Because of the large number of components, the variety and the short life cycle of electronic products, the assembly of electronic products has brought great challenges to production operation scheduling, and many varieties, small batches and variable batches have become the mainstream production mode of electronic manufacturing.
In this mode, the switching time between the various varieties occupies an increasing proportion in the whole assembly Time. By the high-speed SMT machine and multi-functional Mounter Composition. In fact, the entire PCB assembly line also includes the feeder, screen printing presses, dispensing machines, reflow soldering and curing furnace, receiving machine and other equipment, these equipment in series to form a PCB assembly line, but these auxiliary equipment does not constitute the entire pipeline bottleneck process, and thus in the modeling is Omitted. Each SMT machine can hold 20 feeding slots, each of which occupies a feeding slot on the SMT Machine.
As a general rule, the number of components required for a SINGLE-PRODUCT PCB circuit board does not exceed the capacity of the feeder, but the total number of component types required for a variety of PCBs usually exceeds the capacity of the Feeder. The components required for different types of PCB board in the placement process are placed on these feeding slots, and the mounting device is removed from the feeding tank and affixed to the specified position on the PCB. According to the investigation data of the empirical research object, the time of the high-speed mounter to mount one component is 0.06s, and the time of the average switching of a feeding trough is 180s. Multi-function Mounter has two workbench, but only one workbench work, the other one is only for large or profiled components, each table accommodates 10 feeding slots, the average placement of a component requires 0.18s, the average switching time for a feeder is 220s. When switching between different types of pcbs, the placement machine needs a certain amount of time to prepare for switching, usually to switch one component to 6 times times the time of the feed slot, that is, 1200s.
Therefore, the switching time in the electronic product assembly process has a pivotal position. In the Multi-species small batch environment, usually first the PCB grouping, will have similar characteristics of the PCB into a group, so that in the same group, different varieties of PCB between the assembly does not need to replace the feeder, but also do not need to switch time, but when the two sets of PCB need to replace the feeder, you need to consider the switching time between them accordingly, The PCB production scheduling problem is divided into two levels: the first level of scheduling problems called "board-level" scheduling problem, that is, a PCB group in the production sequence of each pcb; the second level of scheduling problem is called "group-level" scheduling problem, that is, to determine the production sequence between the PCB Organization.
