Setting of technical parameters of injection molding machine molding process

Time:2021-05-24 11:39:29 / Popularity: / Source:

technical parameters of injection molding machine molding process 

Setting of injection molding pressure parameters

During injection, in order to overcome flow resistance of molten rubber through nozzle, gate and mold cavity, injection screw must exert sufficient pressure on molten rubber to complete injection. Injection molding machine is mainly composed of injection molding and clamping. Pressure parameters such as injection pressure and clamping pressure (clamping force) are important technical parameters of injection molding. Injection molding pressure parameters include injection pressure, clamping pressure, holding pressure, back pressure, other operating pressures, etc. Specific pressure parameters are as follows:

1. Injection pressure

Injection pressure is the heaviest injection molding pressure parameter. It has a decisive effect on fluidity of molten rubber and filling of mold cavity. It also has a direct impact on dimensional accuracy and quality of injection molded products. Injection pressure parameters are set according to different models.
Among common models, there are generally one, two, and three injection pressures. In specific production, pressure parameters should be reasonably selected and set according to plastic raw materials and specific molded product structure.

2. Setting of clamping pressure parameters

Clamping pressure is set from beginning of low-pressure clamping, after high-pressure clamping, until end of clamping. Clamping action is divided into three stages. At the beginning of clamping, pressure parameters required for rapid movement of mold plate are set to save cycle time and improve efficiency.
When clamping action is about to end, in order to protect mold, remove inertial impact, and reduce clamping pressure parameter. When mold is completely closed, in order to achieve preset clamping force, increase setting value of clamping pressure parameter.

3. Setting of holding pressure

Pressure holding is to continue to compact melted rubber material in horizontal cavity after injection is completed, to feed gaps that occur when product in mold cavity is cooled and molded, and to increase density of product. Holding pressure ensures that cavity pressure is constant until gate is solidified.
Holding time is often set to control holding pressure. Holding pressure determines parameter size of feeding displacement, determines weight performance of product quality such as consistency, uniformity, and compactness, which is of great significance for improving product quality and production efficiency. General principle for setting holding pressure parameters is that holding pressure should be slightly less than filling force, and gate holding time should be longer than curing time.

4. Setting of back pressure parameters

Back pressure is generated during plasticization and metering process of plastic raw material in melt barrel. At the top of screw and front end of melt, pressure of molten rubber when screw rotates back is often called plasticizing pressure. Back pressure female screw retreats too fast to ensure uniformity and fineness of plasticization process.
Properly setting back pressure parameters can increase internal stress of molten rubber, improve uniformity and mixing effect, and improve plasticizing ability of injection molding.

Setting of injection molding flow parameters

Flow parameters include injection speed, melt speed, mold opening speed, mold clamping speed, etc.

1. Injection speed

Injection speed has a direct effect on flow properties of molten rubber, molecular arrangement direction and surface state of plastic products. Injection speed promotes flow of molten rubber, generates a uniform shear force between adjacent flowing layers, and stably drives molten rubber to fill mold, which has a significant impact on product quality and accuracy of injection molded products. Injection speed and injection pressure complement each other and are used in conjunction.
Setting of injection speed is generally from the first stage of injection, after second stage of injection ~~~~ until end of injection. Size of injection speed is also determined by combining characteristics of plastic raw materials, shape, size, precision and other comprehensive parameters of injection molding mold design. Injection speed will affect quality and quality of molded product.

2. Mold clamping and mold opening speed

Parameter setting of mold clamping and mold opening speed is basically same as pressure parameter setting. For example, there are three stages of mold opening speed. In the first stage, in order to reduce mechanical vibration, moving mold plate is required to move slowly at the beginning of mold opening. This is because injection molded product is in cavity. If mold is opened quickly, plastic part may be damaged, too fast mold opening can also produce huge noise;
In second stage of mold opening, in order to shorten cycle time, movable mold plate moves quickly to improve efficiency of machine; in third stage, when movable mold plate approaches end position of mold opening, in order to reduce inertial impact, mold opening speed is slowed down. Combining various factors, stability, speed, and efficiency are purpose of speed parameter setting.

Setting of injection molding temperature parameters

Injection molding temperature parameter is core content of injection molding process, directly related to quality of injection molded product, affects plasticization flow and setting of time parameters of each process of molded product. General temperature parameters mainly include heating temperature of melt, nozzle temperature, mold temperature, material temperature and oil temperature.

1. Temperature setting of glue cylinder

Injection molding is to heat plastic, evenly plasticize granular material into a molten rubber in a melt cylinder to ensure that molten rubber is filled smoothly. Temperature of melt cylinder generally rises gradually from hopper mouth to nozzle. Because plastic is gradually plasticized in melt cylinder.
Frictional heat generated by shearing effect of screw groove directly affects temperature, so temperature parameter setting is carried out in stages. Usually glue cylinder is divided into front, middle and back heating sections, required parameters are set respectively. Temperature of molten rubber is generally higher than flow temperature of plastic and melting point temperature of plastic, lower than decomposition temperature of plastic.
In actual production, it is often determined by experience or according to situation of injection molded products. If temperature of engineering plastics is higher, temperature of melt cylinder can be set higher to make plastics fully plasticized.

2. Nozzle temperature parameter setting

Nozzle is hub that connects mold cavity gate, runner mouth and pouring mouth in melt cylinder. Nozzle temperature setting is reasonable, flow performance of molten rubber is suitable, and it is easy to fill mold. At the same time, properties of plastic product such as welding strength and surface gloss can be improved.
If temperature of nozzle is too low, it will happen that cold material will block nozzle or gate of pouring system, runner mouth, etc., production cannot be carried out normally. Cold material may also cause product to have cold material spots, which affects quality of plastic product; If nozzle temperature is too high, it will cause over-practicing decomposition of molten rubber, resulting in a decrease in physical and mechanical properties of plastic products. Temperature setting of nozzle is generally performed to set temperature to fully maintain constant temperature of nozzle.

3. Setting of mold temperature parameters

Mold temperature generally refers to temperature of contact surface between inner wall of transverse cavity and plastic product. Mold temperature has a great influence on appearance quality and performance of plastic products processed by precision injection molding. Setting of mold temperature parameters is often determined by size and structure of plastic product, characteristics of plastic material, and process conditions of plastic product.
Setting of mold temperature is cooling for molten rubber. Controlling mold temperature can cool plastic molded product and provide conditions for smooth demolding; controlling mold temperature can make temperature of each part of mold cavity uniform, so that degree of heat dissipation of products in cavity is consistent to avoid degradation of product performance due to internal stress and ensure product quality.

4. Material temperature and oil temperature

Plastic raw materials need to be processed before injection molding. Because raw materials will absorb moisture in atmosphere during storage and transportation.

Setting of injection molding time parameters

Injection molding time parameter is an important parameter to ensure normal production. It directly affects labor production efficiency and equipment utilization. Usually, time required to complete one injection molding is called molding cycle. Molding time includes injection time, cooling time, low pressure clamping time, ejector time, cycle time, melting time, mold opening time, blowing time, etc.

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