Tool changing – Process
Patent
1993-09-10
1996-01-23
Briggs, William
Tool changing
Process
483 56, B73Q 3157
Patent
active
054861519
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a Machining Center for machining a workpiece by of one out of at least two, automatically interchangeable, tools that are each clamped in an individually driven work spindle and can be applied alternately to the workpiece by numerically controlled movements.
When machining workpieces, the cycle time required for completion comprises machine time, during which the workpiece is physically modified, and also downtime required for all non-productive operations, such as changing workpieces or changing tools on the machine.
For small components with machining cycles requiting different tools, downtime takes up an important fraction of the total cycle time. Due to the short machine time typical for such components and the relatively long chip-to-chip time due to changing tools, downtime can even exceed machine time. In such cases machining of the workpieces does not represent an economic optimum.
Devices are known with spindles applied alternately that aim also at reducing chip-to chip time. Such a device applicable to existing machine tools is described, for example, in the registered design DEV-9015333. It comprises two work spindles, a drive- and a positioning-motor and groups of pinions and clutches. This device permits the changing of tools simultaneously with machine time but still does not resolve the problem of the long chip-to-chip time, as the individual steps of operation, e.g. "unlock indexing", "brake spindle", "actuate clutch", "accelerate spindle" and "unlock indexing" still are sequential in time. No time is thus gained as compared with rapid conventional solutions.
Also similar machines with two individually driven work spindles are known. They are fitted to a common spindle support in opposite directions by 180.degree.. The changing operation is effected by rotating the spindle support by 180.degree.. An example for this is the metal-cutting machine sold under the trademark MONOPOSTO of the CMS OPTICAL company, that makes it possible to carry out movements in parallel operation. However, the relatively long half-circle described during rotation for changing as well as the need for locking and unlocking operations due to the not numerically controlled changing process do not permit appreciable savings in time as compared with rapid conventional solutions.
In addition devices or machines are known such as the ones mentioned above, in which the attempt is made to compensate for the unfavorable influence of the time required for the tool change on the cycle time used to complete an individual workpiece by applying simultaneously several tools to several workpieces. For example, DE 4020997A1 and CH-654237 show machine tools with several spindles for interchangeable tools, the spindles with axes parallel to each other being fitted to a common spindle support. In these machines each spindle machines one particular workpiece with a single tool. For changing tools, the entire spindle support is moved to a changing position. During the time required for this operation (displacement of the spindle support to the changing position, changing of tools, return of the spindle support to the working position) no workpiece can be machined thereby. The unfavorable ratio for machine time to downtime in such a two-spindle machine can only be improved by using several parallel spindles (actually up to eight spindles are used). A very serious drawback of this solution is that, when changing workpieces adjustment work required for alignment of the workpieces is unproportionally time consuming, thus reducing overall productivity and flexibility.
CH-666432 shows a machine tool with two spindles with parallel axes for the workpieces and with two turrets with parallel axes for various tools. The same workpiece can either be machined simultaneously with two tools or in sequence by one single tool in each of the two turrets whereby, collision of file tools or of the turrets is avoided. Automatic changing of tools stored in a magazine is not provided ho
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Bergmann Klaus
Frauenfelder Martin
Schwab Jacques
Briggs William
Mikron S. A. Agno
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