastic element, the error of the strain experienced by it is 5%, that is,δ=0.05, taking a load cell with a sensitivity of 2mv/v as an example, the maximum stress The variable isε=1000×10-6=10-3, when the resistance strain gage sensitivity coefficient K=2.0, the nonlinear error δ of the bridge output is:

Due to various reasons, the strain experienced by the resistance strain gauge has a 5% deviation, which should be the maximum deviation possible. The influence of the nonlinear error of the load cell is 0.005%, which is acceptable within the allowable error range. From this, it is not difficult to draw a conclusion: the positioning deviation of the resistance strain gage pasted on the set position of the strain zone of the elastic element should be subject to the condition that the sensed strain change is not greater than 5%. In order to meet the positioning error requirements of the resistance strain gauge pasted on the elastic element, manual operation should be avoided as much as possible in the key process of pasting the resistance strain gauge. It is best to use computer-aided pasting resistance strain gauge equipment and intelligent robot pasting resistance strain gauge system.

(2)Strain adhesive curing and post curing process mechanism

Curing is a process in which the strained adhesive itself is cross-linked at a specified temperature and within a certain period of time, and the adhesion between it and the elastic element is formed to bond firmly. Whether the curing is sufficient and complete directly affects the physical and mechanical properties of the strained adhesive, mainly related to the bond strength that affects the strain transfer performance, especially the shear strength does not meet the technical requirements, resulting in the strain of the elastic element cannot be synchronized and accurately transferred Sensitive grid for resistance strain gage. The key issues of the curing process are curing temperature, holding time, and heating rate. Therefore, it must be carried out in strict accordance with the curing process requirements of the strained adhesive, and the accuracy and uniformity of the temperature must be guaranteed. . Strictly speaking, the strained adhesive is not completely homogeneous after curing, and its crosslinking density and even chemical composition vary with different parts, so the heating rate and holding time have a greater impact on the microstructure of the strained adhesive.

The heating rate should be about 50C per minute, and enough heat preservation time should be given to make some components of the strained adhesive volatilize and solidify in turn. When the adhesive is not cured sufficiently or completely, because its molecular bonds are not firmly polymerized, small molecules will be generated when undergoing deformation, which will increase the creep effect, thereby increasing the creep value and making the zero point of the load cell unstable. It should be cured as much as possible, and post-curing treatment should be performed after curing. Post-curing is a process to ensure that the strained adhesive achieves the best comprehensive performance and enters a stable state. Its purpose is to make the strained adhesive more complete curing and eliminate the escape of water molecules and shrinkage of the adhesive layer due to pressure and heating during the first curing. Causes of residual stress. It can also be said that in a short time, the natural curing of the long-term strained adhesive layer can be simulated by heating. The maximum post-curing temperature should be 200C~300C higher than the curing temperature, keep it for 2~3 hours, and the effect of curing after cooling with the heating equipment:

①Expand the temperature limit of the bonding layer between the resistance strain gauge and the elastic element;

②Increase the elastic modulus of the bonding layer;

③Release the residual stress and make the stress of the bonding layer evenly enter a stable working state.

(4)The welding Wheatstone bridge process machine has four resistors R1, R2, R3, R4 connected into a quadrilateral circuit called Wheatstone bridge circuit, as shown in Figure 2, its function is to convert resistance changes into voltage output.

Figure 2 Wheatstone bridge circuit

The four resistors are called the four arms of the bridge. The diagonal BD of the quadrilateral is connected to the output end of the measuring instrument called the bridge, and the diagonal AC of the quadrilateral is connected to the power source and is called the bridge supply end of the bridge. After the bridge supply voltage Ui is applied to the bridge supply terminal AC, there is an initial voltage U0 at the output terminal BD. If the resistance of the bridge arm changes, the output voltage will also change to U0 + △ U0. When power is supplied to the bridge end, each branch in the bridge circuit has current flowing. When the potential between the two BDs is not equal, the bridge will produce unbalanced output, and when the BD between the two points When the potential is equal, the current between BD in the bridge circuit is zero. At this time, the bridge is said to be in a balanced state, namely: R1R3=R2R4 The above formula shows that the product of the bridge relative to the arm resistance is equal when the bridge is balanced, this is The balance condition of the bridge. When working, only one bridge arm resistance changes is called a single-arm bridge; two adjacent bridge arm resistances change is called a half-bridge bridge; four bridge arm resistances all change are called a full bridge Electric bridge.

Wheatstone bridges have the following characteristics when used in load cells:

① In the initial state (the bridge arm resistance has not changed), the output voltage U0 can be zero. When working, the change in output voltage from zero △ U reflects the change in resistance, which can achieve a higher resolution, which is very beneficial for amplification, display and recording;

② Influences such as temperature changes can be offset by the full bridge connection;

③ If the position, direction and bridge assembly of the resistance strain gauge are reasonable, the influence of eccentric load and side load can be eliminated or reduced;

④ It is easy to compensate and adjust various circuits. The bridge output of the load cell is mostly connected with a DC amplifier, and the input resistance R0 of the DC amplifier is much larger than the bridge resistance. Therefore, the bridge output can be regarded as an open circuit, that is, R0 = ∝. This type of bridge is usually called a "voltage output bridge", and its bridge circuit

as shown in picture 2.

Using Ohm's law and Kirchhoff's law, the equation for the bridge output voltage can be derived:

The above two formulas show that the relationship between resistance change rate or strain and output voltage is approximately linear.

(5)Protection and sealing process mechanism

Protection and sealing are key processes in the manufacturing process of load cells, and are the fundamental guarantee for load cells to withstand the impact of the objective environment and the sensing environment and to work stably and reliably. The resistance strain gauge attached to the elastic element of the load cell and the strain adhesive used will be affected by moisture and oxygen in the air, because water can penetrate almost all polymers to produce plasticization. If the protection and sealing are not good, the resistance strain gauge and the strain adhesive will absorb the moisture in the air, which will cause the adhesive layer to expand and plasticize, resulting in a sharp drop in insulation resistance, bonding strength and rigidity, causing zero drift and irregular output changes until the weighing The heavy sensor fails. In some test occasions, the load cell will also be directly sprayed and immersed by water. The penetration of moisture will reduce the bond strength and insulation resistance of the strained adhesive, because moisture is not entirely water, usually many complex aqueous solutions. It can infiltrate various polymers to plasticize and change properties.Salt spray is an aerosol-like body, the main ingredients are calcium chloride, magnesium chloride and other impurities, which have a strong corrosive effect on elastic components, resistance strain gauges and strain adhesives. At this time, no matter how exquisite the manufacturing process of the load cell is, and no matter how good the technical performance index is, it cannot play a role, so stability and reliability are the prerequisite technical indicators of the load cell. To ensure that this indicator must be effectively protected and sealed, the load cell's moisture-proof, water-proof, anti-salt spray performance and the ability to resist vibration and impact are improved. This is the focus of the protection and sealing of load cells. If the protection and sealing are not good, all previous technological achievements will be wiped out, which shows the importance of protection and sealing.

Currently, load cells mostly use three methods: surface sealing, blind hole potting, and diaphragm welding and sealing.

4:Special process and its mechanism analysis

The manufacturing process that is transplanted from the very mature manufacturing process of related products and has a miraculous effect on improving the technical performance of the load cell is called a special process. For example, in order to eliminate the residual stress of elastic components and improve the dimensional stability, the introduced aerospace product parts stabilization treatment technology mainly includes anti-quenching method, thermal cycle method and constant temperature aging method. In order to improve the stability and reliability of the load cell, the introduction of vibration aging technology and so on.

(1) Temperature cycle aging process

In fact, it is a method of "environmental stress screening" for aerospace vehicle parts, and it is very effective to transplant it into the production process of load cells. The main parameters of temperature cycle are the limit value of high temperature and low temperature, residence time, temperature change rate, total time of one temperature cycle and number of cycles. According to the characteristics of the resistance strain gauge, strain adhesive and manufacturing process used in the load cell, the cyclic aging method from room temperature to high temperature and gradually increasing the temperature is often used, that is, the temperature is raised to 60℃ for 4 hours on the first day, and the temperature is naturally reduced to room temperature with the test box Starting from the second day, the maximum temperature will increase by 20°C every day until 140°C on the fifth day, stay for 4 hours, and naturally decrease the temperature to room temperature with the test chamber, which is a temperature cycle. A total of ten days of two temperature cycle aging is enough.

(2) Stability treatment process of heat treatment method

It is mostly used in aluminum alloy weighing sensors, which are processed after the blank is processed into elastic components, mainly including anti-quenching method, cold and heat cycle method and constant temperature aging method.

①Reverse quenching method

Place the aluminum alloy elastic element in liquid nitrogen at -196℃, and after holding it for 12 hours, quickly spray it with new high-speed steam or put it in boiling water. Because of the opposite direction of the stress generated by deep cold and rapid heat, they cancel each other out to achieve the purpose of releasing residual stress. Tests show that the use of liquid nitrogen-high-speed steam method can reduce residual stress by 84%, and the use of liquid nitrogen-boiling water method can reduce residual stress by 50%.

②Cold and hot cycle method

The heat and cold cycle process is -196℃×4 hours/190℃×4 hours, and the cycle is 3 times, which can reduce the residual stress by about 90%, and has a stable structure, high resistance to microplastic deformation, and good dimensional stability. The thermal stress generated by the cold and hot temperature gradient interacts with the residual stress to redistribute it to obtain the effect of reducing the residual stress.

③ Constant temperature aging method

Constant temperature aging can eliminate the residual stress generated by mechanical processing, but also eliminate the residual stress introduced by heat treatment. When LY12 hard aluminum alloy is aging at a high temperature of 200°C under constant temperature, the relationship between the release of residual stress and the aging time shows that the residual stress can be reduced by about 50% by keeping it for 24 hours.

(3) Mechanical stability treatment process

Mechanical stability treatment is usually carried out when the load cell circuit is compensated and adjusted and protected and sealed, and the product is basically formed. The main processes are pulsation fatigue method, overload static pressure method and vibration aging method.

①Pulsating fatigue method

Install the load cell on the low-frequency fatigue testing machine, apply the lower limit of (1/5 to 1/3) rated load, and the upper limit of rated load or 120% of rated load, and perform 5000 to 10000 times at a frequency of 3 to 5 times per second The loop. It can effectively release the residual stress of the elastic element, the resistance strain gauge, and the strain adhesive layer, and the effect of improving the zero point and sensitivity stability is extremely obvious.

②Overload static pressure method

In theory, it is suitable for various ranges, but in actual production, aluminum alloy small-range load cells are used more frequently. The overload static pressure process is: in a dedicated standard weight loading device or a simple mechanical screw loading device, the load cell applies 125% of the rated load and maintains it for 4 to 8 hours, or applies 110% of the rated load and maintains it for 24 hours. Both processes can achieve the purpose of releasing residual stress and improving the zero point and sensitivity stability. Due to the simple equipment, low cost and good effect of the overload static pressure process, it is widely used by aluminum alloy load cell manufacturers.

③Vibration aging method

Install the load cell on a vibration table whose rated sinusoidal thrust meets the requirements of vibration aging, estimate the frequency according to the rated range of the load cell, and determine the applied vibration load, working frequency and vibration time. For a small-range parallel beam load cell, at a frequency of 30 Hz and a vibration acceleration of 10 g, 15 minutes of vibration can achieve better results. Resonance aging is better than vibration aging to release residual stress, but the natural frequency of the load cell must be measured. Before and after the test, an X-ray instrument can be used to measure the stress value at and around the resistance strain gauge. The characteristics of vibration aging and resonance aging process are: low energy consumption, short cycle, good effect, no damage to the surface of the elastic element, and simple operation.

The mechanism of vibration aging is still inconclusive. The theories and opinions put forward by foreign experts mainly include: plastic deformation theory, fatigue theory, lattice dislocation slip theory, energy viewpoint and material mechanics viewpoint. They have only given explanations to varying degrees, but they have not been fully, convincingly, and authoritatively tested. These theories and viewpoints are often intersecting each other, so the mechanism of vibration aging can be regarded as a complicated process.

After experimental research on vibration aging, some experts tend to explain the mechanism of vibration aging from the viewpoint of repeated stress overload in material mechanics. That is, the vibration stress acting on the elastic element interacts with the residual stress inside, which relaxes and releases the residual stress.

IV:The development and innovation of the manufacturing process of the load cell

Today,when the electronic weighing instrument market is increasingly internationalized and manufacturing technology and manufacturing processes are becoming increasingly commercialized, the development of weighing sensor manufacturing technology will inevitably be guided by the needs of the electronic weighing market competition, and will be strongly driven by new technologies, new materials and new processes. . The development of manufacturing process is not an end in itself, but a means to ensure that the load cell can meet the needs of the domestic and foreign electronic weighing market in terms of variety, specification, quantity, quality, and price. It is used to achieve that the enterprise can integrate into the country as soon as possible. Foreign markets, the need to participate in international competition.

1. Support process development and innovation

The manufacturing process of load cells is always evolving, and there is no eternal advanced manufacturing process. With the progress of science and technology, the improvement of industrial automation, digitization, and intelligence has continuously given new connotations to the manufacturing process. The progress of the manufacturing process should promote the improvement of product quality and overall efficiency and benefit. For a long time, the progress in the manufacturing process of the elastic components of load cells and their accessories has been limited to the improvement of the production efficiency of a single machine tool, a single process, and a single tool, which is not suitable for mass production and customized production. In order to achieve mass production and customized production, it is necessary to conduct analysis and research from the entire process of load cell design and manufacturing, and use the opportunities brought by the Internet of Things + thinking and intelligent manufacturing to upgrade the manufacturing process and process flow of the load cell.

Since entering the new century, weighing sensor manufacturing companies, which are in the position of leader in the international market, have combined information technology, automation technology and traditional manufacturing technology. They have generally adopted CNC machine tools, machining centers, and flexible manufacturing units to achieve flexible automated production.. In recent years, it has developed into a digital production line to achieve the comprehensive goals of compatibility with multi-variety production, stabilizing quality, improving efficiency, and reducing costs. In view of the "multi-variety , small batch" product characteristics of load cells, and the "product development and mass production coexisting" manufacturing model, there is no existing experience to learn from. In recent years, in order to meet the needs of mass production and customized production, some domestic enterprises have used Internet + thinking and new opportunities brought by intelligent man ufacturing to upgrade mass production of elastic component cold and hot processing production lines, and combine informatization with industrialization., Completed the technical transformation of the elastic element mechanical processing production line, and established an automated and intelligent production line for the cold and hot processing of elastic elements. This is a powerful measure to realize the upgrading of automation and intelligent technology and keep up with the development of international weighing sensor technology.

2. Development and innovation of basic technology

In recent years, there have been many improvements and innovations in the support technology of load cells such as resistance strain gauges, strain adhesives, protective and sealing materials. Among them, the improvement and innovation of the resistance strain gauge manufacturing process has improved the accuracy and stability of the load cell. Played a vital role.

(1) Automatic and intelligent stability treatment process for strain resistance alloy foil

The resistivity change and temperature performance of the strain resistance alloy foil used to make the resistance strain gauge are all related to the hot and cold processing technology, which is caused by the lattice defects produced by the plastic deformation of the strain resistance alloy foil. The migration of these defects when the temperature is slowly raised is the cause of the unstable electrical and mechanical properties of the strain resistance alloy foil, so effective stability treatment must be carried out.

Strain resistance alloy foils are generally made of resistance alloy ingots with a diameter of 14 inches and a weight of 1 ton, which are made into large coils with a thickness of 1/16 inch through rough rolling processes such as cold rolling, hot rolling, and rolling. After finishing rolling, it is rolled on Sendzimir 20 high-speed rolling mill through cold rolling, annealing treatment, rolling and other processes to a thickness of 0.0001 to 0.0002 inches (2.5 to 5μm), and the thickness change is less than 0.00001 inches (0.2μm). ), then clean and cut to the required width. In the process of multiple rolling and rolling of the strain resistance alloy foil, defects such as dislocations, slippage, vacancies, and cracks are generated in the crystal lattice, and the nearby atoms are in a thermodynamically unstable state. An important reason for stability. Therefore, it is necessary to perform stability treatment, that is, annealing treatment. When the annealing temperature is reached, these atoms absorb heat energy and diffuse, which makes the lattice defects migrate and disappear, and the resistivity and temperature coefficient of resistance tend to stabilize.Annealing temperature, holding time, and cycle times are the three elements of stability treatment. In order to improve the stability of the processing technology, companies that are in the position of the leader in the international resistance strain gauge market may develop or commission an intelligent vacuum heat treatment furnace to heat the resistance alloy foil. The characteristic of the intelligent vacuum heat treatment furnace is to perform heat treatment accurately according to the heat treatment process curve under extremely high vacuum conditions or under the protection of high reducing hydrogen gas. Due to the automatic and intelligent setting and control of various heat treatment elements, the heat treatment is guaranteed The uniformity of the heat output improves and stabilizes the heat output performance, ensures the stability of the resistivity and temperature coefficient of resistance of the resistance strain gauge, and provides a theoretical and material basis for the development and production of high-accuracy load cells.

(2) Integration of the manufacturing process of the resistance strain gauge substrate

In order to control the quality of resistance strain gauges from the manufacturing source and break through the bottleneck of resistance strain gauge substrate manufacturing, in recent years, some resistance strain gauge manufacturers at home and abroad have broken through the shackles of traditional manufacturing processes and considered the multiple processes of manufacturing substrates. It is integrated into a process, that is, the selected base glue is prefabricated into a strip with the required thickness (for example, 25μm), and then cut into the size required by the photolithography, after raising and uniform temperature treatment, and then cutting , The cleaned strain resistance alloy foil is bonded together by strain adhesive, and is cured by an intelligently controlled laminator that simultaneously heats and presses. This is a new process called the integration of resistance strain gauge substrate manufacturing. Its outstanding feature is that the substrate manufacturing process is simple and standardized, suitable for automated and intelligent production; because the film is pre-made with uniform thickness and small errors, it overcomes manual Operation and artificial control of the error caused by throwing the adhesive on the resistance alloy foil; the laminator can heat and press dozens of plates at the same time, the substrate production efficiency is high, and the resistance strain gauge has good uniformity of working characteristics. The clean room that meets the requirements of Shidu guarantees the adhesion of analog and digital load cell resistance strain gauges and the installation quality of digital modules.

(2) Adopt video image to assist paste resistance strain gauge and intelligent robot paste resistance strain gauge system. The video image assist paste resistance strain gauge system is shown in Figure 4.

(3) Adopt a new type of resistance strain gauge base material

Breaking through the dominance of traditional phenolic-acetal, epoxy-phenolic, polyimide and other base materials, the new base material—polyetheretherketone (PEEK) is used to make resistance strain gauges. Polyether ether ketone is a high polymer composed of repeating units containing one ketone bond and two ether bonds in the main chain structure. It is a special polymer material and its characteristics are:

①Good physical and chemical properties such as high temperature resistance and chemical corrosion resistance;

②It can be used as high temperature structural material and electrical insulation material;

③It can be combined with glass fiber or carbon fiber to prepare reinforced materials;

④ High melting point and softening point, high tensile strength (melting point 334℃, softening point 168℃, tensile strength 132~148MPa);

⑤It has good rigidity and flexibility, and has outstanding fatigue resistance under alternating stress, which is comparable to alloy materials;

⑥Good manufacturability, can be made into 25μm, 12.5μm thick film.

The substrate is an important part of the foil resistance strain gauge. Its characteristics not only depend on the performance of the substrate material itself, but its thickness and heat treatment conditions will also have an important influence on the quality of the resistance strain gauge. The properties of polyether ether ketone polymer material and the practice of its manufacturing process show that it is an ideal base material for resistance strain gauges. This type of resistance strain gauge is particularly suitable for high-accuracy load cells.

(4) New technology for fully sealed covering layer of resistance strain gauge

In order to ensure the long-term stability of the resistance strain gauge and prevent external mechanical damage, the ideal manufacturing process is to coat a protective film on the surface of the bare gate, that is, a covering layer of the sensitive gate, to form a fully sealed resistance strain gauge after the resistance value is qualified. structure. Although the single-row sensitive grid filming method in the traditional technology of our country solves the uniformity of the thickness of the covering layer of each resistance strain gauge, only the sensitive grid part is sealed, and the grid wire around the solder joint is not sealed. In fact, This resistance strain gauge is not a fully sealed structure. In recent years, some domestic enterprises have solved the uniformity of the film thickness by improving the process and equipment. The resistance strain gauge manufactured by the new process of the whole-page film method is generally adopted. Because the sensitive grid and the grid wire around the two solder joints are completely covered by the glue film. After covering, the resistance strain gauge is the real fully sealed structure after curing. The process of the whole-page filming method is to clean and dry the strain gage that is qualified for resistance adjustment with absolute ethanol, and then paste the pre-prepared film on the whole page, and place it on a heated and pressurized laminator as required. Carry out curing. Finally, the full-page resistance strain gage integrated with the substrate, the sensitive grid and the cover layer is placed on the laser machine, and the laser beam is used to penetrate the adhesive film at the solder joint to expose all the solder joints, which completes the complete sealing process of the resistance strain gage.

(5) Intelligent laser automatic cutting process

The traditional cutting method is to manually use scissors to cut the horizontal rows and vertical columns of the entire plate of resistance strain gauges, which requires a lot of labor, low efficiency, and large deviation of the substrate size. Using intelligent laser cutting device for cutting, the work efficiency is high, the size of the resistance strain gauge substrate is consistent, and the tolerance from the center line of the sensitive grid to its edge is ±0.13mm, and the substrate shape of the resistance strain gauge can be used as the patch positioning reference.

3. Development and innovation of core technology

(1) Pay attention to the installation environment of resistance strain gauges and digital modules

(2) Pasting the resistance strain gauge in the strain area of the elastic element is a key process in the core manufacturing process, and its working environment and pasting quality directly affect the measurement characteristics of the load cell. In the past, some companies did not pay enough attention to this, and some clean rooms and clean benches did not fully meet the requirements, and the work of pasting resistance strain gauges was very irregular. After certification, forensics and international exchanges, companies generally recognize the impact of the working environment of the resistance strain gauge on the quality of the paste, or purchase a clean room, clean workbench, or build their own temperature, humidity, cleanliness, lighting and anti-static measures;

Figure 4 Video image assisted paste resistance strain gauge system

The video image-assisted paste resistance strain gauge system is a semi-automated process based on the analysis of the advantages and disadvantages of the traditional process of pasting resistance strain gauges, in order to ensure the positioning accuracy of the resistance strain gauges and the consistency of the paste positions of the elastic elements, and improve the efficiency of paste Transformation. The system adopts high-definition LCD video image technology, which can automatically enlarge the paste area according to the elastic element structure, shape size, resistance strain gauge positioning size, and provide a clear dynamic video image suitable for the patch magnification. As long as the magnified resistance strain gauge positioning mark is aligned with the positioning crosshair on the elastic element shown in the video, the correct patch position is obtained. The errors caused by the alignment and positioning with the naked eye are eliminated, and the positioning accuracy of the resistance strain gauge and the consistency of the pasting position are improved. Its structure is characterized by the use of PC operating system control, powerful software, convenient operation, intuitive and practical interface. The main video area mainly provides a real-time preview of the video of the elastic element pasting area. The software positioning crosshair is used to replace the scribing on the elastic element, eliminating the physical damage to the surface of the elastic element due to the scribing. In order to ensure the positioning error of the pasted resistance strain gauge and improve the pasting quality and work efficiency, it is best to use an intelligent robot pasting resistance strain gauge system.

(3) Implement a new process of overall cleaning after the elastic element patch group bridge

80% of the failures of the load cell are process problems, and most of the process problems are the welding and cleaning problems of the lead wires of the resistance strain gauge solder joints, the inner and outer leads. Domestic resistance strain gauge production equipment manufacturers are developing resistance strain gauge lead welding equipment whose contact temperature is adjustable within the range of +260℃～+425℃ to ensure the welding quality of resistance strain gauge leads. After the load cell is welded to the bridge, thoroughly cleaning the solder joints and their surroundings is a prerequisite to ensure its stable and reliable operation. Internationally renowned weighing sensor manufacturers generally adopt the overall cleaning process after the elastic component patch bonding wire assembly bridge to remove the solder and the surrounding flux and dirt, and then apply protective surface glue to ensure that it is not wet during the production process.

(4) New development of coating process for resistance strain gauge surface glue and highly moisture-proof and water-proof sealant

After bonding the wire assembly and bridge, the surface of the elastic element that has been cleaned as a whole is coated with a protective surface glue on the resistance strain gauge. This is an important process in the production process of the load cell, which is usually called the first protective sealing treatment. Its purpose is to protect the resistance strain gauge from damage and moisture during the production process, and to lay a good foundation for the final protective seal. In the past, the coating process required to cover the resistance strain gauge, and the surrounding solder joints and polished metal surfaces were not included in the protection, which buried stability and reliability risks. The improved new process of coating surface glue requires a large coverage area, not only the surface of the resistance strain gauge must also cover all the solder joints and the surface of the polished elastic element.

Highly moisture-proof and water-resistant sealant, which can achieve the purpose of improving water and humidity resistance by introducing halogen into the polymer or embedding it with silicon oxygen bond. Foreign countries have used fluorine-containing polyimide, fluorine-containing epoxy resin, fluorine-containing acrylate, silicone/imide copolymer, phenyl silicone and siliconized styrene as basic materials to make sealants, and they have achieved very good applications. effect.

IV:the development trend of load cell manufacturing process

In order to implement the "Made in China 2025" development strategy, deep integration of information technology and manufacturing technology, to realize digital, networked, and intelligent design and manufacturing, the development trend of load cell manufacturing technology is to gradually transform and upgrade existing production lines to achieve digitalization, Intelligent production lines and digital factories.

1. Development trend of load cell production mode

Breaking the traditional manufacturing method of load cell, implementing the automation, intelligent transformation and innovation of manufacturing process and mass production line of elastic components and accessories is the only way for the development of load cell production mode. Change the original drawing distribution mode, based on the electronic distribution process, to realize the 3D model from design to manufacture directly to the production line. Compared with the traditional two-dimensional drawing distribution, the work efficiency is improved and the process preparation cycle is shortened. Due to the comprehensive use of structured and three-dimensional visualization methods, it is conducive to the realization of three-dimensional process design and inspection, and ensures that the elastic element has high size, shape and position accuracy and product uniformity. To this end, it is necessary to promote digital and intelligent transformation of key manufacturing processes.

The experience of load cell manufacturing companies in the position of leader in the international market is: to promote automation and intelligent transformation of key manufacturing processes, first of all, to automate and intelligentize key manufacturing processes that have a large impact on the quality of load cells. The second is to connect automated and intelligent processes with independent operation and control functions through the network and computer systems, and realize the collection, storage and processing of information under the management of network software. The process information is expressed through various methods such as multimedia videos, such as real-time display of the production status and quality status of each process flow (such as resistance strain gauge curing, post-curing temperature control; zero temperature, sensitivity temperature compensation success rate; performance testing and verification qualified Rate, etc.) in order to control and manage product quality and process operation.

2. The development trend of load cell technology system and manufacturing process support system

The standards for the structural design and manufacturing process of the load cell to form a digital and intelligent technology system are:

(1) Unified product development process

In the overall structure and process design of the load cell, it is necessary to absorb the best practice process design at home and abroad, but also must have the characteristics of the company.

(2) Unified standard specification

Establish standards and specifications for the digital development of weighing sensors in our company, covering design, manufacturing, technology, and testing platform construction.

(3) Unified basic process

Due to different uses, load cells have different structures of elastic elements and different stresses, but the basic manufacturing process is basically the same. A common, scientific, reasonable, and repeatable production process must be formulated.

(4) Unified basic database

Establish basic common databases such as resistance strain gauges, strain adhesives, circuit compensation raw materials, component libraries, general standard parts library, raw material library, and component library for load cells, and employ actual data.

Unified software tools

The three-dimensional design of the load cell structure and process adopts the unified design tools of the enterprise to improve the design efficiency. But it needs to be resolved:

①Three-dimensional labeling method of products;

②Conversion technology from 2D drawing information to 3D model information;

③Establish effective modeling and labeling methods to make 3D digital prototypes the basis for product design and manufacturing.

3. Development trend of quality management model

Change the original organization model and quality management method of load cell design and manufacture, establish rules and regulations in line with digital design and manufacture, take three-dimensional digital prototypes and products as the core, integrate design, process, and inspection into one as soon as possible through practice Quality management ideas and methods under the serial digital design and manufacturing mode.

VI: Concluding Remarks

The manufacturing process of weighing sensors is kept confidential in industrially developed countries in the world. From weighing sensor international academic conferences, essays, technical publications, and related documents, you can find references on working principles, structural design, application examples, etc. However, it is difficult to find information about manufacturing process mechanism, manufacturing process flow, manufacturing process equipment, etc. The domestic weighing sensor manufacturing field is no exception. Its related materials and works are all talking about the structure principle and the manufacturing process is tight-lipped. Another prejudice against the manufacturing process is that the manufacturing process is not theoretically strong, but only a practical experience and skill. In fact, this is not the case, but the manufacturing process has been explored too little, and the research, revealing and mastering of its mechanism and law is not enough. This article only explains the importance of manufacturing process from the key role of manufacturing process in the development and production of load cells, discusses the mechanism and development trend of key manufacturing processes, and hopes to attract enough attention from domestic load cell manufacturers. In the transformation and development of the enterprise,advanced manufacturing technology, effective management methods, and practical market development methods are incorporated to raise the weighing sensor technology and manufacturing process to a new level.