Press release

Ingolstadt, 2009-06-26

Value – raw materials, materials and “look and feel”

AUDI AG
Sylvia Droll, Head of Total Vehicle Materials and Corrosion Engineering

Quality begins with the materials – with their selection, processing and chemistry. Audi sets extremely high standards here and is the driving force of continuous progress.

The company’s quality assurance organization includes an in-house laboratory that employs a whole slew of high-tech devices for extremely detailed studies of materials. Audi’s two computed tomography machines, for example, can scan entire cylinder blocks, and with their extreme magnification of up to 500,000 times, scanning electron microscopes assist in the analysis of fracture sites.

The spectrum of materials is extremely diverse, ranging from metallic materials to rubber, plastics, wood and leather to innovative, dirt-repellent textile trim in the interior. And time and time again, employees turn to their subjective senses to supplement the rigorously scientific analysis. The members of the “Nose Team,” for example, sniff out objectionable odors on board the vehicles and eliminate them.

In the materials sector, Quality Assurance monitors many components from the first step in their development to their everyday use by the customer in production vehicles. They collaborate closely with Technical Development, Production and even the Motorsport Department: Engine and chassis components of the Audi racing cars are also regularly examined in the lab.

Another task area within the material sector are the subjects of operational safety and corrosion, which pertain to the lasting durability of the components and their corrosion resistance. The bar is set high here, as well. Audi uses much more stringent test criteria for alloy wheels than its competitors. And the INKA test (Ingolstadt Corrosion and Aging Test), in which the entire lifetime of an automobile is simulated within five months, has long since become something of a benchmark throughout the entire automobile industry.

Soft and supple – the leather upholstery

AUDI AG
Claudia Lischke, Materials Engineering Interior/Equipment

Leather is a natural material. The unique exterior, the special haptics, the very unique smell – each piece of leather has very sensual properties. Audi handles this emotional material with kid gloves so that it can achieve its uncompromising quality objectives here as well.

The leather Audi uses comes from the natural cycle of agricultural animal husbandry. Every animal is different; every hide is unique. Audi only uses leather from male cows, which have larger and more homogenous hides than females. A large portion of the leather comes from southern Germany – the pastures there are almost entirely devoid of barbed wire fences on which the animals could injure themselves.

A hide has an area of roughly four to five and a half square meters, which the leather experts divide into three quality zones. The best piece is the back (croupon) – the grain is particularly even here and cracks or scars due to injuries are rare. The leather from the core of the back is used in all areas of a car seat where fine appearance and high robustness are most important – on the headrest, in the shoulder area, in the buttocks area and on the side bolsters and seatbacks on the entry side. The leather from the directly adjacent regions of the back are used in all other areas of the seat. Audi does not use the outermost region of the hide.

Tanning of the leather – a process comprising multiple steps – is performed without the use of chromium salts. In a pioneering move for the automobile industry, Audi stopped using these chemicals 15 years ago. They are still used today for shoe and garment leather.

Audi offers its customers an extremely wide selection of leather upholstery for all models. The experts from Quality Assurance divide their “leather pyramid” into three levels. It begins with the basic leather, which is embossed and finished (coated) on machines. The coating covers the hide structures and seals the pores, which makes the seat very durable. Less finishing is involved on the second level of the pyramid; the leather is more natural, breathes more and is softer – to paraphrase: more comfortable.

At the very top is pure aniline leather. There is no machine embossing or coating involved. The top grade of leather shows its natural surface and grain, thus it also requires a greater level of care. Unlike coated leather, it shows authentic characteristics of an animal hide in some areas, such as tiny healed wounds, light rough patches or mosquito bites. As a visible expression of natural processing, these underscore the authentic character of the material.

Regardless of the type of leather, Audi checks all grades of leather in its own laboratory. 45 tests are performed just to determine the durability of the leather. Mounted in automatic fixtures, the leather specimens have to show that they expand evenly, where they begin to tear, when they begin to develop wrinkles and how resistant they are to abrasion and fire.

How they react to exposure to extreme sunlight is just as important as the determination of water vapor permeability or the odor and emission tests.

Besides the classic types of leather, Audi also offers seats covered in a combination of leather and Alcantara in many models. The natural material is applied to the side bolsters and seat backs; the microfiber on the center areas. Audi is also constantly developing new leather grades, particular with respect to breathability, softness and natural appearance.

Strict standards apply not only for the selection of the leather, but also for its application and stitching. Due to their round and concave shapes, a great deal of effort is required to cover the seats – especially the sport seats – without wrinkling, but that is precisely what Audi quality demands. The seams on all seats and trim elements are exactly straight, even and parallel. This can be attributed in part to the special needles used in the sewing machine. The so-called cutting needles minimize the sawtooth effect in the cap seam region that would otherwise occur when the leather is drawn into the needle mark.

Precious material – the wood veneers

AUDI AG
Hermann Wiegel, Head of Non-Metallic Materials

Wood veneers create an atmosphere in the interior; they convey an impression of elegance and cultivations. Wood is a precious natural material – and a demanding one. Audi handles it with particular care.

Audi’s purchasing agents apply strict standards to the raw material. Specialty companies manufacture veneers by machine-peeling thin sheets only 0.5 to 0.6 mm thick from the trunks of trees, from the roots or from outgrowths from the trunk called burls. Because the structure of the wood is constantly changing, each sheet of veneer has its own grain – a “flat” or “living” structure as the experts say. The “clouds” and “eyes” are always different.

These differences are more or less pronounced depending on the type and lightness of the wood. Dark birds-eye maple, for example, has a relatively homogenous appearance, whereas light poplar is particularly variable. Amber-colored vavona, taken from the burls of the California redwood, exhibits a wide range of structures and brilliant, shimmering colors that gives an intense sense of depth. Audi offers its customers a broad selection of inlays, with custom grades such as Fine grain maple copper or Poplar saffron available from the Audi exclusive and Audi S line ranges for various models.

The veneer sheets must satisfy exacting requirements if they are make it past the watchful eyes of Audi Quality Assurance. A veneer trim set for a car generally comes from a single burl or single sheet of veneer. The individual parts are similar. Audi is particularly strict when it comes to obvious differences in areas such as the center console and the ashtray cover fitted there. The veneers must be free of flaws.

Processing of the veneer sheets is a painstaking process. The specialists bond and press a precious veneer with up to four substrate layers, taking into consideration the alignment of the grain in the layers so that they can later achieve perfect dimensional accuracy. Machine pressing, in which the thin package comes in the desired form, also requires a fine sense for the proper temperatures and cooling times. After pressing, the wood skin thus produced is back-injected with plastic.

The next step is bleaching, which is required because the base colors of the wood are different. The final shade is provided by the stain, which is applied thereafter. Wood with a “flat” optical structure is used for the piano finish trim that Audi offers for some models. The wood is painted black and covered with up to ten successive coats of clearcoat.

Most veneers also contain a sealing coating of transparent plastic (polyurethane/PU). It protects against scratches, provides a deep luster and does not yellow even when exposed to intense sunshine. The PU coating is not used with open-pored veneers such as dark ash. Instead the natural surface is retained, which has a slightly structured feel when you run a fingertip over it.

Only after all of these steps have been completed is the part machined. All parts have complex geometries – the door inlays, for example, are not plane but raised, and the large panel on the center console has numerous edges and radii due to the cutouts for the ashtray, shift lever and, if installed, the start-stop button.

Machine cutting requires a high degree of precision, and Audi also requires subsequent manual reworking of the cut pieces. A sanding block is used to sand (“break”) the edges of the veneer very slightly – it takes years of experience to sand down just the right amount. The next step – polishing with soft cloths – is also performed by hand in many areas. The special coating for the edges, which prevents moisture from penetrating into the wood, is also applied manually.

Audi focuses on maximum precision at each step, even when the finished wooden trim elements are bonded with thin chrome frames as is the case with some variants. The permissible tolerances, including those for assembly at the plant, are generally only one to two millimeters. These are essential due to the various rates of thermal expansion of the components. Even at extreme temperatures – and in direct sunshine the interior of a car can reach as much as 70 degrees Celsius – the veneer must not rub against the frame.

Audi Quality Assurance maintains its own testing laboratory for the study of wood veneers, where issues such as fogging (evaporation) or fading are investigated. Specialists carefully study the structure of the woods; other topics include weatherability, geometrical stability and resistance to abrasion and scratching.

Audi is also constantly developing innovations in interior materials. The current trend is toward lighter colors, and thus also toward lighter woods. The “Sportback concept” prototype presented at the Detroit Auto Show early this year featured light veneers into which lateral strips of dark wood were embedded. This solution is very time-consuming and requires a novel process for peeling the veneers but produces a one-of-a-kind atmosphere in the interior.

Cleanliness and gloss forever – Oleophobation and UV paint
Oleophobation

AUDI AG
Helmut Donaubauer, Materials Engineering Interior/Equipment

Stains and discoloration caused by water or dirt in the passenger compartment – that just doesn’t go with an Audi, not even after years of operation by the customer. A Quality Assurance team for interior A- and B-pillar liners therefore developed a coating that repels liquids and provides for easy cleaning.

After the textiles are manufactured, a coating is applied to the fabric intended for the liner. This coating is a type of impregnation that repels liquids such as water or oil similar to the lotus effect. This surface masking stands up to UV radiation and is also resistant to all the other various environmental influences that act on the vehicle interior, which vary depending on the regional conditions prevailing in the sales markets throughout the world. The textile decor elements are placed in molds and back-injected with plastic to produce the finished pillar liners.

The fact that water or coffee beads and can be removed without leaving residues behind is not the only advantage of the coating: Unlike untreated fabric covers, it is also easy to clean. Testing has shown that even heavy soiling such as soot can be removed nearly completely even from light-colored parts.

High gloss and UV paints

AUDI AG
Ronald Schiweck, Head of Materials Engineering Interior/Equipment

Every Audi interior makes a shining impression thanks to its numerous high-gloss control elements – from light switches to the fascia in the doors and the cockpit to the air conditioning system. An increasing number of high-gloss components are being used – a current trend in car making that has also left its mark on Audi.

Even before the classic grand piano, high-quality instruments, furniture and other objects with a high-grade surface in high-gloss black have fascinated the observer. Unfortunately, these decorative items are often not as robust in use as Audi quality standards demand, such as with respect to scratch resistance. Audi therefore insisted that high-gloss components for automotive interior applications must be classified according to the loads that they can withstand. The first step here was to analyze the loads placed on the high-gloss surfaces in daily use by the customers according to comprehensive criteria: see and touch; decorative or functional surface; location within the direct reach of the occupants; low or high frequency of actuation.

The “Guidelines for the Load-based Classification of High-Gloss Components” cover all of these parameters and depending on how high the loading on the part is, specify a maximum permissible change in gloss following the scratch-resistance test.

In the future, Audi will apply a high-gloss finish with a UV-curing topcoat to all high-load control elements. This can also reduce inadvertent damage caused by objects such as rings, keys or mobile phones.

During the conventional painting process, a special topcoat system is applied to the respective part, and the surface is subsequently exposed to UV light. This results in an extreme increase in hardness due to the reaction of certain components in the paint. Curing is extremely fast, eliminating the need for an additional energy-intensive drying line.

Cerapaint® – the perfect protection for aluminum

AUDI AG
Waltraud Betz, Materials Engineering Corrosion Protection

Audi offers its customers a special option – the high-gloss package – for many of its models. This package includes body trim elements such as the window capping trim or the lower door trim made of aluminum. As the first and only car maker in the premium segment, Audi coats these premium parts with the high-end protective coating Cerapaint to keep them shining over the life of the car.

The current standard in the automobile industry is the Eloxal process, a technique in which the aluminum base material is oxidized with oxygen. This is done by applying a direct current and by means of electrolytic anodization – a process in which the workpiece acts as an electrode and accepts electrons, driving an oxidizing reaction. The oxide layer thus produced has column and honeycomb-shaped pores that seem to grow out of the surface of the component. Anodic oxidation requires a final densifying step: The open, porous oxide layer is closed by embedding water in the amorphous oxide. The disadvantage of this is that certain chemicals, such as insect removers or highly alkaline prewash agents in car washes, attack this layer and can cause irreparable damage and corrosion.

The Cerapaint process does not suffer from this weakness. The aluminum is first anodized and then densified in a special process. A thin layer of silicatic gel is then sprayed onto this layer. It is only one to two thousandths of a millimeter thick, but it is characterized by a dense, closed surface, high hardness and excellent chemical resistance.

The protective coating is resistant to acids and bases and thus all types of road salt, repels dirt and is easy to clean. The Cerapaint process can be applied to all versions of the trim elements in colors ranging from the natural color in high-gloss to black.

The scent detectives – the Audi Nose Team

AUDI AG
Heiko Lüßmann-Geiger, Material and Corrosion Engineering Total Vehicle

Audi customers want to experience their cars with all of their senses as a place where they can feel comfortable. Audi applies stringent criteria in this area and here too is a pioneer in the industry. The Audi Nose Team, assigned to Quality Assurance in the lead up to the start of production, combats offensive aromas on board the vehicles.

The smell inside a car is of fundamental importance, although it is generally perceived subliminally. People can differentiate between thousands of aromas and keep them in memory. Smells generate positive or negative associations; they inspire sympathy or antipathy. Unpleasant smells trigger – consciously or subconsciously – defense reactions and can have far-reaching consequences. If a vehicle interior smells unpleasant, the customers may also evaluate the other properties of the car less highly.

The Audi “Nose Team” was formed in 1985; seven years later, the process it developed had become the standard in the German automobile industry. The six-member core team, supported by three outer “bench players,” decides whether materials are suitable from an olfactory perspective for use in the car. Materials that don’t clear this high hurdle are stricken from the procurement list.

The work in the Nose Team is a special assignment; normally the professional sniffers work in the Quality Assurance materials laboratory. They were chosen for the smell team by virtue of their particular sensitive noses, which they have to take good care of: Smoking is prohibited, a cold stops team members from working and team members must not give off any scents of their own during testing – whether perfume, shower gel, after shave or maybe even garlic.

The members of the Nose Team meet daily in the Ingolstadt plant’s Quality Center. The employees cut small pieces out of the components to be tested – from the cockpit to wood inlays to the leather upholstery for the seats. These specimens are then placed in a standard canning jar equipped with an odorless gasket. An oven heats the sealed jar to 80 degrees Celsius for two hours.

Now it is time for the evaluation: Each tester in turn lifts the cover slightly, sniffs briefly at the contents of the jar, reseals it and quickly passes it to his or her colleague. Each team member writes down their grade in secret. After five or six tests, the noses need a one to two hour break before they are again capable of exact evaluations.

The German school grading system is used for scoring the results. Materials given a grade of one (“odorless”) to three (“strong inherent smell, but not yet offensive) pass the test. Materials with the grades four (“offensive”) to six (“unbearable”) fail. Plastic parts that give off unpleasant odors, leather that smells of fish oil or floor mats with an air of onion about them don’t stand a chance at Audi.

The Nose Team analyzes roughly 500 different components from the passenger compartment for each model. It also examines complete components such as dashboards to test the interaction of various materials. They are brought up to temperature in a large custom heat chamber of stainless steel. During the test, the testers stick their heads through a hole in the chamber and assess the smell.

The last step is the evaluation of the entire complete vehicle. This is done by heating the interior in a climate chamber with large heat lamps. When a car sits in the blistering sunshine, the interior can easily reach temperatures of up to 80 degrees Celsius. The members of the Nose Team evaluate the overall impression and also attempt to identify components with dominant smells.

Nose Team members also use highly advanced technical methods in addition to subjective evaluation. All air samples are analyzed in a gas chromatograph, frequently in combination with mass spectroscopy. These enables the Audi specialists to precisely analyze the chemical composition of the substances emitted and unequivocally identify all volatile organic compounds, which enables offensive materials to be precisely identified and eliminated.

The result of this elaborate series of tests is the subtle olfactory impression exuded by every Audi. Internally it is designated as “neutral.” Each part contributes to this neutral smell with the authentic smell corresponding to the respective materials. Audi uses no artificial scents in its cars, in part because there is no one aroma that appeals equally to all customers. The fully scentless car is also not the objective – that is as unappealing as a sound-dead vehicle.

The Audi Nose Team is not only involved in the development of new models, it also checks that the olfactory quality of production vehicles remains at a consistently high level. Individual cars are randomly pulled from Production and sniffed over in the test chamber.

The INKA Test – time-lapse torture

AUDI AG
Werner Piller, Materials Engineering Corrosion Protection

A fog of saltwater solutions sprayed onto the sheet metal panel through countless nozzles. Test drives on gravel roads. A hydropulser in a minus 35 degree Celsius climatic chamber that twists the body. Audi tortures its test vehicles mercilessly. The INKA test (Ingolstadt Corrosion and Aging Test) simulates all the rigors of a 12-year service life in only 19 weeks.

The INKA test is performed at the Audi proving grounds near Ingolstadt. Not only are there various selective test tracks there, but also a large building with eight special test rigs. Weaknesses that would only occur after two or three years of normal wear manifest after just a few weeks on the test rig.

Each test is conducted in five phases. In the first phase, the car placed in a climatic chamber at 35 degrees Celsius and enshrouded in salt fog. It is then subjected to damp heat – up to 50 degrees Celsius at a maximum of 100 percent humidity. In the third phase the temperature is reduced to 42 degrees Celsius, but an artificial sun with an output of 1,000 watts per square meter beats down from the ceiling. This simulates the UV exposure of an African summer. The extreme irradiation heats the body to as much as 90 degrees Celsius. Colors in the interior must not fade and the materials must not become brittle.

Phase four simulates winter conditions at the polar circle. A hydropulser with four activation points – one for each wheel – shakes the car at a temperature of minus 35 degrees Celsius to depict the twisting of the body and the loads on the suspension components and engine mounts when driving on poor roads. This also reveals any trim elements that squeak or rub. In between – in phase five – test drivers do repeated runs totaling 12,000 kilometers over specially prepared routes featuring difficult profiles, pools of saltwater and mud, and gravel tracks where stones constantly rattle off the sheet metal.

At the end of the tests, specialists dismantle the entire car and body down to their individual parts and search for weak spots using sophisticated test equipment. Is there corrosion on an edge somewhere? Did a weld seam weaken? How did the scratches intentionally made in the paint during the test develop? Did adhesives in the body begin to deform? And how did the engine, the transmission, the electrical system and especially the many plugged connections and also the suspension hold up to the torture? The specialists devote particular attention to those areas in which different materials are combined or are joined using innovative techniques.

Although the INKA test has long enjoyed the status of a benchmark within the industry, Audi is not content to rest on its laurels and is continuously refining the test method based on its many years of experience. This enables Audi to achieve optimal design-based corrosion protection in the early stages of development of every car.

Design and safety – alloy wheels

AUDI AG
Andreas Wild, Materials Engineering Corrosion Protection

The alloy wheels from Audi are surely the most eye-catching parts of the vehicle that are of major importance in terms of both design and safety. Accordingly, Quality Assurance devotes a great deal of attention to them. The Materials Engineering specialists track the wheels from development through to their use by the customer.

To satisfy Audi’s stringent requirements, an alloy wheel must complete a demanding testing program comprising a series of material, surface and strength tests and inspections. The wheels are examined for casting defects, anomalies and cracks in the X-ray check. The roll motion test simulates travel through curves with extreme lateral forces. In the recreation of driving over the curb at high speed, the rim flanges must withstand hard impacts without fracturing. Audi wheels can endure such impacts because they are cured by means of a special process that simultaneously enhances strength and strain.

With respect to surfaces, Audi has set the bar higher than any other car maker. Competing products, which periodically run through the test program, repeatedly fail various criteria. The corrosion test, in which acid and temperature intensify the conditions, lasts for over 240 hours. Of equal duration is the paint adhesion test, which is performed at nearly 100 percent humidity. A stone-chip resistance test and tests to determine chemical resistance, weatherability and light stability round out the program.

Aluminum wheels from Audi have complex surfaces, regardless of whether the wheel is cast, forged or rolled. The corrosion protection coating system, comprising a primer, basecoat and clearcoat, is common to all versions. The wheels are tested for tightness prior to coating – Audi does not accept use of the coating as a sealant.

If requested by the customer, Audi also supplies custom wheels – in standard silver and high gloss, with polish and clearcoat or with diamond-cut design surfaces and contrasting paint for a two-color effect. Custom surfaces – with chromed plastic wheel cover or galvanically chromed – are also available. Audi achieves uncompromised quality in the demanding chrome plating process, whereas many competitors have problems here with corrosion and thus diminished visual appeal.

One new development is the Durabright technology, which makes the surface so dirt-repellent that cleaning requires nothing more than soap and water. Audi plans to begin using a special chrome surface in the near future that is characterized by a subtle flat finish (“iridium look”) and simultaneously demonstrates the high level of quality demanded by Audi.

Service life testing – durability

AUDI AG
Reiner Steppan, Head of Materials Engineering Suspension/
Corrosion Protection

At Audi, durability means the guaranteed service life of all vehicle components in the customer’s possession – from the seal strip to the crankshaft, from the wheels to the links in the suspension. Ensuring durability is one of the classic tasks of Quality Assurance.

The work of the quality assurance specialists extends to many different levels, and includes random checks of components used in series production, various concept experiments, the determination of the service life of components and the analysis and recreation of damage. When a defect does occur in practice, Quality Assurance analyzes the environment and background with great precision and recreates the events that led to the damage. It often turns out that the customer was overly ambitious with his car – driving over a traffic island at excessive speed is too much for even the most robust wheel suspension – but the investigation of these extreme cases also provides valuable lessons for continuous improvement.

Durability tests are performed on test rigs that enable the function and behavior of components to be precisely determined. Whether a control arm behaves suspiciously under certain loads or overload situations – such as driving too fast over a curb – can be determined relatively quickly, for example. Road testing takes much longer. The Audi quality assurance specialists often investigate very specific issues, down to the question of whether cleaning procedures for aluminum components or country-specific types of road salt have an effect on service life.

The range of test rigs comprises twelve individual hydropulse cylinders, a three-axis axle test rig and a series of specialized systems for testing such things as joints, crankshafts, rubber-metal bearings and wheels. Audi has codeveloped proprietary test rigs for assessing the wear and function of the ball joints used in the company’s complex multi-link axles.

High-tech measurements – the Audi laboratory

AUDI AG
Martin Poese, Head of Materials Engineering Assemblies/Transmissions

How strong and how durable is a material? What is the distribution of chemical elements in the materials? When does sheet metal start to corrode when sprayed for weeks on end with a concentrated saltwater solution? How do the reinforcing zones of a pivot bearing have to be designed so that the component is as light as possible yet absolutely reliable over a long service life? All of these questions are investigated and answered by Materials Engineering Ingolstadt, a department within Audi Quality Assurance.

The lab is the materials engineering competence center for the entire company and is closely networked with the laboratories at other Audi sites. Established in 1971, it currently employees roughly 70 people. The lab is responsible for all materials engineering matters, from development to use in production vehicles, and is also largely responsible for the corrosion protection of the complete vehicle.

The lab monitors many technical components throughout the entire development process and beyond. As a skilled partner, the lab supports the colleagues in Technical Development, Planning and Production in numerous areas, such as materials consulting and development, damage analysis and the testing/inspection of components. Before a new engine block that was hand-built at great expense is subjected to rigorous, time-consuming and costly testing on the engine test rig, the lab’s specialists preemptively conduct a detailed analysis of the quality of the casting.

The high-tech equipment in the Ingolstadt lab has a replacement value of over 30 million euros. Whether gas analysis using high-performance liquid chromatography, x-ray diffractometry to measure internal stresses in components or inductively coupled plasma for trace analysis of heavy metals – Materials Engineering has the ideal measuring equipment in practically every case.

From aluminum to high-strength steels, from engine to suspension to body – metallic materials are naturally the focus of the lab’s work. However, the Audi specialists also work with rubber and plastics, textiles and leather as well as glass and ceramic. A highly specialized team analyzes the smell of the materials fitted in the interior – gas chromatography devices and mass spectrometers used for measuring are complemented by people with an exceptionally highly trained sense of smell, as there is nothing better than the subjective opinion of the expert. The uncompromising approach to quality at Audi extends to the smallest possible component with the focus always on the ultimate deciding factor – people.

Computer tomography – Technology from the world of medicine

AUDI AG
Stefan Hils, Materials Engineering Suspension

Computer tomography devices are tools for better health – in medicine and at Audi. They serve the same purpose in both cases: to illuminate bodies so that problem areas can be found. Audi uses its two CT machines in the Ingolstadt Quality Assurance Laboratory to non-destructively examine the structures of components – from larger components, such as engine blocks, gearbox housings, alloy wheels or oil coolers, down to the smallest of structures found in electronic units, for example.

Audi has invested 1.2 million euros in its computer tomography devices, which like the medical devices work with x-rays. Because they don’t have to make allowances for living organisms, they are operated at much higher powers, however. The components to be examined are secured in a fixture inside the machine and rotated around their own axis in tiny angular steps. A two-dimensional x-ray image is produced at each step.

The result at the end of the process, which can last anywhere from roughly 30 minutes to several hours, is a collection of digital, 2D images. A powerful computer assembles these individual images into a 3D volume approximately two gigabytes in size. The Audi specialists use the data generated for a wide variety of analyses. They can rotate the virtual component in any direction, take as many slices as they want and take a virtual fly-through through the interior.

This enables them to find potential defects, such as blowholes – voids that occur as the result of material shrinkage during casting. In more complex units – a defective fuel pump or a noisy rubber-metal bearing from the suspension, for example – they can precisely analyze the position of the individual components and their exact interaction.

The CT machines are used at Audi for a wide variety of tasks. They are used to assess hand-built arts during predevelopment, provide information for strength studies and help with the analysis of defective components. Audi also uses the CT machines in motorsports to analyze suspension parts following a race. The wheel suspension of a DTM (German Touring Car Championship) car, for example, is made of high-strength steel to save weight and the slightest crack could prove fatal.

Very unusual objects have found themselves on the turntables of the Audi CT machines from time to time. The machines in Neckarsulm have, for example, examined a roughly 2,000-year old Egyptian animal mummy for the Hessian State Museum – all in the name of science.

The scanning electron microscope – detailed analysis of fracture sites

AUDI AG
Martin Poese, Head of Materials Engineering Engines/Transmissions

Audi quality also means testing under extreme conditions. Engines and transmissions are repeatedly pushed to their limits and beyond on test rigs, with maximum loads that never would occur in normal use. If a component then fails, it undergoes a detailed examination in the Quality Assurance laboratory – under the scanning electron microscope.

Two scanning electron microscopes, abbreviated SEM, are available to the specialists at Audi. The name refers to their basic functional principle: they scan the specimens point-by-point and line-by-line with a focused electron beam in a vacuum. Electrons have a shorter wavelength than light and can be rastered extremely finely in a beam. This enables the SEM to achieve extreme resolutions and magnifications between a factor of 20 and a factor of 500,000. Light microscopes, on the other hand, bump up against their limits at a factor of only 1,000. The black-and-white image of the SEM is high contrast, tack sharp and has a high depth of field.

The team’s primary work is the analysis of fractures and wear sites on engine and transmission components such as valve springs and gears. Large component or fracture planes are broken down accordingly. Viewed under the SEM, typically at 100 to 20,000x magnification, the fracture site of a spring, for example, provides the experts with precise information: They can tell what type of fracture it is, e.g. a fatigue fracture or a fracture initiated by stress cracking, based on characteristic features. The monitor shows the reference point of the fracture – frequently a tiny inclusion of foreign material measuring only a few thousandths of a millimeter – and reveals the series of events that led to the failure.

The precise investigation is facilitated by another technology integrated into the scanning electron microscopes at Audi: micro x-ray fluorescence analysis. This technology takes advantage of the fact that a characteristic x-ray radiation is generated by the interaction of the electron beam with the specimen. Different elements in the sample generate different radiation.

The color graphic of the recorded spectrum and the element distribution image provide key information. An oxygen peak, for example, is indicative of a slag inclusion, a small point of an inferior material mixture, and thus of a manufacturing fault during the melting of the steel. Brittle fractures could provide clues regarding imprecision during the heat treatment of the workpiece; fatigue fractures suggest insufficient material thickness or an unfavorable design geometry. All of this information helps the colleagues in Development and Production make the proper adjustments to resolve the problem.

Damage analysis is the primary focus of the 13-member team’s work. Other tasks include examining components from Audi racing engines and transmissions; the testing of materials, including motor and transmission oils; and consulting on the metallic and non-metallic materials used in engines and transmissions. The damage analysis team monitors all important components from the development process to use in series production to use in customer vehicles.



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