Detection of pinholes during processing of aluminum materials

Together, German/Austrian company Mendel RG-Systems and G. Rauch Präzisionswerkzeugbau GmbH, which has made a name for itself as a manufacturer of foil punching technology, are offering customers a new solution for detecting tiny holes in the material known as pinholes. To do this, the SMARTSCAN 200% inspection system from Erhardt+Leimer has been further developed in collaboration with Mendel RG-Systems so that, in addition to printing defects, it can now also detect holes up to a size of 20 µm in the material. This type of hole detection is particularly important in the processing of closures and sealing devices in the food and beverage sector, where it acts as a quality criterion for ensuring that end products do not have any leaks.

What makes the SMARTSCAN system so unique is its 200% inspection method. Thanks to a special illumination process using a combination of conventional incident light inspection and backlighting, with double image captures of the material under different lighting conditions, new standards have been set for quality assurance. This allows the SMARTSCAN camera to detect printing defects across the full width of the web using the incident light method. In addition, splices, flags, impurities/contamination and color defects can be detected. After a short delay a further image is then taken for which only the rear flash is switched on. By switching off the incident light, the material web is shown entirely in black. By contrast, holes up to a size of 20 µm are reliably displayed thanks to the flash of light from the rear. In addition, the holes are separately classified and can be displayed separately. To do this, the operator switches between print image and pinhole inspection on the multi-touch monitor. SMARTSCAN is available for web widths up to 22 inches (560 mm), with a maximum web speed of 300 m/min.

"In the past, the standard approach was to use two separate camera systems for print inspection and surface inspection, or to carry out inspections solely via the restricted 100% inspection," explains Alexander Thomalla, Product Manager at Erhardt+Leimer. "It is only the double imaging technique that enables the so-called 200% inspection, which combines two separate systems in a single unit."

Mendel RG-Systems will exhibit the SMARTSCAN system for pinhole detection at Drupa 2021.

The 200% technology in detail

In the form of SMARTSCAN, Erhardt+Leimer is offering the first 200% inspection system with pinhole detection for the converting industry. A special illumination and image acquisition process is used here.
The web is diffusely illuminated from above using an incident light source. The camera simultaneously records images, which are displayed in color on the monitor for the machine operator (see figure "Print image inspection"). This is the image that is used to detect printing errors. Here, all image series are recorded at the finishing stage and are then compared with a previously defined reference image (Golden Template).
With the SMARTSCAN 200% inspection, in addition to the incident illumination the web is also illuminated from the rear, during which the incident illumination is briefly switched off. During this time, a further image is taken alongside the main image, and this is then checked for pinhole defects. As a result, the camera image shows holes as bright areas, with the light shining through the material from behind here (see figure "Pinhole detection").
If deviations from the reference image or pinholes are detected, the system triggers a corresponding action in order to e.g. warn the operator (lamp) or to stop the punching process in the area of the defect.

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