Modern gear calculation programs give us the possibility to determine the load carrying capacity and the noise
behavior of a gear transmission considering the shaft and bearing system, the tooth modifications and the
production deviations.While load and stress optimized tooth modifications are quite insensible to the normal
production deviations; noise and vibration optimized tooth modifications need a much higher production
accuracy because of the low values of the transmission errors caused by the changes of the mesh stiffness.
The numerical simulation leads often to more complex modifications which can not be realized with normal
standard modifications like crowning and root or tip relief. Topological modifications are required and have to
be realized in the grinding process. Differences between the common profile grinding method and the
generating grinding method based on the different contact situations between grinding wheel and gear gap
will be shown.
More and more companies discover the high improvement potential of topological modifications with which
gears can be modified where it is required -- the generating engagement relief of a helical gear corresponds to
the normal tip and root relief of a spur gear. The teeth are modified in the area of highest pressure (at the
beginning and the end of the mesh). A contact area with a lower Herzian pressure can transmit more load.
The topological modifications show big advantages for the noise and vibration behavior also due to the much
higher variability in direction of contact pattern. Gears with even overlap ratio should for instance be modified
as less as possible, otherwise the basic advantages of the constant contact line is not given anymore.
Unfortunately, a load optimized tooth flank modification is not always a noise optimized modification also -- a
compromise between optimized load distribution and low noise has to be found.
The basic of the modern gear calculation programs is the exact determination of the mesh stiffness. All the
secondary influences like shaft bending and deflection in the bearings should also to be considered. For the
load distribution calculation a static view is often sufficient. The basic of the dynamic analysis is the load over
the time in form of a FFT analysis. The running speed and the behavior of the oscillating system have also to
be considered. In a practical example the calculation possibilitieswill be shown. Itwill be demonstrated how an
optimized tooth modification can be found. In the calculation possible production deviations have to be
considered -- the feedback from the production to the design department is essential.
To satisfy the new requirements the gear grinders manufactures had and have to improve their machines
every year. Today, a serial production of gears in quality Q=1 according DIN 3962 (AGMA >15) is possible, if
requested. This improvement was basically been possible with the substitution of the mechanical
transmissions in the grinder with themodern CNC controls. By introducing the torque motor as the main table
drive of a grinder the last gear transmission disappeared in the gear grinder field.
The accuracy of a gear grinder depends basically from the accuracy of the table drive. The modern torque
motor shows together with the direct mounted encoder high advantages in comparison to the mechanical
worm/worm gear drive. Problems like worm gear wear, backlash and deviations are not known in a torque
motor anymore. Without excitation, it realizes an incredible constant movement of the table axis. Machine
frequencies -- the main reason for the almost disappearing of the generating grinders in the nineties -- are not
transmitted to the gear anymore. This and the possibility to realize topologicalmodifications could now lead to
a Renaissance of the generating grinders. They can be built in such a way that also form grinding is possible
on the same machine.