G. UZUN, I. KORKUT: THE EFFECTS OF CUTTING CONDITIONS ON THE CUTTING TORQUE ...
275–280
THE EFFECTS OF CUTTING CONDITIONS ON THE CUTTING
TORQUE AND TOOL LIFE IN THE TAPPING PROCESS FOR AISI
304 STAINLESS STEEL
VPLIV POGOJEV REZANJA NA MOMENT PRI REZANJU IN
ZDR@LJIVOST NAVOJNEGA VREZNIKA PRI VREZOVANJU
NOTRANJIH NAVOJEV V NERJAVNO JEKLO AISI 304
Gultekin Uzun, Ihsan Korkut
Gazi University, Faculty of Technology, Manufacturing Engineering, Ankara, Turkey
uzun.gultekin@gazi.edu.tr
Prejem rokopisa – received: 2015-02-22; sprejem za objavo – accepted for publication: 2015-04-09
doi:10.17222/mit.2015.044
In this study tapping operations were carried out using taps of different diameters and with different cutting parameters on AISI
304 austenitic stainless steel. The cutting performances of the taps were determined according to the cutting torques created
during the threading and the depth of cut for each cutting feed (Q). With the aid of the obtained experimental data the solution
suggestions to the problems in the threading operations for AISI 304 steel were developed. As a result it was specified that the
increasing amount of cutting in each pass directly affected the cutting torque. It was determined that there was a tendency to
decrease the cutting torque with the increasing depth of cut for each cutting feed. The best tool-life results for an M5 tap were
obtained at a 5-mm Q value, whereas for M6 taps it was at a 3-mm Q value.
Keywords: tapping, AISI 304, machinability
V {tudiji je bilo izvedeno vrezovanje notranjih navojev z uporabo navojnega vreznika z razli~nimi premeri in razli~nimi nivoji
vrezovalnih parametrov v avstenitnem jeklu AISI 304. Zmogljivosti vrezovanja navojnih vreznikov so bile dolo~ene glede na
moment, ki je nastal med vrezovanjem navojev v globino, za vsako hitrost podajanja pri vrezovanju (Q). S pomo~jo dobljenih
eksperimentalnih podatkov so bili postavljeni predlogi re{itev problemov pri postopku vrezovanja navojev pri jeklu AISI 304.
Pokazalo se je, da pove~anje vrezovanja pri vsakem prehodu neposredno vpliva na moment pri vrezovanju. Ugotovljeno je, da
se zmanj{uje moment vrezovanja s pove~anjem globine reza pri vsakem podajanju pri vrezovanju. Najbolj{a zdr`ljivost orodja
pri M5 vrezniku je bila dose`ena pri vrednosti Q = 5 mm, pri vrezniku M6 pa pri vrednosti Q = 3 mm.
Klju~ne besede: vrezovanje notranjih navojev, AISI 304, strojna obdelava
1 INTRODUCTION
The need for stainless steels in industry is increasing
day by day along with technological developments.
Several types of stainless steels are used, especially in
the manufacturing of the storage tanks, pressure vessels,
heat exchangers and stainless pipes used in the petro-
chemistry, chemistry and food industries. One of the
ways of increasing the strength of stainless steel is to in-
crease the content of the main alloying elements, such as
chrome and nickel, and to decrease the carbon content.
In recent years, rapid improvements in technology have
led to an increase in the expectations from the new me-
thods used in the manufacturing of materials.1,2
The high tensile strength of stainless steels is the
main cause of their poor machinability. The distance
between the yield and rupture points of stainless steels is
more than that of normal carbon steels. Therefore, a
higher cutting force is needed for the machining of stain-
less steels compared to normal carbon steels. The poor
machinability of austenitic stainless steels stems from
their low heat conductivity and high work-hardening
properties.3 In the turning operations of AISI 304 and
AISI 316 austenitic stainless steels, TiC/TiCN/TiN-
coated cutting tools lead to lower cutting forces than
those for TiC/TiCN/Al203-coated cutting tools. In a study
in the literature, it was specified that the cutting speed
did not cause any significant change in the cutting for-
ces, while it affected the surface roughness significantly.4
In the turning process for AISI 304 stainless steel, at
high cutting speeds exceeding the 150 m/min, the tool
wear and the surface-roughness values were decreased
with the increasing of the cutting speed.5
The cutting tools should provide the suitable cutting
parameters required for maximum efficiency. In the
threading process, the selection of the correct tap and the
necessary parameters (feed, revolution, cooling liquid
etc.) are of importance in terms of the threading quality
and the economy of production. Incorrect tap selection
causes increased costs and time loss. In Germany, in the
machine manufacturing industry, the total time spent for
threading is equal to 22 % of the total machining time.6
The operation steps between the cutting tool and the
material during tapping are complicated compared to
other cutting tools. The selection of the correct tap and
the cutting conditions is a necessity for the efficient use
of the tap. In a study, it was emphasized that higher
Materiali in tehnologije / Materials and technology 50 (2016) 2, 275–280 275
UDK 621.7:621.99:669.14.018.8 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(2)275(2016)
forces occurred on the coatings having a lower wear
resistance, in contrast with the higher wear-resistant
coatings. In the tapping, the TiCN-coated taps exhibited
excellent abrasive and adhesive wear resistances.7 It was
specified that during the tapping of deep holes with
small-diameter taps, the reason for frequent tool break-
age was the higher torque during threading.8 The lowest
cutting torque in the tapping operations was obtained
under dry-cutting conditions.9 It was stated that the cutt-
ing liquids containing fluorine formed a lubricant film
layer between the tool and workpiece interface, which
led to an increase in tool life by preventing build-up-
edge formation on the tool and thus the cutting forces
could be decreased by about 18 %.10 The thread pre-
cision of CBN-coated taps exhibited improvements in
the tapping torque and tool life. The tool life and
tapping-torque resistances of CBN-coated taps provided
better results compared to conventionally coated taps.11
In some studies, estimation models were also developed
to predict the torque occurring during the tapping.9–13
As can be seen from the literature, the tapping of
AISI 304 stainless steel is a difficult process owing to its
poor machinability. Tapping is a complicated operation
and this makes it difficult to solve the problems in this
field. There have been limited studies carried out to de-
termine cutting torque, tool life and tool wear regarding
the tapping processes.
2 MATERIALS AND METHOD
Tapping a deep hole in the rigid tapping mode may
be difficult due to chip sticking on the tool. In such
cases, the peck rigid tapping cycle is useful. In this study,
the peck rigid tapping operation was carried out using
the Tapping cycle (G84). The chip breaking command of
G83 and the depth of cut for each cutting feed (Q) in
each pass are entered into G84 and in this way the cutt-
ing tool can break the chip during the tapping operation.
The sample program used is given as follows:
G84 X25. Y25. Z-20. R5. Q5. F203.64 S255.
At the end:
• The effect of different cutting parameters on the
cutting torque,
• The effect of the addition of the Q value to the G84
command on the cutting torque,
• The effects of Q values added to the G84 command
on the tool life were determined.
• The materials and equipment that are used in the tests
are listed below.
2.1 Experimental method
The chemical composition of the AISI 304 austenitic
stainless steel used in the tests is given in Table 1.14
The test samples were prepared as prismatic plates
with a size of 100 mm × 80 mm × 15 mm. A mold was
designed to fix the test samples to the dynamometer. In
the tapping tests, 63 holes were drilled in each sample.
The distribution of holes on the upper surface of the
samples is given in Figure 1. By taking into considera-
tion the hardness distribution around the drilled hole, the
symmetrical placing of holes on the piece was done
carefully.
The cutting forces and moments were measured
using a KISTLER 9272 A type dynamometer. The dyna-
mometer was fixed to the vertical machining center and
thus the three cutting forces (Fx, Fy, Fz) and the moment
(Mz) could be measured simultaneously. A fixing die and
a workpiece were placed on the dynamometer to perform
the cutting tests properly. In the designed system, the
force data is taken from the workpiece by direct contact
between the workpiece and the dynamometer (Figure 1).
The tap types and forms are given in the technical
data in Figure 2.
Drills with diameters of Ø4.2 and Ø5.0 mm were
used for the drilling of the tapping holes. In the tests, for
the purpose of preventing the taps experiencing excess-
ive cutting torques, a tapping cap and a safety tap holder
were used.
The wear and material adhesions on the cutting tools
were examined by using an AM413ZT Polarized Digital
Microscope at 50 × magnification (Figure 3).
In this study, four different cutting speeds (4-6-8-10
m/min) and four different Q (3-5-8-20 mm) values were
used to determine the suitable cutting parameters under
G. UZUN, I. KORKUT: THE EFFECTS OF CUTTING CONDITIONS ON THE CUTTING TORQUE ...
276 Materiali in tehnologije / Materials and technology 50 (2016) 2, 275–280
Figure 1: Drawings of the samples used in the tests and the experi-
mental setup
Slika 1: Risba vzorcev, uporabljenih pri preizkusu in eksperimentalni
sestav
Table 1: Chemical composition of AISI 304 austenitic stainless steel14
Tabela 1: Kemijska sestava avstenitnega nerjavnega jekla AISI 30414
Chemical composition
C Mn Si P max S Cr Ni N
0.07 % 2.00 % 1.00 % 0.045 0.015 % 17.50–19.50 % 8.00–10.50 % 0.11
dry-cutting conditions. Taps with different diameters
were used to evaluate in detail the effects of the cutting
parameters mentioned above on the tapping process. By
considering these parameters and studies in the literature,
appropriate values in the cutting-tool catalogs were taken
into consideration.
2.2 Tapping and measurement of the cutting torque
In the tapping process, a rotating torque (cutting
torque) is produced. The most effective factor in the
tapping process is rotation torque (Figure 4). There are
some factors affecting this, i.e., chip angle, chamfer
length, tap form, work piece material, cutting liquid, etc.
A wider chip angle decreases the cutting torque, but at
the same time decreases the strength of the tap. The main
purpose of using the cutting liquid (emulsion, cutting oil,
etc.) during tapping is to decrease the friction between
the cutting tool and the workpiece. One of the main
reasons for heating and cutting torques as a result of
friction is the chip squeezing in the tap channels. To
prevent this chip squeezing, an appropriate tap form
must be selected in accordance with the workpiece and
hole type, and in this way the chip in the tap channels is
removed. In Figure 4, during the tapping process,
graphical and experimental measurements of the torque
are shown:
1. zone) beginning of cut to full contact of all chamfer
teeth,
2. zone) cutting torque of the tap that is now cutting
with all its chamfer teeth,
3. zone) breaking the machine spindle to a stop,
4. zone) bBeginning reversal of the spindle to contact of
the tooth back with the chip root left standing by the
next cutting tap tooth,
5. zone) shearing off the chip root,
6. zone) squashing back the chip root remains in place
after the shearing off of the chip root (size depending
on the chamfer relief angle of the tap and on the rear
cutting angle of the tap tooth),
7. zone) sliding friction between tap and workpiece.
3 RESULTS AND DISCUSSION
In this study, the type of tap and cutting parameters
were considered as the input, whereas cutting torque
(moment) (Mz), which is very important among the
cutting forces, was considered as the output. The change
of cutting torque (depending on the Q values) that is
created during threading under dry-cutting conditions at
different cutting speeds with the M5 tap is given in Fig-
ure 5.
From Figure 5 it is clear that the increase in the
values of Q led to a decrease in the cutting torque. The
highest cutting-torque values for all cutting speeds were
measured for the Q value of 3 mm. The reason for this is
the formation of a discontinuous cutting operation and
the insufficient heat in the cutting area for the deforma-
tion of the material.3 The second largest cutting-torque
values were obtained for the Q value of 5 mm. For the Q
value of 8 mm, 4 % and 8 % increases were calculated
for the 8 m/min and 10 m/min cutting speeds compared
to the Q value of 5 mm. At the cutting speeds of 4 m/min
G. UZUN, I. KORKUT: THE EFFECTS OF CUTTING CONDITIONS ON THE CUTTING TORQUE ...
Materiali in tehnologije / Materials and technology 50 (2016) 2, 275–280 277
Figure 4: Graphical and experimental measurement of the cutting
torque during tapping16
Slika 4: Grafi~ni prikaz eksperimentalnih meritev momenta pri vrezo-
vanju notranjih navojev16
Tap
Tap shape
(Form DIN
371)
Mouth type Helicalchannel Material
Drill
diameter
(mm)
M 5 × 0.8 Form B(3.5-5 Thread) Oblique Flat
HSS-E
(Normal) 4.2
M 6 × 1.0 Form B(3.5-5 Thread) Oblique Flat
HSS-E
(Normal) 5.0
Tap l1 (mm) l2 (mm) d2 Ø (mm) a (mm) l3 (mm)
M 5 × 0.8 70 13 6 4.9 8
M 6 × 1.0 80 15 6 4.9 8
Figure 2: Technical data of M5 and M6 taps
Slika 2: Tehni~ni podatki za M5 in M6 navojne svedre
Figure 3: Examined zones of the cutting tools through a digital micro-
scope
Slika 3: Preiskovana podro~ja rezalnega orodja, prikazana z
digitalnim mikroskopom
and 6 m/min, the cutting torque decreased in comparison
to that of the Q value of 5 mm. The lowest cutting-torque
values were obtained by increasing the Q value to 20 mm.
This was attributed to the formation of sufficient heat for
cutting in the cutting area due to the lower heat conduc-
tivity of the AISI 304 material.5,15 The continuous cutting
operation provided an easier chip removal. The angular
slope at the cutting mouth makes the chip removal easier.
In this way, there is no chip accumulation and the tap can
make the cutting operation easy. The number of cham-
fers is 4–5 threads and this decreases the moment distri-
buted to the threads, ending up with a lower cutting
moment.9,16,17
The change of cutting torque depending on the Q va-
lues that emerged during threading under dry-cutting
conditions at different cutting speeds with the M6 tap is
given in Figure 6.
For the M6 tap from Figure 6 it is clear that the in-
crease in the values of Q caused a decrease in the cutting
torque. When changing the Q values from 3 mm to 5 mm
an increase was observed, after which the tendency to
decrease continued. The highest cutting-torque values
were obtained with a Q value of 5 mm. The reason for
this was attributed to an inappropriate cutting speed/feed
ratio. In addition, the discontinuous formation of the
cutting operation caused insufficient heat for the material
deformation.11 The second highest cutting-torque values
were seen for the Q values of 3 mm and 8 mm. When Q
was 20 mm the lowest cutting-torque values were ob-
tained. This was explained by the formation of sufficient
heat for cutting in the cutting area due to the lower heat
conductivity of the AISI 304 material.3,5,15 The angular
slope at the mouth of the cutting tool and the continuous
cutting operation made the chip removal easier. Thus, the
tap worked easily and there was no chip pile-up. The
chamfer of the tap along with 4–5 threads led to a de-
crease in the moment, which was distributed to the
threads and caused the cutting moment to have lower
values.18,19
Tool-life tests were carried out at an 8 m/min cutting
speed (average speed). Graphics were drawn by calcul-
ating the distance of the cutting tool as the cutting-tool
life. The distance of the cutting tool was calculated by
multiplying the workpiece thickness by the number of
threaded holes. Tapping processes were repeated until
the breaking of each cutting tool and obtaining the
excessive chip build-up-edge.
Figure 7 shows that in the tool-life tests with the M5
tap the shortest tool life came out to be 60 mm at the
lowest and highest Q values. The best tool life was deter-
mined to be 200 mm for the 5 mm Q value. When the
cutting-tool life for the M5 tap is examined, it is seen
that the tool life decreases with an increasing Q value.
As seen from Figure 8 the chip build-up-edge values
on the cutting tools are the most important factor affect-
ing the tool life.11,13,18 In stainless steels, higher ductility
makes the machinability difficult. In tapping, the mate-
rial build-up-edge to the cutting mouths causes squeez-
ing. As a result of these squeezes there are breakages in
the cutting tools (Figure 8d).
When Figure 7 is examined for the M6 tap, the effect
of Q value is clearly seen. The longest tool life for a
3 mm Q value was 255 mm. The tool life decreased with
G. UZUN, I. KORKUT: THE EFFECTS OF CUTTING CONDITIONS ON THE CUTTING TORQUE ...
278 Materiali in tehnologije / Materials and technology 50 (2016) 2, 275–280
Figure 5: Change of cutting torque (depending on the Q values) at
different cutting speeds with the M5 tap
Slika 5: Spreminjanje momenta pri vrezovanju (odvisno od vrednosti
Q) pri razli~nih hitrostih rezanja z navojnim svedrom M5
Figure 7: Change of tool life for M5 and M6 taps depending on the Q
values
Slika 7: Spreminjanje zdr`ljivosti M5 in M6 navojnega svedra v
odvisnosti od vrednosti Q
Figure 6: Change of cutting torque (depending on the Q values) at
different cutting speeds with the M6 tap
Slika 6: Spreminjanje momenta pri vrezovanju (odvisno od vrednosti
Q), pri razli~nih hitrostih rezanja z navojnim svedrom M6
an increasing Q value. The second best tool life (240
mm) was obtained for a 20 mm Q value.
From Figure 9 it is clear that all of the cutting tools
were broken due to tool squeezing. The main reason for
the breaking of the tools was the build-up-edge of the
chip. The ductile structure of the AISI 304 material pro-
vides the build-up-edge formation at the cutting mouths
of the taps. The filling of cutting mouths makes the cutt-
ing operation difficult and causes breakage of the cutting
tool.11,13
When Figure 7 was examined for the M5 and M6
taps, it was seen that the best tool-life results were ob-
tained with the M6 taps. The effect of Q value was seen
clearly for both the cutting tools. The best tool-life
results for the M5 tap were obtained for a 5 mm Q value,
and for a 3 mm Q with M6. The best results from the
point of view of cutting torques were not obtained at
these values mentioned above, but this did not affect the
tool life significantly. As a result, in threading with
small-scale taps under suitable conditions, it can be said
that the Q value can be used.
4 CONCLUSION
The results obtained from this study are summarized
as below:
• The cutting-torque values for each of the depth of cut
and cutting feed (Q) values have been determined.
This was the case for both cutters. A high cutting
torque was obtained with the lowest and highest Q
values.
• The most important factor affecting the tool life was
the build-up-edge formation on the tools. In the tapp-
ing operation, the build-up-edge chips on the cutting
mouths caused squeezing, which resulted in break-
ages of the cutting tools.
• Tapping operations were carried out using the M5
and M6 taps on the AISI 304 austenitic stainless
steel. It was specified that an increase of the depth of
cut for each cutting feed (Q) directly affected the
cutting torque. The Q value affecting the tool life was
determined.
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280 Materiali in tehnologije / Materials and technology 50 (2016) 2, 275–280