Flexible Manufacturing System (FMS):

P versus Q in Factory Operations

Facilities versus Product Quantities:

• A company designs its manufacturing systems and organizes its factories to serve the particular mission of each plant

Certain types of production facilities are recognized as the most appropriate for a given type of manufacturing:

1. Low production – 1 to 100

2. Medium production – 100 to 10,000

3. High production – 10,000 to >1,000,000

Different facilities are required for each of the three quantity ranges

Low Production:

• Job shop is the term used for this type of production facility

A job shop makes low quantities of specialized and customized products

– Products are typically complex, e.g., space capsules, prototype aircraft, special machinery

Equipment in a job shop is general purpose

Labor force is highly skilled

Designed for maximum flexibility

Medium Production:

• Two different types of facility, depending on product variety:

Batch production

– Suited to hard product variety

– Setups required between batches

Cellular manufacturing

– Suited to soft product variety

– Worker cells organized to process parts without setups between different part styles

High Production:

Often referred to as mass production

– High demand for product

– Manufacturing system dedicated to the production of that product

Two categories of mass production:

– Quantity production

– Flow line production

Quantity Production:

• Mass production of single parts on single machine or small numbers of machines

Typically involves standard machines equipped with special tooling

Equipment is dedicated full-time to the production of one part or product type

Typical layouts used in quantity production are process layout and cellular layout

Flow Line Production:

• Multiple machines or workstations arranged in sequence, e.g., production lines

Product is complex

– Requires multiple processing and/or assembly operations

Work units are physically moved through the sequence to complete the product

Workstations and equipment are designed specifically for the product to maximize efficiency

Types of Plant Layout:

• The production process normally determines the type of plant layout to be applied to the facility:

– Fixed position plant layout

• Product stays and resources move to it.

– Product oriented plant layout

• Machinery and Materials are placed following the product path.

– Process oriented plant layout (Functional Layout).

• Machinery is placed according to what they do and materials go to them.

– Cell Layout

• Hybrid Layout that tries to take advantage of different layouts types.

Product Layout:

Group machines in a line to make a certain product - Assembly line

Ex-rim wheel manufacturer

P-Q Analysis

ProductLayouts

FixedPositionLayouts

Mixed LayoutsProcess Layouts

Quantity

Number of Different Products

Functional layout:

Advantages Disadvantages

Best for products made in large quantitiesLow cost per unitFastLow material handling costsLow storage & inventorySimplified training of

new workersFewer personnel

Large initial investmentVulnerable to stoppageInflexible – new designs not

introducedParts must fit exact – no

rework along lineNot suitable for incentive pay Absenteeism hard to handleAll stations must take same

time

Group Machines in centers which perform similar functions

Advantages Disadvantages

Best use of specialization of machines & employeesFlexible – variety of productsGeneral purpose machines – less costlyAbility to follow diverse pathsLess vulnerable to shutdownsMachine breakdown less of

problemSmall batch product economySuitable for incentive pay

General purpose machines slowerWork routing, scheduling difficultMaterial handling costs highMaterial moves slowlyPartially finished inventory high – large storage spaceCommunication difficultSome limit to size of parts

Manufacturing Support Systems:

• A company must organize itself to design the processes and equipment, plan and control production, and satisfy product quality requirements

Accomplished by manufacturing support systems - people and procedures by which a company manages its production operations

Typical departments:

1. Manufacturing engineering

2. Production planning and control

3. Quality control

Flexible Manufacturing:

• Use of special tools and machines

• Computer-controlled machines allow production run to be small

• Reduced set-up time

• Increased quality control with the use of the computer

• Lots as small as one product can be produced at the cost of continuous manufacturing

(a) Fixed Routing and (b) Variable Routing:

Cellular LayoutProcess (Functional)

Layout

Group (Cellular) Layout

Similar resources placed together

Resources to produce similar products placed

together

T T TMM M T

MSG CG CG

SG

D D DD

T T T CG CG

T T T SG SG

M M D D D

M M D D D

A cluster or cell

Computer Control System:

• Typical computer functions in a manufacturing system:

– Communicate instructions to workers (receive processing or assembly instructions for the specific work unit)

– Download part programs to computer-controlled machines

– Control material handling system

– Schedule production

– Failure diagnosis when malfunctions occur and preventive maintenance

– Safety monitoring (protect both the human worker and equipment)

– Quality control (detect and reject defective work units produced by the system)

– Operations management (manage overall operations)

Part or Product Variety: Flexibility

“The degree to which the system is capable of dealing with variations in the parts or products it produces”

• Three cases:

1. Single-model case - all parts or products are identical (sufficient demand/fixed automation)

2. Batch-model case - different parts or products are produced by the system, but they are produced in batches because changeovers are required (hard product variety)

3. Mixed-model case - different parts or products are produced by the system, but the system can handle the differences without the need for time-consuming changes in setup (soft product variety)

Enablers of Flexibility:

• Identification of the different work units

– The system must be able to identify the differences between work units in order to perform the correct processing sequence

• Quick changeover of operating instructions

– The required work cycle programs must be readily available to the control unit

• Quick changeover of the physical setup

– System must be able to change over the fixtures and tools required for the next work unit in minimum time

Manufacturing Systems for Medium or High Product Complexity:

Three Cases of Product Variety in Manufacturing Systems

(a) Single-model case, (b) batch model case, and (c) mixed-model case

Manufacturing Systems for Low Product Complexity:

Automation:

• Automation is the use of control systems and information technologies reducing the need for human intervention.

• In the scope of industrialization, automation is a step beyond mechanization.

• Whereas mechanization provided human operators with machinery to assist them with the muscular requirements of work, automation greatly reduces the need for human sensory and mental requirements as well.

Flexibility:

• Flexibility in manufacturing means the ability to deal with slightly or greatly mixed parts, to allow variation in parts assembly and variations in process sequence, change the production volume and change the design of certain product being manufactured.

Flexible Automation:

• Ability to adapt to engineering changes in parts

• Increase in number of similar parts produced on the system

• Ability to accommodate routing changes

• Ability to rapidly change production set up

Fms

Industrial FMS Communication:

A Flexible Manufacturing System (FMS) is a production system consisting of a set of identical and/or complementary numerically controlled machine which are connected through an automated transportation system.

each process in FMS is controlled by a dedicated computer (FMS cell computer).

History of FMS:

At the turn of the century FMS did not exist. There was not a big enough need for efficiency because the markets were national and there was no foreign competition. Manufacturers could tell the consumers what to buy. Henry Ford is quoted as saying �people can order any color of car as long as it is black.� This was the thinking of many big manufacturers of the time.

After the Second World War a new era in manufacturing was to come. The discovery of new materials and production techniques increased quality and productivity. The wars end open foreign markets and new competition. Now the market focused on consumer and not the manufacturer. The first FMS was patent in 1965 by Theo Williamson who made numerically controlled equipment. Examples of numerically controlled equipment are like a CNC lathes or mills which is called varying types of FMS.

In the 70�s manufacturers could not stay to date with the ever-growing technological knowledge manufacturers competitors have, so FMS became mainstream in manufacturing.

In the 80�s for the first time manufacturers had to take in consideration efficiency, quality, and flexibility to stay in business.

According to Hoeffer, the change in manufacturing over time was due to several factors. (Hoeffer, 1986)

• Increased international competition,

• The need to reduce manufacturing cycle time, and

• Pressure to cut the production cost.

Benefits of Flexible Manufacturing:

• A major benefit to FM systems is that it can fluctuate as the market fluctuates. FM systems can be changed to produce more or less depending on the need. This characteristic is one that many manufactures seek out when trying to develop a product. Also, when a manufacturer is looking to expand, FM systems can expand with the manufacturer. As time changes and new technologies are developed FM systems can change with them.

List of benefits for using FM systems

• Short-term Changes

• Engineering changes,

• Processing changes,

• Machine unavailability, and

• Cutting tool failure.

• Long term Changes

• Changing product volumes,

• Different part mixes, and

• New Product additions.

Manufacturers Considerations (Maleki, 1991)

For these benefits to work for the manufacture there are two characteristics that the FMS should have. These are:

• Technological consistency of the hardware, and

• Management of the technology and its flexibility.

Equipment of FMS:

• Primary equipment

work centers

• Universal machining centers (prismatic FMSs)

• Turning centers (rotational FMSs)

• Grinding machines

Process centers

• Wash machines

• Coordinate measuring machines

• Robotic work stations

• Manual workstations

• Secondary equipment

Support stations

• Pallet/fixture load/unload stations

• Tool commissioning/setting area

Support equipment

• Robots

• Pallet/fixture/stillage stores

• Pallet buffer stations

• Tools stores

• Raw material stores

• Transport system(AGVs,RGVs,robots)

• Transport units(pallets/stillages)

Two categories of flexibility:

– Machine flexibility, covers the system's ability to be changed to produce new product types, and ability to change the order of operations executed on a part.

– Routing flexibility, which consists of the ability to use multiple machines to perform the same operation on a part, as well as the system's ability to absorb large-scale changes, such as in volume, capacity, or capability.

FMS and FMC:

• Early FMSs were large and very complex, consisting of dozens of CNCs and sophisticated material handling systems. They were very automated, very expensive and controlled by incredibly complex software. There were only a limited number of industries that could afford investing in a traditional FMS as described above.

• Currently, the trend in FMS is toward small versions of the traditional FMS, called flexible manufacturing cells (FMC).

– Today two or more CNC machines are considered a flexible cell and two more more cells are considered a flexible manufacturing system.

– Thus, a Flexible Manufacturing System (FMS) consists of several machine tools along with part and tool handling devices such as robots, arranged so that it can handle any family of parts for which it has been designed and developed.

• A flexible manufacturing cell (FMC) consists of two or more CNC machines, a cell computer and a robot.

• The cell computer (typically a programmable logic controller) is interfaced with the microprocessors of the robot and the CNCs.

The Cell Controller:

• The functions of the cell controller include work load balancing, part scheduling, and material flow control.

• The supervision and coordination among the various operations in a manufacturing cell is also performed by the cell computer.

• The software includes features permitting the handling of machine breakdown, tool breakage and other special situations.

The Cell Robot:

• In many applications, the cell robot also performs tool changing and housekeeping functions such as chip removal, staging of tools in the tool changer, and inspection of tools for breakage or expressive wear. When necessary, the robot can also initiate emergency procedures such as system shut-down.

FMS Goals:

• Reduction in manufacturing cost by lowering direct labor cost and minimizing scrap, re-work, and material wastage.

• Less skilled labor required.

• Reduction in work-in-process inventory by eliminating the need for batch processing.

• Reduction in production lead time permitting manufacturers to respond more quickly to the variability of market demand.

• Better process control resulting in consistent quality.

Advantages of FMS:

• Faster, lower- cost changes from one part to another which will improve capital utilization

• Lower direct labor cost, due to the reduction in number of workers

• Reduced inventory, due to the planning and programming precision

• Consistent and better quality, due to the automated control

• Lower cost/unit of output, due to the greater productivity using the same number of workers

• Savings from the indirect labor, from reduced errors, rework, repairs and rejects

• Limited ability to adapt to changes in product or product mix (e.g., machines are of limited capacity and the tooling necessary for products, even of the same family, is not always feasible in a given FMS)

• Substantial pre-planning activity

• Expensive, costing millions of dollars

• Technological problems of exact component positioning and precise timing necessary to process a component

• Sophisticated manufacturing systems

Application of FMS:

• Metal-cutting machining

• Metal forming

• Assembly

• Joining-welding (arc , spot), glueing

• Surface treatment

• Inspection

• Testing

FMS different strategies:

• The capability of producing different parts without major retooling

• A measure of how fast the company converts its process/es from making an old line of products to produce a new product

• The ability to change a production schedule, to modify a part, or to handle multiple parts

Development of FMS:

Several actions must be decided on before you can have a have a FMS. These actions include.

Selecting operations needed to make the product.

Putting the operations in a logical order.

Selecting equipment to make the product.

Arranging the equipment for efficient use.

Designing special devices to help build the product.

Developing ways to control product quality.

Testing the manufacturing system.

Example of a FMS:

FMS Layouts:

• Progressive Layout:

– Best for producing a variety of parts

• Closed Loop Layout:

– Parts can skip stations for flexibility

– Used for large part sizes

– Best for long process times

• Ladder Layout:

― Parts can be sent to any machine in any sequence

― Parts not limited to particular part families

― Open Field Layout:

― Most complex FMS layout

― Includes several support stations