A Phoenix gear cutting machine, integrated into a closed-loop system for inspection and corrective settings, cuts a spiral bevel gear.

The complex geometry of spiral bevel and hypoid gears makes it a tedious, timeconsuming process to turn a gear design into a finished product that works as intended. Gear manufacturers must go through a trial-and-error process of design, prototype manufacture, inspection, and adjustment of machine settings to refine the part geometry. And they often must repeat the entire process more than once to obtain a dimensionally acceptable gear.

Over the years, advances in computers and software have eliminated much of the tedium involved. But still, this trial-and-error process takes several days.

Now, an integrated, closed-loop gear development and manufacturing system brings the three key elements of this process together so gear manufacturers can perform the trial-and-error steps more efficiently, thereby reducing the time from days to hours, and minimizing the potential for human error. These key elements include:

• Gear design, using software that analyzes the tooth surfaces and their mating contact characteristics before parts are generated.

• Machine settings (CNC program) for the gear-generating machine.

• Gear evaluation, using software to verify that the generated gear matches the design.

In the early 1980s, The Gleason Works, Rochester, N.Y., developed the software for this closed loop system: a gear design and analysis package that was available to gear manufacturers online, via modem. Users could move sequentially through design and analysis programs to calculate machine settings for an optimum gear design. The late ‘80s brought enhancements such as graphic capabilities, and multi-tasking, letting users perform these tasks on desktop workstations.

Evaluating a gear before it exists

The first step in the closed-loop process is to establish an optimum theoretical gear design. Using Gleason’s design and analysis software package, called CAGE (Computer-Aided Gear Engineering), the design engineer enters basic gear parameters, such as number of teeth, diametral pitch, and face width. The software helps the engineer develop and optimize gear tooth geometry of bevel and hypoid gears based on customer application requirements.

As part of the design process, the analysis portion of the software predicts how the theoretical gear will mesh with its mating gear, so the engineer can “test” gearset performance before any metal is cut. At this point, the gear only exists in the computer as a set of mathematical parameters, along with data on the desired contact conditions between the two gears and their desired uniformity-of-motion.

Tooth contact analysis is the primary method for determining the optimum tooth geometry. Software programs such as CAGE simulate tooth contact between two mating gears, commonly called the gear and pinion, in a gearset. The software displays the contact pattern that would occur if the gears were rolled together in a test machine, as well as the smoothness of the rolling motion. It also calculates tooth bending and contact stresses under the expected load. This allows the engineer to optimize the contact pattern — uniformly distributing the load to minimize tooth contact stresses.

Once the theoretical gear design is established, the software produces machine instructions, which the operator transfers to a computer disk and loads into the CNC controller of a gear cutting machine. With Gleason’s Phoenix cutting machine, for example, these instructions enable a Fanuc controller to simultaneously control six axes of machine motion, three linear and three rotational, that generate the tooth shape. An operator then uses the machine instructions to cut a trial gear.

Each axis of motion uses a separate motor — five ac servo motors and one spindle motor in all — to drive the cutter and work head at the required velocities and accelerations. Incremental rotary and linear encoders provide position feedback information for the rotary and linear axes, respectively.

Continue on page 2