Because of the hard grind of some metals such as aluminum, copper and brass, burnishing can be very effective. Burnishing is a non-cutting process in which the surface of the workpiece is plastically deformed by hard work and pressure in the surface layers of the workpiece. In this study, the burnishing process is applied to 2024 aluminum alloy to improve the quality of the final surface and its increasing hardness. In this process, a roller-based tool was used for burnishing with the lathe. The parameters of spindle speed, feed rate and burnishing force were used in three stages, with two repetition phases and in the full factorial method in aluminum 2024 burnishing. Minitab software was used to determine the effects of the different parameters on surface roughness and hardness. Also, the regression method was used to predict the surface roughness and hardness under the influence of the parameters. The results showed that the optimum surface roughness (Ra = 0.05µm) was achieved at a feed rate of 0.11mm/rev, a spindle speed of 1000rpm, and a burnishing force of 1000N.
Research Article
Development of the Burnishing Process: Moving Towards Increasing the Quality and Surface Hardness of Aluminum alloy 2024
https://doi.org/10.21203/rs.3.rs-2725355/v1
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burnishing process
lathe machine
burnishing tool
predict surface roughness
chipless process
aluminum alloy
Burnishing, due to its economy and low cost compared to other surface finishing processes (such as grinding, honing, lapping, etc.), leads to the production of a high quality and low cost product and increases the competitiveness of the product in the market. In this paper, the effect of burnishing process on the surface quality and hardness of 2024 aluminum alloy was studied and tested.
Several variables affect the burnishing process and consequently the hardness and strength as well as the quality of the resulting surfaces. The main effective parameters in this process are burnishing force, feed rate, burnishing speed (rotation speed of the workpiece), lubrication, tool material and its diameter, workpiece material, surface roughness before burnishing and rotation speed of the workpiece[1].
Rao et al[2] studied the Bernsching effect in different types of titanium alloys. They concluded that the optmum burnishing force depends on various factors such as workpiece material, burnishing speed, tool diameter, surface before cutting, and feed rate. Saï et al[3] investigated the generation of residual compressive stresses, surface microhardness and roughness in relation to the surface finishing process (Honing, grinding, polishing and burnishing). The various results showed that burnishing produces excellent surface quality that improves wear resistance, fatigue, tensile strength and corrosion resistance.
El-Axir et al [4] studied the effects of burnishing on mild steel. They reported that at high speeds, the roughness of the burnishing surface begins to increase. The reason given was the low deformation of the surface under the bullet at high speeds, the formation of an umbrella, the inability of oil to penetrate into the contact area of the deformation, and the more uniform flow of material into fewer holes. In this study, the best results in terms of surface roughness or roundness were obtained at a force of 150 N and a feed rate of 0.12 mm/rev.
Babu, P.R., et al [5] studied the effects of burnishing on aluminum and brass alloys. As the speed of burnishing increases at any given depth of penetration and the number of small passes increases, the average roughness of the surface slowly decreases. This is due to the stability of the burnishing tool at high speeds. Increasing the number of passes and the speeds leads to a deterioration of the surface quality, as it causes high hardness and crust formation on the surface. The general trend shows that an increase in the depth of penetration in the area used leads to a decrease in the average surface roughness.
Gharbi, F. et al [6] presented a burnishing tool for improving very large smooth surfaces. They presented a mathematical model to predict surface roughness as a function of speed, power and feed. Results showed that the burnishing of 1050A aluminum sheets softens them and improves their hammerability, but does not increase their microhardness. In addition, the effect of burnishing on compressive residual stress was found to depend on the feed path.
John, M. R., et al[7] investigated surface performance characteristics such as surface roughness, surface hardness, and out-of-roundness during burnishing of 6061 aluminum, using a new innovation in the process: In addition to pressing the surface around the contact point, the roller rotates at 5000 to 11500rpm. The lowest surface roughness of the parts was achieved at a force of 13N and a rotational speed of 580rpm.
Several studies have been conducted on the microhardness of aluminum alloys. In 2014, researchers also studied the microhardness of aluminum internal surfaces[8]. From the final model obtained for the input parameters of burnishing on microhardness, it was found that the low rotational speed of burnishing does not have much influence. This means that the rotational speed of burnishing in the range used for the feed rate, depth of cut, and number of passes does not have a significant effect on the microhardness of the surface. As the feed rate is further increased, the surface microhardness gradually decreases.
Krishna, R.M.et.al[9] studied the effects of burnishing on aluminum and brass alloys. The number of passes is one of the most important parameters for surface finish. An increase in the number of passes leads to an increase in the degree of difficulty of the plane. The difficulty of the plane increases after each pass.Excessive pressure causes more deformation and flaking of the surface and increases the roughness of the surface.
Burnishing is a final surface quality improvement process that is less expensive than traditional polishing methods. The time required for burnishing is much less than that required for machining. By burnishing instead of grinding, lapping and honing, the cost is reduced tremendously. It also has advantages such as residual compressive stresses that increase the life of the workpiece.
In our study, the focus is on the use of roller tools instead of balls in burnishing. Also, due to the flexibility in the design of the tool and the possibility of changing the roller diameter, the effectiveness of the process in terms of surface quality and hardness of the aluminum seat 2024 has been demonstrated. The burnishing tool mounted on the dynamometer during operation on the lathe is shown in Fig. 1.
The questions to be answered here are: What is the influence of the most important parameters on roughness and hardness? What are the optimum values for roughness and hardness when selecting parameters? What is the influence of the tool on the burnishing process?
The objective of the current research is to design and build a burnishing tool that can achieve the most desirable surface quality and hardness for non-metals that are unable to produce suitable surface quality (maximum Ra 1.0) using other machining processes. In addition to producing surface quality, such tools can produce surface hardness by producing residual compressive stresses.
2-1 Equipment And Tools
The Model TN50BR lathe is used to perform various burnishing operations. The control of deviations and sag in the lathe should be done so that they do not exceed the limit. It is clear that if the deviations and backlash of the machine tools are above the specified limit, it will lead to failure or poor quality of the production part, and as a result, the results of the tests will be incorrect. The allowable radial clearance on the lathe is 0.003 to 0.005mm. Angular contact ball bearings take the axial clearance up. These bearings absorb the axial force in two directions and also bear the radial force behind the spindle.
The Roughness Tester, Model RT -620 is a portable instrument for measuring the roughness of machined surfaces. A portable hardness tester based on the LEEB method was used to measure hardness.
A special roller burnishing tool is used (Fig. 2). It carried the series of tests out with this designed and built tool. We used this tool for burnishing on external surfaces with a round cross-section. The roller of the burnishing tool (7) is interchangeable and can be manufactured in different dimensions and materials. After being placed on the workpiece, two support rollers set this roller in rotation (10) and carry out the burnishing operation. In addition to the dynamometer, the burnishing force can be determined by the displacement of the spring, which is measured by the indicator clock. Four screws attached the base of this burnishing tool to the dynamometer of the lathe.
The dynamometer is used to measure the forces acting on the tool. It was developed on the basis of piezo technology and is mounted under the burnishing tool.
Aluminum is one of the light metals with a density of 2.7 g/cm3. Its corrosion resistance is excellent because it has a sticky and stable aluminum oxide layer on its surface. In other words, this oxide layer, whose thickness is about 0.025 micrometers, protects the aluminum from most corrosive substances.Aluminum alloy 2024 is used for the production of parts such as the fuselage and wings of aircraft due to its special properties such as special strength, high toughness, corrosion resistance and good fatigue properties [10].
The originality of aluminum alloy 2024, including chemical composition, mechanical properties and physical properties, must be determined by the seller or by experimental testing.
2-2 Experiment Design
Many factors affect the outcome of this process, but the main factors or parameters that affect the response variables in this research and experiment are:
-
Burnishing rotation speed: the number of rotations of the workpiece in revolutions per minute (rpm).
-
Burnishing feed rate: this is the feed rate of the burnishing tool at each revolution of the workpiece, measured in millimeters per revolution (mm/rev).
-
Burnishing force: the force exerted by the tool on the workpiece, measured in Newtons; instead of burnishing force, the depth of cut can also be used, measured in millimeters. The number of levels that can be achieved for each factor in this test is three levels. Table 1 shows the number of levels for each parameter of spindle speed, feed rate, and burnishing force.
|
Input parameters to branching machining |
|||
|---|---|---|---|
|
Set point Spindle speed (n, rpm) |
a1 |
a2 |
a3 |
|
355 |
710 |
1000 |
|
|
Set point Feed rate (\({F}_{f}\), mm/rev) |
b1 |
b2 |
b3 |
|
0.11 |
0.2 |
0.4 |
|
|
Set point Branching force (\(\text{F}\), N) |
c1 |
c2 |
c3 |
|
300 |
600 |
1000 |
|
Table 2 is the same experimental design based on the full factorial method. In this plan, three main factors, each with three constant values, are entered into the experiment, and a total of three to the power of three, and thus 27 experiments, are performed. Values of 355, 710, and 1000 are considered for spindle speed, values of 0.11, 0.2, and 0.4 for feed rate, and values of 300, 600, and 1000 for burnishing force.
|
N. |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
|---|---|---|---|---|---|---|---|---|---|
|
test |
a1b1c1 |
a1b1c2 |
a1b1c3 |
a1b2c1 |
a1b2c2 |
a1b2c3 |
a1b3c1 |
a1b3c2 |
a1b3c3 |
|
N. |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
|
test |
a2b1c1 |
a2b1c2 |
a2b1c3 |
a2b2c1 |
a2b2c2 |
a2b2c3 |
a2b3c1 |
a2b3c2 |
a2b1c1 |
|
N. |
19 |
20 |
21 |
22 |
23 |
24 |
25 |
26 |
27 |
|
test |
a3b1c1 |
a3b1c2 |
a3b1c3 |
a3b2c1 |
a3b2c2 |
a3b2c3 |
a3b3c1 |
a3b3c2 |
a3b3c3 |
The prepared material is cut into five equal pieces (210 mm). Then the two-headed center drill is applied to both ends of the pieces and the pieces are closed and machined on the lathe (Fig. 3). The outer surface of the parts is cut only to a whiteness of 0.5 mm, and two steps are created on both sides to close them in the chuck. Finally, the dynamometer is installed on the top set of the lathe and the tool is closed with four screws. During the burnishing process, the forces and torques generated by the reaction of the tool are closed by four screws. During the burnishing process, the forces and torques caused by the reaction of the tool and the workpiece are applied to the dynamometer and cause piezoelectric quartz deformation in the dynamometer, which generates an electrical signal. This generated signal is transmitted and amplified via communication cables to a multi-channel amplifier, which measures the values of the various forces.
After the installation of tools and workpieces, the number of tests is carried out according to their parameters and levels in 27 test modes and in two repetitions. Then the roughness and hardness values are measured and recorded in Table 3. Minitab software is used to determine the effects of each parameter on surface roughness and hardness. It is also possible to extract the results from the effect of factors in the form of two effects. Finally, the regression equation in the roughness and hardness of the surface will be done to find the optimum condition.
|
N. |
test |
\({{R}}_{{a}}\) |
\({h}{a}{r}{d}{n}{e}{s}{s}\) |
N |
test |
\({{R}}_{{a}}\) |
\({h}{a}{r}{d}{n}{e}{s}{s}\) |
N. |
test |
\({{R}}_{{a}}\) |
\({h}{a}{r}{d}{n}{e}{s}{s}\) |
|---|---|---|---|---|---|---|---|---|---|---|---|
|
1 |
a1b1c1 |
0.1717 |
174 |
10 |
a2b1c1 |
0.1219 |
172 |
19 |
a3b1c1 |
0.1304 |
169 |
|
2 |
a1b1c2 |
0.1259 |
184 |
11 |
a2b1c2 |
0.0783 |
180 |
20 |
a3b1c2 |
0.0591 |
176 |
|
3 |
a1b1c3 |
0.0307 |
192 |
12 |
a2b1c3 |
0.0669 |
190 |
21 |
a3b1c3 |
0.0328 |
186 |
|
4 |
a1b2c1 |
0.1744 |
174 |
13 |
a2b2c1 |
0.1986 |
170 |
22 |
a3b2c1 |
0.1089 |
167 |
|
5 |
a1b2c2 |
0.1144 |
182 |
14 |
a2b2c2 |
0.1504 |
180 |
23 |
a3b2c2 |
0.0889 |
177 |
|
6 |
a1b2c3 |
0.0493 |
191 |
15 |
a2b2c3 |
0.0843 |
187 |
24 |
a3b2c3 |
0.0545 |
184 |
|
7 |
a1b3c1 |
0.1215 |
172 |
16 |
a2b3c1 |
0.2089 |
166.5 |
25 |
a3b3c1 |
0.0763 |
165 |
|
8 |
a1b3c2 |
0.1130 |
181 |
17 |
a2b3c2 |
0.1770 |
177.5 |
26 |
a3b3c2 |
0.0832 |
176 |
|
9 |
a1b3c3 |
0.0487 |
191 |
18 |
a2b3c3 |
0.1509 |
183.5 |
27 |
a3b3c3 |
0.0856 |
184 |
The primary workpiece has a roughness and hardness of 1.0846Ra and 164HV machined before the burnishing process. Figure 4 shows the machined workpiece surface and the burnished surface.
Aluminum 2024 burnishing was done using a lathe and its results were extracted. These results included roughness and hardness of the surface. By entering this information into the Minitab software, the data processing was completed. This processing includes the effect of the main factors and the effect of the two factors on the roughness and hardness of the surface. The graph related to them was extracted and the regression related to roughness and hardness was obtained according to the components including spindle speed, feed rate, and burnishing force.
3-1 Effects Of Main Factors On Surface Roughness
The separate effect of the three factors of spindle speed, feed rate, and burnishing force by considering three separate values for each on the surface roughness of aluminum 2024 was investigated (Fig. 5). The effect of spindle speed at speeds of 355, 710 and 1000 rpm on surface roughness was 0.137, 0.072 and 0.114 respectively. The second item is the feeding rate, which was obtained for 0.11, 0.20, and 0.40 surface roughness values of 0.100, 0.123, and 0.092 respectively. Finally, the effect of burnishing force with the values of 300, 600, and 1000N the surface roughness was measured, and the values of 0.110, 0.096, and 0.119 were obtained, respectively. The amount of feed rate on surface roughness shows an increasing and then decreasing effect, while it shows the opposite effect for the two factors of spindle speed and burnishing force.
3-2 The Effect Of Two Factors On Surface Roughness
The effect of two factors on the surface roughness resulting from burnishing including spindle speed and feed rate, spindle speed and burnishing force, and feed rate and burnishing force is shown in Fig. 6.
Spindle speed and feed rate: by increasing the spindle speed from 355 to 710 and 1000rpm, with a feed rate of 0.11mm/rev values of 0.137, 0.88, and 0.072µm, with a feed rate of 0.20mm/rev values of 0.168, 0.068 and 0.165µm, With a feed rate of 0.40mm/rev, values of 0.107, 0.062 and 0.103µm were obtained for the surface roughness, respectively. A downward trend and then an upward trend can be seen for the feed rate of 0.200 and 0.400mm/rev and only a downward trend for the feed rate of 0.11mm/rev and with increasing spindle speed in general.
Spindle speed and burnishing force: by increasing the spindle speed from 355 to 710 and 1000rpm, for the burnishing force 300N, the surface roughness value is 0.129, 0.088, and 0.114µm, for the burnishing force 600N, the surface roughness value is 0.130, 0.050 and 0.109µm, and for the burnishing force of 600N, the surface roughness values of 0.154, 0.084 and 0.120µm were obtained, respectively. A downward and upward trend was obtained for all three burnishing forces of 300, 600, and 1000N for surface roughness and with increasing spindle speed.
Feed rate and burnishing force: with increasing feed rates of 0.11, 0.20, and 0.40mm/rev, with the burnishing force of 300N, the surface roughness of 0.115, 0.148, and 0.069µm, with the burnishing force of 600N, the surface roughness of 0.087, 0.104 and 0.105µm, and with The bearing force was 1000N, the surface roughness was 0.100, 0.155 and 0.109µm, respectively. In general, an upward and downward trend can be observed for the roughness surface value for three burnishing forces of 300, 600, and 1000N and with an increase in the feed rate.
3-3 Effects Of Main Factors On Surface Hardness
The effect of three factors of spindle speed, feed rate, and burnishing force in different machining conditions was investigated separately on the surface hardness (Fig. 7). The results show that the spindle speed of 355, 710, and 1000 rpm causes the surface hardness to be 178.4, 181.6 and 176.9 in Vickers, respectively. With the feed rate of 0.11, 0.2, and 0.4, the surface hardness value is 174.8, 180.2, and 181.9 in Vickers respectively. By applying the burnishing force from 300 to 600 and finally 1000 N, the surface hardness was recorded as 178.3, 180.3, and 178.5, respectively. The feed rate has shown an increasing effect on the degree of hardness, while for the spindle speed and burnishing force, it reaches a maximum value from an initial value and then shows a decreasing effect.
3-4 The Effect Of Two Factors On Surface Roughness
The effect of two factors on the surface hardness resulting from burnishing including spindle speed and feed rate, spindle speed and burnishing force, and feed rate and burnishing force are shown in Fig. 8.
Spindle speed and feeding rate: by increasing the spindle speed from 355 to 710 and 1000 rpm, with a feeding rate of 0.11mm/rev values of 176, 175, and 173HV, with a feeding rate of 0.20mm/rev values of 183, 183 and 174HV, with a feed rate of 0.40 mm/rev, values of 175, 186 and 184HV are obtained, respectively, for the surface hardness. An upward and then downward trend can be seen for the feed rate of 0.200 and 0.400 mm/rev and only a downward trend for the feed rate of 0.11 mm/rev and with increasing spindle speed for the overall surface roughness.
Spindle speed and burnishing force: by increasing the spindle speed from 355 to 710 and 1000 rpm, for a burnishing force of 300N, surface hardness values are 180, 178, and 175HV, for a burnishing force of 600N, surface hardness values are 180, 178 and 181HV, and for the burnishing force of 600 N, surface hardness values of 174, 180 and 173HV were obtained, respectively. In total, a downward trend for the burnishing force of 300 N, a downward-upward trend for the burnishing force of 600N, and an upward-downward trend for the burnishing force of 1000N were obtained for surface hardness and with increasing spindle speed.
Feed rate and burnishing force: with an increase in the feed rate of 0.11, 0.20, and 0.40 mm/rev, with a burnishing force of 300N, the surface hardness of 171, 183, and 181HV, with a burnishing force of 600N, the surface hardness of 176, 181 and 185HV, and With a bearing force of 1000N, the surface hardness of 178, 178 and 179 HV was obtained respectively. In general, is visible an ascending-descending trend for the hardness value for burnishing force 300N, an upward trend for the hardness value for burnishing force 600N, and a downward trend for the hardness value for burnishing force 1000N, and with increasing feed rate mm/rev.
3-5 Surface Roughness And Hardness Regression Equation And Model
The regression equation for surface roughness and hardness is given in equations 1 and 2, respectively. In these relationships, the effect of spindle speed, feed rate and amount of burnishing force can be seen in the optimization.
In the present investigation, an attempt was made to carry out the burnishing process with a rolling die on aluminum 2024. The results of the study and analysis of the output parameters of surface roughness (Ra) led to the following factors:
-
Power parameters and spindle speed have a greater effect on surface roughness than feed rate.
-
Increasing the spindle speed improves the quality of the surface with a sharp slope.
-
By increasing the spindle speed, the corresponding surface roughness is achieved, and the effect of the feed is very small.
-
With minimum feed, maximum speed and force in the selected range, the optimum surface roughness is achieved, which is less than 0.05Ra.
This study has shown by software analysis that the quality of the surface with a steep pitch improves when the speed of the spindle is increased. The reason for this can be analyzed as that at high speeds, due to the reduced connection time between the tool and the workpiece, the adhesion between the tool and the material decreases, so there are fewer defects on the surface and the surface roughness improves with a steeper slope.
The debatable point is that according to the results, the amount of feed rate in all three selected areas did not have much effect on the surface roughness, on the other hand, the minimum feed rate in the selected area gave the best surface roughness (although with a small difference from the maximum feed rate). This does not mean that a lower feed rate can be used, since the low feed rate causes the contact between the tool and the metal surface to be prolonged. In this condition, the tendency for adhesion between the tool and the workpiece material increases, the work is harder, the surface of the material peels off, and finally, the quality of the surface decreases.
Another important interpretation of the four results mentioned above is the insignificant effect of feed rate on surface roughness. This means that burnishing can be performed at high speeds and increases the production speed. Therefore, burnishing is economically very suitable and affordable for producing high-level roughness on AL2024 due to its high speed.
Comparing this method with other machining methods, we find that, first, it is impossible to achieve a surface roughness of less than 0.05Ra by machining, and second, more surface roughness is produced at high feed rates.
Comparing this method with other grinding methods, we find that after about 30 seconds of grinding, the holes of the stone are filled and contaminate the surface of the workpiece, so it must be sharpened again. This process is repeated many times. In practice, this work cycle is not possible, and secondly, it is not economical.
From the above results and discussions, the general conclusion is that burnishing is a very suitable method to achieve high surface roughness on AL2024.
In the future, we will investigate the effects of burnishing on strength in corrosive environments and chemical surface corrosion.
In burnishing, there are many observable parameters such as burnishing force, feed rate, burnishing speed, lubrication, burnishing tool material and its diameter, number of burnishing passes, and surface roughness before burnishing. In this study, the surface roughness and microhardness of the surface of Al2024 were analyzed, tested and investigated. The rollers used in the manufactured tools can be replaced and adjusted, and the tool has a longer service life and can be easily maintained. The oil layer in the tool makes the roller work with less friction and less heat. The oil cooler forms a smooth working layer between the roller and the workpiece and prevents the material from sticking to the roller. The results show that the force parameters and the spindle speed have a greater influence on the surface roughness than the feed rate. Moreover, at the minimum feed rate with maximum speed and force, the optimum surface roughness was obtained, which is less than 0.05Ra.
Acknowledgment: Special thanks to Mr. Hamid Yousefian for machining and testing.
Data Availability Statement: All data generated or analyzed during this study are included in this published article.
Conflicts of Interest: None
Funding: No funding was used to support this study.
Ethical Approval: None
- Chomienne, V., et al., Influence of ball burnishing on residual stress profile of a 15-5PH stainless steel. CIRP Journal of Manufacturing Science and Technology, 2016. 13: p. 90-96.
- Rao, D.S., H.S. Hebbar, and M. Komaraiah, Surface hardening of high-strength low alloy steels (HSLA) dual-phase steels by ball burnishing using factorial design. Materials and Manufacturing Processes, 2007. 22(7-8): p. 825-829.
- Saï, W.B. and J. Lebrun, Influence of finishing by burnishing on surface characteristics. Journal of Materials Engineering and Performance, 2003. 12(1): p. 37-40.
- El-Axir, M., An investigation into the ball burnishing of aluminium alloy 6061-T6. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture, 2007. 221(12): p. 1733-1742.
- Babu, P.R., et al., Optimization of burnishing parameters and determination of select surface characteristics in engineering materials. Sadhana, 2012. 37(4): p. 503-520.
- Gharbi, F., et al., Ductility improvement of aluminum 1050A rolled sheet by a newly designed ball burnishing tool device. The International Journal of Advanced Manufacturing Technology, 2012. 60(1): p. 87-99.
- John, M., et al., Surface characteristics of low plasticity burnishing for different materials using lathe. Arabian Journal for Science and Engineering, 2014. 39(4): p. 3209-3216.
- El-Axir, M., O. Othman, and A. Abodiena, Improvements in out-of-roundness and microhardness of inner surfaces by internal ball burnishing process. Journal of materials processing technology, 2008. 196(1-3): p. 120-128.
- Krishna, R.M., An Investigation of the Effect of the process parameters on the Material Properties of burnished components. 2013.
- IJ, P., Recent developments in light alloys. Materials transactions, JIM, 1996. 37(1): p. 12-31.