Papers by Keyword: Sheet Metal

Abstract: Tailor welded blanks (TWB) are commonly used in the automotive industry to achieve heterogeneous components, particularly for creating high strength, lightweight parts. Laser welding is one method for joining TWB. Laser welding was used to create TWB composed of stainless steel 304L, with varied thicknesses, in a “patchwork quilt” pattern forming quadrants within the sample. The mechanical properties and quality of the weld were evaluated via tensile testing and microscopy. Truncated pyramids were then formed with weld seams along the faces, and springback and mechanical properties after forming were analyzed. Optical microscopy revealed that the weld seams remained intact after forming. The weld seam location in the center of the pyramid walls did not have a significant impact on the geometrical accuracy of the formed parts. The results of this study show promise for the use of SPIF with quilted TWB to achieve optimal formed part properties for the intended part application.

Abstract: In the aerospace industry, hot forming processes, using materials like Ti-6Al-4V titanium, are known for their complexity and cost. Senior Aerospace Thermal Engineering (SATE) has traditionally relied on a trial-and-error approach for new product introductions (NPIs), which, while effective, has led to significant time and resource expenditures. This paper examines the transition of SATE's NPI processes to a more efficient digital approach using AutoForm Forming simulation software. By doing so, SATE has been able to accurately predict forming outcomes, optimize tooling designs, and significantly reduce both the number of physical tryouts and the overall project costs. Two case studies are presented to demonstrate the practical applications of this digitalization, highlighting how important engineering decisions were taken. The paper concludes with an assessment of the impact on SATE's operations, noting improvements in development time, feasibility assessments, and overall production efficiency.

Abstract: This paper addresses the unique challenges in processing aluminum materials within metal forming technology, specifically focusing on complex wear conditions involving abrasion and adhesion. A promising research approach to avoid abrasive and adhesive tool wear and reduce the friction coefficient towards aluminum alloys is the use of sufficiently smooth CVD diamond coatings. To achieve this, two approaches are considered. First, wear resistance is enhanced by using tool inserts made of carbide or a tungsten alloy, directly coated with CVD diamond. Second, the friction coefficient is selectively influenced or reduced by refining the polished CVD diamond coating through laser ablation. The study investigates the impact of these surface treatments on friction coefficients during both dry and lubricated forming processes involving the aluminum alloy EN AW-5182. Comparative analyses of various surface treatments are conducted against reference tests using diamond-like carbon (DLC)-coated tools. Through application-oriented strip drawing tests, the paper systematically examines how different surface smoothing techniques affect the coefficient of friction. This research provides valuable insights into optimizing metal forming processes for aluminum alloys through tailored surface treatments, advancing our understanding of friction dynamics in these specific manufacturing conditions.

Abstract: Advanced hardening models accurately describe the transient plastic behavior (reyielding, stagnation, resumption...) after various strain-path changes (reverse, orthogonal...). However, a common drawback of these models is that they usually predict monotonic loading with lower accuracy than the regular isotropic hardening models. Consequently, the finite element predictions using these models may sometimes lose in accuracy, in spite of their tremendous theoretical superiority. This drawback has been eliminated in the literature for the Chaboche isotropic-kinematic hardening model. In this work, a generic approach is proposed for advanced hardening models. Arbitrary models could be successfully compensated to preserve rigorously identical predictions under monotonic loading. A physically-based model involving a 4^th order tensor and two 2^nd order tensors was used for the demonstration. The parameter identification procedure was greatly simplified by rigorously decoupling the identification of isotropic hardening parameters from the other parameters.

Abstract: Computer simulation plays a crucial role in the designing of sheet metal stamping processes for the prediction of process output, before try-out die sets are manufactured. Different commercial software packages are available on the market for sheet forming simulation, but their accuracy can vary, depending on the selection of the pre-processing parameters and on their formulation. Software benchmarking can be used to select the most appropriate package for a given application. Calibration, i.e. the inverse determination of the correct set of pre-processing parameters, can be used for improving the prediction accuracy. The scientific literature on numerical simulations of sheet metal forming processes presents some examples of software calibration and very few examples of benchmarking. The literature generally neglects a critical and important issue: the inherent variability of real forming processes. In this work, the experimental results of two similar multi-stage deep drawing processes are presented and compared to the simulation output of two popular software packages used in the industry. Statistical methods for benchmarking and calibration are proposed. The paper demonstrates how benchmarking can be misleading if process variability is not considered.

Abstract: Miniaturization of parts for technical products is an ongoing trend across all industries over the past decades. Due to the large number of possible applications, several billion micro parts are produced every year. In mass production, cold forming offers technological, economical and ecological benefits in comparison to other manufacturing methods. Unfortunately, due to size effects that negatively influence the part geometry, the process stability, the handling and the tool stress, this manufacturing technology is currently barely used. Previous research results have shown that bulk microforming from sheet metal has the potential to reduce the aforementioned restrictions decisively. Within this paper, a three-stage bulk microforming process from sheet metal is experimentally analysed to form a demonstrator geometry with dimensions in the sub-millimetre range in all spatial directions. In the first stage, material is provided in form of a pin for subsequent forming stages. During the second stage, a cup geometry is formed on the pin. Finally, the micro part is separated from the sheet metal by shear cutting. To ensure a wide range of applications, the investigations are carried out with copper, steel and aluminium material. This study is focused on the evaluation of the achievable part quality and the process stability. For the evaluation of the geometry and the surface quality, the micro parts are optically measured with a three-dimensional surface measuring system. The standard deviation of the part dimensions and the process forces are used to investigate the influence of size effects in relation to the material and the grain structure.

Abstract: Most of the sheet metals in general exhibit high an-isotropic plasticity behavior due to the ordered grain orientation that occurred during the rolling process. This results in an uneven deformation yield property that tends to develop ears in case of deep-drawing operation. The deep drawing process is used for the production of cup-shaped articles having applications in automobiles, beverages, home appliances etc. It is essential to know the formability of sheet metals for minimisation of test runs and reducingthe defects. Forming Limit Diagram (FLD) is one of the methods for assessment of formability of sheetmetals. This paper describes various deformation models, yielding and an-isotropic properties and itsdetermination. Through experimental tests, FLD constructed for aluminium alloy AA6111 sheet metalhaving 0.9 mm thickness.

Abstract: In many areas of product manufacturing constructions consist of individual components and metal sheets that are joined together to form complex structures. A simple and industrial common method for joining dissimilar and coated materials is clinching. During the joining process and due to the service load cracks can occur in the area of the joint, propagate due to cyclic loading and consequently lead to structural failure. For the prevention of these damage cases, first of all knowledge about the fracture mechanical material parameters regarding the original material state of the sheet metals used within the clinching process are essential.Within the scope of this paper experimental and numerical preliminary investigations regarding the fracture mechanical behavior of sheet metals used within the clinching process are presented. Due to the low thickness of 1.5 mm of the material sheets, the development of a new specimen is necessary to determine the crack growth rate curve including the fracture mechanical parameters like the threshold against crack growth ΔK_I,th and the fracture toughness K_IC of the base material HCT590X. For the experimental determination of the crack growth rate curve the numerical calculation of the geometry factor function as well as the calibration function of this special specimen are essential. After the experimental validation of the numerically determined calibration function, crack growth rate curves are determined for the stress ratios R = 0.1 and R = 0.3 to examine the mean stress sensitivity. In addition, the different rolling directions of 0° and 90° in relation to the initial crack are taken into account in order to investigate the influence of the anisotropy due to rolling.

Abstract: In order to reduce the fuel consumption and consequently the greenhouse emissions, the automotive industry is implementing lightweight constructions in the body in white production. As a result, the use of aluminum alloys is continuously increasing. Due to poor weldability of aluminum in combination with other materials, mechanical joining technologies like clinching are increasingly used. In order to predict relevant characteristics of clinched joints and to ensure the reliability of the process, it is simulated numerically during product development processes. In this regard the predictive accuracy of the simulated process highly depends on the implemented friction model. In particular, the frictional behavior between the sheet metals affects the geometrical formation of the clinched joint significantly. This paper presents a testing method, which enables to determine the frictional coefficients between sheet metal materials for the simulation of clinching processes. For this purpose, the correlation of interface pressure and the relative velocity between aluminum sheets in clinching processes is investigated using numerical simulation. Furthermore, the developed testing method focuses on the specimen geometry as well as the reproduction of the occurring friction conditions between two sheet metal materials in clinching processes. Based on a methodical approach the test setup is explained and the functionality of the method is proven by experimental tests using sheet metal material EN AW6014.

Abstract: Lubricant-free deep drawing is motivated by the avoidance of using environmentally harmful lubricants as well as the potential for shortening the process chain by eliminating lubricant application and component cleaning. Central challenges of dry deep drawing are a significant increase in friction as well as in adhesive tool wear due to a lack of a separating lubricant layer between tool and workpiece. An approach to meet these challenges is the modification of the tools through diamond-like coatings. Based on findings from laboratory tests, a-C:H and ta-C coatings were selected and their effectiveness in overcoming these challenges was demonstrated in single stroke tests in previous research. In order to use the process-specific advantages of forming technology, high tool life is required. In this context, this research aims at investigating the application behavior of a-C:H and ta-C coatings during lubricant-free deep drawing of a high number of components made of the aluminum alloy AA5182. For this purpose, a new wear test rig is applied, which enables the time and material efficient production of high quantities. Numerical methods are utilized to identify the drawing die radius as well as the blank holder as the highest loaded areas. Based on these findings, the wear of the coatings as well as that of an uncoated tool as a reference is analyzed in these areas by optical and tactile measurements. In addition, the influence of tool wear on the component surface quality is determined. It is proven that the ta-C coating increases the tool life from 10 components in uncoated condition up to 3,000 components.