Shaft cooler for a tool motor spindle

A shaft cooler (1) for a tool motor spindle (2), which has a rotating shaft (3), a static lance (4), and at least one coolant loop (7), which comprises a coolant inlet (5) and a coolant outlet (6), said shaft cooler being implemented such that the flow of the coolant from the static lance (4) into the rotating shaft (3) is performed via a flow path that includes radially-extending cooling holes (31) to cause the coolant to flow from a radially inside location to a radially outside location.

BACKGROUND OF THE INVENTION

The invention relates to a shaft cooling system for a tool motor spindle, comprising a rotating shaft, a static lance and at least one cooling circuit having a coolant intake and a coolant outlet.

The tool motor spindles are operated at high rotational speeds. These high rotational speeds make great demands on the bearing arrangement via which the spindle is mounted, so as to be rotatable about its spindle axis, in the spindle housing. In particular, the bearing friction must be reduced to an absolute minimum, in order to reduce the generation of heat and the wear. It is therefore necessary to provide a shaft cooling system.

Such a shaft cooling system is described in WO 2006/018394 A1. Described therein is a spindle device comprising a shaft device and a cooling device. The cooling device has at least one convection gap, via which a substantial portion of dissipated heat can be removed from the shaft device in targeted fashion.

Additionally known are tool motor spindles that are externally cooled for the purpose of removing the dissipated power.

The disadvantages that exist in the case of these known shaft cooling systems consist, in particular, in that, owing to the insufficient cooling action, an insufficiently reduced shaft growth occurs as a result of the thermal expansion.

The object of the invention therefore consists in proposing a shaft cooling system that, on the one hand, reduces a longitudinal growth of the shaft to a minimum and, on the other hand, owing to the smallness of the longitudinal growth, ensures a high measurement accuracy in the dimensional checking of the workpiece.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved in that the shaft cooling system is realized in such a way that feeding of the cooling medium into the static lance is effected via cooling bores, from the inside outwards into the rotating shaft.

DETAILED DESCRIPTION

FIG. 1shows a sectional view of a tool motor spindle2. A stator9, usually a 3-phase motor winding, which is fitted into a spindle sleeve, drives a rotor mounted on a through shaft3. The shaft3is realized as a hollow shaft and is multiply mounted in a spindle sleeve by means of a front bearing11and a rear bearing12. Furthermore, the shaft3is provided with a co-rotating chucking device, consisting of a tool chuck15and a collet10, and is located in the shaft bore14. This chucking device serves to chuck a machining tool by means of a collet10. The machining tool, not represented in the figure, is put into rotation by means of a motor. On the one hand, coolant, for internal cooling of the tool, is guided through the bore13of the tool chuck15, and on the other hand compressed air, for cleaning the tool interface, is also routed through the shaft3. The shaft3has cooling bores8, which are constituent parts of the shaft cooling system1.

All media mentioned are fed into the rotating shaft3through the lance4, which is provided with a central bore41. At the start of the cooling circuit7, the cooling medium is introduced into the coolant intake5and, after cooling, it emerges from the coolant outlet6.

The section A-A ofFIG. 1is represented inFIG. 2. In this example, four media are fed in or drawn off. The coolant forward-flow is denoted by16and the coolant return is denoted by17. The coolant leakage is drawn off via the connection18. The connections19and20serve, respectively, to supply the tool inner cooling (cooling lubricant) and to remove the leakage of the cooling lubricant. The taper cleaning air is supplied into the intake21. For the purpose of sealing the system, the sealing air is fed in via the line22.

The front shaft portion is shown, by way of example, in the section B-B inFIG. 3. In this embodiment, the shaft3is arranged with three cooling-circuit loops23,24and25distributed eccentrically and symmetrically. All three cooling loops23,24and25are realized with a forward-flow, axially parallel bore26and with a like second, return bore28adjacent thereto. In the foremost shaft region, these two bores26and28are connected to each other by a transverse bore27that is closed on one side, this constituting a cooling loop in the cooling circuit7.

FIG. 4shows a sectional view of the cooling system in the front portion of the lance4. A cooling medium delivered and temperature-controlled by a cooling device, for example water enriched with chemical stabilizing additives, is fed in under pressure to the connection5of the stationary lance4, which is screwed onto the rear spindle flange. The cooling medium is first brought into the transfer region30through two bores29that extend parallelwise. The radial transfer is effected at the end of the bores29, into a bore31equal in area, perpendicularly relative to the longitudinal axis. The cooling water now emerging from the stationary part passes, via the resultant circulatory flow between the lip-seals33, into the three forward-flow bores26(seeFIG. 3) of the shaft3, which are distributed by 120°. The cooling medium emerging under pressure thereby reinforces the sealing behaviour of the externally sealing lip-seals33in respect of the rotating shaft inner contour. In the region30of the radial transfer of the cooling medium, the latter undergoes additional acceleration, owing to the centrifugal force by the rotating shaft3. The exploitation of this physical property is the key to the realization of the transfer of media from the static portion to the dynamic portion. The cooling medium in the forward-flow bores31passes, via the reversing loops (transverse bores27(FIG. 3) in the foremost shaft portion), into the return bores32. In the region of the lance4, the radial transfer is effected from the rotating portion into the stationary portion, in that the cooling medium passes, via two circulatory flows37,38in two bores31,32extending perpendicularly relative to the longitudinal axis, into two return bores34that extend parallelwise. The integration of the lip-seals33naturally results in a different arrangement for the return, with a theoretically greater leakage at the seal facing away from the pressure chamber. In order to prevent this, in this example two radial transfers are provided for the purpose of halving the return pressure, which has been reduced in any case. This symmetrical seal arrangement (high-pressure flow on both sides enclosed by two low-pressure returns) serves to additionally wet the sealing surfaces of the inwardly facing lip-seals33. Owing to the lubricating effect, this results in an increased service life of the forward-flow seals, which are under greater pressure, as described below inFIG. 5. The leakage cooling medium is taken out of the lance4via the circulatory flows35and via a return of its own. The coolant leakage passes into the circulatory flow36. Finally, the cooling medium is returned into the cooling device via the connection6.

Represented inFIG. 5is the seal symmetry of the lip-seals33of the present invention. The lip-seals33are mounted on the lance4, between the rotating shaft3and the stationary lance4. The two outer lip-seals33are subjected to a lower pressure (1 bar) than are the two inner lip-seals33(3 bar). The forward-flow and return pressures occurring in the example result in differing differential pressures ensuing at the externally sealing lips33. Owing to this symmetrical arrangement, the inner lip-seals33, which are subjected to the greater loading, are lubricated and cooled, which results in an increased service life.

FIG. 6shows the routing of the taper cleaning air and of the sealing air in the tool motor spindle. The taper cleaning air is fed in via the connection44of the lance4, which is provided with a central bore41. This air is used to purge the tool taper, and is connected-in only when the spindle is at a standstill. When the spindle is rotating, the taper cleaning piston43is raised from the rotating sealing surface of the shaft3by the compression spring42. In the standstill state, the pressure of the taper cleaning air is able to move the piston43forwards, in order to lay open to the air the passage into the taper cleaning bore39of the shaft3. The sealing air45, fed into the connection46, serves to seal off the lance4in respect of the outer regions. The two leakage media (cooling medium and cooling lubricant) must be separated by means of the sealing air, because of their differing chemical composition. The radial transfer of the sealing air is effected at the end of the bore40, via the circulatory flow and the small bore to both sides of the shaft3. This positive pressure has the effect that, on the one hand, no leakage cooling water passes into the interior of the shaft and, on the other hand, no leakage cooling lubricant penetrates into the region of the lance4.

FIG. 7shows the leakage routing and the tool inner cooling. The leakage of the cooling water return escaping through the outer lip-seals33collects in the region of the circulatory flows47and48. The radial return of the leakage is effected through the two transverse bores that open perpendicularly into the axial leakage bore49.

Finally, the leakage of the cooling water is routed back into the cooling device via the connection50.

Cooling lubricant for the tool inner cooling is fed in via the connection51. This cooling lubricant is transferred through the stationary lance4to the stationary part52of an integrated rotary leadthrough that is already present. The cooling lubricant, finally, is routed forwards to the tool interface, via the bore56, through the rotating part53of this rotary leadthrough through the rest of the shaft portion.

Emerging or backed-up cooling lubricant from the rotary leadthrough is directed backwards, as leakage, via the axially extending leakage bore54, and routed out of the lance4via the connection55.

FIG. 8shows an exemplary variant of the shaft cooling system. In contrast toFIG. 7, which shows an inner rotary inlet52,53, this shaft cooling system has an outer rotary feeder57. This rotary feeder57can be exchanged without removal of the entire lance4. The sealing-air separation between the inner cooling medium and the shaft cooling medium is omitted. The tool inner cooling is denoted by the reference numeral58.

The purpose, and the advantages resulting therefrom, of cooling the rotating shaft is, on the one hand, to have a “cool shaft”, which limits to a minimum the longitudinal growth that ensues with increasing temperature. This results in improved machining quality of each machining centre where this motor spindle according to the invention is installed. The second advantage of this reduced longitudinal growth of the shaft, or of the tool holder in respect of the spindle nose, is an improved measurement accuracy in the dimensional checking of workpieces. This enables 3-D probes to be inserted in the “cool” tool interface, without the sensitive measuring probe lengthening concomitantly as a result of an excessively warm shaft, this resulting in highly accurate measurement results. Owing to the lesser temperature difference between the shaft and the bearing housing, the bearings can be designed with a narrower tolerance range, this resulting in greater rigidity during operation and in an improved service life of the motor spindle.