Abstract:
A workpiece mounting for a working machine, with a circular mounting plate rotatable in a horizontal plane for chucking a workpiece and with a conveying unit for moving the mounting plate in the horizontal plane, wherein the mounting plate is movable on air support on a horizontal table, and is clampable on the conveying unit in any desired rotational position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a workpiece mounting for a material removal working machine according to the preamble of claim  1 . 
     2. Description of the Prior Art 
     In working machines, such as, for example, drilling and milling machines and in particular laser working machines, the workpiece is chucked onto a workpiece mounting for the working. In order to position the workpiece with respect to the working tools, or with respect to the laser beam, and to generate the working advance, it is known to chuck the workpiece onto a circular mounting plate which is supported rotatably in a horizontal plane and is movable in this horizontal plane by means of a conveying unit. The mounting plate is herein supported rotatably by means of a pivot bearing which is attached on the conveying unit and is moved by means of it. In order to be able to work heavy work pieces, a corresponding high loading capacity of the mounting plate and its pivot bearing is necessary. The bearing is therefore constructionally expensive and has a high weight. Accordingly, the conveying unit, which is conventionally movable in the X and Y axes, must be laid out to be highly loadable. 
     Such expensive workpiece mountings are justified for series productions. The cost of working of single workpieces, for example the laser working of injection molding form tools, however, is excessively increased due to such workpiece mountings. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the task of providing a workpiece mounting which is constructed cost-effectively and also is suitable for heavy workpieces. 
     This task is solved according to the invention through a workpiece mounting with the characteristics of claim  1 . 
     Advantageous realizations of the invention are specified in the dependent claims. 
     The essential concept of the invention comprises chucking the workpiece onto a mounting plate, which, air-supported on a horizontal table surface, is freely movable, in particular can also be rotated about its vertical axis. In the desired rotary position the mounting plate is clamped on the conveying unit. The conveying unit is preferably formed of two linear guidances such that the mounting plate clamped on the conveying unit can be moved under control in the X and Y direction by means of the conveying unit. 
     Based on the air support of the mounting plate on the table surface, the mounting plate is movable free of friction even if heavy workpieces, of, for example, up to 200 kg are chucked. With the clamping disengaged, the mounting plate can be moved, in particular also be moved manually, on the table surface. The mounting plate can in particular also be rotated in order to orient the chucked workpiece in the X and Y directions of the linear guidances of the conveying unit. After rotating the mounting plate for angular positioning, the mounting plate is clamped on the conveying unit. The linear advance in the X direction and the Y direction for the working can now be carried out by means of the conveying unit. Since the mounting plate is air-supported, it can be moved free of friction by the conveying unit such that the conveying unit only needs to apply low displacement forces even with heavy workpieces. The conveying unit can therefore be laid out simply and cost-effectively. 
     Depending on the requirements, the linear guidances of the conveying unit can be driven by motor or manually, wherein, in the case of a motor drive, a joy stick control or also a CNC control can be used. 
     In a useful implementation the mounting plate is clamped at its circumference on the conveying unit. For this purpose the mounting plate can comprise a circumferential flange, which is grasped by a clamping device of the conveying unit. A simple implementation is obtained thereby that the conveying unit comprises a circular-arc form seat, which extends under the circumferential flange of the mounting plate, wherein clamping means, for example, in the form of clamping jaws, clamp the circumferential flange securely on this seat. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the invention will be explained in further detail in conjunction with an embodiment example depicted in the drawing. Therein show: 
     FIG. 1 a top view onto the workpiece mounting, 
     FIG. 2 an enlarged partial representation of FIG. 1, and 
     FIG. 3 a vertical section along line A—A in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiment example shows a workpiece mounting for a laser working machine. In particular with this working machine heavy workpieces can be worked. The working machine can be used, for example for the purpose of eliminating and reworking by means of laser beams defects in injection mold form tools. 
     Underneath the conventional laser beam generator and focusing unit, not shown in the drawing, is disposed a horizontal table surface  10 . The table surface  10  is produced of metal sheets adhered one to the other under pressure and comprises a planarity of better than 0.1 mm. 
     On the table surface  10  is disposed an X-Y conveying unit, which comprises an X linear guidance  12  and a Y linear guidance  14 . The Y linear guidance  14  comprises a positioning drive  16  fixed on the table surface  10 , which comprises an electric motor and a position sender serving for feed back. The positioning drive  16  drives via a spindle  18 , for example a ballscrew, a linearly guided Y carriage  20 . The Y carriage  20  carries a positioning drive  22 , which also comprises an electric motor and a position sender for reporting-back. The positioning drive  22  drives via a spindle  24 , for example a ballscrew, a linearly guided X carriage  26 . Due to the linear guidances  12  and  14  disposed at right angles to one another, the X carriage can be moved via the positioning drives  16  and  22  with coordinate control on the plane of the table surface  10 . The coordinate control can take place via a joy stick, if an individual manual positioning of the workpiece to be worked is desired. A coordinate control via a programmable CNC control is also possible. 
     The linear guidances  12  and  14  are structured in a manner known per se such that a detailed description is not required. 
     For chucking the workpiece a circular mounting plate  28  is provided which has a diameter adapted to the application purpose, for example a diameter of approximately 350 mm. The mounting plate  28  carries at its top side a pattern of apertures known per se which serves for inserting chucking means for the workpiece to be chucked. Formed on at the circumference of the mounting plate  28  is a margin  30  directed downwardly, into which is set a base of a porous sintered aluminum plate. Via a (not shown) connection line and a controllable magnet valve, air under pressure, for example at a pressure of approximately 3 bar, is introduced into the hollow body formed by the mounting plate  28  and the base. This air emanates through the porous base over its entire surface and forms an air cushion which bears the mounting plate  28  with an air gap  32  of up to approximately 0.2 mm between the table surface  10  and the base, or the lower edge of margin  30 . If the compressed air is introduced under the mounting plate  28 , the mounting plate  28  is supported in this way through the air cushion and is mounted freely floating and thus free of friction. At an air consumption of approximately 17 l/min at a pressure of 3 bar, a bearing force of the mounting plate  28  is obtained of, for example, up to 200 kg. If the air supply is switched off via the magnet valve, the mounting plate  28  becomes deposited with its margin  30  on the table surface  10  and is seated immovably and securely. 
     When the air cushion under the base of the mounting plate  28  is built up, the mounting plate  28 , due to its friction-free air support, can readily be displaced manually on the table surface  10  and be rotated about its vertical axis. By rotating the mounting plate  28 , in this way a workpiece chucked on the mounting plate  28  can be aligned, in particular in its angular position, such that the axes of the workpiece correspond to the X and Y axes of the linear guidances  12  and  14 . 
     As soon as the mounting plate  28  is manually aligned, it is clamped on the X-Y conveying unit in order to be securely connected with it. For this purpose the mounting plate  28  comprises at the outer circumference approximately at half the height of its margin  30  a flange  34  extending over the entire circumference and projecting radially outwardly. On the X carriage  26 , displaceable on the X linear guidance  12 , is fastened a metal connection sheet  36  projecting parallel to the plane of the table surface  10 . The metal connection sheet  36  is, as evident in FIG. 3, bolt-connected with the X carriage  26  and projects from it. On the outer edge facing away from the X carriage  26 , of the metal connection sheet  36  is fastened a seat  38  on the underside of the metal connection sheet  36 , which has the form of a circular arc segment with the radius of the mounting plate  28 . If the mounting plate  28  while being air supported is slid against the seat  38 , the seat  38  extends under the flange  34  of the mounting plate  28  and comes to rest on the outer circumference of the margin  30 . Outside of the outer circumference of flange  34  are provided in the seat  38 , offset angularly with respect to one another in the circumferential direction, two threaded bores  40 . Onto the metal connection sheet  36  are set clamping jaws  42  in such position that a vertical continuous bore  44  of the clamping jaw  42  is axially aligned with one of the threaded bores  40  of the seat  38 . Clamping levers  46  are each inserted with a threaded bolt  48  through the bores  44  and screwed into the threaded bores  40 . The clamping levers  46  are each seated on the clamping jaws  42 , in order to tension these axially against the seat  38 . Each of the clamping jaws  42  comprise a jaw segment  50 , which extends over the flange  34  and is in contact on the outer circumference of margin  30 . If the mounting plate  28  is slid with its flange  34  against the seat  38 , such that it extends beneath the flange  34 , the jaw segments  50  are set on the flange  34 . By tightening the clamping levers  46 , the jaw segments  50  are tensioned against the flange  34  such that this flange  34  and, consequently, the mounting plate  28  is clamped on the seat  38  and is securely connected with the X carriage via the metal connection sheet  36 . 
     Through the clamping the mounting plate  28  is attached torsionally tight on the X carriage and thus on the conveying unit. Via the positioning drives  16  and  22  the mounting plate  28  can be moved under control in the X and Y direction. 
     The metal connection sheet  36  has sufficient elasticity in the vertical Z direction, perpendicular to the plane of the table surface  10 , such that the mounting plate  28  can move vertically over the height of the air gap  32  without a force being transmitted in the Z direction onto the X-Y conveying unit. 
     The present invention having been herein described in reference to a preferred embodiment thereof, it will be apparent to one skilled in the art that various changes and modifications may be made to this invention without departing from the scope of the following claims.