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Brief Introduction of Injection Molding Process

Posted by: Mu Ju 2021-11-26 Comments Off on Brief Introduction of Injection Molding Process

The injection molding process includes preparation before molding, injection process and post-processing of plastic parts.


Preparations before molding include the inspection of raw material appearance and the determination of technological properties, preheating and drying, cleaning of injection machine barrel, preheating of inserts and selection of release agent when demoulding is difficult. Sometimes it is necessary to preheat the mold.


During molding, powdered or granular materials are fed from the hopper into the high-temperature barrel for melting and plasticizing to become viscous fluid melt, and then injected through the nozzle at a high speed into the closed mold at a lower temperature under the high pressure of the plunger or screw. The melt fills the cavity under pressure and is compacted. After a period of holding pressure, the plunger or screw returns. At this point, the melt may flow back from the cavity to the gating system. After cooling, the mold can be opened and the product can be removed from the mold cavity.


After the plastic is heated and plasticized in the barrel of the injection machine, it enters the mold cavity through the pouring system of the mold. The final cooling process is called the pouring process.


The injection process usually includes feeding, plasticizing, filling, holding, reverse flow, cooling and demoulding.


  1. addition


The powder is added to the hopper of the injection machine.


  1. plasticizing


The plastics are added in the barrel to make it melt from solid particles and have good plasticity. This process is called plasticization.


  1. mold filling


The plasticized melt is pushed to the front of the barrel by the plunger or screw, and is filled with the cavity through the nozzle and mold pouring system. This stage is called filling.


  1. guaranteed pressure



When the melt in the mold is cooled and contracted, the plunger or screw forces the melt in the barrel to replenish the mold continuously, thus forming a complete and compact plastic part. This stage is called packing.


  1. reflux


At the end of packing, the plunger or screw recedes and the pressure in the cavity is relieved. At this time, the melt pressure in the cavity will be higher than that in front of the gate. If the gate has not been frozen, the melt in the cavity will return to the pouring system through the gate. This process is called backflow.


Reverse flow causes plastic parts to produce shrinkage, deformation and loose texture defects. If the gate is frozen when the pressure is over, there will be no backflow phenomenon.


  1. cooling


The cooling process of a plastic part in a mold refers to the whole process from the time when the plastic melt at the gate is completely frozen to the time when the plastic part will be pushed out of the mold cavity. In fact, the cooling process begins with the injection of plastic into the mold cavity, which includes the period from the completion of filling, the beginning of packing to the time before demoulding.


  1. Demolding


When the plastic parts are cooled to a certain temperature, the mold can be opened, and the plastic parts are pushed out of the mold under the action of the pushing mechanism.


The key parameters that determine the molding quality of products are temperature, time, pressure, speed and position.


PTJMould Industrial Company Limited, established in 2010, is a leading injection moulding manufacturer in China. PTJMould specializes in plastic mould production for household appliances, medical equipments, electronic equipments, safety equipments as well as monitoring system.

The company has over 15000 square metres factory. With plastic injection tooling divisions possessing different machinery and expertise, PTJMould offers tools from small and precise mobile phone parts to as big as automotive parts. Our tools are mainly exported to U.S.A., Europe, Japan and UK. PTJMould’s diversification strategy and full service has won compliment from customers all over the world.

Our mission is to provide our customers high quality moulding products and services. We aim to exceed our customers’ expectations of pricing, quality and on-time delivery. To achieve our mission, PTJMould:

  • Commits to continually improve employee skills and efficiency,
  • Provides our employees a clean and safe working environment,
  • Upgrades machine technology and support equipment through a strict maintenance program, and
  • Maintains customers’ tooling to its highest peak of performance

For more about custom manufacturer of plastic molding products,please visit https://www.plastics-moulding.com/


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