Bonding of Automotive Displays

Fully Automatic Material Application With Henkel’s High-Precision Automated Mixing and Dosing Machines

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.

Our structural bonding solutions for automotive displays meets the needs of market trends, such as the increasing demand for design flexibility. High-precision metering with Sonderhoff fully automatic mixing and dosing systems ensure high contour accuracy during adhesive application.

But how do you ensure perfect display bonding when cost and design considerations are increasingly narrowing the bonding surfaces of the display housing?

Using Active Quantity Adjustment (AQA) technology, we provide solutions to help compensate for component tolerances during adhesive application and achieve a uniform width of adhesive bead after joining. This method makes it possible to adapt the dosing quantity during 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. To achieve this, a 3D line scanner measures the part geometry and compares the data with the previously defined CAD reference of the part before the adhesive is dispensed. The result after joining is an adhesive seam that is consistent in height and width.

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.

Strong Adhesive Bonds on Narrow Bonding Surfaces

Freeform and curved automotive displays designs dominate the interiors of modern cars. They are fully integrated into the overall interior design.

The design and manufacture of automotive displays require a variety of material features, ranging from ensuring the strength of the display housing structure to bonding the cover glass onto the TFT / LCD display.

In order to bond the automotive display to the housing, structural 2K adhesives are used that are designed for elastic bonding with high/medium strength. They are suitable for the multi-substrate bonding of freeform and curved display designs.

This can include the bonding of different substrates, such as plastic to plastic; plastic to glass; and glass to glass. Thanks to its very fast curing properties, the adhesive used achieves a high initial strength at room temperature shortly after the components are joined.

Display housing with adhesive bead before attaching the transparent cover

Cross section of the display housing after joining

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.

Application of adhesive bead onto absolutely flat surface (ideal condition without component tolerances).

Adhesive bead before joining.

 

Adhesive bead after joining shows uniform compression of the adhesive.
 

Application of adhesive bead onto component with height tolerances.
 

Adhesive bead before joining.

 

Adhesive bead after joining shows different dimensioning. The aim is to achieve uniform width after compression.

Application of adhesive bead onto component with height tolerances. Utilizing the height profile, the amount of material in each area is adjusted.

Adhesive bead before joining shows application of different quantities based on height profile.
 

Adhesive bead after joining shows the desired width after compression.
 

Process

Mixing and Dosing Systems With 6-Axis Robot and Shuttle Table for Bonding Display Housings

Efficient and Fully Automatic – To Meet Your Exact Requirements

The adhesive application process for bonding the automotive displays to the housing is fully automatic and carried out using the DM 502 mixing and dosing machine with a 6-axis robot guiding the MK 825 PRO precision mixing head and using WT 1-LEVEL shuttle table for the parts handling. The display housings are attached to the two pick-up plates and positioned within range of the robot in shuttle mode utilizing a single plane, ensuring a continuous adhesive application process. Depending on the type of plastic used for the display housing, it may be necessary to apply plasma to the contour of the display housing beforehand to achieve an improved adhesive effect. For this purpose, the robot can be optionally equipped with a plasma nozzle.

To measure and check part tolerances, a separate pre-dispensing process scans the surface of the housing using a 3D line scanner. The measured data are transmitted to the dosing system’s programmable logic controller (PLC) and compared with the predefined CAD reference of the part. The detected deviations are used to adjust the dosing program in advance for the next adhesive application.

The mixing head mounted on the robot arm moves over the contour of the display housing and applies a precise, narrow bead of adhesive to the contour. Thanks to the AQA process, it is possible to automatically adjust the adhesive discharge quantity to match the dimensional deviations of any part tolerances.

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