Abstract：In the high-speed railway sector, a machine tool is used as a working machine for part processing.The relationship between high-speed rail and the machine tool industry is summarized in this paper, which is followed by a hierarchical analysis of the types of machinable parts of high-speed rail, and finally a summary of the selection principles for general and special machine tools when machining high-speed rail mechanical parts. Then, it introduces the current mainstream special machine tools on the selection of processing technology for machining parts of high-speed rail machinery such as rails, bogies and car bodies. Finally, the development trend of machine tools in the field of high-speed rail is forecasted.

Keywords：machine tool classification; high-speed rail parts; equipment manufacturing; special machine tools.

 

Since the beginning of the 21 st century, China 's high-speed railway has experienced leapfrog development and is at the forefront of the world. The demand for high-speed rail parts to machine tools is facing more and more diversity, and higher standards are put forward for machine tool products in terms of accuracy and efficiency [ 1 ]. Among them, efficient special machine tools are the key points to improve the production and quality of high-speed trains. Therefore, it is very important to study the characteristics of high-speed rail for high-speed rail processing machine tools.   

Firstly, this paper classifies the high-speed rail machining parts and determines the selection of high-speed rail machine tools. Then, it focuses on the types of special machine tools for the application of high-speed rail mechanical machining parts. Finally, it summarizes and discusses the development trend of machine tools in the field of high-speed rail, and provides some reference for the study of high-speed rail machine tools.

1 Classification of high-speed rail machinable parts and selection of high-speed rail machine tools

1. 1. High-speed rail machining parts classification

The application of machine tools in high-speed rail can not only improve the processing efficiency, accuracy and quality of parts [ 2 ], but also save manpower and financial resources. The classification of high-speed rail parts facilitates the analysis of the workpiece processing process and the machine tools applied.

The research on the classification of high-speed rail parts began in 2011, mainly based on the classification of high-speed rail information, including hierarchical classification, surface classification and mixed classification.The hierarchical classification method is a classification system that arranges classification objects into a hierarchical expansion, suitable for classification with clear hierarchy, strong logic, and a large amount of information. The face classification method is to classify the selected classification objects according to their features, which is suitable for classification with complex rules, no commonalities, and a small amount of encoded data. The hybrid classification method is a combination of hierarchical classification and surface classification, suitable for classification with large classification volume and no commonality. Due to the complex structure and numerous components of high-speed rail, as well as the strict membership relationship between systems, components, and parts, adopting the hierarchical classification method is the best solution [3]. Divide the high-speed rail system into systems and subsystems according to its structure, and then disassemble them one by one to the smallest possible processing units. The classification system is shown in Figure 1, and the summarized classification of high-speed rail machinable components is shown in Table 1.

Fig. 1 High-speed rail system and parts classification system

 

Table 1 High-speed rail machinable system and parts classification table

It can be seen from Table 1 that the parts of track, bogie, car body and catenary are mainly mechanical machinable parts, while the parts of air supply and braking device and high voltage traction system are mainly non-mechanical machinable parts.

1. 2. High-speed rail machine tool selection

The key to the stable operation of high-speed rail is to ensure the cooperation between various parts, which is inseparable from the parts manufacturing machine tools. Therefore, the selection of high-speed rail machine tools is extremely important. The demand of high-speed railway for machine tools is divided into four aspects :

( 1 ) Rail and ballastless plate manufacturing in track system.

( 2 ) Frame, wheel set and other manufacturing in the bogie system.

( 3 ) Manufacture of locomotive body.

( 4 ) Daily maintenance and repair of high-speed rail operation.

Because these processing belongs to mechanical manufacturing, the demand for general machine tools and special machine tools is large, so the selection of machine tools is based on the production type of enterprises, the complexity of products and other factors to consider :

( 1 ) The selection of general machine tools. Due to the wide variety of machine tools, and each machine tool should meet the corresponding scope of application and processing conditions in order to meet the requirements. Therefore, in the selection, the typical processing parts are determined by analyzing the processing procedures, and the appropriate machine tools are selected within a certain range. At the same time, the development of the machine tool process should be properly considered to leave room for development. Then, the parts are classified and grouped according to the similarity principle. Finally, the machine tool suitable for workpiece processing is determined [ 4 ].

( 2 ) Selection of special machine tools. Because the special machine tool is a kind of machine tool which is specially suitable for the processing of a specific part or a specific process [ 5 ], and it is usually indispensable in the automatic production line manufacturing system. Therefore, when selecting the machine tool, we first select the machine tool according to the customer 's product requirements, and analyze the processing technology to select the machine tool within a certain range. Then, the processing effect should be considered, and the optimal choice should be combined with economy under the same conditions. Finally, the better processing machine tool is determined.

2 Application status of machine tools for machinable parts of high-speed railway machinery

There are various types of machine tools applied to high-speed rail parts processing. This section will classify the machine tools used in the key mechanical machinable parts of high-speed rail according to the summary of Section 1.1, focusing on mainstream products.

2.1 Rail system processing machine

The track system is the guiding part of the operation of high-speed rail vehicles, and it is a complex overall engineering structure.

2.1.1 Rail processing machine

The rail is the track part that supports and guides the train operation, which is in the shape of " 工. " The processing procedures include derusting, welding, weld normalizing and air cooling, rough grinding, straightening, fine grinding and welding ultrasonic inspection [ 6 ]. The seamless rail laid on the high-speed rail track produces a weld every time it is welded, which requires high-precision machine tools to accurately grind and process the welded parts. In addition, the turnout is one of the weak links of the track. It is a line connecting device that transfers the vehicle from one track to another. The types are diverse, as shown in Figure 2, and its processing is extremely important.

Figure 2 Turnout Type Diagram

2.1.2 Weld processing machine

At present, domestic rail welding joints are finished by fine grinding machine and fine milling machine. The precision grinding machine is a tool machine that uses a grinding tool to grind the workpiece to obtain the required shape, size and precision machining surface. Finish milling machine refers to the tool machine that the milling cutter processes a variety of surfaces of the workpiece to obtain the required processing shape and precision. For the precision shaping treatment of welds, the traditional process at home and abroad is mainly grinding. Due to the shortcomings of the fine grinding machine in the process of processing, such as insufficient weld grinding, increased local temperature of grinding, long processing time, low production efficiency, serious grinding dust pollution and inability to accurately locate, in the early stage, the fine grinding machine was mainly introduced in China, and in the later stage, the fine milling machine was mainly developed in China.

( 1 ) Fine grinding machine

1 MAS150 typical rail fine grinding machine produced by France Giesma Company is mainly used for the smooth grinding of the surface within 500 mm of the welded joint, which is composed of input, output frame and intermediate frame [ 7 ], as shown in Fig.3. It realizes the ' soft ' adjustment of the whole weld grinding process and grinding depth through the control program, and realizes the ' hard ' adjustment of the grinding depth by manually adjusting the limit sensor [ 8 ].At the same time, it has a vacuum device to purify the working space to a certain extent.

Fig. 3 MAS150 fine grinding machine

2 The MMA-14AL typical rail fine grinding machine developed by Laytec, France, is mainly used for the fine grinding of the top surface of the weld rail and the working surface within 500 mm of the rail welding, as shown in Fig.4. The device uses the cradle mechanism to control the movement of the grinding head, swings left and right around the rail axis, and grinds the arc of the rail surface according to the set swing angle to realize the profile grinding of the rail head profile.

Fig. 4 MMA-14AL rail grinding machine

3 The MK-1000 rail finishing mill developed by Shanghai Ruiniu Machinery Co., Ltd. is mainly used for smoothness repair grinding within a range of 1000 mm at the weld seam [10], as shown in Figure 5. The equipment uses a highly sensitive vibration sensor and servo system to position and grind on the left and right of the welding head to determine the rail grinding reference plane, and then adjust the grinding reference beam to be parallel to the straight line determined by the two points to achieve weld grinding.

Fig. 5 MK-1 000 rail weld grinding machine

( 2 ) Finish milling machine

1 GFJX-100 rail weld finish milling machine produced by Shenzhou high-speed railway is mainly used for multi-directional repair of contour surface in the range of 300 ~ 1 000 mm of long rail tread [ 11 ], as shown in figure 6. The biggest feature of the equipment is that the cutter is smooth and smooth at the milling weld, there is no ' hump ' residue, the cutting system is rigid, and there is no tool letting phenomenon. The imported machine clamp tool is adopted, which has a long service life and is easy to replace. At the same time, the indexing of the two rotary tables adopts the synchronous control system of double AC servo motors, which has accurate indexing and high intelligence.

Fig. 6 GFJX-100 rail weld finishing milling machine

2 The JKX-1000 rail weld finishing milling machine jointly developed by Lanzhou Public Works Machinery Section and Shanghai Ruiniu Machinery Co., Ltd.integrates mechanical, electrical, hydraulic and measurement and control. The eddy current sensor is used to measure the small distance data, and then compared. At the same time, the ' two-end point connection method ' is used to calculate the rail straightness and improve the machining accuracy [ 12 ]. The measurement milling synchronization mechanism is adopted to improve the milling efficiency. The shape and angle of the tool are improved, and the flatness of the rail welding joint is improved.

2.1.3 Turnout processing machine tools

High speed railway turnouts are usually formed by milling cutters in one operation, belonging to the heavy cutting type. Not only does the CNC gantry milling machine for turnouts require high dynamic and static stiffness and structural stability, but it also puts forward high requirements for machine tool vibration resistance, machining accuracy, and power.

( 1 ) General technology The XK series turnout special milling machine produced by Qiqihar No.2Machine Tool Co., Ltd.is shown in Figure 7, which can not only ensure high production efficiency, but also obtain high machining accuracy and surface quality. The equipment is characterized by the installation of one or two high-power ram-type boring and milling heads on the beam, which can configure a variety of accessories according to user needs, and can mill, boring, drill and internal thread processing of turnout rails in one clamping. It avoids the errors caused by multiple clamping positioning, alignment and tool setting of the workpiece, and improves the machining accuracy and efficiency. At the same time, the worktable is equipped with permanent magnet furniture, automatic pushing and unloading workpieces and automatic clamping tools, which has a high degree of automation.

Fig.7 XK series fork special milling machine

( 2 ) The XK9720 × 400 CNC gantry mobile turnout boring and milling machine produced by Wuhan Heavy Machine Tool Group Co., Ltd.is dedicated to the processing of high-carbon steel turnouts, as shown in Figure 8. The equipment has a single and double gantry movement to choose from. The biggest feature is that it is equipped with an ATC automatic tool changer for rail processing. At the same time, the gantry movement adopts double motor and double detection synchronous drive. The spindle can automatically broach and realize 90 ° automatic orientation. The ram has a hydraulic balance device. The beam is equipped with a rolling block and a steel guide rail unloading device, which has a high degree of automation.

Fig.8 XK97 fork special milling machine

2.1.4 Ballastless plate processing machine tool

Ballastless slab is a new type of track structure composed of concrete base, CA mortar layer, track slab and fasteners. Its processing flow includes grinding preparation, transportation positioning of blank plate, lifting plate, blank plate measurement, grinding and track plate detection. At present, the ballastless slab track used in China has three structural forms : CRTS I, CRTS II and CRTS III. Among them, type II track plate ( Borg plate ) grinding processing mainly adopts Borg plate CNC grinding machine.

( 1 ) The BZM650 track plate special CNC grinding machine [ 15 ] developed by East China CNC Co., Ltd.and China Railway Sixth Engineering Group Co., Ltd.is the first track plate grinding machine developed in China. It adopts one-time forming grinding technology to realize the forming processing of the plane of the rail bearing platform and the surface of different inclined angles. At the same time, the bridge gantry machine tool structure with beam movement is adopted, and the longitudinal and transverse movements adopt the double servo anti-backlash drive technology to realize the high-precision control of the machine tool. The spindle of the grinding head has two degrees of freedom. At the same time, two grinding heads are used to process two rows of bearing platforms respectively, and the grinding accuracy is higher.

( 2 ) The MKB7025 CNC grinding machine produced by Hangzhou Machine Tool Group is dedicated to the grinding of the rail plate forming table [ 16 ], as shown in Figure 9. The equipment adopts the process of one-time installation and secondary forming of the track plate, and the whole adopts the movement mode of the beam CNC grinding machine. Its high precision and low failure rate make the grinding process simple. At the same time, the machine tool is equipped with contact and non-contact automatic measuring devices, which has a high degree of automation [ 17 ]. The machine also uses the track geometry rating to shorten the pause time between each orbiting platform [ 16 ], and each has a grinding head under the left and right vertical towing plates to improve efficiency.

    

Figure 9 MKB7025 CNC grinding machine processing track plate

2.2 Bogie system processing machine tool

Bogie system is a walking part of high-speed railway [ 18 ], which plays a role in supporting the car body, steering and braking. Its complex structure is shown in Figure 10, which has high functional requirements for machine tools.

Fig. 10 Bogie structure diagram

2.2.1 Frame machining machine tool

The framework is the substrate for carrying and transmitting force on high-speed rail, which is a fully welded structure with poor overall rigidity, compact structure, high processing accuracy, and multiple processing parts, making processing difficult [19]. The processing process includes side beam and crossbeam processing, frame welding, frame reverse processing, frame front processing, finishing and tapping, and frame 3D detection.

The UNIPORT7000 gantry machining center produced by Unisign, Netherlands, has 5-axis machining capability and excellent stiffness and accuracy, which is dedicated to frame processing, as shown in Figure 11. The equipment has a high degree of automation, and the machining accuracy and efficiency of the parts are improved by compiling the machining program. The machining dimensional accuracy is 0.005 ~ 0.01 mm. The biggest feature is that the machining accuracy is not affected by the complexity of the parts.

Fig. 11 UNIPORT7000 gantry machining center

2.2.2 Axle machining machine

The axle bears the weight and load of the vehicle. In order to ensure its sufficient safety, reliability and long service life, extremely high requirements are put forward for axle materials and related technologies. Axle machining process includes blank, heating, forging, heat treatment, rough machining, testing and finishing.

( 1 ) The machine tools produced by Jiangxi Nelson − Simmons − Heggensett Medium Machine Co., Ltd.

1 CK1832 CNC axle series lathe is dedicated to the turning of high-speed rail blank shaft and semi-finishing shaft, which can realize the dry or wet processing of axle outer fillet, transition fillet, chamfer and shaft shoulder, as shown in Figure 12. The machine tool has the functions of hydraulic automatic positioning and clamping axle, automatic detection and turning, automatic center hole positioning. It can choose single and double spindles and single and double tool holders. At the same time, it can also choose embedded drive of top claw end face and special friction chuck drive.

Fig.12 CK1832 CNC axle series lathe

2 The N30 turning center is dedicated to precision machining of axles, as shown in Figure 13. This device can achieve functions such as milling, drilling, and rolling with specific tools, as shown in Figure 14, and integrates these functions into the flexible conveying system. In addition, modular design is adopted for standard interface tools and clamping systems suitable for multiple suppliers, such as spindle/sub spindle and tailstock.

Figure 13 N30 turning center diagram

Fig.14 Machining diagram of N30 turning center

The 7624 axle deep rolling machine is designed to improve the service life of the axle, as shown in Figure 15. The machine has two independent tool holders, each of which can provide three pairs of rollers for specific deep rolling tasks. When two pairs of rollers are rolled on each tool holder at the same time, the shaft processing ability can be optimized. In addition, the device enables deep rolling of specific areas or entire shafts on the same machine, as shown in Figure 16.

Fig. 15 7 624 Axle deep rolling machine

Figure 16 7 624 Axle deep rolling machine processing diagram

( 2 ) The machine tool

1 CK8132C / 1 lathe produced by Qinghai Qingzhong Machine Tool Manufacturing Co., Ltd.is dedicated to the full-axis turning of the precision forging blank axle, as shown in Fig.17. The diameter of the workpiece is 100 ~ 320 mm, and the length is 1 500 ~ 3 000 mm. The machine tool can realize one-time loading to complete the axle semi-finishing and finishing processing. The fuselage adopts an oblique overall layout. Advanced motion and dynamic parameters and efficient structural configuration ensure the high rigidity, high speed and high performance of the machine tool, which can meet the needs of efficient processing.

2 QZ-048A and QZ-056A drilling machines are specifically designed for drilling center holes on axle end faces.

Figure 17 CK8132C / 1 lathe

2.2.3 Wheelset processing machine

The wheel is both a safety component and a consumption component, and its processing and maintenance are extremely important. The high-speed rail wheel steel billet is made into finished products after sawing, forging, heat treatment, machining and other processes, and then subjected to ultrasonic testing, magnetic particle testing, static balance measurement, shot peening strengthening, hardness measurement and full-size measurement.

( 1 ) Wuhan Heavy Duty Machine Tool Group Co., Ltd.produced machine tools

1 PWL1200 gantry lathe is dedicated to high-precision and high-efficiency repair and processing vehicles on the dismantled wheel set and brake disc, as shown in Figure 18. It combines the latest advanced technologies such as mechanical, electrical and hydraulic, and is controlled by SIEMENS 840 DSL CNC system. It has the functions of automatic transmission of wheelsets, automatic lifting and centering, automatic processing and remote diagnosis. Equipped with automatic measurement system, and through the data processing automatically calculate the best cutting parameters, and automatically complete the whole process of wheel set. Using the software based on man-machine dialogue technology, the operator can easily select the processing program of different profiles. After the completion of the processing cycle, the machine can automatically print the results in a format determined by the user.

Fig.18 PWL1200 gantry wheel lathe

2 UGL series CNC non-falling wheel lathe is dedicated to the repair and processing of wheel tread and brake disc. The unique design of the machine allows the processing of wheelsets with inner or outer axle boxes without disassembling any part of the vehicle, as shown in Figure 19. High degree of automation, the entire measurement, processing and result printing process can be completed through the control interface, as shown in Figure 20b. A large boring bar type turning tool bar is installed on the horizontal tool holder, which can complete the processing of various brake discs installed on the inside, outside and middle of the axle tool bar, as shown in Fig.20a.

Figure 19 UGL series CNC non-falling wheel lathe

( a ) Processing map

( b ) Operation interface

Figure 20 UGL series CNC non-falling wheel lathe machining details

In addition, the machine structure is strong and easy to repair.

  ( 2 ) Machine tools produced by Qinghai Huading Heavy Machine Tool Co., Ltd.

1 DLC-25GA pit CNC non-falling wheel-set lathe is dedicated to the repair and processing of wheel flanges and treads. The wheel pair can be operated without any disintegration ( including the end cover of the axle box ) during the whole train formation, as shown in Figure 21. In addition, the machine can also be used for the repair and processing of the flange and tread of a single wheelset and a single bogie.

Fig.21 DLC-25GA pit CNC non-falling wheelset lathe

2 The SLC-25GA lathe is specifically designed for processing wheel sets, wheel rims, and tread surfaces, as shown in Figure 22. Without any disassembly, the entire four wheelsets of the bogie can be operated simultaneously on this machine tool, making it the best method for processing and repairing various vehicle wheelsets in modern times. This machine tool can switch between two independent operating modes of the non falling wheel set lathe, meeting the processing of various wheel set surfaces and brakes.

Figure 22 SLC-25GA lathe

3 TUP650SH is dedicated to repairing the wheel profile of the vehicle. It can work under both disintegration and non-disintegration conditions, and has strong adaptability, as shown in Figure 23. Its processing axle load does not exceed 30 000 daN.

Fig.23 TUP650 non-falling wheelset lathe

( 3 ) The original machine tool

STC14020 intelligent CNC non-falling wheel lathe produced by Shenyang Machine Tool Factory is an advanced equipment integrating the measurement, analysis and repair of the geometric parameters of the wheel set, as shown in Figure 24. All the wheelsets of the whole locomotive can be re-profiled without any disassembly, and the profile error can be corrected, so as to meet the requirements of the geometric parameters of the locomotive wheel set.

Fig.24 STC14020 CNC non-falling wheel lathe

( 4 ) Jiangxi Nelson − Simmons − Heggenset MACHINERY & MACHINERY CO., LTD. 1 U2000-G400 series non-falling wheel lathe is dedicated to the processing of a single wheel set of the vehicle, two wheel sets of the same bogie, and four wheel sets of two bogies of the same vehicle, as shown in Figure 25.Whether in a disassembled or non disassembled state, the wheel flange and tread can be processed online and the equivalent taper and polygon can be detected online, with a maximum chip cross-sectional area of 10 mm2.

Figure 25 U2000-G400 series non-falling wheel lathe

The Mobiturn type mobile non-falling wheel lathe is dedicated to the processing and repair of the wheel set to be repaired, as shown in Figure 26. The machine can be transported to different places by rail or road. It can be simply sent from the standby position on the track network to the position to be repaired when needed by placing it in the track network of the workshop, as shown in Figure 27. Compared with the traditional non-falling wheel lathe, Mobiturn has specific advantages for specific applications. One device can meet the requirements of wheel repair in different locations in the region, and good mobility can save the cost of wheel repair.

Fig.26 Mobiturn mobile non-falling wheel lathe

Figure 27 Mobiturn lathe machining drawing

2.2.4 Bearing processing machine

Bearings are key components connecting wheel axles and bogies, composed of steel balls, steel plates, and collars. The manufacturing process of steel balls includes raw materials, cold heading, smooth grinding, heat treatment, hard grinding, initial research, appearance and precision research; The manufacturing process of steel plates includes raw materials, cutting, ring cutting, finishing, forming, shaping, and punching rivet holes; The manufacturing process of ferrules includes raw materials, forging, annealing, turning, quenching, tempering, grinding, and assembly. The quenching process of the inner and outer rings is extremely important in the processing of bearings, which is used to improve the lifespan and load-bearing capacity of bearings.

The ZCY-2G fully automatic fully enclosed quenching press for inner and outer rings of railway bearings produced by Ningxia Machinery Research Institute Co., Ltd.is shown in Figure 28. It is used to control the hardness and deformation of railway passenger car and freight car bearings during heat treatment and quenching, so as to ensure the quality of railway bearings. It has the characteristics of high degree of automation, good reliability and stable quality of quenching workpiece. The equipment can improve the efficiency of quenching work, reduce labor intensity, reduce scrap rate, and promote the level of heat treatment process in the factory. It is the largest and only special equipment in the country that can realize the quenching of high-speed railway bearings. [ 21 ].

Figure 28 ZCY-2G bearing quenching press

2.2.5 Brake disc processing machine

Disc brake disc is the last guarantee of train braking [ 22 ]. Therefore, the development of high-performance brake discs is crucial to the entire high-speed rail industry. Its structure is complex, and it has high requirements on the toughness, hardness and strength of the forming material. Its processing procedures include rough turning, semi-finishing turning, finishing turning, fine drilling, deburring and inspection warehousing [ 23 ]. At present, the domestic brake disc mainly depends on imports, and the manufacturing technology is subject to foreign countries. It is urgent to vigorously develop independent research and development.

The PWL1200 gantry wheel lathe and UGL series CNC non-falling wheel lathe produced by Wuhan Heavy Machine Tool Group Co., Ltd., mentioned above, are also dedicated to brake disc processing. The flatness of the PWL1200 gantry wheel lathe processing brake disc 100 mm can reach 0.1 mm, and the surface roughness Ra is 3.5 μm. The flatness of the brake disc on 100 mm can reach 0.25 mm, and the surface roughness Ra is 3.5 μm on UGL series CNC non-falling wheel lathe.

2.3 Car body processing machine

The car body is the largest part of the whole vehicle, which is mostly welded by long extruded aluminum profiles. The high-speed gantry machining center and multi-functional industrial robot welding equipment are used to process the car body in the manufacturing workshop. The machining center needs to be equipped with a five-axis linkage advanced CNC system to perform high-precision machining of complex spatial surfaces. [ 24 ]

ENDURA produced by Fokker in Germany ®  The 500 milling machine is dedicated to machining car bodies and is equipped with a linear motor to achieve high-precision machining, as shown in Figure 29. The characteristics of this device are large, fast, and reliable. The mobile gantry milling machine ENDURA produced ®  1006LINEAR, with 2 gantries, specifically designed for processing aluminum alloy profiles, as shown in Figure 30.

Figure 29 ENDURA ® 500 processing map

Figure 30 ENDURA ® 1006LINEAR Processing Map

The GMC45620u super-large gantry mobile five-axis linkage machining center product produced by Shenyang machine tool is the first super-long high-speed rail machining equipment in China, which is dedicated to the complex surface machining of the car body, as shown in Figure 31. The machine adopts the lightweight technology of the whole machine, the high precision machining technology of the whole machine, the precision guarantee technology of the ultra-long stroke bed, the segmented docking technology of the bed, the ultra-high speed movement technology of the X axis and the ' deformation compensation processing ' technology [ 25 ]. The machining precision of complex curved surface is guaranteed, the machining efficiency is improved and the cost is saved.

Figure 31 GMC45620u gantry machining center

3 Conclusion

China's high-speed rail is at the forefront of the world, with demand driving technology. Its manufacturing of machine tools has gradually shifted from being mainly introduced from abroad in the early stage to independent research and development in the later stage. Due to the unique nature of high-speed rail, there are differences in processing techniques for various components, as well as high precision and quality requirements. Therefore, using different specialized machine tools to meet processing requirements can improve processing efficiency. However, in order to further improve production and quality, one of the key points is to form a supporting production line with specialized machine tools for processing discrete key components.

The general trend of machine tool development in the future is ' intelligent ' machine tools [ 26 − 27 ]. The specific performance is as follows : ( 1 ) High speed and high precision. ( 2 ) Intelligent. ( 3 ) Complexization and systematization. ( 4 ) Customization. ( 5 ) Greening [ 28 ]. ( 6 ) High performance [ 29 − 32 ]. High-speed rail machine tools will be further upgraded with the integration of high-speed rail and new generation of information technology [ 33 ].In the future, the development trend of high-speed rail mainly has the following points :

( 1 ) Intelligent. As the future high-speed train will develop in the direction of intelligent high-speed rail [ 34 − 35 ], it is composed of four parts : intelligent high-speed rail brain platform, intelligent construction, intelligent equipment and intelligent operation. [ 36 − 37 ], through the combination of sensors and standard communication interfaces, real-time control processing. The combination of big data, industrial internet of things, digital twin [ 38 ], edge computing / cloud computing and deep learning will help promote the development of intelligent machine tools in the field of high-speed rail in the future [ 39 − 41 ].

( 2 ) Customization and specialization [ 42 − 43 ]. As the future of high-speed rail will move in a faster, heavier, more difficult, updated and broader direction. Aiming at the processing requirements of large complex curved surfaces such as high-speed rail car bodies, it is necessary to develop intelligent grinding and polishing systems and flexible grinding tools. Aiming at the manufacturing requirements of key components such as rails, bogies, and wheelsets, a special and efficient processing complete set of equipment is developed [ 43 ]. Therefore, it is necessary to provide customized development in machine tool structure, system configuration, professional programming, cutting tools and measurement according to user needs, and provide specialized services in processing technology, cutting parameters, fault diagnosis, operation and maintenance. Technologies such as modular design, reconfigurable configuration, networked collaboration, software-defined manufacturing, and mobile manufacturing will provide technical support for customization [ 31 ].

( 3 ) Functional integration. Support the processing of a variety of parts, only need to adjust the relevant control program can be multi-mode production. It not only saves production time, but also reduces the error caused by repeated positioning, which can strengthen the application scope of CNC machine tools and simplify the layout of processing personnel.

( 4 ) Synergy. High-speed rail processing is a huge project. The collaborative operation of machine tools and robots can improve processing efficiency. Combined with the production and operation mode of the enterprise, the machine tool is designed comprehensively and professionally to achieve flexibility and build a flexible manufacturing system.

( 5 ) Double-carbon modeling [ 44 ]. In order to cope with climate change and green development, machine tool manufacturing industry must also face green transformation. First, from the procurement of raw materials to the final packaging and transportation to achieve full carbon neutrality. The second component uses high efficiency and low energy consumption products. The third is to further realize carbon neutralization in the process of machine tool processing parts technically.

Intelligent manufacturing is the hallmark of Industry 4.0 [45]. At present, the process of international industrial transfer is accelerating, and part of the production capacity of the world's equipment manufacturing industry is being transferred to developing countries. Not only is processing and manufacturing being transferred, but also the research and development industry is being transferred. This is an opportunity for China to develop the CNC machine tool industry, and high-speed rail machine tools are also a key development direction.

FAQ 1: What is the current status of machine tool applications for machinable parts in the high-speed railway industry?

Answer: The current status of machine tool applications in the high-speed railway industry shows significant advancements and integration of cutting-edge technologies. Manufacturers are increasingly using precision machine tools, such as CNC (Computer Numerical Control) milling and turning centers, to produce complex and critical components for high-speed trains. These machine tools offer enhanced automation, accuracy, and repeatability, resulting in higher-quality parts and improved overall efficiency in the production process.

FAQ 2: How are machine tools contributing to the development of high-speed railway technology?

Answer: Machine tools play a crucial role in the development of high-speed railway technology by enabling the precise manufacturing of various machinable parts. They are utilized to produce critical components like axles, wheelsets, bearings, and gear systems, which are essential for the safe and reliable operation of high-speed trains. The application of advanced machining techniques ensures that these parts meet stringent performance requirements, contributing to the overall performance, speed, and safety of high-speed railway systems.

FAQ 3: What are the key benefits of using state-of-the-art machine tools for high-speed railway parts production?

Answer: Utilizing state-of-the-art machine tools for high-speed railway parts production offers several advantages:

• High Precision: Modern machine tools deliver exceptional precision, ensuring that each component meets tight tolerances and maintains consistency in quality.
• Faster Production: Advanced automation and optimized machining processes in modern machine tools lead to faster production cycles, reducing lead times for high-speed railway parts.
• Improved Material Efficiency: High-speed machining capabilities allow for efficient material removal, minimizing waste and optimizing material usage.
• Enhanced Innovation: The integration of cutting-edge technologies in machine tools fosters innovation in design and manufacturing, resulting in continuous improvement in high-speed railway technology.

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