Ideal process parameters in injection mouldingPresentation Transcript
In InjECTIOn MOuLDIng
BY DEVANG NAIK
• Injection Molding: -
It is a cyclic process,
where a heat soften material injected
in to close mold, which gives the
It is an organic substance
which can be converted in to any
shape by application of heat and
• TERMS uSED In InjECTIOn
• Injection Pressure.
• It is a maximum
pressure excreting on plastic
melt at screw tip.– measuring
unit kg/cm2 or bar.
Rate of displacement of screw
per second. Measuring unit
gm/sec, cc/sec, mm/sec.
• Back Pressure :-
It is a pressure /force which
force the screw backward direction even as it is
conveying polymer forward.
This back pressure
controlled by throttling the oil behind injection
It is not more than 14 bar.
It is a mechanical device (helical
flighted shaft) which convey the heat
It is a tube like mechanical
device which provide mechanical &
thermal connection from not
cylinder (barrel) to much colder
Types of nozzle:-
1. open channel.
2. Check valve type.
3. Shut off valve
• Size of orifice with respect to
• Up to 180T 4 mm 3 mm
• 350 T 5 mm 4 mm
• 650T 6 mm 5 mm
• 850T 10mm 8 mm
• How to start machine ?
Sprue bush dia.
Cooling line looping.
Water pressure & Water temp. Delta T : 2
to 5 degree
Screw surface speed (SSS) .
Hold on position.
• Process Setting.
Mold temp. 1. Injection
Cavity pressure. 2. System
Sprue bush dia 3. Barrel temp.
System Flow 4. Hot runner
Air pin/Ejector pin
• Hygroscopic Non Hygroscopic
• Polymers with high Very little or no affinity
• Affinity for moisture. For moisture.
• Nylon, ABS Polystyrene.
• Polycarbonate Polyethylene.
• Polyester PVC,PP.
• Polyurethane Acetal.
non return valve
• 1 Set up m/c to run standard
• 2 Turn of pack and hold time
• 3 Weigh the parts and record
• Why Vent?
• Evacuation of latent air that
is in the closed mold.
• Allow the evacuation of
gases produced by low
molecular weight polymers
• What is important barrel temp or melt temp?
• Optimum MELT TEMP is the key to successful
• Factors affecting melt temp.
• Barrel temp setting.
• Screw speed.
• Screw back pressure.
• Residence time.
• in order to reProduce
the same Process on
multiPle machines .
• melt temPerature is
one variable that
must be controlled
• Plastic materials viscosity decreases as
shesr rate increases.
• WHY IS THIS IMPORTANT?
• Screw speed----Lower viscosity at higher
• Inj speed---Flow rate easier with higher inj
• Flow Rate=Time in sec,measured from
start of injection to transfer to pack/hold.
How does velocity profiling help?
• Allows the mold to be filled as fast as
• Reduces burning, splay and other
• Helps with weld line.
• Surface finish.
• Best speed for each area of the segment
can be selected.
• What is pressure?
• Pressure is Resistance to FLOW.
• Injection pressyre-----1st
• Packing pressure-------2nd
• Back pressure.
• Cavity pressure--------Most Important
• Injection pressure must always
be set per requirement of cavity
pressure. This can be done by
gradually increasing the set inj.
Prs. On monitor and observe the
increment in pr.gauge.The set
point after which the gauge pr.
Does not change is your require
HydrauliC pr.vs plastiC
• Hydraulic pressure: Measure of how
much force a machine can generate
against the ram.
• Plastic (Melt) pressure: Pressure
generated in the nozzle of a molding
machine usually derived from the
intensification ratio of the machine.
• Cavity Pressure: Actual pressure in the
• Pack and Hold-----Gate freeze study.
• Mold open.
• Mold close.
• Cooling Time= 150 * Thickest wall of the
• = 150*.100=15sec.
• Screw surface speed=0.052
* Screw Dia*Screw RPM.For
HDPE and PP 750.SSS is
low than definable require
higher barrel temp.
• There are few processing
parameters in the injection process
that have significant influence on
the melt temp., the temp of the melt
as it leaves the injection unit.
• The temp setting of barrel heaters.
• RPM of screw.
• Back pressure applied.
• Residence time.
• Cycle time.
Is the key to