Resumen de Procesos (KALPAKJIAN)

8/10/2019 Resumen de Procesos (KALPAKJIAN)

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General Introduction

L6

Selection

of

Manufacturing

Processes

As will be

described

throughout

this text, there is often

more

than one method that

can

be

employed

to

produce

a

component

for

a

product

from

a

given

material

The

following broad categories of

manufacturing

methods

are

all

applicable

to

metallic

as Well

as

nonmetallic materials:

a.

Casting (Fig.

I.6a):

Expendable

mold

and

permanent

mold (Part Il).

Casting processes

Expendable pattern

Expendable

mold,

is

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Permanent mold casting

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Lost-foam casting

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casting

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casting

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Melt-spinning

process I

Squeeze casting

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___

(H)

FIGURE

l.6a Schematic illustrations

of various casting processes.



Section 1.6 Selection

of Manufacturing

Processes

Forming and shaping (Figs.

I.6b

through I.6d):

Rolling,

forging, extrusion,

drawing,

sheet forming, powder metallurgy, and

molding

(Part III).

Machining

(Fig.

I.6e): Turning, boring, drilling,

milling,

planing, shaping,

broaching;

grinding;

ultrasonic

machining;

chemical,

electrical,

and

electro-

chemical

machining;

and high-energy-beam

machining

(Part

IV).

This broad

category

also includes micromachining for producing ultraprecision parts

(Part

V).

Joining (Fig. l.6f): Welding,

brazing, soldering,

diffusion

bonding,

adhesive

bonding,

and mechanical joining (Part

VI).

Finishing:

Honing, lapping, polishing, burnishing, deburring,

surface

treating,

coating, and

plating

(Chapters 26 and 34).

Microfabrication

and nanofabrication:

Technologies

that are capable of

pro-

ducing

parts with

dimensions at the micro (one-millionth of a meter) and

nano

(one-billionth of a meter) levels; fabrication of microelectromechanical

Bulk-deformation

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Rolling

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Forging

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Extrusion

and

drawing

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Flat rolling I Open-die forging I

Direct

extrusion I

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Shape rolling Closed-die forging

Cold

extrusion

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rolling

Heading

Drawing

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Fioli forging :

Piercing

Tube

drawing

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(b)

FIGURE

l.6b Schematic

illustrations

of various

bulk-deformation

processes.



General introduction

Sheet-metal-forming

Shearing

Bending

and drawing

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Forming I

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forming

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Punching

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Piercing I

Deep

drawing I I Magnetic-pulse forming

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(C)

FIGURE

I.6c Schematic

illustrations

of various

sheet-metal-forming

processes.

systems (MEMS) and nanoelectromechanical

systems (NEMS), typically involv-

ing

processes such

as

lithography,

surface

and

bulk

micromachining,

etching,

LIGA, and

various specialized

processes (Chapters 28 and

29).

Process Selection.

The

selection

of

a

particular

manufacturing

process or, more

often,

sequence

of

processes,

depends on

the geometric

features of the parts to

be

produced, including

the

dimensional tolerances and surface

texture

required,

and on

numerous

factors pertaining to

the

particular workpiece material and its manufac-

turing

properties.

To

emphasize the challenges

involved, consider

the

following two

cases:

a. Brittle and hard materials

cannot be shaped

or formed

without the

risk of frac-

ture, unless

they are

performed

at elevated

temperatures, whereas

these mate-

rials

can

easily

be cast,

machined,

or ground.



Section 1.6 Selection

of

Manufacturing Processes

,

Thermoplastics

I TIIGIITIOSGIS

Polymer-processing

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I Rapid prototyping

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Extrusion Compression

molding Stereolithography

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Blow

molding

Vacuum-bag forming I

Three-dimensional

printing I

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Thermoforming

Transfer

molding I

manufacturing

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ld)

FIGURE I.6d

Schematic

illustrations of

various

polymer-processing methods.

b.

Metals

that

have been

preshaped

at

room

temperature

become

less

formable

during

subsequent processing,

vvhich,

in practice, is often

required to complete

the

part;

this

is because

the

metals have become stronger, harder,

and less duc-

tile

than they were

prior to processing

them

further.

There is a constant demand for new approaches to production problems

and,

especially,

for

manufacturing cost reduction.

For example,

sheet-metal parts

tradition-

ally

have been

cut and

fabricated

using common mechanical tools

such

as punches

and dies.

Although still

Widely

used, some of these operations

are now being

replaced

by laser cutting, as shown in Fig.

1.7

on p. 24, thus eliminating

the

need for hard tools,

which

have

only fixed

shapes

and

can

be

expensive and time consuming to make.

The laser

path

in

this

cutting

operation is computer controlled, thereby

increas-

ing the

operation’s

flexibility

and its

capability

of producing an

infinite variety

of



General

Introduction

Machining

and finishing

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Machining

Advanced

machining

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Finishing 1

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Turning

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Water-jet machining : Electrochemical polishing

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(G)

FIGURE

l.6e Schematic illustrations of various machining and finishing processes.

shapes accurately, repeatedly, and economically. However, because of the high

heat

in-

volved in using lasers, the surfaces produced after cutting have very different charac-

teristics

(such

as discoloration and a

different surface

texture)

than

those

produced

by traditional

methods.

This

difference can have

significant effects

not only

on

the

appearance

of

the material, but especially on its subsequent processing and in the



Section 1.6 Selection of Manufacturing

Processes

Fusion welding I I Other welding

Fastening and

bonding

, _____ ;_I

_________

,

_________

.

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it

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hielded metal-arc welding I Friction-stir welding

Adhesive bonding

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Gas-metal arc welding Resistance

welding Bolted connection

I

li

M

Q

I I

Flux-cored arc welding I Explosion welding Wave soldering I

|

Il

2

I

I Gas-tungsten

arc welding

I Cold

welding

Brazing

(I)

ll

FIGURE l.6f

Schematic illustrations

of

various joining

processes.

service life of

the

product. Moreover,

the

inherent

flexibility

of laser cutting is coun-

tered by

the

fact that it is a

much

slower operation than traditional punching.

In process selection, several factors can have a major role,

such

as

the

part size,

shape complexity, and

dimensional

accuracy and surface finish required. For

example,

° Flat parts and thin

cross sections can be difficult

to cast.

° Complex parts generally

cannot be shaped easily

and

economically

by

such met-

alworking techniques as forging,

whereas,

depending on

the

part size and

the

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