Where - When -
Hardware - Software
I performed FEM simulation for various metal deformation processes
during my Ph.D. study in Germany, and during my employment in Morgan
Construction Company in USA, etc. The simulation was done mainly in HP UNIX workstations
and Silicon Graphics, etc., under application of an multi-purpose code MARC and its
per- and postprocessor MENTAT. MENTAT helped for mesh generation and result
Programming techniques applied
During my FEM simulation, following programming have
been applied to achieve results of high quality:
- Three dimensional definition
for tools. The tools are a pair of cylinder rolls with grooves milled on
each of the rolls. For a roll to press a round bar, for example, the groove
cross-section shape is almost semi-round.
- Contact surface description.
While using a shell to represent groove surface, there are two faces for
each surface. Various contact situations have to be considered.
- Input work piece geometry. In
most cases, the entry shape of the stock (work piece) is irregular. This is
particularly true in the case of multiple pass rolling, in which the rolled
shape of the previous pass has to be accurately entered as the initial shape of
the current pass.
of FEM technical
parameters. Since the incremental, updated Lagrangian approach was
applied in most of the simulation, time step and (number of) auto load should be
determined correctly. For thermo-mechanical solution, the time step should
be much smaller than that of the mechanical approach (without temperature
calculation). In addition, the time step for shape rolling should be much
smaller than for flat rolling.
of the movement for stock
and tools for each pass. During rolling, the stock is bitten into the roll
gap through friction. However, in FEM simulation, a push action has to be
applied to the stock until about one third contact length has been filled
with the stock. This push speed has to be modeled carefully to establish a
steady rolling process.
of the material data and
boundary conditions. Since the code MARC is only a general-purpose
program, complicated material data and boundary conditions have to be
modeled and programmed (e.g. with Fortran) to feed into the code MARC.
Those material data and boundary conditions include flow stress (as function of strain, strain rate, temperature and
initial grain size, etc.), heat transfer coefficient between the stock and the
tools (depending on cooling speed and surface conditions, etc.),
specific heat (depending on temperature and phase for a given metal grade), friction (as function of
e.g. materials, relative speed, temperature and
pressure), and so on.
- Extra models such as
those on microstructure evolution, to simulate metallurgical process. To predict and
plot microstructure parameters, an interface with FEM predicted parameters
(e.g. strain, train rate and temperature, etc.) has to be established.
Usually, the microstructure evolution process is modeled as function of
material, temperature, strain and strain rate for every stage of the rolling
and cooling. The microstructure model is then entered into the FEM model as user
presentation of rolling technical parameters. Since MARC is not specifically
designed for rolling process, most rolling technical parameters can be
neither directly calculated nor graphically presented. Customized programming
has to be done to allow the the program to display metal forming technical
parameters, such as local spread, local recrystallized percentage and local
grain size. As long as a parameter is defined, the code MARC can display it,
either with graphics or the color contour.
simulation operational issues
of FEM algorithm. In
the simulation, coupled thermal and mechanical model and the incremental,
updated Lagrangian algorithm was used.
for grids, process
parameters, etc. to achieve high accuracy and low computational cost
Describing material behaviors and boundary conditions as accurate as possible.
In the simulation, stock was assumed as elastic-plastic, tools were taken as
rigid. Both heat transfer behavior and friction coefficient were determined
through FEM variation together with measurement.
Accurate determination of the temperature during
the measurement of flow stress. For this purpose, an FEM simulation of the
torsion test was done to determine temperature profile in the torsion samples.
- Use of temperature profile in the entry
stock, instead of an average temperature value. Before the stock enter each roll gap, FEM simulation for cooling
process was perform to determine temperature profile in the stock at the
moment it enter the roll gap.
of established model
through comparing simulated results with experiment data.
- 2D flat rolling
- 3D flat rolling, with isothermal model and then coupled
- 6 passes of angle steel rolling (must be 3D
model), with isothermal model
and then coupled thermo-mechanical model. Special attention was paid to
determine local metal flow during rolling, cross-section after rolling,
and load and power requirements, and to validate the calculated results by
comparing them with corresponding measurement. The error of FEM prediction
are normally < 10% in rolling forces, and constantly < 1% in
geometry. Fig. 1 shows predicted temperature profile in the 1st
pass, with the upper and lower rolls represented with rigid shell.
- Rolling with a specially simplified FEM model, which takes only
0.5% of regular computational time and receives sufficiently accurate
output. The model
attactes great attention from engineers and researchers
- 4 main rolling passes of H-beam rolling, with coupled
thermo-mechanical model Castrolling (combined casting and rolling) with
liquid core, with coupled thermo-mechanical model. Fig. 2 is the geometry
after fourth pass, with predicted equivalent plastic strain.
- Steel rod rolling to roll steel
from round cross-section to oval cross-section, and from oval
cross-section to round. Special attention is paid to predict
microstructure formation process.
Fig. 1: FEM simulated
temperature distribution for the angle steel rolling, 1st pass (click on the
picture to enlarge)
Fig. 2: FEM Simulation for angle steel rolling, 2nd pass (click on the picture
Fig. 3: FEM simulated H-beam after 4th pass, with
equiv. Plastic strain (click on the picture to enlarge)
Figure 4: Wire rod rolling pass over-round, distribution of 3rd comp.
of stress (click on the picture to enlarge)
on FEN Investigation and Experimental Verification