The battery tray is the battery receptacle on the car. It must be mechanically stable and fastened to the entire car body. However, it is no longer a single part simply attached to an electric vehicle. Furthermore, the tray has become fully integrated into the car body. The complex aluminium weld design contains all the battery cells, connectors, and control units. Also, the battery packs including various number of battery modules.
Thermal expansion of the battery pack during charging and driving can lead to torsion and bending in the tray. A variety of dimensional characteristics, such as the length, diameter and position of slots, must be measured either using random sampling or a complete automated inspection at the end of the line. The large number of features requires quick inspection cycles involving multi-sensor measurement. ZEISS non-contact optical laser scanners can quickly extract feature data, while tactile probe systems can reach undercuts and other challenging optical features.
The tray must be properly integrated in the car body because of the large amount of energy in the battery cells – and to ensure the safety of the battery in the event of a crash. Connection points (i.e. welded bolts) attach it to the rest of the car body. The size and location of these welded points are important for the fully automated battery tray assembly process, and for the structural connection to take load forces during driving, charging and in case of an accident. All of these requirements lead to a wide range of different characteristics that could be covered with flexible user-defined probe systems or by scanning point clouds with ZEISS optical sensors.
Due to the high number of geometric elements and weld joints to be measured, as well as the size of the battery tray, long measurement and inspection cycles are quickly achieved. Since the battery tray, as a safety-critical component, is very often required to 100% monitoring, an inline solution for production is required in addition to the reference measurement in the measuring room, in which the most important elements are measured. ZEISS offers various sensor systems for inline measurement and inspection technology. The sensors are moved to the features to be measured by industrial robots, which means that a very short measuring time can be achieved without the need to additionally eject the battery tray.
Optical measuring machines from GOM Metrology enable the full-field measurement of the battery tray with high-precision fringe projection. They digitize the part within a short period of time from different viewing directions – with high accuracy and detail resolution. The sensors create absolute, correlation free and traceable measuring data.
The user gets millions of full-field distributed 3D coordinates that can be compared to the CAD model to detect deviations and identify defects such as deformations. By using CAD data and inspection plans, the software fully automatically creates sensor positions and robot paths required for acquisition.
The result of the measurement is the digital copy, a digital twin that shows the real geometry of the battery tray. Process-related inspection features, such as the location of the fixing holes, can be extracted from the 3D point cloud and be evaluated in a trend analysis. With trend analyses based on full-field measurements, changes in the production process can be spotted at an early stage. During problem analysis, the color-coded surface deviations of the 3D point cloud facilitate reaching the desired nominal CAD geometry. By using GD&T functions, the flatness or surface profile of sealing surfaces or individual battery compartments can be calculated. Likewise, the height and position of the sealing bead are easy to capture.
In the digital assembly, the interaction of the battery modules with the battery tray can be assessed. Assembly situations can be simulated and optimized via different local alignments. Questions about gap size changes caused by thermal deformation of the battery modules after cycle tests can also be answered easily. The surface deviations between battery module and battery tray can also be used to calculate the volume of the required heat-conducting paste for the individual battery compartments.