Precision machining and precision assembling method for electric spindle of numerical control machine tool

Abstract

The invention provides an electric spindle precision machining and precision assembling method for a numerical control machine tool. An electric spindle rotating shaft machining process and an electric spindle motor press fitting process are optimally designed. In the rotating shaft machining process, four-section carburizing and quenching, five-section nitriding and hydrogen removing, three-time center hole repairing and grinding and laser beam surface hardening are adopted, and a spherical center and a conical center are used in pairs to serve as the machining standard. In the press-fitting process of the motorized spindle motor, a spiral pressing sleeve tool is designed, and when large-interference thermal expansion and cold contraction press-fitting is carried out on a rotating shaft and a rotor iron core of the motorized spindle motor, a molybdenum disulfide lubricant and an epoxy resin adhesive are coated on the outer circle surface of the rotating shaft and the inner hole surface of the rotor iron core respectively; when large interference hot press fitting is carried out on the water-cooled jacket and the stator iron core, an anti-corrosion and anti-rust agent and a molybdenum disulfide lubricant are sequentially coated on the surface of an inner hole of the stator iron core, and an epoxy resin adhesive is coated on the surface of the water-cooled jacket.

Description

Technical Field

[0001] The present application relates to the field of precision machining and precision assembly of electric spindles, and in particular to a precision machining and precision assembly method of electric spindles for numerically controlled machine tools. Background Art

[0002] Precision machining and precision assembly technology is one of the core technologies of electric spindles, and is the key to ensuring the high-speed operation accuracy of electric spindles. However, machining errors, low assembly accuracy, and unreasonable heat treatment processes will lead to excessive axial eccentricity and vibration of the electric spindle rotor system, which will not only reduce the machining quality of CNC machine tools, but also cause excessive noise, affecting the service life of the spindle. How to optimize the machining and assembly process of electric spindles and improve the quality of electric spindle products is the long-term research direction of the electric spindle industry. The machining accuracy and assembly process of electric spindles play a vital role in the actual use of CNC machine tools and meeting the design index requirements. In the process of electric spindle machining, it is therefore urgent to optimize the machining and assembly processes of key components, adopt advanced process methods and optimized process parameters, and improve the overall accuracy of the electric spindle. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for precision machining and precision assembly of an electric spindle for a CNC machine tool, optimizes the electric spindle shaft machining process, optimizes the electric spindle motor press-fitting process, and improves the overall precision of the electric spindle.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A method for precision machining and precision assembly of an electric spindle for a numerically controlled machine tool, including machining of the electric spindle shaft and press-fitting of the electric spindle motor;

[0006] The electric spindle shaft processing includes: the shaft blank is sequentially subjected to forging, forging annealing, rough turning, four-stage carburizing and quenching, fine turning, rough grinding of the outer circle, semi-fine grinding of the outer circle, five-stage nitriding and dehydrogenation, nitriding layer depth detection, nitriding layer hardness detection, and fine grinding of the outer circle; when rough grinding of the outer circle, semi-fine grinding of the outer circle, and fine grinding of the outer circle, the top hole is respectively repaired three times and the surface is hardened by laser beam, and the spherical top and the conical top are used in pairs as the processing reference during the processing;

[0007] The electric spindle motor press-fitting comprises: firstly, performing cylindricity detection and roughness detection, cooling the rotating shaft with liquid nitrogen and heating the rotor core in an oven, until the sum of the outer diameter shrinkage of the rotating shaft and the inner diameter expansion of the rotor is greater than or equal to the total press-fitting amount, and applying force evenly by using a spiral sleeve press tool.

[0008] Furthermore, the four-stage carburizing and quenching is performed in sequence at 920°C for 18 hours, 950°C for oil quenching for 3 hours, 600°C for insulation for 6 hours and dripping of a 1:1 mixture of triethanolamine and alcohol at a rate of 80-100 drops / min, and 930°C for stress relief and tempering for 4 hours. After the four-stage carburizing and quenching process is completed, the steel piece is taken out of the furnace for air cooling.

[0009] Furthermore, the five-stage nitriding and dehydrogenation is nitriding at 510°C for 5h, nitriding at 550°C for 25h, nitriding at 570°C for 8h, nitriding at 570°C for 18h, introducing ammonia gas and keeping at 200°C for 6h to remove hydrogen, the depth of the nitriding layer is >0.3mm, and the hardness of the nitriding layer is ≥900HV.

[0010] Furthermore, after the three times of grinding and laser beam surface hardening of the top hole, the roughness values ​​of the top hole after grinding are greater than 0.4um, 0.2um, and 0.1um when rough grinding the outer circle, semi-finishing grinding the outer circle, and finishing grinding the outer circle, respectively. The top hole undergoes laser beam surface hardening heat treatment, and the hardness is greater than HRC45.

[0011] Furthermore, any cross-section of the spheres of the spherical top and the conical top is circular, ensuring that the top and the top hole always maintain a circular line contact state on the positioning section.

[0012] Furthermore, the spiral pressing tooling is made of stainless steel non-magnetic material and uses the threaded hole at the end of the shaft as a supporting force point. As the temperature drops, in addition to radial tightening, the axial direction is also gradually tightened. During the cooling process after pressing, the spiral pressing tooling is continuously tightened, and pressure is continuously applied to eliminate the axial tightening gap until the temperature difference between the rotating shaft and the rotor core, or the water-cooling jacket and the stator core is zero, and the axial contraction relative to the rotating shaft or the water-cooling jacket stops.

[0013] Furthermore, when the shaft and the rotor core of the electric spindle motor are pressed together with a large interference fit to cause thermal expansion and contraction, molybdenum disulfide lubricant and epoxy resin adhesive are respectively applied to the outer cylindrical surface of the shaft and the inner hole surface of the rotor core; when the water cooling jacket and the stator core are heated together with a large interference fit, anti-corrosion and rust prevention agent and molybdenum disulfide lubricant are successively applied to the inner hole surface of the stator core and epoxy resin adhesive is applied to the surface of the water jacket.

[0014] Beneficial effects:

[0015] 1. The conventional electric spindle shaft adopts three-stage quenching. The electric spindle shaft processing technology of the present invention adopts non-traditional four-stage carburizing quenching, adding a 1:1 mixture of triethanolamine and alcohol that few people pay attention to. The mixture is dripped at a speed of 80-100 drops / min and kept at 600°C for 6 hours. This process can improve the wear resistance of the shaft and reduce its brittleness.

[0016] 2. The traditional electric spindle nitriding process adopts a two-stage or three-stage process, and few people consider the benefits of dehydrogenation after carburizing. The electric spindle shaft processing process of the present invention adopts a non-traditional five-stage nitriding and dehydrogenation method. With the increase of the number of nitriding stages, the tensile strength and hardness of the spindle surface layer are on the rise, while the tensile strength and hardness of the spindle core are not greatly affected. The present invention adds a process of introducing ammonia gas at 200°C for 6 hours to remove hydrogen. Nitriding can be used to improve the wear resistance and fatigue strength of the workpiece, but anhydrous ammonia is generally used as the nitrogen supply medium during the nitriding process. As N atoms penetrate, H atoms also penetrate into the metal matrix. If a large number of H atoms gather on the surface grain boundaries of the workpiece, H 2 Molecular state, as H 2 The content increased, H 2 The pressure also increases. When H 2 When the pressure reaches the yield strength of the metal itself, plastic deformation occurs, and then microcracks are generated. 2 The molecules are continuously precipitated, the cracks are continuously expanded, and after multiple cracks are connected to each other, the nitride layer will peel off along the grain boundary. At 0.08 mm from the surface, H 2 The content of molecules dropped sharply, H 2 Molecules do not diffuse toward the center, but at the right temperature and in the right atmosphere, H 2 It can diffuse to the outside of the metal, so choosing a reasonable dehydrogenation process can make H 2 The content is reduced to the minimum, thereby reducing or preventing the peeling of the nitride layer.

[0017] 3. The traditional top hole grinding does not have a laser beam surface hardening process. The present invention adopts a laser beam surface quenching heat treatment technology, which can irradiate the spindle surface with a laser beam, so that a high-hardness hardened layer is formed on the spindle surface. The laser beam has high energy and can complete the processing quickly. Especially when performing local processing, it will basically not affect the area that the laser beam cannot irradiate, ensuring the accuracy of the workpiece; the size, shape and other factors of the workpiece will not hinder the use of the laser, and no medium is required for cooling treatment, and the heat treatment speed is fast and efficient.

[0018] 4. Different from the traditional double-conical top, the present invention uses a spherical top and a conical top as a processing reference, with complementary advantages. Any cross section of the sphere is circular, ensuring that the top and the top hole always maintain a circular line contact state on the positioning section. Even if there are obvious taper errors and coaxiality errors in the two top holes, their circular line contact state will not change.

[0019] 5. Few people pay attention to the problem of strain on the two contact surfaces of the interference connection caused by excessive friction during the press-fitting process, and few people pay attention to the anti-corrosion and anti-rust preventive measures at the two contact surfaces of the interference connection during actual use. In the present invention, when the shaft and the rotor core of the electric spindle motor are press-fitted with large interference fit due to thermal expansion and contraction, molybdenum disulfide lubricant and epoxy resin adhesive are respectively applied to the outer cylindrical surface of the shaft and the inner hole surface of the rotor core. When the water-cooling jacket and the stator core are hot-pressed with large interference fit, the anti-corrosion and anti-rust agent and molybdenum disulfide lubricant are successively applied to the inner hole surface of the stator core, and the epoxy resin adhesive is applied to the surface of the water-cooling jacket. Molybdenum disulfide is a wear-resistant lubricant. Applying a small amount at the starting position of the interference fit can improve the success rate of press-fitting. When the electric spindle is working, coolant is passed into the water cooling jacket. The rust inhibitor can prevent the coolant from corroding the stator core. In addition, molybdenum disulfide may corrode copper. Adding a small amount of preservative is also beneficial to improve the corrosion resistance of the stator core. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the precision machining and precision assembly method of the electric spindle;

[0021] Figure 2 Schematic diagram of the use of a spherical top and a conical top in combination.

[0022] The reference numerals in the drawings are: spherical top 1, conical top 2. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. The present application is described in detail below in conjunction with the accompanying drawings.

[0024] The invention discloses a precision machining and precision assembly method of an electric spindle for a numerically controlled machine tool, comprising machining of an electric spindle shaft and press-fitting of an electric spindle motor.

[0025] like Figure 1 As shown, the process of machining the electric spindle shaft includes: the shaft blank is sequentially subjected to forging, forging annealing, rough turning, four-stage carburizing and quenching, fine turning, rough grinding of the outer circle, semi-fine grinding of the outer circle, five-stage nitriding and dehydrogenation, nitriding layer depth detection, nitriding layer hardness detection, fine grinding of the outer circle, etc. The top hole is polished three times during rough grinding of the outer circle, semi-fine grinding of the outer circle, and fine grinding of the outer circle, and the surface is hardened by laser beam. During the machining process, the spherical top and the conical top are used in pairs as the machining reference.

[0026] The four-stage carburizing and quenching is performed in sequence at 920° C. for 18 hours, at 950° C. for oil quenching for 3 hours, at 600° C. for insulation for 6 hours and dripping of a 1:1 mixture of triethanolamine and alcohol at a rate of 80 to 100 drops / min, and at 930° C. for stress relief and tempering for 4 hours. After the four-stage carburizing and quenching process is completed, the steel is taken out of the furnace for air cooling.

[0027] The five-stage nitriding and dehydrogenation are nitriding at 510°C for 5h, nitriding at 550°C for 25h, nitriding at 570°C for 8h, nitriding at 570°C for 18h, introducing ammonia gas and keeping at 200°C for 6h to remove hydrogen, the depth of the nitriding layer is >0.3mm, and the hardness of the nitriding layer is ≥900HV.

[0028] After the three times of grinding and laser beam surface hardening, the roughness values ​​of the top hole after grinding are greater than 0.4um, 0.2um, and 0.1um respectively when rough grinding the outer circle, semi-finishing grinding the outer circle, and finishing grinding the outer circle. The top hole undergoes laser beam surface hardening heat treatment, and the hardness is greater than HRC45.

[0029] like Figure 2 As shown, the spherical tip 1 and the conical tip 2 are used in pairs as the processing reference. The spherical tip 1 is designed at one end and the conical tip 2 is designed at the other end. The spherical tip 1 and the conical tip 2 are used in pairs as the processing reference, and their advantages complement each other. Any cross section of the sphere is circular, ensuring that the tip and the tip hole always maintain a circular line contact state on the positioning section. Even if there are obvious taper errors and coaxiality errors in the two tip holes, their circular line contact state will not change.

[0030] The process of pressing the electric spindle motor comprises: firstly, performing cylindricity detection and roughness detection, the cylindricity is less than 0.003, the roughness is less than 0.8um, cooling the rotating shaft with liquid nitrogen and heating the rotor core in an oven at the same time, until the sum of the cold shrinkage of the outer diameter of the rotating shaft and the expansion of the inner diameter of the rotor is greater than or equal to the total pressing amount, applying force evenly by means of a spiral sleeve pressing tool, and when pressing the rotating shaft and the rotor core of the electric spindle motor with large interference fit due to thermal expansion and cold contraction, applying molybdenum disulfide lubricant and epoxy resin adhesive respectively on the outer cylindrical surface of the rotating shaft and the inner hole surface of the rotor core, and when heating the water cooling jacket and the stator core with large interference fit due to thermal expansion and cold contraction, applying anti-corrosion and anti-rust agent and molybdenum disulfide lubricant successively on the inner hole surface of the stator core and applying epoxy resin adhesive on the surface of the water jacket.

[0031] The spiral pressing sleeve tooling is made of stainless steel non-magnetic material and uses the threaded hole at the end of the shaft as a supporting force point. As the temperature drops, in addition to radial tightening, the axial direction is also gradually tightened. During the cooling process after press-fitting, the spiral pressing sleeve tooling is continuously tightened, and pressure is continuously applied to eliminate the axial tightening gap until the temperature difference between the rotating shaft and the rotor core, or the water-cooling sleeve and the stator core is zero, and the axial contraction relative to the rotating shaft or the water-cooling sleeve stops.

Claims

1. A method for precision machining and precision assembly of an electric spindle for a CNC machine tool, characterized in that: Including electric spindle shaft processing and electric spindle motor press-fitting; The electric spindle shaft processing includes: the shaft blank is sequentially subjected to forging, forging annealing, rough turning, four-stage carburizing and quenching, fine turning, rough grinding of the outer circle, semi-fine grinding of the outer circle, five-stage nitriding and dehydrogenation, nitriding layer depth detection, nitriding layer hardness detection, and fine grinding of the outer circle; when rough grinding of the outer circle, semi-fine grinding of the outer circle, and fine grinding of the outer circle, the top hole is respectively repaired three times and the surface is hardened by laser beam, and the spherical top and the conical top are used in pairs as the processing reference during the processing; The electric spindle motor press-fitting comprises: firstly, performing cylindricity detection and roughness detection, cooling the rotating shaft with liquid nitrogen and heating the rotor core in an oven, until the sum of the outer diameter shrinkage of the rotating shaft and the inner diameter expansion of the rotor is greater than or equal to the total press-fitting amount, and applying force evenly by using a spiral sleeve press tool.

2. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: The four-stage carburizing and quenching is performed in sequence at 920° C. for 18 hours, at 950° C. for oil quenching for 3 hours, at 600° C. for insulation for 6 hours and dripping of a 1:1 mixture of triethanolamine and alcohol at a rate of 80 to 100 drops / min, and at 930° C. for stress relief and tempering for 4 hours. After the four-stage carburizing and quenching process is completed, the steel is taken out of the furnace for air cooling.

3. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: The five-stage nitriding and dehydrogenation are nitriding at 510°C for 5h, nitriding at 550°C for 25h, nitriding at 570°C for 8h, nitriding at 570°C for 18h, introducing ammonia gas and keeping at 200°C for 6h to remove hydrogen, the depth of the nitriding layer is >0.3mm, and the hardness of the nitriding layer is ≥900HV.

4. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: After the three times of grinding and laser beam surface hardening, the roughness values ​​of the top hole after grinding are greater than 0.4um, 0.2um, and 0.1um respectively when rough grinding the outer circle, semi-finishing grinding the outer circle, and finishing grinding the outer circle. The top hole undergoes laser beam surface hardening heat treatment, and the hardness is greater than HRC45.

5. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: Any cross section of the sphere of the spherical top and the conical top is circular, ensuring that the top and the top hole always maintain a circular line contact state on the positioning section.

6. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: The spiral pressing sleeve tooling is made of stainless steel non-magnetic material and uses the threaded hole at the end of the shaft as a supporting force point. As the temperature drops, in addition to radial tightening, the axial direction is also gradually tightened. During the cooling process after press-fitting, the spiral pressing sleeve tooling is continuously tightened, and pressure is continuously applied to eliminate the axial tightening gap until the temperature difference between the rotating shaft and the rotor core, or the water-cooling sleeve and the stator core is zero, and the axial contraction relative to the rotating shaft or the water-cooling sleeve stops.

7. The method for precision machining and precision assembly of an electric spindle for a CNC machine tool according to claim 1, characterized in that: When the shaft and the rotor core of the electric spindle motor are pressed together with a large interference fit to cause thermal expansion and contraction, molybdenum disulfide lubricant and epoxy resin adhesive are applied to the outer cylindrical surface of the shaft and the inner hole surface of the rotor core respectively. When the water-cooling jacket and the stator core are heated with a large interference fit, anti-corrosion and rust-proof agent and molybdenum disulfide lubricant are applied to the inner hole surface of the stator core in turn, and epoxy resin adhesive is applied to the surface of the water jacket.

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