Determination of optimum parameters on delamination in drilling of GFRP composites by Taguchi method
Erol Kilickap*
Department of Mechanical Engineering, Dicle University, 21280 Diyarbakir, Turkey
Received 26 August 2009; accepted 8 June 2010
Drilling is one of the important machining processes in hole making operations. Delamination is a vital problem during any drilling operation. It causes structural integrity reduction and poor assembly tolerance as well as potential for long-term performance deterioration. As a result, drilling of any material requires dimensional stability and interface quality. In this study, glass fibre reinforced plastic composite is selected as experimental material for investigation of cutting parameters (cutting speed, feed rate and tool geometry) affecting delamination in drilling operation. Moreover, the Taguchi method is used to determine optimal cutting parameters for damage-free drilling material. A plan of experiments, based on L’16 Taguchi design method, is performed drilling with cutting parameters in a GFRP composite. The orthogonal array, signal-to- noise (S/N) ratio and analysis of variance (ANOVA) are employed to investigate the optimal drilling parameters of GFRP composites using four different drills. The experimental results demonstrate that the feed rate is the major parameter among the controllable factors that influence the delamination. Additionally, the optimal combinations of the cutting parameters are determined.
Keywords: Taguchi method, Analysis of variance, Design optimization, Drilling, Delamination, Glass fibre reinforced plastic composites
The uses of glass fibre reinforced plastic (GFRP) composites in engineering applications such as automotive, aircraft and manufacture of spaceships and sea vehicles industries have been increased considerably in resent years due to their significant advantages over other materials. They provide high specific strength/stiffness, superior corrosion resistance, light weight construction, low thermal conductivity, high fatigue strength, ability to char and resistance to chemical and microbiological attacks. As a consequence of the widening range of applications of GFRC, the machining of these materials has become a very important subject for research1-3. Drilling is a frequently practiced machining process in industry owing to the need for component assembly in mechanical pieces and structures4. Delamination is a dramatic problem associated with drilling fibre- reinforced composite materials that, in addition to reducing the structural integrity of the material, also results in poor assembly tolerance and has the potential for long-term performance deterioration5. Therefore, a precise drilling needs to be performed to ensure the dimensional stability and interface quality6.
It is necessary to understand the relationship among the various controllable parameters and identify the important parameters that influence the quality of drilling. Mohan et al.7 have performed and analyzed delamination in drilling process of GFRP composite material. Hocheng and Tsao in their study on drilling of composites materials with various drill bits, presents a comprehensive analysis of delamination in use of various drill types, such as saw drill, candle stick drill, core drill and step drill. In their analysis, the delamination is predicted and compared with twist drill8. Davim et al.9 studied the behaviour of two cemented carbide drilling (K10) with distinct geometry (“Stub Length” and “Brad &
Spur”) when drilling glass fibre reinforced plastic (GFRP) manufactured by hand lay-up. Their study’s objective was to establish a correlation between cutting parameters with the specific cutting pressure, thrust force, damage factor and surface roughness.
Moreover, a number of research workers have investigated the drilling of GFRP composite materials using Taguchi design method to investigate the influence to cutting parameters on delamination.
Palanikumar et al.10 studied evaluation of delamination in drilling GFRP composites using HSS twist drill and 4-flute cutter. They developed
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*E-mail: ekilickap@dicle.edu.tr
empirical models to prediction in drilling of GFRP composites using response surface regression. Davim and Reis11 presented an approach using Taguchi’s method and ANOVA to establish a correlation between cutting speed and feed rate with the delamination in a composite laminate. Tsao and Hocheng12 investigated a prediction and evaluation of delamination factor in use of twist drill, candle stick drill and saw drill. The aim of the study was to establish a correlation between feed rate, spindle speed and drill diameter by using Taguchi’s method and analysis of variance. Enemuoh et al.13 presented an approach for development of delamination-free drilling in fibre reinforced plastic. To obtain the optimum cutting parameters, a combination of Taguchi’s experimental analysis and multi-objective optimization criteria was developed. Rao et al.14 presented a comprehensive study of delamination in use of various drill types, three different feed rate and spindle speeds. The influence of drilling parameters on the extension of delamination was examined by conducting the number of experiments as per the design of experiments and analysis of variance techniques of Taguchi. In order to understand the effects of machining parameters in the various machining, a number of researchers used Taguchi techniques15-19.
The objective of this paper is to demonstrate an application of Taguchi parameter design in order to achieve low damage with a particular combination of cutting parameters in drilling of GFRP composite materials.
Experimental Set-up and Machining Conditions
Materials and method
In this study, a GFRP composite manufactured by hand lay-up, with ultimate tensile strength of 240 MPa and modulus of elasticity of 25 GPa, provided by Armaplast Inc (Turkey) was chosen as test materials. The GFRP composites have E-glass fibres and epoxy matrix. The GFRP composite was provided in the size of 400×400×10 mm. The
workpiece material specimens having size of 400×30×10 mm were cut from the plate. The drilling tests were conducted on a SX XHMT vertical drilling machine. Drills used throughout test were all 7 mm diameter with high speed steel (HSS). Drill characteristics are shown in Table 1. All tests were run without coolant at cutting speeds of 5, 10, 15 and 20 m/min and feed rates of 0.1, 0.2, 0.3 and 0.4 mm/rev. The damage around the holes as measured using a microscope, Nikon Epiphot 200 optical microscope, with 10× magnification and 1 µm resolution.
Delamination and calculation of delamination factor
Delamination is recognized as one of the major causes of damage when drilling of GFRP composites. The damage generated associated with drilling glass fibre reinforced composites were observed, both at the entrance and the exit during the drilling.
To determine the delamination factor around the holes, the maximum diameter (Dmax) in the delamination zone was measured (Fig. 1). The value of delamination factor (Fd) can be determined by Eq, (1)9,20:
Table 1—Drill tool types and characteristics
Drill type Description
HSS twist drill, 109 mm long, point angle of 118o
HSS-E TiN coated twist drill, 109mm long, point angle of 135o HSS standard brad point drill, 105 mm long
HSS steel step drill, 105 mm long, step diameter:4mm, step length:10mm, step angle of 90o, point angle of 118o
Fig. 1—The delamination size around the drilled hole
max
drill
Fd D D
= ... (1)
In which, Dmax is the maximum diameter of the delamination zone in mm and Ddrill is diameter of the drill in mm.
Taguchi Method and Design of Experiment
Taguchi method
Traditional experimental design methods could be very complicate and difficult to use. Additionally, these methods could require a large number of experiments, when the number of process parameters increase17,21. In order to minimize the number of tests required, Taguchi experimental design method, a powerful tool for designing high quality system, was developed by Taguchi. This method uses a special design of orthogonal arrays to study the entire parameter space with small number of experiments only.
Taguchi recommends analyzing the mean response for each run in the inner array, and he also suggests analyzing variation using an appropriately chosen signal-to-noise ratio (S/N). These S/N ratios are derived from the quadratic loss function, and three of them (Eqs (2)-(4)) are considered to be standard and widely applicable.
Nominal is the best :
2
10 log 2
S y
N s
= ... (2)
smaller is the best : 2
1
10 log 1 n i i
S y
N n =
∑
= −
... (3)
larger is the best : 2
1
1 1
10 log n
i i
S
N n∑= y
= −
... (4)
where y is the average of observed data, s2 is the variation of y, n is the number of observations, and y is the observed data7,22.
Regardless of category of the performance characteristics, the lower S/N ratio corresponds to a better performance. Therefore, the optimal level of the process parameters is the level with the lowest S/N value. The statistical analysis of the data was performed by analysis of variance (ANOVA) to study the contribution of the factor and interactions and to explore the effects of each process on the observed value19,23,24.
Design of experiment
In this study, two machining parameters were used as control factors and each parameter was designed to
have four levels, denoted 1, 2, 3 and 4 (Table 2). The experimental design was according to an L’16 (4^5) array based on Taguchi method while using the Taguchi orthogonal array would markedly reduce the number of experiments17,19.
A set of experiments designed using the Taguchi method were conducted to investigate the relation between the process parameters and delamination factor. The DESIGN EXPERT 6.07 software was used for regression and graphical analysis of the obtained data.
Results and Discussion
Experimental results
The delamination occurs at entrance and exit during the drilling GFRP composites. Thus, a drilling test was conducted to evaluate the effect of cutting parameters and drill types on the damage at workpiece (entrance and exit sides). After measuring the maximum diameter Dmax in the damage around each hole, the delamination factor (Fd) is determined by using Eq. (1). Tables 3 and 4 show the computed values of the delamination factor at workpiece entrance and exit, respectively.
Analysis of the S/N ratio
In the Taguchi method, S/N ratio is the measure of quality characteristics and deviation from the desired
Table 2—Drilling parameters and levels
Symbol Drilling parameter Level 1 Level 2 Level 3 Level 4
A Cutting speed (m/min) 5 10 15 20
B Feed rate (mm/rev) 0.1 0.2 0.3 0.4
[
Table 3—Experimental design using L’16 orthogonal array and the computed values of Fdentrance
Levels of factors Drill type Trial no.
v f 118o 135o Step Brad
1 1 1 1.20 1.11 1.06 1.06
2 1 2 1.23 1.20 1.15 1.15
3 1 3 1.33 1.33 1.22 1.37
4 1 4 1.44 1.35 1.26 1.43
5 2 1 1.21 1.22 1.06 1.07
6 2 2 1.23 1.44 1.12 1.19
7 2 3 1.42 1.48 1.15 1.37
8 2 4 1.49 1.54 1.27 1.40
9 3 1 1.22 1.27 1.07 1.11
10 3 2 1.27 1.48 1.13 1.25
11 3 3 1.43 1.55 1.20 1.45
12 3 4 1.50 1.56 1.27 1.50
13 4 1 1.24 1.30 1.15 1.12
14 4 2 1.29 1.50 1.15 1.25
15 4 3 1.49 1.52 1.25 1.50
16 4 4 1.52 1.68 1.26 1.56
value. The mean S/N ratio for each level of the cutting parameters and drill types is summarized and called the L’16 experiments is also.
Entrance
After computed values of the delamination factor (Table 3), S/N ratios for each experiment of L’16 (4^5) was calculated by applying the Eq. (3). Table 5 gives the S/N ratio for the workpiece entrance. The objective of using the S/N ratio as a performance measurement is to develop products and processes insensitive to noise factor24. Thus, by utilizing computed values of the delamination factor (Table 3)
and S/N ratios (Table 5), average effect response value (Table 6) and average S/N response ratios (Table 7), respectively, were calculated for each drill types. The S/N ratios response graph for delamination at workpiece entrance is shown in Figs 2 and 3.
Regardless of category of the quality characteristic, a greater S/N ratio corresponds to a better performance. The level of a factor with the highest signal-to-noise ratio is the optimum level24. Therefore, the optimal parameter combination level identified for the present investigation in the drilling process is cutting speed at level 1 (A1) and feed rate at level 1 (B1) for all the drill types(* optimum level). From Fig. 2, it can be observed that raise of cutting speed increases the delamination factor in drilling of GFRP composites by all drill tools. The increase of feed rate increases the delamination factor for all drill tools.
Exit
After calculating values of the delamination factor (Table 4), the next step is to compute the S/N ratios.
S/N ratios for each experiment were calculated by applying the Eq. (3). Table 8 gives the S/N ratio for the workpiece exit. By using computed values of the delamination factor (Table 4) and S/N ratios (Table 8), average effect response value (Table 9) and average S/N response ratios (Table 10), respectively, were calculated for each drill types. The S/N ratios response graph for delamination at workpiece exit is shown in Figs 4 and 5.
Based on the results of the S/N ratio and mean (Figs 4 and 5), the optimal cutting parameters for FdExit were obtained 5 m/min cutting speed (Level 1) and 0.1 mm/rev feed rate (Level 1) for all drills (*Optimum level). It can be observed that decrease of
Table 6—Average effect response table for the Fdentrance
118o 135o Step Brad
Level
v f v f v f v f
1 1.300 1.217 1.247 1.225 1.172 1.085 1.250 1.090 2 1.337 1.255 1.420 1.405 1.150 1.122 1.257 1.210 3 1.355 1.417 1.460 1.470 1.167 1.205 1.327 1.422 4 1.385 1.487 1.500 1.532 1.202 1.265 1.357 1.472 Table 7—Average S/N response table for delamination factor
118o 135o Step Brad
Level
v f v f v f v f
1 -2.257* -1.710* -1.895* -1.750* -1.357-0.697* -1.889* -0.745* 2 -2.495 -1.972 -3.012 -2.917 -1.190* -1.115 -1.946 -1.667 3 -2.610 -2.950 -3.257 -3.300 -1.332 -1.612 -2.398 -3.062 4 -2.722 -3.447 -3.480 -3.680 -1.590 -2.045 -2.593 -3.352
*Optimum level Table 4—Experimental design using L’16 orthogonal array and
the computed values of Fdexit Levels of factors Drill type Trial no.
v f 118o 135o Step Brad
1 1 1 1.35 1.21 1.03 1.25
2 1 2 1.42 1.33 1.07 1.50
3 1 3 1.53 1.35 1.08 1.62
4 1 4 1.62 1.50 1.10 1.75
5 2 1 1.45 1.40 1.05 1.37
6 2 2 1.42 1.35 1.09 1.62
7 2 3 1.70 1.40 1.12 1.75
8 2 4 1.67 1.48 1.18 1.87
9 3 1 1.56 1.50 1.07 1.50
10 3 2 1.55 1.60 1.11 1.62
11 3 3 1.73 1.61 1.14 1.75
12 3 4 1.74 1.68 1.20 2.10
13 4 1 1.56 1.70 1.10 1.56
14 4 2 1.70 1.73 1.12 1.68
15 4 3 1.80 1.78 1.17 1.87
16 4 4 1.87 1.80 1.22 2.10
[
Table 5—S/N response table for the delamination factor at entrance
Levels of factors Drill type Trial no.
v f 118o 135o Step Brad
1 5 0.1 -1.58 -0.91 -0.50 -0.50
2 5 0.2 -1.80 -1.58 -1.21 -1.21
3 5 0.3 -2.48 -2.48 -1.72 -2.73
4 5 0.4 -3.17 -2.61 -2.00 -3.10
5 10 0.1 -1.66 -1.73 -0.50 -0.58 6 10 0.2 -1.80 -3.17 -0.98 -1.51 7 10 0.3 -3.05 -3.40 -1.21 -2.76 8 10 0.4 -3.46 -3.75 -2.07 -2.92 9 15 0.1 -1.76 -2.08 -0.58 -0.90 10 15 0.2 -2.08 -3.40 -1.06 -1.93 11 15 0.3 -3.11 -3.69 -1.58 -3.22 12 15 0.4 -3.52 -3.86 -2.11 -3.52 13 20 0.1 -1.87 -2.28 -1.21 -0.98 14 20 0.2 -2.21 -3.52 -1.21 -2.00 15 20 0.3 -3.17 -3.63 -1.94 -3.52 16 20 0.4 -3.64 -4.50 -2.00 -3.86
cutting speed reduces the delamination factor in drilling of GFRP composites by each drill. The increase of feed rate increases the delamination factor for all drill tools.
Analysis of variance (ANOVA)
Entrance
The relative importance of the cutting parameters with respect to the delamination factor
was investigated to determine more accurately the optimum combinations of the cutting parameters by using ANOVA. The analysis of variance (ANOVA) was applied to study the effect of cutting parameters on the delamination factor. Tables 11-14 give ANOVA results for delamination factor in drilling GFRP composites.
Analysis of variance was carried out for all drill types in Tables 11-14. Feed rate was found to be the major factor affecting the delamination factor at workpiece entrance in all experimental results. It can be observed from the tables that cutting speed also affects delamination factor at workpiece entrance.
From Tables 11-14, values of prob > F less than 0.0500 indicate drilling parameter terms are
Fig. 2—Effect of cutting speed on delamination factor at entrance (οS/N • Mean)
Fig. 3—Effect of feed rate on delamination factor at entrance (οS/N • Mean)
Table 8—S/N response table for the delamination factor at exit Levels of factors Drill type
Trial no.
v f 118o 135o Step Brad
1 5 0.1 -2.61 -1.65 -0.25 -1.94
2 5 0.2 -3.05 -2.48 -0.58 -3.52
3 5 0.3 -3.69 -2.61 -0.66 -4.19
4 5 0.4 -4.19 -3.52 -0.83 -4.86
5 10 0.1 -3.23 -2.92 -0.42 -2.76 6 10 0.2 -3.05 -2.61 -0.75 -4.19 7 10 0.3 -4.61 -2.92 -0.98 -4.86
8 10 0.4 -4.45 3.40 -1.43 -5.43
9 15 0.1 -3.86 -3.52 -0.58 -3.52 10 15 0.2 -3.81 -4.08 -0.90 -4.19 11 15 0.3 -4.76 -4.14 -1.13 -4.86 12 15 0.4 -4.81 -4.51 -1.58 -6.44 13 20 0.1 -3.86 -4.61 -0.82 -3.86 14 20 0.2 -4.61 -4.76 -0.98 -4.50 15 20 0.3 -5.11 -5.01 -1.36 -5.46 16 20 0.4 -5.44 -5.10 -1.27 -6.44
[
Table 9—Average effect response table for the Fdexit
118o 135o Step Brad
Level
v f v f v f v f
1 1.480 1.480 1.347 1.452 1.070 1.062 1.530 1.420 2 1.560 1.522 1.407 1.502 1.110 1.097 1.652 1.605 3 1.645 1.690 1.597 1.535 1.130 1.127 1.742 1.747 4 1.732 1.725 1.752 1.615 1.152 1.175 1.802 1.955
Table 10—Average S/N response table for delamination factor
118o 135o Step Brad
Level
v f v f v f v f
1 -3.385* -3.390 -2.565* -3.175* -0.584* -0.523* -3.627* -3.022* 2 -3.835 -3.360 -2.962 -3.482 -0.898 -0.806 -4.313 -4.101 3 -4.310 -4.540 -4.062 -3.670 -1.053 -1.038 -4.753 -4.842 4 -4.755 -4.722 -4.870 -4.132 -1.225 -1.394 -5.068 -5.796
*Optimum level
Fig. 4—Effect of cutting speed on delamination factor at exit (οS/N • Mean)
Fig. 5—Effect of feed rate on delamination factor at exit (οS/N • Mean)
[
Table 11—Table ANOVA results for the delamination factor for drill point angle 118o
Source of variance SDQa DFb MSc F value p-value Contribution %
Model 0.20 6 0.034 95.05 <0.0001 Significant
Cutting speed 0.012 3 3.842E-003 10.72 0.0025 5.55
Feed rate 0.19 3 0.064 179.37 <0.0001 92.90
Error 3.225E-003 9 3.583E-004 1.55
Total 0.21 15 100.0
S.D. 0.019 C.V. 1.41 R2 0.9845 Pred. R2 0.9509
Mean 1.34 PRESS 0.010 Adj.R2 0.9741 Adeq. Precision 27.354
Table 12—Table ANOVA results for the delamination factor for drill point angle 135o
Source of variance SDQ DF MS F Value Prop>F Contribution %
Model 0.36 6 0.060 44.26 <0.0001 Significant
Cutting speed 0.15 3 0.049 36.74 <0.0001 40.14
Feed rate 0.21 3 0.070 51.78 <0.0001 56.58
Error 0.012 9 1.345E-003 3.28
Total 0.37 15 100.0
S.D. 0.037 C.V. 2.61 R2 0.9672 Pred. R2 0.8964
Mean 1.41 PRESS 0.038 Adj.R2 0.9454 Adeq. Precision 23.084
[
Table 13—Table ANOVA results for the delamination factor for step drill
Source of variance SDQa DFb MSc F Value Prop>F Contribution %
Model 0.091 6 0.015 32.07 <0.0001 Significant
Cutting speed 8.292E-003 3 2.796E-003 5.85 0.0169 8.71
Feed rate 0.083 3 0.028 58.30 <0.0001 86.82
Error 4.252E-003 9 4.724E-004 4.47
Total 0.095 15 100.0
S.D. 0.022 C.V. 1.85 R2 0.9553 Pred. R2 0.8588
Mean 1.18 PRESS 0.013 Adj.R2 0.9255 Adeq. Precision 17.651
important. Therefore, A and B (cutting speed and feed
[
rate) are significant drilling patameter terms for all drills.
Figures 6 and 7 show normal probability plots of the residuals. Figures 6 and 7 revealed that the residuals generally fall on a straight line implying that the errors are distributed normally. This result was also mentioned by various researchers18,25.
Exit
Tables 15-18 show the results of the ANOVA with delamination factor at exit in drilling GFRP composite, for the four drills.
Analysis of variance was carried out for all drill types in Tables 15, 17 and 18. Feed rate was found to
be the major factor affecting the delamination factor at workpiece entrance in all experimental results.
It can be observed from the tables that cutting speed also affects delamination factor at workpiece entrance.
It was noticed that cutting speed was influential parameter affecting the delamination factor at exit 84.71% for drill point 135o in Table 16. It was also observed that feed rate has an effect on delamination factor at workpiece exit 11.55 %.
The values of Prob > F in Tables 15-18 for drilling patameter terms are less than 0.0500 which indicate that drilling patameter terms are noteworthy, which is desirable. Therefore, A and B (cutting speed and feed rate) are significant drilling patameter terms.
Table 14—Table ANOVA results for the delamination factor for brad drill
Source of variance SDQa DFb MSc F Value Prop>F Contribution %
Model 0.42 6 0.070 135.26 <0.0001 Significant
Cutting speed 0.033 3 0.011 21.39 0.0002 7.82
Feed rate 0.39 3 0.13 249.12 <0.0001 91.08
Error 4.664E-003 9 5.182E-004 1.55
Total 0.43 15 100.0
S.D. 0.023 C.V. 1.75 R2 0.9890 Pred. R2 0.9653
Mean 1.30 PRESS 0.015 Adj.R2 0.9817 Adeq. Precision 32.542
Fig. 6—Normal probability plot of residuals for delamination factor at entrance
Fig. 7—Normal probability plot of residuals for delamination factor at exit
Table 15—Table ANOVA results for the delamination factor for drill point angle 118o
Source of variance SDQa DFb MSc F Value Prop>F Contribution %
Model 0.32 6 0.053 28.83 0.32 Significant
Cutting speed 0.14 3 0.047 25.73 0.14 42.42
Feed rate 0.18 3 0.059 31.93 0.18 52.63
Error 0.017 9 1.84E-003 0.017 4.95
Total 0.33 15 0.33 100.0
S.D. 0.043 C.V. 2.67 R2 0.9505 Pred. R2 0.8437
Mean 1.60 PRESS 0.052 Adj.R2 0.9176 Adeq. Precision 17.537
Table 16—Table ANOVA results for the delamination factor for drill point angle 135o
Source of variance SDQ DF MS F Value Prop>F Contribution %
Model 0.47 6 0.078 38.60 <0.0001 Significant
Cutting speed 0.41 3 0.14 67.93 <0.0001 84.71
Feed rate 0.056 3 0.019 9.27 0.0041 11.55
Error 0.018 9 2.008E-003 3.74
Total 0.48 15 100.0
S.D. 0.045 C.V. 2.94 R2 0.9626 Pred. R2 0.8818
Mean 1.53 PRESS 0.057 Adj.R2 0.9377 Adeq. Precision 19.145
From the results of Taguchi method and ANOVA, the best combination levels of the cutting speed and feed rate was obtained at low levels of cutting parameters. The minimum exit delamination is observed at low level of feed rate (0.1 mm/rev) and cutting speed (5 m/min).
Conclusions
The application of Taguchi optimization for investigating the effect of cutting parameters (cutting speed and feed rate) on delamination factor during drilling of GFRP composite has been presented in this paper. The following conclusions can be drawn from this study:
The analysis of experimental results is carried out using Taguchi’s orthogonal array and analysis of variance. The level of the best of the cutting parameters and drill types on the damage is determined by using ANOVA.
Taguchi design can present a systematic procedure that can successfully and efficiently identify the minimum damage in the process control of drilling machines.
The results of ANOVA revealed that feed rate is the dominant cutting parameter, which has greater influence on the delamination factor for four drills.
The feed rate is cutting parameters that have the physical as well as statistical influence on the delamination at entrance and exit in GFRP composite.
The damage increases with both cutting parameters, which means that the composite damage
is bigger for higher cutting speed and feed rate. For achieving minimal delamination on the GFRP composite, always lower feed rates and cutting speeds are preferred.
Based on the S/N, optimal parameters for the minimum entrance damage are the cutting speed at Level 1(5 m/min) and the feed rate at Level 1 (0.1 mm/rev). Similarly, the optimum cutting parameters for minimum exit damage are cutting speed at Level 1(5 m/min) and the feed rate at Level 1 (0.1 mm/rev).
The step drill produces less delamination the GFRP composites (entrance and exit) than three drills, i.e., the delamination factor at entrance and exit is smaller.
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Table 17— Table ANOVA results for the delamination factor for step drill
Source of variance SDQa DFb MSc F Value Prop>F Contribution %
Model 0.042 6 6.998E-003 31.39 <0.0001 Significant
Cutting speed 0.015 3 4.906E-003 22.01 0.0002 33.46
Feed rate 0.027 3 9.090E-003 40.78 <0.0001 61.98
Error 2.006E-003 9 2.229E-004 4.56
Total 0.044 15 100.0
S.D. 0.015 C.V. 1.34 R2 0.9544 Pred. R2 0.8559
Mean 1.12 PRESS 6.341E-003 Adj.R2 0.9240 Adeq. Precision 19.746
[
Table 18—Table ANOVA results for the delamination factor for brad drill
Source of variance SDQa DFb MSc F Value Prop>F Contribution %
Model 1.02 6 0.17 18.65 <0.0001 Significant
Cutting speed 0.25 3 0.083 9.08 0.0044 22.54
Feed rate 0.77 3 026 28.21 <0.0001 70.01
Error 0.082 9 9.126E-003 7.44
Total 1.10 15 100.0
S.D. 0.096 C.V. 5.62 R2 0.9256 Pred. R2 0.7647
Mean 1.70 PRESS 0.26 Adj.R2 0.8759 Adeq. Precision 14.916
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