Car Body Construction Research Articles

ANALYSIS OF INFLUENCE OF PROCESS PARAMETERS ON TEMPERATURE DISTRIBUTION IN PROFILES EXTRUDED FROM 6xxx-SERIES ALUMINUM ALLOYS

Changing market preferences regarding expectations in terms of the functionality, properties, and appearance of a finished product place excessive demands on manufacturers. The 6xxx-series alloys are the most commonly used in extrusion, and they have broad applications (e.g., the construction, electronics, automotive, and shipbuilding industries). The development of deformation technology at the design stage reaps unquestionable benefits when planning the production process. Under real conditions, the extrusion of hollow profiles requires the use of pocket dies, whose proper design is a complex process. This paper presents the results of preliminary numerical investigations of the extrusion process of structural panels from the 6005A aluminum alloy intended for the construction of transport car bodies. The influence of selected parameters of the extrusion process on the temperature distribution was analyzed in the material. The calculations were made using FEM for a three-dimensional deformation state, taking into account the thermal phenomena occurring during the applied deformation scheme in the extrusion process carried out in a flat die.

Scrutinising the electric vehicle material backpack

Conventionally the use phase of a road vehicle contributes to more than 70% of the total environmental impact in terms of energy use or emissions of greenhouse gases. This figure is no longer valid concerning electric vehicles and a shift to other life cycle stages and impacts is expected and should be re-evaluated. The goal of this study is to assess the environmental performance of two prototype vehicle drivetrains; an internal combustion engine and an electric motor, from a life cycle perspective. The assessment is performed in a qualitative manner using the Environmentally Responsible Product Assessment (ERPA) matrix. The two vehicles in this study have similar car body construction, providing an excellent opportunity to highlight the significance of material differences in their drivetrains. The internal combustion vehicle demonstrated a better environmental performance in three out of five lifecycle stages (pre-manufacture, product manufacture, and disposal). In all of these stages, the impact of the electric vehicle is determined by the burden of the materials needed for this technology such as rare earth elements (REE) and by the lack of recycling possibilities. The study demonstrated a need to close the material cycle when it comes to Critical Raw Materials (CRM) such as REE which can only be achieved when the technology but also the incentives for material recovery are provided, i.e. by promoting the development of cost-efficient recycling technologies. Moreover, the need for relevant metrics and assessment indicators is demonstrated to be able to compare the two technologies fairly.

Principal component analysis and singular value decomposition used for a numerical sensitivity analysis of a complex drawn part

The numerical forecasting of car body construction processes is already being used in industry to provide support in the ramp-up process. However, long calculation times are stretching the finite element method (FEM) to the limit, in particular when analyzing the effect of the variation of an input variable on one or more dependent variables. Moreover, there is still a need for experienced users to separate relevant from irrelevant parameters and to determine their variation. This paper presents a method that makes it possible, based on stochastic experimental design (DOE) in combination with both principle component analysis (PCA) and singular value decomposition (SVD), to create mathematical models that separate relevant from irrelevant input variables and that represent the effect of individual variables on all part or assembly areas by means of a variance-based sensitivity analysis. The method is verified in a case study based on realistic front hood geometry. The study examines the deep-drawing process steps as well as the geometrical accuracy in a measuring device. It is shown that it is possible to represent the effects of the most important variables from these processes on the strain and geometry parameters of the car body part and to vary these, based on a model function, interactively.

Improved process robustness by using closed loop control in deep drawing applications

The production of irregular shaped deep-drawing parts with high quality requirements, which are common in today’s automotive production, permanently challenges production processes. High requirements on lightweight construction of passenger car bodies following European regulations until 2020 have been massively increasing the use of high strength steels substantially for years and are also leading to bigger challenges in sheet metal part production. Of course, the more and more complex shapes of today’s car body shells also intensify the issue due to modern and future design criteria. The metal forming technology tries to meet these challenges by developing a highly sophisticated layout of deep drawing dies that consider part quality requirements, process robustness and controlled material flow during the deep or stretch drawing process phase. A new method for controlling material flow using a closed loop system was developed at the IFU Stuttgart. In contrast to previous approaches, this new method allows a control intervention during the deep-drawing stroke. The blank holder force around the outline of the drawn part is used as control variable. The closed loop is designed as trajectory follow up with feed forward control. The used command variable is the part-wall stress that is measured with a piezo-electric measuring pin. In this paper the used control loop will be described in detail. The experimental tool that was built for testing the new control approach is explained here with its features. A method for gaining the follow up trajectories from simulation will also be presented. Furthermore, experimental results considering the robustness of the deep drawing process and the gain in process performance with developed control loop will be shown. Finally, a new procedure for the industrial application of the new control method of deep drawing will be presented by using a new kind of active element to influence the local blank holder pressure onto part flange.

Flow drill screwing of fibre-reinforced plastic-metal composites without a pilot hole

Modern lightweight constructions are increasingly based on the use of multi-material design such as fibre-reinforced plastics (FRP) combined with metallic material. The technology of screwing is rated, especially for applications where high-strength and permanent joints are required, among the established joining methods. To achieve a high-quality lightweight design, often, profile-intensive constructions are used, with the effect of one-sided accessibility to the joining area. Against this background, flow drill screwing offers an innovative solution for car body construction as well as the assembly for joining this combination of material. Currently, flow drill screwing with a pilot hole in FRP materials is used in the assembly process. To use this technology without a pilot hole and use it economically in the body framework, the auxiliary joining elements have to be optimised. This publication includes the latest research findings in the context of the development and qualification of joining by using flow drilling screws. It focuses on the specific adaptation of the auxiliary joining element with regard to the geometry, the material and the coating systems. With macroscopic and microscopic sections, as well as studies of strength, ultrasound and corrosion, it is possible to assess the quality of new and original FDS joints.

Investigations on remote laser beam welding of dissimilar joints of aluminum alloys and steel with varying sheet thicknesses for car body construction

For lightweight construction, different steel and aluminum materials with various thicknesses can be welded together, depending on the dimensions and the individual functions of the workpiece. Specifically for frame and body construction, remote laser beam welding has been established as a suitable and efficient joining method for similar material seams for several years. In contrast to joining similar materials, thermal joining of steel and aluminum alloys includes different technological challenges due to the formation of hard and brittle intermetallic phases, which decreases the strength and the formability of the dissimilar joints. In the context of these requirements, the presented results show, besides the influence of different steel materials, particularly the influence of different sheet thicknesses and thickness ratios on the appropriate process parameters for remote laser beam welded lap joints of steel and aluminum alloys, respectively. Different thickness ratios, process parameters, and material properties affect the geometrical formation of the weld seam regarding penetration depth tE and weld width b, which mainly influences the composition of the molten bath and accordingly the transmittable forces. Within the scope of the presented investigations, dissimilar joints of the steel materials such as HX220LAD+Z100, 22MnB5+AS150, and 1.4301 as well as the aluminum alloy such as AA6016-T4 are characterized. Among others, the influences of the energy per unit length, material grade, and sheet thickness ratio on the achievable strengths were analyzed. The characterization of the dissimilar joints includes tensile shear tests and metallographic analyses, depending on the energy per unit length.

Phases quantification in DP600 steel welded by GTAW process using SEM and atomic force microscopy

The automotive industry is constantly under several challenges in many aspects, such as development of new materials and improvement their manufacturability. In order to achieve light weight, reduced emissions and ensure conductor safety, advanced high strength steels (AHSS) are able to fulfill these requirements. Dual phase steels (DP) are well suited for light weighing car body constructions. The gas tungsten arc welding (GTAW) process is focused in literature as an alternative choice for joining AHSS steels; this study is held to disclose the exhibited microstructural constituents. In addition, quantitative determinations of the volume % of phases in the various weld regions were made. The relative amounts of lower bainite (LB), upper bainite (UB), and polygonal ferrite (PF) in the heat affected zone (HAZ) were determined by image analysis from optical microscopy (OM) and scanning electron microscopy (SEM). It was found that GTAW promoted the development of significant amounts of LB in the HAZ (50.89 %). In contrast atomic force microscopy (AFM) leads to quantify the different phases by the morphology, height and roughness, it was found that martensite (M) dropped down to 7.5% in the intercritical zone (IZ) although PF increases to 92.5% compared with the base metal (BM).

Influence of hydrogen on formability and bendability of DP1180 steel for car body application

In order to reach future light weight targets, it is increasing necessary to use advanced high strength steels with tensile strength 980 MPa or higher in automotive body-inwhite structures. Due to the sensitivity to hydrogen embrittlement and the limited understanding of various aspects of hydrogen embrittlement on processing and function, the wide application of these steels is still limited.In the current work, the influence of hydrogen on the multiaxial forming behavior was investigated by determining the forming limit curve and bending limit curve of DP1180 steel. Hydrogen concentration in the material was modified by cathodic charging. Then Nakajima tests on hydrogen uncharged and pre-charged samples were carried out in order to adjust and study different strain states resulting in the forming limit curve. In the study of bending limit curve, the steel sheets were pre-strained by Marciniak test. Bending load on the uncharged and pre-charged samples was introduced by VDA238-100 bending tests. The experimental results indicated that the presence of hydrogen affected the formability and bendability of DP1180 steel. A clear difference in the influence of hydrogen at different strain states was observed. When formed in a biaxial strain state via the Nakajima test, the material showed the highest degradation in formability. Moreover, the samples with biaxial pre-loading showed more degradation in bendability comparing to those pre-strained in plane strain and uni-axial paths. Fractography by scanning electron microscope gave evidence of hydrogen-induced cleavage fracture on pre-charged Nakajima samples. Thus this investigation improves the understanding of influences of hydrogen on forming processes and provides important evidence for further studies on HE susceptibility of AHSS for the application on car body constructions.

The next generation material for lightweight railway car body structures: Magnesium alloys

While magnesium alloys have the attractive attributes of low density, the application of the metal in transportation industries has been restricted by its low stiffness and strength. The aim of this study was to examine the possibility of lightweight railway car body construction using magnesium alloys from the structural and manufacturing perspectives. Extruded members, making up a car body, were designed employing a gradient-based optimization algorithm. And then, numerical simulations were conducted to confirm the structural performance of the newly designed car body. In addition, one of the designed members was extruded and joined with another via friction stir welding in order to verify its fabrication potential. The work demonstrated that, with just 85% of the weight of an aluminium car body currently in operation, a magnesium-based railway car body can be potentially constructed by extrusion followed by friction stir welding for the next generation rolling stocks; that is to say, the weight saving amount is 10% of the total bare frame weight, or 2% of its total rolling stock weight.

Tolerances and Measuring Strategies in the Virtual Process Chain for Spot Welded Structures; Substitute Modeling and Automating the Calibration Procedure

This paper presents a method with whose help it is possible, to quickly and precisely predict the influence that thermal spot-shaped joining processes has on the dimensional stability of complex component structures even in early planning phase. The welding distortion is calculated in the context of reduced computing time, based upon an experimentally calibrated mechanical substitute model. This expands existing approaches of substitute models and defines both an experimental and numerical procedure for creating adequate calibration samples. In turn, this makes use of the potential obt ained for standardizing the experimental basis for calculating and modelling the distortion to automatically carry out painstaking calibration processes in simulations and experiments in future based upon mathematical model functions. Finally, the limits to applying the substitute spot welding model are verified with reference to its predictability using a complex joining situation of a car body construction.

Improving the Ramp-Up Process of a Body-Construction Line by Numerical Supported Design of Clamping Devices and FEM Based Tolerance Prognosis

The use of FEM (finite element method) to assistant in ramp-up processes of car body construction lines is increasing, thanks to developments in recent years [1-3]. Car body manufacturing begins with sheet metal forming, while in subsequent steps the inner structures of the vehicle are assembled and connected to the outer skin by hemming. With reference to the current state of the art, there is no methodology which can reliably predict the dimensional accuracy of body parts through metal forming [4].Additionally, several methods to predict the distortion of joining and the dimensional effect of clamping during the assembly process were presented and validated [4-11]. Dimensional effects of the clamping process are basically the result of a deliberate alignment, other than the given values of construction to compensate dimensional inaccuracy of single parts from the body shop. These deliberate alignments are generally effected through a translation of clamps and pins in the clamping device. Until now, most of the methods of clamping and joining simulation presented have been verified using academic samples.In this report, the quality of forecasting in real problems during a ramp-up process will be verified and expanded. As part of a national project, co-funded by Sächsische Aufbaubank (SAB), the potential of FEM to assist in the ramp-up process were reviewed in a cooperative effort between Porsche Leipzig GmbH and Fraunhofer Institute for Machine Tools and Forming Technology (IWU). Furthermore, it will be shown that developed methods are able to represent the influence of deliberate positioning of clamps in complex samples. For the first time the quality of forecasting through the translation of locating pins is numerically and experimentally qualified.

Investigating Car Body Construction Influence on the Passive Safety in a Rear Impact

Investigating Car Body Construction Influence on the Passive Safety in a Rear Impact

Welding Simulation in Car Body Construction

AbstractLaser remote welding is a dynamic and flexible joining technology which enables various new approaches in welding sequence and weld position planning. However, the challenge is to find the optimal set‐up within this large parameter space. In this article, numerical welding simulation is used to deal with this challenge. For a car door, different welding sequences and weld positions were numerically analyzed and compared with respect to its welding distortion behavior.

Martensitic Automotive Steel Sheet - Fundamentals and Metallurgical Optimization Strategies

Martensitic sheet steel is increasingly being used in advanced car body construction, especially in areas where high crash loads are expected. Using such steels appropriately the weight of individual components can be reduced by up to 20 percent. Martensitic steel sheet is commercially available in the strength range of 1200 to 1900 MPa, either as cold forming or hot stamping grade. Whereas the strength of such martensitic steels is practically only a function of the carbon content, other properties such as ductility, toughness, bendability and delayed cracking resistance are severely influenced by other alloying elements and the particular thermal processing route. The paper discusses the influence of various key-alloying elements such as Nb, Mo and B on these properties and suggests routes to optimize the steel’s behavior with respect to the manufacturing and application related aspects.Keywords Martensite, prior austenite grain size, delayed cracking, grain boundary segregation, hydrogen trapping, niobium, molybdenum

Diode Lasers and Remote Welding

AbstractFor more than thirteen years, diode lasers are used in series body manufacturing. The first diode laser was installed for brazing tailgates in the Audi A3 in 2001. While nowadays diode lasers in car‐body construction are the industry standard for brazing, cutting and welding of aluminum and steel, a new promising technology in bodyshell work emerges: remote laser welding. What are the main advantages of this technology? What are potential applications? How can fiber‐coupled, high power diode lasers create added value in body‐in‐white (BIW) remote‐welding applications?

Laser-based manufacturing concepts for efficient production of tailor welded sheet metals

Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input, high precision and fast welding speed. Especially when welding high strength steels, which are dominantly used in today’s car body construction, the low heat input by laser welding bears significant advantages with regard to the properties of the weld seam. The exploitation of the full application potential of laser welding in mass production requires an appropriate manufacturing concept and corresponding auxiliary technologies. The present paper demonstrates the integration of laser welding into the surrounding manufacturing concepts by a modular setup with different levels of automation. This approach offers flexible solutions for individual needs thereby optimizing investment cost, labor cost and productivity. Recently available laser sources enable exceptionally high welding speed on thin gauged sheet metals but require efficient material handling concepts to utilize the full speed potential. Industrial concepts are presented offering efficient material handling and high process robustness for mass production welding.

Material Modelling of Short Fiber Reinforced Thermoplastic for the FEA of a Clinching Test

In modern car body construction, multi-material and hybrid design is used, whereby short fibre reinforced plastics combined with light metals represent an interesting class of work-piece materials. In order to realize modern hybrid construction, suitable joining techniques are therefore required. Clinching represents a cost-effective and easy to implement joining method. In this paper the material modelling of the short fibre reinforced thermoplastic sheets considering the fibre orientation tensor for the FEA of the clinching process is presented.

Performance of Different Tool Steels for the Cutting of an CP1000 Advanced High Strength Steel

During the last decade, AHSS (Advanced High Strength Steels) have received growing attention in the construction of light-weight car bodies with excellent crash-performance. With the rising strength of these materials, the requirements for forming and cutting tools are also increasing permanently. To investigate the tool performance for such conditions, four different cold work tool steels (1.2379 – Sverker21, Sleipner, 1.2358 – Carmo and Caldie), one of them (1.2379 – Sverker21) additionally PVD-coated, were used in their typical heat treatment condition to compare the wear behavior and the cutting performance. The tests were performed on semi-industrial forming and cutting press under industrial process parameters on partially preformed test pieces of the steel CP1000. The measurement methods applied include optical as well as tactile measurement methods to measure the tool wear, optical methods to investigate the cutting zone and the burr formation at the workpiece as well as scanning electron-microscopy to characterize the tool surface regarding wear, fracture and adhesion of the zinc coating. Except for the lower alloyed surface hardened and nitride tool steel (1.2358 – Carmo), which showed early failure, all other tooling solutions easily reached 100,000 test pieces with good workpiece quality. Nevertheless, small partial fracturing at the cutting edge was found at all tools. Best results regarding wear, but especially lowest zinc adhesion were found at the PVD-coated tools.

Local Laser Strengthening of Steel Sheets for Load Adapted Component Design in Car Body Structures

The current trend in car body construction concerning light weight design and car safety improvement increasingly requires an adaption of the local material properties on the component load. Martensitic hardenable steels, which are typically used in car body components, show a significant hardening effect, for instance in laser welded seams. This effect can be purposefully used as a local strengthening method. For several steel grades the local strengthening, resulting from a laser remelting process was investigated. The strength in the treated zone was determined at crash relevant strain rates. A load adapted design of complex reinforcement structures was developed for compression and bending loaded tube samples, using numerical simulation of the deformation behavior. Especially for bending loaded parts, the crash energy absorption can be increased significantly by local laser strengthening.

Effects of process time and thread on tensile shear strength of Al alloy lap joint produced by friction stir spot welding

In automotive applications, friction stir spot welding (FSSW) has been practically used in the construction of aluminium car bodies. In this study, the weld strength and factors governing the weld strength in the friction stir spot welded aluminium alloy 6061-T6 were examined. The weld strength increased with the process time during FSSW up to 3 s, beyond which it decreased. The fracture path changed from the lapped interface into the shoulder edge as the process time increased, and the maximum strength was obtained at the process time when the transition of the fracture path occurred. The cross-sectional microstructure depended on the threads on the probe surface, i.e. the elliptical zone was formed in the stir zone by the threads, but an effect of the thread on the weld strength was hardly found. The present study suggests that the weld strength was strongly related to the size of the well-consolidated region, which was larger than the elliptical zone observed in the vicinity of the exit hole.