Processing of Polymers and

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Chapter 10. Properties and Processing of Polymers and

Reinforced Plastics; Rapid Prototyping and Rapid Tooling

Prof. Ahn, Sung-Hoon (

安成勳

)

School of Mechanical and Aerospace Engineering Seoul National University

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Introduction

 Advantages of polymers

 High strength-to-weight ratio

 Design possibilities

 Wide choice of colors and transparencies

 Ease of manufacturing

 Relatively low cost

 Compared with metals

 Low density

 Low strength

 Low stiffness

 Low electrical & thermal conductivity

 Good resistance to chemicals

 High coefficient of thermal expansion

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

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Mechanical properties

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Polymers

 Monomer (단량체), dimer, trimer

 Multimer

 Oligomer

(N=30~200)

 Polymer (many parts)

(N≥200)

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Structure of polymers

 Primary bonds : covalent bonds (공유결합)

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Polymerization

 Monomer → Polymer 중합

(Polymerization)

 Degree of polymerization (DP, 중합도)



 Number of repeat unit per polymer

 Effects of crystallinity (결정도)

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

 Glass-transition temperature (유리전이 온 도)

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

 At low temp. : hard, rigid, brittle, and glassy.

 At high temp. : rubbery and leathery.

)

( unit repeat the

of weight Molecular

)

( polymer the

of weight Molecular

분자량 단위체의

분자량 폴리머의

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Polymer chains

 Secondary bonds :

van der Waals, hydrogen bonds, and ionic bonds

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Crystallinity

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Glass-transition temperature (

유리전이온도

)

Glassy

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Thermoplastics (

열가소성 플라스틱

)

 Linear and branched polymers have weak secondary bonds.

 As the temperature is raised above the T_g or T_m polymers become easier to form or mold into desired shapes.

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

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

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Viscoelastic behavior (

점탄성

) (1)

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Viscoelastic behavior (

점탄성

) (2)

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Thermosetting plastics (

열경화성 플라스틱

)

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

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

 Epoxies (에 폭 시), phenolics (페 놀 수 지), polyesters (폴 리에 스 터), aminos (아미노), silicones

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Elastomers (rubbers,

탄성중합체

)

 Amorphous polymers with low T_g

 Vulcanization (가황처리) - Charles Goodyear

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Reinforced plastics (

강화플라스틱

) (1)

 Composite materials (복합재료)

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.

 History

 Clay (진흙) + straw (짚) (B.C. 2000)

 Concrete + iron rods (1800s)

 Structure of reinforced plastics

 Fibers / particles

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

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

 Plastic matrix : tougher than the fibers.

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Reinforced plastics (

강화플라스틱

) (2)

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Applications of reinforced plastics

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Effect of Nano Scale

Melting point of gold particles as a function of particle size.

 Hall-Petch equation

Material with smaller grain size is stronger

Sintering temperature of ceramic decreases : 1800°C 900°C for nano size.

Ductile cutting for sub-micro meter size machining tool tip

Easier to cut hard materials.

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Reinforcement

 Nano composites :

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

CNT + epoxy Nano Carbon black powder

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Averaged properties

1 1

1 1 1

1 1

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f

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f

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A A

A F



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f m m m

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L L





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1

2 2

2

2 2

2 2 2

2 2

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,

2













 

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2 2

2

2 2 2

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L L_m _m L_f _f L

L

A E A F



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Longitudinal Young’s Modulus

Transverse Young’s Modulus F₁

F₁ L

ΔL

M F M F₂

F₂ L

ΔL

FIGURE 10.21 Tensile strength of glass-reinforced polyester as a function of fiber content and fiber direction in the matrix. Source:After R.M. Ogorkiewicz.

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Classification of reinforced plastics

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Processing of plastics

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Extrusion / Injection molding

Metal inserts

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Sprue, Runner, and Gate

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Types of Gate

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DFM in Injection Molding (1)

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Prevent undercut!

DFM in Injection Molding (2)

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Reaction-injection molding / Blow molding

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Thermoforming / Compression molding

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Transfer molding / Casting

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Polymer matrix reinforced plastics

 Prepregs

 Sheet-molding compound (SMC)

 Bulk-molding compound (BMC)

 Thick molding compound (TMC)

BMC

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Manufacturing of polymer matrix reinforced plastics

 Molding

 Compression molding

 Vacuum-bag molding

• Autoclave

 Contact molding

• Hand lay-up

 Resin transfer molding

 Injection molding

 Filament winding

 Pultrusion

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Sprayed-metal tooling process

FIGURE 10.55 Production of tooling for injection molding by the sprayed-metal tooling process. (a) A pattern and base plate are prepared through a rapid-prototyping operation; (b) a zinc-aluminum alloy is sprayed onto the pattern (See Section 4.5.1); (c) the coated base plate and pattern assembly is placed in a flask and back-filled with aluminum-impregnated epoxy; (d) after curing, the base plate is removed from the finished mold; and (e) a second mold half suitable for injection molding is prepared.

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Automatic tape lay-up

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Vacuum bag molding / Autoclave

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Introduction to 3D Printing

 Other names of 3D printing

 Layered Manufacturing

 Desktop Manufacturing

 Solid Free-form Fabrication (SFF)

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

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

 3D Printing offers advantages compared to conventional subtractive fabrication methods.

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Basic Ideas

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Stair-Step Effect

Surface roughness vs. build time

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Support Structures

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Stereolithography Apparatus (SLA)

 Developed by 3D Systems, Inc

 The laser beam will scan the surface following the contours of the slice.

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Stereolithography Apparatus (SLA)

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Stereolithography Apparatus (SLA)

3D Systems, Inc

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Selective Laser Sintering (SLS)

 Developed by The University of Texas at Austin.

 Powders are spread over a platform by a roller.

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

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Selective Laser Sintering (SLS)

laser beam

bonded powders powders

laser beam

bonded powders powders metal

polymer coating

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Selective Laser Sintering (SLS)

3D Systems, Inc

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Fused Deposition Modeling (FDM)

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Notre Dame CSFC Product Design

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Polymer Jetting (PolyJet)

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Polymer Jetting (PolyJet)

Solid Concepts Inc.

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Laminated-Object Manufacturing (LOM)

 Developed by Helysis.

 LOM uses layers of paper or plastic sheets with a heat- activated glue on one side to produce parts.

 The desired shapes are burned into the sheet with a laser beam, and the parts are built layer by layer.

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LOM process

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Shape Deposition Manufacturing (SDM)

 Developed by Stanford University / CMU.

 Uses deposition and milling.

 Provides good surface finish.

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Laser Engineered Net Shaping (LENS)

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Issues in 3D Printing Materials

 Rapid Fabrication of functional parts

 Structural

 Optical

 Surface Roughness

 Electrical

 Thermal

 Color

 Etc.

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Micro Structure of FDM Part

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Gallery - FDM

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Gallery - Polyjet

* multi-material

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Before surgery

After surgery Virtual surgery

CT Scan 3D printed part

Medical Application

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Component of Hardware

Dispenser

X and Y axis control

Z axis control

High speed spindle

Micro needle

UV lamp Microscope

Granite Base

Micro endmill

1㎛resolution

15 ~ 700 kPa

 140㎛~ 800㎛

 100㎛~ 1000㎛

Max. 46,000rpm

0 ~ 400 W,λ = 365㎚

PMAC (Multi-tasking board)

3 Axes-stage

Dispenser

Micro needle

Micro tool

High speed spindle

UV curing system

Controller SPECIFICATIONS

 _

Deposition; Rapid Prototyping

Cutting; Milling

Hybrid; Both

Micro needle Micro endmill



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Hybrid Process

Deposition Machining

Part material

Support material 3D MODEL

SLICING

DEPOSITION

CURING

POST-PROCESS LAST LAYER ?

DEPOSITION

CURING MACHINING

LAST LAYER ?

CONVENTIONAL DEPOSITON SYSTEM HYBRID SYSTEM

YES

YES NO

NO PROCESS PLANNING

3D PART

Machining

Support

Molding / Casting

Heat

Demolding

Part Deposition

Machining

Deposition and Machining

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Stapes

The smallest bone in human body, width 2.5mm / height 3.5mm

40wt% Hydroxyapatite + Acrylic resin

Dispensing process using 140㎛needle

Micro milling using 100㎛flat endmill

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

PROCESS



Area measurement using imaging processing

Error : 0.26%

3.4mm

3.0mm

200㎛

3-dimesional part

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3D Nano / Micro Parts

 Nano Stereolithography

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.

I n se t i s to p vie w o f th e s t r u c tu re

(a) (b)

SEM images of fabricated micro-Thinker by double- scanning path. The insets are the same micro-Thinker with various view angles, and

Fabricated micro-prototypes of a micro rotor

•D. Y. Yang, KAIST

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Porous Structure

 PCL; poly(e-caprolactone) (The University of Michigan)

 Rehabilitation (Yan, et al)

(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.

CAD modeling 3D printed part Rehabilitated ear

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3D printed prosthetic

 Design of the piece are fit to the individual

3D Printing: Modern Medical Applications, Devin Peek et al. (2010)

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3D printed clothes

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Food

 Tony Cenicola/The New York Times

 2013. 9. 22