Oil film measurement

Quality assurance through oil film measurement

Thin coatings and their properties can be crucial for the quality of products. Taking press plants as an example: They produce stamped and formed parts – for example, for the automotive industry. These are made from large metal sheets, the so-called coils. For the processing of these sheets, it is necessary to oil the material before forming. The thin oil films fulfil three important tasks in sheet metal production: They protect metal sheets from corrosion, prevent mechanical damage, and improve the friction behaviour of the sheets when being formed. The exact oil dosage is decisive: During the forming process, it is crucial to oil the points of a component that are particularly prone to deformation. Corrosion protection requires uniform and complete distribution of the oil film. That is why somewhat thick oil films are often used. This can lead to quality problems in oil-sensitive downstream processes such as gluing, painting, welding, or electrical contacting.

High-resolution surface detection thanks to fluorescence

It is therefore advisable to measure the homogeneity and thickness of the oil layer during production. Conventional inline measuring systems perform selective surface measurements only. But only comprehensive oil film measurement can reliably determine the actual oil distribution on a sheet. 

With its »F-Scanner«, Fraunhofer IPM has developed a process that precisely determines and thus controls the oil distribution on the entire sheet using a fast imaging fluorescence measurement technology. The system detects the thickness and homogeneity of oil films and dry lubricants in real-time – on flat sheets as well as on complex 3D stamped parts. No preparatory homogenization of distribution is necessary. Fast laser scanners measure up to 400 lines per second. With a feed of the metal sheet of several meters per second, 100 percent of the surface is analyzed directly in production. 

Quality through inline measurement technology

The scanning system can be adapted to feed system widths of up to 4.2 m. This allows high area throughput while retaining high sensitivity. In addition to monitoring strip products, components with complex 3D free-form surfaces can also be completely inspected. The UV laser beam scans the entire object. Automated image processing based on pattern recognition makes it possible to evaluate and categorize fluorescence images in real-time. If the defined oil distribution maximum value is exceeded or the minimum not reached, the next process step can be adapted: The component is pulled off the line and the spot is marked or the lubrication quantity adjusted.

In this way, spatially resolved evaluation helps to assess and document the quality of oiling in the production line and thus to optimize it continuouslyn.