Gear manufacturing method

Abstract

To improve process tolerance of a gear by suppressing chattering vibration caused by a tool at the time of processing the gear in skiving process.SOLUTION: A manufacturing method of a gear is a method which machines a workpiece by N path (N≥3) cutting of a skiving process to manufacture a gear. The manufacturing method comprises when a value of an addendum modification coefficient is Xm where maximum value of cutting force becomes the maximum from cutting start to cutting end in a Mth path (M is 2 or N) cutting comprises the steps of: preparing a tool whose addendum modification coefficient is larger than Xm; and machining the workpiece by the tool in the Mth path cutting.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a gear by skiving. [Background technology]

[0002] Skiving is one method for forming a gear from a workpiece. In skiving, the rotation axis of the tool is arranged so that it is inclined at a fixed angle (crossed axes angle) relative to the rotation axis of the workpiece. The tool has multiple cutter blades arranged side by side in the circumferential direction of the tool. The cutter blades are arranged at equal pitches in the circumferential direction of the tool (see, for example, Patent Document 1). As the tool rotates, the workpiece rotates in synchronization with the rotation of the tool, and the tool machines the workpiece. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-33732 Summary of the Invention [Problem to be solved by the invention]

[0004] When machining large-module gears using the above-described skiving process, chatter vibrations may occur during machining, which may result in a decrease in gear machining accuracy. An object of the present disclosure is to suppress chatter vibrations during skiving when machining a gear with a tool, thereby improving gear machining accuracy. [Means for solving the problem]

[0005] A gear manufacturing method according to one embodiment of the present disclosure is a method for manufacturing a gear by machining a workpiece through N (N≧3) cutting passes in a skiving process. The gear manufacturing method according to this embodiment includes: preparing a tool having a addendum modification coefficient greater than Xm, where Xm is the addendum modification coefficient that maximizes the cutting force from the start to the end of cutting in an Mth (=2 to N) cutting pass; and machining the workpiece with the tool in the Mth cutting pass.

[0006] As a result of extensive research, the inventors of the present disclosure have discovered the following. In the second and subsequent passes of N-pass cutting, the maximum value of the cutting force from the start to the end of cutting in one pass varies depending on the addendum coefficient of the tool. The value of the addendum coefficient at which the maximum value of the cutting force is greatest differs for each pass. Furthermore, by making the addendum coefficient of the tool larger than the value of the addendum coefficient at which the maximum value of the cutting force is greatest, the maximum value of the cutting force decreases.

[0007] In the gear manufacturing method according to this aspect, the Mth (=2 to N) cutting pass is performed using a tool with a addendum modification coefficient greater than the addendum modification coefficient Xm at which the maximum cutting force from the start to the end of cutting is maximized. This reduces the cutting force. As a result, chatter vibrations during gear machining with the tool are suppressed, improving gear machining accuracy.

[0008] In the Nth cutting pass, the value of the shift coefficient at which the maximum cutting force from the start to the end of cutting is maximized is defined as Xn, and the tool may have a shift coefficient greater than Xn. The inventors of the present disclosure have found that the value of the shift coefficient at which the maximum cutting force is maximized increases as the number of cutting passes increases. Therefore, by using a tool with a shift coefficient greater than Xn, the cutting force can be reduced in all cutting passes using the same tool.

[0009] Xn may be expressed by the following formula (1). Xn=Xw×(Zt / Zw) / cos(θ)×0.96-0.11 / cos(θ) (1) Zw is the number of grooves on the gear. Zt is the number of teeth on the tool. Xw is the addendum shift coefficient of the workpiece. θ is the crossed axis angle during machining.

[0010] A tool for machining an internal gear can be considered an external gear. Therefore, the tool may be manufactured according to the design criteria of an external gear with the same module, pressure angle, and number of teeth. The tool may have a profile modification coefficient smaller than the value of the profile modification coefficient at which Sa is 0.25 × m. Sa is the apex width of the tooth tip of an external gear with the same module, pressure angle, and number of teeth as the tool. m is the module of the tool. This prevents the cutting edge of the tool from becoming too thin. [Effects of the Invention]

[0011] The gear manufacturing method according to the present disclosure reduces the cutting load when a tool is used in skiving to machine a gear, thereby suppressing chatter vibrations of the tool, improving the gear machining accuracy, and extending the tool life. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a side cross-sectional view showing a cutter head and a workpiece according to the embodiment. [Figure 2] FIG. 2 is a top view showing the cutter head and the workpiece. [Figure 3] FIG. [Figure 4A] FIG. 10 is a diagram showing the operation of a tool in one-pass cutting. [Figure 4B] FIG. 10 is a diagram showing the operation of a tool in one-pass cutting. [Figure 4C] FIG. 10 is a diagram showing the operation of a tool in one-pass cutting. [Figure 5] 4 is a table showing parameters that define the shapes of a workpiece and a tool according to the first embodiment. [Figure 6] FIG. 10 is a diagram showing the depth of cut in each of N cutting passes. [Figure 7] 10 is a graph showing the relationship between the addendum modification coefficient of the tool according to the first example and the maximum cutting force in cutting for each pass. [Figure 8A] 8 is a diagram showing the position of the rake face of the cutter blade of the tool and the cutting width at point P5 (X5) in FIG. 7. FIG. [Figure 8B] 8 shows the position of the rake face of the cutter blade of the tool and the cutting width at point P5 (0.9) in FIG. [Figure 9A] FIG. 10 is a diagram showing the relationship between workpiece speed, tool speed, and cutting speed for a zero-shift tool. [Figure 9B] FIG. 10 is a diagram showing the relationship between workpiece speed, tool speed, and cutting speed for a tool with a positive addendum coefficient. [Figure 10] 10 is a table showing parameters that define the shapes of a workpiece and a tool according to a second embodiment. [Figure 11] 10 is a table showing the relationship between the addendum modification coefficient of the tool according to the second example and the maximum cutting force in cutting for each pass. [Figure 12] 10 is a table showing parameters that define the shapes of a workpiece and a tool according to a third embodiment. [Figure 13] 10 is a table showing the relationship between the addendum modification coefficient of the tool according to the third example and the maximum cutting force in cutting for each pass. [Figure 14] 10 is a table showing parameters that define the shapes of a sample workpiece and a tool. [Figure 15] 1 is a graph showing the results of a regression analysis performed on a sample. DETAILED DESCRIPTION OF THE INVENTION

[0013] A gear manufacturing method according to an embodiment will be described below with reference to the drawings. FIG. 1 is a side cross-sectional view showing a tool 1 and a workpiece 2 according to an embodiment. FIG. 2 is a top view showing the tool 1 and the workpiece 2 according to an embodiment. The tool 1 is a cutter head used in a skiving machine. The tool 1 cuts the workpiece 2 by skiving to form a gear having a plurality of tooth grooves 3. Note that in the drawings, only some of the plurality of tooth grooves 3 are designated by the reference numeral 3, and the reference numerals for the other tooth grooves 3 are omitted.

[0014] The tool 1 and workpiece 2 are rotated synchronously with each other by a driving device (not shown). As shown in FIG. 1, the rotation axis A1 of the tool 1 is inclined with respect to the rotation axis A2 of the workpiece 2. The tool 1 cuts the inner surface of the workpiece 2 to form tooth grooves by moving in a direction parallel to the rotation axis A2 of the workpiece 2 while rotating around the rotation axis A1. The rotation axis A1 of the tool 1 and an axis parallel to the rotation axis A2 of the workpiece 2 intersect at an axis crossing angle θ.

[0015] As shown in FIG. 2, the tool 1 has a plurality of cutter blades 4. Note that in the drawing, only some of the plurality of cutter blades 4 are labeled with the reference numeral 4, and the reference numerals of the other cutter blades 4 are omitted. FIG. 3 is an enlarged view of the tool 1. In FIG. 3, the two-dot chain line indicates the shape of the cutter blade 5 of the zero-displacement tool. The cutter blade 4 of the tool 1 is displaced relative to the cutter blade 5 of the zero-displacement tool. The zero-displacement tool is a tool with zero displacement.

[0016] The cutter blade 4 of the tool 1 is shifted by an amount m × Xt relative to the cutter blade 5 of the zero-shift tool. m is the module of the tool 1. Xt is the shift coefficient of the tool 1. As shown in Figure 3, the tool 1 has a positive shift coefficient. In Figure 3, the dashed line indicates the shape of the cutter blade 4' of the tool 1, which has a negative shift coefficient.

[0017] As a result of extensive research, the inventors of the present disclosure have discovered the following. When manufacturing a gear by machining a workpiece through N (N≧3) cutting passes in skiving, in the second and subsequent cuts, the maximum value of the cutting force from the start to the end of cutting in one pass varies depending on the addendum modification coefficient of tool 1. The value of the addendum modification coefficient at which the maximum value of the cutting force is greatest differs for each pass. As the number of cutting passes increases, the value of the addendum modification coefficient at which the maximum value of the cutting force is greatest increases. Furthermore, by making the addendum modification coefficient of tool 1 larger than the value of the addendum modification coefficient at which the maximum value of the cutting force is greatest, the maximum value of the cutting force decreases.

[0018] 4A to 4C show the operation of the tool 1 in one cutting pass. As shown in Fig. 4A to 4C, one cutting pass is a series of machining operations in which the tool 1 is lowered toward the bottom end 21 of the workpiece 2, the workpiece 2 is cut, and then the tool 1 is raised and returned to the top end 22 of the workpiece 2. D1 indicates the cutting depth in the first pass. The two-dot chain line 10 indicates the circular base of the cutting edge.

[0019] A method for determining the addendum modification coefficient of the tool 1 based on the above findings will be described below.

[0020] (First Example) FIG. 5 is a table showing parameters that define the shapes of the workpiece 2 and tool 1 according to the first embodiment. FIG. 6 is a diagram showing the depth of cut for each of N cutting passes. In the first embodiment, the workpiece 2 is machined using five cutting passes to form tooth spaces. In FIG. 6, 6, indicated by a two-dot chain line, indicates the target shape of the tooth spaces to be formed in the workpiece 2. Furthermore, 7 indicates the cut shape of the workpiece 2.

[0021] In the first embodiment, the cutting depths D1 to D5 of the first to fifth passes are as follows. D1=2.18mm D2=1.61mm D3=1.25mm D4=1.00mm D5=0.2mm (finish) 7 is a graph showing the relationship between the addendum coefficient of the tool 1 according to the first embodiment and the maximum cutting force in each cutting pass. The maximum cutting force is the maximum value of the cutting force from the start to the end of one cutting pass. For example, in FIG. 7, points P1 to P5 indicate the maximum cutting forces in the first to fifth cutting passes when a workpiece 2 is cut using the tool 1, each having a addendum coefficient of 0.64.

[0022] L1 shows the relationship between the addendum shift coefficient of tool 1 and the maximum cutting force in the first cutting pass. L2 shows the relationship between the addendum shift coefficient of tool 1 and the maximum cutting force in the second cutting pass. L3 shows the relationship between the addendum shift coefficient of tool 1 and the maximum cutting force in the third cutting pass. L4 shows the relationship between the addendum shift coefficient of tool 1 and the maximum cutting force in the fourth cutting pass. L5 shows the relationship between the addendum shift coefficient of tool 1 and the maximum cutting force in the fifth cutting pass. As shown in Figure 7, even in the same cutting pass, the maximum cutting force changes depending on the addendum shift coefficient of tool 1.

[0023] As shown in Figure 7, in the second cutting pass, the maximum cutting force is greatest when the addendum shift coefficient Xt is X2. In the third cutting pass, the maximum cutting force is greatest when the addendum shift coefficient Xt is X3. In the fourth cutting pass, the maximum cutting force is greatest when the addendum shift coefficient Xt is X4. In the fifth cutting pass, the maximum cutting force is greatest when the addendum shift coefficient Xt is X5.

[0024] Therefore, in the second cutting pass, using a tool 1 with a modification coefficient greater than X2 reduces the maximum cutting force. In the third cutting pass, using a tool 1 with a modification coefficient greater than X3 reduces the maximum cutting force. In the fourth cutting pass, using a tool 1 with a modification coefficient greater than X4 reduces the maximum cutting force. In the fifth cutting pass, using a tool 1 with a modification coefficient greater than X5 reduces the maximum cutting force.

[0025] As shown in FIG. 7, in the second and subsequent cutting passes, the values ​​of the dislocation coefficients X2 to X5 at which the maximum cutting force is maximized satisfy the relationship of the following formula (2). X2 <X3<X4<X5 (2) The differences between X2 and X3, X3 and X4, and X4 and X5 are positively correlated with the cutting depths D3, D4, and D5 of X3, X4, and X5, respectively. For example, because D5 is smaller than D3 and D4, the difference between X4 and X5 is also smaller than the difference between X2 and X3 and the difference between X3 and X4. Therefore, using a tool 1 with a shift coefficient larger than X5 reduces the maximum cutting force in all passes except the first pass. Note that using a tool 1 with a shift coefficient smaller than X5 also reduces the maximum cutting force in the fifth pass. However, because the maximum cutting force in other passes may be larger, it is preferable for the shift coefficient of tool 1 to be larger than X5.

[0026] The reason for the reduction in maximum cutting force as described above is thought to be as follows. Figure 8A shows the position of the rake face of the cutter blade of tool 1 and the cutting width at point P5 (X5) in Figure 7. In Figure 8A, multiple curves Y1 indicate changes in the position of the rake face, and the hatched portion W1 indicates the cutting width. The cutting width is the portion of the rake face that is in contact with the workpiece 2. Point P5 (X5) indicates the maximum cutting force by tool 1 with a dislocation coefficient of X5 during the fifth cutting pass.

[0027] Figure 8B shows the position of the rake face of the cutter blade of tool 1 and the cutting width at point P5 (0.9) in Figure 7. In Figure 8B, multiple curves Y2 indicate changes in the rake face position, and the hatched portion W2 indicates the cutting width. Point P5 (0.9) indicates the maximum cutting force by tool 1, which has a larger addendum coefficient (0.9) than X5.

[0028] 8A and 8B, in the fifth cutting pass, when a tool 1 having a addendum coefficient larger than X5 is used, the cutting width W2 at each cutting face is smaller than the cutting width W1 at each cutting face when a tool 1 having a addendum coefficient X5 is used. Therefore, when a tool 1 having a addendum coefficient larger than X5 is used, the area of ​​the workpiece 2 simultaneously cut by the tool 1 becomes smaller, which is thought to reduce the maximum cutting force.

[0029] The reason why the cutting width changes depending on the offset coefficient is thought to be as follows. Figure 9A shows the relationship between the speed Vw of the workpiece 2, the speed Vt of the tool 1, and the cutting speed Vc when using a zero-offset shift tool. Both speeds Vw and Vt are peripheral speeds. As shown in Figure 9A, when a zero-offset shift tool is used in a skiving machine, the speed Vw of the workpiece 2 and the speed Vt of the tool 1 are set so that the cutting speed Vc does not have a horizontal component on the pitch circle between the tool 1 and the workpiece 2. In other words, the cutting speed Vc is parallel to the rotation axis of the workpiece 2. With a zero-offset shift tool, both sides of the cutter blade cut the workpiece 2 simultaneously, resulting in a large contact width and a large cutting force.

[0030] FIG. 9B is a diagram showing the relationship between the speed Vw of the workpiece 2, the speed Vt of the tool 1, and the cutting speed Vc when using a tool 1 with a positive addendum modification coefficient. As shown in FIG. 9B, when using a tool 1 with a positive addendum modification coefficient, the speed Vt of the tool 1 increases as the outer diameter of the tool 1 increases. If the speed Vw of the workpiece 2 remains the same, the increase in the speed Vt of the tool 1 changes the horizontal component of the cutting speed Vc. This changes the timing at which each side of the cutter blade cuts the workpiece 2.

[0031] For example, in the case of tool 1, which has a larger dislocation coefficient (0.9) than the above-mentioned X5, the timing at which one side of the cutter blade cuts the workpiece 2 is advanced and the timing at which the other side cuts the workpiece 2 is delayed compared to the zero dislocation tool. As a result, the cutting width becomes smaller and the cutting force is reduced.

[0032] The upper limit of the addendum modification coefficient of tool 1 is determined as follows: As the addendum modification coefficient increases, the apex width of the cutter blade decreases, and the cutting edge of the cutter blade becomes sharper. Therefore, it is preferable that the addendum modification coefficient of tool 1 is smaller than the value of the addendum modification coefficient where Sa is 0.25 × m. Sa is the module of tool 1, the pressure angle, and the apex width of the tooth tip of an external gear that has the same number of teeth. m is the module of tool 1.

[0033] From the above, in the first embodiment, the addendum modification coefficient of the tool 1 is 0.8 to 1.0.

[0034] (Second Example) Fig. 10 is a table showing parameters that define the shapes of the workpiece 2 and the tool 1 according to the second embodiment. Fig. 11 is a table showing the relationship between the addendum coefficient of the tool 1 according to the second embodiment and the maximum cutting force in each cutting pass. In Fig. 11, the column showing the maximum value of the maximum cutting force in each cutting pass is hatched.

[0035] As shown in FIG. 11, in the second and subsequent cutting passes, the values ​​of the dislocation coefficients X2 to X12 at which the maximum cutting force is maximized satisfy the relationship of the following formula (3). X2 <X3<X4<X5<X6<X7<X8<X9 (3) Therefore, by using a tool 1 having a shift coefficient larger than X9, the maximum cutting force in all passes except the first pass is reduced. The upper limit of the shift coefficient of the tool 1 is determined in the same manner as in the first embodiment. In the final pass of the cutting process (finishing pass), the difference from the previous pass is small because the cutting depth D is small. Therefore, the shift coefficients may be approximately equal.

[0036] From the above, in the second embodiment, the addendum modification coefficient of the tool 1 is 0.2 to 0.4.

[0037] (Third Example) Fig. 12 is a table showing parameters that define the shapes of the workpiece 2 and tool 1 according to the third embodiment. Fig. 13 is a table showing the relationship between the addendum coefficient of the tool 1 according to the third embodiment and the maximum cutting force in each cutting pass. In Fig. 13, the column showing the maximum value of the maximum cutting force in each cutting pass is hatched.

[0038] As shown in FIG. 13, in the second and subsequent cutting passes, the values ​​of the dislocation coefficients X2 to X12 at which the maximum cutting force is maximized satisfy the relationship of the following formula (4). X2 <X3<X4<X5<X6<X7<X8<X9<X10<X11 (4) Therefore, by using a tool 1 having a addendum modification coefficient larger than X11, the maximum cutting force in all passes except the first pass is reduced. The upper limit of the addendum modification coefficient of the tool 1 is determined in the same manner as in the first embodiment.

[0039] From the above, in the third embodiment, the addendum modification coefficient of the tool 1 is 0 to 0.4.

[0040] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0041] In the above embodiment, the tool 1 machines the workpiece 2 into an internal gear. However, the tool 1 may also machine the workpiece 2 into an external gear. In the above embodiment, the tool 1 machines the workpiece 2 into a spur gear. However, the tool 1 may also machine the workpiece 2 into a helical gear.

[0042] In the N-th pass of cutting, the value Xn of the dislocation coefficient at which the maximum value of the cutting force from the start to the end of cutting is maximized may be calculated by the following formula (5).

[0043] Xn=Xw×(Zt / Zw) / cos(θ)×0.96-0.11 / cos(θ) (5) Zw is the number of grooves on the gear. Zt is the number of teeth on tool 1. Xw is the addendum modification coefficient of workpiece 2. θ is the crossed axis angle. The second term on the right side of equation (5) can be approximated as 0.12. Equation (5) is derived as follows:

[0044] The timing at which the cutter blade 4 of the tool 1 comes into contact with the tooth flanks on both sides of the tooth space 3 of the workpiece 2 changes due to the change in the horizontal component of the cutting speed Vc described above. When the cutter blade 4 of the tool 1 comes into contact with the tooth flanks on both sides of the tooth space 3 of the workpiece 2 at the same time, the maximum value of the cutting force increases. This situation occurs during the M pass when the addendum modification coefficient of the tool 1 is near Xm.

[0045] The rotation speed St of tool 1 and the rotation speed Sw of workpiece 2 follow the relationship St × Zt = Sw × Zw, since there is one tooth engaged with each other. That is, Sw = St × Xt / Zw. The speed Vt of tool 1 varies depending on the number of teeth Zt of tool 1, module m, crossed axis angle θ, addendum modification coefficient Xt of tool 1, and rotation speed St of tool 1. The peripheral speed of a zero-profile tool is Zt × m / cosθ × St. Taking the addendum modification coefficient into account, the peripheral speed is (Zt × m / cosθ + 2 × m × Xt) × St. The speed Vw of workpiece 2 varies depending on the number of grooves (number of teeth) Zw of workpiece 2, module m, addendum modification coefficient Xw of workpiece 2, and rotation speed Sw of workpiece 2. The peripheral speed of a zero-profile workpiece is Zw × m × Sw. Taking the addendum modification coefficient into account, the peripheral speed is (Zw × m + 2 × m × Xw) × Sw.

[0046] When machining a zero-shift workpiece using a zero-shift tool, the peripheral speed of tool 1 is Zt×m / cosθ×St, and the peripheral speed of workpiece 2 is Zw×m×Sw. The horizontal component is expressed as Zt×m / cosθ×St×cosθ-Zw×m×Sw, and its value is 0.

[0047] When the offset coefficients of tool 1 and workpiece 2 are taken into consideration, the horizontal component can be expressed as (Zt×m / cosθ+2×m×Xt)×St×cosθ-(Zw×m+2×m×Xw)×Sw=2×m×Xt×St×cosθ-2×m×Xw×Sw=2×m×(Xt×St×cosθ-Xw×Sw)=2×m×St×(Xt×cosθ-Xw×Zt / Zw).

[0048] The horizontal component is determined by the magnitude relationship between Xt × cosθ and Xw × Zt / Zw. Therefore, Xn was substituted for Xt, and a regression analysis was performed on the relationship between Xn × cosθ and Xw × Zt / Zw using five samples of tool 1 and workpiece 2 shown in Figure 14. As a result, as shown in Figure 15, a high correlation of R = 0.997 was obtained with Xn × cosθ = 0.96 × Xw × Zt / Zw - 0.11. From the above, the equation Xn = 0.96 × Xw × Zt / (Zw × cosθ) - 0.11 / cosθ is obtained.

[0049] Alternatively, the addendum modification coefficient Xn may be estimated as follows: First, multiple workpieces 2 are experimentally machined using tools 1 each having a different addendum modification coefficient. The cutting force in the Nth pass is measured for each workpiece 2. Then, the addendum modification coefficient Xn is estimated based on the relationship between the maximum measured cutting force and the addendum modification coefficient. [Industrial Applicability]

[0050] The gear manufacturing method according to the present disclosure reduces the cutting load when a tool is used in skiving to machine a gear, thereby suppressing chatter vibrations of the tool, improving the gear machining accuracy, and extending the tool life.

Claims

1. A method for manufacturing a gear by machining a workpiece through N passes (N≧3) of cutting in a skiving process, comprising: In the M-th pass (=2 to N) of cutting, a value of the addendum coefficient at which the maximum value of the cutting force from the start to the end of cutting is maximized is set to Xm, and a tool having an addendum coefficient greater than Xm is prepared; machining the workpiece with the tool in the M-pass cutting; A gear manufacturing method comprising:

2. In the N-th pass of cutting, the value of the dislocation coefficient at which the maximum value of the cutting force from the start to the end of cutting is maximized is defined as Xn, The tool has a shift coefficient greater than Xn. The method for manufacturing a gear according to claim 1 .

3. When the number of grooves of the gear is Zw, the number of teeth of the tool is Zt, the addendum modification coefficient of the workpiece is Xw, and the crossed axis angle formed by the rotation axis of the tool and an axis parallel to the rotation axis of the workpiece is θ, Xn is expressed by the following equation: Xn=Xw×(Zt / Zw) / cos(θ)×0.96-0.11 / cos(θ) The method for manufacturing a gear according to claim 2 .

Images