mold plastic

8/10/2019 Mold Plastic

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Mold Plastic Set textbook for Website

J ETRO SUPPORTING INDUSTRY PROGRAM

J une 2 6


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SET C

1. Mold design chapter1-1 Gate method

1-2 Guidelines for steel materials and mold life1-3 Guidelines for steel material selection intended for plastic injection

materials

1-4 Comparison table of International Standards for steel materials of mold1-5 Heat treatment method of steel materials1-6 General data on steel materials used for mold making

1-7 Computation of deflection on moveable side1-8 Computing necessary thickness of side walls of rectangular shaped

cavities(if bottom surface is integrated)

1-9 Computing necessary thickness of side walls of rectangular shapedcavities(if the bottom surface is separated from the others)

1-10 Computing necessary thickness of side wall of cylindrical cavities

1-11 Mold temperature control method1-12 Cross sectional shape design for runners1-13 Guideline for designing tunnel gate1-14 Head shape design for pinpoint gate

1-15 Runner lock structures for Pinpoint gate1-16 Polishing, finishing of Plastic mold parts

1-17 Outline for food container mold1-18 Outline for medical utensils mold

1-19 Outline for blow molding


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2. Plastic injection materials chapter

2-1 predrying condition of plastic injection materials

2-2 tables showing material properties of plastic injection materials2-3 trouble shooting for rejected works (bubbles)2-4 trouble shooting for rejected works (sink mark)

2-5 trouble shooting for rejected works (flow mark)2-6 trouble shooting for rejected works (burn)

2-7 trouble shooting for rejected works (silver streak)2-8 trouble shooting for rejected works (defective brightness)2-9 trouble shooting for rejected works (short shots)2-10 injection materials and purpose of usage (polyamide)

2-11 injection materials and purpose of usage (polyacetal)2-12 injection materials and purpose of usage (polycarbonate)

2-13 injection materials and purpose of usage (thermoplastic elastomer)


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Examples ofselecting steelmaterialsdepends ontypes of plasticinjectionmaterials

1-3 Guidelines for selecting steel materials depends on types of plastic injection

materials

Types ofResins

Formingsample

expectedspecificationsto resins

expectedspecification to steel

materials

Recom-mendedsteel type

PP

ABS

Bumpers

OA enclosures

Impact

resistance Crepingcontrol

S50C

SCM440

PSPMMAABS

Lighting fixtureMiscellaneousgoodsCosmeticcontainers

design CrepingcontrolMirror finish

SKD61

POMPA

GearsShafts

Abrasionresistant

Abrasionresistant

SKD61

PCPMMA

LensPhoto

conductor

TransparencyOptical

transparency

Mirror finisheasiness

SUS420J2precipitatio

n hardeningtypes ofsteel

PC

PMMA

CD Discs

DVD Discs

Optical

TransparencyLightretractivity

Mirror finish

easinessCorrosionresistant

SUS420J2

PVC

Gutter

Pipes

Heat

resistant

Corrosion

resistant SUS

Fireresistance ABS

TV CabinetAppliances part

Heatresistant

Corrosionresistant

SUS420J2

PBT-GFPA-GF

CameraEnclosureElectricalEquipment

resistance Abrasionresistant

SKD11

Magneticpowder

containing PA

Printer rollersSensor parts

Mold abilityMagneticcharacteristic

Non-magneticAbrasion

resistant

Nonmag-netic steel

Thermo-plastictypes ofresins

Mg

forming

Computer

enclosure

Cellular phoneenclosures

Heat

resistance

Light weight

Heat

resistant

Abrasionresistant

Nonmag-

netic steel


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Phenol resin

Melamine resin

Dishes

Ashtray

Heat

resistant

Heat

resistantAbrasionresistant

SKD11

Phenol resin

unsaturatedpolyester

SwitchesConnectors

HeatresistantFireresistant

abrasionresistantcorrosionresistant

SUS420J2SKD11

Thermo

settingtype ofresins

Epoxy resin IC sealTransistor

Electricinsulation

AbrasionresistantCorrosionresistance

SUS420J2SKD11


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1-4 Comparison tables of International Standards for steel materials of mold

Comparison tables of Standards for steel materials of mold in different countries

JIS AISI SAE AISI ASTMBS 970Part 1.3

DIN 17210,17220

NFA35-551NF EN10083-1,2

OST14959,4543

ISO683/1,10,11

S10C 1010 040A10040A10040M10

CK10C10

XC10 C10

S12C 1012 040A12 XC12

S15C 1015 055M15 CK15C15

C15E4C15M2

S17C 1017 XC18

S20C 1020 070M20 CK22C22

1C222C223C22

S22C 1023

S25C 1025 CK25

C25

1C25

2C253C25

C25

C25E4C25M2

S28C 1029

S30C 1030 080A30080M30

CK30C30

S33C

S35C 1035 CK35C35

1C352C353C35

S38C 1038S40C 1039

1040

080M40 CK40

C40

1C40

2C403C40

S43C 1042

1043

080A42

S45C 10451046

CK45C45

1C452C453C45

S48C 080A47

S50C 1049 080M50 CK50

C50

1C50

2C50

3C50S53C 10501053

S55C 1055 070M55 CK55C55

1C552C553C55

S58C 10591060

CK60C60

1C602C603C60

S09CK 045A10045M10

CK10 XC10

Carbonsteel

formechanicalstructu

res

S15CKS20CK

CK15CK22

XC12XC18


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SK1 Y13 TC140

SK2 W1-11 1/2 Y12 TC120

SK3 W1-10 Y11 TC 105SK4 W1-9 Y10 TC 90

SK5 W1-8 Y9 TC90TC80

SK6 Y8 TC80TC70

Carbon

toolsteels

SK7 Y7

JIS AISISAE

AISIASTM

BS DIN NF OST ISO

SKH2

SKH3

SKH4

SKH10

SKH51

SKH52

SKH53

SKH54

SKH55

SKH56

SKH57

SKH58

Highspeedtoolsteel

SKH59


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SKS11 F2

SKS 2 105WCr6 105WC13 XB4 105WCR1

SKS21SKS 5

SKS51

SKS7

SKS8

SKS4

SKS41

SKS43

SKS44

SKS3

SKS31

SKS93

SKS94SKS95

SKD1

SKD11

SKD12

SKD4

SKD5

SKD6

SKD61

SKD62

SKD7

SKD8

SKT3

Alloytoolsteel

SKD4


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JIS: Japan Industrial Standards

AISI: American Iron and Steel Institute

SAE: Society for Automotive Engineers

ASTM: American Society for Testing Material

BS: British Standards Institution

DIN: Deutche Industrie Normen

NF: Normes Francaises

ost:

ISO: International Organization for Standardization

(Reference literature) JIS Handbooks


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Heat treatment methods of mail steel materials

Types

of steel

Oil quenching

marquenching

aircooling

Heat tempering method

Air cooling

Heat temperinghardness (reference)

Tempering

none


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preheat preheat

air cooling

preheat preheat

air cooling

Standard tempering

Aircooling

High temperature tempering

Aircooling

none


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Primarypreheat

Secondarypreheat

Maintemperature

Cool down

Aircooling

Aircooling

Tempering

none


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1-6 General data on steel materials used for mold making

General data on steel materials used for mold making

ultimate strength

modulus of

longitudinal

elasticity(Young's

modulus)

modulus of

transverse

elasticity

maximum

elasticity

YP (yield

point)

tension com

press

Specific

gravity

coefficient

of linear

expansion

thermal

conductiv

ity

mildsteel

prehaiden

steel


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nickelsteel(2~3%Ni)

209x104 84x10 4

Cast steel

215x104 83x10 4 (2000) (2100) 3500-

7000

(2800) (4000) 7.85 (11.7)

Ni-Cr-Mosteel

210x104 84x10 4 800010000

9000-12000

7.75 17-18

Cast steel75-105x104

27-40x104

1200-2400

7000 -8500

13002600

7.30

Brass(rolling)

63x104 24x10 4 1500 1500 8.50 18-23

Copper(Casting)

105x104 420 -620

1250-1800

8.888.95

16.5


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Aluminum(casting)

extra superduralumin

Zinc alloythird type(ZAS)

Titanium

( ) indicates reference value


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Computation of deflection on moveable side

Attachment plateon movable side


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B: width of mold plate (mm)

L: space inside spacer block (mm)h: thickness of backing plate (mm)l: length of part that receives internal pressure(p)of the cavityb: width of part that receives internal pressure(p)of the cavity

p: internal pressure of cavity (Kgf/)

E: modulus of longitudinal elasticity of materials (Young's modulus) (Kgf/)

max max deflection of backing plate (mm)


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Question: How thick must be bottom part(h) for the followingmovable side plate using carbon steel used inmechanical structure(S55C)?


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Based on Table1

A : E of S55C is E=210 10 kgf/

Therefore

h=35x500x30x1144

32x210x104x250x0.01

= 42.2 (mm)

Answer : at least 42.2mm is needed

In case one allows up to max=0.025

h=3 5x500x30x114 4

32x210x104x250x0.025 =31.1 (mm)

In this case, at least 31.1mm is needed

[Simplified computation when we assume l= L]

max = 5.p.b.L4

32.E.B.h3 (mm)

h =35.p.b.l4

32.E.B.max (mm)


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Table 1. List of value E

material

mild steel

prehaiden steel(SCM440system)

extra super

duralumin


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Table 2. rule of thumb for cavity internal pressure(p)

moldcondition

lower setting

of injectionpressure

higher settingof injection

pressure


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Table 3. rule of thumb for maximum permissible deflection considering

parting burrs

moldingmaterials

maximumpermissible

deflection max(mm)

good flowability (such as

PA,PP etc.)

those which

with generalflow ability

products whichare not affectedby burrgeneration


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[Variation of maximum deflection by insertion of supporting blocks]

Position of supporting block

1 generates when positionis X= 0.421 L/2

One portion at

the center for

supportingblock

Maximum deflection

max = maximum

deflection when there is no

su ortin blocks

(Note) above computation may applied when supporting block is inserted with thewidth equivalent to mold plate width B. On the other hand, above computation will

not applied once there is (are) insertion of supporting pins

Supporting block

Diagram 1 Case that abovecomputation applies

Supportingpin

Diagram 2 Case that above

computation will NOT apply


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Altered condition

Once one creates 1/2 of

inner su ort block s ace

once backing plate

thickness h become h1

Maximum deflection


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omputing necessary thickness of side walls of rectangular shaped cavities (if

bottom surface is integrated)

core

cavit


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Question: How much should be a minimum cavity side wall thicknesshfor the following bottom surface integral hard steel mold?


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p: cavity internal pressure (kgf/ )

l: cavity inner length (mm)h: thickness of cavity side surface (mm)a: sidewall height of cavity internal pressure (p) receiving area (mm)b: cavity height (mm)

E: modulus of longitudinal elasticity(Young's modulus) (kgf/)max: maximum deflection (mm)

h = 312.p.l4.a384.E.b.max

(note) this formula does NOT apply if it is bottom attached type of cavity

Computing necessary thickness of side walls of rectangular shaped cavities (if the

bottom surface is separated from the others)

Core

Cavity

Bottom bushing


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Table 1 Table for value E

Materials E (kgf/cm2)

mild steel 210x104

hard steel 220x104

prehaiden steel(SCM440system)

230x104

cast steel (75-105)X104

extra superduralumin 73x104


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Table 2 Guidance for cavity internal pressure (reference value)

forming condition

lower injectionpressure setting 200 400

higher injectionpressure setting 400 - 600

Question: How much minimum thickness hdo you have to provide on the side wall ofhard steel cavity which the bottom surfaces are divided as drawing?


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A: if the maximum deflection of cavity side wall is max= 0.01mm, we will knowthe modulus of longitudinal elasticity of hard steel is

E = 220 10kgf/ based on Table 1.

Therefore

at least 7.83mm is neededhopefully 10mm is given including some allowance purpose

Computing necessary thickness of side wall of cylindrical cavities

p: cavity internal pressure (kgf/)

R: cavity external radius dimension (mm)r: cavity internal radius dimension (mm) allowable stress of cavity

(kgf/)


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Table 1. value of

material quality

mild steel

hard steel

cast steel


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Question: How much external radius of the following cylindricalcavity shape made of SKD11 is needed?


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Answer: At least 7.07mm is necessary. Giving some extra space, we will make it

10mm.


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1-11 Mold temperature control method

Some of the engineering plastic and super engineering plastic generatecavity temperature over 100 .

It is difficult to raise the cavity temperature by water temperature control,once cavity surface temperature exceeds 90 .Following methods are used generally for countermeasure.

1. Oil temperature control

Temperature is kept constant by oil exhaled from recycling pump passeschannels in mold and cavities, passes joint hose and circulate. Once

temperature will raise up to setting temperature, it is relatively easy tosustain stable temperature.But the weak point is, it takes time to startup temperature.Also, there are other concerns like potential danger of burns, and difficulties

of post treatment.

2. Electric heater

Electric heater (cartridge heater) temperature control may be done withtemperature sensor (thermo-couple etc.) so that temperature will be kept

constant.

Since the heat capacity is big, startup temperature is fast.Difficulty is that heater surroundings become high temperature, but low

temperature at isolated area from heater which means keeping heatdistribution constantly.Heaters have product life, and therefore we must replace heater periodically.For the heater attachment, it is important to provide right clearance at

attachment hole. Too big clearance will cause a situation like boiling withoutwater, and reduce heater life.

MISUMI M-HTM3021 (Temperature controller for cartridge heater) cancontrol temperature by PID control method, therefore quite stabletemperature control than ON-OFF type controller is possible.

It is recommended to provide heat intercepting board in between platen andmold attachment plate of injection machine. It is further recommended toprovide heat intercepting board surrounding mold plate.


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[Table] Example of molding materials with high cavity surface

temperature

Name of plastic cavity surface temperature( )

PPS Glass fiber 30%(polyphenylene sulfide) 130150

LCP Glass 40%(Liquid crystal polymer) 70110

PET

(polyethylene terephthalate) 130150

PA 46

(Polyamide/46 Nylon) 80120

PC(Polycarbonate) 80120

heat resistant PLA(heat resistant polylactic acid) 110120

PEEK(polyether ether ketone) 120160

PI

(polyimide) 170200


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In injection molding of PPS resins and liquid crystal polymer, one need to

maintain the cavity surface temperature above 100 . Therefore it isnecessary for one to control temperature thru oil or cartridge heater.Commercially available Cartridge heater utilize [ON-OFF control] by power

ON and OFF to control temperature.ON-OFF Control is simple structure to shift switch that the cost is cheap.

On the other hand, it has weakness like,() cavity surface temperature gap is big() instability

Instability cavity surface temperature will cause defects such as shrinkage

of dimension, unevenness of surface brightness on precision products.

To stabilize cavity surface temperature, we use PID control.PID control isP: Proportional

I: IntegralD: Derivative

PID control applies above to reduce lead time to stabilize temperature.

Heat intercepting board is very important parts considering that it stabilizes

temperature of injection mold, materialize energy conservation whilekeeping the temperature.

Heat intercepting board has following usage

1. fixed to platen of injection mold machines and use

2. fixed to back of attachment plate of mold and use


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Following are selection standard of Heat intercepting board.

1. Heat resistant temperatureFollowing are recommended working temperature as guidance

recommended working temperature below 100

recommended working temperature below 180 recommended working temperature below 220



2. MaterialMaterials are related to recommend working temperature and crushing

strength.There are following types of materials.

cotton cloth Phenol resins(bakelite)

craft paper Phenol resins(bakelite)

Glass fiber silicate binder

Glass fiber super heat-resistant epoxy resin

Glass fiber phosphate binder

Glass fiber borate binder


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1-12 Cross sectional shape design of runner

Runner is channel to let molted resins to flow from sprue to product.Selection of cross sectional shape of runner depends upon product size,

resin types, expected molding condition etc.Following are basic standard for the selection of runner cross section shape.

[Diagram] shows main runner cross section shape

One may select runner from following 3 types

1) carve on movable side2) carve on fixed side3) carve on both movable and fixed side

Selection depends on shape restriction and mold parting position.

Symbols such as : excellent : proper, : inadequate

Important roll of runner is to let molten resin flow under minimal pressureloss condition. Unnecessary large sized runner will increase scraps, worsen

material costs, prolonged molding cycle, and increase volume of disposingwaste.

Index to indicate runner efficiency is inscribed circle diameter area at

cross sectional shape. The bigger the space of inscribed circle, wider thearea that hot resins will flow, and therefore one can expect better flow of

molten resins.So the ideal is the runner on round cross section shape. But cost wise thisbecomes more expensive for mold cost because one must carve runner on

both movable and fixed side.To comply on such nonconformity, further biting of trapezoidal shape orsemicircle cross section are utilize.

It is better to provide angles on the side of runner so that mold releasebecomes better. On the other hand inner surface of runner must be polished

by rubber wet stone or rapping to avoid pressure loss.


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1-13 Guideline of tunnel gate design

Tunnel gate (submarine gate) is widely used gate method where the

product and gate are automatically cut every time parting surface opensand close.

It is necessary for one to know the basics such as shapes and dimension todesign tunnel gate. But for this time, we are introducing to you the basicvariation of molded products and gate, runner relation.In the [Diagram], shows basic patterns of tunnel gate.

Put parting surface between, there are 4 patterns of gate-runnercombination on fixed side and moving side.


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Fixed side tunnel gateFixed side runner

Fixed side tunnel gateMovable side runner

Movable side tunnel gateMovable side runner

Movable side tunnel gateFixed side runner

Movable side tunnel gateArrangement for hubFixed side runner


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In case if tunnel gate is provided on the fixed side, cutting of product and

gate will be done while parting surface opens. Therefore, gate cuttingcondition varies depending on mold opening speed.On the other hand, in case if tunnel gate is provided on the fixed side,

cutting of product and gate will be done when runner ejector pin pushesrunner. This means, gate cutting condition depends on protruding speed of

runner ejector pins.In case runner is provided on the fixed side, it is necessary to makestructure that the lock pins will pull runner toward movable side, becausethere is a chance that runner itself may be left on fixed side.

In case runner is provided on the movable side, we must set ejector pin topush out runner properly.

In special case, there are times that boss-shaped (sharpen up ejector pin)tunnel gate is provided on the movable side, and fill resins from backsurface of top panel.

In actual practice, we must decide what type of gate and runner to use onmold design based on product characteristics, and material properties.

If specification prohibits any trace of gate mark on side panel or top panel,

we rarely have to provide gate on back surface of products.In such a case, Curved tunnel gate is rarely used.


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Runner Curved tunnel ate

Cavit

Ejector pin

Gate holding hub

E ector in


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In the structure of curved tunnel gate, bulging gate shape extends from

parting surface to inner movable core. Therefore, gate opening locates at

top plate of core.Ejector pins are provided on runner near the gate area, and boss isprovided at the top part of pin part to hold gate. Overall length of boss is

H. During the ejection, so as to undergo smooth gate cutting, it will holdgate until product will be cutout from core completely.

Final shape of bulging part is usually corrected after several trial-and-error.It is wise to set nested split type structure from very beginning, so that thecorrection of mold become easy.

Gate passage is always affected by mold cooling time and pressure keeping

time. Try several variation as sample for prototype.

Whichever method one may choose, cutting condition at cutting area and

scum become common problem upon cutting product and gate.

Following factors may affect cutting condition1. Gate tip shape design

2. gate size (cross-sectional shape)3. distance from gate cutting part to runner lock part

4. acting condition of pressure keeping5. orientation of high molecules at gate part

6. cutting timing of gate and products

Careful analysis must be made before entering into preparing mold for

precision mold and multi-cavity mold.


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1-14 Pinpoint gate tip shape design

Following are potential problems on pinpoint gate structure.

1) Gate tip portion protrude and remain on the product surface, or pluck offpart of product

2) In comparison to high filling pressure and keeping pressure, filling cantbe done smoothly

Above are common problems and headaches of mold designer upon usingPinpoint gate.

Following are technical trouble shooting.

[Diagram1.] Shows general pinpoint gate structure. Gate design withoutany consideration usually looks like this.On the other hand, [Diagram2.] shows contrive design to minimize above

problems.


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2. Gate

Opening angle

1. gate land

Length

3. thickness relief

4. Dimple

(basin)


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Point 1 Gate land length L

If the gate land is unnecessary long length, it may remain as protrusion,because gate will be cut in the middle portion.

From the study, we recommend that Gate length(L) size be 12 times the

diameter of gate tip.

Point 2 Gate open angle A

One must provide tapering to open angle and create cone shape. As long as

it is cone shape, strong chance that contact point of minimal cross sectiongate area and product shall be the cutting point.

Mold release becomes easy too. Value A is usually 1530. Bigger thevalue, more assurance on cutting, but wearing out at the tip portion tends

to become faster.


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Point 3 Slot

Once Slots are provided, they will encroach 1 step into the surface ofmolded products. Because of this, protrusion will not exceed the surfacelevel of products even if it remains at cutting area.

One must first acquire Approval of product designer in prior to set slots onthe drawing.

Point 4. Dimple

Dimples are spherical shape concave provided at the opposite side of the

gate which has almost same wall thickness to product, so that molten resinwill flow stable when slots are created.

One must also first acquire Approval of product designer in prior to setdimples on the drawing.


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457 1-15 Runner lock structures for Pinpoint gate

Runner lock shapes in pinpoint gate structures have several patterns,however usually applied pattern is indicated in Diagram 1.

Diagram 1.

Product

Fixed side mold plate +

Cavit

Runner plate

Fixed side attachment late

Gate

Runner

Narrow

Runner

Runner lock pin


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Place runnerlocks one stepdown

In the [Diagram1.], locate runner lock pin which has undercut shape at the

head area into the runner foundation. When fixed side of mold plate andrunner plate create a space, they will compulsively separate runner andgate.

Runner lock pin will be engage by clearance fit to runner plate, and fixed to

fixed side attachment plate by plate and screw plug.In this method, if one will work on thin product or resin with higherpressure loss, channel within runner from the head portion of runner lockpin becomes narrower. In this case, it is necessary for one to provide higher

filling pressure or pressure keeping as molding condition.

In this case, as indicated in [Diagram2.], one may set lock area one steplower within runner plate. In this manner, one is necessary to createconiform curving on top of runner plate. For this process, mold cost may

become higher, but be able to improve pressure losses during molding.


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Encroach into inner side

also for the purpose forrelief thickness

If incase one wish to reduce the molding cycle, create a pointed conifom

shape at tip of runner lock pin shown in [Diagram3.], which will also act

as slot like lock shape. In this way, excess materials at the runnercenter will be reduced, therefore more efficient cooling is done, thencontribute to reduction of cycle.

But one must take care of coniform shape portion balance, becausepoor balance at the area will cause fracture of cuneiform shape from the

base. One can also provide corner radius to improve strength.

One must select proper runner lock, by first determining expected roll ofrunner lock in prior to design mold.


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1-16 Polishing finish of plastic mold parts

Cavity surface of plastic injection mold undergo mainly hand polish ormachine polishing after milling, EDM, wire cut process to smoothen thesurface.

Transcription surface for products be dull, and surface quality maybecome poor if polishing condition is not good.

surface may become potential undercut upon separating product

from cavity, and cause defective mold release.

Hard wetstone and abrasive grain are utilized for cavity polishing. You

may use rough mesh number (larger grain) to finer mesh number. Usegrinding fluid while making sure that clogging and galling will not take

place.Polishing is not only done one direction but relative position andcircumferential direction so that polishing surface will be uniform.

Following are main polishing materials.

Natural polishing agent - silica group (agate, alcansas)

- Corundum group (emery, garnet)- Diamond powder

Synthetic polishing agent - alumina (Al2O3)

- Silicon carbide (SiC)- Boron carbide (BC)

- Synthetic diamond

Grain size of polishing materials ranges from #10#20000. Smaller the

value, rougher the mesh.

(Ex. Using #10#30 polishing results rough finish, but #1000#2000

polishing results finer finish)

In case one will use fine abrasive grain, we mix olive oil or vegetable oilinto maple, pine, willow, balsa like trees and polish.


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1-17 Food container mold overview

Many plastics are used as food container. PET bottles, food cups,wrappings are mostly plastics.It is necessary to give extra care on food container quality, so that man

can enjoy foods not worrying hygienics, at the same time not todamage lips and tongues by burrs.

Any pores or cracks on plastic will allow bacteria to infiltrate into foodsand spoil them. Such quality defects are not allowed too.

There are following major food containers

margarine container : PP

ice cream container : HIPS, HDPE lactic acid bacteria beverage : HIPS pudding container : PS, PP

confectionary container : HIPS, PP, HDPE soft drink container : PET

Necessity of function depends on food purposes such as thermostability(for foods necessary to heat up), low thermal resistant(for food

necessary to freeze, refrigerate), gas barrier(for those foods that cannot be exposed to oxygen).

For food containers, sales of the foods will also depends on productdesign(beautiful finish), which means 3 dimensional curved surfaceshape and design become significant. Therefore, in product design and

mold design, one needs 3 dimensional solid data.There are always chances of burrs to generate at parting surface,therefore location of parting surface must be paid attention.This is same for gate position and method.

Cavities, and cores must be fabricated by corrosion resistance steelmaterials. It is better that one will not apply grease nor slide promoting

oil. This means non lubricating mold mechanism is recommended.Electric injection machines are ideal, further ideal to work inside cleanrooms.

Its worth trying using valve gate and hot runners. If mass production isexpected, one can also use scrap press effects and high cycling.


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1-18 Medical utensils mold overview

Many plastics are used in medical utensils. In many cases, injection

molding method is used for production.This means many parts of medical utensils have been produced thrumold making.

There are following major plastic medical utensils.

1. syringe (syringe body) : PP, PE2. piston of syringe : PP3. pipet chips : PP4. catheter : PVC, PC

5. blood collecting test tubes : PC6. dish for culturing : PS

For plastic medical utensils materials, only those which are allowed bydrug legislation and quality standard prescribed by Ministry Of Labor

and Health can be utilize. Those materials must withstand exposures ofUV lights and gamma rays used for sterilization, at the same timepassed the clinical test for blood coagulation reaction, allergies etc.Basically, medical utensils are disposable. Therefore those materials

must be environmental friendly upon incineration.

It is recommended that mold materials shall be non rusting type. This isthe reason why many cases, medical utensil molds are made of

stainless, ion plating film, hard chrome plating so as to preventcorrosion of core, cavity.

Valve gate molds are used in mass production items.

Needless to say that burrs for products are defects, therefore useprecision guide to locate movable side and fixed side, and also try toapply contraption preventing the abnormal worn out of core pins ofcentering location structure.

There must be delicate temperature setting for cavities and cores to

produce stable quality products. For this point, one must pay attentionto the structure of cooling circuit and heat pipes.Cooling structure in core becomes very important for cylinder body of

syringe.

Removal of gases and resins on the mold surface is related to quality.Gas vent settings and enforced ventilation structures are applied.


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1-19 Blow molding mold overview

Blow molding method is usually applied to pet bottle containers forjuices (PET : polyethylene terephthalate resin) which blow methods areused.

It is familiar in all over the world because it is used as shampoocontainer, soy sauce and other seasoning container, detergent container

etc.Polyethylene terephthalate, polypropylene, PVC, nylon, polycarbonatemay be used for blow molding method.

Exclusive blow machine is used for blow molding. In the mold, there isonly cavity on female mold, but no core on male mold.

Instead, there is a nozzle prepared to blow air. Balloon like performingshape part called Parison blows, stick to cavity and transcribe shape.

Generally speaking, soft metal materials are used for cavities in blowmolding. These are aluminum alloy, bronze, and special steels.Usually beautiful brightness surface is required to product, thereforepolishing of inner cavity surface must be done properly.

In beverage containers blowing, multi-cavity moldings are practice

generally which means contraption on cooling and temperature controlare important to comply high-cycle operation.

Also design of products that incorporated recycle is important, because

most of those blow items will be disposed after the consumption.


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2-1 pre-drying condition of plastic molding materials

Usually, plastic molding materials comes in pellet form in the paper bagupon their delivery.

Pellets absorbs moisture in the air, therefore hydrolysis may take place

on some resins in the process of molding if pellet still contains moisture,or degrade physical properties of materials. There are also cases thatsilver streak may appear on the surface of product, or short shots mayoccur due to gases, and burns may be generated too.

Many cases, materials are first placed into box shape pre-drying device

before placing them into the hopper dryer.

It is recommended that proper drying temperature and time are take

into consideration. Moisture can not be eliminated completely evenplaced for long period, if drying temperature is below the proper setting.Quick consumption of materials after pre-drying is recommended. Ifthere will be any left over of materials in a daily production, you must

undergo pre-drying again before usage.


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Pre-drying temperature of plastic molding materials

Name of materials symbol predrying temperature drying time(H)

Liquid crystal polymer LCP 110 150 4 - 8

Polyetherimide PEI 120 150 2 - 7

polyamide imide PAI 150 180 8 - 16

thermoplastic elastomer TPE 120 3 - 4

polyether ether ketone PEEK 150 8

polyphenylene sulfide PPS 140 250 3 - 6

polyalylate PAR 120 150 4 - 8

polysulfone PSU 120 150 3 - 4

ABS resin ABS 70 80 2 - 3

Acryl PMMA 70 100 2 - 6

Polycarbonate PC 120 4 - 6

Nylon 6 PA6 80 8 - 15

Nylon 66 PA66 80 8 - 15

Nylon 11 PA11 70 80 8 - 15

Nylon 46 PA46 80 8 - 10

Polyacetal POM 110 2 - 3

PBT PBT 120 4 - 5

Pellets of Plastic molding materials usually absorbs certain degrees ofmoisture in the air. If there will be too much moisture absorption,

hydrolysis may take place (some resins cause chemical decompositionby water) in the cylinder of injection machine during molten andkneading process. Sometimes, silver streak, bubbles, defective

brightness, defective transcription may occur during injection.To avoid above problems, we must first place the pellets in the dryingmachines to remove water content.

Variation of flow of materials, degrading physical properties, defectivemolding may happen if we do not give out predrying properly.


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2 2 Tables showing material properties of plastic molding materials

Main plastic material physical properties list

Thermoplastic type of Plastic

Resin name ABS resin

GradeHigh steel

ability Heat resistance

Filling materialsGlass fiber20 40%

JIS testingmethod

A.S.T.M.Testingmethod Abbreviation ABS

Drying temperature 70~80 70~80 70~80

Drying time 2 2 2

Injection mold cylindertemperature 200~260 250~300 200~260

Injection mold temperature 50~80 50~80 50~80

Injection molding pressure 560~1760 560~1760 1050~2810

Compression moldtemperature 160~180 160~260

Compression mold pressure 0.7~506 0.7~5.6

Mold contraction rate 0.4~0.9 0.4~0.9 0.1~0.2

Moldability

K6911.K7112 D792 Specific gravity (density) 1.03~1.06 1.05~1.08 1.22~1.36

K6911.K7113 D638 Tensile strength 400~530 400~560 570~740

Elongation percentage 3.0~20.0 5.0~25.0 2.5~3.0

Compression strength 127~879 505~702 844~1550

Bending strength 773~914 703~1050 1120~1900Mecha-nical

properties Impact strength (Izod) 10.9~33.7 10.9~35.4 5.4~13.1

Hard ness (Rockwell R107~115 R100~115 M65~100

Heat resistance (continuos) 71~93 88~165 93~110

Heat distortion ( ) a)bending

stress 101~112 85~107ThermalCharac-teristic

K7206.K7207 b) bending stress 99~108 107~122 93~119


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Thermoplastic type of plastic

AS Resin Etylene-vinylacetate Polyamide (Nylon)

General Nylon 6 Nylon 66 Nylon 11.12

Glassfiber 20 30% -

Glass fiber30% -

Glass fiber30%

SAN EVA PA6 PA66 PA11.12

85 85 80 80 80 80 70~80

2~4 2~4 8~15 8~15 8~15 8~15 8~15

200~260 200~260 120~230 240~290 240~290 260~300 260~300 190~270

50~80 50~80 20~60 40~120 40~120 40~120 40~120 20~100

710~2320 1050~2810 562~1410

150~200 90~150

70.3~703 0.04~1.76

0.2~0.7 0.1~0.2 0.7~1.2 0.5~1.5 0.4~0.6 0.8~1.5 0.5 0.3~1.5

1.07~1.10 1.20~1.46 0.92~0.95 1.12~1.4 1.35~1.42 1.13~1.15 1.38 1.03~1.08

600~840 600~1440 95~200 700~850 1650 770~850 1850 530~550

1.5~3.7 1.1~3.8 500~900 200~300 3~6 150~300 3 300~500

984~1200 1550 914 1340 1050 2070

984~1340 1550~1830 1270~2320 429~1200 471~1260

Nondestructive 3.3~5.4 16 4.3~5.4 12 10~30

M80~90 M100~E60 D17~45 R119 M101 R120 M100 R106~109

60~96 93~104 82~121 93~149 82~121 82~121 82~149

88~104 88~110 33.7 88.1 210 74.8 77 54.2

101~115 77~80 203 239 208 236~239 167


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Methacrylate

resin (acryl) Polyacetal

General General GeneralHighimpact

Thermosability

- -Glass fiber20% -

GlassFiber 40%

PMMA POM PP PS HIPS PS

70~100 110 110

2~6 2 2

190~290 180~230 180~230 200~300 200~300 170~280 190~280 199~280

40~90 60~120 60~120 20~90 20~90 20~60 10~80 20~80

703~1410 703~1410 703~1410 703~1410 703~1410 703~2110 703~2110 703~2110

149~218 171~288 171~288 129~204 121~204 129~204

141~703 0.35~0.70 0.35~0.70 70.3~703 70.3~703 70.3~703

0.1~0.4 2~2.5 0.4 1.0~2.5 0.2~0.8 0.4~0.7 0.4~5.7 0.2~0.6

1.07~1.20 1.41~1.42 1.61 0.90~0.91 1.22~1.23 1.03~1.05 1.03~1.06 1.05~1.09

470~770 580~800 1250~1300 210~400 560~1000 350~840 200~350 350~530

2~10 25~75 3 100~800 2~4 3~4 13~50 2~60

844~1270 1270 1200 260~562 387~492 809~1120 281~633

914~1340 991 1970 352~492 492~773 562~984 211~844

1.6~2.7 5.4~13 10 2.2~110 7.6~11 1.4~2.2 3.3~20 2.2~19

M85~105 M78~94 M79 R50~111 R102~75 M60~75 M10~80 M70

59.8~93 90 104 88~115 121~138 65.3~76.5 59.3~79.2

73.7~99 124 110 45.9~59.8 59.8~93 104 90 90

79.2~107 170 158 103~130 117~161 82~110 82~104


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Polycarbonate Polyethylene

GeneralLow

densityModeratedensity

Highdensity

Glass fiberless than

10%Glass Fiber10 40%

Glass fiber20 30%

PC LDPE MDPE HDPE PBT

120 120 120 120 120

>4 >4 >4 4 4

270~380 270~380 270~380 150~270 200~300 200~300 230~280 230~280

80~120 80~120 80~120 20~60 10~60 10~60 40~80 40~80

700~1410 700~1410 1050~2810 562~2110 562~2110 703~1410 562~1800 562~1800

249~326 135~176 149~190 149~232

0.7 7.03~56.2 7.03~56.2 0.35~0.56

0.5~0.7 0.2~0.5 0.1~0.2 1.5~5.0 1.5~5.0 2.0~6.0 1.5~2.0 0.2~0.8

1.19~1.20 1.27~1.28 1.24~1.52 0.91~0.925 0.926~0.940 0.941~0.965 1.31~1.38 1.52

550~700 630~675 840~1760 42~161 84~246 218~387 550~540 110~1340

100~130 5~10 0.9~5.0 90~800 50~600 20~130 50~300 2~4

844 984 914~1480 190~253 605~1020 1270~1650

949 1050 1200~2250 337~492 844~1170 1830

75~100 5.5 11

Non

destructive 2.7~87 2.7~110 4.4~5.4 7.0~8.7

R115~125 M75~85 M88~95 D41~50 D50~60 D60~70 M68~78 M90

121 135 135 82~100 48.7~121 121 49.8~121 115~176

129~140 142 143~149 40.3~48.7 40.3~48.7 43.1~54.2 49.8~85 220

132~143 146 149~154 48.7~73.7 48.7~73.7 59.8~88 115~193 225


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Thermoplastic type of plastic

Polystyrene Polyvinyl chloride Fluororesin Polyphenylene chloride Crystal liquid polymer

Flexible rigid

Glass fiber20 -30% - -

Glass fiber40 %

Glassfiber 40%

PS SPVC HPVC FEP PPS LCP

120~140 120~140 140~160 140~160

3~5 3~5 4 4

170~280 160~190 170~210 370~430 315~330 315~360 250~310 250~310

20~80 10~20 10~60 95~230 130~150 130~150 70~110 70~110

1050~2810 562~1760 703~2810 352~1410 300~1000 300~1000 150~500 150~500

140~176 140~204 315~399

35.2~141 52.7~141 70.3~140

0.1~0.3 1~5 0.1~0.5 2~3 0.6~0.8 0.2~0.4 0.1~0.8 0.1~0.55

1.20~1.33 1.16~1.35 1.30~1.58 2.15~2.17 1.3 1.60~1.67 1.35 1.7

633~1050 100~240 400~500 180~210 630 1500~1550 1060~1335 900

1~2 200~450 40~80 250~330 1~2 0.9~4 1.3~4.5 1.8

949~1270 63~120 562~914 155

738~1410 703~1120

1.4~2.2 2.2~100

Largely

change

Non

destructive


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2-3 Countermeasure on defective molding

Bubble Void are phenomenon where air bubbles are generated withinmolded products. These bubbles or voids will be considered rejected on a

product such as lens, prism because appearance and optical characteristicbe disturb by such defect. It will also reduce strength and become cause of

destruction of machine once those defective items are used as machineparts.

There are 2(two) major cause of bubbles.

One cause is that, air was mixed into molten plastic. This is called bubbles.

Other one is caused in the process of shrinkage of molded articles known asVoid. In the void, insufficient pressure keeping was applied to thick wall

area, and this caused abnormal shrinkage just like this happened in theprocess of generation of Sink mark.

Following can be possible countermeasures for above problems.

Countermeasures for bubbles

1. Countermeasures related to mold

1. There are no air vent or lack of numbers of air vent

2. There is no cold slag well, or it may be too small


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2. Countermeasures related to injection molding condition

1. too fast screw rotational speed2. too high cylinder temperature

3. too fast injection speed

3. Countermeasures on product design

1. insufficient predrying of mold materials

Countermeasures on void

1. Countermeasures on molds

1. There is no air vent, or lacking

2. There is no cold slag well, or it is too small3. too small sprue, runner4. too small gate


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2. Countermeasure related to injection mold condition

1. Too high cavity surface temperature2. Too low pressure keeping3. lack of pressure keeping time

3. Countermeasure on product design

1. insufficient predrying of molding materials2. too thick molded product wall thickness


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2-4 Countermeasures on defective molding (sink mark)

Sink mark is a phenomenon which generate slight concave due to

shrinkage of product surface.It may become defective quality in case product used for surfaceappearance.

There are following methods to control sink mark.


1. Set the cavity surface temperature slight lower2. Make gate size bigger

3. Make runner size larger4. Use larger sprue

5. Review cooling channels of mold to improve cooling efficiency6. Improve the structure where difficult cooling area to become easierto cool. (Ex. Baffle plate structure, cooling pipe structure, heat pipe,

non-ferrous bushing)7. Increase the number of gate8. Relocate gate position to thick wall area


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2. Countermeasures related to injection mold condition

1. Set pressure keeping time longer2. Set pressure keeping to higher setting3. Set the injection speed faster

4. Set nozzle temperature lower5. increase indiscrete value

6. Increase cushion volume7. Change the injection mold machine8. Exchange the backflow prevention ring of injection unit

3. Countermeasure on product design

1. remove the thick wall area of products(Ex. Material relief shape, alter into another parts)2. apply amorphous resins


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2-5 Countermeasure for defective molding (flow mark)

Flow mark is a phenomenon where melted resin flowing marks remainson the surface of products. This may become a cause of reject dependsupon degree of such mark appearance. Products such as electric appliances

or cosmetic product casing are particular about such appearance.

Flow mark is generated in the process that molted resins contact metalsurface in the mold will encounter different degree of cooling at the tip ofresins.

Following methods are considered to improve the flow mark.


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1. Countermeasures related to molds

1. set the cavity surface temperature lower

2. expand the size of the gate3. enlarge the size of the runner4. secure enough cold slag well


1. set the injection pressure higher2. set the injection speed faster

3. secure enough measurement to increase the cushion volume4. set the pressure keeping time longer

5. set the resin temperature higher6. enlarge the nozzle tip diameter larger

3. Countermeasures related to molded article design

1. set the variation of wall thickness of molded articles smaller


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2-6 Countermeasures on defective molding (Burn)

Burn is a phenomenon where black burning materials are generated on

the surface of molding articles. Air which remained in the cavity whilecompressed will generate heat, and this heat burns the plastics whenmolten plastics are filled into cavity.

Burn can be appearance defect, causing missing parts, and decreasing

material properties.

Following are considered countermeasures on burns.


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1. provide the air vent

2. prepare deeper air vent and secure enough vent passage3. dismount mold and wash give out maintenance to air vent4. use insertion mold structure or bushing structure so that air will escape

from parting surfaces5. Use vacuum aspirator device

6. change the gate position


1. set the injection speed slower2. set the cylinder temperature lower

3. make smaller measurement4. avoid staying of resins in the cylinder


1. try to apply design that avoids thinner wall areas of molded articles2. change the wall thickness of molded articles, and flow of plastics

3. alter the design that allows air to stay


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2-7 Countermeasures on defective molding (Silver streaks)

Silver streak (silver film) is a phenomenon where shinny stripe marks aregenerated on the surface of molded articles. This may become potentialrejects as an exterior parts for electric appliances, automobile, bicycle for its

defective appearance quality.

Silver streaks occur because the air and volatile gas in the moldingmaterials come out on the surface of products.

Following are potential countermeasures on silverstreaks.


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1. improve the functions of air vent

2. enlarge the gate size3. enlarge the cold slag well


1. confirm the preheating condition(temperature, drying time) ofmolding materials and apply proper drying.

2. set the injection speed slower to slower filling3. set the cylinder temperature lower

4. reduce the screw rotation speed5. avoid staying in the cylinder

3. Countermeasures related to molded article wall thickness

1. prepare as much as possible the uniform wall thickness


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2-8 Countermeasures on defective molding (defective brightness)

Ideal surface of molded articles must be the transcribed surface appearanceof cavities, but there are times that surface of molded articles exhibitobscured or uneven brightness surfaces.

This may become major defect cause on the product exterior surface which

the appearance quality is considered significant.

Following are potential countermeasures on defective brightness.


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1. there might be NO air vent or lack of air vent2. small gate3. small and narrow sprue and runner

4. cavity plating is NOT good condition5. cavity surface polishing is NOT good condition

6. deposits are attached to the surface of cavity


1. lack of measurement2. too short cushion surface

3. too low pressure keeping4. too short pressure keeping time5. low cavity surface temperature

6. insufficient predrying of molding materials


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2-9 Countermeasures on defective molding (Short shots)

Short shot is a phenomenon where incomplete filling takes place at the part

of molded articles.

There are 2(two) potential cause of short shots.

First cause is, cooling down and solidifies of tip of materials while moltenresins flow.

Second cause takes place in the process of flowing. Because air traps aregenerated depends on the flowing condition.

To take countermeasures on short shots, one must first find out the cause

of problems from the above cause.


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Short shots caused by flow tip solidification


1. Expand further the gate size

2. Expand further the runner size3. use the larger sized sprue4. too small cold slag well

5. provide heat insulating plate at bottom surface of mold plate6. increase the number of gate

7. alter the location of gate


1. set the resin temperature higher2. set the cavity surface temperature higher

3. increase the filling pressure4. set the pressure keeping higher5. set the pressure keeping time longer6. increase the measurement value

7. increase the number of cushon8. change the injection machines9. exchange the backflow prevention rings of injection unit

10.exchange the injection nozzle tip diameter of injection machine larger


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1. increase wall thickness of molded articles

2. provide ribs at the area where there is poor flowing

Short shot due to air trap


1. provide an efficient air vent at air trap generating areas2. change the gate position

3. change the runner balance4. review and improve the structure into heatup possible structure where

there is poor flow

5. change the structure to insertion or bushing structure where there ispoor flow


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1. change the injection speed, to change the flowing patterns

2. relayout the position of screw speed pressure exchange position3. set the injection speed slower4. set the cavity surface temperature higher

5. set the mold clamping pressure slight lower

3. Countermeasures related to mold article design

1. review and apply uneven wall thickness of molded articles2. increase the wall thickness of molded articles


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2-10 Molding materials and its usage (polyamide)

Polyamide is also known as Nylon(trademark). There are PA6,PA66,PA46,and aromatic polyamides.Characteristics of polyamide are that it is outstanding in friction abrasion

character. Because of this characteristics, materials will not cause muchnoise, stable sliding. Its also has superior resistant character to organic

solvents and oils.On the other hand, it has great water permeability and hygroscopic property.This means, one can expect dimensional change of products,There will be an improvement of heat resistant and strength by filling glass

fibers.

Following are main usage:

Automobile parts throttle cam throttle body housing

intake control valve shifting lever set door mirror bracket engine cover

electric oil sensor intake manifold

electric / electronics parts

FPC connector

Coil bobbins Relay

Switch parts

electric appliances / residential related

surfing board electric shaver moving parts

residential window handle levers

electric tool housing

others

fastener chair legs


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2-11 Molding material and its usage (polyacetal)

POM resins (Polyacetal, polyoxymethylene) are superb in mechanicalspecification like breaking strength, and worn out resistance property sothey are known as engineering plastics.

In POM, there are homopolymer and copolymer.There are differences in strength, thermal resistance, molding condition

between homopolymer and copolymer.Biggest feature of POM Resins are self-lubrication. It is valued functionswhen its applied as gear, bearing like parts where there are always facingfrictions.

Crystallinity is high, therefore is shows good result in strength and thermalresistance.

In injection molding, one must take care not this materials to stay longperiod in the cylinder, because they will undergo thermal decomposition.Followings are main usage.

Automobile parts

fuel gauge fuel chamber

door mirror warm gear

mirror stay fuel pump radiator drain cock

Electric / Electronics parts

CD pickup unit

Switch stem

DVD drive unit / pulley. Cum Magnetic memory device roller

precision parts

watch gears

bearing

others

shower bib

fastener gas meter parts flushing toilet parts


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2-12 Molding material and its usage (polycarbonate)

Polycarbonate is a transparent strong thermal resistant material applied in

diverse areas.Recently alloy type of usage of polycarbonate by mixing it with ABS resinsand used for industrial purposes.

It is amorphous and exhibit good light transmittance therefore applied aslens and cover materials. It also exhibits outstanding strength especially

shock resistance among other plastics.However it will be corroded by organic solvents. This is the reason why onemust pay great attention, if ever grease group of chemicals and solventsare applied on the material.

In injection molding, this material exhibits poor liquidity. Therefore fillingpressure must be set higher. One shall also necessary to increase the

temperature up to approx 80 .Following are usage of the materials.

Automobile parts meter panel

head lamp lens

door handle sun roof

instrumental panels wheel cover

Electric / Electronics cellular phone case memory sticks

CD disc

DVD disc

Digital camera case Printer chassis

PC casing

optical components

camera lens

aspheric surface lens prism

light conductor protection goggle

dome shape roofing window glasses


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2-13 Molding material and its usage (Thermoplastic elastomer)

Thermo plastic elastomer (TPE) is a synthetic resin which has rubber likeproperties.Automobile tire is one good example of rubber, but those rubbers are

solidify thru chemical reaction and therefore generally speaking it is notpossible to fabricate by injection process.

On the other hand, TPE can fabricate thru injection molding. It isthermoplastic and therefore one can fabricate without burrs under relativelyfast cycle time.In many cases now, this material is applied to products such as sticker parts,

sports items, toys, writing materials. 1.43M tons(2001) has been consumedin the world.

TPE shows rubber like flexible hypertrophic properties because it containssoft segments and hard segments.

There are following types of TPE available, and being used accordingly.

(1) SBC (styrenic TPE)

Sole, automobile parts, food container, writing material grip, sportsitems

(2) TPVC (vinyl chloride TPE)

Electric wire coating, automobile parts, electric appliance(3) TPO (olefine TPE)

Automobile parts, construction/civil work parts, electric appliance(4) TPE (Polyurethane TPE)

Watch band, sole, automobile parts. etc(5) TPEE (polyester TPE)

Automobile parts, electric appliance, industrial materials. etc.(6) nitryl TPE

(7) TPAE (polyamide TPE)(8) Fluoro-chemical TPE

(9) Silicone TPE


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1) c Michio Komatsu : Molds for beginners. Introduction to plastic injection

mold, molding technology. Mold technologyApril 2004, special issues, [Daily industrial journals]2004

2) c Michio Komatsu : Plastic injection molding design manual, pin gatestructure mold technology. March 1998 special issue, Daily industrial

journals 1998

3) c Michio Komatsu : Plastic injection design manual Daily industrialjournals (1996)

4) Plastic mold standard parts 2005.6 2007.4MISUMI Inc. (2005)

5) Technology course, MISUMI online, MISUMI Inc, www.mol.ne.jp

mold plastic

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