A test method for loading high-speed milling electric spindles in machining centers

Abstract

This invention discloses a loading test method for a high-speed milling electric spindle used in machining centers. Since the electric spindle is simultaneously subjected to the coupled effects of the main cutting force, back force, and feed force during the cutting process, to simplify the loading equipment, the tangential component of the main cutting force is treated as torque loading, the normal component of the main cutting force is combined with the feed cutting force to form a radial force loading, and the back force is treated as an axial force loading. This invention achieves synchronous coupled loading, can simulate the cutting conditions of milling cutters with different helix angles and different lead angles, can apply alternating loads for accelerated life testing, and can also study the dynamic characteristics and thermal fatigue effects of the electric spindle under thermo-mechanical coupling.

Description

Technical Field

[0001] This invention relates to the field of loading tests on high-speed milling electric spindles for machining centers, and more particularly to a loading test method for high-speed milling electric spindles for machining centers. Background Technology

[0002] Numerical control (NC) technology is a crucial standard for measuring a country's ability to manufacture complex and precision parts. Testing electric spindle components using actual cutting operations on CNC machine tools incurs significant costs for both tools and workpiece materials, resulting in long testing cycles and extremely high costs. Traditional loading methods, on the other hand, cannot apply loads in all directions in a coupled manner according to actual conditions, offering poor adjustability and rarely considering issues such as reduced electric spindle lifespan, dynamic characteristic changes, and thermal fatigue effects caused by alternating stress and thermal coupling. Therefore, constructing a high-speed electric spindle test bench to simulate the alternating load coupling of electric spindles and reproduce real cutting conditions is of great significance for researching and improving key performance indicators of electric spindles. Summary of the Invention

[0003] To address the urgent need for performance testing of electric spindles and solve the aforementioned technical problems, this invention proposes a loading test method for high-speed milling electric spindles used in machining centers. This method simulates different cutting conditions of electric spindle tools and, based on this, studies the dynamic characteristics and thermal fatigue effects of electric spindles under accelerated life testing and thermo-mechanical coupling.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for testing the loading of a high-speed milling electric spindle for a machining center includes the following steps:

[0006] Step 1: Simultaneously couple radial force, axial force and torque to simulate the cutting conditions of end mills with different helix angles and different principal cutting edge angles;

[0007] Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in Step 1, the three forces are simultaneously and synchronously alternating in a cycle to conduct an accelerated life test and estimate the service life of the electric spindle.

[0008] Step 3: Based on Step 2, apply temperature stress to the simulated tool holder and study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermo-mechanical coupling.

[0009] Further, step 1 includes: according to the milling force mathematical model, synchronously adjusting the magnitude of radial load, axial load, and torque load; the magnitude of radial force and axial force of the cylindrical milling cutter is related to the helix angle; and the magnitude of radial force and axial force of the end mill is related to the principal cutting edge angle.

[0010] Furthermore, step 2 includes: applying radial force, axial force, and torque in alternating cyclic loading individually or simultaneously in alternating cyclic loading; using fatigue cumulative damage theory, setting the cycle period and fatigue load setpoint to conduct accelerated life tests under different acceleration factor conditions and predict the service life of the electric spindle.

[0011] Furthermore, the reciprocating motion in steps 1-3 is achieved by a hybrid reciprocating ball screw, which consists of a reciprocating screw section and a unidirectional right-hand screw section. The reciprocating screw section consists of two threaded grooves with the same pitch but opposite directions of rotation, connected at both ends by a transition curve.

[0012] Furthermore, when the slider moves to the end of the helical groove of the reciprocating screw section, it automatically enters the threaded groove of another direction.

[0013] Furthermore, step 3 includes: using a ceramic heating ring to heat the simulated tool holder, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation, the rise in tool temperature and the change in cutting force form a thermo-mechanical coupling, and monitoring the change in spindle dynamic stiffness to study the influence of thermo-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

[0014] The advantages of this invention compared to the prior art are:

[0015] 1. Traditional loading methods cannot apply loads in each direction in a coupled manner according to actual conditions, resulting in poor adjustability and minimal consideration of alternating stress. The method of this invention can simultaneously adjust the magnitude of axial loading force, radial loading force, and torque load, simulating the cutting conditions of milling cutters with different helix angles and different principal cutting edge angles. Radial force loading, axial force loading, and torque loading can be alternated in cycles individually or simultaneously in cycles to simulate the alternating loads borne by the milling cutter when the machining path and cutting depth change.

[0016] 2. Traditional loading methods do not consider the combination of loading tests and life prediction tests. Based on loading tests, this invention utilizes the fatigue cumulative damage theory to conduct accelerated life tests under different acceleration factor conditions by setting cycle periods and fatigue load values, and predicts the service life of the electric spindle.

[0017] 3. Traditional loading test benches are fixed at both ends and apply force in the middle, which cannot simulate the cantilever state of an electric spindle with a tool. This invention designs a high-speed gearbox with a floating bearing fixed to the high-speed shaft. The gears have meshing clearance, which ensures that the simulated tool holder is in a cantilever state, and there is room for the axial offset caused by the radial force. The axial force is applied through the thrust ball bearing of the high-speed shaft of the gearbox. Because the gear meshing surface is wide enough, the axial elongation or compression deformation does not affect the gear meshing, and thus does not affect the torque loading.

[0018] 4. The hybrid reciprocating screw structure designed in this invention consists of two parts: a unidirectional right-hand screw and a reciprocating screw. The unidirectional right-hand screw can apply constant stress to test the influence of the axial stiffness of the electric spindle on the dynamic performance of the electric spindle. When switching to the reciprocating screw, the slider can achieve reciprocating motion without changing the rotation direction of the screw shaft, and apply an axial alternating cyclic load.

[0019] 5. Traditional loading methods do not consider the thermo-coupling effect caused by wear and heat generated during actual cutting. This invention designs a ceramic heating ring to heat the simulated tool holder, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation. Monitoring the change in spindle dynamic stiffness allows for the study of the influence of thermo-coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect. The designed ceramic heating ring utilizes a positive temperature coefficient ceramic heating element, generating heat through resistance heating. The outer surface ceramic material is an insulator and can be directly mounted on the simulated tool holder shaft. Attached Figure Description

[0020] Figure 1 A diagram showing the load location distribution for the loading test method;

[0021] Figure 2 This is a schematic diagram illustrating the principle of radial force loading.

[0022] Figure 3 This is a schematic diagram illustrating the principle of axial force loading.

[0023] The attached figures are labeled as follows: 1. High-speed electric spindle; 2. Simulated tool holder; 3. Diaphragm coupling; 4. High-speed gearbox; 5. Torque load; 6. Axial load; 7. Radial load; 8. Ceramic heating ring; 9. Cam mechanism; 10. Radial force sensor; 11. Extension rod; 12. Radial spring; 13. Push rod; 14. High-speed ceramic ball bearing outer ring; 15. Hybrid reciprocating ball screw; 16. Slider; 17. Axial force sensor; 18. Boss; 19. Axial spring; 20. Collar; 21. High-speed thrust ball bearing outer ring; 22. Gearbox high-speed shaft; 23. Reciprocating screw section; 24. Unidirectional right-hand screw section. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. The invention will now be described in detail with reference to the accompanying drawings.

[0025] like Figure 1As shown, in the loading test device of the present invention, the high-speed electric spindle 1 is fixed on the ground iron and connected to the high-speed shaft 22 of the high-speed gearbox 4 through the simulated tool holder 2 and the diaphragm coupling 3. The magnitudes of the radial loading load 7, axial loading load 6, and torque load 5 are adjusted synchronously to simulate the cutting conditions of milling cutters with different helix angles and different principal cutting edge angles. The radial loading load 7 and axial loading load 6 are set on the high-speed shaft 22 of the gearbox.

[0026] The high-speed electric spindle 1 is connected to the simulated tool holder 2 through the tool holder locking mechanism of the HSK interface. The flange hole at one end of the diaphragm coupling 3 is bolted to the flange hole of the simulated tool holder 2. The flange hole at the other end of the diaphragm coupling 3 is bolted to the flange hole of the high-speed shaft of the high-speed gearbox 4. The torque load 5 is applied through the low-speed shaft of the high-speed gearbox 4, and the torque is transmitted through gear meshing.

[0027] A ceramic heating ring 8 is placed on the simulated tool holder 2 to heat the simulated tool holder 2, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation. By monitoring the change in the dynamic stiffness of the spindle, the influence of thermo-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect can be studied.

[0028] like Figure 2 As shown, the outer circle of the cam mechanism 9 is tangent to the radial force sensor 10. The radial force sensor 10 is fixedly connected to the extension rod 11 with screws. The extension rod 11 is welded to the radial spring 12, the radial spring 12 is welded to the push rod 13, and the push rod 13 is tangent to the outer circle of the high-speed ceramic ball bearing outer ring 14. The cam mechanism 9 converts continuous rotational motion into reciprocating radial force loading, which passes sequentially through the radial force sensor 10, the extension rod 11, the radial spring 12, the push rod 13, and the high-speed ceramic ball bearing outer ring 14, and is finally applied to the simulated tool holder 2.

[0029] like Figure 3 As shown, the slider 16 is connected to the threaded groove of the hybrid reciprocating ball screw 15 by threading. The slider 16 is screwed to the axial force sensor 17, which is screwed to the boss 18. The boss 18 is welded to one end of the axial spring 19, and the other end of the axial spring 19 is welded to the collar 20. The collar 20 presses against the outer ring 21 of the high-speed thrust ball bearing. The outer ring 21 of the high-speed thrust ball bearing transmits the axial force to the inner ring of the bearing through the bearing rolling elements. The inner ring of the bearing is fixed to the high-speed shaft 22 of the gearbox by interference fit.

[0030] The hybrid reciprocating ball screw 15 consists of a reciprocating screw section 23 and a unidirectional right-hand screw section 24. The rotation of the hybrid reciprocating ball screw 15 causes the slider 16 to reciprocate axially, passing sequentially through the axial force sensor 17, boss 18, axial spring 19, collar 20, high-speed thrust ball bearing outer ring 21, bearing inner ring, gearbox high-speed shaft 22, and diaphragm coupling 3, ultimately applying force to the simulated tool holder 2.

[0031] The reciprocating lead screw section 23 consists of two threaded grooves with the same pitch but opposite directions of rotation, connected at both ends by a transition curve. When the slider moves to the end of the lead screw helical groove, it automatically enters the threaded groove with the other direction of rotation.

[0032] Figure 3 In this diagram, P represents the pitch, B represents the groove width, R represents the transition radius, H represents the groove depth, and D represents the major diameter of the thread groove.

[0033] Therefore, the loading test method for high-speed milling electric spindles in machining centers of the present invention includes the following steps:

[0034] Step 1: Simultaneously couple radial force, axial force and torque to simulate the cutting conditions of end mills with different helix angles and different principal cutting edge angles;

[0035] Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in Step 1, the three forces are simultaneously and synchronously alternating in a cycle to conduct an accelerated life test and estimate the service life of the electric spindle.

[0036] Step 3: Based on Step 2, apply temperature stress to the simulated tool holder and study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermo-mechanical coupling.

[0037] Further, step 1 includes: according to the milling force mathematical model, synchronously adjusting the magnitude of radial load, axial load, and torque load; the magnitude of radial force and axial force of the cylindrical milling cutter is related to the helix angle; and the magnitude of radial force and axial force of the end mill is related to the principal cutting edge angle.

[0038] Furthermore, step 2 includes: radial force, axial force, and torque can be applied alternately and cyclically individually or simultaneously and synchronously; using the fatigue cumulative damage theory, the cycle period and fatigue load setpoint are set to conduct accelerated life tests under different acceleration factor conditions and predict the service life of the electric spindle.

[0039] Furthermore, in step 3, a ceramic heating ring is designed to heat the simulated tool holder, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation. The rise in tool temperature and the change in cutting force form a thermo-mechanical coupling. Monitoring the change in spindle dynamic stiffness can help study the influence of thermo-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

Claims

1. A method for testing the loading of a high-speed milling electric spindle for a machining center, characterized in that, Includes the following steps: Step 1: Simultaneously couple radial force, axial force and torque to simulate the cutting conditions of end mills with different helix angles and different principal cutting edge angles; Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in Step 1, the three forces are simultaneously and synchronously alternating in a cycle to conduct an accelerated life test and estimate the service life of the electric spindle. Step 3: Based on Step 2, apply temperature stress to the simulated tool holder and study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermo-mechanical coupling. Steps 1-3 all require reciprocating motion, which is achieved by a hybrid reciprocating ball screw. The hybrid reciprocating ball screw consists of a reciprocating screw section and a unidirectional right-hand screw section. The reciprocating screw section consists of two threaded grooves with the same pitch but opposite directions of rotation, and the two ends are connected by a transition curve.

2. The method for testing the loading of a high-speed milling electric spindle for a machining center according to claim 1, characterized in that, Step 1 includes: according to the milling force mathematical model, synchronously adjusting the magnitude of radial load, axial load, and torque load. The magnitude of the radial and axial forces of the cylindrical milling cutter is related to the helix angle, and the magnitude of the radial and axial forces of the end mill is related to the principal cutting edge angle.

3. The method for testing the loading of a high-speed milling electric spindle for a machining center according to claim 1, characterized in that, Step 2 includes: applying radial force, axial force, and torque in alternating cycles or simultaneously in alternating cycles; using fatigue cumulative damage theory, setting the cycle period and fatigue load setpoints to conduct accelerated life tests under different acceleration factor conditions and predict the service life of the electric spindle.

4. The method for testing the loading of a high-speed milling electric spindle for a machining center according to claim 1, characterized in that, When the slider moves to the end of the helical groove of the reciprocating screw section, it automatically enters the thread groove of another direction.

5. The method for testing the loading of a high-speed milling electric spindle for a machining center according to claim 1, characterized in that, Step 3 includes: using a ceramic heating ring to heat the simulated tool holder, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation, the rise in tool temperature and the change in cutting force form a thermo-mechanical coupling, and monitoring the change in spindle dynamic stiffness to study the influence of thermo-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

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