Lightening the load of metal sheeting
In the blanking process, that is the cutting of a blank, the blank holder force (BHF) is of great importance. During the formation of thin, high strength metal sheets, wrinkling of the sheet can become a problem. This is especially true in the case of difficult-to-form materials such as aluminium and stainless steel. To overcome this, the BHF typically has to be relatively large. The BH is that part of the forming die which holds the blank by pressure against a mating surface of the die to control metal flow and prevent wrinkling. Pressure is applied by mechanical means, springs, air, or fluid cushions. The pressure exerted by the blank holder against the blank is normally adjustable to control metal flow during drawing. A new system has been developed which minimises blank holder force, and optimises frequency and amplitude. Compared with conventional processes, this fully automated system results in material reduction since material thickness in the pan production can be reduced by as much as 30%. Drawing depth can be increased by up to 25%, removing the need for additional deep drawing steps. Part strength is also significantly improved, with the weakest edges showing an increase in strength of 4.5%. The resultant sheets are high in tensile strength and light in weight benefiting the automotive industry as well as in all other industries, which require such lightweight metal sheets. The enormous cost savings with regard to raw material reduction and energy savings will improve the competitiveness of the relevant European industries.
