In the injection molding process, mainly
due to product defects is
1) molding plastic parts design is not
(2) mold design, manufacturing
unreasonable;
Nature (3) of the plastic itself;
4) the inappropriate choice of molding
process conditions;
(5) injection molding machine model
matching unreasonable. Therefore, to solve the problem of plastic injection
molding bad, we can start from the injection machine, molding conditions and
mold (including product design), plastics and so on. However, the reasons for
seeking to defect from the plastic is very difficult, because the defect molded
parts are often made in front of several reasons why the mutual coupling formed
by the action (see Table 1), it causes the defect depends on the vast project
experience and judgment of the technical staff
Countermeasure
1, the rational design of plastic parts
Design of plastic parts to uniform
thickness, it is because the molding cycle cooling time is never a given
thickness of plastic parts, if a part of the thick, partially affected by the
thickness of the cooling time and extended cycle times, reduce the efficiency
of the molded ; Also, if uneven wall thickness, is caused by uneven shrinkage,
resulting in reduced pit or internal stress, as well as deformation or
cracking. Plastic stripping designed to have a certain slope to ensure the
smooth stripping of plastic parts. Because the internal stress tends to be
concentrated at the intersection of the surface and the surface, i.e., focused
on the corner, in order to reduce distortion in the root fillet can design
stress dispersion, while also improving the fluidity of the plastic, but also
conducive to the release. Sometimes in order to enhance the plastic parts or to
increase the fluidity of plastics, set the ribs, pay attention to the stripping
direction to be provided with a reverse slope.
2. Improved mold design
Gate design is an important and complex
issue, in the form of a direct gate, side gate, submarine gate, gate and other
points. How to choose the actual manufacturing arrangement runner, gate type
and position, mostly by the shape of plastic parts, dimensional accuracy and
appearance requirements and decisions, while its runner-type system is varied.
In order to make the plastic filling process ends at the same time, the gate
and the runner must be balanced. In the injection molding process, the
injection into the mold cavity of the molten plastic temperature is about
200300 ℃, but when removed from the mold cavity after the plastic parts
which cure temperature 60 0C or less, the mold temperature is lowered due to
the cooling water through the heat away, so a reasonable cooling system
directly affects the dimensional accuracy of plastic parts and mechanical
properties. In the actual injection mold exhaust problem must also be
considered, if the injection mold cavity gas can not be discharged smoothly,
will make products bubble, loose, filling dissatisfaction, welding is not
strong, the workpiece surface fat bird, or at the time of the injection due
produced by high-temperature gas is compressed so that the bottom parts of the
charred charring. Common exhaust many ways, for example using an exhaust vent
grooves, with the gap such as exhaust. Set the top of the system should be
considered in order to avoid distortion, bleaching, catching phenomenon.
3, adjusting the injection molding process
For the different types and grades of
plastics, which drying and molding the melt temperature are clearly defined,
and therefore in the development of the molding process, according to the
specific requirements of products used in plastics, to determine its drying and
heating barrel temperature. Pressure is also forming important process
parameters, the pressure into the injection pressure and holding pressure in
two stages. Injection pressure is pushing the screw will melt into the mold
cavity pressure used, packing pressure is nearing completion filling in, inject
the melt is cooled and solidified to complement the products due to volume
shrinkage caused by replenishment process of pressure used, in molding process,
the right choice injection pressure and holding pressure and injection speed,
is the key to the success of the molding process. Currently, most
computer-controlled injection molding machines, injection to the decentralized
approach.
4, the choice of efficient equipment
Selection of the injection molding machine
should consider matching the mold clamping force is necessary to meet the
requirements can not be too large, each injection is not less than the plastic
parts plus runner condensate material weight. Pay attention to regular
maintenance of equipment to ensure the normal operation of the production. IV
Conclusion
Since the injection molding is a complex
process, a lot of factors affecting the molding products, often a result of
improved product defects caused by forming factors, may cause another
previously insignificant factors stand out, make the product the emergence of
new defects. Thus, in the development and adjustment molding process, not only
to build pressure, speed, the right combination of temperature and the right
choice for screw speed, injection pressure screw each position, holding
pressure. Back pressure and cooling time and other issues should be fully
valued. Advanced tooling, efficient equipment and reasonable modern injection
molding process is the production of three elements. Therefore, in addition to
research as a mold designer and mold structure and processing technology, but
also a certain amount of injection molding technology, especially for products
in the molding process common defects and solutions should have a
full
understanding.
In the process of injection molding, there are still many problems. For example
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