MOULDING DEFECTS 1.PDF

7/27/2019 MOULDING DEFECTS 1.PDF

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1

MOULDING DEFECTSAND

REMEDIES



2

~ HOW MANY KINDS OF DEFECTS ARE THERE?



3

~ HOW MANY KINDS OF DEFECTS ARE

THERE?

31



4

DEFECTS

1. Sink Marks

2. Streaks

3. Blistering

4. Weld Lines

5. Gloss difference



5

6. Jetting

7. Record grooves effect

8. Dull spots near gate area

9. Incompletely filled part ( Shortshots)

10. Diesel effect

DEFECTS



6

11.Over sprayed parts (Flashes)

12.Stress whitening/Cracking

13.Ejector marks

14.Deformation during demolding

15. Ejection Grooves

DEFECTS



7

DEFECTS



8

21. Defects on electroplated parts

22. Broken or ragged film hinge

23. Warpage24. Fish eye

DEFECTS



9

25. Hesitation

26.Over packing

27. Unbalanced flow

DEFECTS



10

28. Nozzle drool

29. Nozzle freeze – off

30 Nozzle spitting31. Screw slip



11

WHAT ARE THE MAIN FACTORS

CAUSING DEFECTS?

4M?



12

SOME MAIN FACTORS CAUSING DEFECTS

The moulding Machine

Mould

Operating conditions i.e..Temperature, pressure, injectionspeed & time

Material. Design of product

Management



13



14

!!"

!"#$%&#

SINKMARKS



15

!"#$%&#

SINK

MARKS



16

!"#$%&#

SINK MARKS



17

Sink marks on a cylindrical core with poor

temperature control

Sinkmarks

!"#$%&#



18

Sink marks appear as depressions on the surfaceof a molded part.

These depressions are typically very small;

however they are often quite visible, because theyreflect light in different directions to the part.

!"#$%&#



19

CAUSE OF SINK MARKS

Sink marks occur during the cooling process ifcertain areas of the part are not cooled

sufficiently causing them to contract

If these contractions are not compensated andthe outside wall is not stable enough due toinsufficient cooling depressions occur



20

!!!"#

$ %&%&$ '($ )&"

$ '(

*+,

-+'!!"

.+/

%'%(%)*&*!"#$%&#



21

Disadvantageous Gating

Moulded part with sink marks

(Gating at the thin wall)

Solidified Peripheral

!"#$%&#



22

0+ "&

*+ "

-+ !&""1("

*!+(,*(')!*"*&!"#$%&#



23

.+ '2+!(3!"(

4+ 3

*!+(,*(')!*"*&!"#$%&#



24

2. STREAKS

Streaks are the prominent stretchy markson the surface of the moldings.

CHARRED STREAKS

MOISTURE STREAKS

AIR STREAKS

COLORED STREAKS

GLASS FIBER STREAKS



25

Charred streaks due to excessive residence time in

the plasticising cylinder

2.CHARRED STREAKS



26

Streaks due to excessive moisture content of thegranules

2.MOISTURE STREAKS:



27

&

2.AIR STREAKS:



28

&5!!

2.COLOUR STREAKS:



29

&&

2.COLOUR STREAKS:



30

/!&631&(7

-(%!+&,)&,%#



31

"""3"

"

""

!!53"!"

%'%(%)*&*&)&,%#

%'%( %)*& *& )&,%#



32

""!

!"(

,1"

%'%(%)*&*&)&,%#

*!+(, *(')!*" *& )&,%#



33

0+ !&1""

3%(%3

*+ !"3+

*!+(,*(')!*"*&)&,%#

*!+(, *(')!*" *& )&,%#



34

-+ !&"'1%""

.+ &!!3

4+ """

*!+(,*(')!*"*&)&,%#

*!+(, *(')!*" *& )&,%#



35

6. Reduce residence time in material hopper

7. Reduce injection rate

8. Round sharp edges of transitions.

9. Reduce depth of engraving

10. Provide for venting

*!+(,*(')!*"*&)&,%#

*!+(, *(')!*" *& )&,%#



36

11. Use smaller colour pigments

12. Check solubility of the used die

13. Use shorter glass fiber

*!+(,*(')!*"*&)&,%#

3.BLISTERS



37

3.BLISTERS

0+ &&&!(!(

AIR BUBBLES

Hollows created on or in the molded part

3.BLISTERS



38

Air traps occur when converging flow frontssurround and trap a bubble of air.

The trapped air can cause

Incomplete filling and packing, Surface blemish in the final part. Air trapped in pockets may compress, heat up

and cause burn marks.

3.BLISTERS

3.BLISTERS



39

3.BLISTERS

(hollows created on or in the molded part)

*+8(+

voids

3.BLISTERS / BUBBLES



403.Bubbles

Bubbles

3.BLISTERS



41

4.Blisters and delamination

DELAMINATION

%'%( %)*& *& +(!),&



42

913"!

!!3

8"&

"

%'%(%)*&*&+(!),&

*!+(,*(')!*"*&+(!),&



43

0+

*+ (

-+ 3

.+ &

* * ' * *

*!+(,*(')!*"*&+(!),&



44

4+

:+ "

;+ ,11

<+ "

4 WELD LINE



45

4.WELD LINE

(Witness marks of two or more melt flow fronts at their joining

zone)

=((!(!&3"31&+

(!

3(!

WELD LINE

%'%(%)*&*.,((!",



46

=( '(

91& 1" =( '13( !"(&"

,!(

*!+(,*(')!*"*&.,((!",



47

0+ '

*+ '

-+ '

.+ 2

*!+(,*(')!*"*&.,((!",



48

4+ 15

:+ 813(

;+ 1"61(1&

7

<+ 1!(

5.GLOSS/GLOSS DIFFERENCES



49

Very glossy impression due to reflection on the polished surface




50

Only slightly glossy impression due to reflection on a roughsurface

5 GLOSS/GLOSS DIFFERENCES



51


"!!"3!!(9"+

3!"!("6!7+

!!"""!!"3"

!""+




52




53

%'%(%)*&*&-(*!,&,",



54

!!"

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9!

,!

*!+(,*(')!*"*&-(*!,&,",



55

0+ !

*+ !"(!"!

-+

.+ 1">

6.JETTING



56

The prominent inhomogeneous snake like strandson the surface of molding

?""""%"1+

JETTINGJETTING

/,))!"-



57

!3'("'

"!(!

1 ! &

Mould filling process in frontal flow and with jetting

/,))!"-



58THREE EXAMPLE OF JETTING

6.JETTING



59

Jetting occurs when polymer melt is pushed at a highvelocity through restrictive areas, such as the nozzle,runner, or gate, into open, thicker areas, without formingcontact with the mold wall. Jetting leads to part weakness,surface blemishes, and a multiplicity of internal defects.

*!+(,*(')!*"*&/,))!"-



60

0+ '

*+ "%(

-+ "

.+ 1"(!13&&(

7.RECORD GROOVES EFFECT



61

83!"1!!

#

0+ !!2

*+ '

7.RECORD GROOVES EFFECT



62

RECORD GROOVE OR ORANGE PEEL

*!+(,*(')!*"*&&,*&-&**0,,,)



63

0+

*+ +

-+ 1

.+ '

4+ 9'

8.DULL SPOTS IN GATE AREA



64

"3&3

0+ "*+ "'+

'((*)!"-%),%&,%



65

!(+

"'"&3"!"'+

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'((*)!"-%),%&,%



66

!(+

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93!+

(3!

*!+(,*(')!*"*&'((*)!"-%),%&,%



67

0+ '

*+ "

-+ !!"13

.+ 1!"

9.INCOMPLETELY FILLED PART (SHORT SHOTS)



68

!1!3+

SHORT SHOT




69

INCOMP0LETELYFILLED




70

A short shot is the incomplete filling of a mold cavitywhich results in the production of an incomplete part.

The flow freezes off before all of the flow paths havefilled.

%'%(%)*&*&1*&)1*)



71

'1617

,1"

'!!

"

%'%(%)*&*&1*&)1*)



72

(%!

3!1&!(

&!!(

13

!!""

*!+(,*(')!*"*&1*&)1*)



73

0+ '%

*+

-+ +!1

.+ !

*!+(,*(')!*"*&1*&)1*)



74

4+131+

:+!511"913

;+""+

!3!3%3@!%"&&113(+!"(%"

1

10.DIESEL EFFECT / BURNED MARKS



75

!!!!(2

1&+

A"(!&3"

3&31&+

BURNED MARKS




76BURN MARKS

BURN MARKS




77

BURNS

BURNS




78

31"&%"""""&+

&%!%(&%(1!(!%!

!(+

0+ "B"

*!+(,*(')!*"*& !,,(,,)



79

" "

*+ '

-+ '

.+ B

4+ 1131"+

83&1(3(&&"&"

11.FLASHES



80

!"!%!1"1%('+

!((&+

>1,C

FLASHES

11.FLASHES



81

Flashing occurs when a thin layer of material is

11.FLASHES



82

forced out of the mold cavity at the parting line orejector pins location.

This excess material remains attached to themolded article, and normally has to be manuallyremoved.

11.FLASHES



83

FLASHES

%'%(%)*&*&(%1,



84

,&"(9%!!"%9"%""!

"!"(

"

!!13!

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85

0+

*+ 1"+831&"!&"

-+ "!3!!3&3D&"E"

*!+(,*(')!*"*&(%1,



86

.+ '&+

4+ 3&"("!("+

:+ 3&"!&"(1+

12.STRESS WHITENING



87

""&3"

&39!+

3&&3&

9&"!

!F3

(!1&+

12.STRESS WHITENING



88STRESS WHITENING

*!+(,*(')!*"*&)&,.1!),"!"-



89

0+ '

*+ 3

-+ 3

.+

*!+(,*(')!*"*&)&,.1!),"!"-



90

4+

:+ !3'

;+ !333B

<+ !3B

13.EJECTOR MARKS



91

'1"&"(3!

!!+

DEPRESSED EJECTORMARKS

%',*&,/,)*&$%&#



92

"""!

"!!(&(('

,"""!

"!"'"

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93

0+ &!!'

*+ !'

-+ "'"3

.+ "

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94

4+ "'3

:+ !

;+ "!!"%"

14.DEFORMATION DURING DEMOULDING



95

&(3""+

3&&+

DEFORMATION ON THE MOULDED PART DUE TO FORCED DE MOULDING

DEFORMATION

*!+(,*(')!*"*&,*&$%)!*"'&!"-,$*'(!"-



96

0+ "

*+ "

-+ "

.+ '

*!+(,*(')!*"*&,*&$%)!*"'&!"-,$*'(!"-



97

4+ )!3"!

:+ !"!"

;+)"

15.EJECTION GROOVES



98

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3

%',*&,/,)!*"-&**0,



99

3

=!+

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!9113+

!!+

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0+ "



100

0+ "

*+ (

-+ !

.+ )(!"

4+ !!

16.FLAKING OF SURFACE LAYER



101

("!3!"!!!!

&"&('3+

FLAKING

0+ ! + &

*!+(,*(')!*"*&(%#!"-*'&%,(%2,&



102

0+ !+&31&39"

&

*+ 3

-+

.+

4+ !!A"+"3"!

17.COLD SLUG



103 "!(!

"&!13!+

COLD SLUG NEAR THE GATE

17.COLD SLUG



104 "!(!

"&!13!+

WELD LINE BEHIND A COLD SLUG

17.COLD SLUG



105 "!(!

"&!13!+

FLOW FRONT TRANSFORT THE COLD SLUG IN TO THE MOULD

%',*&*(('-



106

3&

!

"&&

,&

%',*&*(('-



107

,&

0+ "

*+ "3

-+

.+ 1'&(

18.FILAMENTATION



108

!!"!"%&3!"+

3"!!!1+

"3(

!!!!+

Long filamentation of a cold runner gating system near the machinenozzle

18.FILAMENTATION



109

!!"!"%&3!"+

3"!!!1+

"3(

!!!!+

Long filament near a hot runner gate

0 , !!

*!+(,*(')!*"*&!(%$,")%)!*"



110

0+ ,1!!""3+

*+ 91"+

-+

!!+

.+ ""+

*!+(,*(')!*"*&!(%$,")%)!*"



111

" "

4+ 31&&!("+

:+ +

;+ "

19.DARK SPOTS



112

&&(&"31+

3&

1"!!"%(1"+

19.DARK SPOTS



113Severe black specks

19.DARK SPOTS



114

Poor screw flights design ,dead spots lead to black specks

#%"%

%',*&%&#*)

&



115

,&

0+ !!+

*+ &+

-+ +

.+ +

#%"%

%',*&%&#*)



116

,&

$ 15+

$ ,11+

$ ,""3+

$ 13+

20.PLATE OUT



117

,!!!+"(13!!1+

3,%,,%,A%,%,)%,(1!%&

&'

ROUGH SURFACE DUE TO PLATE OUT IN THE MOULD

20.PLATE OUT



118

PLATE OUT NEAR THE GATE

,!!!+"(13!!1+

3,%,,%,A%,%,)%,(1!%&&'

"91!&

%',*&(%),*')



119

&3!%&&+

3""+

"%91%%+

0+ )&&

*!+(,*(')!*"*&(%),*')



120

*+ "!&+

-+ )!3!1"+

.+ &3!&(1BB&+

4+ 9"+

*!+(,*(')!*"*&(%),*')



121

:+

;+ !!1"+

<+

21.DEFECTS ON ELECTROPLATED PARTS



122

!6%&%!!37+

!'1&+

!(

"+

PIMPLES AND BLISTERS ON A MOULDED PART

21.DEFECTS ON ELECTROPLATED PARTS



123

!6%&%!!37+

!'1&+

!(

"+

BLISTERING DUE TO DRAWN –IN AIR (COMPONENTWITH AND WITHOUT ELECTROLITIC LAYER)

*!+(,*(')!*",,)*",(,)&*(%),%&)



124

0+ '

*+ (("+

-+ +

.

*!+(,*(')!*",,)*",(,)&*(%),%&)



125

.+ 1(1+

4+ 1!"

:+ 1+

;+ ""+

22.BROKEN/ RAGGED FILM HINGE



126

"1"'+

!&!+

STRESS WHITENING ON A FILM HINGE

22.BROKEN/ RAGGED FILM HINGE

STREE

WHITENING



127

!!!"3&3

13+ !"3&33+

1"("+

STRESS WHITENING ON A FILM HINGE

!!!

0+ +

*!+(,*(')!*"*&+&*#,"3&%--,!($1!"-,



128

0+ +

*+ '+

-+ (+

.+ (!!"+

4+ )!(

:+ 1!""(3!"+

*!+(,*(')!*"*&+&*#,"3&%--,!($1!"-,



129

!!>"+

0+ (

*+ )!(!3

-+ ""

!&3!!(+

*!+(,*(')!*"*&+&*#,"3&%--,!($1!"-,



130

3

0+ 1(!!"+

*+ (+

-+ )!"13

.+ !(!!(!

23.WARPAGE



131

"1!!>+

"%,(&"&(%(%&(&3!("

MOULDED PART WITH WARPAGE ON THE EDGE

23.WARPAGE



132

"1!!>+

"%,(&"&(%(%&(&3!("

WARPAGE IN THE FLANGE AREA

WARPAGE

23.WARPAGE



133

Variation in mould temperature will cause

component to warp

23.WARPAGE



134

Warped component

23. WARPAGE

Distortion of the part caused by non-uniform shrinkage of

the plastic.



135

23.WARPAGE



136

Typical warpage in most radiator end tanks.

Article ejected too hot.

Variation in section thickness or contours of the

%'%(%)*&*&.%&%-,



137

a at o sect o t c ess o co tou s o t escrew.

Excessive area discharged or packed into the areaaround the gate.

Non-uniform mould temperature due to improperpositioning if the cooling channels in the mould.

Excessive feed.

'"+

CAUSAL FACTORS FOR WARPAGE



138

!!"+

,3""3+

)&"("+

"+

*!+(,*(')!*"*&.%&%-,

0+ '615%11"7+%



139

"711"7+%

11"7+

*+ "!>+

-+ !"+

.+ >B&!&1+

*!+(,*(')!*"*&.%&%-,



140

4+ '5+

:+ "+

;+ "&+

<+ 3""'+

Fish eyes are a surface defect that results fromun melted material being pushed with the meltstream into the cavity and appearing on the surface

24. FISH EYES



141

y pp gof a molded part.

Remedies for Fish eyes

1. Reduce regrind materialC i l li h d d

24. FISH EYES



142

Contact material suppliers to get the recommended

levels of regrind to use.

2. Optimize melt temperature

3. Modify screw designContact material suppliers to get the right screw

design information to avoid improper melt mix oroverheating that leads to material degradation.

Hesitation is when flow slows down or stops along

a particular flow path. If plastic filling a cavity has the option of filling either

a thin section or a thick section the plastic will tend

25. HESITATION



143

a thin section or a thick section, the plastic will tend

to fill the thick section first as this route offers lessresistance to flow.

Hesitation can occur in ribs and in thin section ofparts that have significant changes in wallthickness.

25. HESITATION



144

Remedies for Hesitation

1. Move the polymer injection location away fromh f h i i h h b lk f h

25. HESITATION



145

the area of hesitation so that the bulk of the

cavity fills before the melt reaches the thin area.

2. Move the polymer injection location to a place

that will cause greater pressure to be appliedwhere the hesitation occurred.

Remedies for Hesitation

3. It is useful to have thin ribs/bosses as the lastpoint to fill

25. HESITATION



146

point to fill

4. Increase the wall thickness where the hesitationoccurred, to reduce the resistance to flow.

5. Use a less viscous material

6. Inject more quickly

7. Increase the melt temp

Over packing is when extra material is compressedin one flow path while other flow paths are stillfilling.

26. OVERPACKING



147

26. OVERPACKING



148

Remedies for Over packing

1. Thicken or thin parts of the model to act as flowleaders or deflectors.

26. OVERPACKING



149

2. Move the injection location to a position that willdefine similar length flow paths.

3. Divide the cavity into imaginary sections, anduse one injection location for each section.

4. Remove unnecessary gates.

Unbalanced flow is plastic completely fillingsome flow paths in the mold before other flow

paths have filled.

27. UNBALANCED FLOW



150

27. UN BALANCED FLOW



151

Remedies for Unbalanced flow

1. By altering the thickness of regions within thepart, flow can be fastened or delayed incertain directions to help balance flows.

27. UN BALANCED FLOW



152

p

28. NOZZLE DROOL



153

28. NOZZLE DROOL



154

29. NOZZLE FREEZE - OFF



155

29. NOZZLE FREEZE - OFF



156

30 . NOZZLE SPITTING



157

31. SCREW SLIP



158

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MOULDING DEFECTS 1.PDF