Advanced Materials Research Vol. 1018

Abstract: Forming complex asymmetric parts lead to high horizontal process forces applied to the ram of a forming machine. These forces entail horizontal ram displacement and influence the quality of the finished parts negatively. By application of horizontal counterforces to the ram, the displacement could be avoided and the process stability could be improved. This paper presents a design of an electromagnetic system, which is capable to apply such high horizontal counterforces. To obtain high counterforces and a high dynamic simultaneously, the techniques premagnetisation and overexcitation have been tested numerically. Both mentioned techniques improve dynamic of electromagnetic systems by a large extent as illustrated in the paper.

Abstract: Due to new material concepts (e.g. boron-manganese steels), hot stamping of sheet metal parts has emerged in order to produce high strength components. Thereby, the design of hot stamping processes by means of finite element simulations requires information about the thermo-mechanical material behaviour up to high strain levels at various temperatures as simulation input. It is known that hot tensile tests are only evaluable until low strain levels. Therefore, a hot gas bulge test for temperatures in the range of 600 °C to 900 °C and strain rates up to 1/s is being developed. In order to design such a hot gas bulge test, the requirements (e.g. forming pressure) are estimated by finite element simulations. The result is a test bench, which already enables a pneumatic forming of specimens at room temperature and pressures up to 200 bar without any unexpected side effects.

Abstract: Increasing demands on vehicle safety and weight reduction in the automotive industry lead to an increased use of “advanced high strength steels” for car body manufacturing purposes. Mentioned material grades are having high levels of tensile strength and are often used in conventional sheet metal forming processes. One of the most significant factors on quality of stamped components as well as its manufacturing process robustness is the friction between tool and sheet material. During the deep drawing process, superposition of tensile stresses is causing enlargement of the sheet surface by a few percent. This effect can damage the zinc layer. Due to that fact, lubricant has to keep tool and work piece separated in order to prevent adhesion and abrasion. For that very reason, sufficient amount of lubricant has to be applied onto the surface texture reservoirs. Furthermore, the viscosity of lubricant is mainly influencing its ability of wetting the surface. The aim of this study is to define the relationship between friction coefficient, surface enlargement and lubrication having different viscosities. In this investigation the same amount of lubricant with viscosity of ϑ=65 mm²/s, ϑ=200 mm²/s and ϑ=400 mm²/s was applied on strips made out of DP1000 and DC04 steel. Then, the strips were stretched uniaxially, and restraining forces were measured by strip draw test considering constant surface pressure and drawing speed. In this paper, the correlation between friction coefficient, viscosity and surface enlargement for two different sheet material grades is shown.

Abstract: In shearing and blanking lubrication is widely used. For future production one aim is to decrease the use of oil or to do without such lubricants. For this purpose it is interesting, if there is an influence of using lubricants on the cut edge quality. Therefore numerical analysis and experiments are carried out with a blanking tool, installed in a servo press, to analyze the cut edge quality of shearing of aluminum 6082-T6. Using FE-simulation with Lemaitre’s damage model, the process is simulated with different friction coefficients for simulate different kinds of lubrication. In this paper the circle punch with 16 mm diameter is used (piercing). In the experiments the cut edge quality and the maximum shearing force do not differ significantly. With a friction coefficient of 0.2 it is possible to give the right cut edge quality by using the damage model of Lemaitre.

Abstract: With cold forging processes it is possible to produce parts characterized by high strength, high dimensional accuracy and high surface quality. In order to optimize the forming process and to be able to use the advantages of cold forging specifically and combined, it is necessary to find correlations between manufacturing parameters on the one side, strength and other properties like hardness distribution and surface quality of the component on the other side. The research work covered in this paper focuses on the correlation of the components properties influenced by its manufacturing history and their fatigue strength. The used component is a gear produced by a lateral cold forging process. For the investigations an experimental setup has been designed. The aim for the design of the setup is to reproduce the real contact condition for the contact of two gears. To obtain different component properties the production process of the gear was varied by producing the parts by a milling operation. First of all, the components’ properties, for example hardness distribution, remaining residual stresses, orientation of fibers and surface quality, were determined. The components’ fatigue behavior was determined using a high frequency pulsator and evaluated in terms of finite life fatigue strength and fatigue endurance limit. These examinations were used to produce Woehler curves for the differently manufactured components with a certain statistical data analysis method.

Abstract: Super high strength steels are used as the importance of lightweight construction increases. They induce a high amount of springback during removal of a tool and this has to be compensated. Previously developed methods of springback compensation [1] have two disadvantages. Firstly springback of a u-shaped profile cannot be compensated in one deep drawing step. Secondly these methods only take the material parameters of one sheet metal batch into account. With varying material properties, problems arise because the tool is especially designed for one sheet metal batch. Therefore the objective of this work is not to compensate springback but to reduce it by a preventive measure which allows the production of a u-shaped profile by one deep drawing step. An additional advantage of the measure, which consists of a geometric change of the punch radii and is defined by several parameters, is that the influence of the sheet metal batch on springback is significantly reduced. This can be realised by a suitable choice of values for these parameters. Apart from this measure a method was developed whereby appropriate values for the parameters can be determined on the basis of a metamodel without the need of individual simulations. By way of example the method is applied to a u-shaped profile, however it can be used for structural components in general.

Abstract: The combination of fibre-reinforced materials with metals is defined as a fibre metal laminate. These material composites have already been a subject of research for several years. The long manufacturing time resulting from the period required for consolidation of the thermosetting resin is a major disadvantage of the fibre metal laminates previously in use (for instance GLARE, which is a combination of aluminium with glass fibre-reinforced plastic). In this paper, a new fibre metal laminate with a thermoplastic resin in the carbon fibre-reinforced plastics (CFRP) is introduced. The application of a thermoplastic resin system results in a general change in the process chain. The cutting of fibre metal laminates by means of the flexible water jet and laser cutting techniques is presented. In the second operation, forming behaviour is represented by the methods of v-bending and deep drawing. Finally, quality assurance by means of computed tomography, which replaces the conventional metallographic method, is described.

Abstract: The increasing use of advanced high strength steels challenges the forming industry. Data on tool life are not available, thus causing uncertainties in the choice of suitable tribological systems. This paper investigates the reliability of a strip drawing test and the effect of the load level on tool life. Reproducibility of wear tests is barely discussed in literature. This study shows that a wear analysis on the base of a strip drawing test allows reproducible data. However, even small differences of the initial parameters can affect the result. A further investigation shows a distinct relationship between tool life and load level. Furthermore, the predominant wear mechanism is also influenced by the applied load. The findings on wear behaviour and reproducibility can be used for a new approach to estimate tool life in industrial forming processes on the base of a model test.

Abstract: Tailored blanks are suitable for the manufacture of lightweight structures due to the load-optimised design. However, the forming of tailored blanks is problematic because of the varying properties. Especially springback is a main challenge to focus on. An innovative process will be discussed which concentrates on the air bending process of sheet metal extended by a local application of a stress superposition to reduce springback.

Abstract: In cold forging, the forming tool takes a key role as it determines accuracy and efficiency of forming process. The present study focuses on the FE based analysis of the influence of die material, interference within prestressing and die splitting on the stress state in and the elastic behaviour of the forming tool. The results reveal a great influence of the workpiece material and the tool layout on the outcome of the forming process and the corresponding tool stresses.