A review of processing science of additive manufacturing(AM)

A review of processing science of additive manufacturing(AM)

on metal

Additive

manufacturing(AM),known

by

people

as

3D

printing,is

a

manufacturing

method which using acomputer controlled laser form component layer by layer from

powder,sheets

ve

manufacturing(AM)

has

grown

and

developed

prosperous

in

the

past

decades

years,many

techniques

such

as:SLM,SLS,LOM,LENS,FDM,SLAhave been developed to manufacturing complex

shapedfunctionalmetallic

components,which

also

has

tremendously

potential

in

the

area

of

aerospace,

defence,bio- medical

industries

this

review,the

processing

science

of

metal

manufacturing

is

focused,the

follow

parts

will

be

explore

d:the

theory

of

metal < /p>

AMtechniques,processingdefects,solidific ation,solid-stateprecipitation,mechanical

properties and present review has established the relation between

metallurgical

mechanism,material

and

process

for

laser

based

AM,furthermore,the

more processing techniques will be discussed more detailed in this review.

Keywords:

Additivemanufacturing,Process ing science, Metals

Introduction

Additive manufacturing(AM),known by people as three dimensional (3D) printing,has

developing

for

decades

years

since

1980s

and

becoming

one

of

the

most

advanced

manufacture

techniques

over

the

there

still

are

several

problems

limit

the

application

of

AM,the

processing

and

materials

both

face

unique

tanding the processing of various techniques and dilemma will be help

for improving the capabilities of the components.

The

earliest

patented

process

relevant

to

metal

AM

is

selective

laser

sintering

(SLS),which

form

parts

from

mixed

metal

and

polymer

first

reported

metal

AM

part

was

manufactured

in

1990

by

Bourell

and

Manriquez-Frayre

form

metal alloy powders (Manriquez-Frayre, 1990).it is significant though the mechanical

property

and

quality

is

far

from

application.A

new

process

was

patented

by

EOS

GnbH,which

can

full

melting

the

metal

powder,called

selective

laser

melting

(SLM).SLM is widely used to make metal parts at now,many companies such as 3D

Systems,Optomec

have

entered

this

market

with

laser

powder-bed

hardware

and

software for metal r process called “three dimensional printing”was

patented by a group of researches at MIT,and now we named it Binder Jetting,which

can be used for form metal parts and other name of “3D printing”has

been

used

to

described

all

kind

of

ed

by

selective

melting

of

a

powder

bed,some

researches

innovated

the

direct

energy

deposition

(DED),which

deposit

feed-stock directly into a molten LENS was the first commercialised DED

technology developed by Sandia National Laboratories In lamination,the

last category of metal AM patented by Dawn White of Solidica in 1999,which uses

ultrasonic

welding

technology

and

computer

numerical

control

(CNC)form

3D

the start of this century,another metal AM technology:electron beam melting

(EBM) patented by Sweden,which also use power-bed feed-stock.

AM

technology

has

been

widely

used

for

Rapid

prototyping

(RP)

and

rapid

manufacturing(RM)

(Gu,

2015).Applied

at

the

area

of

aerospace

structures,Part

repairs,biomedical implants and high temperature there still have big

questions need to discuss ,especially for the processing basic purpose of

this essay is to review the current situation of research and development of metal AM.

Classification of AM technologies

The

category

of

AM

technology

diverse

from

metal

to

polymer,materials

changes

from

powder

to

sheet,the

mew

techniques

developed

more

and

,both

of

them must consolidate the feed-stock into a dense part,form the component layer by

the

purpose

of

discuss

distinct

classes

of

machines,the

ASTM

F42

Committee of Additive Manufacturing has released a standard on process terminology

(ASTM, 2012).There are four categories to metal AM:

?

Powder bed fusion (PBF)

?

Selective laser melting (SLM)

?

Electron beam melting (EBM)

?

Direct energy deposition (DED)

?

Laser vs.e-beam

?

Wire fed fed

?

Binder jetting

?

Infiltration

?

Consolidation

?

Sheet lamination

?

Ultrasonic additive manufacturing (UAM) (Sames, 2015)

In this review,we will focus on PBF and DED,these two kinds of AM technology

were widely used to manufacture metal two could achieve highly quality

micro-structure and mechanical property.

Powder-bed fusion

Selective

laser

melting

(SLM)

and

Electron

beam

melting

(EBM)

are

typical

technologies

of

powder-bed

fusion,which

were

used

to

selectively

sinter

or

melt

a

layer of a powder bed. The SLM is widely used than SLS,The laser sintering much

more used for polymer powder-bed processing of SLM and EBM melting

the

powder

layer

and

previous

layer

allows

current

layer

adhere

the

rest

of

the

,there

still

have

several

important

differences

in

power

for

melting

of

SLM

is

laser,The

prototype

of

BEM

is

scanning

electron

microscope

(SEM),the EBM system

is more power,which include a filament,magnetic coils and

an electron beam powder distribution system is different as well.

As

we

learned

from

the

last

paragraph,SLM

and

EBM

system

has

the

same

processing:machine

set- up,form,powder-bed

recovery

and

substrate

operation

of

a

PBF

machine

is

governed

by

the

details

of

the

scan

strategy

and

processing parameters

.

Before form the part,a build substrate must put the bottom of

chamber,which

give the

build materials

a mechanical

and thermal

support,and must

keep

stay

there

all

over

manufacture

the

complete

the

building,excess powder and substrate need to be removed,the powder could be used at

the

next

substrate

usually

adhere

to

the

part,which

will

be

cut

off,however,sometimes

it

is

easy

to

remove,just

like

Ti-Al-4V

deposit

and

stainless

steel substrate in EBM.

Direct energy deposition

DED

dislike

the

process

of

SLM

and

EBM,which

use

a

laser

generate

a

melting

pool,and

AM

materials

feed

into

this

pool,deposit

the

component

layer

by

ent

from

SLM

and

EBM,the

materials

of

DED

could

be

powder

and

wire,the deposit environment can be outside or in special shield gas.

The

LENS

process

is

one

of

the

most

researched

and

commercialised

forms

of

DED,which use a laser power source to melt a stream of powder feed-stock (Mudge,

2007),widely used to repair machines and rapid biggest challenge of

LENS is

the

feed

rate of the metal

powder must be verified regularly,otherwise the

micro-structure

and

mechanical

will

be

in

PBF,a

powder-feed

system,a

substrate

and

shield

gas

are

necessary

for

DED

finish

the

manufacture,the part will be removed from the build y,the surface of

part

will

be

very

rough,the

part

is

far

from

the

demand

of

working.

Parts

will

be

post- processed

to

reduce

residual,achieve

final

geometry

and

improve

mechanical

property.