Companies in the packaging industry buy sheets of paperboard from mills and merchants and convert them into boxes by printing designs on them, stamping out the required nets and then folding and gluing these together.

Boxes come in all shapes and sizes but the converters' printing presses are less flexible. A very common size takes sheets up to 720 x 1020 mm. In order to use their presses efficiently, converters fit the nets of several copies of a box together onto a single sheet. While this reduces the range of sheet sizes which the converters wish to process, there remains a large number of possible sheet sizes.

Converters have to be able to respond quickly to customers' demands. If a customer places an order, the converter can rarely afford to wait for the mill to supply precisely the sheet size required which would minimize the converter's waste. Instead the converter holds stocks of certain sheet sizes and has to manage his inventory so as to be able to respond to short-notice orders.

Converters have limited storage space and do not like having large amounts of working capital tied up in stocks of sheets. There is therefore a tension between the cost of holding stocks and the desire to minimize waste by holding a large variety of sheet sizes. A further complication is that there is a limit to the amount of waste which can be removed on the press. If the trim on either the width or the length of the sheet exceeds this limit, the sheets must be guillotined before they can be used.

Eudoxus Systems has developed the Sheet Size Selection Model to address this problem. It is an Excel spreadsheet which finds good compromises between the number of sheet sizes held, the trim loss and the amount of guillotining required. It takes a list of the orders which are expected together with maximum and minimum sheet sizes, product thickness, etc.

You press a button and let the model choose the sheet sizes. It generates not just a single solution but a family of solutions with different numbers of sheet sizes. Out of this family of solutions it displays the details of one solution with the number of sheet sizes you have specified.

It plots these on a scatter chart and shows the tonnages required for all the solutions on a bar chart. In this example we are looking at the solution with 5 sheet sizes.

Further information about the Model and a demonstration version are available to converters, as explained on the attached information sheet.