Haibo Lu

Experimental Study and Efficient Prediction on Forming Forces in Incremental Sheet Forming

Incremental sheet forming (ISF) is a promising forming process in which complex 3D shapes are formed from a sheet of metal using a simple moving tool. The efficient prediction of contact forces in ISF is desirable to monitor the forming process, prevent failure, and implement on-line control and process optimization. However, traditional Finite Element (FE) simulation used for force prediction is significantly time-consuming for complex products. The purpose of this study is to investigate the ISF force prediction and characteristics under different forming conditions and build a potential efficient model. In the present work, forces during the cone forming process with different wall angles and step down sizes were recorded and compared. Different force trends were identified and discussed with reference to bending and strain hardening mechanics. Influences of different parameters on designated formability were also qualified which should benefit the product design process. An efficient predictive model based on upper-bound approach was applied for force prediction in this case. Predicted tangential forces were then compared with the experimental results showing relatively good agreement. The limits of the proposed model were also identified and the potential of future improvements were suggested.

Study on Step Depth for Part Accuracy Improvement in Incremental Sheet Forming Process

Incremental Sheet Forming (ISF) is a new-emerging sheet forming process well suited for small batch production or prototyping because it does not need any dedicated dies or punches. In this forming process, sheet metal parts are formed by a smooth-end tool in a stepwise way, during which plastic deformation is highly localized around the tool end. The part geometric accuracy obtained in the current ISF process, however, has not met the industry specification for precise part fabrication. This paper deals with a study on step depth, a critical parameter in ISF, for improving the geometric accuracy, surface quality and formability. Two sets of experiments were conducted to investigate the influence of step depth on part quality. Dimensional accuracy, surface morphology and material fracture of deformed parts were compared and analysed. An optimum value of step depth was suggested for forming a truncated cone. The present work provided significant fundamental information for the development of an advanced ISF control system on tool path control and optimization.

An Experimental and Numerical Study on Forming Force, Fracture Behavior, and Strain States in Two Point Incremental Forming Process

Two-point incremental sheet forming process (TPIF) is an emerging and promising manufacturing process for the production of complex geometries or customized functional sheet components. In this study, the single-pass TPIF process is investigated using experimental and numerical approaches to study the forming force evolution, fracture behavior and strain states with a varied wall angle hemisphere shape. It can be concluded that both the peak force and fracture depth increases with tool diameter and incremental depth in TPIF process. It seems the deformation mechanism or the failure mechanism is strongly dependent on particular forming conditions based on a failure parts morphology observation. FEM simulation results indicated that the major plastic strain is positive while the minor plastic strain is negative in the TPIF process on a hemiphere shape. it can be concluded that the strain increment and total equivalent plastic strain is affected by both tool diameter and incremental depth.