A study on drawbead restraining force effectiveness

Springback phenomenon is mainly a problem of residual stresses, which are released after die opening. The use of drawbeads in the blankholders of forming dies is a widely taken measure in order to influence the stress state through the thickness of the sheet material. Besides, blankholder closing force has implications in die design and energy consumption during production. This paper presents a methodology to evaluate the efficiency of different drawbead geometries regarding restraining capacity. An efficiency parameter was created which allows for a comparison between drawbead geometries. It is based on the measurement of the maximal in-plane strain in the test part which can be generated with a determined blankholder force. Finite element simulations using commercial software have been run on a test part, using different drawbead geometries and closing forces. The simulations were experimentally validated using a test die. With the methodology, it is possible to determine the most efficient drawbead geometry for a definite sheet metal part, allowing for reducing die investments and press energy consumption per part produced.