30079_37.pdf

CHAPTER 37

COMPUTER-INTEGRATED

MANUFACTURING

William E. Biles

Department of Industrial Engineering

University of Louisville

Louisville, Kentucky

Magd £. Zohdi

Department of Industrial and Manufacturing Engineering

Louisiana State University

Baton Rouge, Louisiana

37.1 INTRODUCTION

11 87

37.4 INDUSTRIAL ROBOTS 1 195

37.4.1 Definition 11 95

37.4.2 Robot Configurations 119 6

37.4.3 Robot Control and

Programming 1197

37.4.4 Robot Applications 11 97

37.2 DEFINITIONS AND

CLASSIFICATONS 11 88

37.2.1 Automation 11 88

37.2.2 Production Operations 1189

37.2.3 Production Plants 11 90

37.2.4 Models for Production

Operations

37.5 COMPUTERS IN

MANUFACTURING 11 97

37.5.1 Hierarchical Computer

Control 11 97

37.5.2 CNC and DNC Systems 1198

37.5.3 The Manufacturing Cell 1 198

37.5.4 Flexible Manufacturing

Systems

1190

37.3 NUMERICAL-CONTROL

MANUFACTURING SYSTEMS 1192

37.3. 1 Numerical Control 1 192

37.3.2 The Coordinate System 1192

37.3.3 Selection of Parts for NC

Machining

1198

11 93

37.3.4 CAD/CAM Part

Programming

37.6 GROUP TECHNOLOGY 11 99

37.6. 1 Part Family Formation 1 200

37.6.2 Parts Classification and

Coding 12 00

37.6.3 Production Flow Analysis 1201

37.6.4 Types of Machine Cell

Designs 12 01

37.6.5 Computer- Aided Process

Planning

1 193

37.3.5 Programming by Scanning

and Digitizing 1194

37.3.6 Adaptive Control 11 94

37.3.7 Machinability Data

Prediction

1195

12 03

37.1 INTRODUCTION

Modern manufacturing systems are advanced automation systems that use computers as an integral

part of their control. Computers are a vital part of automated manufacturing. They control stand-

alone manufacturing systems, such as various machine tools, welders, laser-beam cutters, robots, and

automatic assembly machines. They control production lines and are beginning to take over control

of the entire factory. The computer-integrated-manufacturing system (CIMS) is a reality in the modern

industrial society. As illustrated in Fig. 37.1, CIMS combines computer-aided design (CAD),

computer-aided manufacturing (CAM), computer-aided inspection (CAI), and computer-aided pro-

Mechanical Engineers' Handbook, 2nd ed., Edited by Myer Kutz.

Fig. 37.1 Computer-integrated manufacturing system.

duction planning (CAPP), along with automated material handling. This chapter focuses on computer-

aided manufacturing for both parts fabrication and assembly, as shown in Fig. 37.1. It treats

numerical-control (NC) machining, robotics, and group technology. It shows how to integrate these

functions with automated material storage and handling to form a CIM system.

37.2 DEFINITIONS AND CLASSIFICATIONS

37.2.1 Automation

Automation is a relatively new word, having been coined in the 1930s as a substitute for the word

automatization, which referred to the introduction of automatic controls in manufacturing. Automa-

tion implies the performance of a task without human assistance. Manufacturing processes are clas-

sified as manual, semiautomatic, or automatic, depending on the extent of human involvement in the

ongoing operation of the process.

The primary reasons for automating a manufacturing process are to

1. Reduce the cost of the manufactured product, through savings in both material and labor

2. Improve the quality of the manufactured product by eliminating errors and reducing the

variability in product quality

3. Increase the rate of production

4. Reduce the lead time for the manufactured product, thus providing better service for

customers

5. Make the workplace safer

The economic reality of the marketplace has provided the incentive for industry to automate its

manufacturing processes. In Japan and in Europe, the shortage of skilled labor sparked the drive

toward automation. In the United States, stern competition from Japanese and European manufac-

turers, in terms of both product cost and product quality, has necessitated automation. Whatever the

reasons, a strong movement toward automated manufacturing processes is being witnessed throughout

the industrial nations of the world.

37.2.2 Production Operations

Production is a transformation process in which raw materials are converted into the goods demanded

in the marketplace. Labor, machines, tools, and energy are applied to materials at each of a sequence

of steps that bring the materials closer to a marketable final state. These individual steps are called

production operations.

There are three basic types of industries involved in transforming raw materials into marketable

products:

1. Basic producers. These transform natural resources into raw materials for use in manufac-

turing industry—for example, iron ore to steel ingot in a steel mill.

2. Converters. These take the output of basic producers and transform the raw materials into

various industrial products—for example, steel ingot is converted into sheet metal.

3. Fabricators. These fabricate and assemble final products—for example, sheet metal is fab-

ricated into body panels and assembled with other components into an automobile.

The concept of a computer-integrated-manufacturing system as depicted in Fig. 37.1 applies specif-

ically to a "fabricator" type of industry. It is the "fabricator" industry that we focus on in this

chapter.

The steps involved in creating a product are known as the "manufacturing cycle." In general, the

following functions will be performed within a firm engaged in manufacturing a product:

1. Sales and marketing. The order to produce an item stems either from customer orders or

from production orders based on product demand forecasts.

2. Product design and engineering. For proprietary products, the manufacturer is responsible

for development and design, including component drawings, specifications, and bill of

materials.

3. Manufacturing engineering. Ensuring manufacturability of product designs, process plan-

ning, design of tools, jigs, and fixtures, and "troubleshooting" the manufacturing process.

4. Industrial engineering. Determining work methods and time standards for each production

operation.

5. Production planning and control. Determining the master production schedule, engaging in

material requirements planning, operations scheduling, dispatching job orders, and expedit-

ing work schedules.

6. Manufacturing. Performing the operations that transform raw materials into finished goods.

7. Material handling. Transporting raw materials, in-process components, and finished goods

between operations.

8. Quality control. Ensuring the quality of raw materials, in-process components, and finished

goods.

9. Shipping and receiving. Sending shipments of finished goods to customers, or accepting

shipments of raw materials, parts, and components from suppliers.

10. Inventory control. Maintaining supplies of raw materials, in-process items, and finished

goods so as to provide timely availability of these items when needed.

Thus, the task of organizing and coordinating the activities of a company engaged in the manufac-

turing enterprise is complex. The field of industrial engineering is devoted to such activities.

37,2,3 Production Plants

There are several ways to classify production facilities. One way is to refer to the volume or rate of

production. Another is to refer to the type of plant layout. Actually, these two classification schemes

are related, as will be pointed out.

In terms of the volume of production, there are three types of manufacturing plants:

1. Job shop production. Commonly used to meet specific customer orders; great variety of work;

production equipment must be flexible and general purpose; high skill level among

workforce—for example, aircraft manufacturing.

2. Batch production. Manufacture of product in medium lot sizes; lots produced only once at

regular intervals; general-purpose equipment, with some specialty tooling—for example,

household appliances, lawn mowers.

3. Mass production. Continuous specialized manufacture of identical products; high production

rates; dedicated equipment; lower labor skills than in a job shop or batch manufacturing—for

example, automotive engine blocks.

In terms of the arrangement of production resources, there are three types of plant layouts. These

include

1. Fixed-position layout. The item is placed in a specific location and labor and equipment are

brought to the site. Job shops often employ this type of plant layout.

2. Process layout. Production machines are arranged in groups according to the general type of

manufacturing process; forklifts and hand trucks are used to move materials from one work

center to the next. Batch production is most often performed in process layouts.

3. Product-flow layout. Machines are arranged along a line or in a U or S configuration, with

conveyors transporting work parts from one station to the next; the product is progressively

fabricated as it flows through the succession of workstations. Mass production is usually

conducted in a product-flow layout.

37.2.4 Models for Production Operations

In this section, we will examine three types of models by which we can examine production oper-

ations, including graphical models, manufacturing process models, and mathematical models of pro-

duction activity.

Process-flow charts depict the sequence of operations, storages, transportations, inspections, and

delays encountered by a workpart of assembly during processing. As illustrated in Fig. 37.2, a

process-flow chart gives no representation of the layout or physical dimensions of a process, but

Storoge in row moteriols warehouse

Transport to first operation

Delay

First operation

Transport to second operation

Delay

Second operation

Transport to third operation

Delay

Third operation

Workport quality inspection

Fig. 37.2 Flow process chart for a sample workpart.

focuses on the succession of steps seen by the product. It is useful in analyzing the efficiency of the

process, in terms of the proportion of time spent in transformation operations as opposed to trans-

portations, storages, and delays.

The manufacturing-process model gives a graphical depiction of the relationship among the several

entities that comprise the process. It is an input-output model. Its inputs are raw materials, equipment

(machine tools), tooling and fixtures, energy, and labor. Its outputs are completed workpieces, scrap,

and waste. These are shown in Fig. 37.3. Also shown in this figure are the controls that are applied

to the process to optimize the utilization of the inputs in producing completed workpieces, or in

maximizing the production of completed workpieces at a given set of values describing the inputs.

Mathematical models of production activity quantify the elements incorporated into the process-

flow chart. We distinguish between operation elements, which are involved whenever the work part

is on the machine and correspond to the circles in the process-flow chart, and nonoperation elements,

which include storages, transportations, delays, and inspections. Letting T0 represent operation time

per machine, Tno the nonoperation time associated with each operation, and nm the number of ma-

chines or operations through which each part must be processed, then the total time required to

process the part through the plant [called the manufacturing lead time (71,)] is

T, = nm(T0 + Tno)

If there is a batch of p parts,

Tt = nm(pT0 + Tno)

If a setup of duration Tsu is required for each batch,

T, = nm(Tsu + pT0 + Tno)

The total batch time per machine, Tb, is given by

Tb = Tsu + PT0

The average production time Ta per part is therefore

T, + PT

The average production rate for each machine is

#a = l/rfl

As an example, a part requires six operations (machines) through the machine shop. The part is

produced in batches of 100. A setup of 2.5 hr is needed. Average operation time per machine is 4.0

min. Average nonoperation time is 3.0 hr. Thus,

Controls

1 Decisions

Row Materials

Equipment

Completed ^Workpiece

Tooling. Fixtures Manufacturing

Electrical Energy Process

Labor

Scrop and Waste

Fig. 37.3 General input-output model of the manufacturing process.

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