Hole drilling method and rotary tool unit and rotary tool used therefor

Abstract

This invention provides a tool feeding mechanism that controls the thrust force of a rotating tool on a workpiece. [Solution] A method for machining holes in a workpiece, wherein a rotary tool for machining holes is advanced relative to the workpiece using fluid pressure, and the cutting force acting in the direction of the central axis of the rotary tool is variably controlled according to the area in contact between the cutting edge of the rotary tool and the workpiece.

Description

Technical Field

[0001] The present invention relates to a method for drilling holes such as bottomed holes and through holes in a workpiece, and a rotary tool unit and a rotary tool suitable therefor.

Background Art

[0002] When drilling a hole in a workpiece, a hole-making tool such as a drill is inserted from one surface of the workpiece and advanced until it reaches a desired depth or penetrates the opposite surface. At this time, if the hole-making tool slips sideways when the drill or the like is pressed against the workpiece, the shape of the entrance of the hole will deviate greatly from a perfect circle. In addition, in the processing of through holes, when the cutting edge of a drill or the like protrudes from the opposite surface, burrs may occur on the peripheral portion of the hole. Furthermore, chips discharged during hole machining may get entangled with a drill or the like and become an obstacle to cutting.

[0003] As countermeasures for these problems, conventionally, many are aimed at improving the drill shape and optimizing the feed control of the drill (Patent Documents 1 to 13).

[0004] However, although these conventional techniques are effective when performing predetermined hole machining on a predetermined workpiece with a CNC-controlled machine tool or the like, in fields such as the assembly of an aircraft composed of complex three-dimensional shaped members, for example, the parts where hole machining is required are extensive, and the curvature, plate thickness, material, etc. of the machining surface are different from each other. So far, drill machining has been performed manually. This results in poor productivity and improvement has been desired. As a countermeasure, the application of an industrial robot has been considered, but the rigidity of the robot arm is less than 1 / 100 of that of a CNC machine tool, and it has been difficult to ensure a perfect circle in hole machining and suppress the generation of burrs in such an unstable state.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-213121 [Patent Document 2] Japanese Patent Publication No. 2008-296313 [Patent Document 3] Patent No. 6975353 (JP6975353) [Patent Document 4] Japanese Patent Publication No. 2000-263600 [Patent Document 5] Japanese Patent Publication No. 2007-268645 [Patent Document 6] Japanese Patent Publication No. 2003-311520 [Patent Document 7] Special Publication No. 7-472435 [Patent Document 8] Japanese Patent Application Publication No. 2-36009 [Patent Document 9] Japanese Patent Application Publication No. 62-246408 [Patent Document 10] Japanese Patent Publication No. 2004-261928 [Patent Document 11] Patent No. 5631467 (JP5631467) [Patent Document 12] Japanese Patent Publication No. 2009-50942 [Patent Document 13] Japanese Patent Publication No. 2012-16793 [Non-patent literature]

[0006] [Non-Patent Document 1] Burr formation in hole drilling of aluminum plates by soft machining, - Comparison of soft machining and CNC machining -, Takashi Numazawa, Takeshi Arimura, Yasuo Kondo, October 28, 2023, Tohoku Branch Academic Conference of the Japan Society for Precision Engineering [Overview of the project] [Problems that the invention aims to solve]

[0007] In hole machining using CNC-controlled machines, the forward feed amount and feed rate of the rotary tool are controlled, making it difficult to control the cutting force applied by the cutting edge of the rotary tool to the workpiece. Therefore, the inventors investigated a tool feeding mechanism that controls the thrust force of a rotating tool on a workpiece, and as a result, arrived at the present invention. In addition, the present inventors have proposed soft machining using a weight-based tool feed in Non-Patent Document 1, but the present invention enables soft machining not only in the vertical direction but in any direction. [Means for solving the problem]

[0008] The hole machining method according to the present invention is a method for machining holes in a workpiece, wherein a rotary tool for hole machining is advanced relative to the workpiece using fluid pressure, and the cutting force acting in the direction of the central axis of the rotary tool is variably controlled according to the area in contact between the cutting edge of the rotary tool and the workpiece.

[0009] Here, "advancing using fluid pressure relative to the workpiece" means that the rotating tool may be advanced relative to the workpiece, or conversely, the workpiece may be advanced relative to the rotating tool.

[0010] When using fluid pressure, such as air, as the feed mechanism for a rotary tool, a stable thrust force can be applied to the workpiece at a predetermined pressure. Furthermore, because the fluid has elastic properties, the rotary tool can be advanced while absorbing the repulsive force from the workpiece to the rotary tool. Therefore, if a back pressure from the fluid is added to the fluid pressure that advances the rotary tool, the thrust force applied to the workpiece becomes more stable. In this respect, CNC control differs from a feed mechanism using a ball screw or the like, where a forced thrust force is applied regardless of the repulsive force from the workpiece.

[0011] In the present invention, the rotary tool unit suitable for the above-described hole machining method is characterized by having a guide portion for guiding the forward and backward movement of the rotary tool and a fluid pressure control means for controlling the cutting force in the feed direction with respect to the rotary tool. Also in this case, it is preferable that the rotary tool has back pressure control means for controlling the back pressure in the backward direction.

[0012] In the present invention, a general drill or the like may be used as the rotary tool. Furthermore, as a rotary tool with improved entanglement of chips in a drill or the like, it is preferable to use one having a first cutting edge portion on the tip side and a third cutting edge portion on the rear end side, and having a second cutting edge portion with a concave curve shape between the first cutting edge portion and the third cutting edge portion.

Advantages of the Invention

[0013] The hole machining method according to the present invention employs a feed mechanism for a rotary tool using fluid pressure, so that a stable thrust force can be applied to the workpiece, and it can also be used for the end effector of a multi-axis controlled robot arm. As a result, the field of use as a hole machining means expands, and the quality is more stable and the productivity is improved compared to conventional manual hole machining.

Brief Description of the Drawings

[0014] [Figure 1] Shows Example 1 of the rotary tool unit according to the present invention. [Figure 2] Shows Example 2 of the rotary tool unit according to the present invention. [Figure 3] Shows the relationship between the passage of time of hole machining and the cutting force. [Figure 4] [[ID=�4]]Shows a chart comparing the changes in cutting force in the machining method (SM: soft machining) according to the present invention and conventional CNC feed control. [Figure 5] Shows a comparison photo of the appearance of hole machining. <C [Figure 6] Shows a comparison between the shape of the drill used in the present invention and a conventional drill. [Figure 7]Figure 6 shows photographs of the chips produced using drills (a) and (b). [Figure 8] A schematic diagram shows an example of the rotary tool unit according to the present invention being mounted on a robot arm. [Modes for carrying out the invention]

[0015] Figures 1 and 2 show examples of the structure of a rotary tool unit 10 used in the hole drilling method according to the present invention. Figure 1 shows the rotary tool unit of Example 1. The rotating tool 11 has a tool mounting section 12 that utilizes the shank portion of the rotating tool 11 to mount the rotating tool 11. The tool mounting section 12 is capable of moving forward and backward along the cylindrical guide section 13. As a feeding mechanism for the tool mounting section 12, the rear end of the tool mounting section 12 is connected to the piston section 15 via a rod 15a, and this piston section 15 is built into the cylinder section 14. The cylinder section 14 is divided into a pressurized chamber 14a and a back pressure chamber 14b, separated by the piston section 15. In this embodiment, air is injected into the pressurized chamber 14a while the fluid pressure is controlled by the fluid pressure control unit 16. Meanwhile, the back pressure applied to the piston section 15 by a fluid such as air in the back pressure chamber 14b is controlled by the back pressure control unit 17, and air is discharged from the back pressure chamber 14b. Furthermore, a ventilation hole 13a is provided in the guide section 13 to prevent negative pressure from forming inside due to the forward movement of the rotary tool. As a result, by injecting air from the fluid pressure control unit 16 into the pressurizing chamber 14a, a predetermined pressure f1 is applied in the axial direction of the drill via the piston unit 15, and a predetermined thrust force f2 is applied to the tip of the rotary tool 11 relative to the workpiece W. In this case, the thrust force on the drill tends to be unstable if only the internal pressure of the pressurizing chamber 14a is used, but the feeding mechanism of the rod 15a is stabilized by controlling the back pressure of the back pressure chamber 14b.

[0016] Figure 2 shows Example 2, and the differences from Example 1 will be explained. In Example 1, the fluid injected into the pressurized chamber was air, and the back pressure in the back pressure chamber 14b was also controlled by air. In contrast, Example 2 is an example in which a back pressure cylinder 18a is provided via a connecting portion 18d, separate from the cylinder portion 14. The back pressure cylinder 18a is equipped with a back pressure piston 18b, which is connected to the tool mounting section 12 by a rod 18c, and the back pressure is controlled by the back pressure f3. This embodiment is a hydraulic control unit that uses oil as the fluid in the back pressure chamber 14c.

[0017] Next, an example of a hole machining method according to the present invention will be described. Figure 3 shows the ideal feeding mechanism considered by the inventors. When drilling a hole from one side of the workpiece W using a rotary tool 11, the tip of the cutting edge of the rotary tool 11 first contacts the workpiece W. The area S in contact with the workpiece increases according to the depth of penetration of the rotary tool, and the cutting force P increases accordingly, thereby suppressing misalignment (lateral deviation of the cutting edge). Within the range where the outer diameter of the rotary tool and the hole diameter match, there is a constant contact area S. When the cutting edge penetrates the workpiece, the contact area S of the cutting edge decreases, and it was assumed that reducing the cutting force P accordingly would reduce burrs.

[0018] The results of the demonstration experiment are shown in Figure 4. Figure 4 shows a 3mm thick aluminum alloy plate conforming to JIS A 2017 as the workpiece, with holes drilled using an HSS twist drill with a tip angle of 135°. The drill diameter was set to 4 mm and the rotation speed to 2000 rpm. In Figure 4, Chart SM (Soft Machining) uses the rotary tool unit according to the present invention, while CNC, as a comparative example, shows a chart using a ball screw feed mechanism. In the processing method of this invention, a thrust force of 70 N was applied. On the other hand, the CNC was set to an average feed rate of 20 mm / min, taking into consideration the SM of the present invention. At stage (a), when the tip of the cutting edge begins to contact the workpiece W and the hole diameter is smaller than the outer diameter of the drill, the cutting force (N) of the CNC increases proportionally, whereas the fluid-based feed mechanism of the present invention changes along a curve that is higher than the transition curve of the CNC. Next, at stage (b) where the hole diameter matches the outer diameter of the drill, the cutting force (N) in the CNC was greater and more unstable than that in the SM. In contrast, the SM of the present invention was a gradual change. This is presumed to be due to a balance between the fluid pressure in the drill's feed direction and the back pressure from the fluid, resulting in a stable thrust force. Even at stage (c), when the drill bit had penetrated the workpiece, the SM showed a decrease in a curve that was higher than the CNC's.

[0019] Figure 5 shows the appearance of holes machined according to the present invention and holes machined using CNC. It can be seen that the hole machining method according to the present invention has a higher degree of roundness, both on the tool entry surface and the tool penetration surface.

[0020] Next, we considered the shape of the drill. Figure 6 schematically shows the shape of the tip of a drill according to the present invention (a) and the shape of a conventional drill (b). The drill 20 according to the present invention is manufactured to have a first cutting edge portion 21 that expands in diameter in a conical shape from the die at the tip of the cutting edge, a second cutting edge portion 22 that has a profile that changes in a curve to become concave in the axial direction, and a third cutting edge portion 23 that expands in diameter to match the outer diameter of the drill. Figure 6(b) shows a comparative example using a twist drill 30 in which the cutting edge 31 is conically enlarged. Using both of these drills, we experimented with cutting under the same conditions as the hole drilling described above. A photograph of its exterior is shown in Figure 7. It can be seen that the drill according to the present invention results in less chip entanglement.

[0021] Since the present invention uses a fluid-controlled rotary tool unit 10, it can be used as an end effector attached to the tip 1a of a robot arm 1 that can be controlled in the XYZ direction, as schematically shown in Figure 8. [Explanation of symbols]

[0022] 10 Rotary Tool Units 11 Rotary Tools 12 Tool mounting section 13 Guide Section 14 Cylinder section 14a Pressurized chamber 14b Back pressure chamber 15 Piston section 15a Rod 16 Fluid pressure control unit 17 Back pressure control unit 18a Back pressure cylinder 18b Back pressure piston 21 First cutting edge 22 Second cutting edge 23 Third cutting edge Double job

Claims

1. A method for machining holes in a workpiece, This system uses fluid pressure to advance a rotary tool for hole drilling relative to the workpiece. A hole machining method characterized in that the cutting force acting in the direction of the central axis of the rotary tool is variably controlled according to the area in which the cutting edge of the rotary tool contacts the workpiece.

2. The hole machining method according to claim 1, characterized in that a back pressure by the fluid is applied to the fluid pressure that advances the rotary tool.

3. A rotary tool unit used in the hole drilling method described in claim 1 or 2, A rotary tool unit characterized by having a guide section that guides the forward and backward movement of a rotary tool, and a fluid pressure control means that controls the cutting force in the feed direction relative to the rotary tool.

4. The rotary tool unit according to claim 3, characterized in that it has a back pressure control means for controlling the back pressure in the retraction direction relative to the rotary tool.

5. A rotary tool used in the hole drilling method described in claim 1 or 2, A rotary tool characterized by having a first cutting edge portion at the tip and a third cutting edge portion at the rear end, and having a second cutting edge portion with a concave curve shape between the first cutting edge portion and the third cutting edge portion.

Images