During the molding process of converting plastic particles into plastic products, plastics are often subjected to high temperature and high pressure and flow molding at high shear rates. Different molding conditions and processes will have different effects on product quality. Plastic injection molding has plastics. Raw materials, injection molding machines, molds and injection molding processes are composed of four aspects.

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Influence Of Injection Molding Process On Product Quality
Translated By Jasmine HL
During the molding process of converting plastic particles into plastic products, plastics are often
subjected to high temperature and high pressure and flow molding at high shear rates. Different
molding conditions and processes will have different effects on product quality. Plastic injection
molding has plastics. Raw materials, injection molding machines, molds and injection molding
processes are composed of four aspects.
If the plastic raw materials are correctly selected, the technical parameters of the injection
molding machine and the mold structure meet the requirements of the injection molding
conditions, and the quality of the processed products is directly related to the injection molding
process.
The quality of the product includes the quality of the internal material and the appearance. The
quality of the internal material is mainly mechanical strength, and the magnitude of the internal
stress directly affects the mechanical strength of the product. The main reasons for the internal
stress are the crystallinity of the product and the orientation of the molecules in the plastic
molding of.
The appearance quality of the product is the surface quality of the product, but the warpage and
deformation caused by the large internal stress will also affect the appearance quality problem.
The appearance quality of the products are: insufficient products, product dents, weld marks,
flashes, bubbles, silver wires, black spots, deformation, cracks, peeling and discoloration, etc., all
related to the molding temperature, pressure, flow, time and location-related.
1. Molding temperature: barrel temperature, plasticizing temperature, nozzle temperature, mold
temperature and plastic drying temperature, etc.
Barrel temperature: It is the melting temperature of the plastic. The barrel temperature is set too

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high and the viscosity of the plastic is low. Under the same injection pressure and flow rate, the
injection speed is fast, and the molded product is easy to flash, silver wire, discoloration and
brittleness.
The barrel temperature is too low, the plastic is poorly plasticized, the viscosity is high, the
injection speed is slow at the same injection pressure and flow rate, the molded product is easy
to be insufficient, the welding marks are obvious, the size is unstable, and there are cold blocks in
the product.
Nozzle temperature: The nozzle temperature is set high, and the nozzle is easy to drool, causing
cold filaments in the product. Low nozzle temperature causes blockage of the mold casting
system. The injection pressure must be increased in order to inject plastic, but there is a cold
block in the molded product at once.
Mold temperature: The mold temperature is high, the injection pressure and flow rate can be set
lower, but under the same pressure flow rate, the product is easy to flash, warp and deform, and
the product is difficult to eject from the mold. The mold temperature is low. Under the same
injection pressure and flow rate, the product is insufficiently formed, and bubbles and weld
marks are formed.
Plastic drying temperature: Various plastics have different drying temperatures. ABS plastic is
generally set to a drying temperature of 80 ~ 90 ℃, otherwise it will not be easy to dry and
volatilize the moisture and residual solvents, the product is prone to silver wire and air bubbles,
the product strength will be reduced.
2. Molding process pressure: there are pre-plastic back pressures: injection pressure, mold
clamping pressure, holding pressure, mold and neutron pressure, injection table pressure, etc.
Pre-plastic back pressure: high back pressure, high storage density, large storage capacity in the
same storage volume. Low back pressure Low storage density and low storage. After setting the
storage position, adjust the backpressure by a large amount. You must pay attention to reset the
storage position, otherwise the product may be flashed or insufficient.
Injection pressure: Different types of plastics have different melt viscosities, and the viscosity of
non-crystalline plastics changes greatly with the change of plasticizing temperature. The injection
pressure is set according to the welding viscosity of the plastic and the plastic process ratio. If the
injection pressure is set too low, the product is insufficiently shot, and the dents, weld marks, and
dimensions are unstable. The injection pressure is too high, the product flashes, it is difficult to
discolor and eject the sticky mold.
Clamping pressure: It depends on the projection area of the mold cavity and the injection
pressure. If the clamping pressure is insufficient, the product is likely to flash, and the weight
increases. Excessive clamping force makes it difficult to open the mold. The clamping pressure
setting is generally not more than 120par / cm2.
Holding pressure: When the injection is finished, the screw is kept under a pressure called
holding pressure. At this time, the product in the mold cavity has not been frozen. Holding
pressure can continue to fill the mold cavity to ensure that the product is full. The holding

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pressure and pressure are set too high, which brings great resistance to the supporting mold and
the drawing insert, and the product is easy to be whitened and warped. In addition, the mold
runner gate is easily swelled by supplementary plastic and the gate is broken in the runner.
Products with too low pressure have dents and unstable dimensions.
Supporting die and neutron pressure, the setting of supporting die and neutron pressure is based
on the comprehensive conditions of the mold cavity area, the core projection area of the core
insert, and the complexity of the geometric shape of the molded product. size. Generally, it is
necessary to set the pressure of the pallet and the neutron cylinder so that the product can be
pushed.
3. Flow: It is related to the speed of the injection molding machine, including screw speed,
injection speed, carrier mold and neutron speed.
Screw speed: In addition to adjusting the pre-plastic flow, it is mainly affected by the pre-plastic
backpressure. For example, if the pre-plastic flow is adjusted to be large and the pre-plastic back
pressure is high, as the screw rotates, the plastic has a large shear force in the barrel, and the
plastic molecular structure is easily cut off. , And the barrel heating temperature is not easy to
control. If the pre-plastic flow is set too low, the pre-plastic storage time will be extended, which
will affect the molding cycle.
Injection speed: Set the injection speed reasonably, otherwise the product quality will be
affected, the injection speed will be too fast, the product will have bubbles, scorch, discoloration,
etc. If the injection speed is too slow, the product is insufficiently formed, and there are welding
marks.
Undercarriage and neutron flow: It should not be set too large, otherwise the ejection and core
pulling action will be too fast, which will cause the ejection and core insert to be unstable, and
the product will be easily ejected.
3. Time setting: In the injection molding process, there are drying time, injection and dwell time,
and cooling time.
Drying time: It is the drying time for plastic raw materials. Various types of plastics have the best
drying temperature and time. The drying temperature of ABS plastic is 80 ～ 90 ℃, and the
time is 2 hours. ABS plastic generally has a water absorption of 0.2 to 0.4% for 24 hours, while
the water content that can be injection molded is 0.1 to 0.2%.
Injection and dwell time: The control method of the computer injection machine is equipped
with multi-stage injection to grade the pressure, speed and plastic quantity. Make the injection
speed of the plastic in the mold cavity reach a constant speed, and improve the appearance of
the molded products and the quality of the internal materials.
Therefore, the injection process is usually used for position control without time control. Holding
pressure is controlled with time. For example, if the holding time is longer, the product is dense,
the weight is heavy, the internal stress is large, the demolding is difficult, the top is easy to be
white, and the molding cycle is prolonged. The holding time is too short, the product is prone to
dents, and the dimensions are unstable.
Cooling time: It is to ensure the stability of the product set. It is to cool the molding time after

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molding the plastic injected into the mold cavity into the product. Otherwise, the product will
easily warp and deform when ejected, and the product will easily deform and become white. The
cooling time is too long, and the molding cycle is extended, which is uneconomical.
4. Position control: Some injection molding machines have mold transfer position, pallet support
position, material storage and injection position control.
The mold moving position refers to the entire moving distance from mold opening to mold
closing and locking. The best position to move the mold is to remove the product smoothly. The
mold opening distance is too large, and the molding cycle is long.
As long as the position of the supporting mold is controlled from the position of ejection from
the mold, the product can be easily removed.
Storage location: First of all, it is necessary to ensure the amount of plastic injected at one time of
the molded product, and secondly to control the amount of material stored in the barrel. The
storage position is controlled more than once, and the injection volume is too much, and the
product is easy to flash, otherwise the product is insufficiently formed.
Too much stock in the barrel, the plastic stays in the barrel for a long time, the product is easy to
fade, and affects the strength of the molded product. On the contrary, it will affect the
plasticization quality of the plastic, and it will be added to the mold without material during the
holding pressure.
to sum up
The quality of injection molded products involves product design, plastic material, mold design
and processing quality, choice of injection molding machine and process adjustment.
For normal production molds, to ensure and improve product quality, only adjustments to the
injection process; that is, adjustments to temperature, pressure flow rate, time and position.
The process adjustment must be comprehensive and balanced. If the size of the product changes
greatly, consider starting from the plastic raw material, whether it is crystalline or non-crystalline
plastic and the size of the molecular weight of the plastic. It is a crystalline plastic and a
macromolecular plastic. It is necessary to consider the crystallinity and molecular orientation of
the product. The shape of the product changes to the flow during molding, which causes changes
in the stress and size of the product, and changes in the shrinkage of the product.
It can solve the small changes in product size. From the process, it can increase the temperature
of some materials, reduce the temperature of the mold, control the amount of injection material,
reduce the injection pressure, increase the injection speed, and fill the mold cavity instantly,
reduce the holding time, and extend some cooling time Reduce the product density while
ensuring that the product shoots. To reduce the internal stress of the product, and reduce the
shrinkage of the product.
In short, the adjustment of the injection process cannot be started from a single point but must
be started from the principle of the injection process. Comprehensive consideration and
consideration of issues can be adjusted from multiple aspects one by one or multiple issues at a
time. However, the adjustment method and adjustment principle depend on the quality and
process conditions of the products produced at that time.