Do You Know the Process of Plastic Injection Molding?

The process of trial production of injection molding products generally involves modeling design, plastics and molding equipment choice and mold design. The designer determines the mold structure based on the geometry of the product model, based on his own experience and design principles to draw drawings and mold processing. After the mold is completed, we need to try the mold. However, due to inadequate consideration in some aspects of modeling design or lack of experience, it is difficult to succeed immediately when the mold is tested. 

Injection molding is widely used in the field of industrial manufacturing. However, many people still don't know much about the process of injection molding.

The pressure in the injection molding process includes plasticizing pressure and injection pressure, which directly affect the plasticization of plastics and product quality.

⒈ Plasticizing pressure:

When a screw injection machine is used, the pressure on the top of the screw when the screw rotates and retracts is called plasticizing pressure, also known as back pressure. This pressure can be adjusted by the relief valve in the hydraulic system. In the injection, the size of the plasticizing pressure needs to be changed according to the design of the screw, the quality of the product and the type of plastic. If these conditions and the speed of the screw are unchanged, increasing the plasticizing pressure will strengthen the shear. The effect is to increase the temperature of the melt but it will reduce the efficiency of plasticization, the countercurrent and leakage, and the driving power. In addition, increasing the plasticizing pressure during the plastic injection molding can often make the temperature of the melt uniform, mix the color material uniformly and discharge the gas in the melt. In the operation of the pressure curve in general injection molding, the determination of the plasticizing pressure should be as low as possible under the premise of ensuring good product quality. The specific value varies with the type of plastic used, but it rarely exceeds 20 kg / Cm2.

⒉ Injection pressure:

In the current production, the injection pressure of almost all injection machines is based on the pressure exerted on the plastic by the top of the plunger or screw (converted from the oil pressure). The role of injection pressure in injection molding is to overcome the flow resistance of the plastic from the barrel to the cavity, to give the melt filling rate and to compact the melt.

Injection molding cycle

The time required to complete an injection molding process is called the molding cycle, also known as the molding cycle.  Injection molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, the relevant time in the molding cycle should be shortened as much as possible under the premise of ensuring quality. In the entire molding cycle, the injection time and cooling time are the most important. They have a decisive influence on the quality of the product. The filling time in the injection time is directly inversely proportional to the filling rate. The filling time in production is generally about 3-5 seconds. The dwell time in the injection time is the pressure time on the plastic in the cavity, which accounts for a large proportion of the entire injection time, usually about 20-120 seconds (for thick parts, up to 5-10 minutes). Before the melt is frozen at the gate, the amount of holding time will have an impact on the accuracy of the product size.