Methods for CNC Lathes

Abstract

The present invention uses a nominal rake angle (γ n The present invention relates to a turning method for a CNC lathe, comprising at least two machining steps, in which the cutting elements (1, 11) are repositioned between the machining steps such that the cutting element diameter (D) is changed, whereby the useful tool life can be extended and a high quality of the machined surface and a stable cutting process can be achieved even with worn tools. The present invention also relates to a system and a computer program for implementing the method.

Description

[Technical Field]

[0001] This invention belongs to the field of metal cutting. More specifically, this invention belongs to the field of turning. [Background technology]

[0002] In metal cutting, turning is a common machining operation. CNC lathes are commonly used. Especially when machining hard materials, it is common to use turning tools with cutting elements made of cubic boron nitride (CBN) or ceramic. Even though such materials have higher wear resistance compared to, for example, carbide cutting tools, wear on the rake face and flank face of the cutting element ultimately limits the usability of the cutting element and can even lead to tool failure where the cutting element must be replaced. For efficiency and economic reasons, it is sometimes desirable to use the cutting element for as long as possible. Therefore, efforts have been made to reduce the wear of the cutting element. As an example, EP2015881 discloses a CBN tool component having a secondary layer on the rake face that has higher resistance to crater formation. However, even if tool life can be extended to some extent, such a layer does not prevent tool wear from ultimately degrading the cutting properties of the CBN tool.

[0003] Therefore, it is necessary to further extend the tool life of the cutting elements used in the turning process. [Overview of the project]

[0004] The object of the present invention is to mitigate the shortcomings of the prior art and to provide a method for extending tool life, i.e., the time that a cutting element can be used for machining. A further object is to provide a method for consistently producing high-quality machined surfaces. A further object is to obtain a stable cutting process.

[0005] Therefore, according to the first aspect, the present invention relates to a turning method for a CNC lathe, and this method is - The step of providing a workpiece that is rotatable in the rotational direction around its axis of rotation, - A step of providing a turning tool extending along a tool axis, wherein the turning tool comprises a cutting element including a rake face, a flank face, and a cutting edge formed at the boundary between the rake face and the flank face, the cutting element being oriented in different directions relative to the workpiece, each orientation being determined by a nominal rake angle with respect to the surface of the workpiece, and the cutting element having an effective rake angle and an effective flank angle at the contact point between the cutting edge and the workpiece, which depend on the wear of the cutting element, - The steps of positioning a cutting element relative to a workpiece in a first orientation determined by a first nominal rake angle that yields a first effective rake angle and a first effective relief angle, -In the first machining step, the workpiece is machined with the cutting element in a first orientation, After the first machining step, - A step of rearranging a cutting element with respect to a workpiece or another workpiece to be machined in a second orientation determined by a second nominal rake angle that results in a second effective rake angle and a second effective relief angle, wherein the second nominal rake angle is different from the first nominal rake angle. - In the second machining step, the cutting element is in a second orientation while machining the workpiece or another workpiece. Includes.

[0006] This can extend the effective tool life, and even when using worn tools, high-quality machined surfaces and a stable cutting process can be achieved. Surface quality may refer to surface roughness or surface integrity, for example, related to microstructural changes caused by the machining process.

[0007] The turning method is for CNC lathes, i.e., computer-controlled or computerized numerically controlled lathes, i.e., any CNC machine suitable for turning, such as a rotary lathe, multitasking machine, turn mill machine, or sliding head machine. The workpiece may be a metal workpiece including an outer surface which is the radially outward surface. The radially outward surface faces outward from the axis of rotation. This turning method can be used for turning the radially outward surface, i.e., external turning. The workpiece extends between a first end and a second end.

[0008] The workpiece may be made of hardened steel, for example, hardened steel with a hardness of 40 HRC or higher. Alternatively, the workpiece may be made of a superalloy, such as a heat-resistant superalloy (HRSA), for example, a nickel-based alloy.

[0009] The workpiece may be clamped by a clamping mechanism. The clamping mechanism holds the workpiece and is at least partially controlled and driven by a motor or spindle. The clamping mechanism may be in the form of a collet chuck, a face driver, or a three-jaw chuck and may include a tailstock. The headstock end of the machine is preferably located at the first end of the workpiece. The second end of the workpiece opposite the first end may be a free end. Alternatively, the second end may be in contact with a tailstock or a second chuck.

[0010] The turning tool comprises a front end and an opposite rear end in the form of a coupling. The coupling is connected to the CNC lathe, more specifically to the machine interface of the CNC lathe, such as the machine spindle, tool revolver turret, or tool post.

[0011] The connecting portion may have a square or rectangular cross-section. The connecting portion may preferably be conical or substantially conical, according to ISO standard 26623-1, etc. In this context, a frustum of cone is a conical shape. In this context, the tapered portion forming the rear of the connecting portion according to ISO standard 26623-1 is a conical shape. The connecting portion extends along the connecting axis. The connecting portion is preferably conical such that the cone or conical shape is symmetrical or substantially symmetrical about the connecting axis. In this context, 3-fold symmetry is considered symmetrical. The cross-sectional area of ​​the cone or conical shape preferably decreases towards the rear. The connecting portion may be in the form of a hollow tapered shank, such as an HSK, according to DIN 69893.

[0012] The connecting shaft defines the longitudinal axis of the turning tool and corresponds to the tool axis or central axis of the turning tool.

[0013] A turning tool comprises cutting elements. The cutting elements are preferably made from wear-resistant materials, such as cubic boron nitride (CBN), polycrystalline cubic boron nitride (pCBN), ceramics, or cemented carbide. The cutting elements may be mounted, for example, as part of the turning tool, for instance as an integral part of such a turning tool, or as a replaceable and / or indexable cutting insert, or a turning insert that can be attached to the turning tool, for example, within an insert pocket, where the cutting insert may be fastened by any suitable fastening means, such as screws or other means for securely holding the cutting insert within the insert pocket. The cutting elements may also be considered part of such a cutting insert. For example, the cutting elements may be CBN cutting tips brazed to a cemented carbide carrier, which together form a replaceable cutting insert.

[0014] The cutting element comprises an upper surface including a rake face or rake surface. The cutting element further comprises a clearance face or clearance surface adjacent to the rake face. At the boundary between the rake face and the clearance face, a cutting edge is formed. The cutting edge, or a part of the cutting edge, generates a machined surface. The cutting edge may have a convex shape in top view, for example, the cutting edge may be a nose cutting edge in the form of an arc. The cutting element may have a rhombic, triangular, octagonal, square, circular or polygonal shape in top view, especially when in the form of a cutting insert.

[0015] The upper surface may be flat. Alternatively, the surface may be non - flat or non - planar. For example, the surface may comprise one or more chip - breaking means in the form of one or more protrusions and / or depressions. Further, a chamfer may be formed on the upper surface such that the cutting edge is defined at the boundary between the clearance face and such a chamfered surface. In such a case, for the purposes described in the present disclosure, i.e., considering the nominal rake angle and / or the effective rake angle, the chamfered surface corresponds to the rake face.

[0016] During machining, the workpiece is rotated in a rotational direction and the turning tool is controlled such that the cutting edge of the cutting element engages the rotating workpiece. The machining performed during the first machining step includes machining the workpiece. The first machining step may also include further machining of the workpiece.

[0017] The machining may include any method that results in a rotationally symmetric surface about which the workpiece rotates. Thus, the method may be used not only in single - point turning but also in other turning operations such as turning operations where the contact point or contact area between the cutting edge and the workpiece moves along the cutting edge during machining. For example, here, there is a linear feed movement in a direction transverse to the axis of rotation.

[0018] During machining, cutting elements undergo wear, particularly crater wear on the rake face and flank wear on the flank face. Especially in the case of CBN cutting elements used in turning hard parts, the minute geometry of the cutting element is fundamentally altered as wear progresses throughout the cutting element's life. For example, when using a CBN cutting element with a chamfered section that initially has a negative rake angle, the effective rake angle eventually becomes positive due to crater wear on the cutting element. Ultimately, the cutting element will either fail or fail to provide an acceptable machining result and must be replaced. The inventors have discovered that cutting elements can assume tribological stability conditions after a certain period of machining, i.e., conditions maintained for the remainder of the cutting element's life. For example, in the case of a CBN cutting element with a chamfered section, such tribological stability conditions may appear approximately 30% of the estimated tool life. Under tribological stability conditions, the effective rake angle, effective flank angle, and cutting edge radius are normalized. As a result, the wedge angle is also normalized and therefore does not change significantly during stable tribological conditions. Thus, even if crater wear and flank wear may increase during this stable state, the progression of wear is such that the shape of the flank and crater does not change, i.e., the effective rake angle and effective relief angle remain substantially the same. It was found that the cutting edge line of the cutting element maintained good integrity even under stable tribological conditions, despite a significant change in the effective rake angle compared to the original rake angle. However, it was also found that under stable tribological conditions, the effective relief angle is often 0 or near 0, i.e., for a considerable amount of tool life, and this can potentially have various adverse effects. For example, increased contact between the flank and the workpiece can alter the integrity of the machined surface. The inventors found that changing the nominal rake angle before or immediately after reaching stable tribological conditions could improve (or maintain) the integrity of the machined surface and extend effective tool life.

[0019] To put it another way, the inventors have found a way or method that allows cutting elements that were previously considered worn out to be used for a longer period of time. This way involves repositioning the cutting element opposite the workpiece. The inventors have found that this method works particularly well when turning hardened steel or other hard metals such as nickel-based superalloys, etc., using CBN or pCBN cutting elements, i.e., cutting or turning inserts containing CBN or pCBN.

[0020] As used herein, “nominal rake angle” refers to the angle of the original rake face relative to a plane perpendicular to the machined surface, without considering variations in the geometric shape of the cutting element (such as variations caused by wear). In this context, the nominal rake angle may also be considered a “system rake angle,” i.e., one that can be determined by the original geometric shape of the cutting element in a particular machining setting (e.g., the orientation and position of the CNC lathe, tool holder, etc., relative to the workpiece). Correspondingly, “nominal relief angle” refers to the clearance of the original, unworn relief face relative to the workpiece surface, i.e., the desired clearance, without considering tool wear. In contrast, as used herein, “effective rake angle” is the true rake angle effective during machining, i.e., the actual cutting angle, which depends on local variations in the geometric shape of the rake face. Correspondingly, “effective relief angle” refers to the actual clearance of the relief face relative to the machined surface. Both the effective rake angle and the effective relief angle are affected by wear of the cutting element. For example, the effective rake angle may increase compared to the original rake angle due to crater wear on the rake face, and the effective relief angle may decrease due to flank wear. Therefore, when machining with an unworn cutting element, the effective rake angle and effective relief angle are initially equal to the nominal rake angle and nominal relief angle, respectively. match However, as soon as wear occurs and begins to affect these angles, the effective angle becomes, match It deviates from the nominal angle.

[0021] Therefore, during the first machining step, wear of the cutting element affects the actual geometric shapes of the rake face and flank face. This can increase the effective rake angle and decrease the effective flank angle. To compensate for such wear, the nominal second rake angle is different from the first nominal rake angle. In particular, repositioning the cutting element to a second orientation, i.e., changing the nominal rake angle, can increase the effective clearance.

[0022] To achieve this, the second nominal rake angle used in the second machining step may be smaller than the first nominal rake angle used in the first machining step.

[0023] Reducing the nominal rake angle also clearly reduces the effective rake angle, at least compared to the effective rake angle present immediately before the cutting element is repositioned. However, the second effective rake angle may still be larger than the first effective rake angle because the wear caused by the first machining step causes an increase in the effective rake angle compared to the first effective rake angle.

[0024] It is also assumed that the first effective rake angle and the second effective rake angle are the same, that is, the change in the effective rake angle caused by wear from the first machining step corresponds to the difference between the first nominal rake angle and the second nominal rake angle. However, this may often not be true if the first machining step initially involves using a new, unworn cutting element, because the increase in the rake angle due to crater wear is often higher than what is desirable to compensate for when repositioning the cutting element. On the other hand, if the first machining step begins with an already worn cutting element that has been repositioned from a previous state where stable tribological conditions have been reached, and the first machining step proceeds until new stable tribological conditions are reached, it is very likely that the first effective rake angle corresponds to the second effective rake angle, that is, the effective rake angle is restored by the change in the nominal rake angle. However, the original effective rake angle of the unworn cutting element may not be desirable or possible to restore.

[0025] Reducing the nominal rake angle increases the effective clearance, thus reducing contact between the cutting element flank and the workpiece. An increase in the contact area between the cutting element flank and the workpiece alters the distribution of passive and feed forces, resulting in an increased thickness of the white layer on the machined component, which is associated with undesirable microstructural changes on the machined surface. Therefore, increasing the clearance leads to a more stable machining process, reduced white layer formation, and thus improved surface quality.

[0026] The second effective escape angle is equal to the first effective escape angle. match or substantially matchIt is possible. In other words, the difference between the first nominal rake angle and the second nominal rake angle may correspond to the change in the effective clearance angle caused by the first machining step. For example, the first machining step may cause flank wear of the cutting element such that the effective clearance angle is reduced to zero, i.e., friction occurs between at least a portion of the flank face and the workpiece. Then, by making the difference between the first nominal rake angle and the second nominal rake angle correspond to a desired clearance angle, e.g., the clearance angle that exists for an unworn cutting element, the desired (e.g., original) effective clearance angle can be restored by rearranging the cutting element. In other words, the original effective clearance can be restored by changing the nominal rake angle.

[0027] The second nominal rake angle may differ from the first nominal rake angle by only 2 to 10 degrees. In many applications, this is sufficient to restore the gap while maintaining good cutting performance, and by not changing the nominal rake angle too much, it is possible to reposition the cutting element multiple times, further extending the overall life of the cutting element. The second nominal rake angle may differ from the first nominal rake angle by only 4 to 8 degrees, for example, by only 6 degrees, which may be beneficial for at least some applications.

[0028] The step of repositioning the cutting element may be performed when the cutting element is unable to cut. As used herein, “out of cut” refers to a state in which the cutting element is not engaged with the workpiece. Such a state may occur between machining two different workpieces or between two different passes of a turning operation on a workpiece.

[0029] Therefore, the first machining step may include a first set of one or more machining operations, and the second machining step may include a second set of one or more machining operations, where the step of rearranging the cutting elements may be performed between these sets of machining operations, for example, between machining two different workpieces, in which case the machining operations in the second set do not overlap with the machining operations in the first set.

[0030] In this context, a machining operation can be considered an operation performed on a workpiece that may involve one or more passes using a turning tool.

[0031] As described above, the step of rearranging the cutting elements may be performed between two different passes of the machining operation. In this case, the first machining step and the second machining step may each include different parts of a single turning operation. The first machining step may then include, for example, one or more complete machining operations (e.g., machined components) and a first part of a particular machining operation, while the second machining step may include a second part of a particular machining operation, as well as subsequent machining operations and / or parts of subsequent machining operations.

[0032] It is conceivable that the rearrangement of the cutting elements may occur during machining, for example, during the pass of a turning operation. Therefore, the rearrangement of the cutting elements may include stepwise or continuous rearrangement performed during machining. This may be useful, for example, when turning a large HRSA component, where the cutting element wears down in a single pass, which may potentially cause the surface integrity of the component to differ between the beginning of the cut and the end of the cut.

[0033] The duration of each machining step may be selected based on a predetermined time period during which the cutting element was being cut. Therefore, the repositioning of the cutting element may occur after a specific predetermined time period, for example, after a certain number of minutes (i.e., "time in cut") during which the cutting element was active. Thus, the first machining step may include machining for a specific time, without considering the actual number of machining operations performed. A machining step may also be determined to include a machining operation or a path of machining operations such that a predetermined time period ends during which the current machining operation or path ends before the cutting element is repositioned. Instead of a predetermined time, the duration may alternatively be selected based on a predetermined cutting length. As a further alternative, each machining step may relate to a certain number of machining operations; that is, a machining step may be determined to include machining a predetermined number of workpieces. Therefore, the repositioning of the cutting element may occur after a certain number of components have been machined.

[0034] Regardless of the parameters used to determine when the rearrangement of the cutting elements should occur, each machining step may involve machining multiple different workpieces.

[0035] Positioning and rearranging the cutting element between the first and second orientations can be achieved in various ways. According to some embodiments, the relative position between the workpiece and the tool axis can be adjusted. For example, the engagement point between the cutting element and the workpiece can be adjusted by moving the tool axis relative to the workpiece laterally with respect to the axis of rotation from the first tool axis position to the second tool axis position, such that the tool axis at the second tool axis position is parallel to but not coincides with the tool axis at the first tool axis position.

[0036] Therefore, the direction of engagement of the cutting element with respect to the surface of the workpiece can be adjusted by changing the orientation of the tool axis relative to the workpiece, particularly by translation of the tool axis. In particular, considering a Cartesian coordinate system for a lathe where the Z axis points in the direction along the axis of rotation of the workpiece, the X axis points in the radial direction relative to the workpiece (i.e., toward or away from the axis of rotation), and the Y axis points in the direction perpendicular to the plane defined by the Z and X axes, translation may include movement along the Y axis. Thus, such embodiments require the use of a CNC lathe that has the ability to move the turning tool along the Y axis, such as certain types of multitasking machines or mill-turn machines. Thus, when using such a CNC lathe, the step of repositioning the cutting element can be achieved via the machine control system. Such repositioning of the cutting element can be carried out accurately and relatively easily, as it does not require specially designed turning tools or tool holders.

[0037] According to some embodiments, the tool axis is moved a first distance in a first direction from a first tool axis position to a second tool axis position.

[0038] Considering the coordinate system determined above, the first direction may be along the Y-axis. Therefore, if the tool axis is oriented along the X-axis or parallel to the X-axis, the first direction may correspond to a direction lateral to both the tool axis and the axis of rotation of the workpiece. In particular, the first direction may correspond to, or substantially correspond to, the direction of rotation of the workpiece, i.e., the direction of tangential motion of the workpiece at the point of contact between the cutting element and the workpiece. To put it another way, the first direction may be along the Y-axis, away from the direction to which the rake face or top face of the cutting element faces.

[0039] In other words, the movement of the tool axis may have a component along the Y-axis, and the movement may be directed along, or substantially along, the rotational direction of the workpiece at the point of contact between the cutting element and the workpiece, i.e., away from the direction toward which the rake face or top face of the cutting element faces.

[0040] As a result, the cutting element is repositioned relative to the workpiece, where the nominal rake angle is reduced and the effective relief angle is increased.

[0041] The tool axis may be moved not only along the Y-axis but also along the X-axis to compensate for changes in cutting depth caused by movement along the Y-axis. For example, if the tool axis is moved a certain distance along the Y-axis to change the nominal rake angle, the tool axis may also be moved a certain distance along the X-axis to maintain the same cutting depth.

[0042] The tool may not necessarily move linearly between the first and second orientations, nor in two consecutive linear movements (for example, not first in the Y-axis direction and then in the X-axis direction), but may also move along an arc, for example, around the perimeter of the workpiece.

[0043] The first distance moved in the first direction, or the resulting distance moved along the Y-axis, can be between 0.03r and 0.18r, such as 0.07r and 0.14r, where r is the radius of the workpiece. A movement of 0.03r to 0.18r, when performed at least near the center of the workpiece, i.e., in the vicinity of the XZ plane, can result in a change of 2 to 10 degrees of the nominal rake angle. As an example, the first distance, or the resulting distance moved along the Y-axis, can be about 0.1 times the radius of the workpiece, for example, between 0.09r and 0.11r, which can correspond to a change of about 6 degrees of the nominal rake angle.

[0044] An alternative method for repositioning cutting elements that does not require translation of the tool axis may be to mount the cutting elements in different turning tools or tool holders, depending on the desired orientation. For example, before the first machining step, the cutting elements may be mounted in a turning tool body, which is designed so that the cutting elements have a first orientation relative to the workpiece when the turning tool is mounted on a CNC lathe. To reposition the cutting elements before the second machining step, the cutting elements may be mounted in a different tool body, which is designed so that the cutting elements have a second orientation relative to the workpiece when the turning tool is mounted on a CNC lathe.

[0045] The step of rearranging the cutting element in a second orientation may also include changing the direction of engagement of the cutting element with respect to the surface of the workpiece by tilting the tool axis, for example, by the rotational motion of the tool spindle to which the turning tool is attached, or by controlling the angle of the tool turret to which the turning tool is attached. Alternatively, the cutting element may be tilted relative to the tool axis. For example, if a tiltable or otherwise adjustable turning tool or tool holder is used, the positioning and rearrangement of the cutting element may be achieved by such means. For example, a tiltable tool holder, or a tool in which the portion containing the cutting element is tiltable, may be used. Such adjustment may be achieved by manual means or controlled by some kind of actuator, such as a remotely controlled actuator. Rearranging the cutting element by tilting the tool axis or by tilting the cutting element relative to the tool axis preferably involves tilting by an angle corresponding to the difference between a first nominal rake angle and a subsequent nominal rake angle. For example, if several steps of rearranging in a third orientation are carried out by such inclination, the inclination angle for each step is preferably the same or substantially the same, i.e., within + / - 5 degrees. For each step, the nominal rake angle gradually decreases or becomes even more negative.

[0046] According to some embodiments, the turning method is performed after the second machining step, - A step of rearranging a cutting element with respect to a workpiece or another workpiece to be machined in a third orientation determined by a third nominal rake angle that results in a third effective rake angle and a third effective relief angle, wherein the third nominal rake angle is different from each of the first and second nominal rake angles. - In the third machining step, the cutting element is in a third orientation while machining the workpiece or another workpiece. It also includes.

[0047] Therefore, the rearrangement of the cutting element may be repeated multiple times. The second nominal rake angle may be smaller than the first nominal rake angle, and the third nominal rake angle may be smaller than the second nominal rake angle. In other words, the third nominal rake angle may be smaller than both the first and second nominal rake angles. The difference between the first and second nominal rake angles may be the same as the difference between the second and third nominal rake angles. That is, the nominal rake angle may be changed by the same amount each time the cutting element is rearranged. The rearrangement may be repeated more than two times, for example, three, four, or five times, or even more. Each time the cutting element is rearranged, the effective relief angle may be restored to that of the beginning of the machining step. This may further extend the effective life of the cutting element while maintaining the quality of the machined surface.

[0048] According to some embodiments relating to multiple repositioning of cutting elements, in which the step of repositioning the cutting element in a second orientation includes moving the tool axis by a first distance in a first direction from a first tool axis position to a second tool axis position, the step of repositioning the cutting element in a third orientation may include moving the tool axis by a second distance in the first direction from the second tool axis position to a third tool axis position away from the first tool axis position.

[0049] By moving the tool axis away from the first and second tool axis positions, the nominal rake angle is further reduced, and the effective relief angle is increased compared to the effective clearance that existed immediately before the cutting element was repositioned in the third orientation. For example, the effective clearance can be restored to that of immediately after the cutting element was repositioned in the second position. In other words, the third effective relief angle is equal to the second effective relief angle and / or the first effective relief angle. match It is possible.

[0050] The second distance may be the same as the first distance, or it may be smaller than the first distance.

[0051] The change in nominal rake angle caused by the translation of the tool axis depends on the distance along the Y-axis from the center of rotation of the workpiece. For example, the closer to the center, the greater the translation along the Y-axis required to achieve the same change in nominal rake angle as when the tool axis translation occurs further away from the center.

[0052] Therefore, as an example considering this embodiment, if the first machining step is performed using a cutting element located in the XZ plane, the nominal rake angle change is the same for two subsequent rearrangements of the cutting element only if the second distance is smaller than the first distance.

[0053] However, for many applications and workpiece dimensions, this difference may be negligible; that is, it may suffice to move the tool axis the same distance along the Y-axis when repositioning the cutting element. In other words, the second distance may be the same as the first distance. This may also be true, for example, when the first machining operation is performed above the center of the workpiece, the second machining operation is performed at the center, and the third machining operation is performed below the center. In that case, both translations along the Y-axis may be of the same magnitude to achieve the corresponding nominal rake angle change.

[0054] According to a second aspect of the present invention, a system is provided comprising a CNC lathe, a processor, and a turning tool including cutting elements, the system being configured to carry out the method according to the first aspect of the present invention. The processor may be an integral part of the CNC lathe or may be operably coupled to the CNC lathe, and may be configured to execute a computer program that triggers at least some of the steps of the method to be carried out. The system may further include memory for storing such computer programs.

[0055] Accordingly, according to a third aspect, the present invention relates to a computer program having an instruction that causes a system according to a second aspect of the present invention to carry out a method according to a first aspect of the present invention when executed by a system according to a second aspect of the present invention.

[0056] Accordingly, the methods described herein can be embodied by one or more computer programs, which may exist in various forms. For example, they may exist as software programs consisting of program instructions for carrying out some of the steps of the method, and may be embodied on a computer-readable medium. In other words, the rearrangement of cutting elements may be carried out according to instructions determined in the computer program. These instructions may include parameters, for example, the interval for rearranging the cutting elements and the degree of each such rearrangement. Optimal values ​​for these parameters may be determined based on experience in machining similar components, and may be entered by an end user, for example, found in a lookup table. Alternatively, an algorithm may be used to calculate optimal parameters based on user input, for example, the type of insert to be used, the type of component to be manufactured, and information on "normal" wear when manufacturing such components, for example, input relating to the expected tool life when not using the method according to the present invention. Expected tool life may be determined, for example, as machining time or the number of components manufactured before the cutting insert is replaced. Such an algorithm may be based on prior knowledge of wear propagation when manufacturing different components and materials. [Brief explanation of the drawing]

[0057] [Figure 1] This shows a cutting insert with a CBN cutting element. [Figure 2] This shows a cross-sectional view of a cutting element that is not worn during machining. [Figure 3] This shows a worn cutting element under the assumption of stable tribological conditions. [Figure 4] This diagram schematically shows the effect of changing the nominal rake angle of the cutting element. [Figure 5] This is a flowchart showing the steps of the turning method according to the present invention. [Figure 6A-C] A schematic representation of one embodiment of the turning method is shown. [Figure 7] This graph shows the change in the effective rake angle based on a test using another embodiment of the turning method. [Figure 8] This graph, which refers to the same test as Figure 7, shows the progression of flank wear on the cutting element. [Modes for carrying out the invention]

[0058] All figures are schematic and not necessarily to scale, and generally show only the parts necessary to illustrate each embodiment, while other parts are omitted or merely suggested. Unless otherwise indicated, similar reference numerals in different figures refer to the same parts.

[0059] Figure 1 shows a cutting insert 7 to which a CBN cutting element 1 is brazed. The cutting insert is rhomboid in this example and has fastening holes 8 to facilitate the insertion of the insert into the insert pocket of a turning tool (not shown). A magnified view shows a portion of the cutting element, including the top surface 6 which includes a chamfered portion 3 and a flank 4 corresponding to the rake face of the cutting element. A cutting edge 5 is formed between the chamfered portion 3 and the flank 4.

[0060] Figure 2 shows a cross-section of the cutting element 1 during a turning operation in which a metal workpiece 2 is machined, more precisely, a chip 9 is formed and thus the material is removed from the workpiece. The cutting element is positioned in a turning tool mounted on a CNC lathe, with a nominal rake angle γ n_1 and nominal relief angle α n_1 It is oriented relative to the workpiece. The cutting element 1 is in an unworn state, i.e., before crater wear or flank wear begins to occur on the rake face and flank face, respectively. In this state, the effective rake angle γ e and effective escape angle α e These are the nominal rake angles γ, respectively. n_1 and nominal relief angle α n_1 to match As can be seen in the figure, the initial rake angle of this cutting element is negative.

[0061] Figure 3 shows a worn cutting element 1' after assuming stable tribological conditions or states. Under these conditions, even if wear further propagates, the effective rake angle and the effective relief angle do not change significantly. However, as can be seen from the figure, the effective rake angle γ e increases (and is now positive) due to crater wear, and the effective relief angle α e is reduced to 0 due to flank wear. The original unworn cutting element 1 is shown by the dashed line. This stable state can be assumed fairly early, for example, early after 30% of the expected total tool life, and continues for the remainder of the tool life. However, the integrity of the machined surface is affected, at least in part, by an increase in the contact between the relief face and the workpiece.

[0062] Figure 4 schematically shows the effect of changing the nominal rake angle of the cutting element. If a stable tribological state is assumed, or before it is assumed, the nominal rake angle can be changed to restore the effective relief angle. In Figure 4, the original unworn cutting element is shown by the dashed line, the worn cutting element 1' is shown by the dotted line, and the repositioned worn cutting element 1" is shown by the solid line. In this example, the repositioning that brings about the nominal rake angle change Δγ n is being carried out by tilting the cutting element. However, as will be described later, the repositioning of the cutting element can also be achieved by other means.

[0063] Hereinafter, a turning method for a CNC lathe will be described with reference to Figure 5, which is a flowchart showing the steps of the turning method, and Figures 6A to 6C, which are schematic views of one embodiment of the method.

[0064] In step 501, a workpiece 2 that is rotatable in a rotational direction R around its rotational axis is provided.

[0065] In step 502, the turning tool 10 is provided so as to extend along the tool axis L, in this case parallel to the X axis of the lathe. The turning tool 10 comprises a cutting element 11 in the form of a CBN cutting insert. In contrast to the cutting element 1 shown in Figures 1 to 4, the cutting element 11 shown in Figures 6A to 6C does not have a chamfer formed between the cutting edge and the upper surface of the cutting element. The cutting element can be positioned in different orientations relative to the workpiece, each orientation having a nominal rake angle γ with respect to a line perpendicular to the surface of the workpiece at the point of contact between the cutting edge and the workpiece. n It is determined by [the following].

[0066] In step 503, the cutting element has a first nominal rake angle γ (which is 0 in this example). n_1 and nominal relief angle α n_1 It is positioned relative to the workpiece in the first orientation shown in Figure 6A, as determined by [the specified method]. If the cutting element 11 shown in Figure 6A is a non-worn cutting element, the nominal rake angle and nominal relief angle are initially the effective rake angle and effective relief angle, respectively. match Figures 6B and 6C illustrate subsequent machining steps in which wear may occur on the rake face and flank face, causing the effective angle to differ from the nominal angle. However, for improved visibility and ease of understanding, wear and effective angles are not shown in Figures 6A–6C.

[0067] In step 504, the workpiece is machined with the cutting elements in a first orientation.

[0068] In step 505, the cutting element is repositioned relative to the workpiece or to another workpiece being machined, in a different orientation as shown in Figure 6B. Thus, the cutting element 11 is positioned with a different nominal rake angle γ n_2 and different nominal relief angles α n_2 It is positioned as follows. In this example, the new nominal rake angle γ n_2 It is negative, that is, the previous nominal rake angle γ n_1It is smaller than . The rearrangement of the cutting element 11 is achieved by the translational movement of the turning tool 10 relative to the workpiece 2. This movement has a component in the Y-axis direction, i.e., thereby the tool axis L is displaced in the Y-axis direction by a distance ΔY1. As a result, the nominal rake angle decreases and the nominal relief angle increases (i.e., γ n_2 <γ n_1 , α n_2 >α n_1 ).

[0069] In step 506, the workpiece or another workpiece is machined with the cutting elements in the repositioned orientation.

[0070] As indicated by arrow 507 in Figure 5, the steps of repositioning the cutting element in a different orientation and machining the workpiece (or another workpiece) with the repositioned cutting element may be repeated several times.

[0071] Therefore, in Figure 6C, the cutting element 11 is rearranged again by translating the tool axis L in a direction having a component in the Y direction such that the tool axis L is displaced in the Y direction by a distance ΔY2. Thus, the cutting element 11 is rearranged, here with the previous nominal rake angle γ n_2 Nominal skewer angle γ is smaller than or even more negative than n_3 And the previous nominal relief angle α n_2 A larger nominal relief angle α n_3 They are arranged as follows.

[0072] Figure 7 shows how the effective rake angle of a cutting element can change during machining and how the effective rake angle is affected by multiple rearrangements of the cutting element. The graph shows (different nominal rake angles γ) n_1 gamma n_2 gamma n_3 and γ n_4The results of a test in which four differently designed tool holders (providing) were used to reposition the cutting element in different orientations relative to the workpiece are shown. The cutting element used in this test was a CBN cutting element with a chamfered portion (i.e., similar to the cutting element shown in Figure 1). The cutting element was first subjected to a first nominal rake angle γ n_1 (Therefore, the initial effective rake angle γ e The element was positioned relative to the workpiece such that the rake angle was -36 degrees and the relief angle (not shown in the graph) was 6 degrees. After 15 minutes of machining, the cutting element was repositioned so that the nominal (and effective) rake angle was reduced by 6 degrees. Such repositioning was performed again after 30 minutes of machining, and then again after 45 minutes of machining. Each of these repositionings, shown by the dashed line in Figure 7, resulted in an immediate reduction of 6 degrees in the effective rake angle. As seen in the figure, the first repositioning was performed before the stabilization condition was reached, and the second and third repositionings were performed after such a stabilization condition was reached. In this example, the stabilization condition, where the effective rake angle was approximately 15 degrees, was reassured fairly quickly after each repositioning performed during the 30-minute and 45-minute machining periods.

[0073] The vertical axis represents the average width of flank wear, VB. B The graph in Figure 8 shows the propagation of flank wear 81 (indicated by dots) of the cutting element in the test described above. The reference flank wear 82 (indicated by triangles) of the corresponding cutting element that was not repositioned is also shown in the graph. As seen in Figure 8, when using the method according to the present invention, the average width of the flank wear VB B The thickness approaches 200 μm after 60 minutes of machining, but this level of flank wear is already achieved after 36 minutes of machining if this method is not used.

Claims

1. A turning method for a CNC lathe, - A step of providing a workpiece (2) that can rotate in the rotational direction (R) around the axis of rotation, - A step of providing a turning tool (10) extending along a tool axis (L), wherein the turning tool comprises cutting elements (1, 11) including a rake face (3), a flank face (4), and a cutting edge (5) formed at the boundary between the rake face (3) and the flank face (4), wherein the cutting elements (1, 11) can be positioned in different orientations with respect to the workpiece (2), and each orientation is such that the nominal rake angle (γ) is relative to the surface of the workpiece (2). ｎ The effective rake angle (γ) of the cutting element (1, 11) at the contact point between the cutting edge (5) and the workpiece (2) is determined by the wear of the cutting element (1, 11). ｅ ) and effective relief angle (α ｅ ) a step of providing, - First effective rake angle (γ ｅ＿１ ) and the first effective relief angle (α ｅ＿１ The first nominal rake angle (γ) that results in ｎ＿１ The steps include positioning the cutting elements (1, 11) relative to the workpiece (2) in a first orientation determined by ), - In the first machining step, the workpiece (2) is machined with the cutting elements (1, 11) in the first orientation, After the first machining step, - the second effective rake angle (γ ｅ＿２ ), and the second effective relief angle (α ｅ＿２ ), in a second orientation determined by a second nominal rake angle (γ ｎ＿２ ), repositioning the cutting element (1, 11) relative to the workpiece (2) or relative to another workpiece to be machined, the second nominal rake angle (γ ｎ＿２ ) being different from the first nominal rake angle (γ ｎ＿１ ), the step of repositioning, - In the second machining step, the workpiece (2) or the other workpiece is machined with the cutting elements (1, 11) in the second orientation. A turning method, including

2. The turning method according to claim 1, wherein the second nominal rake angle is smaller than the first nominal rake angle.

3. The turning method according to claim 1 or 2, wherein the second effective relief angle matches the first effective relief angle.

4. The turning method according to any one of claims 1 to 3, wherein the second nominal rake angle differs from the first nominal rake angle by only 2 to 10 degrees.

5. The turning method according to any one of claims 1 to 4, wherein the step of rearranging the cutting element is performed when the cutting element is not engaged with the workpiece.

6. The turning method according to any one of claims 1 to 5, wherein the duration of each machining step is selected based on a predetermined time period during which the cutting element was being cut.

7. The turning method according to any one of claims 1 to 6, wherein the step of rearranging the cutting element in a second orientation includes moving the tool axis relative to the workpiece in a plane perpendicular to the axis of rotation from a first tool axis position to a second tool axis position, wherein the tool axis at the second tool axis position is parallel to but not coincides with the tool axis at the first tool axis position.

8. The turning method according to claim 7, wherein the tool axis is moved by a first distance in a first direction from the first tool axis position to the second tool axis position.

9. After the second machining step, - A step of repositioning the cutting element with respect to the workpiece or another workpiece to be machined in a third orientation determined by a third nominal rake angle that results in a third effective rake angle and a third effective relief angle, wherein the third nominal rake angle is different from each of the first nominal rake angle and the second nominal rake angle, - A third machining step in which the workpiece or the other workpiece is machined with the cutting element in the third orientation. A turning method according to any one of claims 1 to 8, further comprising:

10. The turning method according to claim 9, referencing claim 8, wherein the step of rearranging the cutting element in the third orientation includes moving the tool axis by a second distance in the first direction from the second tool axis position to the third tool axis position, away from the first tool axis position.

11. The turning method according to claim 10, wherein the second distance is the same as or less than the first distance.

12. The turning method according to any one of claims 1 to 11, wherein the cutting element includes cubic boron nitride or polycrystalline cubic boron nitride.

13. The turning method according to any one of claims 1 to 12, wherein the workpiece is made of hardened steel or a heat-resistant superalloy having a hardness of 40 HRC or more.

14. - CNC lathe and, - Processor, - Turning tools including cutting elements and A system comprising the above, wherein the system is configured to carry out the method described in any one of claims 1 to 13.

15. A computer program having, when executed by the system described in claim 14, an instruction causing the system to perform the method described in any one of claims 1 to 13.

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