Fuel pumps must operate trouble-free behind the scenes during the whole life of the automobile. A defect-free surface of the pump tube is a prerequisite for perfect corrosion protection and thus a long life of the fuel pump. To guarantee this, Präschu Umformtechnik has chosen an in-line inspection system from Octum for the automatic surface inspection of the pump tubes. 

The company Präzisionsteile Franz Schulz GmbH - or just Präschu Umformtechnik for short - has its key competence in the production of high quality sheet metal parts by deep drawing, stamping and bending. This is followed by further processing with or without cutting, assembly by joining or welding and surface finishing and cleaning.

Octum GmbH implements customised image processing solutions for 100% quality inspection and material flow control in series production. The solutions are implemented with compact, intelligent cameras for simple or distributed inspection or identification jobs, or PC-based multi-camera systems, e.g. for surface inspection or 3D inspection. In the field of surface inspection, Octum has specialised in the inspection of single metal parts.
The tubes of fuel pumps are produced fully automatically in a deep drawing process. Material flaws were already discovered in spot checks prior to deep drawing which are largely due to contamination, blowholes, doubling and scaling of the metal sheets. According to Thomas Hube - Head of Production & Plants at Präschu - the scrap rate is already about 2% on arrival of the material, whilst Präschu promises its customers 100% good parts. This has led to high sorting costs in the past with the risk of flaws slipping through unnoticed, which can never be totally ruled out in manual inspection.

From Manual to Fully Automated ­Control
Other sources of faults such as Thyssen arches and flaking off of the galvanisation were identified during the conception phase of the automatic inspection system. The latter defect lead to a loss of the corrosion protection and thus to failure of the fuel pump. Although the majority of the flaws would already be detectable before deep drawing, an optical inspection system was chosen which does not inspect the parts until after deep drawing. This also enabled tool faults and tool matching problems to be discovered.

The tubes are washed after deep drawing and then presented to the image processing system decollated and in the correct position over a chute with stoppers. A roller mechanism designed by Präschu turns the parts around their longitudinal axis by 380 degrees underneath the camera. The CV-600 system from Octum takes the camera images in high resolution with a line scan camera and evaluates these automatically. The CV-Inspect system software operates with local adaptive methods to cope with brightness fluctuations to compensate for process-related or material-related fluctuations in the appearance of the tubes after the deep drawing. The sensitivity of the defect segmentation and of course also the response limit can be parameterised by the operator. At this time, defects from a size of 0.2 mm x 0.2 mm upwards lead to rejection of the part. All detected defects are colour marked in the grey image. Inspection regions and excluded areas can be set flexibly. The key routines access library functions of Halcon or VisionPro, respectively, depending on the application. The cycle rate is 1.8 seconds.

Future-orientated Investment
At Präschu, more than 2.1 million parts per year are produced. Good parts are transported directly for packing. The system is designed for simple operation and provides multi-level access depending on the qualification of the employees. The access possibilities range from simply calling the inspection program for the part currently being produced to making parameter changes or even modifications in the inspection process. This future-orientated investment is part of the 0 ppm strategy of Präschu Umformtechnik and guarantees the continuing high level of quality in the production. Because of the positive experience made with the installed inspection system and the quick amortisation time as well as other cost savings, additional surface inspection systems are being planned for other lines and products.