PNNL-13501 - Pacific Northwest National Laboratory

Development of Modeling Tools for Joining of Multicomponent Lightweight Structures
Mohammad A. Khaleel, Ken I. Johnson, John E. Deibler, Richard W. Davies
Study Control Number: PN00034/1441
Welded assemblies of hydroformed aluminum structures are critical to developing fuel-efficient vehicles. This project is
developing methods to facilitate the implementation of these lightweight structures.
Project Description
The objective of this project is to develop computational
methods and simulation tools for predicting weld
durability of hydroformed thin-walled aluminum alloy
extrusions and tube assemblies, and to gain a fundamental
understanding of the effects of severe deformations
associated with hydroforming on the weld microstructure,
residual stress state, and distortions in welded assemblies.
The technical work involves developing numerical
procedures to simulate the hydroforming process in a
parallel computing environment and predicting
formability to optimize the process conditions for a given
part geometry and tube or extrusion material.
Computational methods and simulation tools for modeling
welding operations of individual multi-weld joints also
are being developed.
Introduction
The goal of developing more efficient vehicles has
prompted the increased use of lightweight materials.
Hydroforming of aluminum components is a developing
technology for the production of automotive structures.
Complex lightweight assemblies then can be fabricated by
welding or other joining techniques. To date, the
experience of manufacturers with hydroforming is
primarily trial-and-error with little understanding of the
process parameters (pressure, end feed, material behavior)
necessary to achieve geometrically stable parts.
Similarly, the development of welding procedures for
aluminum structures to minimize weld distortions has
been empirical and is complicated by the residual stresses
caused by the severe deformations associated with
hydroforming. In addition, concerns have been raised
concerning weld durability and the effects of material
thinning in long-term fatigue and impact situations. The
goal of this project is to develop modeling tools that can
be used to optimize the process conditions for a given part
geometry and tube or extrusion material and predicting
the distortions of large assemblies composed of
hydroformed components.
Results and Accomplishments
Computational Methods for Optimization of
Hydroforming Process Parameters
The MARC finite element code was used to simulate
expansion of a tube into a conical die. MARC was
chosen for this work because of the ability to develop
user-defined control routines (MSC Software Corporation
2000). During the forming process, several limiting
conditions must be considered in determining the proper
combination of pressure and end-feed. These include the
• axial load required to seal the mandrels in the ends of
the tube
• column buckling of long tubes (high length-todiameter
ratio) during initial sealing and end-feed
• local, axisymmetric wrinkling of shorter tubes (lower
length-to-diameter ratio) during end-feed
• bursting due to eventual unstable, local wall thinning.
Our basic strategy was to apply maximum end-feed
throughout the forming process, which introduces more
material into the die to minimize thinning. Axial
compression also causes yielding and plastic deformation
to occur at lower pressures, which are beneficial from a
forming limit consideration.
A user-subroutine was written to track several parameters
in the finite element solution that indicate the
development of an unsupported wrinkle in the tube.
These include
• localized bending strains that indicate formation of a
wrinkle around the circumference of the tube
Design and Manufacturing Engineering 175