Conveyor Jacket Cut Planning
An application was developed for Gates Power Transmission, Dumfries, to create cutting plans for the production of conveyor belt jackets from stock strips of reinforced material. This case study is an example where a non-standard cutting application can be addressed by the standard SECANT cutting engine with some additional bespoke software development.
In normal bar or pipe cutting, stocks are cut down to create a set of required pieces of different lengths. There will normally be some wasted material at the end of the bar. In this particular case, where the stock material is of high value, we may in certain circumstances be able to use the remnant as a component of some other jacket that is still to be produced.
Although this flexibility allows us to reduce the wastage implicit in cutting it does have disadvantages. Additional material is required to form a hem when two pieces are joined and of course the joining process itself has an associated time and cost. Each jacket is restricted in the number of joins that are permitted in its construction. Some jackets, for example, must be produced as a single piece, others may be so large that they must be produced with one or more hems. In general, however the planner may choose the size of components for a jacket provided that no component is less than some minimum length.
The aim of cut planning is to minimize the total wasted amount of the stock strips. The total waste includes both remnants that are too small to be used as a component and, of course, the additional material used in forming hems.
The components of a jacket are collated and fed to an automatic assembling machine that adds the hems and produces the finished items. Very little marshaling space is available between the cutting and joining operations so components need to be joined as soon as possible after being cut.
In a standard bar cutting operation we can to some extent assess the quality of an individual pattern in terms of cutting speed and the amount of wastage. Such is not the case in this application. A sequence of several cutting patterns need to be examined at the same time to ascertain if the remnant from the first pattern can be efficiently used to produce a component or components for jackets that are then completed in subsequent patterns.
The approach that was taken was to use the SECANT cutting engine to generate super patterns for a remnant (from the immediately preceding cutting pattern) plus a combination of stock strips.
In the super pattern illustrated above the remnant from the previous pattern is too large to be used as a single component (as the remaining component to complete the jacket would then be too small). It is therefore split into components for two jackets that are immediately completed as part of the next pattern. By generating a super pattern for both the remnant and two stock strips we are able to see that this section of the cutting plan is highly efficient will all strips being used without waste and jacket 4 being produced as a single piece without a hem. In addition, all components of a jacket are started and completed within the super pattern ensuring that components are easily marshaled for the assembly machine.
The application was implemented as an automatic process with the jacket requirement and stock availability being imported from the company’s existing database software. Data files detailing the sizes and cutting sequence for the jacket components were generated by the application and used to drive the assembly machine.
The use of super patterns combined with SECANTS standard search procedures generate cutting plans that minimise hems while at the same time almost eliminating waste in the stock strips.