Syntax Error (4742): Illegal character 3f in hex stringSyntax Error (4743): Illegal character 78 in hex stringSyntax Error (4744): Illegal character 70 in hex stringSyntax Error (4747): Illegal character 6b in hex stringSyntax Error (4749): Illegal character 74 in hex stringSyntax Error (4752): Illegal character 6e in hex stringSyntax Error (4754): Illegal character 3d in hex stringSyntax Error (4755): Illegal character 22 in hex stringSyntax Error (4756): Illegal character 77 in hex stringSyntax Error (4757): Illegal character 22 in hex stringSyntax Error (4758): Illegal character 3f in hex stringSyntax Error: Couldn't read xref tableSyntax Warning: PDF file is damaged - attempting to reconstruct xref table...Service TrainingSelf-study Programme 421Body BasicsS421_002What springs to mind when you think about a vehicle? Normally the drive, the engine, the performance and the image come first. But what would a car be without its body? It is the central component of a vehicle that connects all other vehicle components and, at the same time, manages to accommodate the passengers. It meets high technical requirements as well as the comfort expectations of passengers. Furthermore the body in particular bears the characteristic face of a vehicle and thus also of the car brand.A modern body needs to retain a good condition, if possible, for the whole “life” of the car so that no unnecessary costs arise. This prevents a fast moral decline of a vehicle model and the brand will be held in high esteem. It is also important that damage to a body that occurs in any future accidents can be repaired and this highquality vehicle component can thus retain its properties and appearance. This self-study programme will explain the basic associations of material science, steel production and the treatment processes leading up to painting. It will lay the foundations for better understanding of the procedures should body repairs be necessary.The self-study programme portrays the design and function of new developments. The contents will not be updated.For current testing, adjustment and repair instructions, refer to the relevant service literature.Important Note2ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Historical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Basics - Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Basics - General information on materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Basics - Steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Basics - Treatment of steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Basics - Aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Steels for Body Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of steels for body construction . . . . . . . . . . . . . . . . . . . . . . . . . . Increasing the strength of steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Body structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basics - Process Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manufacture of semi-finished products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tailored blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Joining processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coating processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corrosion Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre-treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seam sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stone chip protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protection against galvanic corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Painting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 30 31 38 40 40 46 48 56 60 60 61 62 63 65Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Repair methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 The glossary provides explanations of the CAPITALISED terms3IntroductionHistorical backgroundIntroductionCar bodies yesterday and today - how have requirements and tasks of car bodies changed over the course of technical progress? To begin with, let us define the term “body”, which refers to the complete coachwork of a motor vehicle. Historically, the first superstructure on a vehicle with wheels could be considered as the start of body development. We should then also include the first open and later closed motor carriages. We will describe bodies in the context of motor vehicles throughout this self-study programme.Non-load-bearing bodyThe first bodies were not load-bearing, i.e. they were built on a frame or a chassis. Both ladder frames and tubular frames were used. Ladder frames are still used for lorries and off-road vehicles today. Bodies were not necessarily linked to one vehicle manufacturer. There were chassis manufacturers and coachbuilders. This allowed bodies to be adapted to and built onto different drivable chassis as required. Later on bodies were produced using a platform frame. The body structure was placed on a platform frame that had been specially designed for it and was then attached. Only then was it fitted onto the drivable chassis.… from the start of motor vehicle production to this day …Motor carriage Wood/steelSeparate body on drivable chassis, e.g. Ford Model T4Monocoque bodiesEngineers looked for solutions to make bodies without a separate, heavy frame as it became necessary to reduce weight in car construction. The resulting body featured a structure that could support itself. This development was also aided by technical progress in sheet metal processing. In this design, the load-bearing body structures are joined together securely and permanently using different joining techniques, for example, welding, soldering and bonding. This method of construction is the general standard in car manufacturing today.Use of materialsThe first bodies were made of wood, to which an outer coating of lacquer, fabric or plastic was added to improve the appearance and to also protect it from the elements. Modern bodies are increasingly not just optimised in terms of structure and cross-sections. Special tailor-made materials are being used more and more for specific body areas. The materials are distinguished by their respective composition and their treatment. These different materials are used to continually improve the ability of specific sections of the body to bear mechanical stress and resist corrosion. Above all, steel is used as a material. Aluminium and plastics are also being used more to create lightweight constructions.S421_081 Body with platform frame Current monocoque body5IntroductionBodiesBodies are frequently only perceived and understood as a design. People normally only consider the technical issues and comfort as an afterthought. In a nutshell, the body is first and foremost the part of a vehicle that allows passengers to be transported - it is the actual “transport case” for the people being carried.Requirements for bodiesAs a result of technical progress, today’s bodies have an increasingly complex range of tasks to perform:●Structure of a bodyThe body can be split into two main areas:●Transport space for passengers Fulfilment of human needs, for example, comfort, noise insulation etc. Accommodation of all technical components for drive and power transmission Accommodation of all technical components for convenience systems Accommodation of heating, ventilation and airconditioning systems Accommodation of all safety systems Design of the body for optimum protection against possible interior and exterior damage, e.g. in accidents Image aspects●the inner body structure and the outer panels of the body structure●Due to safety requirements, the inner part of the body structure, also called the passenger cell, needs to be particularly resistant to deformation. The front and rear ends of the body should allow optimum absorption and reduction of impact energy (crumple zones to meet safety requirements in a crash). This also applies increasingly for the side sections and the roofs of modern vehicles.●●●Repairs to a bodyRepairs to the inner body structure are very complex due to its sturdy configuration. Parts fastened to the body structure with bolts (body outer skin) are replaced if badly damaged.●●●6The structure of a body will be shown using the bodies of the current Golf and Passat as examples. The body shows the internal body structure together with parts of the outer panels.Body of Golf model year 2009Body structure, outer panels transparentS421_082With outer panelsS421_005Body of Passat model year 2006Body structure, outer panels transparentS421_083With outer panelsS421_0067Basics - MaterialsBasics - General information on materialsOn modern bodies, specially configured materials are increasingly being used for specific body parts. In order to explain the reasons for the respective materials used, we will look at some principles of material science.Crystalline structuresAll substances are made from different types of ATOMS (iron, sodium, gold, nitrogen, oxygen etc.) regardless of their state of matter (gas, liquid or solid). The ATOMS behave like solid balls, whose size varies depending on their nature. The following descriptions cover the relationships with the crystalline structures using metals as an example. When the metals are still in liquid state during melting, the ATOMS move randomly without staying in a set position. When the materials become solid upon cooling, the ATOMS stop moving and arrange themselves in a set three-dimensional form, i.e. “crystalline structure”. The crystalline structure can be reduced to the respective smallest basic unit. In its simplest form, the basic unit can be, for example, simple cubic. Depending on the type of material, body-centred cubic and face-centred cubic or even hexagonal crystalline forms, for example, are possible in addition to the simple cubic forms. The crystalline structure type determines characteristic material properties like density, HARDNESS or melting point.Crystalline structureBasic unit (simple cubic)S421_092The crystal lattice shown is a random section of a crystalline structure. The ATOMS highlighted in yellow in the illustration show an example of a basic unit of the crystalline structure - in this case a simple cubic crystal. The possible crystalline forms are explained in more detail on the next page.8Metals mostly crystallise in three crystalline forms:●Body-centred cubic crystal The METAL IONS arrange themselves so that the connecting lines between the ions form a cube. Another metal ion is located in the centre of the cube. This crystallisation type is found in chrome, molybdenum, vanadium and tungsten as well as in iron below approx. 900°C.Body-centred cubicMETAL IONSS421_099METAL IONS = electrically charged atoms●Face-centred cubic crystal The basic form of the crystal is also a cube. In addition to the eight METAL IONS at the corners, there is one ion in the centre of the six side surfaces. This crystallisation type is found, for example, in lead, aluminium, copper and nickel as well as in iron above approx. 900°C.Face-centred cubicMETAL IONSS421_100●Hexagonal crystal The basic form of this crystal is a prism with hexagonal top and bottom surfaces. There is also a METAL ION in the centre of the top and bottom surfaces. In addition, three further METAL IONS are arranged inside the crystal. This crystallisation type is found, for example, in magnesium, titanium and zinc.HexagonalMETAL IONSS421_1019Basics - MaterialsMetal structureIn liquid molten metal, METAL IONS and free ELECTRONS move randomly among each other. There is no specific arrangement. An arrangement only forms once solidification begins. Formation of crystallisation seeds begins at the points where the solidification temperature is reached first.Liquid molten metalStart of solidificationMETAL IONSContinuing solidificationCrystallisation seeds Complete solidificationGrowing crystalsGrainsGrain boundaries S421_089As solidification continues, METAL IONS are deposited on these seeds and crystal lattices form. The crystal lattices continue to grow until they meet other neighbouring crystal lattices that are also growing. They cannot grow any further.The crystals formed after complete solidification are irregular in their exterior form - they are also called crystallite or grains - they form the structure of a metal.Iron is not used in its pure form for technical applications. Instead it is used in a wide range of ALLOYS. Iron and alloy components are melted together. The alloy additions dissolve in the iron base metal during this process. Different structure types are formed depending on the mixing ratio of iron and alloy components.10Structure typesSolid solution alloy When ATOMS from the base metal are replaced by an ion from the alloy metal in a crystal, this is known as a substitutional SOLID SOLUTION.Structure with substitutional solid solution crystalsGrainGrain boundaryIf the ions of the alloy metal arrange themselves between the METAL IONS, this is known as an interstitial SOLID SOLUTION .Structure with interstitial solid solution crystalsGrainGrain boundary S421_090Multi-phase alloyStructure with multiple phasesIf alloy components do not mix upon solidification of the melt and each component forms its own crystals, this is known as a multi-phase alloy.Base metalAlloy metalPlain steel has one special feature. The alloy component in this case is carbon. It is chemically bonded in the steel as iron carbide (cementite) and forms thin layers between the grains of the iron crystals (ferrite) - these grains are called pearlite.Structure of plain steelCementiteFerrite grainPearlite grainFerrite S421_09111Basics - MaterialsMechanical propertiesThe mechanical properties of materials are established in laboratory tests. Tensile testing for determining the strength of materials is the most common. In tensile testing, samples of the test material are subjected to a rising pulling force at room temperature. All samples must have a standard size and shape so that the results for different materials can be compared. During the test, the load required to deform the sample until it breaks and the extent of deformation is determined. A stress-strain curve (load in relation to the original cross-section of the sample) can then be drawn up from the results. Depending on the type of material, an extended yield point (yield-point runout) or a continuous transition from the elastic region to the plastic region (with 0.2% offset yield point) can occur on the curve.The following two characteristic curves are examples - they can differ from each other considerably depending on the material or its variation.Stress-strain curve - with extended yield point Stress (MPa) Stress (MPa) Stress-strain curve - with 0.2% offset yield point -Rm ReHZRp 0,2ReL XStrain in % Elastic region Plastic region S421_008Strain in % S421_093The normal unit from the international measuring system, i.e. pascal (Pa), is used. Due to the very high values, megapascals (MPa) are mainly used: 1MPa = 1,000,000Pa. The measuring unit newton (N) per square millimetre is still also used, however: 1MPa = 1N/mm2.12Analysis of the stress-strain curveA detailed analysis of the stress-strain curve provides a range of information among which the following should be highlighted:Yield point ReH and ReLAt the start of load application, the strain on the sample is elastic, i.e. the sample rod returns to its original length once the load is removed. This elastic behaviour continues until the yield point ReH is reached. Therefore this point can also be called the elastic limit. (This is an example and a simplified approach for this self-study programme. In practice, there are, of course, numerous variants of the curve where, for example, the elastic limit can be just in front of the yield point. These cases will, however, not be examined further in this self-study programme). The elastic limit separates the elastic region from the plastic region. The sample starts to deform plastically once the yield point ReH (elastic limit) has been passed. Depending on the type of material, the yield point can also cover a region (the yield-point runout “X”) with an upper yield point ReH and a lower yield point ReL (see figure S421_008). If there is no extended yield point, the 0.2% offset yield point is set as a substitute yield point. This is the point where the 0.2% remaining strain is found. A line is drawn parallel to the linear rise at a distance of 0.2% strain for this purpose. The point where this line crosses the curve is the offset yield point Rp 0.2 (see figure S421_093).Ultimate strength or tensile strength RmThe stress reaches maximum here. The stress Rm is the highest load that a cross-section can withstand. From this point on, the sample starts to neck, i.e. the cross-section area becomes smaller. Since the stress is calculated as a force in relation to the cross-section area, the force required for further deformation decreases after point Rm.Fracture point (Z):The sample fails at this point. This value has no significance for technical practice.13Basics - MaterialsBasics - SteelSteel is one of the most common materials in vehicle body construction. Steel is an ALLOY of iron and carbon with a maximum carbon proportion of 2.06%. Greater proportions result in castings. Further elements like nickel, manganese, phosphor, silicon, chrome etc. can be alloyed to produce the different steel families. There are a large number of steel types, each of which has a different composition and thus different properties.Production of steelIron ore extraction Furnace SteelworksFoundry ladle Distributing troughOre charging Furnace Ingot mould Billet dischargeSlabS421_070The iron ore found in the ground is smelted in a furnace to form iron (pig iron). Depending on the composition of the iron ore used, the smelted pig iron has its own specific composition. The resulting pig iron is then processed at the steelworks to adjust its chemical composition to previously specified and required values. This can be achieved by removing and adding certain elements. The process is also called alloying.Different types of steel can be produced by varying the carbon content and other alloying elements. Setting the carbon content up to around 2.06% in particular makes a steel from the iron. The specific properties of the steel can be specially configured depending on the later use of the material.14At the steelworks, the melt is conveyed to the continuous casting plant and processed into a billet. This billet material then forms the basic product for all further processes, for example, rolling, thermal treatment and surface coating, to produce a wide range of SEMI-FINISHED PRODUCTS.The steel properties are determined by the following main variables:● ●the chemical composition of the steel the later treatment of the steel productsChemical compositionEach type of steel has its own crystalline structure in solid state. This structure gives it mechanical properties that can be determined using a metallographic analysis. One very important aspect of steel production is the speed at which the raw materials are heated and cooled in both the manufacturing process and subsequent procedures. If you examine iron in its pure state, you can determine how its crystalline structure and its magnetic properties and its solubility vary as the temperature rises or falls. To give a better understanding of the properties of a type of steel, first the properties of pure iron, then the properties of different iron-carbon ALLOYS and finally the properties of ALLOYS made from iron, carbon and other components will be explained.Pure ironTo provide a basis for all further observations of the steel types, the temperatures at which pure iron changes its crystalline structure, i.e. the arrangement of its ATOMS need to be known. This new arrangement requires a certain amount of time during which the temperature remains constant. The temperatures where the structure changes are called “critical points” (see diagram “Transformation points of pure iron” on the next page). These “critical points” are shown on the diagram as horizontal lines resembling steps.15Basics - MaterialsTransformation points of pure irone Liquid irond Temperature (°C)Delta ironcGamma ironbBeta ironaAlpha iron or ferrite Cooling curveTime (min.) S421_009Heating curveHeatingAt temperatures between 0 and 790°C, iron is called “alpha iron” or “ferrite” and has a body-centred cubic crystalline structure consisting of nine iron atoms. Alpha iron is very magnetic and does not dissolve carbon. If the iron is heated further to 790 to 910°C, it is called “beta iron”. It still has a body-centred cubic crystalline structure that also does not dissolve carbon, but it loses part of its magnetism. Between 910 and 1,400°C, it is called “gamma iron”. The cubic structure becomes face-centred at this stage. Gamma iron is not magnetic and dissolves carbon. Between 1,400 and 1,535°C, it is called “delta iron”. The crystalline structure is body-centred cubic. Since it only occurs at very high temperatures, it is only of little importance in the investigation of thermal treatment types. At temperatures above 1,535°C, pure iron is liquid. In comparison with heating, the opposite process occurs during cooling (with minor deviations in the “critical points”).At the “critical transformation points”, the absorbed heat is used to change the crystalline structure. Therefore there is no rise in temperature. This means that the iron atoms group themselves in different crystalline structures with different magnetic properties and different carbon solubility depending on the temperature.16Transformation points of iron-carbon alloysSteel crystallises in different microstructures depending on the temperature and carbon proportion. Steel is an iron-carbon alloy with a maximum carbon proportion of 2.06%.Iron-carbon diagram Temperature in °CMelt Austenite + melt Austenite Austenite + cementiteThe illustration shows only the area of the iron-carbon diagram that is relevant to steels. The complete version of the diagram reaches to over 6% carbon.Ferrite + austenite Ferrite Pearlite + ferrite Pearlite + cementiteS421_010 Carbon in %Interpretation of “iron-carbon diagram”The lines on the diagram show the “critical points”, at which the steel changes its crystalline structure. Depending on the carbon proportion, the temperature at which the structural change occurs varies. The areas bordering on the “critical points” show the crystalline structure that the steel adopts in each case. At high temperatures, the steel is molten and all of its components are dissolved - like salt in water. As the steel cools, parts of the iron and the carbon solidify. The so-called “austenite crystals” form (the solidification temperature varies depending on the carbon proportion). If the temperature decreases further, the ALLOY solidifies completely to become austenite. Under approximately 723°C, austenite can form two different structures depending on the carbon proportion in the ALLOY:●● ●If the carbon proportion is below 0.8%, austenite becomes pearlite and ferrite, which are distributed within the steel in crystal form. If the carbon proportion is 0.8%, the steel will only contain combined pearlite crystals. If the carbon proportion is greater than 0.8%, austenite becomes pearlite and cementite.17Basics - MaterialsStructure typesThe table below explains the most important structural and mechanical properties of the compositions listed in the iron-carbon diagram (only the area of the diagram relevant to steel). (The listed compositions also occur above this area i.e. with 2.06% carbon.)Type of microstructure FerriteExplanationFerrite consists of alpha-iron crystals, which form a body-centred cubic crystal lattice. Carbon is deposited between the iron atoms (interstitial SOLID SOLUTION). Ferrite is the softest component of steel. In terms of mechanical properties, ferrite is characterised by an ultimate strength of 28MPa and a strain of 35 to 40%.CarbonPure carbon atoms can be connected to each other in two ways. Graphite or diamond results depending on the type of bonding. Of course, for steels, only carbon in the form of graphite is important. Its bonds are weak and therefore easily broken. Carbon is either incorporated atomically in the lattice (interstitial SOLID SOLUTION) or in the form of bonds - see, for example, cementite.CementiteCementite is a chemical compound of iron and carbon. In chemistry, it is known as iron carbide (Fe3C). Cementite contains 6.67% carbon and 93.33% iron. Cementite can be deposited in the structure in a different form, in separate formations (e.g. rods or needles) or in groups on the grain boundaries of the crystalline structure. Cementite is the hardest, but also most brittle component of steel with an ultimate strength of 215MPa.AusteniteAustenite consists of gamma-iron crystals, which form a face-centred cubic crystal lattice. It contains carbon, which is deposited between the iron atoms like with ferrite (interstitial SOLID SOLUTION). Due to the larger interstices in the face-centred cubic crystal lattice, more carbon can be incorporated compared with ferrite. The carbon proportion varies between 0 and 2.06%. Austenite has an ultimate strength of 88 to 105MPa and a strain of 20 to 23%. It is characterised by a high wear resistance and low HARDNESS and is the substance that occurs most frequently in steels.18Type of microstructure PearliteExplanationPearlite is a mixture of cementite and ferrite layers that results from austenite transformation. The thickness of the layers depends on the cooling speed. The slower the cooling, the thicker the layers. Pearlite has an ultimate strength of 55–70MPa and a strain of 20–28%. The mechanical parameters of pearlite are between those of ferrite and cementite; it is harder and more resistant than ferrite, but softer and easier to shape than cementite.MartensiteMartensite is produced by cooling austenite very quickly. During this process, the face-centred cubic lattice of the austenite is transformed into a body-centred cubic lattice. More carbon is dissolved in the face-centred cubic lattice due to there being more space available than in the body-centred cubic lattice. As a result, the carbon cannot find enough space during the structural transformation, distorts the crystal lattice and expands it. Plate-like crystals are formed, which look like needles in the microsection - so-called martensite needles. The compression stress caused by the greater volume of the martensite results in the greater HARDNESS, but also the brittleness of the martensite. As the cooling speed increases, less and less pearlite is formed so that an almost complete transformation into martensite occurs. After cementite, martensite is one of the hardest components of steel. The ultimate strength of martensite is between 170 and 250MPa and the strain is between 0.5 and 2.5%.BainiteLike pearlite, bainite consists of the ferrite and cementite phases, but differs from pearlite in form, size and distribution. Bainite has a structure containing either bundles of ferrite laths with film-like carbide layers between them or ferrite plates with layers of carbide between them. Bainite is formed by accordingly controlled fast cooling of the austenite at temperatures and cooling speeds between those for pearlite and martensite. After cooling the austenite to temperatures above the martensite start temperature, the conversion into bainite occurs in the so-called bainite phase at a now constantly maintained temperature (isothermal). The cooling speed is controlled so that no pearlite is formed. The ultimate strength ranges between 15 and 220MPa and the strain is 1.5 – 2%.19Basics - MaterialsIn the following section, two examples of structural changes, which occur in the production of steel with a carbon proportion of 0.15 or 1.20%, are explained by way of illustration.Steel with 0.15% carbonLiquid phase AusteniteAusteniteAustenite FerritePearlite FerriteS421_032The starting temperature is over 1,500°C - the steel is liquid. If the temperature falls below 1,400°C, part of the iron and the carbon solidifies and a mixture of a liquid phase and austenite is created. When the temperature drops below 1,300°C, the steel with 0.15% carbon proportion is already completely solid and has become austenite. It remains like this until the temperature falls below 750°C. Between 750 and 723°C, a mixture of austenite and ferrite is formed. Below 723°C, the crystalline structure changes and a mixture of pearlite and ferrite is formed. If, during this phase, the cooling speed changes at any point, differing structure components, like, bainite, martensite etc., can form.20Steel with 1.20% carbonLiquid phase AusteniteAusteniteAustenite CementitePearlite CementiteS421_033This steel type is also liquid at 1,500°C. Between 1,300 and 1,200°C, a mixture of a liquid phase and austenite occurs. When the temperature drops below 1,200°C, the steel with 1.20% carbon is completely solid and has become austenite. Between 1,000 and 723°C, a mixture of austenite and cementite is formed. At temperatures below 723°C, the crystalline structure is transformed into a stable state and forms a mixture of pearlite and cementite.21Basics - MaterialsAlloying steel with further componentsThe carbon proportion is responsible for the STRENGTH of the steel. If selected further alloy elements, for example, silicon, phosphor, titanium, niobium or chrome are added, other specific properties can be created as required. The effects of these elements are even noticeable if they are added only in small quantities in relation to the other alloy components. The ALLOYING of an iron-crystalline structure can happen in the following different forms:●●●Substitution: ATOMS of other elements replace iron atoms in the crystal matrix. Gap: Iron atoms are removed from the crystal matrix and the corresponding space remains free. Interstitial: ATOMS from other elements like titanium occupy interstitial* positions between the iron atoms of the crystal matrix. They hinder possible sliding of the atom surfaces against each other and thus increase the strength, for example. Their quantity in the steel alloy is decisive for the later mechanical properties.*Interstitial - located in an intermediate position within a structureCrystalline structure/crystal matrixATOM of base materialSubstitutionGapInterstitialS421_01522The table shows you how the steel properties can be influenced with examples of some further important alloy elements.Alloying elementChanged properties of the steelChromeIncreases the passivity of the steel towards corrosive influences (it is the main alloying element for increasing the rust- and acid-resistance of steels)ManganeseRefines the grain; increases the STRENGTH; improves the temperability; increases HARDNESS, strain and wear resistance; improves weldability and malleabilityMolybdenumIncreases the STRENGTH and the tenacity; enhances the passivity of the steel towards corrosive influences; improves the temperability, reduces the tempering brittleness in CrNi and Mn steels; favours fine grain formation and improves the weldability.NickelIncreases the STRENGTH and tenacity; contributes to stabilisation of the austenitic lattice structure; improves the formability even at low temperaturesNiobiumNiobium behaves similar to titaniumPhosphorIncreases the STRENGTH; contributes to an equal balance between press-formability and mechanical STRENGTHSiliconIncreases the STRENGTH and the elastic limit; refines the grainNitrogenIncreases the STRENGTH of austenitic steels; improves the mechanical properties at higher temperaturesTitaniumIncreases the STRENGTH and tenacity; inhibits grain growth and thus contributes to a fine-crystal microstructure; suppresses the precipitation of chrome carbide in chrome alloy steels and thus grain boundary corrosion23Basics - MaterialsBasics - Treatment of steelThere are numerous types of treatment that can be grouped into three large families:Treatment typeTreatmentMechanical treatmentsCold forming Hot formingThermal treatmentsHardening Annealing Normalising TemperingThermochemical treatmentsCase hardening Carbonitriding NitratingMechanical treatmentThis includes processes in which permanent forming of the metal occurs using mechanical energy. These processes do not have an effect on the crystalline structure, but instead change the elasticity, tenacity, plasticity and HARDNESS.The most common mechanical processes are:ProcessProcedureCold formingThe steel is formed below its RECRYSTALLISATION temperature. The HARDNESS, the deformation resistance and the elasticity limit of the steel are increased.Hot formingThe steel is formed above its RECRYSTALLISATION temperature. In this treatment, plastic deformation and the RECRYSTALLISATION of the deformed grains occur simultaneously whereby the temperature has to be maintained long enough so that complete RECRYSTALLISATION occurs. This treatment allows the same forming as in cold forming, but with less force requirement resulting in softer, more malleable steels with a more standardised crystalline structure.24Thermal treatmentThermal treatment includes processes in which the properties of the metals are modified by changing their structure and the structural constitution. The resulting material with these new properties can perform the intended tasks better. The application possibilities and performance are much better here than would be the case in normal conditions. Thermal treatment includes the thermal treatment of steel. In general, thermal treatment is simply “heating and maintaining” a certain temperature in the steel for a more or less long period of time. It should then be cooled in a suitable way. This results in changes to the microscopic structure of the steels that are responsible for the required adjustment of HARDNESS and STRENGTH . This means that, in thermal treatment, only the thermal energy has an effect. This effect is on the crystalline structure, but not on the chemical composition.The four most important thermal treatment methods are described in the following section:ProcessProcedureHardeningThe steel is hardened by cooling it quickly to avoid renewed changes to the crystalline structure.AnnealingThe steel is annealed when it has been subjected to deformations through mechanical influences or other causes. The steel is cooled very slowly in this case.NormalisingThe steel is normalised to remove tension in the steel. The normal state of the steel concerned is produced. A medium cooling speed is required for this.TemperingThe steel is heated (tempered) again after hardening. The stability of the structure is improved in the process. Tempering partly reverses the hardening. However, these effects become greater as the temperature to which the material is heated rises.25Basics - MaterialsMicrostructuresThermal treatment methods allow variations in the structural composition of the steel to be achieved. This is, of course, also dependent on the composition of the steel (proportion of alloying elements). The respective variation is obtained using the proportions of certain structural components that have a basic influence on the STRENGTH/HARDNESS of a steel type. The steel can be adapted to the application requirements with this kind of treatment. This approach is used with the body. Depending on the requirements for the different body areas, steels with the necessary structural compositions and thus also the necessary strength parameters are used.The basic structural components with their respective strength areas are shown in the diagram.Elasticity limit Re of selected structural components Bainite: 15–220MPaPearlite: 55–70MPa Martensite: 170–250MPaAustenite: 88105MPaCementite: 215MPa Ferrite: 28MPaElasticity limit ReS421_02326Thermochemical treatmentThis includes processes in which chemical components are involved in the steel treatment in addition to thermal energy (heat, maintain temperature, cool). The microstructure and the chemical composition of the steel vary accordingly. The most important thermochemical treatment methods are:ProcessProcedureCase hardeningIn case hardening, the surface of a steel part is enriched with carbon (carburization) creating the conditions for later hardening. The part is heated and kept at a suitable temperature while simultaneously being in contact with materials that can release carbon. The enrichment with carbon can be achieved, for example, by means of gas carburizing, powder carburizing and carburizing in salt bath. During the subsequent cooling, the layers produced are hardened while the noncarburized material core remains unchanged. The process results in greater tenacity and impact strength.CarbonitridingCarbonitriding is actually an advanced variant of case hardening. In this process, the surface of steel parts is also enriched with nitrogen in addition to carbon. The enrichment is performed in a cyanide salt bath at corresponding temperatures. The material is then cooled in a controlled process. There is little warpage due to the low hardening temperatures and the milder quenchant. In this process, hard outer layers with a low thickness are created in a simple and fast way.NitratingNitration also forms hard layers on the surface of the steel part by forming nitrides. These layers reach a high level of HARDNESS that is even greater than the HARDNESS of the layers formed in case hardening (see above). This process is based on steel absorbing nitrogen in its microstructure. The process occurs at low temperatures which is why deformation is minimal. There is no quenching and no transformation of the structure.27Basics - MaterialsBasics - AluminiumWeight is playing an increasingly important role in vehicle design. This results in particular from constantly rising targets for economic and environmentally friendly vehicles. In addition to optimised solutions in body design, lower weight can be achieved by using lighter materials. Aluminium, for example, is being used more and more. Full aluminium bodies are not used for Volkswagen vehicles. Aluminium is used for individual selected components, for example:● ●Doors and lids on Phaeton Bonnet on TouaregProduction of aluminiumAluminium is extracted from bauxite in a digestion process using caustic soda (NaOH). This method is called the Bayer process. Bauxite:Bauxite●●Formed by the weathering of limestone and silicate stone in the appropriate climatic conditions The name comes from its place of discovery, Les Baux (southern France).Bayer processAluminium is readily found on Earth, but economic extraction has only been possible for around the past 100 years.Titanium oxideSilicon oxideNot until the end of the 19th century was it possible to produce aluminium on a large scale using electrolysis with the dynamo invented by Werner von Siemens.Iron oxideIt is difficult to extract the aluminium from the ore as it is in a very stable oxide bond with oxygen. It cannot therefore be extracted from the ore by smelting with the aid of carbon as in iron production.Aluminium oxideElectrolysisMolten aluminiumPrimary aluminium pigS421_04428On an industrial level, the extraction of aluminium by electrolysis is performed in large iron vats of molten aluminium oxide that are lined with a coating of carbon. The vat serves as the cathode. Carbon blocks submerged in the aluminium oxide are used as anodes.The aluminium is deposited on the floor of the vat since the distance to the floor is shorter than to the side walls. This causes a layer of liquid aluminium to form under the molten aluminium oxide. The aluminium is tapped off every 2–4 days and can be cast in bars.Molten aluminium oxideCarbon block anodesS421_045 Aluminium Cathode Carbon coatingAlloying aluminiumAluminium alloys are used instead of pure aluminium to guarantee optimum material properties for the respective body components. Aluminium is low STRENGTH in its pure state. The properties of aluminium can be changed by adding other elements, i.e. by ALLOYING . This concerns primarily the STRENGTH and the corrosion resistance. The most frequent alloy components are magnesium and silicon. These ALLOYS then form the basis for extruded profiles, cast nodes and aluminium sheet. The STRENGTH of aluminium alloys can be increased by forging and curing. One decisive requirement for the usability of aluminium in technical applications is its curing capability. In curing, precipitation of brittle structure components within the alloy structure can be achieved with specific temperature control. This builds up inner resistance to deformation and results in an increase in STRENGTH.29Steels for Body ConstructionClassification of steels for body constructionDue to the large number of possible steel types, it is useful to classify them according to specific features. This allows steels to be classified according to their mechanical values, for example, ultimate strength and yield point. One example is the differentiation of conventional, high-strength, higher-strength and ultra-high-strength steels.Classification according to strengthUltimate strength in MPaClassification according to steel familyManufacturing methodConventional steels High-strength steelsUp to approx. 300 300-480 350-730Deep-drawn steels Bake-hardening steel Micro-alloyed steel; Isotropic steels Phosphor-alloy steel Interstitial-free (IF) steel Dual-phase (DP) steel Transformation induced plasticity (TRIP) steel Complex-phase (CP) steel Martensite steelRolling Bake hardening Grain refining and precipitation hardening Solid solution hardening340-480Higher-strength steels500-600 600-800Hard phases Hard phasesUltra-high-strength steels Ultra-high-strength thermoformed steels800 1,000Hard phases Hard phasesIt is possible to classify steels according to their mechanical values, but this is imprecise. There is no fixed value for a boundary between the different steels. Normally quite a large bandwidth is involved. There can, for example, be cases where high-strength steels have identical or higher values than higher-strength steels. For this reason, steels are normally and more relevantly also grouped into families according to manufacturing method. Steels from these families will be looked at over the following pages as they are increasingly used in body construction. In particular, the mechanisms for increasing the STRENGTH compared with conventional deep-drawn steels are explained. A balanced ratio between increasing strength and plasticity is decisive here. Basically the STRENGTH of steels can be increased in four ways:● ● ● ●solid solution hardening grain refinement and precipitation hardening, bake hardening hardening using hard phases (hard phases = hard structure phases)30Increasing strength of steelIncreasing strength - with solid solution hardeningNormally, hardening initially calls to mind the thermal treatment of steel for achieving greater HARDNESS. Increasing the STRENGTH and also the HARDNESS can, however, be achieved by ALLOYING with other elements. This method is known as solid solution hardening. The hardening method allows the two steel types higher-strength IF steels (Interstitial Free steels = IF steels) and phosphor-alloy steels to be produced, for example.ATOM of Fe basic latticeFe ATOM replaced with substitution (e.g. phosphor)Alloying material deposited interstitially (IF) (e.g. carbon and nitrogen)S421_014●Higher-strength IF steels: These steels have a ferrite matrix without interstitially (interstitial = inside lattice) dissolved alloying proportions. As early as the steel melt, an accordingly lower proportion of carbon and nitrogen is set with specific treatment. Remaining ATOMS from these elements are bound by microalloying titanium and niobium. The steels have good malleability due to the lack of blockages by carbon and nitrogen (interstitial free). Phosphor and manganese are added to the steel to obtain the required STRENGTH. This is then known as higher-strength IF steel. The steels mostly have a minimum ultimate strength between 340 and 460 MPa or a minimum yield point (here the 0.2% offset yield point RP0.2) between 180 and 340 MPa.●Phosphor-alloy steels: These steels also have a ferrite matrix and contain hardening elements from solid solution hardening with phosphor (substitution), which can have a proportion of up to 0.12%. The steels are characterised by their compromise between “mechanical STRENGTH and press formability”, which is why they have a wide range of applications, for example, in structural or reinforcing parts (longitudinal members, crossmembers, pillars etc.), parts that need to be fatigue-resistant or parts that play an important role in crashes. These steels mostly have a minimum ultimate strength between 340 and 480 MPa or a minimum yield point between 220 and 360 MPa.The steels have a good balance between press formability and mechanical STRENGTH. If repairs are required, the steels weld well in any welding method.31Steels for Body ConstructionIncreasing strength - by means of grain refinement/ precipitation hardeningCrystal grainCrystalline structureMicrostructureATOMSS421_021The STRENGTH of a steel can also be increased by reducing the grain size (grain refinement) and with precipitation hardening. This principle of grain refinement is used, for example, for micro-alloyed steels. Vanadium, niobium and titanium are alloyed in small quantities. This micro-alloying creates a fine dispersion of carbide/nitride precipitation during hotrolling. The grain growth is limited by this and ferrite grains measuring 10 micrometres are formed. Carbide/nitride precipitates again over the course of the transformation, but also during the subsequent slow cooling. These are even finer - they cause precipitation hardening. This produces micro-alloyed fine grain steels with a high STRENGTH and simultaneous limitation of the alloy elements contained. Micro-alloyed steels mostly have a minimum ultimate strength between 350 and 730 MPa or a minimum yield point of 260 to 550 MPa.These steels are, above all, used for parts in the inner body structure that need to have a high fatigue strength, like reinforcing parts and mounts. Their mechanical properties allow lighter reinforcing parts and structural components to be produced. Isotropic steels are one variant of the micro-alloyed steels whose material parameters are not dependent on the rolling direction. The isotropic behaviour is achieved with a special alloying technique using manganese and silicon. The isotropic steels mostly have a minimum ultimate strength between 300 and 400MPa or a minimum yield point of 260 to 550MPa. Isotropic steels are particularly suitable for outer skin parts for which the isotropic behaviour is of great importance. Micro-alloyed fine grain steels can be welded with all methods.32Increasing strength - by means of bake hardeningBake hardening steels are easy to form in their original condition. They do not acquire their final higher strength until the formed component goes through the paint baking process. These steels meet the requirements for good formability and simultaneous component strength very well - this is a great advantage in the production of a body. Raising the elasticity limit Re to Re(BH) is achieved with thermal treatment at a low temperature like paint baking in the paint oven. This is also known as a “bake-hardening effect” (BH effect) - accordingly heating and drying in the oven at 180°C is compared with a baking process. This heating process is sufficient to change the molecular structure of the sheet so that the elasticity limit is increased.Elasticity limit (Re) after thermal treatmentStress (MPa)Original elasticity limit (Re)Increase achieved with BHS421_022 Strain (%)BH steels comprise a ferrite matrix, which contains the carbon required for the “bake-hardening effect” in the form of a solid solution. The improvement achieved through thermal treatment normally exceeds 40MPa. This means a steel with a fracture strength (Rp 0.2) of around 220MPa has a fracture strength of up to 260MPa following the “bake-hardening effect”. Bake-hardening steels mostly have a minimum ultimate strength between 300 and 480MPa or a minimum yield point of 180 to 360MPa. Advantages of “bake-hardening effect”:●●It improves the deformation resistance of all processed parts, even those with a slight deformation level (bonnets, roofs, doors, wings …). Thinner sheets can be used to provide the same mechanical properties. This reduces the weight of the body and, at the same time, increases the deformation resistance.BH steels are used for parts of the body panelling (doors, bonnets, tailgates, front wings and roofs) or for structurally important parts (pillar reinforcements or longitudinal members). Due to the higher elasticity limit, more force is required for reshaping. It welds well with any method thanks to the minor ALLOYING.33Steels for Body ConstructionIncreasing strength - with hard phasesIncreasing the STRENGTH of steels using hard phases leads to so-called “multi-phase steels” that achieve their STRENGTH through the coexistence of “hard” and “soft phases” - i.e. multiple phases - in their microstructure. These hard and soft phases are structural components in the steel, which are characterised by their respective different HARDNESS. When a steel is manufactured with hard phases, the starting steel is subjected to a specific process and is thus transformed into a steel with modified structural composition.Production of multi-phase steelsThe production of multi-phase steel makes use of the property of steel to form different microstructures depending on the forming and cooling conditions. These different structural components and, in particular, also intelligent combinations of them allow a very varied configuration of material properties adapted to customer requirements. Today, multi-phase steels are produced with ultimate strengths ranging from 500 to around 1,400MPa. Different methods can be used for production depending on the manufacturer. For example, the required microstructure can be obtained later on by heating the cold-rolled metal strips. Also the metal strips produced by hot-rolling can immediately be cooled accordingly and the required microstructure configured.The explanation of the multi-phase steels and their production - including simplified illustrations of the temperature and transformation processes - will use the treatment of hot-rolled metal strips (see page 36 – 37).34The category of multi-phase steels includes● ● ● ●DP steels (dual-phase steels) TRIP steels (TRansformation Induced Plasticity steels) CP steels (complex phase steels) MS steels (martensite steels)All of these steels are characterised by a high level of stiffness, high energy absorption and great deformation resistance. The most frequent applications are those in which a high level of energy absorption without deformation of the part is required, for example, in the reinforcement for the B-pillar or the inner reinforcements for the side members. It is generally difficult to reshape this kind of sheet which is why the part is normally just replaced. However, weldability is excellent with any method.TRIP steelsMS steelsDP steelsCP steelsS421_031Ultimate strength Rm 600–800MPa 500–600MPa 800MPa 1,000MPaAustenite FerriteBainiteMartensite35Steels for Body Construction“DP” (dual-phase) steelsDP steels have a high mechanical STRENGTH and good malleability. The ultimate strength Rm is between 500 and 600MPa. The STRENGTH is achieved by fast cooling of the hot metal strip - immediately after the rolling process – in the ferrite area. A cooling pause in the ferrite area allows the formation of sufficient ferrite. Then it is cooled more quickly to a low reeling temperature so that the remaining austenite is turned into martensite. The cooling speed and the steel composition are adjusted to each other so that no pearlite and as little bainite as possible are formed. A mixed structure results with approx. 80–90% ferrite and 10–20% insularly deposited martensite.Temperature Rolling mill Metal strip Ferrite Bainite MartensitePearliteReel* Time S421_028“Dual-phase steels” contain approximately 0.12% carbon, 0.5% silicon and 1.46% manganese. * Reel = reeling device for hot metal strip“TRIP” (TRansformation Induced Plasticity) steelsTRIP steels have a very good ratio of STRENGTH and plasticity; the ultimate strength Rm is between 600 and 800MPa. The STRENGTH is achieved by fast cooling of the hot metal strip - immediately after the rolling process. It is cooled in the ferrite area where ferrite is formed in a cooling pause. The austenite is enriched with carbon during this process. Then the bainite area is cooled and the hot metal strip is reeled up. The enrichment of the austenite with carbon continues. If the martensite starting temperature is below room temperature, the austenite that has not yet been transformed remains as so-called “residual austenite” in the structure. Undesired martensite forming in the bainite is prevented by suitable ALLOYING. The temperature of the reel is decisive for the process.Temperature Ferrite PearliteBainite Martensite Time S421_029“TRIP” steels have up to 20% residual austenite in their structure. This residual austenite is not transformed into martensite until the material is shaped later on and is hardened in the process. TRIP steels normally contain about 0.15–0.4% carbon, 1–2% silicon and 0.5–2% manganese.36“CP” (complex-phase) steelsCP steels mark the transition to the ultra-high-strength steels, which can have an ultimate strength value Rm of over 800MPa.TemperatureCP steels are characterised by high energy absorption and high deformation resistance. The STRENGTH is achieved by fast cooling of the hot metal strip - immediately after the rolling process. It is cooled quickly to a reeling temperature in the bainite range and then reeled. Only a small amount of ferrite and martensite is formed. Micro-alloying additives like niobium and titanium are used for grain refining. This gives the steel a very finegrained structure.Ferrite BainitePearliteMartensite Time S421_097CP steels have a low carbon proportion of less than 0.2%; furthermore they contain alloying elements like manganese, silicon, molybdenum and boron.“MS” (martensite) steelsMS steels are among the highest-strength steels. They are characterised by ultimate strength values Rm of around 1,000MPa to over 1,400MPa. The STRENGTH is achieved by cooling the hot metal strip at maximum speed - immediately after the rolling process. In the process, it is cooled to approximately 200°C and the strip is reeled. A predominantly martensitic microstructure is thus produced. Due to the high STRENGTHS over 1,400MPa, thermoforming is necessary for the later shaping of parts made from martensitic steels.Temperature Ferrite Bainite Martensite Time S421_098PearliteAs even small ferrite proportions need to be avoided due to the danger of material properties being dispersed, the transformation is controlled as required by alloying Mn, B and Cr. The STRENGTH is controlled via the carbon content.37Steels for Body ConstructionBody structureOverall, the body structure is the most important and central part of the body. Today, modern bodies need to meet extensive and very complex requirements. They are therefore optimised according to the following main points:● ● ● ● ●Taking the latest Golf as an example, we will show the different materials that are used in the body assembliesPassive safety Lightweight construction Stability and vibration resistance Pedestrian protection Corrosion protectionIn addition to the geometric/constructive design of the SEMI-FINISHED PRODUCTS and profiles, this optimisation is achieved by using tailor-made materials with different strengths for the respective body areas. Steel is used more than any other material. Aluminium and plastics are also used to create lightweight constructions. Sheets with higher STRENGTHS are increasingly being used – the greatest STRENGTH is provided by thermoformed ultra-high-strength sheets. What characterises these sheets? They are steel sheets that are formed in heated state, for example, at temperatures between 900 and 950°C. A defined cooling process produces a microstructure that provides greater STRENGTH and HARDNESS. There are also die-quenched sheets. These allow, for example, very slim and light body parts to be produced without losing strength.Ultra-high-strength sheets in the assemblies:● ● ● ●●Inner A-pillar Seat brackets Outer side member Front brackets on front longitudinal members Rear bumper cross member38S421_071Legend Steel sheet up to 140MPa High-strength steel sheet from 180 to 240MPa Higher-strength steel sheet from 260 to 320MPa Ultra-high-strength steel sheet from 340 to 700MPaThermoformed ultra-high-strength sheets in the assemblies:● ● ● ● ● ●Ultra-high-strength, thermoformed steel sheet over 1,000MPaFront bumper cross member Cross member in footwell area Inner side members Centre tunnel A-pillar/roof frame area B-pillarThe strength figures in MPa refer to Rm = ultimate strength. 1 MPa = 1 newton/mm239Basics - Process EngineeringManufacture of semi-finished productsConstantly greater and also more differentiated constructive requirements are being set for modern bodies. To meet these requirements, the materials/SEMI-FINISHED PRODUCTS are selected and used so they are precisely tailor-made for the load profile. The body calculations and later tests provide load curves within the body that can be predicted increasingly closer to practice thanks to today’s computing possibilities.Design and calculationLaboratory and practical testsThe calculations and tests are used as a basis for the configuration of the body structure:● ● ●●Defining the semi-finished product profile Selecting the semi-finished product material Selection of the respective body parts and their material that will be treated during production (e.g. hot forming in forming die) Selection of the body areas and the respective parts that have cross-section variations within the part (tailored blanks)40Forming processDifferent processes are used to produce SEMI-FINISHED PRODUCTS. Today’s thin steel sheets are ideal for meeting the requirements of lightweight construction while simultaneously providing high STRENGTH to meet safety requirements. However, they also need accordingly good malleability for shaping. This shows how complex the requirements are!The main forming methods are: Deep drawingHydroformingImpact extrusionRollingExtrusion41Basics - Process EngineeringDeep drawingIn deep drawing, the sheet metal is formed by using the simultaneous effect of pulling and pushing forces. The sheet metal is shaped in one or more operations. Materials with corresponding deformability are used deep-drawn sheet. One special type of deep-drawing is stamping. Embossed structures and shapes, for example, inscriptions, can be added to the surface - this is often performed simultaneously with the deep-drawing process, however.PunchThe cut sheet metal is placed on the drawing die …Blank Drawing dieS421_060Forming force… and clamped by the holder.HolderS421_061FlangeThe punch is then pushed downwards and draws the sheet metal over the drawing edge into the opening in the drawing die. The sheet metal is pressed so firmly onto the drawing die by the holder that creases cannot form in the flange area.Drawing edgeS421_062Upon completion of the drawing process, the punch releases the workpiece as it moves upwards.Pull-off edgeS421_06342HydroformingHydroforming uses pressure to shape metal. In this process, high pressure is used to press a sheet-metal profile against a hollow mould. This method also allows parts with different and complex geometries, e.g. with subsections, to be produced very quickly. Furthermore it allows weld seams to be avoided. The strain hardening that occurs during forming increases the component strength or stiffness.CounterholderMould halfTubeThe sheet-metal profile is placed in the lower half of a two-piece die.Mould halfSealing dieThe die is then sealed and filled with a liquid pressure medium.Pressure mediumThe liquid pressure medium is then pressurized to approx. 170MPa. The resulting forces press the inserted sheet-metal profile against the die and thus produce the required new form.SubsectionUpon completion of the forming process, the mould halves separate and the finished formed part can be removed.Finished T pieceS421_08043Basics - Process EngineeringImpact extrusionImpact extrusion uses pressure to shape metal. The materials used in this process need to have a high level of malleability.RemoverPunchStarting shape (slug)Slug Die Finished partS421_066In impact extrusion, materials are pressed into solid or hollow parts using a punch and a die. A slug is placed in the forming die as the starting material. When the punch pushes this material together under high pressure, it is forced on the other side into the die opening. Forming hardens the material. Furthermore a corresponding surface quality can be achieved with the die.44RollingRolling uses pressure to shape metal.RollerProfiles, sheets, tubes and wires are fed between rotating rollers and shaped in the process. The material is compressed by the rollers and thus hardened accordingly. Furthermore the desired surface qualities can be produced.S421_064ExtrusionPunch Die BilletExtrusion uses pressure to shape metal. In this process, heated materials are pressed through a die and extruded as a billet. Different profiles can be produced depending on the shape of die used.S421_065The material is compressed by the reshaping in the die and thus hardened accordingly.Block Die holderFurthermore the desired surface qualities can be produced.45Basics - Process EngineeringTailored blanksAs the term “tailored” indicates, tailored blanks are parts that are made to measure. “Blanks” are the starting material. Tailored blanks were originally developed to produce sheet metal plates with widths that could not be produced with the rolling technology of the time. Today, producers make use of the advantage that tailored blanks allow different steel grades and sheet thicknesses to be joined together in a finished part. Tailored blanks allow an increasingly better and more precise adjustment of the body structure to the loading of certain body sections. This allows parts with complex shapes and precisely fitting designs to be produced. The individual parts of the tailored blanks are joined together by welding. After welding the blank is then shaped, for example, by deep drawing.Example - floor pan - front with tailored blanksS421_039Front floorFront longitudinal member Increasing sheet thickness46Different welding methods are used to join the individual components of tailored blanks. One method that was frequently used in the past was mash seam welding. Today, this has, however, mostly been replaced by more modern laser welding. Therefore we will not look further into mash seam welding. The seam edges must be prepared well to obtain the necessary seam quality in laser welding.... joining with laser weldingLaser nozzle Welding rod feed Laser beamWelding rod S421_095Sheet metalIn addition to laser welding, high-frequency welding is also used for tailored blanks today. ... joining with high-frequency welding In this process, metal sheets are clamped at a defined gap “x” fr