Injection molding is the most important one of the methods of plastic molding, precision plastic parts with the right performance increasingly high demand for plastic parts required not only has high dimensional accuracy, low warpage, but also has excellent optical performance. To improve the level of injection molding technology to produce high-precision plastic parts, die design as a basis for an important link must not relax. In precision injection molding mold design, in addition to die design should be considered a general matter, we must also give special consideration to the following matters.

A suitable mold dimensional accuracy
A plastic mold dimensional accuracy, dimensional accuracy and relevance
According to plastic parts plans to develop mold design, mold making and plastic molding process. First of all plastic parts from the mold surface measurements obtained surface size, and then press the mold surface size of production molds get the actual size die and then molding plastic parts from the mold to be. Important among these is how to ensure that the actual sizes of plastic parts surface within the required dimensional tolerances.
3, the appropriate shrinkage
Even if the same resin shrinkage will be different due to a difference forming conditions, precision molding shrinkage rate of change required is small, estimated and actual shrinkage shrinkage no difference as far as possible. Determination of the current shrinkage rate mainly through the collation of previous plastic parts like the actual shrinkage rate of the presumption, but also useful to seek the actual shrinkage of experimental mode, and then amended, designed the production model. However, entirely appropriate for presumed shrinkage is almost impossible, and inevitably to die tryout after the amendment. In order to facilitate mold amendment, the Department of dimensions in the design of concave mold shrinkage should be taking a small value, the design size of convex Department will take a small value of shrinkage, design convex when the shrinkage of the Ministry of size to take large values.
Third, to prevent the contraction rate fluctuations
Precision injection molding in order to determine the size to be ashamed as a system of molds premise. However, even if a certain die size, actual size plastic parts may shrink due to the actual rate varies, so in precision injection molding, shrinkage rate control is very important.
One of the main factors affecting shrinkage
Die size size plastic parts can be obtained with shrinkage rate, so in the mold design to be considered the main factors affecting shrinkage. Affect the shrinkage of the main factors: ① the injection pressure; ② resin temperature; ③ mold temperature; ④ gate cross-sectional area; ⑤ injection time; ⑥ cooling time; ⑦ wall thickness of plastic parts; ⑧ reinforcement content; ⑨ directionality; ⑩ injection speed. However, after the plastic molding is still shrinking, affecting a major factor in shrinkage after molding internal stress, crystallinity, temperature, humidity and so on.
(1) injection pressure. Injection pressure a great impact on the shrinkage rate, injection pressure, contraction rate is small, the actual size of large plastic parts. In a single mold cavity, injection pressure of internal plastic parts of different shapes and different, in the multi-mode cavity, the mold cavity injection pressure are different, the results of the shrinkage cavity is not the same.
(2) die temperature. Whether a non-crystalline or crystalline resin, resin, mold temperature is high, shrinkage rate is high. Precision molding mold temperature must be maintained at a specific temperature, so in the mold design, must pay attention to the cooling circuit design.
(3) The gate cross-sectional area. Gate to change the cross-sectional area will change in shrinkage rate, shrinkage rate of the gate with the larger and smaller size, which is related to the mobility of resin.
(4) The wall thickness of plastic parts. For non-crystalline resin, large wall thickness, shrinkage rate is high, for the crystalline resin, then there is a greater change in wall thickness must be avoided. Multi-mode cavity, if there are differences cavity wall thickness, will also produce differences in shrinkage.
(5) The content of reinforcing material. Glass fiber reinforced resin, glass fiber content the more the smaller the shrinkage rate, the flow direction of the shrinkage rate than the small transverse shrinkage. In order to prevent distortion, warping, but also must consider the gate shape, location and number of effects.
(6) directionality. All resins are present orientation, the orientation of crystalline resin, particularly large, and having different wall thickness and molding conditions are different.
2 to take measures to
(1) ensure flow channel, gate balance. Single-mode multi-gate and multi-cavity mold cavity for filling, the gate to balance. As the resin flow and the flow channel in the flow resistance related to the gate in the balance before taking a good idea to take a balanced flow channel.
(2) The cavity arrangement. In order to shape the conditions set easily, pay attention to cavity arrangement. As the molten resin, the heat into the mold cavity arranged in the general case, the mold temperature distribution in order to the gate as the center of the concentric circles-like, the choice of cavity arrangement, they need to take a balanced flow channel, but also to take in order to irrigate mouth as the center of the concentric circles-like arrangement.
(3) The cooling circuit design. Mold temperature on the shrinkage of great impact, while the cooling time will also have a different temperature. From the heat exchange efficiency point of view, the flow of coolant should be a prime flow, the cooling circuit is best designed to be connected in series baffle plate. Cooling cavity and cores at different heat, heat resistance also varies due to loop structure, import the water temperature in the mold cavity and core-Department has greater differences, therefore, precision molding mold cavity and the cooling circuit should be used cores were designed, and were temperature-controlled machine with temperature control.
4, preventing molding deformation
Shape deformation of the cause is non-uniform contraction, there is internal stress, preventing molding deformation measures are:
(1) select the appropriate number of gates. For example, in the design center cylindrical hole injection mold, you must set the gate in the center. However, in the resin flow direction and the vertical direction there is a big difference in shrinkage rate, there is produced an oval shortcomings. When the center hole with high precision roundness requirements, mold must be designed into three or six gates, but also to note the gate balance. Using the side gate, the three gate will increase the diameter of cylindrical plastic parts, when the outer surface of the gate does not allow signs, the use of multi-point inside the sub-gate can meet the requirements.
(2) The gate shape and location. According to shape of plastic parts adopt the appropriate gate, as part of shaping pieces, using side gate, point gate, spoke after the gate and thin-film gate forming different levels of deformation, which is characterized by thin-film gate can be seen as a long rectangular edge gate, usually across the whole degree of the whole cavity to provide greater mobility area, filling speed and filling time uniform warping deformation is small, especially for large amount of warpage of plastic molding.
5, to prevent the deformation Stripping
Precision plastic parts typically small size, thin wall thickness of plastic parts, and some there are many thin bars. Mold design must take into account the deformation of plastic parts is not the case ejection. For the smaller shrinkage of resin, when the molding pressure is high, should pay attention to plastic parts easy to stay in the mold cavity. With the shrinkage of the resin forming a small gear, the gear part of the cavity design in the top of the best out of the side of the template. Using his putter, the putter should pay attention to the number of non-distortion and maximum pressure position. Core hole gears, in order to parallel the top out top out the side of the template to be installed. For the angular plastic parts, you can use the template top of punching out the top with this template that can prevent the development of deformation.
General Precision Plastic Taper Angle smaller, in order to reduce the ejection force required to mirror machining, grinding direction must be the direction for the pull mode, according to the direction of designing easy Taper grinding block-type core.
6, mold manufacturing error
6.1 processing methods required to determine the appropriate part structure
In order to obtain the desired precision plastic parts size, must have a corresponding die size, while the die size needed to ensure a very high-precision machining. In order to maintain precision mold, wear resistance is higher, which requires hardening. With the grinding and EDM precision machining hardened materials up to 0.01mm or less. Surface grinding machine can not be processed due to be closed with the trough, the choice of "]" _-shape processing, but "]"-shaped intensity difference required to use the enhancements shown in Figure 1.
With EDM machining, we must note that the extreme wear and tear of power larger. Processing of the gear shown in Figure 2, with aluminum wire EDM machining, we should as far as possible the structure designed to link up processing. From the prevention of distortion and reduce grinding in terms of processing time, we must select a small quenching deformation of steel, but also to design the shape of a small quenching deformation. Complex shape, the quenching is not easy uniform, easy to produce quenching distortion.