Deep hole processing method

Abstract

To provide a deep hole processing method which moves a cantilevered drill tool along an axis and presses a tip thereof against a work-piece thereby processing a deep hole, and in which bending during processing is detected, and this bending can be quantified and reflected in drill tool control.SOLUTION: Vibration displacement of a drill toll at a rear position along an axis from an opening is measured by a non-contact displacement sensor, frequency analysis of vibration displacement is performed, and movement of the drill tool is controlled from contributions to vibration displacement of a prescribed frequency on a side with a lower frequency than 200 Hz.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a deep hole drilling method in which a cantilevered drill tool is moved along its axis and the tip is pressed against a workpiece to drill a deep hole. [Background technology]

[0002] In deep hole drilling, a cantilevered drill tool is moved along its axis and its tip is pressed against the workpiece to create a borehole (deep hole). Since the bending of the borehole due to axial runout of the drill tool increases the further it goes, it is important to control the straightness of the drill tool.

[0003] For example, Patent Document 1 describes a method for drilling deep holes using a boring bar with a cutter head at the tip, known as the BTA (Boring & Trepanning Association) method, in which cutting oil is supplied between the bar and the borehole and chips are discharged into a chip receiver through a passage hole inside the boring bar. This method discloses a method in which a reflector is provided inside the tip of the boring bar, a laser beam is applied from the rear, the amount of bending displacement of the head is detected by an optical position detector, and the protrusion and retraction of a guide pad are adjusted to correct the bending of the borehole.

[0004] Similarly, Patent Document 2 discloses a method for controlling the boring bar so as to cancel out the strain in the BTA system, in which a strain detector consisting of a strain gauge attached to the outer periphery of a tool holder disposed on the opposite side along the axis of a cutter head including a cutting blade and a guide pad detects the strain of the boring bar generated in the holding portion, and controls the boring bar to cancel out the strain.The boring bar's advancing direction is controlled by pushing and pulling the guide pad away from the cutter head to displace it. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 03-26412 [Patent Document 2] Japanese Utility Model Application Publication No. 06-71047 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, in deep hole drilling, straight-line control of the drill tool is important, but to achieve this, it is necessary to detect bending during drilling, quantify this bending, and reflect it in the control of the drill tool.However, it is difficult to quantify bending of measurement parts such as the tool holder located on the opposite side of the tip of the drill tool because the position of the tool holder relative to the tip of the drill tool changes during drilling, changing the fulcrum.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a deep hole drilling method in which a cantilevered drill tool is moved along its axis and the tip is pressed against the workpiece to drill a deep hole, in which bending during drilling can be detected, this bending can be quantified, and the amount of bending can be reflected in the control of the drill tool. [Means for solving the problem]

[0008] The deep hole drilling method of the present invention is a deep hole drilling method in which a cantilevered drill tool is moved forward along its axis and its tip is pressed against the workpiece to drill a borehole through an opening, and is characterized in that the vibration displacement of the drill tool at a rear position along the axis from the opening is measured with a non-contact displacement sensor, the vibration displacement is frequency analyzed, and the movement of the drill tool is controlled based on the contribution to the vibration displacement of a predetermined frequency lower than 200 Hz.

[0009] According to this feature, even if the measurement position along the axis of the drill tool changes during machining, the bending can be quantified and this can be reflected in the control of the drill tool. [Brief explanation of the drawings]

[0010] [Figure 1]1 is a side cross-sectional view of a drill tool and a workpiece used in an example of a deep hole drilling method according to the present invention. [Figure 2] FIG. 2 is a front view of the head body of the drill tool. [Figure 3] 10 is a graph showing the relationship between hole bending and the integrated value of vibration displacement components in (a) the vertical direction and (b) the horizontal direction. DETAILED DESCRIPTION OF THE INVENTION

[0011] A deep hole drilling method as one embodiment of the present invention will be described with reference to FIGS.

[0012] As shown in Figure 1, a processing device 10 is used for deep hole drilling in this embodiment. The processing device 10 includes a drill tool 1 for cutting a workpiece 20, a chuck unit 2 that holds the workpiece 20 and rotates it about an axis A, and a support unit 3 connected to a feed mechanism (not shown) that moves the drill tool 1 forward (to the left in the figure) along the axis A. The workpiece 20 is a generally rod-shaped body, and one end of the workpiece 20 is held by the chuck unit 2 and the other end is supported by the support unit 3, so that the workpiece 20 is positioned with its longitudinal direction aligned with the axis A and rotated about the axis A.

[0013] The drill tool 1 includes a round bar-shaped head body 12 that cuts the workpiece 20, and a tube 11 that cantilever-supports the head body 12 by attaching it to its tip. The drill tool 1 is supported by a support part 3 at the base side of the tube 11 and can be advanced forward. The head body 12 at its tip end is pressed against the workpiece 20 to drill an opening 25a in the workpiece, and further drills a borehole 25 from the opening 25a.

[0014] Here, the drill tool 1 is of the BTA type and has a mechanism for discharging chips from inside the tube 11. Specifically, it is equipped with a seal 21 that abuts against the other end of the rotating workpiece 20 to seal off the outflow of cutting oil, an oil pressure head 22 that forms a passage for sending cutting oil from an opening 25a of the workpiece 20 through the seal 21 to between the inner periphery of the borehole 25 and the outer periphery of the drill tool 1, and a guide bush 23 that guides the tube 11 inside the oil pressure head 22.

[0015] Referring also to FIG. 2 , the head body 12 has a plurality of cutting edges 13 (13a, 13b, 13c) at its forward end, with one cutting edge 13a attached to its outer periphery. That is, the cutting edges 13 are brought into contact with the workpiece 20 to cut the front and periphery, thereby widening the borehole forward. The head body 12 also has a plurality of guide pads 15 on its outer periphery, including at least a position facing the cutting edges 13a, which can determine the position of the cutting edges 13a relative to the inner periphery of the borehole. The head body 12 also has a through hole 14 on the rake face of the cutting edges 13 for introducing chips, and the through hole 14 is connected to the inside of the tube 11. The guide pad 15 may be movable, and the movement of the drill tool 1 may be controlled by changing the position of the guide pad 15.

[0016] As a result, the cutting oil is guided around the outer periphery of the tube 11 towards the head body 12 inside the borehole formed in the workpiece 20. Furthermore, the cutting chips are carried by the cutting oil guided from the outer periphery of the head body 12, pass through the through hole 14, pass through the inside of the tube 11 and move towards the support part 3, where they are collected. Although not shown in the figures, the cutting oil from which the cutting chips have been collected is circulated and reused. Other details are known and will not be described here.

[0017] In this embodiment, the machining device 10 further includes a non-contact displacement sensor 41 that measures the vibration displacement of the drill tool 1. The non-contact displacement sensor 41 is disposed on the support part 3 side near the oil pressure head 22 to detect the displacement of the outer periphery of the tube 11, thereby measuring the vibration displacement at the rear position of the drill tool 1. The non-contact displacement sensor 41 is also connected to a calculation part 42, which can perform frequency analysis of the vibration displacement. For example, an eddy current displacement sensor can be suitably used as the non-contact displacement sensor 41.

[0018] However, when drilling deep holes using such a drill tool 1, bending becomes a problem because the drill tool 1 is cantilevered to penetrate deep into the borehole. Therefore, controlling the straightness of the drill tool 1 is important. For example, the straightness of the drill tool 1 can be improved by lowering the feed rate relative to the workpiece 20 during its movement. However, using a low feed rate throughout the entire deep hole drilling process significantly reduces work efficiency. Therefore, it is considered to detect bending at an early stage during drilling, quantify this bending, and then reflect this in the control of the drill tool 1.

[0019] However, even if one attempts to detect bending during machining, it is difficult to detect bending in the borehole 25 inside the workpiece 20. Therefore, the inventors experimentally acquired a large number of physical variables in the tube 11 of the drill tool 1 to investigate whether any of them correspond to bending. As a result, they found that the contribution to the vibration displacement obtained by frequency analysis of the vibration displacement can correspond to bending. Here, the contribution is a part of the vibration displacement, and is the vibration displacement component at a predetermined frequency in the frequency spectrum obtained by frequency analysis.

[0020] Therefore, in this embodiment, the vibration displacement of the tube 11 can be measured by the non-contact displacement sensor 41 as described above. Then, the frequency analysis of the measured vibration displacement is performed by the calculation unit 42, and the movement of the drill tool 1 is controlled based on the contribution to the vibration displacement at a predetermined frequency lower than 200 Hz, thereby adjusting, for example, the feed rate for the workpiece 20. Note that, as a result of the frequency analysis, the contribution to the vibration displacement at each frequency was larger at frequencies lower than 200 Hz, so the predetermined frequency was set to be lower than 200 Hz.

[0021] Even if the theoretical relationship between the contribution to vibration displacement at a predetermined frequency and the magnitude of bending is unknown, the magnitude of bending can be quantitatively estimated during drilling by, for example, experimentally creating a table that associates the contribution to vibration displacement with the magnitude of bending. Then, the movement of the drill 1 can be controlled according to the estimated magnitude of bending, thereby preventing the bending from expanding. In other words, even if the position of the drill 1 along the axis A changes during drilling, the bending can be detected and quantified based on the vibration displacement measured at the position of the non-contact displacement sensor 41, and this can be reflected in the control of the operation of the drill 1.

[0022] For example, by observing the contribution of vibration displacement at a predetermined frequency and controlling the feed rate to decrease when a predetermined threshold is exceeded, it is possible to suppress the expansion of the bend without reducing work efficiency. Note that, if the guide pad 15 is movable as described above, the position of the guide pad 15 may be changed to control the movement of the drill tool 1 when a predetermined threshold is exceeded.

[0023] Alternatively, multiple frequencies may be selected as the predetermined frequency. By selecting multiple frequencies, vibrations can be captured more broadly, stabilizing the correspondence with the magnitude of bending. In this case, for example, the contributions to vibration displacement at the selected multiple predetermined frequencies can be integrated, and the calculated integrated value can be reflected in the control of the drilling tool 1. For example, when the integrated value exceeds a threshold, the feed rate of the drilling tool 1 can be reduced. Furthermore, since the predetermined frequency is set to 200 Hz or less, the predetermined frequency can be set within a certain range below 200 Hz, and the contributions to vibration displacement at each frequency can be calculated and integrated, and the integrated value can be reflected in the control of the drilling tool 1 in a similar manner.

[0024] [Vibration measurement test] The vibration displacement during deep hole drilling using the above-described drilling device 10 was measured and analyzed, and the relationship between the measured value of bending and the vibration was determined. The results are described with reference to Figure 3. Two non-contact displacement sensors 41 were installed facing each other at two locations on the top and side of the tube 11, and the vibration displacement in the vertical direction and the vibration displacement in the horizontal direction were measured.

[0025] Here, a φ67 head body was used to drill a deep hole that penetrated the entire length of a round bar with a length of approximately 7700 mm and an outer diameter of approximately 205 mm from one side in a single process. Vibration displacement was measured every 500 mm of feed during machining, and hole bending was measured at each point that was being cut when vibration displacement was measured after machining was completed.

[0026] The measured vibration displacement data for 300 seconds was subjected to a fast Fourier transform to calculate the vibration displacement components (contribution to vibration displacement at each frequency) in increments of 0.03125 Hz from 10 Hz to 200 Hz, obtaining a frequency spectrum. An integrated value was then obtained by adding up all the vibration displacement components. Furthermore, the hole curvature at the point where cutting was taking place when the vibration was measured was plotted on a graph in correspondence with the integrated value of the vibration displacement components.

[0027] As shown in Figures 3(a) and (b), we observed a tendency for the bending to increase as the integrated value of the vibration displacement components increased in both the vertical and horizontal directions. Furthermore, this tendency can be linearly approximated by regression analysis, demonstrating a good correlation. In other words, by creating such a line, it is possible to estimate hole bending even during drilling from the integrated value of the vibration displacement components in a similar drilling operation. Therefore, by setting a threshold value for the integrated value in advance, it is possible to control the movement of the drill tool 1 when this threshold is exceeded, thereby preventing the hole bending from increasing.

[0028] It should be noted that even for the same hole distortion, the integrated value of the vibration displacement component differs depending on the position (machining depth) of the drill tool 1 relative to the borehole. Therefore, for example, a threshold value for the integrated value may be determined according to the machining depth of the borehole. However, the hole distortion will increase as the integrated value increases, and by using a single threshold value throughout the entire machining depth, the movement of the drill tool 1 can be easily controlled to suppress the hole distortion.

[0029] Although typical embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0030] 1 drill tool 10 Processing equipment 11 tubes 12 Head body 13 Cutting edge 20 Workpiece 25 Boreholes A axis

Claims

1. A deep hole drilling method in which a cantilevered drill tool is moved forward along an axis line and a tip portion is pressed against a workpiece to drill a borehole from an opening, A deep hole drilling method characterized by measuring the vibration displacement of the drill tool at a rear position along the axis from the opening using a non-contact displacement sensor, performing frequency analysis of the vibration displacement to select multiple predetermined frequencies lower than 200 Hz, and accumulating the contribution to the vibration displacement for each of the predetermined frequencies to control the movement of the drill tool.

2. The deep hole drilling method according to claim 1, wherein the movement of the drill tool is controlled when an integrated value of the contribution of the vibration displacement exceeds a threshold value.

3. 3. The deep hole drilling method according to claim 1, wherein the movement is controlled by the feed speed of the drill tool.

4. A deep hole drilling method according to any one of claims 1 to 3, characterized in that the drill tool includes a tube and a round bar-shaped head body attached to the tip of the tube, and the head body has a cutting blade attached to the outer peripheral edge of the front end and a guide pad attached at a position opposite the cutting blade and the outer peripheral edge.

5. 5. The deep hole drilling method according to claim 4, wherein the movement is controlled by changing the position of the guide pad.

6. 6. The deep hole drilling method according to claim 1, wherein the non-contact displacement sensor is an eddy current sensor.

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