First, what is thin-walled injection molding
Thin-wall injection molding technology is also known as thin-wall plastic injection molding technology. There are three types of definitions:
First, the ratio of the flow length to the thickness L / T, i.e., the ratio of the flow length L from the melt to the mold to the fuselage must be filled, and the ratio of the corresponding average wall thickness T of 100 or more is Thin wall injection;
Second: the thickness of the plastic parts is less than 1 mm, while the projection area of ​​plastic parts in the 50 c square meters above the injection molding method;
Thirdly, the wall thickness of the molded piece is less than 1 mm (or 1.5 mm), or t / d (plastic part thickness t, plastic piece diameter d, for disc type plastic parts) in 0.05 below the injection molding is defined as thin Wall injection molding.
It can be seen, the thin-walled injection molding definition of the critical value will also change, it should be a relative concept.
Second, the choice of raw materials
The requirements for raw materials: large flow length, high impact strength, high heat distortion temperature, high thermal stability, low directivity and good dimensional stability; also consider the low temperature impact of plastic raw materials, fire resistance, mechanical assembly and appearance Quality and so on.
Commonly used thin-walled injection molding materials are: polycarbonate (PC), propylene-butadiene-styrene (ABS), PC / ABS blends and PA6. As the wall thickness decreases, it is necessary to use plastic with better physical properties to maintain the strength of the product.
Third, the common defects analysis
Although the thinning of plastic parts has many advantages, it reduces the formability of the plastic parts so that these thin-walled plastic parts can not be formed by conventional injection molding methods. In the formation of thin-walled plastic parts, there are the following common problems:
1, short shot
Short shot is due to the mold cavity filling is not entirely caused by incomplete plastic parts of the quality defects, that is, before the completion of filling the melt has been condensed.
Conventional injection molding of the filling process and the cooling process is intertwined. When the polymer melt flows, the melt front encounters a relatively low temperature of the core surface or cavity wall, it will form a layer of condensation on its surface. The melt flows in the condensate layer, and as the thickness of the condensate increases, the actual cavity flow path becomes narrower and the thickness of the condensate layer has a significant effect on the flow of the polymer. Because the conventional injection molding plastic parts of the thickness of thick, so at this time the impact of the injection layer on the injection molding is not great. However, in the thin-walled injection molding, when the thickness of the condensate layer and the thickness of the plastic parts with the thickness of the thinning gradually increased, the impact is great. In particular, the size of the two can be more prominent when compared to each other.
When the thickness of the plastic parts decreases, the effect of the condensate on the flow will increase exponentially, which also shows that the condensation layer in the thin-walled injection molding in the great impact. If injection molding is required only, the injection molding machine is required to have a high injection rate so that the rate of filling the cavity of the plastic melt exceeds the rate of growth of the condensate (or the growth rate of the condensate is slowed down) so that the flow rate Close the filling before the completion of the action, the injection molding of thin-walled plastic parts.
When the flow length of 300mm, plastic wall thickness of 3.0 mm, this time L / T is 100, with conventional injection molding technology is easy to achieve; but when the plastic wall thickness dropped to 1.0mm below, this was easy The ratio of the length to thickness (100) becomes very difficult to achieve.
2, warping deformation
Warping deformation is uneven due to internal stress caused by plastic parts defects. The reason for the warping deformation is uneven shrinkage, uneven orientation and uneven cooling.
 Improve the method: you can balance the cooling system, adjust the cooling time, holding pressure and pressure time and other measures to improve the plastic parts of the warping deformation defects.
3, welding line
The weld line is the boundary formed by the fusion of two or more melt flows in the cavity. In the welding line is easy to produce stress concentration, weaken the mechanical strength of plastic parts, plastic parts, especially thin-walled plastic parts of the mechanical properties is particularly unfavorable, by the external force after the plastic parts are very easy to crack at the weld line.
 Improve the method: in the design can reduce the number of gates or change the gate position to reduce or change the location of the weld line to meet the design requirements of plastic parts.
4, lack of material
Finished small parts, corners can not be fully formed, because the mold is not in place or poor exhaust, forming due to injection dose or pressure is not enough and other reasons, resulting in design defects (lack of meat).
Improve the method: can correct the lack of mold at the mold, take or improve the exhaust measures, plus flesh, gate improvement (increase the gate, increase the gate), increase the injection dose, increase the injection pressure and other measures to improve.
5, shrink
Often occurs in the molded product wall thickness or uneven meat, due to hot melt plastic cooling or curing shrinkage caused by different. Such as the back of the ribs, the edge of the side wall, BOSS column on the back of stealing meat, but at least 2/3 of the flesh.
  Improve the method: through the thickening of the runner, increase the gate, plus exhaust, raise the material temperature, increase the injection pressure, to extend the pressure time and other measures to improve.
6, the surface image
Often occurs in the stolen BOSS column, or the back of the tendons, or because the core, thimble design is too high stress caused by reduced.
Improve the method: by correcting the core, thimble, the mother face sandblasting and other ways to deal with the use of reducing the mold surface brightness, reduce the injection speed, reduce the injection pressure and so on.
7, gas pattern
Occurred in the gate, and more because the mold temperature is not high, the injection speed, the pressure is too high, improper setting of the gate, pouring plastic encountered spoiler structure.
Improve the method: through the change into the gate, runner lighting, runner cold area increased, into the gate to increase the surface plus bite flower (by adjusting the machine or repair mode can also be combined), increase the mold Temperature, reduce the injection speed, reduce the injection pressure, etc. to solve.
8, combined line
Occurs in the intersection of two streams, such as the two gate of the material flow, bypass the core of the material flow is due to the temperature drop, poor exhaust caused.
 Improve the method: through the change into the gate, plus cold material wells, open exhaust slot or public mold surface bite flowers, etc., can also raise the material temperature, increase mold temperature and so on.
9, burr
Often the combination of male and female mold, due to poor mold caused by, or mold surface corner improper processing, molding often due to clamping force is not enough, temperature, pressure is too high.
 Improve the method: can mold correction, re-mold, increase the clamping force, reduce the material temperature, reduce the injection pressure, reduce the pressure time, reduce the pressure and so on.
10, deformation
Slender parts, large area of ​​thin-walled parts, or structural asymmetry of the larger finished product due to uneven cooling stress or erection of the force caused by different.
Improve the method: can be modified thimble, set the tension from the pull of the pin, etc., if necessary, plus the bimono mold deformation, adjust the mold temperature and reduce the pressure, etc., small pieces of deformation mainly by the pressure size and Time, large deformation of the adjustment generally rely on mold temperature.
11, the surface is dirty
Is due to the rough surface of the mold.
Improve the method: for the PC material, sometimes due to mold temperature is too high, mold surface residual glue, grease, need to promptly clean up the mold surface, lighting treatment, reduce mold temperature and so on.
12, pull white
Easy to occur in the thin-walled corner of the molded product or the thin-walled RIB root, due to poor force caused by stripping, thimble set improper or draft angle is not enough.
Improve the method: increase the corner of the R angle, increase the stripping angle, increase the thimble or increase its cross-sectional area, mold surface lighting, thimble or diagonal flash, reduce the rate of fire, reduce the injection pressure, reduce the pressure And time.
13, drawing die
Manifested as bad mold or mold injury, pull flowers. Mainly due to draft angle is not enough or mold surface roughness, forming conditions are also affected.
Improve the method: to increase the draft angle, mold surface lighting, sticky mother mold surface can increase or change the pull pin, horn feeding attention horn diameter, the public mold plus bite, reduce the injection pressure, reduce the pressure and Time and so on.
14, stomata
Transparent finished PC material is easy to form. As the injection process of the gas is not exhausted, improper mold design or improper molding conditions have an impact.
Improve the method: increase the exhaust, change the gate (into the gate to increase), PC material flow path must be light, strict drying conditions, increase the injection pressure, reduce the injection speed.
15, broken poor
Occurs in the male and female modules, sliders, diagonal, and other joints, the performance of the level of the joint surface is uneven, due to improper mold or die itself.
 Improve the method: modify the mold, or re-mold.
16, size tolerance
Mold the problem itself, or improper molding conditions caused by improper molding shrinkage.
Improved method: usually change the holding time, injection pressure (the second paragraph) on the size of the greatest impact. For example: to improve the pressure, to improve the role of pressure filling can significantly increase the size, reduce the mold temperature can also increase the gate or increase the gate can improve the regulation effect.