Cutting method and cutting device

Abstract

To provide a machining method and a machining apparatus which can impart a suitable compressive residual stress onto a surface of workpiece by a simple procedure.SOLUTION: A machining apparatus 10 for machining workpiece 20 by an end mill 13 having a cutting edge formed on its tip performs final machining of cutting off a partial surface of the workpiece 20 into a product dimension by up-cutting so as to generate a compressive residual stress on the surface of the workpiece 20. The machining apparatus 10 may continuously perform such up-cutting that a cut-off amount becomes zero after final machining a plurality of times.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cutting method and a cutting apparatus.

Background Art

[0002] Conventionally, as an aircraft material, an aluminum alloy that is lightweight and has high specific strength has been used. Products made of aluminum alloy used in aircraft are given their shape by cutting. However, during cutting, plastic deformation occurs on the material surface due to a large shear stress generated between the material surface and the tool. When plastic deformation occurs, residual stress is generated on the material surface. Residual stress generated during cutting includes compressive residual stress and tensile residual stress. Generally, tensile residual stress is considered disadvantageous in terms of fatigue, corrosion, and strain generation compared to compressive residual stress.

[0003] Therefore, as described in Patent Document 1, various measures are implemented to apply compressive residual stress to the material surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when performing cutting, it is desirable to preferably apply compressive residual stress with as simple a procedure as possible. In this regard, there is room for improvement in the cutting method of Patent Document 1.

[0006] The present invention has been made in view of the above problems, and an object thereof is to provide a cutting method and a cutting apparatus capable of applying suitable compressive residual stress to the surface of a workpiece with a simple procedure.

Means for Solving the Problems

[0007] The first cutting method for solving the above problems is a cutting method for cutting a workpiece made of a metal material with a tool having a cutting edge provided at its tip. When performing a final cutting operation to scrape off a part of the surface of the workpiece so as to obtain a product dimension, the gist is to perform the final cutting operation in an up-cut manner so that compressive residual stress is generated on the surface of the workpiece.

[0008] Thereby, suitable compressive residual stress can be imparted to the surface of the workpiece by a simple procedure.

[0009] The cutting device for solving the above problems is a cutting device for cutting a workpiece made of a metal material with a tool having a cutting edge provided at its tip. When performing a final cutting operation to scrape off a part of the surface of the workpiece so as to obtain a product dimension, the gist is to include a control unit that performs the final cutting operation in an up-cut manner so that compressive residual stress is generated on the surface of the workpiece.

[0010] Thereby, suitable compressive residual stress can be imparted to the surface of the workpiece by a simple procedure.

Brief Description of Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments embodying the "cutting method" and "cutting apparatus" according to the present invention will be described with reference to the drawings. In each of the following embodiments, parts that are identical or equivalent to each other are denoted by the same reference numerals in the drawings, and the description of the parts with the same reference numerals is incorporated by reference.

[0013] (First Embodiment) As shown in FIG. 1, the cutting apparatus 10 includes a table 11 on which a workpiece 20 is fixed, a moving mechanism 12 that moves the table 11 in the front-rear, left-right, up-down directions, an end mill 13 as a tool that has a cutting edge provided at its tip and cuts the workpiece 20 fixed to the table 11, a rotating mechanism 14 that rotates the end mill 13, a control unit 15 that controls the moving mechanism 12 and the rotating mechanism 14, and the like. Note that the cutting apparatus 10 of the present embodiment moves the table 11 to move the workpiece 20 relative to the end mill 13, but may be provided with a mechanism that moves the end mill 13 relative to the workpiece 20.

[0014] Next, based on FIG. 2, a general process of cutting is described. First, rough machining is performed to cut a raw material (the source of the workpiece 20) that has not been processed into a roughly shaped form according to the design dimensions (the first step S101). In rough machining, a workpiece 20 with a determined allowance (machining allowance) remaining is generated.

[0015] Next, in order to prepare for finish machining, semi-finish machining is performed on the rough-machined workpiece 20 (the second step S102). In this semi-finish machining, the workpiece 20 is cut so as to leave an allowance for finishing.

[0016] Then, according to the requirements of the product specifications (such as dimensional accuracy), finish machining is performed to cut the workpiece 20 so as to obtain the final product dimensions determined in advance in the design (the third step S103).

[0017] In this finish machining, for example, as shown in FIG. 3, the cutting device 10 moves the workpiece 20 together with the table 11 in a predetermined direction (for example, the direction of the arrow) by the moving mechanism 12 with respect to the end mill 13 rotating by the rotating mechanism 14, thereby cutting the workpiece 20. Note that FIG. 3 shows the state of side machining in which the outer peripheral edge of the end mill 13 cuts the workpiece 20.

[0018] The rough machining, semi-finish machining, and finish machining are carried out by different cutting devices 10. Thereby, the load during machining is dispersed to maintain the accuracy during machining. However, part or all of them may be performed by the same cutting device 10. Even in this case, in order to disperse the load on parts such as the end mill 13 and maintain the dimensional accuracy, it is desirable to replace parts such as the end mill 13 for each process. Also, the semi-finish machining and rough machining may be omitted.

[0019] Incidentally, in the finishing process, when machining the surface of the workpiece 20 (in the case where the workpiece 20 is assembled into the final product, the portion corresponding to the surface of the final product), it is common for residual stress to occur on the surface of the workpiece 20. Residual stress includes compressive residual stress and tensile residual stress, and tensile residual stress is considered disadvantageous in terms of fatigue, corrosion, and strain generation compared to compressive residual stress. Therefore, in the machining method and the machining apparatus 10 of the present embodiment, measures are taken in the finishing process so that compressive residual stress is preferably applied to the surface of the workpiece 20. This will be described in detail below.

[0020] First, before explaining the measures in the finishing process, up-cut (upward cutting) and down-cut (downward cutting) will be explained. As shown in FIG. 4, up-cut is a machining method in which the cutting edge of the end mill 13 cuts the workpiece 20 upward. That is, as shown in FIG. 4, the method of feeding the surface of the workpiece 20 that contacts the right-rotating end mill 13 from left to right is up-cut. In up-cut, a rubbing portion occurs before the start of cutting, and flank wear occurs on the end mill 13.

[0021] As shown in FIG. 5, down-cut is a machining method in which the cutting edge of the end mill 13 cuts the workpiece 20 downward. That is, as shown in FIG. 5, the method of feeding the surface of the workpiece 20 that contacts the right-rotating end mill 13 from right to left is down-cut. Generally, down-cut has less chatter vibration and less impact on tool life, so it is often used in metal processing.

[0022] Next, with reference to the drawings, the experiment on how the residual stress changes by changing the machining content (way of cutting) in the finishing process and the experimental results will be described.

[0023] (First Experiment) The premise of the first experiment will be explained. The end mill 13 used in the first experiment is a carbide two-flute end mill. Its tool diameter is 20 [mm], the rake angle is 10 [degrees], the first peripheral relief angle is 10 [degrees], and the lead angle is 30 [degrees]. Also, the rotational speed of the end mill 13 is 3000 [rpm], the feed is 900 [mm / min], and the feed per tooth is 0.15 [mm / 1 tooth]. Further, the specimen (corresponding to the workpiece 20) used in the experiment is an A7050-T7451 aluminum alloy used for aircraft structures.

[0024] Also, the residual stress was measured by X-ray residual stress measurement using an X-ray residual stress measuring device. That is, the crystal grains in the case of no residual stress are composed of regularly arranged crystal lattices, but when stress is applied to the crystal grains, the spacing between the crystal lattice planes changes depending on the direction of the stress and the angle of the crystal. Therefore, in X-ray residual stress measurement, X-rays are irradiated onto the metal material that is the specimen, and the residual stress is calculated from the crystal lattice plane spacing. This X-ray residual stress measurement is a non-destructive inspection.

[0025] In this experiment, the X-ray residual stress measurement method by the cosα method, which is a non-destructive inspection, was used. Also, since the aluminum alloy has coarse crystal grains, it is necessary to horizontally oscillate the specimen in order to mitigate the influence on the Debye ring during measurement. For this reason, a specimen oscillation device was used. The specimen oscillation device oscillated the specimen at a stroke of 2.0 [mm] and a moving speed of 1.0 [mm / s] during X-ray irradiation, increasing the X-ray irradiation area. The diameter of the X-ray irradiation diameter is approximately 2.0 [mm], and the X-ray irradiation area is approximately 8.3 [mm^2].

[0026] Next, each machining content in the first experiment will be explained based on FIG. 6.

[0027] In the machining content (No1), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then the process ends as it is. In the figure, a down cut with a depth of cut of A [mm] may be displayed as "Down (A mm)". Similarly, in the figure, an up cut with a depth of cut of B [mm] may be displayed as "Up (B mm)". Also, the cutting process of removing a part of the surface of the workpiece to achieve the product dimensions is referred to as the final cutting. The cutting process of removing a part is a cutting process where the depth of cut is not zero, and the final cutting is the cutting process that is performed last among the cutting processes with a non-zero depth of cut in the finishing process. Also, performing an up cut (or down cut) once means counting as one time the movement of the end mill 13 during rotation from one end to the other end of the workpiece 20.

[0028] In the machining content (No2), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, three down cuts with a depth of cut of 0 [mm] are to be performed. Note that a down cut with a depth of cut of 0 [mm] means performing a down cut at a distance where the end mill 13 and the test specimen either touch or do not touch during machining. Specifically, without changing the distance between the end mill 13 and the workpiece 20 set in the final cutting, a down cut can be realized by performing a down cut while maintaining the same distance. When the depth of cut is 0 [mm], it may be referred to as zero cut machining. Since the depth of cut in zero cut machining is zero, even if it is performed after the final cutting, it does not become the final cutting. Incidentally, even if the depth of cut is zero, if there is remaining material after the final cutting, the remaining material will be removed during zero cut.

[0029] In the machining content (No3), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, five down cuts with a depth of cut of 0 [mm] are to be performed.

[0030] In the machining content (No4), an up cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then the process ends as it is.

[0031] In the machining content (No5), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed three times. Note that the up cut with a depth of cut of 0 [mm] means performing an up cut at a distance where the end mill 13 and the specimen either touch or do not touch during machining. Specifically, by performing an up cut while maintaining the same distance between the end mill 13 and the workpiece 20 set in the final cutting without changing the distance, an up cut with a depth of cut of 0 [mm] can be achieved.

[0032] In the machining content (No6), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed five times.

[0033] In the machining content (No7), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once.

[0034] In the machining content (No8), first, a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once. After that, a down cut with a depth of cut of 0 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once, and this is repeated twice (2 reciprocations of repetitive machining). Note that performing an up cut with a depth of cut of 0 [mm] once after performing a down cut with a depth of cut of 0 [mm] once may be referred to as repetitive machining.

[0035] In the machining content (No9), first, a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once. After that, a down cut with a depth of cut of 0 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once, and this is repeated 4 times (4 reciprocations of repeated machining).

[0036] In the machining content (No10), first, a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once. After that, a down cut with a depth of cut of 0 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once, and this is repeated 19 times (19 reciprocations of repeated machining).

[0037] The experimental results in the first experiment will be described based on Figure 7. In Figure 7, when the residual stress [MPa] indicated by the vertical axis is a positive value, it indicates a tensile residual stress, and when the residual stress [MPa] is a negative value, it indicates a compressive residual stress.

[0038] When the cutting of the machining content (No1) was carried out, it was found that tensile residual stress was generated. On the other hand, when the cutting of the machining content (No4) was carried out, it was found that compressive residual stress was generated. From this, it was found that in the finishing process, it is possible to generate compressive residual stress when the final cutting is carried out by up cut.

[0039] Also, from the comparison results between the case where the cutting of the machining content (No1) was carried out and the case where the cutting of the machining content (No7) was carried out, it was found that it is possible to generate compressive residual stress when an up cut with a depth of cut of 0 [mm] is carried out after the final cutting.

[0040] When comparing the case of performing the cutting process of the processing content (No7) with the case of performing the cutting process of the processing content (No5), it was found that the compressive residual stress of the processing content (No5) is larger (the residual stress becomes larger on the negative side). From this, it was found that when multiple up-cuts with a cutting depth of 0 [mm] are continuously performed after the final cutting process, the compressive residual stress becomes larger.

[0041] When comparing the case of performing the cutting process of the processing content (No5) with the case of performing the cutting process of the processing content (No8), it was found that the compressive residual stress of the processing content (No8) is slightly larger. On the other hand, when comparing the case of performing the cutting process of the processing content (No5) with the case of performing the cutting process of the processing content (No6), the values of the compressive residual stress were almost the same. However, when comparing the case of performing the cutting process of the processing content (No8) with the case of performing the cutting process of the processing content (No9), it was found that the compressive residual stress of the processing content (No9) is smaller (the residual stress becomes larger on the positive side). Furthermore, when comparing the results in the processing content (No8) to the processing content (No10), it was found that the compressive residual stress of the processing content (No10) is the smallest (the residual stress becomes larger on the positive side).

[0042] From this, it was found that when multiple up-cuts with a cutting depth of 0 [mm] are continuously performed after the final cutting process, it is preferably below a predetermined number of times (for example, 3 times). Furthermore, it is considered more desirable to continuously perform multiple (for example, 3 times) up-cuts with a cutting depth of 0 [mm] without sandwiching a down-cut with a cutting depth of 0 [mm].

[0043] Summarizing the above results, as shown in Fig. 7, by performing up-cutting with a cutting depth of 0 [mm] after down-cutting, it was possible to apply a larger compressive residual stress than when performing down-cutting with a cutting depth of 0 [mm] after down-cutting. Therefore, it is considered that even in zero-cut machining (cutting depth of 0 [mm]), the final machining method has a significant impact on the residual stress. On the other hand, the machining contents (No5 and No8) with up-cutting with a cutting depth of 0 [mm] performed three times resulted in the highest compressive residual stress. However, the compressive residual stress decreased as the number of zero-cut machining increased. Therefore, it is considered that there is an appropriate number of repetitions to apply a large compressive residual stress. In addition, in the first experiment, the same tendency was obtained even when the specimen used in the experiment was changed to carbon steel (S50C).

[0044] (Second Experiment) The premise of the second experiment will be explained. The end mill 13 used in the second experiment is a carbide two-flute end mill. Its tool diameter is 26 [mm], the rake angle is 10 [degrees], the first peripheral relief angle is 10 [degrees], and the lead angle is 30 [degrees]. However, since the relief angle has been re-sharpened, the tool diameter is 25 [mm] as measured. Also, the specimen (corresponding to the workpiece 20) used in the experiment is an aluminum alloy of A7050-T7451, the same as in the first experiment. Also, the method for measuring the residual stress is the same as in the first experiment.

[0045] Next, each machining content in the second experiment will be explained based on Fig. 8. In the second experiment, the residual stress when the rotational speed was changed was compared. For each machining content (No11~No18, No21~No28), the rotational speed [rpm] of the end mill 13 and the feed [mm / min] are shown. In all cases, the feed per tooth is 0.15 [mm / tooth], and they are all the same. The results of this second experiment are shown in Fig. 9.

[0046] As shown in Fig. 9, compressive residual stress occurred in up-cut, while tensile residual stress occurred in down-cut. Also, when the rotational speed was about 7000 [rpm] or more, the increase in tensile residual stress due to the increase in rotational speed became gentle in down-cut. On the other hand, in up-cut, the compressive residual stress increased (the residual stress became larger on the negative side) due to the increase in rotational speed up to about 7000 [rpm]. However, when it was about 7000 [rpm] or more, the compressive residual stress decreased (the residual stress became larger on the positive side). The minimum value (absolute value of residual stress) of the compressive residual stress in up-cut was about 180 [MPa], and the maximum was about 340 [MPa], showing a change nearly twice as large. In up-cut, since the end mill 13 advances in a way that cuts upward with respect to the specimen, a rubbing portion occurs before the contact between the end mill 13 and the specimen. At this time, it is considered that the pressing and flattening force due to the cutting edge rounding of the end mill 13 and the thermal influence due to rubbing act on the machined surface. In addition, in the second experiment, the same tendency was obtained even when the specimen used in the experiment was changed to carbon steel (S50C).

[0047] (The Third Experiment) The premise of the third experiment will be explained. The end mill 13 used in the third experiment is a high-speed two-flute end mill. Its tool diameter is 20 [mm], the rake angle is 12 [degrees], the first peripheral relief angle is 11 [degrees], and the lead angle is 25 [degrees]. Also, the rotational speed of the end mill 13 is 750 [rpm], the feed is 150 [mm / min], the feed per tooth is 0.10 [mm / tooth], and the peripheral speed is 47 [m / min]. Also, the specimen (corresponding to the workpiece 20) used in the experiment is carbon steel (S50C). Also, the method for measuring residual stress is the same as that in the first experiment.

[0048] Next, each machining content in the third experiment will be explained based on Fig. 10. In the third experiment, the residual stresses when the final machining method was changed were compared.

[0049] In the machining content (No31), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then the process ends as it is.

[0050] In the machining content (No32), an up cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then the process ends as it is.

[0051] In the machining content (No33), a down cut with a depth of cut of 0.2 [mm] is performed once, and then a down cut (final cutting) with a depth of cut of 0.1 [mm] is performed once.

[0052] In the machining content (No34), a down cut with a depth of cut of 0.2 [mm] is performed once, and then an up cut (final cutting) with a depth of cut of 0.1 [mm] is performed once.

[0053] In the machining content (No35), an up cut with a depth of cut of 0.2 [mm] is performed once, and then a down cut (final cutting) with a depth of cut of 0.1 [mm] is performed once.

[0054] In the machining content (No36), an up cut with a depth of cut of 0.2 [mm] is performed once, and then an up cut (final cutting) with a depth of cut of 0.1 [mm] is performed once.

[0055] Next, the results of this third experiment are shown in Fig. 11. As shown in Fig. 11, if the final cutting is performed by an up cut, it is considered that compressive residual stress can be applied regardless of the machining content before that. In addition, in the third experiment, the same tendency was obtained even when the specimen used in the experiment was changed to an aluminum alloy of A7050-T7451.

[0056] From the results of the above first experiment to the third experiment, in the cutting apparatus 10 of the present embodiment, the following cutting method is implemented.

[0057] When the cutting device 10 performs final cutting to remove a part of the surface of the workpiece 20 so as to obtain the product dimensions, the final cutting is carried out by up-cutting so that compressive residual stress is generated on the surface of the workpiece 20. That is, when the control unit 15 of the cutting device 10 performs various machining controls such as rotation control of the end mill 13 and movement control of the table 11 to perform final cutting, up-cutting is carried out so that compressive residual stress is generated on the surface of the workpiece 20.

[0058] In addition, after the final cutting, the cutting device 10 may perform up-cutting with a cutting depth of zero (0 [mm]). When performing up-cutting with a cutting depth of zero (0 [mm]) after the final cutting, it is desirable to perform it multiple times. However, when performing up-cutting with a cutting depth of zero (0 [mm]) multiple times after the final cutting, the number of up-cuts is preferably not more than a predetermined number of times (for example, 3 times) at which the compressive residual stress becomes the largest. Also, it is desirable to continuously perform multiple up-cuts (zero-cut machining) without sandwiching down-cut (zero-cut machining).

[0059] Also, when performing up-cutting in the final cutting or when performing up-cutting (zero-cut machining) after the final cutting, the rotational speed is desirably within a predetermined range set based on the rotational speed at which the compressive residual stress becomes the largest. The predetermined range is desirably, for example, within the range of 0.7 times to 1.4 times the rotational speed at which the compressive residual stress becomes the largest. As in the second experimental result, when the compressive residual stress becomes the largest at about 7000 [rpm], it is desirable to be within the range of 5000 to 10000 [rpm].

[0060] The effects of this embodiment will be described.

[0061] When the cutting device 10 performs the final cutting process of shaving a part of the surface of the workpiece 20 so as to obtain the product dimensions, the final cutting process is carried out by up-cut so that compressive residual stress is generated on the surface of the workpiece 20. For this reason, compressive residual stress can be suitably applied to the surface of the workpiece 20 by a simple procedure.

[0062] Also, after the final cutting process, an up-cut with a cutting depth of zero may be carried out. Thereby, compressive residual stress can be suitably applied to the surface of the workpiece 20 by a simple procedure. Further, when an up-cut with a cutting depth of zero is carried out after the final cutting process, the up-cut may be carried out a plurality of times. Thereby, the compressive residual stress can be increased by a simple procedure. Further, when the up-cut with a cutting depth of zero is carried out a plurality of times after the final cutting process, the number of times of the up-cut is set to be equal to or less than a predetermined number of times (for example, 3 times) at which the compressive residual stress becomes the largest. Thereby, while increasing the compressive residual stress, it is not necessary to carry out unnecessary up-cuts.

[0063] When the up-cut with a cutting depth of zero is carried out a plurality of times after the final cutting process, a plurality of up-cuts are continuously carried out without sandwiching a down-cut therebetween. Thereby, in the case of carrying out the up-cut the same number of times, the compressive residual stress can be made higher. Also, unnecessary labor can be saved.

[0064] Also, when the up-cut is carried out in the final cutting process, or when the up-cut (zero-cut process) is carried out after the final cutting process, the rotational speed of the end mill 13 is set within a predetermined range based on the rotational speed at which the compressive residual stress becomes the largest. Thereby, the compressive residual stress can be increased.

[0065] (Second Embodiment) The following describes the fourth experiment conducted in the second embodiment. Note that the description of the same conditions as in the first experiment is omitted. Also, in the fourth experiment, a cutting device 10 (with the same configuration) different from the cutting device 10 used in the first to third experiments is utilized. Therefore, even with the same machining content, the results may vary slightly.

[0066] (Fourth Experiment) The premise of the fourth experiment is described. The end mill 13 used in the fourth experiment is a carbide two-flute end mill. Its tool diameter is 20 [mm], the rake angle is 10 [degrees], the first peripheral relief angle is 10 [degrees], and the lead angle is 30 [degrees]. Also, the rotational speed of the end mill 13 is 3000 [rpm], the feed is 900 [mm / min], and the feed per tooth is 0.15 [mm / 1 tooth]. Further, the specimen used in the experiment (corresponding to the workpiece 20) is an A7050-T7451 aluminum alloy.

[0067] Next, each machining content in the fourth experiment will be described based on FIGS. 12 to 14.

[0068] As shown in FIG. 12, in the machining content (No101), a down cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then it is finished as it is.

[0069] In the machining content (No102), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once.

[0070] In the machining content (No103), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once.

[0071] Hereafter, similarly, for the machining content (No104, No106, No108, No110), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, down cuts with a depth of cut of 0 [mm] are each performed 2 to 5 times.

[0072] Also, similarly, for the machining content (No105, No107, No109, No111), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, up cuts with a depth of cut of 0 [mm] are each performed 2 to 5 times.

[0073] As shown in Figure 13, for the machining content (No112), an up cut (final cutting) with a depth of cut of 0.2 [mm] is performed once and then it is finished as it is.

[0074] For the machining content (No113), an up cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then a down cut with a depth of cut of 0 [mm] is performed once.

[0075] For the machining content (No114), an up cut (final cutting) with a depth of cut of 0.2 [mm] is performed once, and then an up cut with a depth of cut of 0 [mm] is performed once.

[0076] Hereafter, similarly, for the machining content (No115, No117, No119, No121), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, down cuts with a depth of cut of 0 [mm] are each performed 2 to 5 times.

[0077] Also, similarly, for the machining content (No116, No118, No120, No122), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, up cuts with a depth of cut of 0 [mm] are each performed 2 to 5 times.

[0078] As shown in Fig. 14, the machining content (No123) is the same as the machining content (No8). That is, after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once, and the repetitive machining is carried out for 2 reciprocations. Also, the machining content (No124) and the machining content (No125) are the same as the machining content (No9) and the machining content (No10), respectively.

[0079] In the machining content (No126), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once. Then, a down cut with a depth of cut of 0 [mm] is performed once.

[0080] In the machining content (No127), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once. Then, after performing a down cut with a depth of cut of 0 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once.

[0081] In the machining content (No128), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once. Then, after performing a down cut with a depth of cut of 0 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once, and finally, a down cut with a depth of cut of 0 [mm] is performed once.

[0082] In the machining content (No129), after performing a down cut (final cutting) with a depth of cut of 0.2 [mm] once, an up cut with a depth of cut of 0 [mm] is performed once. Then, a down cut with a depth of cut of 0 [mm] → an up cut with a depth of cut of 0 [mm] → a down cut with a depth of cut of 0 [mm] → an up cut with a depth of cut of 0 [mm] are performed in this order.

[0083] In the machining content (No130), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once. Then, an up cut with a depth of cut of 0 [mm] is performed once.

[0084] In the machining content (No131), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once. Then, after performing an up cut with a depth of cut of 0 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once.

[0085] In the machining content (No132), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once. Then, after performing an up cut with a depth of cut of 0 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once, and finally, an up cut with a depth of cut of 0 [mm] is performed once.

[0086] In the machining content (No133), after performing an up cut (final cutting) with a depth of cut of 0.2 [mm] once, a down cut with a depth of cut of 0 [mm] is performed once. Then, an up cut with a depth of cut of 0 [mm] → a down cut with a depth of cut of 0 [mm] → an up cut with a depth of cut of 0 [mm] → a down cut with a depth of cut of 0 [mm] are performed in this order.

[0087] The experimental results in the fourth experiment will be described based on FIGS. 15 to 17. In FIGS. 15 to 17, when the residual stress [MPa] indicated by the vertical axis is a positive value, it indicates a tensile residual stress, and when the residual stress [MPa] is a negative value, it indicates a compressive residual stress. Also, when an up cut is performed at the end of the finishing process, the results are shown in white, while when a down cut is performed at the end of the finishing process, the results are shown in hatching.

[0088] Figure 15 summarizes the results of the machining operations (No101 - No111) where the final cutting operation is downcut. Figure 16 summarizes the results of the machining operations (No112 - No122) where the final cutting operation is upcut. Figure 17 summarizes the results of the machining operations (No123 - No133) that include repetitive machining with alternating downcut and upcut operations.

[0089] When the cutting operation of machining content (No101) was performed, it was found that tensile residual stress occurred. On the other hand, when the cutting operation of machining content (No112) was performed, it was found that compressive residual stress occurred. From this, it was found that when the final cutting operation is performed as upcut, it is possible to generate compressive residual stress.

[0090] When the machining of machining content (No102) and machining content (No113) was performed, it was found that little residual stress (tensile residual stress and compressive residual stress) occurred. On the other hand, when the machining of machining content (No103) and machining content (No114) was performed, it was found that compressive residual stress occurred. From this, it was found that regardless of whether the final cutting operation is upcut or downcut, in the finishing operation, when upcut is performed, it is possible to generate compressive residual stress. On the other hand, regardless of whether the final cutting operation is upcut or downcut, in the finishing operation, even if downcut is performed only once, it is found that it is difficult to generate compressive residual stress. This is considered to be because in the first pass of the finishing operation, the remaining material to be cut is removed.

[0091] When the machining of machining content (No104 - 111, No115 - 133) was performed, it was found that compressive residual stress occurred. From this, it was found that regardless of whether the final cutting operation is upcut or downcut, in the finishing operation, when zero - cut machining with a cutting depth of 0 [mm] is performed multiple times, it is possible to generate compressive residual stress.

[0092] In particular, from the experimental results of the machining details (No106 - 111, No117 - 125, No127 - 129, No131 - 133), it was found that when zero-cut machining is performed three times, regardless of whether the finishing machining is up-cut or down-cut, it is possible to suitably generate compressive residual stress. On the other hand, it was found that even if zero-cut machining is performed four or more times, it is difficult to increase the compressive residual stress.

[0093] From the results of the machining details (No102, No104) and the machining details (No113, No115), it can be seen that in finishing machining, even if down-cut is performed one or two times, it is not possible to appropriately impart compressive residual stress, or it is not possible to impart a large compressive residual stress. This is probably because in the first two down-cuts (zero-cuts) in finishing machining, the remaining material is being removed, so the compressive residual stress generated by zero-cut machining cannot be imparted. This can also be inferred from the results of the machining details (No103) and the machining details (No114), because when the remaining material is removed by up-cut in finishing machining, the same compressive residual stress as in the case where the final cutting is up-cut is imparted.

[0094] From this, it is considered that if there is no remaining material, compressive residual stress can be appropriately imparted by zero-cut machining. Therefore, if the specifications of the end mill 13 (such as hardness) and the specifications of the cutting device 10 (such as the force for fixing the end mill 13) are adjusted so that the remaining material can be eliminated in the first finishing machining (zero-cut machining), it is considered that compressive residual stress can be appropriately imparted in the zero-cut machining from the second time onwards.

[0095] Also, from the experimental results of the machining details (No127 - 129, No131 - 133), it was found that when up-cut and down-cut are alternately performed, if zero-cut machining is performed three or more times, it is possible to appropriately impart compressive residual stress.

[0096] Also, from the experimental results of the machining details (No126 - 133), it was found that when the final finishing machining is up - cut, it is easier to increase the compressive residual stress compared to the case where the final is down - cut.

[0097] From the results of the above - mentioned fourth experiment, in the cutting machining apparatus 10 of the second embodiment, the following cutting machining method is implemented.

[0098] When the cutting machining apparatus 10 performs the final cutting machining to cut off a part of the surface of the workpiece 20 so as to obtain the product dimensions, the final cutting machining is carried out by up - cut so that compressive residual stress is generated on the surface of the workpiece 20. And, after the final cutting machining, the cutting machining apparatus 10 may perform an up - cut with the cutting depth being zero (0 [mm]), or may perform zero - cut a plurality of times.

[0099] In addition, when performing zero - cut a plurality of times, if continuously performing down - cuts with the cutting depth being zero (0 [mm]), it is desirable to perform 3 or more times. Also, when performing zero - cut a plurality of times and performing up - cuts and down - cuts alternately, it is desirable to perform zero - cut a total of 2 or more times. Further, in the finishing machining, when performing zero - cut a plurality of times, it is desirable to perform an up - cut with the cutting depth being zero (0 [mm]) last.

[0100] The effects according to the second embodiment will be described.

[0101] By a simple procedure of performing the final cutting machining by up - cut, compressive residual stress can be suitably applied to the surface of the workpiece 20. Also, by performing the final cutting machining by up - cut and performing one or more up - cuts with the cutting depth being zero (0 [mm]) in the finishing machining, or by performing zero - cut a plurality of times in the finishing machining, compressive residual stress can be more suitably applied to the surface of the workpiece 20.

[0102] At that time, even if up-cutting with a cutting depth of zero (0 [mm]) and down-cutting with a cutting depth of zero (0 [mm]) are alternately performed, compressive residual stress can be suitably applied. Further, when zero-cutting is performed multiple times in the finishing process, if up-cutting with a cutting depth of zero (0 [mm]) is performed last, the compressive residual stress can be easily increased.

[0103] Also, if the final cutting process is performed by up-cutting and down-cutting (zero-cutting) with a cutting depth of zero (0 [mm]) is performed three or more times in the finishing process, compressive residual stress can be appropriately applied.

[0104] (Modification example) · As long as the cutting device 10 in the above embodiment can perform cutting using the end mill 13, its configuration can be arbitrarily changed. For example, as the cutting device 10, any of a vertical milling machine, a horizontal milling machine, a universal milling machine, and an NC milling machine may be employed. Also, a lathe or a machining center may be used. Further, the shape of the end mill 13 may be arbitrarily changed.

[0105] · In the above second embodiment, the final cutting process does not have to be performed by down-cutting. Also, if the final cutting process is performed by up-cutting, zero-cutting does not have to be performed in the finishing process. Thereby, compressive residual stress can be easily applied.

[0106] · In the above second embodiment, if up-cutting is performed in the finishing process, it may be performed only once. Thereby, compressive residual stress can be easily applied.

[0107] · In the above second embodiment, when zero-cutting is performed multiple times in the finishing process, up-cutting and down-cutting do not have to be alternately performed. For example, either one may be continuously performed multiple times and then the other may be performed one or more times.

[0108] · In the above second embodiment, when zero-cut machining is performed multiple times in the finishing process, the last cut may be a down cut.

Explanation of Signs

[0109] 10... Cutting device, 11... Table, 12... Moving mechanism, 13... End mill, 14... Rotating mechanism, 15... Control unit, 20... Workpiece.

Claims

1. In a cutting method for cutting a workpiece made of a metallic material with an end mill having a cutting edge provided at its tip, when performing a final cutting operation for shaving off a part of the surface of the workpiece to the product dimensions, the final cutting operation is carried out in an up-cut manner so that compressive residual stress is generated on the surface of the workpiece, the workpiece is composed of an aluminum alloy or steel, A cutting method in which the up-cut in the final cutting operation is carried out by side machining for machining the workpiece with the side surface of the end mill.

2. The cutting method according to claim 1, wherein after performing the final cutting operation, a plurality of zero cuts with a cutting depth of zero are carried out.

3. The cutting method according to claim 2, wherein after performing the final cutting operation, three down-cuts with a cutting depth of zero are continuously carried out.

4. The cutting method according to claim 2, wherein after performing the final cutting operation, an up-cut with a cutting depth of zero and a down-cut with a cutting depth of zero are alternately carried out.

5. The cutting method according to claim 2 or 4, wherein after performing the final cutting operation, an up-cut with a cutting depth of zero is carried out last.

6. The cutting method according to claim 1, wherein after performing the final cutting operation, a zero cut with a cutting depth of zero is not carried out.

7. The cutting method according to claim 1, wherein after performing the final cutting operation, an up-cut with a cutting depth of zero is carried out.

8. In a cutting apparatus for cutting a workpiece made of a metallic material with an end mill having a cutting edge provided at its tip, when performing a final cutting operation for shaving off a part of the surface of the workpiece to the product dimensions, a control unit is provided for carrying out the final cutting operation in an up-cut manner so that compressive residual stress is generated on the surface of the workpiece, the workpiece is composed of an aluminum alloy or steel, A cutting apparatus in which the up-cut in the final cutting operation is carried out by side machining for machining the workpiece with the side surface of the end mill.

Images