Plastics Manufacturing SolutionsSince 1989

Injection Molding Basics

P.O. Box 782, 134 Industrial Dr.La Vernia, TX 89121

Phone: (830) 779-2289 Fax: (830) 779-2396

THE INJECTION MOLDING CYCLE

In the following pages we will go through the basics of the injection molding cycle. The various stages of the cycle are carefully considered when analizing part design, tool creation and efficient production of injection molded products.

Any unfamiliar terms used in this guide can be found in the Aire Plastics Injection Molding Glossary of Terms online at: http://www.aireplastics.com/glossary-of-terms/

STEP 1

STEP 1: THE MOLD CLOSES. The Injection Molding cycle timer begins when the mold closes.*

*Note: In some cases, as with the use of robots, the cycle runs “part to part” which means the cycle begins and ends when the robot recieves a new part or the new part touches the conveyor belt.

STEP 2: INJECTION. The heated plastic is injected into the mold. As the melt enters the mold, the displaced air escapes through vents in the injection pins and along the parting line. Runner, gate and vent design are important to insure the mold is properly filled.

STEP 2

STEP 3

STEP 3: COOLING. Once the mold is filled the part is allowed to cool for the exact amount of time needed to harden the material.

Cooling time is dependent on the type of resin used and the thickness of the part.

Each mold is designed with internal cooling lines where refrigerated water is cycled through the mold to maintain a constant temperature.

STEP 4

STEP 4: PLASTICIZING THE RESIN. While the part cools, the barrel screw retracts and draws new plastic resin into the barrel from the material hopper.

The heater bands maintain the needed barrel temperature for the type of resin being used.

STEP 5

STEP 5: EJECTION The mold opens and the ejector rod moves the ejector pins forward.

The part falls and is captured in a bin located below the mold.

STEP 6

STEP 6: REMOVING THE RUNNER AND PACKAGING. Although the injection molding machine’s cycle ends on Step 5, the process continues. Periodically the machine operators, or robots separate the usable parts from the left over runner.

The runner is the pathway that the plastic takes to fill the mold cavity.

In many cases the runners are ground and recycled to reduce costs and environmental impact.

The usable parts are then weighed, counted and packaged for assembly or shipping.

Plastics Manufacturing Solutions

For more information about the many solutions that Aire Plastics offers please visit us at:

http://www.aireplastics.com