(Microsoft Word - 22-31\343\325\330\335\354)

Al-Khwarizmi

Engineering

Journal

Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, March, (2020)

P. P. 22- 31

The Influence of Process Variables for Milling Sculptured Surfaces

on Surface Roughness

Mustafa Mohammed Abdulrazaq
Department of Production Engineering and Metallurgy / University of Technology

Email: mustafaalneame@yahoo.com

(Received 8 October 2019; accepted 19 January 2020)

https://doi.org/10.22153/kej.2020.01.001

Abstract

Increasing the variety of products that are being designed with sculptured surfaces, efficient machining of these

surfaces has become more important in many manufacturing industries. The objective of the present work is the
investigation of milling parameters for the sculptured surfaces that effecting of surface roughness during machining
of Al-alloy. The machining operation implemented on C-TEK CNC milling machine. The influence of the selected
variables on the chosen characteristics have been accomplished using Taguchi design approach, also ANOVA had
been utilized to evaluate the contributions of each parameter on process outcomes. Three strategies of tool path (Zig,
Zig-Zag and follow periphery), and three levels of spindle speeds (1700, 2200 and 2700 rpm), with three feed rates
(200, 400 and 600 mm/min). The results showed that low surface roughness values produced with the zig-zag
strategy, higher speeds (2700) rpm and lower feed rates (200) mm/min. The analysis of variance approach ANOVA
showed that the strategy of tool paths was the most affecting variables on surface roughness with percentage of
contribution of (42.25 %).

Keywords: Sculptured surface, surface roughness, ANOVA, tool path strategy.

1. Introduction

Milling sculptured part surfaces is different
from milling the regular surface parts, the cause of
that is, it could be traced back to the differences of
sculptured and regular surfaces nature especially
in the freedom of sculptured surface modeling [1].
The main characteristics of machined sculptured
surfaces are the shape and the actual designing
parameters. They strongly depend on the
parameters for the operation of the surface

generation [2]. Milling sculptured surface in
carried out with two stages: rough milling and
finishing. The first stage of cutting used for
removing the large amount of work-piece material
and leaves slightly oversized material of the part
that removed in the next stage. Finishing is the
processes that remove the remaining material

from the roughing of the sculptured surfaces work
piece and gives final dimensions for machining
the desired parts. The result surfaces are produced
with a numbers of scallop heights. Thus that lead
to the surface roughness on the machined parts
and it is important to be investigated for
improving the surface quality for the final product
[3]. Surface roughness of engineering parts is very
important variable, where the quality of any
machined part depending on it. Detailed
assessment is essential for carrying out precisely
and analyzing the micro geometry of surfaces [4].
The roughness of surfaces for the manufactured
part is one of the important characteristics to
insure the quality of the products.

In 2013 Jatin & Sharma [5] investigated the
effecting of a various cutting variables (feed rate,
cutting speeds depth of cuts) in end mills on the

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

Surface Roughness. The calculations have done
by utilizing Taguchi designing method. In
addition to the S/N Ratio, also ANOVA have
illustrated to clarify the Impact of variables
through the result data. Their studies has been
illustrated in milling process for hardened die
steel H-13, using flat-end cutter with four flue of
solid carbide for finishing process. The results
show that surface roughness decreases at the
increasing of cutting speeds.

Simunovic (2013) [6] Studied the influence of
milling parameters (number of revolution, feed
rate and depth of cut) on the surface roughness of
aluminum alloy. A statistical (regression) model
has been developed to predict the surface
roughness by using the methodology of
experimental design. Central composite design is
chosen for fitting response surface. Also,
numerical optimization considering two goals
simultaneously (minimum propagation of error
and minimum roughness) has been performed
throughout the experimental region. It has been
found that feed rate and number of revolutions, as
well as the interaction between the feed rate and
number of revolutions are significant.

Zeljkovic M., et al. (2017) [7]: identify
optimum machining parameters on surface quality
of sculptured parts. The effect of various
machining process parameters such as machining
strategy, feed, depth of cut and spindle speed on
roughness of surfaces through three-axis end-mill
of sculptured parts have been studied by
performing a number of experiments constructed
according to standard Taguchi’s L9 orthogonal
array design matrix. Grey relational analysis
method was used to find the optimal machining
process parameters and analysis of variance was
carried out to find the significance and
contribution of each machining parameter on
performance characteristics.

2. Taguchi Experimental Design Method

Taguchi method is depending on that the
machined parts quality must be computed by the
deviation amount from the required value. He
takes into consideration not only the process
mean, but also by the variation magnitudes or
"noise" created with manipulating inputs
parameters or operation variables. This technique
is depending on two groups; a unique kind of
matrix called "orthogonal array (OA)", the
columns include a number of tests depending on
the no. of levels of controlling parameters, and

(S/N) the signals to noise ratio [8,9]. The
expression ‘signal’ indicating of the required of
the output characteristics values "mean" and the
expression ‘niose’ indicating of unrequired
values. S/N ratios calculation is varying based on
objectives functions, i.e., a characteristics amount.
Designing the method using MINITAB16
program as follow:

3. Variance Analysis

The experimental work results could be
investigated by (ANOVA) variance analysis to
discover the effecting of machining variables (tool
path strategies, spindle speeds and feed rates) on
surface roughness through the entire process. In
the analysis, the ratio between mean square errors
and residual called F- ratio and it utilized for
determining the importance of a parameter. F ratio
correspondent to 95% reliable levels in
calculations of the operation variables. P values
are the report of importance levels of each
parameter (appropriate and inappropriate) [10,
11].

4. Sculptured Surface Representation

In this paper Bezier technique illustrated for
representing the proposed study surface. Using the
sixth order degree with seven control points to the
entire surface for representing the required surface
of the product, and the equation of the proposed
Bezier surfaces is:

BB
WPMUMwuF =),( …(1)

=
b





























−

−−

−−−

0000001

0000066

0000150315

00020600632

001560900615

06306060306

1615321561

]1[
23456

uuuuuuU =

]1[
23456

uuuuuuW =

Where U and W are the vectors of surface
parameters, Mb is the Bezier basis function matrix

STAT DOE Taguchi Create Taguchi

design

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

that represents the Bezier surface and (P) is the
vertex information matrix (control point) with
(49) control points. The Bezier basis functions are
derived from Bernstein polynomial for the
parametric coefficients [12].

The creation of CAD modeling has been
implemented utilizing Bezier technique depend on
the algorithm through selecting the required
control point matrices using MATLAB software,
and transferring the CAD data to UG-NX
software for generating the tool paths and post-
processing that required for implementing the
machining process. The CAD module, where
profile of the curves generating the surfaces is
modeled-using MATLAB and then transferred to
the UGS-NX9-through TXT data-exchanges file
to view the required shape. After the construction
of the Bezier surface converted to a series of
curves using Iso-parametric conversion scheme
Figure (1) shows the proposed surface using
MATLAB software and the part after transferring
the CAD data to UG-NX.

The data of the curves have been represented
and saved in a single matrix of (n x 3), where n is
the number of rows which is equal to n =1+ 1/Δu,
where Δu is the increment of the independent
parameter. Each matrix is saved as (txt) file and
exported to the UG-NX program.

After importing the curves in UG-NX
software, a skinning procedure for these curves
have been implemented to accomplish the final
shape of the surface.

(a)

(b)

Fig. 1. (a) The proposed surface using MATLAB,

(b) Transferring the CAD data to UG-NX software.

5. Tool Path Generation

After the completion of representing CAD
models, it is followed by the tool path generation
for designed part utilizing UG-NX software.
There are several steps had to be taken for the
creation of the actual tool paths, the process has
two phases, first one is creating tool paths for
roughing, where the requirement must be chosen
for this stage, such as (Machining method, tool
Geometries, tools diameter, strategy of tool paths
…etc.). The second phase is creating tool path for
finish machining. In finishing process the side
step value of the tool paths is very small
compared to roughing process three deferent
strategies have been implemented in this work;
Zig, Zig-Zag and follow periphery strategies.
Figure (2) shows the three illustrated types of tool
path strategy.

(a)

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

(b)

(c)

Fig. 2. Deferent strategies of tool paths (a) Zig, (b)

Zig-Zag, (c) Follow periphery.

6. Machines and Tools

The experiments have been conducted on 3-
axis CNC milling machine which is existed in
workshop training Center in University of
technology, with work piece dimension (40 x 40)
mm and thick (40) mm. This operation needs
some accessories and experimental setup, the
main elements that must be used in the milling
machine can be divided into the following
elements:

6.1. Machine of Milling Process

Figure (3) shows the 3-axis CNC machine of
milling operation type (C-TEK) with model
(KM80D) that used in the machining process of
the samples which machined in the present work.

Fig. 3. CNC C-TEK milling machine.

6.2. Cutting Tool

Flat-end milling tools (Ø 10 mm) dia., with
four flutes and flute length equal to (40 mm) of
High-Speed Steel (HSS) utilized for rough milling
phase, and ball-end milling tools (Ø 12 mm) dia.
for finishing. The cutting tools are shown in figure
(4).

Fig. 4. Cutting tools.

6.3. Work Piece

Al-7024 alloy work piece is chosen to be
milled. The chemical composition was tested in
the "Central Organization for Standardization and
Quality Controls". Tables (1) and (2) show the
chemical composing and the mechanical
properties of the work piece respectively.

Flat-end tool D=10

Ball-end tool D=12

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

Table 1,

Chemical composition of Aluminum 7024.

Table 2,

Mechanical properties of Aluminum 7024.

6.4. Designing of Experiments

The designing of experimental tests using
Taguchi approach had a great influence on the
required experimental tests numbers.
Accordingly, the experiments of machining

required an appropriate design. The overall
number of machining experimental tests is (9)
experiments, on the basis of (3) levels and (3)
variables (33). The levels of milling parameters
are listed in Table (3).

Table 3,

Cutting variables.

No Parameter Level 1 Level 2 Level 3

1 Spindle 1700 2200 2700
2 Speed Zig Zig-Zag Follow Periphery
3 Strategy 200 400 600

The final distributional division of the
experimental tests and the level of each

experiment are clarified on table (4) depending on
the Taguchi experimental design method:

Table 4,

Experimental design of work.

No.

Spindle Speed

(r.p.m)
Tool path Strategy

Feed rate

(mm/min)

1 1700 Zig 200

2 1700 Zig-Zag 400

3 1700 Follow Periphery 600

4 2200 Zig 400

5 2200 Zig-Zag 600

6 2200 Follow Periphery 200

7 2700 Zig 600

8 2700 Zig-Zag 200

9 2700 Follow Periphery 400

6.5. Implementation the Machining Process

The milling process is done in two processes;
rough machining and finishing, removing
materials take place on a rapid way as much as
possible in rough machining. In this process, a
higher material removal rate is used for
minimizing the process time. Rough machining in
most cases illustrated in parallel levels of layers
accessing to the exact depths. The quality of the

final surfaces is not reliable, where that layers
removed by subsequent process (finishing
process). Figure (5) shows the samples after
machining.

Si % Fe% Cu % Mn% Mg% Cr% Ni%
0.18 0.41 2.17 0.19 1.57 0.092 0.014
Zn% Ti% Ga % V % Pb % Other AL%
4.91 0.039 0.012 0.009 0.072 0.134 90.21

Ultimate Tensile

Strength (MPa)

Tensile Yield Strength

(MPa)

Elongation to

Failure (%)

Modulus of Elasticity

(GPa)
Hardness Brinell

469 324 20% 73.1 231

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

Fig. 5. Samples after machining.

6.6. Surface Roughness Inspection

Pocket-Surf, the portable gauge of surface
finish (Mahr Federals patented). The gauge is a
pocket sized, which has a suitable economical
price, integral portable device, provides a tracing
for surface roughness measurement through
widely surface types. The instrument probe has a
durable cast-aluminum structure to obtain long
time accurately dependable surface roughness
inspection shown in fig (6-a).

Since the proposed surface in the present work
is sculptured surface, the measurement process of
the surface roughness for such surfaces needs to
make the instrument inclined with suitable angles
which make the tracer parallel to the surface, so a
special holder has been used to fix the instrument,
this holder has the ability to move up and down
with inclined motion of multi angles to ensure
tracing the surface geometry in parallel way as it
illustrated in fig (6-b).

(a)

(b)

Fig. 6. (a) Pocket-surf gauging instrument,

(b) measurement process using the movable

holder.

7. Result and Discussions

Table (5) represents the experimental results of
machining the Al-alloy samples and the surface
roughness according to the orthogonal array

Table 5,

The values of measured roughness

No. Speed Strategy Feed rate
Surface

Roughness

1 1700 Zig 200 1.12

2 1700 Zig-Zag 400 1.06

3 1700
Follow
Periphery

600 1.336

4 2200 Zig 400 1.048

5 2200 Zig-Zag 600 1.096

6 2200
Follow
Periphery

200 1.056

7 2700 Zig 600 1.24

8 2700 Zig-Zag 200 0.776

9 2700
Follow
Periphery

400 1.26

7.1. Effect of Tool Path Strategies and Feed

Rate on Surface Roughness

The figure (7) shows the effecting of tool path
strategy and the feed rate on surface roughness,
the graph clarified that increasing the feed rate
give a high values of the surface roughness and
the reason of that belong to increasing the

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

temperature of cutting and the reason of that
belongs to increasing the friction between the tool
and the metal surface leading to overheat states,
and thus will oxidize the outer surface and
producing a rough surface finish. On the other
hand the better surface finish obtained using Zig-
Ziag tool path strategy among them.

Fig. 7. Effect of the strategy and feed rate on

surface roughness.

7.2. Effect of Spindle Speed and Tool Path

Strategies on Surface Roughness

Figure (8) shows the effects plot of machining
factors (spindle speed and the tool path strategy)
on surface roughness, it can be noted that
increasing the spindle speed values decreasing
the surface roughness, where increasing the
revolutions of the cutter will repeat the passing
of cutter edge on closer regions removing the
numbers of scallop heights. On the other hand
the maximum values of surface roughness
obtained by using the follow periphery strategy,
while the lower values obtained using Zig-Zag
strategy.

Through testing multi tools for implementing
the finishing stage, it found that using ball-end
tool with (12 mm) in diameter for generating tool
paths giving lower values of scallop heights
which leads to less surface roughness in
machined surface in case the diameter doesn't
exceed the lowest value of concavity that
existing in the surface to prevent occurring the
gauging areas. Beside, implementing the follow
periphery strategy for generating the required
tool path for the surfaces will effect on
machining time, where it takes shorter time than

using Zig and Zig-Zag strategies. And the reason
of that belongs to the distribution of the tool
paths, where in this type of strategy the cutter
path tracing the regions of the required geometry
and its not necessary to reach the regions that
doesn’t need to be machined, contrariwise with
other types that may reach to regions doesn’t
need for machining just to complete the straight
line along the path.

Fig. 8. Effect of spindle speed and strategy on

surface roughness.

7.3. Analysis of Variance

The experimental results are analyzed by using
analysis of variance (ANOVA) to determine the
effect of machining parameters on the surface
roughness, surface roughness as the dependent
variable, tool path strategy, spindle speed and feed
rate as independent variables. The F ratio value
of 2.19 for the tool path strategy is greater among
the parameters (see Table 6). Therefore, the most
influential parameter is tool path strategy (42.3 %)
for minimum surface roughness, and the next
significant parameter is feed rate with (41.2%).
Finally, the spindle speed has the smallest
influence with (8.57%). Mean value of surface
roughness Ra and signal to noise ratio are shown
in figures (9 and 10). These figures clarifies the
effect of process parameters on the output
roughness, it can be seen that increasing the feed
rate increasing the roughness, where the best
surface roughness obtained with (200 mm/min).
On the other hand, the lower spindle speeds
increase the surface roughness values, where
heights Ra given with (1700 rpm). And the best
surface roughness obtained using Zig-Zag tool
path strategy.

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

Table 6,

Analysis of Variance for Roughness

2 7 0 02 2 0 01 7 0 0

1 . 2 0

1 . 1 5

1 . 1 0

1 . 0 5

1 . 0 0

Z ig - Z a gZ igF o llo w P e r ip h e r y

6 0 04 0 02 0 0

1 . 2 0

1 . 1 5

1 . 1 0

1 . 0 5

1 . 0 0

S p in d le S p e e d

M
e
a
n
o

f
S

u
rf

a
c
e
R

o
u
g
h
n
e
ss

S t r a t e g y

F e e d r a t e

M a i n E f f e c t s P l o t f o r M e a n s

D a t a M e a n s

Fig. 9. Main effect plot for means of roughness.

2 7 0 02 2 0 01 7 0 0

0 . 0

- 0 . 5

- 1 . 0

- 1 . 5

- 2 . 0

Z ig - Z a gZ igF o llo w P e r ip h e r y

6 0 04 0 02 0 0

0 . 0

- 0 . 5

- 1 . 0

- 1 . 5

- 2 . 0

S p in d le S p e e d

M
e
a
n
o

f
S

N
r

a
ti
o
s

S t r a t e g y

F e e d r a t e

M a i n E f f e c t s P l o t f o r S N r a t i o s

D a t a M e a n s

S ig n a l- t o - n o is e : S m a lle r is b e t t e r

Fig. 10. Main effect plot for means of roughness.

From figure (11) it can be seen that the tool
path strategy the most significant parameter
affecting on surface roughness, this is because
the strategy of motion of tool is responsible for
generating the final surface. Then the feed rate,
while the spindle speed is the less effective
parameter on the process among the other
variables.

Fig. 11. The percentage of contribution of the three

parameters on the process.

Source of variance DOF Sum of squares Variance V F ratio P (%)

Spindle speed 2 0.0181 0.009 0.28 8.57
Strategy 2 0.0894 0.045 2.19 42.3
Feed rate 2 0.038 0.019 2.10 41.2
Error ,e 2 0.118 0.059 8.02
Total 8 2.07 100

Mustafa Mohammed Al-Khwarizmi Engineering Journal, Vol. 16, No. 1, P.P. 22- 31 (2020)

8. Conclusions

To summarize the concluded influences that
deduced from these experiments could be sum up
in:

• The best combination of machining factors for
giving the minimum surface roughness (Ra)
among (tool path strategies, spindle speed and
feed rate) is: (Zig-Zag tool path, 2700 rpm and
200 mm/min) respectively.

• Tool path strategy has the highest effect with
(42.25%) the feed rate and the spindle speed
has the smallest influence on the surface
roughness.

• Using ball-end tool with (12 mm) in diameter
for generating tool paths, will give lower value
of scallop heights which leads to less surface
roughness in machined surface in case the
diameter doesn't exceed the lowest value of
concavity that existing in the surface to prevent
occurring the gauging areas.

• Implementing follow periphery strategy for
generating the required tool path for the
surfaces will effect on machining time, where
it takes shorter time than using Zig and Zig-
Zag strategies.

9. References

[ 1] J. Paulo Davim, "Machining of Complex
Sculptured Surfaces", Department of
Mechanical Engineering University of
Aveiro, Springer-Verlag London Limited,
2012.

[ 2] B. Mikó, J.Beňo, and I. Maňková,
"Experimental Verification of Cusp Heights
when 3D Milling Rounded Surfaces", Acta
Polytechnica Hungarica, vol. 9, no. 6, pp.
101-116, 2012.

[ 3] A. Helleno, K. Schützer, "Contribution for
the Manufacturing of Sculptured Surfaces
with High-Speeds Based on New Methods of
Tool Path Interpolation", 20th International
Congress of Mechanical Engineering,
Gramado-RS, Brazil, November, pp. 15-20,
2009.

[ 4] A. R. Silva, A. X. Morales, L.A. Morales-
Hernandez and F. G. Funes,
"Characterization of the Surface Finish of
Machined Parts Using Artificial Vision and
Hough Transform", National Polytechnic

Institute of Mexico and Autonomous
University of Queretaro Mexico, 2012.

[ 5] K. Jatin and Pankaj Sharma, "Effect of
machining parameters on output
characteristics of CNC milling using Taguchi
optimization technique", International
Journal of Engineering, Business and
Enterprise Applications, vol. 6, pp. 64-67,
2013.

[ 6] K. Simunovic, "Predicting the Surface
Quality of Face Milled Aluminium Alloy
Using a Multiple Regression Model and
Numerical Optimization", Measurement
Science Review, vol. 13, pp. 265–272, 2013.

[ 7] S. Tzeng Yih- fong, "Parameter design
optimization of computerized numerical
control turning tool steel for high
dimensional precision and accuracy",
Material and Design. vol.27, pp. 665-675,
2006.

[ 8] H. Shukry, and A. M. Laith , “Studying
parameters of EDM based micro-cutting
holes using ANOVA”, Eng. &Tech. Journal,
vol.31, no.15, pp. 2876-2887, (2013).

[ 9] K. Wissam, “Feasibility Development of
Incremental Sheet Metal Forming Process
Based on CNC Milling Machine”, PhD.
thesis, University of Technology, 2009.

[ 10] A. S. Bedan, and H. A. Habeeb “An
investigation study of tool geometry in single
point incremental forming (SPIF) and their
effect on residual stresses Using ANOVA
Model”, Al-Khwarizmi Enginering Journal,
vol. 14, no.2, pp. 1-13, 2018.

[ 11] M. Mustafa, S. K. Ghazi and M. Q.
Ibraheem, “Investigation the Influence of
SPIF Parameters on residual stresses for
angular surfaces based on iso-planar tool
path”, Al-Khwarizmi Engineering Journal,
vol. 15, no.2, pp. 50-59, 2018.

[ 12] R. Goldman "Bezier Curves and Surfaces" in
an Integrated Introduction to Computer
Graphics and Geometric Modeling, Taylor
and Francies, pp. 379-384, 2009.

)2020( 22- 31، صفحة 1العدد ، 16دجلة الخوارزمي الهندسية المجلم مصطفى محمد عبد الرزاق

تأثير متغيرات عملية التفريز لالسطح الحرة على الخشونة السطحية

مصطفى محمد عبد الرزاق
الجامعة التكنولوجية / هندسة االنتاج والمعادن قسم

mustafaalneame@yahoo.comEmail:

الخالصة

لتشغيل عينات من االلمنيوم. عملية التشغيل على الخشونة السطحية ان الهدف البحث هو التحقيق في مدى تأثير متغيرات عملية التفريز لالسطح الحرة

تأثير هذه المتغيرات التي تم تحديدها تمت بأستخدام طريقة تاكوشي، كذلك تم استخدام تقنية تحليل العناصر .C-TEKنفذت على ماكنة تفريز مبرمجة نوع
ثالث و )، Follow peripheryو Zig ،Zig-Zagألختبار نسبة مساهمة كل متغير وتأثيره على العملية. ثالث استرتيجيات من مسارات العدد وهي (

). النتائج اظهرت دقيقة ملم /٦٠٠و ٤٠٠، ٢٠٠. اضافة الى ثالث معدالت للتغذية ()دورة بالدقيقة ٢٧٠٠و ٢٢٠٠، ١٧٠٠مستويات من السرع الدورانية (
٢٠٠( معدل تغذية واقل )دورة بالدقيقة ٢٧٠٠ة (واعلى سرعة دوراني Zig-Zagعند استخدام استراتيجية ان اقل قيم للخشونة السطحية تم الحصول عليها

.%) ٤٢٬٢٥بنسبة مساهمة وصلت الى (.ان طريقة تحليل العناصر اظهرت ان استرتيجيات مسار العدد هي االكثر تأثيرا من باقي المتغيرات ملم/دقيقة)