Gear cutting – milling – or planing – Milling – Process
Patent
1995-08-11
1998-03-17
Pitts, A. L.
Gear cutting, milling, or planing
Milling
Process
409 80, 409 84, B23C 900
Patent
active
057279128
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a controller and a method for optimization of metal-working on CNC-operated machine tools, especially on CNC-operated milling machines and machining centers.
While CNC-operated machine tools have existed for years, their efficiency and usefulness has been limited by their incapability to take into account many factors in the programming stage which influence production efficiency, including: number of workpieces in a run, operating cost, tool replacement time, tool cost, etc. In addition, the rigidly deterministic nature of CNC-operated machine tool programming is incapable of allowing for unforseeable changes in real-time cutting conditions such as depth and width of metal cutting, tool wear, non-uniformity of workpiece blank, etc.
A recent development in the field of CNC-operated machine tools provides for apparatus for controlling a machine tool as a function of torque load on a cutting tool when the torque load respectively exceeds or falls below a predetermined upper or lower critical torque load. For example, U.S. Pat. No. 4,237,408 describes critical torque loads including, inter alia, a catastrophic torque limit relative to the machine structure, a catastrophic torque limit relative to a particular tool and a minimum torque limit that should be present if a cutting tool is in contact with the workpiece.
It is one of the objects of the present invention to overcome the limitations and disadvantages of today's CNC-operated machine tools and to provide an optimizing controller for machine tools, in particular for CNC-operated milling machines and machining centers, which calculates the optimal cutting modes according to production efficiency criteria, and automatically provides adaptive feed and spindle speed control responding to real-time cutting conditions, maintains a constant and presettable spindle torque and/or tool life, ensures optimal machining operation, prevents tool breakage and indicates tool status.
According to the invention, this is achieved by providing a controller for optimization of metal-working on CNC-operated machine tools, having a main drive powering the tool spindle of said machine tools and feed drives powering the feed mechanism of said machine tools, said feed drives being controllable to produce a feed rate determined either by a predetermined setting of the cutting torque produced by said tool spindle, or by said controller overriding said setting in a teaching mode of said controller, comprising a first unit for monitoring the torque of the main drive of said machine tool to establish the actual, instantaneous cutting torque; a second unit for setting the rated cutting torque in said teaching mode in dependence on said main-drive torque as monitored; a third unit for calculating the feed rate required to maintain said cutting torque at a constant level and controlling the feed drive of said machine tool; a fourth unit responsive to said monitored main-drive torque and providing feed rate limiting signals to said third unit for protecting the tool against breakage, characterized in that said unit for calculating said feed rate is addressed by a compensator unit responsive, on the one hand, to signals from a comparator unit comparing said torque as set with the actual, instantaneous torque as indicated by said first unit and, on the other hand, to signals from an identifier unit calculating the instantaneous cross-sectional area of the cut in response to signals from both said first, main-drive torque monitoring unit and said feed-rate calculating unit, said compensator unit facilitating a high-precision stabilization of said torque.
The invention furthermore provides a method for optimization of metal-working on CNC-operated machine tools having a main drive powering the tool spindle of said machine tools and feed drives powering the feed mechanism of said machine tools, said feed drives being controllable to produce a feed rate determined by a predetermined setting of the cutting torque produced by said tool spindle, or by said controll
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Fainstein Boris
Karasin Igor
Rubashkin Igor
Tabachnik Eduard
Warshawski Joel P.
Kirkman Christopher
Omat Ltd.
Pitts A. L.
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