Flow Drill Screws – A new joining technology
Audi has developed a process for the TT and TT Roadster bodies that significantly reduces weight while optimizing the axle loads. The front end and floor assembly are made of aluminum, the rear end of sheet steel. Because these two materials have differing coefficients of expansion when heated, they cannot be fastened to one another by means of welding. Audi is using a new technology here – self-tapping screws.
230 of these so-called Flow Drill Screws (FDS) assure the integrity of the body of the Audi TT Coupé, 250 in the TT Roadster. One of their most important areas of application is in the heel plate in the rear-end floor assembly, where they are closely spaced at between 60 and 100 millimeters. Structural adhesives further increase the strength of 80 percent of the connections.
The Flow Drill Screws are installed by a robot. Because of the high speed of the electric motor – up to 5,000 rpm – and the high pressure that is applied, the 18-millimeter long screws melt the workpiece slightly. The robot system, which is sensor-controlled, repeatedly modifies speed and force during the three-second process – as a result, the screws tap a metric thread into the material without damaging it.
Flow Drill Screws offer numerous advantages. They can even be used where the workpieces are difficult to access or can only be accessed from one side. The sequence of the screwing process is flexible and secure. The threads are so durable that they can even be re-used in connection with repairs. And because the process does not involve any thermal distortion, it is ideally suited to the strict quality standards that Audi applies in the Body Shop.
Audi anticipates enormous potential in the coming years for the principle of aluminum and steel composite construction. With its Flow Drill Screw technology, which is also suitable for employment in mass production environments, the brand with the four rings once again enjoys a crucial technological lead, Vorsprung durch Technik.
Remote laser beam welding – Fast and accurate
Audi also utilizes a high-end technology for connecting sheet steel workpieces – remote laser beam welding is employed in the doors of the Audi A4 and Audi Q5. It is fast and highly efficient, and it affords customers a key safety advantage: It enables narrow welding bosses to be provided on the inside of the door frames. Because of them, the A-pillars can be narrower – which increases the driver’s field of vision.
Remote laser beam welding is performed in the N24 hall at the Ingolstadt site, in which the doors for the newest Audi model lines are produced. It occurs in two steps in an enclosed cell. In the first step, a 7 kW laser fires pulses onto the surface of the inside of the door in extremely short cycles. This produces the small, 0.15 millimeter high bosses that are required for welding galvanized sheet metal – they create the gap joint in which the zinc can degas in a controlled manner.
In the second step, a robot with an optical focusing system produces the laser welds. 48 welds create a strong connection between the inside of the door and its frame. The two mirrors of the optical system that are used for aligning the laser beam reposition themselves extremely quickly in accordance with a preprogrammed sequence as the robot moves – a weld can be completed in around 40 milliseconds, and the next one is already being performed after only a few milliseconds.
This remote technology reduces the cycle time to between 19 and 20.5 seconds per door, around one half of the former time. And energy input, too, is much lower – the efficiency factors of the new laser units are six times higher than their predecessors.
Remote laser beam welding produces welding bosses with a width of around five millimeters – in the predecessor to the Audi A4, in which traditional resistance spot-welding was employed, they were 13 millimeters wide. As a result of the narrow bosses, the total weight of each door is 60 grams lighter – representing a weight reduction of nearly 0.25 kilograms in the Audi A4.
Flexible manufacturing – Different doors on one and the same line
Hall N24, which was constructed only two years ago on the Ingolstadt site, is the door center for the cars from the mid-size model line. This is where the doors are produced for the Audi A4 Sedan, the Audi A4 Avant, as well as the Audi A5 and the Audi Q5 – in a modern, flexible and efficient process.
Hall N24 is divided into two main areas. The doors for the Audi A5 are produced in a somewhat smaller zone at the periphery; their frameless design makes them a special case. Located in the center of the building is the combination system for all of the other doors; it is divided into four fields of equal size. In each of them, a door – front left, rear left, rear right or front right – is manufactured from between 13 and 15 individual components. Whether they are destined for the Audi A4 Sedan, the Audi A4 Avant or the Audi Q5 plays only a subordinate role in the production process.
Although the geometries of the doors differ greatly from one another, their engineering is identical, and they incorporate many identical and similar components. The reinforcing elements can always be installed in the doorframes in the same manufacturing sequence. And the connection between the inside of the door and the frame by means of remote laser beam welding is performed on one and the same system. Production of the left- and right-hand doors is performed identically, although as a mirror image of one another.
The large components are delivered by a conveyer that runs beneath the roof of the building; this conveyer also carries away the finished doors. The screw elements for attaching the components are placed fully automatically by robots – in the predecessor model, this was still being done manually. Robots move all heavy components and glue the soundproofing mats into the door bodies – a further automation step.
This compact layout of the production operation saves on floor space – amounting to 2,720 square meters, the footprint of the combination system is 35 percent smaller than in the case of conventional individual systems. Many components are stored on rotary tables and in rotary drums, which further improves floor space utilization. Every working day, 7,800 doors for 1,950 automobiles are produced in the combination system. Audi can be 100-percent flexible in apportioning this volume between the Audi A4 Sedan, the Audi A4 Avant and the Audi Q5.
Paris Red and Inuit While – New paint technologies from Audi
Automobiles from Audi offer impressive, pioneering design – and their paint finishes play a major role in this connection. New technologies make the cars with the four rings even more attractive out on the road, while simultaneously reducing the energy input requiring for the painting process.
The latest developments include the color Inuit White – a mother-of-pearl effect paint finish that is reminiscent of the glittering brightness of the polar region; mother-of-pearl colors have a long tradition at Audi. Development of the new Inuit White began two years ago using two different approaches, both of which led to the desired result.
The first approach was a paint finish that was produced by two painting runs, with a base coat and a clear coat being applied in each of these two runs. The first base coat produces the color, the second provides the mother-of-pearl effect by means of pearlescent pigments. This four-coat paint finish is around 180 microns – nearly one-fifth of a millimeter – thick.
As an alternative, the Audi specialists also investigated an only 135-micron thick three-coat paint finish using the so-called wet-in-wet process, in which the individual coats are applied in one painting run, without intermediate baking. Although the end result produces no discernable difference to the four-coat paint finish, the elimination of the second painting run and one clear coat means that the three-coat paint finish offers considerable savings in terms of energy input and weight.
A further forward-looking technology that Audi is investigating in the paint sector consists of so-called nanodispergent pigments. In this process, tiny pigment particles of only 10 to 80 nanometers (0.01 to 0.08 micron) in size are produced and dispersed – a human hair is 1,000 times thicker than one of these particles. The results are strong depth and high gloss, as demonstrated by an initial red test paint finish, which is tentatively being called Paris Red. At the same time, development work is also under way on a very low-gloss clearcoat paint that specifically produces a satin-finish appearance, which can lend a totally unique effect to sporty automobiles.
Audi is working on a further issue in collaboration with the Ingolstadt University of Applied Sciences – a new mixing process for the filler coat colors on the basis of eight basic colors. In this process, the volume of paint required for each automobile is individually mixed just prior to painting in order to assure the best possible match to the base coat. The better the filler used as the primer coat is matched to the color of the base coat, the more security there is in also using new effect paints. Moreover, this technology also enables the painting process to be designed more efficiently.