What is a precision injection molding
Precision injection molding
generally refers to a process that requires high accuracy and surface quality
of molded products. Some people also believe that precision injection molding
refers to an injection molding process that has a dimensional accuracy of 0.01
to 0.001 mm. With the rapid development of medical, communications, automotive and
other industries, people's requirements for the accuracy and height of plastic
products are increasing day by day. Traditional plastic molding processes have
been difficult to meet the current high standards. At the same time, injection
molding is one of the most important plastic molding methods. First, as a
result, precision injection molding technology is receiving more and more
attention from people. Therefore, precision injection molding technology
continues to advance, and new technologies continue to emerge.
Precision injection molding
requires that the product not only has high dimensional accuracy, minimal
warping deformation, excellent transfer characteristics, but also excellent
optical performance, etc., so it has an excellent performance on injection molding
machines, injection molds, molding processes, and raw materials. And formula
are always special requirements, many factors affect precision injection
molding.
What are the factors that
affect precision injection molding?
Generally, PS, ABS, AS, PMMA, PC,
PPO, PSU can be used to form products with level 3 and 4 accuracies; PA series
can be used to form products with level 4 accuracy; and POM, PP, PE, TPE, etc.
are not suitable for forming level 4 or higher Precision products.
In addition, due to the low shrinkage
and high dimensional stability of inorganic-filled or glass-reinforced
plastics, they are often used to form precision products. Process
characteristics of precision injection molding are mainly high injection pressure, fast injection
speed, and precise temperature control.
(1) High injection pressure the test proves that for different plastic varieties, shapes, and sizes, the pressure required for precision injection molding should be 180-250MPa (the
injection pressure used for ordinary injection molding is generally 40-200MPa),
in some special cases, the requirements are higher. The highest has reached
about 450MPa.
(2) Fast injection speed The
size of the injection speed obviously affects the size of the product, and more
importantly, it can reduce the dimensional tolerance of the product. In order
to improve the accuracy of injection molded parts, especially for the molding
of products with complex shapes, variable-speed injection must be developed,
that is, the injection speed is changed, and the change rule is determined by
the structural shape of the part and the properties of the plastic.
(3) Temperature control must be
precise. The temperature has a great influence on the molding quality of the product
and is one of the three major process conditions for injection molding. For
precision injection molding, there are both temperature problems and
temperature control accuracy issues. In the process of precision injection
molding, if the temperature is not accurately controlled, the fluidity of the
plastic melt and the molding performance and shrinkage of the product will not
be stable, so the accuracy of the product cannot be guaranteed.
From this perspective, when
precision injection molding is used, the temperature range must be strictly
controlled for both the barrel and the nozzle and the injection mold.
For example, during precision injection
molding, PID controllers are used for the temperature at the barrel and nozzle,
and the temperature range is controlled within 1 ° C. For ordinary injection
molding machines, the temperature can reach 20 ° C to 300 ° C. In order to
ensure the accuracy of the product during injection molding production, in
addition to strictly controlling the temperature of the barrel, nozzle and
mold, attention must also be paid to the impact of the ambient temperature on
the accuracy of the product after demolding.
