Plastic Molding

Plastic Injection molding is a manufacturing process for producing plastic parts by injecting molten raw plastic material into a plastic injection mold. It is typically used when the same plastic part is being created by thousands or even millions of times in succession.

The plastic raw material is fed into the hopper of the plastic injection machine, it will be heated and plasticized in the injection barrel, the molten plastic flow will be injected into the closed mold cavity through the injection nozzle and mold runner system under pressure, and finally, the desired plastic part will be shaped after being cooled.

As the primary molding method for thermoplastic materials, plastic injection molding is able to produce customized plastic parts with complicated structures and accurate dimensions, as well as with metal or non-metal inserts.

The features of the plastic injection molding process are short cycle, high production efficiency, and easy automation. Until now, plastic injection molding is applicable to almost all thermoplastic materials. Some thermosetting plastics with high fluidity can also be molded via this process.

The weaknesses of plastic injection molding include high injection molding equipment price, complicated mold structure, high production cost, and not suitable for small quantity production of a single plastic part.

Injection plastic molding system
The workflow chart of injection molding
The process of plastic injection molding

During the plastic injection molding process, the plastic resin will be firstly fed into the high-temperature injection barrel through a funnel-shaped hopper where they are heated, melted, and plasticized into a sticky molten flow. The reciprocating screw will convey the melt plastic material into a lower temperature closed mold by the injection nozzle at a high speed under the great pushing pressure.

Under the great pressure, the molten plastic will fill the entire cavity and will also be compacted. After that, the reciprocating screw will return after a period of pressure holding.

When the mold opens after cooling and forming, the product will be ejected from the mold cavity.

The main process usually includes the following steps: plastic material feeding, Raw material plasticization, molten material injection, pressure holding, mold cooling, and mold ejection.

Plastic material feeding: Pellets are fed into the hopper.

Raw material plasticization: It is heated in the barrel and turned from solid pellets into a molten flow.

Injection: The plasticized molten flow will be pushed to the forepart of the barrel by the reciprocating screw, and then injected to fill the mold cavity through the injection nozzle and sprue & runner system of the mold.

Pressure holding: When the molten material is shrinking inside the mold due to cooling, the reciprocating screw will continuously force the molten material in the barrel into the mold for replenishment, to ensure that a complete structured and the densely textured product is produced.

Cooling: The in-mold cooling process usually refers to the entire process from the moment the molten material at the gate is fully solidified to the plastic part is ejected from the mold cavity; but actually the cooling step starts the minute the molten plastic flows into the cavity, covering the time period from completion of the injection, pressure holding to the moment before mold release starts.

Mold Ejection: Mold release is allowed when it is cooled to a certain temperature, through which the plastic part is pushed out of the mold by the ejectors.

The key parameters which determine the quality of molding product including:

Mold clamping force
Mold temperature
Injection temperature
Injection pressure
Injection speed
Pressure holding time
Cooling time

Injection Molding Process Capabilities:

Presses range in size from 50 to 3000 tons
Environmentally controlled molding facility with 24 hour operation
Shot sizes up to 76 ounces of plastic
Mold design /build is in same facility for best customer service of part and tool changes
Cavity from one to 96 cavities per mold
Process hot /insulated runner, stack, unscrewing, insert, and cam /hydraulic core pull molds

Injection Molding Raw Material:

Commercial grades of polypropylene, polyethylene, nylon, polystyrene, and ABS
Engineering resins including polycarbonate, polyester, urethane, PVC, acrylic, acetal, PPO, PBT, and TPR
Glass, mineral, foam and Teflon filled materials and Teflon filled materials
High temperature (oil-cooled) molding resins
Protein and starch based thermoplastic resins
All colors are available

Value Added Secondary Operations:

Hot stamping, painting, pad printing and silk screening
Sonic welding and adhesive bonding
Drilling, tapping and secondary CNC machining
Assembly of molded /stamped parts to a finished product
Special packaging for commercial or retail

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