At the beginning of human civilization, the status and role of manufacturing technology and manufacturing process were recognized. Labor creates the world. Manufacturing technology and manufacturing process have always been the active connotation of productivity, the most active factor in the materialization process of engineering technology, and the bridge for the transformation of scientific research results into commodities. Weighing sensor technology and products are no exception. Since its advent in the 1940s, it has been completely based on and relied on manufacturing processes. Although the elastic elements of weighing sensors have various structural forms due to different stresses, their manufacturing processes are basically the same. In the process of research and development of weighing sensors, the world's market-leading weighing sensor manufacturing companies have almost all shifted the focus of weighing sensor development to the field of manufacturing process research and application through analysis and research. They have many new understandings and new experiences, and have created and applied some effective new processes and new process equipment. Among them, the most representative are the technology and process of temperature compensation for the sensitivity of weighing sensors researched and implemented by BLH Company of the United States; the technology and process of linear compensation for weighing sensors using semiconductor strain gauges researched and implemented by VISHAY Company of the United States (US Patent No. 3.034346); the technology and process of linear compensation for weighing sensors using nickel foil strain gauges researched and implemented by PHILIPS Company of Germany while taking into account the technology and process of sensitivity temperature compensation; the technology and process of linear compensation using nonlinear disc-shaped diaphragms and lateral force compensation in French Patent No. 1204850. In various countries around the world, weighing sensor manufacturers have achieved good application results. The experience of these weighing sensor manufacturers is that the manufacturing process of weighing sensors is definitely not the "workshop craft" in the minds of some people, but a comprehensive technology integrating machinery, electronics, information, materials and management. With the inclusion and promotion of artificial intelligence technology and modern management technology, the concept and connotation of manufacturing technology are constantly expanding, from narrow to broad, from local to overall, from single to system, so that the traditional weighing sensor manufacturing process is combined with modern digital intelligent manufacturing process technology, and technology is combined with management to form a new modern manufacturing process system. The above understanding is increasingly accepted by domestic weighing sensor manufacturers, and the development and application of manufacturing technology are increasingly valued and concerned by technicians engaged in the research and production of weighing sensors. 1  The status and role of manufacturing technology in the development and production of weighing sensors It is well known that there are four key issues in the development and production of weighing sensors, namely structure, material, process, and detection. Among them, the manufacturing process and its process equipment have a great influence on the accuracy, stability and reliability of weighing sensors. Only by scientifically and rationally selecting and integrating effective manufacturing processes can the technical level and product quality of weighing sensors be continuously improved. Conversely, the improvement of the technology and application level of weighing sensors promotes the innovative development of manufacturing processes. Therefore, manufacturing process and weighing sensor technology are complementary and promoting relationships. Manufacturing process is an important means for weighing sensor manufacturers to strengthen their competitiveness and improve economic benefits. The enterprise that attaches importance to the research and application of manufacturing process will benefit more and make faster progress. Weighing sensor manufacturers must rely on diverse product varieties, excellent quality, low cost and timely delivery to occupy the market in order to survive, develop and achieve economic benefits in today's fierce and almost cruel market competition. The main means to achieve these comprehensive advantages is to rely on product development, scientific and reasonable selection of manufacturing processes and continuous improvement and innovation. The German weighing industry is well-known in the world weighing market for manufacturing high-precision and cutting-edge technology products, and has a high level of professional technology in the field of weighing technology. Especially in the research, manufacturing and application of weighing sensors, there are a group of manufacturing experts in weighing sensors such as HBM Electronic Measurement Technology Co., Ltd. and Balluff Sensor Co., Ltd., who can produce high-precision products with excellent stability and reliability, based on advanced manufacturing technology and manufacturing processes. Dr. Manfred Kochsiko, senior consultant of the German Institute of Engineering Physics, believes that this is due to the increasing technical and process innovation capabilities and insatiable innovative spirit of the German weighing instrument manufacturing industry. As an international manufacturing professional expert commented: "If product development takes ten times the effort, then the development of mass production technology takes a hundred times the effort." Weighing sensor manufacturing companies in some industrially developed countries in the United States and Europe have taken a hundred times the effort in developing mass production technology, and they are in a leading position in international weighing sensor technology and market competition, and have maintained it to this day. In my country, the important role of weighing sensor manufacturing technology in research and production is often not recognized by people, and not given enough attention. Some companies' weighing sensor product design accommodates the process, and the process design accommodates the equipment. This is the fundamental reason for the long-term lag in weighing sensor technology and manufacturing process, and it is the result of not paying attention to technological transformation. The reason is that the research work of the manufacturing process itself is relatively arduous, requiring certain test equipment, and repeated manufacturing process tests, accumulating years of practical experience, and working hard for several years before overcoming certain technical and process difficulties. Therefore, it is difficult to produce results, talents, and benefits in a relatively short period of time. However, the quality and cost of weighing sensors are closely related to the manufacturing process, and enterprises must pay attention to it. As far as weighing sensor products are concerned, despising the manufacturing process technology is to relax product quality. Only by paying attention to and grasping the process technology can a large number of hidden dangers be eliminated in the bud. It is understandable to grasp product quality, but there will be no peace if you don’t grasp the manufacturing process. In order to overcome the problems of some enterprises’ business strategy ideas adapting to market changes slowly, poor manufacturability of designed products, long development cycles, and neglecting to continuously improve product performance and improve the level of manufacturing technology, the United States proposed that design and process should be parallel and work together, and carry out "concurrent engineering" (Concurrent Engineering), and determined the four principles of simultaneity, constraint, coordination, and consistency. That is, the design and process are carried out in parallel within the same time frame, shortening the product development cycle to varying degrees. Of course, under the current conditions of rapid development and widespread application of CAD/CAM/CAE technology and three-dimensional digital design and manufacturing technology, "simultaneous engineering" has a new connotation. It can connect CAD/CAM/CAE and databases through the network, or use three-dimensional digital design technology to share information and resources, combine on the computer screen, and carry out parallel operations within the same time frame. Analyze various constraints and closely coordinate to select the best combination of requirements such as cost, quality, and delivery cycle. In this way, the conditions of the manufacturing process are considered as the constraints of the design of weighing sensor products, and the work efficiency is higher. In the current situation where the competition in weighing sensor technology and products is becoming increasingly fierce and the weighing sensor market is becoming increasingly international, the manufacturing process is playing a more important role. 2  Analysis of the hot and cold processing technology and mechanism of weighing sensor elastic elements The manufacturing process of weighing sensors is from the preparation of resistance strain gauges and elastic elements to the completion of all manufacturing processes. Among them, it is very important to select relatively ideal metal materials for elastic elements, eliminate the residual stress generated by elastic elements in hot and cold processing such as forging, machining, and heat treatment; select resistance strain gauges and strain adhesives that have the best working characteristics and the best matching with elastic elements; repeatable, precise and scientific production process; high-precision test and detection equipment; effective quality control procedures, that is, the use of traceable measuring equipment to control and ensure the stability of the manufacturing process. In the manufacturing process of weighing sensors, weighing sensor manufacturers, which are in the position of international market leaders, pay special attention to the preparation process of elastic elements at all costs. This concept is worth learning from for weighing sensor manufacturers in my country. 2.1 Analysis of the process mechanism of forging, machining and heat treatment of elastic elements There are many types of steel used in the elastic elements of weighing sensors, but they are mainly high-strength medium-carbon alloy structural steel with excellent comprehensive mechanical properties, supplemented by martensitic precipitation hardening stainless steel. The most representative medium carbon alloy structural steels are AISI 4340 from the United States, 30CrNi8 from Germany, En26 from the United Kingdom, 35XгCA from Russia and 40CrNiMoA from China (GB3077-1999). Precipitation hardening stainless steels are widely used, such as 17-4PH and 15-5PH from the United States, 630/631 from the United Kingdom, SUS630 from Japan and 0Cr17Ni4Cu4Nb from my country. Among them, 40CrNiMoA steel from China has high strength, plasticity and hardenability under appropriate process conditions and is widely used. The hot and cold processing technology of the elastic element of the weighing sensor should strictly control and test the residual stress, especially the surface residual stress caused by the fine processing of the strain zone of the elastic element should be tested by X-ray diffractometer to achieve the purpose of controlling and reducing the surface residual stress in the strain zone. The elastic elements of medium and large weighing sensors must be processed by forging process, so that the blank is repeatedly forged to break the coarse grains, so that it is refined and uniform and the structure is dense. At the same time, the direction of the metal fiber of the blank is required to be consistent with the force direction of the elastic element, and no crossing or overlapping is allowed. This is the most important link to improve the accuracy and stability of the weighing sensor. Therefore, in the forging process, try to stretch only, not upsetting, and prevent overburning and coarse grains. After forging, the elastic element must be annealed to make its metallographic structure: pearlite + ferrite + carbide. When the elastic element of the weighing sensor is machined, no matter which manufacturing technology is used, such as planing, milling, turning, or grinding, or an advanced machining center, residual stress will be generated on the elastic element. This is mainly because during the cutting process, compression deformation occurs in the cutting direction, and tensile plastic deformation (plastic protrusion effect) occurs perpendicular to the machined surface, resulting in residual tensile stress on the surface. In addition, the squeeze effect of the tool contact point and the thermal effect during cutting also produce residual compressive stress and residual tensile stress respectively. Therefore, the residual stress generated by machining is the superposition of the plastic protrusion effect of the area in front of the tool contact point, the squeeze effect of the area below the tool contact point and the thermal effect during cutting. In order to reduce the residual stress of the elastic element during machining, the cutting amount of fine machining should be reduced as much as possible, and it is best not to use the grinding process, because the last process of the elastic element strain zone using grinding can produce more than 60kgf/mm2 of compressive stress. Although from the overall point of view of the elastic element, the residual stress generated by machining only appears in the thin layer of about 300μm on its surface, and the resistance strain gauge is attached to this surface with uneven stress distribution and large grinding stress, with the action of time, temperature and external force, slip lines will be generated in the metal material structure of the elastic element and the residual stress will be continuously released. Since residual stress is a kind of energy retained in the deformed crystal, this energy is manifested as pushing atoms to unstable positions, causing the atomic spacing to change and release energy. In the process of releasing residual stress, a small permanent deformation will also occur, which directly affects the stability of the zero point and sensitivity of the weighing sensor. After the elastic element of the weighing sensor is processed by forging and annealing processes, it must also be processed by quenching and tempering processes to make the elastic element material have a higher proportional limit and good comprehensive performance. Determining scientific and reasonable heat treatment process specifications and strictly implementing them can ensure that the weighing sensor has excellent mechanical properties and a higher fatigue life. The general quenching process of 40CrNiMoA alloy steel is: quenching temperature 840~860℃, holding time 10~30 minutes (determined by the size of the elastic element), oil cooling, and the metallographic structure after quenching is quenched martensite. The tempering process is: tempering temperature 200~560℃, holding time 2 hours, air cooling. For small and medium-sized elastic components, the tempering system of 500℃ is mostly used.
At this time, the metallographic structure is troostite, but the martensite direction is still retained. The hardness is about HRC39, the strength limit is 1250N/mm2, the yield limit is 1130N/mm2, and the average elastic hysteresis is 0.024%.