Single point incremental forming (SPIF) is an innovative sheet forming process with a high economic pay-off. The formability in this process can be maximized by executing forming with a tool of specific small radius, regarded as threshold critical radius. Its value has been reported as 2.2 mm for 1 mm thick sheet materials. However, with a change in the forming conditions specifically in the sheet thickness and step size, the critical radius is likely to alter due to a change in the bending condition. The main aim of the present study is to undertake this point into account and develop a relatively generic condition. The study is composed of experimental and numerical investigations. The maximum wall angle (θmax) without sheet fracturing is regarded as sheet formability. A number of sheet materials are formed to fracture and the trends correlating formability with normalized radius (i.e., R/To where R is the tool-radius and To is the sheet thickness) are drawn. These trends confirm that there is a critical tool-radius (Rc) that maximizes the formability in SPIF. Furthermore, it is found that the critical radius is not fixed rather it shows dependence on the sheet thickness such that Rc = βTo, where β varies from 2.2 to 3.3 as the thickness increases from 1 mm to 3 mm. The critical radius, however, remains insensitive to variation in step size ranging from 0.3 mm to 0.7 mm. This is also observed that the selection of tool with R < Rc narrows down the formability window not only on the higher side but also on the lower side. The higher limit, as revealed by the experimental and FEA results, diminishes due to excessive shearing because of in-plane biaxial compression, and the lower limit reduces due to pillowing in the bottom of part. The new tool-radius condition proposed herein study would be helpful in maximizing the formability of materials in SPIF without performing experimental trials.
Single point incremental forming (SPIF) is an innovative sheet forming process with a high economic pay-off. The formability in this process can be maximized by executing forming with a tool of specific small radius, regarded as threshold critical radius. Its value has been reported as 2.2 mm for 1 mm thick sheet materials. However, with a change in the forming conditions specifically in the sheet thickness and step size, the critical radius is likely to alter due to a change in the bending condition. The main aim of the present study is to undertake this point into account and develop a relatively generic condition. The study is composed of experimental and numerical investigations. The maximum wall angle (θmax) without sheet fracturing is regarded as sheet formability. A number of sheet materials are formed to fracture and the trends correlating formability with normalized radius (i.e., R/To where R is the tool-radius and To is the sheet thickness) are drawn. These trends confirm that there is a critical tool-radius (Rc) that maximizes the formability in SPIF. Furthermore, it is found that the critical radius is not fixed rather it shows dependence on the sheet thickness such that Rc = βTo, where β varies from 2.2 to 3.3 as the thickness increases from 1 mm to 3 mm. The critical radius, however, remains insensitive to variation in step size ranging from 0.3 mm to 0.7 mm. This is also observed that the selection of tool with R < Rc narrows down the formability window not only on the higher side but also on the lower side. The higher limit, as revealed by the experimental and FEA results, diminishes due to excessive shearing because of in-plane biaxial compression, and the lower limit reduces due to pillowing in the bottom of part. The new tool-radius condition proposed herein study would be helpful in maximizing the formability of materials in SPIF without performing experimental trials.
[1] H Wang, F Ye, L Chen, et al. Sheet metal forming optimization by using surrogating modeling techniques. Chinese Journal of Mechanical Engineering, 2017, 30(1): 22-36.
[2] SBM Echrif, M Hrairi. Research and progress in incremental sheet forming processes. Materials & Manufacturing Processes, 2011, 26(11): 1404-1414.
[3] J Jeswiet, F Micari, G Hirt, et al. Asymmetric single point incremental forming of sheet metal. CIRP Annals, 2005, 54(2): 88-114.
[4] L Lei, W Zhou, G Hussain. Prediction of single point incremental forming limit. Chinese Journal of Mechanical Engineering, 2010, 46(18): 102-107.
[5] G Ambrogio, L Filice, F Gagliardi. Improving industrial suitability of incremental sheet forming process. International Journal of Advanced Manufacturing Technology, 2012, 58(9-12): 941-947.
[6] G-J Dong, C.C Zhao, M. Y Cao. Flexible-die forming process with solid granule medium on sheet metal. Transactions of Nonferrous Metals Society of China, 2013, 23 (9): 2666-2677.
[7] KA Al-Ghamdi, G Hussain. The pillowing tendency of materials in incremental forming: Experimental and FE analyses. Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2015, 229(5): 744 -753.
[8] J-C Li, C Li, T Zhou. Thickness distribution and mechanical property of sheet metal incremental forming based on numerical simulation. Transaction of Nonferrous Metals Society of China, 2012, 22(1): s54-s60.
[9] G Fan, L Gao, G Hussain, et al. Electric hot incremental forming: A novel technique. International Journal of Machine Tools and Manufacture, 2008, 48(15): 1688-1692.
[10] F Han, J. H Mo, H Qi, et al. Springback prediction for incremental sheet forming based on FEM-PSONN technology. Transactions of Nonferrous Metals Society of China, 2013, 23 (4): 1061-1071.
[11] X Shi, G Hussain, G Zha, et al. Study on formability of vertical parts formed by multi-stage incremental forming. International Journal of Advanced Manufacturing Technology, 2014, 75(5-8): 1049-1053.
[12] M S Shim, J J Park. The formability of aluminum sheet in incremental forming. Journal of Materials Processing Technology, 2001, 113(1-3): 654-658.
[13] L Fratini, G Ambrogio, R D Lorenzo, et al. Influence of mechanical properties of the sheet material on formability in single point incremental forming. CIRP Annals, 2004, 53(1): 207-210.
[14] G Hussain, L Gao, N Hayat. Empirical modelling of the influence of operating parameters on the spifability of a titanium sheet using response surface methodology. Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2009, 223(1): 73-81.
[15] Kathryn Jackson, Julian Allwood. The mechanics of incremental sheet forming. Journal of Materials Processing Technology, 2009, 209(3): 1158-1174.
[16] A Hadoush, AH Van Den Boogaard, WC Emmens. A numerical investigation of the continuous bending under tension test. Journal of Materials Processing Technology, 2011, 211(12):1948-1956.
[17] M B Silva, P S Nielsen, N Bay, et al. Failure mechanisms in single point incremental forming of metals. International Journal of Advanced Manufacturing Technology, 2011, 56: 893-903.
[18] G Centeno, I Bagudanch, AJ Martinez-Donaire, et al. Critical analysis of necking and fracture limit strains and forming forces in single-point incremental forming. Materials and Design, 2014, 63(21): 20-29.
[19] L Filice, L Fratini, F Micari. Analysis of material formability in incremental forming. CIRP Annals, 2002, 51(1): 199- 202.
[20] M Hama, J Jeswieta. Single point incremental forming and forming criteria for AA3003. CIRP Annals, 2006, 55(1): 241-248.
[21] G Hirt, J Ames, M Bambach, et al. Forming strategies and process modelling for CNC incremental sheet forming. CIRP Annals, 2004, 53(1): 203-206.
[22] M B Silva, M Skjoedt, P.A.F. Martins, et al. Revisiting the fundamentals of single point incremental forming by means of membrane analysis. International Journal of Machine Tools and Manufacture, 2007, 48(1): 73-83.
[23] M B Silva, M Skjoedt, A G Atkins, et al. Single point incremental forming and formability-failure diagrams. Journal of Strain Analysis for Engineering Design, 2008, 43(1): 15-35.
[24] Y Fang, B Lu, J Chen, et al. Analytical and experimental investigations on deformation mechanism and fracture behavior in single point incremental forming. Journal of Materials Processing Technology, 2014, 214(8): 1503-1515.
[25] KA Al-Ghamdi, G Hussain. Threshold tool-radius condition maximizing the formability in SPIF considering a variety of materials: experimental and FE investigations. International Journal of Machine Tools and Manufacture, 2015, 88: 82-94.
[26] G Hussain, L Gao. A novel method to test the thinning limits of sheet-metals in negative incremental forming. International Journal of Machine Tools and Manufacture, 2007, 47(3-4) 419-435.
[27] G Hussain, L Gao, N Hayat, et al. On the effect of curvature radius on the spifability. Advanced Materials Research, 2010, 129-131: 1222-1227.
[28] P Eyckens, B Belkassem, C Henrard, et al. Strain evolution in the single point incremental forming process: digital image correlation measurement and finite element prediction. International Journal of Material Forming, 2011, 4(1): 55-71.
[29] S Kweon, A J Beudoin, R J Mcdonald. Experimental characterization of damage processes in aluminum AA2024-O. Journal of Engineering Materials and Technology, 2010, 132(3): 1-9.
[30] G Hussain, KA Al-Ghamdi, H Khalatbari, et al. Forming parameters and forming defects in incremental forming Process: Part B. Materials and Manufacturing Processes, 2014, 29(4): 454-460.
