I. warpage refers to the shape of the
injection molded article deviates from the shape of the mold cavity, it is one
of the defects of plastic products common. Warpage occurs because many
parameters alone are often powerless to solve. Combined with relevant
information and practical experience, the following factors affecting the
injection-molded articles warpage brief analysis.
Second, the structure of the impact of the
injection mold warpage of. In molds, plastic deformation of the main factors
affecting the gating system, cooling system and ejector system.
1. Gating system
Injection mold gate location, gate number
and form will affect the plastic in the mold cavity filling state, causing
plastic deformation. The longer the distance the flow, the greater the internal
stress between the frozen layer and the central layer consists of flow-induced
flow and feeding; the other hand, the shorter flow distance, the shorter the
article flow from the gate to the end of the flow of time, freeze time filling
layer thickness decreases, reduce internal stress, warpage will therefore
greatly reduced. Some flat shaping parts, use only a center gate, due to
shrinkage in the diameter direction is larger than the shrinkage in the
circumferential direction, molded plastic parts will produce distortion; if the
switch multiple-point gate or a film type gate, can effectively prevent
warpage. When molded using point gate, also due to the plastic shrink
anisotropy, gate location, number of all have a great influence on the degree
of deformation of plastic parts. In addition, the use of multiple gates also
enable the plastic flow ratio (L / t) shortened so that the density of the melt
in the cavity become more uniform, more uniform shrinkage. Also, the entire
plastic parts can be filled in less injection pressure. While smaller injection
pressure can be reduced tendency of molecular orientation of the plastic,
reducing its
2. Cooling system
In the injection process, the cooling rate
is non-uniform plastic parts will be uneven shrinkage forming plastic parts,
such differences lead to shrinkage leaving a bending moment produced warping
plastic parts. If the mold cavity during injection molding flat shaping parts
(such as mobile phone battery shell) is used, the core temperature difference
is too large, as close to the cold mold cavity surface melt quickly cooled
down, and close to the hot surface of the mold cavity the material layer will
continue to shrink, uneven shrinkage will warp the plastic parts. Therefore, it
should be noted injection mold cooling cavity, core temperature tends to
balance the temperature difference between the two is not too large (in this
case, consider using two mold temperature). In addition to considering the
appearance of the temperature within the plastic tends to balance In addition,
the plastic parts should be considered consistent with the temperature of each
side, that you want to keep the cooling mold cavity, core temperature is
uniform throughout, so that the entire plastic cooling rate balanced, so that
the contraction become more uniform throughout to effectively prevent the
generation of distortion. It is therefore crucial cooling water holes disposed on
the mold. After the wall cavity surface to determine the distance, as far as
possible so that the distance between the small cooling water holes, walls, in
order to ensure uniform temperature. Meanwhile, since the temperature of the
cooling medium increases with the length of the cooling water rises, so that
the mold cavity, core temperature difference along the waterways. Therefore,
the required length of each cooling circuit is less than 2 m waterways. In
large mold cooling circuit should be set several import a loop located near the
exit of another loop. For long shaped Part should be used straight-through
waterways. (And we die mostly based S-type loop ---- is not conducive to
cycling, but also extend the period. Top of the system design has a direct impact
plastic deformation. If the top of the system layout imbalance will result in
ejection force of unbalanced leaving the plastic deformation. Therefore, the
ejection system design should strive to be balanced with the release
resistance. In addition, the cross-sectional area of the ejection lever can not be too small to
prevent the plastic force per unit area is too large
(especially in When the temperature is too high under the premise of the
release) leaving the plastic deformation. jack should be arranged as close to a
large release resistance area. Without prejudice to the quality of plastic
(including requirements, dimensional accuracy and appearance) should When the
jack is provided in order to reduce as much as possible the overall plastic deformation
(in other rams for the top block is the truth). with plastic (such as TPU) to
produce thin-walled plastic parts deep cavity, since the release resistance is
large, The material has a softer, if at all using a single mechanical push-up,
will produce plastic deformation, even top wear caused by folding or produce
scrap plastic parts, such as switching to a multi-element joint or gas (liquid)
pressure and mechanical Top of the combination would be better (will be used
later).
Third, the impact of plastics stage WARPAGE
Plasticizing stage of the glass pellets
into the viscous flow state of melt processes (talked about changes in raw
material plasticized Tristate training). In this process, the temperature of
the polymer in the axial, radial (screw relative terms) the temperature
difference will produce plastic stress; In addition, the injection pressure of
the injection machine, speed and other parameters will greatly affect the
degree of molecular orientation during filling, thereby causing warpage.
Fourth, the plastic filling and cooling
stages influence on warpage molten state under the action of the injection
pressure, filled into the mold cavity and the cavity is cooled, solidified.
This process is the key injection molding. In this process, temperature,
pressure, speed of the three mutual coupling effects, the impact on the quality
and productivity of plastic parts are great. Higher pressures and flow rates
will produce a high shear rate, thereby causing difference in parallel to the
flow direction and perpendicular to the flow direction of molecular
orientation, while producing "freezing effect." "Freezing
effect" will produce frozen stress, internal stress formed plastic parts.
Effect of temperature on warpage is reflected in the following aspects:
(1) plastic parts, lower surface
temperature difference causes thermal stress and deformation;
(2) Plastic temperature difference between
the different regions will cause uneven shrinkage between different regions;
(3) different temperature conditions will
affect the shrinkage of plastic parts.
Fifth, the effect of stripping stage
WARPAGE
Plastic parts from the mold cavity and
allowed to cool to room temperature in the process, mostly glassy polymer.
Stripping force imbalance, launch mechanism movement is not smooth or stripping
the top of the area is easy to make inappropriate product deformation (As
already mentioned). Meanwhile, in the filling and cooling stages
"frozen" stresses within the plastic parts due to loss of external
constraints, it will be released in the "deformed" form, leading to
warpage.
Sixth, the direct cause of the contraction
injection products injection warpage warpage impact on that uneven shrinkage of
plastic parts. If you do not consider the shrinkage of the filling process in
the mold design stage, the geometry of the product design requirements will
vary greatly, resulting in a serious distortion products will be scrapped (ie
problem of shrinkage). In addition to filling stage will cause deformation, the
mold temperature difference between the upper and lower wall will cause
contraction of the upper and lower plastic surface differences, resulting in
warpage. Warpage analysis, the contraction itself is not as important
differences on shrinkage. In the injection molding process, the molten plastic
in the injection mold filling stage because the polymer molecules are arranged
along the flow direction of the plastic shrinkage in the flow direction is
larger than the shrinkage in the vertical direction, leaving the injection produce
warpage (ie each anisotropy). Generally uniform volumetric shrinkage caused
only plastic parts, only uneven shrinkage will cause warpage. Differential
shrinkage of crystalline plastics in the flow direction and the perpendicular
direction than non-crystalline plastics large, and the shrinkage rate than
non-crystalline plastics large, large shrinkage after its crystalline plastic
shrinkage anisotropy effect superimposed result warpage tendency crystalline
plastic parts is much greater than that of non-crystalline plastic.
Seven of the influence of the residual
thermal stress warpage in injection molding process, the residual thermal
stress is an important factor in causing warpage, and have a greater impact on
the quality of injection products. Due to residual thermal stress on warpage is
very complex, not repeat them here.
Eight, influence of warpage insert metal to
put inserts plastic products, due to the shrinkage of plastic than the large
metal, so easily lead to distortion (some even cracking); to reduce this case,
First preheat metal (generally not less than 100 ℃), and then put into
production. IX Conclusion Influence of Injection warpage many factors,
structure, physical properties of plastic materials and heat molding process
conditions and parameters of the mold are different degrees of influence on
warpage articles. Therefore, warpage of injection molding process must consider
these factors.
more information www.cnmoulding.com www.chinamoldmaker.org
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