material handling injection molding precision injection molding - sooperarticles.com

by:Hengju     2019-06-23
Precision Injection Molding---The concept of precision injection molding and the specific requirements of plastic injection molding machine.With the development of information technology and automatic control technology, the market has put forward higher requirements for precision injection molding machines, and the demand is also growing rapidly.There are two indicators for general precision injection molding machines: one is the repeatability error of product size and the other is the repeatability weight error of the product.
Due to the different size and thickness, the former is difficult to compare.The latter represents the degree of aggregation of plastic injection molding machines.The repeated weight error of an ordinary injection molding machine is about 1%, and a better machine can reach 0.
8%, precision injection molding machine is less than 0.5%, called ultra-Precision Machine with error less than 0.3%.Injection pressure of 25 MPa;The injection speed is 300 mm/s;Product Size accuracy 0.
001mm;The standard deviation coefficient (change speed) of product quality is 0.1%;opening ≦ 0.03mm, close 0.The accuracy of the injection position (maintaining the pressure end point) is 0 ‰.03 mm;The force balance of the tie bar is 1%;Pre-The positioning accuracy of plastic is 0.
03mm;≦ 0.
The clamping force is 03mm at zero;≦ 0.
The maximum clamping force is 005mm;The temperature control accuracy of the barrel and screw is 0.5 ℃;In the process of precision injection molding, the machine generally needs a higher injection pressure (250 250), otherwise it is difficult to form.However, it should be noted that the size and thickness of precision injection molding products are relatively small, so not all products have high requirements for clamping force.
On the contrary, if the clamping force is too large, or the four corners are uneven, or unstable, it will lead to uneven molding on the mold, and ultimately affect the quality of the molding product.The precision injection molding process needs to adjust the clamping force reasonably, conveniently and accurately, overcoming the problem of the length and size difference caused by the deformation of the clamping force unit and the unstable clamping force caused by changes in room temperature and mold temperature.The uniformity of plasticization not only affects the molding quality of the product, but also affects the resistance when the molten plastic passes through the gate.
In order to get the uniform effect of adding plastic, special screw and adding plastic process need to be designed.In addition, the barrel temperature should be precisely controlled.In order for the plastic product to maintain a high degree of stability, the injection plastic for each injection cavity must be equal, which means that the screw reset accuracy must be the same when feeding.
However, in fact, the screw reset position cannot be completely unchanged. the larger the screw diameter, the greater the inertia of the system, and the more difficult the position accuracy control.We generally control the screw reset accuracy at 0.
3mm, perfect in 0.
2 mm.
Injection speed is an important indicator of precision injection molding machine, because there is a time difference between the injection from the hot melt plastic to the cavity to complete the injection.During this period, the hot melt plastic begins to cool, and in order for the material in the gate and mold cavity to cool evenly, a high-speed injection should be selected.In order to increase the injection speed, you must configure one or more accumulators that can quickly release energy to shorten the time difference.
For precision injection molding, it is advantageous to increase the original injection speed by more than 3 times, reaching 300 ~ 800 mm/s.Precision injection molding requires a large injection pressure to increase the density of plastic, reduce shrinkage, and ensure the accuracy of the product.However, the injection pressure is not the bigger the better.
if the pressure is too large, it will flash.The injection cycle time should not exceed 0 at optimal injection pressure.05 seconds.Keeping the pressure has a great impact on precision plastics.
To be accurate, keeping the pressure can feed well, reduce plastic deformation and control the accuracy of the product.The stability of the holding pressure determines the molding accuracy, and the fixed screw end position determines the holding effect.For precision injection molding, the mold cavity temperature should be controlled at ± 1 °, and PID control must be used.
But for ultra-This is not enough.
The more advanced method is to use fuzzy control )
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