METHOD FOR MACHINING GEAR WORKPIECES

Description

Field of the invention

[0001] The subject of the invention is a method for (gearing) machining of gear workpieces.

[0002] There are various processes for cutting bevel gears. Milling processes for manufacturing bevel gears can be characterized as follows: Indexing processes ∘ as a single-part process (also called intermittent indexing process, single indexing process, or face milling) and ∘ as a continuously indexing process; rolling ∘ as a generating process and ∘ as a plunging process without rolling. Examples of processes for chip-generating machining of gear workpieces are described in DE 10 2012 012617 A1, DE 10 2005 058536 A1, EP 2 570 217 A1, and US 2015 / 038058 A1.

[0003] A distinction is also made between completing and semi-completing processes, which depend on the number of cuts required to create the final geometry. In completing, one tool cuts with one machine setting, while in semi-completing, a tool cuts with two separate machine settings. In semi-completing, one machine setting is used for cutting the concave flanks and the other for cutting the convex flank. There are also single-sided cutting processes, in which one tool cuts the concave flank with one machine setting, and another tool cuts the convex flank with different machine settings.

[0004] These attributes of the above-mentioned processes can be combined with each other and are also predominantly used in industry.

[0005] The single-part completing method and the continuous completing method are commonly used. Fig. 1A Examples of basic principles of a single part process are shown. To be specific, this is a single part completing process. The single part completing process is in Fig. 1Ashown schematically. For the sake of simplicity, the joint rolling motion of the bevel gear workpiece 11 and the cutter head 20, which occurs much slower than the rotation ω1 of the cutter head 20, is not shown. This illustration is essentially a snapshot of the rolling process. The outer cutting edges 21.a and the inner cutting edges 21.i of the cutter head 20 perform a continuous circular arc-shaped movement. The rotational movement of the cutter head 20 (here counterclockwise) is indicated by an arrow labeled ω1. The pivot point of the tool spindle, or rather the intersection point with the plane of the drawing, is identified by reference numeral 102. To produce further tooth gaps, the cutter head 20 is retracted and the bevel gear workpiece 11 is rotated by a pitch angle (called pitch rotation). The step-by-step further rotation (here clockwise) is shown in Fig. 1Aindicated by arrows a, b, and c. Thus, one tooth gap is always created at a time.

[0006] Extended-epicycloidal (also called extended-epicycloidal) bevel gears are manufactured using a continuous indexing process (also called continuous hobbing, continuous indexing process, or face hobbing). A corresponding example is shown in Fig. 1B shown schematically. A bar cutter head 30 is used as the tool here.

[0007] When producing the epicycloid in the continuous dividing process (see Fig. 1B) the ratio of the number of teeth to the number of threads of the bar cutter head 30 (number of cutter groups) corresponds to the ratio of the radius of the base circle G and the radius of the rolling circle R. One speaks of an extended epicycloid if the nominal cutter head radius on which the cutting edges of the bar cutters sit is greater than the radius of the rolling circle R. In this continuous indexing process, both the cutter head 30 and the workpiece 11 rotate in a temporally coordinated movement sequence. The indexing is therefore continuous and all tooth gaps are created more or less simultaneously. The rotary movement of the cutter head 30 is symbolized here by ω2, while the rotary movement of the workpiece 11 is symbolized by ω3. This is made up of the required indexing movement and the rolling movement. Fig. 1B shows a snapshot of the rolling process. Fig. 1BIt can be seen that the bar knives 33.a, 33.i of the bar knife head 30 are typically arranged in pairs (in groups, with two knives per group). The arrangement of the bar knives 33.a, 33.i is not concentric along a nominal circle N, as in the bar knife head 20 of the Fig. 1A . In Fig. 1B It can be seen that the rolling circle R of the cutter head 30 rolls along the base circle G of the workpiece 11. M here denotes the center of the cutter head 30 and Z1 denotes the flight circle radius.

[0008] The Figures 1A and 1B The processes shown can also be used as immersion processes for the production of ring gears if they are carried out without rolling.

[0009] Furthermore, there are various process options for implementing the aforementioned methods. For example, there are single rolling, plunge rolling, double rolling, and others. A wide variety of variations can be used by combining rolling and plunge passes, as well as the start and end values and speed profiles.

[0010] It is based on the Figures 1A and 1B It is easy to see that the kinematics of these processes can be very complex, as several movement sequences are coordinated with one another.

[0011] You can Figures 1A and 1B It can also be seen that, depending on the snapshot, several knives may be engaged in cutting operations. This can lead to dynamic load changes.

[0012] Fig. 1Cshows a schematic sectional view of a first machining phase of an exemplary individual part semi-completion process according to the prior art. During this first machining phase, a left flank 53f of a bevel gear workpiece 11 is finish-toothed, and simultaneously a right flank 54v is pre-toothed. In the first machining phase, the active area 26 of a bar cutter is in a first relative position RP1. At the moment shown, a portion of the outer cutting edge 21.a, a portion of the inner cutting edge 21.i, and the tip cutting edge 21.k are being machined. Those portions of the cutting edges 21.a, 21.i, and 21.k that are being machined are highlighted by dotted lines.

[0013] Fig. 1Dshows a schematic sectional view of a second machining phase of the exemplary single-part semi-completion process, according to the prior art. During this second machining phase, the right flank 54f of the bevel gear workpiece 11 and a portion of the gap base 114 are finished. At the moment shown, part of the outer cutting edge 21.a and the tip cutting edge 21.k are being machined. The inner cutting edge 21.i is not used.

[0014] You can also use the Figures 1C and 1D It should be noted that, depending on the machining phase, different areas of the cutting edges may be engaged in cutting operations. Changing machining phases can also lead to dynamic load changes.

[0015] The schematic representations of the Figures 1A to 1Dare only partially suitable for illustrating the complexity of dynamically changing loads. In practice, the relationships are considerably more complex. Dynamically changing loads depend on numerous factors. Among other things, the chip thickness, the number of cuts per unit of time, the cutting speed, the rigidity of the gear cutting machine and tool, the rigidity of the cutting part of the gear cutting tool blades, the shape and orientation of the cutting edges of the cutting part of the gear cutting tool blades, as well as the material properties (such as the machinability of a material) of the gear workpiece can play a role, to name just a few of the influencing factors.

[0016] Added to this is the fact that suppliers are striving to increase the productivity of the processes described. One of the focuses is increasing cutting speed. This is placing increasing demands on the materials of the gear cutting tools and on tool life. Cutter head systems are being used more and more frequently because they offer greater flexibility.

[0017] Cutter heads are the most commonly used tool type. Depending on the cutter head type and process, these can be bar cutters, profile cutters, or cutters with cutting inserts. For example, bar cutters are arranged in so-called cutter groups. A cutter group can consist of three cutters (internal cutter, center or head cutter, and external cutter), two cutters (internal and external cutter), or one cutter (full cutter or internal or external cutter).

[0018] Details of the exemplary cutter head system are shown in the Figures 2A, 2B and 2C Since this is a prior art cutter head 20, the same reference numerals are used here.

[0019] A corresponding knife head 20 can, for example, carry several bar knife groups with at least one inner knife 21.i and one outer knife 21.a per knife group, as already described in Fig. 1A shown.

[0020] The knife head 20 of the Figures 2A, 2B and 2C can, for example, carry several bar knives 23, each with an inner cutting edge 21.i and an outer cutting edge 21.a per bar knife 23, as in Fig. 2A Unlike in the Figures 1C and 1D , the active area 26 of the bar blade 23 has an asymmetrical shape.

[0021] The outer cutting edge 21.a removes, depending on the gear cutting process, e.g. material from the right flank 54v of a tooth gap 12 (see Fig. 1C) to pre-tooth this right flank 54v. At the same time, the inner cutting edge 21.i removes, depending on the tooth cutting process, e.g. material from the left flank 53f of the tooth gap 12 in order to finish tooth cutting this left flank 53f (see Fig. 1C ).

[0022] In a subsequent process step, the outer cutting edge 21.a can then remove further material from the right flank 54v of the tooth gap 12 (see Fig. 1D ) to complete the toothing of this right flank 54v. The finished toothed flanks are designated by the reference symbols 53f and 54f.

[0023] In order to be able to remove material from the flanks of a tooth gap 12, the gear cutting machine in which the cutter head 20 is used specifies appropriate machine settings, as already mentioned.

[0024] Based on the Figures 2A - 2CFurther details of the exemplary cutter head 20 are explained below. These are merely exemplary details.

[0025] A bar cutter 23 can comprise a shaft 25, which is secured in a receiving opening of a base body 22 of the cutter head 20. Reference numeral 27 denotes the cutting face of the bar cutter 23. The cutting face 27 is the surface of the active area 26 over which the chips run during machining. Reference numeral 28 denotes the head clearance surface, and reference numerals 28.a, 28.i denote the two lateral clearance surfaces. Furthermore, a head cutting edge 21.k is provided.

[0026] In principle, the individual surfaces and the angles between the surfaces of the active area 26 are defined by the assumed cutting direction and the feed direction of the gear cutting tool. The basic terms can be found, for example, in the DIN standard DIN 6581 "Terms of Machining Technology - Reference System and Angle on the Cutting Part of the Tool," Beuth Verlag, Berlin, 1985. However, other definitions and reference systems can also be used.

[0027] Strictly speaking, the 3-dimensional geometry of the cutting edge(s) of the active area 26 is primarily defined by the 3-dimensional geometry of the tooth gaps to be milled on the gear workpiece and by the process kinematics. Therefore, there are corresponding limits to the design / modification of the 3-dimensional geometry of the cutting edge(s).

[0028] The NC controls of modern gear cutting machines are sometimes designed to slowly accelerate a gear cutting tool, such as a bar cutter head, or to follow a predetermined acceleration profile as the tool plunges into the gear workpiece material. This can, for example, prevent sudden load changes or reduce their negative effects on the tool and workpiece. This can sometimes increase tool life.

[0029] In addition, (software) modules designed to interact with the NC control of a gear cutting machine are increasingly being used. Such a module can, for example, monitor and control the power consumption of an axis drive (e.g., the rotary drive of the tool spindle). This approach assumes that the power consumption increases proportionally with the load acting on the gear cutting tool. To prevent load peaks on the gear cutting tool, for example, such a module can temporarily throttle the drive's power supply.

[0030] Despite these measures, significant tool wear or even premature failure of a gear cutting tool may occur, or unexpected vibrations may occur during gear cutting, for example.

[0031] It is therefore an object of the invention to provide a method and a device to prevent premature tool wear or even failure of a gear cutting tool and / or to prevent vibrations that can have an influence on the surface quality of the gears.

[0032] It is also an object of the invention to enable an optimization of the use of the tool, whereby the term "optimization" is not to be understood in the sense of a mathematical optimization, but in the sense of a technical optimization or change.

[0033] The invention is based on an approach that is intended to make it possible to control the relative force acting on the cutting edges of a gear cutting tool.

[0034] This approach should make it possible, in at least some of the embodiments, to prevent excessive forces from occurring momentarily and / or locally at individual cutting edges.

[0035] Furthermore, at least some of the embodiments should allow the tool, or rather the tool's cutting edges, to be used as productively as possible without exceeding any limit values at the cutting edges. This approach allows chip-generating machining to be carried out as quickly as possible without exceeding any limit values or leaving any boundary areas.

[0036] The present invention relates to the machining (also called gear cutting) of a gear workpiece with a cutting tool that comprises at least two geometrically defined cutting edges.

[0037] The method of the invention, in all or at least some of the embodiments, is designed for chip-generating (gear cutting) machining of a gear workpiece in a machine with a cutting tool comprising at least two geometrically defined cutting edges, wherein the cutting edges produce material in chip form on the gear workpiece during the chip-generating machining. Chip-generating machining is defined by process parameters, and the method of the invention comprises the following steps: (1) Carrying out a computer-aided analysis of the generation of chips at the cutting edges of the cutting tool, (2) Carrying out a computer-aided determination of relative forces that will occur when generating chips at the cutting edges of the cutting tool, (3) Optimizing the chip-generating machining to prevent the relative forces from exceeding a predetermined limit value or reaching a limit range, wherein, as part of the optimization, adapted process parameters are provided by adjusting at least one of the process parameters, and (4) Carrying out the chip-generating machining (V6) of the gear workpiece (11) with the adapted process parameter(s).

[0038] In all embodiments, the at least two geometrically determined cutting edges can be arranged on a common knife or on different knives.

[0039] The method of the invention is divided in all, or at least in some of the embodiments, into preparatory steps (1) - (3) and into a step (4) which serves for the actual chip-generating machining of the gear workpiece.

[0040] In at least some of the embodiments, steps (1) and (2) can be carried out partially overlapping or even simultaneously.

[0041] In order to be able to plan the chip-generating machining of the gear workpiece and to subsequently carry out the chip-generating machining in a controlled manner, the relative force effect can be defined, depending on the approach and design, as force per unit length of a cutting edge, as torque per unit length of a cutting edge, as force per unit volume of a cutting edge, as torque per unit volume of a cutting edge, or as relative force effect depending on the material of the blade.

[0042] In order to be able to make a statement about the relative force acting on the cutting edges of the gear cutting tool, according to the invention, in part or in all embodiments of the invention, the process forces in the preparatory steps (1) - (3) are determined analytically (e.g. based on systematic investigations and their evaluation), which act on the various cutting edges of the active area of a blade of the gear cutting tool during the cutting process.

[0043] Thus, in all embodiments, it is a matter of a relative quantity (e.g. a force or a torque) which is related in some way to a cutting edge of the gear cutting tool.

[0044] In at least some of the embodiments, the forces leading to shearing of the gear workpiece material are determined in the preparatory steps (1) - (2) for chip formation on the gear workpiece. For example, a mechanistic model can be used that depicts the formation of shear planes and / or shear zones. This means that in this case, the shear planes and / or shear zones are modeled by modeling the forming process.

[0045] In at least some of the embodiments, a linear relationship between the chip thickness and the corresponding cutting force is assumed in the preparatory steps (1) - (2) for the chip formation on the gear workpiece, which helps to reduce the effort required for analytically determining the process forces.

[0046] In at least some of the embodiments, a potential model or an exponential model can also be used in the preparatory steps (1) - (2) for chip formation on the gear workpiece.

[0047] When analyzing and / or modeling the forming process or when using a linear, potential or exponential model, one can, for example, rely on existing models and / or data, or one's own models and / or data can be used and / or one's own systematic investigations and their evaluations can be carried out.

[0048] Since there are currently no generally valid analytical formulas for modeling the forming process during bevel gear milling, and since the kinematic conditions can change significantly during bevel gear milling, the milling of bevel gears according to the invention can be broken down into individual process steps (referred to here as segmentation) for better analytical investigation and evaluation in all embodiments. For each of these process steps (also referred to here as segments), the relative cutting forces acting on individual cutting edges of the active area, or acting on shorter sections of the individual cutting edges, can then be analytically determined.

[0049] If the method of the invention results in a force being applied at at least one point on at least one of the cutting edges of the gear cutting tool, which is above a limit value, which reaches or leaves a limit range, the procedure may provide for / trigger one or more of the following reactions: Issuing a warning (visual and / or acoustic); generating a (graphic) display on a screen, preferably indicating at least that location of the at least one cutting edge at which excessive force is expected; sending a message (e.g., to a mobile system or via a network); starting a (new) design routine in order to be able to change at least one process parameter of the machining process.

[0050] Since the process can calculate the expected force application using process simulation and chip analysis, a software module can be provided that, in the event of an expected local overload, determines which process parameters lead to this local overload. Once these process parameters have been identified, the software can suggest changes in an optional step. In this case, the user can be prompted to accept a suggested change. The steps are then preferably repeated with the modified process parameter(s). At the end of the corresponding optimization, the process then branches off to the machining of the gear workpiece.

[0051] For the purposes of this description and claims, process parameters include, among others, the following quantities, parameters and values: Cutting speed, and / or feed rate, and / or plunge speed, and / or roll speed, and / or angular speed(s) in the machine, and / or the speed of other linear movements in the machine, and / or type of interpolation of axis movements of the machine, and / or pressure, and / or acceleration(s).

[0052] For the purposes of this description and claims, process parameters also include controlled variables and / or control parameters. The cutting edge geometry of the knife(s) is also considered a process parameter, such as the cutting edge position, wedge angle, rake angle, clearance angle, and cutting edge preparation.

[0053] For the purposes of the present description and claims, the choice of the cutter head and / or the cutter head pitch, the material of the cutters and / or the choice of the cutting process (e.g., immersion rolling instead of rolling in) are also considered as process parameters.

[0054] If it results from the method of the invention that a force should be applied at at least one location on at least one of the cutting edges of the gear cutting tool which, for example, is significantly below a limit value or outside a limit range, at least one process parameter of the machining process can be changed for the purpose of optimizing the method so that the force applied at the location of the affected cutting edge is closer to the limit value or within the limit range.

[0055] Since the process can calculate the expected force effect using process simulation and chip analysis, a software module can be provided that, in the event of insufficient loading of a cutting edge, determines backwards (e.g., numerically iteratively) which process parameters lead to this insufficient load. Once these process parameters have been identified, the software can suggest changes in an optional step. In this case, the user can be prompted to accept a suggested change. The steps are then preferably repeated with the modified process parameter(s). At the end of the corresponding optimization, the process then branches off to the machining of the gear workpiece.

[0056] However, there are also other cutting tools (e.g., one-piece cutter heads) that can be used in the process of the invention. Generally, these are cutting tools that comprise at least two geometrically defined cutting edges on one or two different cutters.

[0057] By using the invention, tooth flanks with high-quality surfaces can be manufactured efficiently and cost-effectively / productively, whereby the force acting on the individual cutting edges can be planned / controlled.

[0058] As a result, the use of the invention provides gears, e.g. spiral bevel gears, with high precision and high-quality surfaces, whereby the maximum possible service life of the cutting tool is utilized as far as possible.

[0059] The invention is particularly applicable to gear cutting tools in which more than one geometrically defined cutting edge is used simultaneously for cutting. In particular, all embodiments of the invention are applicable to gear cutting tools equipped with at least two profile blades, at least two bar blades, or at least two cutting inserts.

[0060] The invention makes it possible to utilize the maximum possible service life of the cutting tool by avoiding thermal and / or mechanical overloading of gear cutting tools through targeted planning.

[0061] Using the method of the invention, the expected load on the cutting edges can be determined in part or for all (time) segments of the machining process. If excessive forces are predicted, other process parameters can be selected, for example. If excessive forces are predicted, other process parameters can be selected, for example, to achieve optimization. DRAWINGS

[0062] An embodiment of the invention is described in more detail below with reference to the drawings. FIG. 1A shows a schematic illustration of a single part process according to the state of the art in order to be able to describe the basics of a single part process; FIG. 1Bshows a schematic illustration of a continuously rolling dividing process (e.g. a cyclo-palloid process), according to the state of the art, in order to be able to describe the principles of a continuous dividing process; FIG. 1C shows a schematic sectional view of a first machining phase of a semi-completing single-part process, according to the prior art, during the finish tooth cutting of a left flank and the simultaneous pre-tooth cutting of a right flank of a bevel gear workpiece; FIG. 1D shows a schematic sectional view of a second machining phase of the semi-completing single part process, according to the state of the art, during the finish toothing of the right flank of the bevel gear workpiece of the Fig. 1C ; FIGS. 2A-2C show details of an exemplary ARCON cutter head from Klingelnberg, according to the state of the art; FIG. 3shows a schematic perspective view of a rake face and the three cutting edges surrounding this rake face; FIG. 4 shows a schematic flow diagram of the steps of a method of the invention; FIG. 5 shows a tabular representation of exemplary intermediate results of a method of the invention; FIG. 6 shows a tabular representation of exemplary intermediate results of another method of the invention; FIG. 7A shows a schematic perspective view of a rake face and the three cutting edges surrounding this rake face; FIG. 7B shows in the form of a schematic diagram the force acting on the three cutting edges as a function of the distance x; FIG. 7C shows a tabular representation of exemplary intermediate results of a method of the invention according to Fig. 7B . DETAILED DESCRIPTION

[0063] In order to better describe the dynamically changing loads that can occur on a gear cutting tool, the following example refers purely schematically to a cutter head system from Klingelnberg.

[0064] This is a cutter head system designed for use in a single-part gear cutting process (single-part process). The basic aspects of such a single-part process were initially explained using the Fig. 1A The invention can also be applied to a continuously dividing method, as explained above with reference to Fig. 1B explained, and apply to other processes.

[0065] In the above-described Fig. 2AThe cutting force is indicated by an arrow S (the length of the arrow is proportional to the magnitude of the force, and the orientation indicates the direction). The cutting force S is essentially perpendicular to the rake face 27. This cutting force S is a vector that is a function of time t; therefore, the reference symbol S(t) is used here.

[0066] Since this is about the force acting on the cutting edges of tool 20, Fig. 3 The cutting force S is broken down into three small arrows or vectors Ki, Ka, and Kk, which act in opposite directions. A force distribution is performed here to allow for a more precise assessment of the forces acting on the individual cutting edges.

[0067] The three vectors Ki, Ka, and Kk, together with the cutting force S, form a force equilibrium in 3-dimensional space. Ki describes the sum of all partial forces acting on the inner cutting edge 21.i, Ka describes the sum of all partial forces acting on the outer cutting edge 21.a, and Kk describes the sum of all partial forces acting on the head cutting edge 21.k. However, this is only a highly simplified snapshot on the time axis.

[0068] During the gear cutting of a gear workpiece 11 with the cutting edges of tool 20, the sums of these partial forces are subject to constant change. Not only their magnitude but also their orientation can change. Furthermore, the starting points along the cutting edges can shift. The starting points are those points on the cutting edges where the sums of the respective partial forces Ki, Ka, and Kk are applied.

[0069] Since the tool 20 is rotationally driven by a tool spindle of a machine whose dimensions are known, the relative forces can always be expressed as relative torques. If the orientation and length of the cutting edges in space, as well as the distance of the relative forces from the rotational axis of the tool spindle, are known, the relative forces can be converted into relative torques.

[0070] In all embodiments, relative forces and / or relative torques can be used to assess the force acting on at least two cutting edges. Since the spindle drive of the tool spindle is powered by electricity, the current consumption of the spindle drive (or a winding of the spindle drive) per millimeter of cutting edge length can also be used in all embodiments.

[0071] In a plunging process, for example, straight tooth flanks on the gear workpiece result from the straight cutting edges of the gear cutting tool 20. In a generating process, the tooth flanks on the gear workpiece result from the envelope of numerous enveloping cuts. In this case, the movements are significantly more complex, and the forces acting on the cutting edges can only be determined with a significantly greater computational effort.

[0072] If, for example, modifications to the tooth flank topography are made when cutting gear workpieces, the corresponding relative movements of the gear cutting tool and the gear workpiece are even more complex.

[0073] Accordingly, the magnitude, orientation, and point of application of the cutting force S can also change, whereby the cutting force S, as already mentioned, forms a force equilibrium with the partial forces Ki, Ka, and Kk. The partial forces are therefore also functions of time t, as indicated by the reference symbols Ki(t), Ka(t), and Kk(t).

[0074] In all embodiments, the cutting edges can be divided into smaller sections (e.g., individual segments or points). In this case, the relative forces and / or the relative torques and / or the relative current and / or power consumptions are also divided into sections.

[0075] As mentioned at the beginning in connection with the Figures 1A - 1Ddescribed, the number of knives that are cutting at a given time can vary. This means that the total drive force (or the current consumption) of the spindle drive of the tool spindle of the tool 20 is broken down into several cutting forces S, each of which can have a different size, orientation and a different point of application on the chip surfaces 27 in use. If the gear cutting tool 20 is to be driven at a constant speed of the tool spindle despite the counter forces changing over time, for example, then the NC control of the spindle drive must constantly adjust the current. With increasing partial forces on the cutting edges, the spindle drive must respond with a greater drive torque, i.e. the current that is impressed must be increased. If the sum of the partial forces decreases, then the current must be reduced in order to reduce the drive torque and thus keep the speed constant.

[0076] The invention is based on an approach that is intended to enable the relative force acting on the cutting edges of a gear cutting tool to be controlled as precisely as possible and to identify the relationships / effects of individual process parameters.

[0077] According to the invention, the expected forces KiKa and Kk can be calculated as a function of time before the actual gear cutting.

[0078] If only one force is applied per cutting edge and if one simplifies the assumption that the forces act over the entire cutting length (which does not affect the snapshot of the Fig. 1C applies), then the relative force can be calculated by dividing the currently acting force by the absolute cutting edge length. 1000 N acting on a cutting edge with a short cutting edge length results in a significantly higher relative force than 1000 N acting on a cutting edge with a longer cutting edge length.

[0079] In all embodiments, a cutting edge-specific maximum force can be defined for each cutting edge and / or a relative, cutting edge-specific, maximum force can be defined for each cutting edge.

[0080] Thus, all embodiments involve relative sizes that are related in some way to the cutting edges of the gear cutting tool.

[0081] In order to cover the various variants of this inventive approach, these relative quantities are referred to here as relative, cutting-edge-specific force specifications or, for short, as relative, cutting-edge-specific force. This means that these relative quantities can, for example, be a (maximum) force related to a specific cutting edge, or they can be a (maximum) force related to a geometric specification (e.g., a (partial) length, (partial) area, or a (partial) volume) of a specific cutting edge. The area and volume are directly related to the (partial) length of the corresponding cutting edge. Conversion is therefore possible.

[0082] As already mentioned, torque and / or current consumption can also be used as relative quantities instead of force.

[0083] In addition, there is also a direct relationship between the force acting on a (partial) length of the corresponding cutting edge and the cutting work acting on the corresponding (partial) volume to separate a chip.

[0084] In embodiments that operate with a relative force related to a specific cutting edge, this relative force can be defined, for example, for the first blade of a tool 20 as K.i1 [N] for the inner cutting edge, K.a1 [N] for the outer cutting edge, and K.k1 [N] for the tip cutting edge. The relative force for the second blade of the same tool 20 is then defined as K.i2 [N] for the inner cutting edge, K.a2 [N] for the outer cutting edge, and K.k2 [N] for the tip cutting edge, etc. Thus, each cutting edge of each blade of a tool 20 can be assigned a relative force. The nomenclature used here is for illustrative purposes only.

[0085] If a tool 20 comprises, for example, several knife groups (e.g., an outer knife, a center cutter and an inner knife), then in all embodiments, for example, the same relative forces can be assigned to each knife of such a group.

[0086] In order to prevent temporary overloading or even the failure of a cutting edge, maximum values (as limit values) can be specified individually for each cutting edge in all designs.

[0087] The force can be expressed as an absolute value in N if the length of the respective cutting edge is a known quantity. For example, an outer cutting edge 21.a with a length of 20 mm can be assigned a maximum relative force Ka max = 2000 N (the word "relative" in this context indicates that the force is related to a specific cutting edge). This essentially corresponds to a relative, cutting-edge-specific maximum force of rK.a max = 2000 N / 20 mm = 100 N / mm.

[0088] This approach makes it possible to prevent excessive forces from occurring momentarily and / or locally at individual cutting edges during the tooth cutting of a gear workpiece.

[0089] For this purpose, depending on the approach and design, the relative force can also be defined as force per unit length of a cutting edge, as torque per unit length of a cutting edge, as force per unit volume of a cutting edge, as torque per unit volume of a cutting edge, or as current consumption per unit length of a cutting edge. To stick with the numerical example, which previously assumed a force Ka max of 2000 N, the relative force can be defined as force per unit length of this cutting edge with a maximum value of 100 N / mm (as the limit value).

[0090] Based on the Fig. 4 , which shows a flow chart in schematic form, the exemplary steps of a first embodiment of a method of the invention are described.

[0091] In all embodiments, the method can begin, for example, with the simulation (here also referred to as planning) of a gear cutting process. A first preparatory step is Fig. 4 marked with the reference symbol V1. Here, for example, the hobbing of a bevel gear workpiece can be simulated computationally (i.e., computer-aided). Suitable software (e.g., software that uses FEM) can be used to simulate the gear cutting process.

[0092] The computational (ie computer-aided) simulation in step V1 can be fed, for example, by data {D}, as in Fig. 4indicated. These data {D} can be taken from a memory 150. The data {D} can be provided beforehand, for example, as part of a design of the gear workpiece to be machined, by a combination of computer and software 151. However, the data {D} can also be transferred directly (without (intermediate) storage) to step V1 by a combination of computer and software 151.

[0093] In all embodiments, the computational (i.e. computer-aided) simulation in step V1 can be fed, for example, with information / data on the 3-dimensional definition of the gear workpiece, referred to here as WG.

[0094] In all embodiments, the computational (i.e., computer-aided) simulation in step V1 can be fed, for example, with information / data for the 3-dimensional definition of the gear cutting tool 20 and / or the relevant cutting edges, referred to here as VG. The information / data can, for example, describe the geometry of the cutter head 20 equipped with bar cutters 23 and the cutting edge geometry (e.g., as a 2- or 3-dimensional polygon).

[0095] In all embodiments, the computational (i.e. computer-aided) simulation in step V1 can be fed, for example, with information / data for defining the machine and / or the kinematics, referred to here as KG.

[0096] These quantities are collectively referred to as process parameters.

[0097] In Fig. 4 It is indicated that the simulation in step V1 can be fed with information / data WG and / or VG and / or KG.

[0098] In a subsequent step V2, for example, a type of segmentation can be performed. Segmentation refers to a subprocess that allows the gearing process to be broken down into time windows and / or length segments and / or volumetric size segments.

[0099] In Fig. 4 The result of segmentation V2 is represented by several squares, labeled Δ1 to Δn. Here, n denotes the number of segments. The larger the number n of segments, the more accurate the statements regarding chip formation and the forces occurring at the individual sections of the cutting edges of the active area 26 can be.

[0100] The more complex the gear cutting process, i.e., the more dynamic load changes are expected during gear cutting, the more segments Δn (e.g., time windows and / or length segments and / or volumetric size segments) should be used. A gear cutting process subject to only minor load fluctuations can be defined with sufficient precision using a few time windows, length segments, or volumetric size segments. A gear cutting process subject to numerous load fluctuations, however, should be defined using more time windows, length segments, or volumetric size segments.

[0101] For each of the n segments, in all embodiments, for example, the geometry of the chips to be expected can be determined mathematically. The chip geometry can be determined, for example, using a penetration calculation, whereby this penetration calculation describes the movement of the cutting edges of the active region 26 through the material of the gear workpiece. During the penetration calculation, for example, the current tool envelope can be calculated for each of the n segments based on the cutting edge geometry and the kinematics by subtracting two surfaces or bodies. The geometry of the chips, for example, can be calculated from the current tool envelope. As part of the penetration calculation, it is also possible, for example, to calculate for each of the n segments which area of the workpiece is machined by which (longitudinal) section of the tool cutting edges.The corresponding length specifications are required if the method of the invention takes into account the force effect related to the cutting length currently in use (e.g. in N per millimeter).

[0102] In a subsequent step V3, a computer-assisted chip analysis is carried out.

[0103] If more than one chip is created in one of the n segments (e.g., due to chip breakage), an average of all chips for this segment can be calculated as part of the chip analysis V3. This provides the geometry of a mean fictitious chip for the corresponding segment. The geometry of the mean fictitious chip can then be used in the subsequent steps.

[0104] If more than one chip is generated in one of the n segments, a statistical evaluation of all chips for this segment can be performed as part of the V3 chip analysis. This provides the geometry of a statistical, fictitious chip for the corresponding segment. The geometry of the statistical, fictitious chip can then be used in the subsequent steps.

[0105] If more than one chip is generated in one of the n segments, a maximum value analysis can be performed as an alternative within the scope of chip analysis V3, for example, to determine the largest (thickest) chip for the corresponding segment. The geometry of the largest (thickest) chip can then be used in the subsequent steps. The maximum value analysis assumes that the greatest forces occur at the cutting edges of the active area 26 when generating the largest (thickest) chip.

[0106] The Span Analysis V3 can be used in all versions, as in Fig. 4 As indicated, it can be implemented as a functional block or module, whereby this functional block or module evaluates the geometry of the chips of the n segments. If no segmentation of geometric variables is performed, then the functional block or module can evaluate the geometry of the chips of the cutting edges.

[0107] In all embodiments, the chip analysis V3 can be based on a calculation, evaluation or observation of the geometry of the chips (optional step V3.2 in Fig. 4 ). The geometry is then used in a subsequent step (e.g. sub-steps V4.1, V4.2 in Fig. 4 ) a statement is made about the forces that occur at the cutting edges of the active area 26.

[0108] Limit values and / or limit ranges can be specified (these can be loaded from a memory, for example), or a user can be prompted to enter one or more limit values (e.g. rK max ), which can be Fig. 4 indicated by the optional step V4.3.

[0109] In all embodiments, the chip analysis V3 can also be based on a calculation, evaluation or observation of the chip formation process (optional step V3.1 in Fig. 4 ). In a subsequent step, based on the chip formation process, a statement is made about the forces (e.g. sub-steps V4.1, V4.2 in Fig. 4 ) that occur at the cutting edges of the active area 26.

[0110] In all embodiments, the chip analysis V3 can also comprise n parallel functional blocks or modules, whereby each of the functional blocks or modules evaluates the geometry of the chips of one of the cutting edges or one of the n segments in parallel.

[0111] In order to be able to make a statement about the relative force acting on the cutting edges of a gear cutting tool (e.g. sub-step V4.1, V4.2 in Fig. 4 ), in some or all embodiments of the invention, the process forces are determined analytically (e.g. from the geometry of the chips V3.2 and / or from the chip formation process V3.1) which act on the various cutting edges of the active area 26 of a knife during tooth cutting.

[0112] In order to be able to make a statement about the relative force acting on the cutting edges of a gear cutting tool (e.g. sub-steps V4.1, V4.2 in Fig. 4), in some or all embodiments of the invention, the process forces are determined dynamically analytically, ie the relative movements changing with time t are included in the analysis.

[0113] In at least some of the embodiments, for chip formation (optional step V3.1 in Fig. 4 ) on the gear workpiece, the forces that lead to shearing of the gear workpiece material are determined. For example, a mechanistic model can be used that depicts the formation of shear planes and / or shear zones. In this case, the approach involves modeling the forming process.

[0114] In at least some of the embodiments, for chip formation (optional step V3.1 in Fig. 4) on the gear workpiece, a linear relationship between the chip thickness and the corresponding cutting force is assumed, which helps to reduce the effort required to analytically determine the process forces.

[0115] In at least some of the embodiments, for chip formation (optional step V3.1 in Fig. 4 ) a potential model or an exponential model can also be used on the gear workpiece.

[0116] When modeling the forming process or using a linear, potential, or exponential model, one can, for example, rely on existing models and / or data, or one can apply one's own models and / or data and / or analyses. The data can, for example, be defined in advance based on empirical values and / or determined experimentally and / or empirically and / or analytically.

[0117] As in Fig. 4As shown in the example, the determination of the forces can optionally be divided into two substeps, V4.1 and V4.2. This division has been made here only for clarity. The corresponding forces can also be determined in a single step.

[0118] After the chip analysis in step V3, the absolute forces that occur during machining of the gear workpiece can be determined (substep V4.1). These forces can be determined, for example, as a function of time, or the forces can be determined for each of the segments n.

[0119] From these forces, the relative forces can then be determined in substep V4.2. The relative forces are characterized by the fact that, as already described, they are related to the cutting edges in use.

[0120] A possible nomenclature for the designation of relative forces has already been described previously, which can be used here. This nomenclature is intended only as an example and is intended to better explain the relationships.

[0121] In Fig. 5 The result of sub-step V4.2 is presented using n tables (each of these tables reflects the relative forces that occur for one of the segments 1 - n). Each of the n tables has the designation of the affected segment (e.g., Δ1) in the top row. This is followed by three columns: K.i1, K.a1, K.k1, where K.i1 indicates the relative force in [N] acting on the inner cutting edge 21.i, K.a1 indicates the relative force in [N] acting on the outer cutting edge 21.a, and K.k1 indicates the relative force in [N] acting on the tip cutting edge 21.k.

[0122] As in Fig. 5As can be seen, the n tables include a bottom row in which an individual maximum force can be specified as a limit value in [N] for each of the three cutting edges 21.i, 21.a, 21.k. In the present numerical example, 2000N was specified as the upper limit value for each of the cutting edges 21.i, 21.a for each of the n segments. For the head cutting edge 21.k, 500N was specified as the upper limit value for each of the n segments.

[0123] An analysis of these numerical examples yields the following picture. During the first segment, n=1, all forces are significantly below 2000 N or 500 N. However, during the second segment, n=2, the force on the outer cutting edge 21.a exceeds 2000 N by 500 N. The corresponding field in the table is highlighted in gray. During the last segment, n, all forces are again below 2000 N or 500 N.

[0124] The determination of the relative forces (step V4.2) is preferably carried out in a computer-aided manner in all embodiments in order to be able to assess the expected forces before the actual machining of the gear workpiece with the cutting edges of a tool.

[0125] In the example shown, step V4.2 would indicate or inform the machine operator or another user that an inadmissibly high force may be applied, for example, to the outer cutting edge 21.a during the second segment n=2.

[0126] The operator / user can now decide whether to proceed with machining the gear workpiece in the planned form, or whether to change the specifications for the process simulation, which was designated as step V1. For this purpose, the process can, for example, return to the combination of computer and software 151 to enable a different design and / or to specify different kinematics (e.g., with a reduced cutting depth). Selecting a different design and / or different kinematics is referred to here as adjusting the process parameters.

[0127] In Fig. 4 The calculation, evaluation, or viewing of the results of step V4.2 is designated with reference symbol V5. If all values are acceptable, or if the operator / user still wants to machine the gear workpiece in the planned shape, the gear cutting operation follows in step V6.

[0128] If at least one of the values is not okay, the procedure can be, for example, as in Fig. 4 indicated by branch 152, branch back to the interpretation.

[0129] The arrow 153 points in Fig. 5 that the procedure can generally branch here (e.g. as in Fig. 4 shown).

[0130] If the method of the invention shows that a force should be applied at at least one point on at least one of the cutting edges of the gear cutting tool that exceeds a limit value, the method can provide / trigger one or more of the following reactions: Issuing a warning (visual and / or acoustic); generating a (graphic) display on a screen, preferably indicating at least that location of the at least one cutting edge at which excessive force is expected; sending a message (e.g., to a mobile system or via a network); starting a (new) design routine in order to be able to change at least one process parameter of the machining process.

[0131] Since the method can calculate the expected force application using process simulation V1 and chip analysis V3, a software module can optionally be provided that, in the event of an expected local overload, determines backwards which process parameters lead to this local overload. Once these process parameters have been found, the software can suggest changes in an optional step (e.g., by displaying them on a screen). In this case, the user can be prompted to accept a suggested change (e.g., by pressing a key combination). Steps V1-V5 are then preferably carried out again with the changed process parameter(s). In step V5, the method then branches off to V6.

[0132] After a new design, or after a changed design, i.e. as soon as changed process parameters are available, steps V1 up to and including V5 can be carried out again.

[0133] Since the calculation of chip geometry, or rather chip thickness, during the various phases of the machining process cannot always be completely accurate, a variance in chip thickness can be taken into account in all embodiments of the invention. For example, if tests have shown that the calculated chip thickness can fluctuate by ±10%, then the currently determined values in the tables can be assigned a variance (abbreviated as "Var.") of ±10%. A corresponding numerical example is shown in Fig. 6 shown.

[0134] A look at these numerical examples of Fig. 6This results in the following diagram. During the first segment, n=1, all forces are significantly below 2000N or 500N. However, during the second segment, n=2, the force on the outer cutting edge 21.a can exceed 2000N by 750N, and the force on the head cutting edge 21.k can exceed 500N by 28N. The corresponding fields in the table are highlighted in gray. Here, the process branches back, as symbolized by arrow 153. During the last segment, n, all forces are again below 2000N or 500N.

[0135] In the Figures 7A and 7B Details of another embodiment are shown using a further example. Fig. 7A shows, analogous to Fig. 3 , Details of the active area 26, e.g., of a bar knife. The three cutting edges of this bar knife are, as already described, designated by reference numerals 21.a, 21.i, and 21.k. Fig. 7Bshows a linear arrangement of these three cutting edges 21.a, 21.i, and 21.k, with the relative force rK (e.g., in [N / mm]) plotted on the vertical axis and the distance x plotted on the horizontal axis. The force acting on the cutting edges 21.a, 21.i, and 21.k can, for example, be represented as a function of the distance x. Fig. 7B However, an example is shown in which the relative force acting at four points on the outer cutting edge 21.a and four points on the inner cutting edge 21.i is represented by one bar. The relative force acting at the head cutting edge 21.k is represented by two bars.

[0136] As segment Δ2, which can define a time window, a time point t = ta has been defined here.

[0137] The force acting on the cutting edges 21.a, 21.i and 21.k can be determined in all embodiments per segment Δn in the form of one or more discrete values (here represented by bars), or the force acting on the cutting edges 21.a, 21.i and 21.k can be determined in all embodiments per segment Δn, for example, in the form of a function of the distance x.

[0138] If the force is applied, for example, as a function of distance x, the maximum of the corresponding curves can be determined in all embodiments using a maximum value analysis. This maximum value can then be used to determine whether a specified maximum value (e.g., 100 N / mm) is exceeded.

[0139] In Fig. 7CThe result of sub-step V4.2 is presented using two tables (each of these tables reflects the relative forces that occur for one of the segments Δ1 and Δ2). Each of the two tables has the designation of the affected segment (Δ1 and Δ2) in the top row. This is followed by three columns K.a1, K.k1, K.i1, where K.i1 specifies the data set of the relative forces in [N / mm] acting on the inner cutting edge 21.i, K.a1 specifies the data set of the relative forces in [N / mm] acting on the outer cutting edge 21.a, and K.k1 specifies the data set of the relative forces in [N / mm] acting on the head cutting edge 21.k. The two data sets of the outer cutting edge 21.a and the inner cutting edge 21.i each comprise four discrete values and the data set of the head cutting edge 21.k comprises two discrete values.

[0140] A look at these numerical examples of Fig. 7CThe following diagram is obtained. During the first segment, n=1, all forces are significantly below the 100 N / mm specified as the limit value rK max. During the second segment, n=2, the relative force at the outer cutting edge 21.a exceeds 100 N / mm by a value of 10 N / mm and a value of 5 N / mm. The corresponding values in the table are highlighted in gray. Here, too, the process branches back, as symbolized by arrow 153.

[0141] Instead of tables, an interactive graphical representation is also possible in which the respective relative load is shown graphically (color-coded and height-coded) above the cutting edge (e.g. as a projection into a drawing plane or even 3D) as a function of time, rolling angle, and / or plunge path (interactively movable via a controller).

[0142] It is preferable to divide the cutting edges into length sections, as shown in the example of Figures 7A - 7CThis is illustrated by the data analysis. This allows us to determine in which length sections of a cutting edge the highest local forces currently occur.

[0143] Instead of dividing into length segments, a division into time segments can be made additionally or alternatively.

[0144] In all embodiments, the relative forces acting on the cutting edges can be calculated from the respective chip thickness. For simplicity, it can be assumed that generating the greatest chip thickness also requires the application of the greatest forces on the corresponding cutting edge. Thus, in these embodiments, a direct proportionality between chip thickness and relative force is assumed.

[0145] In all embodiments, however, the chip formation (optional step V3.1) and / or the 3-dimensional geometry of the chips (optional step V3.2) can be analyzed in more detail instead of just the chip thickness. In doing so, for example, different types of chip formation or the different zones on the chip can be observed. It is known, for example, that on a cutting wedge in front of the main cutting edge in the transition area between the rake face 27 and the adjoining flank face (e.g. the flank face 28.a) a congestion and separation zone forms. This is where the forces acting on the cutting edge are greatest, i.e. this is also where the relative force is typically at a maximum. This is the zone in which the material is separated.

[0146] In addition to the jam and separation zone, one can also consider the shear zone at rake face 27. There, the relative forces are somewhat lower than in the jam and separation zone.

[0147] When machining a gear workpiece with the cutting edges of a tool, these cutting edges are subject to a certain amount of wear. Various forms of wear are known. Based on worn tools, the types of wear that typically develop in the various length sections of the various cutting edges can be determined. If, for example, the tip cutting edge is subject to a different form of wear (e.g., cracking) than the outer and inner cutting edges (e.g., edge rounding due to abrasion), different maximum values can be specified specifically for the tip cutting edge than for the outer and inner cutting edges. This approach ultimately enables an improvement in the service life of the entire (rod) blade. Reference symbol

[0148] Gear workpiece / bevel gear / bevel gear workpiece 11 Gap between teeth 12 Cutting tool / cutter head / bar cutter head / face cutter head 20 inner cutting edge / inner knife 21.i Outer cutting edge / outer knife 21.a head edge 21.k Basic body 22 Bar knife 23 shaft 25 active area 26 chip surface 27 Headroom 28 Open spaces 28.a, 28.i Tool / (bar) cutter head 30 External blade / external cutting 33.a Inner knife / inner cutting 33.i finished left flank 53f pre-toothed right flank 54v finished right flank 54f Pivot point of the tool spindle / intersection point 102 Gap reason 114 memory 150 Software / Computer 151 branch 153 branch 152 Arrows (division rotation) a, b, c Segments Δ1, Δ2, Δ3, ... Δn Data {D} Base circle G Information / data for the definition of the machine and / or kinematics KG Cutting forces Ki, Ka, Kk, Ki(t), Ka(t), Kk(t) Center M Number of segments n Nominal circuit N Rolling circle R relative force rK first relative position RP1 Cutting force S, S(t) Force acting on cutting edges Ki, Ka Time t time ta Procedural steps V1, V2, V3, V3.1, V3.2, V4.1, V4.2, V4.3, V5, V6 Rotational movement of the tool ω1 Rotational movement of the tool ω2 Rotational movement (generator wheel rotation) ω3 Information / data for defining the gear cutting tool VG Information / data for defining the gear workpiece shared apartment Flight circle radius Z1 Coordinate axis / distance x

Claims

1. Method for chip-generating machining of a gear workpiece (11) in a machine having a cutting tool (20) which comprises at least two geometrically defined cutting edges (21.a, 21.i, 21.k) which generate material in chip form on the gear workpiece (11) as part of the chip-generating machining, the chip-generating machining being defined by method parameters, comprising the steps of: (1) performing a computerised analysis (V3) of the generation of chips on the plurality of cutting edges (21.a, 21.i, 21.k) of the cutting tool (20), (2) performing a computerised determination of relative forces that will occur when generating chips on the multiple cutting edges (21.a, 21.i, 21.k) of the cutting tool (20), (3) optimising the chip-generating machining to prevent the relative forces from exceeding a predetermined limit value or reaching a limit range, wherein adapted process parameters are provided as part of the optimising by adjusting at least one of the process parameters, and (4) carrying out the chip-generating machining (V6) of the gear workpiece (11) with the adapted process parameter(s).

2. Method according to claim 1, characterised in that, in steps (1) - (3), the expected load on the plurality of cutting edges (21.a, 21.i, 21.k) of the cutting tool (20) is determined for a part or for all (time) sections of the machining operation.

3. Method according to claim 1 or 2, characterised in that a segmentation is carried out in a method step which is carried out before step (1) or as part of step (1).

4. Method according to claim 3, characterised in that the segmentation is used to divide the cutting edges (21.a, 21.i, 21.k) into time points, time sections or length sections, the relative forces for each of these segments then being determined as part of step (2).

5. Method according to one of claims 1 to 4, characterised in that a computer-aided chip analysis (V3) is carried out as part of step (2), which comprises a determination of the chip formation process (V3.1) and / or a determination of the chip geometry (V3.2).

6. Method according to one of claims 1 to 5, characterised in that a computer-aided chip analysis (V3) is carried out as part of step (2), which is based on one or more of the following approaches: - mechanistic model that maps the formation of shear planes and / or shear zones, - Assumption of a linear relationship between chip thickness and the corresponding force required for chip-forming machining, - Potential model, - exponential model.

7. Method according to one of claims 1 to 5, characterised in that at least one limit value and / or one limit range are / is predetermined, or in that a user is requested to enter at least one limit value and / or one limit range (V4.3).

8. Method according to one of claims 1 to 7, characterised in that the following steps are carried out as part of the optimisation of the chip-forming machining: (3a) Checking (V5) whether one of the relative forces exceeds the predetermined limit value or reaches the limit range, ∘ If one of the relative forces exceeds the predetermined limit value or reaches the limit range, then making at least one change to the planned machining of the gear workpiece (11) by adjusting the at least one of the process parameters to bring the one of the relative forces below the predetermined limit value or outside the limit range, ∘ repeating step (3a) as long as one of the relative forces exceeds the predetermined limit value or reaches the limit range, ∘ If none of the relative forces exceeds a specified limit value or reaches the limit range, then carry out step (4).

9. Method according to one of claims 1 to 7, characterised in that the following steps are carried out as part of the optimisation of the chip-forming machining: (3b) Checking whether one of the relative forces is below the predetermined limit value or the limit range, ∘ If one of the relative forces is below the predetermined limit value or outside the limit range, then making at least one change to the planned machining of the gear workpiece (11) by adjusting the at least one of the process parameters to bring the one of the relative forces closer to the predetermined limit value or into the limit range, ∘ repeating step (3b) until one of the relative forces reaches the predetermined limit value or is within the limit range, ∘ If one of the relative forces reaches the predetermined limit value or is within the limit range, then carrying out step (4).

10. Method according to one of claims 1 to 9, characterised in that the method for chip-forming machining is an individually dividing method or a continuously dividing method.