High-speed milling motorized spindle loading test method for machining center

Abstract

The invention discloses a high-speed milling motorized spindle loading test method for a machining center, and the method comprises the steps: enabling a tangential component of a main cutting force to serve as a torque for loading in order to simplify a loading device because the motorized spindle is subjected to the coupling effect of the main cutting force, a back force and a feeding force in a cutting process; the normal component of the main cutting force and the feeding cutting force are synthesized into radial force to be loaded, and back force is regarded as axial force to be loaded. Synchronous coupling loading is realized, cutting working conditions of milling cutters with different helical angles and different tool cutting edges can be simulated, an alternating load can be applied to carry out an accelerated life test, and dynamic characteristics and a thermal fatigue effect of the motorized spindle under a thermal-mechanical coupling effect can be researched.

Description

Technical Field

[0001] The invention relates to the field of loading test of a high-speed milling electric spindle for a machining center, and in particular to a loading test method of a high-speed milling electric spindle for a machining center. Background Art

[0002] CNC technology is one of the important standards for measuring a country's ability to manufacture complex precision parts. Using actual cutting processing on CNC machine tools to test electric spindle components consumes a lot of tool and workpiece raw materials, has a long test cycle and is extremely costly. The traditional loading method cannot couple the loads in all directions according to the actual situation, has poor adjustability, and rarely considers the problems of alternating stress and thermal coupling that cause the electric spindle's service life to decrease, dynamic characteristics change, and thermal fatigue effects. Therefore, building a high-speed electric spindle test bench to simulate the electric spindle's alternating load coupling and restore the electric spindle's real cutting conditions is of great significance to the research and improvement of the key performance indicators of the electric spindle. Summary of the invention

[0003] In view of the urgent need for electric spindle performance testing and to solve the above-mentioned technical problems, the present invention proposes a loading test method for a high-speed milling electric spindle for a machining center, which simulates different cutting conditions of the electric spindle tool, and on this basis studies the dynamic characteristics and thermal fatigue effects of the electric spindle under accelerated life testing and thermal-mechanical coupling.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme: A loading test method for a high-speed milling electric spindle for a machining center comprises the following steps: Step 1, synchronously coupling loading of radial force, axial force and torque to simulate the cutting conditions of milling cutters with different helix angles and main deflection angles; Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in step 1, the three forces are synchronously alternating and cycled simultaneously to perform 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 to study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermal-mechanical coupling.

[0005] Furthermore, step 1 includes: according to the mathematical model of milling force, synchronously adjusting the magnitude of radial loading load, axial loading load and torque load, the magnitude of radial force and axial force of cylindrical milling cutter is related to the helix angle, and the magnitude of radial force and axial force of end milling cutter is related to the main deflection angle.

[0006] Furthermore, step 2 includes: radial force, axial force, and torque are individually or synchronously loaded in alternating cycles, and fatigue cumulative damage theory is used to set cycle periods and fatigue load given values ​​to conduct accelerated life tests under different acceleration factors and estimate the service life of the electric spindle.

[0007] Furthermore, the reciprocating motion of step 1 to step 3 is realized by a hybrid reciprocating ball screw, which consists of a reciprocating screw segment and a unidirectional right-hand screw segment. The reciprocating screw segment is two thread grooves with the same pitch and opposite rotation directions, and the two ends are connected by a transition curve.

[0008] Furthermore, when the slider moves to the end of the spiral groove of the reciprocating screw section, it automatically enters the thread groove of another rotation direction.

[0009] Furthermore, step 3 includes: using a ceramic heating ring to heat the simulated tool handle, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation, forming thermal-mechanical coupling due to the increase in tool temperature and the change in cutting force, monitoring the change in spindle dynamic stiffness, and studying the influence of thermal-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

[0010] The beneficial effects of the present invention compared with the prior art are: 1. In the traditional loading method, the loads in various directions cannot be coupled and applied according to the actual situation, the adjustability is poor, and the alternating stress is rarely considered. The method of the present invention can synchronously adjust the size of the axial loading force, the radial loading force, and the torque load, and can simulate the cutting conditions of milling cutters with different helix angles and different main deflection angles; radial force loading, axial force loading, and torque loading can be cycled alternately separately, or they can be cycled alternately synchronously at the same time to simulate the alternating loads borne by the milling cutter when the processing path changes and the cutting depth changes.

[0011] 2. The traditional loading method does not consider the combination of loading test and life prediction test. On the basis of loading test, the present invention uses fatigue cumulative damage theory, sets cycle period and fatigue load given value to conduct accelerated life test under different acceleration factor conditions and predict the service life of the electric spindle.

[0012] 3. The two ends of the traditional loading test bench are fixed, and force is applied in the middle position, which cannot simulate the cantilever state of the electric spindle with the tool. The present invention designs a high-speed gearbox, and the high-speed shaft of the gearbox adopts a floating bearing fixing method, and the gears have a meshing clearance, which ensures that the simulated tool holder is in a cantilever state, and there is room for the axis offset caused by the application of 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 meshing of the gears, thereby not affecting the torque loading.

[0013] 4. The hybrid reciprocating screw structure designed in the present invention consists of two sections: 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 switched to a reciprocating screw, the slider can achieve reciprocating motion without changing the rotation direction of the screw shaft, applying an axial alternating cyclic load.

[0014] 5. The traditional loading method does not consider the thermal coupling effect caused by the wear and heat of the tool during actual cutting. The present invention designs a ceramic heating ring to heat the simulated tool handle, reducing the cutting heat generated when the metal undergoes elastic and plastic deformation. Monitoring the change in the dynamic stiffness of the spindle can study the influence of thermal coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect. The designed ceramic heating ring uses a positive temperature coefficient ceramic heating element to generate heat through the principle of resistance heating. The ceramic material on the outer surface is an insulator and can be directly installed on the simulated tool handle shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Load position distribution diagram for loading test method; Figure 2 It is a schematic diagram of radial force loading principle; Figure 3 Schematic diagram of axial force loading principle.

[0016] Among them, the accompanying drawings are marked as: high-speed electric spindle 1, simulated tool handle 2, diaphragm coupling 3, high-speed gearbox 4, torque load 5, axial loading load 6, radial loading load 7, ceramic heating ring 8, cam mechanism 9, radial force sensor 10, extension rod 11, radial spring 12, push rod 13, high-speed ceramic ball bearing outer ring 14, hybrid reciprocating ball screw 15, slider 16, axial force sensor 17, boss 18, axial spring 19, collar 20, high-speed thrust ball bearing outer ring 21, gearbox high-speed shaft 22, reciprocating screw segment 23, unidirectional right-hand screw segment 24. DETAILED DESCRIPTION

[0017] 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 invention is described in detail below in conjunction with the accompanying drawings.

[0018] 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 is connected to the gear box high-speed shaft 22 of the high-speed gear box 4 through the simulated tool handle 2 and the membrane disc coupling 3, and the radial loading load 7, the axial loading load 6, and the torque load 5 are synchronously adjusted to simulate the cutting conditions of milling cutters with different helix angles and different main deflection angles. The radial loading load 7 and the axial loading load 6 are set on the gear box high-speed shaft 22.

[0019] The high-speed electric spindle 1 is connected to the simulated tool handle 2 through the tool handle locking mechanism of the HSK interface, the flange hole at one end of the diaphragm coupling 3 is connected to the flange hole of the simulated tool handle 2 through bolts, the flange hole at the other end of the diaphragm coupling 3 is connected to the flange hole of the high-speed shaft of the high-speed gear box 4 through bolts, the torque load 5 is applied through the low-speed shaft of the high-speed gear box 4, and the torque is transmitted through gear meshing.

[0020] The ceramic heating ring 8 is arranged on the simulated tool handle 2 to heat the simulated tool handle 2, reduce the cutting heat generated when the metal undergoes elastic and plastic deformation, monitor the change of the dynamic stiffness of the spindle, and study the influence of thermal-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

[0021] like Figure 2 As shown, the cam 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 screw of the extension rod 11, 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 the continuous rotational motion into a reciprocating radial force loading, which passes through the radial force sensor 10, the extension rod 11, the radial spring 12, the push rod 13, the high-speed ceramic ball bearing outer ring 14 in sequence, and is finally applied to the simulated tool handle 2.

[0022] like Figure 3 As shown, the thread of the slider 16 is embedded in the thread groove of the hybrid reciprocating ball screw 15 for connection, the slider 16 is screwed to the axial force sensor 17, the axial force sensor 17 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 supports 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 element, and the inner ring of the bearing is fixed on the high-speed shaft 22 of the gear box by interference fit.

[0023] The hybrid reciprocating ball screw 15 is composed of a reciprocating screw segment 23 and a unidirectional right-hand screw segment 24. The hybrid reciprocating ball screw 15 rotates to make the slider 16 perform axial reciprocating motion, and passes through the axial force sensor 17, the boss 18, the axial spring 19, the collar 20, the high-speed thrust ball bearing outer ring 21, the bearing inner ring, the gear box high-speed shaft 22, the diaphragm coupling 3 in sequence, and finally applied to the simulated tool handle 2.

[0024] The reciprocating screw segment 23 is composed of two thread grooves with the same pitch and opposite rotation directions, and the two ends are connected by a transition curve. When the slider moves to the end of the screw spiral groove, it automatically enters the thread groove of the other rotation direction.

[0025] Figure 3 In the figure, P represents the pitch, B represents the groove width, R represents the transition arc radius, H represents the groove depth, and D represents the major diameter of the thread groove.

[0026] Therefore, the loading test method of the high-speed milling electric spindle for a machining center of the present invention comprises the following steps: Step 1, synchronously coupling loading of radial force, axial force and torque to simulate the cutting conditions of milling cutters with different helix angles and main deflection angles; Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in step 1, the three forces are synchronously alternating and cycled simultaneously to perform 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 to study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermal-mechanical coupling.

[0027] Furthermore, step 1 includes: according to the mathematical model of milling force, synchronously adjusting the magnitude of radial loading load, axial loading load and torque load, the magnitude of radial force and axial force of cylindrical milling cutter is related to the helix angle, and the magnitude of radial force and axial force of end milling cutter is related to the main deflection angle.

[0028] Furthermore, the step 2 includes: radial force, axial force, and torque can be loaded in an alternating cycle individually or synchronously; using fatigue cumulative damage theory, setting cycle period and fatigue load given value, conducting accelerated life tests under different acceleration factors and estimating the service life of the electric spindle.

[0029] Furthermore, in step 3, a ceramic heating ring is designed to heat the simulated tool handle and reduce the cutting heat generated when the metal undergoes elastic and plastic deformation. The rise in tool temperature and the change in cutting force form thermal-mechanical coupling. Monitoring the change in spindle dynamic stiffness can study the influence of thermal-mechanical coupling on the dynamic characteristics of the electric spindle and the thermal fatigue effect.

Claims

1. A loading test method for a high-speed milling electric spindle for a machining center, characterized in that: The steps include: Step 1, synchronously coupling loading of radial force, axial force and torque to simulate the cutting conditions of milling cutters with different helix angles and main deflection angles; Step 2: Based on the synchronous coupling loading of radial force, axial force and torque in step 1, the three forces are synchronously alternating and cycled simultaneously to perform 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 to study the dynamic characteristics and thermal fatigue effect of the electric spindle under thermal-mechanical coupling.

2. A loading test method for a high-speed milling electric spindle for a machining center according to claim 1, characterized in that: The step 1 comprises: according to the mathematical model of milling force, synchronously adjusting the magnitude of radial loading load, axial loading load and torque load, the magnitude of radial force and axial force of cylindrical milling cutter is related to the helix angle, and the magnitude of radial force and axial force of end milling cutter is related to the main deflection angle.

3. The method for loading test of a high-speed milling electric spindle for a machining center according to claim 1, characterized in that: The step 2 includes: radial force, axial force, and torque are individually or synchronously subjected to alternating cyclic loading, and the cycle period and fatigue load given value are set by using fatigue cumulative damage theory to conduct accelerated life tests under different acceleration factors and estimate the service life of the electric spindle.

4. A loading test method for a high-speed milling electric spindle for a machining center according to claim 1, characterized in that: Steps 1 to 3 all require reciprocating motion, which is achieved by a hybrid reciprocating ball screw. The hybrid reciprocating ball screw consists of a reciprocating screw segment and a unidirectional right-hand screw segment. The reciprocating screw segment is two thread grooves with the same pitch and opposite rotation directions, and the two ends are connected by a transition curve.

5. A loading test method for a high-speed milling electric spindle for a machining center according to claim 4, characterized in that: When the slider moves to the end of the spiral groove of the reciprocating screw section, it automatically enters the thread groove of the other rotation direction.

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

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