Chromatic sensors – multipoint measurement for e-mobility

Fuel cell stacks made of bipolar plates, such as those used for motor vehicles, enable vehicles to operate without emitting exhaust gases. Two half plates (anode and cathode) are joined together to form a bipolar plate. These serve on the one hand to supply gas or liquid, and on the other hand as electrodes with the aid of which electricity is generated from the oxidation of hydrogen by chemical reaction.

The ScopeCheck® FB is suitable for measuring the plates. These and the associated embossing tools are measured, for example, at a renowned automotive supplier with a VideoCheck® HA (High Accuracy)..

Tools measurement

The production time for the embossing tools is about 80 hours. To avoid product rejects, 100 % inspection is required with tolerances between 3 μm and 10 μm. For this purpose, the Werth image processing sensor automatically scans the entire tool in the patented Raster Scanning HD mode. By superimposing many individual images taken during the movement, an overall image of the tool is created. All visible two-dimensional geometric properties can then be evaluated very quickly from this.

Since the wave profiles of the tools have the smallest radii of 0.1 mm, conventional probes are unsuitable for measurement. The patented Werth Fiber Probe WFP® 3D with glass stylus tips as small as 20 μm or the non-contact measuring Chromatic Focus Point CFP can be used for highly accurate and fast measurements. Area measurements are possible with the Chromatic Focus Line CFL. The line sensor allows the entire workpiece surface to be measured with 10 000 points/mm2. From this, surface profile deviation, line profile deviation, embossing depth, flank angle and pitch can be determined. After measuring the tool center offset, a virtual pairing of the upper and lower tool plates is possible.

Non-contact measurement of bipolar plates

Since conventional probes would lead to deformation of the thin-walled sheets, the Werth Fiber Probe® or an optical distance sensor are also ideal for these measurements. The CFP 1000 offers an optimum ratio between the measuring range of around 1000 μm, the large working distance to the workpiece surface and the aperture for picking up the light reflected from the surface. This allows fast scanning without moving the sensor relative to the workpiece surface with little risk of collision. If too few points are available on the flank despite the large aperture, the CFP can be brought into the optimum alignment for the respective flank side using the Werth swivel joint. In this way, the flow field can also be analyzed in individual sections: it is possible to measure the line profile shape, channel depth, mold center offset, and flank angle. Deformations in the port area at the inlet and outlet openings for the gases as well as the sealing lips can also be measured.

The bipolar plates are uniquely identified via data matrix code (DMC) detection with the CFP and the flatness is measured. The CFP on the swivel joint can also be used to measure the offset of the welding of two half plates. In addition, the chromatic sensors enable layer thickness measurements for testing the sealing lips.