Hariharasudhan Palaniswamy

Optimization of blank dimensions to reduce springback in the flexforming process

Abstract In sheet metal forming operations, springback of the part during unloading largely determines whether the part conforms to the design dimensions and tolerances. Finite element simulations were performed in order to study the interrelationship of the blank dimensions and interface conditions on the springback for an axisymmetric conical part manufactured by flexforming. Sensitivity analysis done using the finite element method (FEM) demonstrated that the magnitude of springback and the overall dimensional quality are highly influenced by the initial dimensions of the blank. A conventional optimization method combined with FEM was used to obtain optimum blank dimensions that can reduce springback.

Optimal Programming of Multi-point Cushion Systems for Sheet Metal Forming

Numerical optimization technique coupled with finite element analysis of the stamping/sheet hydroforming process was developed to predict four possible modes for application of blank holder force (BHF) in multiple-point cushion systems, namely a) BHF constant in space/location and time/stroke, b) BHF variable in time/stroke and constant in space/location, c) BHF variable in space/location and constant in time/stroke and d) BHF variable in space/location and time/stroke. The BHF was predicted by (a) minimizing the risk of failure by tearing (thinning) in the formed part and (b) avoiding wrinkling. The developed technique was applied to predict the BHF to form a) an automotive part (liftgate-inner) from AA6111-T4 aluminum alloy, b) an asymmetric part from aluminum alloy AA5083-H32 by sheet hydroforming process with die (SHF-D) and c) a round cup by sheet hydroforming with punch (SHF-P). Experimental results showed that the FEM based optimization methodology can reduce trial and error effort and is able to predict the blank holder force necessary to form the parts without fracture and wrinkling in the investigated stamping and sheet hydroforming operations.

Tube and Sheet Hydroforming-Advances in Material Modeling, Tooling and Process Simulation

Tube Hydroforming is a well accepted production technology in automotive industry while sheet hydroforming is used in selected cases for prototyping and low volume production. Research in advanced methods (warm sheet and tube hydroforming, double blank sheet hydroforming, combination of hydroforming and mechanical sizing, use of multi-point and elastic blank holders) is expanding the capabilities of hydroforming technologies to produce parts from Al and Mg alloys, as well as Ultra High Strength Steels. In the development of advanced hydroforming methods, experience based knowledge is not readily available. Thus, robust process simulation is required, along with adequate material modeling and identification of friction coefficients as input to process simulation. This paper gives an overview of advanced hydroforming methods, including examples of novel machine and tooling designs. The use of reliable process simulation is illustrated with examples that demonstrate the significance of material and friction date for making accurate predictions. Advanced simulation methods for warm forming and for programming multiple-point blank holder are also discussed. This review illustrates that hydroforming continues to make advances and has the potential to make many contributions to production technology in the near future.

Prediction of Blank Holder Force in Stamping Using Finite Element Analysis

Introduction of multiple point cushion technology in stamping press has provided an additional degree of freedom to improve the formability of the materials by changing the blank holder/binder/cushion force in space/location and in stroke during the process. However, this advanced capacity of die cushion is being underutilized in production because it is difficult to estimate the force required in each pin and its variation throughout the press stroke to form a part with desired quality. This paper describes two methods namely, a) Numerical Optimization, b) Adaptive simulation coupled with finite element analysis of the stamping process to predict constant and variable binder force (variation in stroke) to form the part without failure and with reduced springback. The blank holder force is predicted by detection of a) wrinkles, b) thinning and c) stress variation through thickness direction during the FE simulation to eliminate potential defects such as wrinkles and thinning and reduce springback in the p...