Stapler Anvil Groove Profile Optimization

Staplers are tools that commonly use staples to perforate and join sheets of paper or fabric. The staple, first, punches the paper or fabric and then folds in contact with a solid surface of an anvil. This work aims to develop an optimized rigid anvil to reduce the maximum force required during staple folding for stapling between 2 and 25 sheets of paper. A commercial stapler is used as a case study. Force curves for stapling 0 to 25 sheets of paper in intervals of 5 sheets were measured for this stapler and the maximum forces are always found to occur during the folding of the staple legs. Finite Element Analysis (FEA) models were developed and fitted to real results to be used in an optimization job of the anvil groove profile. An asymmetric anvil is proposed capable of stapling between 2 and 25 sheets of paper in good conditions and indicates that an asymmetric anvil has potential to reduce maximum forces during folding. Results show a reduction of 32% on maximum force for stapling 25 sheets when compared with the commercial stapler anvil and maximum forces are only 8% higher than the maximum forces for paper punching. For fewer sheets the reduction in maximum force lessens and stapling 2 sheets of paper with the proposed anvil results in an increase of 23% in maximum force. However, the maximum forces are still less the less sheets are stapler, therefore, the proposed anvil reduces the overall maximum forces required for the entire system.