Threshold tool-radius condition maximizing the formability in SPIF considering a variety of materials: Experimental and FE investigations

Abstract In the current study, a new level of understanding on the influence of using small tool radii on the formability (θmax) is identified for single point incremental forming (SPIF). The relative value of tool radius and blank thickness (i.e., R/TB, where R is the tool radius and TB is the blank thickness) was varied over a range (from 1.1 to 3.9), and a formability diagram in the R/TB–θmax space was obtained. The formability was observed to show an inverse V-type pattern which revealed that there is a critical radius of tool (Rc) that maximizes the formability in SPIF. Further, this radius which was found to be independent of the material type (or property) is a function of blank thickness related as, Rc≈2.2TB. This radius was termed as threshold radius. The formability, in agreement with general opinion in the literature, was noticed to increase with the decrease in the tool radius above the threshold value. However, contrarily it reduced with the decrease in the tool radius below the threshold value. In fact, undue surface cutting and metal squeezing was detected when the tests were performed with pointed tools, i.e., below threshold radius. This unstable deformation, which according to the FE analyses was found to be an outgrowth of in-plane compression under the tool center, increasingly weakened the material by inducing corresponding increase in damage (quantified by stress triaxiality) with the decrease in the tool radius. On the other hand, the damage was also observed to increase due to decrease in compression with the increase in the tool radius above the threshold value. This revealed high compression with low damage constitutes the most conducive condition that maximizes the formability in SPIF, which is realized when R≈2.2TB.

[1]  Ghulam Hussain,et al.  Electric hot incremental forming: A novel technique , 2008 .

[2]  J. J. Park,et al.  Effect of process parameters on formability in incremental forming of sheet metal , 2002 .

[3]  B. Lu,et al.  Analytical and experimental investigations on deformation mechanism and fracture behavior in single point incremental forming , 2014 .

[4]  L. Gao,et al.  A novel method to test the thinning limits of sheet metals in negative incremental forming , 2007 .

[5]  Paulo A.F. Martins,et al.  Revisiting the fundamentals of single point incremental forming by means of membrane analysis , 2008 .

[6]  Joost R. Duflou,et al.  Improved SPIF performance through dynamic local heating , 2008 .

[7]  Yonggang Huang,et al.  Studies of Size Effect on the Formability of a Domed Part in Incremental Forming , 2008 .

[8]  J Jeswiet,et al.  Wall thickness variations in single-point incremental forming , 2004 .

[9]  Nasir Hayat,et al.  On the Effect of Curvature Radius on the Spif-Ability , 2010 .

[10]  Meftah Hrairi,et al.  Research and Progress in Incremental Sheet Forming Processes , 2011 .

[11]  Niels Bay,et al.  Failure mechanisms in single-point incremental forming of metals , 2011 .

[12]  Paulo A.F. Martins,et al.  Revisiting single-point incremental forming and formability/failure diagrams by means of finite elements and experimentation , 2009 .

[13]  Fabrizio Micari,et al.  Analysis of Material Formability in Incremental Forming , 2002 .

[14]  M. Shim,et al.  The formability of aluminum sheet in incremental forming , 2001 .

[15]  Julian M. Allwood,et al.  The mechanics of incremental sheet forming , 2009 .

[16]  N. Hayat,et al.  Guidelines for Tool-Size Selection for Single-Point Incremental Forming of an Aerospace Alloy , 2013 .

[17]  W. Hosford,et al.  Metal Forming: Mechanics and Metallurgy , 1993 .

[18]  Markus Bambach,et al.  Forming strategies and Process Modelling for CNC Incremental Sheet Forming , 2004 .

[19]  R. J. McDonald,et al.  Experimental Characterization of Damage Processes in Aluminum AA2024-O , 2010 .

[20]  G Hussain,et al.  Empirical modelling of the influence of operating parameters on the spifability of a titanium sheet using response surface methodology , 2009 .

[21]  Niels Bay,et al.  Single‐point incremental forming and formability—failure diagrams , 2008 .

[22]  Ghulam Hussain,et al.  An experimental study on the effect of thinning band on the sheet formability in negative incremental forming , 2008 .

[23]  Jack Jeswiet,et al.  Single Point Incremental Forming and the Forming Criteria for AA3003 , 2006 .

[24]  W. C. Emmens,et al.  A numerical investigation of the continuous bending under tension test , 2011 .

[25]  Z. Xia,et al.  Modeling and validation of deformation process for incremental sheet forming , 2013 .

[26]  Joost Duflou,et al.  Asymmetric single point incremental forming of sheet metal , 2005 .

[27]  Dong-Yol Yang,et al.  Investigation of a new incremental counter forming in flexible roll forming to manufacture accurate profiles with variable cross-sections , 2014 .

[28]  Jun Gu,et al.  Strain evolution in the single point incremental forming process: digital image correlation measurement and finite element prediction , 2011 .

[29]  G. Centeno,et al.  Critical analysis of necking and fracture limit strains and forming forces in single-point incremental forming , 2014 .

[30]  R. J. Alves de Sousa,et al.  On the use of EAS solid‐shell formulations in the numerical simulation of incremental forming processes , 2011 .

[31]  Dongkai Xu,et al.  Mechanism investigation for the influence of tool rotation and laser surface texturing (LST) on formability in single point incremental forming , 2013 .

[32]  Paulo A.F. Martins,et al.  Single Point Incremental Forming using a Dummy Sheet , 2007 .

[33]  G. Hussain,et al.  A new formability indicator in single point incremental forming , 2009 .

[34]  F. Micari,et al.  Influence of mechanical properties of the sheet material on formability in single point incremental forming , 2004 .