Vibration damping method for long workpieces

Abstract

[Problem] The purpose of the present invention is to provide a vibration-control machining method effective in suppressing the occurrence of chatter vibrations in a long workpiece when the workpiece is subjected to turning machining. [Solution] The present invention is characterized in that a long workpiece is turned with both end sections of the long workpiece each being held, and a torsional load is applied to the long workpiece when an outer circumferential section of the long workpiece is subjected to turning machining by means of a turning tool.

Description

[Technical Field]

[0001] The present invention relates to a machining method using vibration damping to suppress the occurrence of chatter vibrations when turning a long workpiece. [Background technology]

[0002] When a relatively long workpiece is turned using a machine tool such as a lathe, the workpiece may vibrate, causing chattering, which may prevent the desired machining. In order to suppress the occurrence of chatter vibrations during turning of such a workpiece, the following methods have been conventionally adopted. (1) A method of monitoring the relationship between the rotational speed of the spindle and the amplitude and period of fluctuation of the workpiece, and controlling the machining conditions (Patent Documents 1 and 2). (2) The workpiece is held midway by a touch-prevention device, or two cutting tools are positioned opposite the workpiece (Patent Document 3). (3) Improving the turning tool shape, for example, by reducing the nose R of the insert. (4) The applicant has previously proposed a method for applying a tensile axial force to a long workpiece while controlling the axial force (Patent Document 4), but the present invention makes it possible to apply a vibration damping effect based on new findings. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-70138 [Patent Document 2] Japanese Patent Application Publication No. 2012-91283 [Patent Document 3] Japan Special Publication No. 2012-525983 [Patent Document 4] Japanese Patent Application Publication No. 2012-196748 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a vibration-damping method that is effective in suppressing chatter vibrations from occurring in a workpiece during turning of a long workpiece. [Means for solving the problem]

[0005] The vibration-damping processing method for a long workpiece according to the present invention is characterized in that the long workpiece is rotated while holding both ends of the long workpiece, and a torsional load is applied to the long workpiece when the outer periphery of the long workpiece is turned with a turning tool.

[0006] In the present invention, the term "long workpiece" is particularly effective when the ratio of the length L of the workpiece to the outer diameter D is L / D=5 or more.

[0007] The state in which both ends of a long workpiece are held refers not only to the case where both ends of the long workpiece are held by a rotation-controlled spindle, but also to the case where one end of the workpiece is held by a chuck on a rotation-controlled spindle while the other end is held by a core stock or various auxiliary tools, in which a rotational resistance force is applied to the core stock, etc., and a torsional force (torsional load) is applied to the long workpiece in some way during turning.

[0008] A typical embodiment of the present invention is one that comprises a first spindle and a second spindle arranged opposite each other on the same axis, and a torsional load is applied to the long workpiece by giving different rotation speed commands to the first spindle and the second spindle, which respectively hold both ends of the long workpiece. In this way, when a long workpiece is double-supported and machined by the first and second spindles, if an NC control device or the like issues different rotation speed commands for each, the rotation of the long workpiece is controlled in a state in which a torsional load occurs between the first and second spindles due to the difference in rotation speed.

[0009] In this case, when different rotation speed commands are given to the first spindle and the second spindle, the rotation speed of one or both of the rotation speed commands of the first spindle and the second spindle may be varied, and further, the first spindle and the second spindle may be controlled to move in the approaching direction and the separating direction, and a tensile force or a compressive force may be applied to the long workpiece. By variably adjusting the tensile or compressive force applied to the long workpiece depending on the length and diameter of the long workpiece, or the cutting edge shape of the tool, the apparent rigidity of the long workpiece is improved, which acts to suppress the occurrence of chatter vibrations. [Effects of the Invention]

[0010] The present invention applies a torsional external force (torsional load) to a long workpiece when it is turned from both ends, thereby temporarily improving the rigidity of the long workpiece and temporarily changing the direction of the turning load applied by the turning tool, thereby easily suppressing chatter vibrations in the long workpiece. [Brief explanation of the drawings]

[0011] [Figure 1] This shows how a long workpiece is supported on both sides during machining. [Figure 2] (a) shows a frequency analysis chart when turning a long workpiece without applying a torsional load, and (b) shows a frequency analysis chart when turning a long workpiece with a torsional load. DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 shows an example of double-supported machining using an NC-controlled two-spindle opposed lathe, in which one end of a long workpiece W is chucked by a first spindle 11 and the other end is held by a second spindle 12. The long workpiece W was made of S45C, had an outer diameter of 11 to 13 mm, and was 300 mm long. The gripping distance of each spindle was set to 20 mm. The turning conditions were a depth of cut t of 0.3 mm and a feed rate f of 0.15 mm / rev.

[0013] First, a rotation speed command of 1800 / min was set for the first spindle, and the second spindle was allowed to follow in a free state. When turning was performed using turning tool 13 under these conditions, chatter marks occurred in the center of the workpiece, and frequency analysis revealed that chatter vibrations occurred around 1500 Hz, as shown in the chart in Figure 2(a).

[0014] Next, a rotation speed command of 1800 / min was set for the first spindle and a different rotation speed command of 1750 / min was set for the second spindle, so that a torsional load was applied to the long workpiece, and similar turning processing was performed with the turning tool 13. By doing this, the long workpiece can be turned normally without chattering, and the frequency analysis results are shown in Figure 2(b). It can be seen that the chatter vibration around 1500 Hz that occurred in Figure 2(a) has disappeared.

[0015] The comparative experiments shown above revealed that when a long workpiece is turned while being subjected to a torsional external force, a vibration damping effect is produced in the long workpiece, making it possible to suppress the occurrence of chatter vibrations. Here, the magnitude of the torsional load applied to the long workpiece may be set appropriately according to the length and outer diameter of the workpiece. Furthermore, when performing turning processing while holding a long workpiece with the first and second spindles, it is possible to adjust the magnitude of the torsional load according to the turning state of the long workpiece by not only setting a difference between the rotation speed commands for the first and second spindles but also varying the rotation speed command for one or both spindles within a predetermined range between the low-speed side and the high-speed side. Furthermore, applying a tensile or compressive force along the axial direction of the long workpiece in accordance with the torsional load can temporarily improve the rigidity of the long workpiece, suppressing chatter vibrations, and the tensile or compressive force can also be adjusted in accordance with thermal fluctuations of the long workpiece. [Industrial Applicability]

[0016] The present invention can be widely applied to turning long workpieces. [Explanation of symbols]

[0017] 11 1st spindle 12 Second kind of axis 13 Turning tools

Claims

1. A vibration-damping method for a long workpiece, characterized in that a torsional load is applied to the long workpiece when the long workpiece is rotated while holding both ends of the long workpiece, and the outer periphery of the long workpiece is turned with a turning tool.

2. 2. A vibration-damping method for machining a long workpiece according to claim 1, characterized in that the method comprises a first spindle and a second spindle arranged opposite each other on the same axis, and a torsional load is applied to the long workpiece by giving different rotation speed commands to the first spindle and the second spindle, which respectively hold both ends of the long workpiece.

3. 3. The vibration-damping machining method for a long workpiece according to claim 2, wherein when different rotation speed commands are given to the first spindle and the second spindle, the rotation speed of the rotation speed command for one or both of the first spindle and the second spindle is varied.

4. 4. The vibration-damping method for machining a long workpiece according to claim 2 or 3, wherein the first spindle and the second spindle are controlled to move in a direction approaching and a direction separating, and a tensile force or a compressive force is applied to the long workpiece.

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