Metal 3D printing technology is a new type of modern additive manufacturing technology. It is mainly based on three-dimensional digital model technology and forms physical parts by stacking additive manufacturing methods layer by layer. By describing the current status and development trend of metal 3D printing technology and combining the latest maintenance methods and requirements of large-scale railway maintenance machinery and equipment at this stage, this paper discusses the application of metal 3D printing technology in the maintenance of large-scale railway maintenance machinery, such as remanufacturing of damaged parts and repair of parts with slight surface damage. It effectively reduces the maintenance time and cost, improves the stability, reliability and safety of the technical performance of large-scale railway maintenance machinery and equipment, prolongs the service life of the equipment, and helps promote metal 3D printing technology in the maintenance of large-scale railway maintenance machinery.
Traditional metal processing mainly involves turning, milling, boring and other processes to remove the outer layer of metal to form parts and products with accuracy, size and appearance that meet the requirements [1]. Metal 3D printing technology, also known as additive manufacturing technology, is different from traditional metal machining manufacturing technology. Metal 3D printing technology is a new additive manufacturing process based on three-dimensional digital model technology, which forms physical products by stacking the materials of parts layer by layer [2]. Therefore, metal 3D printing technology can accelerate the update and iteration of product models, and can also quickly propose processing technology solutions for the production and manufacturing of parts with complex structures. It is a new development direction in the field of modern production and manufacturing [3].
Among them, the processes of metal 3D printing technology include selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM), fused deposition modeling (FDM), arc additive manufacturing (WAAM), laser cladding forming technology (LMD) and direct metal laser forming (DMLS) and other 17 types [4]. Metal 3D printing technology is suitable for a variety of environments and has high economic value. In the analysis of the current status of large-scale railway maintenance machinery maintenance, it is found that there are many types of large-scale railway maintenance machinery and a wide variety of actual accessories. In the maintenance of large-scale railway maintenance machinery, there is not only the problem of long supply cycle of imported parts, which affects the maintenance progress, but also the problem of high degree of wear or damage of parts after the dismantling of the machine body [5]. Applying metal 3D printing repair and remanufacturing technologies to the maintenance of large-scale railway maintenance machinery can save time and materials for the maintenance of large-scale machinery, improve maintenance efficiency, and increase equipment utilization [6].
1 Maintenance methods and requirements for large-scale railway maintenance machinery
1.1 Current problems in the maintenance of large-scale railway maintenance machinery
1.1.1 Traditional maintenance methods cannot meet new needs
When the railway transportation industry was in its early stages of development, my country’s industrialization capacity was relatively low, the degree of mechanization application was also low, and the use time of machinery was basically fixed. Therefore, large-scale railway maintenance machinery was concentrated in winter for maintenance [7]. However, the current volume of my country’s railway transportation tasks has far exceeded the demand by hundreds of times in the initial stage, resulting in the growth rate of maintenance technicians and maintenance sites for large-scale railway maintenance machinery and equipment, which cannot keep up with the growth rate of maintenance machinery and equipment. Therefore, the traditional maintenance method of large-scale railway maintenance machinery and equipment can no longer meet the new needs at this stage [8].
1.1.2 Inadequate awareness of maintenance prevention
At present, people pay more attention to the use of large-scale maintenance machinery and equipment, and pay less attention to the maintenance of these maintenance machinery and equipment. However, once a large-scale railway maintenance machinery and equipment fails, it will have a huge impact and may cause considerable economic losses to the railway transportation industry [9]. Therefore, prevention should be the main focus for these large-scale maintenance machinery and equipment, and preventive maintenance measures should be taken to ensure the normal operation of large-scale maintenance machinery and equipment.
1.2 Maintenance methods and requirements
At present, there are three main methods for the maintenance of large-scale railway maintenance machinery and equipment, namely, planned preventive maintenance of machinery and equipment, special maintenance of machinery and equipment-specific projects, and fault maintenance of machinery and equipment when failure occurs. Among them, the maintenance and repair of mechanical equipment projects is generally mainly for outsourced inspection and maintenance services for instruments and meters that require third-party calibration agencies to conduct inspection and repair; the maintenance method for mechanical equipment failure is mainly to repair and deal with faulty equipment or legacy problems [10]. Planned preventive maintenance is conducive to early detection of potential faults or safety issues, and targeted maintenance work can effectively improve the accuracy and service life of large-scale railway maintenance machinery and equipment. The requirements of planned preventive maintenance are as follows.
First, before comprehensive maintenance of large-scale railway maintenance machinery and equipment, targeted maintenance work should be carried out on the relevant parts of these machinery and equipment, such as lubrication and adjustment of the power transmission structure of the machinery and equipment according to the requirements of the specifications and standards, or tightening inspection of some key parts of the machinery and equipment, so as to effectively reduce the degree of wear and damage of large-scale maintenance machinery and equipment during use, reduce the number of inspections of machinery and equipment, and avoid affecting the normal operation of railway lines. At the same time, it can also effectively extend the service life of large-scale maintenance machinery and equipment.
Second, carry out routine special maintenance work on the important devices of large-scale railway maintenance machinery and equipment, especially lubrication and adjustment of relevant parts in the power device of the machinery and equipment, maintenance and maintenance of related fastening devices, etc. When testing the power source of the engine and other power systems, it is necessary to focus on the electrical system, hydraulic system and measurement system, and carry out special maintenance from the aspects of safety, stability and accuracy.
Third, in the periodic maintenance of large-scale railway maintenance machinery and equipment, it is necessary to carry out in-depth maintenance of the working device system, measurement system, engine system, power transmission system, hydraulic system and walking brake system, which are important parts related to the normal operation of the maintenance machinery and equipment, and timely standardize the maintenance or replacement of internal parts to ensure that the performance of the machinery and equipment meets the use requirements.
Fourth, the demand for railway transportation is high, and the use of large-scale railway maintenance machinery and equipment is also relatively frequent. Mechanical equipment needs to ensure normal operation in different seasons. Therefore, it is necessary to carry out targeted maintenance and maintenance on some parts of large-scale maintenance. For example, when changing seasons, it is necessary to carry out pre-maintenance and protection work. Some parts of mechanical equipment will deform under the influence of temperature changes, and the external temperature will also cause abnormal operation of the system. To ensure that mechanical equipment reaches the same standard of performance under different working temperature environments, it is necessary to carry out special treatment on these special equipment or parts, such as replacing parts of different materials.
2 Application of metal 3D printing technology in the rail transit industry
2.1 Application of metal 3D printing technology
The application of metal 3D printing technology in the rail transit industry is mainly focused on the production and manufacturing of mechanical equipment and the repair of the surface of mechanical parts. The traditional mechanical production and manufacturing process in the rail transit industry requires a large number of personnel to develop and design the process, and relies on high-precision processing machine tools and skilled operators to complete the production and manufacturing of machinery. Metal 3D printing technology can combine three-dimensional design models with mechanical production and manufacturing equipment, reduce the various processes of mechanical subtraction production and manufacturing, directly use the production and manufacturing method of mechanical additives, stack materials layer by layer, and form a complete entity of metal parts, while ensuring the accuracy, size, appearance and quality requirements of metal parts. At the same time, it greatly reduces the production and manufacturing cycle of metal parts, reduces the waste of raw materials, and improves the work efficiency of the production and manufacturing of mechanical parts in the rail transit industry.
2.2 Advantages of Metal 3D Printing Technology
Metal 3D printing technology has the advantages of reducing the production and manufacturing costs of parts and improving the production and manufacturing efficiency of metal parts in the metal production and manufacturing of the rail transit industry. Compared with the traditional metal parts production and manufacturing process, the metal 3D printing technology process does not require the production process of castings, surface heat treatment processes, etc., and at the same time reduces the number of operators in each process of the production and manufacturing of traditional metal parts. In the whole process of the metal 3D printing technology process, a technician can operate the metal 3D printing technology equipment for production and manufacturing, and can quickly complete the production and manufacturing of parts, greatly reducing the production and manufacturing costs of metal parts. Moreover, metal 3D printing technology does not need to use traditional metal production and manufacturing tools such as tools and fixtures in the production and manufacturing process, saving the time of changing tools and fixtures, and shortening the production and manufacturing cycle of metal parts. While ensuring the accuracy, size, appearance and quality requirements of metal parts, it also greatly improves the production and manufacturing efficiency of metal parts.
3 Application of metal 3D printing technology in the maintenance of large-scale railway maintenance machinery
Compared with other industries, the application of metal 3D printing technology in the maintenance of large-scale railway maintenance machinery is still in the initial stage of research and exploration. The current application research mainly focuses on the remanufacturing of damaged parts and the repair of slightly damaged parts in the maintenance of large-scale railway maintenance machinery.
3.1 Remanufacturing of damaged parts during maintenance
During the maintenance of large-scale railway maintenance machinery, the loss or damage of parts in mechanical equipment often occurs. When a certain part is a non-standard part, or the model and specification of the part is not in production, if the damaged part is produced alone, the manufacturing time and economic cost will be greatly increased. At this time, by adopting metal 3D additive printing technology, additive production can be directly carried out without mold opening and other processes, so that complex parts can be quickly produced to meet the abnormal parts replacement needs of large-scale railway maintenance machinery and equipment. For example, by optimizing the design of damaged bearing parts in large-scale railway maintenance machinery and equipment, new bearing parts can be produced using metal 3D printing technology, and the wear resistance and vibration resistance of the parts can be effectively improved.
In large-scale railway maintenance machinery and equipment, some working device parts are produced and assembled by two connection processes, electric welding or riveting. The strength of the connection of the parts is low, and the connection mode is often damaged due to the action of torsional stress. By using metal 3D printing technology to manufacture the working device parts in an integrated manner, the strength performance, compressive performance and other related mechanical properties of the connection are effectively improved, and the dimensional accuracy of the parts is improved, which effectively meets the use requirements of large-scale railway maintenance machinery and equipment.
3.2 Repair of slightly damaged parts during maintenance
With the development of metal 3D printing technology, domestic and foreign countries have begun to use metal 3D printing technology to repair the surface damage of couplers, axles, and wheel cakes, and fatigue tests are carried out on the repaired axles and the original axles of the same model. The repaired axles are stronger in fatigue performance than the original axles. Further improvement and upgrading of the repair process parameters and the required repair materials have greatly improved the stability and reliability of related technologies.
Domestic related research institutes and other units have also begun to study the metal 3D printing repair technology of surface damaged parts and have achieved good results. In the inspection and maintenance of large-scale railway maintenance machinery and equipment, if the relevant axles, rims, gears and other parts are found to have surface damage, the computer 3D modeling technology can be used to restore the prototype 3D model of the parts, and the metal 3D printing additive repair technology can be combined to repair them, thereby effectively reducing the replacement cost of parts of large-scale railway maintenance machinery and equipment, the running-in time between parts after assembly, etc., and improving the efficiency of inspection and maintenance of large-scale railway maintenance machinery and equipment.
4 Conclusion
This paper studies and analyzes metal 3D printing technology, combines the current methods and requirements for the maintenance of large-scale railway maintenance machinery, and explains the application of metal 3D printing technology in the maintenance of large-scale railway maintenance machinery, such as remanufacturing of damaged parts in large-scale railway maintenance machinery and equipment, and repairing parts with slight surface damage such as axles and gears. At the same time, it ensures that the remanufactured parts or parts with surface damage after repair meet the use requirements in terms of mechanical properties, etc., effectively improving the work efficiency of large-scale railway maintenance machinery maintenance, reducing the cost and maintenance cycle of parts replacement during the maintenance process, and promoting the application of metal 3D printing technology in the maintenance of large-scale railway maintenance machinery and equipment.
