In terms of remanufacturing basic research. Many domestic units, such as the National Defense Science and Technology Key Laboratory of Equipment Remanufacturing Technology of the Armored Forces Engineering College, Shanghai Jiaotong University, Hefei University of Technology, Shandong University, Lanzhou Institute of Chinese Academy of Sciences, etc., have carried out basic research on remanufacturing. On the theoretical basis, the calculation method of residual stress of coating is improved, and the life prediction evaluation model is explored and preliminarily established. For example, the introduction of the uniformity coefficient, the classical formula of residual stress, Stoney equation [8], is studied. The calculation method of residual stress in remanufactured parts coating is studied and proposed. The nonlinear dynamics is studied for the crankshaft of used diesel engine. Analyze the model, explore the mapping relationship between the fatigue test data of the waste parts and the model analysis data, and initially establish the residual life prediction model [9]; based on the metal magnetic memory principle and the contact fatigue life assessment criteria, the remaining parts of the waste parts are preliminarily proposed. Life assessment and methods for predicting service life of remanufactured components [10]. In terms of technology foundation, a number of key technologies for remanufacturing have been developed and innovated, and relevant basic theories have been deeply studied. For example, the formation mechanism of Fe-Al intermetallic compounds under high temperature conditions was studied. The method of combining high-speed arc spraying technology with powder core wire was applied to the surface repair of remanufactured parts for the first time, and Fe-Al (base) was realized. Intermetallic compound preparation and coating forming integration technology [11]; Invented a "two-channel, dual-temperature zone" supersonic plasma spraying new technology, which solved the over-melting, entrainment and burning of coating droplets Problem [12]; Using high-energy mechanochemical method with independent intellectual property rights, the problem of uniform dispersion and suspension stability of nanoparticles in multi-ion solution system is solved, and non-conductive nanoparticles and conductive in nano-brush plating process are realized. High-efficiency co-deposition of matrix metal nickel [13]; preparation of nanometer soft metal, nano-oxide and nano-rare earth compound and other excellent nano-anti-friction self-repair additives, and initially realized nano self-repairing additive during equipment operation In-situ dynamic self-repair of the wear site [14].
4. The development trend of China's remanufacturing
Remanufacturing, as a new direction for the development of China's new century, is characterized by saving resources, energy and protecting the environment. It takes the high-tech of information technology, nanotechnology and biotechnology as the core, fully embodies the characteristics of independent innovation with Chinese characteristics. . Remanufacturing is highly compatible with the strategic needs of building a circular economy and implementing energy conservation and emission reduction, and will certainly make greater contributions to the implementation of circular economy and energy conservation and emission reduction. Looking to the future, China's remanufacturing should focus on three major breakthroughs, namely, “exploring the scientific basis of remanufacturing, key technologies for innovative remanufacturing, and setting industry standards for remanufacturingâ€:
1) Exploring the scientific basis of remanufacturing, that is, in-depth exploration of the basic theory of remanufacturing represented by the product life cycle theory, the life expectancy prediction theory of used parts and remanufactured parts, etc., to reveal the scientific nature of the evolution of product life. Remanufacturing is an engineering science from practice that is more empirical. Is the remaining life of the used parts sufficient and can the life of the remanufactured parts be maintained for a full service life? Such major problems, due to the lack of theoretical basis, are sometimes accomplished by simple inspection equipment or even visual inspection or empirical judgment by the worker's master. In order to solve this major problem, we must explore more and more effective non-destructive testing and life prediction theory and technology. The current research has achieved initial results. When studying the residual life of metal magnetic memory theory, it is found that the metal magnetic memory signal is the stray magnetic field signal on the surface of ferromagnetic material, and the distribution of metal magnetic memory signal under fatigue damage is summarized by combing. The characteristics and variation laws are used to construct the residual life prediction model for fatigue crack initiation and propagation of waste parts of ferromagnetic materials by using the magnetic memory signal normal component. When the acoustic emission theory is predicted to predict the service life, the typical acoustic emission signal is solved. The selection of characteristic parameters and the analysis of their information provide a true and accurate reflection of the microcrack initiation, propagation and fracture of the surface coating of remanufactured parts, and initially grasp the evolution of the surface coating life of remanufactured parts.
In the future, under the premise of continuing to deepen the above theory and technology, it is necessary to explore new theories and techniques, and to find the characteristic parameters to quickly and easily represent the life law.
2) The key technology of innovative remanufacturing is to continuously innovate and develop advanced surface engineering technology group for remanufacturing, so that the surface coating of remanufactured parts has higher strength and longer life, ensuring that the quality of remanufactured products meets or exceeds new products. . Has successfully developed nano surface engineering technology and automated surface engineering technology, the former includes nanoparticle composite brush plating technology, nano thermal spray technology, nano antifriction self-repair additive technology, etc., the latter includes automated arc spray technology, automated nanoparticle composite electricity Brush plating technology, etc. The core of nano-surface engineering technology is to use the small size effect of nano-particle materials to achieve atomic-scale chemical bonding between nanoparticles and matrix metals through uniform and diffuse distribution in coatings or additives, thereby significantly improving the strength of coatings. And tribological performance; the core of automated surface engineering technology is to replace the manual operation with robot or manipulator. By automatically controlling the planning path, real-time feedback adjusts the coating forming process parameters to realize the automation and intelligentization of surface coating preparation. The above technology has been applied to the engine remanufacturing production line. For example, the nano-particle composite brush plating technology successfully repaired the imported aircraft engine compressor blades, and the 300-hour bench test meets the requirements, breaking through the bottleneck of the localized maintenance technology for foreign imported products. The remanufacturing cost is only 1/10 of the foreign technical cost; the automatic arc spraying technology is used for the remanufacturing of heavy-duty automobile engine block, crankcase and other parts. The remanufacturing time of the single-piece engine case is shortened from 90min to 20min. And the material consumption is only 0.5% of the weight of the part body, and the cost is not more than 10% of the price of the new product. In addition to continuing to improve nano-surface engineering technology and automated surface engineering technology, it is necessary to develop new directions such as bio-surface engineering technology.
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