Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B53/00—Devices or means for dressing or conditioning abrasive surfaces
  • B24B53/04—Devices or means for dressing or conditioning abrasive surfaces of cylindrical or conical surfaces on abrasive tools or wheels
  • B24B53/047—Devices or means for dressing or conditioning abrasive surfaces of cylindrical or conical surfaces on abrasive tools or wheels equipped with one or more diamonds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B53/00—Devices or means for dressing or conditioning abrasive surfaces
  • B24B53/04—Devices or means for dressing or conditioning abrasive surfaces of cylindrical or conical surfaces on abrasive tools or wheels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B53/00—Devices or means for dressing or conditioning abrasive surfaces
  • B24B53/06—Devices or means for dressing or conditioning abrasive surfaces of profiled abrasive wheels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B53/00—Devices or means for dressing or conditioning abrasive surfaces
  • B24B53/06—Devices or means for dressing or conditioning abrasive surfaces of profiled abrasive wheels
  • B24B53/062—Devices or means for dressing or conditioning abrasive surfaces of profiled abrasive wheels using rotary dressing tools

Definitions

• the present invention relates to a method for machining workpieces in a gear grinding machine with a grinding tool that is designed as a profile grinding wheel or grinding worm and has vitrified bonded abrasive grains made of a super abrasive material, in particular cBN, and a gear grinding machine that is designed to carry out the method.
• a disadvantage of vitrified-bonded cBN tools is that an undesirable grinding behavior occurs (research report FVA 778 I, IGF no. 18580 N, retrieved on November 16, 2020 from www.fva-net.de).
• the grinding-in behavior describes the phenomenon that thermal damage to the edge zone of heat-treated workpieces (so-called grinding burn) can occur immediately after dressing when using a vitrified bonded cBN tool.
• thermal damage to the surface zone is often documented in the first machined gear gaps after dressing.
• There are different approaches to explain this grinding-in behavior insufficient chip space, exposed bond, flattening of the cBN grains).
• US2005272349A1 discloses a method for conditioning a superabrasive grinding tool, in which a plurality of cuts are made in a sacrificial element after the grinding tool has been dressed.
• the geometry of the sacrificial element corresponds to the geometry of the workpieces that are then machined with the grinding tool.
• a method for machining workpieces in a gear grinding machine with a grinding tool that is ceramic bonded abrasive grains made of a super abrasive material, in particular cBN comprises the steps: a) dressing the grinding tool; b) conditioning of the dressed grinding tool in such a way that a desired state of wear of the grinding tool is generated, with the gear grinding machine performing conditioning kinematics; and c) machining pre-geared workpieces with a predetermined basic shape using the dressed and conditioned grinding tool, with the gear grinding machine performing machining kinematics.
• the method is characterized by the fact that the conditioning kinematics differ from the processing kinematics.
• a sacrificial workpiece is not machined with the machining kinematics for conditioning, but rather the conditioning takes place with a conditioning tool that is moved relative to the grinding tool with special conditioning kinematics.
• the conditioning kinematics can, in particular, correspond to dressing kinematics such as can be used for dressing the grinding tool.
• a conditioning tool can be used for conditioning that has a different basic shape than a workpiece, in particular the basic shape of a dressing tool.
• the conditioning tool is preferably not also gear-shaped.
• the conditioning tool may instead be, for example, a rotating, disc-shaped conditioning tool, or a stationary, e.g. pin- or tooth-shaped conditioning tool.
• the conditioning can take place in a much more targeted manner, since the movement sequences can be adapted in a targeted manner in order to achieve an optimal conditioning result.
• technological parameters such as the infeed of the conditioning tool radially to the axis of rotation of the grinding tool, the speeds of the grinding tool and, if applicable, of the conditioning tool, the direction of action (synchronous or counter-rotating) and, if conditioning does not take place in line contact along the complete useful profile of the grinding tool, the web feed rate and the degree of coverage can be specifically adjusted.
• conditioning tool with Separate conditioning kinematics can also reduce unproductive idle times that would otherwise arise after conditioning to exchange a sacrificial workpiece for a workpiece to be machined.
• the conditioning tool can also be used several times. This significantly reduces material consumption.
• a “super abrasive material” is understood to mean a material whose Vickers microhardness at room temperature is higher than the microhardness of corundum.
• the class of superabrasive materials includes, in particular, cubic boron nitride (cBN) and diamond.
• CBN is particularly important for the hard finishing of pre-geared workpieces made of steel because, unlike diamond, it has no chemical affinity for typical gear materials.
• the present invention relates in a special way to grinding tools whose grinding body is formed by vitrified bonded cBN grains.
• a damage pattern as specified in ISO 14104:2017-04 is referred to as "thermal damage to the edge zone" of a workpiece or "grinding burn”.
• the nital etching method defined in ISO 14104:2017-04 is used to test whether there is thermal damage to the peripheral zone or not.
• thermal damage to the edge zone of a workpiece is present if the workpiece does not meet classification FA/NB2 after type 3 etching.
• basic shape in the present document denotes the geometric shape of an object abstracted from small differences in dimensions.
• two spur gears with the same helix, the same module and the same number of teeth are viewed as objects with the same basic shape, even if the tooth thickness, the profile shape or the tooth trace of the spur gears differ.
• a disc without spur gear teeth or a stationary pin, tooth, or rod are considered objects that have a different basic shape than a spur gear.
• dressing or “truing” is understood to mean a process with which, on the one hand, a desired geometric Shape of a grinding tool produced or restored and on the other hand the grinding tool is sharpened by the rotating grinding tool is brought into engagement with a dressing tool.
• conditioning is understood to mean the targeted bringing about of a desired state of wear.
• the geometric shape of the grinding tool, as produced during dressing is preferably no longer changed.
• the conditioning can be used in particular to remove binders between the abrasive grains after dressing in order to partially expose the abrasive grains.
• dressing kinematics mean the sequence of movements that the grinding machine executes during the “dressing”, “conditioning” or “machining” process.
• dressing kinematics is understood to mean a sequence of movements in which a dressing tool is brought into engagement with the rotating grinding tool in order to dress the grinding tool.
• the dressing kinematics can include movements of the grinding tool relative to a machine bed of the grinding machine and/or movements of the dressing tool relative to the machine bed.
• the dressing kinematics are generated by one or more numerically controlled axes (NC axes) of the grinding machine.
• conditioning kinematics means a movement sequence in which a conditioning tool is brought into engagement with the rotating grinding tool in order to condition the grinding tool
• machining kinematics means a movement sequence in which the rotating grinding tool interacts with the workpiece in Intervention is brought to edit this machining.
• Two kinematics are considered to be different if the associated movements not only differ in individual parameters such as movement length, speed, etc., but the basic sequence of movements is different.
• the machining kinematics in continuous generating grinding with a grinding worm differ from dressing kinematics in which the grinding worm is dressed with a rotating dressing wheel.
• the machining kinematics in continuous generating grinding include a forced coupling of the rotational speeds of the grinding worm and the workpiece in order to meet the generating condition, while the dressing kinematics do not require such a forced coupling.
• the machining kinematics in discontinuous profile grinding with a profile grinding wheel also differ fundamentally from dressing kinematics when dressing the profile grinding wheel with a rotating dressing wheel. The machining kinematics require that the profile grinding wheel is brought into engagement with the next tooth gap after machining one tooth gap. This element is completely missing in the dressing kinematics.
• the conditioning kinematics differ from the processing kinematics, i.e. a different sequence of movements is carried out during conditioning than the sequence of movements used to process the workpieces.
• the conditioning tool is preferably clamped on a conditioning device that differs from the workpiece spindle, i.e., unlike when sacrificial workpieces are used, conditioning does not take place with the aid of the workpiece spindle, but with the aid of a separate conditioning device.
• the conditioning device can in particular be integrated into a dressing device or be combined with it.
• the basic shape of the conditioning tool can in particular correspond to the basic shape of the dressing tool that is specifically used for dressing the grinding tool, or when using several dressing tools, to the basic shape of one of these dressing tools. If, for example, a rotating, disc-shaped dressing tool is used for dressing, the conditioning tool can also be disc-shaped and have similar dimensions to the dressing tool.
• the conditioning kinematics can then correspond to the dressing kinematics for this dressing tool.
• the basic shape of the conditioning tool can also deviate from the basic shape of the dressing tool actually used.
• the dressing can be done with a rotating, disk-shaped dressing tool, while the conditioning tool is a stationary element, e.g. B. as a pin, tooth or rod is formed.
• the conditioning kinematics can deviate from the dressing kinematics actually used.
• the conditioning kinematics are kinematics that could also be used for dressing, and in this respect the conditioning kinematics also correspond to dressing kinematics in this case.
• the conditioning tool is preferably in an area used in conditioning comes into contact with the grinding tool, made of metal, in particular steel. It is preferably a steel with similar properties to the steel from which the workpieces are made. In particular, it can be the same type of steel as for the workpieces. In particular, the conditioning tool can correspond to the steel base body of a dressing tool whose hard material coating has been omitted.
• the conditioning tool stands still during the conditioning process.
• the conditioning tool rotates during the conditioning process, it being possible for this rotation to take place in the same direction or counter to the grinding tool.
• the conditioning tool may have the basic shape of a dressing roll, i.e. a disc-shaped basic shape.
• the conditioning tool can have the form of a so-called profile roller or a form roller.
• a profile roller is understood to mean a dressing roller that is provided for dressing the grinding tool in line contact in such a way that a profile shape of the dressing roller is transferred to the grinding tool.
• the line contact can, for example, only take place in the area of one flank of the grinding tool, it can take place on two adjacent flanks, or it can also include the head and/or foot areas of the grinding tool lying in between.
• a form roller is understood to mean a dressing roller that is provided for dressing the grinding tool with point contact.
• the conditioning tool preferably corresponds to the steel base body of a dressing roller without a coating of hard material.
• the conditioning tool may be in general line contact with at least a portion of the wear profile of the abrasive tool during the conditioning process, or it may be in point contact with a portion of that wear profile. If the conditioning tool is not in line contact along the entire useful profile of the grinding tool, it can be provided that the gear grinding machine performs a relative movement between the grinding tool and the conditioning tool in such a way that the contact position between the conditioning tool and the grinding tool moves along the profile of the grinding tool during conditioning changes.
• Step c) are machined with identical machining parameters, in particular with an identical infeed perpendicular to the workpiece spindle axis and an identical feed rate along the workpiece spindle axis.
• These machining parameters can be selected in such a way that thermal damage to the peripheral zones would occur during the machining of at least one first workpiece in step c) if step b) were not carried out. This is possible because in step b) the conditioning is carried out in such a way that during the processing in step c) thermal damage to the peripheral zones no longer occurs.
• Steps a) to c) can be repeated several times.
• the conditioning process b) can be carried out several times with the same conditioning tool. Unlike a sacrificial workpiece, the conditioning tool does not have to be discarded after a single conditioning process, but can be reused several times.
• the workpiece machining in step c) can be carried out in particular by continuous generating grinding or by discontinuous profile grinding.
• the grinding tool can be a grinding worm or a profile grinding wheel.
• the present invention also provides a gear cutting machine which is specially designed for carrying out the method indicated above.
• the gear grinding machine has: a tool spindle on which a grinding tool can be clamped; at least one workpiece spindle on which a workpiece can be clamped; a dressing device on which a dressing tool can be clamped; a plurality of machine axes for driving and moving the tool spindle, the workpiece spindle and the dressing device relative to one another; and a controller for controlling the machine axes.
• the gear cutting machine is characterized in that it has a conditioning device that differs from the workpiece spindle, and a conditioning tool can be clamped on the conditioning device.
• the control device is then designed to control the machine axes in such a way that the machine tool executes a method of the type specified above, so that the conditioning is carried out with conditioning kinematics that differ from the machining kinematics and preferably correspond to dressing kinematics.
• FIG. 1 shows a gear grinding machine according to an exemplary embodiment in a perspective view
• FIG. 2 shows a detail from the gear grinding machine of FIG. 1 in the area of the dressing device, with parts of the gear grinding machine not being shown for the sake of simplicity;
• FIG. 3 shows the detail of FIG. 2, a profile grinding wheel being provided as the grinding tool instead of a grinding worm;
• Fig. 4 is a sketch showing a grinding worm engaged with a workpiece
• Fig. 5 is a sketch showing a profile grinding wheel in engagement with a workpiece.
• FIG. 6 shows a flow chart for a method according to the present invention.
• FIG. 1 a machine tool for hard fine machining of gears by generating grinding is shown as an example.
• Horizontal spatial directions are denoted by X and Y, the vertical spatial direction (direction of gravity) is denoted by Z.
• the machine has a machine bed 100 on which an infeed carriage 210 is arranged to be displaceable along an infeed direction X1.
• the infeed direction X1 corresponds to the horizontal spatial direction X.
• a tower-like tool carrier 200 is mounted on the infeed slide 210 so as to be pivotable about a vertical pivot axis C1, referred to below as the C1 axis.
• a feed slide 220 is arranged on the tool carrier 200 so that it can be displaced along a feed direction Z1.
• the feed direction Z1 corresponds to the vertical spatial direction Z.
• the feed carriage 220 carries a tool head 300 which can be pivoted relative to the feed carriage 220 about a horizontal pivot axis A1, hereinafter referred to as the A1 axis.
• the A1 axis runs parallel to the infeed direction X1.
• a tool spindle 310 is arranged on the tool head 300 so as to be displaceable along a shift direction Y1.
• the Shift direction Y1 runs perpendicularly to the A1 axis and at an angle to the feed direction Z1, which depends on the pivoting angle of the tool head 300 about the A1 axis.
• a grinding tool 320 in the form of a grinding worm is clamped on the tool spindle 310 in order to rotate it about a tool spindle axis B1 (see FIGS. 2 to 5).
• the tool spindle axis B1 runs parallel to the shift direction Y1.
• a dressing device 400 is arranged on the machine bed 100 .
• a workpiece spindle 500 On a side of the tool carrier 200 facing away from the dressing device 400, a workpiece spindle 500, only partially visible in Fig. 1, is arranged on the machine bed 100 in order to rotate a workpiece 510 clamped on it about a vertical workpiece spindle axis C (see Figures 4 and 5).
• the tool carrier 200 can be pivoted through 180° between a machining position and a dressing position about the C1 axis.
• the grinding tool 320 In the machining position of the tool carrier 200, the grinding tool 320 can be brought into engagement with the workpiece 510 (see FIGS. 4 and 5).
• the dressing position the grinding tool 320 can be brought into engagement with dressing tools of the dressing device 400, which are described in more detail below (see FIGS. 2 and 3). 1 shows the tool carrier 200 in the dressing position.
• a machine control 600 shown only symbolically, receives signals from sensors in the machine and controls the linear and swivel axes of the machine, the tool spindle, the workpiece spindle and the dressing device.
• FIG. 1 A machine concept according to FIG. 1 is disclosed in US5857894A. Corresponding machines are available under the designation RZ 400 from Reishauer AG, Wallisellen, Switzerland.
• FIG. 2 illustrates a detail from the machine of FIG. 1 from a different viewing direction. Parts of the machine were omitted in order to achieve a clearer representation.
• Abrasive tool 320 is illustrated floating in FIG. 2 . However, it goes without saying that the grinding tool is still clamped on the tool spindle 310, as illustrated in FIG. For the discussion below, it is assumed that the abrasive tool 320 comprises a vitrified cBN abrasive grits.
• the structure of the dressing device 400 in particular can be seen from FIG. 2 .
• the dressing device 400 has a first dressing spindle 410, which can be pivoted about a vertical axis C_P1 relative to the machine bed and can be moved linearly along two orthogonal horizontal directions X_P, Y_P.
• a disk-shaped dressing tool 415 is clamped to rotate on the first dressing spindle 410 .
• the dressing device 400 also has a second dressing spindle 420, which can be swiveled about a vertical axis C_P2 relative to the machine bed with the aid of a swivel drive 421.
• a second disk-shaped dressing tool can be clamped to rotate on the second dressing spindle 420 .
• a disk-shaped first conditioning tool 425 is clamped on the second dressing spindle 420 instead of a dressing tool.
• a stationary second conditioning tool 416 can be provided.
• the stationary conditioning tool 416 is held in a holder 417 which is arranged in a stationary manner on the housing of the first dressing spindle 410 in the example in FIG. 2 .
• the dressing device 400 thus assumes the function of a combined dressing and conditioning device. Strictly speaking, only the first dressing spindle 410 with the dressing tool 415 clamped on it forms the actual dressing device, while the second dressing spindle 420 with the conditioning tool 425 clamped on it and the holder 417 with the fixed conditioning tool 416 form a conditioning device.
• the grinding tool 320 can be selectively brought into engagement with each of the three dressing or conditioning tools 415, 416 and 425 with the aid of NC axes for generating movements with respect to X1, Y1, Z1, A1, X_P, Y_P, C_P1 and C_P2.
• FIG. 3 illustrates the use of a grinding tool 321 in the form of a profile grinding wheel. All of the considerations outlined here also apply analogously to this type of grinding tool.
• tangential feed direction is usually used for direction Y1 instead of "shift direction”.
• the rotating grinding tool 320, 321 is first brought into engagement with the dressing tool 415, which is also rotating. As a result, the desired outer contour of the grinding tool 320, 321 is produced or restored, and the grinding tool 320, 321 is sharpened.
• the rotating grinding tool 320, 321 is then brought into engagement with the rotating conditioning tool 425 and/or with the stationary conditioning tool 416.
• the conditioning is carried out until it is ensured that there is no thermal damage to the edge zone of the workpieces during the subsequent machining of the workpieces, even if the machining for all workpieces is carried out with the same technological parameters.
• the dressing and conditioning device can also be configured differently.
• Dressing tool 415 may be any dressing tool suitable for dressing a vitrified bonded cBN abrasive grits. Dressing tools of this type are known in a variety of configurations from the prior art. They can be used in different ways for dressing.
• a grinding worm can be dressed with line contact between the dressing tool and the grinding tool in order to map the profile of the dressing tool to the profile of the grinding tool.
• profile dressing can each flank of a worm flight can be dressed individually, both flanks of a worm flight can be dressed at the same time, or the flanks of two or more worm flights of a multi-start grinding worm can be dressed at the same time. It is also possible, in addition to the flanks, to also dress the head and/or foot areas of the worm threads simultaneously or one after the other.
• the same dressing tool or a different dressing tool can be used for this (cf. eg US6234880B1).
• disc-shaped dressing tools dressing rollers
• the dressing tool then often has a disc-shaped base body made of steel, on which an abrasive coating, e.g. made of diamond grains, is applied.
• Other types of dressing tools on the other hand, are fixed.
• Dressing tools of this type can also have a base body made of steel, which is coated with abrasive material.
• a profile grinding wheel can also be dressed in line contact or in point contact. This can in turn be done with a rotating, disk-shaped dressing tool of the type of dressing tool 415 or with a stationary dressing tool, in which case the dressing tool can have a base body made of steel and an abrasive coating.
• the conditioning process and the conditioning tool used for this purpose can be in line contact or in point contact.
• the conditioning tool can be rotating or stationary. In particular, it can be formed by the steel base body of a dressing tool in which the abrasive coating has been omitted, so that the grinding tool is conditioned directly with the steel of the base body.
• the conditioning tool can be the same as the dressing tool.
• both the dressing tool and the conditioning tool can be a disk-shaped tool that is rotated during dressing or conditioning.
• the conditioning tool can also be of a different type than the dressing tool.
• the dressing tool can be rotating while the conditioning tool is stationary.
• the conditioning does not take place with a sacrificial workpiece that is clamped on the workpiece spindle for conditioning, but with a separate conditioning tool.
• the conditioning tool is not clamped on the workpiece spindle, and the conditioning does not take place with kinematics that correspond to the kinematics during workpiece machining, but conditioning takes place with kinematics that correspond to the kinematics of a typical dressing process.
• the kinematics during conditioning can differ from the kinematics actually used during dressing (e.g. because the dressing tool and the conditioning tool are not of the same type), but it is nevertheless a kinematics that could also be used during dressing.
• the same movement axes that can also be used for dressing can be used for conditioning.
• These axes are pure dressing and conditioning axes that are not relevant to workpiece machining. The movement sequences during conditioning are therefore obviously completely different in the examples in FIGS. 1 to 3 than in the case of workpiece processing.
• the workpieces are processed. For the sake of completeness, this is shown in FIG. 4 for the example of continuous generating grinding and in FIG. 5 for the example of discontinuous profile grinding (Pitch profile grinding) illustrated.
• the grinding tool 320 is a grinding worm which is in rolling engagement with the workpiece 510 .
• the workpiece 510 rotates about the workpiece spindle axis C at a speed that is in a predetermined speed ratio to the speed of the grinding tool 320 .
• This rolling coupling is established electronically by the machine controller 600.
• the grinding tool 320 is continuously advanced along the feed direction Z1 over the entire width of the workpiece and, if necessary, shifted along the shift direction Y1. It is obvious that these kinematics differ significantly from the kinematics in dressing and conditioning.
• the grinding tool 321 is a profile grinding wheel.
• the rotating grinding tool 321 is successively introduced into the individual tooth gaps of the workpiece 510 in order to machine them.
• the workpiece 510 stands still and the grinding tool 321 is continuously advanced along the feed direction Z1 over the entire width of the workpiece.
• the workpiece is then twisted to machine the next tooth gap. It is obvious that this kinematics also differs significantly from the kinematics during dressing and conditioning.
• step 701 the grinding tool is dressed.
• step 702 it is conditioned.
• step 703 the workpieces are then machined. If the grinding tool is so worn that it needs to be reprofiled and/or resharpened, steps 701 and 702 are performed again.
• the invention is not limited to the above embodiments, and other modifications are possible.
• the invention is not limited to a specific machine concept, but can be used with any gear grinding machine that allows both dressing and conditioning.

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