FMS - Industrial Systems Design          


FMS - Flexible Manufacturing Systems
Integrated Methodology for the Design of FMS – Flexible Manufacturing Systems


Generating a modelling approach for the design of Flexible Manufacturing Systems (FMS) using a concurrent engineering approach assumes independent operation of four modules:


¤ Automation and Robotics
¤ Command and Control
¤ Production Planning and Plant Layout
¤ Maintenance Planning and Logistics.




A FMS is defined as an integrated and automated production system containing:

(a) Flexible process equipment, normally automated machines with numeric control and equipped with quick tool change ability,

(b) Material handling equipment including transfer lines or conveyor belts, forklifts, elevators, automated guided vehicles (AGVS) as well as automated storage and inventory-handling systems such as automated storage and retrieval systems (ASRS),

(c) Sophisticated computerised communication and control systems integrating process and material handling equipment, and

(d) A modern maintenance support structure that can bring the system quickly back to normal after equipment failure. The design of such facilities is a time-consuming multidisciplinary effort with several production-related objectives that may include the minimisation of the transfer cycle duration, work-in-progress and other inventory, set-up times and the amount of fixed investment required.

Other operational objectives such as the maximisation of flexibility, reactivity (or the ability to handle contingencies), availability and productivity should also be taken into account in particular for FMS designed to do batch jobs, small and medium-sized series in addition to mass production volumes.

Design costs are significant as they include system engineering, project preparation and test, installation, personnel training in addition to direct and indirect operating costs after installation.

Flexibility is a particular important design objective implying that the same production line can be used for different products, either sequentially or simultaneously without major transformation costs. Stigler first introduced the concept in 1939 as the slope in the production cost function. A system is said to be flexible if the production cost function is almost flat for a given volume interval, meaning that a slight increase in volume will increase productions costs very little.

A graphic representation is provided below showing that technology II is much more flexible than technology I in the production interval VI - V2. In today's literature, this concept is known as volume flexibility but the concept has been extended to cover other areas as well.



Browne proposed a taxonomy of flexibility that is often used as a reference6. Combining that taxonomy with the one generated by Sethi and Sethi (1990) (7) flexibility may be define with regards to:


¤ Volume
¤ Product mix (allowing simultaneous processing of different products),
¤ Parts (can be added to or eliminated from a production line or equipment),
¤ Routing (alternative production paths available in case of breakdown or sudden changes in demand patterns),
¤ Product design changes,
¤ Process sequence changes,
¤ Machine tools and
¤ Expansion of the overall system.


The advice is to prioritise these types of flexibility and to define the required type of flexibility for the specific system under consideration (8).

The main economic advantage of such systems is the capability to manufacture parts and products economically and in small volumes with the ability to respond to market changes, quality problems, design changes, scheduling conflicts with a low break-even volume, low supervisory costs and low reject levels. The disadvantages are well known: high initial acquisition costs and dependence on highly skilled maintenance and computer programming personnel (9).

The concept has been applied to a wide range of manufacturing industries processes requiring shape and form changing (machining, metal forming, plastic moulding and forming, wood and fibre processing), chemical transformation (plastics, pharmaceutical), assembly (where robots have had a major impact in design), information (to monitor and control manufacturing, co-ordination and decision-making) and transportation (raw materials, in-process goods, finished products and other resources).

The process determination implies a choice of technology (labour, machines, energy sources and other inputs) for which the most important criteria are feasibility and cost.




The choice of technology requires close link with product design, a function that is concerned with functional and aesthetic requirements necessary to meet actual or potential market needs at an acceptable rate of return (10).

Design for Manufacturing methods have been developed as an alternative to decrease total development time and improve the consideration of life cycle issues during product design11. Concurrent engineering methods suggest that product and process development should proceed in parallel, if possible. The ISO 9000 standard for quality assurance also stresses the coherence needed between product and process design processes. The argument is particularly important given the short average product life and the relatively long product development cycles observed in modern industry.

In process design, the choice of equipment, the set or processing steps and their sequence will determine the material flow through the future plant, volumes and physical placement of raw materials, in-process and finished good inventory as well as bottlenecks and congested areas, most of which are useful information for layout decisions. Graphs are widely used internationally to represent alternative choices in FMS process design (12).

Equipment choice is particularly important in FMS design and the decision criteria should include total investment, maintainability, future obsolescence, labour skill requirements, quality consistency, tools requirements, output rate and overall flexibility. There is often a choice between general and special purpose equipment, the former designed to accommodate a wide range of transformations.

The complete set of criteria to evaluate process design choices should include technological feasibility, financial considerations, training requirements for operators and maintenance personnel, compatibility with existing facilities, raw material requirements, equipment size and weight as well as other physical requirements (safety, temperature, water, waste, etc.), maintainability and spare part requirements.

In general, economic pressures on the manufacturing industry require quick response to new markets and products, all subject to uncertain demand patterns in a very competitive global environment. The trends are towards (13):

a) Increasing global competition and pressure for lower costs,
b) Demanding customers with rapidly changing expectations;
c) Accelerating technical evolution;
d) Pressures to shorten lead times and to decrease work-in-progress throughout the production system; e) Shorter product life cycles and longer R&D cycles,
f) Demand for increased production system flexibility and overall efficiency.

Effective facility layout alone can reduce material handling costs by 10% to 30%(14). In addition, plant layout can reduce initial investment costs, work-in-progress inventories and manufacturing lead times15;. Projected future research needs points out towards concurrent consideration of layout and production system design issues (16).

Serial engineering leads to unacceptable delays due to the sequential nature of main design activities and necessary corrections (17). Local decisions made by various experts are isolated in time, space and function. Concurrent engineering on the other hand is "a systematic approach to the integrated, concurrent design of products and their related processes, including manufacture and support". This approach is intended to cause the developers, from the outset, to consider all elements of the product life cycle from conception through disposal, including quality, cost, schedule and user requirements (18). It is a common-sense approach to product and process design as well as support.

The clear specification of product requirements through its life cycle from the start of conception can lead to significant cost reductions both in design and production as well as shorten the development process.

Concurrent engineering approaches integrate the functions of product design, process planning, installation, production and final distribution as well as the experts from various functions such as company designers, R&D specialists, industrial engineers, experts in automation and robotics, production planners and schedulers, marketing managers and others. As a consequence, the simultaneity of the activities integrates the views from various sectors and functions to reduce the total design time significantly. There is particular interest in functions that increase product quality and performance, reduce product manufacturing or investment costs as well as reduce lead-time for design and manufacturing (19).

In process design, concurrent engineering means the integration of conceptual design, concept optimisation, factory design, detailed design (CAD, CAM and CIM plus 3D Simulation), detailed process plans including NC programs and machine tooling.


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