Batch manufacturing has always had inherent limitations on account of mid-volume, mid variety nature of manufacturing. Work- in- process levels are generally high and machine utilization tends to be low. Job spend a high proportion of time waiting for machine to be set up, waiting to be moved or waiting for other jobs on the machines to be completed. Batch production often requires an army of expeditors, progress chasers to keep jobs flowing through the manufacturing facilities. In batch type manufacturing, some studies conducted revealed that only 5 percent of the total time spent on the shops unnecessary waiting of jobs and so on. One way to improve productivity is to use technology to obtain a better process. These requirements could be met with the aid of computers and numerical control techniques using the basic concepts of Flexible Manufacturing Systems (FMS)
Job shops are designed to produce a variety of products. They usually tend to have low production rate, high manufacturing lead time, more WIP, and more inventories of finished goods. On the other hand, flow shops are designed for mass production. Consequently, they are less flexible to change. The change over a period of time is very high, as it involves redesigning of template, cam switches, dies; fixtures etc. FMS is a combination of job shopped flow in the sense that a limited variety with reasonably quick change over time is possible.
An FMS is a manufacturing system that actually consists of numerical control (NC) machines connected by an automated material handling system. It is operated through central computer control and is capable of simultaneously processing a family of parts with low to medium demand, different process cycles and operation sequences. We can characterize the typical features of FMS as follows:
- It is an attempt to solve the production problem of mid-volume and mid variety parts for which neither high production rate transfer lines nor highly flexible stand-alone NC machines are suitable.
- It is designed to process simultaneously several types of parts in the given mix.
- It is equipped with sophisticated flexible machine tools that are capable of processing a sequence of different parts with negligible tool change over time.
- Parts are transferred from machine to machine by Computer controlled machine handling system.
- It consists of three subsystems (i) the machining system (ii) the material handling systems (iii) the control system
FNS technology results in the reduction of direct and indirect labor force. With the level of automation that is employed in the subsystem, it is possible for a worker to attend to a group of machines in the system. The following is the role of human labor in the FMS:
- Loading and unloading,, tool set up, tool replacement, work piece set up off-line
- Maintenance of the system, multi-task monitoring (3to8 machines)
- Supervision of the overall system taking decisions using the information supplied by the computer system.
The technologically advanced features of the FMS, in part, simplify process designs and complexities in flow in an intermittent flow system in batch manufacturing by offering the following flexibilities;
- Machine flexibility
- Process flexibility
- Routing flexibility
- Volume flexibility
