Accuracy, reliability and validity of finite element analysis in metal forming: a user's perspective

Abstract

PurposeThe purpose of this paper is to provide industrial, education and academic users of computer programs a basic overview of finite elements in metal forming that will enable them to recognize the pitfalls of the existing formulations, identify the possible sources of errors and understand the routes for validating their numerical results.Design/methodology/approachThe methodology draws from the fundamentals of the finite elements, plasticity and material science to aspects of computer implementation, modelling, accuracy, reliability and validation. The approach is illustrated and enriched with selected examples obtained from research and industrial metal forming applications.FindingsThe presentation is a step towards diminishing the gap being formed between developers of the finite element computer programs and the users having the know‐how on the metal forming technology. It is shown that there are easy and efficient ways of refreshing and upgrading the knowledge and skills of the users without resorting to complicated theoretical and numerical topics that go beyond their knowledge and most often are lectured out of metal forming context.Originality/valueThe overall content of the paper is enhancement of previous work in the field of sheet and bulk metal forming, and from experience in lecturing these topics to students in graduate and post‐graduate courses and to specialists of metal forming from industry.

Coupled Finite Element Flow Formulation

“…Despite the many contributions in literature, it is becoming more evident that industrial, and to some degree also academic, use of finite element modeling is relying on existing commercial computer programs, where the user naturally has limited access to implementation details and the physical models behind the calculations. This leads to potential pitfalls if the users are not aware of the best use and potential limitations of such programs, as recently discussed by Tekkaya and Martins [20].…”

Meshing and Remeshing

“…However, the simplification is not always feasible as shown by Tekkaya and Martins [2] by means of a metal forming example displaying significant erroneous tool force when assuming the tool rigid instead of elastic. In such situations there is a need to take the elastic deformation of tooling into consideration.…”

“…Node k (2) is discarded as second candidate because it is diagonally opposed to P (that is, line segment drawn from k (2) to P is a diagonal of the quadrilateral face). Node k 2 is selected as candidate 2, and during selection of candidate 3, k (3) is discarded for also being diagonally opposed to P, and k 3 is selected instead.…”

“…Furthermore, standard tetrahedral elements suffer from locking due to the incompressibility constraint in plasticity. Second-order tetrahedral elements overcome this problem but perform poorly in the tool-workpiece contact interfaces, often leading to stability problems in the contact algorithms as stated by Tekkaya and Martins [2]. As a result of this, special tetrahedral elements with interior nodes have been developed for preventing locking.…”

Determination of the flow stress of a magnetorheological fluid under three-dimensional stress states by using a combination of extrusion test and FEM simulation

“…The finite element method, which is the most widespread numerical methodology for the analysis of complex industrial processes, can provide accurate predictions of displacements, stresses, strains, strain rates and temperature distribution throughout the workpiece [13]. In sheet flexible-die forming, accurate determination of the flow stress of pressure-carrying medium is of significant importance.…”