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Singer M.,Institute for Metal Forming Technology IFU | Liewald M.,Institute for Metal Forming Technology IFU | Feuer A.,University of Stuttgart
Key Engineering Materials | Year: 2015

Ecological aims and political requirements today are increasing demands on lubricants in sheet metal forming and their impact on environment. For that reason, metal forming industry wants to reduce the amount of lubricants containing polluting additives with a long-term goal of avoiding lubrication entirely. Additionally, dry metal forming will reduce the cleaning steps after the forming operation. This paper shows a new tribological system in which lubrication is replaced by CO2 in a liquid state. Here, CO2 is expanding directly into contact area between workpiece and tool surface and changes its state from gas to solid. The combination of this particular dry ice as well as the pressure of approximately 57 atm affects resulting friction coefficient significantly. After forming operation, CO2 medium vaporizes and a dry component can be used immediately for the next process steps. In this case, the lubricant is applied directly into the contact area. Therefore, laser drilled micro holes are located in the contact area of the tool. Very first gained experimental results disclose such feasibility, the effects and the potential of this new lubrication system at that moment is based on strip draw tests. Different numbers of micro holes are examined to support blank holder pressure ranging between 5 MPa and 6 MPa. In this investigation a mild strength steel DC04 is used as sheet material. This knowledge is aimed to be used for further investigation and later transfer into real deep and stretch forming processes. © (2015) Trans Tech Publications, Switzerland.

Kappes J.,Institute for Metal Forming Technology IFU | Liewald M.,Institute for Metal Forming Technology IFU | Jupp S.,Hydro Aluminium | Pirchl C.,ALU SPF AG | Herstelle R.,ALU SPF AG
Production Engineering | Year: 2012

Relatively low tooling costs, high design complexity coupled with low forming speeds make the superplastic sheet metal forming process attractive, especially for smaller lot sizes. Due to the relatively small lot size, the effort and budget for designing superplastic forming processes is usually limited (Kappes and Liewald in J Mater Sci Eng B1:472-478, 2011). For this reason the tool design and corresponding pressure profiles in superplastic forming processes are often based on trial and error (Franchitti et al. in 11th international Esaform conference on material forming, 2008; Barnes in J Mater Eng Perform 4:440-454, 2007). Consequently a process chain should be established to design superplastic forming processes accurately and efficiently. This paper deals with the process chain to form an aluminium part superplastically. At the beginning of the process chain, there is a new, developmental aluminium alloy sheet (AA5456, s 0 = 1.6 mm) designed for superplastic forming supplied by Hydro Aluminium Rolled Products GmbH. The relevant material parameters of this sheet are then determined via pneumatic bulge testing with and without in situ measurement of strains. Using these experimentally determined parameters superplastic forming process can be simulated by FE modelling (PAM-STAMP 2G). Due to in situ measurement of strains during pneumatic bulging, the comparison of experiment and FE-simulation results over the whole pneumatic bulging process could be done. This comparison shows good correlation for the observed conditions. Furthermore a cylindrical cup was simulated, evaluated via determined isobar Superplastic Forming Limit Curve (at fracture) and finally formed by pneumatic bulging. Material characterisation of the bottom of this cup showed that excessive cavitation was observed as a result of the iron-silicon particles. Superplastic forming of a bracket usually formed out of AA5083 was also simulated using material parameters of AA5456. The simulation was able to show that this part is not able to be manufactured out of AA5456 under these forming conditions, which was confirmed by forming trials performed at ALU-SPF AG. © 2012 German Academic Society for Production Engineering (WGP).

Bolay C.,Institute for Metal Forming Technology IFU | Liewald M.,Institute for Metal Forming Technology IFU
AIP Conference Proceedings | Year: 2011

Composite materials with metallic cover sheets have been established based on their low weight potential in industrial applications. Further requirements such as high stiffness of component, vibration damping and formability today are only partially met by these composites. For that reason, in current research work, great efforts are being made to develop materials which can be adapted to their later use and load in terms of improving noise, vibration and harshness. Thus, greater stiffness of component structure with a simultaneous reduction of weight can be achieved. This article presents a new composite material which consists of a plane sheet, a thin intermediate damping-layer and a sheet with formed elements to increase stiffness of component such as beads. The plane side can be used as the visible part side. The shape elements increase strength due to work hardening and can be used as design or functional elements. Thus, this composite material results in several advantages within the single layers. Possible flexibility in component design enables new semi-finished or tailored components. © 2011 American Institute of Physics.

Liewald M.,Institute for Metal Forming Technology IFU | Kappes J.,Institute for Metal Forming Technology IFU
AIP Conference Proceedings | Year: 2011

Superplastic forming of sheet metal aluminum alloys exhibits numerous technical and economical advantages for manufacturing of complex part geometries in niche type production. For virtual engineering tasks prior manufacturing of superplastic forming equipment such as forming dies, numerical sheet metal forming simulations and material parameters are crucial. In such context the selected testing procedure should be as similar as possible to the subsequent forming technique. For that reason the pneumatic bulge test represents an appropriate testing procedure for the most common superplastic forming process-the blow forming process. In-situ strain measurement of pneumatic bulging AA5083 at 500°C results in high requirements in terms of the grid applied on the blank surface due to process temperature and large strain values. These large strain values result into pole heights up to 70 mm of the bulge test specimens using an initial blank thickness of 1.5 mm and a circular die opening of 100 mm. This paper describes the influence of different grid types and finally proposes adequate grid types for in-situ strain measurement for pneumatic bulging of AA5083. Furthermore the capabilities of in-situ measurement of strains during pneumatic bulging of AA5083 are highlighted. © 2011 American Institute of Physics.

Kappes J.,Institute for Metal Forming Technology IFU | Wagner S.,Institute for Metal Forming Technology IFU | Schatz M.,ViALUX GmbH
International Journal of Material Forming | Year: 2010

Material characterisation is of prime importance in understanding its response to forming loads, which in turn influence the product design. The flow stress in plastic loading defines the evolution of the yield surface and depends on a variety of factors such as strain, strain rate and temperature. The degree of influence of the strain rate increases at higher temperatures. This effect can be well described with superplastic forming, in which the material is loaded very slowly at superplastic temperatures. This paper deals with monitoring of process parameters during superplastic sheet metal forming of magnesium alloys, with special emphasis on in-process measurements for bulge test purposes at elevated temperatures. The strain evolution near the part's pole region has been recorded in-process by using the ViALUX photogrammetric strain analysis system AutoGrid. The recorded data provides a lot of information about the forming process such as evolution of strains, strain rate, flow stress and the limit strains, which allows determining all relevant material and process parameters for superplastic forming. © 2010 Springer-Verlag France.

Jarrar F.S.,The Petroleum Institute | Liewald M.,Institute for Metal Forming Technology IFU | Schmid P.,Institute for Metal Forming Technology IFU | Fortanier A.,Institute for Metal Forming Technology IFU
Journal of Materials Engineering and Performance | Year: 2014

The superplastic forming process is used to form light weight components with complex features in one manufacturing step. However, the non-uniformity of the produced part thickness and the possibility of severe thinning are among its major disadvantages. The goal of this parametric study was to investigate feasible geometries for triangular channels to be manufactured by superplastic forming. The channels considered had sharp radii and served as secondary features extending along a circular path at the base of a shallow cup. An axisymmetric finite element model in ABAQUS™ was used to simulate the forming process. Effects of the aspect ratios of both the cup and the triangular channel on the thickness distribution and the pressure profiles were investigated. An experimental setup was used for validating the simulation results for AA5083 at 500 °C. © 2014 ASM International.

Liewald M.,Institute for Metal Forming Technology IFU | Bolay C.,Institute for Metal Forming Technology IFU | Thullner S.,Institute for Metal Forming Technology IFU
Journal of Manufacturing Processes | Year: 2013

New lightweight sandwich materials challenge existing forming processes as well as following process steps. As such the manufacturing potential of shear cutting has to be evaluated. Two cutting methods are compared. Method commonly used is shear-cutting within one stroke engaged, the other one is known as counter-shear cutting, which uses two strokes. The challenges of cutting sandwich materials are variation of hole diameter within the different layers, fraying of the textiles, deformation of the hole contour and burr formation. These effects occur in conventional shear cutting as the intermediate layer and the lower sheet metal are cut by the scrap of the upper sheet instead of the cutting punch. The following methodology included shear cutting with closed cutting edge i.e. cutting of holes into five different sandwich materials. The sandwiches exemplarily represent multiple kinds of possible material designs. For instance, aluminum and steel face sheets, different thicknesses of intermediate layers and different intermediate layers materials such as integrated textile fibers have been used. Adequate cutting parameters such as die clearance and the use of a blank holder have been determined. To achieve good results a stiff machine design with good guidance and precise control of punch position was crucial. Observations of conventional shear cutting revealed the need of small cutting clearance of 4%. High burnish area is possible for the upper face sheet due to the superimposed force by the lower face sheet. The major conclusion depicted that high cutting quality of sandwich materials requires counter shear cutting. Hence, the roll-over of the lower sheet facing the intermediate layer, the burnish area at the lower sheet, good cutting quality of the fibers improve significantly and burr formation is avoided completely. Summarized this paper provides cutting parameters for sandwich materials based on experimental work. © 2013 The Society of Manufacturing Engineers.

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