Determining stock-sheet-sizes to minimise trim loss

Abstract

This paper discusses the methods developed by an automobile press shop to determine stock-sheet-sizes to minimise total-trim-loss. The shop stocks sheets in a few sizes and manufactures a number of parts using them. When a part is to be produced, the most economic stock-sheet-size is selected and cut into blanks of required size. From one sheet, blanks of only one size are cut. Cutting blanks of more than one size from a sheet is not done to avoid coordination problems. However, the same sheet size may be used for another part at another time. The stock-sheet-sizes are determined by: (a) suggesting sheet sizes which are likely to give low trim loss for major parts, (b) generating a trim-loss matrix giving trim loss for every combination of suggested sheet sizes and parts, and (c) using a heuristic method to select a given number of sheet sizes. This method was used to determine stock-sheet-sizes for Extra Deep Drawing (EDD) steel sheets. The shop used 8364 tons of sheets in a year and generated 625 tons of trim loss. This could be reduced to 332 tons by selecting the best existing size for every part, without changing the sheet sizes. It could be further reduced to 74 tons by determining stock-sheet-sizes using the method described in this paper.