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Machine structure

The PRÄZOPLAN is a planarly guided three-axis high precision machining center with the possibility to add a 4th and 5th axis. The two horizontal axes (X and Y) are generated by the planarly guided slide. It has a horizontal clamping surface on the workpiece side. A vertical axis (Z) supports the vertically arranged motor spindle.

A large natural granite is used as machine base. The upper side is a precisely lapped surface with a high flatness, which serves as guiding surface for the planarly guided slide and is comparable to a measuring plate with a high degree of accuracy. The planar guiding is aerostatic and, for this, the slide has aerostatic guiding areas directly at the bottom side. Thanks to the planar aerostatics, the movement in vertical direction and the pitch and roll is accurately guided. For the degrees of freedom in horizontal direction as well as for the yaw, a traverse which moves and drives a planarly guided slide is used. A ball screw is directly coupled to the planarly guided slide in X direction. In Y direction, an aerostatic lateral guide is used between the planarly guided slide and the traverse. Thus the slide has aerostatic lateral guides which are also integrated directly in the slide and is running against a precision-ground lateral surface of the traverse. This lateral guide is able to drive the degrees of freedom in Y direction and the yaw with a very high rigidity toward the traverse. This aerostatic arrangement does not induce a constraint between the rigid traverse and the planar guide, vertical degrees of freedom are decoupled.
The traverse can be moved in Y direction and serves as sliding block guide for the slide. The traverse is also consequently driven in an aerostatic way on the machine base made of natural granite. It is provided with a lateral guide which uses the entire lateral surface of the granite for taking the feed forces for the X direction. For this, the lateral faces of the granite are also precision-lapped to assure the required rectangularity and flatness.

A large-dimensioned column which carries the vertical axis is flanged directly to the rear side of the natural granite. This column forms, together with a counter holder, a gantry in a closed O-arrangement. The counter holder closes the structure on the front granite surface. Thanks to a lateral offset of the counter holder, the work area remains widely accessible from the front and the left side. A Z axis designed as a quill guarantees an ideal rigidity / mass ratio whereas the quill carries the guide rails and the motor spindle is directly integrated. The machine structure is mounted on a base frame consisting of a welded steel construction installed on air-spring damping elements.

The axis drive is realized for all axes by means of ball screws of the latest generation. The X drive is equipped with a driven nut and the Y axis is provided with a gantry combination. The planar guide is not a stack arrangement and therefore the center of mass of the slide and the drive kinematics are in alignment with one another. This allows an extremely quick and low-vibration positioning.

Linear scales are integrated in all axes. Due to the low axis structure compared to a stacked compound table, there are very small offsets between the axes and the TCP. Thereby rotational deviations will only have a small influence on the positioning accuracy.

The planar guiding system of the X and Y axis is protected against the penetration of chips, dirt and coolant by a novel sliding panel. A steel strip made in one piece and therefore easy to seal is provided with wipers on both longitudinal sides and can be rolled up in travel direction. The two- axis motion principle has been systematically put into practice and offers the advantage of a stack- free, very low structure and very small masses. Thanks to the rollable strip, the installation space of the cover in one direction may have a very compact design. There will be enough space for a stiff machine structure and perfect ergonomics. The machine operator can step close to the slide and the clamped workpieces from the front without leaning into the machine. The work area enclosure includes also a casing made of stainless steel which is easy to clean, a wiper for the quill from above and a perfectly positioned work area illumination.

The enclosure with a size of only 2 x 2 m is very compact and covers, besides the cooling device, all units of the machine. The bottom part is designed as a pan in which the entire machine structure is placed. This design allows the low- frequency, damping and vibration insulating installation of the machine; the machine can move freely on the air spring damper elements inside the enclosure. Furthermore, this design guarantees highest tightness against escaping coolant. The enclosure is a part of the thermal concept and encapsulates the machine completely against environmental influences and emissions. A coolant unit is located in the pan, the chip disposal is realized in the basic version by means of an easily accessible chip collecting device. The protective doors of the work area can be completely opened so that the workpiece is easily accessible.

Included in the ergonomic concept is the perfect height of the work area so that the operator can recognize finest machining details without bending forward. This is particularly important when using the machine for high-precision milling.

The standard version of the machine is equipped with a work spindle with lifetime grease lubrication which facilitates the machining of graphite and dust-generating materials. The spindle with HSK-E40 reaches 35000 rpm and is, with a power of 8 kW in S6-60 %, also suitable for roughing. The spindle temperature is balanced by a low-hysteresis cooling unit.

Further spindles are available including a high-precision spindle with aerostatic bearings and HSK-E25 reaching 80000 rpm.

On the right side of the work area, there is a tool change system with a 30-fold disk magazine and a quick tool changer. Due to the high dynamics, a chip-to-chip time according to VDI 2582 of 2.5 s is possible. The disk magazines in the system can be replaced by chain magazines which increases the number of tools to 100 or 150.

The left side of the work area is used for the automatic workpiece change. Different loading systems are available for this. The coolant unit included in the standard version can be replaced by a chip conveyor or by an extraction system for the dust generated during machining. The chips do not come into contact with the machine structure. Therefore a dry machining and a minimum lubrication is possible without affecting the thermal stability.

Various other options can be provided in modular design in order to optimize the machine for different applications. Thus the machine can be configured individually. You can compose the ideal mold milling machine or a machine for dynamic graphite machining, a milling machine for medium-sized batches of high-precision parts or an ergonomic shop floor machine for very high accuracy.

Developed with inspire AG / IWF of the ETH Zürich

A company of Krause & Mauser Group