Eric S. Stanfield

Dimensional metrology of bipolar fuel cell plates using laser spot triangulation probes

As in any engineering component, manufacturing a bipolar fuel cell plate for a polymer electrolyte membrane (PEM) hydrogen fuel cell power stack to within its stated design tolerances is critical in achieving the intended function. In a bipolar fuel cell plate, the dimensional features of interest include channel width, channel height, channel parallelism, side wall taper, straightness of the bottom or side walls, plate parallelism, etc. Such measurements can be performed on coordinate measuring machines (CMMs) with micro-probes that can access the narrow channels. While CMM measurements provide high accuracy (less than 1 µm), they are often very slow (taking several hours to measure a single plate) and unsuitable for the manufacturing environment. In this context, we describe a system for rapid dimensional measurement of bipolar fuel cell plates using two laser spot triangulation probes that can achieve comparable accuracies to those of a touch probe CMM, while offering manufacturers the possibility for 100% part inspection. We discuss the design of the system, present our approach to calibrating system parameters, present validation data, compare bipolar fuel cell plate measurement results with those obtained using a Mitutoyo UMAP (see footnote 1) fiber probe CMM, and finally describe the uncertainty in channel height and width measurements.

Minimizing error sources in gauge block mechanical comparison measurements

Error sources in gage block mechanical comparisons can range from classical textbook examples to a completely counter- intuitive example of diamond probe tip wear at low applied force. Fortunately, there are methods available to metrologists that can successfully be applied to minimize these and other effects. Techniques such as statistical process control, use of check standards, thermal drift eliminating measurement algorithms, improved sensor calibration, and well-tested deformation modeling are used at the National Institute of Standards and Technology to minimize errors. These same methods can be applied by anyone making mechanical comparison gage block measurements.

Metrology for Fuel Cell Manufacturing

The project was divided into three subprojects. The first subproject is Fuel Cell Manufacturing Variability and Its Impact on Performance. The objective was to determine if flow field channel dimensional variability has an impact on fuel cell performance. The second subproject is Non-contact Sensor Evaluation for Bipolar Plate Manufacturing Process Control and Smart Assembly of Fuel Cell Stacks. The objective was to enable cost reduction in the manufacture of fuel cell plates by providing a rapid non-contact measurement system for in-line process control. The third subproject is Optical Scatterfield Metrology for Online Catalyst Coating Inspection of PEM Soft Goods. The objective was to evaluate the suitability of Optical Scatterfield Microscopy as a viable measurement tool for in situ process control of catalyst coatings.

Case against optical gauge block metrology

The current definition of the length of a gage block is a very clever attempt to evade the systematic errors associated with the wringing layer thickness and optical phase corrections. In practice, most laboratories wring to quartz or fused silica reference plates, and in addition there are very large systematic operator and surface effects. We present quantitative data on these effects and how that the current definition of gage block length is a primary source of measurement uncertainty.

High Accuracy Measurements Using a Scanning System with a Single Point Triangulation Sensor

Abstract: The capabilities of non-contact laser spot triangulation sensors for high accuracy measurements have slowly increased over the past decade, and now have usable resolution below 0.1 μm. The Dimensional Metrology Group at the National Institute of Standards and Technology (NIST) has developed a simple scanning system to work with these sensors, and presents the system details and data from a variety of geometries. The features measured include screw threads, fuel cell channels, and computer tomographic (CT) scanner phantoms.

New Capabilities at NIST In Dimensional Metrology

Abstract: A number of new or revised services in dimensional metrology are presented. Included are: a lower cost, high accuracy calibration for sphere diameter; reduced uncertainty in roundness calibration; a new instrument for measurement of the thermal expansion coefficient of gauges and other material, extended capabilities of ring gauge calibration on the M48 CMM, and a system for in-situ calibration of deformation of gauge blocks in mechanical comparison.