Automotive Skin Research Articles

Thermal‐Oxidative Aging Behavior and Factors of Polystyrene‐Based Thermoplastic Elastomers‐Based Automotive Interior Skin

ABSTRACTCompared to traditional polyvinyl chloride (PVC), polyurethane (PU), and thermoplastic olefin (TPO) materials, thermoplastic elastomers (TPEs) offer advantages of complete recyclability, absence of plasticizers and solvents, superior mechanical properties, pleasing tactile characteristics, low volatile organic compounds (VOCs) emissions, and cost‐effective processing. Making it an exceptional choice for environmentally friendly automotive skin materials. The automotive skin is frequently subjected to harsh conditions, such as high temperatures and oxygen exposure during use, presenting a significant durability challenge. Therefore, this study focuses on polystyrene (PS)‐based thermoplastic elastomers (TPE‐S) as the subject and investigates the influence of molecular weight, PS content, and chain structure in the blend on the mechanical properties of TPE‐S using an accelerated thermal‐oxidative aging method. Meanwhile, the changes of TPE‐S during the aging process are discussed via molecular weight, crystalline structure, molecular chain structure, microphase separation structure, and tactile sensation, providing a scientific foundation for guiding the selection of TPE‐S in automobile skin and heat oxidative aging resistance ability.

The Effect of NCO Content in Polyurethane Foam for Automotive Instrument Panel

A thermoplastic polyurethane (TPU) series for automotive panels with high durability have been newly synthesized using the reacting process based on polyester polyol (BTG), polycaprolactone triol (PCL), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and 1,4-butanediol chain extender as a function of NCO/OH ratio (NCO index). The dependence of varying NCO index of synthesized TPUs on tensile strength and hardness have evaluated. To form PU foams with suitable rigidity and uniform skin-pores, the optimal synthetic process was controlled precisely by the amount of solvent, foaming agent, silicone surfactant, and catalysts content. A considerable NCO index dependence was observed in the range of 0.96 ≤ NCO index ≤ 0.99 at almost same molecular weight. When NCO index of TPU was 0.98, mechanical properties achieved maximum value due to the uniform open cell structure of molding PU foam. With the ratio of NCO/OH increasing, the hardness of PU foam also increased until 0.98 NCO index while the hardness of 0.99 NCO index decreased. The designed TPU with 0.98 NCO could be a promising formulation for molding foams of automotive skin panels and seating.

Optimization of <i>Durio zibethinus </i>(Durian) Fiber-Reinforced Composite as Automotive Skin Material

Medium-density fiberboard (MDF) was developed from Durio zibethinus (durian) husk using urea formaldehyde (UF) as a binder. The output will be applied as an automotive panel, realigning the conventional application of MDFs. Fiberboards were prepared at varying mixing ratios and pressing pressure to determine the optimal conditions. The fibers and optimized fiberboard were characterized in terms of surface morphology, elemental analysis, FT-IR analysis, and thermal stability. Moreover, the physical and mechanical properties of fiberboard were also studied. Results showed that the fiberboard was optimized at a 1:4 fiber-to-resin ratio by mass and press pressure of 640 kPa. It has a density of 0.71 g/cm3, thickness swelling (TS) of 3.33%, water absorption (WA) of 62.44%, internal bond (IB) of 2.85 MPa, modulus of elasticity (MOE) of 3008.06 MPa, and modulus of rupture (MOR) of 22.25 MPa. These were compared against properties of commercial MDF based on American National Standards Institute (ANSI) specifications (0.5≤D≤1, TS≤15%, IB≥0.6 MPa, MOE≥2500 MPa, and MOR≥22 MPa). Based on the results, the optimized fiberboard demonstrated high potential for commercial application in the automotive industries.

Understanding novel gap-bridged remote laser welded (RLW) joints for automotive high-rate and temperature applications

This paper investigates the microstructure, high-rate and temperature dependent tensile behaviour of fillet edge joints produced by novel ‘gap-bridged’ remote laser welding (RLW) using an automotive grade aluminium alloy AA6014, commercially known as AC-170PX, extensively used for automotive skin panel applications. Three part-to-part gap-bridged RLW fillet edge welds, produced with different gaps (0.2 mm, 0.4 mm and 0.6 mm) were examined for joint geometry and microstructure. Relatively larger columnar grains resulting from directional solidification were observed in the fusion zone and microhardness was reduced by ~15- 20% due to precipitates disappearance. Moderate (0.1 m/s) to high speed rate (10 m/s) tensile tests performed at room temperature (~23°C) were used to determine high-rate tensile performance. Although the strain rate dependency was found to be low, an increase in tensile extension was obtained. Additionally, the joint tensile performance was evaluated over a range of temperatures between -50°C and 300°C. Using digital image correlation (DIC), fracture strains were obtained in the range from 0.21 to 0.25 for all gap and speed conditions. Fusion zone based finite element simulations were performed using the Johnson-Cook material failure model to predict joint strength. Additionally, the suitability of gap-bridged RLW joints for automotive applications was determined by comparison with two industrial joining methods, self-piercing riveting (SPR) and resistance spot welding (RSW).

Experimental and numerical investigations on springback in V-bending of tailor-welded blanks of interstitial free steel

Tailor-welded blanks of interstitial free steel are commonly used in complex automotive skin panels. The presence of weld zone, difference in thickness and high anisotropic behaviour affect forming behaviour of tailor-welded blanks significantly. Therefore, incorporation of anisotropy of the sheets and properties of the weld zone in finite element simulations is very important for accurate prediction of springback in bending of tailor-welded blanks. In this study, experimental and finite element simulations of V-bending were carried out on tailor-welded blanks of three thickness combinations, prepared by Nd-YAG laser welding of interstitial free steel sheets of thicknesses 0.8, 1.2 and 1.5 mm. The orientation of the weld line in longitudinally welded blanks was kept at 0°, 45° and 90° with respect to the rolling direction to study the effects of anisotropy on springback in V-bending. The tensile properties of the weld zone in different thickness combinations were determined and incorporated in finite element simulations for prediction of springback. It was observed that springback results were mainly governed by the springback behaviour of the thicker sheet in a particular thickness combination. Weld zone properties affect the springback of tailor-welded blanks more significantly than the anisotropy of the sheets. Accuracy of predicted values of springback in simulations increased when the properties of the weld zone were incorporated in the material model.

Characterization of Roping on AA6xxx Alloy Sheet by Numerical Analysis for Surface Topography

AA6xxx alloys are known to suffer from a phenomenon called roping, which is a ridge and valley pattern appearing after stamping is treated as a fatal surface defect for the automotive skin panels. Although the roping is the important factor to determine the exterior quality, it is commonly evaluated by visual check done by inspecting staff, which is very subjective and difficult to measure quantitatively. In this study, to quantify the roping level in detail and easily, a new calculation method based on Fourier transform and using simple device to measure topography is proposed. As a result of analyses for several different AA6022 alloy sheets, it is found that the strong roping surface has the intensive directional pattern along the rolling direction with a specific wavelength. The roping level can be expressed numerically as the ratio between the amplitude of the rolling directional pattern and the average amplitude of each directional pattern. This value shows good agreement with the roping level determined by human observation. Moreover, it is found that the proposed method can be applied to the surface appearance obtained by digital camera without a 3D profiler.

Holistic life cycle approach for lightweight automotive components

Since sustainability and environmental issues rose lately, lightweighting has been the point of interest for automotive and aerospace sectors. Lightweighting reduces the fuel consumption of the vehicles and as a result of this reduces emissions. Aluminum, especially wrought aluminum alloys, have large potentials for dramatic weight reduction of structural parts while maintaining the safety and performance. Wrought aluminum alloys are used in automotive skin, bumpers and suspension parts etc. Lightweight suspension parts improve the ride quality and handling, additional to fuel consumption and emission reduction. Holistic life cycle approach takes into account the material flows and related information flows in order to achieve these material flows through the life cycle of the components as well as performance characteristics not only in technical and economic terms but also environmental and social terms. It is necessary to have seamless information flow through the life cycle of the components that could be enabled by the closed-loop product life cycle management (PLM). Closed-loop PLM may also help collection of life cycle information which is necessary to generate performance characteristics and distribution of performance characteristics among life cycle actors.

A novel inspection method for determining the cosmetic quality of automotive skin panels

The cosmetic quality of automotive skin panels affects the perceived valuation and quality of an automotive vehicle. The human eye is sensitive to optical distortions caused by geometric deviations and the severity of these distortions is related to wavelength and depth of the defects. This paper describes the development and evaluation of a physically based inspection method that uses the wavelet transform to identify shapes in panel topology that the human eye is specifically sensitive to and to estimate their depths. We then relate their depths to a perceived severity. Using a structured lighting system, geometric data was first collected from panels at each stage of a five-stage stamping process and then analysed with the wavelet-based inspection method. The results were then compared to a conventional inspection and two outcomes were found. First, the wavelet-based method was capable of detecting the location and sizes of subtle cosmetic defects in the panel and secondly, the stages of the stamping process were found to influence the location and severity of the defects found in panels.

Subtle Cosmetic Defects in Automotive Skin Panels

Cosmetic defects such as ‘hollows’ are the result of deviations in a skin panel. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem: the springback or buckling of the panel, the optics of the painted panel and the ability of an observer to perceive the defect. In particular, it will be argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a simple way of locating and quantifying the severity of these defects. The transform was applied to two physical parts and a simulation model.

Detecting subtle cosmetic defects in automotive skin panels

Cosmetic defects, such as ‘hollows’, are deviations in topology of automotive skin panels that form as a result of springback at the end of the forming process. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem. The first is the springback of the panel, the second is the optics of the painted panel, and the third is the ability of human sight to perceive a defect. In particular, it is argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a way to relate the geometry of a hollow to the resulting optical distortion. The transform was applied to two physical parts and the paper will discuss the effectiveness of the transform in locating and quantifying the relative severities of the defects that were present.

Effect of Quenching Temperature on Age Hardening of AA6016 Sheets

Heat treatable AlMgSi alloys are being used increasingly for automotive skin sheet. AA6016 sheets produced from direct chill (DC) cast ingots are the material of choice in Europe. However, manufacturing of sheets using twin-roll casting (TRC) is a cost effective alternative to DC casting. The effect of processing parameters on the age hardening of TRC AA6016 sheets was assessed. The influence of quenching temperature after solution annealing and subsequent pre-aging at 100 °C was studied. Sheets in the artificially aged condition were prepared using a simulated car-body paint baking procedure (180 °C/30 min). The precipitation kinetics, resulting dispersion of the agehardening phase and their correlations with properties were investigated by differential scanning calorimetry, transmission electron microscopy and tensile tests. It is demonstrated that pre-aging results in increased age hardening effect, especially in the material quenched to 20 °C after solution annealing. The differences in strength are ascribed to the differences in the nucleation rate of β'' precipitates during stabilisation and the formation of stable GP-I zones in naturally aged specimen. The differences in precipitate microstructure inherited from the pre-treatment affect precipitation kinetics during paint baking and result in different precipitate dispersion and sheet strength.

Tailored blank design and prediction of weld line movement using the backward tracing scheme of finite element method

To achieve weight and cost reductions in component manufacturing, tailored blank is introduced for forming automotive structural skin components. In order to obtain successful application of tailored blanks without necessarily trimming after the forming process, it is critical to design an initial welded blank and to predict the weld line movement, which is usually determined by intuition and experience with the trial-and-error approach. A systematic approach method of the backward tracing scheme, which is confirmed by experiment, is extended to design the initial tailored blank for net-shape production in this study. The optimised tailored blank by the backward tracing scheme appears to be successful in obtaining a net-shape stamping product. This blank also improves the forming condition during stamping process. All simulation results show that the backward tracing scheme can be applied to more general blank design.

Effects of Si on the aging behaviour and formability of aluminium alloys based on AA6016

The heat treatable 6xxx series (Al–Mg–Si–(Cu)) aluminium alloys are finding increasing use in automotive skin panel applications where relatively high formability and in-service strength for dent resistance are major requirements. In Europe, the alloy of choice for such applications is currently the low Cu-containing alloy AA6016, which typically contains approximately 0.4 wt.% Mg and 1.0 wt.% Si, and which derives its strength from the precipitation hardening phase, Mg 2Si. The volume fraction of Mg 2Si is, in turn, affected primarily through the level of Mg within the alloy, although the Si content is also important. The level of Si within the alloy influences the solution heat treated (T4) strength and the subsequent aging response of the 6xxx series alloys, again predominantly through its effect on the volume fraction of Mg 2Si. In this paper, the effects of Si content on the aging behaviour and mechanical properties (formability) of alloys based on the AA6016 composition are described.

Improvement in Bake Hardening Response of Al-Si-Mg Alloys

Although heat treatable Al-Si-Mg-based 6000 alloys have become increasingly attractive for automotive skin panel applications, the potential of these alloys is not fully explored in the current automotive body paint bake cycle due to a low temperature and a short duration. In order to improve the bake hardening response in such a cycle, many efforts have been made in past years by means of microstructural modification. This paper presents our recent results in developing pre-aged (T4P) Al-Si-Mg alloys. Two types of processes have been investigated which differ in the holding time between the solid solution heat treatment and the pre-ageing heat treatment, and can be denoted (a) fresh pre-ageing treatment and (b) reversion pre-ageing treatment. The mechanism of microstructural evolution during these processes is discussed, also considering the effect of processing parameters and alloy chemistry on the bake hardening response.

Evolution of Texture during Thermo-Mechanical Processing of an Al-Mg-Si-Cu Alloy

Heat-treatable 6000-series alloys are currently used in selected automotive skin components, and are being considered in further applications towards reducing the weight of automobiles and aircrafts. Despite the advantage in terms of strength to weight ratio, these alloys exhibit lower forming limits. The microstructural characteristics produced during recrystallization, such as grain structure and crystallographic texture, play a dominant role in controlling the mechanical properties and formability of sheet in the T-4 condition. Crystallographic texture plays an important role in forming of materials, as it controls the plastic anisotropy like wall thickness reduction (R-value) and earring properties. It is, therefore, important to understand the evolution of texture and microstructure of these alloys. In recent years, the quantitative texture analysis using three dimensional orientation distribution function (ODF) plots has contributed to improved understanding of the deformation behavior of materials. This technique provides more accurate description of the texture and its correlation with the microstructure developed during deformation. This paper describes some preliminary results of experiments designed to obtain information about the effects of deformation temperature on microstructural changes and development of crystallographic texture in an Al-Mg-Si-Cu alloy. The recrystallization behavior and its effect on the crystallographic texture during solution treatment of hotmore » rolled Al-Mg-Si-Cu alloy has also been studied. The relationship between texture and formability will be reported in a subsequent publication.« less