Influences of process and material parameters on quality of small-sized thin sheet-metal parts drawn with multipoint tooling

Multi-point tooling forming is one of the special categories of sheet metal forming techniques with good operational flexibilities due to using two sets of adjustable pins along the machine ram direction (vertical direction usually), which represent the acting points of desired forming-tool surface contours. Nevertheless, some defects may develop during forming under different process and machine-set conditions, such as wrinkles and undesired surface indents. This paper presents a study of the influences of possible process variations by adjusting the tooling as well as associated quality control when thin sheet-metals were drawn into the cap-type parts, being focused on the small-sized components. Effects of the curvatures to be formed, sheet material and geometry, holding force, lubrication condition and use of rubber as cushions on the formed component-geometry and surface quality have been investigated. The formed parts were measured with a Co-ordinate Measuring Machine and observed on the indentation with a high resolution Camera. The results showed that careful control of the process parameters and machine setup for the forming of thin sheet-metals for a particular type of the material and geometry is needed prior to the forming production uses with multi-point tooling forming, and use of rubber cushions and proper design of blank-holding are extremely important for successfully forming thin, small sized sheet-metal components with discrete pin-tools.