3D finite element modeling of thin-wall machining of aluminum 7075-T6 alloy

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3D finite element modeling of thin-wall machining of aluminum 7075-T6 alloy
Conference Paper · December 2014
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
IIT Guwahati, Assam, India
135-1
3D finite element modeling of thin-wall machining of aluminum
7075-T6 alloy
Gururaj Bolar1, S. N. Joshi2*
1Department of Mechanical Engineering, Indian Institute of Technology
Guwahati, Guwahati, 781 039, E-Mail: [e-mail]
2*Department of Mechanical Engineering, Indian Institute of Technology
Guwahati, Guwahati, 781 039, E-Mail: [e-mail]
Abstract
This paper presents the modeling and simulation of deformation of thin-wall section using finite element method
(FEM). A 3D non-linear numerical model was developed by employing Johnson-Cook material constitutive
model for aluminum 7075-T6 alloy. Johnson-cook damage law was adopted to account for damage initiation
and chip formation during cutting tool penetration into the work material. The deformation of thin-walled part
under the action of cutting forces during milling operation was studied for a set of process conditions and the
preliminary results are discussed.
Keywords: Thin-wall machining, numerical simulation, deformation, aluminum 7075-T6
1 Introduction
Aerospace industry needs monolithic thin-wall
components to manufacture the sections of aircraft
fuselage, wings, aircraft door frame, and engine
blades. Monolithic parts are machined from a single
block of workpiece to their final shape. Monolithic
parts are preferred over the traditional riveted-welded
parts due to the high set-up cost and long time of
production associated with the later [Campa et al.
(2007)]. During the machining of thin-wall parts,
their sections deform under the action of cutting
forces. This leads to geometrical errors which in turn
influence the quality and accuracy of final product.
The geometrical error produced during machining of a
thin-wall part is shown in figure 1. The material
ABCD needs to be cut away ideally. However, under
the action of machining forces, the low rigidity thin-
wall structure deflects, which results in cutting away
of material A’BCD. When the cutter moves away
from the milled surface, the wall elastically recovers,
and material C’CD remains uncut. This was a
common problem observed in the machining of thin-
wall components. This causes the shape of the wall to
be thicker atthe top and thinner atits bottom.
Researchers proposed that the machining errors can
be minimized either by trial and error approach or by
repetitive feeding techniques. However this may lead
in longer production time and higher costs.
Finite element modeling can be used to simulate
machining of thin-wall parts to predict the deflection
and deformation of thin-walls. Literature reports
research on various aspects of thin-wall machining
such as deflection, deformation, machining mechanics
and dynamics, error prediction and control.
Ratchev et al. (2003) (2004) developed a flexible
cutting force model and investigated the deflection of
the low rigidity parts under the action of the
calculated cutting forces. In the similar way, Tang and
Liu (2008) studied the deformations of thin-walled
plate under the action of static end milling forces.
Figure 1 Error in thin-wall machining
Tanase et al. (2010) analyzed the deformation
during milling thin-walled parts. The cutting forces
were determined separately based on the cutting
power measured during experiments.Few attempts
have been reported on 3D finite element modeling of
milling process. Pittalà and Monno (2010) simulated
the face milling of aluminum alloy. Soo et al. (2010)

3D finite element modeling of thin-wall machining of aluminum 7075-T6 alloy
135-2
developed a 3D finite element model for high speed
ball end milling process. Wu and Zhang (2014)
worked on 3D simulation of milling of titanium alloy.
However it has been noted that during these reported
numerical studies, the machining forces are calculated
either based on the cutting force model
developed[Ratchev et al. (2003) (2004)] [Tang and
Liu (2008)] or based on experimental values [Tanase
et al. (2010)].The cutting force values are computed
based on certain assumptions viz.simplification of
milling force as linear load, the normal line being
straight and vertical to the middle plane both before
and after deformations, direct stress on the plane
parallel to the middle plane etc. These assumptions
limit the applications of these models. Reported 3D
models reported were limited to general end milling
operation [Soo et al. (2010)] [Wu and Zhang (2014)]
and face milling [Pittalà and Monno (2010)]. Very
scant work is reported on 3D modeling of deformation
during thin-wall machining process.
In this work, a 3D numerical FEM based model
was developed to simulate the thin-wall machining
process. The model employs the material constitutive
criterion which describesthe material behavior of
aluminum7075-T6 alloy and material damage law
which account for chip formation.Details regarding
model development are presented in the next sections
followed by preliminary results and conclusions.
2 Finite element modeling of thin-wall
machining
By using 2D orthogonal or oblique cutting
models, it is not possible to simulate the interaction of
helical teeth and workpiece and to predict the
workpiece deformation and surface roughness.
Therefore it was felt that a 3D finite element model
would provide a realistic approach to simulate the
thin-wall machining operation. In the present work,
commercial FEM solver ABAQUSTM was used.
2.1 Geometrical modeling, boundary conditions
and mesh configuration
The thin-wall workpiece was modeled as an
inverted cantilever structure as shown in figure 2. The
workpiece was constrained at the bottom, whilst the
other three ends of the thin-walled parts are not
constrained as shown in figure 3. The milling tool was
made to move in in the feed direction and is provided
with rotation motion. The workpiece was meshed with
3D solid element C3D8R. It is 8-node linear brick
element with reduced integration and hourglass
control. The mesh density is kept higher at the cutting
region where tool and workpiece interaction takes
place. It captures accurately the chip formation
process at the cutting region and minimizes the use of
total numbers of elements at the non-interacting
regions. This increases computational efficiency of
the simulation.
Figure 2 Work dimensions and boundary
conditions
The workpiece was discretized into 304640
elements. The cutting tool was considered to be rigid
body and the suitable constraint was applied to it. The
cutting tool was meshed using 4-node, bilinear
quadrilateralR3D4 rigid element. The cutting tool was
discretized into 4325 elements. The helical milling
cutter was assumed to be having sharp cutting edges.
Cutting tool parameters are listed in table 1.
Figure 3 Boundary conditions and meshing