How Molded Plastic Is Made

To make a plastic part for a product a mold making company is contracted to design and produce the mold. This starts as a block of high chromium steel, a steel that can withstand the injections of high pressure plastic. The block is then milled, machined and grinded down to hundredths of millimeters of precision. The mold has strategically placed holes for the guide pins and bushings that will eventually hold the mold together.

A CNC (numerically controlled) machine does the fine details, and can go for hours or even days as the mold is shaped to near perfection, and is then sometimes polished for even finer detail. Electronic measuring devices check the specifics of the size of the mold, and if any letters are needed in the cast, they are placed on in reverse. The final piece of the puzzle is the creation of cooling lines, where fluid can be injected to cool off the plastic.



CNC company in the United States (this company does fuel filters)
http://reccofilters.com

Injection molding images and further explanation
http://www.vulcanmold.com/article/Plastic-Injection-molding-process.html