STEINBICHLER ABIS II
AUDI AG Ingolstadt
OPTICAL SYSTEM FOR THE INSPECTION OF BODYSHELL PARTS
Truth in Engineering – AUDI relies on automated optical surface inspection of bodyshell parts in their press shop quality assurance processes.
Customers see the surface quality of a vehicle in close relation to the quality of the overall vehicle. This is why automobile manufacturers are eager to make sure that the bodyshell surface of their vehicles is absolutely perfect. During all steps of the process chain, starting with a single press shop part, as in the example of AUDI AG in Ingolstadt (Germany), to the body shop and the finishing belt, through to the top coat section, experienced staff members constantly inspect the surface and rework it, if required. Significant cost reduction can be achieved if defects are found quickly and as early in the production cycle as possible and then classified objectively according to their severity.
Truth in Engineering – this also reflects in press shop 3 at AUDI Ingolstadt. Here, the QA staff rely on ABIS II, the optical surface inspection system from Steinbichler Optotechnik. During the manufacture of a press lot of bodyshell parts, the surface quality of single parts is checked every hour using the ABIS II system. While in earlier times, a whetstone was used for this purpose, taking at least 30 minutes to inspect a side panel, today's robot-assisted system performs the surface inspection in less than 2 minutes, i.e. the surface quality feedback to the press staff can be given much faster. The resulting dramatic time and cost savings are the result of a forward-looking quality management strategy.
Truth in Engineering – AUDI consistently adhered to this philosophy when adopting this new technology. Partnering with Steinbichler Optotechnik, AUDI took up a development project on automated optical surface defect detection in unpainted bodyshell parts (the name of the project was OPAQ) in 2003 and designed a pilot facility tailored to the requirements of a press shop which was completed in 2006.
Today, the surface inspection system is an integral part of the quality assurance process at the GRS 13 and GRS 14 large-capacity suction presses. Surface specialist Uwe Walcher from AUDI is responsible for setting up the ABIS II system, i.e. he programs the panel measurement programs, performs operator training and, together with the auditors, defines the boundary samples. He puts it in a nutshell: “The optical surface inspection system must be ready to run day and night. It now replaces the whetstone formerly used by the QA staff. Thus, we can check more parts and classify them objectively in the same time period.” What is more, scrap costs caused by whetstone-based inspection could be reduced significantly, continues Uwe Walcher, since at AUDI, whetstone-inspected, scratched bodyshell panels may not be returned to the production process due to the high surface quality requirements.
The heart of the surface inspection system is the ABIS II sensor (ABIS – Automatic Body Inspection System). The robust design of the ABIS II sensor in its sealed aluminum housing ensures the secure acquisition of the measured data not only under the typical acceleration stress of robot applications, but also under production-related ambient conditions (vibration, shop floor lighting, temperature, etc.). Conceptually, the sensor is based on the so-called fringe projection technology where a periodical grid is projected onto the object and the fringe pattern is captured by a camera placed perpendicularly to the surface. Using a single image technology ensures an extremely short image acquisition time of 0.1 msec so that vibrations, which always occur in the workshops during the production process, are entirely negligible. Due to the integrated touch screen, operators can easily use the offline system even when wearing protective gloves. When designing a facility, the position and size of the robot are determined using simulation, based on the largest panels to be measured. The robot can either stand on a pillar or, as in press shop N58 at AUDI Ingolstadt, it can be an overhead robot. In both cases, the panel is put on a table and the operator selects the panel on the screen in order to start measurements. An optical position adjustment system determines the panel position on the table and corrects the robot path accordingly.
The integrated classification of the measurable defects represents an essential part of the data evaluation and builds the basis for an automatic application of the corresponding quality criteria in the subsequent decision processes. With the ABIS software, defect characteristics and severity classification (based on auditor experience) can be generated – not every defect affects the paint and requires reworking. Moreover, the defect tolerance is often higher at production start, i.e. the quality objectives change with production time. For this reason, the severity classification tolerances are adjustable. The detected and classified surface defects are color-marked in the CAD representation of the test panel. Corresponding defect statistics (trend analyses) enable the users to enhance the process (e.g. by tool optimization) and to document the influence of material modifications (e.g. in case of a supplier change).
The ABIS II system in press shop 58 is used to inspect the bodyshell parts (side panels, doors, fenders, hoods and trunk lids) of the AUDI TT, AUDI A3, and AUDI A4 models for their surface quality. The results are included in the series quality evaluation. Including all variants, currently more than 30 panels have been set up on the inspection system, and more panels are to come. “The surface inspection system in our North press shop (in Ingolstadt) convinces through its reliability and it is an integral part of our inspection process,” said Uwe Walcher from AUDI at a meeting early in 2010, “and we are seriously considering to extend our testing capacities, i.e. to duplicate the system for our South press shop (also in Ingolstadt)”.