Special machine tool with clamping self-centering for turning and grinding and machining method of shaft sleeve parts

Abstract

The application discloses a special machine tool with clamping and self-centering for turning and grinding and a machining method of shaft sleeve parts. The machine tool comprises a bed, a main shaft, a sub-main shaft, a power cutter tower, a centering tool movable along a Z axis, a translation driving mechanism and a servo feeding mechanism. The centering tool is provided with upper and lower centering clamping blocks which are symmetrical and openable and closable, and rollers are rotatably installed on clamping surfaces of the upper and lower centering clamping blocks. During clamping, one end of a workpiece is first inserted into the main shaft for pre-tightening, the centering tool is moved to the other end of the workpiece, the upper and lower centering clamping blocks are driven to be closed, four rollers are used to forcibly correct and center the free end of the workpiece, and gravity deflection is overcome; then the sub-main shaft is moved forward along the Z axis, an inner tightener disc of the sub-main shaft is accurately inserted into the other end of the workpiece and is tightly expanded; and the power cutter tower is fed to complete turning and grinding machining. The application solves the problems of difficult insertion of the sub-main shaft and clamping stress deformation of long shaft sleeve workpieces caused by a large length-diameter ratio, and improves production efficiency and product quality.

Description

Technical Field

[0001] This invention belongs to the field of mechanical processing equipment technology, specifically relating to a special machine tool for grinding and compound processing of long shaft sleeve workpieces, and a method for processing shaft sleeve parts using the machine tool. Background Technology

[0002] In the manufacturing of large-scale equipment such as power, transmission, and metallurgy, long shaft sleeves (such as large motor rotor sleeves, transmission sleeves, and long cylindrical support sleeves) are widely used. These parts are typically characterized by a length much greater than their diameter, relatively thin walls, and high requirements for the coaxiality of their inner and outer circles and the perpendicularity of their end faces. Typical machining processes include rough machining, semi-finishing, finishing, and possible grinding.

[0003] Currently, for the machining of the outer diameter of high-precision long shaft sleeve parts, a dual-spindle turning and grinding compound machine tool with coaxial drive at both ends is an effective solution to improve machining accuracy and efficiency. Its basic principle is: the workpiece is clamped at both ends by a relatively movable main spindle and a secondary spindle. The main spindle drives the workpiece to rotate, while the secondary spindle follows and provides auxiliary support. Simultaneously, the power turret feeds to complete the cutting or grinding. This "dual-spindle opposing" clamping method theoretically can simulate the real state of the workpiece's axis of rotation to the greatest extent, reducing clamping errors caused by traditional chuck + center methods.

[0004] However, in actual machining of long shaft sleeve parts, especially during the clamping stage, existing twin-spindle turning and grinding machines have a significant drawback: difficulty in inserting the secondary spindle and problems of clamping stress deformation. A detailed analysis follows: First, clamping interference caused by gravitational deflection: Due to their large axial dimensions and heavy weight, long shaft sleeves inevitably experience downward deflection (sag) at their free end (the other end) under gravity after one end is internally tensioned by the main spindle. In existing technologies, such as the "twin-spindle turning machine for machining slender shafts" disclosed in patent document CN208913144U, although the secondary spindle can move along the Z-axis, it lacks an active correction mechanism for the sagging state of the workpiece's free end. Because the internal tensioning mechanism of the secondary spindle (such as a hydraulic internal tensioning plate) has a limited tensioning stroke, typically only a few millimeters, while the gravitational deflection of the free end of the long shaft sleeve can reach tens of millimeters, even if the secondary spindle moves into position along the axis, its tensioning mandrel is difficult to accurately insert into the inner hole of the workpiece end. Forced insertion may even damage the inner hole of the workpiece or cause equipment malfunction.

[0005] Secondly, there is the risk of clamping stress and workpiece deformation: If precise alignment cannot be achieved, and internal tension is forcibly applied through the sub-spindle, the workpiece will be clamped in a bent state. This unnatural clamping state introduces huge residual stress into the workpiece. When the workpiece is turned or ground to remove the surface material, the residual stress rebalances, which can easily lead to quality problems such as bending and out-of-roundness deviations in the machined workpiece, and in severe cases, may even cause the workpiece to be scrapped.

[0006] In summary, existing turning-grinding composite machining tools, when machining long shaft sleeve-type workpieces, cannot effectively solve the problem of gravity deflection at the free end before workpiece clamping, resulting in difficulties in clamping the sub-spindle, easy occurrence of clamping stress deformation, and limitations in machining accuracy and automation.

[0007] Therefore, there is an urgent need in this field for a special machine tool and method that can actively center and correct the attitude of the free end of the long shaft sleeve workpiece during the clamping process, so as to assist the sub-spindle to complete the clamping smoothly and without stress, and realize the composite processing of high-precision processes such as turning and grinding. Summary of the Invention

[0008] This invention aims to solve the aforementioned problems in the prior art, and provides a turning-grinding composite machining tool and machining method with a self-centering clamping function that can automatically overcome the gravitational disturbance during the clamping of long bushing workpieces, achieve interference-free and precise insertion of the sub-spindle, and effectively eliminate clamping stress. This machine tool is particularly suitable for high-precision machining of large, ultra-long bushing parts through one-time clamping and turning-grinding composite machining.

[0009] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A special turning and grinding machine tool with self-centering clamping includes a bed, a main spindle, a sub-spindle, and a power turret; the main spindle is mounted at one end of the bed and can rotate autonomously; The secondary spindle is arranged coaxially with the primary spindle and can move along the Z-axis. Each end of the primary and secondary spindles is connected to a hydraulic internal tensioning disc, which is connected to a hydraulic drive mechanism. The axis of the primary spindle is parallel to the horizontal plane. The primary spindle is connected to a power drive mechanism that drives its spindle body to rotate, and the secondary spindle is a follower.

[0010] A centering fixture that can move along the Z-axis is slidably connected to the machine bed; the centering fixture and the power turret are arranged between the main spindle and the secondary spindle; The centering fixture includes a pair of upper and lower centering clamps that can be opened and closed. The secondary spindle and the primary spindle are arranged coaxially facing each other. The machine bed is provided with a translation drive mechanism that drives the secondary spindle to move along the Z-axis. The translation drive mechanism includes a first lead screw arranged in the Z-axis direction. One end of the first lead screw is connected to a first servo motor that drives it to rotate. Both ends of the first lead screw are rotatably connected to the machine bed. The first servo motor is fixed to the machine bed and electrically connected to the machine tool controller. The bottom of the housing of the secondary spindle is fixed with a first lead screw nut, which is screwed onto the first lead screw.

[0011] The first servo motor drives the first lead screw to rotate, and the first lead screw drives the sub-spindle to translate through the first lead screw nut, thereby enabling the sub-spindle to move closer to or further away from the workpiece.

[0012] The machine bed is also equipped with a servo feed mechanism that drives the power turret to feed obliquely along the X-axis and feed along the Z-axis. The machine tool controller controls the translation drive mechanism, servo feed mechanism, main spindle, power turret, centering fixture opening and closing, power drive mechanism, and hydraulic drive mechanism.

[0013] When clamping long workpieces, the workpiece is hoisted between the main spindle and the sub-spindle of the machine tool using a gantry crane provided in the workshop. One end of the workpiece is then inserted into the main spindle, positioned between the upper and lower centering blocks. The main spindle pre-clamps one end of the workpiece, and the centering fixture is manually pushed to the other end. After pre-tensioning the workpiece at one end, the upper and lower centering blocks move closer together, clamping the other end of the workpiece between them. This overcomes the deflection caused by gravity at the other end of the workpiece, thus centering it. Finally, the sub-spindle moves closer to the workpiece and inserts it into the workpiece end, then tightens it internally, completing the clamping and centering of both ends of the workpiece. The main spindle then rotates the workpiece, and the power turret feeds the workpiece for turning or grinding. By actively rotating the main spindle and tightening the auxiliary spindle with the hydraulic internal tensioning plate, the coaxial centering clamping of both ends of long shaft workpieces is achieved. The whole machine adopts integrated CNC centralized control, with strong process linkage. It can complete the turning and grinding composite processing of long shaft workpieces in one go, with fewer clamping times and significantly improved processing efficiency and finished product accuracy.

[0014] Furthermore, the centering fixture also includes a first guide rail fixed to the bed, a centering slide block slidably connected to the first guide rail, a first rack and pinion slider that drives the upper centering clamp block to rise and fall, and a second rack and pinion slider that drives the lower centering clamp block to rise and fall; the first rack and pinion slider and the second rack and pinion slider are arranged opposite to each other and both mesh with gears; The first rack and pinion slider and the second rack and pinion slider are slidably connected to the centering slide block, and the gear is rotatably connected to the centering slide block; The second rack and pinion slider is fixed to the end of the telescopic rod of the electric cylinder. The electric cylinder is fixedly connected to the centering slide and electrically connected to the machine tool controller.

[0015] Through the above technical solution, the electric cylinder drives the second rack and pinion slider to move up or down, which in turn drives the gear to rotate. The gear then drives the corresponding first rack and pinion slider to move down or up. The first rack and pinion slider drives the upper centering block to rise and fall, and the second rack and pinion slider drives the lower centering block to rise and fall. This allows the upper and lower centering blocks to move closer to or further apart, thus achieving the centering, clamping, and releasing of the workpiece. The upper and lower centering blocks are powered by the electric cylinder. The machine tool controller monitors the current fluctuations generated when the electric cylinder clamps the workpiece, which allows for a certain degree of control over the clamping degree.

[0016] Furthermore, the upper centering clamp is fixed to one end of the swing arm, and the other end of the swing arm is fixed to the rotating shaft; the rotating shaft is fixedly connected to the piston rod of the rotary cylinder; the rotating shaft is rotatably connected to the centering slide, and the rotary cylinder is fixedly connected to the centering slide; the rotary cylinder is connected to a high-pressure air source through an air pipe, and the machine tool controller controls the operation of the rotary cylinder through a solenoid valve set on the air pipe.

[0017] The lower centering clamp is fixedly connected to the second rack and pinion slider.

[0018] The rotary cylinder can drive the rotating shaft to rotate, the rotating shaft can drive the swing arm to swing, and the swing arm can drive the upper centering clamp to rotate, thereby moving the upper centering clamp to the space area directly above the lower centering clamp, thus avoiding interference during the installation, disassembly and processing of the workpiece.

[0019] Furthermore, the end of the swing arm that is fixed to the rotating shaft is provided with a first limiting surface and a second limiting surface; The first rack and pinion slider is fixed with a first limiting rod and a second limiting rod; When the first limiting surface is abutting against the first limiting top rod, the upper centering clamp and the lower centering clamp are symmetrically arranged vertically.

[0020] When the second limiting surface abuts against the second limiting top rod, the upper centering block moves out of the area directly above the lower centering block. Through the cooperation of the limiting surface and the limiting top rod, the stopping position of the upper centering block can be precisely controlled to ensure the centering effect.

[0021] Furthermore, each of the upper centering clamp and the lower centering clamp is formed with a pair of arc protrusions of equal height, and the two pairs of arc protrusions are symmetrically arranged about the opening and closing center surface. The axes of the main spindle and the secondary spindle are coplanar with the opening and closing center plane; The centers of the two pairs of convex inscribed circles coincide with the axis of the principal axis.

[0022] The above settings ensure that the workpiece is centered and clamped by the upper and lower centering blocks.

[0023] Furthermore, each of the upper and lower centering clamps is rotatably connected to a pair of rollers of equal height, with one side of the outer wall of the rollers extending beyond the arc protrusion; the axis of the rollers is parallel to the axis of the main shaft.

[0024] When clamping the workpiece, four rollers replace the arc protrusions in contact with the workpiece, thus centering it. Compared to the fixed arc protrusion centering structure, the centering fixture using roller clamping changes the sliding friction between the workpiece and the fixture to rolling friction, which can effectively prevent scratches and pressure damage to the outer diameter of shaft-type workpieces, reduce wear on the fixture contact surface, and maintain centering accuracy better over long-term use. At the same time, the rollers can adapt to the workpiece shaft diameter tolerance and slight roundness deviation, ensuring smooth clamping without jamming. There is no hard compressive stress during the clamping process, which is less likely to cause workpiece deformation. Furthermore, the workpiece can be flexibly rotated and indexed for alignment during lathe machining. Its adaptability, machinability, and service life are all superior to the fixed arc protrusion structure.

[0025] Furthermore, the secondary spindle is slidably connected to the first guide rail.

[0026] The sub-spindle and centering fixture share a single guide rail, ensuring consistency between the center height of the sub-spindle and the height of the opening / closing center plane.

[0027] Furthermore, the servo feed mechanism includes a sliding seat, a second guide rail fixed to the bed in the Z direction, and a second lead screw rotatably connected to the bed in the Z direction. The sliding seat is slidably connected to the second guide rail. A second lead screw nut is fixed to the bottom of the sliding seat and screwed onto the second lead screw. One end of the second lead screw is connected to a second servo motor that drives it to rotate. The upper part of the sliding seat is rotatably connected to a third lead screw arranged in the X direction, and the third lead screw is screwed with a third lead screw nut. The power turret and the third lead screw nut are both fixedly connected to the turret seat. The turret seat is slidably connected to a third guide rail arranged in the X direction. The third lead screw is connected to a third servo motor that drives its rotation. The third guide rail and the third servo motor are fixed to the sliding seat. The second servo motor and the third servo motor are both electrically connected to the machine tool controller.

[0028] The third servo motor drives the third lead screw to rotate, and the third lead screw drives the turret base to move along the X-axis through the third lead screw nut. The turret base drives the power turret to move along the X-axis (i.e., move closer to or away from the spindle axis). The power turret performs turning or grinding on the outer diameter of the workpiece.

[0029] The second servo motor drives the second lead screw to rotate, and the second lead screw drives the sliding seat to move along the Z-axis direction through the second lead screw nut. The sliding seat drives the power turret to move in the Z-direction through the third guide rail and the turret seat.

[0030] Furthermore, the Z-axis is set parallel to the horizontal plane, and the X-axis makes an angle of 45° with the horizontal plane.

[0031] The 45° X-axis angled layout decomposes the feed force of the power turret into horizontal and vertical components, resulting in more balanced force distribution and higher turret feed rigidity. It also facilitates the natural sliding of chips without accumulation, reducing the impact of chip residue on workpiece machining accuracy and machine tool guideway wear. The 45° angled structure also optimizes the overall machine space layout, reduces the machine tool footprint, and facilitates workpiece loading, unloading, inspection, and maintenance, making it suitable for the high-precision and high-stability operation requirements of long-shaft workpieces in combined turning and grinding processes.

[0032] A method for machining bushing-type parts using a turning and grinding machine tool with clamping and self-centering features includes the following steps: Step 1: Insert one end of the workpiece into the main spindle and pre-tension the main spindle to the workpiece end; Step 2: Push the centering fixture to the other end of the workpiece. After the main spindle pre-tensions one end of the workpiece, the upper and lower centering clamps move closer to each other, clamping the other end of the workpiece between the upper and lower centering clamps, thus centering the other end of the workpiece. Step 3: After the secondary spindle approaches and inserts into the end of the workpiece, it is internally tightened to complete the clamping and centering of both ends of the workpiece. Step 4: Release the centering fixture and return it to the safe area; Step 5: The main spindle drives the workpiece to rotate, and the power turret feeds the workpiece to perform turning or grinding.

[0033] The outstanding effects of this invention are: Compared with existing technologies, this invention introduces a centering fixture that can move along the Z-axis and has an active opening and closing function. Before the sub-spindle is inserted, it precisely radially centers the free end of the long shaft sleeve workpiece, actively counteracting the deflection deformation caused by its own weight. This ensures that the inner tensioning disc of the sub-spindle can be easily and without collision inserted into the inner hole of the workpiece, fundamentally solving the problem of difficult automatic clamping of long shaft workpieces on twin-spindle machine tools.

[0034] Since the two ends of the workpiece have been aligned coaxially before clamping, the clamping action of the sub-spindle does not introduce additional bending stress. The workpiece is clamped in a natural, relaxed state, and will not deform due to the release of residual stress after machining. Especially for high-precision workpieces that require subsequent grinding, stress-free clamping is a key prerequisite for ensuring the roundness, cylindricity, and straightness of the finished product.

[0035] With a power turret that combines oblique and axial feed, this machine tool can perform multiple processes such as rough turning, finish turning, and external cylindrical grinding after the workpiece is clamped without stress. This avoids the secondary clamping error that requires removing the workpiece from the turning machine and then putting it back on the grinding machine in traditional processes, and greatly improves processing efficiency and product consistency.

[0036] By employing a rotatable roller structure as the contact element for the centering clamp, traditional sliding friction is transformed into rolling friction, effectively preventing scratches or indentations on the outer surface of the long shaft sleeve workpiece (especially the surface after precision machining) during the centering process. Simultaneously, rolling contact offers better adaptability to workpiece shaft diameter tolerances, resulting in a smoother and more reliable centering process. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of the present invention with the casing removed; Figure 3 This is a top view of the main structure of the present invention; Figure 4 This is a cross-sectional view of the invention from the left view direction; Figure 5 This is a schematic diagram of the centering fixture of the present invention; Figure 6 This is a schematic diagram of another state of the centering fixture; Figure 7 This is a schematic diagram of the servo feed mechanism and power turret of the present invention.

[0038] Reference numerals: 1. Bed; 2. Main spindle; 3. Sub-spindle; 4. Power turret; 5. Centering fixture; 6. Translation drive mechanism; 7. Servo feed mechanism; 31. Shell; 51. Upper centering clamp; 52. Lower centering clamp; 53. First guide rail; 54. Centering slide; 55. First rack and pinion slider; 56. Second rack and pinion slider; 57. Gear; 58. Electric cylinder; 59. Swing arm; 510. Rotating shaft; 511. Rotary cylinder; 512. First limiting rod; 513. Second limiting rod; 514. Roller; 500. Opening / closing center surface; 501. Arc protrusion; 502. First limiting surface; 503. Second limiting surface; 61. First lead screw; 62. First lead screw nut; 71. Sliding seat; 72. Second guide rail; 73. Second lead screw; 74. Second lead screw nut; 75. Third lead screw; 76. Third lead screw nut; 77. Turret seat; 78. Third guide rail; 79. Third servo motor. Detailed Implementation

[0039] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0040] The following is for reference Figures 1 to 7 The present invention will be described as follows: Reference Figures 1 to 4 A special turning and grinding machine tool with self-centering clamping mechanism includes a bed 1, a main spindle 2, and a sub-spindle 3. The bed 1 is a single cast iron component with a mounting reference surface machined on its upper surface. The housing of the main spindle 2 is bolted to the upper left end of the bed 1. The main spindle 2 is connected to a power drive mechanism and a hydraulic internal tensioning plate. The power drive mechanism drives the spindle body of the main spindle 2 to rotate via a belt or direct drive. The hydraulic internal tensioning plate is supplied with oil by an external hydraulic station, enabling radial tensioning of the inner hole at the left end of the workpiece. The axis of the main spindle 2 is parallel to the horizontal plane and coincides with the longitudinal centerline of the bed 1. The sub-spindle 3 is arranged coaxially with the main spindle 2 and is located at the right end of the bed 1. The sub-spindle 3 itself does not have an active drive motor; its internal hydraulic internal tensioning plate is also controlled by a hydraulic station, enabling tensioning of the inner hole at the right end of the workpiece. During machining, the sub-spindle 3 passively rotates with the workpiece, acting as a follower.

[0041] The machine bed 1 is equipped with a translation drive mechanism 6 for driving the sub-spindle 3 to move along the Z-axis (horizontal longitudinal direction). This mechanism includes a first lead screw 61, a first lead screw nut 62, a first servo motor, and a coupling, all positioned along the Z-axis. The two ends of the first lead screw 61 are rotatably connected to the machine bed 1 via bearing seats. One end of the first lead screw 61 is connected to the output shaft of the first servo motor via a coupling. The first servo motor is fixed to the right end face of the machine bed 1 and electrically connected to the machine tool controller. The first lead screw nut 62, fixedly connected to the bottom of the sub-spindle 3 housing 31, is threadedly engaged with the first lead screw 61. When the first servo motor receives a command from the controller to rotate, the first lead screw 61 rotates, driving the first lead screw nut 62 to move linearly along the Z-axis, thereby precisely moving the sub-spindle 3. By controlling the direction and speed of the first servo motor, the sub-spindle 3 can be moved closer to or further from the workpiece, and its speed can be varied.

[0042] A centering fixture 5 is positioned between the main spindle 2 and the secondary spindle 3 to center the free end of the workpiece before the secondary spindle 3 inserts into the workpiece. Two parallel first guide rails 53 extending along the Z-axis are fixed on the bed 1. The centering fixture 5 includes a centering slide 54, the bottom of which has a slider that slides along the first guide rails 53, allowing the entire centering fixture 5 to be manually moved along the first guide rails 53. Simultaneously, the bottom of the housing 31 of the secondary spindle 3 is also slidably connected to the same set of first guide rails 53, allowing the secondary spindle 3 and the centering fixture 5 to share guide rails and ensuring their center heights are consistent. The centering fixture 5, positioned between the main spindle 2 and the secondary spindle 3, is used to center the free end of the workpiece during clamping.

[0043] like Figure 5 As shown, a first rack slider 55 and a second rack slider 56 are slidably connected vertically on a centering slide 54. A gear 57 is provided between the first rack slider 55 and the second rack slider 56, rotatably connected to the centering slide 54 and meshing with both the first rack slider 55 and the second rack slider 56. The lower end of the second rack slider 56 is fixedly connected to the end of the telescopic rod of an electric cylinder 58. The cylinder body of the electric cylinder 58 is fixed on the centering slide 54. The electric cylinder 58 is electrically connected to the machine tool controller and has a built-in position sensor and current monitoring function. When the electric cylinder 58 pushes the second rack slider 56 upward, the first rack slider 55 moves downward through the transmission of the gear 57; when the electric cylinder 58 retracts, the second rack slider 56 moves downward and the first rack slider 55 moves upward.

[0044] The upper centering block 51 and the lower centering block 52 are respectively connected to the two rack and pinion sliders. Specifically, the lower centering block 52 is directly fixed to the upper end of the second rack and pinion slider 56 and rises and falls with the rise and fall of the second rack and pinion slider 56. The upper centering block 51 is connected to the first rack and pinion slider 55 through a flipping mechanism: the upper centering block 51 is fixed to one end of a swing arm 59, the other end of the swing arm 59 is fixed to a rotating shaft 510, and the rotating shaft 510 is rotatably connected to the first rack and pinion slider 55 through a bearing; one end of the rotating shaft 510 is fixedly connected to the piston rod of a rotary cylinder 511, and the cylinder body of the rotary cylinder 511 is also fixed to the first rack and pinion slider 55. The rotary cylinder 511 is connected to a high-pressure air source through an air pipe, and a solenoid valve is installed on the pipe, which is controlled by the machine tool controller. When the piston rod of the rotary cylinder 511 rotates, it drives the rotating shaft 510 and the swing arm 59 to swing, thereby switching the upper centering block 51 between the working position and the clearance position. Since both the rotating shaft 510 and the rotary cylinder 511 are mounted on the first rack and pinion slider 55, when the first rack and pinion slider 55 moves up and down, the entire flipping mechanism, together with the centering clamp 51 on it, rises and falls together, ensuring the coordination of the clamping action.

[0045] To precisely control the stopping position of the upper centering block 51, a first limiting rod 512 and a second limiting rod 513 are fixed on the first rack and pinion slider 55. The end of the swing arm 59 fixed to the rotating shaft 510 has a first limiting surface 502 and a second limiting surface 503. When the rotary cylinder 511 drives the swing arm 59 to rotate until the first limiting surface 502 is against the first limiting rod 512, the upper centering block 51 is positioned directly above the lower centering block 52, symmetrically positioned in the working position. When the rotary cylinder 511 drives the swing arm 59 to rotate in the opposite direction until the second limiting surface 503 is against the second limiting rod 513, the upper centering block 51 is lifted and rotated out of the area directly above the lower centering block 52, in a clearance position, facilitating the loading and unloading of workpieces.

[0046] On the opposing surfaces of the upper centering block 51 and the lower centering block 52, two arcuate protrusions 501 of equal height are formed. The two upper arcuate protrusions 501 and the two lower arcuate protrusions 501 are symmetrical about the opening and closing center plane 500. The axes of the main spindle 2 and the auxiliary spindle 3 are coplanar with the opening and closing center plane 500. When the electric cylinder 58 drives the upper and lower centering blocks to close, the center of the inscribed circle of the four arcuate protrusions 501 coincides with the axis of the main spindle 2, thereby forcibly correcting the center of the workpiece to the spindle axis.

[0047] As a further improvement, rollers 514 are rotatably mounted at each arc protrusion 501 position of the upper centering clamp 51 and the lower centering clamp 52. The rollers 514 are made of bearing steel with a surface hardening hardness of HRC55-60 and a cylindricity ≤0.005mm. The axis of the rollers 514 is parallel to the axis of the main spindle 2, and the outer surface of the rollers 514 is 3mm to 5mm higher than the surface of the arc protrusions 501, ensuring that only the rollers 514 contact the outer diameter of the workpiece when clamping it. When the electric cylinder 58 drives the upper and lower centering clamps to close, the four rollers 514 simultaneously contact the outer surface of the workpiece from both the upper and lower sides. Due to the downward droop of the workpiece's free end, the two lower rollers 514 contact the workpiece first. As the clamps continue to close, the two upper rollers 514 push the workpiece upward until the outer diameter of the workpiece is constrained by all four rollers 514, and the workpiece center is forcibly corrected to coincide with the spindle axis. Throughout the centering process, roller 514 maintains rolling contact with the workpiece, preventing scratches on the workpiece surface and adapting to the roundness error and diameter tolerance of the workpiece's outer diameter. During subsequent rotational machining of the workpiece, roller 514 passively rotates without interfering with the workpiece's rotation.

[0048] like Figure 4 and Figure 7As shown, a servo feed mechanism is arranged at the middle-rear part of the bed 1. Two parallel second guide rails are fixed on the bed 1, and the second guide rails are arranged along the Z-axis direction. The second lead screw is rotatably connected to the bed 1 through a bearing seat and is parallel to the second guide rails, and one end of the second lead screw is connected with a second servo motor. A sliding block is fixed at the bottom of the sliding seat 71 to be in sliding fit with the second guide rails, and a second lead screw nut is fixed at the bottom of the sliding seat at the same time, and the second lead screw nut is in threaded fit with the second lead screw. The second servo motor drives the second lead screw to rotate, so as to drive the sliding seat 71 to move along the Z-axis direction. Two parallel third guide rails and a third servo motor 79 are fixed on the sliding seat 71. The third lead screw is arranged at a 45° oblique angle relative to the X-axis, two ends of the third lead screw are rotatably connected to the sliding seat 71 through bearings, and one end of the third lead screw is connected with the output shaft of the third servo motor 79 through a coupling. A sliding block is fixed at the bottom of the tool post seat 77 to be in sliding fit with the third guide rails, and a third lead screw nut is fixed at the bottom of the tool post seat 77 at the same time, and the third lead screw nut is in threaded fit with the third lead screw. The power turret 4 is fixed on the tool post seat 77 by bolts. The third servo motor 79 drives the third lead screw to rotate, so as to drive the tool post seat 77 and the power turret 4 to move along the X-axis (45° oblique direction), that is, to approach or move away from the axis of the main shaft. Both the second servo motor and the third servo motor 79 are electrically connected to the machine tool controller, and can realize linkage. The power turret 4 is a general 12-station or 8-station power turret, which can be equipped with turning tools, boring tools, rolling heads and grinding spindles to realize composite machining of turning and grinding. The 45° oblique layout decomposes the feed force into a horizontal component force and a vertical component force, with balanced stress, smooth chip removal, and optimized space layout.

[0049] The machine tool controller (such as Siemens 828D or FANUC 0i-TF system) is connected through cables to actuators such as the first servo motor, the second servo motor, the third servo motor 79, the power drive mechanism of the front spindle 2, the solenoid valve of the hydraulic station, the servo driver of the electric cylinder 58, and the solenoid valve of the rotary cylinder 511, and receives signals from various sensors. A machining program is preset in the controller to control the actions of each component in sequence.

[0050] The method for machining a long shaft sleeve workpiece using the above-mentioned machine tool is described in detail below. Taking a long shaft sleeve workpiece with a length-to-diameter ratio of about 8 as an example, the material is 42CrMo, the total length is 2200mm, the outer diameter is 270mm, and the inner hole is 250mm, and composite machining of turning and grinding is performed.

[0051] The first step is loading and pre-tensioning of the left end. Use a crane with a nylon sling to lift the workpiece horizontally, align the left end of the workpiece with the hydraulic internal expansion chuck of the front spindle and fully insert it. The operator presses the "left end pre-clamping" button, the controller controls the solenoid valve to make the hydraulic internal expansion chuck of the front spindle 2 slightly expand, the expansion force is set to 30% of the rated force, and only the left end of the workpiece is fixed.

[0052] The second step is right-end centering. After the left end of the workpiece is pre-tensioned, the right end deflects downward due to its own weight. The operator manually pushes the centering fixture 5 along the first guide rail 53 to the vicinity of the right end of the workpiece, about 80mm away from the right end face, confirming that the upper centering clamping block 51 is in the working position with the first limit surface 502 against the first limit top rod 512. Pressing the "centering and clamping" button activates the controller to start the electric cylinder 58. The telescopic rod of the electric cylinder 58 extends, pushing the second rack slider 56 upward, which in turn drives the first rack slider 55 downward through the gear 57. The upper centering clamping block 51 descends, and the lower centering clamping block 52 rises. The four rollers 514 gradually contact and clamp the outer circle of the right end of the workpiece. The controller monitors the drive current of the electric cylinder 58. When the current reaches the set threshold (corresponding to a clamping force of about 200N), the electric cylinder 58 stops and self-locks. At this time, the center of the right end of the workpiece is forcibly corrected to coincide with the axis of the main spindle 2, and the deflection is overcome.

[0053] The third step involves inserting and tightening the secondary spindle. The controller sends a command to the first servo motor, driving the first lead screw 61 to rotate, which in turn moves the secondary spindle 3 slowly to the left along the first guide rail 53 (at a speed of 500 mm / min). Since the right end of the workpiece has been precisely aligned by the centering fixture 5, the hydraulic inner tensioning disc (in its retracted state) of the secondary spindle 3 enters the inner hole at the right end of the workpiece without obstruction. The secondary spindle 3 continues to move to the left until the end face contacts the trigger limit switch. The controller stops the first servo motor and activates the hydraulic tensioning solenoid valve of the secondary spindle 3, causing the inner tensioning disc to tighten to 80% of its rated force. At the same time, the tensioning force of the main spindle 2 also increases to 80%. At this point, the workpiece is clamped without stress at both ends.

[0054] The fourth step is to reset the centering fixture. The controller commands the electric cylinder 58 to retract, the upper and lower centering blocks to move away from each other, and the roller 514 to release the workpiece. Then, the controller opens the solenoid valve of the rotary cylinder 511, and the high-pressure gas drives the rotary cylinder 511 to move. The rotating shaft 510 rotates, causing the swing arm 59 to flip upward until the second limit surface 503 abuts against the second limit rod 513, and the upper centering block 51 is raised to the avoidance position. The operator then pushes the entire centering fixture 5 back to its original position to the right.

[0055] Step 5: Combined turning and grinding machining. The controller activates the power drive mechanism of spindle 2, accelerating the spindle to 300 rpm (roughing speed). The 95° roughing tool on the power turret 4 is positioned at the starting point on the right end of the workpiece, and performs Z-axis reciprocating feed at 0.3 mm / r and 2.5 mm depth of cut to complete the rough turning of the outer diameter. After rough turning, the finishing tool is automatically switched on, and the spindle speed is increased to 500 rpm. Finish turning is performed with a feed rate of 0.1 mm / r and a depth of cut of 0.3 mm to φ269.5 mm, Ra3.2. After finishing turning, the CBN grinding wheel is automatically switched on to the grinding spindle (12000 rpm), and the spindle speed is adjusted to 60 rpm. Plunge grinding is used, with a depth of cut of 0.005 mm per pass, and two reciprocating finish grinding passes are performed. The final outer diameter is φ269.0 ± 0.01 mm, Ra0.4.

[0056] Step 6, unloading. The controller stops the spindle rotation and issues commands sequentially: sub-spindle 3 releases tension, main spindle 2 releases tension. The translation drive mechanism 6 drives sub-spindle 3 to move 500mm to the right. The operator uses a gantry crane to lift the workpiece horizontally, completing one processing cycle.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications assumed above should also be considered within the scope of protection of the present invention.

Claims

1. A special machine tool for turning and grinding with self-centering clamping, comprising a bed (1), a main spindle (2), a secondary spindle (3), and a power turret (4); characterized in that: The main spindle (2) is installed at one end of the bed (1) and can rotate autonomously; The secondary spindle (3) is arranged coaxially opposite to the primary spindle (2), and the secondary spindle (3) can move along the Z-axis. A centering fixture (5) that can move along the Z-axis is slidably connected to the bed (1); the centering fixture (5) and the power turret (4) are arranged between the main spindle (2) and the secondary spindle (3); The centering fixture (5) includes a pair of openable and closable upper centering clamps (51) and lower centering clamps (52). The secondary spindle (3) is arranged coaxially with the primary spindle (2) facing each other, and the bed (1) is provided with a translation drive mechanism (6) that drives the secondary spindle (3) to move along the Z-axis. The bed (1) is also provided with a servo feed mechanism (7) that drives the power turret (4) to feed obliquely along the X-axis and feed along the Z-axis. The centering fixture (5) also includes a first guide rail (53) fixed on the bed (1), a centering slide (54) slidably connected to the first guide rail (53), a first rack slider (55) that drives the upper centering clamp (51) to rise and fall, and a second rack slider (56) that drives the lower centering clamp (52) to rise and fall; the first rack slider (55) and the second rack slider (56) are arranged opposite to each other and both mesh with the gear (57); The first rack and pinion slider (55) and the second rack and pinion slider (56) are slidably connected to the centering slide (54), and the gear (57) is rotatably connected to the centering slide (54); The second rack and pinion slider (56) is fixed to the end of the telescopic rod of the electric cylinder (58), and the electric cylinder (58) is fixedly connected to the centering slide (54); The upper centering clamp (51) is fixed to one end of the swing arm (59), and the other end of the swing arm (59) is fixed to the rotating shaft (510); the rotating shaft (510) is fixedly connected to the piston rod of the rotary cylinder (511); The lower centering clamp (52) is fixedly connected to the second rack and pinion slider (56); The swing arm (59) is fixed to the rotating shaft (510) at one end and is provided with a first limiting surface (502) and a second limiting surface (503). The first rack slider (55) is fixed with a first limiting rod (512) and a second limiting rod (513); When the first limiting surface (502) abuts against the first limiting top rod (512), the upper centering clamp (51) and the lower centering clamp (52) are symmetrically arranged vertically. When the second limiting surface (503) abuts against the second limiting top rod (513), the upper centering block (51) moves out of the area directly above the lower centering block (52).

2. The turning and grinding machine tool with self-centering clamping as described in claim 1, characterized in that: The upper centering clamp (51) and the lower centering clamp (52) are each formed with a pair of arc protrusions (501) of equal height, and the two pairs of arc protrusions (501) are symmetrically arranged about the opening and closing center plane (500). The axes of the main spindle (2) and the secondary spindle (3) are coplanar with the opening and closing center plane (500); The center of the inscribed circle of the two pairs of circular arc protrusions (501) coincides with the axis of the positive principal axis (2).

3. The turning and grinding machine tool with self-centering clamping as described in claim 2, characterized in that: The upper centering clamp (51) and the lower centering clamp (52) are each rotatably connected to a pair of rollers (514) arranged at the same height. One side of the outer wall of the roller (514) extends out of the arc protrusion (501). The axis of the roller (514) is parallel to the axis of the main shaft (2).

4. The turning and grinding machine tool with self-centering clamping as described in claim 1, characterized in that: The secondary spindle (3) is slidably connected to the first guide rail (53).

5. The turning and grinding machine tool with self-centering clamping as described in claim 1, characterized in that: The servo feed mechanism (7) includes a sliding seat (71), a second guide rail (72) fixed on the bed (1) in the Z direction, and a second lead screw (73) rotatably connected to the bed (1) in the Z direction. The sliding seat (71) is slidably connected to the second guide rail (72). A second lead screw nut (74) is fixed at the bottom of the sliding seat (71), and the second lead screw nut (74) is screwed onto the second lead screw (73). One end of the second lead screw (73) is connected to a second servo motor that drives it to rotate. The upper part of the sliding seat (71) is rotatably connected to a third lead screw (75) arranged in the X direction. The third lead screw (75) is screwed with a third lead screw nut (76). The power turret (4) and the third lead screw nut (76) are both fixedly connected to the turret seat (77). The turret seat (77) is slidably connected to a third guide rail (78) arranged in the X direction. The third lead screw (75) is connected to a third servo motor (79) that drives it to rotate. The third guide rail (78) and the third servo motor (79) are fixed on the sliding seat (71).

6. The turning and grinding machine tool with self-centering clamping as described in claim 5, characterized in that: The Z-axis is set parallel to the horizontal plane, and the X-axis makes an angle of 45° with the horizontal plane.

7. A method for machining bushing-type parts using a turning and grinding machine tool with self-centering clamping as described in any one of claims 1-6, characterized in that: Includes the following steps: Step 1: Insert one end of the workpiece into the main spindle (2) and pre-tighten the main spindle (2) on one end of the workpiece; Step 2: Push the centering fixture (5) to the other end of the workpiece. After the main spindle (2) pre-tensions one end of the workpiece, the upper centering clamp (51) and the lower centering clamp (52) move closer to each other, clamping the other end of the workpiece between the upper centering clamp (51) and the lower centering clamp (52), so that the center of the other end of the workpiece is positioned. Step 3: The secondary spindle (3) moves closer to the workpiece and inserts into the end of the workpiece, then internally tightens to complete the clamping and centering of both ends of the workpiece; Step 4: Release the centering fixture (5) and return it to the safe area; Step 5: The main spindle (2) drives the workpiece to rotate, and the power turret (4) feeds the workpiece to perform turning or grinding.

Images