The wbk Institute of Production Science—an offshoot of the Germany-based Karlsruhe Institute of Technology (KIT) focussed on application-oriented research, teaching and innovation in production science—and Dentsply Sirona, a US-based manufacturer of dental equipment and consumables, are working together on the ProIQ project, the main objective of which is to reduce dental instrument noise and vibration.
In the project, approaches for function-oriented quality assurance (QA) of microgears are being investigated by integrating inline measurement technology, namely the µCMM optical coordinate measuring machine (CMM) from Austria-based Bruker Alicona. The aim is to adaptively control the hobbing process to increase component quality while reducing scrap.
Key functions of complex products require high-precision components
The trend towards miniaturisation and the increasing use of high-precision components with tolerances of a few micrometres pose great challenges for manufacturing companies. Vivian Schiller and Daniel Gauder, PhD students at the wbk Institute of Production Science and members of the ProIQ project, are researching intelligent quality control (QC) loops, measurement technology (in-line and in-process) and component pairing strategies for the production of high-precision components. Their goal is to create QC loops in the sense of closed loop manufacturing. Thus, the integration of in-line metrology into production systems improves product quality and increases efficiency in production.The Federal Ministry of Education and Research (BMBF) in Germany is funding the ProIQ project as part of its photonics programme, which includes testing the suitability of the µCMM in the production environment.
After its initial installation at the wbk Institute of Production Science, the µCMM was integrated directly into Dentsply Sirona's production environment on the shop floor. Schiller commented: “As part of the ProIQ project, we measure the surface topography of microgears with involute profiles in the module range smaller than 0.3, focusing on the tooth flanks. Geometric parameters are then extracted from the captured point clouds. In addition, we derive function-oriented parameters, such as the rotary path deviation, from the point clouds.” Smallest possible deviations lead, for example, to reduced vibration of dental instruments, which benefits dentists and patients alike.
Attention must be paid not only to the metallic components’ surfaces, due to reflections, but also their steep flanks. “The tooth root area poses the greatest challenge, since the opposing flanks of a tooth space converge in this area,” explained Schiller.
The µCMM optical coordinate measuring machine (CMM) performing a 3D measurement of a microgear.
Low measurement uncertainty and short measurement times
To find the right measuring system for the task, various metrology systems were considered during the project preparation phase. In general, various criteria, such as measurement uncertainty, measurement speed and even information density, play an important role in the field of microgear measurement. Tactile measuring systems have been used for a long time due to having low measurement uncertainty, but their in-line integration presents a challenge because of the filigree geometries of microgears. Volumetric measurement systems provide a high level of information and enable 3D acquisition, even with undercuts, but they have a relatively high measurement uncertainty and require longer measurement times.
When evaluating the different systems, particular emphasis was placed on low measurement uncertainty and short measurement times. The µCMM was chosen on account of these factors as well as its providing focus variation, which combines a limited depth of focus with vertical scanning to deliver topographical and colour information. “If the workpiece material is optically cooperative and undercuts are not considered reasons for exclusion, focus variation offers non-contact, two-dimensional measurement recordings with high measurement point density,” explained Schiller.
A 3D image of the microgear produced by the µCMM.
Increased component quality with less scrap
Measurements obtained using the µCMM have proved exceptionally beneficial. Standard parameters (according to VDI/VDE 26121) as well as function-describing parameters (according to VDI/VDE 26082) after a single-flank rolling test can be derived based on the measurement data recorded in-line. Sustainable quality improvements can also be achieved. Starting from the evaluated parameters, the hobbing process can be adaptively controlled, which means increased component quality with less scrap.
Artificial intelligence for function prediction of the entire product
In the future, the wbk Institute of Production Science research team would like to rely increasingly on artificial intelligence (AI). In addition to adaptive control of the hobbing process, a method for adaptive assembly of microgears is being developed. Based on the measurement data and the features derived from the point clouds, AI models will predict the function of possible microgear pairs. Subsequently, an optimisation algorithm will enable the individual or selective assembly of the gears produced.
wbk Institute of Production Science
Dentsply Sirona
Bruker Alicona
References
1 VDI (2018–11). VDI/VDE 2612 Blatt 1 Measurement and testing of gears—evaluation of profile and helix measurements on cylindrical gears with involute profile.Available at: https://bit.ly/3Pol3ud
2 VDI (2001–03). VDI/VDE 2608 Tangential composite and radial composite inspection of cylindrical gears, bevel gears, worms and worm wheels.
Available at: https://bit.ly/3FG7QIx