Patent Application
20190255670
The invention relates to a drilling and/or milling device which is fastened to a tool holding fixture of a numerically controlled machine tool, in particular a turning center or a machining center. Turning centers are often equipped with a tool turret. This field of use is a main field of application of the device according to the invention; however, the invention is not restricted thereto and can be used in all tool holding fixtures of numerically controlled machine tools.
A power tool of this kind is known from DE 39 30 787 C2, for example. It comprises a spindle in which the tool is received and a drive shaft which is driven by means of a drive shaft of the machine tool.
DE 20 2015 008 987 U1 discloses a further generic embodiment of a drilling-milling device. These drilling and/or milling devices are not restricted to drilling and milling. In principle, any desired tool can be clamped into the spindles of these devices. The name “drilling-milling device” will be used in the following for the sake of linguistic simplicity, without intending to restrict the field of use of the device according to the invention to these machining processes.
These drilling-milling devices are built such that the spindle and the drive shaft are often arranged at right angles to one another. Other angles+/−β that deviate from 90° or angles+/−β that can also be adjusted in this additional plane (−180° to 0° to +180°) are likewise possible and are already known from power tools that are available on the market. The angle β is explained in more detail below with reference to
If the angle is β=0° or =180°, the rotational axes of the spindle and the drive shaft are in parallel. If an angle is β=0°, the tool points away from the machine holding fixture. If an angle is β=180°, the tool points towards the machine holding fixture. With these angles β, the spindle and the drive shaft usually have an axial offset, and a spur gear mechanism transmits power from the drive shaft to the spindle. In the specific case where the angle β=0° and the axial offset likewise=0°, the gear mechanism is not required, and the drive shaft is part of the spindle at the same time.
The axis of the spindle is also pivotable (angle+/−α) relative to the axis of the drive shaft, such that slanted holes, surfaces or profiles can also be produced. The pivot angle α is explained in more detail below with reference to
The increasing requirements for efficient machining production on turning or machining centers and other numerically controlled machine tools comprising power tools are associated with ever greater requirements in terms of the quality or the precision with which the workpieces can be produced.
The problem addressed by the invention claimed is that of providing a drilling-milling device which achieves an even greater cutting capacity and/or an improved quality of the machined surfaces for a wide range of applications. At the same time, the operational life of the tool and the service life of the drilling-milling device are intended to be significantly increased.
In the case of a drilling-milling device that comprises a housing, a drive shaft and a spindle, the drive shaft and the spindle being coupled to one another by means of a gear mechanism, this problem is solved by the drilling-milling device comprising a device for evening out the torque and/or the rotational velocity of the spindle and by said device being coupled to or integrated into the spindle.
In a first embodiment, the evening-out of the torque and/or the rotational velocity of the spindle is achieved by means of an increased flywheel mass of the spindle itself or by means of an additional mounted flywheel mass that is connected to the spindle. The desired large mass moment of inertia of the spindle or of the flywheel mass can be achieved by means of the geometry of the spindle and the flywheel mass (diameter, length). Furthermore, by using materials with a particularly high relative density, for example lead, tantalum or tungsten, a large mass moment of inertia can be achieved in very compact dimensions.
The damping action of this flywheel mass can be further increased if the flywheel mass is designed as a dual-mass flywheel. A resilient (spring) element is provided between the two flywheel masses. This principle is known from the field of automotive engineering in the form of dual-mass flywheels or dual-mass clutches.
In an enhanced embodiment, the mass distribution of the flywheel mass can be adjusted. The more remote the mass is from the rotational axis of the spindle, the greater the mass moment of inertia. As a result, the evening-out action of the flywheel mass is also adjusted. In particular, the eigenfrequencies of the “tool, spindle, flywheel mass and drive shaft” system are adjusted in a targeted manner by changing the mass moment of inertia of the flywheel mass such that the machining quality and/or the operational life of the tool is optimized. The two target variables cannot always be optimized at the same time. Consequently, one target variable has to take priority.
This change to the flywheel mass is made ideally during the operation of the drilling-milling device according to the invention when the spindle and the drive shaft are rotating.
These adjustments are controlled by a control loop that processes signals from suitable sensors (rotational speed, torque, temperature, vibrations) and determines the most favorable distribution of the flywheel mass according to the “optimization of the machining quality and/or service life of the cutting tools and/or service life of the drilling-milling device” target variable/s.
In a second, preferred embodiment, the desired evening-out is achieved by means of a brake that is coupled to the spindle and transmits the braking torque to the housing of the drilling-milling device.
By means of the brake, the torques resulting from the cutting that are transmitted from the drive shaft to the spindle are, from the outset, superimposed by a braking torque that is independent of the cutting. This braking torque causes a torque to always be transmitted from the drive shaft to the spindle during the machining, even if the cutting is carried out with an interrupted cut. As a result, in a toothed gearing between the drive shaft and the spindle, the same faces of the tooth flanks of the gears involved always remain in contact. The pressing force with which the tooth flanks are pressed together can be adjusted by means of the braking torque. This pressing force leads to the elimination of a backlash which, for production reasons, is always present between the engaged gears of the gear mechanism, and thus does not affect the precision of the machining of a workpiece.
In addition, the bearing systems are preloaded before the cutting process by the braking torque produced by the brake. This further improves the machining quality. The use of the drilling-milling device according to the invention in turning or machining centers that are already available and in production results in clear improvements in the machining quality and the service life of the cutting tools and the drilling-milling device.
In an enhanced embodiment, the braking action can be adjusted, as a result of which the superimposed torque is adapted. These adjustments are established by a control loop that processes signals from suitable sensors (rotational speed, torque, temperature, vibrations) and optimizes same with respect to the machining optimization and/or the service life of the cutting tools and/or the service life of the drilling-milling device.
It is also possible to use the drilling-milling device according to the invention in hob peeling by means of this brake. Hob peeling very particularly depends on an accurate coordination of the position of the rotational angle of the workpiece or the workpiece spindle with the position of the rotational angle of the tool which is clamped in the spindle of the drilling-milling device according to the invention.
In principle, all known braking devices, such as any type of friction brakes (e.g. drum brakes, shoe brakes, disk brakes), magnetic brakes, electric brakes, hydrodynamic brakes and fluid brakes, can be used as the brake.
In an advantageous embodiment of the drilling-milling device according to the invention, a viscous coupling known from the prior art is used as the brake. A coupling usually interconnects two shafts, whereas, when used according to the invention as a brake, one face of the coupling is coupled directly or indirectly to the spindle and the other face of the coupling is connected to the housing. A viscous coupling of this kind comprises two groups of plates which are arranged so as to be at a small axial distance from one another.
According to the invention, the first group of plates is connected to the spindle for conjoint rotation. The second group of plates is conjoined with the housing of the drilling-milling device. A fluid medium (e.g. an oil or fat, or a rheological fluid, which is a fluid of which the viscosity changes if the field strength of a magnetic field to which the fluid is exposed changes) having a high viscosity is located in the gaps between the two groups of plates. Shear stress between the plates of the first group and the plates of the second group results from this when the spindle is driven. This results in the desired braking torque.
An advantage of this viscous coupling that is repurposed as a brake can be considered to be that of being able to easily and also retroactively adjust the braking action of the brake. This takes place by changing the filling amount and/or the viscosity of the fluid medium (e.g. oil or fat).
Advantageously, silicone oils that can be purchased on the market with different viscosities can be used.
If more silicone oil is poured in, the braking action is increased when the viscosity is the same. Of course, it is also possible to deactivate the brake by removing the silicone oil in its entirety from the brake.
The silicone oil can be easily replaced by unscrewing a screw plug from the housing and draining or sucking out the silicone oil present and pouring in new silicone oil or another fluid medium.
Furthermore, the braking action can be set by adjusting the number of plates and the distance between the plates, and adjusting the geometric form of the plate geometry.
If the viscous brake is filled with a rheological fluid, the braking action can be easily controlled by applying or adjusting a magnetic field that captures the brake.
Furthermore, retarder couplings that are known from the coupling industry can be used as fluid brakes. One face of said retarder couplings is conjoined with the housing rotation; the other face is connected to the spindle.
The amount of the fluid in a viscous coupling or a retarder—and therefore the braking action also—can also be changed during operation.
Alternatively, it is also preferably possible for the evening-out according to the invention to be achieved by means of a magnetic brake or for an electric generator to be used. Preferably, both the magnetic brake and the electric generator can be controlled such that, in this case too, it is easy to set the braking torque and therefore the damping according to requirements. If an electric generator is used as the brake, then the mechanical energy output when the spindle is braked can be converted back into electrical energy (recovery).
Coupling the machine control system and connected sensors (e.g. (torsional) vibration, rotational speed and/or torque sensors) to the electronic controls of the magnetic brake or of the electric generator can result in a monitored and controlled braking action in order to achieve optimal workpiece surfaces and the above-described increased operational life of the cutting tools.
Since mechanical energy is converted into heat energy in the brake according to the invention, it is advantageous if the brake according to the invention is actively cooled.
Particularly advantageously, this can occur by the drilling-milling device comprising an internal cooling-lubricant supply and the brake being cooled by the cooling lubricant that flows through the cooling-lubricant supply.
Cooling-lubricant supplies have been part of the prior art in efficient drilling-milling devices for many years.
According to the invention, the cooling-lubricant lines in the housing of the drilling-milling device should be positioned so that they actively cool the brake. This cooling lubricant, which is heated by a few degrees Celsius, then fulfills its actual purpose, namely cooling and lubricating the cutting tool or the workpiece. The increase in the temperature of the cooling lubricant by a few degrees Celsius caused by the heat absorption at the brake does not affect its suitability as a cooling lubricant. This type of active cooling is therefore not only very efficient, but also very cost-effective.
The drilling-milling device according to the invention is suitable for being used in a wide range of turning centers and machining centers. In particular, it is compatible with all conventional mechanical interfaces of star, disk and crown turrets. The drilling-milling device according to the invention can therefore be used in turning centers or machining centers from a wide range of manufacturers.
This compatibility of the drilling-milling device according to the invention also applies to the drive shaft. The drive shaft is formed at its end facing towards the turret in such a way that it can be driven by the turret. For this purpose, it can be equipped with a dihedron, for example.
However, there are also turrets that comprise inner teeth on the driven shaft thereof. Correspondingly, the drive shaft of the drilling-milling device according to the invention comprises external teeth. As already mentioned, all variants that allow a drilling-milling device according to the invention to be mounted on a turret available on the market are possible with respect to the interface between a turret and the driven drilling-milling device. The drilling-milling device according to the invention can of course also be easily adapted to mechanical interfaces appearing on the market in the future.
In order to further expand the field of use of the drilling-milling device according to the invention, the drilling-milling device comprises a pivoting means. Said means makes it possible to pivot the spindle about a rotational axis of the drive shaft. This is frequently necessary when drilling or milling. Such pivotability is also needed for hob peeling. Pivoting means of this kind are known from the prior art.
In a further advantageous embodiment of the invention, the spindle of the drilling-milling device according to the invention comprises a tool holding fixture. All tool holding fixtures available on the market can be used. It is of course a prerequisite for the tool to be tensioned with sufficient accuracy and securely clamped in order to be able to transmit the driving power and forces necessary for machining. Collets, expansion chucks, hollow-shank taper holders (such as HSK, PSC, Coromant Capto®, KM) and milling arbor holders have been proven to be particularly suitable tool holding fixtures.
Further advantages and advantageous embodiments of the invention can be found in the following drawings, the description thereof and the claims.
In the drawings:
The drawings show an embodiment in different views. All of the reference numerals are therefore the same across the drawings.
Furthermore, the forces and torques acting between the drilling-milling device 1 and the turret are also transmitted. The drilling-milling device 1 is screwed to the turret by means of the screws 7.
Since the drilling-milling device 1 is a power tool, a drive shaft 9 is formed in the region of the mechanical interface 3 and, in this embodiment, comprises a dihedron 11 on its end that is at the bottom in
In this embodiment, the cylindrical portion 5 and the drive shaft 9 are arranged concentrically to one another.
In
The tool (not shown) necessary for machining is clamped to the left-hand end of the spindle 17 in
The spindle 17 is rotatably mounted in a housing 19 of the drilling-milling device 1. A brake (not shown in
This type of pivot mounting is known from machine vices and other tools, for example. The design details of said pivoting means are therefore not explained in more detail.
In order to be able to directly read off the set pivot angle α, a scale is arranged on the housing 19.
As a result of this design, the rotary table 21 can be fastened to the turret beforehand by means of the screws 7.
It is therefore not problematic if said screws 7 are no longer accessible after assembling the housing 19 on the rotary table 21. In a further step, the housing 19 is fastened to the rotary table 21 independently of the positions of the screws 7 by means of the aforementioned clamping brackets and clamping screws 23.
In this embodiment, the tool holding fixture 25 is designed as an expansion chuck. This allows for very accurate concentricity and short tool-change times. Nevertheless, other embodiments of tool holding fixtures are also possible. In particular, it is possible to tension the tools (not shown) in the spindle 17 or the tool holding fixture 25 by means of a collet holder (also not shown).
The turret or the tool holding fixture of the machine tool comprises a similar hole at the opposite point and conveys the cooling lubricant into the hole 27. In order for the drilling-milling device 1 to be offset by 180° and operated on the tool holding fixture, a second hole 27 is provided opposite the first hole 27 in the drilling-milling device 1. The hole 27 that is not needed is then optionally closed by a set screw.
A first bevel gear 33 is connected for conjoint rotation to the drive shaft 9 at the end of the drive shaft 9 that is at the top of
The spindle 17 is mounted in the region of the tool holding fixture 25 in zero-clearance bearings. This mounting can be achieved by an O-shaped arrangement of angular contact ball bearings, for example. This design variant is shown in detail “X”. In order to further increase the radial rigidity of the mounting, the spindle 17 can be mounted in the region of the tool holding fixture 25 in a cylindrical roller bearing 37, as is shown in
The inner ring of the cylindrical roller bearing 37 is slightly conical in this embodiment. In a complementary manner, the spindle 17 is in the shape of a frustum in said region. When the inner ring of the cylindrical roller bearing 37 is pressed against the frustum of the spindle 17 by means of a nut 39, said ring enlarges slightly. Zero-clearance mounting of the spindle 17 can be thus achieved during assembly. It may even be advantageous if a certain amount of preloading is set by tightening the nut 39 accordingly.
Due to this design, zero-clearance and, in the radial direction, extremely resilient mounting of the spindle 17 or of the tool (not shown) clamped in the tool holding fixture 25 is achieved in the region of the tool holding fixture 25. This is, inter alia, very important for hob peeling in order to achieve good machining quality.
In
In order for the second bevel gear 41 to be connected to the spindle 17 without rotational backlash, a conical recess 45 is formed in the spindle 17 opposite the feather key 43. A threaded hole 47 is formed in the second bevel gear 41, slightly offset from this conical recess 45. The offset between the recess 45 and the threaded hole 47 is provided both in the axial direction and in the circumferential direction.
Because of this slight offset between the recess 45 and the threaded hole 47, the second bevel gear 41 is braced against the feather key 43 and therefore also against the spindle 17 in the circumferential direction by screwing in the set screw 49. A backlash-free connection is thus produced. The same design is also included in the connection of the drive shaft 9 to the first bevel gear 33, but cannot be seen here as the set screws are offset from the feather key 43 by 90°.
The outer rings of the ball bearings 53 are supported against a step in the housing part 19. The inner ring of the left-hand ball bearing 53 in
For reasons relating production and/or assembly, the housing 19 is formed in three parts. The largest part is denoted by 19.1 and supports the mounting of the spindle 17. Below this housing part 19.1 is a second housing part 19.2. In
In the embodiment shown, the brake 55 is designed as a multi-plate coupling, in which a first group of plates is rotatably connected to the spindle 17 for conjoint rotation and the second group of plates is connected to the third housing part 19.3 or the first housing part 19.1 for conjoint rotation. For the sake of clarity, the two groups of plates are not shown in detail in
In this magnified view, it is clear that a support element (having no reference numeral) supports a first group of plates 57 in the housing 19.3. Correspondingly, a second group of plates 59 is fastened to the spindle 17. For the sake of clarity, only one plate, 57 or 59 as is the case, is provided with a reference numeral. The plates 57 and 59 are mutually spaced in the axial direction. The first plates 57 are connected to the housing 19 for conjoint rotation and the second plates 59 are connected to the spindle 17 for conjoint rotation.
Silicone oil (not shown) is located in the spaces between the plates 57 and 59. Owing to the shearing forces between the plates 57 and 59 and the silicone oil, a braking torque dependent on rotational speed is produced in the brake 55 as soon as the spindle 17 rotates.
Said braking torque also depends on the dimensions of the brake 55. It can be adjusted very easily by varying the filling amount of the silicone oil. Furthermore, the braking torque can be controlled by selecting the viscosity of the silicone oil. For this purpose, different silicone oils with different viscosities are available on the market. When the brake 55 is intended to be switched off, the silicone oil is simply removed from the housing or the brake 55. This results in an air gap between the plates 57 and 59 that has almost no braking action because the viscosity of air is extremely low.
In order to be able to discharge the heat produced in the brake 55 even when operating the drilling-milling device 1 continuously, the cooling-lubricant supply 27 of the drilling-milling device 1 is designed such that holes are provided in the housing 19 that surround the brake 55 especially in the third housing part 19.3. Said holes are part of the cooling-lubricant supply and therefore have reference numeral 27. The cooling-lubricant supply 27 ends in the rotational axis 15 of the spindle 17.
In the embodiment shown, the spindle 17 is bored hollow such that the cooling lubricant, after cooling the brake 55, enters the region of the tool holding fixture 25 via a central through-hole 61 of the spindle 17. A corresponding hole that guides the cooling lubricant to the tool can be provided on the tool (not shown) in said region.
Alternatively, it is also possible to guide the cooling lubricant outwardly and then direct it towards the workpiece. In
In particular, it is clear from
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 118 766.6 | Oct 2016 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/075253 | 10/4/2017 | WO | 00 |
