12.1: Introduction

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Consider a manufacturing facility that is required to produce multiple part types. Demand is insufficient to warrant a dedicated work cell for any part type. However, demand for all part types together is sufficient to potentially justify automating the production process.

What is needed in this case is a flexible manufacturing system (FMS). Such a system operates efficiently and cost effectively regardless of the mix of part types produced. It is comprised of flexible machines that perform a range of operations on a variety of parts with only minor setup required when switching between part types. Such machines must be programmable or computer numerically controlled (CNC). They must be capable of storing, automatically setting up (loading), and using a variety of tools. A new part type could be introduced without significant additional capital investment, at least if it was sufficiently similar to existing part types.

An FMS requires automated material handling capabilities to move parts between machines as well as into and out of the system. An FMS must be highly automated and thus requires co- ordinated, computer based control.

The initial capital cost of an FMS is high relative to a work cell dedicated to a single part. This investment is worthwhile if the FMS can effectively produce a mix of part types more economically than can a set of dedicated work cells, one per type of part. A flexible manufacturing system could have as many as 20 machines. A system consisting of one or two flexible machines is called a cell.

An FMS operates in a similar manner to a work cell. A part arrives to a single load-unload station where it is attached to a fixture that is mounted on a pallet. More than one part could be attached to the fixture. Parts need not be batched by type upon arrival since machines are able to adapt to processing different part types with relatively little setup time. Measuring the WIP is important since the WIP level is proportional to the number of pallets and fixtures needed.

Since machines are flexible, more than one machine can perform each operation the part requires. Thus, breakdowns do not hamper the operation of an FMS to the same degree as for a dedicated work cell.

One aspect of the design of an FMS is the scheduling of parts on specific machines. In this case study, the assignment of parts to machines using an optimization algorithm is compared with the use of a heuristic dynamic scheduling rule. The performance measure of interest is the total time to produce a given number of parts.