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Metrology-Grade Inspection Accuracy Through Real-Time Calibration

Aluminium Die-Cast Shock Tower Inspection

As a global Tier-1 auto part supplier began mass producing single-piece die-cast aluminium shock towers for a popular SUV, they required an 100% inline inspection solution with metrology-grade accuracy to ensure the casted parts conformed to GD&T and design specifications. Aluminum high-pressure die-cast shock tower offers many advantages over traditional steel-sheet parts, including much improved stiffness and lighter weight that translate to better vehicle handling and fuel economy.

The Need for 100% Inline Inspection

Bluewrist offered a complete inspection solution in which 100% inline quality control of die-cast shock towers was performed to ensure that no defective parts were passed onto the customer. Powered by our NIST-certified ScanXtream 3D vision and SPCWorks software, Bluewrist helped the manufacturer monitor the production process by inspecting every part that came down the die-casting line and even flagging deviations in process stability before it led to an actual defect. What made this project unique and challenging was the customer’s need to performing 16-plus feature inspections in under 20 seconds to meet its high-volume cycle-time requirements. A shock tower is found in every vehicle on the road and acts as an attachment point for the upper end of the suspension damper, which consists of a strut or shock absorber. As a result, the mounting holes on the shock tower must be manufactured with high precision and in the correct location, with minimal deviation from their design. Any deviations will lead to misfits, affect a vehicle’s driveability, and lead to costly fixes and recalls.

Metrology-Grade Inspection Accuracy through Real-Time Calibration & Innovation

A 100% inline solution is a prerequisite for this critical component and rules out traditional sampling-based quality control using a CMM, which may take more than 40 minutes of manual inspection. To accomplish this task, both the Bluewrist engineering team’s ingenuity and the flexibility of the in-house designed software solutions were put to full use to achieve metrology-grade accuracy.

To inspect the 16-plus features within the required 20-second window, a robot-mounted, high-resolution 3D-structured light snapshot camera is used for the inspection process. A robot arm loads and unloads the shock tower onto a custom-designed fixture that is vibration-isolated from the rest of the manufacturing plant to improve the point cloud-capture accuracy. The 3D camera captures high-resolution point clouds of multiple features on the shock tower which are then streamed in real time to the ScanXtream software for dimensional analysis. The captured data are then compared to the CAD design and GD&T specifications for deviations.

Off-the-shelf industrial robots typically have poor absolute accuracy, and the effect is further compounded by the changing ambient temperature of the manufacturing plant. Bluewrist’s KinOptim robot calibration toolbox addresses this issue using built-in volumetric and temperature calibration that continuously monitors the kinematic performance of the robot performing the 3D scan. This provides continuous corrections for the robot arm and compensates for dimensional changes in the shock tower caused by fluctuating ambient temperatures. Together, this ensures true metrology-grade accuracy and inspection results with standard off-the-shelf components.

Real-Time Quality Reporting and Process Monitoring

ScanXtream software is optimized for use in fast-paced manufacturing environments and promises accurate, efficient, and stable performance. The software effortlessly processes the large amount of data streamed from the 3D camera in real time to perform the inline 3D scanning and dimensional measurements of the shock tower. Parts that pass the inspection are delivered to another manufacturing facility for the next steps in the assembly process. When defects or deviations are detected, the shock tower is automatically removed from the inspection station after a visual and audible warning to notify the operator. The defect location is also indicated in the SPCWorks software.

The Bluewrist customer also leveraged SPCWorks software to monitor the real-time dimensional data of inspected shock towers to minimize defects at source. Since SPCWorks statistically analyzes every shock tower coming down the die-cast line, automated notifications will be triggered if the dimensional data trend towards a custom threshold. This might indicate issues with the casting process, and alerts will be sent to the rest of the team so they can take preventative measures to prevent an actual defect.

System Flexibility

The custom inline inspection solution consists of a 3D snapshot camera mounted on an industrial robot, and PLCs for pass or rejection of the inspected shock tower. Bluewrist comXtream industrial communications software links all these components together in one cohesive system to trigger the measurements and the inter-device, sensor and robotic communications. Bluewrist software is platform and hardware agnostic and compatible with all major robot, PLC, and 3D vision sensors on the market. As a result, the solutions can be integrated into our customer’s manufacturing facility with minimal delay or costly custom engineering work.

Should the customer change the shock tower design for future vehicle models, the Bluewrist system can be modified and reprogrammed onsite to meet any evolving requirements. The inline 3D inspection system is actively used at the customer’s manufacturing facility, performs thousands of shock inspections per day, and has met and exceeded all requirements.

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