Analysis of the hottest depth laser additive reman

In depth analysis: laser additive remanufacturing technology and application

this paper introduces the technical characteristics of laser additive remanufacturing, introduces the application status of this technology in national defense, energy and power, industrial equipment and other fields, and shows its application prospects. Four key problems of laser additive remanufacturing technology are deeply analyzed: residual stress, matrix heat affected zone, interface matching, remanufacturing process intelligence and automation. It is pointed out that these four problems are the "bottleneck problems" that restrict the large-scale commercial application of laser additive remanufacturing technology

I. Introduction

laser additive manufacturing technology, also known as laser 3D printing technology, is a laser manufacturing technology that, with the help of computer, slices three-dimensional solid models into two-dimensional slices, and then discretizes the two-dimensional slices into one-dimensional lines. It uses laser cladding technology to stack point by point, and finally realizes the forming of three-dimensional solid parts (its basic principle and process are shown in Figure 1). Compared with traditional manufacturing technology, this technology is flexible, easy to realize intellectualization, short production cycle, and can produce parts with high mechanical properties. This technology has been widely used in aviation, national defense, transportation, energy, metallurgy, mining and other fields, and shows an attractive prospect

laser additive remanufacturing is a technical behavior based on laser cladding technology to restore geometric shape and mechanical properties of service failure parts and mismachined parts. Many major equipment in modern industry and national defense have complex production processes, long processes and high costs. During the service process of these equipment, some key parts often fail due to wear, corrosion, fatigue, accidents and other reasons, which affects the normal operation of the equipment. If these high value-added parts can be repaired and remanufactured, the normal operation of the equipment can be guaranteed, the cost can be saved and great economic benefits can be created. The processing procedures of some parts are complex and difficult, and they are prone to accidental damage. Many times, the wrongly processed parts can only be scrapped, which will cause great waste and loss. Adding materials to these wrongly processed parts for manufacturing and repair can greatly improve the qualification rate of parts, shorten the production cycle, improve economic benefits, and recover losses. Laser additive remanufacturing is an advanced remanufacturing repair method. The heat source energy of this technology is concentrated, which can realize the high-quality recovery of the geometric shape and mechanical properties of parts under the condition of little impact on the performance of the matrix. Using this technology to remanufacture and repair the service failure and misprocessed parts has a good practical significance. At present, laser additive remanufacturing technology has been widely used in aeroengines, gas turbines, steel metallurgy, military accompanying support and other fields

the principle of laser additive remanufacturing technology is similar to that of laser 3D printing technology, but it has its own characteristics. The typical laser additive remanufacturing process is as follows: disassembly - Cleaning - Classification - Detection - discrimination - remanufacture and repair - (heat treatment) - post processing - inspection. For the parts to be remanufactured after disassembly and cleaning, it is necessary to carry out nondestructive testing and life evaluation first, then remanufacture and repair the remanufactured parts, then carry out post heat treatment and post-processing, and finally test and evaluate the quality of the remanufactured parts to determine whether the remanufactured products are qualified. The core stage is the repair stage. Compared with laser 3D printing technology, laser additive remanufacturing technology also needs to pay attention to the thermal damage of the remanufacturing process to the matrix, the interface between remanufactured materials and the matrix, and the physical property matching between remanufactured materials and the matrix, which is more complex. For laser 3D printing technology, the whole part is formed by scanning and stacking point by point. Therefore, its manufacturing cycle is relatively long and the cost is high. In contrast, laser additive remanufacture takes invalid or misprocessed parts as the matrix, and the size that needs to be restored is often very limited. Its manufacturing cycle is short and the cost is low. Therefore, its economic and social benefits are more significant

II. Application status of laser additive remanufacturing technology

laser additive remanufacturing technology is an advanced technology for high-performance repair of equipment, and has been widely used in the maintenance of high-end equipment and high value-added parts in different industrial fields. British Rolls Royce company applied laser cladding technology to the repair of rb211 gas turbine blades; Optpmec design company of the United States uses laser cladding technology to repair the wear of T700 aircraft engine parts; Huffman also used laser cladding technology to repair nickel base superalloy and titanium alloy aviation blades; The "mobile parts hospital" (MPH system for short) successfully developed by the U.S. military uses laser cladding technology to rapidly manufacture and remanufacture metal parts. This system has been installed in the U.S. Navy and army, and has played an important role in the battlefield in Afghanistan. At present, laser cladding technology has been widely studied and applied in major industrial countries in the world

in China, laser additive remanufacturing technology has also made great progress in recent ten years, and its engineering application scope has gradually expanded, playing an important role in the aviation industry and weapon equipment maintenance field. A factory adopts laser additive remanufacturing technology to repair and remanufacture Aeroengine Blades and other aircraft bearing parts. The Institute of automation of the Chinese Academy of sciences applied additive remanufacturing technology to the repair of Aeroengine Turbine guides and ship blades. The national defense science and Technology Key Laboratory of equipment remanufacturing technology is the only national key laboratory in the remanufacturing field in China. In terms of laser additive remanufacturing, it has undertaken and completed a series of national, military and enterprise scientific research tasks such as equipment pre research projects, National Natural Science Foundation projects, national 973 projects and enterprise cooperation projects, and has made in-depth research and exploration in the materials, processes, performance characterization and other aspects of laser additive remanufacturing, It solves the technical problems of remanufacturing typical equipment parts such as heavy-duty vehicle engine camshaft, cast iron cylinder head, carburized gear, high-speed train axle, large compressor impeller and various shaft parts, and creates significant economic and social benefits

laser additive remanufacturing technology has become an important technical means in the field of high-end equipment services. There are nearly 300 laser additive remanufacturing enterprises in China. Among them, Shenyang continental Laser Technology Co., Ltd. is the first high-tech company in China to carry out laser additive remanufacturing services based on laser cladding technology. It has applied laser additive remanufacturing technology to many industrial fields and successfully solved the emergency repair and remanufacture problems of important parts and components such as aviation equipment, metallurgical equipment, petrochemical equipment, energy and power equipment and mining equipment, It has created significant economic and social benefits

at present, scientific research institutes and enterprises such as Zhejiang University of technology, Northwest University of technology, Huazhong University of science and technology, Tianjin University of technology, armored forces Engineering College, Guangzhou Institute of advanced technology, Nanjing Institute of advanced technology, Shenyang continental Laser Technology Co., Ltd., Liaoning starsk Industrial Co., Ltd. have conducted in-depth research and Practice on the technology, equipment, materials and applications of laser additive remanufacturing technology, It has formed a pattern of competition and collaborative development among universities, scientific research institutes and factories and enterprises, and constitutes the main force in the research and application of laser additive remanufacturing technology in China

III. key problems of laser additive remanufacture

although laser additive remanufacture has been widely used, there are still a series of key problems that need to be further studied and solved

1. residual stress is one of the most difficult problems in laser additive remanufacturing. The additive part of remanufactured parts is formed by scanning and stacking point by point through laser cladding technology. In this nonlinear strong coupling process, the temperature and physical properties of materials are extremely uneven, which inevitably accompanies the evolution of stress and strain, resulting in cracks and deformation of remanufactured parts, and the high residual stress state will also affect the static, corrosion resistance, fatigue and other properties of parts, and ultimately affect the service performance and safety of remanufactured parts

compared with laser 3D printing technology, the problem of residual stress in laser additive remanufacturing is more prominent. For laser 3D printing, the uniformity of temperature field in the cladding process can be adjusted through reasonable stacking strategy, and the actual restraint of materials can be adjusted to avoid excessive accumulation of tensile stress; In the process of laser additive manufacturing, the shape and size of the matrix are often fixed, and its restraint is generally large, which is easy to cause the accumulation of high-level residual tensile stress. In addition, in the process of laser additive remanufacturing, the matrix material and remanufactured material are often heterogeneous materials, and their yield strength, thermal expansion coefficient and other key parameters that affect the evolution of residual stress usually differ greatly, which is easy to cause the accumulation of high-level residual tensile stress level and improve the uneven distribution of stress. Professor Wang Huaming of Beihang called the problem of residual stress the "first bottleneck problem" of laser additive manufacturing. For laser additive manufacturing, this problem is more serious than others, and further work is needed

2. The performance degradation of heat affected zone is another important problem in laser additive remanufacturing. As we all know, the heat affected zone is usually the fragile part of the welded joint. Although the heat source energy density is concentrated and the heat affected zone is small in the laser additive remanufacturing process, the evolution of material properties in the heat affected zone is still a problem that needs to be paid attention to. The thermal cycle of laser additive remanufacturing causes changes in the microstructure of the material, which ultimately affects the performance of the material. The thermal process may affect the size and uniformity of grains, the type, distribution and size of precipitates, the solid solubility of the material, the degree of element grain boundary segregation, etc., and ultimately affect the hardness, strength, plasticity, corrosion resistance and other properties of the heat affected zone. From the matrix to the interface, the typical heat affected zone can be roughly divided into incomplete recrystallization zone, recrystallization zone, overheating zone, etc. The uniformity of grain size and properties in the incomplete recrystallization zone are poor; The microstructure of recrystallization zone is usually fine; There are many abnormally grown grains in the superheated zone, and their grain size and property uniformity are also poor. Common matrix materials for laser additive remanufacturing include nickel base, cobalt base, titanium base, iron base, aluminum base, etc., and their heat treatment states are diverse, including as cast, forging, aging, rolling, carburizing and nitriding, etc. Therefore, the performance of the heat affected zone of laser additive manufacturing. 3. There are great differences in the degradation mode and degree of normal testing but the light is not on. Targeted exploration and research should be carried out according to specific materials. Generally, The research results of the heat affected zone in the welding process have certain reference value, but we need to pay attention to the difference between the thermal cycle of laser additive remanufacturing and that of general welding process. In the process of laser additive remanufacturing, the temperature gradient in the heat affected zone is larger, the temperature change is more intense, and the number of thermal cycles may be more

3. The interface matching between matrix and remanufactured materials is also an important problem in laser additive remanufacturing. Different from laser 3D printing, the chemical composition and heat treatment state of laser additive remanufactured materials and matrix materials are often different, and there must be certain differences in their structural characteristics and physical and chemical properties, which will affect the bonding quality of the interface and lead to defects. There are mainly the following types of interface problems: one is the interface brittle phase. When the matrix material is mixed with the cladding material, it is possible to generate some brittle phases. For example, gray iron castings laser