Jiuzhi knowledge: single-variation variation of injection molded parts

Product weight stability is the result that every injection molding manufacturer hopes to achieve, and product weight is also an important control parameter in quality management.

The weight stability of injection molded parts is not a sufficient condition for production stability, but it is a necessary condition. If the weight deviation is large, the production stability must be low. Such production is unstable production, or production is not "precise".

High weight stability is an important indicator of precision production. Precision injection molding, although the main body is an injection molding machine, but the precision production is the production of all aspects of the same stable effect, including materials, molds, injection molding machines and peripheral equipment. If other indicators are well controlled, the machine can exert stability. If other parameters are unstable, precision production will certainly not be achieved.

What is the surrounding indicator?

The five control parameters of the injection molding machine---pressure, speed, position, time, and temperature all have an effect on the weight change, and the temperature that affects the weight stability of the product in the case of continuous production without changing parameters.

(1) Temperature and purity of hydraulic oil. The temperature of the hydraulic fluid directly affects the viscosity of the oil, affecting the control pressure and speed, especially when the equipment is not fully closed loop controlled. When the purity is low, it may block the proportional valve flow valves. Therefore, hydraulic oil will affect the weight stability. The main factor affecting the oil temperature is the efficiency of the oil temperature cooler, so pay attention to the hardness and cleanliness of the external circulating water. If the hardness is high and the cleanliness is poor, the efficiency of the cooler must be poor, and the oil temperature rise is inevitable.

(2) The mold temperature, especially the temperature of the cavity surface. This depends on two points, the stability of the molding cycle and the stability of the cooling water, the cooling water flow is large, the cooling effect is good, and the hardness is low, and the water path is not blocked.

(3) Stability of barrel temperature and flow rate. The temperature stability is mainly because the back pressure is reasonable, and there is no excessive shear temperature rise, but generally the back pressure is less than 30 kg and the barrel will not heat up automatically. The stability of the flow is mainly the sealing property, and the small three parts of the screw head are worn. If there is no wear, the flow will be stable.

(4) Other: The drying effect of the material. The cleanliness of the material, if there is foreign matter, the melt flow fluctuation will not be stable.

If all of the above is done, the rest is to look at the precision of the machine. The weight repeatability in precision injection molding is a very important indicator. It is generally considered that “the weight of the ordinary injection molding machine is 1%, and the weight of the precision injection molding machine is repeated. Below 0.5%, the ultra-precision injection molding machine has a weight repeat of less than 0.3%".