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Development of Friction Stir Incremental Forming Process Using Penetrating Tool
ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
Available online at www.sciencedirect.com
www.elsevier.com/locate/procedia
Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 207 (2017) 789–794
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017,
Development of Friction Stir Incremental Forming Process Using Cambridge, United Kingdom Penetrating Tool Development of Friction Stir Incremental Forming Process Using Wei Jianga,*, Takuya Miuraa,Penetrating Masaaki Otsua,Tool Masato Okadaa, Ryo Matsumotob, Hidenori Yoshimurac, Takayuki Muranakad Wei Jianga,*, Takuya Miuraa, Masaaki Otsua, Masato Okadaa, Ryo Matsumotob,
a Department of Mechanical Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan Division of Materials and Manufacturing Science, Osakac University, 2-1 Yamadaoka, Suita,dOsaka 565-0871, Japan c Department of Intelligent Mechanical Systems Engineering, Kagawa University, 2210-20 Hayashicho, Takamatsu, Kagawa 761-0396, Japan d DepartmentaDepartment of Mechanical Engineeering, Fukui National College Technology, Geshi-cho, FukuiJapan 916-8507, Japan of Mechanical Engineering, University of of Fukui, 3-9-1 Bunkyo, FukuiSabae, 910-8507, b Division of Materials and Manufacturing Science, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan c Department of Intelligent Mechanical Systems Engineering, Kagawa University, 2210-20 Hayashicho, Takamatsu, Kagawa 761-0396, Japan d Department of Mechanical Engineeering, Fukui National College of Technology, Geshi-cho, Sabae, Fukui 916-8507, Japan b
Hidenori Yoshimura , Takayuki Muranaka
Abstract
In order to form sheet metals into concave-convex shape without using special machines or dies, a new forming method called Abstract friction stir incremental forming using penetrating tool was proposed. A forming tool called a penetrating tool was originally developed and this tool was composed of two dome shape tools, which located between an upper tool and a lower tool In order to form sheet metals intoofconcave-convex shape without special machines a newofforming called symmetrically and were jointed a screw. Pure aluminum JIS: using A1050-O sheets havingora dies, thickness 2 mm method were used for friction stirSheets incremental forming using penetrating tool was proposed. A forming tool called a shapes penetrating tool was originally workpiece. were formed into a truncated cone shape. Concave, convex and concave-convex were formed successfully developed and this tool The waseffect composed two dome shape tools, which locatedclockwise, between was an upper tool and a lower tool by the proposed method. of toolof rotation direction, clockwise and counter also investigated. symmetrically and were jointed of a screw. Pure aluminum JIS: A1050-O sheets having a thickness of 2 mm were used for workpiece. were formed into a truncated © 2017 TheSheets Authors. Published by Elsevier Ltd.cone shape. Concave, convex and concave-convex shapes were formed successfully by the proposed method. The effect of tool rotation direction, clockwise counter clockwise, was also on investigated. Peer-review under responsibility of the scientific committee of theand International Conference the Technology
of2017 Plasticity . © The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. Peer-review under responsibility of the scientific committee of the International Conference on the Technology Keywords: Friction of Plasticity . stir incremental forming, Penetrating tool, Pure Aluminum, Concave-convex shape, Keywords: Friction stir incremental forming, Penetrating tool, Pure Aluminum, Concave-convex shape,
* Corresponding author. Tel.: +81-776-27-9838; E-mail address: [email protected] * Corresponding Tel.: +81-776-27-9838; 1877-7058 © 2017 author. The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Peer-review under responsibility of the scientific committee Plasticity.
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee Plasticity.
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.830
790 2
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
1. Introduction Product lead time is becoming shorter in lots of fields, like automotive, electronic and machine tool industries. Shorter product lead time promotes a challenge to research, development and trial manufacture of new products. To reduce the product lead time, various rapid manufacturing technologies such as additive manufacturing were proposed. Incremental sheet metal forming is a rapid manufacturing method, which has great potential in the sheet metal forming. In the sheet metal forming, nowadays the most widely used process are stamping and deep drawing, which are based on costly dies and presses. Due to these forming methods need a large initial investment, they are only profitable for mass production. However, Incremental sheet metal forming is different. Manufacturing principle of incremental sheet metal forming is a layer by layer modelling. A complex 3-dimensional shape is disassembled into contour lines. A sheet is formed by locally deformed with a hemispherical tool along the contour lines. Those local deformations accumulate and finally achieve the desired shape. Since no die is need in this method, cost and time can be saved extremely. Therefore, it is suitable for small batch production, rapid prototyping and product repairing. In the most typical incremental sheet forming process, a blank sheet is fixed to a table and a tool is pushed from one side of the sheet. In this method, it is easy to form a bulged shape but hard to form a concave-convex shape. In order to form a sheet into concave-convex shapes, several methods were proposed. One of the proposed method is putting a supporting blank in the opposite side from the tool of the sheet [1]. Another method is double side incremental forming which employs two tools to form the sheet from the both sides simultaneously [2]. Although these two methods can form a sheet into concave-convex shapes, in the former method, the production of the supporting blank making cost and time and in the latter method, a dedicated forming machine having tools in both sides of the sheet is needed. If concave-convex shapes can be formed within a common 3-axis NC machine without using any die or supporting blank, incremental sheet metal forming process will be used for greater application. Friction stir incremental forming (FSIF) is a variation of incremental sheet metal forming which combined friction stir welding (FSW) and incremental sheet metal forming together. FSIF can be used to form magnesium alloys and aluminum alloys successfully without using any heating appliance [3, 4]. FSW is a welding method characterized by easy operation and high welding efficiency. Bobbin tool friction stir welding is a variation of FSW. Bobbin tool consists of two cylinders called shoulder, which are arranged facing each other and connected by a probe. During welding process, probe penetrates plates and each shoulder contact to the top surface and the bottom surface of the plates, respectively. There are many merits of bobbin tool friction welding such as abbreviation of backing support, lower machine load, full penetration weld and so on. In this study, FSIF using penetrating tool was proposed. This new forming process is an application of bobbin tool to FSIF. A penetrating forming tool was developed for forming metal sheets into concave-convex shapes with only this tool and without using die based on the bobbin tool. Aluminum sheets were formed into concave, convex and concave-convex shapes as substantiative experiment of FSIF using penetrating tool. 2. Development of penetrating tool 2.1. Forming principle by penetrating tool A typical shape of a bobbin tool used in FSW, a hemispherical tool used in incremental sheet metal forming and a developed penetrating tool are shown in Fig. 1 (a), (b) and (c), respectively. The penetrating tool consists of two dome shaped shoulders, constituted by flat surface and curved corner, connected by a probe as shown in Fig. 1 (c). During the forming, a sheet is clamped by an upper tool and a lower tool, and then the tool rotates at high rotation rate and friction heat is generated by friction between the shoulder and the sheet surface. Sheet material becomes softer with temperature elevation and a material flow occurs around the probe. By the material flow, probe can pass through the sheet without leaving any hole. If the tool is moved upward and downward during this process, it become possible to deform the sheet into concave-convex shape from the one side of the sheet. 2.2. Designing penetrating tool
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
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There are severe problems in manufacturing and using penetrating tool in a case of making the tool in monolithic structure. The problems are as follows: 1. It is troublesome to make a gap between two shoulders with accuracy. 2. It is impossible to adjust the gap after fabricate. 3. Whole part of the tool has to be discarded when the probe is fractured. 4. It is difficult to remove the tool from the sheet when the tool is left within a sheet. In order to overcome the shortages listed above, a separable penetrating tool was designed as shown in Fig. 2 and Fig. 3. The separable penetrating tool is composed of five parts, base, upper tool, lower tool, middle screw and screw locker. Middle screw, lower tool and screw locker were jointed together by two joint screws. Since the middle screw can be fixed to upper tool and base by “double nut” effect between upper tool and base, the gap can be adjusted by changing the fixing position of the middle screw. Due to upper and lower parts can be separated, only the middle screw is need to replace when probe is fractured. 3. Friction stir incremental forming using penetrating tool 3.1. Experimental apparatus and workpiece A machining center (Okuma Corp., MILLAC44VⅡ) was used for forming. The developed penetrating tool was used as forming tool and its size was illustrated in Fig. 4. Pure Aluminum JIS: A1050-O was used for workpiece which size of 200 mm × 200 mm × 2 mm. Sheet was put in a table and clamped by a special jog which have stage in the outside of jog as shown in Fig. 5. A hold was drilled in the table for the tool leading.
Fig. 1. (a) Bobbin tool; (b) Incremental forming tool; (c) Penetrating tool.
Fig. 3. Photo of separable penetrating tool.
Fig. 4. Tool dimension.
Fig. 2. Structure of separable penetrating tool.
Fig. 5. Experimental apparatus for FSIF.
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
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3.2. Experimental method Friction stir welding using penetrating tool was carried out as a pre-experiment to find suitable welding parameters. And the main parameters in pre-experiment were gap size between upper and lower tool Ga, tool rotation speed ω and tool feed rate v. The results of the pre-experiment shown that welding can be achieved by using penetrating tool and welding was easy success when Ga = 1.8 mm. Based on the results of pre-experiment, forming sheets into concave shape, convex shape and concave-convex shape by friction stir incremental forming using penetrating tool were carried out. Objective forming shape was a truncated cone with a base diameter of 57 mm and a wall angle of θ = 45 °. A tool path for friction stir incremental forming is shown in Fig. 6. Red line in the tool path is the path of tool leading into the sheet in v =200 mm/min. Black line is the path of incremental forming. Since it is hard to obtain conical spiral tool path, multi-circular helix tool path, which tool moves as the circular helix to complex the movement in Z direction, then moves in x-y plane and repeat it, was used to approximate it in this experiment. After leading, the tool was moved at the forming feed rate v and a pitch of tool move up or down per one round pz = 1 mm. Forming depth was 20 mm, but during forming, forming was stopped, when a groove defect, which commonly occurrs in friction stir welding under unsuitable condition, occurred. The forming depth before a groove defect occurring was defined as maximum formable depth in present study. The gap Ga was kept 1.8 mm and tool rotation speed ω and tool feed rate v were changed to do experiment to find maximum formable depth. After forming, a surface profile was measured by a laser displacement meter. 3.3. Experimental results One sets of forming results which maximum depths of 9 mm for concave shape forming, 6 mm for convex shape forming and 2 mm for concave-convex shape forming were shown in this paper. Fig. 7 shows the appearance of formed sheets and the measured surface profiles are plotted in Fig. 8. In these experiments, the tool rotation rate and tool feed rate were ω = 1000 rpm and v = 200 mm/min, respectively. A tool path direction was counter clockwise when viewed from upper side. From the results above, it is clarified that 3 kinds of objective shapes, concave, convex and concave-convex can be formed by friction stir incremental forming using penetrating tool.
Fig. 6. (a) Top view of tool path for FSIF; (b) Sectional view of tool path for FSIF.
Fig. 7. Photos of formed sheet by FSIF using penetrating tool; (a) Concave shape; (b) Convex shape; (c) Concave-convex.
Wei Wei Jiang et al./ Engineering 00 (2017) 000–000 Jiang et Procedia al. / Procedia Engineering 207 (2017) 789–794
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Fig. 8 Sectional profile of formed sheet by FSIF using penetrating tool; (a) Concave shape; (b) Convex shape; (c) Concave-convex.
4. Effect of tool rotation direction on formed shape 4.1. Experimental purpose and method In FSW, advancing side (AS) is the side which a tool rotation direction and a welding direction are same, while retreating side (RS) is opposite. In FSW, a groove defect generally occurs in the specific side. To clarify the reason why the groove defect occurs and to get a better forming, experiments for studying effect of a tool rotation were carried out. Since the developed separable penetrating tool can be used in only counter clockwise (CCW) direction as its structure, the tool path direction was changed equivalently as a way to study the effect of the tool rotation direction. When the tool path is CCW, the center side is AS and the peripheral side is RS. When the tool path is CW, the center side is RS and the peripheral side is AS. In other hand, it was found that the groove defect occurred in FSIF using penetrating tool become deeper with the increase of forming circles. It was assumed that the reason of groove defect occurred have relationship with material flow. So, thickness of formed sheet were measured as a judgement factor of material flow. Forming method and forming conditions were the same in chapter 3. The tool was stopped when a groove defect occurred. After forming, the sheet was cut along the symmetry line by wire cutting machining. A sectional profile was measured by a photo scanner. The thicknesses of sheet formed by the tool path of CCW and CW were measured from the photos of sectional profile by using a graphic processing software. 4.2. Experimental results By using both tool paths of CCW and CW, the sheets can be formed until 9 mm depth. Photos of sectional profile were shown in Fig.9. For a better understanding of material flow, sectional profile was classified to an unformed part, a formed part, a tool place part and a center part. Sheet thickness distributions with the classification are shown in Fig.10. When the tool path was CCW (Fig. 10(a)), the thickness of the unformed part was nearly 2 mm which is equal to the initial sheet thickness. The thickness at the formed part (RS) is greater than 2 mm, but that at the tool place (AS) was much smaller than 2 mm. On the contrary, when the tool path was CW, the thickness at the formed part (AS) was smaller than 2 mm, but that at the tool place (RS) was larger than 2 mm. The thickness distributions are understood in the different point of view. The thickness of the formed sheet in Z direction were also measured. The measured thickness distributions in Z direction are shown in Fig. 11. Because no chips were generated, the volumes of the sheet before and after forming are same. So the material flow can be obviously understand from the thickness distributions in Z direction. The thickness in Z direction at the RS after forming was larger than that before forming. That at the AS after forming was smaller than that before forming. This means that the material flows form the AS to the RS during friction stir incremental forming using penetrating tool.
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
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Fig. 9. Photos of cross sectional of formed sheet by FSIF using Penetrating tool; (a) CCW tool path strategies; (b) CW tool path strategies.
Fig. 10. Thickness distribution of formed sheet; (a) CCW tool path strategies; (b) CW tool path strategies.
Fig. 11. Thickness distribution in Z direction; (a) CCW tool path strategies; (b) CW tool path strategies.
5. Conclusions A friction stir incremental forming experiments by using penetrating tool undertake by using the developed tool. Following results were obtained. 1. Concave, convex and concave-convex shapes can be formed by friction stir incremental forming using penetrating tool. 2. A material flows from the advancing side to the retreating side occurs during friction stir incremental forming using penetrating tool process and eventually causes a groove defect on formed sheet. References [1] J.M. Allwood, D. Braun, O. Music, The effect of partially cut-out blanks on geometric accuracy in incremental sheet forming, J. Mater. Process. Technol. 210 (2010) 1501-1510 [2] H. Meier, V. Smukala, O. Dewald, J. Zhang, Two Point Incremental Forming with Two Moving Forming Tools, Key Eng. Mater. Vol. 344 599-605 [3] M. Otsu, H. Matsuo, M. Matsuda, K. Takashima, Friction stir incremental forming of aluminum alloy sheets, Steel Res. Int. 81 (2010) 942–945. [4] M. Otsu, T. Ichikawa, M. Matsuda, K. Takashima, Improvement of formability of magnesium alloy sheets by friction stir incremental forming, Steel Res. Int. Special Eds. (2011) 537–541.
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000
ScienceDirect
Available online at www.sciencedirect.com
www.elsevier.com/locate/procedia
Procedia Engineering 00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 207 (2017) 789–794
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017,
Development of Friction Stir Incremental Forming Process Using Cambridge, United Kingdom Penetrating Tool Development of Friction Stir Incremental Forming Process Using Wei Jianga,*, Takuya Miuraa,Penetrating Masaaki Otsua,Tool Masato Okadaa, Ryo Matsumotob, Hidenori Yoshimurac, Takayuki Muranakad Wei Jianga,*, Takuya Miuraa, Masaaki Otsua, Masato Okadaa, Ryo Matsumotob,
a Department of Mechanical Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan Division of Materials and Manufacturing Science, Osakac University, 2-1 Yamadaoka, Suita,dOsaka 565-0871, Japan c Department of Intelligent Mechanical Systems Engineering, Kagawa University, 2210-20 Hayashicho, Takamatsu, Kagawa 761-0396, Japan d DepartmentaDepartment of Mechanical Engineeering, Fukui National College Technology, Geshi-cho, FukuiJapan 916-8507, Japan of Mechanical Engineering, University of of Fukui, 3-9-1 Bunkyo, FukuiSabae, 910-8507, b Division of Materials and Manufacturing Science, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan c Department of Intelligent Mechanical Systems Engineering, Kagawa University, 2210-20 Hayashicho, Takamatsu, Kagawa 761-0396, Japan d Department of Mechanical Engineeering, Fukui National College of Technology, Geshi-cho, Sabae, Fukui 916-8507, Japan b
Hidenori Yoshimura , Takayuki Muranaka
Abstract
In order to form sheet metals into concave-convex shape without using special machines or dies, a new forming method called Abstract friction stir incremental forming using penetrating tool was proposed. A forming tool called a penetrating tool was originally developed and this tool was composed of two dome shape tools, which located between an upper tool and a lower tool In order to form sheet metals intoofconcave-convex shape without special machines a newofforming called symmetrically and were jointed a screw. Pure aluminum JIS: using A1050-O sheets havingora dies, thickness 2 mm method were used for friction stirSheets incremental forming using penetrating tool was proposed. A forming tool called a shapes penetrating tool was originally workpiece. were formed into a truncated cone shape. Concave, convex and concave-convex were formed successfully developed and this tool The waseffect composed two dome shape tools, which locatedclockwise, between was an upper tool and a lower tool by the proposed method. of toolof rotation direction, clockwise and counter also investigated. symmetrically and were jointed of a screw. Pure aluminum JIS: A1050-O sheets having a thickness of 2 mm were used for workpiece. were formed into a truncated © 2017 TheSheets Authors. Published by Elsevier Ltd.cone shape. Concave, convex and concave-convex shapes were formed successfully by the proposed method. The effect of tool rotation direction, clockwise counter clockwise, was also on investigated. Peer-review under responsibility of the scientific committee of theand International Conference the Technology
of2017 Plasticity . © The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. Peer-review under responsibility of the scientific committee of the International Conference on the Technology Keywords: Friction of Plasticity . stir incremental forming, Penetrating tool, Pure Aluminum, Concave-convex shape, Keywords: Friction stir incremental forming, Penetrating tool, Pure Aluminum, Concave-convex shape,
* Corresponding author. Tel.: +81-776-27-9838; E-mail address: [email protected] * Corresponding Tel.: +81-776-27-9838; 1877-7058 © 2017 author. The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Peer-review under responsibility of the scientific committee Plasticity.
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee Plasticity.
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.830
790 2
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
1. Introduction Product lead time is becoming shorter in lots of fields, like automotive, electronic and machine tool industries. Shorter product lead time promotes a challenge to research, development and trial manufacture of new products. To reduce the product lead time, various rapid manufacturing technologies such as additive manufacturing were proposed. Incremental sheet metal forming is a rapid manufacturing method, which has great potential in the sheet metal forming. In the sheet metal forming, nowadays the most widely used process are stamping and deep drawing, which are based on costly dies and presses. Due to these forming methods need a large initial investment, they are only profitable for mass production. However, Incremental sheet metal forming is different. Manufacturing principle of incremental sheet metal forming is a layer by layer modelling. A complex 3-dimensional shape is disassembled into contour lines. A sheet is formed by locally deformed with a hemispherical tool along the contour lines. Those local deformations accumulate and finally achieve the desired shape. Since no die is need in this method, cost and time can be saved extremely. Therefore, it is suitable for small batch production, rapid prototyping and product repairing. In the most typical incremental sheet forming process, a blank sheet is fixed to a table and a tool is pushed from one side of the sheet. In this method, it is easy to form a bulged shape but hard to form a concave-convex shape. In order to form a sheet into concave-convex shapes, several methods were proposed. One of the proposed method is putting a supporting blank in the opposite side from the tool of the sheet [1]. Another method is double side incremental forming which employs two tools to form the sheet from the both sides simultaneously [2]. Although these two methods can form a sheet into concave-convex shapes, in the former method, the production of the supporting blank making cost and time and in the latter method, a dedicated forming machine having tools in both sides of the sheet is needed. If concave-convex shapes can be formed within a common 3-axis NC machine without using any die or supporting blank, incremental sheet metal forming process will be used for greater application. Friction stir incremental forming (FSIF) is a variation of incremental sheet metal forming which combined friction stir welding (FSW) and incremental sheet metal forming together. FSIF can be used to form magnesium alloys and aluminum alloys successfully without using any heating appliance [3, 4]. FSW is a welding method characterized by easy operation and high welding efficiency. Bobbin tool friction stir welding is a variation of FSW. Bobbin tool consists of two cylinders called shoulder, which are arranged facing each other and connected by a probe. During welding process, probe penetrates plates and each shoulder contact to the top surface and the bottom surface of the plates, respectively. There are many merits of bobbin tool friction welding such as abbreviation of backing support, lower machine load, full penetration weld and so on. In this study, FSIF using penetrating tool was proposed. This new forming process is an application of bobbin tool to FSIF. A penetrating forming tool was developed for forming metal sheets into concave-convex shapes with only this tool and without using die based on the bobbin tool. Aluminum sheets were formed into concave, convex and concave-convex shapes as substantiative experiment of FSIF using penetrating tool. 2. Development of penetrating tool 2.1. Forming principle by penetrating tool A typical shape of a bobbin tool used in FSW, a hemispherical tool used in incremental sheet metal forming and a developed penetrating tool are shown in Fig. 1 (a), (b) and (c), respectively. The penetrating tool consists of two dome shaped shoulders, constituted by flat surface and curved corner, connected by a probe as shown in Fig. 1 (c). During the forming, a sheet is clamped by an upper tool and a lower tool, and then the tool rotates at high rotation rate and friction heat is generated by friction between the shoulder and the sheet surface. Sheet material becomes softer with temperature elevation and a material flow occurs around the probe. By the material flow, probe can pass through the sheet without leaving any hole. If the tool is moved upward and downward during this process, it become possible to deform the sheet into concave-convex shape from the one side of the sheet. 2.2. Designing penetrating tool
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
791 3
There are severe problems in manufacturing and using penetrating tool in a case of making the tool in monolithic structure. The problems are as follows: 1. It is troublesome to make a gap between two shoulders with accuracy. 2. It is impossible to adjust the gap after fabricate. 3. Whole part of the tool has to be discarded when the probe is fractured. 4. It is difficult to remove the tool from the sheet when the tool is left within a sheet. In order to overcome the shortages listed above, a separable penetrating tool was designed as shown in Fig. 2 and Fig. 3. The separable penetrating tool is composed of five parts, base, upper tool, lower tool, middle screw and screw locker. Middle screw, lower tool and screw locker were jointed together by two joint screws. Since the middle screw can be fixed to upper tool and base by “double nut” effect between upper tool and base, the gap can be adjusted by changing the fixing position of the middle screw. Due to upper and lower parts can be separated, only the middle screw is need to replace when probe is fractured. 3. Friction stir incremental forming using penetrating tool 3.1. Experimental apparatus and workpiece A machining center (Okuma Corp., MILLAC44VⅡ) was used for forming. The developed penetrating tool was used as forming tool and its size was illustrated in Fig. 4. Pure Aluminum JIS: A1050-O was used for workpiece which size of 200 mm × 200 mm × 2 mm. Sheet was put in a table and clamped by a special jog which have stage in the outside of jog as shown in Fig. 5. A hold was drilled in the table for the tool leading.
Fig. 1. (a) Bobbin tool; (b) Incremental forming tool; (c) Penetrating tool.
Fig. 3. Photo of separable penetrating tool.
Fig. 4. Tool dimension.
Fig. 2. Structure of separable penetrating tool.
Fig. 5. Experimental apparatus for FSIF.
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
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3.2. Experimental method Friction stir welding using penetrating tool was carried out as a pre-experiment to find suitable welding parameters. And the main parameters in pre-experiment were gap size between upper and lower tool Ga, tool rotation speed ω and tool feed rate v. The results of the pre-experiment shown that welding can be achieved by using penetrating tool and welding was easy success when Ga = 1.8 mm. Based on the results of pre-experiment, forming sheets into concave shape, convex shape and concave-convex shape by friction stir incremental forming using penetrating tool were carried out. Objective forming shape was a truncated cone with a base diameter of 57 mm and a wall angle of θ = 45 °. A tool path for friction stir incremental forming is shown in Fig. 6. Red line in the tool path is the path of tool leading into the sheet in v =200 mm/min. Black line is the path of incremental forming. Since it is hard to obtain conical spiral tool path, multi-circular helix tool path, which tool moves as the circular helix to complex the movement in Z direction, then moves in x-y plane and repeat it, was used to approximate it in this experiment. After leading, the tool was moved at the forming feed rate v and a pitch of tool move up or down per one round pz = 1 mm. Forming depth was 20 mm, but during forming, forming was stopped, when a groove defect, which commonly occurrs in friction stir welding under unsuitable condition, occurred. The forming depth before a groove defect occurring was defined as maximum formable depth in present study. The gap Ga was kept 1.8 mm and tool rotation speed ω and tool feed rate v were changed to do experiment to find maximum formable depth. After forming, a surface profile was measured by a laser displacement meter. 3.3. Experimental results One sets of forming results which maximum depths of 9 mm for concave shape forming, 6 mm for convex shape forming and 2 mm for concave-convex shape forming were shown in this paper. Fig. 7 shows the appearance of formed sheets and the measured surface profiles are plotted in Fig. 8. In these experiments, the tool rotation rate and tool feed rate were ω = 1000 rpm and v = 200 mm/min, respectively. A tool path direction was counter clockwise when viewed from upper side. From the results above, it is clarified that 3 kinds of objective shapes, concave, convex and concave-convex can be formed by friction stir incremental forming using penetrating tool.
Fig. 6. (a) Top view of tool path for FSIF; (b) Sectional view of tool path for FSIF.
Fig. 7. Photos of formed sheet by FSIF using penetrating tool; (a) Concave shape; (b) Convex shape; (c) Concave-convex.
Wei Wei Jiang et al./ Engineering 00 (2017) 000–000 Jiang et Procedia al. / Procedia Engineering 207 (2017) 789–794
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Fig. 8 Sectional profile of formed sheet by FSIF using penetrating tool; (a) Concave shape; (b) Convex shape; (c) Concave-convex.
4. Effect of tool rotation direction on formed shape 4.1. Experimental purpose and method In FSW, advancing side (AS) is the side which a tool rotation direction and a welding direction are same, while retreating side (RS) is opposite. In FSW, a groove defect generally occurs in the specific side. To clarify the reason why the groove defect occurs and to get a better forming, experiments for studying effect of a tool rotation were carried out. Since the developed separable penetrating tool can be used in only counter clockwise (CCW) direction as its structure, the tool path direction was changed equivalently as a way to study the effect of the tool rotation direction. When the tool path is CCW, the center side is AS and the peripheral side is RS. When the tool path is CW, the center side is RS and the peripheral side is AS. In other hand, it was found that the groove defect occurred in FSIF using penetrating tool become deeper with the increase of forming circles. It was assumed that the reason of groove defect occurred have relationship with material flow. So, thickness of formed sheet were measured as a judgement factor of material flow. Forming method and forming conditions were the same in chapter 3. The tool was stopped when a groove defect occurred. After forming, the sheet was cut along the symmetry line by wire cutting machining. A sectional profile was measured by a photo scanner. The thicknesses of sheet formed by the tool path of CCW and CW were measured from the photos of sectional profile by using a graphic processing software. 4.2. Experimental results By using both tool paths of CCW and CW, the sheets can be formed until 9 mm depth. Photos of sectional profile were shown in Fig.9. For a better understanding of material flow, sectional profile was classified to an unformed part, a formed part, a tool place part and a center part. Sheet thickness distributions with the classification are shown in Fig.10. When the tool path was CCW (Fig. 10(a)), the thickness of the unformed part was nearly 2 mm which is equal to the initial sheet thickness. The thickness at the formed part (RS) is greater than 2 mm, but that at the tool place (AS) was much smaller than 2 mm. On the contrary, when the tool path was CW, the thickness at the formed part (AS) was smaller than 2 mm, but that at the tool place (RS) was larger than 2 mm. The thickness distributions are understood in the different point of view. The thickness of the formed sheet in Z direction were also measured. The measured thickness distributions in Z direction are shown in Fig. 11. Because no chips were generated, the volumes of the sheet before and after forming are same. So the material flow can be obviously understand from the thickness distributions in Z direction. The thickness in Z direction at the RS after forming was larger than that before forming. That at the AS after forming was smaller than that before forming. This means that the material flows form the AS to the RS during friction stir incremental forming using penetrating tool.
Wei Jiang et al. / Procedia Engineering 207 (2017) 789–794 Wei Jiang et al./ Procedia Engineering 00 (2017) 000–000
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Fig. 9. Photos of cross sectional of formed sheet by FSIF using Penetrating tool; (a) CCW tool path strategies; (b) CW tool path strategies.
Fig. 10. Thickness distribution of formed sheet; (a) CCW tool path strategies; (b) CW tool path strategies.
Fig. 11. Thickness distribution in Z direction; (a) CCW tool path strategies; (b) CW tool path strategies.
5. Conclusions A friction stir incremental forming experiments by using penetrating tool undertake by using the developed tool. Following results were obtained. 1. Concave, convex and concave-convex shapes can be formed by friction stir incremental forming using penetrating tool. 2. A material flows from the advancing side to the retreating side occurs during friction stir incremental forming using penetrating tool process and eventually causes a groove defect on formed sheet. References [1] J.M. Allwood, D. Braun, O. Music, The effect of partially cut-out blanks on geometric accuracy in incremental sheet forming, J. Mater. Process. Technol. 210 (2010) 1501-1510 [2] H. Meier, V. Smukala, O. Dewald, J. Zhang, Two Point Incremental Forming with Two Moving Forming Tools, Key Eng. Mater. Vol. 344 599-605 [3] M. Otsu, H. Matsuo, M. Matsuda, K. Takashima, Friction stir incremental forming of aluminum alloy sheets, Steel Res. Int. 81 (2010) 942–945. [4] M. Otsu, T. Ichikawa, M. Matsuda, K. Takashima, Improvement of formability of magnesium alloy sheets by friction stir incremental forming, Steel Res. Int. Special Eds. (2011) 537–541.