Influence of cutting parameters on the surface quality of machined metal “Applied materials: St70-2 and
Cf45”
H. Bouhabila
Transport Laboratory, Institute of Mechanical Engineering, Faculty of Science and Technology
University-Constantine1
Campus Shaab Ersas, 25000 Constantine, Algeria hamoudi_bouhabila@yahoo.fr
S.Boukebbab, L.Bidi,
Transport Laboratory, Institute of Mechanical Engineering, Faculty of Science and Technology
University-Constantine1
Campus Shaab Ersas, 25000 Constantine, Algeria
Abstract— The quality of the machined parts is generally determined by the errors of shape and degree of finishing of the surface of the items during their machining [1]. The state surface of a machined workpiece plays an important role in the wear resistance, ductility, and fatigue of the piece. This surface state therefore cannot be neglected in the design phase of the work [2].
A machined surface is the result of the geometric and kinematic reproduction of the shape and the trajectory of the tip of the tool on the machined material [5]. In practice, several factors such as the nature of the material being machined, the cutting conditions, the geometry of the tool, the vibration of the machine tool during machining, the influence on chip formation and thus the roughness of the surface produced [7]. This complex system requires explaining the influence of each machining parameter on the state surface of the finished product in order to master the machining process and to meet the requirement of dimensional accuracy of the parts produced. Our work is to investigate variation of the roughness of the machined feature cutting parameters selected when cutting metal parts.
Index Terms— Roughness / State surface / Parameters cutting / Factors influences / Experiences Plan.
I. INTRODUCTION
In a rapidly changing world, the mechanical industries must adapt to new constraints, such as the globalization of markets leading to increased competition [4]. This also applies to the market prototyping and machining room. This rivalry can only be overcome by two forms: a better quality product or a quality / price unbeatable report competition.
Mechanics production market , whatever the mode of machining material removal, the final goal is to obtain a product whose quality of execution will be characterized by a dimensional accuracy of geometric shapes and a degree of cleanliness surfaces directly linked to the notion of roughness.
The state surface is one of the most relevant aspects of machining operations, it represents the final phase of the production cycle. This state of surface determines the degree of
surface finish and dimensional and geometric properties of the machined workpieces. It is therefore necessary to define the influence of different factors involved in the process of cutting in order to choose the appropriate parameters to achieve the desired quality of surfaces [7,8].
II. DESCRIPTION ANDMODELING II.1 Template Gilbert:
According to the theoretical models of Gilbert [10], for different combinations of cutting conditions (f, p, Vc, Rc).
Criteria to consider are roughness Ra, Rz and Rt The goal here is to develop correlations between these criteria and machining parameters in the form of the following equation:
R (Ra, Rz, Rt) = C1. k1f. k2ap. k3Vc. k4Rc (1) Where: C1: is a constant; k1, k2, k3, k4: are exponents that indicate the influence of each parameters (f, ap, Vc, Rc) on the roughness.
II.2 Model developed:
In the case of a dressing operation of a surface on a turn parallel “Fig. 1”, the generator point of the tool moving describes a spiral whose center is on the axis of rotation of the spindle. This spiral shape is due to the continuous linear movement of the cutting tool on the one hand, and the rotation of the workpiece on the other [4].
The shape of the machined surface depends on the geometrical characteristics of the cutting tool edge and advance. In this case, we seek to know the influence factor of each of the cutting parameters on the quality of machined surface (see later developed model).
Since the generator point of the tool describes a spiral whose origin lies on the perimeter of the piece and the center on the axis of the spindle. The distance between the peaks corresponds to the advance per revolution of the tool (f). The furrows are generated by the tool tip. In the case of a rounded
trenchant shall adopt, these furrows are portions of circles of radius (R) to a first approximation and altitude (Rt) “Fig. 2”.
Fig. 1. Description of the machining of the surface.
Fig. 2. Modélisation de l’usinage de la surface [4].
III. EXPERIMENTAL STUDY III.1 Machine Tool:
The machine used “Figure 3”, is a model parallel turn EMCO "MANURHIN KMX" 1.30 m, with a power P = 4.9 kW, machining and reading roughness are performed in the laboratory of IUT of St-Brieuc-Renne1-, France.
Fig. 3. Model Parallel Turn “1.30 m”, with a power “P = 4.9KW”
The workpiece is fixed by means of a mandrel of a rotating side and between the other edge side (mixed mounting), we made several operations with different cutting parameters selected according to the theoretical model developed, the cutting speed [300.600] m / min, the advance speed of tool [0.1, 0.25] mm / rev, the operations made are finishing dressage and roughing 0.5mm the pass “Fig. 4”.
"Mixed mounting" "Mounting on air"
Fig. 4. Operations turning "Roughing and dressage”
III.2 Tools:
The tools allow removing the chip, the tool geometry directly affects machinable shapes of the workpiece. On distinguishes wafers-holder and wafers figure I-5, according to their shapes, the geometry and the material. Wafers were used metal carbide in figure 6, whose beak radius varies from [0.5, 1.5] mm in the following geometric characteristics “Table 1”:
Fig. 5. Wafers-holder
a/ Rc=0.5mm b/ Rc=1 mm c/ Rc=1.5mm Fig. 6. Varied forms wafers
TABLE I. CHARACTERISTIC OF USED WAFERS[18]
III.3 Machined Material:
We chose two pieces of steel “200x50mm”, different nuance "St 70-2 and Cf 45" “Fig. 7”. Which have mechanical properties and chemical composition, performed at the MANOIRE company in France. Shown in “Table II” below:
a / Nuance "St 70-2" b / Nuance "Cf 45"
Fig. 7. Machined workpieces
Brands SECO T&O SANDVIK
Designation KPMT16T300
FM CPMT09T302
FM CCMT06T302 FM
Characteristics
h 11.86 12.0 11.9
h1 12.09 12.14 12.1
f 15.06 16.04 15.8
L1 81.89 80.44 81.0
L2 18.32 14.34 16.1
b 11.90 12.16 12.0
b1 4.11 4.2 4.09
β 55° 75° 80°
γ 11° 11° 7°
A. Chemical Composition
TABLE II. THE CHEMICAL COMPOSITIONS OF THE MATERIAL“CF45”AND
“ST70-2”
B. Mechanical Properties
TABLE III. MECHANICAL PROPERTIES
Standard Designation Cf45 Designation St70-2 Limit elastic
≥ N/mm2 370 370
Tensile strength
N/mm2 620-760 700-850
Elongation % 17 10
Pinch the rupture
% 45 -
Resilience J 28 27
Hardness HRC 55-61 55-61
Hardness HB 207 -
Hardness HV
20kg load 219 208
III.4 Apparatus for measuring the roughness:
For measuring the roughness values R (Ra, Rt, Rp), We used a profilometer "Alti Serf 500" equipped with software for processing 3D image and profile roughness in 2D.
Fig. 8. Profilometer type "Alti Surf 500"
IV. METHOD OF EXPERIENCES PLANS
Usually, technological systems are very complex due to the high number of parameters involved in the evolution of these systems. Accordingly, for studying and especially to obtain an experimental model of the evolution of the system, it is necessary to make many tests. In this context, the volume of required tests is subject to two contradictory trends [13]:
One hand, it is necessary to include all factors with multiple levels to obtain a representative model .
Other hand, it is necessary to minimize the number of attempts to reduce the duration and cost of experimentation.
One of the main applications of experiences plans design is the search for factors having a significant influence on one or many objective functions. Generally among the factors studied, many will be low impact and only a few will play an important role in the variation of these functions Objective. Thus, all the influential factors have been detected and their variations studied with minimal testing. Experiences plans allow on one hand to analyze a large number of parameters and goal hierarchy of parameters depending on the effect caused on the physical value (Functions Objective studied). And secondly to obtain empirical models that relate the parameters to the objective functions [13,14].
IV.1 First experimental Experiences Plans (Nuance St70-2):
The purpose of this Experimental Experiences Plans is to highlight the influence of three (3) selected parameters: Speed Cutting (Vc), the beak radius (Rc) and the advance speed (f), on the roughness for nuance St70-2.
IV.1.1 Influence Factors (FI):
We have awarded two (2) levels in each of the three (3) parameters “Table IV”; The choice of these levels has been defined with the knowledge gained by the laboratory.
TABLE IV. INFLUENCEFACTORS AND LEVELS OF VARIATION
IV.1.2 Objective Functions (FO):
The Roughness is an important value from an industrial point of view; in our study we chose this grandeur as objective function (FO) “Fig. 9”.
Desig
nation Additi elemenon
t
ISO standard value Experimental value
Cf45 St70-2 Cf45 St70-2
Chemical Composition
C % 0,43-0,49 0,5-0,62 0,481 0,473
Mn % 0,5-0,8 0,5-0,8 0,814 0,758
Si % 0,15-0,35 0,17-0,37 0,216 0,254
P % 0,025-
0,035 0,05 0,028 0,011
S % <0,035 0,055 0,024 0,018
Cr % 12.16 12.16 0,194 0,184
Mo % 4.2 4.2 0,016 0,044
Cu % 75° 75° 0,25 0,037
Ni % 11° 11° 0,071 0,043
B % 5 9
V % 0,004 0,003
Sn % 0,009 0,002
Ti % 0,005 0,001
N % 1,007 0,007 43,67 0
Fe % 97,85 98,15
Factors of Influence Domain exploration
Cutting speed, Vc [m.min-1] [300 ; 600]
Beak radius, Rc [mm] [0,5 ; 1,5]
advance Speed, f [mm.rev-1] [0,1 ; 0,25]
a / profile "2D" b / image in "3D"
Fig. 9. Profile roughness Ra (objective function) IV.1.3 Matrix Program (MP):
The Matrix Program retained for experimental conditions (Three (3 Influence) Factors with two (2) levels and a single (1) objective functions) includes eight (8) trials (23trials) [15].
The measured values of the roughness (Ra) are shown in
“table V”:
TABLE V. MATRIX PROGRAM AND MEASURED VALUES OF THE OBJECTIVE FUNCTIONRA
Ra = 4.461 [µm], Ra = 0.591 [µm], Vc = 300[ m.min-1], Vc = 600 [m.min-1],
Rc = 0.5 [mm], Rc= 1.5 [mm], f = 0.15 [mm.rev-1] , f = 0.15 [mm.rev-1]
Fig. 10. Diversity results vis-à-vis the roughness
On ”Figure 9”, we see a great variety of results with respect to the workpiece surface. However, we observe significant changes in roughness.
IV.1.4 Results of parameters affect: :
The results of affects are presented as a histogram of Pareto [16]. “Figure 11”, shows the effects caused by factors and their interactions influence on the objective function (Ra).
“Figure 10”, shows that the roughness is mainly influenced by the beak radius (Rc), and to a lesser degree by the cutting speed (Vc) and the interaction between the cutting speed and radius of the beak. If the beak radius varies from 0.5 to 1.5 [mm], the surface roughness Ra decreases to 2.20 [µm], whereas if the advance speed varies from 0.15 to 0.25 [mm.rev-1] the roughness Ra increases to 0.94 [µm].
Case of nuance "St 70-2"
Fig. 11. Influence of Factors on Roughness
The main influence factors and their interactions are listed in
“Table VI”, in descending order with respect to the effect caused by these factors..
TABLE VI. EFFECTS OFINFLUENCEFACTORS AND THEIR INTERACTIONS ON THE ROUGHNESS
Trial N°
Factors of Influence Functi
on Objecti Codified Values Physical Values ve
Vc Rc f Vc
mm/min Rc
mm F
mm/rev Ra
[µm]
1 -1 -1 -1 300 0,5 0,15 4,461
2 +1 -1 -1 600 0,5 0,15 2,060
3 -1 +1 -1 300 1,5 0,15 0,742
4 +1 +1 -1 600 1,5 0,15 0,590
5 -1 -1 +1 300 0,5 0,25 5,245
6 +1 -1 +1 600 0,5 0,25 2,390
7 -1 +1 +1 300 1,5 0,25 2,338
8 +1 +1 +1 600 1,5 0,25 1,660
Effects of factors
Factors Total effect [µm]
beak radius, Rc - 2,207 Cutting speed, - 1,520
Vc Rc + 1,106
Advance speed, f + 0,945
The variations of roughness depending on the significant influence factors or insignificant can be observed in the
“figures (12, 13)” [11, 12];” Figure 12”, is observed that the beak radius (Rc) and cutting speed (Vc) and their interaction have significant effects on the roughness (in the area explored).
Under these conditions, the effect of the cutting speed on the roughness is influenced by the level on which the roughness is.
For low speeds, the effect of the beak radius on the roughness is more important than for high speeds. In contrast observed in
“Fig. 13”, as the cutting speed (Vc) and advance speed (f) generally have non-significant direct effects on the roughness (in the area explored).
Fig. 12. Vatiriaon of roughness Ra with the Vc and Rc
Fig. 13. Variation of roughness Ra with the Vc and f
From histograms Pareto “Fig. 11”, and the coefficients of the Factors Influence, we can write the law of variation (2) of the roughness (Ra) depending on the cutting parameters (Vc, Rc, f) [11].
Final Equation of influencing factors:
Ra = 2,436- 0,760Vc - 1,103Rc + 0,472f + 0,553 VcRc –
0,122 Vcf +0,194 Rcf (2)
For the roughness, the average value was obtained in
“Table VI”,is 2.436 [µm], the coefficients associated with each influence factor are equal to half of the amplitudes presented in histogram shown in Figure 12, (for exemple, Rc -2.206 / 2 = - 1.103 [µm]).
Finally Vc, Rc and f values entered in the estimating equation are the values calculated by the following expression:
iphys phys i iphys
icod I
X
X X 0
With Xi0phys: Central Level Influence Factor (i) (3) Iiphys: Interval Influence variation of factor (i).
And i = 1 , 2
To validate the experimental model, we compared the values of roughness estimated by the model to the measured roughness
“Fig. 14”. We note that there is a good agreement between the measurements and the estimated values using (Eq. 2).
TABLE VII. COMPARING“MEASURES-ESTIMATES” VALUES OF ROUGHNESSTHEIR
N°
Trial
Ra exp [µm]
Ra mod
[µm] Rate %
1 4,461 4,452 0,22
2 2,06 2,069 -0,44
3 0,742 0,751 -1,21
4 0,59 0,581 1,53
5 5,245 5,254 -0,11
6 2,39 2,381 0,38
7 2,338 2,329 0,47
8 1,66 1,669 -0.54
Fig. 14. Graph “Measures Estimates”of roughness Ra
IV.2 Second Experimental Experiences Plans “Cf 45”:
The objective of this second Experimental Experiences Plans is to highlight the influence of three selected parameters:
cutting speed, the beak radius and advance speed of the roughness for the nuance Cf 45.
IV.2.1 Influence Factors (FI):
We retained the same influence factors with the same areas of exploration, as shown in Table 5, the roughness is the only objective function study “Fig. 9”.
IV.2.2 Matrix Program (MP):
The Matrix Program retained for experimental conditions (Three (3) Influence Factors with two (2) levels and a single objective functions) includes eight (8) trials (23 trials). The measured values of the objective functions are presented in
“Table VIII”.
TABLE VIII. MATRIX PROGRAM AND MEASURED VALUES OF THE OBJECTIVE FUNCTIONRA
Ra = 3.694 [µm], Ra = 2.414 [µm], Vc = 300 [m.min-1], Vc = 300 [m.min-1],
Rc = 0.5 [mm], Rc = 0.5 [mm], f = 0.25 [mm.rev-1], f = 0.15 [mm.rev-1]
Fig. 15. Diversity results vis-à-vis the roughness
On “Figure 15”, we see a great variety of results with respect to the workpiece surface. On all trials and In view of the variation domains of operating parameters cutting explored, all surface states have good quality according to the selected parameters. However, we observe significant changes in roughness.
IV.2.3 Results of parameters affect: :
Figure 16, shows that the roughness is mainly influenced by the beak radius (Rc), to a less degree by the advance speed (f) and the cutting speed. If the beak radius varies from 0.5 to 1.5 [mm], the roughness Ra decreases to 1.46 [µm], whereas if the advance speed varies from 0.15 to 0.2 [mm.rev-1] the roughness Ra increases to 0.86 [µm].
Case of Nuance "Cf45"
Fig. 16. Influence of Factors on Roughness
The main influence factors and their interactions are listed in
“Table IX”, in descending order with respect to the effect caused by these factors.
TABLE IX. EFFECTS OFINFLUENCEFACTORS AND THEIR INTERACTIONS ON THE ROUGHNESS
Trial N°
Factors of Influence Functi
on Objecti Codified Values Physical Values ve
Vc Rc f Vc
mm/min Rc
mm F
mm/rev Ra
[µm]
1 -1 -1 -1 300 0,5 0,15 2,414
2 +1 -1 -1 600 0,5 0,15 1,566
3 -1 +1 -1 300 1,5 0,15 0,815
4 +1 +1 -1 600 1,5 0,15 0,636
5 -1 -1 +1 300 0,5 0,25 3,694
6 +1 -1 +1 600 0,5 0,25 2,39
7 -1 +1 +1 300 1,5 0,25 1,717
8 +1 +1 +1 600 1,5 0,25 1,064 Effects of factors
Factors Total effect [µm]
beak radius, Rc -1,458 Advance speed, f 0,859 Cutting speed, Vc -0,746
Vc Rc 0.330
Vc f -0.233
Rc f - 0.194
The variations of the roughness depending on the influence factors significant or not significant can be observed in Figures (17, 18). On the “Figure 17”, we see that the beak radius (Rc), the advance speed, the cutting speed (Vc) and the interaction between cutting speed (Vc) and the beak radius (Rc) have significant effects on the roughness (in the area explored). In these conditions, the effect of the cutting speed on the roughness is influenced by the level on which the roughness is situated; For low speeds, the effect of the beak radius on the roughness is more important than for great speeds. In contrast observed in Figure 18, that the cutting speed (Vc) and advance speed (f) generally have non-significant direct effects on the roughness (in the area explored).
Fig. 17. Vatiriaon of roughness Ra with the Vc and Rc
Fig. 18. Variation of roughness Ra with the Vc and f
From histograms Pareto “Fig. 16”, and coefficients of Influence Factors, we can write the law of variation of the roughness (Ra) depending on operating parameters (Vc, Rc, f).
Final Equation of influences::
Ra = 1,787- 0,373Vc - 0,729Rc + 0,429f + 0,165VcRc -
0,116Vcf – 0,097Rcf (4)
To validate the experimental model, we compared the values of roughness estimated by the model to the measured roughness Figure 19. We note that there is a good agreement between the measurements and the estimated values with the (eq.4).
TABLE X. COMPARING“MEASURES-ESTIMATES” VALUES OF ROUGHNESS
N°
Trial
Ra exp [µm]
Ra mod
[µm] Rate %
1 2,390 2,388 -0.094
2 1,717 1,715 -0,131
3 1,064 1,066 0,211
4 3,694 3,696 0,061
5 1,566 1,568 0,143
6 0,815 0,817 0,275
7 2,414 2,412 -0,093
8 0,636 0,634 -0,355
Fig. 19. Graph “Measures Estimates”of roughness Ra
V. CONCLUSION
To achieve our goal, is to prove the relationship between the theoretical state of surface and dimensional quality of mechanical machined workpiece, we have developed a mathematical model that permits the virtual reproduction of theoretical profile of surface topography obtained by dressage or Roughing operation. This model is elaborated on a description base of experience plans method. The model we proposed expresses the influence factor of three key parameters and their interaction are the cutting speed, the beak radius and the advance speed of the tool. The overlay of graphics results obtained by the theoretical model allows us to draw the following conclusions:
There is a decreasing relationship between the cutting speed and the theoretical roughness of surface, inversely to the beak radius, and an increasing relationship with the advance
speed of the tool. The interaction between the different cutting parameters allows having good quality surfaces. The influence factors of each parameter and the interaction section is a very important factor in order to determine the actual and precise state the machined surface. The variation of the influence factor of a parameter to another also depends on the matter of the workpiece.
According to the numerical and graphical results obtained by theoretical and experimental study, we can say that the developed mathematical model gives very satisfactory results.
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