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Injection Molding Basics
Date:2019-11-26 11:40:50

Most solid plastic materials are produced by a process called injection molding. During the 

process of plastic injection molding, plastic resin pellets are heated until they melt. The 

melted liquid plastic is introduced, under pressure (injected), into a mold. The mold may 

be made up of any metal such as steel or aluminum. The molten form is then allowed to cool 

down and set into a solid form. The plastic material thus formed is then retrieved out of 

the mold.

The injection-molding process has been around for nearly 150 years. Reciprocating screw 

injection molding machines were introduced in the 1960s and are still used today. The 

injection molding machine comprises an injection unit, where material is prepared for 

injection into the mold, and a clamping unit, where the injected plastic is captured in the 

mold under conditions of temperature and pressure to form the finished product.

The actual process of plastic molding is just an expansion of this basic process. The 

plastic goes into a barrel or chamber by gravity or is force-fed. As it moves down, the 

increasing temperature melts the plastic. Then, the molten plastic is forcibly injected 

into the mold under the barrel with an appropriate shape. As the plastic cools, it 

solidifies. The plastic molded like this has a reverse shape of that of the mold. A variety 

of shapes can be produced by the process. The process of plastic molding is cheap due to 

the simplicity involved, and the quality of the plastic material is modifiable by changing 

the factors involved in the custom injection molding basics process:

Knowledge Base Subjects

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The pressure of injection can be varied to change the hardness of the final product. 

Injection pressure causes the material to flow. Pressure increases as mold filling becomes 

more complex. There is a direct relationship between injection pressure and injection line 

The thickness of the mold affects the quality of the part produced. On average, the minimum 

wall thickness of an injection molded part ranges from 2mm to 4mm (.080 inch to .160 inch). 

Parts with uniform walls thickness allow the mold cavity to fill more precisely since the 

molten plastic does not have to be forced through varying restrictions as it fills.
The temperature for melting and cooling determine the quality of the plastic formed. In 

plastic injection molding, the temperature of the melt in the cavity is generally between 

200 and 300 degrees, the melt is formed in the cavity, cooled, and solidified into a 

product profile.

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