With development of science and technology ,home appliances become diversified, meanwhile, they are developing towards integration, miniaturization, and intelligence.
In
context of home appliance market becoming more mature and over-performance,
consumers not only pay attention to performance of home appliances, but
also put forward higher requirements for appearance of product design. Shells
of household appliances are mainly divided into two categories: plastic
materials and metal materials. Due to advantages of plastic materials,
such as good plasticity, strong melt fluidity, simple manufacturing process,
and low cost, materials of parts of household appliances are mostly plastic. Common
injection molding materials include polypropylene PP, polycarbonate PC,
polystyrene PS, acrylonitrile-butadiene-styrene triblock copolymer resin ABS.
Molding process of plastic parts includes blow molding, extrusion, injection
molding, etc., among which injection molding is the most widely used molding
technology.
Design points of injection project for household appliances,professional home appliance mould maker will pay attention to:
1. Wall thickness design
Wall thickness of a plastic part is mainly
determined by its external dimensions and materials, but when designing plastic
products, uniform wall thickness is primary principle. Uneven wall thickness
can cause defects in appearance of plastic parts, such as shrinkage,
depression, deformation, and even internal stress, resulting in appearance
cracks.
If wall thickness is too thin, it will increase
flow resistance of molten plastic, hinder flow of material in cavity, finally
make it difficult to fill material, and plastic parts will have unfilled and
poor strength.
Of course, the thicker wall thickness is not the
better, the thicker wall thickness, product is prone to bubbles, shrinkage,
depression, deformation and other appearance defects, the thicker product, the
heavier its weight, resulting in an increase in cost of entire product. In
addition, the thicker wall thickness of product, the longer molding time,
mainly because pressure holding and cooling time during molding become longer,
resulting in low production efficiency. However, sometimes due to strength of
product, local wall thickness will be thicker. At this time, it is necessary to
make a gradual transition between thick and thin to avoid sharp changes or
sudden changes in thickness.
2. Design of fillet and draft angle
Stress at sharp corners of injection molded case
is relatively concentrated, and brittle failure is likely to occur in plastic
sharp corners. Eliminating sharp corners of product can reduce stress
concentration and increase strength of reinforcing ribs of plastic product,
thereby enhancing product's ability to resist external impact.
Therefore, in the appearance and structure design
of home appliances, outer arc corner should be increased as much as possible.
Of course, a too large rounded transition will produce a shrinkage effect,
especially arc at the corners of raised column roots and ribs. Under normal
circumstances, it is more reasonable to control arc size range between
0.3mm-0.8mm.
Drafting is for smoother demolding of plastic
parts during mold production. Generally, draft angle of a plastic part is
determined by multiple factors such as size of plastic part, wall thickness,
shrinkage, and surface roughness of mold cavity. Because plastic parts in mold
cavity will shrink continuously, it will be difficult to take out plastic parts
if there are design defects in draft angle. Forcible removal will also increase
the damage rate, such as napping and scratching. According to different types
of plastics and structure of plastic parts, demoulding angle should be
controlled between 20'~1°30'.
3. Reinforcing rib design
Reinforcing ribs can increase structural strength
of plastic part, reduce probability of warping deformation, plastic
consumption, product weight, and cost during production process without
increasing wall thickness of plastic part. In design of ribs, position of
ribs should be strictly controlled, not too high, not too small, and evenly
distributed as much as possible to avoid cold shrinkage of thick rib bottom.
Try to keep consistency of rib distribution direction and melt filling
direction as much as possible, which is more helpful for opening and closing of
injection mold. Reinforcement rib adopts arc transition method, no parts can be
arranged on reinforcement rib, so as to avoid excessive stress concentration.
Reinforcing ribs are usually about 50% to 70% of wall thickness of plastic part.
For this reason, we usually round corners at the bottom of ribs. Purpose is to
improve fluidity of melt and improve stress concentration. Value of R angle is
generally 1/8 of wall thickness.
In summary, structural design of plastic shell of
home appliances must pay attention to design details. Under conditions of
ensuring appearance, mechanical properties, and cost of shell, optimal design
plan can be selected, design work can be completed more quickly with the help
of computer design software to ensure design quality. At the same
time, it is also necessary to adopt corresponding solutions to quality problems
of injection molded case to ensure design quality of injection molded case. Of
course, in actual design, a reasonable choice must still be made based on
specific design schemes and design requirements.
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