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How to set the injection speed and pressure?

October 08,2022

As we know from our experience, general simple small products can be set at a high speed and high pressure first, and the products with about 90% integrity can be produced by changing positions. The pressure holding speed is also set at a high speed, and the pressure holding pressure is set at about half or slightly higher than the injection pressure, and the pressure holding time is increased from 1s to 1s, and the time when the product unit weight is stable is selected as the pressure holding time. Back pressure can choose an empirical value according to the machine. Generally, a simple product can be molded at a high speed, but the requirements for molds and equipment are relatively high.

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Generally, based on this, the second or multi-stage process should be adjusted. If the mold is opened without considering the deformation of the product or the exhaust is not done well, it is necessary to adjust the mold temperature and use low-speed and low-pressure processes. The trial mode is a debugging process, and specific problems should be analyzed in detail.
Under normal circumstances, 90% of the product is hit, and then the pressure is increased, so you need to find the switching position on the premise of knowing the measurement of this product. As for the speed, it is determined according to the material of the product. ABS material should be low-speed and low-pressure, and nylon material should be high-speed and high-pressure. In short, we should consider the fluidity of the material and the bone position of the product. Of course, it is best to use a mold temperature machine to improve the mold temperature when necessary, so that the fluidity of the material in the mold cavity can be improved.
First, the pressure
The action pressure provided by the pressure system (oil pump) or servo motor of the injection molding machine is mainly used in various action programs, such as injection device, glue melting device, mold unlocking device, ejection device, injection table device, core pulling device, etc. After the relevant parameters are input into the control panel of the injection molding machine, the processor converts them into signals of each program action, thus controlling the pressure required for the execution of each action program.
The setting principle of pressure is: the corresponding strength to overcome the resistance of the action, but the parameter value needs to be adjusted accordingly to match the speed of the action.
Second, the speed
Cooperate with the above pressure to complete the required activity speed (flow rate of hydraulic oil in the system) of each action program. The basic grades of speed are: slow flow 0.1-10, slow flow 11-30, medium speed 31-60 and high speed 61-99.
1. The control of injection rate is applied to different product structures and materials to set the size values. It is easy to confuse people here (engineering/general plastics, crystalline/amorphous plastics, high-temperature/low-temperature plastics, soft/hard plastics), and make a more understandable explanation. Injection rate is a process factor that is difficult to control in injection molding, unlike other process factors, which have standard data for reference (a detailed introduction will be made later)

The numerical setting of glue injection speed mainly follows the following points:

According to the fluidity of materials, soft plastics such as PP, LDPE, TPE, TPR, TPU, PVC, etc. have good fluidity, and their cavity resistance is small when filling. Generally, a lower injection speed can be used to fill the cavity.
Commonly used medium viscosity plastics such as ABS, HIPS, GPPS, POM, PMMA, PC+ABS, Q glue, K glue, HDPE, etc. have a slightly poor fluidity. When the appearance gloss of the product is not high or the meat thickness of the product is moderate (the wall thickness or bone thickness of the product is more than 1.5MM), the injection speed can be filled at a medium speed. On the contrary, the filling speed should be appropriately increased according to the product structure or appearance requirements.
For example, engineering plastics such as PC, PA+GF, PBT+GF, LCP, etc. have poor fluidity, so it is generally necessary to inject glue at a high speed when filling, especially for materials with increased GF (glass fiber). If the glue injection speed is too slow, the floating fibers (silvery surface) on the product surface will be serious.
2. Control of glue melting speed
This parameter is one of the most easily overlooked processes in daily work, because most colleagues think that this process has little influence on molding, and products can be made by adjusting the parameters casually. However, in injection molding, the melting parameter is as important as the injection speed, which can directly affect the melt mixing effect, molding cycle and other important links.
3. Speed control of unlocking die
Setting different parameters for different mold structures, such as adjusting high-speed mold locking before starting low-pressure mold locking and adjusting to fast mold opening after the product leaves the mold cavity, can effectively improve production efficiency.
However, when adjusting the speed of the unlocking die for the die with row position, the fast and slow switching of the unlocking die should be determined according to the height and structure of row position. Due to the complicated structure of special die structure and core-pulling die, a detailed explanation will be made in the following chapters.
4. Control of thimble speed
It depends on the demoulding condition of the product. In principle, it should be as fast as possible on the premise of ensuring that the product does not appear top white, top height or deformation. On the contrary, it is necessary to adjust the parameters appropriately according to the actual situation. Of course; Under normal circumstances, it is better to adjust the jacking speed for the first time at medium and low speed (15%-35%), which can effectively prolong the service life of thimble and thimble cylinder.
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