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Effects of Process Parameters on Surface Roughness in Incremental Sheet Forming
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 28026–28032
www.materialstoday.com/proceedings
ICCMMEMS_2018
Effects of Process Parameters on Surface Roughness in Incremental Sheet Forming Ajay Kumara,*, Vishal Gulatia, Parveen Kumarb a
Department of Mechanical Engineering, Guru Jambheshwar University of Science & Technology, Hisar 125001, Haryana, India b
Rawal Institute of Engineering & Technology, Faridabad 121004, Haryana, India
Abstract Incremental Sheet Forming (ISF) process significantly reduces the tooling costs as compared to other conventional sheet metal processes where expensive dies are used to produce any product. Hence, multi-variety components in small batches can be manufactured at lower cost with ISF technology which prevents limitations of traditional sheet metal forming processes. This paper represents effects of process parameters on surface roughness of formed components on AA2024-O sheets. Surface roughness has been measured by a roughness tester. Average roughness was found to increase with decrease in tool diameter. Hemispherical ended tools produced better surface quality of formed components as compared to that produced by flat end tools. © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Composite Materials: Manufacturing, Experimental Techniques, Modeling and Simulation (ICCMMEMS-2018). Keywords: ISF; Process Parameters; AA-2024-O; Tool Shape; Average Roughness.
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. * Corresponding author. Tel.: +91-9467717120. E-mail address:[email protected] 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Composite Materials: Manufacturing, Experimental Techniques, Modeling and Simulation (ICCMMEMS-2018).
Kumar et al./ Materials Today: Proceedings 5 (2018) 28026–28032
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1. Introduction Small and medium volume production of precision conventional forming processes has still been a problem of the metal working industry. In order to meet production of rapid prototyping for lower cost, complex parts and higher quality level, a new sheet metal forming method can be used in industry called as Incremental Sheet Forming (ISF). This method is more suitable by virtue of shorter cycle time and economical tooling cost for batch type and prototype production. ISF is also suitable to form non-symmetrical geometries without using expensive dies for manufacturing complex components of sheet metal [1]. ISF has sought global attention in the field of metal forming processes. This process is beautified with process flexibility and capable of eliminating storage of costly dies of parts. Aerospace industry faces the problems of replacing fuselage components of old aircrafts. The forming dies of these kinds of unique parts are generally not available in the required form. These problems can be overcome by a process like ISF which is a purely die-less forming process. It requires minimum energy in order to form the components. It also significantly reduces the tooling costs as compared to other conventional sheet metal processes where expensive dies are used to produce any product. Hence, multi-variety components in small batches can be manufactured at low cost with ISF technology which prevents limitations of traditional sheet metal forming processes [2-3]. According to forming methods ISF is categorized as Single Point Incremental Forming (SPIF), Two Points Incremental Forming (TPIF), Double Sided Incremental Forming (DSIF) and Hybrid forming. SPIF is also known as negative incremental forming as shown in Fig. 1a. It is truly die less forming technology as envisioned by Leszak [4]. In DSIF, forming tool is supported by a counter tool or slave tool in order to increase dimensional accuracy of the formed components (Fig.1b). TPIF process can be accomplished with partial die (Fig. 1c) or full die (Fig. 1d). The sheet metal moves vertically on bearings, which move on sheet holder posts, along the z-axis, as the forming tool pushes into the metal sheet. Araghi et al. [5] presented a hybrid process which is the combination of asymmetric incremental forming and stretch forming in order to produce spherical cap with circumferential. The process combination offer new possibilities to overcome the thinning limits of ISF and forming time are reduced even for a large part.
Fig.1. Various variants of ISF.
Although, a large amount of work has been performed in ISF, still it has not been employed in manufacturing sectors. For complex geometry, SPIF is more flexible and economical having higher formability and lesser lead time
28028
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as compared to conventional forming processes. This process finds application in head light casing of automobiles, producing complex shapes, automotive service panels, and customized bio-medical components such ankle support, plate prosthesis, implants for arthoplasty and cranial implants etc. SPIF is characterized by different input parameters and responses. Surface roughness of the components is one of the important responses in the field of sheet metal process. In the past few years, substantial research has been carried out by researchers but still there is a lack of intensive understanding of the mechanism of surface roughness of parts in ISF, which is very crucial in optimizing the process for better response qualities [2]. Cavalar et al. [6] studied impact of tool radius, surface coating of tool and step size on AISI 304 steel sheets. Surface roughness was found to decrease with increase in step size and tool diameter. Coated tools produced better surface finish than the surface finish produced by uncoated tools. Removal of metal occurred even after using lubricant. Color of lubricant changed to grey from yellow due to involvement of particles of metal in it. Babu and Kumar [7] investigated effects of step depth, spindle speed and feed rate on deep drawing IS513Cr3 steel sheets and found that surface roughness increased with increase in spindle speed because surface become rough due to increase in temperature. Increase in feed rate and step size resulted in decreasing surface roughness. De Bruyn and Treurnicht [8] investigated effects of step down and lubricants (MoS2 and graphite) on Ti-6Al-4V sheets. Results showed that dry run produced rougher surface of work piece as compared to that produced with lubricants. Roughness was found to decrease with increase in step size. Moreover, work material tends to adhere with tool tip in case of dry run and reduces tool life and surface finish. Gulati et al. [9] optimized the SPIF process by investigating effects of input parameters on AA6063 sheets. Results showed that surface roughness increased with increase in step size, sheet thickness and feed rate. Lubrication was found to be most affecting factor. Liu et al. [10] optimized effects of punch radius, sheet thickness, feed rate and step down using RSM technique. They found that thickness of sheet affected the roughness of surface the most followed by tool diameter and feed rate. External roughness of surface was found greater than inner surface roughness. Literature reports that effects of process parameters like tool diameter, step size, spindle speed and lubrication are significant on surface roughness of the components. Moreover, this die-less process is still limited in manufacturing industry due to lack of information about the effecting process variables. A significant knowledge about the process variables is required to obtain which would help the process engineer to implement the SPIF process in industrial sector. [11-12]. This paper focuses on investigation of process variables on surface roughness for AA-2024 sheets which finds application in aerospace and automobile industries. Truncated cone shape objects were formed in order to study influence of tool diameter, tool shape and wall angle. Three different shapes of forming tools have been investigated. Table 1 represents geometry of forming tools used in this study. Table 2 shows the investigated parameters with their levels. Each parameter is studied at three levels taking other process variables constant as tool diameter 11.60 mm, wall angle 64o, spindle speed 1000 rpm, feed rate 1500 mm/min, sheet thickness 1.2 mm and step size 0.5 mm. Castrol lubricant oil Alpha SP 320 was applied on sheet in order to reduce friction at tool-sheet interface. Table 1. Geometrical details of forming tools. Tool diameter 7.52
11.60
15.66
Side radius of
Radius of hemispherical
flat-end tool
end tool
Symbol
1.40
-
FlatEnd-R1
2.00
-
FlatEnd-R2
-
3.76
Hemispherical
1.98
-
FlatEnd-R1
2.85
-
FlatEnd-R2
-
5.80
Hemispherical
1.85
-
FlatEnd-R1
3.76
-
FlatEnd-R2
-
7.83
Hemispherical
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Table 2. Process parameters and their levels. Parameter
Level 1
Level 2
Level 3
Tool Diameter (mm)
7.52
11.60
15.66
Tool Shape
Flatend-R1
Flatend-R2
Hemispherical
Wall angle (o)
60
64
68
Table 3. Chemical compositions of aluminum alloy used. Chemical composition (weight %) AA 2024-O
Al
Cr
Cu
Fe
Mg
Mn
Si
Ti
Zn
91.50
0.10
4.60
0.30
1.70
0.80
0.50
0.10
0.20
2. Materials and methods Experimental tests were performed using a 3-axis VMC (Fig.2a) on AA2024-O sheets of 1.2 mm thickness. Chemical compositions of alloy sheets are given in Table 3. Forming tools are made of HSS and hardened to 64 HRC before finishing operation. Truncated cone shape parts of 120 mm upper diameter and 70 mm height are formed for different wall angles. Helical tool path has been used in CAM package for tool trajectory. In this work, average roughness (Ra) value is studied which is an international parameter of roughness measurement and arithmetic mean of profile departure. Ra value of work-pieces was measured by a roughness tester Mitutoyo SJ-400 as shown in Fig.2b. Ra value of each specimen was measured five times and average value was represented to increase statistical accuracy of results. Cutoff length and evaluating length were fixed as 0.8 mm and 4 mm respectively.
(a)
(b) Fig.2. (a) Experimental set up (b) Surface roughness measurement set-up.
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3. Results and discussion Experimental test results of different process variables for average roughness (Ra) are given in Table 4. Ra is measured in direction of step size of the inner surface of formed cones. Fig.3 shows the effects of tool shape with different tool diameters on average roughness of formed parts. Ra was found to decrease with increase in tool diameter. Higher tool diameter allows reduction in waviness on the tool-sheet interface resulting in better surface quality and this is in accordance of previous results [10, 12, and 13]. It is very interesting to show influence of tool shape. As the side radius of flat end tools was increased, roughness of surface decreased for all three levels of tool diameters (7.52, 11.60, 15.66 mm) and reached to minimum value for hemispherical end tools. When tool shape was changed from FlatEnd-R1 to Hemispherical end, Ra decreased approximately 28.34 %, 40.38 % and 47.05 % for 7.52 mm, 11.60 mm and 15.66 mm tool diameters respectively. Similarly, Ra was found to decrease 46.45 %, 52.33 % and 60.43 % for FlatEnd-R1, FlatEnd-R2 and Hemispherical shape respectively when tool diameter was increased from 7.52 mm to 15.66 mm. Fig.4 shows the effects of tool shape with different wall angles on average roughness of the formed parts. It has been observed from experimental investigations that Ra increases with increase in wall angle of conical parts. When wall angle is increased, higher lateral area of punch tip touches the blank. Hence, steeper surface is formed which leads to increase in waviness on the surface of the component. This is also in accordance with [9, 13]. This trend of increasing Ra value with increase in wall angle was consistent with all three shapes of forming tools (Fig.4). Moreover, sheet fracture was observed with specimens having 68o wall angle for all three shapes of forming tools. This may be due to that higher wall results in excessive sheet thinning according to sine law [22] which leads to earlier fracture of the sheet material. In case of conical frustum of 64o wall angle, fracture occurred for FlatEnd-R1 and FlatEnd-R2 tool shape. This can be due to the fact that smaller radius of tool increases penetration into sheet and removes materials in the form of chips. Hence, smaller radius of tool tip leads to cracking of sheet material resulting lower forming depth. When tool shape was changed from FlatEnd-R1 to Hemispherical end, Ra decreased approximately 40.44 %, 40.18 % and 27.27 % for 60o, 64o and 68o wall angles respectively. Similarly, Ra was found to decrease by 26.44 %, 27.18 % and 39.77 % for FlatEnd-R1, FlatEnd-R2 and Hemispherical shape respectively when wall angle was reduced from 68o to 60o. Table 4. Average roughness test results with different process parameters. Ra test results for tool diameter and tool shape
Ra test results for wall angle and tool shape
Sr. no.
Tool Diameter
Tool Shape
Ra (μm)
Sr. no.
Wall Angle
Tool Shape
Ra (μm)
1
7.52
FlatEnd-R1
1.27
10
60
FlatEnd-R1
0.89
2
7.52
FlatEnd-R2
1.07
11
60
FlatEnd-R2
0.75
3
7.52
Hemispherical
0.91
12
60
Hemispherical
0.53
4
11.60
FlatEnd-R1
1.04
13
64
FlatEnd-R1
1.07
5
11.60
FlatEnd-R2
0.87
14
64
FlatEnd-R2
0.84
6
11.60
Hemispherical
0.62
15
64
Hemispherical
0.64
7
15.66
FlatEnd-R1
0.68
16
68
FlatEnd-R1
1.21
8
15.66
FlatEnd-R2
0.51
17
68
FlatEnd-R2
1.03
9
15.66
Hemispherical
0.36
18
68
Hemispherical
0.88
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FlatEnd-R1 FlatEnd-R2 Hemispherical
1.3 1.2 1.1
Ra (µm)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3
6
8
10
12
14
16
Tool Diameter (mm) Fig.3. Effects of tool diameter and tool shape on average roughness.
1.2 1.1
FlatEnd-R1 FlatEnd-R2 Hemispherical
Ra(µm)
1.0 0.9 0.8 0.7 0.6 0.5
60
62
64
66
68
Wall Angle (o) Fig.4. Effects of wall angle and tool shape on average roughness.
4. Conclusion This work focused on influence of tool diameter, tool shape and wall angle on surface roughness of the components formed during SPIF. Experimental investigation showed that average roughness of surface of conical frustums increased with decrease in tool diameter and side radius of flat end tools. Increase in wall angle led to increase in surface roughness of the components. Combination of higher wall angle and flat end tool with lower side radius results in fracture of components at lower depth which is an indicator of loss of formability. Best condition of surface finish in terms of minimum Ra (0.36 μm) was obtained with combination of larger tool diameter (15.66 mm)
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and hemispherical tool shape, whereas, surface condition was worst (Ra = 1.27 μm) with combination of lower tool diameter and flat end tool with lower side radius. Analysis of formability and geometrical accuracy of the formed components would be focused in future work. Acknowledgements The authors have no conflict of interest. The authors would like to thank A.R.K. Mould & Tools Ltd., Gurgaon and A.K. Automatics Pvt. Ltd., Rohtak for their assistance. The authors would also like to thank Mr. Udayveer Singh, Mr. Bissan Singh and Er. Narender Saini for their appreciable contribution in developing experimental set-up analysis of results. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
S. H. Wu, A. Reis, F. M. Andrade Pires, A. D. Santos & A. Barata da Rocha, Study of tool trajectory in incremental forming, Advanced Materials Research. 472 (2012) 1586-1591. P. Li, J. He, Q. Liu, M. Yang, Q. Wang, Q. Yuan & Y. Li, Evaluation of forming forces in ultrasonic incremental sheet metal forming, Aerospace Science and Technology. 63 (2017) 132-139. Y. Li, W. J. T. Daniel & P. A. Meehan, Deformation analysis in single-point incremental forming through finite element simulation, The International Journal of Advanced Manufacturing Technology 88 (2017) 255-267. L. Edward, Apparatus and process for incremental dieless forming, U.S. Patent No. 3, (1967) 342,051. 19. B. T. Araghi, G. L. Manco, M. Bambach & G. Hirt, Investigation into a new hybrid forming process: Incremental sheet forming combined with stretch forming, CIRP annals, 58 (2009) 225-228. L. C. C. Cavaler, L. Schaeffer, A. S. Rocha & F. Peruch, Surface roughness in the incremental forming of AISI 304L stainless steel sheets, J. Mechan. Eng. Phys, 1 (2010) 87-98. S. C. Babu & V. S. Kumar, Effect of process variables during incremental forming of deep drawing steel sheets, Eur. J. Sci. Res, 80 (2012) 50-56. R. De Bruyn & N. Treurnicht, An investigation into lubrication strategies for the incremental sheet forming of Ti-6Al-4V, in Computers and Industrial Engineering, 42 (2012). V. Gulati, A. Aryal, P. Katyal & A. Goswami, Process parameters optimization in single point incremental forming, Journal of the Institution of Engineers (India): Series C, 97 (2016) 185-193. Z. Liu, S. Liu, Y. Li & P. A. Meehan, Modeling and optimization of surface roughness in incremental sheet forming using a multiobjective function, Materials and Manufacturing Processes, 29 (2014) 808-818. G. Ambrogio, L. De Napoli, L. Filice, F. Gagliardi, M. Muzzupappa, Application of IF process for high customised medical product manufacturing, Int. J. Mater. Process. Techno, 162-163 (2005) 156-162 M. C. Radu & I. Cristea, Processing Metal Sheets by SPIF and Analysis of Parts Quality, Materials and Manufacturing Processes, 28 (2013) 287-293. S. B. Echrif & M. Hrairi, Significant parameters for the surface roughness in incremental forming process, Materials and Manufacturing Processes, 29 (2014) 697-703.
ScienceDirect Materials Today: Proceedings 5 (2018) 28026–28032
www.materialstoday.com/proceedings
ICCMMEMS_2018
Effects of Process Parameters on Surface Roughness in Incremental Sheet Forming Ajay Kumara,*, Vishal Gulatia, Parveen Kumarb a
Department of Mechanical Engineering, Guru Jambheshwar University of Science & Technology, Hisar 125001, Haryana, India b
Rawal Institute of Engineering & Technology, Faridabad 121004, Haryana, India
Abstract Incremental Sheet Forming (ISF) process significantly reduces the tooling costs as compared to other conventional sheet metal processes where expensive dies are used to produce any product. Hence, multi-variety components in small batches can be manufactured at lower cost with ISF technology which prevents limitations of traditional sheet metal forming processes. This paper represents effects of process parameters on surface roughness of formed components on AA2024-O sheets. Surface roughness has been measured by a roughness tester. Average roughness was found to increase with decrease in tool diameter. Hemispherical ended tools produced better surface quality of formed components as compared to that produced by flat end tools. © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Composite Materials: Manufacturing, Experimental Techniques, Modeling and Simulation (ICCMMEMS-2018). Keywords: ISF; Process Parameters; AA-2024-O; Tool Shape; Average Roughness.
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. * Corresponding author. Tel.: +91-9467717120. E-mail address:[email protected] 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Composite Materials: Manufacturing, Experimental Techniques, Modeling and Simulation (ICCMMEMS-2018).
Kumar et al./ Materials Today: Proceedings 5 (2018) 28026–28032
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1. Introduction Small and medium volume production of precision conventional forming processes has still been a problem of the metal working industry. In order to meet production of rapid prototyping for lower cost, complex parts and higher quality level, a new sheet metal forming method can be used in industry called as Incremental Sheet Forming (ISF). This method is more suitable by virtue of shorter cycle time and economical tooling cost for batch type and prototype production. ISF is also suitable to form non-symmetrical geometries without using expensive dies for manufacturing complex components of sheet metal [1]. ISF has sought global attention in the field of metal forming processes. This process is beautified with process flexibility and capable of eliminating storage of costly dies of parts. Aerospace industry faces the problems of replacing fuselage components of old aircrafts. The forming dies of these kinds of unique parts are generally not available in the required form. These problems can be overcome by a process like ISF which is a purely die-less forming process. It requires minimum energy in order to form the components. It also significantly reduces the tooling costs as compared to other conventional sheet metal processes where expensive dies are used to produce any product. Hence, multi-variety components in small batches can be manufactured at low cost with ISF technology which prevents limitations of traditional sheet metal forming processes [2-3]. According to forming methods ISF is categorized as Single Point Incremental Forming (SPIF), Two Points Incremental Forming (TPIF), Double Sided Incremental Forming (DSIF) and Hybrid forming. SPIF is also known as negative incremental forming as shown in Fig. 1a. It is truly die less forming technology as envisioned by Leszak [4]. In DSIF, forming tool is supported by a counter tool or slave tool in order to increase dimensional accuracy of the formed components (Fig.1b). TPIF process can be accomplished with partial die (Fig. 1c) or full die (Fig. 1d). The sheet metal moves vertically on bearings, which move on sheet holder posts, along the z-axis, as the forming tool pushes into the metal sheet. Araghi et al. [5] presented a hybrid process which is the combination of asymmetric incremental forming and stretch forming in order to produce spherical cap with circumferential. The process combination offer new possibilities to overcome the thinning limits of ISF and forming time are reduced even for a large part.
Fig.1. Various variants of ISF.
Although, a large amount of work has been performed in ISF, still it has not been employed in manufacturing sectors. For complex geometry, SPIF is more flexible and economical having higher formability and lesser lead time
28028
Kumar et al./ Materials Today: Proceedings 5 (2018) 28026–28032
as compared to conventional forming processes. This process finds application in head light casing of automobiles, producing complex shapes, automotive service panels, and customized bio-medical components such ankle support, plate prosthesis, implants for arthoplasty and cranial implants etc. SPIF is characterized by different input parameters and responses. Surface roughness of the components is one of the important responses in the field of sheet metal process. In the past few years, substantial research has been carried out by researchers but still there is a lack of intensive understanding of the mechanism of surface roughness of parts in ISF, which is very crucial in optimizing the process for better response qualities [2]. Cavalar et al. [6] studied impact of tool radius, surface coating of tool and step size on AISI 304 steel sheets. Surface roughness was found to decrease with increase in step size and tool diameter. Coated tools produced better surface finish than the surface finish produced by uncoated tools. Removal of metal occurred even after using lubricant. Color of lubricant changed to grey from yellow due to involvement of particles of metal in it. Babu and Kumar [7] investigated effects of step depth, spindle speed and feed rate on deep drawing IS513Cr3 steel sheets and found that surface roughness increased with increase in spindle speed because surface become rough due to increase in temperature. Increase in feed rate and step size resulted in decreasing surface roughness. De Bruyn and Treurnicht [8] investigated effects of step down and lubricants (MoS2 and graphite) on Ti-6Al-4V sheets. Results showed that dry run produced rougher surface of work piece as compared to that produced with lubricants. Roughness was found to decrease with increase in step size. Moreover, work material tends to adhere with tool tip in case of dry run and reduces tool life and surface finish. Gulati et al. [9] optimized the SPIF process by investigating effects of input parameters on AA6063 sheets. Results showed that surface roughness increased with increase in step size, sheet thickness and feed rate. Lubrication was found to be most affecting factor. Liu et al. [10] optimized effects of punch radius, sheet thickness, feed rate and step down using RSM technique. They found that thickness of sheet affected the roughness of surface the most followed by tool diameter and feed rate. External roughness of surface was found greater than inner surface roughness. Literature reports that effects of process parameters like tool diameter, step size, spindle speed and lubrication are significant on surface roughness of the components. Moreover, this die-less process is still limited in manufacturing industry due to lack of information about the effecting process variables. A significant knowledge about the process variables is required to obtain which would help the process engineer to implement the SPIF process in industrial sector. [11-12]. This paper focuses on investigation of process variables on surface roughness for AA-2024 sheets which finds application in aerospace and automobile industries. Truncated cone shape objects were formed in order to study influence of tool diameter, tool shape and wall angle. Three different shapes of forming tools have been investigated. Table 1 represents geometry of forming tools used in this study. Table 2 shows the investigated parameters with their levels. Each parameter is studied at three levels taking other process variables constant as tool diameter 11.60 mm, wall angle 64o, spindle speed 1000 rpm, feed rate 1500 mm/min, sheet thickness 1.2 mm and step size 0.5 mm. Castrol lubricant oil Alpha SP 320 was applied on sheet in order to reduce friction at tool-sheet interface. Table 1. Geometrical details of forming tools. Tool diameter 7.52
11.60
15.66
Side radius of
Radius of hemispherical
flat-end tool
end tool
Symbol
1.40
-
FlatEnd-R1
2.00
-
FlatEnd-R2
-
3.76
Hemispherical
1.98
-
FlatEnd-R1
2.85
-
FlatEnd-R2
-
5.80
Hemispherical
1.85
-
FlatEnd-R1
3.76
-
FlatEnd-R2
-
7.83
Hemispherical
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Table 2. Process parameters and their levels. Parameter
Level 1
Level 2
Level 3
Tool Diameter (mm)
7.52
11.60
15.66
Tool Shape
Flatend-R1
Flatend-R2
Hemispherical
Wall angle (o)
60
64
68
Table 3. Chemical compositions of aluminum alloy used. Chemical composition (weight %) AA 2024-O
Al
Cr
Cu
Fe
Mg
Mn
Si
Ti
Zn
91.50
0.10
4.60
0.30
1.70
0.80
0.50
0.10
0.20
2. Materials and methods Experimental tests were performed using a 3-axis VMC (Fig.2a) on AA2024-O sheets of 1.2 mm thickness. Chemical compositions of alloy sheets are given in Table 3. Forming tools are made of HSS and hardened to 64 HRC before finishing operation. Truncated cone shape parts of 120 mm upper diameter and 70 mm height are formed for different wall angles. Helical tool path has been used in CAM package for tool trajectory. In this work, average roughness (Ra) value is studied which is an international parameter of roughness measurement and arithmetic mean of profile departure. Ra value of work-pieces was measured by a roughness tester Mitutoyo SJ-400 as shown in Fig.2b. Ra value of each specimen was measured five times and average value was represented to increase statistical accuracy of results. Cutoff length and evaluating length were fixed as 0.8 mm and 4 mm respectively.
(a)
(b) Fig.2. (a) Experimental set up (b) Surface roughness measurement set-up.
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Kumar et al./ Materials Today: Proceedings 5 (2018) 28026–28032
3. Results and discussion Experimental test results of different process variables for average roughness (Ra) are given in Table 4. Ra is measured in direction of step size of the inner surface of formed cones. Fig.3 shows the effects of tool shape with different tool diameters on average roughness of formed parts. Ra was found to decrease with increase in tool diameter. Higher tool diameter allows reduction in waviness on the tool-sheet interface resulting in better surface quality and this is in accordance of previous results [10, 12, and 13]. It is very interesting to show influence of tool shape. As the side radius of flat end tools was increased, roughness of surface decreased for all three levels of tool diameters (7.52, 11.60, 15.66 mm) and reached to minimum value for hemispherical end tools. When tool shape was changed from FlatEnd-R1 to Hemispherical end, Ra decreased approximately 28.34 %, 40.38 % and 47.05 % for 7.52 mm, 11.60 mm and 15.66 mm tool diameters respectively. Similarly, Ra was found to decrease 46.45 %, 52.33 % and 60.43 % for FlatEnd-R1, FlatEnd-R2 and Hemispherical shape respectively when tool diameter was increased from 7.52 mm to 15.66 mm. Fig.4 shows the effects of tool shape with different wall angles on average roughness of the formed parts. It has been observed from experimental investigations that Ra increases with increase in wall angle of conical parts. When wall angle is increased, higher lateral area of punch tip touches the blank. Hence, steeper surface is formed which leads to increase in waviness on the surface of the component. This is also in accordance with [9, 13]. This trend of increasing Ra value with increase in wall angle was consistent with all three shapes of forming tools (Fig.4). Moreover, sheet fracture was observed with specimens having 68o wall angle for all three shapes of forming tools. This may be due to that higher wall results in excessive sheet thinning according to sine law [22] which leads to earlier fracture of the sheet material. In case of conical frustum of 64o wall angle, fracture occurred for FlatEnd-R1 and FlatEnd-R2 tool shape. This can be due to the fact that smaller radius of tool increases penetration into sheet and removes materials in the form of chips. Hence, smaller radius of tool tip leads to cracking of sheet material resulting lower forming depth. When tool shape was changed from FlatEnd-R1 to Hemispherical end, Ra decreased approximately 40.44 %, 40.18 % and 27.27 % for 60o, 64o and 68o wall angles respectively. Similarly, Ra was found to decrease by 26.44 %, 27.18 % and 39.77 % for FlatEnd-R1, FlatEnd-R2 and Hemispherical shape respectively when wall angle was reduced from 68o to 60o. Table 4. Average roughness test results with different process parameters. Ra test results for tool diameter and tool shape
Ra test results for wall angle and tool shape
Sr. no.
Tool Diameter
Tool Shape
Ra (μm)
Sr. no.
Wall Angle
Tool Shape
Ra (μm)
1
7.52
FlatEnd-R1
1.27
10
60
FlatEnd-R1
0.89
2
7.52
FlatEnd-R2
1.07
11
60
FlatEnd-R2
0.75
3
7.52
Hemispherical
0.91
12
60
Hemispherical
0.53
4
11.60
FlatEnd-R1
1.04
13
64
FlatEnd-R1
1.07
5
11.60
FlatEnd-R2
0.87
14
64
FlatEnd-R2
0.84
6
11.60
Hemispherical
0.62
15
64
Hemispherical
0.64
7
15.66
FlatEnd-R1
0.68
16
68
FlatEnd-R1
1.21
8
15.66
FlatEnd-R2
0.51
17
68
FlatEnd-R2
1.03
9
15.66
Hemispherical
0.36
18
68
Hemispherical
0.88
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FlatEnd-R1 FlatEnd-R2 Hemispherical
1.3 1.2 1.1
Ra (µm)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3
6
8
10
12
14
16
Tool Diameter (mm) Fig.3. Effects of tool diameter and tool shape on average roughness.
1.2 1.1
FlatEnd-R1 FlatEnd-R2 Hemispherical
Ra(µm)
1.0 0.9 0.8 0.7 0.6 0.5
60
62
64
66
68
Wall Angle (o) Fig.4. Effects of wall angle and tool shape on average roughness.
4. Conclusion This work focused on influence of tool diameter, tool shape and wall angle on surface roughness of the components formed during SPIF. Experimental investigation showed that average roughness of surface of conical frustums increased with decrease in tool diameter and side radius of flat end tools. Increase in wall angle led to increase in surface roughness of the components. Combination of higher wall angle and flat end tool with lower side radius results in fracture of components at lower depth which is an indicator of loss of formability. Best condition of surface finish in terms of minimum Ra (0.36 μm) was obtained with combination of larger tool diameter (15.66 mm)
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and hemispherical tool shape, whereas, surface condition was worst (Ra = 1.27 μm) with combination of lower tool diameter and flat end tool with lower side radius. Analysis of formability and geometrical accuracy of the formed components would be focused in future work. Acknowledgements The authors have no conflict of interest. The authors would like to thank A.R.K. Mould & Tools Ltd., Gurgaon and A.K. Automatics Pvt. Ltd., Rohtak for their assistance. The authors would also like to thank Mr. Udayveer Singh, Mr. Bissan Singh and Er. Narender Saini for their appreciable contribution in developing experimental set-up analysis of results. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
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