A. Erman Tekkaya

State-of-the-art of simulation of sheet metal forming

Abstract The paper starts with a brief historical overview to the attempts of numerical simulation of sheet metal forming. Comparison between bulk and sheet metal forming processes from the simulation point of view is given. Basic requirements of the applier to the simulation tools are summarized. Various possible methodologies are briefly discussed. Special emphasis is given to the static explicit and dynamic implicit finite element procedures. Also different element types are overviewed. Available important commercial finite element packages are given. The current state of the application of the simulation tools is discussed. Some typical industrial applications are reviewed to demonstrate the current abilities of analysis. Finally, an attempt to prognosticate some future developments is made.

The increased forming limits of incremental sheet forming processes

Incremental sheet forming is known to give higher forming limits than conventional sheet forming processes, but investigation of this effect has been impeded by the computational cost of process models which include detailed predictions of through thickness behaviour. Here, a simplified process is used to gain insight into the mechanics of a broad class of incremental forming processes. The simplified process is described and shown to give increases in forming limits compared to a conventional process with the same geometry. A model of the process is set up with a commercial finite element package, validated, and used to trace the history of a ‘pin’ inserted perpendicularly into the workpiece. The history of the deformation of the ‘pin’ demonstrates significant through thickness shear occurring in the direction parallel to tool motion. This insight is used to modify an existing analysis used to predict forming limit curves. The analysis shows that for a sheet with uniform proportional loading, the forming limit is increased when through thickness shear is present, and this is proposed as an explanation for the increased forming limits of incremental sheet forming processes.

Numerical investigation of non-homogeneous plastic deformation in quenching process

Abstract The aim of the study is to investigate the evolution of internal stresses and non-homogeneous plastic deformation in quenching by numerical simulation. This paper presents the finite element model of quenching of axisymmetric components and the results of various numerical experiments. In the simulation, first the temperature distribution is determined as a function of geometry and time. Then, a model is described to give the volume fractions of phases as a function of time for the corresponding cooling curves. Next, thermo–elastic–plastic approach is applied to describe the stress–strain response during cooling, and to predict the residual stresses of the first order. The computer program was written in Fortran, and material properties were input as a function of the individual phases and temperature.

RESIDUAL STRESS STATE AND HARDNESS DEPTH IN ELECTRIC DISCHARGE MACHINING: DE-IONIZED WATER AS DIELECTRIC LIQUID

ABSTRACT Procedures and results of experimental work to measure residual stresses and hardness depth in electric discharge machined surfaces are presented. Layer removal method is used to express the residual stress profile as a function of depth caused by a die sinking type EDM. Thin stressed layers are removed from machined samples by electrochemical machining. Corresponding deformations due to stress relaxation are recorded for each removal to determine the stress profile from elasticity theory. The relational dependence of the machining parameters with residual stresses is obtained and a semi-empirical model is proposed for plastic mold steel for de-ionized water as dielectric liquid. These stresses are found to be increasing rapidly with respect to depth, attaining to its maximum value, around the yield strength, and then fall rapidly to compressive residual stresses in the core of the material since the stresses within plastically deformed layers are equilibrated with elastic stresses.

Developing Tele-Operated Laboratories for Manufacturing Engineering Education. Platform for E-Learning and Telemetric Experimentation (PeTEX)

The aim of the PeTEX-project is to establish an e-Learning platform for the development, implementation, and delivery of educational training programs in the field of manufacturing engineering. The PeTEX team designs both: a technical platform for eLearning based on â??Moodle

Platform for e-Learning and Telemetric Experimentation (PeTEX). Tele-operated laboratories for production engineering education

The development of tele-operated experimentation and its provision to distance learners opens new dimensions of knowledge acquisition, particularly where experiments are the core elements of engineering education. The finalized EU-funded project PeTEX-Platform for e-Learning and Telemetric Experimentation has developed a prototype of an e-learning platform based on Moodle for the design and implementation of educational and training programs in the field of manufacturing engineering. The principle goal of this project was to establish individual and group oriented learning for different target groups like students and professional workers within a platform-system able to sustain a multi-country learning community. Hence, an educational model was designed which integrates the tele-operated experimentation platform with teaching content and learning activities in order to support a successful learning walkthrough for different target groups.

Shape optimization with the biological growth method: a parameter study

Studies the effect of parameters controlling the biological growth method by applying it to the classical optimization problem of a plate with a central hole under biaxial stress state. It has been found that the optimization character of the method depends strongly on the so‐called reference stress. Depending on the magnitude of this parameter either a local or global optimum is approached. A global optimum corresponds to the minimum possible v. Mises stress along the hole boundary (and hence in the plate), whereas a local optimum presents the modified shape of the hole yielding an uniform stress distribution whose magnitude is larger than the minimum possible value and which is equal to the specified reference stress. The magnification factor applied to the iterative displacement results influences the optimization speed. Too large factors lead to divergence of the solution. Furthermore, it has been found that the dimension of the optimization domain has a critical effect on the optimization result.

Stresses induced by different loadings around weak abutments

Stresses and deflections of abutments induced by various loadings were analyzed with a two-dimensional finite element model. The biomechanic system consisted of the mandibular posterior three-unit fixed partial denture (FPD). Four different loading types were analyzed: (1) a distributed force of 600 N; (2) concentrated nonaxial and (3) axial 300 N forces at the marginal ridge of the molar; and (4) a concentrated vertical 300 N force at the center of the pontic. All computations were conducted for three different alveolar bone levels. The premolar exerted a greater pressure during occlusal loadings (except axially) on the alveolar bone than the molar. According to the stresses induced in the alveolar bone, the most critical loading was the distributed force. With diminishing periodontal support, stresses elevated in the biomechanic system and critical increases were noted for the concentrated nonaxial load on the molar.

Innovative Machine Concepts for 3D Bending of Tubes and Profiles

The paper deals with two new processes and developed special machines for profile and tube bending. The first process is a new roll-based machine for three-dimensional bending of profiles with symmetrical and asymmetrical cross-sections that has been developed. Compared to conventional processes like stretch bending, the advantage of Torque Superposed Spatial (TSS) Bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency especially in small batch production. The second process is the new process of Incremental Tube Forming (ITF). This process is based on a combination of a spinning process and kinematic free form bending of tubular semi-finished products. It is suitable for bending tubes two- and three-dimensionally to arbitrary contours and for manufacturing tailored tubes. The combined spinning and bending process leads to low bending forces with the possibility of a significant springback reduction.

Surface reconstruction for incremental forming

In spite of extensive efforts being made with regard to virtual process optimization technology, the production of prototype parts is still a necessity. With respect to the production of sheet metal parts in low quantities, incremental sheet metal forming (ISMF) is a highly interesting process. ISMF allows the production of complex parts with drastically reduced costs in tooling and machinery compared to conventional processes like deep drawing. However, ISMF, with it’s incremental nature, introduces the need for generating a tool path considering both final geometry and process-induced deviations or constraints. Consequently, for the generation of the tool path a (tool path) surface, with an adequate offset, is necessary. That is why, within the scope of extensive research work at the Institute of Forming Technology and Lightweight Construction (IUL), a special correction module has been developed, determining this offset e.g. depending on the workpiece geometry. This paper presents the algorithm, the application, and the effect on the produced parts. Furthermore, a concept for an extension regarding further constraints like elastic workpiece behavior is presented.