ENDMILL SPECIFICATION DESIGN METHOD, CUTTING CONDITION DETECTING METHOD, AND PROCESSING METHOD

Abstract

Provided is an endmill (5). The maximum spindle speed, per one minute, of a main spindle to which the endmill is attached is Smax. The number of teeth of the endmill (5) is N. The outer shape of the endmill (5) is Da. The natural frequency at which vibrations at the end of the endmill (5) reach a maximum level is 1. 1 and/or N are set so that when the diameter-direction infeed amount of the endmill (5) is set to Rd: i) 160/N6<Smax, if Rd is at least 4% of Da; and ii) 160/N3<Smax, if Rd is less than 4% of Da.

Claims

1. An endmill specification design method, comprising: setting 1 and/or N so as to satisfy the following, wherein when a maximum spindle speed per one minute of a main spindle having an endmill attached thereto is defined as Smax, the number of teeth of the endmill is defined as N, an outer shape of the endmill is defined as Da, a natural frequency at which a vibration is maximized in a tool tip of the endmill is defined as 1, and a radial depth of cut of the endmill is defined as Rd, i) in a case where Rd is equal to or greater than 4% of Da, 160/N6<Smax is satisfied, and ii) in a case where Rd is smaller than 4% of Da, 160/N3<Smax is satisfied.

2. The endmill specification design method according to claim 1, wherein bottom surface machining is performed in a case of i), and side surface machining is performed in a case of ii).

3. A cutting condition detecting method, comprising: setting a rotation speed of a main spindle having an endmill attached thereto so as to satisfy the following, wherein when a maximum spindle speed per one minute of the main spindle is defined as Smax, the number of teeth of the endmill is defined as N, an outer shape of the endmill is defined as Da, a natural frequency at which a vibration is maximized in a tool tip of the endmill is defined as 1, and a radial depth of cut of the endmill is defined as Rd, i) in a case where Rd is equal to or greater than 4% of Da, a range of 160/N6 to Smax is satisfied, and ii) in a case where Rd is smaller than 4% of Da, a range of 160/N3 to Smax is satisfied.

4. The cutting condition detecting method according to claim 3, wherein bottom surface machining is performed in a case of i), and side surface machining is performed in a case of ii).

5. The cutting condition detecting method according to claim 3, wherein the rotation speed of the main spindle is set to a rotation speed so as to avoid 60/N(m0.5) (m is a natural number), when the natural frequency that is a frequency higher than oil serving as the natural frequency at which the vibration is maximized in the tool tip of the endmill, that has a vibration peak independent of 1, and that has a peak value of the vibration which is equal to or greater than 1/10 of a peak value of 1 is defined as .

6. A processing method comprising: performing machining on a workpiece by using the cutting condition detecting method according to claim 3.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a schematic configuration diagram illustrating an endmill according to an embodiment of the present invention.

[0033] FIG. 2 is a graph illustrating a stable pocket.

[0034] FIG. 3 is a graph illustrating a stable region existing on a rotation speed higher than that of the stable pocket in FIG. 2.

[0035] FIG. 4 is a graph illustrating a ratio of each stable spindle speed to a radial depth of cut.

[0036] FIG. 5 is a graph illustrating vibration response characteristics of a tool tip of the endmill.

[0037] FIG. 6 is a graph illustrating the stable region for two vibration peaks.

DESCRIPTION OF EMBODIMENTS

[0038] As illustrated in FIG. 1, an endmill 10 has a shaft 14 extending in an axial direction, and a plurality of teeth 15 disposed in an outer periphery of the shaft 14. One end of the endmill 10 is attached to a main spindle 5 by using a fixing tool such as a chuck. The main spindle 5 is connected to a rotary shaft of a machine tool (not illustrated), and is rotated at a predetermined rotation speed instructed by a control unit. A maximum spindle speed Smax of the main spindle 5 is determined depending on capacity of the machine tool, and is set to 10,000 to 40,000 (rpm), for example.

[0039] A length from the main spindle 5 to a tool tip of the endmill 10 is set as an overhang length L. The overhang length L is set to be changed in accordance with processing conditions. The endmill 10 is mainly used in processing aluminum alloy, and is used in performing pocket processing on a member having a thickness of 100 mm to 500 mm, for example. For example, specific processing targets include aircraft structural components (keel beams or main wing center beams). A ratio L/Da of the overhang length L to a tool diameter Da of the endmill 10 is set to 5 or greater.

[0040] The tool diameter Da of the endmill 10 is set to 16 mm to 25 mm, and the number of teeth N is set to 10 to 25.

[0041] In machining performed by the endmill 10, a stable spindle speed Sn at which the endmill 10 can stably perform the machining without generating a regenerative chatter vibration is determined as the following equation.

Sn=160/N/n [rpm](1)

[0042] 1 is a natural frequency of the tool tip of the endmill 10, N is the number of teeth, and n is a natural number. For example, the natural frequency 1 can be obtained by performing tapping on the endmill 10 attached to the main spindle 5, and is a frequency indicating a largest vibration peak.

[0043] The rotation speed region within a predetermined range around the stable spindle speed Sn becomes the stable pocket. If the main spindle 5 is rotated inside the stable pocket, the regenerative chatter vibration can be avoided.

[0044] FIG. 2 illustrates a plurality of the stable pockets. In the drawing, a horizontal axis represents a main spindle rotation speed [rpm], and a vertical axis represents a horizontal cutting amount [mm]. The stable region is located below a curve, and an unstable region where the regenerative chatter vibration is generated is located above the curve.

[0045] The drawing illustrates a first stable pocket SP1 at a first stable spindle speed S1 defined as n=1 in Equation (1) above, a second stable pocket SP2 at a second stable spindle speed S2 defined as n=2, and a third stable pocket SP3 at a third stable spindle speed S3 defined as n=3. Each stable pocket is 1/n.sup.th of the first stable pocket SP1 (refer to Equation (1)).

[0046] In a case of using the stable pocket SP illustrated in FIG. 2, there are problems as follows. In the endmill 10 where L/Da is 5 or greater, the overhang length L is long. Accordingly, the natural frequency 1 decreases, and the main spindle rotation speed at which the stable pocket SP appears decreases. Therefore, the machining is less likely to be performed at high speed. In addition, a rotation speed width of the stable pocket SP is narrowed. Accordingly, the rotation speed is less likely to be adjusted. In addition, as the natural frequency 1 decreases, the stable pocket SP is closer to the natural frequency 1. Accordingly, a forced vibration is likely to be generated.

[0047] In contrast, the present inventor has found the following. As illustrated in FIG. 3, a stable pocket where the regenerative chatter vibration is not generated exists in a region exceeding the first stable pocket SP1 and further exceeding the natural frequency 1. The horizontal axis represents the main spindle rotation speed [rpm], and the vertical axis represents the horizontal cutting amount [mm]. The stable region is located below a curve, and an unstable region where the regenerative chatter vibration is generated is located above the curve.

[0048] The drawing illustrates a simulation of the endmill 10 where the number of teeth N is defined as 19, the tool diameter Da is defined as 25 mm, and the overhang length L is defined as 170 mm. This simulation is performed using a stability limit analysis of the regenerative chatter vibration in endmill processing, based on the above-described tool geometry and frequency characteristics thereof.

[0049] As can be understood from the drawing, a first high-speed stable pocket SP1 exists in a region of 6,000 [rpm] to 10,000 [rpm] which greatly exceeds the first stable pocket SP1, and a large second high-speed stable pocket SP2 exists in a region of 18,000 [rpm] or higher. The present embodiment adopts the high-speed stable pockets SP1 and SP2.

[0050] Furthermore, the present inventor has found the following. A shape of each stable pocket SPs illustrated in FIG. 3 is changed depending on the natural frequency 1 and the radial depth of cut Rd [mm] of the endmill 10. Therefore, the simulation is performed for various types of the endmill 10 by changing the natural frequency 1 and the radial depth of cut Rd. As a result, the present inventor has found that there is a predetermined relationship between the first stable spindle speed S1 and the first high-speed stable spindle speed S1 as illustrated in FIG. 4.

[0051] In FIG. 4, the horizontal axis represents Rd/Da [%], which is the percentage of the radial depth of cut Rd to the tool diameter Da of the endmill 10, and the vertical axis represents a ratio of the first high-speed stable spindle speed S1 to the first stable spindle speed S1. As can be understood from the drawing, S1/S1 is approximately 3 in a case where Rd/Da is smaller than 4%, and S1/S1 is approximately 6 in a case where Rd/Da is equal to or greater than 4%. That is, the meaning is as follows. In the case where Rd/Da is smaller than 4%, the first high-speed stable spindle speed S1 exists around 3 times the first stable spindle speed S1. In the case where Rd/Da is equal to or greater than 4%, the first high-speed stable spindle speed S1 exists around 6 times the first stable spindle speed S1. If the first high-speed stable pocket SP1 including the first high-speed stable spindle speed S1 is used, the machining can be stably performed at high speed by using the endmill 10.

[0052] Next, referring to FIGS. 5 and 6, influence on a vibration peak of the endmill 10 at the frequency higher than the natural frequency 1 will be examined. The above-described natural frequency 1 is the frequency which indicates the highest vibration peak in a case where the frequency of the tool tip of the endmill 10 is analyzed. In some cases, the frequency indicating an independent vibration peak may exist in the frequency higher than the natural frequency 1. Specifically, as illustrated in FIG. 5, in some cases, the independent vibration peak on the frequency side higher than the natural frequency 1 which is the first vibration peak may be recognized as a second peak frequency 2. As expressed in Equation (1), the stable spindle speed also exists in the second peak frequency 2, and an unstable region exists in a region having no stable spindle speed. FIG. 6 illustrates a result of examining the stable region and the unstable region for the second peak frequency 2.

[0053] In FIG. 6, the horizontal axis represents the main spindle rotation speed [rpm], and the vertical axis represents the horizontal cutting amount [mm]. The drawing illustrates a curve L1 indicating the stable region corresponding to the natural frequency 1, a curve L2 indicating the stable region corresponding to the second peak frequency 2, and a curve L3 obtained by superimposing the curves L1 and L2 on each other. As can be understood from the drawing, a region where L3 is greatly recessed downward exists around 14000 [rpm] indicated by a line segment L4. The reason is the influence caused by the curve L2 of the second peak frequency 2. The rotation speed region indicated by the line segment L4 is the unstable region. Accordingly, it is preferable to avoid the rotation speed region. Therefore, the main spindle rotation speed is limited as follows.

[0054] The natural frequency that is a frequency higher than 1 serving as the natural frequency at which the vibration is maximized in the tool tip of the endmill 10, that has the vibration peak independent of the natural frequency 1, and that has the peak value of the vibration which is equal to or greater than 1/10 of the peak value of 1 is defined as . It is assumed that the m-number of exists (m is a natural number). In this case, the rotation speed of the main spindle 5 is set so as to be the rotation speed avoiding 60/N/(m0.5). In this manner, it is possible to avoid the center rotation speed between the adjacent stable pockets.

Endmill Specification Design Method

[0055] Next, an endmill specification design method used based on the above-described concept will be described. Smax represents the maximum spindle speed of the main spindle 5. 1 and/or N are set so as to satisfy (160/N6<Smax, i) in a case where the radial depth of cut Rd is equal to or greater than 4% of the tool diameter Da, and so as to satisfy 160/N3<Smax, ii) in a case where the radial depth of cut Rd is smaller than 4% of the tool diameter Da.

[0056] In this manner, the rotation speed can be increased up to the main spindle rotation speed close to the maximum spindle speed Smax of the main spindle 5. Accordingly, the machining can be stably performed at high speed. For example, the natural frequency 1 is decreased by increasing the protrusion amount of the endmill. The first stable spindle speed S1 is decreased by increasing the number of teeth N. In this manner, the first high-speed stable pocket SP1 having the higher rotation speed than the first stable spindle speed S1 can be widely used.

[0057] In this case, bottom surface machining is preferably performed in the above-described case of i), and side surface machining is preferably performed in the above-described case of ii).

[0058] In the case of i), the radial depth of cut Rd is larger than that in the case of ii). Accordingly, the case of i) is suitable for the bottom surface machining in the pocket processing, particularly for the bottom surface finishing in the deep pocket processing. In the case of ii), the radial depth of cut Rd is smaller than that in the case of i). Accordingly, the case of ii) is suitable for the side surface machining, particularly for the single finishing processing in the deep axial cutting of the endmill.

Cutting Condition Detecting Method

[0059] Next, a cutting condition detecting method used based on the above-described concept will be described. Smax represents the maximum spindle speed of the main spindle 5. The rotation speed of the main spindle 5 is set so as to satisfy a range of 160/N6 to Smax, i) in a case where the radial depth of cut Rd is equal to or greater than 4% of the tool diameter Da, and so as to satisfy a range of 160/N3 to Smax, ii) in a case where the radial depth of cut Rd is smaller than 4% of the tool diameter Da.

[0060] The processing conditions are set to the above-described conditions. In this manner, a workpiece can be processed in the first high-speed stable pocket SP1 having the higher rotation speed than the first stable spindle speed S1. Therefore, the machining can be stably performed at high speed.

[0061] In this case, bottom surface machining is preferably performed in the above-described case of i), and side surface machining is preferably performed in the above-described case of ii).

[0062] In the case of i), the radial depth of cut Rd is larger than that in the case of ii). Accordingly, the case of i) is suitable for the bottom surface machining in the pocket processing, particularly for the bottom surface finishing in the deep pocket processing. In the case of ii), the radial depth of cut Rd is smaller than that in the case of i). Accordingly, the case of ii) is suitable for the side surface machining, particularly for the single finishing processing in the deep axial cutting of the endmill.

[0063] Furthermore, it is preferable to add the following conditions when the processing conditions are set. The rotation speed of the main spindle 5 is set so as to avoid +60/N(m0.5) (m is a natural number), when the natural frequency that is the frequency higher than the natural frequency 1 at which the vibration is maximized in the tool tip of the endmill 10, that has the vibration peak independent of 1, and that has the peak value of the vibration which is equal to or greater than 1/10 of the peak value of 1 is defined as .

[0064] Since has the frequency higher than 1, the stable spindle speed of may appear at the frequency higher than 1 in some cases. On the other hand, the regenerative chatter vibration appears between the adjacent stable spindle speeds (for example, between m=1 and 2) (refer to FIG. 6). Therefore, a median value that may be an unstable region between the adjacent stable spindle speeds of can be expressed by +60/N(m0.5). The rotation speed of the main spindle 5 is set so as to avoid the median value. In this manner, the processing can be more stably performed.

Processing Method

[0065] Next, a processing method used based on the above-described concept will be described. As the processing method, the machining is performed using the endmill 10 under the conditions of the above-described cutting condition detecting method. In this case, the endmill 10 obtained based on the above-described endmill specification design method is used. In this manner, the processing can be stably performed at high speed.

[0066] For example, in a case of the bottom surface finishing, the axial cutting amount is set to 1 mm or smaller, and the feeding amount per one tooth is set to 0.1 mm/tooth or smaller. In a case of the side surface finishing, the feeding amount per one tooth is set to 0.03 to 0.05 mm/tooth, and the axial cutting amount is set to the length corresponding to the protrusion amount of the endmill. Therefore, a single tool can cope with processing for workpieces having various depths. The above-described cutting amounts or feeding amounts are merely examples, and can be obtained through simulation or processing tests.

REFERENCE SIGNS LIST

[0067] 5: main spindle [0068] 10: endmill [0069] 14: shaft [0070] 15: tooth [0071] Da: tool diameter (of endmill) [0072] L: overhang length (of endmill) [0073] Smax: maximum spindle speed (of main spindle) [0074] Rd: radial depth of cut [0075] 1: natural frequency (of endmill tool tip) [0076] S1: first stable spindle speed [0077] S1: first high-speed stable spindle speed [0078] SP, SP1, SP2, SP3: stable pocket [0079] SP1: first high-speed stable pocket [0080] SP2: second high-speed stable pocket