Automated manufacturing system

Automated manufacturing systems can be classified into three basic types: (1) fixed

automation, (2) programmable automation, and (3) flexible automation. They generally

operate as fully automated systems although semiautomated systems are common in

programmable automation. The relative positions of the three types of automation for

different production volumes and product varieties are depicted in Figure 1.5.

Fixed Automation. Fixed automation is a system in which the sequence of processing (or assembly) operations is fixed by the equipment configuration. Each operation

in the sequence is usually simple, involving perhaps a plain linear or rotational motion or

an uncomplicated combination of the two, such as feeding a rotating spindle. It is the integration and coordination of many such operations in one piece of equipment that makes

the system complex. Typical features of fixed automation are (1) high initial investment

for custom-engineered equipment, (2) high production rates, and (3) inflexibility of the

equipment to accommodate product variety.

The economic justification for fixed automation is found in products that are made

in very large quantities and at high production rates. The high initial cost of the equipment

can be spread over a very large number of units, thus minimizing the unit cost relative

to alternative methods of production. Examples of fixed automation include machining

transfer lines and automated assembly machines.

Programmable Automation. In programmable automation, the production

equipment is designed with the capability to change the sequence of operations to accommodate different product configurations. The operation sequence is controlled by a

program, which is a set of instructions coded so that they can be read and interpreted by

the system. New programs can be prepared and entered into the equipment to produce

new products. Some of the features that characterize programmable automation include

(1) high investment in general-purpose equipment, (2) lower production rates than fixed

automation, (3) flexibility to deal with variations and changes in product configuration,

and (4) high suitability for batch production

Programmable automated systems are used in low- and medium-volume production. The parts or products are typically made in batches. To produce each new batch of

a different item, the system must be reprogrammed with the set of machine instructions

that correspond to the new item. The physical setup of the machine must also be changed:

Tools must be loaded, fixtures must be attached to the machine table, and any required

machine settings must be entered. This changeover takes time. Consequently, the typical

cycle for a given batch includes a period during which the setup and reprogramming take

place, followed by a period in which the parts are produced. Examples of programmable

automation include numerically controlled (NC) machine tools, industrial robots, and

programmable logic controllers.

Flexible Automation. Flexible automation is an extension of programmable

automation. A flexible automated system is capable of producing a variety of parts or

products with virtually no time lost for changeovers from one design to the next. There

is no lost production time while reprogramming the system and altering the physical

setup (tooling, fixtures, machine settings). Accordingly, the system can produce various mixes and schedules of parts or products instead of requiring that they be made

in batches. What makes flexible automation possible is that the differences between

parts processed by the system are not significant, so the amount of changeover between

designs is minimal. Features of flexible automation include (1) high investment for a

custom-engineered system, (2) continuous production of variable mixtures of parts or

products, (3) medium production rates, and (4) flexibility to deal with product design

variations. Examples of flexible automation are flexible manufacturing systems that

perform machining processes.

1.2.2 Computerized Manufacturing Support Systems

Automation of the manufacturing support systems is aimed at reducing the amount of

manual and clerical effort in product design, manufacturing planning and control, and

the business functions of the firm. Nearly all modern manufacturing support systems are

implemented using computers. Indeed, computer technology is used to implement automation of the manufacturing systems in the factory as well. Computer-integrated manufacturing (CIM) denotes the pervasive use of computer systems to design the products,

plan the production, control the operations, and perform the various informationprocessing functions needed in a manufacturing firm. True CIM involves integrating all

of these functions in one system that operates throughout the enterprise. Other terms

are used to identify specific elements of the CIM system; for example, computer-aided

design (CAD) supports the product design function. Computer-aided manufacturing

(CAM) is used for functions related to manufacturing engineering, such as process planning and numerical control part programming. Some computer systems perform both

CAD and CAM, and so the term CAD/CAM is used to indicate the integration of the

two into one system.

Computer-integrated manufacturing involves the information-processing activities

that provide the data and knowledge required to successfully produce the product. These

activities are accomplished to implement the four basic manufacturing support functions

identified earlier: (1) business functions, (2) product design, (3) manufacturing planning,

and (4) manufacturing control