A component that is frequently made in plastic by various car manufacturers is the fuel filler flap. Because it has a predestined position in the best area of visibility, the highest requirements are placed on the surface. Despite state-of-the-art technologies, small sink marks cannot be completely avoided on the visible side of the flap. “Although these sink marks are only a couple of micrometres deep, they can become visible after painting. But by then, it’s too late to fix it”, said Wolfram Schmidt, head of sales at INB Vision AG, outlining the problem. “It is extremely difficult to detect variations in the surface on unpainted injection moulded parts”, noted Schmidt.
He recalled, “In summer 2011, more than a year before the series start-up of the Golf VII, the plastics specialists at Volkswagen AG set out to find a suitable surface inspection system for fuel filler flaps.” Volkswagen found it at INB Vision AG in Magdeburg, the developer of the surfaceCONTROL measuring system.
INB evaluates 3D data to detect surface deformities. To do this, the surface is scanned with a stereo sensor based on strip light projection. INB’s experience shows that the information content of this data is higher compared to other procedures. The 3D surface inspection addresses a variety of challenges. Concave and convex surfaces alternate with different curvatures within the free-form surfaces. The surface can also have a varying degree of gloss. However, one of the biggest challenges is detecting local form variations. With some 100th of a millimetre deep, they are usually ten times smaller than the geometric tolerances of the part.
To detect local surface variations that show up in the 3D data, INB offers a variety of patented processes. For example, there is the option of training the system offline using faultless parts. The system learns the reliable geometric tolerances of the sound parts in series production.
The Magdeburg company has developed another process for inspecting the fuel filler flap. It is based on a tried-and-tested inspection method that is widely used on metal sheets in pressing plants and car body manufacture – the whetting stone. An employee whets the surface with an oblong whetting stone in order to make the smallest faults visible.
In case of the “digital whetting stone” procedure by INB, the whetting is not carried out physically but virtually. The surface is not physically “whetted” but rather visually, and consequently it is not damaged. After the visual scan of the surface with the 3D sensor, the digital whetting stone is “guided” point by point across the 3D data of the part. It then stops over each of the highest points. The distance between the line and the 3D surface data is then determined. The result is shown in colour on a defect map. Using pre-set threshold values, the system makes an automatic satisfactory/unsatisfactory decision.
Initial examinations on sample parts convinced the engineers at Volkswagen. The tests showed that variations from a depth/height of 5 µm were reliably detected.
INB’s surface inspection system was installed at Volkswagen in 2012 and the communication with the line control of the existing injection moulding system was established.
About every 60 seconds, the tool on the injection moulding machine opens up and releases two fuel filler flaps for the new Golf. A robot grips the two fuel filler flaps and puts them into the inspection system one after the other. A few seconds later, the result of the inspection is determined. The fault-free fuel filler flaps are placed on an outfeed conveyor and packaged for subsequent painting. If a faulty part is discovered, the result of the inspection is documented automatically. The part goes into a separate container and is later recycled.
Author: Frauke Flenker-Manthey
Head of Sales INB Vision
INB Vision AG
Leipziger Str. 44 (Zenit II)
ph: +49 391 6117 300