Reinforced Plastics; Rapid Reinforced Plastics; Rapid Prototyping and Rapid Tooling

Chapter 10. Properties and p p Processing of Polymers and

Reinforced Plastics; Rapid Reinforced Plastics; Rapid Prototyping and Rapid Tooling

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering

Seoul National University

Introduction

ƒ Advantages of polymers

ƒ High strength to weight ratio

ƒ High strength-to-weight ratio

ƒ Design possibilities

ƒ Wide choice of colors and transparencies

ƒ Ease of manufacturing

ƒ Relatively low cost

ƒ Compared with metals

ƒ Low density

ƒ Low strength

ƒ Low stiffness

ƒ Low electrical & thermal conductivity Low electrical & thermal conductivity

ƒ Good resistance to chemicals

ƒ High coefficient of thermal expansion

L f l t t ( t 350°C)

ƒ Low useful temperature range (up to 350°C)

Polymers

ƒ Monomer (단량체), dimer, trimer

ƒ Multimer

ƒ Oligomer

(N=30~200)

ƒ Polymer (many parts)

(N≥200) (N≥200)

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Structure of polymers

ƒ Primary bonds : covalent bonds covalent bonds (공유결합)

Ref.

Polymerization

ƒ Monomer → Polymer

중합

(Polymerization)

ƒ Degree of polymerization (DP, 중합도)

) (

l th f i ht

M l l 폴리머의 분자량

ƒ

ƒ Number of repeat unit per polymer

)

( unit repeat the

of weight Molecular

) (

polymer the

of weight Molecular

분자량 단위체의

분자량 폴리머의

ƒ Effects of crystallinity (결정도)

ƒ

High crystallinity : stiffer, harder, less ductile, more dense, less rubbery, and more resistant, y, to solvents and heat.

ƒ Glass-transition temperature (유리전이 온 도 )

도 )

ƒ

Distinct change in mechanical behavior across a narrow range of temperature.

ƒ

At low temp. : hard, rigid, brittle, and glassy.p g g y

ƒ

At high temp. : rubbery and leathery.

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Polymer chains

ƒ Secondary bonds :

van der Waals hydrogen bonds van der Waals, hydrogen bonds,

and ionic bonds

Ref.

Crystallinity

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Thermoplastics (열가소성 플라스틱) ( )

ƒ Linear and branched polymers have weak secondary bonds. y

ƒ As the temperature is raised above the T

_g

or T

_mm

polymers become easier to form or p y mold into desired shapes.

ƒ If the polymer is then cooled, it returns to If the polymer is then cooled, it returns to its original hardness and strength; in other words the effects of the process are reversible

reversible.

ƒ Polymethylmethacrylate (PMMA, 아크릴), cellulosics (셀룰로오스) nylon (나일론) cellulosics (셀룰로오스), nylon (나일론), ABS (acrylonitrile-butadiene-styrene), polyesters (폴리에스터), polyethylene (폴 리에틸렌 ) PVC (polyvinyl chloride)

리에틸렌 ), PVC (polyvinyl chloride)

Ref.

Viscoelastic behavior (점탄성) (1) ( ) ( )

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Viscoelastic behavior (점탄성) (2) ( ) ( )

Ref.

Thermosetting plastics (열경화성 플라스틱) g ( )

ƒ When the long-chain molecules in a polymer are cross-linked in a three dimensional arrangement the structure in effect becomes three-dimensional arrangement, the structure in effect becomes one giant molecule with strong covalent bonds.

ƒ During polymerization, the network is completed, and the shape of the part is permanently set.

ƒ Epoxies (에폭시), phenolics (페놀수지), polyesters (폴리에스터), aminos (아미노) silicones

aminos (아미노), silicones

Elastomers (rubbers, 탄성중합체) ( )

ƒ Amorphous polymers with low T _g

ƒ Vulcanization (가황처리) Charles Goodyear

ƒ Vulcanization (가황처리) - Charles Goodyear

Ref.

Reinforced plastics (강화플라스틱) (1) ( ) ( )

ƒ Composite materials (복합재료)

A combination of two or more chemically distinct and insoluble phases whose A combination of two or more chemically distinct and insoluble phases whose properties and structural performance are superior to those of the constituents acting independently.

ƒ History

ƒ

Clay (진흙) + straw (짚) (B.C. 4000)

ƒ

Concrete + iron rods (1800s)

ƒ

Concrete + iron rods (1800s)

ƒ Structure of reinforced plastics

Fibers / particles

ƒ Fibers / particles

• Glass, graphite, aramids (Kevlar), boron, talc, mica

• Strong and stiff, but brittle, abrasive, and lack toughness

ƒ Plastic matrix : tougher than the fibers

ƒ Plastic matrix : tougher than the fibers.

Reinforced plastics (강화플라스틱) (2) ( ) ( )

Ref.

Effect of Nano Scale

ƒ Hall-Petch equation

Material with smaller grain size is stronger

Melting point of gold particles as a D ctile c tting for s b micro meter si e Melting point of gold particles as a

function of particle size.

ƒ

Ductile cutting for sub-micro meter size machining tool tip

Easier to cut hard materials.

ƒ

Sintering temperature of ceramic decreases :

1800°C 900°C for nano size.

Reinforcement

ƒ Nano composites :

Carbon Nano Tube (CNT) nano platelets Carbon Nano Tube (CNT), nano platelets, nano particles

CNT + epoxy Nano Carbon black powder

Ref.

Averaged properties

A A

A

F = σ = σ + σ Δ L = ε L = ε L = ε L

Longitudinal Young’s Modulus

1 1

1 1 1

1 1

1 1

m m f

f

m m f

f

v v

E

A A

A F

σ σ

ε σ

σ σ

σ

+

=

=

+

=

=

1 1 1

1 1

1

1 1

1

f f f

m f

m f

E

L L

L L

=

=

=

=

=

= Δ

ε σ

ε ε

ε

ε ε

F ₁ ε

1 1 1 1 1

1 1 1

m m f

f m m m

E v E v E

E +

=

= ε

F ₁ σ

L ΔL

Transverse Young’s Modulus L

2 2

2 2 2

2

2 ⎟⎟ ⎠

⎜⎜ ⎞

⎝

⎛ +

=

=

^m _m ^f _f

L L L

E L

E ε ε ε

2

σ

2 2

2

L

A E A

F σ ε

Δ

=

M =

F M F ₂

2 2

2

2 2 2

2 2

2

,

=

=

=

=

m f

f f f

m m

m

E E

σ σ

σ

ε σ ε σ

2 2

2

2 L

_{m m}

L

_{f f}

L

L

ε ε

ε

+

= Δ

=

F ₂ ΔL

1

2 2

2

−

⎟ ⎟

⎠

⎞

⎜ ⎜

⎝

⎛ +

=

f f m

m

E v E

E v

L

Classification of reinforced plastics

Ref.

Processing of plastics

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Extrusion / Injection molding

Metal inserts

Ref.

Sprue, Runner, and Gate

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Types of Gate

Ref.

Reaction-injection molding / Blow molding

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Thermoforming / Compression molding

Ref.

Transfer molding / Casting

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Polymer matrix reinforced plastics

ƒ Prepregs

ƒ Sheet molding compound (SMC)

ƒ Sheet-molding compound (SMC)

ƒ Bulk-molding compound (BMC)

ƒ Thick molding compound (TMC) g p ( )

Ref.

Manufacturing of polymer matrix reinforced plastics

ƒ Molding

ƒ Compression molding Compression molding

ƒ Vacuum-bag molding

• Autoclave

ƒ Contact moldingg

• Hand lay-up

ƒ Resin transfer molding

ƒ Injection molding j g

ƒ Filament winding

ƒ Pultrusion

Ref.

S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3^rd/4^th ed. Addison Wesley

Introduction to Rapid Prototyping (RP)

ƒ Other names of RP

ƒ Layered Manufacturing

ƒ Layered Manufacturing

ƒ Desktop Manufacturing

ƒ Solid Free-form Fabrication (SFF)

ƒ A group of related technologies is used for fabricating physical objects directly from CAD data.

objects directly from CAD data.

ƒ Objects are formed by adding and then bonding the materials in layers.

ƒ The RP offers advantages compared to conventional subtractive g p

fabrication methods.

STL File

ƒ Developed for StreoLithography

ƒ De facto standard for RP data

ƒ Most CAD systems support STL format

Stair-Step Effect

Surface roughness vs. build time

Stereolithography Apparatus (SLA)

ƒ Developed by 3D Systems Inc 3D Systems, Inc

ƒ The laser beam will scan

the surface following the g

contours of the slice.

Selective Laser Sintering (SLS) (1)

ƒ Developed by The University of Texas at University of Texas at Austin.

ƒ Powders are spread over p a platform by a roller.

ƒ A laser sinters selected areas causing the particles to melt and then solidify

solidify.

Selective Laser Sintering (SLS) (2)

laser beam polymer coating laser beam

laser beam laser beam

metal

bonded powders powders bonded powders powders

Laminated-Object Manufacturing (LOM)

ƒ Developed by Helysis.

ƒ LOM uses layers of paper or plastic sheets with a heat- p

activated glue on one side to produce parts.

ƒ The desired shapes are

burned into the sheet with a

burned into the sheet with a

laser beam, and the parts

are built layer by layer. y y y

Fused Deposition Modeling (FDM)

3D Printers

ƒ Developed at MIT.

ƒ Parts are built upon a platform situated in a bin p

full of powder material.

Solid Ground Curing (SGC)

ƒ Developed and commercialized by Cubital Ltd (Israel)

by Cubital Ltd. (Israel).

ƒ Uses a photopolymer, which is i i UV li h

sensitive to UV-light.

ƒ The vat moves horizontally as y well as vertically.

ƒ The horizontal movements take

ƒ The horizontal movements take

the workspace to different

stations in the machine.

Shape Deposition Manufacturing (SDM)

ƒ Developed by Stanford University / CMU.

ƒ Uses deposition and milling

ƒ Uses deposition and milling.

ƒ Provides good surface finish.

Issues in RP Materials

ƒ Rapid Fabrication of functional parts

ƒ Structural

ƒ Structural

ƒ Optical

ƒ Surface Roughness

ƒ Electrical

ƒ Thermal

ƒ Color Color

ƒ Etc.

Micro Structure of FDM Part

Post-processes of FDM

FDM Process

Assembled Part

Resin Infiltration

Raw FDM ABSi During Infiltration After Infiltration Raw FDM ABSi During Infiltration After Infiltration

0.6

25

Raw material Infiltration Infiltration+Sanding

0.3 0.4 0.5

issivity(%)

15 20 25

ssivity(%)

0 0.1 0.2

Transmi

0 5 10

Transmis

0

800 760 720 680 640 600 560 520 480 440 400 Wave length(nm)

0

-0.003 0 0.003

Air Gap(inch)

Flash Memory Reader

CATIA modeling:

5 hours

FDM process:

10 hours

Post-processes : 24 hours

Post-processes : 24 hours

Total prototyping time : 39 hours

Component of Hardware

Z axis control 9 Deposition; Rapid Prototyping

High speed spindle

9 Cutting; Milling 9 Hybrid; Both

Dispenser

UV lamp Microscope

Micro needle

UV lamp Microscope

Micro

Micro needle Micro endmill

X d Y i

Micro needle Micro endmill

ƒ1㎛ resolution

ƒ15 ~ 700 kPa

ƒ3 Axes-stage

ƒDispenser SPECIFICATIONS

X and Y axis control Granite Base

15 700 kPa

ƒ 140 ㎛ ~ 800 ㎛

ƒ 100 ㎛ ~ 1000 ㎛

ƒMax. 46,000rpm

ƒ0 ~ 400 W, λ = 365 ㎚

ƒPMAC (Multi-tasking board) Dispenser

ƒMicro needle

ƒMicro tool

ƒHigh speed spindle

ƒUV curing system

ƒController

φ φ φ

φ

Hybrid Process

Deposition Machining

3D MODEL

Part Support

3D MODEL

SLICING

Part material

Support material

DEPOSITION DEPOSITION

YST EM

PROCESS PLANNING

CURING CURING

MACHINING

D EPOSIT O N S Y D SYST EM

P t

Deposition and Machining

POST-PROCESS

LAST LAYER ? MACHINING

LAST LAYER ?

NVENTIONAL D HYBRI D

YES NO

NO

Machining

Support

Molding / Casting Part

Deposition

CO

YES

3D PART

Support / Casting

Heat

Demolding

Machining

Stapes

9 Th ll t b i h b d idth 2 5 / h i ht 3 5

3-dimesional part

9 The smallest bone in human body, width 2.5mm / height 3.5mm 9 40wt% Hydroxyapatite + Acrylic resin

9 Dispensing process using 140㎛ needle 9 Micro milling using 100㎛ flat endmill

φ φ

3.4mm

9 Micro milling using 100㎛ flat endmill φ

3.0mm

200㎛

200㎛

Mold (using wax) machining → part deposition → surface machining → demolding

PROCESS

Error : 0.26%

Mold (using wax) machining → part deposition → surface machining → demolding

Area measurement using imaging processing

3D Nano / Micro Parts

ƒ Nano Stereolithography

D Y Yang KAIST

(a) (b) •D. Y. Yang, KAIST

SEM images of fabricated islands with (a) actual and (b) exaggerated ratio of height vs. width by controlling both exposure time and laser power simultaneously time and laser power simultaneously.

Inset is top view of the structure

Fabricated micro-prototypes of a micro rotor

SEM images of fabricated

micro-Thinker by double-

scanning path The insets

scanning path. The insets

are the same micro-Thinker

with various view angles, and

the scale bars are 10 ㎛

Porous Structure

ƒ PCL; poly(e-caprolactone)

(The University of Michigan)

(a) An actual pig condyle, (b) surface rendering of STL design file for pig condyle scaffold, (c) front view, and (d) back view of pig condyle PCL scaffold fabricated by SLS.

ƒ Rehabilitation

(Yan, et al)

CAD modeling RP part Rehabilitated ear