DE3804963C1 - Pneumatic-mechanical tool-clamping system for hollow work spindles carried in rolling bearings - Google Patents

Abstract

The invention relates to a pneumatic-mechanical tool-clamping system for hollow work spindles carried in rolling bearings, with provision for automatic tool change, the collet being pneumatically released and mechanically tightened. In this arrangement, the back-up force for the release force, by means of a differential cylinder which is axially displaceable in a ball box and secured against rotation, is passed into the hollow work spindle via a sleeve in such a way that the rolling bearings remain unaffected by it, the hollow work spindle being given a fluid column which encourages a uniform temperature distribution. The release force is transmitted by the fluid column between a rear pressure piston and a front pressure piston in the hollow work spindle to the collet, the closing force being transmitted by a rotating tension wire of the smallest possible cross-section from the rear pressure piston, which can be acted upon by tension springs, to the front pressure piston and to the collet. The fluid column advantageously has as high a heat capacity as possible and/or as low a specific weight as possible.

Description

The invention relates to a pneumatic-mechanical tool clamping system for roller bearing, hollow work spindles according to the generic term of Claim 1.

Are known for pressure medium (for releasing) and mechanical (for tensioning) actuated tool clamping systems, for example, from the genus used DE-PS 25 45 713 and from DD-PS 2 19 137 or DE- OS 35 33 623. In the known clamping systems, the clamping force is through Tension springs applied, which a tension via a push-pull rod pull the pliers into the spindle cone. The loosening power is a pressure acted upon cylinder and generated via the push-pull rod on the Transfer collet. The reaction opposite to the release force Force can be absorbed in different ways. It can be a force flow within the spindle can be adjusted by the cylinder with the Spindle is installed directly coupled. Through the rotating cylinder becomes the bending critical speed  the spindle is reduced, which is particularly the case with high-frequency work spindles is disadvantageous, since this usually at a limit speed of Be operated 10% -15% below the critical speed, in addition, a complex rotary union would have to be used for the printing medium be used. Another option is the cylinder not to be firmly connected to the spindle. Thereby the recreational power taken up by the roller bearings of the spindle, which thereby an unzu can experience casual stress. It is also a construction with special ball bearings known in which a bearing ring relative to another is axially displaceable in one direction. Through a cylinder the spindle turns against a housing that absorbs the reaction force pressed. However, only spring-loaded single bearings can be used for this be used and not for reasons of the required rigidity the spindle against radially attacking cutting forces, especially with milling spindles Often chosen construction of two rigidly matched bearing pairs with working fixed bearing and rear floating bearing. Common feature of the ge called tool clamping systems is that working in the hollow spindle is a pull-push rod, which the inner cross section of the hollow work spindle. The through the rotor and the rolling bearings generated heat can not be optimally distributed, which leads to locally high Temperatures.

The invention has for its object a tool clamping system to create the kind outlined in the preamble of claim 1 that the avoids disadvantages mentioned, in particular the rotating masses should not be enlarged, no impermissible forces during the Tool change should act on the rolling bearing, the heat discharge from the  Rolling bearings and the rotor should not be affected, the main dimensions of a comparable conventional work spindle should be preserved as well as the thermal state in the hollow Work spindle should be improved.

This object is achieved by the invention according to claim 1 solved.

The invention essentially provides the following advantages achieved: The reaction force when releasing the tool is not achieved by the Rolling bearings added, so that impermissible, permanent deformation The rolling elements are already on at relatively low loads kick, avoided. At the same time, the rotating masses do not enlarged. By using a liquid column inside The hollow work spindle for releasing the collet can be attached to a rotating push-push rod are dispensed with and thus the permissible subcritical speed of the spindle can be increased. The density of the Liquid column is ½ of density when using water of the steel bar material. Becomes a liquid with high thermal conductivity ability, d. B. water, also results in a clear better heat dissipation from the rotor and the bearings, because inside the convection of liquid occurs through which the temperature differences along the spindle are compensated, and because of missing joint gaps the heat transfer to the liquid column is optimal.

The dissipation of the heat loss from the hollow work spindle and extensive compensation of different temperatures along the spindle is critical for two reasons:

Grease-lubricated spindle bearings are maintenance-free and do not require any Additional units, but for thermal reasons, do not allow them Oil mist or cooling oil lubrication achievable speeds. With the invent According to the internal cooling, the permissible speed for grease-lubricated bearings can be increased. This eliminates auxiliary units,  or applications are opened up that do not use oil lubrication allow, e.g. B. drilling circuit boards for the otherwise expensive air storage would have to be used. Another advantage is that Increasing the clamping accuracy. With known high frequency working pin For milling, temperatures are often measured in the cone, which results in a dimension change of the cone that is no longer negligible to have. Depending on the temperature gradient in the longitudinal direction of the spindle the cone angle changes so that the tool wobbles in µm Range is possible. This immediately worsens the work result.

A further development of the invention results from claim 2.

The tool clamping system according to the invention is illustrated below using the example a PCB drilling spindle described in more detail.

Fig. 6 shows a complete PCB drilling spindle with the possibility of automatic tool change. The

Fig. 1 to 5 are enlarged sections.

The bearing pairs 14 and 18 for a hollow work spindle 15 are each rigidly matched, the rear bearing pair 14 acts as a floating bearing, the front bearing pair 18 as a fixed bearing. A rotor 16 is located between the bearing pairs 14, 18 .

The release force for a collet 20 is generated by a pneumatic cylinder 1, 2, 6 having a piston 1 , the cylinder housing 2 of which is mounted in a longitudinally displaceable manner in the spindle housing 17 via a ball bushing 4 .

As can be seen from FIGS. 4 to 6, by loading a working space 3 of the cylinder, the piston 1 is moved forward until it comes to rest on the end face of a rear pressure piston 11 . At the same time, the cylinder housing 2 is moved backwards. As a result, an annular driver 6 comes into contact with a sleeve 9 . At this moment, a pressure force builds up on the rear pressure piston 11 and a reaction force on the cylinder housing 2 .

The cylinder housing 2 of the pneumatic cylinder is axially movable in relation to the bearing housing 8 and secured against rotation by a pin 7 .

The force transmitted from the piston 1 of the pneumatic cylinder to the rear pressure piston 11 ( FIG. 4, FIG. 3) corresponds to the piston area in the working chamber 3 multiplied by the working pressure. The supporting force for the hollow work spindle 15 , which is transmitted from the driver 6 to the sleeve 9 , is the same amount, since the friction of the ball bushing 4 can be neglected. The bearing pairs 14 and 18 remain unaffected by the release force.

The release force deforms the tension springs 10 (FIGS . 3, 6) and displaces the rear pressure piston 11 in the direction of the collet 20 . A liquid column 13 located in the interior of the hollow work spindle 15 is compressed ( FIGS. 1, 3, 6) and, when a pressure proportional to the releasing force of the collet 20 is reached, displaces a front pressure piston 19 which is fixedly connected to the collet 20 , so that the collet 20 opens in the cone 21 .

After the tool is changed, the pneumatic cylinder becomes Clamping of the tool relieved of pressure.

The piston 1 is moved back by springs 5 ( FIGS. 4, 6) and the cylinder housing 2 is pushed forward.

The tension springs 10 move the rear pressure piston 11 back and this pulls the front pressure piston 19 back via a high-strength puller wire 12 (FIGS . 1, 3, 6).

As a result, the collet 20 is pulled back into the cone 21 and thereby closed. The closing or clamping force, which is applied by the tension springs 10 , is supported by the hollow work spindle 15 .

Claims (2)

1. Pneumatic-mechanical tool clamping system for roller-bearing, hollow work spindles with the possibility of automatic tool change, the tool gripping collet of the clamping system being released pneumatically and mechanically clamped under the action of clamping springs arranged outside the spindle, characterized in that the supporting force For the release force with a piston ( 1 ) having a differential cylinder ( 1, 2, 6 ) which is axially displaceable in a ball bushing ( 4 ) and secured against rotation ( 7 ), so via a sleeve ( 9 ) into the hollow work spindle ( is initiated 15) that the rolling bearings (14, 18) derArbeitsspindel (15) of which remain unaffected in that the hollow work spindle (15) contains a column of liquid (13), which promotes uniform temperature distribution, that the release force through the liquid column (13 ) between a rear pressure piston ( 11 ) and a front, with the collet ( 20 ) which pressure piston ( 19 ) in the hollow work spindle is transferred to the collet ( 20 ) and that the closing force by a co-rotating pull wire ( 12 ) with the smallest possible cross-section from the rear pressure piston ( 11 ), which can be acted upon by the tension springs ( 10 ) the front pressure piston ( 19 ) and thus transferred to the collet ( 20 ). 2. Tool clamping system according to claim 1, characterized in that the liquid column ( 13 ) has the highest possible heat capacity and / or the lowest possible specific weight.