Mold Plastic Set textbook for Website

JETRO SUPPORTING INDUSTRY PROGRAM

June 2006

SET C 1. Mold design chapter

1-1 Gate method 1-2 Guidelines for steel materials and mold life 1-3 Guidelines for steel material selection intended for plastic injection

materials 1-4 Comparison table of International Standards for steel materials of mold 1-5 Heat treatment method of steel materials 1-6 General data on steel materials used for mold making 1-7 Computation of deflection on moveable side 1-8 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 shaped

cavities(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 method 1-12 Cross sectional shape design for “runners” 1-13 Guideline for designing tunnel gate 1-14 Head shape design for pinpoint gate 1-15 Runner lock structures for Pinpoint gate 1-16 Polishing, finishing of Plastic mold parts 1-17 Outline for food container mold 1-18 Outline for medical utensils mold 1-19 Outline for blow molding

2. Plastic injection materials chapter 2-1 predrying condition of plastic injection materials 2-2 tables showing material properties of plastic injection materials 2-3 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)

From page 3…

1 ‒ 1 Gate method

Gate Method

∅d= gate tip diameter θ= penetrating angle

α= angular aperture

l = gate land length

[Submarine gate (tunnel gate)]

==Characteristics== ① gates are automatically cut

when mold open

② gate marks are small and not

obvious

③ gating are possible on both

movable and fixed side

④ pressure keeping is difficult

to apply due to fast gate sealing

runner

Parting surface

[Tab gate]

b= gate width

l= gate length

h= gate depth

==Characteristics==

① gate mark is same as that of

side gate

②after staying in the tab area

for a moment, melted resins

will enter into cavities. This

is the reason why flow marks

tend to generate at the area.

Tab

runner cavity

Parting surface core

[Disc gate]

l= gate land length

h= gate depth

==Characteristics==

①gate mark appears toroidally

at the inner surface of

molded items

② it is necessary to include

cutting out process of gate

③ cylindrical filling becomes

homogeneity parting surface

sprue

Disc gate

cavity

core

[Film gate]

sprue

runner

parting surface

cavity

core

b= gate length

l= gate land length

h= gate depth

==Characteristics==

① gate mark will remain on the

side surface of the product

② it is necessary to include

cutting process of film

shaped gate

③ it is suited to filling of

thin plate shaped products

b= gate width

h= gate depth

l= gate length

==Characteristics==

① gate mark will remain on the

side surface of products

② it is necessary to include

gate cutting process

③ machine fabrication of

cavities at gate areas are

easy

④ filling of resins is

relatively easy

[Side gate]

core

cavity

Parting surface

Runner

side gate

b= gate width

h= gate depth

l= gate length l1= inflow area l2= gate land length l3= runner overlapping length

[Under gate]

==Characteristics==

①gate mark will remain at bottom

surface of products but not on

side surface

②it is necessary to include gate

cutting process

③gates are done by scrive

process on the core side

④it is relatively easy to fill

resins

under gate

runner

parting surface

cavity

core

[Direct gate]

parting surface

sprue

cavity

core

∅D= gate diameter

θ= sprue removal pitch

==Characteristics==

① large gate mark will remain

at the bottom surface of

product

② it is necessary to include

gate cutting process

③ it is relatively easy to

fill resins

[fan gate]

runner

parting surface

cavity

core

α= opening angle

l = gate land lengthh = gate depth

==Characteristics==

① gate mark will remain

on the side surface of

products

② it is necessary to

include gate cutting

process, but cutting is

difficult

③ it is suited for thin

plate shaped items

[Pinpoint gate]

runner lock part

parting surface

runner lock pin

runner plate

cavity

core

∅d= gate diameter

l= gate land length α= opening angle

SR= runner tip radius

θ= runner removing taper

h1= gate relief depth

h2= depth of the basin

SR’= radius of basin

∅dr1= runner lock pin diameter

∅dr2= runner lock area diameter

h3= runner lock pin undercut length

h4= runner lock area depth

==Characteristics==

① one can locate gate at random area at flat surface of product

② gate mark appears small, and not obvious

③ tend to use multiple point gate

④ scrive process of gate area is relatively difficult

⑤ countermeasures for gate cutting remains must be establish

Guidelines of steel

materials and mold

life sample

appliances /

general items automobile / OA

electronic parts /

mass production /

optical parts

Hardness(HRC)

marageing steel

prehaiden steel

mold life(expected shots) (×10,000 shots)

- non heat treated type

of steel

- prehaiden steel

- age hardening type of

steel

- quenching and tempered

type of steel

1-2 Steel materials and mold life guidelines

Examples of selecting steel materials depends on types of plastic injection materials

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

materials

Types of Resins

Forming sample

expected specifications to resins

expected specification to steel materials

Recom-mended steel type

PP ABS

Bumpers OA enclosures

Impact resistance

Creping control

S50C SCM440

PS PMMA ABS

Lighting fixture Miscellaneous goods Cosmetic containers

design

Creping control Mirror finish

SKD61 prehaiden

steel

POM PA

Gears Shafts

Abrasion resistant

Abrasion resistant

SKD61 prehaiden

steel

PC PMMA

Lens Photo conductor

Transparency Optical transparency

Mirror finish easiness

SUS420J2 precipitation hardening types of steel

PC PMMA

CD Discs DVD Discs

Optical Transparency Light retractivity

Mirror finish easiness Corrosion resistant

SUS420J2

PVC

Gutter Pipes

Heat resistant

Corrosion resistant

SUS

Fire resistance ABS

TV Cabinet Appliances part

Heat resistant

Corrosion resistant

SUS420J2prehaiden

steel

PBT-GF PA-GF

Camera Enclosure Electrical Equipment

resistance

Abrasion resistant

SKD11 prehaiden

steel

Magnetic powder containing PA

Printer rollers Sensor parts

Mold ability Magnetic characteristic

Non-magnetic Abrasion resistant

Nonmag-netic steel

Thermo-plastic types of resins

Mg forming

Computer enclosure Cellular phone enclosures

Heat resistance Light weight

Heat resistant Abrasion resistant

Nonmag-netic steel

Phenol resin Melamine resin

Dishes Ashtray

Heat resistant

Heat resistant Abrasion resistant

prehaiden

steel SKD11

Phenol resin unsaturated polyester

Switches Connectors

Heat resistant Fire resistant

abrasion resistant corrosion resistant

SUS420J2 SKD11

Thermo setting type of resins

Epoxy resin IC seal Transistor

Electric insulation

Abrasion resistant Corrosion resistance

SUS420J2 SKD11

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 ASTM

BS 970 Part 1.3

DIN 17210, 17220

NFA35-551 NF EN10083-1,2

ΓOST 14959, 4543

ISO 683/1,10,11

S10C 1010 040A10 040A10 040M10

CK10 C10

XC10 C10

S12C 1012 040A12 XC12 S15C 1015 055M15 CK15

C15 C15E4

C15M2 S17C 1017 XC18 S20C 1020 070M20 CK22

C22 1C22 2C22 3C22

S22C 1023 S25C 1025 CK25

C25 1C25 2C25 3C25

C25 C25E4 C25M2

S28C 1029 S30C 1030 080A30

080M30 CK30 C30

S33C S35C 1035 CK35

C35 1C35 2C35 3C35

S38C 1038 S40C 1039

1040 080M40 CK40

C40 1C40 2C40 3C40

S43C 1042 1043

080A42

S45C 1045 1046

CK45 C45

1C45 2C45 3C45

S48C 080A47 S50C 1049 080M50 CK50

C50 1C50 2C50 3C50

S53C 1050 1053

S55C 1055 070M55 CK55 C55

1C55 2C55 3C55

S58C 1059 1060

CK60 C60

1C60 2C60 3C60

S09CK 045A10 045M10

CK10 XC10

Carbon steel for mechanical structures

S15CK S20CK

CK15 CK22

XC12 XC18

SK1 Y13 TC140 SK2 W1-11 1/2 Y12 TC120 SK3 W1-10 Y11 TC 105 SK4 W1-9 Y10 TC 90 SK5 W1-8 Y9 TC90

TC80 SK6 Y8 TC80

TC70

Carbon tool steels

SK7 Y7

JIS AISI SAE

AISI ASTM

BS DIN NF OST ISO

SKH2 SKH3 SKH4 SKH10 SKH51 SKH52 SKH53 SKH54 SKH55 SKH56 SKH57 SKH58

High speed tool steel

SKH59

SKS11 F2 SKS 2 105WCr6 105WC13 XB4 105WCR1 SKS21 SKS 5 SKS51 SKS7 SKS8 SKS4 SKS41 SKS43 SKS44 SKS3 SKS31 SKS93 SKS94 SKS95 SKD1 SKD11 SKD12 SKD4 SKD5 SKD6 SKD61 SKD62 SKD7 SKD8 SKT3

Alloy tool steel

SKD4

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

Гost:

ISO: International Organization for Standardization

(Reference literature) JIS Handbooks

1-5 Heat treatment methods of steel materials

Heat treatment methods of mail steel materials

Types of steel Quenching method

Standard quenching

Oil quenching

marquenching

air cooling

Heat tempering method

Air cooling

Heat tempering hardness (reference)

Tempering ℃ none

Standard quenching

preheat preheat

air cooling

marquenching

preheat preheat

cool down

air cooling

Standard tempering

Air cooling

High temperature tempering

Air cooling

Tempering

℃

none

Primary preheat

Secondarypreheat

Main temperature

Cool down

Air cooling

Air cooling

Tempering℃

none

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 oftransverse elasticity

maximum elasticity

YP (yield point)

tension com press

shear

ing

Specific gravity

coefficient of linear expansion

thermal conductivity

Specific

ation

Material

quality E

Kgf/cm2

G

Kgf/cm2

S

mild steel

210 x 104 81 x 104 (1800) (1900) 3400

~

4500

1900 2900

~

3800

7.85

11.7

39

S55C 210 x 104 81 x 104 (2500) (2800) 6600 (2800

)

(4000

)

7.86 11.7 (39)

SKD11 210 x 104 81 x 104 7000 ~

10000

8500

~

12000

7.85 11.7

prehaiden steel (SCM440)

210 x 104 10800 7.80 11.5 (25)

nickel steel (2~3% Ni)

209x104 84x104

Cast steel

215x104 83x104 (2000) (2100) 3500- 7000

(2800) (4000) 7.85 (11.7)

Ni-Cr-Mo steel

210x104 84x104 8000 – 10000

9000- 12000

7.75 17-18

Cast steel

75-105x104

27-40x104

1200- 2400

7000 - 8500

1300 – 2600

7.30

Brass (rolling)

63x104 24x104 1500 1500 8.50 18-23

Copper (Casting)

105x104 420 - 620

1250- 1800

8.88– 8.95

16.5

Aluminum (casting)

68x104 26x104 930 2.56 (23) 197

extra super duralumin (Alcuin300)

73x104 27.5x104 5100 2.80 23.4 (202)

Zinc alloy third type (ZAS)

13x104 2600 6.9 27.4 (97)

Titanium

68x104 8500-

12500

8800-

15000

4.51 8.2

( ) indicates reference value

Computation of deflection on moveable side

Cavity

Projected area

Cavity

mold plate

Backing plate

spacer block

Attachment plate on movable side

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 cavity b: 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/㎠) δmax ： max deflection of backing plate (mm)

<Computation sample>

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

Based on Table1 A : E of S55C is E=210 ×10�kgf/㎠ Therefore h=3√⎯5x500x30x1144

32x210x104x250x0.01 = 42.2 (mm) Answer : at least 42.2mm is needed In case one allows up to σmax=0.025 h=3√ 5x500x30x1144

32x210x104x250x0.025 =31.1 (mm) In this case, at least 31.1mm is needed [Simplified computation when we assume l= L]

δmax = 5.p.b.L4

32.E.B.h3 (mm)

h =3√5.p.b.l4

32.E.B.δmax (mm)

Table 1. List of value “E”

material E (kgf/ cm2)

mild steel 210x104

prehaiden steel (SCM440system)

230x104

(75-105)x104

extra super duralumin

73x104

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

mold condition

P (kgf/ cm2)

lower setting of injection pressure

200 - 400

higher setting of injection pressure

400 – 600

Table 3. rule of thumb for maximum permissible deflection considering

parting burrs

molding materials

maximum permissible deflection σmax (mm)

good flow ability (such as PA,PP etc.)

0.025

those which with general flow ability

0.03 – 0.05

products which are not affected by burr generation

0.1 – 0.2

[Variation of maximum deflection by insertion of supporting blocks]

Position of supporting block

σ1 generates when positionis X= 0.421 × L/2

One portion at the center for supporting block

Maximum deflection σ

※ δmax = maximum deflection when there is no supporting 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 willnot applied once there is (are) insertion of supporting pins

Supporting block

Diagram 1 Case that above computation applies

Supporting pin

Diagram 2 Case that abovecomputation will NOT apply

Altered condition

Once one creates 1/2 of inner support block space

once backing plate thickness h become h1

Maximum deflection σ

Computing necessary thickness of side walls of rectangular shaped cavities (if bottom surface is integrated)

core

cavity

l/a C

1.0 0.044

1.1 0.053

1.2 0.062

1.3 0.070

1.4 0.078

1.5 0.084

1.6 0.090

1.7 0.096

1.8 0.102

1.9 0.106

2.0 0.111

3.0 0.134

4.0 0.140

5.0 0.142

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)

E: modulus of longitudinal elasticity(Young's modulus) (kgf/㎠)

c: constant derived from l/a ratio σmax: maximum deflection (mm)

<Computation sample>

Question: How much should be a minimum cavity side wall thickness “h”for the following bottom surface integral hard steel mold?

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/㎠) σmax: maximum deflection (mm) h = 3√12.p.l4.a 384.E.b.σmax (note) this formula does NOT apply if it is bottom attached type of cavity

380 From Table 1. E= 220 × 10⁴kgf/㎠

381 yh, l/a value is considered as modulus of longitudinal elasticity ofhard steel

382 l/a= 40/10 = 4

from the table it becomes

384 therefore

385 Answer : at least 2.95 is needed

386 at least approx.5mm is needed including over design thoughts

Computing necessary thickness of side walls of rectangular shaped cavities (if the bottom surface is separated from the others)

Core

Cavity

Bottom bushing

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 super duralumin

73x104

Table 2 Guidance for cavity internal pressure (reference value)

forming condition lower injection pressure setting

200 – 400

higher injection pressure setting

400 - 600

<Computation sample>

Question: How much minimum thickness “h”do you have to provide on the side wall of hard steel cavity which the bottom surfaces are divided as drawing?

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

E = 220 × 10⁴kgf/㎠ based on Table 1. Therefore at least 7.83mm is needed hopefully 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) σℷ：tangential allowable stress of cavity

(kgf/㎠)

Table 1. value ofσℷ

material quality

mild steel 900 ‒ 1500

hard steel 1200 ‒ 1800

cast steel 500 ‒ 750

<Computation sample>Question: How much external radius of the following cylindrical cavity shape made of SKD11 is needed?

Answer : SKD11 is hard steel materials, and therefore value ofσ ℷ from

Table1.becomesσ₁= 1200 ～ 1800 kgf/㎠. Just to give allowance on the

computation, we use smaller value to setσℷ= 1200 kgf/㎠.

430 therefore

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

10mm.

1-11 Mold temperature control method

Some of the engineering plastic and super engineering plastic generate cavity 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 passes channels in mold and cavities, passes joint hose and circulate. Once temperature will raise up to setting temperature, it is relatively easy to sustain 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 with temperature 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 heat distribution 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 without water, and reduce heater life. MISUMI M-HTM3021 (Temperature controller for cartridge heater) can control temperature by PID control method, therefore quite stable temperature control than “ON-OFF type controller” is possible. It is recommended to provide heat intercepting board in between platen and mold attachment plate of injection machine. It is further recommended to provide heat intercepting board surrounding mold plate.

[Table] Example of molding materials with high cavity surface temperature Name of plastic cavity surface temperature(�) PPS Glass fiber 30% (polyphenylene sulfide) 130～150 LCP Glass 40% (Liquid crystal polymer) 70～110 PET (polyethylene terephthalate) 130～150 PA 46 (Polyamide/46 Nylon) 80～120 PC (Polycarbonate) 80～120 heat resistant PLA (heat resistant polylactic acid) 110～120 PEEK (polyether ether ketone) 120～160 PI (polyimide) 170～200

In injection molding of PPS resins and liquid crystal polymer, one need to maintain the cavity surface temperature above 100�. Therefore it is necessary 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,

(ア) cavity surface temperature gap is big (イ) 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 is

P: Proportional I: Integral D: 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 while keeping 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

Following are selection standard of Heat intercepting board. 1. Heat resistant temperature Following are recommended working temperature as guidance ● recommended working temperature below 100� ● recommended working temperature below 180� ● recommended working temperature below 220� ● recommended working temperature below 400� ● recommended working temperature below 500� 2. Material Materials 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

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 side 2) carve on fixed side 3) 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 pressure loss condition. Unnecessary large sized runner will increase scraps, worsen material costs, prolonged molding cycle, and increase volume of disposing waste. Index to indicate runner efficiency is “inscribed circle diameter area” at cross sectional shape. The bigger the space of inscribed circle, wider the area 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 this becomes 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 or semicircle cross section are utilize. It is better to provide angles on the side of runner so that mold release becomes better. On the other hand inner surface of runner must be polished by rubber wet stone or rapping to avoid pressure loss.

parting surface fixed side

movable side angle

angle inscribed circle

thin

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 opens and close. It is necessary for one to know the basics such as shapes and dimension to design tunnel gate. But for this time, we are introducing to you the basic variation 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-runner combination on fixed side and moving side.

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 hub Fixed side runner

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 cutting condition 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 pushes runner. 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 make structure that the lock pins will pull runner toward movable side, because there 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 to push 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 back surface of top panel. In actual practice, we must decide what type of gate and runner to use on mold 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.

Runner Curved tunnel gate

Cavity

Ejector pin

Gate holding hub

Ejector pin

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 is provided 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 hold gate 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 the correction 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 condition 1. 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 keeping 5. 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.

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 off

part of product 2) In comparison to high filling pressure and keeping pressure, filling cant

be done smoothly Above are common problems and headaches of mold designer upon using “Pinpoint gate”. Following are technical trouble shooting. [Diagram1.] Shows general pinpoint gate structure. Gate design without any consideration usually looks like this. On the other hand, [Diagram2.] shows contrive design to minimize above problems.

2. Gate

Opening angle

1. gate land

Length

3. thickness relief

4. Dimple

(basin)

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 1～2 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 section gate area and product shall be the cutting point. Mold release becomes easy too. Value A is usually 15°～30°. Bigger the value, more assurance on cutting, but wearing out at the tip portion tends to become faster.

Point 3 Slot Once “Slots” are provided, they will encroach 1 step into the surface of molded products. Because of this, protrusion will not exceed the surface level of products even if it remains at cutting area. One must first acquire “Approval” of product designer in prior to set slots on the 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 resin will flow stable when slots are created. One must also first acquire “Approval” of product designer in prior to set dimples on the drawing.

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 +

Cavity

Runner plate

Fixed side attachment plate

Gate

Runner

Narrow

Runner

Runner lock pin

Place runner locks one step down

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 and runner plate create a space, they will compulsively separate runner and gate. 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 higher pressure loss, channel within runner from the head portion of runner lock pin 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 step lower within runner plate. In this manner, one is necessary to create coniform curving on top of runner plate. For this process, mold cost may become higher, but be able to improve pressure losses during molding.

Encroach into inner side also for the purpose for relief 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 runner center will be reduced, therefore more efficient cooling is done, then contribute to reduction of cycle. But one must take care of coniform shape portion balance, because poor 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 of runner lock in prior to design mold.

1-16 Polishing finish of plastic mold parts

Cavity surface of plastic injection mold undergo mainly hand polish or machine polishing after milling, EDM, wire cut process to smoothen the surface. Transcription surface for products be dull, and surface quality may become poor if polishing condition is not good. 凹凸 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. Use grinding fluid while making sure that clogging and galling will not take place. Polishing is not only done one direction but relative position and circumferential 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 oil into maple, pine, willow, balsa like trees and polish.

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 to damage lips and tongues by burrs. Any pores or cracks on plastic will allow bacteria to infiltrate into foods and 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 can not be exposed to oxygen). For food containers, sales of the foods will also depends on product design(beautiful finish), which means 3 dimensional curved surface shape 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 steel materials. 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 clean rooms. Its worth trying using valve gate and hot runners. If mass production is expected, one can also use scrap press effects and high cycling.

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 thru mold making. There are following major plastic medical utensils. 1. syringe (syringe body) : PP, PE 2. piston of syringe : PP 3. pipet chips : PP 4. catheter : PVC, PC 5. blood collecting test tubes : PC 6. dish for culturing : PS For plastic medical utensils materials, only those which are allowed by drug legislation and quality standard prescribed by Ministry Of Labor and Health can be utilize. Those materials must withstand exposures of UV lights and gamma rays used for sterilization, at the same time passed 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 is the reason why many cases, medical utensil molds are made of stainless, ion plating film, hard chrome plating so as to prevent corrosion of core, cavity. Valve gate molds are used in mass production items. Needless to say that burrs for products are defects, therefore use precision guide to locate movable side and fixed side, and also try to apply contraption preventing the abnormal worn out of core pins of centering location structure. There must be delicate temperature setting for cavities and cores to produce stable quality products. For this point, one must pay attention to 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.

1-19 Blow molding mold overview

Blow molding method is usually applied to pet bottle containers for juices (PET : polyethylene terephthalate resin) which blow methods are used. It is familiar in all over the world because it is used as shampoo container, soy sauce and other seasoning container, detergent container etc. Polyethylene terephthalate, polypropylene, PVC, nylon, polycarbonate may be used for blow molding method. Exclusive blow machine is used for blow molding. In the mold, there is only cavity on female mold, but no core on male mold. Instead, there is a nozzle prepared to blow air. Balloon like performing shape part called “Parison” blows, stick to cavity and transcribe shape. Generally speaking, soft metal materials are used for cavities in blow molding. These are aluminum alloy, bronze, and special steels. Usually beautiful brightness surface is required to product, therefore polishing 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 control are 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.

2-1 pre-drying condition of plastic molding materials Usually, plastic molding materials comes in pellet form in the paper bag upon 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 that silver streak may appear on the surface of product, or short shots may occur 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 even placed for long period, if drying temperature is below the proper setting. Quick consumption of materials after pre-drying is recommended. If there will be any left over of materials in a daily production, you must undergo pre-drying again before usage.

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 of moisture in the air. If there will be too much moisture absorption, hydrolysis may take place (some resins cause chemical decomposition by water) in the cylinder of injection machine during molten and kneading 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 drying machines to remove water content. Variation of flow of materials, degrading physical properties, defective molding may happen if we do not give out predrying properly.

2 – 2 Tables showing material properties of plastic molding materials

Main plastic material physical properties list

Thermoplastic type of Plastic

Resin name ABS resin

Grade High steel

ability Heat resistance

Filling materials Glass fiber 20 – 40%

JIS testing

method

A.S.T.M. Testing method Abbreviation ABS

Drying temperature 70~80 70~80 70~80

Drying time 2 2 2

Injection mold cylinder temperature 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 mold

temperature 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

Mold ability

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 1120~1900 Mecha-

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 85~107

Thermal Charac-teristic

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

Thermoplastic type of plastic

AS Resin Etylene-vinyl acetate Polyamide (Nylon)

General Nylon 6 Nylon 66 Nylon 11.12

Glass fiber 20 – 30% -

Glass fiber 30% -

Glass fiber 30%

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

Non

destructive 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

Thermoplastic type of Plastic Methacrylate resin (acryl) Polyacetal

General General General High impact

Thermos ability

- - Glass fiber 20% -

Glass Fiber 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

Thermoplastic type of Plastic

Polycarbonate Polyethylene polybutylene

terephthalate

General Low

density Moderate density

High density

Glass fiber less than

10% Glass Fiber 10 – 40%

Glass fiber 20 – 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

Thermoplastic type of plastic

Polystyrene Polyvinyl chloride Fluororesin Polyphenylene chloride Crystal liquid polymer

Flexible rigid Glass fiber

20 -30% - - Glass fiber

40 % Glass

fiber 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 <2.7 5~8 13~21 8.7

M70~95 A50~100 D68~85 D60~80 R123 R123 R60~63 R79

82~93 54.2~79.2 204

90~104 59.8~76.5

97~110 57.0~82 69.8 135 250~265 332~335 319

2-3 Countermeasure on defective molding

“Bubble” “Void” are phenomenon where air bubbles are generated within molded products. These bubbles or voids will be considered rejected on a product such as lens, prism because appearance and optical characteristic be disturb by such defect. It will also reduce strength and become cause of destruction of machine once those defective items are used as machine parts. 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 as “Void”. In the void, insufficient pressure keeping was applied to thick wall area, and this caused abnormal shrinkage just like this happened in the process 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

2. Countermeasures related to injection molding condition

1. too fast screw rotational speed 2. 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 small 3. too small sprue, runner 4. too small gate

2. Countermeasure related to injection mold condition

1. Too high cavity surface temperature 2. Too low pressure keeping 3. lack of pressure keeping time

3. Countermeasure on product design

1. insufficient predrying of molding materials 2. too thick molded product wall thickness

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 surface appearance. There are following methods to control sink mark. 1. Countermeasures related to mold

1. Set the cavity surface temperature slight lower 2. Make gate size bigger 3. Make runner size larger 4. Use larger sprue 5. Review cooling channels of mold to improve cooling efficiency 6. Improve the structure where difficult cooling area to become easier

to cool. (Ex. Baffle plate structure, cooling pipe structure, heat pipe, non-ferrous bushing)

7. Increase the number of gate 8. Relocate gate position to thick wall area

2. Countermeasures related to injection mold condition

1. Set pressure keeping time longer 2. Set pressure keeping to higher setting 3. Set the injection speed faster 4. Set nozzle temperature lower 5. increase indiscrete value 6. Increase cushion volume 7. Change the injection mold machine 8. 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

2-5 Countermeasure for defective molding (flow mark)

“Flow mark” is a phenomenon where melted resin flowing marks remains on the surface of products. This may become a cause of reject depends upon 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 metal surface in the mold will encounter different degree of cooling at the tip of resins. Following methods are considered to improve the flow mark.

1. Countermeasures related to molds 1. set the cavity surface temperature lower 2. expand the size of the gate 3. enlarge the size of the runner 4. secure enough cold slag well

2. Countermeasures related to injection molding condition 1. set the injection pressure higher 2. set the injection speed faster 3. secure enough measurement to increase the cushion volume 4. set the pressure keeping time longer 5. set the resin temperature higher 6. enlarge the nozzle tip diameter larger

3. Countermeasures related to molded article design 1. set the variation of wall thickness of molded articles smaller

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 while compressed will generate heat, and this heat burns the plastics when molten plastics are filled into cavity. Burn can be appearance defect, causing missing parts, and decreasing material properties. Following are considered countermeasures on burns.

1. Countermeasures related to mold 1. provide the air vent 2. prepare deeper air vent and secure enough vent passage 3. dismount mold and wash give out maintenance to air vent 4. use insertion mold structure or bushing structure so that air will escape

from parting surfaces 5. Use vacuum aspirator device 6. change the gate position

2. Countermeasures related to injection molding condition 1. set the injection speed slower 2. set the cylinder temperature lower 3. make smaller measurement 4. avoid staying of resins in the cylinder

3. Countermeasures related to molded article design 1. try to apply design that avoids thinner wall areas of molded articles 2. change the wall thickness of molded articles, and flow of plastics 3. alter the design that allows air to stay

2-7 Countermeasures on defective molding (Silver streaks)

Silver streak (silver film) is a phenomenon where shinny stripe marks are generated on the surface of molded articles. This may become potential rejects 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 molding materials come out on the surface of products. Following are potential countermeasures on silverstreaks.

1. Countermeasures related to mold

1. improve the functions of air vent 2. enlarge the gate size 3. enlarge the cold slag well

2. Countermeasures related to injection molding condition

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

2. set the injection speed slower to slower filling 3. set the cylinder temperature lower 4. reduce the screw rotation speed 5. avoid staying in the cylinder

3. Countermeasures related to molded article wall thickness

1. prepare as much as possible the uniform wall thickness

2-8 Countermeasures on defective molding (defective brightness)

Ideal surface of molded articles must be the transcribed surface appearance of cavities, but there are times that surface of molded articles exhibit obscured 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.

1. Countermeasures related to mold 1. there might be NO air vent or lack of air vent 2. small gate 3. small and narrow sprue and runner 4. cavity plating is NOT good condition 5. cavity surface polishing is NOT good condition 6. deposits are attached to the surface of cavity

2. Countermeasures related to injection mold condition 1. lack of measurement 2. too short cushion surface 3. too low pressure keeping 4. too short pressure keeping time 5. low cavity surface temperature 6. insufficient predrying of molding materials

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 molten resins flow. Second cause takes place in the process of flowing. Because air traps are generated depends on the flowing condition. To take countermeasures on short shots, one must first find out the cause of problems from the above cause.

■ Short shots caused by flow tip solidification 1. Countermeasures related to mold

1. Expand further the gate size 2. Expand further the runner size 3. use the larger sized sprue 4. too small cold slag well 5. provide heat insulating plate at bottom surface of mold plate 6. increase the number of gate 7. alter the location of gate

2. Countermeasures related to injection mold condition

1. set the resin temperature higher 2. set the cavity surface temperature higher 3. increase the filling pressure 4. set the pressure keeping higher 5. set the pressure keeping time longer 6. increase the measurement value 7. increase the number of cushon 8. change the injection machines 9. exchange the backflow prevention rings of injection unit 10.exchange the injection nozzle tip diameter of injection machine larger

3. Countermeasures related to molded article design 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. Countermeasures related to mold

1. provide an efficient air vent at air trap generating areas 2. change the gate position 3. change the runner balance 4. 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 is

poor flow

2. Countermeasures related to injection mold condition

1. change the injection speed, to change the flowing patterns 2. relayout the position of screw speed pressure exchange position 3. set the injection speed slower 4. 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 articles 2. increase the wall thickness of molded articles

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 much noise, 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

2-11 Molding material and its usage (polyacetal)

POM resins (Polyacetal, polyoxymethylene) are superb in mechanical specification like breaking strength, and worn out resistance property so they 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 functions when its applied as gear, bearing like parts where there are always facing frictions. Crystallinity is high, therefore is shows good result in strength and thermal resistance. In injection molding, one must take care not this materials to stay long period 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

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 resins and used for industrial purposes. It is amorphous and exhibit good light transmittance therefore applied as lens 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 one must pay great attention, if ever grease group of chemicals and solvents are applied on the material. In injection molding, this material exhibits poor liquidity. Therefore filling pressure 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

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

Thermo plastic elastomer (TPE) is a synthetic resin which has rubber like properties. Automobile tire is one good example of rubber, but those rubbers are solidify thru chemical reaction and therefore generally speaking it is not possible to fabricate by injection process. On the other hand, TPE can fabricate thru injection molding. It is thermoplastic and therefore one can fabricate without burrs under relatively fast 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 consumed in the world. TPE shows rubber like flexible hypertrophic properties because it contains soft 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, sports items

(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

<reference/citation list>

1) �c Michio Komatsu : “Molds for beginners. Introduction to plastic injection mold, molding technology.” Mold technology April 2004, special issues, [Daily industrial journals]2004 2) �c Michio Komatsu : “Plastic injection molding design manual, pin gate structure” mold technology. March 1998 special issue, Daily industrial journals 1998 3) �c Michio Komatsu : “Plastic injection design manual” Daily industrial journals (1996) 4) “Plastic mold standard parts 2005.6 ～2007.4”MISUMI Inc. (2005) 5) Technology course, MISUMI online, MISUMI Inc, www.mol.ne.jp