Patent Application
20110081844
The invention relates to a hard finish machine for hard finishing of a workpiece, comprising at least two different hard finish tools which are arranged on a tool spindle, wherein the tool spindle is arranged movable in the direction of its axis on a tool carrier, wherein the tool carrier is translational movable relatively to a machine bed and wherein the hard finish machine furthermore comprises cooling lubricant supplying means for the supply of cooling lubricant to the machining region between the workpiece and the hard finish tool.
Such hard finish machines which are well known in the state of the art are employed e.g. in the production of gears as gear grinding machines. Often, a division of the stock is provided which has to be ground so that the gear is firstly rough machined and subsequently finish machined. For rough machining a grinding worm can be used, wherein the continuous generation grinding method is employed; the finish machining can take place with a profile grinding wheel using the profile grinding method.
In order to carry out the grinding process properly and to prevent especially thermal overload of the tooth flank a reliable supply of the contact area between the grinding tool and the workpiece must be ensured which takes place by the arrangement of cooling lubricant supply means.
For the two mentioned methods significant different demands with respect to the cooling lubricant supply exist in terms of a secure prevention of thermal damages of the workpiece:
When using the continuous generative grinding method usually cutting speeds, i.e. circumferential velocities of the grinding worm, of ca. 60 m/s and higher are used due to the connection between the cutting speed and the machining time. For a secure prevention of thermal damages of the workpiece peripheral zone a difference between the circumferential velocity of the grinding worm and the exit velocity of the stream of cooling lubricant being as small as possible is aimed for, i.e. a relatively high exit velocity of the cooling lubricant from the cooling lubricant nozzle is required. This high velocity is created by a small cross sectional area of the nozzle and a high supply pressure. Under such circumstances a relatively low volume flow rate is given which, however, has no negative influence to the grinding process or to the reached workpiece quality.
In contrast, when using the profile grinding method usually low cutting speeds between 25 and 35 m/s are employed. This method demands a secure coverage of the whole grinding wheel profile by the stream of cooling lubricant. Thereof the demand results for a relatively large cross sectional area of the nozzle depending on the respective profile width and height, wherein a stream of cooling lubricant having a low exit velocity and a low pressure results, but having a relatively high volume flow rate.
Beside the mentioned specific application of the hard finishing method of gears other general cases are possible in which several tools are employed one after the other with significant different demands to the cooling lubricant supply.
According to a usual manufacturing method in the case of several tools those tools are arranged flushing on a mandrel which is clamped between a spindle motor and a counter bearing. The whole unit consisting of spindle motor, counter bearing, mandrel and tools is arranged on a slide (tool carrier) movable in axial direction of the tools (mostly nominated as the “Y” axis) by which the tools can be brought into the axial position relatively to the workpiece which is necessary for the machining.
The worm-shaped tools which are used for the generative grinding process are usually significantly wider than the pure contact width which results from the contact between the tool and the workpiece. This is done for the purpose to use different shifting methods to grind the gears in a specific way: Firstly, the discontinuous shifting in the direction of the axis of the tool (Y axis) is employed between rough machining and finish machining and between the machining of single workpieces respectively to bring new fresh regions of the grinding worm into contact. With the continuous shifting in the direction of the axis of the tool (Y axis) during the grinding process of a workpiece (also designates as diagonal grinding) a specific influence of the tooth flank topology and/or surface structure can take place.
The cooling lubricant nozzles which are used here can be designed as fixed elements, i.e. they are optimized for a specific changeless workpiece diameter which is especially recommended for non-dressable CBN grinding tools which does not change their diameter. In the case of tools with changeable diameter, i.e. namely for dressable tools, the cooling lubricant nozzle can be installed in such a way that it is arranged movable in a plane which is perpendicular to the axis of the tool spindle, so that the cooling lubricant nozzle can be tracked correspondingly when the diameter of the tool decreases. This adjustment of the nozzle position to the actual tool diameter can take place by a rotatory or translational movement.
In the pre-known applications the workpiece is either machined only with a single tool (e.g. with a dressable grinding worm; the rough machining and the finish machining take place with different width regions of the same tool) or two tools of the same type and the same size are used (e.g. non-dressable profile grinding with CBN rough machining and finish machining wheels). In those cases the use of a single nozzle is possible without problems—with optimized properties for the used tool and method respectively.
Usually, a combination of several tools and machining methods of different kind respectively is used for the machining of several gears of the same workpiece in one clamping (e.g. gear box shafts) or for the machining of a gear with different methods for the rough machining and for the finish machining (e.g. rough machining by dressable generative grinding, finish machining by non-dressable profile grinding—as explained above).
In those cases the following variants of cooling lubricant supply are known:
It is known to use the same nozzle (with or without the above mentioned tracking in the case of changes of the diameter) for the different tools. Here it is the drawback that the conditions of the cooling lubricant supply cannot be optimized for each used tool. Therefore the machining with at least one of the used tools is possible only with reduced feed rate, so that longer machining times and thus a loss of efficiency result.
Furthermore, it is known that several nozzles are arranged on the slide of the Y axis which travel with the slide, wherein the nozzles do not change their position relatively to the respective tool. In this case the following drawbacks exist: To be able to use the above mentioned shifting process in the case of the generative grinding method with a worm-shaped tool the nozzle which travels with the slide of the Y axis must be as wide as the whole tool, i.e. thus significantly wider than it would be necessary due to the effective contact width between the tool and the workpiece. Given a constant exit height of the nozzle opening the cross sectional area of the nozzle increases when the nozzle becomes wider which is in conflict with the conditions which are ideal for the generative grinding. Also in this case the machining can take place only with a reduced feeding rate due to the non-optimal conditions of the cooling lubricant supply and thus the machining times are longer and the efficiency is reduced.
Thus, it is an object of the invention to further develop a hard finish machine of the kind mentioned above with respect to the cooling lubricant supply means so that the above mentioned drawbacks are avoided and that the use of all possible combinations of tools and methods can take place under optimized cooling lubricant supply conditions. It should become possible to adjust the respective conditions for the supply of cooling lubricant which have been found optimal for each type of tool and for each machining method. Furthermore, an automated adjusting of the conditions for the supply of cooling lubricant for a used tool and a used machining method respectively should become possible within a machining cycle without intervention by an operator, i.e. managed by the machine control.
The solution of this object by the invention is characterized in that the cooling lubricant supplying means comprise at least one nozzle element, wherein the nozzle element comprises at least two nozzle chambers each having a stream exit opening, wherein the at least two stream exit openings are arranged at the same working position in the direction of the axis of the tool spindle and wherein the nozzle element is movable in a plane which is perpendicular to the axis of the tool spindle.
The nozzle element can have at least two separate nozzle bodies each having a nozzle chamber, wherein the stream exit openings are arranged at the outlet end of the nozzle bodies.
Alternatively, the nozzle element can also have only a single nozzle body with the at least two nozzle chambers, wherein the stream exit openings are arranged at the outlet end of the nozzle body.
The form of the stream exit openings is preferably different. Preferably, the stream exit openings have a rectangular shape. The differences in the form relate then preferably to the width and the height of the stream exit openings.
All stream exit openings arc preferably arranged symmetrically to a plane which is perpendicular to the axis of the tool spindle.
The nozzle element can be arranged pivotable around an axis which is parallel to the axis of the tool spindle for the purpose of positioning or of tracking the diameter.
Alternatively, the nozzle element can be arranged translational movable in a plane which is perpendicular to the axis of the tool spindle for the mentioned purpose. The nozzle element is here preferably arranged movable on a linear guide.
The nozzle element can be designed for charging each of the nozzle chambers individually controlled with cooling lubricant. Alternatively, it is also possible that at least two nozzle chambers of the nozzle element are designed for the simultaneous charging with cooling lubricant.
The nozzle element can be arranged stationary in the direction of the axis of the tool spindle at or on the tool carrier. It can also be arranged movable on a linear guide in this direction relatively to the tool carrier. Furthermore, it is possible that the nozzle element is arranged stationary in the direction of the axis of the tool spindle at or on the machine bed. Finally, it is possible that the nozzle element is arranged movable on a linear guide in the mentioned direction relatively to the machine bed.
According to a preferred embodiment of the invention the hard finish tools are gear machining tools, especially a grinding wheel or a grinding worm.
Thus, it is proposed the combination of several—especially of two—nozzles at one working position of the tool spindle which are equipped with actuation means for maintaining and adjusting respectively of the optimal position. The nozzles thus have a possibility for displacement in a plane which is perpendicular to the axis of the tool spindle.
Beneficially, the above mentioned object is solved completely with the proposed solution. Accordingly, it becomes possible that also in the case of the use of very different hard finish tools, especially of grinding tools, the cooling lubricant supply conditions are optimized. The adjustment of the cooling lubricant supply means is possible in an easy manner automated by means of the machine control unit.
Consequently, solutions are proposed for the cooling lubricant supply for machining methods in which several tools are used one after the other in the same position relatively to the workpiece to be machined and wherein the requirements for the cooling lubricant supply (especially in terms of the exit cross sectional area, the exit speed, the volume flow rate and the pressure) differ significantly depending on the used tools and machining methods.
In the drawing embodiments of the invention are shown.
In
The tool spindle 5 has an axis 6. The tool spindle 5 can be moved in the direction of this axis on the tool carrier 7 in the marked direction Y to bring the tools 3, 4 selectively into engagement with the workpiece 2. Insofar, the gear grinding machine corresponds to the pre-known designs. The further necessary machine axes which are of course necessary for the machining are not further discussed as they are not relevant for the invention.
Relevant are now the cooling lubricant supply means 9 which serve for supplying cooling lubricant to the contact area between tool 3, 4 and workpiece 2.
According to the invention the cooling lubricant supply means 9 comprise a nozzle element 10 as can be seen in
Hereby, it is important that the nozzle element 10 is movably arranged in a plane E (see
The two stream exit openings 13 and 14 are designed differently. They have a rectangular shape in each case, wherein the height and width of the exit openings arc optimal adapted to the concrete tool application (see the below-mentioned remarks in connection with
The nozzle chambers 11, 12 can selectively be charged with cooling lubricant what is arranged by the machine control unit.
The relatively thin but relatively wide stream exit opening 13 is optimal for the lubrication of the grinding worm 4 during generative grinding. However, the relatively thick but less wide stream exit opening 14 is suitable for the lubrication of the grinding wheel 3 during profile grinding.
In
As can be seen in the section A-A according to
Accordingly, during the outlet of cooling lubricant via the nozzle chamber 11 a wide but relatively thin stream is obtained which is optimal for lubricating of the grinding worm 4 during generative grinding.
Contrary to this, the cooling lubricant flows with a relatively thick stream during the outlet from the nozzle chamber 12 which stream however is significantly smaller and is optimal for lubricating of the grinding wheel 3 during profile grinding.
If applicable, a further movement for the displacement of the nozzle element can be superposed to the displacement movement V and the pivoting movement S respectively to not only adjust the tools in an optimal way due to changes in the diameter but also to bring the respective optimal stream exit opening for the concerned grinding tool 3, 4 in the working position.
As far as above an (absolute) stationary arrangement of the nozzle at or on the machine bed is mentioned the following should be noted: On the actual machine bed mostly a machine stand is (movably) arranged, wherein in turn a swivelling part is arranged (movably) on the machine stand. Then, e.g. a slide is arranged movably on a linear guide (for the Y axis) on the swivelling part.
The stationary arrangement of the nozzle at or on the machine bed has to he understood in that way that the nozzle is not moved during the intended use during the grinding process. Thus, this is also the case by definition if the nozzle—as it may be mostly the case—is fixed on the swivelling part and thus not directly fixed, but indirectly fixed via the swivelling part and the machine stand with the machine bed so that however the nozzle is arranged stationary relatively to the bed during the intended use (although it can be moved (adjusted) by the swivelling part and the machine stand relatively to the actual machine bed).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 043 677.4 | Oct 2009 | DE | national |
