Flexible Manufacturing Systems(FMS) Applications and Benefits

      FMS APPLICATIONS  AND BENEFITS

In this section, we explore the applications of FMSs and the benefits that result from these applications. Many of the findings from the industrial survey on cellular manufacturing (reported in Section 15.5.2) are pertinent to FMSs, and we refer the reader to that report .

        FMS Applications

The concept of flexible automation is applicable to a variety of manufacturing operations. In this section, some of the important FMS applications are reviewed. FMS technology i~ most widely applied in machining operations. Other applications include sheet metal pressworking, forging, and assembly. Here some of the applications are examined using case study examples to illustrate.

Flexible Machining Systems. Historically. most of the applications of flexible machining systems have been in milling and drilling type operations (non rotational parts), using NC and subsequently CNC machining centers. FMS applications for turning (rotational parts) were much less common until recently, and the systems that are installed tend to consist of fewer machines. For example, single machine cells consisting of parts storage units, part loading robots, and CNC turning centers are widely used today, although not always in a flexible mode. Let us explore some of the issues behind this anomaly in the development of flexible machining systems.

By contrast with rotational parts, nonrotational parts are often too heavy for a human operator to easily and quickly load into the machine tool. Accordingly, pallet fixtures were developed so that these parts could be loaded onto the pallet offline and then the part on. pallet could be moved into position in front of the machine tool spindle. Non rotational pans also tend to be more expensive than rotational parts, and the manufacturing lead times tend to be longer. These factors provide a strong incentive to produce them as efficiently as possible, using advanced technologies such as FMSs. For these reasons, the technology for FMS milling and drilling applications is more mature today than for FMS turning applications

EXAMPLE             16.1         FMS  at Ingersoll-Rand in Roanoke, Virginia

One of the first FMS installations in the United States was at the Roanoke, Virginia. plant of the Tool and Hoist Division of Ingersoll-Rand Corp. The system was installed by Sundstrand in the late 1960& It consists of two five-axis machining centers, two four axis machining centers, and two four-axis drilling machines. The machines are each equipped with 6Otool storage drums and automatic 1001 changers and pallet changers. A powered roller conveyor system is used for the primary and secondary workpart handling systems. Three operators plus one foreman run the system three shifts. Up to 140 part numbers are machined on the system. The parts begin as cast iron and aluminum castings and are machined into motor cases, hoist casings, and so on. Part size capability ranges up to a 0.9 m cube (36.0 in). Production quantities for the various part numbers range from 12 per year to 20,000 per year. The layout of the system is presented in Figure 16.12.

crankcase halves for aircraft engines. The layout is an open field type and is illustrated in Figure 16.13. The handling of work-parts between machines is performed by an in-floor towline cart system with a total of 2~ pallet carts. The system contains 14 machine tools: one duplex multispindle bead indexer, two simplex multi-spindle head indexers, and 11 machining centers. In a multispindie head indexer, machining heads are attached to an indexing mechanism that indexes (rotates in specified angular amounts) to bring the correct machining head into position to address the work. A simplex unit processes the work on one side only, while a duplex has two indexers on opposite sides of the work. Machining centers are described in Section 14.3.3.

EXAMPLE 16.3   Vought  Aerospace       FMS

An FMS installed at Vought Aerospace in Dallas. Texas, by Cincinnati Milacron is shown in Figure 16.14. The system is used to machine approximately 600 different aircraft components. The FMS consists of eight CNC horizontal machining centers plus inspection modules. Part handling is accomplished by an automated guided vehicle system using four vehicles. Loading and unloading of the system is done at two stations. These load/unload stations consist of storage carousels that permit parts to be stored on pallets for subsequent transfer to the machining stations by the AGVS. The system is capable of processing a sequence of single, one-of-a-kind parts in a continuous mode. permitting a complete set of components for one aircraft to be made efficiently without batching.

Other FMS Applications. Pressworking and forging arc two other manufacturing processes in which efforts are being made to develop flexible automated systems.

 The following example illustrates the development efforts in the pressworking area.

EXAMPLE          16.4   Flexible  Fabricating System

The term flexible fabricating system (FFS) is sometimes used in connection with systems that perform sheet metal press working operations. One FFS concept by Wiedemann is illustrated in Figure 16,15. The system is designed to unload sheet metal stock from the automated storage/retrieval system (AS/RS), move the stock by rail-guided cart to the CNC punch press operations, and then move the finished parts back to the AS/RS, all under computer control.

Flexible automation concepts can be applied to assembly operations. Although some examples have included industrial robots to perform the assembly tasks, the following example illustrates a flexible assembly system that makes minimal use of industrial robots.

EXAMPLE      16.5       Assembly    FMS at Allen-Bradley

An FMS for assembly installed by Allen-Bradley Company is reported in {421. The "flexible automated assembly line" produces motor starters in 125 model styles. The line boasts a 1 day manufacturing lead time on Jot sizes as low as

one and production rates of 600 units/hr. The system consists of 26 workstations that perform all assembly, subassembly, testing, ami packaging required to make the product. The stations are linear and rotary indexing assembly machines with pick-and-place robots performing certain handling functions between the machines. 100% automated testing at each step in the process is used to achieve very high quality levels. The flexible assembly line is controlled by a system of Allen-Bradley programmable logic controllers.

        FMS Benefits

A number of benefits can be expected in successful FMS applications. The principal benefits are the following:

Increased machine utilization. FMSs achieve a higher average utilization than machines in a conventional batch production machine shop. Reasons for this include:

(1) 24 hr/day operation. (2) automatic tool changing ar machine tools. (3) automatic pallet changing at workstations. (4) queues of parts at stations, and (5) dynamic scheduling of production that takes into account irregularities from normal operations. It should be possible to approach 80-90%  asset utilization by implementing FMS technology [23].

   Fewer machines required Because of higher machine utilization. fewer machines are required.

   Reduction in factory floor space required. Compared with a job shop of equivalent capacity, an fMS generally requires less floor area. Reductions in floor space requirements  are estimated to he 40-50%, [23].

   Greater responsiveness to change. An FMS improves response capability to part design changes. introduction of new part s, changes in production schedule and product mix. machine breakdowns. and cutting tool failures. Adjustments can be made in the production schedule from one day to the next to respond to rush orders and special customer requests.

   Reduced inventory requirements, Because different parts are processed together rather than separately in batches. Work-in-process (WIP) is less than in a batch production mode. The inventorv of starting and finished parts can be reduced as well. Inventory reductions of 60-80% are estimated.

   Lower manufacturing lead times. Closely correlated with reduced WIP is the time spent in process by the parts. This means faster customer deliveries

   Reduced direct labor requirements and higher labor productivity. Higher production rates and lower reliance on direct labor translate to greater productivity per labor hour with an FMS than with conventional production methods. Labor savings of 30-.50%, arc estimated [23].

   Opportunity for unattended production. The high level of automation in an FMS allows it to operate for extended periods of time without human attention. In the most optimistic scenario, parts and tools are loaded into the system at the end of the day shift, and the FMS continues to operate throughout the night so that the finished parts can be unloaded the next morning.