Method for generating control instruction data for controlling CNC lathe

Abstract

To provide a method for generating control instruction data for controlling a CNC lathe so as to execute a turning operation with a turning tool.SOLUTION: A method for generating control instruction data for controlling a CNC lathe so as to execute a turning operation with a turning tool includes a step for generating control instruction data for instructing a turning tool so as to execute a first turning pass 52 and a second turning pass 50. In the method for generating the control instruction data for controlling the CNC lathe, the maximum cutting depth of the second turning pass is larger than the maximum cutting depth 64 of the first turning pass 52.SELECTED DRAWING: Figure 4

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 with 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 clamped. Typically, the turning tool comprises 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 in a direction perpendicular to the axis of rotation of the metal blank, which is commonly called a radial feed or a facing cut. Other movement angles, or feed directions, are also possible, which is commonly known as a copy or copy turning. The sequence from entering the cut to leaving 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 plank may be called a tool path. This tool path corresponds to instructions or commands. Typically, the volume of material can be removed in many different ways. For example, the commands may differ with respect to factors such as feed direction, cutting depth, 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. Thus, 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 larger 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] It is a primary object of the present invention to provide an improved method for generating control command data, and one particular object is to improve the manner in which depth of cut is selected.

[0006] This object is realised by a method of generating control instruction data for controlling a CNC lathe to perform a turning operation by means of a turning tool, the method comprising the steps of selecting a representation of a metal blank, selecting a representation of the turning tool, selecting a volume of material to be removed by the turning tool from the metal blank, said volume being bounded by an inner and an outer surface, the metal blank being bounded by a circumferential surface, the circumferential surface comprising the outer surface, and generating control instruction data based on the above to instruct the turning tool to perform a first turning pass and a second turning pass, the first turning pass and the second turning pass being parallel or nearly parallel, the first turning pass comprising turning of the circumferential surface, and a maximum cutting depth for the second turning pass being greater than a maximum cutting depth for the first turning pass.

[0007] In such a way tool life can be improved: since the outer surface is part of the periphery of the blank, machining of this surface may result in more tool wear, since the outer shell of the blank may be harder and / or have a less uniform surface.

[0008] The method is for generating 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 is for generating 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 the 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 of importing a representation of the machined workpiece.

[0011] A representation of the metal blank is selected. The representation of the metal blank 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 may 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, said 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 location defined below to an end location 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 and second cutting edges. Preferably, the nose angle formed between the first and second cutting edges is 85° or less in plan view. The nose cutting edge may have a shape of a circular arc or may have a shape that deviates slightly from a perfect circular arc. Preferably, the nose cutting edge has a radius of curvature of 0.2-2.0 mm. Preferably, the first and second cutting edges are straight in plan view. Alternatively, the first and second cutting edges may be slightly convex or concave, and have a radius of curvature that is more than two times, preferably more than ten times, greater than the radius of curvature of the convex nose cutting edge.

[0018] The inner surface is formed only, 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 A1.

[0019] Preferably, the first cutting edge is positioned or oriented to be active at a cutting angle 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 volume of material to be removed from the metal blank by the turning tool is selected.

[0021] It is not necessary that the volume is 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.

[0022] The volume is defined by an inner surface (preferably the machined workpiece includes the inner surface) and an outer surface (the periphery of the metal blank comprises the outer surface), the distance from the machined workpiece to the outer surface being greater than the distance from the machined workpiece to the inner surface.

[0023] The volume is selected such that the volume can be removed using a selected turning tool.

[0024] The turning operation is for removing at least a portion of the volume.

[0025] Preferably, an end location is selected, the end location being defined as a point or area along the inner surface where the turning tool will be located when said volume is removed.

[0026] The turning tool is commanded or controlled to perform a first or initial turning pass and a second or subsequent turning pass, the second turning pass being performed after the first turning pass, the turning passes being chronologically defined as the time between entering and exiting the cut.

[0027] The first and second turning passes are spaced apart and parallel or nearly parallel, and each of the first and second turning passes is at least partially linear.

[0028] The first turning pass includes turning the peripheral surface.

[0029] Preferably, during the second turning pass, a volume of material is removed that lies between the inner surface and the volume of material removed during the first turning pass.

[0030] Preferably, the method includes the step of selecting a maximum cutting depth for the turning tool.

[0031] The method includes the step of selecting a recommended cutting depth for a turning tool.

[0032] The maximum or greatest depth of cut of the second turning pass is greater than the maximum or greatest depth of cut for the first turning pass.

[0033] It is preferred that the respective maximum depths of cut for the first turning pass and the second turning pass are each less than or equal to a recommended depth of cut for the turning tool.

[0034] Preferably, the method includes the step of positioning the turning tool such that the second cutting edge forms a front 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 rear 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°.

[0035] Preferably, the maximum cutting depth of the second turning pass is less than or equal to the recommended cutting depth for the turning tool.

[0036] Preferably, the method comprises the further step of selecting a maximum depth of cut for the turning tool and selecting a maximum depth of cut for the second turning pass and a maximum depth of cut for the first turning pass, respectively, to be less than or equal to the maximum depth of cut for the turning tool, in other words the depth of cut during the first turning pass and the second turning pass, preferably during all turning passes, is less than or equal to the selected maximum depth of cut of the turning tool.

[0037] A maximum cutting depth for the turning tool is selected, i.e. an upper threshold or an upper threshold function for the turning tool. The maximum cutting depth is an upper threshold or an 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 cutting depth can be understood as the distance away from and perpendicular to the inner surface.

[0038] Preferably, the method can include the step of selecting a recommended depth of cut for the turning tool, which may be equal to, and preferably less than, the maximum depth of cut for the turning tool.

[0039] Preferably, the maximum cutting depth or upper threshold function may be selected to correspond to a point along the first cutting blade or along the second cutting blade.

[0040] The maximum cutting depth 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 cutting depth can therefore be understood as an upper threshold function that depends on the direction of the feed.

[0041] Preferably, the method includes the step of selecting a recommended cutting depth for the turning tool.

[0042] The method includes selecting a maximum depth of cut for the second turning pass and a maximum depth of cut for the first turning pass, each being less than or equal to a maximum depth of cut for the turning tool.

[0043] Preferably, the maximum cutting depth for the second turning pass is equal to the recommended cutting depth.

[0044] The first turning pass and the second turning pass may be linear, for example parallel to the axis of rotation of the metal blank.

[0045] The cutting depth for the first turning pass and the second turning pass may each be constant.

[0046] Preferably, the second turning pass comprises machining a cylindrical surface which, when measured along the axis of rotation of the metal blank, is longer than any other metal cylindrical surface forming part of the inner surface.

[0047] According to one embodiment, the method comprises the further steps of selecting the volume of material to have at least one partial surface whose inner surface is cylindrical, conical or planar, calculating a length of each of the partial surfaces, setting a baseline along the longest of said lengths, and instructing the turning tool to move at least partially along or parallel to the baseline during the first turning pass and the second turning pass.

[0048] 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.

[0049] The length is measured along the axis of rotation of the metal blank if the surface is cylindrical, perpendicular to the axis of rotation if the surface is planar, and along the envelope surface and towards the axis of rotation if the surface is conical.

[0050] A baseline, i.e., an imaginary line, is established or selected along the longest of these lengths.

[0051] According to one embodiment, the method includes the further step of instructing the turning tool to form a part surface relative to the baseline during the second turning pass.

[0052] According to one embodiment, the method includes the further step of instructing the turning tool to remove a volume of material through a series of turning passes, wherein a maximum cutting depth for the turning passes relative to the baseline is greater than a maximum cutting depth for the first turning pass.

[0053] Preferably, the first turning pass is the turning pass associated with the outermost line. The maximum cutting depth for the turning pass associated with the baseline is measured orthogonal to the plane associated with the baseline.

[0054] The respective maximum cutting depths for all turning passes after the first turning pass until the turning pass is relative to the baseline are less than or equal to the maximum cutting depth of the turning tool, and preferably equal to the recommended cutting depth for the turning tool.

[0055] Preferably, the method includes the steps of selecting a minimum depth of cut for the turning tool, and selecting respective depths of cut for all turning passes to be greater than or equal to the minimum depth of cut for the cutting tool.

[0056] According to one embodiment, the turning passes are parallel or at least partially parallel.

[0057] Preferably, the parallel turning passes are spaced apart a distance equal to the recommended cutting depth of the turning tool.

[0058] Preferably the method includes the further step of commanding the turning tool to move in the same direction during at least two or more, preferably all, of the turning passes.

[0059] By such a method, tool paths can be generated or selected in a simple manner.

[0060] According to one embodiment, the method includes the further steps of selecting a minimum cutting depth for the turning tool, selecting a recommended cutting depth for the turning tool, and selecting the respective cutting depth for each turning pass, starting from the first turning pass: if, If the maximum remaining depth MODULO perpendicular to the baseline, which is the recommended cutting depth for the turning tool, is greater than or equal to the minimum cutting depth for the turning tool, Equal to the recommended cutting depth of the turning tool, Or, if not, If the maximum remaining depth perpendicular to the baseline divided by FLOOR [the maximum remaining depth perpendicular to the baseline divided by the recommended cutting depth for the turning tool] is less than or equal to the maximum cutting depth for the turning tool, Equal to the maximum remaining depth perpendicular to the baseline divided by FLOOR [the maximum remaining depth perpendicular to the baseline divided by the recommended cutting depth of the turning tool] If not, and selecting a maximum remaining depth perpendicular to the baseline minus a minimum cutting depth for the turning tool to be equal to FLOOR [maximum remaining depth perpendicular to the baseline divided by a recommended cutting depth for the turning tool]; However, MODULO is an operator that finds the remainder after dividing one number by another, FLOOR is a function that takes a real number as input and gives as output the largest integer less than or equal to the real number.

[0061] The parentheses "(" and ")" above have been added for computational clarity. Thus, the subject matter within the parentheses should not be construed as optional or the like.

[0062] By such methods, machining time may be reduced and / or chip breakage may be ameliorated.

[0063] The above formula or flow chart is a method for calculating the depth of cut for parallel turning passes starting from the first or outermost pass. The turning tool is then commanded to machine each pass at the calculated depth of cut. The maximum remaining depth perpendicular to the baseline may be understood as the distance from the baseline to the outer surface, or, if the outer surface is machined, to the boundary between the volume of machined material and the volume of unmachined material.

[0064] According to one embodiment, the method includes the further step of decreasing the feed rate upon exiting the cut.

[0065] By such methods, tool life can be improved.

[0066] Thus, the feed rate is reduced for at least one turning pass, preferably for two or more turning passes. Typically, the feed rate is measured in millimeters per revolution. Preferably, the reduction in the feed rate 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 the reduction.

[0067] According to one embodiment, the method includes the further step of commanding the turning tool to enter the cut along an arc during at least one of the turning passes.

[0068] By such methods, tool life can be improved.

[0069] Preferably said arc is tangent to the inner surface, preferably in the direction in which the turning tool moves away from the inner surface.

[0070] 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.

[0071] According to one embodiment, the method includes the further step of selecting the inner surface such that the inner surface comprises a 90° corner.

[0072] A nose angle of 85° or less gives the advantage that a 90° corner, i.e. two walls at right angles to each other, can be machined with one of the noses of the turning insert without changing the orientation of the turning insert. The two walls have one flat surface perpendicular to the axis of rotation and one surface at a constant distance to the axis of rotation.

[0073] Preferably the method includes the step of commanding the turning tool to move away from said flat surface.

[0074] A 90° corner in this context is a 90° corner that is preferably an outside corner formed on or in the outside 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 inner surface of an interior or inner hole concentric with the axis of rotation. A circular or curved segment is in cross section in a plane that contains the axis of rotation in the shape of an arc in the shape of a quarter of a circle having the same radius of curvature as the nose cutting edge of the turning insert, or a quarter of a shape that is approximately a circle. Alternatively, the circular or curved segment has a radius of curvature that is greater than the nose cutting edge of the turning insert.

[0075] Preferably the method includes the step of commanding the turning tool to move away from said 90 degree corner.

[0076] 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.

[0077] 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.

[0078] The feed rates given above are the recommended feed rates for turning tools.

[0079] 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 said calculation. Preferably, the feed rate is set in millimeters per revolution. Preferably, the chip thickness value is set in millimeters.

[0080] According to one embodiment, the method includes the further step of commanding the turning tool to move in a direction away from the inner surface and towards the outer surface during at least one of the first turning pass and the second turning pass.

[0081] The turning tool is preferably commanded to move away from the inner surface when the depth of cut reaches a value that is equal to or greater than a recommended depth of cut for the turning tool, or when the turning tool reaches a predetermined position, where the turning tool is commanded to move away from the inner surface.

[0082] The predetermined location is defined as an intersection between an inner surface and one of the defined lines. Upon reaching the predetermined location, the turning tool is commanded to move away from the predetermined location and along the line away from the inner surface.

[0083] When the turning tool is commanded to move in a direction away from the inner surface, it is preferably moved along one of the defined lines, i.e. the line that intersects the inner surface and at the intersection that defines said predetermined position.

[0084] 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.

[0085] The first cutting edge is an active cutting edge. The second cutting edge is an inactive cutting edge. The second cutting edge is inactive for all turning passes.

[0086] 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 a plan view.

[0087] 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.

[0088] In other words, all the passes are either without a longitudinal component, i.e. simply or purely radial, i.e. towards and perpendicular to the axis of rotation, i.e. facing, or longitudinal, i.e. with a longitudinal component, i.e. in the same direction along the axis of rotation. The longitudinal direction is therefore to be understood as copy cutting, which includes both radial and longitudinal components, or copy cutting, which has only a longitudinal component, i.e. parallel to the axis of rotation. For clarity, all turning passes are either radial, or of the same longitudinal direction, or a combination thereof.

[0089] According to one embodiment there is provided a computer program comprising control instruction data for controlling a CNC lathe to perform turning operations generated by any of the methods described above.

[0090] According to one embodiment, a computer program is provided for generating instruction data according to any of the methods described above.

[0091] Preferably, the computer program is CAM software.

[0092] One aspect of the invention relates to a method of dividing or partitioning a volume of material from a representation of a metal blank into sub-portions, the volume being bounded by an inner surface and an outer surface, the metal blank being bounded by a periphery, the periphery including the outer surface, comprising the steps of identifying partial surfaces of the inner surface that are cylindrical, conical or planar, calculating a length of each of the partial surfaces, setting a baseline along the longest of said lengths, and placing lines within the volume of material, the lines being parallel to the baseline, the lines representing boundaries between adjacent sub-portions, the baseline and an outer line adjacent the baseline being separated by a distance greater than the orthogonal distance between the outermost line and the outer surface.

[0093] The volume of material is to be understood as a representation of the volume of material.

[0094] Dividing the volume of material is a pre-machining step that can, for example, assist the machine operator in selecting the tool path. By dividing in the above manner, the first turning pass can have a smaller cutting depth than subsequent passes, thereby improving tool life. This is due to the outer surface having diameter variations and / or being a more difficult surface to machine. The inventors have found that having a relatively small first cutting depth is advantageous in terms of tool life, i.e. tool wear or insert wear.

[0095] According to one aspect of the invention, the method of dividing or separating a volume of material includes the further steps of selecting a turning tool, selecting a recommended cutting depth for the turning tool, and arranging the lines such that the distance between adjacent lines is equal to the recommended cutting depth for the turning tool.

[0096] Preferably, the distance between adjacent lines is constant. Preferably, the turning tool includes a tool body and a turning insert mounted in an insert seat of the tool body, the turning insert includes 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 the nose angle formed between the first cutting edge and the second cutting edge is 85° or less in plan view. Preferably, the nose cutting edge has a curvature radius of 0.2 to 2.0 mm, and the first cutting edge and the second cutting edge are straight lines in plan view.

[0097] The invention will now be explained in more detail by the description of different embodiments of the invention and with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0098] [Figure 1] FIG. 1 is a perspective view showing a metal blank. [Diagram 2] FIG. [Diagram 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 made from the metal blank of FIG. 1. [Diagram 5] 3A-3C are cross-sectional views showing several passes through which the machined piece of FIG. 2 is made 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 PREFERRED EMBODIMENTS

[0099] Please refer to FIG. 1, which shows in a perspective view a metal blank 2, which is limited by a peripheral surface 80 and is rotatable about a rotation axis A1. The metal blank 2 can be represented by a 3D model. The metal blank can be of cast or forged material. The metal blank can also be a machined workpiece. The metal blank can have a substantially cylindrical shape as in FIG. 1 or any other shape. For example, the metal blank can be provided with 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 surface or limit for a volume of material to be removed from the metal blank, thereby forming or generating the machined workpiece.

[0100] Reference is now made to FIG. 2, which shows a machined workpiece 81 or a machined component in a perspective view. The machined workpiece 81 can be represented by a 3D model. The machined workpiece 81 is rotatable around and symmetrical about the axis of rotation A1. The axis of rotation A1 is the same for both the metal blank 2 and the machined workpiece 81. The machined workpiece 81 is made from the metal blank 2 by a turning process, i.e. a metal cutting process, the volume of the machined workpiece 81 being smaller than the volume of the metal blank 2. The machined workpiece 81 comprises an inner surface 3, which is a boundary surface or limit for the volume of material to be removed from the metal blank 2. The inner surface 3 comprises at least part faces 21-26, which may be cylindrical with respect to the part faces 21, 23 and 25, i.e. all points at a constant distance from the axis of rotation A1 of the machined workpiece 81. The part faces may be conical like the part face 26, i.e. all points at a linearly increasing or decreasing distance from the axis of rotation 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 be provided with additional portions, such as curved partial surfaces.

[0101] For each of said partial surfaces 21-26 a respective length 31-36 can be defined. Said lengths 31-36 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) and along the envelope surface and towards the axis of rotation if the surface is conical (see 36). As can be seen, partial surface 33 is the longest.

[0102] Reference is now made to FIG. 3, which shows the machined workpiece 8 of FIG. 2 in a side view, together with a turning tool 7 connected to a CNC lathe (not shown) via a machine interface 85. The turning tool 7 comprises a tool body 81 and a turning insert 82 mounted in an insert seat 81 of the tool body. The turning insert 82 comprises a primary cutting edge 19, a secondary 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 comprises a front end and a rear end, with a longitudinal axis A2, i.e., a central axis, extending from the front end to the rear end. The rear end is connected to the machine interface. The front end comprises the insert seat. The longitudinal axis A2 is perpendicular to the axis of rotation A1 of the machined workpiece 81.

[0103] The turning insert 82 is mounted in the insert seat so that a bisector extending equidistantly from the first and second cutting edges forms an angle of 35 to 55° with respect to the longitudinal axis A2 of the tool body.

[0104] 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 .

[0105] The first cutting blade 19 is an active cutting blade. The second cutting blade 83 is an inactive cutting blade.

[0106] 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.

[0107] A recommended cutting depth 5 for a turning tool 7 is shown as a dotted line 5 when machining the inner surface from a start position 10 to an end position 11. The recommended cutting depth can be understood as a distance 6 away from and perpendicular to the inner surface 3. Said 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.

[0108] 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.

[0109] The maximum cutting depth for the turning tool 7 (not shown) can be understood in an analogous manner.

[0110] Reference is now made to FIG. 4, which shows the machined piece 81 of FIG. 3 being machined using the turning tool (not shown) of FIG. 3. The orientation of the turning tool with respect to the axis of rotation A1 is as in FIG. 3. The machined piece 81 is machined from the metal blank 2 shown in FIG. 1. A volume 1 of material limited by an outer face 4 and an inner face 3 is removed through several turning passes 52, 51, 50, 53, 54. A baseline 40 is set so that it intersects with the longest face 23. Further lines 41, 42, 43 in the volume 1 of material are added. Said lines 40-43 are parallel and spaced apart by a distance equal to the recommended cutting depth 5 of the turning tool 7. Said volume 1 of material is divided into sub-portions 70, 71, 72, 73, 74, said lines 40-43 representing the boundaries between adjacent sub-portions 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.

[0111] 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.

[0112] The maximum cutting depth 60 for the turning pass 50 relative to the baseline 40 is greater than the maximum cutting depth 64 for the first turning pass 52 .

[0113] When machining the inner surface, i.e., paths 51, 50, 53, 54, a turning tool (not shown) is commanded to enter the cut at the point of the inner surface 3 that is not machined, which is furthest away from the start position 10, i.e., the end position 11. The turning tool 7 is commanded to move along the inner surface 3 in path 51 towards the end position 11. The movement in path 51 is first longitudinal towards 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 the 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 the line 41 towards the right hand side until it exits the cut.

[0114] 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 the inner surface 3, first downward in FIG. 4, then toward the right hand side along the baseline 40 until it exits the cut. As the turning tool moves parallel to the axis of rotation A1, it is moving away from the 90° corner.

[0115] 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 the inner surface 3 is completed.

[0116] Reference is now made to FIG. 5, which is the same as FIG. 4 except that the turning passes are slightly different since 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 is straight and parallel to the longest partial surface 23 of the inner surface 3, as in FIG. 4. As in FIG. 4, said pass 52 follows the line 42. The lines 40, 41, 42, 43 are spaced apart in a manner corresponding to those 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 smaller than the maximum cutting depth for the subsequent turning pass 53, which is equal to the recommended cutting depth 5 for the turning tool.

[0117] After the first pass 52, in the 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 Figure 4.

[0118] Reference is now made to FIG. 6, which shows a metal blank 2 from which a machined workpiece 81 is formed by the removal of 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 machined 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 such that it intersects the longest part face 21. Further lines 41, 42, 43, 44, 45 are drawn in the volume 1 of material parallel to the baseline 40, adjacent lines being spaced apart by a distance equal to the recommended cutting depth 5 of the turning tool. Said lines 40-45 divide said 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 cutting depth 62 of the first pass 52 is less than the recommended cutting depth 5 of the turning tool. Similarly, the subsequent pass 51 is straight and parallel to the baseline 40, but has a cutting depth equal to the recommended cutting depth 5 of the turning tool. In the next and final pass 50, the turning tool is commanded to start at the starting point 10 and move along the inner surface 3 to the end point 11. During the final pass 50, the cutting depth is less than or equal to the recommended cutting depth of the turning tool.

[0119] Reference is now made to FIG. 7, which shows a metal blank 2 from which a machined piece 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 machined piece 81. The inner surface 3 comprises one flat part surface 22 and one conical part surface 21. The flat part surface 22 lies in a plane perpendicular to the axis of rotation A1. The length 31 of the conical part surface 21 is greater than the length 32 of the flat part surface 22. A baseline 40 is drawn along the conical part surface 21. Further lines 41-45 are arranged inside the volume 1 of material, parallel to the baseline 40, such that adjacent lines are 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 sub-portions of the volume 1 of material. Each sub-portion 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 the maximum cutting depth for all subsequent passes 50-54. The lines 41-43 intersect the inner surface at a point representing a predetermined position. During a pass 51-53, when the turning tool reaches such a predetermined position, the turning tool is commanded to move along the respective line 41-43 away from the inner surface and away from the predetermined position.

[0120] Attention is now directed to Figure 8 which illustrates a metal blank 2 from which a machined workpiece 81 is formed by the removal of a volume 1 of material by a turning tool (not shown). Figure 8 differs from Figure 7 in that the geometry 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.

[0121] 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.

[0122] The turning tool is commanded to enter the cut at a start location 10 in pass 51 and move along the inner surface 3. Between line 43 and line 42, the depth of cut is greater than the recommended depth of cut but less than the maximum depth of cut for the turning tool. When the turning tool reaches the intersection between line 42 and inner surface 3, the turning tool is commanded to move away from said intersection along line 42, 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 or termination location 11. During pass 50, the depth of cut never reaches or exceeds the recommended depth of cut 5 for the turning tool.

[0123] Reference is now made to FIG. 9, which shows the machined workpiece 81 and the turning tool 7 of FIG. 3 in a side or cross-sectional view. The turning tool is connected to a CNC lathe (not shown) via a machine interface 85. The turning tool 7 comprises 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 with respect to 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 comprises a front end and a rear end, and a longitudinal axis A2, i.e., a central axis, extends from the front end to the rear end. During a turning pass, i.e., when removing material from a metal blank, a cutting angle 17 is defined as the angle between the direction of feed 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 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).

[0124] 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 should decrease.

[0125] 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 .

[0126] Preferably, the feed rate is reduced by 20-80%, even more preferably 40-70%, before exiting the cut, preferably by 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.

[0127] Reference is now made to FIG. 10, which shows a machined workpiece 81, for example, in a side or cross-sectional view together 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 comprises 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 shown at 18, 18', 18'', 18'''. Thus, if the orientation of the axis A2 is not changed, the cutting angle may be different in dependence of the feed direction 18, 18', 18'', 18'''. The recommended cutting depths 5, 5', 5'', 5''' for the turning tool 7 may be different depending on 18, 18', 18'', 18'''. Preferably, the recommended cutting depths 5, 5', 5'', 5''' for the turning tool 7 are selected to correspond to points 90, 91 along the first or second cutting edge, 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.

[0128] 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.

[0129] Reference is now made to Figures 11 and 12, in which the volume of material bounded by the inner surface 3 and the outer surface 4 is shown in cross section. A baseline 40, corresponding to the longest partial surface of the inner surface 3, intersects the inner surface 3. The inner surface and the outer surface 3, 4 are spaced apart by a distance 95. In both Figures 10 and 11, the volume of material is divided into sub-portions 70-72, and one or more lines 41, 42 represent the boundaries between adjacent sub-portions 70-72. Said line 41 or line 42 is parallel to the baseline 40 and spaced apart from it. In Figure 11, the volume of material is divided into three sub-portions 70, 71, 72. In Figure 12, the volume of material is divided into two sub-portions 70-71. In Figure 11, the distances 60, 61 are equal to 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 surface and the outer surface 3, 4. As always, the recommended cutting depth for a turning tool is to be understood as the recommended cutting depth of the turning tool relative to the feed direction, i.e. the movement of the turning tool.

[0130] In Figures 11 and 12, distance 95 is 4.3 mm. The recommended depth of cut for the turning tool is 2.0 mm. The minimum and maximum depth of cut for the turning tool are 0.5 and 2.5 mm, respectively. Thus, during the first pass in Figure 11, when removing the 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, Figure 11's illustration of separating material volumes and tool paths (passes) may be improved, since a depth of cut less than the recommended depth of cut of the turning tool may provide acceptable results, but may not provide optimal results with respect to, for example, chip breakage.

[0131] In Figure 12, the distances 60, 61 are 2.15 mm, in other words, less than the maximum cutting depth of the turning tool and more than the minimum cutting depth of the turning tool. Thus, Figure 12 is preferred over Figure 11.

[0132] 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 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).

[0133] Here, m is the maximum remaining depth perpendicular to the baseline 40, 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. Hence, m mod a_p is 4.3mod2.0=0.3. The first segment is false since 0.3 is less than a_p min (the minimum cutting depth for the turning tool). Thus, 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 as output the largest integer less than or equal to said real number. Thus, 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 since a_p max is the maximum cutting depth for the turning tool, which in this example is 2.5 mm. Therefore, a_p actual=m / FLOOR(m / a_p), which means that the cutting depth (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 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.

[0134] It is to be understood that the described methods of generating control instruction data and methods of dividing a volume of material are computer implemented, and therefore the objects, movements, and other entities are to 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 by means of 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 by the turning tool (7) from the metal blank (2), said volume (1) being bounded by an inner surface (3) and an outer surface (4), said metal blank (2) being bounded by a periphery (80), said periphery (80) comprising said outer surface (4); Commanding said turning tool (7) to perform a first turning pass (52, 55) and a second turning pass (50). and generating control instruction data based on said selection for said the first cutting pass and the second turning pass (52, 55, 50) are parallel or nearly parallel; said first turning pass including turning said peripheral surface (80); A method of generating control command data, wherein a maximum cutting depth for a second turning pass (50) is greater than a maximum cutting depth (64) for said first turning pass (52, 55).

2. - selecting said volume of material (1) such that said inner surface (3) comprises at least one partial surface (21, 22, 23, 24) which is cylindrical, conical or planar; - calculating the lengths (31, 32, 33, 34) of each of said partial surfaces (21, 22, 23, 24); setting a baseline (40) along said partial surface (31, 32, 33, 34) having a maximum length; generating control data for instructing said turning tool (7) to move at least partially along or parallel to said baseline (40) during said first turning pass and said second turning pass (52, 55, 50); The method of claim 1 further comprising:

3. generating control command data for instructing said turning tool (7) to form said part surface (23) relative to said baseline (40) during said second turning pass (50); The method of claim 2 , further comprising:

4. generating control instruction data for instructing said turning tool (7) to remove said volume of material (1) through a series of turning passes (50, 51, 52, 53, 54, 55); a maximum cutting depth (60) for the turning pass (50) relative to the baseline (40) is greater than a maximum cutting depth (64) for the first turning pass (52, 55); The method according to claim 2 or 3.

5. said turning paths (50, 51, 52, 53, 54, 55) being parallel or at least partially parallel; The method according to claim 4.

6. selecting a minimum cutting depth (9) for said turning tool (7); selecting a recommended cutting depth for the turning tool; Further comprising: The cutting depths (60, 61, 62, 63, 64) for each of the turning passes (50, 51, 52, 53, 54, 55) starting from the first turning pass are if, if a maximum remaining depth MODULO perpendicular to the baseline (40), which is a recommended cutting depth for the turning tool (7), is equal to or greater than the minimum cutting depth (9) for the turning tool (7); is generated as being equal to the recommended cutting depth of the turning tool (7), Or, if not, (the maximum remaining depth perpendicular to the baseline (40) divided by FLOOR [the maximum remaining depth perpendicular to the baseline (40) divided by the recommended cutting depth of the turning tool (7)]) is less than or equal to the maximum cutting depth for the turning tool (7), then equal to the maximum remaining depth perpendicular to the baseline (40) divided by FLOOR [the maximum remaining depth perpendicular to the baseline (40) divided by the recommended cutting depth of the turning tool (7)]; If not, [the maximum remaining depth perpendicular to the baseline (40) minus the minimum cutting depth (9) for the turning tool (7)] divided by FLOOR [the maximum remaining depth perpendicular to the baseline (40) divided by the recommended cutting depth for the turning tool (7)], where MODULO is the operator that finds the remainder after dividing one number by another, 6. The method of claim 5, wherein FLOOR is a function that takes a real number as input and gives as output the largest integer that is less than or equal to the real number.

7. generating control command data for instructing the turning tool to reduce the feed rate upon exiting the cut. The method of claim 1 , further comprising:

8. generating control command data for commanding said turning tool (7) to enter into a cut along an arc during at least one of said turning passes (50, 51, 52, 53, 54, 55); The method of claim 1 , further comprising:

9. selecting said inner surface (3) such that said inner surface (3) comprises a 90° corner; The method of claim 1 , further comprising:

10. selecting a chip thickness value (16) for said turning tool (7); selecting said feed rate such that said feed rate is equal to said chip thickness value (16) divided by a sine function of a 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).

10. The method according to any one of claims 1 to 9.

11. generating control instruction data for instructing said turning tool (7) to move in a direction from said inner surface (3) towards said outer surface (4) during at least one of said first turning pass and said second turning pass (52, 55, 50); The method of claim 1 , further comprising:

12. The turning tool (7) includes a tool body (81) and a turning insert (82) attached to an insert seat portion of the tool body (81), said turning insert (82) comprising a first cutting edge (19), a second cutting edge (83) and a convex nose cutting edge (84) connecting said first cutting edge (19) and said 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. said nose cutting edge (84) having a radius of curvature of 0.2 to 2.0 mm; The first cutting edge and the second cutting edge (19, 83) are straight lines in a plan view.

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

14. 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 longitudinal component or in a longitudinal direction thereof; 14. The method of claim 1, further comprising:

15. A computer program comprising control instruction data for controlling a CNC lathe to perform a turning operation provided by any one of claims 1 to 14.

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

17. A method for dividing a volume (1) of material from a representation of a metal blank (2) into sub-portions (70, 71, 72, 73, 74), said volume (1) being bounded by an inner surface (3) and an outer surface (4), said metal blank (2) being bounded by a periphery (80), said periphery (80) including said outer surface (4), - identifying partial surfaces (21, 22, 23, 24) of said inner surface (3) which are cylindrical, conical or planar; calculating the lengths (31, 32, 33, 34) of each of said partial surfaces (21, 22, 23, 24); - setting a baseline (40) along said partial surface (21, 22, 23, 24) having a maximum length (31, 32, 33, 34); Placing lines (41, 42, 43, 44) within said volume of material (1); Including, The lines (41, 42, 43, 44) are parallel to the baseline (40); said lines (41, 42, 43, 44) represent boundaries between adjacent sub-portions (70, 71, 72, 73, 74); The baseline (40) and the outer lines (41) adjacent to the baseline (40) are spaced apart by a distance (14) greater than a distance (15) between the outermost lines (42, 44, 45) and the outer surface (4).

18. selecting a turning tool (7); selecting a recommended cutting depth (5) for said turning tool (7); positioning said lines (40, 41, 42, 43, 44) such that the distance between adjacent lines is equal to said recommended cutting depth (5) of said turning tool (7); 20. The method of claim 17, further comprising:

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