L. M. Alves

Single-stage nosing of thin-walled tubes into hollow spheres using a die

In recent work, the present authors reported a thorough analysis of the mechanics of nosing thin-walled tubes into hollow spheres using a die and proposed enhancement of the formability limits of the process by means of preforming stages and preliminary tube-end preparation schemes. In an effort to improve the surface quality and dimensional accuracy and to extend further the formability of thin-walled hollow spheres, the present authors now report a new single-stage process based on the utilization of an innovative tool design consisting of two sharp-edge dies and a floating ring. The overall performance of the new proposed process is evaluated by means of numerical simulations based on the finite element method and experimentation on industrial aluminium alloy 6060 tubes under laboratory-controlled conditions.

On the formability, geometrical accuracy, and surface quality of sheet metal parts produced by SPIF

Conventional sheet metal forming processes are not suitable for flexible small-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles, development and production lead times. In fact, the present need for flexible sheet metal forming techniques requires the development of innovative technological solutions that are capable of reducing the fixed and capital costs of sheet metal forming to a level where small-batch production becomes economically feasible. Single point incremental forming (SPIF) is a new sheet metal forming process with a high potential economic payoff for rapid prototyping applications and for small quantity production. In general terms a typical SPIF set-up makes use of a small number of low cost active tools components; (i) a blankholder, (ii) a backing plate and (iii) a single point forming tool. The tool path is generated in a CNC machining center and during the process there is no backup die supporting the back surface of the sheet. Despite the contributions of many researchers on the development of industrial applications and better characterization of the forming limits of the process, several key topics related to the mechanics of deformation, likely mode of failure, geometric accuracy and surface quality of the formed parts remain little understood and scarcely systematized. This paper attempts to provide new contributions about the abovementioned issues by means of a comprehensive experimental investigation performed under laboratory controlled conditions.

Coupled Finite Element Flow Formulation

This chapter presents a coupled finite element approach for thermo-mechanical modeling of metal forming and for electro-thermo-mechanical modeling of resistance welding. The finite element approach is based on the flow formulation which was described in Chapter 2 as one of the implicit quasi-static formulations.

Finite Element Formulations

The governing equations for problems solved by the finite element method are typically formulated by partial differential equations in their original form. These are rewritten into a weak form, such that domain integration can be utilized to satisfy the governing equations in an average sense.

Material, Friction and Contact Characterization

Awareness and understanding of the basic procedures to determine the flow stress, the frictional response and the electric and thermal contact resistances under different conditions of strain-rate and temperature are fundamental for improving the quality of data to be inserted in finite element computer programs. Because accuracy and reliability of numerical simulations are critically dependent on input data, the following sections will provide a brief overview of the most widespread experimental techniques that are utilized for material, friction and contact characterization.

Innovative tube forming and joining technologies

This paper introduces new manufacturing technologies for shaping tubes into metallic liners for composite overwrapped pressure vessels (COPVs) that are commonly utilized in aerospace applications and for joining tubes in a wide range of applications comprising plumbing, air conditioned, refrigeration, process piping and lightweight structures, among others. The presentation gives emphasis to the tooling systems and to the numerical modeling and experimentation with the objective of describing the technical details and demonstrating the flexibility, versatility and cost effectiveness of the proposed technologies.

Parallelization of Equation Solvers

When solving large finite element problems, solution time becomes a factor which cannot be ignored. It is among the concerns when considering modeling in three dimensions instead of two dimensions. Different approaches are available to reduce the computational cost.

Meshing and Remeshing

A significant amount of time in finite element modeling of manufacturing processes is spent in mesh generation. Setting up three-dimensional meshes is a cumbersome task due to complexity of the processes and the involved geometries. Moreover, additional meshing challenges often appear due to the fact that manufacturing processes based on large plastic deformations present progressive mesh distortion (or degeneracy), potential interference between mesh and contour of the tools and possible contact of the mesh with itself. This poses the need for robust, automatic, mesh generation and regeneration (remeshing) procedures in order to ensure that complex processes are modeled from the beginning to the end with high levels of accuracy both in terms of geometry and distribution of field variables.

Cold end forming of thin-walled PVC tubes using a die

The aim of this paper is to evaluate the applicability of tube end-forming processes, currently applied in metals, to polyvinyl chloride (PVC). The presentation is focused on four different processes (expansion, reduction, internal and external inversion) and its contents are expected to provide new fundamental level of knowledge and understanding about the mechanics of deformation and the expected modes of deformation of PVC tubes. The formability limits are defined in terms of the major operating variables with the purpose of predicting the behaviour of PVC tubes across a wide range of working conditions. The experimental findings are interpreted in the light of an innovative extension of the finite element flow formulation that is capable of modelling cold plastic deformation of pressure-sensitive materials under a non-associated flow rule. Special emphasis is placed on the analysis of load-displacement, local buckling, ductile damage and crazing. The overall results confirm that end-forming of thin-walled PVC tubes at room temperature have potential for the manufacture of custom and specific shapes.