Five Important Parameters of Injection Molding Production
Injection molding production is very improtant to our industries, its main advantages: production speed, high efficiency and can realize automation operation, the breed of design and color are much, shape from Jane to numerous, the size from big to small etc, and the precise in dimension and product easy to be upgraded. Injection molding is suitable for mass production with complex shape products and machining fields.
Under a certain temperature, the plastic material is fused completely by the screw, and with high pressure inject into mold cavity, after cooling and curing. This machining method is suitable for mass production of complex parts and also is one of the important machining methods.
Below are five improtant parameter for injection molding production
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Injection pressure
Injection pressure is provided by the hydraulic system of the injection molding system. The hydraulic cylinder pressure is passed injection molding machine screw into the plastic melt. Under the impetus of the plastic melt in the pressure, the injection molding machine nozzle into the mold of the vertical follow channel, mainstream channel, distributary channel to the final molding cavity. This process is known as injection molding production or filling process.
In fact, the pressure exists to overcome resistance in the process of melt flow, or conversely, existing in the process of flow resistance need to offset the pressure of the injection molding machine, to ensure that the filling process smoothly.
Of course, there are many factors that influence the filling pressure of melt. But they’re mainly summarized in three categories:
- Material factor, such as: the types of the material and viscosity etc.
- Structural factor, such as: the type of casting system, number and location, the shape of molding cavity and the thickness of the parts.
- The forming process elements.
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Injection time
Injection time refers to the time required for the plastic melt filling the cavity, not including the auxiliary time of mold opening and closing. Although the injection time is very short, and the influence on the molding cycle is very small. But the adjustment of injection time has a great effect on the pressure control of gate, runner and cavity. Reasonable injection time will help melt ideal filling, and it’s very important for improving the surface quality of products and reducing dimensional tolerance.
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Injection Temperature
Injection temperature is an important factor affection injection pressure. The injection molding machine has 5-6 heatingn sections, each of which has its proper machining temperature. This injection temperature must be controlled within a certain range.
When this temperature is too low, the melt plasticization is bad and affect the final quality of the parts and increase the machining difficulty; when this temperature is too high, the raw material are easily decomposed. In the process of practical injection molding, injection molding temperature are often higher than the cylinder temperature, higher values associated with injection rate and material performance, up to 30 ℃. This is due to the high heat caused by the cutting of the material through the injection port. To avoid this phenomenon, we can through two ways to compensate for this difference in the flow analysis. One is to try to measure the temperature of the molten material in the air injection molding, and the other is to include the nozzle when modeling.
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Keep pressure and time
At the end of the injection molding production, the screw stops rotating and just pushes forward, while the injection molding will enters the pressure protection stage. The nozzle of the injection molding machine is continuously filling the cavity to fill the volume that is empty due to shrinkage. If the cavity is filled, no keep the pressure, it will contract about 25%, especially the tendon is contracted because of shrinkage. So keep pressure and time is crucial to in injection molding process.
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Back Pressure
Back pressure is the pressure that to be overcome when the screw is reversed. High back pressure is advantageous to the pigment dispersion and the melting of the plastic, but it also extend the time of the screw retraction and reduce the length of the plastic fiber, and increase the pressure of injection molding machine, so the back pressure should be lower, generally no more than 20% of the injection pressure.
When plastic foam is injected, the back pressure should be higher than the gas, otherwise the screw will be pushed out. Of course, there are some injection molding machines can program the back pressure to compensate for the shrinking of the screw length during melting, if so, the input heat and cools the temperature will reduce. However, due to this result of this change is difficult to estimate, so it’s not easy to adjust the machine accordingly.
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