Austrian plant engineering firm Vescon developed a solution for producing modern LED headlights for the Slovakian plant of well-known Tier 1 supplier. The focus was on efficient handling systems, the correct processing of time-critical production steps and end-to-end traceability. Specialists from Festo's Technical and Application Center, who were taking care of the turnkey handling systems, made up part of the team.
A lot has changed in the area of lighting technology since the first motorized "carriages" took to the road. At the dawn of automotive history, it was normal to have lamps either mounted on the side of the vehicle or on the hood. Later, these were replaced by electrically-operated lights. With the lamps, you could literally refer to them as "fire points", derived from the light source, usually acetylene flame lamps, that were actually burning.
Equipment for switching from main beam to low beam was designed in 1908: Using a Bowden cable, you could operate a lever that shifted the gas flame from the fire point of the reflector. The world looks very different a century or so later - "and there was light". With new technologies and powerful LED lamps, these days we are, in the full sense of the word, "light years" ahead. This however has called for innovative semi- or fully-automated production systems, in order to guarantee the precision needed for the manufacture of these sensitive vehicle parts. This was an exercise for the experienced plant engineers at Vescon.
The headlight assembly system
Vescon Systemtechnik GmbH is headquartered in Gleisdorf, near Graz, Austria. Here, the company implements a wide range of projects from automation and process engineering right up to power engineering and software development. One of these sophisticated automation and process engineering solutions that was developed specially for the Slovakian plant of Tier 1 supplier ZKW Group, was for the production of full LED headlights. The solution is an LED light module that avoids dazzling other road users thanks to a "matrix arrangement" of the LEDs and the ability to dip individual LED segments, while at the same time ensuring good visibility for the road ahead.
Visual sensors identify the presence of oncoming traffic or vehicles ahead and the segments are selectively switched on or off, depending on the traffic conditions. Coordinated transitions between the light scenarios mean that the driver enjoys a homogeneous and optimized illumination of the road, without that sudden change of light that we are used to when switching from main to dipped beam. The driver's eyes can adjust to the new light setting more easily. This represents an active safety plus because the rest of the surroundings remain well lit by the main beam.
The design had to take processes such as the tricky application of a two-component thermally conductive paste into account. Christoph Legat, Project Manager at Vescon Systemtechnik GmbH: "The paste has very rapid hardening properties. At the design stage we had to ensure that the process would not cause the so-called pot life to be exceeded. This defines how long a reactive material can be processed or, as in this case, how long the LED components can be repositioned in the paste before the material has hardened too much."
Thermally conductive paste is used here because powerful LEDs produce heat that has to be dissipated. With finished headlight modules, additional small fans also ensure that the heat is diverted towards the front of the headlight, which supports the deicing and defrosting properties of the headlight. "It is important to check whether the correct amount of heat-conducting paste has actually been applied to all required surfaces as otherwise, partial overheating can occur. Without doubt, this is one of the main challenges we were faced with, with this system," says Project Manager Legat.
A second, particularly challenging part of the headlight assembly system is the hot riveting. A plastic dome is deformed at a precisely determined temperature to create a rivet head. Christoph Legat: "This rivet head sits on the reflector and it has to hold it and the printed circuit board on the cooling element, completely securely and reliably. The riveting has to be so accurate that no gap can occur, which could cause the components to wobble during the subsequent vibration test or under normal operating conditions. In the worst case, this could impact on the illumination while driving."
The customer opted for a semi-automatic solution where multiple operators are involved. On the one hand, this opened up the opportunity for greater flexibility while keeping costs down. On the other, it made it easier for the manufacturer to take different components or product versions into consideration. In spite of the manual interventions, the complete system is monitored at every step by a controller. Primary control is done through a database that manages all the product data and information relating to the production process of each headlight. At the end of the manufacturing process, each headlight is fully traceable.
As the first step of the process, the operator removes the headlight housing and places it in the processing station. Then the type code or the variant that is to be produced is selected. "A good example is a headlight that is intended for a vehicle that is exported to other, non-European markets. In such cases, other indicator modules are sometimes used because local statutory regulations define that there must be switching between the indicator and the daytime running light," explains Legat.
Each operator works at two or three different assembly stations while locking cylinders ensure that the workpieces are held securely in place. These don't just hold them in place, but in addition, they only release the component once all the necessary processing steps have been carried out correctly. The operator positions the different components and accompanies the headlight until it reaches the first fully automated processing station, the application of the thermal paste. Once it reaches this position, the headlight is already fully wired, and it has been fitted with the adjusting system and the main beam module. Now a turnkey three axis handling system is deployed that was delivered to the Vescon system, by the specialists from the Festo Technical and Application Center.
The basic axes are two EGC-120, stroke 250 toothed belt axes, synchronized via a connecting shaft and with a space-saving right-angle gear unit. The y-axis is a heavy duty Type EGC-HD-160-TB axis with a sturdy double guide. In the z direction, an EGSL-BS-75, stroke 100 electrical slide (screw actuator with ball bearing cage guide) performs its duty. All axes are equipped with servo actuator packages. Three type CMMP-M3 Premium motor controllers with PROFIBUS Interface and safety module operate as controllers. Festo builds and delivers complete ready-to-install handling systems – with a performance guarantee and documentation.
A ready-to-install handling system ensures the even application of a two-component thermally conductive paste.
The operator places the cooling element (with holes for insertion of the reflectors) in the station and the thermally conductive paste is applied automatically on both sides using the Festo handling system. It always brings the two-component dispensing system to exactly the right position on the right track. In the next step, the printed circuit board with the five LEDS is positioned in the paste on the cooling element. Then the reflectors, with their guide pins to ensure optimum positioning, are applied. Once this is done, the operator removes the complete cooling element and takes it to the next station, where a further Festo handling system takes care of the movement of the rivet head tool.
Here, there are two EGC-80 toothed belt axes with guide slides, synchronized via a connecting shaft and with a space-saving right-angle gear unit (x-axis). There is also a type EGC-HD-160-BS heavy-duty axis with sturdy double guide (y-axis) and a type PLFN flange gear. All axes are equipped with servo actuator packages with multi-turn encoders.
Project Manager Legat is delighted with the ready-to-install handling solutions: "We just gave details of the required characteristics, we defined the loads and the paths or tracks that had to be traveled and then we didn't have to give any more thought to this part. This simplified our work enormously as did being able to use the handling system CAD data that Festo provided us, with for the design of the complete system."
The rivet head tools mounted on the handling system are moved out of the way by ADN cylinders controlled by VTUG. The checks of the pin length at the reflectors before riveting and the correct end position are done using SMAT position sensors located on the cylinders. If the pins have the right length, the protruding ends are thermally reshaped into rivet heads by the rivet head tools. This creates permanent connections that hold the sensitive component parts in place throughout the working life of the car. Now, the completed component, consisting of the cooling element, PCB and the riveted reflectors is removed by the operator and built into the headlight.
In order to test that the components are firmly fixed in place, the headlight comes to the pull test station where rotary- and linear-driven hooks are located under the module and by pulling, test for tightness. Then it goes to the light adjustment station. The operator places the headlight on a turntable. The headlight is clamped into position and the turntable is swiveled into the working position. Then the headlight is connected up and the various lighting scenarios and the indicator module are tested using cameras. In addition, the correct positioning of the lighting module is checked and, as in a car workshop, set to the ideal level.
Then, the design panels that conceal all the technology are installed, and in a gluing cell, the external, see-through lenses at the front of the headlight are glued into place using silicon-free, hot-melt adhesive. This is a time-critical process as the parts can only be glued together in an optimum way, during a particular period of time. After a period of pre-heating to reduce the surface tension, and the application of the glue, a robot presses the lens together with the headlight housing. Then a leak test is carried out on the headlight. If the unit passes this final test, another innovative "bringer of light" is ready to start its journey around the world.