Injection molding is a kind of injection and molding method. The advantages of injection molding method are fast production speed, high efficiency, operation can be automated, many varieties, shapes can be from simple to complex, size can be from large to small, and product size is accurate, products are easy to replace, can be shaped into complex parts, injection molding is suitable for mass production and shape complex products and other molding processing fields.
Under a certain temperature, the completely melted plastic material is stirred by a screw pump, injected into the mold cavity with high pressure, and the molding product is obtained after cooling and curing. This method is suitable for mass production of complex parts and is one of the important processing methods
The development of injection molding technology is very rapid, there are many new technologies and processes, such as multi-color injection molding, gas assisted injection molding, micro-injection molding and so on,These technologies can better meet the production needs of complex and high-quality products. At the same time, with the application of computer technology, the simulation and optimization of the injection molding process is becoming more and more common, which can predict the quality of the product and the rationality of the mold design before the actual production, greatly improving the production efficiency and product quality.
Injection molding is a common plastic processing technology. Injecting the molten plastic material into the mold, after cold hardening to obtain the required plastic products. The injection molding process includes raw material preparation, injection molding, cooling and curing, demolding and post-treatment. The following will introduce the injection molding process in detail.
8 stages of the injection molding process
Drying Plastic Granules
The drying temperature of plastic granules is an important step to ensure the quality of plastic products. Different plastic materials have different requirements for drying temperatures. Generally speaking, the drying temperature is too high or too low will affect the performance and processing effect of plastics. The proper drying temperature can remove the moisture and volatile in the plastic granules, and prevent the defects such as bubbles and silver lines during the injection molding process.
Drying temperature and drying time for different plastic granules:
ABS plastic : The drying temperature is 80~85, the drying time is 2~4 hours.
HIPS plastic : Generally do not need to dry, but if the degraded material is added, the drying temperature is 70~75, and the drying time is 1.5~2 hours.
PMMA (Acrylic) : The drying temperature is 70~80, the drying time is 2~4 hours.
PC plastic : The drying temperature is 120~130, the drying time is 2~4 hours.
PPO plastic : The drying temperature of adding degraded material is 100~120, and the drying time is 2~3 hours.
The drying temperature is 80±5, the drying time is 2~3 hours.
PA (nylon) : drying temperature is 90~100, drying time is more than 4 hours.
PP plastic : Generally do not need to dry.
The proper drying temperature can remove the moisture and volatiles in the plastic, and prevent the defects such as bubbles and silver lines during the injection molding process. If the drying temperature is too high, it may lead to the thermal degradation of the plastic, but the melting viscosity increases, the injection molding is more difficult, and the mechanical properties of the parts are reduced. Therefore, choosing the right drying temperature is crucial to ensure the quality of injection molded products.
Loading into molding machine
During the injection molding process, the first step is to put the plastic pellets into the hopper of the injection molding machine, after the plastic pellets are heated and melted and then to be a molten condition of the material and injected into the mold. In this step, it is necessary to adjust the suitable temperature, pressure and other parameters.
Adjustment parameter
According to the actual situation to adjust the injection pressure, nozzle temperature, melting temperature and pressure, cycle time and cooling system and other parameters to achieve the best molding effect and quality.
Ejection
During the injection stage of the injection molding process, the melted plastic flow to the injection cylinder and is pushed by the screw pump of the injection molding machine into the injection outlet of the mold to form the outline of the product. In this process, it is necessary to control the injection speed and volume to ensure the quality of the product.
Pressure holding
In the pressure holding stage of the injection molding process, the plastic in the injection cylinder begins to solidify, keep same injection pressure at this time, make the plastic continues to fill the mold cavity to ensure the smooth surface of the product and the dimensional accuracy.
Cooling
In the cooling stage of the injection molding process, the plastic in the mold begins to cool and solidify, and the cooling time needs to be controlled at this time to ensure product quality, appearance and other needs.
Opening mold
The last step in the injection molding process is the opening mold, need to move the mold while the workbench is opened, and the plastic product is ejected from the mold and sent out for post processing. This step needs to control the strength and speed of the mold opening to avoid deformation or damage of the product.
In summary, the injection molding process of the injection molding machine needs to go through a number of steps, each step requires precise control and parameter adjustment to ensure the quality and efficiency of plastic molding products.
Operating rules for injection molding
Our friends who struggle in the production line know that injection molding processing has some operating rules, to know that safety is productivity.
Injection molding machine is a complex machine with high temperature, high pressure and fast operation. The operator is often negligent for a moment, resulting in irreparable physical harm and lifelong regret. Every step of the operation of the injection molding machine is risky, especially when the mold is opened and locked. In order to avoid danger, in the injection molding process, the operator must pay attention to the following details of safe operation:
- The injection molding factory keeps the injection molding machine and its surrounding environment clean at any time, the space around the injection molding machine should be kept unobstructed as far as possible, and after adding lubricating oil or pressure oil, the leaking oil should be wiped clean as soon as possible. Before turning on the electric heating, please clean the debris (such as plastic particles) on the hopper to avoid fire. If the machine is not repaired or necessary, the heat insulation shield on the hopper shall not be removed.
- Before injection, check whether the mold locking can be terminated during operation by pressing the emergency button or opening the safety door.
- When the injection table moves forward, it is not allowed to remove the deep glue leaking out of the injection nozzle by hand, in order to avoid the hand being caught between the injection table and the mold, causing body injury. When cleaning the cylinder, adjust the nozzle temperature to a suitable high temperature to keep the nozzle unobstructed, and then use a lower injection pressure and speed to remove the residual plastic material in the cylinder. When cleaning, don’t directly contact the newly injected plastic by hand, in order to prevent burning hand.
- Avoid heat-sensitive and corrosive plastics are stored in the hopper for too long, and strictly follow the closing and cleaning methods provided by the plastic supplier. When replacing the plastic, it is necessary to ensure that the new and old plastics will not produce chemical reactions after mixing (such as POM and PVC have been mixed and heated, will produce toxic gases); Otherwise, it is necessary to use other plastic material to clean the residue in hopper.
- Do not remove safety doors or safety switches to increase production speed. Before injection molding, check if the mold is firmly installed on the moving plate and head plate of the injection molding machine. Notice if the ground wire and other wires of the injection molding machine are firmly connected.
- When installing the mold, the lifting ring must be completely screwed into the mold lifting hole before lifting. After the mold is installed, the length of the safety rod of the injection molding machine should be adjusted according to the size of the mold, so that when the safety door is opened, the machine safety block (mechanical lock) can fall down to prevent the injection molding machine to lock the mold.
- In the normal injection molding process, it is strictly prohibited that the operator to remove the injection parts from top or bottom of the injection molding machine without opening the safety door. When the mold is repaired or temporarily stopped, the oil pump motor of the injection molding machine should be closed in time.
- Injection molding can be operated by one person, do not allow multiple operation. Do not allow one person to operate the control panel while the other person adjusts the mold or does other operations.
Every operator of the injection molding factory should keep in mind the above provisions to ensure production safety and creating benefits.
