Cleanliness is critical in fluid circuit components

  • 13-Jul-2012 02:19 EDT
Particles on membrane.jpg

Particles on a membrane that are typically found and analyzed during the inspection of cleanliness during the manufacturing process.

As the automotive industry transforms with new technologies, timely, accurate, and quality production becomes increasingly critical to manufacturers. The evolving nature of the industry has resulted in strict standards concerning cleanliness in the fluid circuit and most other components of road vehicles such as brake systems, fuel injector nozzles, power steering pumps, and fluid hoses. An important part of the challenge is to develop and monitor adequate cleaning procedures.

But how do manufacturers know if their protocol is performing optimally?

As the physical sizes and tolerances of these precision devices continue to shrink with fuel-efficiency concerns that result in lighter engines, quality-conscious manufacturers find it increasingly necessary to ensure the critical cleanliness of their parts and processes. Possible issues associated with fluid circuit component contamination can cause both long- and short-term limitations in vehicle performance.

Further, components must be proven 99.9% reliable to avoid costly insurance claims and increased warranty costs, creating manufacturer interest in reducing these lapses in performance. Before they can minimize performance issues, however, manufacturers need a system to specify the contaminants involved and how they entered the fluid circuit.

ISO (International Organization of Standards) developed 16232-07, which is based on VDA19-2. This set of general specific directives for contamination testing of fluid components in road vehicles regulates which particle extraction methods and measuring equipment must be used.

Adhering to standardized regulations creates mutual understanding between manufacturers and customers. European and American manufacturers lead the automotive industry in adherence to the ISO mandate, resulting in an explosion of innovative techniques for determining the cleanliness of fluid components.

Gravimetric analysis, a traditional testing method, calculates the total mass of contaminants, reducing cost and providing clarity. However, this method fails to produce precise measurements. As a result components with tight tolerances may pass gravimetric testing yet still fail to function, which trivializes the money saved by using an obsolete technique.

Conversely, microscopy provides efficient, accurate microanalysis that identifies contaminant particles. By sizing and quantifying particles, this method produces the information manufacturers need to identify problem particulates and, more importantly, can help them know where the contamination is coming from. Due to new high-precision components, some carmakers are already looking to “dangerous” abrasive contaminants that are just 2 µm (70-µin) in size.

The automated SEM/EDX (scanning electron microscope/energy-dispersive X-ray spectroscopy) method supplements contaminant information by providing the elemental composition of each debris particle over an entire sample. Discerning the elemental composition of these microscopic inclusions assists in discovering the contaminant origin and, subsequently, minimizing the quantity of contaminant present. Also, knowing the composition of contaminant particles affords concrete information that allows manufacturers to conduct quality control analysis and attempt to improve their production process while eliminating risks associated with fluid circuit contamination.

When a manufacturer needs to verify that its product is suitably free of a specific kind or class of particulate contaminant, such as a toxic or abrasive material, other methods waste time analyzing the “benign materials” the sample contains, decreasing accuracy and delaying production. Integrated microscopy allows for rapid search of large areas in a sample, targeting problem particles while disregarding the “empty” space the sample contains.

By appropriate selection of the back-scatter contrast thresholds and the dynamic search grid, large areas of empty sample can be rapidly traversed without sacrificing sensitivity to the "bad actors." The analysis can automatically terminate when the necessary precision is fulfilled, and go/no-go decisions can be automatically generated. These systems can also rapidly characterize large numbers of particles, employing user-defined rules to automatically classify particles in appropriate classes, and include provisions for employing or suppressing elemental analysis and storing thumbnail images for post-analysis.

These integrated microscopy tools—hardware, software, and reporting—can be used to analyze hundreds of thousands of particles per hour rapidly and automatically, without operator intervention, which increases efficiency in terms of both cost and processes. However, while the data gathered in this analysis is critical to quality control, it does so only if provided in a meaningful and actionable format.

For instance, an automated instrument can easily produce a deluge of data that would be overwhelming without the aid of appropriate report-generating software that consolidates the measurements into readily interpreted metrics and trends. Ideally, such reporting software is further structured—i.e., customized—with knowledge of the particular kind of application so that the reports express the metrics most important to the automotive industry and specific application being served. Furthermore, the ability to access historical data from stored reports allows for long-term trend analysis that, over time, aids in a continuous quality improvement process.

Comprehensive reports that organize informative, relevant data upon which critical decisions can be made quickly and with confidence are the true measure of any SEM/EDX solution.

As consumer and engineering demands for “smaller, lighter, faster” continue to increase, so will increase the importance of cleanliness in parts with lower thresholds for contaminants. The ISO standards for contaminant particles during manufacture have met these industry changes with equally progressive customer-specific directives. While traditional methods to meet these standards aid in the process, integrated microscopy provides rapid, automatic identification and detection in quality control. What’s more, the data-driven knowledge, and not just information, derived from this analysis provides a firm foundation upon which confident decisions can be made to improve the production process and minimize the risks of contaminants in automotive manufacturing.

This article was written for AEI by Marion T. Graf and Bernhard E. Heneka of RJL Micro & Analytic GmbH and Timothy J. Drake, Ph.D., of Aspex Corp.

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