Minimizing wastage of sheet metal for economical manufacturing

Large quantities of sheet metal are consumed every month in various sectors of industry, the automotive, furniture, white and brown goods, electrical and body building (including coaches and containers) being the chief consumers. A large number of “critical” automotive sheet metal parts lead to rejections leading to wastage of sheet metal during manufacturing. Here, a product that permits a smaller window of variation in material properties compared to that permitted by the standards is said to be “critical”. The wastage due to layout (utilization) of blanks on the sheet and that on account of rejections constitutes total wastage. While a number of algorithms are available to maximize sheet utilization and curtail the wastage, there appears to be none to minimize rejections. Thus, it will always be helpful to an industry to use a system capable of predicting and minimizing these rejections at the sheet layout stage. This paper views wastage in totality and attempts to minimize the total wastage arising from layout as well as rejections. Highly strained regions in a sheet metal blank are identified. Based on the permissible window of variation in the material properties, a ‘defect map’ is generated on the sheet. The blanks are laid out and the possible number of rejections is predicted probabilistically, leading to the prediction of the actual utilization of the material.