Lead screw, method for producing a lead screw and use of a lead screw

Abstract

The application relates to the technical field of composite metal materials, in particular to a screw rod and a preparation method and application thereof. The screw rod comprises a cylindrical steel rod base material and a metal ceramic layer on the outer surface of the steel rod base material, the metal ceramic layer is a multilayer structure, and the metal ceramic layer comprises a ceramic base layer coated on the whole circumferential outer surface of the steel rod base material and a thread layer on the ceramic base layer. The metal ceramic powder is divided into multiple layers and is fused on the steel rod base material in a laser cladding mode, and the screw rod is obtained through deep cooling treatment and polishing; the cladding process comprises the following steps: firstly, a cladding layer is fused on the whole outer circumferential surface of the steel rod base material to form the ceramic base layer, then multiple cladding layers are fused on the ceramic base layer along helical lines, and the width is gradually reduced layer by layer to obtain the thread layer with the required thickness. The thread part of the screw rod is made of metal ceramic material, which can significantly improve the hardness, wear resistance and corrosion resistance of the surface of the screw rod, thereby improving the precision retention of the screw rod.

Description

Technical Field

[0001] This invention relates to the field of composite metal materials technology, and more specifically, to a lead screw, its preparation method, and its application. Background Technology

[0002] High-precision lead screws are one of the core functional components of industrial machine tools, directly determining their performance, technological level, quality, and reliability. They represent a crucial challenge that my country's manufacturing industry must overcome during its transformation and upgrading. Compared to foreign counterparts, my country's highest-level lead screw products can achieve initial precision comparable to international advanced levels. The main gap lies in aspects such as wear resistance and fatigue life, which determine precision retention and functional reliability. These are related to various factors, including basic materials and forming processes. Therefore, breakthroughs in high-precision lead screw materials and their manufacturing technologies are urgently needed.

[0003] Currently, the metal materials commonly used for lead screws are high-carbon chromium bearing steel GCr15 and medium-carbon steel 4150H. These raw materials undergo annealing or tempering, followed by medium-frequency or high-frequency induction hardening and tempering, and finally a series of machining processes to obtain the lead screw product. While the initial precision of lead screw products manufactured using the above raw materials and processes is comparable to that of foreign products, there is still a significant gap in precision retention. Therefore, providing a wear-resistant, high-precision lead screw product with good precision retention, along with its manufacturing method, is of great significance in overcoming the technical challenge of poor precision retention in lead screw products manufactured using existing technologies.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The primary objective of this invention is to provide a lead screw that, by setting a metal-ceramic layer on a steel rod substrate and using a metal-ceramic material for the threaded portion, can significantly improve the surface hardness, wear resistance, and corrosion resistance of the lead screw, thereby enhancing its accuracy retention and enabling it to operate in complex environments.

[0006] The second objective of this invention is to provide a method for manufacturing a lead screw as described above, in which a metal-ceramic thread is formed on a steel rod substrate by laser cladding layer by layer, and the shape and size of the thread are controlled by controlling the width and thickness of each cladding layer. The resulting lead screw has high precision, small deformation increase, good wear resistance, good precision retention, and long mean time between failures.

[0007] A third objective of the present invention is to provide a ball screw assembly, comprising a screw as described above or a screw manufactured by the screw preparation method described above.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] A lead screw includes a cylindrical steel rod substrate and a metal-ceramic layer on the outer surface of the steel rod substrate. The metal-ceramic layer has a multi-layer structure, including a ceramic base layer covering the entire circumferential outer surface of the steel rod substrate and a threaded layer on the ceramic base layer.

[0010] Preferably, the thickness H of the metal-ceramic layer and the diameter D of the lead screw satisfy the following relationship: H = (0.08~0.15)D.

[0011] Preferably, by mass percentage, the metal-ceramic layer comprises 10%–60% WC, 0%–40% TiC, 0%–40% SiC, and 20%–60% iron-based material consistent with the composition of the steel rod substrate;

[0012] And / or, the steel bar substrate includes any one of 42CrMo steel, GCr15 steel, and 40Cr steel.

[0013] Preferably, the number of metal-ceramic layers n is 4 to 6, wherein the first layer is the ceramic base layer, the second to nth layers constitute the threaded layer, and the thread width of the threaded layer decreases layer by layer from the second layer.

[0014] Preferably, in the multilayer structure of the metal-ceramic layer, the thread width of the second layer is 0.85 to 0.95 times the screw pitch; and / or, the thickness of any layer is 0.01 to 0.04 times the screw diameter.

[0015] A method for preparing a lead screw according to any one of the foregoing embodiments includes the following steps:

[0016] The steel rod substrate is heat-treated, and the metal ceramic powder is fused into the outer peripheral surface of the steel rod substrate in multiple layers by laser cladding to form a metal ceramic layer. Then, it is subjected to deep cryogenic treatment and ground to obtain the final product.

[0017] The cladding step includes cladding a layer of cladding on the entire outer circumferential surface of the steel rod substrate to form a ceramic base layer, then cladding along a spiral line on the ceramic base layer to obtain a spiral second cladding layer, and continuing to clad along a spiral line on the second cladding layer, repeating this process until a threaded layer of the required thickness is obtained.

[0018] Preferably, by mass percentage, the cermet powder comprises 10%–60% WC, 0%–40% TiC, 0%–40% SiC, and 20%–60% iron-based powder with the same composition as the steel rod substrate.

[0019] Preferably, the laser power of the laser cladding is 1000-5000W.

[0020] Preferably, the powder feeding rate for laser cladding is 10-50 g / min.

[0021] Preferably, the laser cladding spot size is 2–6 mm.

[0022] Preferably, the linear speed of the laser cladding is 5-50 mm / s, and the overlap rate is 5%-80%.

[0023] Preferably, the cladding process uses an inert gas to protect the cladding area, and the flow rate of the inert gas is 10-50 L / min.

[0024] Preferably, the number of laser cladding layers is 4 to 6.

[0025] Preferably, the cryogenic treatment temperature is -80℃ to -120℃, and the cryogenic treatment time is 1 to 5 hours.

[0026] A ball screw assembly includes a screw as described in any of the foregoing embodiments or a screw manufactured by the method for manufacturing a screw as described in any of the foregoing embodiments.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention involves cladding a high-temperature resistant, corrosion-resistant, chemically stable, high-hardness, high-strength, and wear-resistant metal-ceramic material onto a steel rod substrate to form a composite metal material with a gradient structure. The threaded layer and the bottom of the grooves between the threads are both composed of metal-ceramic material, which significantly improves the surface hardness, wear resistance, and corrosion resistance of the lead screw, thereby enhancing its accuracy retention and enabling it to operate in complex environments. Lead screws prepared using laser cladding combined with cryogenic treatment technology exhibit high precision, high accuracy retention, good stability, are not easily deformed, have a long service life, and reduce the risk of failure. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 A cross-sectional view of the lead screw before grinding, provided in an embodiment of the present invention;

[0031] Figure 2 For the present invention Figure 1 A magnified view of a portion of the image;

[0032] Figure 3This is a partially enlarged view of the ground lead screw provided in an embodiment of the present invention.

[0033] Figure label:

[0034] 1-Steel rod substrate; 2-Metal-ceramic layer; 21-Ceramic base layer; 22-Threaded layer. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0036] like Figure 1 and Figure 2 As shown, a first aspect of the present invention provides a lead screw, comprising a cylindrical steel rod substrate 1 and a metal-ceramic layer 2 located on the outer surface of the steel rod substrate 1. The metal-ceramic layer 2 has a multi-layer structure, including a ceramic base layer 21 covering the entire circumferential outer surface of the steel rod substrate 1 and a threaded layer 22 located on the ceramic base layer 21. The cross-sectional structure of the threaded layer 22 along the axial section (the section passing through the center line of the steel rod substrate) is a trapezoidal structure with rounded sides (e.g., ...). Figure 3 (As shown).

[0037] Ceramic materials possess many excellent properties, such as high temperature resistance, corrosion resistance, good chemical stability, high hardness, high strength, and good wear resistance. Therefore, they can be used to manufacture products and components that operate under harsh conditions involving high temperature, corrosion, wear, and tension / compression. Fusing cermet materials onto a steel rod substrate to form a composite metal material with a gradient structure can improve the surface hardness, corrosion resistance, and wear resistance of the material. The lead screw provided by this invention has its thread layer and the bottom of the groove between the threads both composed of cermet materials, which can significantly improve the surface hardness, wear resistance, and corrosion resistance of the lead screw, thereby improving the lead screw's accuracy retention and enabling it to operate in complex environments.

[0038] If the threaded layer of the cermet material is directly placed on the steel rod substrate, the bonding between the threaded layer and the steel rod substrate is poor due to the small contact area and the fact that they are dissimilar materials. This also leads to severe deformation of the steel rod substrate. To address this problem, this invention increases the contact area between the cermet layer and the steel rod substrate by setting a fully covered ceramic base layer on the entire outer circumference of the steel rod substrate. This improves the bonding force between the cermet layer and the steel rod substrate and reduces the deformation of the steel rod substrate. Then, the threaded layer is set on the ceramic base layer. The threaded layer and the ceramic base layer are made of the same material, resulting in good bonding. This structural design can improve the bonding force between the threaded layer and the steel rod substrate, prevent the threaded layer from falling off during use under complex working conditions, and further improve the accuracy retention of the lead screw.

[0039] In some specific embodiments of the present invention, the thickness H of the cermet layer and the diameter D of the lead screw satisfy the following relationship: H = (0.08~0.15)D, that is, the thickness H of the cermet layer is 0.08 to 0.15 times the diameter D of the lead screw. For example, it can be any one value or a range of any two values ​​from 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, and 0.15. Too small a thickness of the cermet layer will lead to a decrease in wear resistance, thus affecting its service life; too large a thickness of the cermet layer will lead to insufficient toughness of the lead screw, increased brittleness, and a higher risk of breakage.

[0040] In some specific embodiments of the present invention, the cermet layer comprises, by weight percentage, 10%–60% WC, 0%–40% TiC, 0%–40% SiC, and 20%–60% iron-based material consistent with the composition of the steel rod substrate. Adding a portion of iron-based material consistent with the composition of the steel rod substrate to the cermet layer can improve the bonding between the cermet layer and the steel rod substrate, thereby improving the precision retention of the lead screw.

[0041] In some embodiments, typically but not limitingly, for example, in the cermet layer, the mass percentage of WC can be any one value or a range of any two values ​​from 10%, 20%, 30%, 40%, 50%, and 60%; the mass percentage of TiC can be any one value or a range of any two values ​​from 0%, 10%, 20%, 30%, and 40%; the mass percentage of SiC can be any one value or a range of any two values ​​from 0%, 10%, 20%, 30%, and 40%; and the mass percentage of iron-based material consistent with the composition of the steel rod substrate can be any one value or a range of any two values ​​from 20%, 30%, 40%, 50%, and 60%.

[0042] In some specific embodiments of the present invention, the steel bar substrate used includes any one of 42CrMo steel, GCr15 steel, and 40Cr steel.

[0043] In some specific embodiments of the present invention, the number of metal-ceramic layers, n, is 4 to 6 layers, for example, 4, 5, or 6 layers; wherein the first layer (the cladding layer closest to the steel rod substrate) is a ceramic base layer, and the second to nth layers constitute the threaded layers, with the thread width decreasing progressively from the second layer onwards. Too many metal-ceramic layers result in excessively thin individual ceramic layers and poor bonding between layers; too few layers result in excessively thick individual ceramic layers, increasing the brittleness of the ceramic layers and potentially causing sudden chipping during use. Therefore, both too many and too few layers lead to a decrease in the accuracy retention of the lead screw, and the number of metal-ceramic layers must be reasonably controlled.

[0044] In some specific embodiments of the present invention, in the multilayer structure of the metal-ceramic layer, the thread width of the second layer is 0.85 to 0.95 times the lead screw pitch, for example, it can be any one value or a range of any two values ​​among 0.85, 0.87, 0.9, 0.92, and 0.95; and / or, the thickness of any ceramic layer is 0.01 to 0.04 times the lead screw diameter, for example, it can be any one value or a range of any two values ​​among 0.01, 0.02, 0.03, and 0.04.

[0045] In some specific embodiments of the present invention, the number of metal-ceramic layers is 5. The first layer covers the entire outer circumference of the steel rod substrate and has a thickness of 0.01 to 0.04 times the diameter of the lead screw. The second layer has a thread width of 0.85 to 0.95 times the pitch of the lead screw and a thickness of 0.01 to 0.02 times the diameter of the lead screw. The third layer has a thread width of 0.7 to 0.9 times the pitch of the lead screw and a thickness of 0.01 to 0.03 times the diameter of the lead screw. The fourth layer has a thread width of 0.5 to 0.8 times the pitch of the lead screw and a thickness of 0.01 to 0.03 times the diameter of the lead screw. The fifth layer has a thread width of 0.4 to 0.75 times the pitch of the lead screw and a thickness of 0.02 to 0.04 times the diameter of the lead screw.

[0046] A second aspect of the present invention provides a method for preparing a lead screw according to any one of the foregoing embodiments, comprising the following steps:

[0047] The steel rod substrate is heat-treated, and the metal ceramic powder is clad in multiple layers on the outer peripheral surface of the steel rod substrate by laser cladding to form a metal ceramic layer. Then, it is subjected to deep cryogenic treatment and precision grinding to obtain the final product.

[0048] The cladding step includes cladding a layer of cladding on the entire outer circumference of the steel rod substrate to form a ceramic base layer, then cladding along a spiral line on the ceramic base layer to obtain a spiral second cladding layer, and then continuing to clad along a spiral line on the second cladding layer, repeating this process until a threaded layer of the required thickness is obtained. When cladding the threaded layer, the width of the cladding layer decreases layer by layer, with the aim of making the cross-sectional structure of the threaded layer along the axial section direction into a trapezoidal structure with rounded sides after grinding.

[0049] The method of this invention uses laser cladding to clad high-hardness, high-corrosion-resistance, and high-wear-resistance metal-ceramic powder onto a steel rod substrate. After cladding to form a ceramic base layer, threads are formed on the ceramic base layer along a spiral line. This ensures that the thread layer and the bottom of the groove between the threads of the lead screw are made of metal-ceramic material, which can significantly improve the wear resistance of the lead screw and thus improve its accuracy retention. Deep cryogenic treatment after cladding can improve the mechanical properties and adhesion of the cladding layer, further improving the accuracy retention and service life of the lead screw.

[0050] In some specific embodiments of the present invention, the cermet powder used, by mass percentage, comprises 10%–60% WC, 0%–40% TiC, 0%–40% SiC, and 20%–60% iron-based powder with the same composition as the steel rod substrate. The present invention utilizes cermet materials to increase the wear resistance of the lead screw, while simultaneously adding iron-based powder with the same composition as the steel rod substrate to the cermet powder improves the bonding force between the cermet material and the steel rod substrate, preventing the cermet layer from detaching during use. The synergistic effect of both significantly improves the accuracy retention of the lead screw.

[0051] In some specific embodiments of the present invention, the laser power of laser cladding is 1000 to 5000W. For example, it can be any one value or a range of any two values ​​among 1000W, 1500W, 2000W, 2500W, 3000W, 3500W, 4000W, 4500W, and 5000W.

[0052] In some specific embodiments of the present invention, the powder feeding rate of laser cladding is 10 to 50 g / min. For example, it can be any one value or a range of any two values ​​among 10 g / min, 18 g / min, 25 g / min, 30 g / min, 35 g / min, 40 g / min, 45 g / min, and 50 g / min.

[0053] The parameter settings for laser cladding power and powder feeding amount are related to the thickness of the cladding layer.

[0054] In some specific embodiments of the present invention, the laser cladding spot size is 2 to 6 mm. For example, it can be any single value or a range of any two single values ​​among 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm.

[0055] In some specific embodiments of the present invention, the moving linear speed of the laser cladding is 5 to 50 mm / s, for example, it can be any one value or a range of any two values ​​among 5 mm / s, 10 mm / s, 15 mm / s, 20 mm / s, 30 mm / s, 40 mm / s, and 50 mm / s; the overlap rate is 5% to 80%, for example, it can be any one value or a range of any two values ​​among 5%, 10%, 20%, 40%, 50%, 60%, and 80%.

[0056] In some specific embodiments of the present invention, the cladding process uses an inert gas to protect the cladding area. The flow rate of the inert gas is 10 to 50 L / min. For example, it can be any one value or a range of any two values ​​from 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 40 L / min, and 50 L / min.

[0057] In some specific embodiments of the present invention, the number of laser cladding layers is 4 to 6, for example, 4, 5 or 6 layers. Too many cladding layers will reduce the bonding strength, while too few cladding layers will result in excessive thickness of a single layer and increased brittleness of the cladding layer.

[0058] In some specific embodiments of the present invention, the laser cladding consists of 5 layers. The specific process is as follows: First, a first cladding layer (ceramic base layer) is clad onto the entire outer surface of the steel rod substrate, with a thickness of 0.01 to 0.04 times the diameter of the lead screw. The second layer is clad along a spiral line, with a width of 0.85 to 0.95 times the lead screw pitch and a thickness of 0.01 to 0.02 times the lead screw diameter. The third layer continues cladding along a spiral line on top of the second cladding layer. The width is 0.7 to 0.9 times the screw pitch, and the thickness is 0.01 to 0.03 times the screw diameter. The fourth layer continues to be clad along the spiral line on the third cladding layer, with a width of 0.5 to 0.8 times the screw pitch and a thickness of 0.01 to 0.03 times the screw diameter. The fifth layer continues to be clad along the spiral line on the fourth cladding layer, with a width of 0.4 to 0.75 times the screw pitch and a thickness of 0.02 to 0.04 times the screw diameter.

[0059] In some specific embodiments of the present invention, the cryogenic treatment temperature is -80℃ to -120℃, for example, it can be any single value or a range of any two values ​​among -80℃, -90℃, -100℃, -110℃, and -120℃; the cryogenic treatment time is 1 to 5 hours, for example, it can be any single value or a range of any two values ​​among 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours. If the cryogenic temperature is too high, the microstructure transformation temperature will not be reached, and the effect will be unsatisfactory; if the cryogenic temperature is too low, the thermal shock will be large, which will easily cause the workpiece to crack, and the improvement effect on mechanical properties will not be obvious.

[0060] In some specific embodiments of the present invention, the cryogenic treatment process includes: cooling the workpiece temperature to -80°C to -120°C at a cooling rate of 2 to 8°C / min, holding it at that temperature for 1 to 5 hours, and then slowly raising the temperature to room temperature at a rate of 2 to 10°C.

[0061] In some specific embodiments of the present invention, the ratio of the lead screw pitch to its diameter is not greater than 0.5.

[0062] A third aspect of the present invention provides a ball screw assembly comprising a screw as described in any of the foregoing embodiments, or comprising a screw manufactured by the method for manufacturing a screw as described in any of the foregoing embodiments.

[0063] The following detailed description of some embodiments of the present invention is provided in conjunction with specific examples. Unless otherwise specified, all raw materials used in the embodiments are commercially available.

[0064] Example 1

[0065] This embodiment uses a lead screw with a diameter of 40.0 mm, a pitch of 10.0 mm, and a steel ball diameter of 6.35 mm as an example. Laser cladding is used to clad cermet powder onto the surface of a bright metal steel rod substrate, followed by cryogenic treatment. The steel rod used is made of 42CrMo, and its heat treatment process is quenching and tempering (830-850℃ for 2.5 hours followed by oil quenching, then holding at 560-580℃ for 4 hours, followed by furnace cooling to 350℃ and air cooling). The steel rod has a diameter of 31 mm, the cermet layer thickness is 5 mm, and the outer diameter of the clad lead screw is 41.0 mm. After a series of grinding processes, the final outer diameter is 40 mm. By mass percentage, the cermet powder composition is 25% WC, 15% TiC, 10% SiC, and 50% 42CrMo; the hardness of the cladding layer is 63-65 HRC.

[0066] The laser cladding process parameters are as follows: laser power 2000W, powder feed rate 18g / min, spot size 4mm, moving linear speed 15mm / s, overlap rate 40%, and inert gas flow rate 15L / min.

[0067] The cryogenic treatment process is as follows: cooling rate 5℃ / min, holding temperature -80℃, holding time 2 hours, and heating rate 5℃ / min to room temperature.

[0068] The specific laser cladding steps are as follows:

[0069] First, a 1.2mm thick metal-ceramic layer is clad onto the surface of the steel rod; the second layer is clad along the spiral line, with a width of 0.9 times the pitch (9.0mm) and a thickness of 0.8mm; the third layer is clad along the same spiral line, with a width of 0.7 times the pitch (7.0mm) and a thickness of 1.0mm; the fourth layer is clad along the same spiral line, with a width of 0.5 times the pitch (5.0mm) and a thickness of 1.0mm; the fifth layer is clad along the same spiral line, with a width of 0.4 times the pitch (4.0mm) and a thickness of 1.0mm.

[0070] Example 2

[0071] This embodiment uses a lead screw with a diameter of 63.0 mm, a pitch of 16.0 mm, and a steel ball diameter of 10.0 mm as an example. Laser cladding is used to clad cermet powder onto the surface of a bright iron-based steel rod substrate, followed by cryogenic treatment. The steel rod used is made of GCr15, and its heat treatment process is spheroidizing annealing (isothermal spheroidizing annealing: 770-790℃×2h, furnace cooling to 690-710℃×3h, then furnace cooling to below 500℃ and air cooling). The steel rod has a diameter of 50.0 mm, a ceramic layer thickness of 7.0 mm, and an outer diameter of 64.0 mm after cladding. After a series of grinding processes, the final outer diameter is 63.0 mm. By mass percentage, the cermet powder composition is 25% WC, 20% TiC, 15% SiC, and 40% GCr15; the hardness of the cladding layer is 63-65 HRC.

[0072] The laser cladding process parameters are as follows: laser power 2300W, powder feed rate 25g / min, spot size 5mm, moving linear speed 18mm / s, overlap rate 50%, and inert gas flow rate 18L / min.

[0073] The cryogenic treatment process is as follows: cooling rate 6℃ / min, holding temperature -100℃, holding time 3 hours, and heating rate 6℃ / min to room temperature.

[0074] The specific laser cladding steps are as follows:

[0075] First, a 1.5mm thick metal-ceramic layer is clad onto the surface of the steel rod; the second layer is clad along the spiral line, with a width of 0.9 times the pitch (14.4mm) and a thickness of 1.0mm; the third layer is clad along the same spiral line, with a width of 0.7 times the pitch (11.2mm) and a thickness of 1.0mm; the fourth layer is clad along the same spiral line, with a width of 0.55 times the pitch (8.8mm) and a thickness of 1.5mm; the fifth layer is clad along the same spiral line, with a width of 0.45 times the pitch (7.2mm) and a thickness of 2.0mm.

[0076] Example 3

[0077] This embodiment uses a lead screw with a diameter of 80mm, a pitch of 40mm, and a steel ball diameter of 12.7mm as an example. Laser cladding is used to clad cermet powder onto the surface of a bright iron-based steel rod, followed by cryogenic treatment. The steel rod used is made of 40Cr, and its heat treatment process is quenching and tempering (830-850℃ for 2 hours followed by oil quenching, then holding at 600-620℃ for 4 hours, followed by furnace cooling to 350℃ and air cooling). The diameter of the rod is 64mm, the thickness of the cermet layer is 8.5mm, and the outer diameter after cladding is 81.0mm. After a series of grinding processes, the final outer diameter is 80.0mm. By mass percentage, the cermet powder composition is 30% WC, 20% TiC, 20% SiC, and 30% 40Cr; the hardness of the cladding layer is 63-65 HRC.

[0078] The laser cladding process parameters are as follows: laser power 2500W, powder feed rate 30g / min, spot size 5mm, moving linear speed 20mm / s, overlap rate 60%, and inert gas flow rate 25L / min.

[0079] The cryogenic treatment process is as follows: cooling rate 8℃ / min, holding temperature -120℃, holding time 4 hours, and heating rate 10℃ / min to room temperature.

[0080] The specific laser cladding steps are as follows:

[0081] First, a 1.5mm thick metal-ceramic layer is clad onto the surface of the steel rod; the second layer is clad along the spiral line, with a width of 0.95 times the pitch (38.0mm) and a thickness of 1.0mm; the third layer is clad along the same spiral line, with a width of 0.85 times the pitch (34.0mm) and a thickness of 1.5mm; the fourth layer is clad along the same spiral line, with a width of 0.76 times the pitch (30.4mm) and a thickness of 1.5mm; the fifth layer is clad along the same spiral line, with a width of 0.72 times the pitch (28.8mm) and a thickness of 3.0mm.

[0082] Comparative Example 1

[0083] Comparative Example 1 did not have a metal-ceramic layer fused onto the surface of the steel rod substrate. Instead, it used a steel rod with the same material as in Example 1, with a diameter of 41 mm. The rod was processed into a finished product using the traditional method of "induction hardening - straightening - cyclone milling - straightening - precision grinding". The induction hardening process was as follows: a 200kW, 10kHz induction hardening machine tool was used, the workpiece moving speed was 0.5m / min, and the workpiece temperature was 860-880℃.

[0084] Comparative Example 2

[0085] Comparative Example 2 is similar to Example 1, except that the number of laser cladding layers is changed to 7 layers. The thickness of the first cladding layer is 1.2 mm; the thickness of the second cladding layer is 0.5 mm and the width is 9.5 mm; the thickness of the third cladding layer is 0.5 mm and the width is 9.0 mm; the thickness of the fourth cladding layer is 0.5 mm and the width is 7.5 mm; the thickness of the fifth cladding layer is 0.5 mm and the width is 7.0 mm; the thickness of the sixth cladding layer is 0.8 mm and the width is 5.5 mm; and the thickness of the seventh cladding layer is 1.0 mm and the width is 4.0 mm. The laser power is 4100 W, the powder feed rate is 10 g / min, the moving linear speed is 30 mm / s, the overlap rate is 80%, and the inert gas flow rate is 18 L / min. The other conditions are the same as in Example 1.

[0086] In this comparative example, because the thickness of the single-layer cladding layer has become thinner, the laser cladding parameters have been adjusted to ensure the cladding effect. If they are not adjusted, there is a risk that the cladding will not be completed or the substrate will be severely damaged.

[0087] Comparative Example 3

[0088] Comparative Example 3 is similar to Example 3, except that the number of laser cladding layers is changed to 3 layers. The first cladding layer has a thickness of 2.0 mm, the second cladding layer has a thickness of 3.0 mm and a width of 37.0 mm, and the third cladding layer has a thickness of 3.5 mm and a width of 34 mm. The moving linear speed during the laser cladding process is 15 mm / s, and the overlap rate is 40%. The other conditions are the same as in Example 3.

[0089] Comparative Example 4

[0090] Comparative Example 4 is similar to Example 1, except that: a 35mm diameter rod was selected, and the cladding thickness was 0.07 times the diameter, i.e., 2.8mm; first, a 1.2mm thick metal-ceramic layer was clad onto the surface of the metal rod; the second layer was 9.0mm wide and 0.4mm thick; the third layer was 0.7 times the pitch, i.e., 7.0mm wide and 0.4mm thick; the fourth layer was 0.5 times the pitch, i.e., 5.0mm wide and 0.4mm thick; the fifth layer was 0.4 times the pitch, i.e., 4.0mm wide and 0.4mm thick; the laser power was 3800W, the powder feed rate was 12g / min, the moving linear speed was 35mm / s, the overlap rate was 85%, and the inert gas flow rate was 20L / min; the remaining conditions were the same as in Example 1.

[0091] Comparative Example 5

[0092] Comparative Example 5 is similar to Example 1, except that: a 28mm diameter rod is selected, and the cladding thickness is 0.16 times the diameter, i.e., 6.4mm; first, a 2mm thick metal-ceramic layer is clad on the surface of the metal rod; the second layer has a width of 9.0mm and a thickness of 1.0mm; the third layer has a width of 0.7 times the pitch, i.e., 7.0mm, and a thickness of 1.0mm; the fourth layer is clad along the spiral line, with a width of 0.5 times the pitch, i.e., 5.0mm, and a thickness of 1.0mm; the fifth layer is clad along the spiral line, with a width of 0.4 times the pitch, i.e., 4.0mm, and a thickness of 1.4mm; the remaining conditions are the same as in Example 1.

[0093] Comparative Example 6

[0094] Comparative Example 6 is similar to Example 2, except that the holding temperature of the cryogenic treatment process is changed to -60°C, and all other conditions are the same as in Example 2.

[0095] Comparative Example 7

[0096] Comparative Example 7 is similar to Example 2, except that the holding temperature of the cryogenic treatment process is changed to -140°C, and all other conditions are the same as in Example 2.

[0097] Comparative Example 8

[0098] Comparative Example 8 is similar to Example 1, except that the iron-based powder 42CrMo is replaced with an equal amount of 40Cr, and all other conditions are the same as in Example 1.

[0099] Test case

[0100] The deformation increase, wear, accuracy retention and mean time between failures (MTBF) of the lead screws obtained in each embodiment and comparative example were tested. The test method was based on the method in industry standard JB / T 13813.2-2020. The test results are shown in Table 1.

[0101] Table 1

[0102] Example 1 0.08mm / m 0.8mg 6015h 15236h Example 2 0.06mm / m 0.6mg 6225h 16123h Example 3 0.05mm / m 0.5mg 6486h 16585h Comparative Example 1 0.8mm / m 2.5mg 4002h 10423h Comparative Example 2 0.2mm / m 1.5mg 4200h 8500h Comparative Example 3 0.08mm / m 1.2mg 3000h 6000h Comparative Example 4 0.08mm / m 5.3mg 2000h 4000h Comparative Example 5 0.2mm / m 1.0mg 3500h 7000h Comparative Example 6 0.1mm / m 1.2mg 4525h 8983h Comparative Example 7 0.08mm / m 0.8mg 5432h 12581h Comparative Example 8 0.08mm / m 1.0mg 3800h 7500h

[0103] As shown in Table 1, the lead screw prepared by the method of the present invention exhibits less deformation, less wear, better wear resistance, longer accuracy retention time, and longer mean time between failures (MTBF). Compared with the traditional processing method in Comparative Example 1, the wear is significantly reduced, and the accuracy retention and MTBF are significantly improved. A comparison between Comparative Example 2 and Example 1 shows that excessive laser cladding layers lead to reduced adhesion, significantly decreasing wear resistance, accuracy retention, and MTBF. A comparison between Comparative Example 3 and Example 3 shows that insufficient laser cladding layers and excessive single-layer thickness result in reduced toughness, increased brittleness, and poor wear resistance and accuracy. The wear resistance and accuracy retention were significantly reduced. A comparison of Comparative Examples 4, 5, and Example 1 shows that both excessively large and small total thicknesses of the cermet layer lead to decreased wear resistance and accuracy retention. Comparative Examples 6 and 7, compared to Example 2, show that cryogenic treatment temperature has a significant impact on the wear resistance and accuracy retention of the lead screw; excessively high or low cryogenic treatment temperatures lead to decreased wear resistance and accuracy retention. A comparison of Comparative Example 8 and Example 1 shows that adding iron-based powder with the same composition as the steel rod substrate to the cermet powder can improve the bonding force between the cermet layer and the steel rod substrate, thereby improving the wear resistance and accuracy retention of the lead screw.

[0104] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A lead screw, characterized in that, It includes a cylindrical steel rod substrate and a metal-ceramic layer on the outer surface of the steel rod substrate. The metal-ceramic layer has a multi-layer structure, including a ceramic base layer covering the entire circumferential outer surface of the steel rod substrate and a threaded layer on the ceramic base layer. The thickness H of the metal-ceramic layer and the diameter D of the lead screw satisfy the following relationship: H = (0.08~0.15)D; the number of metal-ceramic layers n is 4~6 layers, wherein the first layer is the ceramic base layer, the second to nth layers constitute the thread layer, and the thread width of the thread layer decreases layer by layer from the second layer; in the multi-layer structure of the metal-ceramic layer, the thread width of the second layer is 0.85~0.95 times the lead screw pitch; the thickness of any layer is 0.01~0.04 times the lead screw diameter; By mass percentage, the metal-ceramic layer comprises 10%~60% WC, 0%~40% TiC, 0%~40% SiC, and 20%~60% iron-based material with the same composition as the steel rod substrate.

2. The lead screw according to claim 1, characterized in that, The steel bar substrate includes any one of 42CrMo steel, GCr15 steel, and 40Cr steel.

3. The method for preparing the lead screw according to claim 1 or 2, characterized in that, Includes the following steps: The steel rod substrate is heat-treated, and the metal ceramic powder is fused into the outer peripheral surface of the steel rod substrate in multiple layers by laser cladding to form a metal ceramic layer. Then, it is subjected to deep cryogenic treatment and ground to obtain the final product. The cladding step includes cladding a layer of cladding on the entire outer circumferential surface of the steel rod substrate to form a ceramic base layer, then cladding along a spiral line on the ceramic base layer to obtain a spiral second cladding layer, and continuing to clad along a spiral line on the second cladding layer, repeating this process until a threaded layer of the required thickness is obtained.

4. The method for preparing the lead screw according to claim 3, characterized in that, By mass percentage, the cermet powder comprises 10%~60% WC, 0%~40% TiC, 0%~40% SiC, and 20%~60% iron-based powder with the same composition as the steel rod substrate.

5. The method for preparing a lead screw according to claim 3, characterized in that, It contains at least one of the following features: (1) The laser power of the laser cladding is 1000~5000W; (2) The powder feeding rate of the laser cladding is 10~50g / min; (3) The laser cladding spot size is 2~6mm; (4) The linear speed of the laser cladding is 5~50mm / s, and the overlap rate is 5%~80%; (5) The cladding process uses inert gas to protect the cladding area, and the flow rate of the inert gas is 10~50L / min; (6) The number of laser cladding layers is 4-6.

6. The method for preparing a lead screw according to claim 3, characterized in that, The cryogenic treatment temperature is -80℃ to -120℃, and the cryogenic treatment time is 1 to 5 hours.

7. A ball screw assembly, characterized in that, The lead screw includes the lead screw as described in claim 1 or 2, or the lead screw prepared by the method described in any one of claims 3 to 6.

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