An Experimental-Numerical Study on Curling Process for Metallic Caps Production

In the field of food industry, adoption of metallic caps for the storage of agri-food products is widespread. This type of caps is obtained through a sequence of forming processes executed on a tinplate. First, the plane metal sheet is deep drawn to obtain a cup whose edge is slightly shaped inward, then a curling process forms the edge into a hollow ring. This paper is focused on the curling, which allows to assess the final cap shape immediately before the application of the cups on the jars. Since the process is generally made on packaging lines with high production rates, the design of a proper curling machine needs to consider the effect of fatigue as well as maximum load values. Because of the different cap dimensions and shapes contemporary worked on the line, the loads definition is not easy. The scope of this work is the development of a model for the prediction of curling loads for different cap shapes and sizes. The analytical solutions, available in literature, together with numerical simulations of the process were compared to experimental compression tests made on two different caps type. Considerations on caps geometry and size influence on curling force represent a contribution to the fitness for service evaluation as well as a starting point for the design of new curling machines.