How to generate control command data for controlling a CNC lathe

Abstract

1. A method for generating control instruction data for controlling a CNC lathe to perform a turning operation with a turning tool (7), the method comprising: generating control instruction data to command the turning tool (7) to enter the cut at a point on the unmachined inner surface (3) that is furthest from an end position (11); and generating control instruction data to command the turning tool (7) to move along the inner surface (3) toward the end position (11) until the turning tool (7) reaches the end position (11), or the cutting depth (8) is equal to or greater than either the maximum allowable cutting depth or the recommended cutting depth (5), thereby commanding the turning tool (7) to move away from the inner surface (3), or until the turning tool (7) reaches a predetermined position, thereby commanding the turning tool (7) to move away from the inner surface (3).

Description

[Technical Field]

[0001] The present invention is in the field of metal cutting, and more particularly in the field of generating control command data for controlling a CNC lathe to perform turning operations with a turning tool. [Background technology]

[0002] The present invention relates to a method for generating control instruction data for controlling a CNC lathe. Turning is a form of metal cutting commonly performed using a computer numerically controlled (CNC) lathe. A metal blank is clamped by a clamping means, such as jaws, and the metal blank is rotated by a spindle. Typically, a CNC lathe includes one or more machine interfaces to which a turning tool can be removably fastened. The turning tool generally includes a turning insert, typically made of a wear-resistant material such as cemented carbide. During the actual cutting, the turning tool is moved relative to the metal workpiece. This relative movement is called a feed. The movement of the turning tool can be in a direction parallel to the axis of rotation of the metal blank, which is commonly called a longitudinal feed or axial feed. Additionally, the movement of the turning tool can be perpendicular to the axis of rotation of the metal blank, which is commonly called a radial feed or facing. Other movement angles, or feed directions, are also possible, and this is commonly known as copy or copy turning. The sequence from entering the cut to exiting the cut is known as a pass. The sum of the paths made by a particular turning tool to remove a volume of material from a metal blank can be called a tool path. This tool path corresponds to instructions or commands. Typically, the volume of material can be removed in many ways. For example, the commands can differ with respect to factors such as feed direction, depth of cut, feed, cutting speed, etc. Although the volume of material can be removed in many ways, not all ways are equal with respect to factors such as machining time, tool life, chip breakage, etc. Therefore, there is a need for guidance in how to intelligently select the command data.

[0003] A method for generating control command data for controlling a CNC lathe to perform a turning operation with a turning tool is described in U.S. Patent Application Publication No. 2016 / 0089760 A1. In FIG. 4, it is explained that the cutting depth should be set to be a value greater than the nose radius of the turning insert.

[0004] However, the inventors have discovered a further need to generate instructional data to improve metal removal results. Summary of the Invention

[0005] The primary objective of the present invention is to provide an improved method for generating control command data, and one particular objective is to improve the manner in which depth of cut is selected to improve the machining of metal blanks.

[0006] The object is to provide a method for generating control instruction data for controlling a CNC lathe to perform a turning operation with a turning tool, the method comprising the steps of: selecting a representation of a metal blank; selecting a representation of a turning tool; selecting a volume of material to be removed from the metal blank by the turning tool, said volume being bounded by an inner surface and an outer surface, the metal blank being bounded by a circumferential surface, the circumferential surface comprising an outer surface; selecting an end position; selecting a recommended cutting depth for the turning tool; selecting a recommended allowable cutting depth for the turning tool; and generating the control instruction data based on the above. and (c) generating control instruction data for commanding the turning tool to move along the inner surface toward the end position until the turning tool reaches the end position, or until the cutting depth is equal to or greater than either the maximum allowable cutting depth or the recommended cutting depth, thereby commanding the turning tool to move away from the inner surface, or until the turning tool reaches a predetermined position, thereby commanding the turning tool to move away from the inner surface.

[0007] By such a method, the workpiece, and in particular the inner surface, can be machined by a turning operation in a shorter time. For example, by not commanding the turning tool to move away from the inner surface until the cutting depth reaches a certain value, the machining time can be reduced compared to when such machining is performed by several machining steps. By such a method, control command data can be generated for various metal blanks to machine various workpieces in an efficient manner.

[0008] The method generates control instruction data, such as NC code (Numerical Control Code), for controlling a CNC lathe to perform a turning operation on a metal workpiece with a turning tool. In other words, the method generates a turning tool path for the CNC lathe. In this context, a CNC lathe is a CNC machine tool suitable for performing a turning operation with a turning tool.

[0009] The CNC lathe includes a machine interface to which a turning tool is connected or connectable.

[0010] The method may comprise a step of importing an electronic CAD (Computer Aided Design) model, such as a STEP-file or an IGS-file, of the desired shape of the machined workpiece, i.e. the blank after the turning operation. In other words, the method may comprise a method for importing a representation of the machined workpiece.

[0011] A representation of the metal blank is selected, which may be preferably imported in the form of a CAD model, such as a STEP-file (for example as defined in ISO 10303-21) or an IGS-file. Preferably, said representation can be obtained by a step of shape measurement of the physical metal blank, preferably by means of a Coordinate Measuring Machine (CMM). The metal blank is defined by a periphery.

[0012] A representation of a turning tool is selected, preferably the turning tool is selected from an electronic tool library, preferably the electronic tool library is a representation of a turning tool from a tool magazine connected to or to part of the CNC lathe.

[0013] The turning tool may be selected manually or automatically.

[0014] Preferably, the turning tool is selected taking into account geometric and other limitations such as the geometry of the turning tool, the geometry of the internal surface, the geometry of the machined workpiece, the surface quality requirements of the machined workpiece, the orientation of the relative turning tool on the metal blank, the orientation of the machine interface, the geometry of the means for clamping the metal blank to the spindle of the CNC lathe, the material of the metal blank, etc.

[0015] The turning tool is selected to be suitable for machining along the inner surface in a direction from a start position defined below to an end position defined below.

[0016] Preferably, the turning tool comprises a tool body and a turning insert mounted in an insert seat of the tool body, the tool body being mounted in or connected to a CNC lathe.

[0017] Preferably, the turning insert comprises a first cutting edge, a second cutting edge, and a convex nose cutting edge connecting the first cutting edge and the second cutting edge. Preferably, the nose angle formed between the first cutting edge and the second cutting edge is 85° or less in plan view. The nose cutting edge may have an arc shape or a shape that deviates slightly from a perfect arc. Preferably, the nose cutting edge has a radius of curvature of 0.2 to 2.0 mm. Preferably, the first cutting edge and the second cutting edge are straight in plan view. Alternatively, the first cutting edge and the second cutting edge may be slightly convex or concave, with a radius of curvature that is more than two times, preferably more than ten times, that of the convex nose cutting edge.

[0018] The inner surface is formed solely, or at least to the greatest extent, or at least partially, by the nose cutting edge. The inner surface is rotationally symmetric about the axis of rotation.

[0019] Preferably, the first cutting edge is positioned or oriented to be active at a cutting angle 17 of 10 to 45°, preferably 20 to 40°. The cutting angle is the angle between the feed direction and the active cutting edge, in this case the first cutting edge.

[0020] The entering angle can vary during one or more passes as the volume of material is removed, but preferably the turning tool should be positioned so that the entering angle is within the above interval when machining the longest face.

[0021] The volume of material to be removed from the metal blank by the turning tool is selected.

[0022] It is not necessary that the volume be selected after the turning tool is selected, in other words, the method may include selecting the turning tool before selecting the volume, or the method may include selecting the volume before selecting the turning tool.

[0023] The volume is defined by an inner surface (preferably, the machined piece includes the inner surface) and an outer surface (the periphery of the metal blank comprises the outer surface), the distance from the machined piece to the outer surface being greater than the distance from the machined piece to the inner surface.

[0024] The volume is selected such that the volume can be removed using the selected turning tool. Alternatively, specifically, the turning tool is selected such that the volume can be removed using the selected turning tool.

[0025] The turning operation is for removing at least a portion of the volume.

[0026] An end location is selected, which is defined as the point or area along the inner surface where the turning tool will be located when the volume is removed.

[0027] Preferably, the end position is selected such that it is at the end of the inner surface. Preferably, the inner surface extends along a line between two points when viewed in cross section, for example as in Figure 3. Preferably, the other of the two points is selected as the start position.

[0028] If the longest partial surface of the inner surface is cylindrical, the end position is preferably selected as one of the two points located closest to the axis of rotation.

[0029] If the longest partial surface of the inner surface is flat, ie perpendicular to the axis of rotation, then the end position is preferably selected as one of the two points located furthest from the axis of rotation.

[0030] A maximum depth of cut for the turning tool, i.e., a maximum allowable depth of cut for the turning tool, i.e., an upper threshold or upper threshold function for the turning tool, is preferably selected. The maximum depth of cut is an upper threshold or upper threshold function for the turning tool depending on the feed direction of the turning tool and takes into account the shape of the inner surface and the orientation of the turning tool. The maximum depth of cut can be understood as the distance away from and perpendicular to the inner surface.

[0031] The method includes selecting a recommended depth of cut for the turning tool, which may be equal to, or preferably less than, the maximum depth of cut for the turning tool.

[0032] Preferably, the maximum cutting depth or upper threshold function may be selected to correspond to a point along the first cutting edge or along the second cutting edge.

[0033] The maximum depth of cut may be selected to a certain value for longitudinal turning in one direction of movement (feed direction) and a different value for longitudinal turning in the opposite direction. For one or more feed directions, the value may be zero. The maximum depth of cut can therefore be understood as an upper threshold function that depends on the feed direction.

[0034] The recommended cutting depth of a turning tool can be understood in a corresponding way as the maximum allowable cutting depth of the turning tool.

[0035] When referring to the position of the turning tool, this should be understood as the position of the surface that produces the point or area of the turning tool. In other words, the position of the turning tool is the position of the nose cutting edge.

[0036] The turning tool is commanded to perform a turning pass by entering the cut at a start location, which is defined as the point on the unmachined inner surface that is furthest away from the end location. The turning tool is commanded to move along the inner surface toward the end location until one of the following criteria is met:

[0037] The turning tool reaches an end position, i.e. the inner surface is machined in one single turning pass, and the depth of cut for this single turning pass is always less than or equal to the maximum allowable depth of cut of the turning tool.

[0038] Alternatively, the turning tool reaches a point while it is moving along the inner surface where the depth of cut is equal to or greater than the maximum depth of cut for the turning tool. The maximum allowable depth of cut for the turning tool is an upper threshold beyond which the turning tool is prohibited from operating, thereby causing the movement of the turning tool along the inner surface to be halted. Thus, "the depth of cut is" should be understood in this context as "the depth of cut is reached."

[0039] After movement of the turning tool along the inner surface is stopped, the turning tool is commanded to move away from the inner surface, preferably in a predetermined direction, thereby exiting the cut. The predetermined direction is parallel to the longest cylindrical, flat, or conical subsurface of the inner surface, if the inner surface includes such a surface. Otherwise, the turning tool is commanded to move away from the inner surface and in a direction perpendicular to the inner surface.

[0040] Alternatively, the turning tool may reach a point while the turning tool is moving along the inner surface where the depth of cut is equal to or greater than the recommended depth of cut for the turning tool, and the movement of the turning tool may be stopped and the turning tool may be commanded to move away from the inner surface.

[0041] Alternatively, the turning tool is commanded to stop when the turning tool reaches a predetermined position, preferably the depth of cut is equal to or greater than the recommended depth of cut of the turning tool when the turning tool reaches said predetermined position.

[0042] Such a predetermined position may be defined under the condition that the inner surface includes one or more cylindrical, flat, or conical subsurfaces. An imaginary line, or baseline, may be drawn intersecting the longest of the surfaces. The predetermined position is defined as the intersection between the inner surface and a line parallel to the recommended cutting depth of the turning tools and spaced from the baseline by the recommended cutting depth, the baseline intersecting the longest conical, flat, or conical inner surface subsurface. After reaching the predetermined position, the turning tool is commanded to move away from the predetermined position and away from the inner surface.

[0043] Preferably, the method includes positioning the turning tool such that the second cutting edge forms a leading clearance angle during at least a portion of the turning pass that is preferably greater than 90°, preferably greater than 100°. The second cutting edge is a trailing edge. In other words, the angle between the feed direction, i.e., the direction of movement of the turning insert, and the second cutting edge is preferably less than 90°, preferably less than 80°.

[0044] The movement away from the inner surface is preferably in a direction perpendicular to the inner surface or within + / - 30° of perpendicular to the inner surface.

[0045] According to one embodiment, the method includes, before step (b), a further step of (a) instructing the turning tool to remove a portion of the volume of material through one or more turning passes until the cutting depth at the point on the inner surface that is furthest from the end position is less than or equal to the maximum allowable cutting depth of the turning tool.

[0046] The method includes the step of commanding the turning tool to remove a portion of the volume of material through one or more preferably parallel turning passes until the depth of cut at the start location, i.e., the point on the inner surface furthest from the end location, is less than or equal to the maximum depth of cut.

[0047] The step is a rough cutting step, which involves machining the peripheral surface of the metal blank.

[0048] Preferably, the turning tool is commanded to remove a portion of the volume of material until the depth of cut at the point on the inner surface furthest from the end location is equal to or less than the recommended depth of cut for the turning tool.

[0049] Preferably, the portion of the volume of material is removed by one or more turning passes that are straight and parallel to the longest partial face of the inner surface.

[0050] According to one embodiment, the method includes the further step of instructing the turning tool to perform two or more turning passes during step (a) and the further step of selecting a maximum depth of cut for a first turning pass to be less than the maximum depth of cut for all successive turning passes during step (a).

[0051] In such a way, tool life can be improved. Because the outer surface is part of the periphery of the blank, machining of this surface can result in more tool wear because the outer shell of the blank can be harder and / or have a less uniform surface.

[0052] Preferably, the turning passes are successively closer to the inner surface, in other words the volume of material removed during a subsequent turning pass is between the inner surface and the volume of material removed during the previous turning pass.

[0053] According to one embodiment, the method comprises the further step of repeating step (c) until the turning tool reaches an end position.

[0054] By such a method, the machining can be performed in a shorter time.

[0055] In other words, the method includes performing one or more additional turning passes, i.e., the inner surface is formed by two or more turning passes.

[0056] According to one embodiment, the method includes the further step of selecting a turning tool during steps (a) and (c) such that the minimum cutting depth for the turning tool is less than the cutting depth.

[0057] By such methods, machining can be performed in a more trouble-free manner, for example, chip breakage and / or chip control can be improved because the depth of cut is not less than the recommended minimum depth of cut of the turning tool.

[0058] According to one embodiment, the method comprises the further step of selecting the material inner surface such that the inner surface comprises at least one part surface that is cylindrical, conical or planar.

[0059] The inner surface comprises at least one partial surface or part of a surface that is either cylindrical, i.e., all points at a constant distance from the axis of rotation of the metal blank, conical, i.e., all points at a linearly increasing or decreasing distance from the axis of rotation of the metal blank, or planar, i.e., lying in a plane.

[0060] According to one embodiment, the method comprises the further step of moving the turning tool during step (c) in a direction that is parallel or approximately parallel to the longest of the cylindrical, conical or flat part surfaces.

[0061] Such a method may reduce the number of passes and therefore the machining time.

[0062] The turning tool is moved during at least a portion of step (c) in a direction parallel or approximately parallel to the longest part surface. Preferably, the direction is parallel to the baseline. Preferably, the direction is away from the inner surface. Preferably, the direction is parallel to the axis of rotation.

[0063] According to one embodiment, the method includes the further step of instructing the turning tool during step (a) to remove material through a series of parallel turning passes.

[0064] Preferably, said parallel turning passes or passes are parallel to the baseline. Preferably, the turning tool moves in the same direction during at least most of the turning passes, preferably all of the turning passes.

[0065] Preferably, the movement of the turning tool is along each line, starting at the outermost line and moving inwards.

[0066] Preferably, the movement of the turning tool is in a direction away from the inner surface and towards the outer surface during at least most, and preferably all, of the turning passes.

[0067] According to one embodiment, the method includes the further step of removing a volume of material by the turning tool in a series of turning passes, wherein a maximum depth of cut for the turning passes relative to the baseline is greater than a maximum depth of cut for the first turning pass.

[0068] The first turning pass is the turning pass associated with the outermost line.

[0069] According to one embodiment, the method includes the further steps of selecting a chip thickness value for the turning tool and selecting a feed rate such that the feed rate is equal to the chip thickness value divided by a sine function of the lead angle, the lead angle being defined as the angle between the direction of feed and the main cutting edge of the turning tool.

[0070] In such a way, tool life is improved.

[0071] Said chip thickness value can be selected manually, preferably taking into account the material of the metal blank, or can preferably be imported from a database.

[0072] The feed rates given above are recommended feed rates for turning tools.

[0073] In other words, the method includes the step of commanding the turning tool to move at a speed related to the rotation of the metal blank and related to the direction of feed according to the above calculation.

[0074] According to one embodiment, the method includes the further step of reducing the feed rate upon exiting the cut.

[0075] In such a way, tool life is improved.

[0076] Thus, the feed rate is reduced for at least one turning pass, preferably two or more turning passes. Typically, the feed rate is measured in millimeters per revolution. Preferably, the feed rate reduction begins between 1 and 10 mm, more preferably 2-8 mm, before exiting the cut. Preferably, the feed rate is reduced by 10-70%, more preferably 20-50%, compared to the feed rate before the selected feed rate, i.e., the feed rate before reduction.

[0077] According to one embodiment, the method includes the further step of commanding the turning tool to enter the cut along an arc during step (b).

[0078] By such methods, tool life can be improved.

[0079] Preferably, at least during step (b), the turning tool is commanded to move or begin the cut along an arc, i.e., when entering the cut. Preferably, at least during step (b), said arc is tangent to the inner surface, preferably tangent to the direction in which the turning tool moves away from the inner surface.

[0080] Preferably, said arc is a circular arc, preferably said circular arc has its radius of curvature between 1 and 10 mm, even more preferably between 2 and 5 mm.

[0081] According to one embodiment, the method includes the further step of selecting the inner surface such that the inner surface comprises a 90° corner.

[0082] A nose angle of 85° or less offers the advantage that a 90° corner, i.e., two walls at right angles to each other, can be machined with one of the turning insert's noses without changing the turning insert's orientation. The two walls have one flat surface perpendicular to the axis of rotation and one surface at a fixed distance from the axis of rotation.

[0083] Preferably, the method includes the step of commanding the turning tool to move away from said flat surface.

[0084] A 90° corner in this context is preferably an exterior corner formed on or in the exterior or outer surface of a metal workpiece, such that a cylindrical wall or surface is faced away from the axis of rotation, preferably along or parallel to the baseline. This is in contrast to any corner that may be formed on or in the interior surface of a bore concentric with the axis of rotation. A circular or curved segment lies in a cross section in a plane containing the axis of rotation in the shape of an arc in the shape of a quarter of a circle or a nearly circular shape having the same radius of curvature as the turning insert's nose cutting edge. Alternatively, the circular or curved segment has a larger radius of curvature than the turning insert's nose cutting edge.

[0085] Preferably, the method includes the step of commanding the turning tool to move away from said 90° corner.

[0086] According to one embodiment, a turning tool comprises a tool body and a turning insert mounted in an insert seat of the tool body, the turning insert comprising a first cutting edge, a second cutting edge, and a convex nose cutting edge connecting the first cutting edge and the second cutting edge, and a nose angle formed between the first cutting edge and the second cutting edge is 85° or less in a plan view.

[0087] The first cutting blade is the active cutting blade. The second cutting blade is the inactive cutting blade. The second cutting blade is inactive for all turning passes.

[0088] According to one embodiment, the nose cutting edge has a radius of curvature of 0.2 to 2.0 mm, and the first cutting edge and the second cutting edge are straight in plan view.

[0089] According to one embodiment, the method includes the further step of generating control command data for commanding the turning tool in all turning passes to move in a radial direction having no longitudinal component or in the longitudinal direction.

[0090] In other words, all passes have no longitudinal component, i.e., are solely or purely radial, i.e., towards and perpendicular to the axis of rotation, i.e., facing cuts, or are longitudinal, i.e., have a longitudinal component, i.e., are in the same direction along the axis of rotation. The longitudinal direction should therefore be understood as copy cuts, which include both radial and longitudinal components, or copy cuts, which have only a longitudinal component, i.e., parallel to the axis of rotation. For clarity, all turning passes are radial, or in the same longitudinal direction, or a combination thereof.

[0091] According to one embodiment, there is provided a computer program comprising instruction data according to any of the methods described above.

[0092] According to one embodiment, a computer program is provided for generating instruction data by a method according to any of the methods described above.

[0093] The invention will now be explained in more detail by description of different embodiments of the invention and with reference to the accompanying drawings. [Brief explanation of the drawings]

[0094] [Figure 1] FIG. 1 is a perspective view showing a metal blank. [Figure 2] FIG. [Figure 3] FIG. 3 is a side view of the machined product of FIG. 2 and a turning tool. [Figure 4] 3A-3C are cross-sectional views showing several passes through which the machined workpiece of FIG. 2 is formed from the metal blank of FIG. 1. [Figure 5] 3A-3C are cross-sectional views showing several passes through which the machined piece of FIG. 2 is formed from a metal blank. [Figure 6] 1 is a cross-sectional view showing several passes through which a machined piece is formed from a metal blank. [Figure 7] 1 is a cross-sectional view showing several passes through which a machined piece is formed from a metal blank. [Figure 8] 1 is a cross-sectional view showing several passes through which a machined piece is formed from a metal blank. [Figure 9] FIG. 1 is a side view showing a machined workpiece and a turning tool. [Figure 10] FIG. 1 is a side view showing a machined workpiece and a turning tool. [Figure 11] FIG. 2 is a cross-sectional view showing the inner and outer surfaces. [Figure 12] FIG. 2 is a cross-sectional view showing the inner and outer surfaces. DETAILED DESCRIPTION OF THE INVENTION

[0095] Referring to FIG. 1 , a perspective view of a metal blank 2 is shown, bounded by a peripheral surface 80 and rotatable about a rotation axis A1. The metal blank 2 can be represented by a 3D model. The metal blank can be made of cast or forged material. The metal blank can also be a machined workpiece. The metal blank can have a generally cylindrical shape as in FIG. 1 or any other shape. For example, the metal blank can have a hole, such as a hole concentric with the axis of rotation. The peripheral surface 80 comprises an outer surface 4, which is a boundary or limit for the volume of material to be removed from the metal blank, thereby forming or creating the machined workpiece.

[0096] Referring now to FIG. 2, a perspective view of a machined workpiece 81 or machined component is shown. The machined workpiece 81 can be represented by a 3D model. The machined workpiece 81 is rotatable about and symmetrical with respect to the rotation axis A1. The rotation axis A1 is the same for both the metal blank 2 and the machined workpiece 81. The machined workpiece 81 is produced from the metal blank 2 by a turning process, i.e., a metal cutting process, and the volume of the machined workpiece 81 is smaller than the volume of the metal blank 2. The machined workpiece 81 has an inner surface 3, which is a boundary or limit for the volume of material removed from the metal blank 2. The inner surface 3 has at least part surfaces 21 to 26, which can be cylindrical with respect to part surfaces 21, 23, and 25, i.e., all points at a constant distance from the rotation axis A1 of the machined workpiece 81. The part surfaces can be conical, like part surface 26, i.e., all points at a linearly increasing or decreasing distance from the rotation axis of the metal blank. Partial surfaces such as partial surfaces 22 and 24 may lie in a plane perpendicular to the axis of rotation A1. The inner surface may comprise additional portions such as curved partial surfaces.

[0097] For each of the partial surfaces 21 to 26, a respective length 31 to 36 can be defined. The lengths 31 to 36 are measured along the axis of rotation A1 if the surface is cylindrical (see 31, 33 and 35), perpendicular to the axis of rotation A1 if the surface is flat (see 32 and 34), or along the enveloping surface and towards the axis of rotation if the surface is conical (see 36). As can be seen, partial surface 33 is the longest.

[0098] Reference is now made to FIG. 3, which illustrates a side view of the machined workpiece 8 of FIG. 2, along with a turning tool 7 connected to a CNC lathe (not shown) via a machine interface 85. The turning tool 7 includes a tool body 81 and a turning insert 82 mounted in an insert seat 81 of the tool body. The turning insert 82 includes a major cutting edge 19, a minor cutting edge 83, and a convex nose cutting edge 84 connecting the first and second cutting edges 19, 83. The nose cutting edge 84 generates the inner surface 3 of the machined workpiece 81. The turning tool 7 includes a front end and a rear end, with a longitudinal axis A2, or central axis, extending from the front end to the rear end. The rear end is connected to the machine interface. The front end includes the insert seat. The longitudinal axis A2 is perpendicular to the rotation axis A1 of the machined workpiece 81.

[0099] The turning insert 82 is mounted in the insert seat so that a bisector extending equidistantly from the first cutting edge and the second cutting edge forms an angle of 35 to 55° with respect to the longitudinal axis A2 of the tool body.

[0100] In FIG. 3, the turning tool 7 is moved along the inner surface 3 generally towards the right hand side, starting from a start position 10 and moving towards an end position 11 .

[0101] The first cutting blade 19 is the active cutting blade. The second cutting blade 83 is the inactive cutting blade.

[0102] The distance from the longitudinal axis A2 of the turning tool 7 to the first cutting edge 19 is less than the distance from the longitudinal axis A2 of the turning tool 7 to the second cutting edge 83. Said distances are measured to corresponding points on the first and second cutting edges 19, 83, respectively, i.e., points that are equidistant from the nose cutting edge 84.

[0103] A recommended depth of cut 5 for a turning tool 7 is shown as a dotted line 5 when machining the inner surface 3 from a start position 10 to an end position 11. The recommended depth of cut can be understood as a distance 6 away from and perpendicular to the inner surface 3. The distance 6 may or may not be constant in all directions, e.g., a different distance in the horizontal direction compared to the vertical direction.

[0104] Correspondingly, the minimum cutting depth 9 for the turning tool 7 can be shown as a dotted line 9, and the minimum cutting depth 9 for the turning tool 7 can be understood as a distance 85 away from the inner surface 3 and perpendicular to the inner surface 3.

[0105] The maximum cutting depth (not shown) for the turning tool 7 can be understood in an analogous manner.

[0106] Reference is now made to FIG. 4, which illustrates the workpiece 81 of FIG. 3 being machined using the turning tool (not shown) of FIG. 3. The turning tool is oriented relative to the axis of rotation A1 as in FIG. 3. The workpiece 81 is machined from the metal blank 2 shown in FIG. 1. A volume of material 1, bounded by an outer surface 4 and an inner surface 3, is removed through several turning passes 52, 51, 50, 53, 54. A baseline 40 is established so that it intersects with the longest face 23. Additional lines 41, 42, 43 within the volume of material 1 are added. The lines 40-43 are parallel and spaced apart a distance equal to the recommended cutting depth 5 of the turning tool 7. The volume of material 1 is divided or segmented into subportions 70, 71, 72, 73, 74, and the lines 40-43 represent the boundaries between adjacent subportions 70-74. Each subsection 70-74 is removed through one of the respective turning passes 50-54 in the following order: 52, 51, 50, 53, 54. The passes 50-53 are all at least partly in the same direction towards the right hand side and at least partly parallel.

[0107] The baseline 40 and an outer line 41 adjacent to the baseline 40, i.e., a line next to the baseline and perpendicular to the longest face 23, are spaced apart by a distance 14, which is greater than the perpendicular distance 15 between the outermost line 42 and the outer face 4.

[0108] The maximum depth of cut 60 for the turning pass 50 relative to the baseline 40 is greater than the maximum depth of cut 64 for the first turning pass 52 .

[0109] When machining the inner surface, i.e., passes 51, 50, 53, 54, a turning tool (not shown) is commanded to enter the cut at a point on the unmachined inner surface 3 that is furthest away from start location 10, i.e., end location 11. The turning tool 7 is commanded to move along the inner surface 3 toward end location 11 in pass 51. The movement in pass 51 is first longitudinal toward the right-hand side and then radially downward in the figure. When the turning tool, or more specifically, the nose cutting blade, reaches a predetermined position in the form of an intersection between line 41 and the inner surface 3, the turning tool is commanded to move away from the inner surface. The turning tool is commanded to move along line 41 toward the right-hand side until it exits the cut.

[0110] After pass 51, pass 50 begins at the predetermined point where the turning tool stopped moving along the inner surface in pass 51. In pass 50, the turning tool is moved along inner surface 3, first downward in FIG. 4, and then toward the right-hand side along baseline 40 until it exits the cut. As the turning tool moves parallel to rotation axis A1, it is moving away from the 90° corner.

[0111] After pass 50, in pass 53 the turning tool moves towards the axis of rotation, then away from the 90° corner and along the inner surface towards the right hand side, then away from the inner surface and along line 43. The final pass 54 is along the inner surface, more specifically along the conical part surface shown at 26 in Figure 2. After the last two passes 53, 54 the machining of inner surface 3 is completed.

[0112] Reference is now made to FIG. 5, which is the same as FIG. 4 except that the turning passes are slightly different because the volume of material is different compared to FIG. 4. In other words, the shape of the metal blank 81 is different compared to FIG. 4, resulting in a different machining sequence or tool path. As in FIG. 4, a first portion of the volume of material 1 is removed by the turning tool through a first turning pass 52, which, as in FIG. 4, is straight and parallel to the longest partial surface 23 of the inner surface 3. As in FIG. 4, said pass 52 follows line 42. The lines 40, 41, 42, and 43 are spaced apart in a manner corresponding to that in FIG. 4, i.e., by a distance equal to the recommended cutting depth 5 of the turning tool 7. The maximum cutting depth 62 during the first turning pass 52 is less than the maximum cutting depth for the subsequent turning pass 53, which is equal to the recommended cutting depth 5 for the turning tool.

[0113] After the first pass 52, in subsequent turning passes 50, the turning tool begins at the starting point 10 and moves along the inner surface 3 until the cutting depth 8 is greater than the recommended cutting depth 5 of the turning tool and until the turning tool reaches a predetermined location in the form of an intersection between the line 40 and the inner surface 3. The turning tool is then commanded to move away from the inner surface 3 towards the right-hand side along the baseline 40 until it exits the cut. The final two passes 53, 54 are performed as in FIG. 4.

[0114] Reference is now made to FIG. 6, which shows a metal blank 2 from which a workpiece 81 is formed by removing a volume 1 of material, followed by the removal of a further volume 90 of material. The first mentioned volume 1 of material is removed by a turning tool (not shown), preferably with its longitudinal axis oriented parallel to the axis of rotation A1 of the workpiece 81. The inner surface 3 of the volume 1 of material comprises two part faces 21, 22, of which the flat part face 21 is the longest. The flat part face 21 lies in a plane perpendicular to the axis of rotation A1, as can be seen in FIG. 6. A baseline 40 is drawn so that it intersects the longest part face 21. Further lines 41, 42, 43, 44, and 45 are drawn within the volume 1 of material parallel to the baseline 40, with adjacent lines spaced apart by a distance equal to the recommended cutting depth 5 of the turning tool. The lines 40-45 divide the volume 1 into subparts 70-75. In other words, the lines 40-45 represent the boundaries between adjacent sub-portions 70-75. The first pass 52 is straight and parallel to the baseline 40, and the maximum depth of cut 62 of the first pass 52 is less than the recommended depth of cut 5 of the turning tool. Similarly, the subsequent pass 51 is straight and parallel to the baseline 40, but has a depth of cut equal to the recommended depth of cut 5 of the turning tool. In the next and final pass 50, the turning tool is commanded to start at the start point 10 and move along the inner surface 3 to the end point 11. During the final pass 50, the depth of cut is less than the recommended depth of cut of the turning tool.

[0115] Reference is now made to FIG. 7, which shows a metal blank 2 from which a workpiece 81 is formed by the removal of a volume 1 of material by a turning tool (not shown). Preferably, the turning tool may be the turning tool shown in FIG. 3, and preferably, the turning tool may be oriented like the turning tool of FIG. 3, i.e., with its longitudinal axis oriented perpendicular to the axis of rotation A1 of the workpiece 81. The inner surface 3 comprises one flat partial surface 22 and one conical partial surface 21. The flat partial surface 22 lies in a plane perpendicular to the axis of rotation A1. The length 31 of the conical partial surface 21 is greater than the length 32 of the flat partial surface 22. A baseline 40 is drawn along the conical partial surface 21. Further lines 41-45 are arranged inside the volume 1 of material parallel to the baseline 40, with adjacent lines spaced apart by a distance equal to the recommended cutting depth 5 of the turning tool. The lines 41-45 represent the boundaries between adjacent subportions of the volume 1 of material. Each subportion is removed by a respective turning pass 50-55. The turning passes 50-55 are at least partially parallel and at least partially in the same direction, more specifically, away from the flat part surface 22. The maximum cutting depth 65 for the first pass 55 is greater than or less than the maximum cutting depth for all subsequent passes 50-54. The lines 41-43 intersect the inner surface at points representing predetermined positions. During passes 51-53, when the turning tool reaches such predetermined positions, the turning tool is commanded to move along the respective line 41-43 away from the inner surface and away from the predetermined positions.

[0116] Attention is now directed to Figure 8, which illustrates a metal blank 2 from which a volume 1 of material is removed by a turning tool (not shown) to form a machined workpiece 81. Figure 8 differs from Figure 7 in that the shape of the metal blank 81 is different and, as a result, the machining sequence or tool path, i.e., the total number of passes, is different.

[0117] A baseline 40 and lines 41-44 are drawn within the volume 1 of material to be removed in a manner corresponding to that for FIG.

[0118] The turning tool is commanded to enter the cut at start position 10 in pass 51 and move along inner surface 3. Between line 43 and line 42, the depth of cut exceeds the recommended depth of cut but is less than the turning tool's maximum allowable depth of cut. When the turning tool reaches the intersection between line 42 and inner surface 3, the turning tool is commanded to move along line 42 away from said intersection, thereby exiting the cut. In the next pass 50, the turning tool is commanded to enter the cut where the turning tool was commanded to move away from the inner surface during the first pass 51, i.e., at the intersection between line 42 and inner surface 3. The turning tool is commanded to move along inner surface 3 toward an end point or termination position 11. During pass 50, the depth of cut never exceeds the turning tool's recommended depth of cut of 5.

[0119] 4-8 , the inner and outer surfaces can have several shapes, depending on, for example, the shape of the metal blank and the shape of the machined workpiece. Therefore, it is preferable to provide a method for generating control instruction data for controlling a CNC lathe to perform a turning operation with a turning tool, the method comprising the steps of: selecting a representation of the metal blank; selecting a representation of the turning tool; selecting a recommended depth of cut for the turning tool; and selecting a volume of material to be removed from the metal blank by the turning tool, the volume being bounded by inner and outer surfaces, the metal blank being bounded by a periphery, the periphery comprising an outer surface; and based on the above, generating control instruction data for a machining strategy as a result of: (I) the recommended depth of cut for the turning is less than or equal to the depth of cut; (II) the recommended depth of cut for the turning tool is greater than the depth of cut; or (III) the recommended depth of cut for the turning tool varying between less than the depth of cut and greater than the depth of cut.

[0120] (II) If the recommended depth of cut of the turning tool exceeds the cutting depth, the method preferably includes the further step of removing a volume of material by making sequential turning passes by moving the turning tool along parallel lines, starting from the outermost line. Preferably, said lines are spaced a distance equal to the maximum allowable depth of cut of the turning tool. Preferably, the method includes the further step of moving the turning tool in the same direction during at least most, preferably all, turning passes. Preferably, the method includes the further step of moving the turning tool in a direction away from the inner surface and towards the outer surface during at least most, preferably all, turning passes.

[0121] (I) If the recommended cutting depth is less than or equal to the cutting depth, the method includes the further steps of selecting a start position and an end position and moving the turning tool along the inner surface from the start position to the end position. Preferably, the method includes the further step of selecting the start position and the end position such that the distance from the rotation axis of the metal blank to the start position is greater than the distance from the rotation axis of the metal blank to the end position.

[0122] Reference is now made to FIG. 9 , which illustrates a side view or cross-section of the machined workpiece 81 and the turning tool 7 of FIG. 3 . The turning tool is connected to a CNC lathe (not shown) via a machine interface 85. The turning tool 7 includes a tool body 81 and a turning insert 82 mounted in an insert seat of the tool body 81. As shown in FIG. 9 , the turning insert 82 is symmetrical or nearly symmetrical about a bisector (not shown) extending between the first and second cutting edges 19, 83 in a plan view of the turning tool 7. The nose cutting edge 84 generates the inner surface 3 of the machined workpiece 81. The turning tool 7 has a leading end and a trailing end, and a longitudinal axis A2, i.e., a central axis, extends from the leading end to the trailing end. During a turning pass, i.e., when removing material from a metal blank, a leading edge angle 17 is defined as the angle between the feed direction 18, i.e., the movement of the turning tool 7, and the main cutting edge 19 of the turning tool 7. The first cutting edge 19 is positioned or oriented so as to be active at a cutting angle 17 of 10 to 45°, preferably 20 to 40°, when machining in a feed direction 18 parallel to a baseline (not shown).

[0123] If the angle between the longitudinal axis A2 of the turning tool 7 and the axis of rotation A1 is constant, changing the feed direction 18 will change the lead angle 17. For example, in Figure 9, when changing the feed direction 18 from parallel to the axis of rotation A1 to an inclined direction relative to the axis of rotation, i.e., to a conical section, the lead angle will increase and therefore the feed rate will decrease.

[0124] Preferably, a chip thickness value is selected for the turning tool 7 and a feed rate is selected such that the feed rate is equal to the chip thickness value divided by a sine function of the cutting angle 17 .

[0125] Preferably, the feed rate is reduced by 20-80%, even more preferably 40-70%, before exiting the cut, preferably over a distance of 1-20 mm, more preferably 3-10 mm. In other words, the turning tool is commanded to move at a slower pace before exiting the cut.

[0126] 10, which shows a machined workpiece 81 in a side view or cross section, for example, along with the turning tool 7 of FIGS. 3 and 9. The turning tool is connected to a CNC lathe (not shown) via a machine interface 85. The turning tool 7 includes a tool body 81 and a turning insert 82 mounted in an insert seat of the tool body 81. The feed direction may be in different directions, as indicated by 18, 18', 18'', and 18'''. Thus, if the orientation of the axis A2 is not changed, the cutting angle may vary depending on the feed direction 18, 18', 18'', and 18'''. The recommended cutting depths 5, 5', 5'', and 5''' for the turning tool 7 may vary depending on 18, 18', 18'', and 18'''. Preferably, the recommended cutting depths 5, 5', 5'', and 5''' for the turning tool 7 are selected to correspond to points 90 and 91 along the first and second cutting edges, respectively. Preferably, the minimum cutting depth for the turning tool and the maximum cutting depth for the turning tool, respectively, are selected in a corresponding manner.

[0127] Preferably, the turning tool 7 is commanded to move along an arc when entering or starting a cut, i.e. when entering a cut, as seen by path 50. Preferably, said arc is tangent to the inner surface 3, and preferably tangent to the direction in which the turning tool moves away from the inner surface 3 (horizontally towards the right hand side). The arc is a circular arc.

[0128] Referring now to Figures 11 and 12, a cross-sectional view of a volume of material bounded by an inner surface 3 and an outer surface 4 is shown. A baseline 40, corresponding to the longest surface of the inner surface 3, intersects the inner surface 3. The inner and outer surfaces 3 and 4 are spaced apart by a distance 95. In both Figures 10 and 11, the volume of material is divided into subportions 70-72, and one or more lines 41 and 42 represent boundaries between adjacent subportions 70-72. The lines 41 or 42 are parallel to and spaced apart from the baseline 40. In Figure 11, the volume of material is divided or split into three subportions 70, 71, and 72. In Figure 12, the volume of material is divided into two subportions 70 and 71. In Figure 11, the distances 60 and 61 equal the recommended cutting depth of the turning tool. In Figure 12, each distance 60, 61 is equal to half the distance 95 between the inner and outer surfaces 3, 4. As always, the recommended depth of cut for a turning tool should be understood as the recommended depth of cut of the turning tool relative to the direction of feed, i.e., the movement of the turning tool.

[0129] 11 and 12, distance 95 is 4.3 mm. The recommended depth of cut for a turning tool is 2.0 mm. The minimum and maximum depth of cut for a turning tool are 0.5 and 2.5 mm, respectively. Thus, during the first pass in FIG. 11, when removing small portion 72, the depth of cut is 0.3 mm, which is less than the minimum depth of cut of the turning tool. Thus, FIG. 11's illustration of separating material volumes and tool paths (passes) can be improved, as a depth of cut less than the recommended depth of cut for the turning tool may provide acceptable results but may not provide optimal results, for example, with respect to chip breakage.

[0130] In Figure 12, the distances 60 and 61 are 2.15 mm, respectively, which is less than the maximum allowable cutting depth of the turning tool and more than the minimum cutting depth of the turning tool. Therefore, Figure 12 is preferable to Figure 11.

[0131] In FIG. 12, the respective cutting depths are as follows: If m mod a_p≧a_p min is true, then a_p actual=a_p If m mod a_p ≥ a_p min is false, and If m / FLOOR(m / a_p)≦a_p max is true, a_p actual=m / FLOOR(m / a_p), If m / FLOOR(m / a_p)≦a_p max is false, Let a_p actual = (m-a_p min) / FLOOR(m / a_p).

[0132] Here, m is the maximum remaining depth perpendicular to the 40-point baseline, i.e., 4.3 mm. a_p is the recommended cutting depth for the turning tool, i.e., 2.0 mm. mod is an operator that finds the remainder after dividing one number by another. Therefore, m mod a_p is 4.3 mod 2.0 = 0.3. Since 0.3 is less than a_p min (the minimum cutting depth for the turning tool), the first segment is false. Therefore, the next step is to calculate m / FLOOR(m / a_p), where FLOOR is a function that takes a real number as input and gives the largest integer less than or equal to that real number as output. Therefore, FLOOR(m / a_p) is equal to floor(4.3 / 2.0), which is equal to FLOOR(2.15), which is equal to 2.0, which means that m / FLOOR(m / a_p) is equal to 3 / 2.0 = 2.15. Since 2.15 is less than or equal to 2.5, the equation m / FLOOR(m / a_p)≦a_p max is true because a_p max is the maximum depth of cut for the turning tool, which is 2.5 mm in this example. Therefore, a_p actual = m / FLOOR(m / a_p), which means the depth of cut (a_p actual) is set to 2.15. In other words, line 41 in FIG. 12, which defines the material removed during the pass along with outer surface 4, is located 2.15 mm below the outer surface in FIG. 12. The same equation is used to calculate the next pass, the only slight difference for the next pass in FIG. 12 is that m is 2.15 mm.

[0133] It is to be understood that the described methods of generating control instruction data and methods of dividing volumes of material are computer-implemented, and therefore, objects, movements, and other entities should be understood as representations, preferably electronic representations, of such entities.

Claims

1. 1. A method for generating control command data for controlling a CNC lathe to perform a turning operation with a turning tool (7), comprising: selecting a representation of a metal blank (2); selecting a representation of a turning tool (7); selecting a volume (1) of material to be removed from the metal blank (2) by the turning tool (7), the volume (1) being defined by an inner surface (3) and an outer surface (4), the metal blank (2) being defined by a periphery (80), the periphery (80) comprising the outer surface (4); - selecting the inner surface (3) so that it comprises at least one cylindrical, conical or flat partial surface (21, 22, 23, 24); selecting an end position (11); selecting a recommended cutting depth (5) for said turning tool (7); selecting a recommended allowable cutting depth for said turning tool (7); generating control command data based on the selection, (b) control instruction data for instructing the turning tool (7) to enter cutting at a point on the inner surface (3) that is not machined and is furthest from the end position (11); and (c) - the cutting depth (8) is equal to or greater than either the maximum allowable cutting depth or the recommended cutting depth (5), whereby the turning tool (7) is commanded to move away from the inner surface (3) and in a direction parallel or nearly parallel to the longest of the cylindrical, conical or flat part surfaces (21, 22, 23, 24), or - the turning tool (7) reaches a predetermined position, whereby the turning tool (7) is commanded to move away from the inner surface (3) and in a direction parallel or approximately parallel to the longest of the cylindrical, conical or flat part surfaces (21, 22, 23, 24), control command data for commanding the turning tool (7) to move along the inner surface (3) towards the end position (11) until generating a Including, The method for generating control command data, wherein the predetermined position is defined as an intersection of the inner surface (3) with straight lines (41, 42, 43, 44, 45), the straight lines (41, 42, 43, 44, 45) being parallel to a baseline (40) and spaced from the baseline (40) by a multiple of the recommended cutting depth (5) of the turning tool (7), the baseline (40) being an intersection of the inner surface (3) with the longest cylindrical, conical or flat part surface (21, 22, 23, 24).

2. Before step (b), (a) instructing the turning tool (7) to remove a portion of the volume of material (1) through one or more turning passes (51, 52, 53, 54, 55) until the cutting depth (8) at a point on the inner surface (3) that is furthest from the end position (11) is less than or equal to the maximum allowable cutting depth of the turning tool; a further step of generating control instruction data for The method of claim 1 , comprising:

3. generating control instruction data for instructing said turning tool (7) to perform two or more turning passes (51, 52, 53, 54, 55) during step (a); During step (a), the maximum depth of cut for a first said turning pass (52, 54, 55) is less than the maximum depth of cut for all successive turning passes (51, 53); The method of claim 2.

4. a further step of repeating step (c) until said turning tool (7) reaches said end position (11) 4. The method of claim 1, comprising:

5. a further step of selecting said turning tool (7) during steps (a) and (c) such that a minimum cutting depth (9) for said turning tool (7) is less than said cutting depth (8).

5. The method of claim 1, comprising:

6. During step (a) material is removed through a series of parallel turning passes (51, 52, 53, 54). generating control instruction data for 6. The method according to any one of claims 1 to 5.

7. generating control instruction data for instructing said turning tool to remove said volume of material (1) in a series of turning passes (50, 51, 52, 53, 54); a maximum depth of cut (60) for the turning pass (50) relative to the baseline (40) is greater than a maximum depth of cut (64) for a first turning pass (54); 7. The method according to any one of claims 1 to 6.

8. selecting a chip thickness value for said turning tool (7); selecting the feed rate such that the feed rate is equal to the chip thickness value divided by a sine function of the lead angle (17); The cutting angle (17) is defined as the angle between the direction of feed (18) and the main cutting edge (19) of the turning tool (7).

8. The method according to any one of claims 1 to 7.

9. a further step of generating control command data for instructing said turning tool (7) to reduce its feed rate when exiting the cut.

9. The method of claim 1, comprising:

10. a further step of generating control command data for commanding said turning tool (7) to enter into a cut along an arc during step (b).

10. The method of claim 1, comprising:

11. the further step of selecting said inner surface (3) such that said inner surface (3) comprises a 90° corner.

11. The method of claim 1, comprising:

12. The turning tool (7) comprises a tool body (81) and a turning insert (82) attached to an insert seat portion of the tool body (81), the turning insert (82) comprises a first cutting edge (19), a second cutting edge (83), and a convex nose cutting edge (84) connecting the first cutting edge (19) and the second cutting edge (83); A nose angle formed between the first cutting edge (19) and the second cutting edge (83) is 85° or less in a plan view.

12. The method according to any one of claims 1 to 11.

13. the nose cutting edge (84) has a radius of curvature of 0.2 to 2.0 mm; The first cutting edge and the second cutting edge (19, 83) are straight in a plan view. The method of claim 12.

14. a further step of generating control command data for commanding said turning tool (7) in all turning passes (50, 51, 52, 53, 54, 55) to move in a radial direction having no axial component or in an axial direction.

14. The method of any one of claims 1 to 13, comprising:

15. A computer program for executing control instruction data generated by the method according to any one of claims 1 to 14.

16. A computer program for generating control instruction data according to the method of any one of claims 1 to 14.

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