(Report Producer/Author: Hua Chuang Securities, Fan Yimin, Hu Mingzhu)
1. Lead screw processing technology and core equipment
(1) Ball/column screw processing process
Grinding is the main processing method of precision lead screws, and the core processes include threading, lead screw straightening and heat treatment. There are two kinds of grinding and cold rolling processing methods of the lead screw, and the difference between the two is that the processing of the lead screw and the processing of the nut are all made by grinding technology. Grinding is the use of high-speed rotating abrasives or abrasives to remove the excess material on the surface of the workpiece, belongs to the finishing method, the accuracy level can reach C5 or even higher, the disadvantage is that the production efficiency is low, the process cycle is about 30-50 days, and the manufacturing cost is high. Cold rolling is roll forming, which is more efficient than grinding, with a process cycle time of about 1-3 days, but the accuracy of the lead screw made is generally only C7 or C10, which is suitable for mass production. The common method for producing precision ball/column screws is "rough turning + fine grinding", including more than 20 processes from blank blanking to assembly and warehousing. Regardless of the lead screw or nut to go through the cutting process, heat treatment process and auxiliary process, etc., the cutting process arrangement follows the general principle of "rough first and then fine", "base surface first" and "primary and secondary".
1. Threading processing
There are two common threading methods: rolling and cutting. Thread rolling is based on the principle of plastic deformation, using the forming die to extrude the workpiece to obtain the method of thread, according to the mold can be divided into two kinds: thread rolling and thread rolling. The metal fiber obtained by cutting processing is disconnected, and rolling processing can produce continuous metal fiber, thus processing surface finish is good, hardness and strength are high, and its production efficiency is also several times or dozens of times higher than cutting processing, is a kind of cost-effective processing mode suitable for trapezoidal lead screw that does not require high precision. However, the roll forming method has high requirements for material hardness, material brittleness, threaded hole shape and outer diameter, etc., and the scope of application is greatly limited. Thread cutting is the method of machining threads on the surface of a workpiece using forming tools or abrasives, including turning, grinding, milling, tapping, and threading. Turning, grinding, milling belongs to the category of machining, the degree of production automation is higher, the product consistency is better, generally speaking, machining accuracy: grinding> milling> turning, processing efficiency is the opposite. Tapping and threading are generally manual operations, and the quality of the machining depends both on the accuracy of the tap or die and on the proficiency of the worker, and is usually only used for the processing of small diameter threads.
Ball screws with higher accuracy levels require higher threading accuracy, especially the threading of planetary roller screws directly affects the success of product manufacturing. At present, the western developed countries generally adopt grinding or milling method, and cyclone milling can mill out the target accuracy at one time, and relying on the existing domestic cutting technology, the lead screw still needs further grinding to obtain higher precision after processing on the lathe or milling machine.
2. Straighten the lead screw
Straightening is the bending correction of the lead screw to return it to a straight state. Slender lead screw parts are easy to deform due to the compound effect of thermal stress and tissue stress after heat treatment, or can be bent due to vibration caused by force in the cutting process, resulting in deformation beyond the tolerance range, and then affect the quality of the workpiece and even hinder subsequent heat treatment, threading and other processes. To restore the bending screw to a straight line, the part can be reversed by applying external force (i.e., compressive straightening) until the residual deformation is equal to the initial deformation, then the screw is just straightened. Straightening is divided into cold state correction and hot state alignment, the latter is more conducive to maintaining the accuracy of parts. Cold state straightening is a straightening method that applies external force at room temperature, and is divided into cold press straightening, cold positive strike straightening and cold counter impact straightening. Take cold pressing straightening as an example, place the protruding part of the part after measurement upwards horizontally, apply pressure to the convex side to make it plastically deformed, according to the principle of "overkill", generally need to press to a little lower than the horizontal line, and then use the part itself rebound to offset the excessive reverse bending. Thermal straightening is carried out at a certain temperature, either by local heating of the deformed part and then by quenching and shrinking, such as hot spot straightening, or after heat treatment, when the part cools to a certain extent, it can be quickly measured and pressurized, such as hot press straightening. The hot state straightened parts can maintain the size and shape within the process requirements for a long time, while the cold state straightening may rebound back due to external forces, resulting in the reduction of part accuracy.
The main equipment is the automatic straightening machine of the lead screw, which is mature and independently supplied in China. At present, domestic and foreign countries have basically completed the upgrade from the traditional manual calibration to the automatic straightening of the machine, the automatic straightening machine is completed by the control system to complete the straightness inspection and straightening process of the parts, the machine is equipped with a special test sensor and high-precision encoder, etc., can achieve stable measurement and precise positioning, compared with manual straightening, its efficiency and accuracy are greatly improved. In terms of suppliers, foreign leading screw automatic straightening machines include German MAE, Italian Galdabini, Japanese Kokusai and German KBH, etc., domestic manufacturers have Chinese machine test equipment, Shanghai Beiyou, Changchun Shangke Machinery, etc., automation equipment is basically replaced by domestic production, which can meet the downstream lead screw processing needs.
3. Heat treatment
Heat treatment refers to a process in which the workpiece is heated, insulated and cooled in a solid state to transform its internal structure to obtain the required mechanical, physical and chemical properties. According to the different heating and cooling methods, heat treatment can be divided into three categories: integral heat treatment, surface heat treatment and chemical heat treatment.
(2) Grinding equipment
The equipment used for grinding is a grinding machine. From the perspective of the industrial chain, the upper reaches of the grinding machine include CNC systems, structural parts, electrical components, transmission systems and auxiliary materials, and the midstream takes automated and high-efficiency CNC grinding machines as the main type, and the downstream involves automobile manufacturing, construction machinery, aerospace and other fields.
1. Upstream: The cost of CNC system accounts for a high proportion, and the mid-to-high-end products lack domestic competitiveness
The main mechanical components of the grinding machine include electric spindle, ball screw, grinding head, tailstock and grinding wheel frame, etc., which can be supplied independently in China, but the competitiveness in the high-end market is insufficient. According to the China Machine Tool Industry Association, in 2023, the cumulative import of machine tool functional components (including parts) will be 1.42 billion US dollars, ranking second among all machine tool products, and the cumulative export will be 1.76 billion US dollars, the same as the previous year. At present, the domestic functional components can basically meet the batch supply of the machine tool host, and the capable machine manufacturers will also make some parts by themselves, which is conducive to reducing costs on the one hand, and on the other hand, it is more conducive to accurate adaptation with the performance of the host. At this stage, there is still a gap between domestic machine tool parts and overseas in terms of variety, quantity and grade, which is highlighted by the low market share of mid-range products and the fact that high-end products have not gotten rid of import dependence. The product consistency of core functional components is closely related to the reliability of machine tools, and technical optimization and strict quality control from functional components are one of the key issues to be solved to enhance the competitiveness of high-end grinding machine market.
The core component of the CNC grinding machine is the CNC system, which is technically difficult and valuable. CNC grinding machine, also known as Computer Numerical Control (CNC) grinding machine, refers to a kind of automatic machine tool that can receive, process and convert digital instructions to control the action of mechanical equipment. The numerical control system is the "brain" of the CNC grinder, including three parts: the control system, the servo system and the detection system: the control system has the function of input and output, and it sends instructions to the servo system, which can realize point control, linear control, contour control, linear interpolation control, etc.; The servo system receives the instruction from the control system and drives the movement of the mechanical parts of the bed body; The detection system helps to detect speed, displacement and measurement size, etc., and feeds back the results to the control system and servo system in time to automatically correct the processing program, forming a closed-loop control. The design and development of numerical control systems requires long-term technology accumulation and a large amount of capital investment, the industry has high barriers to entry, and new entrants have obvious shortcomings in providing one-stop solutions and service quality, which is difficult to meet customer needs.
Medium and high-end CNC system products have high added value and more profitability, and the main suppliers are Siemens of Germany, Fanuc of Japan, etc. China Machine Tool Industry Association divides CNC systems into three categories: economical, standard and high-end. The entry threshold of the economical CNC system is relatively low, and the domestic brands with high cost performance basically occupy the domestic market share; The standard type or mid-range popular type, the key lies in the reliability and stability of the product, which is the main track of domestic and imported competition, and the leader is the Japanese Fanuc; The high-end CNC system has the linkage control capability of 5 axes and above, which is a typical symbol of the technical level of the manufacturer, and the market share is mainly occupied by Siemens of Germany, Fanuc of Japan and Mitsubishi Electric. Grinding machine manufacturers import CNC systems not only have extremely high external costs, but may also face export restrictions on high-end products in policy (for example, Japan basically does not export high-end CNC system products to China), so the realization of domestic substitution of high-end CNC systems plays a key role in improving the international competitiveness of local CNC grinding machines.
2. Midstream: The value of a single domestic grinding machine is low, and the problem of accuracy and reliability still needs to be solved in the high-end
The grinding machine is a high-precision machining machine used in the grinding process, as the final machining equipment of the ball/column screw production line, which plays a key role in the accuracy of the lead screw after assembly. The basic working principle of the grinding machine is to remove the excess layer on the surface of the workpiece with the help of abrasive abrasives, so that the workpiece can achieve the predetermined machining accuracy and surface roughness requirements. According to the different processing methods and uses, the grinding machine can be divided into cylindrical grinder, internal cylindrical grinder, surface grinder, centerless grinder and other general grinders, as well as the special grinder for processing for a certain type of parts, according to the placement mode of the spindle can be divided into vertical, horizontal and gantry three categories, according to the control mode and divided into CNC grinder and non-CNC grinder. The grinding motion varies depending on the abrasive tool used, the process method, and the surface and shape of the workpiece, but usually the main motion is the high-speed rotation of the abrasive, and the feed motion is the displacement of the workpiece and the abrasive.
The accuracy index is one of the most important indicators to evaluate the performance of the grinding machine, and the geometric error, force error and especially the thermal error have the greatest impact on the precision grinding machine. The error of cutting machine tools such as grinding machines comes from many factors, such as the design, manufacturing and assembly of the machine tool itself, that is, geometric errors; or the deviation caused by the control link of the machine tool, that is, the control error; Or the motion error of workbench, rotary spindle etc. in the process of machine tool movement, motion error also belongs to the category of original error of machine tool, and has a greater influence on the precision of high-speed grinding machine tool; and dynamic errors generated during the use of machine tools, including force (deformation) errors and thermal (deformation) errors. Among them, geometric error, thermal error, force error are the main error sources that affect the accuracy of machine tools, and the more precise the machine tool, the greater the proportion of thermal error, so the high-precision grinding machine needs to pay extra attention to the consideration of thermal rigidity.
In addition to the accuracy of the machine tool, reliability is the manufacturing barrier of high-end CNC grinding machines. Reliability is defined as "the ability of a product to complete the specified function under specified conditions and within a specified time period", which reflects the level of the industry in design concepts, failure analysis methods, test data precipitation and parts manufacturing. The reliability of the CNC grinding machine depends first of all on the design of the machine itself. Failure analysis is often used in the industry to improve the reliability of machine tools, and mean time between failures (MTBF) is an important indicator for judging machine reliability. MTBF refers to the average working time between two adjacent failures of repairable machine tools, can also be called the average time between failures, the MTBF of high-end CNC machine tools in mainland China has achieved a leap from 600 hours to 2000 hours, and the accuracy index has increased by 20%, but there is still a certain gap compared with the leading level of more than 5000 hours abroad. According to the type of enterprise and competitiveness, the competition in the mainland CNC grinding machine market can be roughly divided into three levels: the first level is the leading international well-known manufacturers, such as EMAC of Germany, Lemat of the United States, Mitsui Seiki of Japan, etc., with its rich experience in the industry for many years and strong R&D and innovation capabilities, occupy the main share of the high-end CNC grinding machine market in the mainland; The second level is the high-end enterprises with core competitiveness in China, such as Qinchuan Machine Tool, Huachen Equipment, Yuhuan CNC and other national specialized and new "little giant" grinding machine enterprises, as well as Wuxi Machine Tool and Shanghai Machine Tool Factory, which were restructured from the original "Eighteen Arhats"; The third level is a large number of low-end enterprises, which have not formed a large business scale, but also lack representative technology in subdivided fields, and the product homogeneity is more serious.
The value of a single domestic grinding machine is low, and the import substitution space in the high-end market is broad. According to the data of the General Administration of Customs, it is calculated that the average price of imported grinding machines in mainland China in 2022 will be US$223,900 per unit, while the average price of exported grinding machines will only be US$12,100 per unit, reflecting that most of the domestic low-end products and high-end products rely on imports. With the improvement of the competitiveness of domestic brands, the import amount of grinding machines in mainland China from 2018 to 2023 is generally on a downward trend, according to the China Machine Tool Industry Association, it will be 770 million US dollars in 2023, and there is still a large space for domestic substitution in the market. Domestic enterprises in the competition with international enterprises have natural location advantages, equipment price advantages and rapid response service advantages, and CNC grinding machine industry barriers are high, the threat of new entrants is small, the future development prospects of second-level enterprises are considerable.
3. Downstream: The application industry has released its growth potential, and the demand for high-precision and CNC grinding machines has risen
As the market expands, the application scenarios of high-precision and high-efficiency CNC grinding machines increase. According to Global Market Insights, the global grinding machine market size was valued at USD 5.7 billion in 2023 and is expected to reach USD 8.9 billion by 2032, growing at a CAGR of 5.1% during 2024-2032. In terms of industries, 1) the rapid growth of the automobile manufacturing industry, especially the new energy vehicle manufacturing industry, is one of the main driving factors of the market, and the higher standards for metal processing of camshafts, steering pistons and reducer gears and other parts will provide a stable expansion of the grinding machine market space; 2) Industrial manufacturing accounts for the largest proportion of downstream applications, mainly due to the increase in the degree of automation in the industry and the increase in preference for CNC grinders; 3) In addition, the growing demand for high precision and high surface quality in industries such as aerospace, 3C consumer electronics, medical, and humanoid robotics is expected to increase the share of precision grinding machines in the sub-category.
The automobile manufacturing industry chain has made efforts to effectively drive the grinding machine industry. In the process of automobile manufacturing, the processing of precision parts is inseparable from the grinding machine. Grinding machines play an indispensable role in a wide range of applications in automotive manufacturing, from engine crankshafts and camshafts, to worms and gears in steering systems, to key components such as pistons. At the heart of the grinding process is the precise assembly and high-quality performance of the components. The key components of automotive systems need to operate stably for a long time at high speeds and loads, which places extremely high demands on their machining accuracy. The grinding machine is able to achieve micron-level accuracy through its fine machining capabilities, thus guaranteeing its excellent performance.
The construction machinery industry has a large demand, and the equipment is updated to expand the consumption of grinding machines. Grinding machine is widely used in the processing of hydraulic parts and gears in the construction machinery industry, hydraulic parts mainly have three types of hydraulic cylinders, hydraulic pumps and hydraulic valves, hydraulic cylinders with connecting rods for cylindrical grinding and centerless grinding demand is larger, heavy cylindrical grinders and centerless grinders are used, gears (especially bulldozer final transmission gears) processing are used to form gear grinding machines. The core components of construction machinery are characterized by large size and large quality, in order to reduce human error in the manufacturing process and achieve accurate and efficient production, the penetration rate of CNC grinding machine will continue to increase. In March 2024, the Ministry of Housing and Urban-Rural Development issued the "Notice on Promoting the Implementation Plan for the Renewal of Construction and Municipal Infrastructure Equipment", proposing to "update and eliminate construction machinery and equipment that have been used for more than 10 years, high pollution, high energy consumption, serious aging and wear, and backward technology, including excavation, lifting, loading, concrete mixing, lifts, bulldozers and other equipment (vehicles)", so the demand for equipment renewal is expected to boost upstream machine tool consumption.
(3) Whirlwind milling equipment
1. Whirlwind milling is an efficient green cutting process, which is suitable for semi-finishing of large lead screws
The economic benefits of cyclone milling are better than grinding, and the domestic ones stay at the level of semi-finishing, and some foreign manufacturers can achieve finishing. High-speed hard whirlwind milling (referred to as rotary milling) is a method that uses 6~12 forming tools evenly distributed on the cutterhead, with the help of the eccentricity of the rotary milling cutter head and the workpiece and the coupling movement of multiple degrees of freedom, to realize the progressive high-speed forming cutting of the threaded raceway. The traditional "rough turning + fine grinding" method in screw thread processing has cumbersome processes and low processing efficiency, and a large number of cutting fluids are easy to cause environmental pollution. In contrast, the milling speed of the hard rotary milling process can reach 400m/min, taking the ball screw as an example, the specific process route is: quenching and tempering→ semi-fine turning→ stress removal→ fine turning→ rough grinding of the outer → quenching → grinding of the outer → whirlwind milling→ aging treatment→ fine grinding, the general screw rotary milling thread can be directly assembled and shipped out of the factory, and the high-precision lead screw only needs to be finely ground again. The characteristics of one-time clamping of rotary milling process reduce the machining error, and more than 90% of the cutting heat in the cutting process is carried away by the chips, which reduces the pollution of cutting fluid and also makes the thermal deformation of the workpiece smaller.
According to the relative position of the tool and the workpiece, it can be divided into two types: internal rotary milling and external rotary milling. The cutter of internal rotary milling is distributed along the inner side of the annular cutterhead, and the cutterhead rotates at high speed during work, and the workpiece rotates at low speed in the same direction, and the angle between the rotation axis of the cutterhead and the workpiece axis is the spiral rising angle, and the thread of left-handed, right-handed can be processed by changing the size and direction of the spiral rising angle. Internal rotary milling can only process external threads, and the number of tools and the milling speed are greatly limited by the size of the cutter head, and it is also difficult to realize the processing of large lead screw. External rotary milling can machine both external and internal threads and works on a similar principle to internal rotary milling, with the main difference being that the cutter is distributed along the outside of the cutterhead. The milling speed of external rotary milling is slightly higher than that of internal rotary milling, but the cutting stability is relatively poor, and this structure occupies more space, especially brings inconvenience to the threading of large lead screw.
2. CNC cyclone milling machine has risen in China in recent years, and new advanced equipment still needs deep understanding
The basic components of the CNC cyclone milling machine include a head frame, a milling head, a carriage plate, a tailstock, a steady rest and a tool holder. Thread milling is completed by headstock rotation motion (C) and milling head longitudinal movement (Z), linkage, the headstock is driven by servo motor to rotate thereby driving the workpiece to rotate, and the milling head is also driven by the motor so that the cutterhead rotates at high speed, and linkage refers to the C-axis rotation 360 °, and the Z-axis goes a pitch. In order to ensure a strict linkage relationship during milling, the longitudinal movement of the milling head is equipped with a high-precision grating ruler, and the headstock rotation is equipped with a high-precision angle encoder to achieve full closed-loop position feedback. The left and right heel turrets are used for clamping and unclamping the workpiece, and the four center rests are used to lift and release the workpiece by moving the V-shaped support blocks up and down. The clamping action with the tool holder and the support action of the center frame also need to be controlled by the computer control system to achieve the coordination with the C-axis and Z-axis linkage.
The development history of rotary milling equipment at home and abroad is relatively short, and the mainland is gradually breaking the technological monopoly. The specialization of overseas CNC cyclone milling machines Large-scale production began in the 80s of the 20th century, such as the German Leistritz company produced the first rotary milling machine in 1986, and the rotary milling machine was put on the market in 1993 and used for the hard machining of ball screws, similar to the German GWT company, BurgsMuller company, as well as the Austrian Weingartner company, Linsinger company, etc. At the turn of the century, with the development of theoretical processes such as high-speed hard cutting and tool manufacturing, CNC cyclone milling machines in western developed countries represented by Germany have made phased progress in the direction of intelligence and compounding, and have now reached the level of precision machining. The introduction of rotary milling technology in the 60s of the last century was usually installed on the original lathe, mainly for soft milling of threads. Around 2012, Shaanxi Hanjiang Machine Tool Co., Ltd. developed an 8-meter CNC thread whirlwind milling machine HJ092×80, breaking the technical blockade of foreign countries in the efficient processing of large ball screws.
There is a certain gap between the level of domestic CNC cyclone milling machine for thread hard milling and foreign countries, which is mainly reflected in the workpiece lead accuracy and surface roughness, and domestic manufacturers still need to further precipitate relevant theoretical and practical experience.
3. The cyclone milling tool is one of the key elements of the process, and the domestic substitution process in the high-end market is accelerating
The performance of the tool largely determines the quality of the rotary milling process, and the tooth shape consistency and material of the cutting consumables are the key variables. The milling cutter consists of a tool holder, a cutter body and cutting consumables. One end of the tool holder is directly connected with the machine tool spindle, and the other end is connected with the tool body or the whole type of tool, and is the device that transmits the rotation accuracy and rotation torque of the machine tool spindle to the workpiece to be processed. The design of the cutter body structure determines the realization of the milling process, which has a great impact on the machining efficiency and machining accuracy. The cutting consumables are the parts that interact directly with the workpiece to be machined, which can be inserts or integral tools, the former is mounted on the tool body, and the latter can be installed on the tool body or directly connected to the tool holder. Wherein, cutting material is the main part of milling processing, directly determines the quality of thread machining, taking the insert as an example, if a plurality of inserts on the rotary milling cutterhead have tooth shape deviation or chamfer size difference, then it is bound to cause the difference of adjacent milling cross-section, cause the lead screw raceway to fluctuate periodically. In addition, the surface of the insert is gradually worn out by the strong friction between the chip and the surface of the workpiece during milling, especially during conventional milling, which affects the tool life and thus affects the machining cost.
Due to their high hardness and stability, CBN/PCBN tools are the first choice for thread milling of ball screws. The ball screw raceway requires high wear resistance and dimensional stability, and the lead screw and nut material is usually selected GCr15 (high carbon chromium bearing steel) with a hardness of more than 60HRC. According to the characteristics of the workpiece material, CBN (cubic boron nitride)/PCBN (polycrystalline cubic boron nitride) cutter is widely used as a high-speed hard milling tool, and its advantages are: 1) high hardness and wear resistance: CBN has a similar crystal structure and lattice coefficient to diamond, and its fine powder hardness is 8000~9000HV, and the hardness of PCBN micro powder is generally more than 3000; 2) High thermal stability: It can still be used for cutting at about 1300 °C, and the thermal stability is almost twice that of diamond; 3) Good chemical stability: neutral and reducing gases are stable to acid and alkali, not easy to be oxidized at high temperatures, and chemical reactions with iron materials at 1200~1300 °C; 4) Strong thermal conductivity: CBN thermal conductivity is 1300W/(M·°C), second only to diamond; 5) Low friction coefficient: about 0.1~0.3, the friction coefficient decreases with the increase of cutting temperature.
The domestic high-end tool market is dominated by international giants and a small number of domestic enterprises, and the low-end market is scattered. The world's high-end CNC tool leaders include Sweden Sandvik, Germany Walter, the United States Kennametal and other European and American enterprises, as well as Japan Mitsubishi, Japan Kyocera and South Korea Taguck and other Japanese and South Korean enterprises, its development pattern in the international market shows the characteristics of "high starting point, large investment, scale, internationalization", accounting for about two-thirds of the market share of modern high-efficiency tools. Domestic CNC tool enterprises represented by Zhuzhou Diamond, Hengfeng Tools, Wald, Huarui Precision and Oukeyi, etc., have obtained a number of important patents in technology research and development, forming the core competitive advantage of enterprises in subdivided fields. The overall consumption scale of the mainland tool market continues to expand, and the localization of high-end products represented by cemented carbide tools has accelerated. In 2016~2018 and 2019~2021, the annual sales of knives in mainland China grew rapidly, and in 2022, due to the lack of new orders, sales fell by 2.7% year-on-year to 46.4 billion yuan. Among them, the annual sales of domestic knives are about 33.8 billion yuan, accounting for 73%, an increase of 8 percentage points over 2018, and imported knives (including foreign brands produced and sold in China) are 12.6 billion yuan, accounting for 27%. According to the statistics of the association, in terms of grades, the performance of high-end tools is better than that of low-end, mainly due to the upgrading of the demand for tools by key industry users in the mainland; In terms of varieties, the main high-speed steel tools decreased significantly (-10% year-on-year), while cemented carbide blades maintained a growth momentum (+17% year-on-year), and the demand for superhard tools increased to a certain extent driven by the new energy vehicle industry.
The self-sufficiency of knives in the mainland has been enhanced, and the dependence on imports has been reduced. In the past five years, the import and export scale of mainland cutting tools has diverged, the import scale has decreased as a whole, and the export scale has expanded significantly, with an average annual compound growth rate of 6.14% during 2019~2023. Among the varieties of cutting tools, the proportion of inserts and milling cutters is high in import and export, but the import unit price of cutting tools is much higher than the export unit price, the average import price of coated blades is 2.83 times the average export price, the uncoated inserts are 4.70 times, and the milling cutter is 2.12 times.
(4) Induction hardening equipment
1. Heat treatment is the basic process of machinery manufacturing, which has a key impact on product performance
The heat treatment process is one of the basic processes of equipment manufacturing, which participates in multiple links of material pretreatment and subsequent finishing, and plays a vital role in the hardness, toughness, dimensional stability and accuracy of metal workpiece products. In the case of ball/column screws, the main heat treatment processes include spheroidizing annealing, induction hardening and tempering, as well as aging treatment:
Spheroidization annealing: Due to the high hardness of GCr15 material, it is necessary to pre-heat treat the lead screw or nut before cutting, and obtain a spherical or granular carbide structure evenly distributed on the ferrite matrix by spheroidizing the carbide in the GCr15 material, so as to reduce the hardness of the workpiece, increase plasticity and toughness, and prepare for subsequent cutting and heat treatment.
Induction hardening and tempering: Induction hardening is the most important and complex process in the heat treatment process of lead screws, which determines the quality of the product to a large extent. The principle behind induction hardening is the skin effect of alternating current, that is, when the induction coil is passed through alternating current, the induced current generated by the workpiece in the magnetic field is unevenly distributed, and the current density near the surface layer is the largest, and the center is almost zero, so the surface of the workpiece is rapidly heated to the austenite state. Subsequently, the martensite can be obtained by spraying water and cooling quickly, and the surface induction hardening is completed. Induction hardening heating time generally only takes a few seconds or tens of seconds, and the surface hardness of the workpiece is improved after quenching, and the deformation is small and the toughness is retained at the same time because the center is not heated, but the quality control of the process is difficult, and it is more difficult to deal with the workpiece with complex shape. After induction hardening, it is generally necessary to temper immediately to eliminate residual compressive stress and reduce the brittleness of the workpiece.
Aging treatment: The lead screw will be stressed and deformed after quenching or cutting, which not only affects the dimensional stability and accuracy, but also causes the product to be prone to fatigue and wear during use. Aging treatment is a kind of thermal treatment method that eliminates the internal stress of the workpiece, specifically refers to the deformed workpiece is placed at room temperature (natural aging) or a specific temperature (artificial aging) for a period of time, so that the workpiece obtains a stable internal structure. From the perspective of the industrial chain, the upstream of the heat treatment industry is basic raw materials and general accessories, and the midstream covers three categories: heat treatment equipment manufacturing, heat treatment processing services, heat treatment process materials (quenching oil and medium, chemical heat treatment infiltration agent, anti-impermeable agent, cleaning agent, etc.) and auxiliary material manufacturing, with a wide range of downstream application scenarios, mainly for the machinery manufacturing industry.
Upstream raw materials and general accessories can meet general needs, but the localization rate of high-end categories is low. At present, the performance of steel/copper, coolers, sensors, hydraulic systems, etc., required for the manufacture of heat treatment equipment in mainland China has reached or approached the international advanced level, and the rest of the raw materials and components can be supplied independently except for the numerical control system. However, the key problem of domestic accessories is that the reliability and stability of the product are low, resulting in the domestic heat treatment equipment in terms of accuracy and life inferior to the first-class products of the same type at home, so the key sensitive components and core materials still need to rely on imports.
Midstream heat treatment equipment manufacturing and heat treatment processing services dominate, and the transformation and upgrading of the industry has achieved remarkable results. According to the heat treatment industry association, by the end of the "13th Five-Year Plan", there were about 1,000 heat treatment equipment and process material manufacturing enterprises in the mainland, and the numerical control rate of heat treatment process equipment reached 80%. In 2020, the scale of heat treatment equipment and process materials in mainland China will be about 20 billion yuan, of which about 15 billion yuan will be heat treatment equipment, which will nearly double that at the end of the "Twelfth Five-Year Plan".
The downstream applications are broad and the customer loyalty is high. The application field of heat treatment equipment covers almost all equipment manufacturing and mechanical processing scenarios, and new application fields are still emerging, which makes heat treatment equipment manufacturing enterprises less affected by the cyclical fluctuations of the downstream industry, and secondly, it is conducive to enhancing customer stickiness and forming a strong brand barrier.
2. The number of domestic induction hardening equipment manufacturers is small, and the application scenario opens up a new growth space
Continental's induction heat treatment technology has gone through four stages of development: comprehensive introduction, self-reliance, rapid development and independent innovation, and digital and intelligent technology is becoming an important engine for industrial development. The formation of the basic theory of induction heat treatment began with Faraday's discovery of the electromagnetic induction heating phenomenon in 1831, and was gradually systematized through the expansion and improvement of Joule, Maxwell, Foucett and others. In foreign countries, induction heating equipment has been successfully developed at the end of the 19th century, has been widely used in the industrial field in the middle of the 20th century, and further with the advent of thyristors, MOSFETs and IGBTs for a new round of induction heating technology revolution. The development of induction heat treatment technology in the mainland relies on the theoretical and material foundation of 156 major projects in the former Soviet Union in the 50s of the 20th century, since then the mainland has experienced a long period of independent and arduous research and development of "self-reliance" and "rapid development" stage, although the overall technical level is not high, there is an imbalance in the product structure, but these two periods have greatly improved the scale of the domestic induction heating industry and research and development strength, after entering the 21st century, the mainland is in the "independent innovation" stage of induction heat treatment automation, intelligence and green developmentInduction heating related equipment is further extended to high-tech applications such as precision medicine, CNC machine tools, and industrial robots.
Surface induction hardening is the core link of screw heat treatment, and the corresponding equipment induction hardening machine tool has a high technical content. The induction hardening machine tool is composed of five parts: induction heating power supply, numerical control system, other key functional components (including inductors and transformers, etc.), cooling equipment and the main body of the bed. Induction hardening machine tools are expensive, and the price of high-end CNC products ranges from 100~3 million yuan, mainly according to the size of the machine tool and has a large adjustment.
The induction heating power supply is the core equipment of the whole machine, and the thyristor medium frequency and transistor high (ultrasound) frequency are the mainstream types. Induction heating power supply has experienced the development from mechanical intermediate frequency generator set, electron tube type high-frequency power supply, thyristor type intermediate frequency power supply to transistor ultrasound and high-frequency power supply, wherein mechanical intermediate frequency generator set due to low electrical efficiency, low single-hit rated power, noise and other shortcomings have been eliminated in the eighties and nineties of the last century, and the tube-type high-frequency power supply also has the problem of low heating efficiency and unstable control, so the latter two are the power supply mainly used in induction hardening machine tools. The induction heating power supply determines the stability, accuracy and reliability of heating, and is currently continuing to develop in the direction of higher efficiency and frequency, higher reliability, intelligent control and low cost.
The CNC system can greatly improve the processing quality and efficiency, and the components rely on overseas procurement. The numerical control system is used to realize the automatic setting and real-time monitoring of process parameters such as temperature, power, voltage, etc., to realize automatic material transfer, positioning, cooling, tempering and other processes, to realize the continuous heating and quenching/tempering of parts, etc., so as to obtain a uniform and stable quality of the surface of the parts, and is also conducive to the processing of parts with non-circular curves and complex shapes. At present, the application of the CNC system of the continental induction hardening machine tool is not as mature as abroad, and the components of the CNC system are basically purchased from outside, such as the purchase from Siemens of Germany, Fanuc of Japan or Mitsubishi of Japan, the purchase price is high, and in extreme cases may face the risk of banning and restricting sales, and the industry is constrained.
Other key functional components are varied, mainly inductors and transformers. The inductor is a terminal component that uses the principle of electromagnetic induction heating to heat the workpiece, and is specially designed according to the material, hardening layer distribution and shape of the workpiece to be heated, with a high degree of customization. The transformer is used for step-down/step-up, isolation and impedance matching for the heating power supply, and the product has basically achieved import substitution.
Induction hardening machine tools are divided into two types according to the production method: special machine tools and general machine tools. Special machine tools can be subdivided into a variety of categories according to different application scenarios, with a high degree of customization, strong completeness, and high accuracy, and are suitable for mass production of specific workpieces. General-purpose machine tools are suitable for single or small batch production that requires frequent workpiece changes, and has relatively low product quality requirements.
The number of domestic induction hardening machine manufacturers is small, and the R&D strength of the industry vanguard is outstanding. Leading induction hardening machine tool manufacturers include IFTI in Norway, EMAC in Germany, Say Induction in Italy, DHF and Inductotherm in Japan, etc., with business in many regions around the world, with first-mover advantages in scale and R&D. Manufacturers in the field of induction hardening machine tool manufacturing in mainland China are relatively few, and the larger ones are mainly Hengjin induction, constant precision induction and sublimation induction, and their equipment income is more than 10 million yuan. The ability of the equipment of the three enterprises to process large and medium-sized workpieces is not inferior to that of foreign countries, and the induction heating power supply can also reach a higher power, but the overall degree of automation is insufficient. With the acceleration of the implementation of the national innovation-driven strategy, the local cutting-edge enterprises in the industry will continue to narrow the gap with developed countries in terms of technical level.
The prosperity of the downstream wind power and automobile industries has risen, stimulating the growth potential of induction hardening equipment. According to the fourth heat treatment equipment user survey and analysis report, during the "14th Five-Year Plan" period, the investment in induction hardening machine tools accounted for ≥ 30% of the construction machinery and wind power industries, and > 20% of the automobile/motorcycle manufacturing and heat treatment professional factory industries. In 2023, the construction machinery industry will still be in a downward cycle, and domestic demand will continue to be under pressure due to the impact of real estate and infrastructure; The wind power equipment industry continues to grow rapidly in the context of the strategic adjustment of the national energy structure, and the cumulative installed capacity of wind power in China will be about 440 million kilowatts in 2023, a year-on-year increase of 21%; At the same time, the automobile manufacturing industry has grown steadily, with both production and sales reaching a record high in 2023; In addition, the development trend of precision in the machine tool and aerospace industry has given rise to more demand for medium and high-end induction hardening machine tools. It is expected that driven by the downstream machinery manufacturing industry, the industry will usher in huge growth opportunities.
Second, the vigorous development of downstream industries has driven the prosperity of domestic manufacturers to rebound
(1) Huachen Equipment: a leading manufacturer of roll grinders, cooperating with Best to develop high-end linear guide grinders
The company is an innovative leading enterprise specializing in R&D, manufacturing and service of high-end precision grinding equipment in China. The company's core product, the automatic precision CNC roll grinder, has established a global technology leadership position in the field of high-speed and high-precision grinding, breaking the monopoly of foreign brands on high-end roll grinding equipment in mainland China. At the same time, the company continues to expand its business extension, and actively promotes the research and development and market application of new sub-micron high-end composite grinding products, precision thread grinding machines, and CNC linear guide grinding machines, so as to enrich the downstream market coverage and help improve performance and long-term development.
In recent years, the company has focused on launching sub-micron high-end composite grinding series products with the function of grinding outer circle, inner circle, non-circle, end face, contour, thread, etc., which can be used for the grinding of lead screw and nut, and the roundness of product clamping grinding can reach up to 0.2μm, and the related core technical indicators are comparable to the international first-class level, which is expected to promote the domestic substitution process of high-precision grinding machines in the upstream of lead screws. The precision index of the precision thread grinding machine is also comparable to the world's first-class similar products, and the machining accuracy of the standard lead screw specimen grinding can reach up to P0 level, which has been widely used in many fields such as industrial machine tools, robots, aerospace, and auto parts manufacturing. In October 2023, the company said that it would cooperate with Best to jointly promote the key core technology research of domestic high-end CNC linear guide grinding machines around the project needs of Best's rolling functional components.
(2) Qinchuan machine tool: the leading backbone of the machine tool industry, the ball screw production capacity continues to expand
Qinchuan Machine Tool is the leading backbone of China's machine tool industry, China's precision CNC machine tools and complex tools R & D and manufacturing base and industrial robot reducer R & D and manufacturing base, with Baoji machine tool, Hanjiang machine tool, Hanjiang tool, Walker gear, Qinchuan Grande, Qinchuan Baoyi and many other enterprises. Focusing on the development strategy of "adhering to the main engine, creating high-end manufacturing, strong support for core components, breaking through key technologies of intelligent manufacturing and numerical control, and taking the initiative to undertake major national special research and development tasks", the company has developed four major business segments of machine tool host, high-end manufacturing, functional components and intelligent manufacturing, the main products include high-end digital control lathes, machining centers, industrial robot reducers, rolling functional components and high-end CNC systems, etc., which are the most categories in the mainland machine tool industry, the highest degree of precision complexity, and the most complete industrial chain. One of the enterprises with significant comprehensive competitive advantages.
In terms of screw products, the ball screws produced by the subsidiary Hanjiang Machine Tool have a stable accuracy of P2 level, and some of them reach P1 and P0 levels, which can basically meet the requirements of medium and high-end CNC machine tools, and have realized the localization and application of rolling functional parts and precision screw pairs in the field of new energy vehicles. In terms of machine tool products, in 2023, the company's CNC cylindrical grinding machine will break through the high-speed and high-efficiency grinding technology, and the new generation of CNC internal thread grinding machine can meet the grinding needs of large-size threads and planetary screw nuts. In May 2023, the company plans to use the raised funds of 1.23 billion yuan to invest in high-end industrial machine tool innovation bases, R&D and industrialization construction of rolling functional components in the field of new energy vehicles, and construction of new energy passenger vehicle parts, among which the rolling functional parts project is expected to increase the production capacity of ball screws/precision screws by 280,000 pieces/year after reaching production, thereby increasing the production capacity to 380,000 pieces/year.
(3) Zhejiang Hydeman: an expert in lathe turning, and has achieved remarkable results in the development of composite technology
Zhejiang Hydeman is committed to the independent innovation of high-end CNC lathe basic technology and core technology, product positioning "benchmarking Germany and Japan, replacing imports", has realized the spindle technology, servo turret technology, servo tailstock technology is completely autonomous, and has made important breakthroughs in thermal compensation, with a complete high-end CNC lathe development platform and manufacturing platform. The company has four categories: high-end digital control lathes, automated production lines, parallel compound machining centers, and popular CNC lathes, which are mainly used in automobile manufacturing, construction machinery, general equipment, aerospace, military industry and other industries.
CNC lathes and milling machines play an important role in the process of lead screw processing, and the company will make substantial progress in the development of composite technology in 2023. There has been a five-axis linkage of vertical turning and milling compound center into the trial production stage, another five-axis linkage of gantry type milling compound center is being designed, through the five-axis linkage technology on the turning platform to develop all kinds of composite processing technology and technology, can realize the processing process is highly intensive. Parallel compound machining center series (Hi series, V series, HTD series) has entered the prototype trial production stage and small batch production stage, the product can be equipped with double turret and milling function, through parallel composite processing technology to fundamentally improve the processing efficiency of the machine tool. In 2024, the company will actively lay out downstream application fields, and will further expand applications in humanoid robots, semiconductors, military aerospace, molds, and energy storage industries.
(4) Yuhuan CNC: a leading enterprise of CNC grinding machines in China, helping to optimize the processing technology of "titanium alloy" products
The company has been specializing in the research and development, production, sales and service of CNC grinding equipment and intelligent equipment, providing customers with comprehensive solutions for precision grinding and intelligent manufacturing technology, and is a leading enterprise in the field of precision CNC grinding machines and CNC grinding and polishing equipment in China. The company's products are mainly divided into CNC grinding machines, CNC grinding and polishing machines and intelligent equipment series products, which are widely used in consumer electronics, automotive industry, energy and power, new materials, powder metallurgy and other industries. In 2023, the company signed a contract with Jabil Technology for grinding and polishing equipment and transformation equipment with a total amount of 253 million yuan, and the company's brand awareness as a professional provider of comprehensive solutions for precision grinding and intelligent manufacturing technology was further consolidated.
3. Industry views and key focus on individual stocks
Grinding is the main processing method of precision lead screws, and the core processes include threading, lead screw straightening and heat treatment. Grinding is a processing method that uses abrasives or abrasives to remove excess material on the surface of the workpiece, which belongs to the finishing method, and the accuracy level can reach C5 or even higher, but the disadvantage is that the production efficiency is low, the process cycle is about 30-50 days, and the manufacturing cost is high. Cold rolling, i.e. roll forming, is more productive than grinding, with a cycle time of about 1-3 days, but the accuracy of the lead screws made is generally only C7 or C10. The common method for the production of precision ball/column screws is "rough turning + fine grinding", which needs to follow the principles of "rough first and then fine", "base first" and "primary and secondary", and has more than 20 processes such as cutting, grinding and heat treatment.
Threading: The corresponding processing equipment is grinding machine and cyclone milling equipment. There are two common processing methods: rolling and cutting. Ball screws with higher accuracy levels require higher threading accuracy, especially the threading of planetary roller screws directly affects the success of product manufacturing.
Lead screw straightening: The corresponding processing equipment is an automatic straightening machine. Straightening is the bending correction of the lead screw, which is often divided into cold state correction and hot state alignment. At present, domestic straightening machine manufacturers include Zhongji Test Equipment, Shanghai Beiyou, etc.
Heat treatment: The corresponding processing equipment is induction hardening equipment. Heat treatment refers to the process of heating, holding and cooling a workpiece in a solid state to achieve the desired properties. According to the different heating and cooling methods, heat treatment can be divided into three categories: integral heat treatment, surface heat treatment and chemical heat treatment.
The grinding machine is a high-precision machining machine used in the grinding process, as the final machining equipment of the ball/column screw production line, which plays a key role in the accuracy of the lead screw after assembly. According to the data of the General Administration of Customs, it is calculated that the average price of imported grinding machines in mainland China in 2022 will be US$223,900 per unit, while the average price of export grinding machines will only be US$12,100 per unit, reflecting the majority of low-end products in China and the dependence on imports of high-end products. With the improvement of the competitiveness of domestic brands, the import value of grinding machines in mainland China is generally declining, according to the China Machine Tool Industry Association, it will be 770 million US dollars in 2023, and there is still a large space for domestic substitution. At present, in the mainland CNC grinding machine market, international well-known manufacturers such as EMAC of Germany, Lemart of the United States, and Mitsui Seiki of Japan occupy the main share of the high-end CNC grinding machine market in mainland China; Domestic manufacturers such as Qinchuan Machine Tool, Huachen Equipment, and Yuhuan CNC still have great potential in the high-end grinding machine market.
(This article is for informational purposes only and does not represent any investment advice from us.) To use the information, please refer to the original report. ）
Selected report source: [Future Think Tank]. Future Think Tank - Official Website