Bonding of Automotive Displays

The digitalization of the car for modern mobility requires interfaces that offer a more individualized and interactive approach to road users. With increased development of self-driving vehicles, multidimensional infotainment and safety functions are required to accommodate networking. In addition to creating a comfortable cockpit environment, automotive displays support driver safety by providing up-to-date information about traffic events and car functionality.

Automotive infotainment systems provide audio or video entertainment for all occupants via their displays. Advanced driver-assistance systems (ADAS) provide graphical visualization of driver information such as parking assistance, navigation, traffic assistance, control functions and internet connectivity. All setting options in the car can be operated via touch displays.

Freeform and curved automotive displays are the future, enabling larger and more attractive dashboard displays. Housing designs are evolving to better utilize interior space and accommodate these larger and more responsive screens.

The trend towards larger displays in vehicles, combined with the need for space-saving installation has led to narrow-edged display solutions. The challenge is to still achieve strong adhesive bonding with narrow display bonding surfaces and thus thin bonding lines.

The adhesive must not protrude at the edges once joining the display to the housing. Fully automatic adhesive application and tolerance compensation are handled by Sonderhoff mixing and dosing systems.

Flexibly Adjustable Dosing Quantity for Compensation of Component Tolerances

Henkel's Active Quantity Adjustment (AQA) allows the amount of adhesive dispensed for bonding displays to the housing to be controlled. This ensures the correct dosage at all times based on the respective height profile of the component, making it possible to adapt the dosing quantity during the application of the adhesive to the part contour. This compensates for production-related differences and irregularities in the bonding surfaces as well as applies a precisely calculated and accurately metered quantity of adhesive.

Before dispensing, a 3D line scanner scans the geometry of the components. The scanned data are transmitted to the dosing machine’s programmable logic controller (PLC) and compared with the predefined CAD reference of the component. Any deviations detected are used to adjust the dosing program in advance for the next adhesive application.

Wavy or uneven bonding surfaces can occur during the injection molding of the display housing. In order to compensate for this, the robot travels slower over slightly recessed application areas, depositing more adhesive in those areas, then travels faster over the slightly raised areas, so that less adhesive is dispensed there. The result is a bead of adhesive that compensates for the height tolerances and will remain consistent after the display glass is joined to the housing.

The AQA process can compensate for differences in the dimensional tolerances of the component. With a target glue gap of 1 mm, the specified tolerance for pressing the glue line is +/- 0.5 mm when the display and frame are joined. Since cost and design factors are increasingly resulting in narrower display housing bonding edges, the AQA process ensures that the adhesive trace on the housing contour, despite possible dimensional tolerances, remains uniform after the display glass is attached. A visual example of this process is shown below.