The invention relates to a process and a machine for the machining of pre-machined cogged or toothed workpieces, especially gears.
Pre-machined toothed or cogged workpieces are used in all technical areas. In many cases, the gear teeth are pre-machined and finished, after heat treatment, by means of, for example, grinding. In the case of automated machining, the problem of finding the pre-machined gear tooth gap exists, which is to allow for collision-free entrance of a finishing tool which may be a grinding wheel or a grinding worm. In present machines, which have only one spindle for clamping the workpiece, the problem is solved by known means of, for example, the scanning of the outer diameter of the gear teeth by means of an inductive sensor. During this so-called centering operation, the workpiece spindle generally rotates with a reduced number of revolutions in comparison to the machining, in order to measure the actual position of all or, at least, several of the tooth flanks, including the right as well as the left tooth flanks. In a subsequent evaluation process, the average value of the actual position is obtained, in order to balance out varying measurement deviations or hardening distortions. The position determined in such a way is specified as the target value of the control, in order to enter the finishing tool into the middle of the gear tooth gap. Afterwards the actual machining process can be started.
In machines which work according to a continuous grinding principle, the workpiece spindle still first has to be accelerated up to machining speed prior to entrance of the grinding worm into the gear tooth gaps of the workpiece and synchronized to angular position of the grinding spindle, before machining can begin.
All of these individual processes, namely workpiece exchange, measurement of the tooth flank positions, calculation of the average value, rotation of the workpiece into the target position and acceleration to the speed for machining, are unproductive times which make ground workpieces expensive.
To grind the gearing of toothed gears in continuous generating grinding, grinding machines with a multitude of NC axes are necessary. The trueing of the grinding worm requires in conventional trueing apparatuses still a number of additional trueing NC axes. A reduction of the number of axes reduces the manufacturing cost and thus the amortization cost which has to be charged onto the ground workpieces.
It is the object of the invention to reduce the costs of the fine machining of pre-machined toothed or cogged workpieces.
This object is achieved with the present invention which in one aspect, is directed to a process of the machining of pre-machined toothed or cogged workpieces on a finishing machine which comprises a machine base. A first slide is movable on the base. A tool spindle is mounted on the first slide for clamping a finishing tool. A carrier is movably positioned on the base and is movable into at least two positions. At least two workpiece spindles are rotatably mounted on the carrier and driven by one motor each. At least one centering probe is arranged. The centering operation for a collisionfree entrance of the tool into the workpiece tooth gaps is performed on an unmachined workpiece newly placed onto one of the workpiece spindles before the carrier reaches the position in which this unmachined workpiece meshes with the tool.
In another aspect this object is achieved by a machine for machining of pre-machined toothed or cogged workpieces. The machine comprises a base. A tool spindle for clamping a finishing tool is rotatably supported about a first axis and driven by a first motor. A carrier is movable by a second motor into at least two positions. At least two workpiece spindles are rotatably supported on the carrier for clamping a workpiece. Each workpiece spindle is driven by a third motor. Both workpiece spindles are connected to an rotary encoder each. At least one centering probe is arranged for measuring gear tooth flanks of one of the workpiece outside of the position of the carrier, in which this workpiece can be brought into mesh with the tool.
Other aspects of the present invention will become apparent as the description progresses.