Technical Cleanliness Inspection and Analysis of Automotive Components in Compliance with Industrial Standards

Effects of contamination on automotive components

Important automotive components include those used in engines. For example, pistons that repeatedly reciprocate with a clearance of only a few micrometres in an engine block cylinder liner are kept air-tight with engine oil. If a slight amount of metal contamination adheres to the side surface of a piston ring, repeated reciprocation will damage the inner wall of the cylinder liner, causing engine problems.
Also, with an increase in the number of automobiles equipped with high-capacity batteries, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), the importance of paying attention to the metal contamination of components and materials, a problem that may cause lithium ion batteries to generate heat or fire, has also been increasing.
In addition to the complete cleaning of these components after manufacturing, cleanliness management through cleanliness inspection/cleanliness analysis in compliance with international industrial standards is also required.

International industrial standards ISO 16232 and VDA 19 for technical cleanliness inspection

As standards related to technical cleanliness inspection for automotive components, VDA 19 was issued in 2002 by the German Association of the Automotive Industry followed by ISO 16232 issued in 2007 as international standards. These standards have made measurement and composition analysis of foreign particles in compliance with quality requirements mandatory.
These standards define the management of technical cleanliness for oil- and water-related fluid parts such as tanks, pumps, valves, pipes, ducts, and casing—which are important parts for automotive components such as engines, turbochargers, and transmissions—as well as for lithium ion batteries and electronic/electrical components. Particle contaminants generated in the manufacturing processes of these automotive components are removed as much as possible in the cleaning process. Hence it is necessary to perform measurements and analyses to ensure that the technical cleanliness requirements defined in ISO 16232 and VDA 19 are satisfied.
Also, for oil, which is commonly used in automobiles, there is an international industrial standard related to technical cleanliness inspection in liquids. ISO 4406 defines the cleanliness code for (cumulatively) counting particles per millilitre of sample to summarise how contaminants are distributed in fluids.

Methods of technical cleanliness inspection and analysis

There are various methods of technical cleanliness inspection and analysis, and the following two methods are defined in ISO 16232 and VDA 19 as standard technical cleanliness analysis methods for the automotive industry.

Gravimetric method (gravimetric inspection)

This inspection is based on weight and is thus regarded as a relatively easy method, but analysis is conducted only using information related to the difference in weights.
With this inspection, it is impossible to investigate the size of each particle contaminant, the particle size distribution, and the properties of minute particles such as metals and fibres. That means you cannot obtain information useful for determining the cause of contamination or preventing its reoccurrence.

Light scattering method (light scattering analysis)

Optical microscopes are used for inspection and analysis. It is possible to determine not only the presence and volume of contamination but also the size of each particle, the particle size distribution, and the properties of particles (such as metals and fibres).
In the field of automobile manufacturing where contamination by minute particles may greatly affect the quality, performance, and safety of important safety components, technical cleanliness inspection using microscopes based on this light scattering method is most common.

Flow of extracting, measuring, and analysing contamination using the light scattering method

For technical cleanliness analysis of automotive components, inspection is not possible after assembly for components such as engines, which consist of complicated and important parts. Hence, the following procedure is used to conduct analyses for each component.

1. Wash the part (product) with a method such as pressure rinsing to extract foreign particles.
2. Filter the rinsed liquid through a membrane filter to trap foreign particles.
3. Analyse the used membrane filter as a sample using a microscope.

In measurement and analysis using microscopes, the number of particles (contaminant count), the particle sizes, and the type of foreign particles (such as metals and fibres) are measured, analysed, and compared under the same settings to prevent variation in measured values. Then, they are investigated in detail, including a determination of whether these items are risk factors in automotive components.
In ISO 16232 and VDA 19, various standards are defined, from methods to extract foreign particles to the minimum particle size for which analysis is required. For automatic measurement, they also define the pixel count and how to extract foreign particles. Furthermore, reports must be created in the format compliant with these standards.

Making technical cleanliness inspection and analysis compliant with ISO 16232 and VDA more accurate and easier

With the VHX Series 4K Digital Microscope

The VHX Series enables users to carry out technical cleanliness inspections compliant with the ISO 16232 and VDA 19 technical cleanliness standards for the automotive industry. By analysing a high-resolution image with a deep depth of field taken with the 4K Digital Microscope, even targets with uneven surfaces can be measured with high accuracy.

In Detailed Analysis mode, all you have to do is select a target contaminant on the image of the entire membrane filter. The stage moves automatically, enabling you to continue detailed observation at high magnification. Foreign particles can be identified easily and quickly. Furthermore, detailed observation and quantification are possible even for uneven shapes by using depth composition and 3D height measurement at the same time.

Enabling time reduction and quantification by way of automatic reproduction of conditions and automatic calibration

With the VHX Series 4K Digital Microscope

The microscope saves and reproduces past image capture conditions. By simply selecting an image from an album of captured images, its image capture settings (such as lens magnification, shutter speed, gain, light shift, edge enhancement, white balance, and light adjustment conditions) are loaded and reproduced automatically. This automatic reproduction of settings not only significantly reduces work hours but also enables different users to observe targets under the exact same conditions, thereby providing stable analysis results.

The high-resolution lenses and the motorised revolver enable a seamless zoom function that quickly switches lenses from 20x to 6000x magnification according to the size of contamination, eliminating the need for lens replacement. Additionally, the VHX Series automatically identifies the connected lens and can manage magnification data together with captured images.
Furthermore, the one-push calibration function automatically loads the required calibration values when the user simply performs a one-click operation. The ability to reproduce conditions used for extracting (binarising) contamination prevents variation in measured values.