#diagram efek shrinkage

8/8/2019 #Diagram Efek Shrinkage

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Injection Molding

2.810 Fall 2008

Professor Tim Gutowski


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Short history of plastics

1862 first synthetic plastic

1866 Celluloid

1891 Rayon

1907 Bakelite

1913 Cellophane

1926 PVC1933 Polyethylene

1938 Teflon

1939 Nylon stockings1957 velcro

1967 The Graduate


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Outline

Basic operation

Cycle time and heat transfer

Flow and solidification

Part design

Tooling

New developments

Environment


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Readings

Tadmore and Gogos

Molding and Casting pp584 -610

Boothroyd Dewhurst

Design for Injection Molding pp 319 - 359

Kalpakjian (5th ed) see Ch 19

Injection molding case study;Washing machine

augers; see on web page


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30 ton, 1.5 oz (45 cm3) Engel

Injection Molding Machinefor wheel fabrication


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Process & machine schematics*

* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_process.htm

*

Schematic of thermoplastic Injection molding machine
http://www.idsa-mp.org/proc/plastic/injection/injection_process.htmhttp://www.idsa-mp.org/proc/plastic/injection/injection_process.htm


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Process Operation

Temperature: barrel zones, tool, die zone

Pressures: injection max, hold

Times: injection, hold, tool opening

Shot size: screw travel

Flash

Melt

Thermaldegradation

Short-shot

Temp.

Pressure

Processing w indow


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Typical pressure/temperature cycle

( )

polymersforsec10

thicknesshalf

23

2

cm

tcool

==

Time(sec)

Cooling time generally dominates cycle time

Time(sec)

* Source: http://islnotes.cps.msu.edu/trp/inj/inj_time.html

**
http://islnotes.cps.msu.edu/trp/inj/inj_time.htmlhttp://islnotes.cps.msu.edu/trp/inj/inj_time.html


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Calculate clamp force, & shot size

F=P X A = 420 tons

3.8 lbs = 2245 cm3

=75 oz

Actual ; 2 cavity 800 ton


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Clamp force and machine cost


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Heat transfer Note; Tool > polymer

yxx

q

yxTct

x

p

=

)(

)()'(kind3rd

constant)'(kind2nd

constant)'(kind1st

==

==

==

TThxxx

Tk

xxxTk

xxTBoundary Conditions:

1-dimensional heat conduction equation :

The boundary condition of 1st kind applies to injection molding since thetool is often maintained at a constant temperature

x

Tkqx

=

qx qx + qx

2

2

2

2

orx

TtT

xTk

tTcp

=

=

Fouriers law


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Heat transfer

TW

Tii

t

x+L-L

Let Lch = H/2 (half thickness) = L ; tch = L2/ ;

Tch = Ti TW (initial temp. wall temp.)

Non-dimensionalize:2

;1;L

tF

L

x

TT

TTO

Wi

W =+=

=

2

2

=

OFDimensionless equation:

Initial condition 10 == OF

Boundary condition

02

00

==

==

Separation of variables ;matching B.C.; matching I.C. = )()(),( gFfF OO


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Centerline, = 0.1, Fo = t/L2 = 1

Temperature in a slab

Bi-1 =k/hL


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Reynolds Number

* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_process.htm

VL

LV

L

V

==sviscou

inertia

Re

2

2

Reynolds Number:

For typical injection molding

231

32433

10;

1

10

timeFill

lengthPart

essthickn10;101

msN

s

V

mLsmNcmg Z

==

===

410Re =

For Die casting

300

10

1010103Re

3

313

=
http://www.idsa-mp.org/proc/plastic/injection/injection_process.htmhttp://www.idsa-mp.org/proc/plastic/injection/injection_process.htm


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Viscous Shearing of Fluids

vF

h

h

v

A

F

F/A

v/h

1

Newtonian Viscosity

h

v

=

Generalization: &=

)( &&=

&

Injection molding

rateshear:&

Typical shear rate forPolymer processes (sec)-1

Extrusion 102~103

Calendering 10~102

Injection molding 103~104

Comp. Molding 1~10

Shear Thinning

~ 1 sec-1 for PE


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Viscous Heating

Rate of Heating= Rate of Viscous Work

2

==

=

h

v

h

v

A

F

Vol

vF

Vol

P

Rate of Temperature rise 22

or

=

=

h

v

cdt

dT

h

v

dt

dTc

p

p

Rate of Conduction out

22

2

~h

T

c

k

dx

Td

c

k

dt

dT

pp

=

Tk

v

=

2

Conduction

heatingViscous Brinkman number

For injection molding, order of magnitude ~ 0.1 to 10


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Non-Isothermal Flow

v

Flow rate: 1/t ~V/Lx

Heat transfer rate: 1/t ~a/(Lz/2)2

x

zz

x

z

L

LVL

L

LV=

4

1

4~

rateHeat xfer

rateFlow 2

For injection molding

5.210

1.0

/10

1.0/10

4

1~

rateHeat xfer

rateFlow23

=

cm

cm

scm

cmscm

For Die casting of aluminum

2

210

10

1.0

/3.0

1.0/10

4

1~

rateHeat xfer

rateFlow

cm

cm

scm

cmscm

* Very small, therefore it requires thick runners

Small value=> Short shot


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Injection mold die cast mold


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Fountain Flow

* Source: http://islnotes.cps.msu.edu/trp/inj/flw_froz.html ; ** Z. Tadmore and C. Gogos, Principles of Polymer Processing

*

**
http://islnotes.cps.msu.edu/trp/inj/flw_froz.htmlhttp://islnotes.cps.msu.edu/trp/inj/flw_froz.html


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Shrinkage distributions

* Source: G. Menges and W. Wubken, Influence of processing conditions on Molecular Orientation in Injection Molds

V=3.5cm/s

V=8cm/s

sample Transverse direction


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Gate Location and Warping

Center gate: radial flow severe distortion

Diagonal gate: radial flow twisting End gates: linear flow minimum warping

Gate

Air entrapment

Edge gate: warp free, air entrapment

Sprue

2.0

2.0 60

Before shrinkage

60.32

1.96

1.976

After shrinkage

ShrinkageDirection of flow 0.020 in/in

Perpendicular to flow 0.012

ff f


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Effects of mold temperature and

pressure on shrinkage

0.030

0.000

0.010

0.005

0.015

0.020

0.025

100 120 140 160 180 200 220 240

Mold Temperatu re (F)

LDPE PP

Nylon 6/ 6

PMMA

Acetal

Shr

inkage

0.030

0.000

0.010

0.005

0.015

0.020

0.025

Shrinka

ge

6000

8000

10000

12000

14000

16000

Pressure on injection plunger (psi)

Acetal

LDPE

Nylon6/ 6

PP withflow

18000

PP acrossflow

PMMA


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Where would you gate this part?


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Weld line, Sink mark

* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htm

Weld l ine

Mold Fill ing

Gate

Solidified part

Sink mark Basic rules in designing ribsto minimize sink marks
http://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htmhttp://www.idsa-mp.org/proc/plastic/injection/injection_design_7.htm


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Injection Molding

*

*

* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_design_2.htm
http://www.idsa-mp.org/proc/plastic/injection/injection_design_2.htmhttp://www.idsa-mp.org/proc/plastic/injection/injection_design_2.htm


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Where is injectionmolding?

Eff t f ld


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Effects of mold pressure on

shrinkage0.030

0.000

0.010

0.005

0.015

0.020

0.025

Shrin

kage

6000

8000

10000

12000

14000

16000

Pressure on injection plunger (psi)

Acetal

LDPE

Nylon6/ 6

PP w ithflow

18000

PP across

flow

PMMA


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Tooling Basics

Cavity Plate

Cavity

MouldingCore

Core Plate

Basic mou ld consisting of cavity and core plate

Runner

Cavity

Gate

NozzleSprue

Melt Delivery


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Part

Cavity

Core

Stripper plate

Tooling for a plastic cup

Runner

Knob

Nozzle


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Tooling for a plastic cup

Runner

Part

Cavity

Nozzle

Part

Cavity

Knob

Stripper

plate

Runner

Part

Cavity

Nozzle


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Tooling

* Source: http://www.idsa-mp.org/proc/plastic/injection/; ** http://www.hzs.co.jp/english/products/e_trainer/mold/basic/basic.htm (E-trainer by HZS Co.,Ltd.)

*

*

* **

**

*
http://www.idsa-mp.org/proc/plastic/injection/http://www.hzs.co.jp/english/products/e_trainer/mold/basic/basic.htmhttp://www.hzs.co.jp/english/products/e_trainer/mold/basic/basic.htmhttp://www.hzs.co.jp/english/products/e_trainer/mold/basic/basic.htmhttp://www.idsa-mp.org/proc/plastic/injection/


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Part design rules

Simple shapes to reduce tooling cost

No undercuts, etc. Draft angle to remove part

In some cases, small angles (1/4) will do

Problem for gears Even wall thickness

Minimum wall thickness ~ 0.025 in

Avoid sharp corners Hide weld lines

Holes may be molded 2/3 of the way through thewall only, with final drilling to eliminate weld lines

New developments- Gas


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New developments- Gas

assisted injection molding

New developments ; injection


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New developments ; injection

molding with cores

Cores andPart Molded in Clear Plastic

Cores used in Injection Molding

Injection Molded Housing


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Environmental issues

System boundaries

Polymer production

Compounding

Machine types

Out gassing & energy during processing

CRADLE

N hth Oil A illi R

Additives


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Polymer Delivery

Injection MoldingEmissions to air, water, & land

Scrap

Note to Reader: FACTORY GATE

= Also included in the Paper

Polymer

Delivery

Naphtha, Oil.

Natural Gas

Ancilliary Raw

Materials

Thermoplastic Production(Boustead)

Internal Transport

Compounder

Pelletizing

Building (lights,heating, ect..)

Energy Production Industry

Anciliary Raw

Materials

Emissions to

air, water, &land

Internal Transport Drying

= Focus of this Analysis

Waste Management

Drying

Building (lights,heating, ect..)

Packaging

Injection Molder

Extrusion

Service Period

1 kg of Injection Molded Polymer

Emissionsto air,

water &

land

Emissions

to air,water &

land

Polymer Production


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Polymer Production

Largest Player in the Injection Molding LCI

Sources HDPE LLDPE LDPE PP PVC PS PC PETBoustead 76.56 77.79 73.55 72.49 58.41 86.46 115.45 77.14

Ashby 111.50 ------- 92.00 111.50 79.50 118.00 ------- -------

Patel ------- ------- 64.60 ------- 53.20 70.80 80.30 59.40

Kindler/Nickles

[Patel 1999]------- ------- 71.00 ------- 53.00 81.00 107.00 96.00

Worrell et al.

[Patel 1999]------- ------- 67.80 ------- 52.40 82.70 78.20

E3

Handbook

[OIT 1997]131.65 121.18 136.07 126.07 33.24 ------- ------- -------

Energieweb 80.00 ------- 68.00 64.00 57.00 84.00 ------- 81.00

What is a polymer:

How much energy does it take to make 1 kg of polymer = a lot !!!

Values are in MJ per kg of polymer produced. Thiriez 06


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Compounding - extrusion

An extruder is used to mix additives with a polymer base, tobestow the polymer with the required characteristics.

Similar to an injection molding machine, but without a moldand continuous production.

Thus it has a similar energy consumption profile.

Environmentally Unfriendly Additives:

Fluorinated blowing agents (GHGs)

Phalates (some toxic to humanliver, kidney and testicles)

Organotin stabilizers (toxic and

damage marine wildlife)

I j i M ldi P


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Injection Molding Process

Source:http://cache.husky.ca/pdf/brochures/br-hylectric03a.pdf

Machine types: Hydraulic, electric, hydro-electric

All-electrics have very low fixed energy costs (small
http://cache.husky.ca/pdf/brochures/br-hylectric03a.pdfhttp://cache.husky.ca/pdf/brochures/br-hylectric03a.pdfhttp://cache.husky.ca/pdf/brochures/br-hylectric03a.pdfhttp://cache.husky.ca/pdf/brochures/br-hylectric03a.pdf


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All electrics have very low fixed energy costs (small

idling power). SEC is constant as throughput increases.

vpSEC

0

1

2

3

4

5

6

7

8

9

0 5 10 15 20Throughput (kg/hr)

All-Electric - 85 tons

Hydraulic - 85 tons

SEC(MJ/k

g)

Material: PP

Source: [Thiriez]

For Hydraulics and Hybrids as throughput


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For Hydraulics and Hybrids as throughputincreases, SEC k.

0

1

2

3

4

5

6

7

8

0 50 100 150 200Throughput (kg/hr)

SE

C

(MJ/kg)

HP 25

HP 50

HP 60HP 75

HP 100

Low Enthalpy - Raise Resin to Inj. Temp - PVC

High Enthalpy - Raise Resin to Inj. Temp - HDPE

Variable Pump Hydraulic Injection Molding Machines.

Does not account for the electric grid. Source: [Thiriez]

Enthalpy value to melt plastics is just 0.1 to 0.7 MJ/kg !!!

All l t i h b id


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All-electric vs. hybrid

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Time (seconds)

PowerRequired

(kW)

MM 550 Hybrid NT 440 All-Electric

PlasticizeInject high

Clamp open-close

Inject low

Cool

Ton

Buildup

Source: [Thiriez]

The hydraulic plot would be even higher than the hybrid curve

Driers


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Driers Used to dry internal moisture in hygroscopic polymers and external

moisture in non-hygroscopic ones. It is done before extruding and injection molding.

W150

W200

W300

W400

W600

W800

W1000

W1600

W2400

W3200W5000

R2

= 0.8225

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 500 1000 1500 2000 2500 3000 3500

Throughput (kg/hr)

Power Trendline

SpecificPowerConsumptio

(M

J/kg)

kmPSEC

mE

mP +===

&&

0

Source: [Thiriez]

Same as

LCI Summarized Results


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HDPE LLDPE LDPE PP PVC PS Consumed Inj. Molded PC PET

avg 89.8 79.7 73.1 83.0 59.2 87.2 81.2 74.6 95.7 78.8

low 77.9 79.7 64.6 64.0 52.4 70.8 69.7 62.8 78.2 59.4

high 111.5 79.7 92.0 111.5 79.5 118.0 102.7 97.6 117.4 96.0

avg

low

high

avg

low

high

avg

low

high

avg

low

high

0.990.09

-----

Thermoplastic ProductionGeneric by Amount Extras

Building (lights,

heating, ect..)Pelletizing

Polymer Delivery

0.19

Compounder

0.24

Internal

Transport

0.19

0.12

0.24

Polymer Delivery

3.57

3.25

8.01

0.30 1.82

5.001.62

Extrusion

0.70 0.16

-----

0.06 -----

0.31

Subtotal

0.12

-----

5.51

Drying

ENERGY CONSUMPTION BY STAGE in MJ/kg of shot

DryingInternal Building (lights,

Injection Molder

Injection MoldingScrap (Granulating)


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avg

low

high

avg

low

high

avg

low

high

avg

low

high

avg

low

high

Notes Drying - the values presented assume no knowledge of the materials' hygroscopia. In order words, they are

averages between hygroscopic and non-hygroscopic values. For hygroscopic materials such as PC and PET

additional drying energy is needed (0.65 MJ/kg in the case of PC and 0.52 MJ/kg in the case of PET)

DryingTransport

3.11 1.80

1.62

-----0.30

-----

heating, ect..)

0.99

-----

0.04 0.70

69.46

117.34

7.35 6.68

124.18

87.87 87.20

70.77

Hybrid All-Electric93.60

Subtotal

TOTAL w/

Generic Inj.

Molded

Polymer

71.65

178.68

Hydraulic

72.57

-----

13.08

5.35

11.29

3.99

69.79

5.56 4.89

Hydraulic Hybrid All-Electric

Injection Molding - Choose One

19.70 26.54

4.47 3.17

11.22 18.06

8.45 15.29

TOTAL w/o

Polymer Prod

18.97

81.04

Granulating - a scarp rate of 10 % is assumed

Pelletizing - in the case of pelletizing an extra 0.3 MJ/kg is needed for PP

13.24 12.57

8.84 7.96 6.66

(look below)Scrap (Granulating)

0.05

0.03

0.12

Source: [Thiriez]

Energy Production Industry


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The Grid is about 30% efficient

Hydro Nuclear Other Coal Oil Gas

Waste/

Renewable

7.1% 19.6% 0.0% 50.7% 3.1% 16.7% 2.2%

United States Electricity Composition by Source

For every MJ of electricity we also get:

171.94 g of CO2

0.76 g of SO2

0.31 g of NOx

6.24 g of CH4

0.0032 mg of Hg

Scale


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Scale

6 Main Thermoplastics

Compounder and Injection

Molder

4.01E+08

2.06E+08 6.68E+08

U.S.

GJ/year

9.34E+07

Global

All Plastics

GJ/year

HDPE,LDPE,LLDPE,PP, PS,

PVC

The Injection Molding Industry in the U.S. consumes 6.19 x107 GJ of electricity (or 2.06 x 108 GJ in total energy).

This is larger than the entire electric production of somesmall countries.

In such a scale imagine what a 0.1 % energy savings mean !!!

The printer goes in the hopper


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The printer goes in the hopper

And comes out


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And comes out.

Readings


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Readings

1. Z. Tadmore et al., "Molding and Casting" p. 584 - 610

2. G. Boothroyd et al., "Design for Injection Moldingp.319 - 360

3. S. Shingo, "Single Minute Exchange of Dies

4. Thiriez et al, "An Environmental Analysis of Injection

Molding

5. "Injection Molding Case Study

6. Kalpakjian Chapter 19 (Chapter 18)
http://web.mit.edu/2.810/www/Thiriez_ISEE_2006.pdfhttp://web.mit.edu/2.810/www/Thiriez_ISEE_2006.pdfhttp://web.mit.edu/2.810/www/lecture/maytag.pdfhttp://web.mit.edu/2.810/www/lecture/maytag.pdfhttp://web.mit.edu/2.810/www/Thiriez_ISEE_2006.pdfhttp://web.mit.edu/2.810/www/Thiriez_ISEE_2006.pdf

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