Strategies to improve the geometric accuracy in asymmetric single point incremental forming

Abstract

Asymmetric incremental sheet forming (AISF) is a manufacturing process for the small batch production of sheet metal parts. In AISF, a sheet metal part is formed by a forming tool that moves under CNC control. AISF currently has two dominant process limits: sheet thinning and a limited geometric accuracy. This paper focuses on the latter limit. It is shown with a pyramidal part that multistage forming can yield an increased accuracy compared to single-stage forming. However, due to residual stresses induced during forming, the accuracy of the as-formed part can be lost if the part is trimmed after forming. A case study with a car fender section shows that the geometric accuracy of the final part can be improved compared to single-stage forming by a combination of multi-stage forming and stress-relief annealing before trimming.

Fabricate 2017

“…A characteristic of formative fabrication processes, particularly mouldless, freeform approaches, is that their positional accuracy is more highly dependent upon a combination of material behaviour and forming parameters than subtractive or additive approaches. Research into resultant incrementally formed geometries has shown significant deviations from the planned geometries (Bambach et al, 2009), and that parameters including the forming velocity, the toolpath, the size of material and distance to supports and particularly the material springback of the sheet during forming all affect the geometric accuracy of the resulting shape. These geometric deviations are a key deterrent from the widespread take-up of the process (Jeswiet et al, 2008).…”

Part accuracy improvement in two point incremental forming with a partial die using a model predictive control algorithm

“…Without using dedicated dies, it uses a simple tool with a hemispherical end to form the sheet parts. By travelling along a 3D CAM toolpath on the surface of the sheet, the tool end deforms the sheet incrementally with the plastic deformation localised near the tool end [2] The simple dies are generally made of cheap materials like timber or resin [3] so that the cost in the fabrication and storage of dies is not huge. With the use of supporting dies, TPIF generally leads to better geometric accuracy of the formed parts than SPIF [4].…”

“…In order to improve the poor geometric accuracy, some attempts have been presented in the literature, including experimental investigation of process parameters [4,6], hybrid ISF processes [7][8][9], the use of partially cut-out blanks [10], and a multi-stage strategy [3]. Recently, many studies concentrated on the toolpath correction/optimisation.…”

Tool path generation for single point incremental forming using intelligent sequencing and multi-step mesh morphing techniques

“…In particular, incremental forming has been carried out on a wide range of materials including polymers [4][5], many of which have low forming limits, typically defined by a maximum wall angle at which no failure occurs. In addition, several efforts have been made to improve the accuracy of parts [6][7][8][9]. For instance, Verbert et al developed a feature based approach, where the behavior of individual features such as planes, ruled, freeform and ribs is taken into account to manufacture parts with high accuracy [7].…”