F LEXIBLE M ANUFACTURING S YSTEMS

(Steve Krar, Consultant – Kelmar Associates)

The present era of intense global competition is leading U.S. companies toward a renewed commitment to excellence in manufacturing. Attention to the quality of products and processes, the level of inventories, and potential improvements in productivity gained through high tech automation has made manufacturing once again a key element in the strategies of companies intending to be world-class competitors.

To meet the demand for a good selection of high quality, reasonably-priced products, flexible manufacturing systems (FMS) allow manufacturers to quickly change manufacturing operations to produce any product, at any time, while maintaining an economical operation. Flexible manufacturing systems (FMS) are one of the most efficient ways of reducing or eliminating manufacturing problems. FMS is a manufacturing solution that leads to improved profitability by reducing lead times and inventory levels, rapid response to market changes, lower labor costs, and improved manufacturing productivity.

Fig. 10-4-1 FMS consists of a variety of CNC machine tools serviced by a material-handling system under the control of computers. (Cincinnati Machine, A UNOVA Co.)

A flexible manufacturing system generally consists of a number of CNC machine tools and a material-handling system that is supervised (controlled) by one or more dedicated executive (supervisory) computers, Fig. 10-4-1. A typical flexible manufacturing system can completely process the members of one or more part families on a continuing basis without human intervention. FMS brings flexibility to manufacturing so that a part can be produced when the market requires it, and not when it is most suitable for production. The system is also flexible enough to suit changing market conditions and product type without buying other equipment. FMS can use equipment in off-hours (second and third shifts) when it is not normally used. This is a major stepping-stone to unmanned manufacturing and the factory of the future.

WHAT IS FMS?

There are many definitions of FMS depending on the user’s point of view. The following definition applies in most cases:

• A group of CNC machine tools, linked together with an automated material-handling and inspection system, and controlled by a central computer that can randomly process a group of parts and adapt automatically to changes in parts production, mixes, and levels of output.

NEED FOR FMS

The key objective in manufacturing is to get the right raw materials or parts to the right machines at the time they are required. Leaving too much material or getting to the machine too soon creates too much material tied up in in-process inventory. Too little or too late causes delayed work schedules and idle machines. The result in many cases is a poor use of capital, in the form of excess in-process inventory or underutilization of equipment.

Fig. 10-4-2 The use of equipment and facilities in an average manufacturing operation during a year.

There are a total of 8760 hours in one year that can be available to manufacturing operations, Fig. 10-4-2. In a typical manufacturing operation:

• About 44% of the total time available is lost due to incomplete use of second and third shifts.
• 34% of the total time is taken up by vacations and holidays.
• 12% is lost while machines are being set up for the next operation or parts are being loaded or unloaded.
• About 4% of the time is lost due to process difficulties or unforeseen material, tooling, or quality-control problems.
• This leaves only 6% of the total time for actual production.

The manufacturer’s capital investment for equipment, and facilities is working, trying to pay for itself, less than one hour in seventeen.

Fig. 10-4-3 A percentage of time spent on typical manufacturing operations.

Studies have shown that in a typical manufacturing operation a part moving through a metal-cutting operation would be on an individual machine tool only 5-6% of its total time in manufacturing, Fig. 10-4-3. When a part is on a metal-cutting machine tool, and a cutting tool is removing material 1.5-2% of the part’s total manufacturing time and actually performing work and adding value. The other 95% of the time, the part is either moving through the shop or waiting in line for the next operation.