Visual inspection systems have been used to inspect adhesive beads and sealants in automotive engineering for the last 20 years. However, not until the introduction of in-process solutions did the systems feature the required durability to withstand ambient impacts. Moreover, today’s inspection systems also take on the function of robot vision and are even able to monitor the bead height. They play a critical role when it comes to adhering to the most stringent tolerance specifications: Car bodies can be bonded and sealed perfectly with these kinds of systems.
In countless applications, adhesives and sealants have proven to be successful as a modern adhesion technology in the automotive industry as well as with industry suppliers. These days, in many critical applications, adhesive connections have come to replace classic methods such as screw or rivet connections and even welded connections. Today, for example, sealants and support adhesives are used extensively in the assembly of roof, side frames, A and B columns, engine hoods, trunk lids, doors and spare tire wells. The sealant and adhesive application process must be monitored to assure that the finished vehicle is not limited in terms of its functionality, safety and optical appearance.
In addition to bonding and sealing in the automotive manufacturing sector, applications in the electronics industry and in the packaging industry – in this case typically in applications that inspect how glue is applied – are also popular. In any application, what is critical is that the adhesive and sealant being used are dosed exactly and positioned accurately. This is why the application is carried out in a fully automated process during which robots and other controlled application systems interact in harmony.
Accurate Process MonitoringVisual inspection systems have been used to inspect adhesive beads and sealants for the last 20 years, because only the most precise monitoring of these processes makes it possible to adhere to the specified parameters with the most stringent tolerances. After parts have been assembled, it is very difficult or even impossible to inspect whether adhesives or sealants were applied in accordance with specifications. In day-to-day operations, however, the first inspection systems were still very complicated and were also very costly. One of the main disadvantages of these systems was also that they proved to be unstable when fluctuations in the process were involved or when they were subject to varying ambient conditions.
Over the last few years, prices for systems have dropped significantly and as a result the number of installed systems has increased. And yet, the ambient impacts affecting the inspection results and fluctuations in processes still remain. Frequently, operators are unable to draw the correct conclusions from the results obtained and to then alleviate the cause of defects. It is not uncommon for systems to shut down as a result of a detected production defect. What this shows is that not all of the inspection systems’ requirements are met. Practical applications are still far from achieving a closed quality control loop.
In this case, new visual inspection systems for quality inspection and robot vision can supply and realize the ideal visual inspection solution based on standard modules for each work piece size, each application type, each bead geometry and any type of adhesive.
The First In-Process SolutionWith the introduction of an in-process solution for inspecting adhesives and sealants up to 1 m/s, it has become possible to carry out a majority of applications more cost effectively, while at the same time offering ease of use and a system that is much more durable when dealing with ambient impacts. During an especially efficient in-process, the application of adhesives or sealants are inspected during the application itself and therefore no additional processing time needs to be scheduled. The system inspects dimensions, width, geometry, position and penetrability. The compact camera sensor is mounted directly onto the application jet and with a 360-degree panoramic vision it can even monitor safety-relevant components 100% of the time.
During the post-process, the adhesive or sealant is usually applied at a separate station or during a separate cycle. These inspection systems are used if it can no longer be assured that the sensor head can mechanically access a specific location, for example during an application involving a curved nozzle or a triple nozzle.
Before the adhesive or sealant is actually applied, oftentimes the position of the component (such as a car body) needs to be defined in 3-D in order to be able to apply the material at the exactly specified location. In order for this function to be realized without needing any additional measuring systems, the triple camera head system was introduced, which integrates 3-D robot vision and adhesives inspection in one compact system. For the robot vision function, the system determines the exact position of the car body part to be connected in -3-D. The integrated streak sensor not only uses hole properties, but also any kind of edges, contours and rims of the car body part as measuring properties. Based on the individual measurements respectively, the accurate 3-D position of the part to be bonded is determined with an accuracy level of up to 0.1 millimeter. The robot then receives an exact correction vector for its application path.
The quality of the applied adhesive and sealant is monitored early on during the application process itself making it no longer necessary to perform any additional inspections later. The new inspection systems have been used successfully in a total of 23 processing applications at automotive manufacturing companies such as Opel, VW, Mercedes, Ferrari, Seat, Fiat and BMW.
Includes Height MeasurementsThe new sensor head expands the inspection of the adhesives and sealant application process by adding yet another dimension: In addition to its ability to determine exact positions and its capability of inspecting bead widths as well as assuring that adhesives and sealants are applied evenly, the system can now also reliably monitor heights of up to 15 millimeters and integrate these into the evaluation. What is so impressive is that the system can reach a processing speed of up to 500 mm/s, up until now unheard of in the industry. Despite this high speed, an accuracy level of ± 0.5 millimeter is achieved at 240 hertz. This means that during the beading application, the system inspects the process every 2 millimeters.
The sensor's working distance can be set flexibly at 50, 75, 100, 125 or 150 millimeters. The particular set-up of the camera increases the durability of the inspection. The sensor design makes it possible to inspect 360 degrees all around the application jet. A 100% inspection can be performed no matter how the sensor or the robot is aligned. Special mounting holes make it possible to attach the sensor head easily. Large-spaced LED fields ensure optimum and constant illumination for each camera.
The compact sensor, with a diameter of 200 millimeters and a height of 60 millimeters, inspects any kind of seam without being limited in terms of color and form; this includes triangular seams. Even black seams on a black background are monitored reliably.
The system makes use of the latest software technology: The software that comes with the system is easily manageable and can be used for both in-process as well as for post-process inspections. It offers a clearly arranged overview of all essential system parameters and an extensive visualization of defects by presenting meaningful statistics. The auto-teach function assures that the parameters of the material's geometry are set automatically and in a manner that saves time. The time needed to set up the sensor is significantly reduced.
Key to Process OptimizationBy being able to adjust the system to the actual application, using innovative and proven inspection systems, the user is now enabled to react to the specific requirements in place for each adhesive and sealant application. These innovative inspection systems are already successfully being used by almost every leading automotive manufacturer and they play a critical role at these locations in improving the quality of the product as a whole.
The fully automated inspection process by means of sensors offers a high level of processing reliability and is at the same time cost-effective and easy to use. It plays a key role in process optimization and in increasing revenue, increases customer satisfaction and conserves resources by minimizing the amount of rejects. With these state-of-the-art inspection systems, the challenges facing the application of adhesives and sealants today and in future are overcome confidently.
For more information, contact ISRA Vision Systems Inc. (Lansing, MI).
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