With plastic gears, often all teeth have to be measured due to the manufacturing process. Computed tomography allows the entire workpiece to be captured in a single measuring process, thus achieving an enormous time advantage.

Using the CT data, gear evaluation conforming to international standards is possible. In addition, the deviations from the CAD model can be determined for the entire surface by tomography and internal geometries or voids can be measured.

Complete Measurement of Plastic Gears

Gears are used primarily for transmitting torques with zero slippage and are used in nearly every technical device. Examples can be found in electric motors, auto transmissions, robots, pumps, and printers. Plastic gears produced by injection molding are being used more frequently, which places new demands on manufacturing and metrology. Due to varying process parameters, such as the mold fill level or shrinkage, each tooth can theoretically look different, so every tooth must be measured. This makes tactile measurement very time-intensive, taking up to several hours.

Computed tomography coordinate measuring machines (CT-CMM) provide an enormous time advantage. The measurement and evaluation take just a few seconds. As the entire workpiece is always captured, the time required is nearly independent of the number of geometrical characteristics to be measured. Further reduction in measurement time can be achieved by loading several workpieces in the machine at the same time, which are then separated automatically by the software.

The CT always provides a complete measurement point cloud of the workpiece instead of individual scan lines. This means that all teeth can be evaluated at every point, with as many sections as desired, without increasing the measurement time. The captured measurement point cloud can also be used for a color- coded comparison to the CAD model. The volume data that is also generated allows inspection of the gear for voids, for example. The areas of application range from incoming goods and manufacturing monitoring to quality assurance and development.

Because measuring the gears is not limited by the diameter of a probe sphere, even very small moduli can be measured. Without the mechanical filtering effect of the probe sphere, higher detail resolution can be achieved. CT sensor systems are relatively easy to operate, and the workpiece fixtures are typically easily produced, even for very small gears. The measurement point cloud can also be used for pinpoint analysis and simulation of tactile scanning paths or point distributions. With identical measurement positions, CT measurements can thus be compared with conventional tactile measurements.
The automated analysis of measured data with Win-Werth® GearMeasure provides further time savings. The analysis complies with standards and has appropriate filter options to ensure optimal comparability with classical methods. In the WinWerth® 3D measurement software, the teeth can be analyzed with any references desired, based on the subsequent application. For example, teeth on a shaft can be evaluated referring to different datums on the shaft. With WinWerth® Gear-Measure, a uniform software solution is available for a wide range of gear types. Spur gears with involute teeth, with or without lead angle, external and internal teeth, worm wheels (ZI, ZA, ZN, ZK, ZX), and any arbitrary profile forms such as cycloid teeth or rotors can be analyzed.