Patent Application
20200061723
The present invention relates to an endmill specification design method, a cutting condition detecting method, and a processing method.
In recent years, aircraft structural components are progressively integrated with each other, and component shapes thereof are more complicated. A product height increases. Consequently, there is an increasing need for shape processing using a protruding long tool protruding beyond L/D (overhang length/diameter)=5. These components become joint parts as primary structural members in many cases. Accordingly, processed surface characteristics of the components are important. However, the protruding long tool has a problem of a regenerative chatter vibration generated on the tool side, thereby causing a problem in that a processed surface may be defective and a processing time may be lengthened. In general, rigidity is proportional to the cube of a protrusion amount. Accordingly, when the components are processed using the long tool, a worker uses a stable pocket serving as a rotation speed region which can avoid the regenerative chatter vibration. In this manner, the worker further reduces a load as much as possible. Therefore, the processing time is extremely lengthened. Moreover, since one surface is processed in multiple paths, a mismatch occurs between the paths. Accordingly, hand finishing is required after the surface is processed. In addition, the stable pocket is an integral fraction of natural vibration frequencies. Accordingly, as the rigidity is lowered (as natural vibration is small), rotation speed is lowered, thereby degrading efficiency.
In order to cope with this problem, the following processing method called single finishing has been recently promoted. In a case of side surface finishing, a side surface is finished in one step. However, this processing also has the following problems.
In addition, in a case of bottom surface finishing for a deep pocket, processing is performed using a whole diameter of the tool. Accordingly, the chatter vibration is likely to be generated. Therefore, cutting is generally performed by reducing radial cutting or feeding.
In view of these circumstances, as a tool which is less likely to vibrate, there are provided some inventions and products relating to a tooth shape. However, tool manufacturers in the related art have insufficient viewpoints of vibration characteristics. Therefore, dedicated tools have narrow application conditions. The single finishing is very unstable, and a user has difficulties in using the single finishing.
PTL 1 discloses a processing method of an endmill focusing on vibration characteristics. That is, PTL 1 discloses a method of using an effect (process damping) in which a tool and a workpiece are damped by coming into contact with each other during processing in a case of low-speed cutting.
[PTL 1] Specification of U.S. Pat. No. 8,875,367
However, according to PTL 1, the natural frequency is raised through weight reduction of the tool so that the process damping in a low-speed region is used in a medium-speed region. Consequently, there is a limitation in further using the process damping in a high-speed region.
In view of these problems, the present disclosure aims to perform processing by stably using an endmill at a high speed.
According to an aspect of the present invention, there is provided an endmill specification design method including setting ω1 and/or N so as to satisfy the following. 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 ω1, 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, ω1×60/N×6<Smax is satisfied, and ii) in a case where Rd is smaller than 4% of Da, ω1×60/N×3<Smax is satisfied.
A stable spindle speed at which the endmill can stably perform machining without generating a regenerative chatter vibration is defined as ω1×60/N/n (n is a natural number). Through examinations, the present inventor has found that the rotation speed higher than a first stable spindle speed at which n is defined as 1 also has a wide stable region. Then, this stable region is changed by the radial depth of cut Rd of the endmill. Therefore, ω1 and/or N are set so as to satisfy the following.
i) In a case where Rd is equal to or greater than 4% of Da, ω1×60/N×6<Smax is satisfied.
ii) In a case where Rd is smaller than 4% of Da, ω1×60/N×2<Smax is satisfied.
In this manner, the main spindle can be increased to the rotation speed close to the maximum spindle speed Smax, and high speed and stable machining can be performed. For example, the natural frequency ω1 is decreased by increasing a protrusion amount of the endmill. The first stable spindle speed is decreased by increasing the number of teeth N. In this manner, a stable region having a higher rotation speed than the first stable spindle speed can be widely used.
In the endmill specification design method according to the aspect of the present invention, bottom surface machining may be performed in a case of i), and side surface machining may be performed in a case of ii).
In the case of i), the radial depth of cut is larger than that in the case of ii). Accordingly, the case of i) is suitable for bottom surface machining in pocket processing, particularly for bottom surface finishing in deep pocket processing. In the case of ii), the radial depth of cut is smaller than that in the case of i). Accordingly, the case of i) is suitable for side surface machining, particularly for single finishing processing in
According to another aspect of the present invention, there is provided a cutting condition detecting method including setting a rotation speed of a main spindle having an endmill attached thereto so as to satisfy the following. 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 ω1, 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 ω1×60/N×6 to Smax is satisfied, and ii) in a case where Rd is smaller than 4% of Da, a range of ω1×60/N×3 to Smax is satisfied.
The stable spindle speed at which the endmill can stably perform the machining without generating the regenerative chatter vibration is ω1×60/N/n (n is a natural number). Through examinations, the present inventor has found that the rotation speed higher than the first stable spindle speed at which n is defined as 1 also has the wide stable region. Then, this stable region is changed by the radial depth of cut Rd of the endmill.
Therefore, the rotation speed of the main spindle is set so as to satisfy the following.
i) In a case where Rd is equal to or greater than 4% of Da, a range of ω1×60/N×6 to Smax is satisfied.
ii) In a case where Rd is smaller than 4% of Da, a range of ω1×60/N×3 to Smax is satisfied.
In this manner, a workpiece can be processed at the rotation speed higher than the first stable spindle speed, and the machining can be stably performed at high speed.
In the cutting condition detecting method according to the aspect of the present invention, bottom surface machining may be performed in a case of i), and side surface machining may be performed in a case of ii).
In the case of i), the radial depth of cut 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 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.
In the cutting condition detecting method according to the aspect of the present invention, the rotation speed of the main spindle is set to a rotation speed so as to avoid ω′×60/N(m−0.5) (m is a natural number), when the natural frequency that is a frequency higher than ω1 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 ω1, and that has a peak value of the vibration which is equal to or greater than 1/10 of a peak value of ω1 is defined as ω′.
When the natural frequency that is a frequency higher than ω1 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 ω1, and that has a peak value of the vibration which is equal to or greater than 1/10 of a peak value of ω1 is defined as ω′, the stable spindle speed is also set as ω′×60/N/n for ω′ (n is a natural number). Since ω′ has the frequency higher than ω1, the stable spindle speed of ω′ may appear at the frequency higher than ω1 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). Therefore, a median value that may be an unstable region between the adjacent stable spindle speeds of ω′ can be expressed by ω′×60/N(m−0.5). The rotation speed of the main spindle is set so as to avoid the median value. In this manner, the workpiece can be more stably processed.
According to still another aspect of the present invention, there is provided a processing method including performing machining on a workpiece by using any one of the cutting condition detecting methods.
The workpiece can be stably processed at high speed by using the above-described cutting condition detecting method. For example, in a case of the bottom surface finishing, an axial cutting amount is set to 1 mm or smaller, and a 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 a 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.
The workpiece can be stably processed at high speed by using the endmill.
As illustrated in
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.
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.
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=ω1×60/N/n [rpm] (1)
ω1 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 ω1 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.
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.
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/nth of the first stable pocket SP1 (refer to Equation (1)).
In a case of using the stable pocket SP illustrated in
In contrast, the present inventor has found the following. As illustrated in
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.
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′.
Furthermore, the present inventor has found the following. A shape of each stable pocket SPs illustrated in
In
Next, referring to
In
The natural frequency that is a frequency higher than ω1 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 ω1, and that has the peak value of the vibration which is equal to or greater than 1/10 of the peak value of ω1 is defined as ω′. It is assumed that the m-number of ω′ 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 ω′×60/N/(m−0.5). In this manner, it is possible to avoid the center rotation speed between the adjacent stable pockets.
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. ω1 and/or N are set so as to satisfy (ω1×60/N×6<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 ω1×60/N×3<Smax, ii) in a case where the radial depth of cut Rd is smaller than 4% of the tool diameter Da.
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 ω1 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.
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).
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.
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 ω1×60/N×6 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 ω1×60/N×3 to Smax, ii) in a case where the radial depth of cut Rd is smaller than 4% of the tool diameter Da.
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.
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).
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.
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 ω+×60/N(m−0.5) (m is a natural number), when the natural frequency that is the frequency higher than the natural frequency ω1 at which the vibration is maximized in the tool tip of the endmill 10, that has the vibration peak independent of ω1, and that has the peak value of the vibration which is equal to or greater than 1/10 of the peak value of ω1 is defined as ω′.
Since ω′ has the frequency higher than ω1, the stable spindle speed of ω′ may appear at the frequency higher than ω1 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
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.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/038581 | 10/25/2017 | WO | 00 |
