Method for cutting metal threads

Abstract

A machining method for a CNC lathe for forming a predetermined thread in a metal workpiece (19), comprising the following steps: providing a metal workpiece (19); providing a thread machining tool (1), wherein the thread machining tool (1) comprises a first cutting edge (11) and a second cutting edge (12); rotating the metal workpiece (19) around its rotation axis (A1); moving the thread machining tool (1) in a longitudinal (Z) direction through a set of passes (P1-P6), wherein the longitudinal (Z) direction is parallel to or coincides with the rotation axis (A1); during a first pass (P1), oscillating the thread machining tool (1) in a radial (X) direction at a first frequency, so that the thread machining tool (1) moves between a first radial distance (D1) and a second radial distance (D2), wherein the first radial distance (D1) is greater than the second radial distance (D2) (moving forward between D1 and D2, and moving backward between D2 and D1); During the second pass (P2), the thread machining tool (1) is oscillated in the radial (X) direction at a second frequency so that the thread machining tool (1) moves between a third radial distance (D3) and a fourth radial distance (D4), wherein the third radial distance (D3) is greater than the fourth radial distance (D4) and less than the first radial distance (D1), and wherein the fourth radial distance (D4) is less than the second radial distance (D2); and during the last pass (P4, P6), the tool is moved without oscillation in the radial (X) direction, the method comprising the following further steps: setting the second frequency different from the first frequency; setting the third radial distance (D3) to be greater than the second radial distance (D2); arranging the second pass (P2) so that for each oscillation of the second pass (P2), the trajectory of the second pass (P2) intersects the trajectory of the first pass (P1) twice or more.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal cutting. More specifically, the present invention belongs to the field of the turning operation known as threading. Background Art

[0002] The present invention relates to a machining method according to the present invention. In other words, the present invention relates to a machining method of a CNC lathe for forming a predetermined thread in a metal workpiece, comprising the following steps: providing a metal workpiece, providing a thread machining tool including a first cutting edge and a second cutting edge, rotating the metal workpiece around its rotation axis, moving the thread machining tool in a longitudinal direction through a set of passes; wherein the longitudinal direction is parallel to or coincides with the rotation axis; during the first pass, oscillating the thread machining tool in a radial direction at a first frequency so that the thread machining tool moves between a first radial distance and a second radial distance, wherein the first radial distance is greater than the second radial distance, during the second pass, oscillating the thread machining tool in a radial direction at a second frequency so that the thread machining tool moves between a third radial distance and a fourth radial distance, wherein the third radial distance is greater than the fourth radial distance and less than the first radial distance, wherein the fourth radial distance is less than the second radial distance, and wherein the third radial distance is greater than the second radial distance, and during the last pass, moving the tool without oscillating in the radial direction.

[0003] In threading, a thread is formed. Threading can be done in a turning operation. The metal workpiece rotates. The threading tool moves longitudinally relative to the rotating workpiece. The thread is gradually formed by a series of one or more passes.

[0004] EP3241637A1 discloses a method for threading a workpiece, wherein the threading tool is oscillated in the radial direction or in the X direction. This method is said to reduce the problem of long chip strips.

[0005] The inventors have discovered that there is a need for further improved threading methods. Summary of the invention

[0006] The object of the present invention is to improve chip breaking or chip control and to increase tool life.

[0007] At least one of the objects is achieved by the method initially defined, comprising the further steps of: setting a second frequency different from the first frequency; and arranging the second tool pass so that for each swing of the second tool pass, the trajectory of the second tool pass intersects the trajectory of the first tool pass two or more times.

[0008] By this method, the chips can be shortened. The chips are separated at least during the second pass when the trajectory of the second pass intersects the trajectory of the first pass, in other words, the chips are separated when the threading insert is out of the cut. For each swing, the chips will break when they are out of the cut.

[0009] Because for the second pass, the first cutting edge or leading edge arranged to cut the first thread tooth side and the second cutting edge or trailing edge arranged to cut the second thread tooth side are alternately cut, the chip breaking is further improved. More precisely, during cutting, either the connecting cutting edge (which can be in the form of a convex cutting edge, for example) and the first cutting edge are in cutting, or the connecting cutting edge and the second cutting edge are in cutting. The connecting cutting edge should be understood as the part of the cutting edge that forms the thread tooth bottom. Due to the cross section of the chip, this results in the chip having a more favorable shape. The method in which all passes have the same oscillation frequency will result in the chip having a shape that can generally be described as a V-shaped cross section. In other words, the chip is formed when the first cutting edge and the second cutting edge are in cutting at the same time as the connecting cutting edge. This shape description is particularly suitable for common thread profiles, such as V-profile 55 degree or 60 degree threads, or metric or UN 60 degree threads. This V-shaped chip is less favorable in shape, which leads to poor chip control. In addition, the V-shaped chip increases the risk of built-up edge on the rake face of the insert, thereby shortening the tool life. This V-shaped chip will be the one in EP3241637A1 Figure 3 The result of oscillating pass number 2 is shown in .

[0010] By this method, the inventors have found that more than one point along the cutting edge enters and exits the workpiece during the second pass, which is an advantage over methods reportedly entering and exiting the workpiece at one point along the cutting edge. The inventors have found that the entry and exit points are more susceptible to wear.

[0011] During the second cutting pass, the first cutting edge and the second cutting edge act alternately, thereby distributing the wear relatively evenly along the cutting edges, which is advantageous in terms of tool life.

[0012] Machining methods are metal cutting methods. A CNC lathe is any computer or computer numerically controlled machine suitable for turning. A thread or screw tooth is a spiral structure. The thread extends between the start of the thread and the end of the thread. The thread has a constant or substantially constant pitch, i.e., the distance traveled along the axis of rotation per turn of the thread, i.e., the number of threads per unit length. The thread can be straight (i.e., cylindrical) or tapered (i.e., conical). The thread can be an external thread or an internal thread. The thread can be a right-handed thread or a left-handed thread. The cross-sectional shape of the thread is called the thread form. The thread form or thread profile can have various shapes, such as, for example, ISO, trapezoidal, UNC. The thread form preferably includes a first thread flank, a second thread flank, a crest, and a root.

[0013] The thread is preferably a single thread. The metal workpiece is, for example, made of steel. The metal workpiece is preferably at least partially cylindrical or substantially cylindrical. The threading tool preferably comprises a tool body and a threading insert. The threading insert is preferably at least partially made of a wear-resistant material (such as, for example, cemented carbide). The threading tool (preferably, the threading insert) comprises a cutting edge.

[0014] The cutting edge comprises a first cutting edge and a second cutting edge. The first cutting edge and the second cutting edge are preferably connected by a connecting cutting edge. The connecting cutting edge is preferably arranged to cut the thread root. The connecting edge may be convex in a top view. The connecting edge may have a shape that is an arc in a top view. The first cutting edge is preferably arranged to cut the first thread tooth side. The second cutting edge is preferably arranged to cut the second thread tooth side.

[0015] The shape of the cutting edge preferably corresponds or substantially corresponds to the thread form.

[0016] The threading tool, preferably the threading insert, preferably comprises one or more teeth.

[0017] The metal workpiece rotates in one direction about its axis of rotation, wherein the axis of rotation preferably coincides with a longitudinal axis of symmetry of the metal workpiece.

[0018] The method comprises the following steps: the threading tool is moved in a longitudinal direction in a set or a series of passes. The thread is formed by a set of passes. The number of passes is preferably 3-25, even more preferably 4-20. For each pass, material is removed from the metal workpiece. The final pass generates the final shape of the thread, i.e., the predetermined thread.

[0019] This method can be used for radial infeed, side infeed or with alternating side infeed.

[0020] The longitudinal direction is parallel to the axis of rotation of the metal workpiece. For each pass, the threading tool moves longitudinally in one direction and removes metal from the metal workpiece by metal cutting. At the end of each pass, the threading tool is disengaged from cutting by retracting the threading tool, i.e., moving the threading tool in a direction away from the metal workpiece. Before the subsequent pass, the threading tool moves longitudinally in a direction opposite to the one direction without cutting.

[0021] In each pass, the threading tool moves from the start of the thread to the end of the thread, or from a position near the start of the thread to a position near the end of the thread. In other words, the threading tool enters the cutting near the start of the thread and leaves the cutting near the end of the thread. In this context, "near" should be understood as within one turn from the start of the thread.

[0022] If the thread is an external thread, the passes gradually approach the axis of rotation. In other words, during the first pass, the threading tool is on average at a greater radial distance from the axis of rotation than during the second pass. During the last pass, the threading tool is on average at a smaller radial distance from the axis of rotation than during the penultimate pass.

[0023] The movement of the threading tool in the longitudinal direction (i.e. along the Z axis) is called longitudinal feed. The longitudinal feed is preferably constant on average during all passes, i.e. has the same average value. The average value is preferably equal to the pitch of the thread. The longitudinal feed during the last pass is constant, i.e. has a constant value.

[0024] During the first pass, the thread machining tool oscillates in the radial direction at a first frequency. The oscillation is preferably a periodic oscillation with a periodic waveform, such as, for example, a triangular wave or a sine wave. The waveform includes crests and troughs. The oscillation of the thread machining tool oscillates between crests and troughs. If the thread is an external thread, the crests are radially outside and the troughs are radially inside.

[0025] During the first pass, the threading tool performs a forward movement between the first radial distance and the second radial distance, and performs a backward movement between the second radial distance and the first radial distance. If the thread is an external thread, the forward movement is toward the axis of rotation, and if the thread is an internal thread, the forward movement is away from the axis of rotation.

[0026] The first frequency is preferably constant. The frequency refers to one swing per time unit or unit time. For example, if one swing takes 2s, i.e. two seconds, the frequency is 0.5s. -1 .

[0027] Preferably, during the first pass, the threading tool oscillates between once per one revolution of the metal workpiece (ie one cycle) and once per four revolutions of the metal workpiece.

[0028] Even more preferably, during the first pass, the threading tool oscillates once for every two revolutions of the metal workpiece, ie one cycle. One cycle is understood to be starting from a first radial distance, moving to a second radial distance, and then returning to the first radial distance.

[0029] The time for the metal workpiece to make one revolution around its rotation axis is preferably equal to the time for one oscillation or a multiple of the time for one oscillation, or equal to the time for one oscillation divided by an integer.

[0030] The oscillation of the threading tool is radial so that during a first pass the threading tool moves between a first radial distance from the last pass and a second radial distance from the last pass. The first radial distance corresponds to a crest and the second radial distance corresponds to a trough. The distance is the distance from the last pass. The peak-to-peak amplitude of the oscillation during the first pass is equal to the difference between the first radial distance and the second radial distance. Regardless of whether the thread is straight or tapered, the radial distance is in a direction perpendicular to the axis of rotation of the metal workpiece. The oscillation during each oscillating pass causes the threading tool to repeatedly engage and disengage the metal workpiece and generate chips.

[0031] Oscillation during the first pass means that the cutting depth or the feed rate varies during the first pass. The active part of the cutting edge of the threading tool varies during the first pass.

[0032] Preferably, if the thread is an external thread, the first radial distance is greater than the radius of the metal workpiece. In other words, preferably, the trajectory of the first tool pass intersects the peripheral surface or outer surface of the metal workpiece.

[0033] Therefore, the first pass is preferably an interrupted cut, ie the cutting edge acts in an interrupted manner, ie the metal is cut in an interrupted manner. The effect is that the chips can be shorter during the first pass.

[0034] The movement of the threading tool during the first pass therefore comprises two components: a longitudinal component in which the threading tool moves in one direction along or parallel to the longitudinal Z axis, and a radial component in which the threading tool oscillates radially perpendicular to the axis of rotation.

[0035] After the first pass, the threading tool is moved in a direction opposite to the longitudinal direction of the first pass without longitudinal cutting.

[0036] During the second pass, the threading tool oscillates in radial direction at a second frequency which is different from, and even more preferably higher than, the first frequency, thereby even further reducing the length of the chips during the second pass. The second frequency is preferably a multiple of the first frequency.

[0037] Preferably, during the second cutting pass, the thread machining tool oscillates once for every rotation of the metal workpiece, ie, one cycle.

[0038] The oscillation of the threading tool causes the threading tool to move between a third radial distance and a fourth radial distance from the last pass.During the second pass, the threading tool moves longitudinally in a direction along the Z axis, which is in the same direction as the direction of the first pass.

[0039] The third radial distance is greater than the fourth radial distance. If the thread is an external thread, the third radial distance is preferably smaller than the outer surface or peripheral surface of the metal workpiece.

[0040] The first radial distance is greater than the third radial distance, and the second radial distance is greater than the fourth radial distance. In other words, if the thread is an external thread, the diameter of the second pass is on average smaller than the diameter of the first pass.

[0041] The difference between the first radial distance and the second radial distance (ie the radial distance) is preferably different from the difference between the third radial distance and the fourth radial distance.

[0042] The trajectory of the second tool pass intersects the trajectory of the first tool pass. Preferably, for each time period of the second tool pass, that is, for each swing of the second tool pass, the trajectory of the second tool pass intersects the trajectory of the first tool pass twice. In this case, the trajectory of the second tool pass is such that the order of each exit from cutting and entry into cutting corresponds to the backward movement of the threading tool during the first tool pass, or to the forward movement of the threading tool during the first tool pass. In other words, relative to the nearest point or adjacent point along the Z axis corresponding to the second radial distance, the adjacent intersection points are all located on the same side along the longitudinal direction or Z axis.

[0043] The trajectory of the second pass preferably intersects once during forward movement and once during backward movement, wherein backward and forward are opposite directions relative to the axis of rotation. An intersection represents either exiting the cut or entering the cut.

[0044] Preferably, if the thread is an external thread, the trajectory of the second pass is radially below the trajectory of the first pass for a greater time or distance than the trajectory of the second pass is radially above the trajectory of the first pass. For external threads, radially above means radially outside or a larger radial distance, and radially below means radially inside or a smaller radial distance.

[0045] During the last pass, the threading tool moves linearly in the radial direction, i.e. without oscillation. If the thread is a cylindrical thread, the linear movement is parallel to the axis of rotation. The longitudinal feed during the last pass is equal to the pitch of the thread. The last pass forms the final shape of the thread.

[0046] According to an embodiment, the method comprises the further step of setting the second frequency to be twice as large as the first frequency or substantially twice as large as the first frequency.

[0047] In other words, the second frequency is twice the first frequency. This results in shorter chips during the second pass because the chip length is shorter as the frequency increases. The chip breaks every time the blade completely exits the cut. During the second pass, the blade exits the cut once and enters the cut once per swing. In other words, the trajectory of the second pass intersects the trajectory of the first pass twice per swing. This results in shorter chips during the second pass because if the chip breaks at each swing, the chip length decreases as the frequency increases.

[0048] According to an embodiment, the method comprises the further step of phasing the oscillation during the second pass such that the fourth radial distance coincides with the first radial distance and the second radial distance along the Z-axis.

[0049] In this way, insert wear is more evenly distributed on the first and second cutting edges during the second pass, thereby increasing tool life.

[0050] Coincidence in this context may be understood as coincidence along the Z axis, i.e., longitudinal coincidence. In other words, the crest of the second pass defined by the third radial distance is longitudinally located midway between adjacent crests and troughs of the first pass, wherein the crest of the first pass is defined by the first radial distance, and wherein the trough of the first pass is defined by the second radial distance.

[0051] According to an embodiment, the method comprises the following further steps: during the third pass, causing the thread machining tool to oscillate in the radial direction at a third frequency so that the thread machining tool moves between a fifth radial distance and a sixth radial distance, wherein the fifth radial distance is greater than the sixth radial distance and less than the third radial distance, and wherein the sixth radial distance is less than the fourth radial distance; setting the third frequency to be different from the second frequency; setting the fifth radial distance to be greater than the fourth radial distance; arranging the third pass so that for each oscillation of the third pass, the trajectory of the third pass intersects the trajectory of the second pass twice or more; and setting the frequency of the third pass to be lower than the frequency of the second pass or lower than the frequency of the first pass.

[0052] In this way, the oscillation frequency can be set relatively low compared to a method where the frequency is continuously increased, thereby avoiding machine limitations or problems associated with high frequency control and / or the mechanics of the CNC machine.

[0053] In this way, the chip can be broken during the third pass.

[0054] During the third pass, the threading tool is oscillated in a radial direction at a third frequency, which is preferably different from the second frequency. Preferably, the third frequency is equal to or substantially equal to the first frequency. Preferably, the third frequency is lower than the second frequency. The third frequency is preferably half the second frequency. The oscillation of the threading tool causes the threading tool to move between a fifth radial distance and a sixth radial distance from the last pass. The third pass may or may not be the penultimate pass.

[0055] During the third pass, the threading tool moves longitudinally in a direction along the Z-axis, which is in the same direction as the first and second passes.

[0056] The fifth radial distance is greater than the sixth radial distance.

[0057] The fifth radial distance is less than the third radial distance.

[0058] The sixth radial distance is less than the fourth radial distance.

[0059] The trajectory of the third knife pass intersects the trajectory of the second knife pass. Preferably, for each time period of the third knife pass, the trajectory of the third knife pass intersects the trajectory of the second knife pass twice. Preferably, the time or distance that the trajectory of the third knife pass is below the trajectory of the second knife pass is greater than the time or distance that the trajectory of the third knife pass is above the trajectory of the second knife pass.

[0060] The threading tool performs a forward movement between the fifth radial distance and the sixth radial distance, and performs a backward movement between the sixth radial distance and the fifth radial distance.

[0061] According to an embodiment, the method comprises the further step of setting the last oscillating pass to have a higher frequency than all previous oscillating passes.

[0062] This method allows for shorter chips near the thread root, which is beneficial because chipping problems are more likely near the root.

[0063] The last oscillating pass is the penultimate pass. During the penultimate pass, the threading tool oscillates radially between an outer radial distance and an inner radial distance from the last pass, wherein the inner radial distance is zero or less than half the difference between the first radial distance and the second radial distance.

[0064] In other words, during the penultimate pass, the threading tool oscillates radially between two radial distances from the last pass, wherein the radial distance of the radial distance closest to the last pass in radial direction is zero, i.e. intersecting the last pass, or is less than half the difference between the first radial distance and the second radial distance. Preferably, the radial distance is less than 0.10 mm, even more preferably, less than 0.06 mm.

[0065] In other words, preferably, during the penultimate pass, the threading tool is swung in a radial direction so that the trajectory of the penultimate pass intersects or substantially intersects the trajectory of the last pass. "Substantially" in this context should be understood to be within 0.10 mm, even more preferably within 0.06 mm.

[0066] As a result, chip control can be further improved both for the penultimate and final pass.

[0067] The penultimate pass may be the third pass. Alternatively, the penultimate pass may be the fourth pass, the fifth pass, or a higher numbered pass. The penultimate pass is the pass immediately preceding the last pass.

[0068] Preferably, the second radial distance is greater than the fifth radial distance.

[0069] Preferably, the oscillation frequency during the penultimate pass is less than or equal to eight times the oscillation frequency during the first pass. Even more preferably, the oscillation frequency during the penultimate pass is less than five times the oscillation frequency during the first pass. This is an advantage, in particular if the number of oscillating passes is high, for example three or more or five or more oscillating passes. In particular, if compared to an exponentially increasing frequency. In this way, the method can be used for more types of CNC machines, since not all CNC machines allow high-frequency radial oscillation. The inventors have realized that if the frequency is kept relatively low, the risk of damage to the moving parts of the CNC lathe is reduced.

[0070] The peak-to-peak amplitude of all oscillating passes is preferably less than 1.0 mm. In other words, the difference between the first radial distance and the second radial distance is preferably less than 1.0 mm. Preferably, all oscillating passes are all passes except the last pass.

[0071] The inventors have realised that if the peak-to-peak amplitude is relatively low, the risk of damage to moving parts of a CNC lathe is reduced.

[0072] According to an embodiment, the method comprises the further step of setting the frequency of all oscillating passes after the first pass to be less than or equal to four times the frequency of the first pass.

[0073] In this way, the maximum frequency can be set relatively low, thereby reducing the risk of damaging the moving parts of the CNC lathe.

[0074] According to an embodiment, the method comprises the further step of oscillating the threading tool during the penultimate pass between an outer radial distance and an inner radial distance from the last pass, wherein the inner radial distance is zero or less than half the difference between the first radial distance and the second radial distance.

[0075] In this way, chip control during the final cut is improved.

[0076] The penultimate pass may be the third pass or a higher order pass. The fifth radial distance is greater than the sixth radial distance, the fifth radial distance is less than the third radial distance, and the sixth radial distance is less than the fourth radial distance.

[0077] According to an embodiment, the method comprises the further step of setting the frequency of the penultimate knife pass to be higher than the frequency of the first knife pass and higher than the frequency of the second knife pass.

[0078] With this approach, the chips are shorter during the penultimate pass, which is beneficial because chip problems are more likely near the thread root.

[0079] According to an embodiment, the difference between the first radial distance and the second radial distance is different from the difference between the third radial distance and the fourth radial distance.

[0080] In this way, chip breaking or chip control is further improved and / or the tool life is increased.

[0081] In other words, the amplitude of the oscillation during the first pass and the second pass is different. Preferably, the amplitude of the oscillation during the first pass is greater than the amplitude of the oscillation during the second pass. This is an advantage because it increases the chance of leaving the workpiece during all oscillations during the first pass. The diameter of the outer surface may be non-uniform.

[0082] In other words, the peak-to-peak amplitude of the oscillation during the first pass is different from the peak-to-peak amplitude of the oscillation during the second pass. Preferably, the difference between the first radial distance and the second radial distance is less than the difference between the third radial distance and the fourth radial distance. In other words, preferably, the peak-to-peak amplitude of the oscillation during the first pass is less than the peak-to-peak amplitude of the oscillation during the second pass.

[0083] Preferably, the difference between the fifth radial distance and the fourth radial distance is smaller than the difference between the third radial distance and the fifth radial distance.

[0084] According to an embodiment, the difference between the first radial distance and the third radial distance is smaller than the difference between the third radial distance and the second radial distance.

[0085] In this way, chip breaking or chip control is further improved and / or the tool life is increased.

[0086] According to an embodiment, the third frequency is the same or substantially the same as the first frequency.

[0087] Preferably, the first and third passes are in phase, ie, there is no phase shift.

[0088] According to an embodiment, the second radial distance and the sixth radial distance coincide or substantially coincide in the longitudinal direction.

[0089] In this way, chip breaking or chip control is further improved and / or the tool life is increased.

[0090] In other words, the trough of the oscillation during the first cutting pass coincides longitudinally with the trough of the first cutting pass.

[0091] Preferably, the first and third passes have the same or substantially the same frequency. Preferably, there is no phase shift, ie zero or substantially zero phase shift, between the first and third passes. The longitudinal direction is the Z direction.

[0092] According to an embodiment, the threading tool is moved in the longitudinal direction at a longitudinal feed rate of 0.5-3.0 mm / revolution for all passes.

[0093] By this method, threads having a pitch of 0.5-3.0 mm can be machined in a more efficient manner.

[0094] Preferably, the longitudinal feed rate is the same for all passes. In other words, preferably, the longitudinal feed rate has a constant value that is the same for all passes. The value is equal to the pitch of the thread. The longitudinal direction is along the Z axis or parallel to the Z axis.

[0095] According to an embodiment, a thread machining tool includes a thread machining insert and an insert seat, wherein the thread machining insert includes a top surface and a bottom surface, wherein the top surface and the bottom surface are connected by a side surface, wherein a first cutting edge and a second cutting edge are formed at a boundary between the top surface and the side surface, and wherein the bottom surface includes an engagement device for contacting a corresponding structure formed in the insert seat.

[0096] By this method, surprisingly, it was found that the surface quality of the machined surface was improved. By this method, the risk of blade movement was reduced. For all oscillating passes except the first pass, the first cutting edge and the second cutting edge are alternately in cutting, resulting in a change in the direction of the cutting force. This increases the risk of blade movement and the risk of poor surface quality. The engagement device in the bottom surface of the blade reduces this risk. Other engagement surfaces, such as side surfaces, may also be present. It was surprisingly found that when using the method described herein, the situation where the flat bottom surface and / or contact surface of the threading insert is only located on the side surface increases the risk of poor surface quality of the thread.

[0097] The threading insert is preferably at least partially made of a wear-resistant material such as, for example, cemented carbide. The threading insert comprises a cutting edge. The shape of the cutting edge preferably corresponds to or substantially corresponds to the thread form. The top surface comprises a rake face. The cutting edge is formed at the boundary between the top surface and the side surface. The side surface comprises a clearance surface. The top surface preferably comprises a chip breaking or chip forming device, which is preferably in the form of one or more protrusions and / or depressions.

[0098] The bottom surface of the threading insert comprises engagement means for contacting or cooperating with corresponding engagement means, i.e. corresponding structures formed in the insert seat, also referred to as insert pockets. When mounted in the insert seat, the engagement means prevent movement, in particular rotation, of the threading insert.

[0099] The threading insert is preferably mountable in the insert seat by means of a clamping member, such as a screw or bolt or a top clamp. The threading insert may preferably include a through hole for a screw or bolt, wherein the through hole extends between the top surface and the bottom surface of the threading insert.

[0100] The engagement means formed in the bottom surface of the threading insert may be in the form of one or more cavities, for example one or more grooves. Alternatively, the engagement means may be in the form of one or more protrusions. Alternatively, the engagement means may be in the form of one or more inclined surfaces.

[0101] If the engagement means formed in the bottom surface of the threading insert is in the form of a cavity, such as a groove, then the corresponding engagement means formed in the insert seat is preferably in the form of a protrusion, such as a ridge.

[0102] The threading tool, in particular the base and the insert seat of the threading insert, may preferably be arranged as shown and described in EP 1 935 539 A1, which is incorporated herein by reference.

[0103] According to an aspect of the present invention, there is provided a computer program having instructions which, when executed by a CNC lathe, cause the CNC lathe to perform steps according to any one of the aforementioned methods.

[0104] The computer program or computer program product may be comprised in a CAM software product, ie software for computer aided manufacturing.The computer program may be in the form of a computer readable medium, such as a USB stick, CD-ROM or data stream.

[0105] The method may include more passes than described above. For example, according to an embodiment, during a fourth pass, the threading tool is oscillated in a radial direction at a fourth frequency such that the threading tool moves between a seventh radial distance and an eighth radial distance from the last pass; wherein the seventh radial distance is greater than the eighth radial distance; wherein the seventh radial distance is less than the fifth radial distance, and wherein the eighth radial distance is less than the sixth radial distance.

[0106] By this method, chip breaking or chip control is further improved and / or tool life is increased. By this method, threads with larger cross sections can be machined in a more risk-free and / or economical manner.

[0107] Preferably, the difference between the seventh radial distance and the eighth radial distance is less than the radial distance between the third radial distance and the fourth radial distance. In other words, preferably, the peak-to-peak amplitude of the fourth pass is less than the peak-to-peak amplitude of the second pass. Preferably, the difference between the seventh radial distance and the eighth radial distance is less than the difference between the first radial distance and the second radial distance. In other words, preferably, the peak-to-peak amplitude of the fourth pass is less than the peak-to-peak amplitude of the first pass. Preferably, the difference between the seventh radial distance and the eighth radial distance is greater than the difference between the fifth radial distance and the sixth radial distance. In other words, preferably, the peak-to-peak amplitude of the fourth pass is greater than the peak-to-peak amplitude of the third pass. Preferably, the fourth frequency is the same or substantially the same as the second frequency. Preferably, there is no phase shift between the swing during the second pass and the swing during the fourth pass.

[0108] Preferably, the seventh radial distance is greater than the sixth radial distance. Preferably, the trajectory of the fourth tool pass intersects the trajectory of the third tool pass.

[0109] The method may include an even greater number of passes. According to an embodiment, during a fifth pass, the threading tool is oscillated in a radial direction at a fifth frequency such that the threading tool moves between a ninth radial distance and a tenth radial distance from the last pass; wherein the ninth radial distance is greater than the tenth radial distance; wherein the tenth radial distance is less than the eighth radial distance.

[0110] By this method, chip breaking or chip control is further improved and / or tool life is increased. By this method, threads with larger cross sections can be machined in a more risk-free and / or economical manner.

[0111] Preferably, the difference between the ninth radial distance and the tenth radial distance is less than the difference between the third radial distance and the fourth radial distance. Preferably, the difference between the ninth distance and the tenth distance is less than the difference between the first radial distance and the second radial distance. Preferably, the difference between the ninth radial distance and the tenth radial distance is greater than the difference between the fifth radial distance and the sixth radial distance. Preferably, the difference between the ninth radial distance and the tenth radial distance is greater than the difference between the seventh radial distance and the eighth radial distance.

[0112] The fifth frequency is preferably different from the fourth frequency.

[0113] If the fifth pass is the second to last pass, the fifth frequency is preferably higher than the first frequency. If the fifth pass is the second to last pass, the fifth frequency is preferably higher than the second frequency.

[0114] If the fifth pass is not the second to last pass, the fifth frequency is preferably equal to or substantially equal to the first frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The present invention will now be explained in more detail by describing embodiments of the present invention and with reference to the accompanying drawings.

[0116] Figure 1 is a perspective view of a metal workpiece and clamping jaws showing the X-axis and Z-axis.

[0117] Figure 2 is a side view of a threading method showing four passes.

[0118] Figure 3 yes Figure 2 Perspective view of the threading tool in Figure 1.

[0119] Figure 4 is a schematic diagram of a first embodiment of the present invention, showing a tool path traced by a threading tool as viewed from the Z-axis direction.

[0120] Figure 5 Schematic diagram showing the position of the thread machining tool relative to the metal workpiece in the first embodiment of the present invention.

[0121] Figure 6 Schematic diagram showing the position of the thread machining tool relative to the metal workpiece in the second embodiment of the present invention. DETAILED DESCRIPTION

[0122] refer to Figure 1 , which shows a metal workpiece 19 connected to a spindle (not shown) of a CNC lathe (not shown) by a clamping device 22 in the form of a clamping jaw. The clamping device 22 is connected to the spindle and contacts the outer peripheral surface 21 of the metal workpiece 19. Rotation of the spindle causes rotation of the metal workpiece 19. The clamping device 22 may have other configurations. In this case, the metal workpiece 19 is cylindrical. However, the metal workpiece 19 may have other shapes. An X-axis and a Z-axis are shown. Depending on the type of CNC lathe, the metal workpiece 19 may be movable in the Z-axis, such as for a CNC lathe equipped with a bar feed device. For other CNC lathes, the metal workpiece 19 may be immovable in the Z direction.

[0123] Reference now Figure 2 . A threading tool 1 and a metal workpiece 19 are shown. The threading tool 1 includes a threading insert 2 and a tool body 9. The threading insert 2 includes a cutting edge 10. The metal workpiece 19 rotates in one direction 20 about its rotation axis A1. The CNC lathe (not shown) includes a spindle (not shown). The metal workpiece 19 is clamped by a clamping device 22 in the form of a clamping jaw. A helical thread is formed in an outer peripheral surface 21 of the metal workpiece 19. Figure 2 In the embodiment of the present invention, the outer peripheral surface 21 is a radial outer surface, in other words, the thread is a male thread. Alternatively, the thread can be a female thread. The thread form includes a first thread flank 15, a second thread flank 16, a crest or thread crest 17 and a root or thread root 18.

[0124] The thread is formed by several passes P1-P4. The number of passes may vary. In this case, the fourth pass P4 is the last pass. During each pass P1-P4, the cutting edge 10 removes metal from the metal workpiece 19 by metal cutting. The thread machining tool 1 moves in the same longitudinal direction during all passes P1-P4. In other words, the thread machining tool 1 moves along the rotation axis A1 and / or along the Z axis. Preferably, the thread machining tool 1 moves at the same or substantially the same longitudinal feed rate (i.e., along the Z axis) during all passes. The feed rate is equal to the pitch of the thread. During all passes except the last pass P4, the thread machining tool 1 swings along the X axis. During the last pass P4, the thread machining tool 1 does not swing. Between these passes, the thread machining tool 1 retracts to the starting position, i.e., the position where the thread starts along the rotation axis A1. Figure 2 The arrows of the tool paths P1-P3 in FIG. 1 are horizontal. However, in detail, the arrows are not horizontal, but wavy. The wavy shape will be Figure 5 and Figure 6 Explained in.

[0125] The CNC lathe (not shown) is controlled by a computer program. The computer program includes readable and executable code. The code includes information about the relative movement of the thread machining tool 1 relative to the metal workpiece 19 and about the rotation of the metal workpiece 19 around its rotation axis A1. In other words, the computer program includes instructions, such as the number of passes, radial oscillation, longitudinal feed rate and rotation of the metal workpiece.

[0126] Figure 3 Shows Figure 2 A thread machining tool 1 is provided in the tool body 9. The thread machining tool 1 comprises a tool body 9 and a thread machining insert 2. An insert seat 6 is formed in the tool body 9. The thread machining insert 2 comprises three teeth. Only one tooth is installed in an active state, i.e., installed so that the tooth can cut a thread. The thread machining insert 2 is clamped in the insert seat 6 by means of a screw 14. The thread machining insert 2 is indexable so that it can be rotated 120° or 240° to set the next tooth in an active position. Each tooth comprises a cutting edge. Each cutting edge comprises a first cutting edge 11 and a second cutting edge 12 connected by a connecting cutting edge 13. The connecting cutting edge 13 is arranged to cut the thread bottom.

[0127] The bottom surface of the threading insert comprises engagement means in the form of a groove 7. The insert seat comprises a ridge 8. The shape of one groove 7 corresponds or substantially corresponds to the shape of said ridge 8.

[0128] Figure 4 Schematic diagram showing the passes P1-P4 traced by the thread machining tool 1 on the metal workpiece 19 when viewed in the Z-axis direction. The cutting conditions are adapted so that the number of swings of the thread machining tool 1 is one for the first pass P1 and the third pass P3 relative to two rotations of the spindle, and one for the second pass P2 relative to one rotation of the spindle. For the first pass P1, one swing is from D1 to D2 and back to D1. For the second pass P2, one swing is from D3 to D4 and back to D3. For the third pass P2, one swing is from D5 to D6 and back to D5. The fourth pass P4 has no swing. After the second pass P2, the shape of the metal workpiece in the cross section (i.e., when viewed in the Z-axis direction) is close to an ellipse, more precisely, it is formed into an ellipse with two cuts.

[0129] During the first pass P1 and the third pass P3, there is air cutting once for every two revolutions of the metal workpiece 19. Air cutting is from the time when the threading tool is out of cutting until the threading tool is in cutting. The trajectory of the first pass P1 (i.e., the path traced by the threading tool 1 during the first pass P1) intersects the outer peripheral surface 21 of the metal workpiece 19.

[0130] Figure 5 A graph illustrating the position of a cutting tool in a method of forming a thread by four passes P1-P4 is shown, such as in FIG. Figure 2 middle. Figure 2 The vertical axis in is the X-axis of the CNC lathe, ie, the radial direction. Figure 2 The horizontal axis in is the Z axis of the CNC lathe. The horizontal axis can also be understood as time. It can be seen that all passes P1-P3 except the last pass P4 are wavy or corrugated. The longitudinal motion (i.e., the Z axis motion of the threading tool during passes P1-P4) is represented by the extension of the line representing passes P1-P4 along the horizontal axis. The oscillation of the threading tool in the radial direction (i.e., the X axis direction) during passes P1-P4 is represented by Figure 5 The extension along the vertical axis (i.e., the X axis of the CNC lathe) is represented. The peripheral surface 21 is shown as a line. The radial distance from the peripheral surface to the last pass P4 is shown as D11. The radial distance D11 can be understood as the radial distance between the thread root and the peripheral surface 21.

[0131] During the first pass P1, the thread machining tool radially oscillates between a first radial distance D1 and a second radial distance D2 from the last pass P4. The difference or radial distance between the first radial distance D1 and the second radial distance D2 is the peak-to-peak amplitude of the oscillation during the first pass P1. The oscillation is at a first frequency F1. It has been shown that the period or time period of the first pass P1 is B1. It has been shown that during the first pass P1, the thread machining tool disengages from cutting and enters cutting once at each oscillation. In other words, for each oscillation, the trajectory of the first pass P1 intersects the outer peripheral surface 21 of the metal workpiece twice, that is, twice per time period. The time when the line representing the first pass P1 is above the line representing the outer peripheral surface 21 is the time when the cutting edge is not active during the first pass P1, that is, the idle time.

[0132] During the second pass P2, the thread machining tool radially oscillates between the third radial distance D3 and the fourth radial distance D4 from the last pass P4. The difference or radial distance between the third radial distance D3 and the fourth radial distance D4 is the peak-to-peak amplitude of the oscillation during the second pass P2. The period or time period of the second pass P2 is B2. Period B2 represents one rotation of the metal workpiece. Period B2 is different from period B1. More specifically, period B2 is less than period B1. In other words, the oscillation frequency during the second pass P2 is higher than the oscillation frequency during the first pass P1. For each period, the trajectory of the second pass P2 intersects the first pass twice. The trajectory of the second pass P2 (i.e., the path traced by the thread machining tool 1 during the second pass P2) does not intersect the outer peripheral surface 21 of the metal workpiece 19. The time when the line representing the second pass P2 is higher than the line representing the first pass P1 is the time when the cutting edge is not active during the second pass P2, that is, the idle time. In other words, during the second pass P2, there is one air cut for each rotation of the metal workpiece 19. During the penultimate pass as the third pass P3, the thread machining tool radially swings between the fifth radial distance D5 and the sixth radial distance D6 from the last pass P4. The sixth radial distance D6 is zero or less than half of the difference between the first radial distance D1 and the second radial distance D2, preferably less than 0.10 mm. The cutting depth reaching zero or close to zero increases the possibility of short chips during the subsequent last pass (i.e., during the fourth pass P4). The difference or radial distance between the fifth radial distance D5 and the sixth radial distance D6 is the peak-to-peak amplitude of the swing during the third pass P3. The period or time period of the third pass P3 is B3. Period B3 is different from period B2. More specifically, period B3 is greater than period B2. In other words, the swing frequency during the second pass P2 is higher than the swing frequency during the third pass P3. Period B3 is the same or substantially the same as period B1. For each cycle, the trajectory of the third pass P3 intersects the trajectory of the second pass P2 twice. The time when the line representing the third pass P3 is above the line representing the second pass P2 is the time when the cutting edge is not active during the third pass P3, that is, the idle time. Figure 5, it can be seen that the third radial distance D3 is greater than the fourth radial distance D4; the first radial distance D1 is greater than the third radial distance D3; the second radial distance is greater than the fourth radial distance D4; the fifth radial distance D5 is greater than the sixth radial distance D6; the fifth radial distance D5 is less than the third radial distance D3, and the sixth radial distance D6 is less than the fourth radial distance D4. During the first pass P1, the first cutting edge and the second cutting edge cut simultaneously, resulting in a chip with a V-shaped cross-section. During the second pass P2, if the feed direction is from right to left, the first cutting edge enters the cutting from the lowest point of the second pass P2 to the left of the lowest point until it is out of the cutting. When entering the cutting, the second cutting edge is in cutting and remains in cutting until the second pass reaches its lowest point, which corresponds to D4, where the first cutting edge enters the cutting. Therefore, as long as the turning tool is in cutting during the second pass P2, the first cutting edge and the second cutting edge are alternately active or in cutting. During the third pass P3, the first cutting edge enters the cutting from the right point corresponding to D6 until the point along the trajectory of the third pass P3 is vertically aligned with the right crest of the trajectory of the second pass P2, at which point the second cutting edge enters the cutting. Thereafter, the turning tool is disengaged from the cutting. When entering the cutting, the first cutting edge is active and remains active until the point along the trajectory of the third pass P3 is vertically aligned with the left crest of the trajectory of the second pass P2, at which point the second cutting edge enters the cutting.

[0133] Reference now Figure 6 . Figure 6 Shown with Figure 5 The difference is that in Figure 6 There are six passes P1-P6 in Figure 5 Only four passes are shown in FIG. The first three passes P1-P3 are Figure 5. During the fourth pass P4, the thread machining tool swings between the seventh radial distance D7 and the eighth radial distance D8, wherein the radial distance is the radial distance from the last pass as the sixth pass P6. The radial distance between the seventh radial distance D7 and the eighth radial distance D8 is the peak-to-peak amplitude of the swing during the fourth pass P4. For each cycle, the trajectory of the fourth pass P4 intersects the trajectory of the third pass P3 twice. The period of the fourth pass P4 is B4, which is different from the period B3 of the third pass P3. The period B4 of the fourth pass P4 is equal to or substantially equal to the period B2 of the second pass P2. During the penultimate pass as the fifth pass P5, the thread machining tool swings radially between the ninth radial distance D9 and the tenth radial distance D10 from the last pass P6. The tenth radial distance D10 is zero or less than half of the difference between the first radial distance D1 and the second radial distance D2, preferably less than 0.10 mm. A cutting depth of zero or near zero reached during the penultimate pass (i.e., the fifth pass P5) increases the likelihood of short chips during the subsequent final pass (i.e., during the sixth pass P6). The difference or radial distance between the ninth radial distance D9 and the tenth radial distance D10 is the peak-to-peak amplitude of the oscillation during the fifth pass P5. The period or time period of the fifth pass P5 is B5. Period B5 is different from period B4. More specifically, period B5 is less than period B4. In other words, the oscillation frequency during the fifth pass P5 is higher than the oscillation frequency during the fourth pass P4. For each cycle, the trajectory of the fifth pass P5 intersects the trajectory of the fourth pass P4 twice. The time when the line representing the fifth pass P5 is higher than the line representing the fourth pass P4 is the time when the cutting edge is not active during the fifth pass P5, i.e., the idling time.

[0134] During the last pass, which is the sixth pass P6, the threading tool moves without oscillation in the radial direction (ie, the X direction).

Claims

1. A CNC lathe machining method for forming a predetermined thread in a metal workpiece (19), comprising the following steps: providing a metal workpiece (19), Provide thread machining tools (1), The thread machining tool (1) comprises a first cutting edge (11) and a second cutting edge (12). Rotating the metal workpiece (19) around its rotation axis (A1); Moving the thread machining tool (1) in a longitudinal (Z) direction through a set of passes (P1-P6), wherein the longitudinal (Z) direction is parallel to or coincides with the rotation axis (A1); During a first pass (P1), the thread machining tool (1) is oscillated at a first frequency in a radial (X) direction so that the thread machining tool (1) moves between a first radial distance (D1) and a second radial distance (D2), wherein the first radial distance (D1) is greater than the second radial distance (D2), During the second pass (P2), the thread machining tool (1) is oscillated at a second frequency in the radial (X) direction so that the thread machining tool (1) moves between a third radial distance (D3) and a fourth radial distance (D4), wherein the third radial distance (D3) is greater than the fourth radial distance (D4) and less than the first radial distance (D1), wherein the fourth radial distance (D4) is less than the second radial distance (D2), and wherein the third radial distance (D3) is greater than the second radial distance (D2), and during the last pass (P4, P6), the tool is moved without oscillation in the radial (X) direction, It is characterized in that The method comprises the further steps of: setting the second frequency to be different from the first frequency, and The second tool pass (P2) is arranged so that for each swing of the second tool pass (P2), the trajectory of the second tool pass (P2) intersects the trajectory of the first tool pass (P1) two or more times. 2 . The machining method according to claim 1 , comprising the further step of setting the second frequency to be twice as large as the first frequency or substantially twice as large as the first frequency.

3. The machining method according to any one of the preceding claims, comprising the further step of setting the phase of the swing during the second pass (P2) so that the fourth radial distance (D4) coincides with the first radial distance (D1) and the second radial distance (D2) along the Z axis.

4. The machining method according to any one of claims 1 to 2, comprising the following further steps: during a third pass (P3), causing the thread machining tool (1) to oscillate at a third frequency in the radial (X) direction, so that the thread machining tool (1) moves between a fifth radial distance (D5) and a sixth radial distance (D6), wherein the fifth radial distance (D5) is greater than the sixth radial distance (D6) and less than the third radial distance (D3), and wherein the sixth radial distance (D6) is less than the fourth radial distance (D4), setting the third frequency to be different from the second frequency, The fifth radial distance (D5) is set to be greater than the fourth radial distance (D4), The third knife path (P3) is arranged so that for each swing of the third knife path (P3), the trajectory of the third knife path (P3) intersects the trajectory of the second knife path (P2) twice or more, And the frequency of the third knife pass (P3) is set to be lower than the frequency of the second knife pass (P2) or lower than the frequency of the first knife pass (P1).

5. The machining method according to any one of claims 1-2, comprising the further step of setting the last oscillating pass (P3, P5) to have a higher frequency than all previous oscillating passes (P1-P2; P1-P4).

6. The machining method according to any one of claims 1-2 comprises the further step of setting the frequency of all oscillating passes (P2-P3; P2-P5) after the first pass (P1) to be less than or equal to four times the frequency of the first pass (P1).

7. The machining method according to any one of claims 1 to 2, comprising the further step of: during the penultimate pass (P3, P5), oscillating the thread machining tool (1) between an outer radial distance (D5, D9) and an inner radial distance (D6, D10) from the last pass (P6), wherein: The inner radial distance (D6, 10) is zero or less than half of the difference between the first radial distance (D1) and the second radial distance (D2).

8. The machining method according to any one of claims 1-2, comprising the further step of setting the frequency of the penultimate tool pass (P3, P5) to be higher than the frequency of the first tool pass (P1) and higher than the frequency of the second tool pass (P2).

9. The machining method according to any one of claims 1 to 2, in, A difference between the first radial distance (D1) and the second radial distance (D2) is different from a difference between the third radial distance (D3) and the fourth radial distance (D4).

10. The machining method according to any one of claims 1 to 2, in, A difference between the first radial distance (D1) and the third radial distance (D3) is smaller than a difference between the third radial distance (D3) and the second radial distance (D2).

11. The machining method according to claim 4, in, The third frequency is the same as or substantially the same as the first frequency.

12. The machining method according to claim 4, in, The second radial distance (D2) and the sixth radial distance (D6) coincide or substantially coincide in the longitudinal (Z) direction.

13. The machining method according to any one of claims 1 to 2, in, For all passes (P1-P6), the threading tool (1) moves in the longitudinal (Z) direction at a longitudinal feed rate of 0.5-3.0 mm / revolution.

14. The machining method according to any one of claims 1 to 2, in, The thread machining tool (1) comprises a thread machining blade (2) and a blade seat (6). The thread machining insert (2) has a top surface (3) and a bottom surface (4). wherein the top surface (3) and the bottom surface (4) are connected via a side surface (5), wherein the first cutting edge (11) and the second cutting edge (12) are formed at a boundary between the top surface (3) and the side surface (5), Therein, the bottom surface (4) comprises an engagement means (7) for contacting a corresponding structure (8) formed in the insert seat (6).

15. A computer program product having instructions which, when executed by a CNC lathe, cause the CNC lathe to perform the steps of any one of claims 1-14.

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