Kinsey / Wu Tailor Welded Blanks for Advanced Manufacturing

1. Auflage 2011
ISBN: 978-0-85709-385-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 240 Seiten

Reihe: Woodhead Publishing Series in Welding and Other Joining Technologies

Tailor welded blanks are metallic sheets made from different strengths, materials, and/or thicknesses pre-welded together before forming into the final component geometry. By combining various sheets into a welded blank, engineers are able to 'tailor' the blank so that the properties are located precisely where they are needed and cost-effective, low weight components are produced. Tailor welded blanks for advanced manufacturing examines the manufacturing of tailor welded blanks and explores their current and potential future applications.Part one investigates processing and modelling issues in tailor welded blank manufacturing. Chapters discuss weld integrity, deformation during forming and the analytical and numerical simulation modelling of tailor welded blanks for advanced manufacturing. Part two looks at the current and potential future applications of tailor welded blanks. Chapters review tailor welded blanks of lightweight metals and of advanced high-strength steel and finally discuss the uses of tailor-welded blanks in the automotive and aerospace industries.With its distinguished editors and international team of expert contributors, Tailor welded blanks for advanced manufacturing proves an invaluable resource for metal fabricators, product designers, welders, welding companies, suppliers of welding machinery and anyone working in industries that use advanced materials such as in automotive and aerospace engineering. Engineers and academics involved in manufacturing and metallurgy may also find this book a useful reference. - Examines the manufacturing of tailor welded blanks and explores their current and potential future applications - Investigates processing and quality issues in tailor welded blank manufacturing including weld integrity and deformation - Reviews both current and potential future applications of tailor welded blanks as well as specific applications in the automotive and aerospace industries

Autoren/Hrsg.

Kinsey, B.

Wu, X.

Leseproben

2 Deformation of tailor welded blanks during forming
K. Narasimhan,     IIT Bombay, India R.G. Narayanan,     IIT Guwahati, India Abstract:
The reliability of tailor welded blanks (TWBs) in industrial applications depends on many factors affecting TWB formation. The impacts of base metal thickness ratios, strength ratios and welding conditions are explored. The forming behavior of TWBs can be simulated either by incorporating the properties of the weld zone or by assuming the weld region as a weld line without considering the properties of constituent base metals. Weld line movement is a common phenomenon during the drawing of TWBs and can lead to significant reduction in formability. Weld zone properties can be evaluated by tensile testing of subsize samples using the rule of mixtures technique feeding into finite element simulation models for accurate forming behavior predictions. Key words tailor welded blanks rule of mixtures finite element method forming limit curve weld region weld zone drawbead blank holder force 2.1 Introduction
The deformation and forming behaviors of tailor welded blanks (TWBs) are affected in a synergetic manner by many factors. Important factors include base metal properties, thickness/strength ratio, weld process and weld orientation. Prediction of forming behavior of TWBs can significantly reduce the lead time for the manufacturing of sheet metal components using TWBs. The accuracy of such predictions depends greatly on proper estimation of the properties of the weld, in addition to the base metal properties. The following topics will be addressed in this chapter. The estimation of the constitutive behavior of the weld and the effect of the weld parameters on the tensile behavior of TWBs will be detailed. A section will cover factors affecting the forming limit strains of TWBs, with emphasis on the effect of the various TWB parameters. Weld line movement is a common phenomenon observed during the forming of steel TWBs. The factors affecting weld line movement and its control will be discussed. Finally, design issues pertaining to the forming of TWBs will also be discussed and the chapter will conclude with a section on the simulation issues of TWB forming. 2.2 Estimation of the constitutive behavior of the weld region
TWBs are typically manufactured by laser welding processes, which minimize the weld-affected zone (i.e. weld pool and heat-affected zone HAZ), usually in the order of a few millimeters. In TWBs of steel sheets, the strength and hardness of the weld is significantly higher than the base metal properties. Correspondingly, the work hardening exponent of the weld zone is much lower than that of the base steel sheets. In order to better understand and simulate the forming behavior of TWBs, it is essential to have an accurate description of the constitutive behavior of the weld zone in the TWBs. In this section, the procedure based on rule of mixture is discussed for estimating the weld zone properties. The constitutive behavior of the weld region is important from both the formability and simulation points of view in TWBs. Evaluating the constitutive behavior of the weld region is not a new issue, as it was performed even before the advent of tailor welded blanks (TWBs). But most applications use arc welding processes where the weld region is in the order of 15 mm, so that the weld properties can be obtained quite easily. In the case of TWBs, since laser welding is widely used for welding, obtaining the properties of a smaller weld zone (1–2 mm) accurately is difficult and cumbersome. Longitudinal welded blank Few published works1–6 deal with the methodology to evaluate the weld zone properties. In Abdullah et al.,2 the rule of mixtures (ROM) technique with TWBs having a longitudinal weld (see Fig. 2.1) is used to evaluate the stress–strain behavior of the TWB and weld region. 2.1 Schematic of load sharing by base metals and weld region in longitudinal TWBs. The stress–strain relationship of base metals is first obtained by tensile testing and fitting an appropriate hardening law like the Hollomon equation giving, [2.1] where ‘K’ and ‘n’ refer to the strength coefficient and strain hardening exponent of the two base metals, 1 and 2 respectively. According to ROM, the total load, P, applied is distributed on the three areas – namely the base metal 1 (P1), base metal 2 (P2) and the weld zone (Pw). In the tensile testing of the welded specimen, the total load ‘P’ on the sample is represented as, [2.2] where ‘A’ refers to the cross sectional area, ‘w’ refers to the weld region and subscripts 1 and 2 refer to base metal 1 and base metal 2 respectively. Substituting s1 and s2 from equation [2.1] in [2.2] gives, [2.3] where represents the average stress in the weld region, as the hardening behavior of weld may vary along its length. Longitudinal strain is assumed to be constant in all of the regions during deformation and hence, [2.4] Substituting equation [2.4] in [2.3] results in the relationship [2.5] Equation [2.5] defines the stress–strain relation in the weld region. Here, with the exception of and ew, all other values can be obtained using subsize tensile tests on the base metal. Area of the weld region ‘Aw’ can be calculated by knowing the area of cross-sections of base metals 1 and 2 or from weld microstructure. Measuring the area of the weld region is critical to the successful implementation of this method. In Ghoo et al.,3 the same method was followed to establish an understanding of the effect of different tensile specimen sizes and offset weld position on the stress–strain behavior of weld region. It was found that tensile specimen size shows little effect on the stress–strain behavior of TWBs. Also, the offset position of weld in the longitudinal TWB showed negligible effect on the ‘K’ value obtained because the same total load absorbed by the TWB is independent of the offset values. In Auger et al.,7 the same methodology of ROM is used to determine the weld stress–strain behavior. 2.3 Methods to evaluate the weld width (or cross-sectional area) in tailor welded blanks (TWBs)
Evaluating the constitutive behavior of TWBs by ROM depends on the accuracy of measuring the cross-sectional area of the weld region. The following are the few methods available to perform this: 1. The cross-sectional area of the weld region can be obtained by multiplying the thickness of the weld region by the weld width. Here, weld width can be obtained by subtracting the widths of base metals (base metal 1 and 2) from the total sample width. This method is subjected to approximations in measuring dimensions. 2. Another reliable method is by measuring micro-hardness, which is found in many published papers.1–10 The weld region exhibits different hardness when compared to that of the base metal. One can perform hardness measurements perpendicular to the weld region. The sudden hardness change can yield weld width and hence the weld cross-sectional area can be obtained. This is also an approximate method as the weld thickness is assumed to be the same as the average base metal thickness (say 1 mm), without considering the actual shape of the weld region. 3. An accurate way to obtain weld cross-sectional area is through a micrograph. An optical micrograph with an image analyzer can yield accurate measurement of the exact shape of the weld region and hence the cross-sectional area of the weld zone. This method is followed in Bhagwan et al.11 to study the effect of weld properties and geometry in numerically predicting the forming behavior of Al TWBs. 2.3.1 Application of rule of mixtures (ROM)
As described in the methodology, chosen weld properties are evaluated from the tensile testing of welded blanks and base material. Subsize 3 type samples made from welded blanks under desired or optimized welding conditions (welding power = 3.5 kW, welding speed = 5.5 m/min, 300 mm focal length mirror and 360 microns focal diameter in donut mode) were tested for this purpose. In this study, the TWB is produced by CO2 laser welding of the same steel sheet (interstitial free steel (IFS)) and therefore both the base metals 1 and 2 will have identical tensile behaviors. Figure 2.2 shows the engineering stress–strain behavior of base material, welded blank (with longitudinal...