JP2000317773A - Helical machining method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a helical machining method capable of efficiently carrying out a cutting machining. SOLUTION: An intended machining area R is divided into plural partial machining areas RD capable of being machined by a closed curved line C of an optimum length. The optimum length LD of the closed curved line CL' is determined based on the shape, dimension and so on of an end mill. In each partial machining area RD, if machining is carried out by means of the closed curved line CL' close to the optimum length, there is no need for restricting a process for making relative moving speed small, under control, and the amount of cutting per hour can be made great, so that a cutting machining can thereby be efficiently carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a helical machining method for machining a workpiece by drawing a spiral trajectory on the workpiece at the end of an end mill, and a recording medium on which a helical machining program is recorded. Things.

[0002]

2. Description of the Related Art An example of a helical machining method is disclosed in
No. 04303. The helical machining method described in this publication is such that the end mill and the workpiece are rotated relative to each other along the same closed curve when viewed from a direction parallel to the end mill axis in a direction perpendicular to the end mill axis. At the same time, the end mill is moved in a direction parallel to the axis of the end mill by a predetermined amount with respect to the unit amount of relative movement in the direction orthogonal to the axis of the end mill, so that the tip of the end mill draws a helical trajectory. This is a helical machining method that cuts and removes a portion of a workpiece along the helical trajectory, and thereafter repeats the same cutting and removal while changing a closed curve, thereby cutting a desired region of the workpiece. The closed curves are set in multiples substantially parallel to the contours of the desired area, and the end mill and the workpiece are relatively moved along the helical trajectory determined for each of the multiple closed curves. The helical trajectory is
It is determined from the closed curve and the cutting depth of the end mill.

[0003] However, the conventional helical machining method has room for improvement in terms of machining efficiency. Processing efficiency is
The product can be improved by increasing the product of the relative movement speed (feed speed) between the end mill and the workpiece and the axial depth of cut, that is, the amount of cutting per hour (amount of chips discharged per hour). The amount of cutting can be increased when the bending component applied to the end mill is small and cutting can be performed stably. The bending force applied to the end mill is
It is known that it changes according to the relationship between the shape of the end mill and the length of the closed curve, and becomes the smallest when the length of the closed curve is an optimum length determined based on the shape and dimensions of the end mill. However, as described above, when multiple closed curves are set, not all closed curves can be set as closed curves of the optimum length. If the closed curve is not the optimum length, the cutting becomes unstable, and the cutting amount per hour must be reduced as compared with the case where the cutting is stable, so that the cutting cannot be performed efficiently.

[0004] In addition, the minimum amount of cutting per unit time allowed in each of the multiple closed curves of the desired region is often set to the cutting amount per unit time for the entire desired region. In this case, In addition, the cutting for all the closed curves is performed with the minimum cutting amount per time, and the processing efficiency is further deteriorated. If the area of the machining area is large, the difference between the length of the outermost or innermost closed curve and the optimal length increases, and the amount of cutting per hour when machining the entire machining area is limited to a small amount. In particular, the processing efficiency becomes particularly poor.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has an object to provide a helical machining method capable of efficiently machining a desired region of a workpiece. According to the present invention, a helical processing method and a recording medium according to the following embodiments can be obtained. As in the case of the claims, each aspect is divided into sections, each section is numbered, and if necessary, the other sections are cited in a form in which the numbers are cited. This is for the purpose of facilitating the understanding of the present invention and should not be construed as limiting the technical features and combinations thereof described in the present specification to those described in the following sections. . Further, even when a plurality of items are described in one section, the plurality of items need not always be employed together, and only some of the items may be employed. (1) The end mill and the workpiece are relatively moved in a direction orthogonal to the axis of the end mill so as to rotate along the same closed curve when viewed from a direction parallel to the axis of the end mill, and the end mill is moved. By approaching each other in a direction parallel to the axis of the end mill by a predetermined amount with respect to the unit amount of relative movement in the direction orthogonal to the axis, the helical trajectory is drawn at the tip of the end mill and the helical trajectory of the workpiece is In the helical machining method for cutting a desired area of the workpiece by cutting and removing the portion along the same area and thereafter repeating the same cutting and removing the closed curve, the desired area is defined as the closed curve. The length is divided into partial areas that can be machined only by a closed curve that is near the optimum length where cutting by the end mill is most stable, By sequentially performing the cutting of the divided regions, the helical machining method characterized by cutting the desired area total (claim 1). According to the helical machining method described in this section, since cutting can be performed in the most stable state or a state close thereto in each of the partial regions, the amount of cutting per hour can be increased, and efficient cutting can be performed. it can. The optimal length of the closed curve is a length at which cutting can be performed most stably. The state in which the cutting process is most stable is, for example, a state in which the bending component applied to the end mill is the smallest, and the length at which the bending component is the smallest is the optimum length. It is known that in the case where the end mill has one cutting edge, the bending component force applied to the end mill becomes the smallest when the amount of front cutting and the amount of rear cutting accompanying rotation of the cutting edge are equal. If the cutting operation is in the most stable state, the cutting amount per time can be increased. The ratio between the forward cutting amount and the rearward cutting amount corresponds to the shape and dimensions of the end mill (for example, the number, arrangement, and turning radius of the cutting edges. Is determined based on the distance between the center line of rotation of the end mill and the outermost peripheral edge of the cutting edge) and the length of the closed curve. Therefore, when the ratio is 1, the length of the closed curve can be set as the optimum length. It is.
Note that the optimum length of the closed curve can be determined in the same manner even when a plurality of cutting edges are provided. When cutting is performed in each partial region, the end mill and the workpiece are relatively moved along a helical trajectory corresponding to a closed curve. The helical trajectory is determined from the closed curve and the cutting depth. The cutting depth is set according to the end mill capacity (shape, size, bending rigidity, etc.) together with the feed speed. In many cases, the cutting depth is set to maximize the cutting depth per hour. The speed can be changed to some extent in relation to other conditions. Further, depending on the shape and dimensions of the desired region, there are cases where the partial region cannot be set so that the closed curve has the optimum length, or it is not desirable to set such a portion for some reason. In this case, the desired region may be divided so that the processing of the partial region can be performed only by the closed curve near the optimum length. The number of the “closed curve near the optimum length” may be one or a plurality. The effect of the present invention can be enjoyed if the lengths of all the closed curves of the partial area are made closer to the optimum length as compared with the closed curves when helical machining is performed without dividing the desired area. Note that the helical processing method described in this section can be applied to a case where a concave portion is formed in a desired processing region, or can be applied to a case where a convex region is cut down to lower it. In addition, it is desirable to apply to roughing (cutting), for example,
It can be carried out by holding the end mill on the tool spindle of the milling machine. (2) The helical machining method according to item (1), further including a one-closed-curve-corresponding dividing step of dividing the desired area into partial areas that can be machined by one closed curve having a length substantially equal to the optimum length. If the desired area is divided into a partial area that can be processed by only one closed curve having a length substantially equal to the optimum length, processing can be performed most efficiently. (3) An isometric closed curve-corresponding division step of dividing the desired area so that the lengths of the closed curves set for the respective partial areas are substantially the same as each other. (1) Item or (2)
The helical machining method described in the paragraph. If the lengths of the closed curves set for each of the partial areas are substantially the same,
It is possible to perform cutting processing under the same conditions for all partial regions. In addition, the effect of simplifying the algorithm for dividing the desired area can be obtained. Unlike the feature of this section, in the desired area, set as many partial areas as possible so that the length of the closed curve is just the optimal length, and as a result, the remaining area is determined based on another rule. It is also possible to divide. The processing efficiency is improved as the number of partial regions in which the length of the closed curve is just the optimum length increases. (4) The end mill and the workpiece are relatively moved in a direction orthogonal to the axis of the end mill so as to rotate along the same closed curve when viewed from a direction parallel to the axis of the end mill, and the end mill is moved. By approaching each other in a direction parallel to the axis of the end mill by a predetermined amount with respect to the unit amount of relative movement in the direction orthogonal to the axis, the helical trajectory is drawn at the tip of the end mill and the helical trajectory of the workpiece is In a helical machining method for cutting a desired area of a workpiece by cutting and removing a portion along the edge and then repeating the same cutting and removing while changing the closed curve, the length of the closed curve is changed to the end mill. Characterized in that the entire desired area is cut only by a closed curve near the optimum length where cutting by cutting is most stable. Cal processing method. In the case of the conventional helical machining method, first, a closed curve (length and contour shape) is determined according to the shape and size of the machining area, and a helical trajectory determined based on the closed curve and the cutting depth is determined. The end mill and the workpiece are relatively moved along.
In contrast, in the case of the helical machining method described in this section, the optimal length of the closed curve is determined based on the shape of the end mill and the like, and the helical machining determined based on the closed curve near the optimal length and the cut amount. It is relatively moved along the trajectory. The closed curves are set adjacent to each other in the processing area, and are not set multiple. It is not always necessary to divide the processing area. (5) The end mill and the workpiece are relatively moved in a direction perpendicular to the axis of the end mill so as to rotate along the same closed curve when viewed from a direction parallel to the axis of the end mill, and the end mill is moved. By approaching each other in a direction parallel to the axis of the end mill by a predetermined amount with respect to the unit amount of relative movement in the direction orthogonal to the axis, the helical trajectory is drawn at the tip of the end mill and the helical trajectory of the workpiece is Helical machining for determining the closed curve in a helical machining for cutting a desired area of a workpiece by cutting and removing a portion along the same and thereafter repeating the same cutting and removing by changing the closed curve. Program for obtaining the optimum length of the closed curve at which the cutting process of the end mill is most stable. Line length acquisition processing, while dividing the desired area into partial areas that can be processed only by a closed curve having a length near the optimal length acquired in the optimal closed curve length acquisition processing, and the closed curve for each partial area 3. A recording medium according to claim 2, wherein a program for helical machining including an area division / closed curve setting process to be set is recorded so as to be readable by said computer. If the computer reads and executes the helical processing program recorded on the recording medium according to this section, the desired area is divided into a partial area that can be processed only by a closed curve having a length near the optimum length, A closed curve is set for each of the partial regions. The optimum length of the closed curve can be obtained based on the shape of the end mill, for example, as described above. However, even if it is obtained by calculation according to a program, the optimum length is obtained in advance for each end mill. May be obtained by reading out information of the optimum length recorded on the same recording medium as the program according to the above or another recording medium. further,
A program for implementing the helical machining method according to each of the above (1) to (4), or a program for implementing a part relating to setting of a closed curve in the helical machining method is readable by a computer. It is also possible to manufacture a recorded recording medium.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A milling machine capable of performing a helical machining method according to an embodiment of the present invention will be described in detail with reference to the drawings. The milling machine, as shown in FIG.
It includes a main body 10, a table 12, and a tool spindle 14. The table 12 has an X axis and a Y
It is provided so as to be relatively movable in the axis and Z-axis directions. The tool spindle 14 is provided to be rotatable relative to the column of the main body 10 and to be relatively movable in the Z-axis direction.
In the present embodiment, an end mill 16 is attached to the tool spindle 14.
Is attached, and the work piece 18 is held on the table 12.

The operation of the milling machine is controlled by a control device 30. As shown in FIG. 3, the control device 30 is mainly composed of a computer including an input unit 32, a CPU 34, a ROM 36, a RAM 38, an output unit 40, and the like.
The input unit 32 includes an X-axis direction, a Y-axis direction,
A work X direction position sensor 42, a work Y direction position sensor 43, a work Z direction position sensor 44 for detecting a position in the Z axis direction, a tool Z direction position sensor 46 for detecting a position of the end mill 16 in the Z axis direction, and the like are connected. And an input device 48 is connected. Various conditions at the time of processing are input via the input device 48. In addition, the output unit 40 includes a table 12 for holding the workpiece 18,
A work X-direction movement motor 52, a work Y-direction movement motor 53, and a work Z-direction movement motor 54, which move along the Y, Z, and Z axes, respectively, are driven by driving circuits 56 and 5, respectively.
7 and 58, a tool Z-direction moving motor 60 for moving the tool spindle 14 in the Z-axis direction, and a tool spindle rotation drive motor 62 for rotating the tool spindle 14
Are connected via drive circuits 64 and 65, respectively. Further, a monitor 67 is connected. The operator inputs the shape and the like of the processing area on the workpiece 18 via the input device 48 while viewing the display screen of the monitor 67.
The ROM 36 stores a machining area dividing program shown in the flowchart of FIG. 4 and the end mill 16 and the workpiece 1 along the helical trajectory, although illustration of the flowchart is omitted.
8 such that the motors 52, 53,
Various programs such as a motor control program for controlling the motor 60, tables, and the like are stored.

In this embodiment, the relative position of the end mill 16 and the workpiece 18 at the start of machining is determined by the movement of the table 12 (workpiece 18) in the X, Y, and Z directions. X and Y of the workpiece 18
These are relatively moved by the directional movement and the Z-direction movement of the end mill 16, and helical processing is performed on a desired processing area of the workpiece 18. The end mill 16 is relatively moved while rotating. In the helical machining, the end mill 16 is covered with a helical trajectory CL as shown in FIG. 5 (the helical trajectory is a set of positions of the end mill 16 and can be referred to as cutter location data or simply cutter location). The workpiece 18 is relatively moved. Helical trajectory CL
To the X and Y planes (planes perpendicular to the axis of the end mill 16)
Is a closed curve CL ′, but since the inclination angle θ (helical gradient) of the helical trajectory is very small, the helical trajectory CL and the closed curve CL ′ can be regarded as the same.

Through an input device 48, data representing a cutting amount Z, a diameter D (rotational diameter) of the end mill 16, a contour line defining a machining area R, and the like are input. According to the execution of the machining area dividing program, the machining area R is divided into a plurality of partial machining areas RD, and the relative movement locus (helical locus CL) between the end mill 16 and the workpiece 18 is determined. The processing region R is divided in a state where the processing efficiency is improved. Specifically, the cutting is performed in a state where the cutting amount per time is large and no machining residue occurs. In this embodiment, the area is divided into a plurality of partial regions RD that can be machined only by one closed curve CL 'having a length near the optimum length. The optimal length of the closed curve CL 'is
The helical trajectory CL is determined according to the shape, size, etc.
Is determined from the closed curve CL ′ and the cutting amount Z.

The cutting amount Z is determined based on the capacity of the end mill 16 (shape, size, bending rigidity, etc. of the cutting blade 72).
In order to increase the cutting amount per time, it is desirable to set the cutting amount Z to the maximum value. However, it is not essential that the maximum value be set, and a smaller value can be used. In the present embodiment, the number of the cutting blades 72 provided on the end mill 16 is one. The optimal length of the closed curve CL 'is set to a length at which cutting can be performed most stably. Cutting is performed stably when the bending component applied to the end mill 16 is the smallest. As shown in FIGS. 7 and 8, the bending component force applied to the tool may be smaller when the inclination angle θ is larger than 0 than when the inclination angle θ is 0 (horizontal) when the cutting amount Z is the same. Are known. Also,
As the inclination angle θ changes, the ratio between the front cutting amount and the rear cutting amount of the cutting blade 72 of the end mill 16 changes. It is known that, when the front cutting amount and the rear cutting amount are equal, the bending component force applied to the cutting edge 72 becomes the smallest, and the length of the closed curve where the front cutting amount and the rear cutting amount are the same. Is the optimum length.

In FIG. 6, D is the rotation diameter of the cutting blade 72, which is twice as large as the distance from the center axis of the end mill 16 to the outermost peripheral edge of the cutting blade 72. Backward cutting amount t2
Is expressed by an equation t2 = D · tan θ (1) where helical gradient is θ, and a forward cutting amount t1 is expressed by an equation t1 = Z−D · tan θ (2) expressed. On the other hand, the formula tan θ = Z / L (3) is established between the helical gradient θ, the cutting amount Z, and the length L of the closed curve. From the expressions (1) to (3), the ratio between the front cutting amount t1 and the rear cutting amount t2 can be expressed by the following expression: t1 / t2 = L / D-1 (4). Here, the ratio (t1 / t2) is set to 1
Then, the equation L = 2D (5) holds, and it can be seen that the optimum length L of the closed curve CL 'is twice the rotation diameter D of the cutting blade 72. Equation (5) indicates that the front cutting amount t1 and the rear cutting amount t2 are １ ／ of the cutting amount Z.
Can also be determined based on the size of

Thus, the optimum length L of the closed curve CL '
^{Although *} is determined, in the present embodiment, as described above, the processing region R is divided into a plurality of partial regions RD that can be processed only with the closed curve CL ′ having a length near the optimum length L ^*. Because Hereinafter, a case where the processing region R is rectangular will be described.

In the flowchart of FIG. 4, in step 1 (hereinafter abbreviated as S1; the same applies to other steps), the longitudinal direction of the processing region R is divided according to a predetermined rule. In the present embodiment, as shown in FIG.
Is determined according to a predetermined rule. The distance from the outer edge (contour line) of the processing region R to the closed curve CL 'is D / 2, and the inner dimension M1 of the closed curve CL' is D / 2.
The length is slightly smaller (D / 2-α), the distance M2 between adjacent closed curves CL 'is a length slightly smaller than D (D-α'), and the closed curve is included in one partial region. Are not overlapped. Adjacent closed curve C
If the distance M2 between L 'is larger than D, machining residue occurs between them, and if the distance M2 is reduced, the processing efficiency deteriorates. Further, if the inside dimension M1 of the closed curve CL 'is set to a size near D / 2, the closed curve can be made square.
It is desirable. In S2, the optimal length L of the closed curve
^* Is determined as described above. In S3, the number of divisions N in the width direction is set to an initial value N0 (for example, 2), and in S4, the width direction of the processing region R is divided by the number of divisions N0.
The division line DL2 orthogonal to the short side B is determined.
In the present embodiment, the rectangular processing region R is first divided in the longitudinal direction and then in the width direction to be divided into a plurality of partial regions. When dividing the processing region R into a plurality of partial regions RD, dividing lines DL1,
DL2 is determined in this order.

Thereafter, in S5, a closed curve is obtained in each of the partial regions RD, and the length LD is obtained.
In S6, it is determined whether or not the absolute value of the difference between the optimum length L ^* and the length LD is equal to or smaller than a predetermined allowable value δ. If the value is equal to or smaller than the allowable value δ, in S7, the dividing lines DL1 and DL2 for dividing the processing region into a plurality of partial regions are determined, and the helical trajectory corresponding to the closed curve is determined. On the other hand, from the length L D of the closed curve to the optimum length L ^*
If the value obtained by subtracting is larger than the allowable value δ, the number of divisions N is increased by 1 in S8, and then in S4, the width direction of the processing region R is divided by the number of divisions N, and the same is performed in the same manner. You. If the value obtained by subtracting the optimum length L ^* is smaller than the allowable value −δ, the number of divisions is reduced by 1 in S9, and the same processing is performed.

As a result, the processing region R is divided into a plurality of partial regions RD as shown in FIG. The length of the closed curve CL 'in each of all the partial regions RD is the optimum length L ^*
It becomes the size of the neighborhood. Then, the end mill 16 and the workpiece 18 are relatively moved in accordance with the helical trajectory CL determined from the closed curve CL ′ and the cutting amount Z, thereby performing cutting. There is no need to limit the relative movement speed to a small value, and processing can be performed efficiently. Further, when cutting and removing the convex processing region R, it is desirable that the distance between the contour and the closed curve is set to a size such that the difference between the corner of the contour and the closed curve is D / 2. In the present embodiment, the ROM 36 is a recording medium on which a helical machining program is recorded.

In the above embodiment, one closed curve is set for one partial region RD. However, two or more closed curves may be set. In the above embodiment, the rectangular processing area is divided in the longitudinal direction, and then divided in the width direction.However, after dividing in the width direction, divided in the longitudinal direction or both. It may be divided at the same time. further,
The processing area is not limited to a rectangular area, and may be an area having another shape. In any case, the method of dividing the processing region R is not limited to the above-described embodiment, and any method may be used.

In the above embodiment, the cutting amount Z
Is set to the maximum value, but it is also possible to set a value smaller than the maximum value and determine the helical trajectory according to the value. Further, it is not always necessary to determine the dividing lines DL1 and DL2, and a closed curve C having a length near the optimum length L '
If L ′ is set in parallel, a similar effect can be obtained.

Further, depending on the shape and dimensions of the processing region R, it may not be possible to set a partial region so that the closed curve has an optimum length, or it may not be desirable to set such a region for some reason. In this case, the processing region R can be divided so that the processing of the partial region can be performed only by the closed curve near the optimum length. It is also possible to set as many partial areas RD as possible in the processing area R such that the length of the closed curve is just the optimum length, and to divide the remaining area according to another rule. The processing efficiency is improved as the number of partial regions in which the length of the closed curve is just the optimum length increases.

Further, the end mill 16 may have a plurality of cutting edges, and the workpiece 18 and the end mill 16 may be provided.
By moving any one of the above in the X, Y, and Z directions, cutting can be performed. Further, in the above-described embodiment, the recording medium is the ROM 36 fixedly provided in the control device 30. However, the recording medium is not limited to the ROM 36, and may be a RAM 38 or an EEP.
It can also be a RAM. The medium may be removable from the control device 30. The medium may be a medium on which a program is recorded magnetically or an optically recorded medium, such as a floppy disk or a compact disk. Further, the control device may be provided inside the milling machine, or may be provided separately. As described above, some embodiments of the present invention have been described in detail. However, this is merely an example, and the present invention has been described in the section [Problems to be Solved by the Invention, Problem Solving Means and Effects]. Various modifications and improvements can be made based on the knowledge of those skilled in the art including the embodiments.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state in which a processing region is divided into a plurality of partial regions by a helical processing method according to an embodiment of the present invention. FIG. 7 is also a diagram illustrating a result of reading and executing a helical machining program recorded on a recording medium according to an embodiment of the present invention.

FIG. 2 is a schematic view illustrating an example of a milling machine capable of performing the helical machining method.

FIG. 3 is a block diagram showing a control device provided on the milling machine and its periphery.

FIG. 4 is a flowchart showing a part of a helical machining program (machining area division program) recorded in a ROM of the control device.

FIG. 5 is a diagram showing a helical trajectory when an end mill and a workpiece are relatively moved according to the helical machining method.

FIG. 6 is a diagram showing a state in which the workpiece is cut by the relative movement of the end mill and the workpiece along a helical trajectory;

FIG. 7 is a diagram illustrating a state of a bending component and a thrust component applied to the end mill when the end mill and the workpiece are relatively moved along a helical trajectory.

FIG. 8 is a diagram showing a relationship between a helical gradient and a cut amount of a workpiece when an end mill and a workpiece are relatively moved along a helical trajectory.

[Explanation of symbols]

 12: Table 14: Tool spindle 16: End mill 30: Control device 36: ROM 52: Workpiece X direction movement motor 53: Workpiece Y direction movement motor 60: Tool Z direction movement motor 62: Tool spindle rotation drive motor

Claims (2)

[Claims] An end mill and a workpiece are relatively moved in a direction perpendicular to the axis of the end mill so as to rotate along the same closed curve when viewed from a direction parallel to the axis of the end mill. A unit amount of relative movement in a direction perpendicular to the axis of the end mill is brought close to each other in a direction parallel to the axis of the end mill by a predetermined amount, so that a helical trajectory is drawn at the end of the end mill, and the helical path of the workpiece is drawn. In the helical machining method of cutting a desired area of the workpiece by cutting and removing a portion along the trajectory and thereafter repeating the same cutting and removing by changing the closed curve, the desired area is The length of the closed curve is divided into partial regions that can be machined only by a closed curve that is near the optimum length where cutting by the end mill is most stable. A helical machining method wherein the desired regions are all cut by sequentially performing the cutting process on the divided regions. The end mill and the workpiece are relatively moved in a direction perpendicular to the axis of the end mill so as to rotate along the same closed curve when viewed from a direction parallel to the axis of the end mill. A unit amount of relative movement in a direction perpendicular to the axis of the end mill is brought close to each other in a direction parallel to the axis of the end mill by a predetermined amount, so that a helical trajectory is drawn at the end of the end mill, and the helical path of the workpiece is drawn. By cutting and removing a portion along the trajectory, and then repeating the same cutting and removing by changing the closed curve, the computer determines the closed curve in helical machining for cutting a desired area of the workpiece. A program for helical machining, wherein an optimal length of the closed curve at which cutting of the end mill is most stable is obtained. Optimal closed curve length acquisition processing, and dividing the desired area into partial areas that can be processed only by a closed curve having a length near the optimal length acquired in the optimal closed curve length acquisition processing, and the closed curve for each partial area A helical machining program including an area dividing / closed curve setting process for setting the following.