Revisiting Formability and Failure of AISI304 Sheets in SPIF: Experimental Approach and Numerical Validation

Abstract

Single Point Incremental Forming (SPIF) is a flexible and economic manufacturing process with a strong potential for manufacturing small and medium batches of highly customized parts. Formability and failure in SPIF have been intensively discussed in recent years, especially because this process allows stable plastic deformation well above the conventional forming limits, as this enhanced formability is only achievable within a certain range of process parameters depending on the material type. This paper analyzes formability and failure of AISI304-H111 sheets deformed by SPIF compared to conventional testing conditions (including Nakazima and stretch-bending tests). With this purpose, experimental tests in SPIF and stretch-bending were carried out and a numerical model of SPIF is performed. The results allow the authors to establish the following contributions regarding SPIF: (i) the setting of the limits of the formability enhancement when small tool diameters are used, (ii) the evolution of the crack when failure is attained and (iii) the determination of the conditions upon which necking is suppressed, leading directly to ductile fracture in SPIF.

On the Free-Surface Roughness in Incremental Forming of a Sheet Metal: A Study from the Perspective of ISF Strain, Surface Morphology, Post-Forming Properties, and Process Conditions

“…where c is a factor by which σm in the Cu layer is greater than that in the monolithic Cu sheet. Bearing in mind that the hydrostatic stress in ISF has a tensile nature on the free surface [32,33] and it promotes the formation of defects like orange peel, it is possible to infer that the free Cu layer (in Cu/Steel/Cu bonded sheet) experienced more surface defects resulting in rougher texture than texture in a monolithic Cu sheet due to enduring greater tensile hydrostatic stress. The textures For comparison, the roughness results of monolithic DCO4 Steel sheet are also presented in Table 4.…”

“…The above force condition will ultimately change the state of stress, thereby increasing the hydrostatic stress (σ m ) on the free Cu surface in comparison to the monolithic Cu sheet, i.e., σ m(Cu layer) = c σ m(Cu) (13) where c is a factor by which σ m in the Cu layer is greater than that in the monolithic Cu sheet. Bearing in mind that the hydrostatic stress in ISF has a tensile nature on the free surface [32,33] and it promotes the formation of defects like orange peel, it is possible to infer that the free Cu layer (in Cu/Steel/Cu bonded sheet) experienced more surface defects resulting in rougher texture than texture in a monolithic Cu sheet due to enduring greater tensile hydrostatic stress. The textures shown in Figure 13, which were discussed earlier, witness this point.…”

Advances in Plastic Forming of Metals

“…Some of the contributions examine forming limits and defects in the context of actual manufacturing processes. Centeno et al [17] examine formability and failure in single point incremental forming (SPIF) of AISI304-H111 sheets and compare it to conventional forming conditions, e.g., the Nakajima and stretch-bending tests. Among other things, they determine the conditions upon which necking is suppressed, so that failure in SPIF is by ductile fracture.…”

Guidelines for Selecting Plugs Used in Thin-Walled Tube Drawing Processes of Metallic Alloys

“…The finite element software used in this analysis is DEFORM (Scientific Forming Technologies Corporation, v11.0, Columbus, OH, USA) [42]. This program is a specific purpose code that is especially designed to simulate both bulk [43] and sheet metal forming processes [44]. The design of the tools (die and mandrel) has been previously developed in AutoCAD (Autodesk Developer Network, 2013, San Rafael, CA, USA) and subsequently imported into DEFORM™-F2.…”