Plastic_MATERIALS_introduction.ppt

Training Manual on
Operation
of
Injection Molding Machines
ISSUE DATE 15/10/2003
REV.NO. 00
NEXT REVIEW FEB 04

TEAM LEADER
MR. BIMAL BEDI
TEAM
1) P.MOHAN
2) ARUN KUMAR
3) MALAI BANERJI
4) KUND RAJAN SINGH
5) GULSAN GANDHI
6) VIJAY SRIVASTAV
7) ANOOP PAL
8) SACHIN FULSUNDER
9) C. S. TYAGI
10) AMIT NIGAM
11) ABHIJEET
12) PROMOD SATIJA
13) ASHUTOSH MISHRA

INDEX
TOPICS
1. INTRODUCTION TO PLASTICS
2. INTRODUCTION TO INJECTION MOULDING
3. BASIC PROCESSING
4. PROCESS OPTIMISATION
5. TROUBLE SHOOTONG
6. CASE STUDY

INTRODUCTION TO PLASTICS
Plastics is a general term that describes
materials composed
of very large molecules called polymers that are
synthetically made or modified from small
components
called monomers.
Plastics are solids that in some stage have.
been shaped by flow or molding in the liquid, molten or
softened form.
Plastics are those materials which are considered to be
plastics by common acceptance.

PP,PE
Nylons
Polyacetals
PET, PBT
PTFE
Crystalline
PS, ABS, PPO
Acrylic
Polycarbonate
PVC
PES
Amorphous
Thermoplastics
undergo only a physical
change during processing
PF, UF, MF
Epoxides
PUR
Polyesters
Thermosets
undergo a physical as well as
chemical change during processing
which is irreversible
PLASTICS
CLASSIFICATION OF PLASTICS

THERMOSETS Vs THERMOPLASTICS
Thermoplastics
•Processing is reversible change --> Recyclable
•Lower total part cost
•Greater design freedom due to higher ductility
•Stable Electrical Properties
Thermosets
•Processing is irreversible change --> Not Recyclable
•Lower Material Cost
•High Heat/Creep resistance
•High arc resistance

CLASSIFICATION OF PLASTICS
BASED ON APPLICATION
Commodity plastics
Mainly used as a replacement for conventional packaging materials like
glass, wood and paper. They are characterized by their low cost, easy
processibility and average properties.
Engineering plastics
An engineering plastic is expected to support loads more or less indefinitely.
They are characterized by their ability to sustain loads at higher working
temperatures.
Specialty plastics
These polymers offer high temperature performance which is far superior to
anything available so far. Service temperatures in excess of 200O C for
unfilled grades and over 300O C for fiber filled grades are possible.

THERMOPLSATICS
Polyolefins
LDPE, HDPE, PP
Styrenics
PS, HIPS, ABS, SAN
Vinyl chlorides
PVC, PVDC
Ethylene copolymers
EVA
Others
PMMA, Cellulosics
Commodity thermoplastics
Polyamides
Nylon-6, Nylon-66
Polyacetals
Homopolymers, copolymers
Polyphenylenes
PPE, PPS
Polycarbonate
Thermoplastic Polyesters
PET, PBT
Engineering thermoplastics
Polyethers
PES, PEK, PEEK
Polyimides
PEI, PI, PAI
Fluoropolymers
PTFE, FEP
Speciality plastics
THERMOPLASTICS

POLYMERIZATION
Monomer Polymer
polymerization
Ethylene
Monomer
H H
C=C
H H
H H H H H H H H
C C C C C C C C
H H H H H H H H…n
polymerization
Polyethylene
Repeating
unit
A long chain of
polyethylene
molecule

SOME COMMON POLYMERS
H H
C C
H CH3
n
H H
C C
H C6H5
n
H H
C C
H Cl
n
Polypropylene Polystyrene Polyvinyl Chloride
H H
C C
H COOCH3
n
H
C O
H
n
Acrylic Acetal(homopolymer)

CRYSTALLINE VS AMORPHOUS
Crystalline and Amorphous polymers
In crystalline polymers clusters
of polymer chains aggregate into
a regular structure
eg., Nylon, Acetal, HDPE
In amorphous polymers the
molecules do not arrange
themselves in any order.
eg., PC, PMMA, PS

CRYSTALLINE VS AMORPHOUS
Differences between amorphous and crystalline plastics
PROPERTY CRYSTALLINE AMORPHOUS
Melting point Sharp melting point Softens over a range
of temperatures
Transparency Usually opaque/translucent TRANSPARENT
Shrinkage High Low
Chemical resistance LOW HIGH
Permeability Low High
Heat content High Low
Fatigue & wear resistance High Low
Tensile strength High Low
Process conditions which promote Crystallinity
Higher mould/melt temperatures
Slow cooling

GLASS TRANSITION TEMPERATURE (Tg)
The temperature at which a rigid, hard amorphous plastic
changes into a soft rubbery state is called glass transition
temperature
The glass transition is associated with amorphous polymers
and amorphous regions of crystalline polymers
Below their Tg , polymers are glassy and rigid; above their Tg
polymers are rubbery and flexible.
Material: PC POM PA(66) PMMA PS PVC PP PE
Tg (OC) :: 150 -85 56 105 100 80 -10 -120

INTRODUCTION
TO
INJECTION MOLDING
PLASTIC INJECTION MOLDING IS A PROCESS
WHICH DEPENDS FOR ITS SUCCESS ON THE
PROPER FUNCTIONING OF A MACHINE WHICH IS
OPERATING WITH MATERIAL AND PRODUCING
THE SHAPES REQUIRED BY MEANS OF A MOLD

CLAMP UNIT INJECTION UNIT
CONTROLS HYDRAULICS

Mould locating ring
diameter should match the
bore diameter in the fixed
platen
MOULD SETUP CHECKLIST
The shut height (H) of
the mould should be
within the min. and
maximum limits of the
machine
T W The width (W) of the
mould should be lesser
than the distance between
tie-bars (T)
I.e. W < T
H

S
L
The opening stroke required by the
mould (S) should be within the
maximum opening stroke (L) of the
machine
The weight of the
mould should not
exceed the
recommended
maximum mould
weight
The minimum mould
diameter must be greater
than the specified lower
limit.

Nozzle orifice must be lesser than the sprue bush orifice
WRONG RIGHT
Nozzle nose cone radius
(r) must be lesser than the
sprue bush radius (R).
Any mis-match (as shown
in the figure left will lead to
material drool and sprue
getting stuck
r
R

Ensure that the nozzle heater and
thermocouple do not foul with the
mould while the nozzle makes
contact with the sprue bush.
Likely fouling points
If the sprue bush
is located deep
inside the mould,
use extended
nozzles

MOULD SETUP - Loading the mould
Close the mould fully till the
toggles are straight. Take
the end platen backwards
by ‘Mould Height’ gear, till
sufficient gap is created for
lowering the mould. Lower the mould from
the top.
Take care to see that
the mould doesn't
touch the tie-bars
while being lowered
Locate the mould properly
and bring the moving platen
forward by ‘Mould Height’
adjustment till the moving
platen touches the back
plate of the mould
1
2
3
Clamp the mould halves to
the platens and Remove
the link piece (if any).
Remove the crane chain.
4
Change the
operating
mode to
“setting”
during mould
setting
X

1. Start with low opening speeds. (V1)
2. Increase the speed after the mould opens slightly. (V2)
3. Decrease the speed again in the end to avoid jerk and over-
ride during stopping at end position.(V3)
V1
V2
V3
MOULD SETTING - Mould Open
Change the
operating
mode to
“setting”
during mould
setting
X
1
2
3

1. Start with low closing speeds. (V1)
2. Increase the speed after the mould starts closing. (V2)
3. Decrease the speed again just before the two mould halves
make contact. (V3)
V3
V2
V1
MOULD SETTING - Mould Close
Change the
operating
mode to
“setting”
during mould
setting
X
3
2
1

Change the
operating
mode to
“setting”
during mould
setting
X
Set the ‘start mould sensing’ at a
point just before the projecting
surfaces of the moving half (such as
guide pins, finger cams, core etc.)
start entering into the fixed half of
the mould.
Set the ‘mould sensing stop’ at a
nominal minimum distance from the
fixed half of the mould. Normally this
will about 2 to 3mm.
Set minimum mould
sensing pressure which is
just sufficient to move the
mould in the sensing zone
Sensing
zone
Lock
Set mould sensing time
slightly higher than the
time taken by the moving
platen to clear the sensing
zone

Change the
operating
mode to
“setting”
during mould
setting
X
Switch off mould cooling
Normally mould cooling will be “ON” starting from the
point of mould locking to the point of mould open. If
necessary, cooling water circulation can be continued by
setting the required time.
Setting the tonnage
1. Ensure that the toggles are fully stretched and
the two mould halves are touching each other.
2. In this position, open the mould and
lightly press and release mould height adjustment
forward button
3. Close the mould in Manual mode and read
the tonnage via the reading on the dial gage.
4. Repeat steps 2 and 3 till the required value of
tonnage is reached.
5. Release the screw below the dial gage after
setting the tonnage.

07 HYDRAULIC EJECTOR
Max Set Set Actual
HYDRAULIC EJECTOR FORWARD
Delay start 1.0s
Forward pressure 127 25
Forward step 1 -V1 31 10 Start -V2 55.0 mm
Forward step 2 -V2 31 6 Stop 65.0 mm 70.0mm
Stay forward time 1.0s
HYDRAULIC EJECTOR RETURN
Return pressure 127 15
Return speed -V 31 12 Stop 15.0 mm
Return position (multi stroke) Stop 25.0 mm
Hydraulic ejector
Multi stroke operation 2 Ejector L.S.in mould 
Forward with door open 
Return with door open  2-Y5 on in stay fwd time 
Cycle start with door close  2-Y6 off at end position 

Setting Hydraulic Ejector
Ejector Rod
Ejector Plate
Ejector Pin
Ejector Return
Position
Ejector Forward
Position
Change the
operating
mode to
“setting”
during mould
setting
X
Set the ejector
forward
pressure to the
minimum
required
While setting the
forward stop position,
the actual space for
ejector plate in the
mould must be kept in
mind.
In case if the ejector
rod is coupled to the
ejector plate in the
mould, the forward
and return stops of
ejector movement
are dependent on
the space available
for ejector plate
movement in the
mould
X

Ejector Rod Dimensions
Ejector Rod
Ejector Plate
D1
E1
DL
40,60,85,100
125, 150
DL
200, 250
A1 24.5 44.5
B1 17.5 29.5
C1 24.5 44.5
D1 7.8 9.5
E1 20 26
Select length to
suit mould

Setting Hydraulic Ejector
Hydraulic ejector
Multi stroke operation  2 Ejector L.S.in mould 
Forward with door open 
Return with door open  2-Y5 on in stay fwd time 
Cycle start with door close  2-Y6 off at end position 

Enable this option to select the hydraulic ejector
Enable this option to select multi stroke option
Enable this option for forward and return movements
of ejector while the door is open
Enable this option to start the cycle when the
guard door closes in semi-auto cycle
Enable if there is a need for applying pressure in
forward direction during stay forward time (as in
the case of spring loaded ejectors)
Enable this option when there is a limit switch in
the mould. Ejector movements will be controlled
by the limit switch actuation.
Enable this option when there is a need to
switch off ejector at end position (as in
the case of unscrewing moulds)

08 PROCESS OPTIMISATION
Set Act. Set Act.
Cycle time [s] 100 22.8 Scr.retr.aft.dos.[mm] 53 58
Cycle time -last shot[s] - 22.6 Dosing stop [mm] 48 48
Blocking time [s] 25 Scr.retr.bef.dos.[mm] 0
Pause time [s] 1.5
Injection time [s] - 2.3
Dosing time [s] - 6.7 Melt cushion [mm] 4.3
Delay Injection [s] 1.0
Injection pressure(127) 65 Swovr sc.stroke [mm] 9.0 9.0
Injection speed (63) 22 Swovr time [s] 3.0 2.1
Holding time step1 [s] 2 STEPPED DOSING
Holding pressure step1 25 Screw speed step2[mm]
Cooling time [s] 12 Screw speed step2
Dosing delay [s] Back pressure step2
Screw speed step1(63) 25
Back pressure step1 5 Stepped injection 
Back pressure manual 1 Stepped hold on 
Screw retr.before dosing(V)0
Screw retr. after dosing(V)5 Actual screw stroke[mm] 5.4

PROCESS OPTIMISATION TERMINOLOGY
Cycle time
Set: The set cycle time acts as a monitoring time for the completion of cycle. If, due to
some reason, the cycle fails to complete within the set time, the machine will signal an
alarm.
Actual: The time taken by the machine to complete one cycle
The set cycle time should be higher than the actual cycle time.
Cycle time - last shot
The time taken by the machine to complete the previous shot. Useful for checking the
effect of a change in the process parameter
Blocking time
Blocking time starts after the set cycle time expires. At the end of blocking time the
machine goes into shut-off mode as per the switch-off matrix setting.
Pause time
The time between two consecutive cycles while the machine is in auto mode. Pause time is
necessary to prevent mould closing before the ejected components clear the mould area
NOTE
Injection time, dosing time, melt cushion and actual
screw stroke are only measured and displayed on the
screen. They are not settable on the IBED

Delay Injection
A small delay (of the order of 0.4 - 0.7 sec) before injection compensates for the time required for the
nozzle contact force to build-up before injection can start.
Injection Pressure
The pressure during injection is limited to the set value. The injection pressure should be
set by taking the geometry and material of the component being moulded. Viscous materials like
acrylic, polycarbonate and ABS need higher pressures to fill the cavity. Long flow paths and thin wall
thickness also demand high injection pressure.
Injection Speed `
Injection speed is also dependent on the geometry of the component and the material
used. Slower speeds should be used for shear sensitive materials (like PVC). Slower speeds are also
desirable while gating into thick sections to avoid jetting. On the other hand, thin walled components
with long flow paths need high injection speeds to avoid freezing of the flow front before the cavity
is filled up. It is advisable to bring down the injection speed just before the switch over point is
reached to avoid overpacking and flashing.
Holding time
Holding time is dependent on the wall thickness of the component being moulded. Thick
walled components need longer holding times. Crystalline materials also need longer cooling times
as they exhibit higher shrinkage. Holding time should not be prolonged beyond the gate freezing
time of the component.
Holding Pressure
As a thumb rule, the initial holding pressure can be set at around 75% of the peak injection pressure.
Holding pressure can be progressively reduced for more uniform packing. Reducing the holding
pressure in steps will also prevent the screw jumping back after the end of holding phase.

Cooling time
The time to cool the component depends upon a host of factors such as, wall thickness,
material thermal properties, cooling channel layout, temperature and rate of flow of the
coolant. Start with high cooling time and optimize it later.
Dosing delay Dosing
delay can be set if the cooling time is considerably longer than the dosing time. By
delaying dosing, the degradation of heat sensitive materials can be prevented.
Screw Speed
Set the screw speed as per the recommendations. Try to match the end of dosing with
the end of cooling.
End of
holding &
start of
dosing
Cooling time
Dosing
delay Dosing
time

Back Pressure Step1
Maintaining a suitable level of back pressure behind the injection cylinder is essential for
proper homogenization and mixing of the melt and as well as to remove any air
inclusions in the melt.
Back Pressure Manual
Before the machine is put into auto or semi auto mode the screw should be in the dosing
stop position. The back pressure requirement during manual mode is usually set lower
than what is required during the semi or fully auto mode. This will bring the screw to
dosing stop position without drooling.
Screw retraction before dosing (V)
The speed of screw retraction before refill can be set here.
Screw retraction after dosing (V)
This speed setting determines the speed of screw retraction after refill (suck back
speed).
Screw retraction after dosing (mm)
The end position of the screw after retraction is set here.
Dosing stop (mm)
The end position of the screw after dosing. This determines the shot weight of the screw
after dosing.
Screw retraction before dosing (mm)
The end position of the screw retraction before dosing is set here.

Melt Cushion
The position of the screw immediately after the completion of holding stage is displayed
on the screen as melt cushion. Ensure that the melt cushion doesn't drop to zero as this
may restrict the pressure transmitted during hold on stage. A melt cushion of 3 to 5 mm
is ideal.
Swovr sc. stroke
The position of the screw at which the injection phase ends and the hold on phase
starts. Switchover stroke is usually set to occur after 95 - 99% of filling is over. When the
switchover is stroke based, ensure that the switchover time is set to a value slightly
higher than the actual time taken by the screw to cross the switchover point
Swovr time
If the switchover is set to occur in time based option, the injection phase ends and the
holding phase starts after the set time is elapsed. When the switchover by time is
selected, ensure that the switchover stroke is set to a value which can be reached within
the set time.
Note
Switchover from injection to hold on pressure can be triggered by either
stroke or time. If stroke based switchover is chosen, the time is monitored and if time
based switchover is chosen screw stroke is monitored.

INJECTION MOLDING MACHINE- CLAMPING
UNIT
Function :
* Open and close the mould
* Keep the mold locked when subjected to
injection and follow-up pressure
* Eject the moulded part.
*To accommodate different size of MOULD

FACTORS INFLUENICING
MOLDING QUALITY
MOLDING
Mould
- rigidity
- gate
- temperature
control
Environment
- man
- peripheral
equipments
- climatic conditions
Molding Compound
- formulation
- granule shape
- moisture content
Machine
- Injection Unit
- Clamping Unit
- Controls

Injection molding - basic process
•MELTING OF PLASTIC RESIN -
PLASTICATION/DOSING/REFILL
•INJECTION OF MELT INTO THE MOLD- INJECTION +
HOLDING
•COOLING OF THE MOLD
•REMOVING THE PART- EJECTION

CLOSE
MOLD
INJECT
INTO
MOLD
COOL IN MOLD
CAVITY
OPEN
MOLD
EJECT
PART
Injection molding - basic process
TOTAL CYCLE TIME

Injection molding MACHINE
-THE PRE-REQUISITES
Fast Cycling
 Reliable
 Energy Efficient
 High Moulding Quality
 High Mold Safety
 User-friendly

-THE preliminary checks
PRELIMINARY CHECKS
Shot weight requirement
Tonnage requirement
Mould shut height
Mould open stroke
Locating ring diameter
Nozzle radius / orifice diameter
Ejector stroke
Injection pressure
Injection rate
Plasticising rate

-THE machine setup
Settin temperatures
Mould clamping
Speeds / Strokes / Tonnage
Mould protection
Ejector strokes / speeds
Dosing stroke
Screw speed / back pressure
Injection speed / pressure
Switchover point
Holding pressure & time
Cooling time

-THE clamping unit setup
•Mounting the Mould
•Setting the Strokes / Speeds
•Setting the Tonnage
•Setting Mould Sensing
•Setting Ejector Strokes

-THE clamping unit setup
B
A= Mould open
stroke
Setting the strokes of the moving platen
A
B= Mould shut
height with
toggles fully
stretched

-THE MOLD OPEN/CLOSE PROFILE
A
Stroke
Stroke
Mould open speed
Mould close speed

-THE TONNAGE SETTING
LOW TONNAGE….
Leads to mould flashing
VERY HIGH TONNAGE….
Leads to mould damage
OPTIMUM TONNAGE SHOULD BE
BASED ON THE ESTIMATED
AVERAGE CAVITY PRESSURE

-THE EJECTOR STROKE SETTING
E
E = Maximum permissible stroke

-THE INJECTION UNIT setup
CHECKPOINTS:
 Barrel Temperature  Feed throat temperature
Metering Stroke Screw speed
Back pressure IU retract stroke

-THE INJECTION UNIT setup
1 3 4
2
1End point of injection stroke
2 Melt cushion
3 Switchover point
4 Dosing stop

-THE FINE TUNING PARAMETERS
 Mould open stroke
 Closing/Opening speeds
 Mould safety pressure /
stroke
 Ejector strokes/pressure
 Injection speed / pressure
 Switchover point
 Holding pressure/time
 Screw speed / back pressure
 Cooling time
 Temperatures

Injection molding PROCESS
-THE CRITICAL PARAMETERS
AND
THEIR EFECTS
MELT TEMPERATURE
Melt temperature too high:
Thermal degradation
Discoloration
Increased shrinkage
Prolonged cooling time
Inferior mechanical properties (brittleness)
Melt temperature too low:
Inhomogeneous melt
Increased stresses in the molded part
Higher pressure requirements during injection
Poor surface quality
Weak weld lines

AND
THEIR EFECTS
MOULD TEMPERATURE
In general, a high mould temperature ensures:
Less orientation and less warpage
Less internal stresses
Lower pressure requirements
Improved crystallinity
Mould temperature too low:
Matt finish
Ripple effect / Flow lines
Weak and visible weld lines
Increased stresses in molded part

AND
THEIR EFECTS
INJECTION SPEED
Injection speed too high:
Flash formation
Surface defects near the gate
Burn marks at the extremities of flow front
High clamp force requirement
Injection speed too low:
Ripple effect
Part not completely filled up
Warpage
Visible weld lines

AND
THEIR EFECTS
SWITCHOVER POINT
Switchover too early:
Short shot
Sink marks
Dimensions undersized
Visible weld lines
Switchover too late:
Mould flashing
Increased clamp force requirement
Increased stress level in the moulding
Over packing and ejection problems

AND
THEIR EFECTS
HOLDING PRESSURE
Holding pressure too high
Mould flashing
Increased clamp force requirement
Over packing and ejection problems
Over sized components
Ejector marks on the moulding
Holding pressure too low:
Sink marks and voids
Undersized components
Weight inconsistency
Poor reproduction of surface details

AND
THEIR EFECTS
HOLDING TIME
Holding time too long:
Increased energy consumption
Holding time too short:
Undersized components
Melt cushion variation
Variations in component weight and
dimensions
Sink marks and voids

AND
THEIR EFECTS
SCREW SPEED
Screw speed too low:
Variations in dosing time
Melt inhomogeneity
Screw speed too high
Shear / thermal degradation of the material
Temperature variations in the melt
Increased wear and tear of screw and non-return valve

AND
THEIR EFECTS
BACK PRESSURE
Back pressure too high:
Material degradation due to high internal friction
Long dosing times
Back pressure too low:
Melt inhomogeneity
Surface imperfections due to streaking effect of entrapped air

AND
THEIR EFECTS
SUCK BACK
Screw retraction too high:
Air streaks around the gate
Material discolouration
Screw retraction too low:
Material drool from the nozzle

AND
THEIR EFECTS
COOLING TIME
Cooling time too short:
Component distortion during ejection
Ejector pin marks on the component
Increased post-moulding shrinkage

L& T DEMAG INJECTION MOLDING
MACHINES- YOUR BENEFITS
HOW L&T DEMAG ADDS VALUE TO YOUR OPERATIONS
•PRODUCT VALUE
•SERVICE VALUE
•PERSONNEL VALUE
•IMAGE VALUE

Productive Use Of IMM (Optimization)
We Optimize –
 Productivity  Quality
Other Benefits:
Optimum Weight
Minimum Power Consumption
What we work on
Shortest Possible Average Cycle Time
Least Down Time
Low Rejects

Least Down Time
Influenced by:
•Quality of design of Machine, Mould, Accessories
•Reliability of components used in constructions of
above
•Care we take of Machine, Mould, Accessories
•Preventive maintenance
•Oil Quality
•Start up & Shut Down procedures
•Quick - Mould change, Material change

Low Rejects
Important requirements
•Precise reproducibility of parameters by the machine
•Steady state of mould wall temperature
•Consistency in plastics material being fed
•Same batch
•Consistency in virgin & re-grind (if used)
proportions
•Regrind free from flakes and fines
•Consistency in pre-heating, drying & feeding

Before we discuss-
how to optimize Cycle time,
Quality, Shot Weight & Power
Consumption Let us
understand Injection Molding
Process

Complexities in Injection Moulding Process
What Happens in Moulding Process?
A predetermined quantity of melt of constant density at constant
temperature in a cavity is cooled at constant rate to obtain full-bodied,
stress free component.
What Happens during Melt Cooling?
Melt starts cooling the moment it enters mould cavity
With fall of melt temperature – melt shrinks
With Melt Shrinkage – Melt Pressure Falls
With Melt Pressure Fall – Melt expands to touch mould wall
Melt packed under pressure within cavity together with melt in front of
screw tip (provided sprue/gate is not frozen) supply mass required to
compensate shrinkage.

Complexities Arise Because….
Melt is a non-newtonian fluid
Melt is compressible
Melt viscosity changes with - Shear rate and/or Melt temperature
Melt flow advances into cavity following “fountain-head flow pattern”.
It is not a “plug” flow.
So It Is a Chaotic Situation

Disturbance Variables
Environmental Influences
Injection
Molding
Process
Weight
Dimensional accuracy
Surface quality
Orientation
Flow lines
Strength
Mould Geometry
Raw Material Properties
Control Variables
-Temperature
-Pressure
-Speeds
-Time
-Strokes
-Screw speed
Influencing Factors On Quality Criteria of Mouldings
Variations of raw material
properties
Processing Influences
Input Variables Output Variables
(Quality Criteria of Moulding)

Steps to Find Solution Inspite of Chaos
Target - Productivity & Quality
Mould
• Constant mould wall temp.,
• Constant rate of cooling
Machine
• Homogenous melt at constant
temp.,
• Fill as fast as possible
• Keep melt flow front velocity
constant
• Changeover from fill to pack as late
as possible
• Precise changeover
• Consistency of follow up (hold on)
pressure and time
Monitored Parameters
Plasticising Time – Cycle Time
Fill Time
Changeover Position
Melt Cushion
Peak Injection pressure – short hold on
time
Pressure integral – long hold on time
Material
From Single Grade and Same Batch

Understanding Injection Moulding
Process
Melt homogenity is excellent
• When screw rotates slow during plasticising
• Shot weight used below 1.6D stroke of 20.1 L/D ratio
screw
• Consistency in material feeding in screw is dependent
on – feed throat temperature regulation, back pressure
control and barrel temperature control

Recommended Minimum & Maximum Utilization of Dosing
Stroke for Cylinder L:D 20:1 & 24:1

Velocity
profile of
the main
flow
Cross flow
of the flow
front
Frozen
surface
layer
Highly
viscous
skin
Velocity
Profile of the
flow front
Wall
thickness
Melt flow in the cavity resembles “fountain
head” at the flow front. Hot melt in cavity
streaks between the frozen layers at cavity
wall, and, at the flow front, it flows out
towards the wall, and, get deposited.
If the fill rate is slow, hot melt has to flow
between constantly narrowing gap (as frozen
layer against wall is constantly thickening)
demanding higher injection pressure. Melt
flow in such condition drag the freezing
molecules and sets in orientation.
To get stress free moulding, orientation
should relax. To give sufficient time for
relaxation to molecules, cooling has to be
slowed down. To shorten the cooling time,
cavity should be filled fast enough before
freezing layers at cavity wall thicken, and,
thus avoid high injection pressure, and,
orientation in freezing layers.
To summarize, to get stress free /
warpage free moulding at short cooling
time, fill as fast as possible. Only
guard against melt jetting – Melt does
not leave the wall.
Melt flow
Velocity Profile
Understanding Injection Moulding Process

Surface (roughness,
gloss colour)
Distortion,
orientation in the skin
Crystallinity
Contour
definition
Flash
formation
Wt
dimensions
Weight dimensions
shrinkage
Voids, sink marks
Inner orientations
Injection speed
Cylinder temp.
Mould temp.
Switchover
point
Cylinder
temp.
Mould temp.
Level of follow up pressure
Follow up pressure time
Cylinder temp.
Mould temp.
Inj. Time
Inj. Pressure integral
Melt Temp.
Mould temp.
Maximum
hydraulic or
mould cavity
pressure
Mould cavity pressure
integral
Melt temp.
Mould temp.
Mould cavity
pressure
Time
Injection
Phase
Compression
Phase
Phase of follow up
pressure
Quality
Characteristics
Machine
Parameters
Monitoring
Parameters
Relation of quality
characteristics to
process parameters,
represented by the
profile of the mould
cavity pressure

Influences of process parameters on the five most
important quality characteristics (Blue: Great
Influence)
Process
parameters
Quality
characteristics
Injection
Speed
Mould
Temp-
erature
Melt
Temp-
erature
Follow
up
Pressure
Follow
up
Pressure
time
Clamp
Close
Screw
Speed
Screw
back
Pressur
e
Dimension
stability
Low Shrinkage
Good Surface
Homogeneity
Colour
dispersion

Injection Moulding Cycle Time
machine times (1)
injection
hold
rest cooling
plasticising
machine times (2)
removal
cycle time
time t
process times
Wt

For the Shortest Cycle Time
 Machine time shall be shortest – don’t use oversized
machine.
 Melt should afford shortest cooling – depends on
homogenity of melt and least orientation in molecules
(influenced by filling process)
 Plasticise within cooling time, or, should run parallel to
mould open close.
 Ejector, Core, Carriage movement to run during
essential time segments of cycle – Mould Open-Close-
Inject-Cool

Selection of an IMM
Part
- Material
- Ratio F/W
- ...
Mould
- no. of cavities
- gate
- ...
Shot
weight
Residence
time
Cooling
time
Req.
Injection
pressure
Injection
time
holdtime
Machine type
Clamp force
Injection
Unit
Machine
movement
time
Plasticizing
time
Screw
geometry
Screw drive

PLEASE OPEN ABOVE
LINK FILE

0,88
SAN
1,12
PVC
0,95
PUR
0,86
PS
1,05
PPS
0,98
PPO+30%GF
0,9
PPO
0,73
PP
1,1
POM
0,94
PMMA
1,1
PES
1,17
PC+30%GF
0,98
PC
1,15
PBTP+30%GF
1,05
PBTP
1,15
PA 66 + 35% GF
0,95
PAG
0,7
LDPE
0,72
HDPE
0,88
ABS
Discharge Factors
Type
Conversion into Shot-weight
Shot Wt (g) = swept volume (cm3) x
discharge factor (g/cm3)

2.7
2.6
2.5
2.4
2.3
2.2.
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Flow-up pressure higher than injection
pressure
Injection and flow-up pressure the same
Injection pressure
higher than
flow-up pressure
Accumulator
required
Check need
for
accumulator
Wall thickness zones requiring use of
accumulator injection & flow-up pressure
Wall
Thickness
(mm)

Barrel Temperature Profile
Ascending profile is most common, use of a hump or reverse profile produces
optimum melt quality quality with minimal component wear. The
recommendations are:
a. Flat profile – for unfilled resins where shot capacity is 20-40% of barrel capacity.
b. Ascending profile – for unfilled resins with >4 minutes residence time and shot size less
than 30% of barrel capacity.
c. Hump profile – Excellent for most
unfilled materials with 2-4 minutes
residence time and
with shot
capacity around 25-50% of barrel
capacity.
d. Reverse Profile – Excellent for
all heavily filled and shear
sensitive materials. Suitable
where shot size is minimum
50% of barrel capacity with
low residence time.
Front Zone
Nozzle
Zone
Rear Zone
Middle Zone
b
c
d
+40o
C
+30o
C
+10o
C
+20o
C
0oC
-10oC
-20oC
-40oC
-30oC
a
+40o
C
+30o
C
+10o
C
+20o
C
0oC
-10oC
-20oC
-40oC
-30oC

Feed Throat Temperature
Control
• Influences the co-efficient of friction
of plastics granules with steel.
• To maintain desired feed rate feed
throat temp. control is necessary.
• It also regulates packing of screw
flights by granules / melt
• Effects the torque requirement for
Plasticising
• By keeping the temperature in
narrow range, consistency of melt
quality is ensured.
40oC
CP
40oC
CAP
40oC
CAB
40oC
CA
40oC
PPO
40oC
PVC, plast
30-40oC
PVC, Rigid
70-90oC
PC
50-60oC
PMMA
30-40oC
POM
20-30oC
PP
20-30oC
PE
60-80oC
PA
35-40oC
ABS
20-30oC
SB
20-30oC
PS
Temp.
Material

Immediate purging with natural, non-flame retardant resin,
mixed with 1% sodium stearate.
Flame Retardant compounds
Cast acrylics
Filled Matrial
GPPS, Cast Acrylics
PPO
PC regrind, Extrusion grade PP
Polysulphones
Polystyrene, avoid anycotnact with PVC
Acetal
Cast acrylic or PC regrind, follow with PC regrind
Polucarbonate
GPPS, Cast acrylics, High flow HDPE
PET
Next material to be run
PBT
GPPS, Cast Acrylics, High Flow HDPE
Nylon
GPPS, Cast Acrylics
ABS
GPPS, ABS, Cast Acrylics
PVC
Cast acrylic
Polystyrene
HDPE
Polyolefins
Purging Material
Material to be purged
NOTE:There are some special purging compounds available to suit particular category of plastics
material.
General Guideline About Purging
Materials

PVC
PE
PC
PVC
PC
ABS
PE
PC
ABS
PC
Acrylic
-
PC
Acrylic
PC
ABS
PE
PBT
ABS
PBT
PVC
PE
Nylon
PVC
Nylon
PC
-
PC
PC
Nylon
Nylon
-
Acrylic
Nylon
Acrylic
PP
-
Acrylic
PP
Acrylic
Any
material
-
PE
Any
material
Acetal
PC
PE
Acetal
PC
Acetal
PBT
PE
ABS
PBT
ABS
PC
PE
ABS
PC
ABS
Polysulp
hone
PE
ABS
Polysulp
hone
ABS
SAN
-
SAN
SAN
ABS
PP
-
ABS
PP
ABS
Follow
with
Temp.
Bridging
material
Mix with
rapid
purge &
soak
Material
changin
g to
Material
in m/c
SAN
-
SAN
PP
SAN
Acrylic
-
Acrylic
Acrylic
SAN
PVC
-
LLDPE/H
DPE
PVC
PVC
New
material
-
LLDPE/H
DPE
Any
material
PVC
PP
-
PP
PP
PSU
PP
-
PP
PP
PP
PE
-
PE
PE
PP
Acrylic
-
Acrylic
Acrylic
PP
ABS
-
ABS
ABS
PP
ABS
PE
PSU
ABS
PSU
PSU
-
PET
PSU
PET
PS
-
PS
PS
PE
PE
-
PE
PE
PE
PP
-
PP
PP
PE
PPS
PE
PE
PPS
PE
Follow
with
Temp.
Bridging
material
Mix with
rapid
purge &
soak
Material
changing
to
Material
in m/c
General Guideline for Resin Changes Productive Use Of IMM (Optimization)

Trouble shooting chart for
general defects in
plastic
Compiled by:- P. MOHAN

Increase holding pressure time and pressure.
Increase injection pressure.
Enlarge the gate if restricted gate is used.
Reduce melt temp.
 mould temp increase in case of void
formation.
Increase cooling time in machine.
Redesign the part avoiding sudden changes
in wall thickness.
Relocate the large gate into thick section.
Relocate the restricted gate to thin section.
Balance cooling must be provided in the
mold.
holding pressure cannot help
anymore to compensate for the
shrinkage.
Injection pressure too low.
Short of shot capacity.
Mould temp.
Part ejected too hot.
Wall thickness difference is too
great.
Round or
elongated
bubbles,visible
only in
transparent
plastics.
Voids
Suggested remedy
Possible causes
Possible
appearance
Fault

Increase holding pressure time and pressure.
Increase injection pressure.
Enlarge the gate if restricted gate is used.
Reduce melt temp.
Reduce mould temp in case of sink mark.
Increase cooling time in machine.
Redesign the part avoiding sudden changes
in wall thickness.
Relocate the large gate into thick section.
Relocate the restricted gate to thin section.
Balance cooling must be provided in the
mold.
holding pressure cannot help
anymore to compensate for the
shrinkage.
Injection pressure too low.
Short of shot capacity.
Mould temp.
Part ejected too hot.
Wall thickness difference is too
great.
No cushion
depression in
round shape on
the surface of
the moulding.
sink
marks
Suggested remedy
Possible causes
Possible
appearance
Fault

Increase clamping force or use machine
with higher clamping force.
Reduce injection speed and holding
pressure.
Reface the both halves of moulds.
Mould plate should have sufficient strength
and steel used should be of required quality.
Improve matching.
Reduce mold and melt temperature.
Runner and gate should be balanced.
Mould temperature should be uniform.
Optimize the no. of cavities.
Clamping force inadequate.
Cavity pressure too high.
Mould face warped.
Core and cavity not matched
properly.
Viscosity of the material is too
high.
Unequal or interrupted filling of
cavities.
Poorly distributed cooling
channels.
Polymer melt
penetrates mold
gaps(e.g parting
line)
flashes
Suggested remedy
Possible causes
Possible
appearance
Fault

Increase melt and mold temp. improve flow
condition.
Increase injection speed.
Increase wall thickness.
Improve mould venting.
Relocate gate or use multiple gates.
Enlarge runner and gates.
If it is not possible to remove a weld/meld
line, it should be positioned in the least
sensitive area possible. This can be done by
changing the polymer injection location or
altering wall thicknesses to set up a different
fill time
Provide an overflow.
Use textured surface.
Plastic does not have
sufficiently good flow.
Injection speed too low.
Wall too thin.
Mold venting inadequate.
Distance from gate to welded
joint too long.
Multiple gates.
Position of the gate.
Gate size too low.
Clearly visible
line where two
flow fronts
meet.
Weld
lines
Suggested remedy
Possible causes
Possible
appearance
Fault

Check and reduce melt temperature.
Reduce cycle time ,use a smaller
plasticating unit.
Check venting channels for dirt
Decrease injection speed
Decrease injection pressure
Check heater malfunctioning
Decrease nozzle temp.
Add vents
Enlarge gate to reduce frictional burning
Purge with an appropriate material.
Check for impurities..
Check and adjust melt temperature.
Check for screw wear.
Melt temp.too high .
Residence time too long.
Problem with back flow valve.
injection speed too fast.
Back pressure too high.
Inadequate venting.
Frictional buring.
Down time too long
Poor purging( Nozzle
contaminated)
Dirty material
Barrel switched off over a long
period of time
Degradation by other resins
Brownish
discoloration
with streaking
Black mark on
the surface of
the moulding.
Burn
marks
Black
spot
Suggested remedy
Possible causes
Possible
appearance
Fault

Increase melt and mold temperature.
Increase injection speed and injection
pressure.
Make wall thicker.
Increase nozzle contact pressure,check raddi
of nozzle and check centering.
Enlarge gate and runner.
Pre dry the material properly
Lower nozzle temp.
Lower material temp.
Increase back pressure
Increase back pressure stroke
Allow for adequate venting
Move mould to smaller shot size machine
Plastics does not have
sufficiently good flow.
Injection speed too low.
Walls of part tool thin.
Insufficient contact between
nozzle and mold.
Diameter of gating system too
small.
Moisture in material.
Back pressure too low.
Frictional burning at gate, in
machine nozzle or hot runner.
Melt too hot.
Degradation of material.
Incomplete
filling of cavity
,especially at
end of flow path
or near thin
walled areas.
Elongated
silvery streaks.
Short
moulding.
Silver
streakes
Suggested remedy
Possible causes
Possible
appearance
Fault

observe mould for uniform part ejection
Increase hold time
Increase cooling time
Use fixture
 Change gate location
Review part design
Increase/reduce no. of gates
Increase melt temp.
Increase mould temp.
eliminate contamination
Check % of regrind
Decrease injection speed
Change material
Wrong part design
Insufficient cooling time
too high injection pressure
Wrong gate location : different
shrinkage in diff. Direction
Inadequate ejector pins
cavity too hot
Wrong material choice
Injection speed too high
Mould too could
Melt too hot
Incompatible master batch
Too much use of recycled
material.
Cross contamination with other
polymers
Parts are not
flat,are
distorted,do not
fit together.
Surface near
sprue flakes
off(especially
with blends.)
Warpage
delaminat
ion
Suggested remedy
Possible causes
Possible
appearance
Fault

Reduce mold temperature.
Increase cycle time.
Polish well.
Give maximum possible draft.
Cavity wall temperature too
high in certain places.
Part elected too soon.
Poorly polished.
Insufficient draft angle.
Dull spot ,finger
like or clover
leaf shaped
shiny hollow on
surface(usually
near sprue.)
Part
sticks to
mold
Suggested remedy
Possible causes
Possible
appearance
Fault

Plastic_MATERIALS_introduction.ppt

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