Experimental analysis and numerical simulation of the stainless AISI 304 steel friction drilling process/Nerudyjancio plieno AISI 304 frikcinio grezimo proceso eksperimentinis tyrimas ir skaitinis modeliavimas.
Krasauskas, P. ; Kilikevicius, S. ; Cesnavicius, R. 等
1. Introduction
Thread machining is a widely used manufacturing process. However,
sometimes its applicability is complicated due to the insufficient
thickness of a workpiece, for example, during thread tapping in
thin-walled parts.
Therefore, various design decisions in the automotive industry,
furniture manufacturing and other applications, such as speed nuts and
clips, for joining irresponsible parts, fasteners, square weld nuts,
riveted anchors for a reliable fixture of parts are used. Usage of these
fastening methods requires additional elements and technological
operations, so it makes the manufacturing process more labour
expenditure.
For this reason, non-traditional drilling and tread tapping
processes are used. One of them is friction drilling, which is carried
out using a special tungsten carbide tool. Applying this method, the
metal becomes plastic due to significantly increased temperature in the
drilling zone caused by the friction between the tool and the workpiece
and, as a consequence, the tool penetrates the workpiece material. At
that time, the tool forms an additional molten flange (a neck) on the
underneath side of the sheet, which later can be frictionally tapped
using a special tapper.
The main stages of the friction drilling process are presented in
Fig. 1.
[FIGURE 1 OMITTED]
When a rotating punch-type tool is forced into a metal strip, the
heat, generated from the friction between the tool and plate surfaces,
heats the surrounding zone up to 700-900 C. Therefore, the material
becomes plastic and the tool forms a cylindrical hole without removal of
the metal. The excess of the material forms a neck on the lower side of
the hole and a bushing on the upper side of the sheet, by these means
increasing the wall thickness and strength of the hole.
The literature review on the subject showed that experimental
investigations and numerical simulations of the influence of mechanical
and physical properties on the friction drilling process was mainly
carried out on aluminium, magnesium and stainless steel alloys [1-3].
The majority of works dealing with frictional drilling of stainless
steel [4, 5] are focused only on experimental investigations and analyse
the drilling force and moment along with surface roughness of the
drilled holes and tool wear. The review showed that the numerical
simulation of this process is conditioned by a lot of conventionalities
and uncertainties as well as highly depend on various factors such as
material properties, drilling regimes, geometrical parameters of a tool
and a workpiece, etc. [1, 2], therefore a numerical simulation of
friction drilling for each new material is complicated and specific.
Besides, the influence of cutting regimes was investigated in very short
range. Since this method is a recently new metal machining method, the
friction drilling process still is not investigated deep enough.
The purpose of our investigation was to perform drilling
experiments of AISI 304 steel, to obtain drilling parameters, to perform
a simulation of the process and to compare results with the experimental
ones.
2. Materials and experiment technique
Drilling experiment was performed using AISI 304 steel sheet strips
with 1.5 mm in thickness.
The chemical composition of the steel as received is presented in
Table 1.
The experiments were carried out on a CNC milling machine
"DMU-35M" with a "Sinumerik 810D/840D" controller
and "ShopMill" software using a tungsten carbide tool with a
diameter of 5.2 mm. The experimental setup is shown in Fig. 2.
The axial force and torque were measured using a universal
laboratory charge amplifier Kistler type 5018A and a press force sensor
Kistler type 9345B mounted on the CNC table. Measuring ranges of the
sensor: -10 ... 10 kN for force, -25 ... 25 Nm for torque; sensitivity:
[approximately equal to] -3.7 pC/N for force, [approximately equal to]
-200 pC/Nm for torque. The amplifier converts the charge signal from the
piezoelectric pressure sensor into a proportional output voltage.
The variation of the axial drilling force and torque was recorded
to a computer using a "PICO ADC-212" oscilloscope. The
drilling temperature on the upper side of the plate at the contact zone
was measured using a "Fluke574" optical pyrometer (measuring
range: -30 ... 900[degrees]C; accuracy: [+ or -] 0.75% of reading;
response time 250 ms) and recorded to the computer as well.
[FIGURE 2 OMITTED]
3. Experimental results and discussion
During the experiment, spindle rotation speed was set to 3000 rpm
and the drilling feed rate of 100 mm/min was assigned.
The experimental axial force and torque variation is shown in Fig.
3.
[FIGURE 3 OMITTED]
An analysis of the experimental data showed that the axial force,
during the drilling process (from the initial contact until the end of
the hole forming) varies in a very wide range. It was defined, that the
axial force reaches its maximum value when the conical part of the tool
fully penetrates into the strip ("b" step, Fig. 1). When the
sheet is pierced, the axial force drastically decreases ("c"
step), meanwhile the torsion moment increases. The maximum torque is
reached in the "c" step of hole forming when the conical part
of the tool is fully penetrated into the sheet. The force is increasing
again when the tool on the upper sheet surface forms a bushing
("d" step).
The experiment showed that the maximum axial drilling force for a
1.5 thickness sheet of AISI 304 steel is about 1480 N and the maximum
torque is up to 2.5 Nm. The measured temperature on the upper side of
the plate at the contact zone reaches 569[degrees]C.
4. Theoretical background of the friction drilling process
During friction drilling, heat is generated from two sources:
plastic energy dissipation due to the shear deformation and heating due
to the friction in the tool and workpiece contact zone.
The heating from the friction between the tool and the workpiece is
the main heat source and comprises 98-99% of the total heat, therefore
the heat transfer during tool penetration into workpiece is described
[2]:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (1)
where [rho] is the material density; c is the specific heat, T is
the temperature, t is the time, k is the heat conductivity in x, v, and
z coordinates; [[??].sub.f] is the heat generated by the friction
between the tool and the workpiece, it is expressed:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (2)
where [omega] is the angular velocity of the tool and [T.sub.f] is
the friction moment in the contact zone.
For the finite element method simulation the temperature and strain
rate dependent Johnson-Cook model was used [6]. In this case, the flow
stress is expressed:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)
where parameter A is the initial yield strength of the material at
room temperature, B is the hardening modulus; C is the parameter
representing strain rate sensitivity; [[bar.[epsilon]].sub.pl] is the
effective plastic strain; [[??].sub.pl] is the effective plastic strain
rate [[??].sub.0] is the reference strain rate; n is the strain
hardening exponent; m is the parameter which evaluates thermal softening
effect, [theta] is temperature, [[theta].sub.melt] and
[[theta].sub.tran] are material the melting and transition temperatures.
A failure criterion is required to characterize the material
properties degradation due to the tool penetration into the material.
The Johnson-Cook failure model based on the plastic strain was used in
this study. In this model, failure occurs when the parameter D reaches a
value of 1:
D = [integral 1/[[epsilon].sub.f] d [[bar.[epsilon]].sub.pl]. (4)
The equivalent strain to fracture [[epsilon].sub.f] is defined by
[7]:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (5)
where [d.sub.1] to [d.sub.5] are material constants, which can be
determined from experiments, p is the hydrostatic pressure, i.e. the
third of the trace of the Cauchy stress tensor.
5. Finite element model of the friction drilling process
A three-dimensional geometry model of the tool and the workpiece
was created in SolidWorks software and imported in ABAQUS/EXPLICIT
finite element analysis software. The workpiece was created as a disk of
18 mm diameter and 1.5 mm thickness. The 3D model and dimensions of the
tool are presented in Fig. 4.
[FIGURE 4 OMITTED]
One of the primary difficulties in the simulation is the excessive
mesh distortion in the plunge phase, so ABAQUS/EXPLICIT finite element
code based on the adaptive mesh technique, allows automatically
regenerate the mesh when the elements due to large deformation are
distorted. The adaptive meshing technique in ABAQUS/ EXPLICIT creates a
new mesh and remaps the solution parameters from the existing mesh to
the newly created mesh. In this study, the adaptive meshing was carried
out for every three increments of the tool and five mesh sweeps per
adaptive mesh increment was performed. The tool and the workpiece was
meshed using element type C3D8RT, which has 8-node tri-linear
displacement, temperature and reduced integration with hourglass
control. A global element size of 0.3 mm was used to mesh the workpiece.
An element size of 0.15 mm was used in the center of the workpiece where
the tool penetrates the material. 10 layers of elements through the
thickness were generated in the workpiece. The mesh of the workpiece
contained 89710 elements. The mesh is shown in Fig. 5.
In order to save computational time, the mass scaling technique
that modifies the densities of the materials in the model and improves
the computational efficiency was used [8]. In this study, mass scaling
was performed every 10 increments to obtain a stable time increment of
at least 0.0001 s step time.
It was assumed that the tool is rigid and adiabatic, the frictional
contact is described by Coulomb's friction law with the constant
coefficient of friction [mu] and 100% of dissipated energy caused by
friction between the parts was converted to heat. The coefficient of
friction was set to 0.1.
[FIGURE 5 OMITTED]
The boundary conditions (Fig. 5) were set as follow: the outer
surface of the workpiece was fixed in all degree of freedom; the top and
bottom surfaces of the workpiece were under free convection with the
convection coefficient of 30 W/[m.sup.2]K; the ambient air temperature
and the initial temperature of the workpiece were set to 295 K
(22[degrees]C). The tool rotation was set to 3000 rpm and the feed rate
to 100 mm/min.
Material properties and the Johnson-Cook parameters used for the
simulation of the drilling process are presented in Table 2 [9].
The Jonson-Cook material damage parameters used in the simulation
were as follow: [d.sub.1] = 0.69, [d.sub.2] = [d.sub.3] = [d.sub.5] = 0,
[d.sub.4] = 0.0546 [9].
6. Numerical simulation and comparison to the experimental results
The simulation of the friction drilling process was carried out ant
results were obtained.
Figs. 6 and 7 show how the equivalent plastic strain and the Von
Mises stress change during the drilling process. Throughout the whole
process, the maximum value of equivalent plastic strain was 2.39.
The simulation showed that the maximum temperature is reached when
the conical part of the tool penetrates the workpiece. It is up to 1180
K (907[degrees]C) (Fig. 8, c) at that moment. The temperature is up to
969 K (696[degrees]C) in the final stage of the drilling (Fig. 8, d).
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
Figs. 6 and 7 show that the shape of workpiece deformation i.e.
formation of the neck is close to the actual shape obtained by the
experiments.
Dependencies of the axial force (Fig. 9, a) and the torque (Fig. 9,
b) on time were obtained and compared to the experimental ones. The
profiles of the experimental and simulated dependencies were quite
similar.
[FIGURE 8 OMITTED]
[FIGURE 9 OMITTED]
A temperature variation on the upper side of the workpiece at the
contact zone is shown in Fig. 10.
[FIGURE 10 OMITTED]
The surface temperature variation of the simulation was obtained
from the identical position where the surface temperature was measured
in the experiments.
The maximum temperature value on the upper side of the workpiece at
the contact zone obtained by simulation was 589[degrees]C. The
simulation and the experiments both showed very similar results.
7. Conclusions
An experimental analysis and a numerical simulation of a stainless
AISI 304 steel plate were carried out.
The experiment showed that the maximum axial drilling force for a
1.5 thickness sheet of AISI304 steel is about 1480 N and the maximum
torque is up to 2.5 Nm. The measured temperature on the upper side of
the workpiece at the contact zone reaches 569[degrees]C.
The simulation showed that the maximum temperature in the workpiece
is reached when the conical part of the tool penetrates the workpiece.
During that time, it is up to 1180 K (907[degrees]C), and it is up to
969 K (696[degrees]C) in the final stage of the drilling. The variation
of temperature on the upper side of the workpiece at the contact zone
obtained by the simulation and the experiments was very similar. The
comparison of the experimental force and torque variations with the
simulated ones also showed a good agreement.
The obtained results of the presented study lead to a conclusion
that the presumptions taken in the simulation are correct and
realistically define the friction drilling process. The computational
model could be useful for prediction of rational frictional drilling
regimes in order to lower drilling forces and, as a consequence, to
decrease tool wear.
Received August 15, 2014
Accepted November 17, 2014
References
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P. Krasauskas *, S. Kilikevicius **, R. Cesnavicius ***, D. Pacenga
****
* Kaunas University of Technology, Studentu 56, 51424, Kaunas,
Lithuania, E-mail: povilas.krasauskas@ktu.lt
** Kaunas University of Technology, Studentu 56, 51424, Kaunas,
Lithuania, E-mail: sigitas.kilikevicius@ktu.lt
*** Kaunas University of Technology, Studentu 56, 51424, Kaunas,
Lithuania, E-mail: ramunas.cesnavicius@ktu.lt
**** Kaunas University of Technology, Studentu 56, 51424, Kaunas,
Lithuania, E-mail: domas.pacenga@stud.ktu.lt
ref http://dx.doi.Org/ 10.5755/j01.mech.20.6.8664
Table 1
Chemical composition of AISI 304 steel
C, Mn, P, S, Cr, Ni, Si,
% % % % % % %
0.08 2.0 0.0045 0.03 18-20 8-10.5 1.0
Table 2
AISI 304 steel properties and the Johnson-Cook
parameters
Parameter Units Value
Young modulus, E MPa 207.8
Poisson's ratio, v -- 0.3
Density, [rho] N/[m.sup.3] 8000
Melting temperature, [[theta].sub.meit] K 1673
Transition temp, [[theta].sub.tran] K 1000
Specific heat capacity J/(kgK) 452
Thermal expansion, [[alpha].sub.L] [10.sup.-6] 17.8
[K.sup.-1]
Initial yield strength A MPa 280
Hardening modulus B MPa 802.5
Strain hardening exponent n -- 0.622
Thermal softening exponent m -- 1
Strain rate constant C -- 0.0799
Reference strain rate [[??].sub.0] 1/s 1
