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.
Precision – fit, finish and workmanship
Deeply lustrous paint, precise light-refracting edges, uniformly tight body joints – every Audi embodies perfection on the road. The interior is also finely honed and conveys a confident air of quality. A tremendous amount of effort goes into the precision handling of surfaces.
At Audi, this maximum precision begins with the manufacture of the dies for the sheet metal presses, as this is the only way to achieve the extremely tight tolerances allowed by the brand. New high-end joining technologies are constantly being used in body construction – the invisible joint in cars like the A4, for example, is produced by means of plasmatron welding. An extreme amount of effort is also dedicated to corrosion protection; Audi floods cavities in the car body with hot wax in a sophisticated procedure.
This strict dedication to quality is also reflected in the paint – a layer a tenth of a millimeter thick. The effect finish, in which tiny metal particles in the pigments change the shade depending on the light and angle, is applied in such as way as to subtly underscore the lines of the design. Strict specifications also apply to areas such as the engine compartment and the inside of the rear hatch. Modern instruments control the quality and color values of the finish, and Audi also performs painstaking color matching in the interior.
The flawless finish of every car demands perfection across the board, and Audi operates a whole series of measuring systems and mock-ups called master jigs. Car bodies and their sub-sections as well as interiors are built by hand; this “zero-reference environment” enables the specialists from Quality Assurance to check and fine-tune the fit, the impression and a number of other criteria.
Perfect interiors – the interior master jig
AUDI AG
Antonio Gloria, Head of Master Rigs / Measuring Technology for Geometric Vehicle Analysis
A solid interior door handle that can be moved without play. A trunk lid that does not rattle thanks to strips of foam mounted out of sight. Inlays with maximum tolerances of two tenths of a millimeter. Audi takes precision to new heights in its vehicle interiors, and a key instrument that makes this possible is the interior master jig at Quality Assurance.
The interior master jig serves as the reference for the complete vehicle interior. It comprises a body with no dimensional deviations at any mounting point for interior components and thus is the ideal basis for coordinating interior components with one another. Besides functional criteria – easy motion of all components, firm seating, installability, sounds when actuated – the focus here is on visual properties, i.e. the general impression, the fit and the surfaces, as well as the haptics. Do any parts show any damage – scoring, sink marks or dents – from when they were removed from the die? Does the coin holder in the MMI operating system harmonize with the overall impression of the center console, or does the fit still need to be optimized and the surface upgraded with a fine finish?
The pillar trim, the sun roof, the glove box, the seats, the headlining, the dashboard, the center console, the carpets and even the mat under the trunk floor – every single compartment of the interior is evaluated on the interior master jig and must meet Audi’s exacting quality standards. Additional modules known as cubes, in which key individual assemblies of the interior equipment can be coordinated, supplement the central interior master jig body.
Two real-world examples: The flanks of the door liners are somewhat more stable and stiffer than those of the competition because their substructure is elaborately reinforced with ribs. In the rear hatch lining of the new A5 Sportback, a clip bent into the shape of an omega holds the service flap for the taillights. It is more expensive than a simple clip, but of much higher quality and more solid. The clasp into which the latch of the rear hatch engages is covered by a flap to prevent it from getting dirty. When the rear hatch is opened, a spring pushes the clasp cover upward; a thin layer of foam rubber dampens the impact so that the cover moves precisely and smoothly.
The interior master jig is the platform on which the last bit of precision is squeezed out of the parts. It is a central element of quality assurance at Audi, where all involved – the in-house engineers and specialists from the suppliers – can check the progress of development. The Board of Management also stops in from time to time because at Audi, quality is a matter of leading importance.
The “zero-reference environment” – the exterior master jig
AUDI AG
Antonio Gloria, Head of Master Rigs /
Measuring Technology for Geometric Vehicle Analysis
The master jig is a central instrument of Quality Assurance at Audi. The rather traditional-sounding name refers to a collection of measuring systems housed in its own building. Quality Assurance’s aim on the master jig is to fine-tune the dimensions of a vehicle project prior to the start of series production. All fits visible from the outside are fine-tuned on the exterior master jig. The parts involved here range from the doors, the hood and rear hatch to the bumpers, and all the way down to the trim strips.
The bodies are assembled on a rack of solid aluminum profiles. The work on this “zero-reference environment” begins roughly nine months prior to the start of production. The exterior master jig enables the specialists to analyze the dimensional compliance of individual parts, their flush alignment and the alignment of joints on the vehicle and fine-tune them down to tenths of a millimeter, thus continuously and iteratively optimizing the fit.
The gaps in the body are a testament to the strict commitment to precision at Audi. But not only purely measurable criteria are optimized: subjective impressions also play a major role in the tuning process. This means, for example, that a joint in the new Audi A5 Sportback between the fender and the hood varies intentionally in certain areas so that viewers perceive the joint alignment as being uniform.
Besides fit, the exterior master jig provides answers to a number of other questions: Do the colors, gloss, haptics and continuous lines fit together?
Are all components firmly seated and can they be easily installed? Are moving parts free-moving and do they make any unwanted sounds?
Other optimization tools also fall within the scope of the exterior master jig. The joint master jig substructure is used to assess the dimensional accuracy of load-bearing parts and the vehicle floor and for checking and fine-tuning the installability of the substructure. Care is also taken here to ensure that the individual sheet metal parts can be joined together tension-free. The substructure serves as the basis for the final optimization of the general impression of the complete vehicle on the exterior master jig.
The exterior function cubes are used to check the vehicle’s add-on parts, such as the doors with their seals or the taillights, bumpers and trim strips. These parts are first assessed separately in their environment. If they fit there, they move on to the next check on the exterior master jig. The final check takes place on a completely assembled pre-production vehicle. This last check reflects later practice during manufacturing.
Hardly any other manufacturer goes to the lengths that Audi does, always with the aim of offering each customer a vehicle that makes a perfect impression and exceeds even the high expectations of Audi customers.
Tight control – geometric vehicle analysis in the Master Rig Center
AUDI AG
Antonio Gloria, Head of Master Rigs / Measuring Technology for Geometric Vehicle Analysis
Precise analysis is the basis for quality assurance. Audi has therefore established a special analysis team in the Master Rig Center – the Geometric Vehicle Analysis team. In contrast to the interior and exterior master rigs, the focus here is not on individual components, but rather the entire vehicle as a unit. Vehicles at various stages of maturity – pre-production, just prior to the start of series production, the start of production (SOP) and the first production vehicles – are monitored and analyzed.
At the heart of geometric vehicle analysis are tactile measurements with a double-column coordinate measuring machine and optical metrology, which record the geometry and compare the measured values against the specified values from the design. This comparison shows whether all exterior and interior parts have the specified fit and function.
The experts are constantly tracking down minor problem areas. These can be individual parts that diverge slightly from the specification during series production. An injection-molded plastic part, for example, can take on different dimensions if the supplier changes the cooling process. Another example: as a welding robot ages, one or the other spot weld can differ very slightly. Small deviations during assembly can also result in the seat belt latch being installed slightly skewed or the procedure for bolting on the rear hatch not going exactly as planned.
Audi’s Production division has its own analysis teams that study such minor fit and function problems. They call in the colleagues from vehicle analysis in the case of geometric deviations. These might be a door that doesn’t close with a satisfying sound, tight spots in the cockpit where two parts come into contact with one another or switches that are not mounted with the proper fit.
In such cases, the specialists from Geometric Vehicle Analysis remeasure the specific individual parts. If a component does not fit precisely – when its precise function is not guaranteed, regardless of whether the dimensions are in specification or outside the tight tolerances – they consult with Purchased Parts Quality Assurance, Production, Technical Development or the supplier. Audi’s fundamental motto applies here as well: A precise analysis provides the basis for a rapid improvement in quality.
Quality from outset – the body
AUDI AG
Thomas Heußer, Head of Paint Shop Quality Assurance
Homogenous, perfect sheet metal surfaces, tight radii, uniform curvatures, precise light-refracting edges: Audi also sets standards with the exterior finish. Many workstations work together to ensure the perfect appearance and thus to adequately implement the multiple award-winning, sporty and elegant design.
Manufacturing precision begins where the dies for working the sheet metal are made. The Audi Toolmaking Division is an industry benchmark, as multiple awards prove. The “tornado line” characterizes the side view of all Audi models. Its contour is first machined into the die as a negative. Once it is mounted in the press, the lines are optimized again by hand. This demand a great deal of care, skill and experience, because even the slightest irregularities can affect the individual parts made with the die. At 20 to 30 microns, the specified tolerances are correspondingly tight. A human hair is twice as thick.
Strict surface specifications apply to the cold-drawn sheet metal, and thus only electrolytically galvanized sheets are used in addition to aluminum components. The zinc layer applied by means of electrolysis, i.e. by applying an electric voltage in a zinc solution, is substantially more even than that obtained with conventional hot-dip galvanization. These sheets thus combine optimal corrosion protection with a perfect surface.
The striking Audi design poses great manufacturing challenges. Sharp edges and radii, wide, expansive surfaces and tight component transitions require the utmost in precision through the entire manufacturing process, from the press shop to the body shop. Inline measurement systems constantly monitor the joining processes, adjusting them in response to the slightest deviations. But a trained eye and steady hand are still essential for process control. Despite state-of-the-art technology, the most critical testing instrument for surfaces remains the human eye and sensitive hand of the tester. Some irregularities in the surface can often only be detected by a very experienced hand.
Elaborate fixtures are used to join parts in the body shop to ensure, for example, a precise gap with a tolerance of less than 0.1 millimeters between the roof and the side of the car. The brazing of the roof seam is performed by a robot under constant process control; in some cases a camera system is also used. After brazing, the seam is rounded into shape by a second robot operation, giving it a smooth and defined fillet. Thanks to the quality of the surface, this joint does not require an overlay – a highly elegant solution. This is typical of the Audi philosophy, which in all processes takes full advantage of the most modern methods available and to continuously invent new solutions.
To ensure that the top finish lasts for the life of the car, Audi takes additional elaborate measures to prevent corrosion. One of these is to seal the cavities with hot wax. Because the load-bearing sheet metal parts must satisfy increasingly stringent strength requirements, they have highly complex, convoluted shapes. In the door sill of an Audi A4, for example, there are four folded layers of sheet metal similar to the principle of an onion. Often there is also a material mixture of high-strength steels, stainless steel and galvanized sheet. This offers strength and weight advantages, but also requires particular attention to corrosion protection.
Audi therefore coats all cavities at risk of corrosion in hot wax in addition to the dip primer. Audi was the first to use this process, which has been continuously refined. The wax is liquefied in an immersion bath at approximately 120 degrees Celsius. Those areas of the body to be coated are heated to between 60 and 70 degrees Celsius in a continuous oven. The cavities are then filled with the hot wax in fixtures called flooding frames. This low-viscosity wax reaches even the smallest of cavities and prevents the later intrusion of moisture. Upon conclusion of the process, a large portion of the wax runs back out of the hot sheet metal structures, but a small portion remains behind as a thin but reliable protective film.
Sensational and brilliant – the paint finish
AUDI AG
Thomas Heußer, Head of Paint Shop Quality Assurance
Is the finish brilliant with a deep luster? Is it evenly applied and resistant to stone chipping and environmental influences? Do the colors shine the way the designer had in mind? Every Audi owes its shining appearance to the paint finish, for which a team from Quality Assurance is largely responsible.
An Audi wears a coat of paint roughly a tenth of a millimeter thick. That doesn’t sound like much, but these 100 micrometers are packed with pure high-tech. First a cathodic primer to protect against corrosion is applied in an immersion bath and dried at 200 degrees Celsius in a continuous oven. This is followed by application of the filler, which ensures elasticity and protects against damage.
These and the following coats are applied automatically using high-speed rotary atomizers. An electrostatic field ensures that swirling of the paint droplets in the spray booth is minimized, and the paint is precisely applied to the body as if by an invisible hand. Dried, cleaned and dust-free, the bodies continue on their way.
The basecoat, which gives the bodies their shade, is the third and, at roughly 10 thousandths of a millimeter, the thinnest coat in the paint system. The effect finishes – metallic or pearl effect – have tiny particles called effect agents in the color pigments. These are responsible not only for the sparkle but also for what is known as shade flop. The shade changes depending on the viewing angle and the angle at which the light is falling – an effect that in the interplay of light and shadow effectively underscores the lines of the exterior design. The final step is the application of a two-component clearcoat, which imparts gloss to the paint system and protects the body.
The work of the Audi specialists is characterized by the unwavering pursuit of the ideal finish. Styling and visual quality together with technological characteristics are top priorities.
And indeed, in these areas too, Audi stands out clearly from its competitors. For example, the brand is at the forefront of the industry in the development and use of colorimetry. The color – or more accurately the light reflected by a colored object – is broken down into its spectra by a special instrument. The colorimetric values can then be calculated from the measured spectral intensities. This method enables an objective control of the painting process as well as the transfer and comparison of color values of add-on parts painted by external suppliers, for example.
Audi’s specifications for painted surfaces are not restricted to the visible exterior areas of the body. Unlike most of its competitors, Audi also devotes a great deal of attention to visible areas of the interior. Whereas competitors often only paint the entry sills and interior surfaces of the doors or the trunk with the just the basic shades without clearcoat, Audi always uses the body color here.
In many areas the stringent requirements for the exterior also apply. Innovative mixing systems are often used to ensure optimal matching with the shade of the body.
To ensure that all add-on parts in the body color perfectly match the body, some of these parts – such as fuel tank covers, door handles and exterior mirror housings – are painted directly at the Ingolstadt plant. The paint system and the painting process are identical to those used to paint the body.
Flexibility and customization are an additional Audi strength. Even outlandish custom colors that the customer orders through the Audi exclusive customization program can be applied on the regular line.
To ensure that the perfect finish does not suffer en route to the customer and arrives at the dealership in showroom quality, no Audi leaves the factory without protection. Transport protection for the surface is standard, even for short shipments by truck within Germany. For certain overseas markets – or at the request of the dealership – the factory will also install a full-body cover, which is a shroud that protects the entire vehicle.
Harmony through precision – color coordination in the interior
AUDI AG
Anette Ludwig, Interior Materials Engineering / Trim
The visual impression of harmony and quality conveyed by the interior of every Audi is due in no small part to the colors. All shades defined in the design must be precisely matched and coordinated in practice. This sounds simple, but it is actually a complex task that falls under the responsibility of Quality Assurance.
One challenge is posed by the different materials, which in many areas are directly adjacent to one another. In the Audi A4, for example, three different materials come together at the front end of the door map pocket on both the driver and the passenger sides: a support element with a film coating, the polypropylene back wall of the pocket and the thermoplastic speaker grille.
All of these materials must be identically colored in the selected shade, but each requires different pigments due to their respective chemistries. Another challenge is posed by the different surface structures. When smooth plastic and grained leather meet, such as in the area of the door armrest, differences in reflectivity can result in color differences.
Audi Quality Assurance uses advanced technology to solve these problems. The analysis is performed in an in-house light studio with a critical eye and a spectral photometer, which analyzes and evaluates the colors. The measurements are performed in a fully-assembled interior and thus from the customer’s exact viewing angle.
If the coloration processes for the individual parts are not precisely matched, a phenomenon known as metamerism can occur. The components look the same in bright daylight, for example, but appear different under a different type of light. The lighting system in the light studio is therefore capable of producing three different moods – daylight, dusk and cold artificial light.
Fascination – the total car experience, customer-relevant testing and running costs/cost efficiency
An Audi is more than the sum of its parts – it is a total car experience characterized by elegant sportiness, by high quality and attention to detail, and by precision and emotion. The harmonic interplay of all components is a theme to which Audi devotes special attention.
A team at Quality Assurance is responsible for the “comfort audit.” The aim here is to translate the subjective perception of comfort into data, such as by measuring the amount of force needed to close a door and analyzing the sound made by the closing door. The glove box, the adjustable center arm rest or control elements such as the controls for adjusting the seats are areas where Audi puts in a tremendous amount of finishing work.
Another portion of the team is dedicated to the prevention of intrusive noises such as rattles or squeaks – from the first dataset on the CAD computer to road tests with pre-production cars at the Arctic Circle or in the Sahara to being driven by the customer. An extensive testing program totaling roughly two million kilometers assures the quality and proper function of the new models in every regard.
Customer satisfaction is the focus of everything that Audi does. Due in no small part to the fact that this depends on affordable running costs, the specialists from Service Technology begin working on intelligent and innovative solutions very early in the development process. These ensure that Audi cars receive favorable insurance classifications and that service and repair costs remain low.
Total Vehicle Quality Assurance – Shakedown testing: millions of kilometers for maximum customer satisfaction
AUDI AG
Burkhard Knodel, Head of Quality Assurance for Pilot Series / Acoustics
At Audi, Total Vehicle Quality Assurance has a strong position as a core strategic matter. This is clearly illustrated by the fact that Quality Assurance, in coordination with the Board of Management, issues a total vehicle release at the end of each development project. Quality Assurance thus has the ultimate responsibility for the final release for series production.
This release follows shakedown testing, a comprehensive series of road tests by Quality Assurance. All aspects of the new vehicles that could result in customer complaints under certain stressful conditions are examined here. Total Vehicle Quality Assurance begins with pilot production and zero-series vehicles roughly six months prior to the start of production as soon as all the parts of a new model are available from production dies. If complaints arise during this strenuous test phase, there is still sufficient time to define measures in collaboration with the colleagues from Technical Development and Production that can be implemented prior to the start of production of vehicles for customers. The specialist departments at Technical Development also perform their own long-term tests and road tests involving their individual assemblies.
During shakedown testing, Quality Assurance employees drive the cars in everyday situations on public roads under the same conditions that will later be encountered when driven by the customer. In addition to checking the practicality of the design and proper manufacturing, they also assess the quality level of the components, for this is the first time that the parts in the car were produced on the dies that will later be used to manufacture the production parts. The cars log roughly 150,000 kilometers on public roads to ensure that each car delivered to the customer continues to deliver the same satisfying levels of quality, precision and reliability over the entire service life of the car.
Shakedown testing is not restricted to the immediate vicinity of the Audi plants, rather it is conducted worldwide on a number of continents.
