How to define precision injection molding machine chapter 1

                                       How to define precision injection molding machine chapter1 

precision injection molding machine TaiWang brand  is suitable for high quality plastic
products.So,let’s see how to measure or judge a precision injection machine ?
Generally, precision injection molding machine has two indexs: one is repeated deviation of product
size;The another one is repeated weight deviation of product.The former is difficult to compare because
they are different from size and thickness.The latter represents comprehensive level of injection
molding machine.
In fact,the repeated weight error of common one is about 1%,the better one can reach 0.8%, lower than
0.5% is precision machine,lower than 0.3% is super precision machine.As mentioned above, the size accuracy of products is required within 0.01 ~ 0.001mm.

Plentiful precision injection molding machines also are required :
High injection pressure and high injection speed;
The clamping system has sufficient rigidity and locking precision.The locking precision means it has
uniformity, adjustability, stability and repeatability and high precision opening and closing.
Can control pressure, flow, temperature, metering precisely and adopt multistage injection,also ensure
the quality of reproduction .

What are the requirements of precision injection molding ?
1. Characteristics of technical parameters:
injection pressure:
Common injection molding machine: 147 ~ 177Mpa; Precision injection molding machine: 216 ~ 243 Mpa;
Uhv injection molding machine: exceed 243MPa, usually between 243 and 392 MPa.

The advantages of precision injection molding machine :
A. Improve the precision and quality of finished products.
The injection pressure has the most obvious influence on shrinkage rate of product.When the injection
pressure reach 392 MPa, the shrinkage rate of product is near 0.At this time, precision of product is
only effected by mold control or environment.The experiment shows that the injection pressure is from
98 ~ 392 MPa, and the mechanical strength of the parts can be improved 3 ~ 33%.
B. The thickness of precision products can be reduced and the length can be increased.
Take PC as an example, normal machine injection pressure which is 177 Mpa can produce products with
0.8mm thickness, while precision machine injection pressure which is 392 Mpa can make products with
0.45mm thickness or more.
C. Enhance injection pressure ,can fully balance the injection rate.

In order to achieve the rated injection rate, there are two ways: one is to increase the system of
maximum injection pressure ;The second is to modify parameters of injection device or injection system,
including screw parameters;
Injection speed:
The injection speed of precision injection machine is high and the injection speed of precision
hydraulic injection molding machine is required to reach over 200mm/s, and the full electric injection
molding machine can reach above 300mm/.

2. Controling features of precision injection machine:
Repeatable precision (reproducibility) of injection parameters needs high demand and suit multistage
injection feedback control
1. Multi-stage position control;
2. Multi-speed control;
3. Multi-stage pressure maintaining control;
4. Multi-stage backpressure control;
5. Multi-stage screw speed control.

Written by Jerry-Ho


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