Tomaž Pepelnjak

Optimization of sheet metal forming processes by the use of numerical simulations

Abstract If the final part is to be produced without any defects, the development process has to be supported by means of numerical simulations based on finite element method (FEM). The experiences gained with optimization of sheet metal forming processes are presented on the industrial examples. The presented examples are carefully selected in order to present all important issues concerning sheet metal forming: determination of optimal product shape and optimal initial blank geometry, prediction of fracture, prediction of final sheet thickness, prediction of wrinkling, prediction of loads acting on the active tool surfaces, prediction of springback and residual stresses in the product. The results of the numerical simulations were compared to the samples from the production processes. Reliability of the results, costs, benefits, and times required for performing numerical simulations are evaluated.

Numerical simulations in optimisation of product and forming process

Abstract Modern systems for the development and manufacturing of new products are strongly connected to market demand. To achieve fast and effective response to market needs, the concept and design phase must take place in a virtual CA-x environment. Once the approximate product geometry is known, a numerical simulation has to be performed to study the forming process and appropriate tool design. After some iterations, product geometry, with some variants, is known and the best of them is chosen for further development. The number of stamping steps and the exact tooling geometry are determined. The stamping processes which are widely used in the manufacturing of sheet metal parts are hard to control, since they depend on numerous parameters relating to geometry and material type. The purpose of this paper is to present the industrial application of 3D numerical simulations using the PAM-STAMP program in the product and process development cycle. The simulations were performed during product and process development including tool design and manufacturing. The issues theoretically discussed in the first part of the paper will be explained by example. The time, costs and benefits analysis of using the numerical simulation in the product and process development cycle will also be discussed.

Computer-assisted engineering determination of the formability limit for thin sheet metals by a modified Marciniak method

Development of a new sheet-metal-forming technology in a digital environment demands accurate and reliable mechanical properties and forming limits of the selected material. It is essential to determine the forming limits for thin sheets and foils. Implementation of the Marciniak procedure with strip-shaped specimens defining the left-hand side of the forming limit diagram (FLD) results in tearing outside the observed area of the specimen. Therefore, new shapes of test pieces were designed with a strip-shaped central area and enlarged outer areas, which were in contact with the die during the forming process. The radius of the specimen enlargement enabled a co-axial contact of its edge and direction of the material flow over the die radius during the forming process. The shape of the redesigned geometry of the specimen was analysed using the finite element (FE) program ABAQUS to minimize undesired stress concentrations at the die radius. Finally, strain paths variations due to shape change were analysed. The new specimen concept was verified on TS-275 tinplate steel with a thickness of 0.24 mm. By implementing the necessary redesigned specimen shapes and by analysis of the tearing limit of the TS-275 material, the forming limit curve for the tinplate material under investigation was constructed.

Adaptable tooling sets for metal forming of geometrically similar products

Abstract This paper presents the concept of a layered tooling structure for flexible metal forming tools. The adaptation of tooling geometry is possible through such layered tooling sets. The active forming tool parts are built with multiple layers, with layer thicknesses ranging from 1 to 20 mm and more. Layers are manufactured with conventional cutting technologies and/or three-dimensional laser beam cutting, wire electro-discharge machining (wire EDM) or abrasive water jet cutting (AWJ). The production times of new tool sets can also be shortened using existing tool plates. The developed optimisation model for the design of tool layers used in the crafting of new layered tools for metal forming, or the redesign of existing ones, consists of many significant parameter groups: geometrical parameters, tool load parameters, tooling material and tool set assembly. The geometry of layered tooling sets is chosen on the basis of these parameters and tested with regard to the accessibility of tooling materials. The developed system for the optimisation of tooling design has been verified via the redesign of a laminated deep drawing die for rotational cups used for the production of cups with several different diameters. The tooling set redesign, tool plate geometry, and clamping and positioning methods have been chosen on the basis of all the affected parameters. The tool geometry defined with the optimisation system was analysed using finite-element method (FEM) simulations in order to verify the geometry with respect to the defined forming process. Last but not least, deep drawing experiments were performed to confirm the geometry of the chosen tooling set and forming process parameters achieved by FEM simulation.

First Results of Energy Saving at Process Redesign of Die Forging Al‐Alloys

The contribution deals with eco‐friendly solutions for shortened production chains of forging light alloys. During the die forging operations a remarkable amount of material goes into the flash and later on into chips during finish machining. These low value side products are rich with embedded energy therefore recycling or reprocessing could be very energy saving procedure.In cooperation with a die forging company a shortened reprocessing cycle has been studied starting from re‐melting the forging flash and without additional heating to cast preforms for subsequent die forging. As such preforms have not as good formability characteristics as those done from extruded billets the isothermal forging process has been adopted. First results showed that without cracks and other defects the formability is sufficient for a broad spectrum of forgings.To improve the formability a homogenization process of cast preforms has been implemented. As the process started immediately after casting, amount of additional ene...