Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes Page: 99 of 108
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6. Summary and Conclusions
The research and development work for this project was conducted by a team consisting of Lehigh
University and ORNL members. Industrial support was provided by Plymouth extruded products.
The project goals were focused on physical and numerical analysis of the extrusion process for the
production of bimetallic tubes. The project goals were met through a multitool approach to simulate
the extrusion process for bimetallic tubes. The numerical model used was FEM code DEFORM-2D,
which described the material flow during the extrusion process. The FEM simulations, based on
DEFORM-2D were also used to predict the state variables of strain and strain rate that are used to
physically model the bonding and interface development that occurs between the alloys during the co-
The results of multitool approach were validated by preparing bimetallic billets composed of 1020
carbon steel for the outside and 304 stainless steel for the core. The 1020 validation was performed on
two types of billets: (1) the traditional design, where core and outside are the same length and (2) a
new design, where the core is reduced in length by 8-20%. The geometrical results from the FEM
simulations were validated on experimental extrusions by measuring the thickness of the inside tube
as a function of distance. There was good agreement for all conditions tested. In addition to wall
thickness, measurements were also made for the wall thickness eccentricity and no adverse effects
were noted from the new billet design using core shortening.
The FEM simulation of the state variables was validated by detailed investigation of the
microstructure at and on either side of the interface of the co-extruded tubes. The simulation and
microstructural analysis indicated that the majority of carbide precipitation in 304 stainless steel and
decarburization of the carbon steel occurs after extrusion during cool down to room temperature.
The accurate simulation of the microstructure was possible through the FEM modeling to determine
the state variables of strain and strain rate, and thermomechanical means, such as Gleeble, provided
the means to apply the TT profile, including the anticipated cool-down profile, to room temperature
from the extrusion temperature.
The core-shortening billet design method, developed in this project, uses 8-20% less billet material
for core and also reduces scrap in the final product by having to cut shorter lengths because of
extrusion defects as opposed to the traditional billet design. These aspects produce savings in energy
from a combination of (a) the use of less material in initial billet assembly, (b) the use of less energy
in the preheating and extrusion process because of reduced billet mass, and (c) the reduction in the
amount of scrap produced from extrusion defects in the final product.
* Use of the simulation based on FEM code DEFORM-2D was successful in predicting the
geometrical changes of wall thickness as a function of tube length. Based on the validated
simulation method, a new billet design based on core shortening was developed with significant
reduction in scrap produced during the traditional billet design.
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Misiolek, W. Z. & Sikka, V. K. Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes, report, August 10, 2006; United States. (digital.library.unt.edu/ark:/67531/metadc884646/m1/99/: accessed December 10, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.