Molding defects and solutions
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Reliable Package:
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Plastic Injection Molding Solutions Effective Techniques:-
1. Plastic Parts Deformation
Plastic design, mold design, plastic materials selection and injection parameters are the 4 keys in affecting final plastic quality. The plastic part design is dominated the others. With uneven wall thickness and differential shrinkage at different locations, mold design and raw plastic materials will make up a little effect, injection molding parameters setting will then be more demanding for reducing deformation of parts under constant part weight and tool gating size by means of
@ lower mold temperature
@ longer cooling time
@ lower holding pressure
Plastic design, mold design, plastic materials selection and injection parameters are the 4 keys in affecting final plastic quality. The plastic part design is dominated the others. With uneven wall thickness and differential shrinkage at different locations, mold design and raw plastic materials will make up a little effect, injection molding parameters setting will then be more demanding for reducing deformation of parts under constant part weight and tool gating size by means of
@ lower mold temperature
@ longer cooling time
@ lower holding pressure
Cause of deformation (warpage)
Deformation and dimension change by warpage are often being a problem of resin molded product.
Following factors are the cause of the warpage deformation, but actually it will happen when several factors overlap intricately.
Cause of warpage deformation :-
① Design
・ Lack of shape stiffness ・ Uneven thickness ・ Shape asymmetric property
② Material property
・ Crystalline ・ Anisotropy ・ Lack of material stiffness
③ Molding process
・ Resin and filling material orientation ・ Uneven inner pressure ・ Uneven cooling speed (mold temperature) ・ Shrinkage restriction by mold core
④ Fabricating
・ Thermal process （printing paint, adhesive setting process） ・ After contraction ・ After processing， After insert
⑤ Usage environment
・ High and low temperature atmosphere ・ Creep
Deformation and dimension change by warpage are often being a problem of resin molded product.
Following factors are the cause of the warpage deformation, but actually it will happen when several factors overlap intricately.
Cause of warpage deformation :-
① Design
・ Lack of shape stiffness ・ Uneven thickness ・ Shape asymmetric property
② Material property
・ Crystalline ・ Anisotropy ・ Lack of material stiffness
③ Molding process
・ Resin and filling material orientation ・ Uneven inner pressure ・ Uneven cooling speed (mold temperature) ・ Shrinkage restriction by mold core
④ Fabricating
・ Thermal process （printing paint, adhesive setting process） ・ After contraction ・ After processing， After insert
⑤ Usage environment
・ High and low temperature atmosphere ・ Creep
2. Flash in plastic injection parts
Molding Flashes debug !
It occurs when a thin layer of material is forced out of the mold cavity at the parting line or ejector pins location.
Causes:-
@ worn or poorly fitting parting surface, including mold plate deformations and obstructions (grease,dirt, debris).
@ insufficient clamp force of which mold plates shut off are not holding sufficiently.
@ over-packing on sections, thus increasing localized pressure. @non-optimal molding conditions, including material viscosity, injection rate, mold temp. and runner system, etc.
@ improper venting due to poor designed venting system.
Solutions:
# ensure correctly fitting mold plates, set up the mold to seal properly, clean the machine from any obstructions, add pillar or thicken the mold plates if there is any deformation of the mold plate during molding process.
# avoid over packing
# select machine with higher clamp force #vent effectively, especially at materials joining lines
# optimize processing conditions with reducing pressure and shot size to the minimum required.
3. Sink Marks
Description: Sink marks are small depressions that develop in thick areas of the injection molded prototype when shrinkage occurs in the inner portions of the finished product.
Causes: Sink marks are often caused
@when the cooling time or the cooling mechanism is insufficient for the plastic to fully cool and cure while in the mold.
@by inadequate pressure in the cavity, or by an excessive temperature at the gate.
@All else being equal, thick sections of the injection molded part take longer to cool than thin ones and so are more likely to be where sink marks are located.
Remedies:
#1 Mold temperatures should be lowered, holding pressure increased, and holding time prolonged to allow for more adequate cooling and curing.
#2 Reducing the thickness of the thickest wall sections will also ensure faster cooling and help reduce the likelihood of sink marks. .
Causes: Sink marks are often caused
@when the cooling time or the cooling mechanism is insufficient for the plastic to fully cool and cure while in the mold.
@by inadequate pressure in the cavity, or by an excessive temperature at the gate.
@All else being equal, thick sections of the injection molded part take longer to cool than thin ones and so are more likely to be where sink marks are located.
Remedies:
#1 Mold temperatures should be lowered, holding pressure increased, and holding time prolonged to allow for more adequate cooling and curing.
#2 Reducing the thickness of the thickest wall sections will also ensure faster cooling and help reduce the likelihood of sink marks. .
4. Jetting
Causes:
Jetting occurs mostly when the melt temperature is too low and the viscosity of the molten plastic becomes too high, thereby increasing the resistance of its flow through the mold. When the plastic comes in contact with the mold walls, it is rapidly cooled and the viscosity is increased. The material that flows through behind that viscous plastic pushes the viscous plastic further, leaving scrape marks on the surface of the finished product.
Remedies:
@Increase mold and melt temperatures.
@Increase the size of the gate so that the injection speed becomes slower.
@Optimize gate design to ensure adequate contact between the molten plastic and the mold.
Jetting occurs mostly when the melt temperature is too low and the viscosity of the molten plastic becomes too high, thereby increasing the resistance of its flow through the mold. When the plastic comes in contact with the mold walls, it is rapidly cooled and the viscosity is increased. The material that flows through behind that viscous plastic pushes the viscous plastic further, leaving scrape marks on the surface of the finished product.
Remedies:
@Increase mold and melt temperatures.
@Increase the size of the gate so that the injection speed becomes slower.
@Optimize gate design to ensure adequate contact between the molten plastic and the mold.
5. Warp (Warping, Warpage)
Plastic Part Warp (Warping, Warpage)
Description:
The molded component is twisted, uneven, or bent shape where one was not intended. Warping is usually caused by non-uniform cooling of the mold material. Different cooling rates in different parts of the mold cause the plastic to cool differently, thus creating internal stresses. These stresses, when released, lead to warping.
Solutions:
@Ensure that the cooling time is sufficiently long and that it is slow enough to avoid the development of residual stresses being locked into the part.
@Design the mold with uniform wall thickness and so that the plastic flows in a single direction.
@Select plastic materials that are less likely to shrink and deform. Semi-crystalline materials are generally more prone to warping.
Description:
The molded component is twisted, uneven, or bent shape where one was not intended. Warping is usually caused by non-uniform cooling of the mold material. Different cooling rates in different parts of the mold cause the plastic to cool differently, thus creating internal stresses. These stresses, when released, lead to warping.
Solutions:
@Ensure that the cooling time is sufficiently long and that it is slow enough to avoid the development of residual stresses being locked into the part.
@Design the mold with uniform wall thickness and so that the plastic flows in a single direction.
@Select plastic materials that are less likely to shrink and deform. Semi-crystalline materials are generally more prone to warping.
