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Study of milling on [Al.sub.2][O.sub.3] ceramic/GFRP component using sintering diamond tools.

1. Introduction

Lightweight materials have been extensively used in modern armours in recent years. One of those is [Al.sub.2][O.sub.3] ceramic/GFRP component, which plays an important role in improving the bulletproof ability and reducing armour vehicle weight for its excellent physical and mechanical properties such as high hardness, high compressive strength and low density; as a result, many of the current and foreseeable applications for [Al.sub.2][O.sub.3] ceramic/GFRP component can be seen in modern armours and aerospace.

However, machining difficulties and high costs have been associated with the uses. After the composite components are manufactured, secondary machining processes such as milling are required for the purpose of joining and assembling, which is very difficult due to the different properties of the material, such as high hardness and low fracture toughness of ceramic and high hardness and easy laying of the GFRP. Milling is often a manufacturing process to machine irregular holes of different sizes and shapes, such as square holes and hexagonal holes to meet the assembly requirements. However, rare articles are found on studying milling technology on components made of ceramic and GFRP; more articles focus on processing of single material. For instance, Basile et al. (2016) studied the processing of a glass ceramic surface by selective focused beam laser treatment. Zhang et al. (2002) analysed a drilling tool's rotation with fixed abrasives and the machining mechanism of drilling based on the fracture mechanics concept, and a new theoretical model of the material removal rate is proposed. Huang and Liu (2003) studied the machining characteristics and surface integrity of advanced ceramics including alumina, aluminatitania and yttria partially stabilised tetragonal zirconia. Abdul Majeeda et al. (2008) studied the machinability of [Al.sub.2][O.sub.3]/[LaPO.sub.4] ceramic composites using ultrasonic machining methods. Rubio et al. (2013) have done drilling tests using three kinds of cemented carbide drill on glass fibre and analysed the influence of tool parameters. Lazar and Xirouchakis (2011) carried out drilling tests on carbon fibre- and glass fibre-reinforced composite, which studied the distribution of the load and the determination process parameters. Jin, Yuan, and Xiao (2004) studied the drilling characteristics using brazing of diamond drill bit on [Al.sub.2][O.sub.3] ceramics. Li, Chen, and Huang (2006) machined the alumina ceramics using brazing craft production diamond drill bit. Klocke, Verlemann, and Schippers (1999) studied various process strategies for high speed grinding of aluminium oxide and silicon-infiltrated silicon carbide at high removal rates. Ferreira, Coppini, and Miranda (1999); Ferreira, Coppini, and Levy Neto (2011) studied the effects of cutting speed, feed rate, cutting depth and other parameters on tool wear, machining quality and cutting force using carbide and CBN cutting tools. Davim, Reisa, and Antonio (2004) studied the relationship between process parameters and cutting force and surface quality. Slamani, Gauthier, and Chatelain (2015) studied the effect of process parameters on cutting force. Pecat, Rentsch, and Brinksmeier (2012) studied the influence of milling process parameters on the surface integrity of CFRP. And in these works: (Kaczmar, Pietrzak, and Wlosinski 2000; Jarzabek, Chmielewski, and Wojciechowski 2015; Kaczmar, Naplocha, and Morgiel 2014; Chmielewski et al. 2014; Anup Shetty, Rajesh Mathivanan, and Mahesh 2016), there are no detailed investigations of the effects of milling conditions on the milling efficiency and milling force has been reported.

Based on these, milling technology on [Al.sub.2][O.sub.3] ceramic/GFRP component is investigated, which could solve the problem of difficulty in material cutting, thereby improving the milling efficiency and obtaining regular law when milling composite component. This investigation is helpful to improve the application of ceramic/GFRP component in the field of armour protection, and promote the lightweight of special vehicles.

2. Experimental design

2.1. Diamond tool

The diamond tool is mainly made of a diamond layer and a steel matrix, which is shown in Figure 1. Diamond layer is manufactured by compression derived from shrinkage upon sintering of a metal powder and diamond particles; steel matrix (45 steel, tempered to 45HRC hardness) is linked to the diamond layer by welding. According to the test results of references (Zheng, Yuan, and Li 2007; Gao et al. 2011), on sintering diamond tools, this paper uses SMD40 type diamond (supplier: Nanjing Lide grinding tools factory) and the sintering diamond tool manufacturing parameters are shown in Table 1. The dimensions of the diamond tool in this experiment are 20 mm in outside diameter, 8 mm in working layer height, 3 mm in wall thickness and grit size is 50/60 US mesh (300-250 [micro]m).

2.2. Composite component

The component is made up of three parts from top to bottom, namely fibreglass layer (2.0 mm), alumina ceramic (10.0 mm) and fibreglass layer (12.0 mm) and it has dimensions of 50 mm x 50 mm x 24 mm, which are shown in Figure 2.

[Al.sub.2][O.sub.3] (99.5 wt%) ceramic used in this study is produced by hot isostatic pressing; alumina powder size is 0.35-0.75 [micro]m and its mechanical properties are listed in Table 2. GFRP is stacked by a fibreglass mono-layer plate, which is bound by thermosetting epoxy resin among each layer; the volume fraction of the fibre is maintained at 60% and its mechanical properties are listed in Table 3.

2.3. Experimental conditions

Milling experiments were performed on a milling machine whose power of the spindle drive motor was 750 W with available rotating speeds of 1890-3200 r/min. The way of feed processing was constant pressure and feed force was 605-835 N, which were achieved by hanging specific weights on the driving wheel of the machine. Ordinary water coolant was used during the experiment to reduce milling cutter surface temperature; water pressure was 0.3 MPa, and flow rate was 120 cc/s.

Milling force experiments were carried out on the vertical machining center ZX6350A, whose spindle speed range was 20-8000 r/min and feed speed(X, Y, Z) was 1-15000 mm/min, which are shown in Figure 3. The milling force data were collected and recorded by a data acquisition system, which is shown in Figure 4. The schematic diagram of milling force measurement system is shown in Figure 5, which mainly consists of YDX-9702 piezoelectric sensor (the measurement range of X, Y and Z is [+ or -]3000 N, the sensitivity of Z is [+ or -]42 pc/kgf, the sensitivity of X, Y is [+ or -]80 pc/kgf and the size of resolution is [+ or -]0.001 kgf), YE5850 charge amplifier, A/D converters, data acquisition board, computer and virtual instruments.

2.4. Experimental steps

Since [Al.sub.2][O.sub.3] ceramic has a dominant influence on processing efficiency when compared with GFRP when milling composite component; therefore, the milling time of ceramic was used to evaluate the milling efficiency on composite component. First, the influencing rules of feed force, spindle speed and milling depth on milling efficiency were investigated in the milling experiments, and an orthogonal test was designed to further analyse the influence on milling efficiency; the GFRP layer of 2 mm should be milled off in advance; milling length of 50 mm and the milling time were saved under different process parameters for analysing the milling efficiency. Then, the milling force experiments were carried out using nine milling cutters under the different spindle speeds, feed speeds and milling depths; another orthogonal experiment was designed to further analyse the effect of process factors on milling force; the experimental data were acquired by a milling force measurement system. Finally, single-factor tests were conducted to find out empirical formula of milling force, which was used to further investigate the influence of processing factors on milling force.

3. Experimental results and discussion

3.1. The influence of feed force on milling efficiency

Figure 6 shows the milling time under different feed forces when spindle speed is 2600 r/min and milling depth is 5 mm.

It is clear that the milling time decreases with the increase in feed force, i.e. the milling efficiency is enhanced. The reason is that the milling depth of each cutting abrasive becomes greater with a higher feed force, which increases the volume of the removed material per unit time, so the milling efficiency increases. However, the milling efficiency is decreased when the feed force rises up to 770 N, which might be caused by the permitted feed speed of [Al.sub.2][O.sub.3] being very small; the difficulty in crushing the material increased when the diamond cutting depth increased with a higher feed force. Besides, the efficiency is also influenced by the spindle torque; when feed force is too high, the machine tool power provided to the main shaft torque is insufficient, thus the milling efficiency declined. Figure 6 shows the limitation of 770 N for feed force.

3.2. The influence of spindle speed on milling efficiency

Figure 7 shows the milling efficiency by varying the spindle speed under the feed force of 770 N and the milling depth is 5 mm.

It can be seen from the diagram, when the spindle speed is below 2600 r/min, that the efficiency enhanced with the increase in spindle speed because of the increase in volume of the removed material per unit time per unit grain; but when the speed reaches 3200 r/min, the efficiency decreases. There are major two reasons: first, with the spindle speed increasing, tangential velocity of the working diamond in the worn surface increases, then the impact load acting on the diamonds increases, which leads to the diamond's early pulling out or fragmentation; second, the increasing tangential velocity reduces the diamond's cutting depth in unit time when the feed force is being constant, which gives rise to the cutting distance of each diamond; furthermore, the temperature of the milling zone also increases which may cause diamond graphitising easily, then the diamond tends to wear flat. Figure 7 shows that the highest spindle speed should not exceed 2600 r/min.

3.3. The influence of milling depth on milling efficiency

Figure 8 shows the milling efficiency by varying milling depth under the condition of spindle speed is 2600 r/m and feed force is 770 N.

It can be found that milling time is the shortest when the milling depth is 3 mm, which implies the milling efficiency is highest. The milling efficiency declines with the increase in the milling depth; the reason is that the load acting on the single diamond abrasive decreases with the increase in contact area between materials and tools, so the volume of the removed material declines, which leads to the decrease in milling efficiency.

Additionally, the milling efficiency declines more significantly when the range of milling depth is from 5 to 7 mm. The reason is that greater milling depth results in greatly declined load born on single diamond abrasive, which results in the milling depth of each cutting abrasive to become smaller.

3.4. Orthogonal experiment

3.4.1. Experimental design

In order to further analyse the influence of milling parameters on milling efficiency, an orthogonal test with three factors and three levels was designed. The influences of milling parameters on milling efficiency was studied by range analysis. The levels and factors are listed in the Table 4.

3.4.2. The results and analysis of orthogonal experiment

The results of orthogonal experiment are listed in Table 5; range analysis results are shown in Table 6, among them: [K.sub.i] (i = 1, 2, 3) is the sum of the experimental results of 1, 2, 3 levels at various factors; [k.sub.i] (i = 1, 2, 3) is the average value of the sum of the experimental results of 1, 2, 3 levels at various factors; R is range.

The range analysis shows that [R.sub.A] > [R.sub.C] > [R.sub.B]; therefore, the influencing capacity order of each factor is feed force > milling depth > spindle speed, feed force has the greatest influence on milling efficiency, milling depth has a second impact and the spindle speed has the least influence on milling efficiency. Optimal level can be selected to optimise the milling efficiency according to the average values of the sum of the experimental results at various factors, [A.sub.3] (770 N) is the optimal level of feed force because of [k.sub.A3] < [k.sub.A2] < [k.sub.A1]; similarly: [B.sub.3] (2600 r/min) is the optimal level of spindle speed.

Since milling efficiency and milling times are required to be high and minimised separately, considering the ceramic thickness as 10 mm, it is the most reasonable that the milling depth is 5 mm in this experiment. Therefore, [A.sub.3][B.sub.3][C.sub.2] is the best optimal level combination of the experimental factors, which is 770 N in feed force, 2600 r/min in spindle speed and 5 mm in milling depth. Under such conditions, milling efficiency is the highest. And the results indicate that feed force is the most significant factor influencing the efficiency of milling [Al.sub.2][O.sub.3] ceramic and the influencing capacity order is feed force > milling depth > spindle speed.

3.5. The analysis of milling force

3.5.1. The design scheme of orthogonal experiment

Since feed force is the most significant factor influencing the efficiency based on the above experiment results, [L.sub.9]([3.sup.3]) orthogonal milling force tests were arranged to further analyse the effect of process factors on milling force and milling efficiency; a total of nine milling cutters with SMD40 diamond grain were used in this experiment and the experimental data were saved by a milling force measurement system. Because GFRP is easier to mill than ceramic, the latter was focused. The effect of technological factors on the milling force and the processing efficiency was analysed through the scheme of orthogonal experiment; then, the influence level size of various factors on milling force and processing efficiency was evaluated by range analysis and variance analysis; finally, the most reasonable processing parameters were found out. The levels and factors are listed in the Table 7.

3.5.2. The results and analysis of orthogonal experiment

Results of the [L.sub.9]([3.sup.3]) orthogonal test are listed in Table 8. The data of groups (1, 2, 3) indicate that the resultant force increases with the increase in feed speed and milling depth under the same spindle speed; at the same time, the milling time reduces gradually, which means that the milling efficiency increases. In order to distinguish the influence of feed speed and milling depth on milling force and machining efficiency. It can be easily observed that the data of groups (4, 5, 6), two of those are groups (4, 5), of the milling force and the processing time are changed when there is an increase in feed speed and milling depth, which are similar to the groups (1, 2, 3). But in the group of 6, the milling force falling suddenly under the condition of the milling depth increases and the feed speed decreases; at the same time, the processing time doubles; it is clear that the milling force and processing efficiency decline due to the decrease in feed speed.

Furthermore, Table 9 contains the range analysis based on the experimental results for more accurate analysis of the influence of processing parameters (feed speed, milling depth, spindle speed) on milling force, among them: ([F.sub.xi], [F.sub.yi], [F.sub.i] (i = 1 - 3)) is the average value about milling force corresponding to results of the three levels for each influencing factor; R is range.

The range analysis shows that feed speed is the most significant factor influencing the milling force and the influencing capacity order of each factor is C > B > A, and this range analysis is consistent with the observation analysis; therefore, the key factor of milling [Al.sub.2][O.sub.3] ceramic/GFRP component is that the feed speed is controlled reasonably.

Based on range analysis, Table 10 contains the variance analysis for more accurate evaluation of the effect of various process factors on milling force.

The variance analysis shows the feed speed is the most significant factor influencing the milling force, so the variance analysis is consistent with the range analysis.

The analysis results show that the influencing capacity order of each factor is C > B > A, but it can't be judged which group's processing parameters are the most reasonable. The mathematical formula relevant to processing parameters is proposed based on the above analysis in order to determine the most reasonable processing parameters, which can be expressed as follows:

u = [[F.sub.mx] * T * [V.sub.f]/[a.sub.]] (1)

where [F.sub.mx] is the resultant milling force, T is the milling time, [V.sub.f] is the feed speed and [a.sub.p] is the milling depth.

According to the formula (1), when [mu]-value is small, it indicates that the tool can remove more volume of the material under the condition of low milling force, short time and low feed speed; in other words, the milling efficiency is high and this kind of process parameters is the most reasonable. Table 11 contains calculation results of the formula (1) based on the experimental results in Table 8.

The calculation results indicate that the sixth group can achieve the highest milling efficiency under the condition of small cutting force, small feed speed and large milling depth, which can account for the fact that the processing parameters of the sixth group are the most reasonable. Accordingly, high spindle speed, large milling depth and small feed speed should be used on milling [Al.sub.2][O.sub.3] ceramic/GFRP component, which is consistent with the literature (Davim, Reisa, and Antonio 2004).

3.5.3. Single-factor experiments

Since each of the parameters gives conflicting solutions, it is important to arrive at an optimised solution. This is achieved by developing a normalised objective function that includes all the milling parameters, which are obtained by the least square method of linear regression equation. The multivariable linear regression model is used to further accurately investigate the influence of processing factors on milling force. Experiment equipment is the same as the orthogonal experiment; the normal milling force and tangential milling force were collected and recorded, respectively.

3.5.3.1. Mathematical model of milling force. The multivariable linear regression model is dependent on feed speed ([V.sub.f]), milling depth ([a.sub.p]) and spindle feed (n), which are shown in the formula (2):

F = C[V.sub.f.sup.[alpha]][a.sub.p.sup.[beta]][n.sup.r] (2)

where C is a constant which relates to material properties, [V.sub.f] (mm/min) is the feed speed, [a.sub.p] (mm) is the milling depth and n (r/min) is the spindle speed.

The mathematical models of milling force about spindle speed, feed speed and milling depth are expressed, respectively, in formulas (3), (4), (5):

F = C[n.sup.r] (3)

F = C[V.sub.f.sup.[alpha]] (4)

F = C[a.sub.p.sup.[beta]] (5)

3.5.3.2. The empirical formula of milling force

(1) The influence of spindle speed on milling force Experimental conditions: feed speed, [V.sub.f] = 5 mm/min; milling depth, [a.sub.p] = 4 mm/min; the size of milling force was adjusted by changing spindle speed. The experimental scheme and results are listed in the Table 12.

The empirical formula of milling force about spindle speed was obtained using the linear regression equation of the least square method, which can be expressed, respectively, as formulas (6) and (7):

[F.sub.n] = 6.1983[n.sup.-0.0862] (6)

[F.sub.t] = 6.6688[n.sup.-0.2992] (7)

The empirical formulas about spindle speed indicate that the milling force decreases with the increase in the spindle speed, which is caused by the increase in diamond abrasive particle per unit time; the reason is that the maximum milling thickness of single diamond abrasive particle decreases with the increase in diamond abrasive particle per unit time.

(2) The influence of milling depth on milling force

Experimental conditions: feed speed, [V.sub.f] = 5 mm/min; spindle speed, n = 3200 r/min; the size of milling force was adjusted by changing milling depth. The experimental scheme and results are listed in the Table 13.

The same method to calculate the empirical formula of milling force about milling depth is used, which can be expressed, respectively, as the formulas (8) and (9):

[F.sub.n] = 5.3491[a.sub.p.sup.0.1522] (8)

[F.sub.t] = 4.1269[a.sub.p.sup.0.1378] (9)

It should be noted that the milling force increases with the increase in milling depth, but because the machine tool power provided to the main shaft torque is insufficient, the milling depth can't be increased indefinitely in the actual process; otherwise, it will lead to the decline of milling efficiency when milling machine reaches the maximum power; this results are consistent with the above experimental results.

(3) The influence of feed speed on milling force

Experimental conditions: spindle speed, n = 3200 r/min; milling depth, [a.sub.p] = 4 mm/min; the size of milling force was adjusted by changing feed speed. The experimental scheme and results are listed in the Table 14.

The empirical formula of milling force about feed speed is expressed, respectively, as the formulas (10) and (11):

[F.sub.n] = 5.1454[V.sub.f.sup.0.2155] (10)

[F.sub.t] = 3.842[V.sub.f.sup.0.2959] (11)

It is clear that the milling force increases with the increase in feed speed, but the milling force tends to be stable when feed speed reaches a certain value. The reason is that the increase of feed speed leads to the increase in milling force of a single diamond abrasive particle, which causes diamond grain pulling out or shedding early; at the same time, matrix binder wears seriously; what's worse is that the phenomenon of skidding occurs and finally, the milling force tends to be stable.

3.6. Milling samples of composite component

Due to the high brittleness of the armour ceramic, cracks or breakouts are often found in the entrance and exit sides of the hole during the milling; therefore, [Al.sub.2][O.sub.3] ceramic has a dominant influence on the milling efficiency and milling quality. According to the above experimental results, high milling efficiency and good processing quality can be achieved under the condition of spindle speed of 2600 r/min, milling depth of 5 mm and feed force of 770 N. The milling sample of composite component is shown in Figure 9.

4. Conclusions

The results outlined in this study indicate that processing parameters play a significant role in the milling of [Al.sub.2][O.sub.3] ceramic/GFRP component. Conclusions are drawn as follows:

(1) Feed force is the most significant factor influencing the efficiency when milling [Al.sub.2][O.sub.3] ceramic/GFRP component using sintering diamond tools and the influencing capacity order is feed force > milling depth > spindle speed.

(2) Higher milling efficiency and good quality can be achieved under the conditions of spindle speed of 2600 r/min, milling depth of 5 mm and feed force of 770 N when milling the component.

(3) Feed speed is the most significant factor influencing milling force; spindle speed has a minimum influence on the milling force and the influencing capacity order is feed speed > milling depth > spindle speed.

(4) Milling force decreases with the increase of the spindle speed, and increases with the rise in milling depth and feed speed. It tends to be stable when feed speed rises.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by the Natural Science Foundation of Jiangsu High Education Institutions of China [grant number 14KJB460008].

Notes on contributors

Chao Gao constructed the article, designed the main experiments setting. Chao analyzed the results and did the paper writing.

Sheng Wang assisted in experiments setup and milling force analyzing. Sheng also participated in paper writing.

Guorong Wu did the literature surveying and reviewing, and designed experiments setting.

References

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Chao Gao, Sheng Wang and Guorong Wu

Department of Mechanical Engineering, Jiangsu University of Science and Technology, Zhenjiang, China

CONTACT Chao Gao gaochaozibo@qq.com

ARTICLE HISTORY

Received 29 November 2016

Accepted 9 March 2017

https://doi.org/10.1080/14484846.2017.1325153
Table 1. Sintering diamond tool manufacturing parameters.

Binder compo-        Sintering           Holding time    Sintering
sition (wt%)   temperature ([degrees]C)      (min)     pressure (MPa)

Cu50Co25Sn-             600                    2            14.7
   18Ti7

Table 2. Property parameters of [Al.sub.2][O.sub.3] ceramic.

Density (g/[cm.sup.3])  Modulus of elasticity (GPa)

3.90                             350

Density (g/[cm.sup.3])  Flexural strength (MPa) (25 [degrees]C)

3.90                                     370

Density (g/[cm.sup.3])  Vickers hardness (GPa)

3.90                             24

Density (g/[cm.sup.3])  Fracture toughness ([(MPa.m).sup.1/2])

3.90                                     4.4

Table 3. Property parameters of glass fibre-reinforced plastic.

                                                Tensile modulus of
Density (g/[cm.sup.3])  Tensile strength (MPa)   elasticity (GPa)

1.8                            439-503               22-35.6

                        Bending strength  Bending modulus of
Density (g/[cm.sup.3])        (MPa)        elasticity (GPa)

1.8                          530-705           21.7-25.0


Density (g/[cm.sup.3])  Barcol hardness(HB)

1.8                            70-80

Table 4. The table of orthogonal experiment factors and levels.

                                  Spindle speed    Milling depth
Levels, factors  Feed force (N)  (r [min.sup.-1])      (mm)

1                    600              1800               3
2                    650              2200               5
3                    700              2600               7

Table 5. The results of orthogonal experiment.

                             Spindle       Milling  Test results
             Feed force       speed         depth     Milling
Test number     (N)      (r [min.sup.-1])    (mm)     time (s)

1               600            1800            3        662
2               600            2200            5        671
3               600            2600            7        698
4               650            1800            5        672
5               650            2200            7        684
6               650            2600            3        615
7               770            1800            7        623
8               770            2200            3        483
9               770            2600            5        435

Table 6. Range analysis.

                                         B. Spindle
                         A. Feed force     speed (r    C. Milling
Factors                       (N)       [min.sup.-1])  depth (mm)

Milling time  [k.sub.1]      2031          1957          1760
              [k.sub.2]      1971          1838          1778
              [k.sub.3]      1541          1748          2005
              [k.sub.1]       677           652.3         586.7
              [k.sub.2]       657           612.7         592.7
              [k.sub.3]       513.7         582.7         668.3
                     R        163.3          69.6          81.6

Table 7. The table of orthogonal experiment factors and levels.

Levels, factors  Spindle speed  Milling depth      Feed speed
                   n (r/min)    [a.sub.p] (mm)  [V.sub.f] (mm/min)

1                    1800             3                 3
2                    3200             4                 5
3                    4500             5                 7

Table 8. the results of orthogonal experiment.

      Spin-    Cut-                       Experiment results
      dle      ting       Feed
      speed    edge       speed             Milling force

Test                    [V.sub.f]  Tangential   Normal    Resultant
num-  n (r/  [a.sub.p]    (mm
ber   min)     (mm)       /min)     [F.sub.x]  [F.sub.y]  [F.sub.max]

1     1800      3          3         75.6       218.5      231.2
2     1800      4          5         81.3       265.4      277.6
3     1800      5          7         90.2       285.7      299.6
4     3200      3          5         70.3       246.2      256.0
5     3200      4          7         85.6       253.7      267.7
6     3200      5          3         69.3       237.9      247.8
7     4500      3          7         73.7       240.9      251.9
8     4500      4          3         60.4       226.4      234.3
9     4500      5          5         68.8       248.7      258.0

      Experiment results

        Milling force


Test
num-        Time
ber         T (s)

1           23.3
2           14
3           10
4           14
5           10
6           23.3
7           10
8           23.3
9           14

Table 9. Range analysis results.

                        A: Spindle    B: Milling         C: Feed
                          speed         depth             speed
                        n (r/min)   [a.sub.p] (mm)  [V.sub.f] (mm/min)

Tangential         Fx1    82.36         73.2              68.43
milling force      Fx2    75.07         75.77             73.47
([F.sub.x])        Fx3    67.6          76.1              83.17
                    R     14.76          2.90             14.74
Normal milling     Fy1   256.63        235.2             227.6
force ([F.sub.y])  Fy2   245.93        248.6             253.53
                   Fy3   238.67        257.43            260.1
                    R     17.97         22.23             32.5
Resultant          F1    269.46        246.36            237.76
milling force      F2    257.16        259.86            263.86
([F.sub.max])      F3    248.06        268.46            273.06
                    R     21.40         22.10             35.3

Table 10. Variance analysis results.

                   Sum of
                  square of   Degree               F      -
                   devia-    of free-           critical  Significance
Factor              tions      dom     F ratio   value        level

Tangen-        A    325.616     2       1.442     5.14         **
tial           B     15.109     2       0.067     5.14
milling        C    336.496     2       1.491     5.14         **
force          D    677.22      6

Normal         A    490.096     2       0.488     5.14
milling        B    751.909     2       0.748     5.14         *
force          C   1771.909     2       1.764     5.14         **
([F.sub.y])    D   3013.91      6
resultant      A    692.06      2       0.602     5.14         *
milling        B    744.62      2       0.648     5.14
force          C   2011.94      2       1.75      5.14         **
([F.sub.max])  D   3448.62      6

Note: Remarks: A: spindle speed, n (r/min); B: Milling depth, [a.sub.p]
(mm); C: Feed speed, [V.sub.f] (mm/min); D: Error.

Table 11. [mu]-value calculation results.

Number    1     2      3       4       5       6       7       8

Results  5387  4853  4194.4  5973.3  4684.8  3464.2  5877.7  4094.4

Number     9

Results  3612

Table 12. Single-factor test results of spindle speed.

Experiment
number                  1      2      3      4      5      6

Spindle speed n       1800   2200   2600   3200   3600   4500
(r/min)
Milling  Normal        265.4  253.7  250.1  247.5  242.7  236.7
force
         ([F.sub.n])
         Tangential     81.3   79.8   76.3   72.3   67.2   62.4
         ([F.sub.t])

Table 13. Single-factor test results of milling depth.

Experiment
number                     1      2      3      4      5      6

Milling depth [a.sub.p]    1      2      3      4      5      6
(mm)
Milling  Normal          210.8  237.4  246.2  251.3  272.3  281.3
force
         ([F.sub.n])
         Tangential       62.7   68.2   70.3   74.2   78.5   80.2
         ([F.sub.t])

Table 14. Single-factor test results of feed speed.

Experiment
number                  1      2      3      4      5      6

Feed speed n            1      2      3      5      7      9
(r/min)
Milling  Normal       178.5  197.6  207.2  237.2  253.7  295.4
force    ([F.sub.n])
         Tangential    48.6   57.2   60.1   72.3   85.6   92.5
         ([F.sub.t])
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Author:Gao, Chao; Wang, Sheng; Wu, Guorong
Publication:Australian Journal of Mechanical Engineering
Article Type:Report
Date:Mar 1, 2018
Words:5922
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