Patent Publication Number: US-2023158582-A1

Title: Machining method and machined product

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application Number 2021-188662 filed on Nov. 19, 2021. The entire contents of the above-identified application are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a machining method and a machined product. 
     2. Description of Related Art 
     Aircraft components such as a fuselage or a main wing of an aircraft are formed of structure members such as a long sheet frame. 
     Such a sheet frame is bent and molded from a plate-like member so that the cross section in the longitudinal direction has a desired sectional shape for the purpose of improving the strength or the like. Further, since a fuselage, a main wing, and the like to which a sheet frame is applied each have a curved surface shape, the sheet frame is molded so as to have a curved shape curved in the longitudinal direction. 
     Thus, the sheet frame has a complex surface shape. 
     Machining to thin the plate thickness (hereafter, also referred to as “plate thinning machining”) may be performed on such a sheet frame used for an aircraft for the purpose of weight reduction or the like. 
     Conventionally, chemical milling is used in plate thinning machining for a structure component having a complex surface shape. Chemical milling is a machining method to remove a metal by chemical edging using alkaline or acid. Such chemical milling is used to thin the structure component to a constant thickness, and thereby a weight reduction of a structure component is realized. 
     Japanese Patent Application Laid-Open No. 2019-206065 is an example of the related art. 
     In recent years, however, there has been a demand for eliminating chemical milling in terms of an environmental load, an issue of waste liquid treatment, or a reduction in energy usage. 
     To address this, it is conceivable to perform plate thinning machining on a sheet frame by mechanical working (for example, Japanese Patent Application Laid-Open No. 2019-206065). 
     However, when a sheet frame having a plurality of surfaces is machined without a set-up change, reforming one surface will cause distortion in another surface, and it is difficult to reform a plurality of surfaces at the same time. It is thus required to make a strategy as to how to reform respective surfaces. 
     BRIEF SUMMARY 
     The present disclosure has been made in view of such circumstances, and an object of the disclosure is to provide a machining method that can perform plate thinning machining on a plurality of surfaces without requiring a set-up change and also provide a machined product. 
     To achieve the above object, a machining method and a machined product of the present disclosure employ the following solutions. 
     The machining method according to one aspect of the present disclosure is a machining method for machining a machining target material by using a tool, the machining target material is set in a jig, the machining target material has a plate-like web part having an arc shape in plan view and a flange part bent and arranged vertically from an edge along the arc shape of the web part, the tool has an end cutting edge and a peripheral cutting edge, and the jig has a supporting surface on which the web part is placed and a contacting surface with which the flange part comes into surface contact. The machining method includes: a pressing step of pressing the flange part against the contacting surface; a flange cutting step of cutting the flange part by the peripheral cutting edge of the tool by feeding the tool in an arc direction of the arc shape; and a web cutting step of cutting the web part by the end cutting edge of the tool by feeding the tool in the arc direction. 
     Further, the machined product according to one aspect of the present disclosure is a machined product having a plate-like web part having an arc shape in plan view and a flange part bent and arranged vertically from an edge along the arc shape of the web part, one surface in the web part is a machined surface, a plurality of cutter marks extending from one end to the other end of the web part are formed on the machined surface, and the machined product has a portion where a pitch between the cutter marks that are adjacent to each other changes along an extending direction of the cutter marks. 
     According to the present disclosure, plate thinning machining can be performed on a plurality of surfaces without requiring a set-up change. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is a plan view of a workpiece according to one embodiment of the present disclosure. 
         FIG.  2    is a top perspective view of the workpiece according to one embodiment of the present disclosure. 
         FIG.  3    is a top perspective view of a jig according to one embodiment of the present disclosure. 
         FIG.  4    is a top perspective view of the jig according to one embodiment of the present disclosure (clamps are omitted). 
         FIG.  5    is a top perspective view of a state where the workpiece is set in the jig according to one embodiment of the present disclosure. 
         FIG.  6    is a cross-sectional view taken along a cut line VI-VI illustrated in  FIG.  5   . 
         FIG.  7    is a cross-sectional view taken along a cut line VII-VII illustrated in  FIG.  5   . 
         FIG.  8    is a diagram illustrating a concept of a tangential load method. 
         FIG.  9    is a cross-sectional view illustrating a supporting surface of the jig according to one embodiment of the present disclosure. 
         FIG.  10    is a diagram illustrating a displacement of a machined surface after a workpiece is attached to the jig and before the workpiece is machined according to one embodiment of the present disclosure. 
         FIG.  11    is a perspective view illustrating a state where a workpiece is machined by an end mill according to one embodiment of the present disclosure. 
         FIG.  12    represents diagrams illustrating a displacement of a machined surface after a workpiece is attached to the jig and then machined according to one embodiment of the present disclosure. 
         FIG.  13    is a schematic configuration diagram illustrating an example of a hardware configuration of a machining system according to one embodiment of the present disclosure. 
         FIG.  14    is a function block diagram illustrating functions of the machining system according to one embodiment of the present disclosure. 
         FIG.  15    is a diagram illustrating an example of machining on a web surface according to one embodiment of the present disclosure. 
         FIG.  16    is a diagram illustrating an example of machining on a web surface according to one embodiment of the present disclosure. 
         FIG.  17    is a diagram illustrating an overview of a flow of machining on a web surface according to one embodiment of the present disclosure. 
         FIG.  18    is a diagram illustrating an example of machining on a flange surface according to one embodiment of the present disclosure. 
         FIG.  19    is a diagram illustrating an overview of a flow of machining on a flange surface according to one embodiment of the present disclosure. 
         FIG.  20    is a diagram illustrating an example of measurement of an R-surface according to one embodiment of the present disclosure. 
         FIG.  21    is a diagram illustrating an example of measurement of the R-surface according to one embodiment of the present disclosure. 
         FIG.  22    is a diagram illustrating an example of measurement of the R-surface according to one embodiment of the present disclosure. 
         FIG.  23    is a diagram illustrating an example of measurement of the R-surface according to one embodiment of the present disclosure. 
         FIG.  24    is a diagram illustrating an overview of a flow of machining on the R-surface according to one embodiment of the present disclosure. 
         FIG.  25    is a diagram illustrating an example of machining on R-surfaces according to one embodiment of the present disclosure. 
         FIG.  26    is a flowchart illustrating an example of a procedure of a machining process according to one embodiment of the present disclosure. 
         FIG.  27    is a flowchart illustrating an example of the procedure of the machining process according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of a machining method and a machined product according to the present disclosure will be described below with reference to the drawings. 
     [Machining Target Material] 
     First, a workpiece (a machining target material)  10  on which machining is performed by the machining method according to the present embodiment will be described. 
       FIG.  1    illustrates a plan view of the workpiece  10 .  FIG.  2    illustrates a top perspective view of the workpiece  10 . 
     The workpiece  10  is a sheet frame used as a structure component such as a fuselage or a main wing of an aircraft, for example. The workpiece  10  is made of a metal, for example. 
     An example of the metal may be an aluminum alloy (for example, 7000-series aluminum alloys or 2000-series aluminum alloys) or a titanium alloy (for example, 6-4Ti). 
     The workpiece  10  is a long member having a web part  11 , an upper flange part  12  (also simply referred to as “flange part  12 ”), and a lower flange part  13  (also simply referred to as “flange part  13 ”). 
     The web part  11  and the upper flange part  12  are connected to each other via an R-part  14 . Further, the web part  11  and the lower flange part  13  are connected to each other via an R-part  15 . Further, an R-part  16  is formed to the lower end (edge) of the lower flange part  13 . 
     The workpiece  10  has a plan-view shape that is substantially an arc shape including the upper flange part  12  and the lower flange part  13  and has a cross-sectional shape that is substantially a Z-shape. The length dimension along the arc direction of the workpiece  10  in plan view is about 6 m, for example. 
     Respective parts forming the workpiece  10  will be described below. 
     The web part  11  is a plate-like portion forming substantially an arc shape in plan view. 
     The width dimension (the dimension in the radial direction) of the web part  11  is substantially constant in the circumferential direction. 
     The thickness dimension (the plate thickness) of the web part  11  is about 0.05 inches to 0.15 inches (1.27 mm to 3.81 mm) before machining described later is performed. 
     The upper flange part  12  is connected to the outer circumferential edge of the two edges along the arc shape of the web part  11  and has a plate-like portion bent from the edge and arranged perpendicularly upward. The upper flange part  12  is connected to the web part  11  via the round part (R-part)  14  that is smoothly curved. 
     The height dimension (the dimension in the perpendicular arrangement direction) of the upper flange part  12  is substantially constant in the circumferential direction. 
     The thickness dimension (the plate thickness) of the upper flange part  12  is about 0.05 inches to 0.15 inches (1.27 mm to 3.81 mm) before machining described later is performed. 
     The lower flange part  13  is connected to the inner circumferential edge of the two edges along the arc shape of the web part  11  and has a plate-like portion bent from the edge and arranged perpendicularly downward. The lower flange part  13  is connected to the web part  11  via the round part (R-part)  15  that is smoothly curved. Further, the round part (R-part)  16  smoothly curved circumferentially outward in the arc shape of the web part  11  is formed to the lower end (edge) of the lower flange part  13 . 
     The height dimension (the dimension in the perpendicular arrangement direction) of the lower flange part  13  is substantially constant in the circumferential direction. 
     The thickness dimension (the plate thickness) of the lower flange part  13  is about 0.05 inches to 0.15 inches (1.27 mm to 3.81 mm) before machining described later is performed. 
     [Jig] 
     Next, a jig  20  to which the workpiece  10  is attached when the machining method according to the present embodiment is performed will be described. 
     The jig  20  is a device for securing the workpiece  10  in a suitable position in a suitable state in order to suitably perform machining described later on the workpiece  10 . 
       FIG.  3    illustrates a top perspective view of the jig  20 .  FIG.  4    and  FIG.  5    illustrate the top perspective views of the jig  20  in a state where the workpiece  10  is placed. FIG.  6  illustrates a sectional view taken along the cut line VI-VI illustrated in  FIG.  5   .  FIG.  7    illustrates a sectional view taken along the cut line VII-VII illustrated in  FIG.  5   . 
     Note that, in  FIG.  4   , some of the clamps  50  are omitted for simplified illustration. 
     As illustrated in  FIG.  3   , the jig  20  has a base  30 , a setting block  40 , and four clamps  50 . 
     The base  30  is a plate-like member having a predetermined thickness dimension. 
     The thickness dimension of the base  30  is set at a dimension that exhibits rigidity sufficient to be bearable against a loading occurring when the workpiece  10  is fixed. 
     As illustrated in  FIG.  3    to  FIG.  6   , the setting block  40  is a component arranged on the top face of the base  30  and fixed to the base  30  and is a portion to which the workpiece  10  is set. 
     The setting block  40  has a supporting surface  41 , an upper flange contacting surface  42  (also simply referred to as “contacting surface  42 ”), and a lower flange contacting surface  43  (also simply referred to as “contacting surface  43 ”). 
     The supporting surface  41  is a surface on which the web part  11  of the workpiece  10  is placed. Specifically, the supporting surface  41  is a surface that, when the workpiece  10  is placed thereon, comes into contact with a supported surface  11   b  that is the backside of a machined surface  11   a  of the web part  11 . 
     The supporting surface  41  has substantially an arc shape as with the web part  11  in plan view. 
     The upper flange contacting surface  42  is a surface with which the upper flange part  12  of the workpiece  10  comes into contact. Specifically, the upper flange contacting surface  42  is a surface that, when the workpiece  10  is placed thereon, comes into contact with a contacted surface  12   b  that is the backside of a machined surface  12   a  of the upper flange part  12 . 
     The upper flange contacting surface  42  is a surface extending perpendicularly upward with respect to the supporting surface  41 . 
     The lower flange contacting surface  43  is a surface with which the lower flange part  13  of the workpiece  10  comes into contact. Specifically, the lower flange contacting surface  43  is a surface that, when the workpiece  10  is placed thereon, comes into contact with a contacted surface  13   b  that is the backside of a machined surface  13   a  of the lower flange part  13 . 
     The lower flange contacting surface  43  is a surface extending perpendicularly downward with respect to the supporting surface  41 . 
     Note that, while each shape of the contacted surface  12   b , the supported surface  11   b , and the contacted surface  13   b  of the workpiece  10  substantially matches each shape of the upper flange contacting surface  42 , the supporting surface  41 , and the lower flange contacting surface  43  of the setting block  40  (substantially a Z-shape), it is apparent that what serves as a reference for the shape is each surface formed in the setting block  40  that has higher rigidity than the workpiece  10 . 
     As illustrated in  FIG.  3    to  FIG.  5    and  FIG.  7   , each clamp  50  is a component arranged on the top surface of the base  30  and fixed rotatably to the base  30  and has a function of pressing the contacted surface  12   b  and the contacted surface  13   b  of the workpiece  10  against the upper flange contacting surface  42  and the lower flange contacting surface  43  of the setting block  40 . 
     Respective clamps  50  are arranged near positions corresponding to four corners of the workpiece  10  set on the setting block  40 . 
     Each clamp  50  has a clamp body  51 , a load bolt  52 , and a load block  53 . 
     The clamp body  51  is substantially an inverse U-shaped component having a rotating part  51   a  and a leg part  51   b.    
     The rotating part  51   a  is a portion fitted to an inner wheel of a bearing  32  provided on the base  30  and implements rotation of the clamp  50  together with the bearing  32 . Note that the rotation axis X of the clamp  50  (that is, the rotation axis X of the rotating part  51   a ) is orthogonal to the top surface of the base  30 . 
     The leg part  51   b  is a portion that slidably engages with a base-side step  31  formed in the base  30  and thereby bears against a load working on the clamp  50 . 
     Specifically, as illustrated in  FIG.  7   , the base-side step  31  formed so as to be recessed from the top surface of the base  30  and a clamp-side step  51   c  corresponding to the shape of the base-side step  31  are engaged with each other, and thereby the leg part  51   b  bears against a load working on the clamp  50  (a load due to a reaction received from the load bolt  52  described later). 
     Note that, as illustrated in  FIG.  4   , the base-side step  31  and the clamp-side step  51   c  are formed in an arc shape about the rotation axis X of the clamp  50 . Thus, the base-side step  31  and the clamp-side step  51   c  slide smoothly without preventing the rotation of the clamp  50 . 
     As illustrated in  FIG.  3    to  FIG.  5    and  FIG.  7   , the load bolt  52  is a bolt screwed into the rotating part  51   a  of the clamp body  51 . 
     The load bolt  52  is provided in the rotating part  51   a  with the tip on the workpiece  10  side being inclined downward. 
     The load block  53  is a component connected to the tip of the load bolt  52 . 
     The load block  53  is connected so as to rotate three-dimensionally to the tip of the load bolt  52 . This is realized by the tip of the load bolt  52  being formed in a spherical shape, for example. 
     The workpiece  10  is attached as follows to the jig  20  configured as described above. 
     As illustrated in  FIG.  4    and  FIG.  5   , first, the workpiece  10  is set to the setting block  40 . At this time, the workpiece  10  is positioned by causing the end surface of the workpiece  10  to come into contact with a positioning pin  33  erected from the base  30 . 
     Accordingly, the contacted surface  12   b , the supported surface  11   b , and the contacted surface  13   b  of the workpiece  10  come into contact with the upper flange contacting surface  42 , the supporting surface  41 , and the lower flange contacting surface  43  of the setting block  40 . 
     Next, the load bolt  52  is rotated about the axis and pressed in the axis direction to press the load blocks  53  against the end surface of the workpiece  10 . In detail, the load block  53  is slightly pressed against the end surface of the upper flange part  12  (two portions in the arc direction) and the end surface of the lower flange part  13  (two portions in the arc direction). 
     At this time, since the load block  53  is configured to rotate three-dimensionally with respect to the tip of the load bolt  52 , the load block  53  is pressed perpendicularly against the end surface of the upper flange part  12  and the end surface of the lower flange part  13 . Accordingly, the load from the load bolt  52  can be input in the tangential direction of the arc. 
     Further, since the load bolt  52  is inclined downward, the web part  11  of the workpiece  10  is pressed against the setting block  40 . 
     Next, the load bolt  52  is further pushed in to press the end surface of the upper flange part  12  and the end surface of the lower flange part  13  with predetermined force. Herein, the predetermined force is force of 30 kN to 70 kN per one load bolt  52  (fastening torque of 100 Nm to 190 Nm) when a bolt of M 16  is used as the load bolt  52 , for example. 
     At this time, as illustrated in  FIG.  8   , the upper flange part  12  and the lower flange part  13  are naturally pressed against the upper flange contacting surface  42  and the lower flange contacting surface  43  by a force component (Fcosθ), which is directed to the upper flange contacting surface  42  side and the lower flange contacting surface  43  side, of the load F working in the tangential direction (this is called “tangential load method” (see Japanese Patent Application Laid-Open No. 2019-141981)). 
     Accordingly, it is possible to cause the contacted surface  12   b  of the upper flange part  12  to be in close contact with the upper flange contacting surface  42  of the setting block  40  and cause the contacted surface  13   b  of the lower flange part  13  to be in close contact with the lower flange contacting surface  43  of the setting block  40  by using the shaft force of the load bolt  52 . 
     Further, it is possible to finely control the shaft force by adjusting the fastening torque of the load bolt  52 . 
     Once the contacted surface  12   b  of the upper flange part  12  is in close contact with the upper flange contacting surface  42  and the contacted surface  13   b  of the lower flange part  13  is in close contact with the lower flange contacting surface  43 , distortion in the upper flange part  12  and the lower flange part  13  is reformed. On the other hand, the reformed distortion is aggregated into the web part  11 . 
     Thus, this method reforms the distortion in the upper flange part  12  and the lower flange part  13  and intentionally aggregates the distortion of the workpiece  10  into the web part  11 . 
     When the distortion is aggregated into the web part  11 , the supported surface  11   b  of the web part  11  separates from and rises above the supporting surface  41  of the setting block  40 . 
     Accordingly, to suitably support the web part  11  (supported surface  11   b ) even after separation and rising, a lifting mechanism  44  (for example, an air cylinder) as illustrated in  FIG.  9    may be used to cause the supporting surface  41  to follow the supported surface  11   b.    
     Note that, in pushing the load bolt  52 , the upper flange part  12  and the lower flange part  13  may be pushed to the upper flange contacting surface  42  side and the lower flange contacting surface  43  side by some device (not illustrated) as illustrated in  FIG.  4    so that the upper flange part  12  and the lower flange part  13  are reliably guided to the upper flange contacting surface  42  side and the lower flange contacting surface  43  side. 
     The portions to be pushed can be three portions of both ends and the center of the upper flange part  12  and three portions of both ends and the center of the lower flange part  13  regardless of the length of the workpiece  10 . 
     Note that, after the workpiece  10  is attached to the jig  20 , the pushing action is released. 
     In the workpiece  10  attached to the jig  20  as described above, a distribution of distortion (corrugation/separation and rising) as illustrated in  FIG.  10    has occurred in the machined surface  11   a  of the web part  11 . 
     Note that  FIG.  10    represents the arc-shaped machined surface  11   a  in an orthogonal coordinate system (the same applies for  FIG.  12   ). 
     Further, each hatched legend represents a difference in the actual position of the workpiece  10  from the CAD model when the XYZ origin is defined in the base  30 . It is thus noted that the numeric value thereof is not an absolute value but a relative value (the same applies for  FIG.  12   ). 
     [Machining Method] 
     After completion of attachment of the workpiece  10 , a tool is used to cut the machined surface  11   a  of the web part  11 , the machined surface  12   a  of the upper flange part  12 , and the machined surface  13   a  of the lower flange part  13 . 
     As illustrated in  FIG.  11   , the tool is a known end mill (square end mill)  60  having an end cutting edge  61  and a peripheral cutting edge  62 . Note that the tool may be a radius end mill. 
     The end mill  60  is preferably an end mill whose surface used for performing machining formed by the end cutting edge  61  is flat. 
     Note that the following description is provided with an example of a square end mill. 
     The overview of the machining method is as follows. 
     First, the machined surface  12   a  of the upper flange part  12  where distortion has been reformed is cut with a single path by using the peripheral cutting edge  62  of the end mill  60  (flange cutting step). In this step, the end mill  60  is fed from one end to the other end in substantially an arc-shaped manner. 
     Next, the machined surface  11   a  of the web part  11  where distortion has been aggregated is cut with a plurality of paths by using the end cutting edge  61  of the end mill  60  (web cutting step). In this step, the end mill  60  is fed from one end to the other end in substantially an arc-shaped manner. 
     When the pitch of the end mill  60  per path is P,  0  P end mill diameter is met. 
     Cutting of the machined surface  11   a  of the web part  11  is performed so as to follow the shape (distribution) of the distortion that has occurred in the machined surface  11   a  of the web part  11  after the attachment to the jig  20  and before the machining. Accordingly, it is possible to perform plate thinning machining on the web part  11  at a constant cut amount in accordance with the shape of distortion. 
     As a result, as illustrated in  FIG.  12   , distortion has occurred in the machined surface  11   a  of the web part  11  obtained after cutting machining, and the distortion is substantially direct transfer of the shape of distortion that has occurred after the attachment to the jig  20  and before the machining. However, it can be seen that the plate thickness of the web part  11  is thinned for a portion cut by the end mill  60 . 
     In machining of the web part  11 , the attitude of the end mill  60  is controlled so as to follow the shape of distortion (details will be described later). Thus, a plurality of cutter marks M along the feed direction formed on the machined workpiece  10  (machined product) have the shape as illustrated in  FIG.  11   . 
     Thus, the pitch between the adjacent cutter marks M may change gradually in the extending direction of the cutter marks M, a smooth wave-shaped portion may appear in a continuous linear cutter mark M, and a cuspidal point without cutting-in may appear in a continuous linear cutter mark M. Further, the machined surface  11   a  has a multifaceted shape caused by the end cutting edge  61 . 
     Next, the machined surface  13   a  of the lower flange part  13  where distortion has been reformed is cut with a single path by using the peripheral cutting edge  62  of the end mill  60  (flange cutting step). In this step, the end mill  60  is fed from one end to the other end in substantially an arc-shaped manner. 
     By going through the steps described above, it is possible to perform plate thinning machining on each machined surface of the upper flange part  12 , the web part  11 , and the lower flange part  13  without performing a set-up change. 
     Note that, in the machining method described above, a step of cutting the R-part  14  by using a cutting tool having a cutting edge in accordance with the shape of the R-part  14  (for example, a ball end mill (see reference numeral  97  indicated in  FIG.  25   ) or a radius end mill) (R-part cutting step) may be included between the first web cutting step and the flange cutting step. In this step, the cutting tool is fed from one end to the other end in substantially an arc-shaped manner. Accordingly, efficient plate thinning machining without a set-up change and with less paths can be performed on the R-part  14  of the workpiece having a shape error. 
     Further, a step of cutting the R-part  15  by using a cutting tool having a cutting edge in accordance with the shape of the R-part  15  (for example, an inverse R-cutter (see reference numeral  98  indicated in  FIG.  25   )) (R-part cutting step) may be included between the flange cutting step and the second web cutting step. In this step, the cutting tool is fed from one end to the other end in substantially an arc-shaped manner. Accordingly, efficient plate thinning machining without a set-up change and with less paths can be performed on the R-part  15  of the workpiece having a shape error. 
     Further, a step of cutting the R-part  16  by using a cutting tool having a cutting edge in accordance with the shape of the R-part  16  (for example, an inverse R-cutter) (R-part cutting step) may be included after the second web cutting step. In this step, the cutting tool is fed from one end to the other end in substantially an arc-shaped manner. Accordingly, efficient plate thinning machining without a set-up change and with less paths can be performed on the R-part  16  of the workpiece having a shape error. 
     [Machining System] 
     Next, a machining system  70  will be described. 
     The machining system  70  performs a machining control on a workpiece (target component)  10 . Specifically, the machining system  70  controls a drive device that drives the end mill  60 . 
     In the following description, a surface in the end mill  60  used for performing machining with the end cutting edge  61  is referred to as a “bottom surface” of the end mill  60 , and a surface in the end mill  60  used for performing machining with the peripheral cutting edge  62  is referred to as a “side surface” of the end mill  60 . Further, a machined surface machined by the bottom surface of the end mill  60 , such as the machined surface  11   a  of the web part  11 , is referred to as a “web surface” for illustration. A machined surface machined by the side surface of the end mill  60 , such as the machined surface  12   a  of the upper flange part  12  and the machined surface  13   a  of the lower flange part  13 , is referred to as a “flange surface” for illustration. A machined surface of an R-part connecting the web surface to the flange surface, such as the R-part  14  and the R-part  15 , is referred to as an “R-surface”. 
       FIG.  13    is a schematic configuration diagram illustrating an example of a hardware configuration of the machining system  70  according to one embodiment of the present disclosure. As illustrated in  FIG.  13   , the machining system  70  is a so-called computer and has a central processing unit (CPU)  81 , a main memory  82 , a storage unit  83 , an external interface  84 , a communication interface  85 , an input unit  86 , a display unit  87 , and the like. These components are connected to each other directly or indirectly via a bus and perform various processes in cooperation with each other. 
     The CPU  81  performs control by using operating system (OS) stored in the storage unit  83  connected via a bus, for example, and performs various processes by executing various programs stored in the storage unit  83 . 
     The main memory  82  is formed of a writable memory such as a cache memory, a random access memory (RAM), or the like, and is used as a working region where an execution program of the CPU  81  is loaded and writing of processing data or the like by the execution program is performed. 
     The storage unit  83  a non-transitory computer readable storage medium, which may be, for example, a read only memory (ROM), a hard disk drive (HDD), a flash memory, or the like. For example, the storage unit  83  stores OS such as Windows (registered trademark), iOS (registered trademark), Android (registered trademark), or the like used for performing overall control of the apparatus, Basic Input/Output System (BIOS), various device driver used for hardware operation of peripherals, various application software, various data or files, or the like. Further, the storage unit  83  stores a program used for implementing various processes or various data required for implementing various processes. 
     The external interface  84  is an interface for connection to an external device. An example of the external device may be an external monitor, a USB memory, an external HDD, or the like. Note that, although only one external interface is depicted in the example illustrated in  FIG.  13   , a plurality of external interfaces may be provided. 
     The communication interface  85  functions as an interface for communicating with another device through connection to a network and transmitting and receiving information. 
     For example, the communication interface  85  communicates with another device via a wired connection or a wireless connection, for example. Wireless communication may be communication using Bluetooth (registered trademark), Wi-Fi, a dedicated communication protocol, or the like. An example of wired communication may be a wired local area network (LAN) or the like. 
     The input unit  86  is a user interface used for providing an instruction, such as a keyboard, a mouse, a touch pad, or the like. 
     The display unit  87  is a liquid crystal display, an organic electroluminescence display, or the like. Further, the display unit  87  may be a touch panel display on which a touch panel is overlapped. 
       FIG.  14    is a function block diagram illustrating functions of the machining system  70 . As illustrated in  FIG.  14   , the machining system  70  includes a setting unit  71 , a measurement path setting unit  72 , a measuring unit  73 , a surface model generation unit  74 , a component model generation unit  75 , a machining path setting unit  76 , a movement control unit  77 , and a remeasurement path setting unit  78 . 
     The function implemented by each of these units is implemented by processing circuitry, for example. For example, a series of processes for implementing functions illustrated below are stored in the storage unit  83  in a form of a program as an example, and various functions are implemented when the CPU  81  loads such a program into the main memory  82  and performs information processing and calculation processes thereon. 
     Note that an applicable form of the program may be a form in which a program is installed in advance in the storage unit  83 , a form in which a program is provided in a state of being stored in another computer readable storage medium, a form in which a program is delivered via a wired or wireless communication scheme, or the like. The computer readable storage medium may be a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. 
     The setting unit  71  sets machining target surfaces corresponding to the bottom surface and the side surface of the end mill  60  for the workpiece  10 , respectively, based on a design model of the workpiece  10 . The design model is a model representing a design shape (ideal shape) of the workpiece  10 . The design model is CAD data, for example. In the present embodiment, a case where the workpiece  10  is divided into a web surface (machined-by-bottom surface) machined by the bottom surface of the end mill  60 , a flange surface (machined-by-side surface) machined by the side surface of the end mill  60 , and the R-surface will be described as an example. In such a way, the setting unit  71  divides the machined surface of the workpiece  10  into a plurality of machining target surfaces. 
     The measurement path setting unit  72  sets a measurement path based on a design model of the workpiece  10 . Specifically, the measurement path setting unit  72  sets measurement paths on for each divided machining target surface. Each measurement path indicates a position where measurement is performed on the workpiece  10 . For example, a plurality of measurement paths is set at a predetermined pitch. 
     The measuring unit  73  measures the three-dimensional shape of the workpiece  10 . The measuring unit  73  controls a measuring instrument to perform measurement. The measurement instrument may be, for example, a line laser, a scan probe, a 3D scanner, or the like. Measurement of respective measurement paths is performed, and thereby the three-dimensional shape of the workpiece  10  is measured. The measurement is performed at a predetermined interval on the measurement path, and a measurement result is represented by point cloud information having three-dimensional coordinate values. 
     The measurement is performed in a state where the workpiece  10  is fixed to the jig  20  so that the workpiece  10  approaches the design shape. Specifically, the workpiece  10  is fixed by the jig  20  as illustrated in  FIG.  4    to  FIG.  7   . 
     Accordingly, the workpiece  10  is reformed to approach the design shape indicated by the design model of the workpiece  10 . In particular, the flange surface is reformed to approach the design shape. By performing measurement in this state, it is possible to measure the three-dimensional shape of the workpiece  10  with higher precision. 
     The surface model generation unit  74  generates a surface model corresponding to respective machining target surfaces based on three-dimensional measurement data of respective machining target surfaces. Specifically, the surface model generation unit  74  acquires measurement data corresponding to respective machining target surfaces from the measuring unit  73 . Since measurement data is point cloud information, respective measured positions are interpolated to generate information indicating a surface shape (surface model). Thus, the surface model is surface information indicating respective actual shapes of respective machining target surfaces. Various schemes can be applied to the method of generating a surface model without limitation. 
     The component model generation unit  75  combines respective surface models to generate a component model. Specifically, the component model generation unit  75  connects respective divided, measured, and generated surface models to each other to generate a component model indicating the actual shape of the workpiece  10 . Accordingly, the workpiece  10  is modeled as a whole. 
     The component model generation unit  75  may perform anomaly determination based on continuity of a connection between surface models when combining respective surface models. For example, when surface models are combined, if at least any one of a gap and a level difference between the surface models is greater than or equal to a predetermined value (if there is discontinuity), it is determined that there is an anomaly. In other words, when there is an error in a process such as measurement or generation of a surface model and thus a component model is not accurately expressed, it is determined that there is an anomaly. 
     The machining path setting unit  76  sets a machining path based on a three-dimensional shape of the measured workpiece  10 . Specifically, the machining path setting unit  76  acquires a component model and then sets a machining path based on the component model. A machining path is set by using a component model in which respective surface models are combined, and thereby a machining path which takes a relationship between a plurality of surfaces into consideration can be set. A machining path indicates positions where machining is performed on the workpiece  10 . When a machining path is set on the machined surface  11   a  that is a web surface, for example, a machining path is set in an arc-shaped manner in accordance with the arc shape of the machined surface  11   a . When a machining path is set on the machined surface  12   a  that is a flange surface, for example, a machining path is set in an arc-shaped manner in accordance with the arc shape of the machined surface  12   a . The shape of the machining path is not limited. 
     A machining path includes not only the guideline function but also information indicating a tilt angle of the end mill  60 . The machining path setting unit  76  sets a tilt angle. Specific setting of the tilt angle will be described later. 
     The movement control unit  77  performs control to move the end mill  60  along a machining path. As illustrated in  FIG.  14   , the movement control unit  77  includes a feed direction control unit  77   a , a pitch direction control unit  77   b , an orthogonal direction control unit  77   c , and a tilt control unit  77   d.    
     The feed direction control unit  77   a  moves the end mill  60  in a feed direction in which the end mill  60  is moved along a machining path. Thus, the feed direction control unit  77   a  moves the end mill  60  on a machining path so that the end mill  60  passes on the machining path. For example, control is performed so that the center of the bottom surface of the end mill  60  moves on a machining path. 
     The pitch direction control unit  77   b  moves the end mill  60  in a pitch direction. The pitch direction is a vertical direction to the feed direction. The feed direction, the pitch direction, and the z direction described later (for example, the perpendicular direction) are in an orthogonal relationship to each other ( FIG.  11   ). A plurality of machining paths are provided at a predetermined pitch (stepover) P in the pitch direction on the web surface, for example. Thus, the pitch direction control unit  77   b  moves the end mill  60  by the predetermined pitch P in the pitch direction and thereby moves the end mill  60  from one machining path to another. For example, after machining on one machining path ends, the end mill  60  is moved to another machining path (adjacent machining path) where next machining is performed. 
     The orthogonal direction control unit  77   c  moves the end mill  60  in the z direction (cut-in direction). Thus, the orthogonal direction control unit  77   c  moves the end mill  60  in the z direction to adjust the position in the z direction in which machining is performed by the side surface or the bottom surface of the end mill  60 . 
     The tilt control unit  77   d  controls the tilt angle about an axis in the feed direction of the end mill  60  (for example, about a machining path). Specifically, the end mill  60  is tilted in accordance with a tilt angle set for a machining path. Thus, attitude control of the end mill  60  is performed by the tilt control unit  77   d . The tilt angle is defined by the inclination of the center axis of the end mill  60  based on the initial attitude of the end mill  60  (for example, the center axis of the end mill  60  is parallel to the perpendicular direction) as a reference. For example, when the tilt angle of the initial attitude of the end mill  60  is 0 degree and the end mill  60  is then tilted by 5 degrees about the axis in the feed direction, the tilt angle is 5 degrees. A specific example of machining by the end mill  60  involving attitude control will be described later. 
     The remeasurement path setting unit  78  is used when a machining target surface having a large error with respect to a design model is measured. In the present embodiment, as an example, the process by the remeasurement path setting unit  78  is not performed on the web surface or the flange surface but performed on the R-surface. 
     The remeasurement path setting unit  78  sets a remeasurement path based on the three-dimensional shape of the workpiece  10  measured based on a measurement path. Thus, the measurement path setting unit  72  sets a measurement path based on a design model, and the remeasurement path setting unit  78  sets a measurement path based on a surface model. When a process is performed by the remeasurement path setting unit  78  (that is, when the R-surface is targeted), the machining path setting unit  76  sets a machining path based on the three-dimensional shape of the workpiece  10  measured based on a remeasurement path. 
     Machining is performed based on the actual shape of the workpiece  10  in accordance with the processes performed by respective units described above. Machining is performed in a state where the workpiece  10  is fixed to the jig  20  so that the workpiece  10  approaches a design shape. It is possible to improve the continuity of a machined surface by performing attitude control on the end mill  60 . 
     [Machining of Web Surface] 
     Next, specific machining of the web surface will be described. 
       FIG.  15    illustrates an example of a case where no attitude control of the end mill  60  is performed.  FIG.  16    illustrates an example of a case where attitude control of the end mill  60  is performed.  FIG.  15    and  FIG.  16    illustrate a unmachined surface  91  and an ideal machined surface  92 . 
     A plurality of machining paths are set at a predetermined pitch P in the pitch direction on the web surface in order to perform machining by the bottom surface of the end mill  60 . For example, the machining path for the web surface is set at positions in a predetermined depth from the surface of the component model (that is, the unmachined surface  91 ). The end mill  60  is moved so that the center of the bottom surface of the end mill  60  passes on the machining path, and thereby cutting with a predetermined depth can be performed. The end mill  60  is a square end mill, and the bottom surface is flat. Thus, the web surface is subjected to cutting with a surface (a plane) by the bottom surface of the end mill  60 . In the example of  FIG.  15    and  FIG.  16   , a case where two machining paths (a first machining path PP 1  and a second machining path PP 2 ) are set is illustrated as an example. After machining on the first machining path PP 1  is performed, machining on the second machining path PP 2  is performed. 
     As illustrated in  FIG.  15   , when the surface of the workpiece  10  is not flat and has distortion, if machining is performed without attitude control and with only the control of the feed direction, the pitch direction, and the z direction, a z direction error appears as a mismatch (level difference) ΔM between machining on the first machining path PP 1  and machining on the second machining path PP 2 . Thus, if the attitude control is not performed, unevenness may occur on the surface of the web surface due to machining on respective machining paths. 
       FIG.  16    illustrates a case where control is performed on the feed direction, the pitch direction, the z direction, and the tilt direction (attitude) as with the present embodiment. When attitude control is performed, tilt angles are set in association with respective machining paths. Note that the tilt angle is set on a position basis even for the same machining path, and in machining on a particular machining path, the tilt angle is controlled in accordance with the position on the particular machining path. 
       FIG.  16    illustrates a case where the tilt angle of the first machining path PP 1  is 0 degree, and the tilt angle of the second machining path PP 2  is α degrees (α≠0). In such a way, by rotating the end mill  60  about the axis in the feed direction to control the attitude thereof, it is possible to perform machining so that the mismatch ΔM is reduced and the machined surface approaches the ideal machined surface  92 . 
     The tilt angle is set so that, when adjacent machining paths are the first machining path PP 1  and the second machining path PP 2 , the mismatch ΔM between a machined surface machined by the bottom surface of the end mill  60  on the first machining path PP 1  and the machined surface machined by the bottom surface of the end mill  60  on the second machining path PP 2  is less than or equal to a threshold. Thus, the tilt angle is set so that the mismatch ΔM as occurring in  FIG.  15    is less than or equal to the threshold. Note that it is more preferable to set the tilt angle so that not only the mismatch ΔM but also a machining error (plate thickness error) ΔE is less than or equal to the threshold. The machining error ΔE is a distance between the unmachined surface  91  and a machined surface (machined depth). Because the tilt angle is set so that the mismatch ΔM (and the machining error ΔE) is less than or equal to the threshold and machining is performed, unevenness in the machined surface is reduced. 
     For example, when the diameter of the bottom surface of the end mill  60  is 10 mm or greater and 25 mm or less, the predetermined pitch P can be set to about 5 mm or greater and 20 mm or less. By performing plane machining by using the bottom surface of the end mill  60 , it is possible to widen the predetermined pitch P to reduce the number of machining steps. 
     Although the case where a plurality of machining paths are set at a predetermined pitch P when a web surface is machined has been described in the above example, control may be performed on the predetermined pitch P. Specifically, the machining path setting unit  76  sets the predetermined pitch P based on the amount of slope in the pitch direction of the web surface. For example, by making the pitch of machining paths wider when the amount of slope in the pitch direction is smaller, it is possible to reduce duplication of machining and reduce the number of steps while performing machining by using the bottom surface of the end mill  60 . On the other hand, when the amount of slope in the pitch direction is larger, the pitch may be made narrower to perform finer machining. 
       FIG.  17    is a diagram illustrating the overview of a flow of the machining of a web surface. First, a web surface is set as a control point (SW 1 ), and a measurement path is set for the web surface (SW 2 ). Interference check is then performed (SW 3 ), and measurement is performed (SW 4 ). The interference check in SW 3  is an operation to check whether or not the jig  20  interferes with measurement. If there is interference, no subsequent process is performed, or the path is corrected. A surface model of the web surface is then generated (SW 5 ), and a machining path is set for the web surface (SW 6 ). Interference check is then performed (SW 7 ), and the machining is performed on the web surface (SW 8 ). The interference check in SW 7  is an operation to check whether or not the jig  20  interferes with machining to be performed. If there is interference, no subsequent process is performed, or the path is corrected. 
     As described above, when a web surface is machined, a plurality of machining paths are set in the pitch direction, and tilt angles are set for respective machining paths. This makes it possible to machine the web surface more flexibly with higher precision. In particular, in machining of adjacent machining paths, the tilt angles are set so that the level difference (mismatch) between respective machined surfaces machined by the bottom surface of the end mill  60  is less than or equal to a threshold. Therefore, between the machining paths, the machined surface can be made smooth and discontinuity can be controlled. 
     [Machining of Flange Surface] 
     Next, specific machining of a flange surface will be described. 
       FIG.  18    illustrates an example of a case where a flange surface (the machined surface  12   a  of the upper flange part  12 ) of the workpiece  10  is machined. Note that the width (height dimension) of the flange surface is narrower than the range that can be machined by the side surface of the end mill  60 . 
     As illustrated in  FIG.  18   , one machining path is set on a flange surface for the tool tip so that the flange surface can be machined from the lower end to the upper end. Thus, the end mill  60  is moved so that the center of the bottom surface of the end mill  60  passes on the machining path (tool tip point control). 
     Furthermore, one tilt angle (fixed tilt angle) is set on a machining path of the flange surface. Thus, the tilt control unit  77   d  controls the tilt angle of the end mill  60  to be constant at the fixed tilt angle while the end mill  60  moves along one machining path to machine the flange surface. Thus, one-shot machining is performed on one flange surface without a change of the attitude. The end mill  60  is moved along the machining path with the angle being fixed, and thereby cutting with a predetermined depth can be performed. 
     For the fixed tilt angle, it is preferable to use the mean value or the center value of slope angles (slope angles of the flange surface) at a plurality of positions in the longitudinal direction of the flange surface found from a measurement result of the flange surface. Even if the slope varies on the flange surface, by using the mean value or the center value as the fixed tilt angle, it is possible to reduce excessive cutting or insufficient cutting to make the slope of the flange surface even. 
       FIG.  19    is a diagram illustrating the overview of a flow of machining of the flange surface. First, a flange surface is set as a control point (SF 1 ), and a measurement path is set for the flange surface (SF 2 ). Interference check is then performed (SF 3 ), and measurement is performed (SF 4 ). The interference check in SF 3  is an operation to check whether or not the jig  20  interferes with measurement. If there is interference, no subsequent process is performed, or the path is corrected. A surface model of the flange surface is then generated (SF 5 ), and a machining path is set for the flange surface (SF 6 ). Interference check is then performed (SF 7 ), and the machining is performed on the flange surface (SF 8 ). The interference check in SF 7  is an operation to check whether or not the jig  20  interferes with machining to be performed. If there is interference, no subsequent process is performed, or the path is corrected. 
     In such a way, for a flange surface, one tilt angle (fixed tilt angle) is set for one flange surface, and the tilt angle is fixed when machining is performed. It is thus possible to machine a flange surface to have an even slope angle. 
     [Measurement and Machining of R-surface] 
     Next, specific measurement and machining of an R-surface will be described. 
     The R-surface is a portion to connect a flange surface and a web surface to each other and is likely to have a large error with respect to a design model. Thus, multiple times of measurement are performed by using a process of the remeasurement path setting unit  78 . 
       FIG.  20    is a diagram illustrating an example of a case where the workpiece  10  is measured based on a design model. Note that a case where the probe  93  is used to perform measurement will be described as an example. When a measurement path is set based on a design model, a measurement point (a point on the measurement path) is set for the workpiece  10  of a design shape.  FIG.  20    illustrates measurement points P 1 , P 2 , and P 3  on a design model R-surface  94 . For example, when measurement is performed on the measurement point of P 1 , the result of the measurement will be recognized as a measurement result for P 1  on the machining system  70  side. 
     However, as illustrated in  FIG.  21   , when an R-surface having a large shape error with respect to a design model is measured, even though it is intended to measure Pa 1 , Pa 2 , Pa 3 , which are measurement points of an actual R-surface  95  of the workpiece  10  that are supposed to correspond to measurement points (P 1 , P 2 , P 3 ), the measurement positions provided by the probe  93  may be positions (Pb 1 , Pb 2 , Pb 3 ), which are displaced from the measurement points. In such a case, for example, the measurement result of Pbl will be recognized as the measurement result of Pa 1  on the machining system  70  side. Thus, if a surface model is generated based on measurement results including measurement errors, a surface model  96 , which is different from the actual R-surface  95  of the workpiece  10  may be generated as illustrated in  FIG.  22   . 
     Thus, when measurement on an R-surface is performed, the process performed by the remeasurement path setting unit  78  is applied. Specifically, as with the case of a web surface or the like, a measurement path is set based on a design model to perform measurement (corresponding to  FIG.  21   ). A surface model is then generated based on a measurement result (corresponding to  FIG.  22   ). The measurement path is then set by the remeasurement path setting unit  78  based on the surface model (the surface model  96  of  FIG.  22   ). Thus, a measurement path (remeasurement path) indicating portions on which measurement is to be performed is set on the surface model. As illustrated in  FIG.  23   , measurement is then performed based on the remeasurement path. This reduces the error between a measurement point set for the surface model and a measurement position actually measured for the workpiece  10 . A surface model is then regenerated based on the measurement result in accordance with the remeasurement path. 
     The machining path setting unit  76  generates a machining path based on the regenerated surface model. Accordingly, it is possible to accurately make a surface modeled for the R-surface having a large error with respect to a design model to perform machining. 
       FIG.  24    is a diagram illustrating the overview of a flow of machining of an R-surface. First, an R-surface is set as a control point (SR 1 ), and a measurement path is set for the R-surface (SR 2 ). Interference check is then performed (SR 3 ), and measurement is performed (SR 4 ). The interference check in SR 3  is an operation to check whether or not the jig  20  interferes with measurement. If there is interference, no subsequent process is performed, or the path is corrected. A surface model of the R-surface is then generated (SR 5 ). Then, a remeasurement path is set for the R-surface (SR 6 ). Interference check is then performed (SR 7 ), measurement based on the remeasurement path is performed (SR 8 ), and a surface model of the R-surface is regenerated (SR 9 ). The interference check in SR 7  is the same as the interference check in SR 3 . A machining path is then set for the R-surface (SR 10 ). Interference check is then performed (SR 11 ), and machining is performed on the R-surface (SR 12 ). The interference check in SR 11  is an operation to check whether or not the jig  20  interferes with machining to be performed. If there is interference, no subsequent process is performed, or the path is corrected. 
     In such a way, a surface model is generated and a machining path is set for an R-surface through multiple times of measurement. 
       FIG.  25    is a diagram illustrating an example of a case where an R-surface is machined.  FIG.  25    illustrates a case where an inside corner R-surface  99   a  that is the R-surface of the R-part  14  and an outside corner R-surface  99   b  that is the R-surface of the R-part  15  are machined. When the inside corner R-surface  99   a  is machined by a ball end mill having a radius of curvature equal to the design shape, if the workpiece  10  has a shape error with respect to the design shape, this may cause excessive cutting, and a mismatch may occur. Thus, when the inside corner R-surface  99   a  is machined, it is preferable to perform machining by a ball end mill unlike the above or a radius end mill with cutting path following measured result. Note that the inside corner R-surface  99   a  may be machined by a ball end mill  97  having a smaller radius of curvature than the radius of curvature of the design shape of the inside corner R-surface  99   a.    
     When the outside corner R-surface  99   b  is machined by an inverse R-cutter having a radius of curvature equal to the design shape, if the workpiece  10  has a shape error with respect to the design shape, this may cause insufficient or excessive cutting, and a mismatch may occur. Thus, when the outside corner R-surface  99   b  is machined, it is preferable to perform machining by using an inverse R-cutter (corner R-cutter)  98  having an inverse R-part whose radius of curvature is larger than the radius of curvature of the design shape of the outside corner R-surface  99   b  and an angle range of the inverse R-part that is less than 90 degrees (the R-part angle as a cutting edge is less than 90 degrees). As illustrated in  FIG.  25   , in the inverse R-cutter  98 , the R-angle of the R-part is less than 90 degrees. Both ends of the R-part of the inverse R-cutter  98  are provided with nose r-parts, and these nose r-parts prevent cut-in of the edge or a mismatch and thereby smooth the machined surface. The r-angle of the nose r-part can be the minimum necessary and is, for example, 10 degrees or greater. 
     Further, as illustrated in  FIG.  25   , machining paths are set for respective R-surfaces, and machining is performed while attitude control is performed on respective machining paths. Machining can be performed with at least three paths for a connecting part between the R-part and the upper surface thereof, a connecting part between the R-part and the lower surface thereof, and the R-part. Specifically, the machining paths are each set in association with the connecting part between the flange surface and the R-surface, the connecting part between the web surface and the R-surface, and the R-surface of the R-part, and thereby machining can be efficiently performed with three paths. Note that the number of paths may be adjusted in accordance with surface roughness. This reduces occurrence of a mismatch with respect to another surface. In particular, for a portion of an outside corner R such as the outside corner R-surface  99   b , even with a workpiece having an angular error, such as a sheet frame, the inverse R-cutter  98  is used to follow the R-shape to perform machining. With the use of the special inverse R-cutter  98  whose radius of curvature of the inverse R-part is less than 90 degrees (in typical inverse R-cutters, the inverse R-part is 90 degrees), it is possible to reduce the number of paths (for example, the minimum three paths) to efficiently machine the outside corner R-surface  99   b . To perform additional machining along the R-shape, as illustrated in  FIG.  25   , it is possible to perform machining with high precision by using the entire surface of the inverse R-cutter  98 . Thus, machining is performed so that the entire surface of the R-part, which is a portion of the inverse R-cutter  98  to perform machining, is fitted along the outside corner R-surface  99   b . For example, typical inverse R-cutters are to perform machining by abutting a part of the R-part (not the entire surface thereof) against the outside corner of a workpiece. 
     Note that, although the case where the R-surface is machined by the tool as illustrated in  FIG.  25    has been described in the above example, a radius end mill may be used. Note that the R-surface (the outside corner R-surface) of the R-part  16  may be machined in the same manner. 
     [Machining Process] 
     Next, an example of the machining process performed by the machining system  70  described above will be described with reference to  FIG.  26    and  FIG.  27   .  FIG.  26    and  FIG.  27    are a flowchart illustrating an example of a procedure of the machining process according to the present embodiment. The flow is divided into parts of  FIG.  26    and  FIG.  27    for illustration. 
     First, a design model of the workpiece  10  is loaded (S 101 ). Next, machining target surfaces are set (S 102 ). The machining target surfaces are a web surface, a flange surface, and an R-surface. Next, one of the divided machining target surfaces is selected (S 103 ). Next, it is determined whether or not the R-surface is selected (S 104 ). If the R-surface is not selected (S 104 , NO), a measurement path is set for the selected machining target surface based on the design model (S 105 ). Measurement is then performed based on the measurement path (S 106 ). 
     Next, it is determined whether or not the difference between the design model and the measurement result is less than or equal to a threshold (S 107 ). For example, if there is even one portion where the difference (displacement) between the design model and the measurement result is not less than or equal to the threshold, NO is determined in S 107 . If the difference between the design model and the measurement result is not less than or equal to the threshold (S 107 , NO), an alarm is issued to notify that the measurement result has an error or the shape of the workpiece  10  is significantly different from the design model (S 108 ). With this alarm, it is possible to notify that there is a failure in a phase before machining. 
     Next, if the difference between the design model and the measurement result is less than or equal to a threshold (S 107 , YES), a surface model is generated based on the measurement result for the selected machining target surface (S 109 ). Next, it is determined whether or not all the measurement operations on respective divided machining target surfaces are completed (S 110 ). If not all the measurement operations are completed (S 110 , NO), a different machining target surface from the selected machining target surface is selected (S 111 ), and S 104  is again performed. 
     If the R-surface is selected (S 104 , YES), a measurement path is set based on the design model of the R-surface (S 112 ). Measurement is then performed based on the measurement path (S 113 ). Next, it is determined whether or not the difference between the design model and the measurement result is less than or equal to a threshold (S 114 ). If YES is determined in S 114 , the process proceeds to S 107 . If the difference is not less than or equal to the threshold (S 114 , NO), a surface model of the R-surface is generated based on the measurement result (S 115 ). A remeasurement path is then set based on the generated surface model (S 116 ), and measurement is again performed (S 113 ). With the process of S 115  and S 116 , the measurement error is reduced, and YES is likely to be determined in S 114 . 
     Then, if all the measurement operations are completed (S 110 , YES), respective surface models are combined to generate a component model (S 117 ). Next, it is determined whether or not there is inconsistency in the component model 
     (S 118 ). In S 118 , specifically, if at least any one of the gap and the level difference between the surface models is greater than or equal to a predetermined value, it is determined that there is inconsistency (S 118 , YES). If YES is determined in S 118 , an alarm is issued to notify that the component model is not accurately generated (S 119 ). 
     If NO is determined in  5118 , a particular machining target surface is selected (S 120 ), and a machining path corresponding to the selected machining target surface is generated based on the component model (S 121 ). The machining path is set so as to also include tilt angle information used for attitude control. It is then determined whether or not machining paths are set for all the machining target surfaces (S 122 ). If machining paths are not set for all the machining target surfaces (S 122 , NO), a different machining target surface from the selected machining target surface is selected (S 123 ), and S 121  is again performed. If machining paths are set for all the machining target surfaces (S 122 , YES), machining on respective machining target surfaces is performed based on the machining paths (S 124 ). In S 124 , machining on respective machining target surfaces is performed in the order set in advance, such as the order of the flange surface, the web surface, and the R-surface, for example. 
     According to the present embodiment, the following advantageous effects are achieved. 
     Thus, since the method includes a pressing step of pressing the flange parts  12 ,  13  against the contacting surfaces  42 ,  43 , a flange cutting step of cutting the flange parts  12 ,  13  by the peripheral cutting edge  62  of the end mill by feeding the end mill  60  in an arc direction of the arc shape, and a web cutting step of cutting the web part  11  by the end cutting edge  61  of the end mill  60  by feeding the end mill  60  in the arc direction, it is possible to perform plate thinning machining on each surface of the flange parts  12 ,  13  and the web part  11  without requiring a set-up change. 
     Further, because of the contacting step, the flange parts  12 ,  13  are shaped along the contacting surfaces  42 ,  43 , and distortion is intentionally caused on the web part  11 . This makes the flange parts  12 ,  13  be smooth surfaces without having distortion and therefore facilitates plate thinning machining using the peripheral cutting edge  62  of the end mill  60 . Further, although the web part  11  thus has a surface having distortion, it is possible to realize cutting (plate thinning machining) in accordance with the shape of the distortion by controlling the attitude of the end mill  60 . 
     Further, with the use of a tool (the ball end mill  97  or the inverse R-cutter  98 ) having cutting edges in accordance with the shapes of the R-parts  14 ,  15 ,  16 , the R-parts  14 ,  15 ,  16  can be machined efficiently with less paths and with high precision. 
     Herein, when the inverse R-cutter  98  is used, the R-parts  15 ,  16  can be cut by the entire surface of the cutting edge. Note that, in general, an inverse R-cutter is used for forming a round shape to an outside corner part having a ridgeline. In such a case, the entire surface of the cutting edge is not used for cutting. 
     Further, in the pressing step, since a load along the tangential direction is input to the end of the flange parts  12 ,  13  and thereby the flange parts  12 ,  13  are pressed against the contacting surfaces  42 ,  43 , the flange parts  12 ,  13  can be pressed evenly and forcefully against the contacting surfaces  42 ,  43  by a simple load input method. 
     Further, in the flange cutting step, since the flange parts  12 ,  13  are cut with a single path, a machined surface (a surface that has been machined) having a smooth single contour can be obtained. 
     Further, in the web cutting step, since the web part  11  is cut with a plurality of paths, it is possible to realize cutting in accordance with the shape of distortion by controlling the attitude of the end mill  60 . 
     Further, in the web cutting step, since the end mill  60  is fed while the attitude of the end mill  60  is changed in accordance with the shape of distortion generated in the web part  11  due to the pressing step, plate thinning machining on the web part  11  can be performed at a constant cut amount regardless of the shape of distortion. Thus, the plate thinning machining on the web part  11  can be performed so as to substantially transfer the shape of distortion. 
     Further, a plurality of cutter marks M extending from one end to the other end of the web part  11  are formed on the machined surface, and a portion where the pitch between the adjacent cutter marks M changes in the extending direction of the cutter marks is provided. Thus, the shape of distortion can be predicted from the shape of the cutter marks M. Further, it is possible to determine from a change in the shape of the cutter marks M whether or not the end mill  60  has passed on a planned path, whether or not there is an anomaly in the action (attitude) of the end mill  60 , or the like. 
     Since the level difference (mismatch) is reduced on the machined surface  11   a  of the web part  11  on which such cutter marks M are formed, stress concentration at a mismatch portion can be reduced. Accordingly, the plate thickness of the web part  11  required in terms of strength is ensured without requiring manual finishing, and a machined product in which stress concentration due to a mismatch is reduced can be provided. 
     The machining method and the machined product according to the embodiment described above are recognized as follows, for example. 
     Thus, the machining method according to one aspect of the present disclosure is a machining method for machining a machining target material ( 10 ) by using a tool ( 60 ), the machining target material is set in a jig ( 20 ), the machining target material has a plate-like web part ( 11 ) having an arc shape in plan view and a flange part ( 12 ,  13 ) bent and arranged vertically from an edge along the arc shape of the web part, the tool has an end cutting edge ( 61 ) and a peripheral cutting edge ( 62 ), and the jig has a supporting surface ( 41 ) on which the web part is placed and a contacting surface ( 42 ,  43 ) with which the flange part comes into surface contact. The machining method includes: a pressing step of pressing the flange part against the contacting surface; a flange cutting step of cutting the flange part by the peripheral cutting edge of the tool by feeding the tool in an arc direction of the arc shape; and a web cutting step of cutting the web part by the end cutting edge of the tool by feeding the tool in the arc direction. 
     According to the machining method of the present aspect, provided is a machining method for machining a machining target material by using a tool, the machining target material is set in a jig, the machining target material has a plate-like web part having an arc shape in plan view and a flange part bent and arranged vertically from an edge along the arc shape of the web part, the tool has an end cutting edge and a peripheral cutting edge, the jig has a supporting surface on which the web part is placed and a contacting surface with which the flange surface comes into contact, and the machining method includes: a pressing step of pressing the flange part against the contacting surface; a flange cutting step of cutting the flange part by the peripheral cutting edge of the tool by feeding the tool in an arc direction of the arc shape; and a web cutting step of cutting the web part by the end cutting edge of the tool by feeding the tool in the arc direction. Thus, plate thinning machining can be performed on each surface of the flange part and the web part without requiring a set-up change. 
     Further, the flange part is shaped along the contacting surface, and distortion is intentionally caused on the web part by the contacting step. This makes the flange part be smooth surface without having distortion and therefore facilitates plate thinning machining using the peripheral cutting edge of the tool. Further, although the web part thus has a surface having distortion, it is possible to realize cutting (plate thinning machining) in accordance with the shape of the distortion by controlling the attitude of the tool. 
     Further, the machining method according to one aspect of the present disclosure is a machining method for machining a machining target material by using multiple types of tools, the machining target material is set in a jig, the machining target material has a plate-like web part having an arc shape in plan view, a flange part bent and arranged vertically from an edge along the arc shape of the web part, and an R-part ( 14 ,  15 ) smoothly connecting the web part and the flange part to each other, one of the tools has an end cutting edge and a peripheral cutting edge, another one ( 97 ,  98 ) of the tools has a cutting edge corresponding to a shape of the R-part, and the jig has a supporting surface on which the web part is placed and a contacting surface with which the flange part comes into surface contact. The machining method includes: a pressing step of pressing the flange part against the contacting surface; a flange cutting step of cutting the flange part by the peripheral cutting edge of the one of the tools by feeding the one of the tools in an arc direction of the arc shape; a web cutting step of cutting the web part by the end cutting edge of the one of the tools by feeding the one of the tools in the arc direction; and an R-part cutting step of cutting the R-part by the cutting edge of the other one of the tools by feeding the other one of the tools in the arc direction. 
     According to the machining method of the present aspect, plate thinning machining can be performed on each surface of the flange part, the web part, and the R-part without requiring a set-up change. Further, with the use of a tool having a cutting edge in accordance with the shape of the 
     R-part, the R-part can be machined efficiently with less paths and with high precision. 
     Further, in the machining method according to one aspect of the present disclosure, the pressing step includes pressing the flange part against the contacting surface by inputting a load along a tangential direction to an end of the flange part. 
     According to the machining method of the present aspect, in the pressing step, since a load along a tangential direction to an end of the flange part is input and thereby the flange part is pressed against the contacting surface, the flange part can be pressed evenly and forcefully against the contacting surface by a simple load input method. 
     Further, in the machining method according to one aspect of the present disclosure, the flange cutting step includes cutting the flange part with a single path. 
     According to the machining method of the present aspect, in the flange cutting step, since the flange part is cut with a single path, a machined surface (a surface that has been machined) having a smooth single contour can be obtained. 
     Further, in the machining method according to one aspect of the present disclosure, the web cutting step includes cutting the web part with a plurality of paths. 
     According to the machining method of the present aspect, in the web cutting step, since the web part is cut with a plurality of paths, it is possible to realize cutting in accordance with the shape of distortion by controlling the attitude of the tool. 
     Further, in the machining method according to one aspect of the present disclosure, the web cutting step includes feeding the tool while changing an attitude of the tool in accordance with a shape of distortion generated in the web part by the pressing step. 
     According to the machining method of the present aspect, in the web cutting step, since the tool is fed while the attitude of the tool is changed in accordance with the shape of distortion generated in the web part due to the pressing step, plate thinning machining on the web part can be performed at a constant cut amount regardless of the shape of distortion. Thus, the plate thinning machining on the web part can be performed so as to substantially transfer the shape of distortion. 
     Further, an machined product according to one aspect of the present disclosure is a machined product having a plate-like web part having an arc shape in plan view and a flange part bent and arranged vertically from an edge along the arc shape of the web part, one surface of the web part is a machined surface, a plurality of cutter marks extending from one end to the other end of the web part are formed on the machined surface, and the machined product has a portion where a pitch between the cutter marks that are adjacent to each other gradually changes along an extending direction of the cutter marks. 
     According to the machined product of the present aspect, a plurality of cutter marks (M) extending from one end to the other end of the web part are formed on the machined surface, and a portion where the pitch between the adjacent cutter marks changes in the extending direction of the cutter marks is provided. Thus, the shape of distortion can be predicted from the shape of the cutter marks. Further, it is possible to determine from a change in the shape of the cutter marks whether or not the tool has passed on a planned path, whether or not there is an anomaly in the action (attitude) of the tool, or the like. 
     Further, in the machined product according to one aspect of the present disclosure, at least one of the cutter marks has a portion formed in a wave shape on a continuous line from the one end to the other end. 
     Further, in the machined product according to one aspect of the present disclosure, at least one of the cutter marks has a cuspidal point on a continuous line from the one end to the other end. 
     LIST OF REFERENCE SYMBOLS 
     
         
           10  workpiece (target component) 
           11  web part 
           11   a  machined surface 
           11   b  supported surface 
           12  upper flange part 
           12   a  machined surface 
           12   b  contacted surface 
           13  lower flange part 
           13   a  machined surface 
           13   b  contacted surface 
           14  R-part 
           15  R-part 
           16  R-part 
           20  jig 
           30  base 
           31  base-side step 
           32  bearing 
           33  positioning pin 
           40  setting block 
           41  supporting surface 
           42  upper flange contacting surface 
           43  lower flange contacting surface 
           44  lifting mechanism 
           50  clamp 
           51  clamp body 
           51   a  rotating part 
           51   b  leg part 
           51   c  clamp-side step 
           52  load bolt 
           53  load block 
           60  end mill 
           61  end cutting edge 
           62  peripheral cutting edge 
           70  machining system 
           71  setting unit 
           72  measurement path setting unit 
           73  measuring unit 
           74  surface model generation unit 
           75  component model generation unit 
           76  machining path setting unit 
           77  movement control unit 
           77   a  feed direction control unit 
           77   b  pitch direction control unit 
           77   c  orthogonal direction control unit 
           77   d  tilt control unit 
           78  remeasurement path setting unit 
           81  CPU 
           82  main memory 
           83  storage unit 
           84  external interface 
           85  communication interface 
           86  input unit 
           87  display unit 
           91  unmachined surface 
           92  ideal machined surface 
           93  probe 
           94  R-surface 
           95  R-surface 
           96  surface model 
           97  ball end mill 
           98  inverse R-cutter 
           99   a  inside corner R-surface 
           99   b  outside corner R-surface 
         P predetermined pitch 
         PP 1  first machining path 
         PP 2  second machining path 
         ΔE machining error 
         ΔM mismatch (level difference)