S. I. Oh

Metal forming and the finite-element method

Introduction Metal forming process Analysis and technology in metal forming Plasticity and viscoplasticity Methods of analysis The finite element method (1) The finite element method (2) Plane-strain problems Axisymmetric isothermal forging Steady state processes of extrusion and drawing Sheet metal forming Thermo-viscoplastic analysis Compaction and forging of porous metals Three dimensional problems Preform design in metal forming Solid formulation, comparison of two formulations, and concluding remarks Index.

Finite element analysis of metal forming processes with arbitrarily shaped dies

Abstract A method of discretizing the die boundary conditions is considered for the analysis of metal forming processes by the rigid viscoplastic finite element method. The method is natural to the finite element method and general enough to treat the boundary conditions of arbitrarily shaped dies in a unified way. Solutions of the spike forging process are obtained by using the method. The deformation mechanics of the spike forging process are discussed and the solutions are compared with experiments.

Finite element analysis of plane-strain sheet bending

Abstract Sheet bending between the die and the punch is analyzed as a bulk deformation process under the plane-strain condition by the finite-element method. The two finite-element formulations used for the analysis are the rigid-plastic analysis using the incremental theory and the elastoplastic analysis with large-stain formulation. The two solutions are compared in terms of detailed mechanics during bending. Spring-back and residual stresses upon unloading are obtained by rigid-plastic loading and elastoplastic unloading calculations as well as by the elastoplastic calculations for loading and unloading. The solutions agree with each other very well with minor differences.

Analysis of stretching of sheet metals with hemispherical punch

Abstract The variational formulation applicable to sheet metal forming is derived by considering solution uniqueness and the effect of geometry change. From this variational formulation, a finite element model based on the membrane theory is developed, and the stretching of sheet metals with hemispherical punches is analyzed. Agreement of the computed solutions with experiments was generally good. The examination of the effects of interface friction and of modeling of constitutive relations by computation revealed importance of these parameters in deformation characteristics of punch stretching.

BID: A knowledge-based system to automate blocker design

Abstract In closed-die forging with flash, design of blockers is of critical importance. However, while finite element method-based computer simulation programs are gaining wider acceptance to evaluate completed die designs, actual die design itself still remains predominantly manual because determination of the proper blocker configuration is a very difficult task, an art acquired only through years of experience. Efforts to computerize blocker design so far are primarily based either on interactive graphics, or a set of fixed design procedures which do not take into account design variations due to geometry and/or process variables. This paper describes the development of an automated blocker design system named BID (Blocker Initial-guess Design), developed using the knowledge-based systems approach, which attempts to take these design variations into consideration.

Topology-based geometry representation to support geometric reasoning

The geometry of parts and components is traditionally represented in the computer using some form of coordinate data in three-dimensional Euclidean space. Such a representation is at too low a level of detail to enable deep reasoning based on an understanding of the geometric relationships that exist in the part. It is suggested that an application-specific hierarchic representation of part geometry, where geometric details at lower levels of the hierarchy are embedded within the higher level topological description of the object, provides a powerful framework for enabling such geometric reasoning capabilities. Such a representation can facilitate high-level topological queries, linguistic means for human-machine interaction, development of an intelligent interactive design aid, and an extension to more complex geometries. It can provide a language for expressing the appropriate domain heuristics, thereby leading to a smooth interface between the heuristics and the geometry representation. The authors analyze these issues and illustrate the concepts in the context of blocker design, which is encountered in the process of forging die design. >

Investigation of Defect Formation in a 3-Station Closed Die Forging Operation

Summary The objective of this study was to investigate, via finite element modelling, the effects of process parameters on the development of a lap type defect in forging a ring gear blank. This part was made of AISI 4320 steel and hot forged in three operations: busting, blocking and finishing. Each operation was simulated using the FFM code ALPID to understand the formation of the defect and to design a new blocker shape. The new blocker design was evaluated by simulating the metal flow in the finishing stage and was found to result in sound forgings.

A knowledge based approach to automate forging design

This paper describes a method and a system to automate the design of forging geometries. The method is derived from the principles and the actual practices of forging design used by experienced forging designers. Due to the diversity of the knowledge and problem solving techniques required for forging design, a combination of knowledge-based and algorithmic techniques was employed to implement the AFD (automated forging design) system. Given a set of design specifications, that is, machined part geometry, processing conditions, and special design considerations, the AFD system designs the forging section geometry automatically. Initial results from AFD show that it can be a powerful tool for designing geometries for the rib-web type of forgings.

Use of Electronic Geometry Transfer and FEM Simulation in the Design of Hot Forming Dies for a Gear Blank

Summary The increased utilization of computer aided design and manufacturing (CAD/CAM) in forging technology requires that the design of a machined part to be forged or that of a forging is transferred from one CAD/CAM system to the other. The first system may be located at the design department of the end user and the second system may be located in a forge company or in the forge shop owned by the forging user. Metalflow simulation using the FEM based program ALPID has been applied in the past to forging of various round parts and plane strain sections of non-round forgings. This paper reports the results of an example die design procedure that is expected to be routine in the future. In this study the 2-D section geometries of a gear blank (machined part, finish forging and the suggested blocker geometry) were transferred from Eaton Corporations ANVIL 4000 CAD/CAM system to Battelles Computervision. At Battelle forging load and stresses were estimated and the forging process was simulated using ALPID. The results helped to optimize the design of the finisher and blocker dies as well as the estimation of the stock volume.