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Plastic Injection Molding Process

While there are many different types of injection molding process, as the name implies, plastic injection molding in its most basic process can be best described as a process where liquid (viscous) molten thermoplastic, thermoset, elastomer, liquid, and/or metal(s), etc. is injected under high pressure (injection pressure) into a mold, which is held closed using a force (tonnage) greater than that exerted during injection of the material being forced into the same, and allowed to cure (cure time) to a predetermined temperature.

There are as many, if not more, injection molding machine (IMM) configurations as there are injection molding processes. From Horizontal, Vertical, Rotary, Single Color, Multi-Component, Gas Assist, custom machine configurations, etc., and the lists go on and on but there is bound to be a IMM to fit your specific needs.

With the introduction of "all electric" injection molding machines in as early as circa 1996, and Hydroelectric IMM's equipped with Servo-Electronic Injection, today's IMM manufacturers and suppliers are focused on manufacturing IMM's that reach the needs of the plastic manufacturers focused on meeting the world's ever-growing demand for a "greener" marketplace.

Furthermore , plastic injection molding is widely regarded as the most complicated of the plastic manufacturing processes, capable of producing plastic parts typically stronger and at a higher per/part cost than that of its plastics manufacturing counterparts.

Plastic Injection Molding Process Schematics and Injection Molding Machine Exemplar:

Copyright2009. Wittmann Battenfeld® EcoPower

Plastic Extrusion Process

Similar to the plastic injection molding process, the plastic extrusion manufacturing process consists of a barrel, screw, and hopper (Feed) section, whereby raw plastic resin granules or "chips" are first loaded via a hopper or automated "material loading" system, then fed into a rotating screw, typically driven by a hydraulic power source and heated using a series of  electric barrel heaters, that along with the shear heat developed by the friction created by the rotating screw, melt the thermoplastic resins to their softening point.

Once the molten thermoplastic resin is pliable enough to be extruded into the desired shape, i.e. profile, pipe, sheet, film, etc., the molten plastic resin is forced thru a die (mold) that is constructed in a manner consistent with the shape of the intended part. In fact, the plastic extrusion process utilizes a barrel and screw assembly very much like the same assembly found in an injection molding machine.

In contrast, the screw on an extrusion machine does not reciprocate (back and forth motion), instead the screw continuously rotates in a counterclockwise manner, constantly feeding the material in one direction and forcing the molten resin thru the die, thereby creating the desired shape. Similarly, the plastic products produced using the extrusion process are typically not as strong as their plastic injection molded counterpart and are less expensive to manufacture, both in the die (mold) up-front cost, and in the cost to manufacture, as the machine costs are substantially lower when compared to plastic injection molding process.

Plastic Blow Molding Process

In general, there are three primary types of blow molding, extrusion blow molding, injection blow molding, and stretch blow molding.

In its most basic form, the plastic blow molding process can be best described as a processes whereby, molten thermoplastic resin (parison)  is first injected into a mold, then pressure, usually air is injected (Blown) thru the center of the molten resin and forces this plastic to the mold cavities (surfaces) to create a hollow part, i.e. bottle, container, vial, etc.

There are a wide variety of plastic resins that are used in the manufacture of blow molded components, including PE, PP, ABS, PC, PET, etc. In fact, without the blow molding process, a lot of the products we use everyday, such as milk and coke bottles, garbage cans, stadium seats, etc.  would not possible.

Plastic Thermoforming Process

Thermoforming, vacuum forming, and pressure forming are all methods whereby are really secondary processes in the plastics manufacturing process, the primary process being that which produces the plastic sheet or film intended to be formed.

The earliest method, vacuum forming, uses as the name implies, negative pressure to draw the plastic sheet into a mold cavity. and pressure forming, as the name implies, uses positive pressure to force the heated plastic sheet into the mold cavity.

Regardless, the process of thermoforming plastic in its most basic process, consists of two main steps, heating the plastic sheet or film to its softening point, where it is then deformed into the desire shape.

Plastic Manufacturing Safety, Injury, and Standards

Plastic injection molding safety standards are defined and enforced by the Occupational Safety and Health Administration, herein OSHA (www.osha.gov), the American National Standards Institute, herein ANSI (www.ansi.org) and approved State Occupational Safety and Health Plans, such as Michigan’s OSHP.

Plastic manufacturing employers must conform to OSHA’s general industry standard 29 CFR 1919 , which applies to the major percentage of plastics processors operating under SIC code 3089.

ANSI, a private non-profit organization (501(c)3) administers and coordinates the U.S. voluntary standardization and conformity assessment system . As with most industries, organizations such as ANSI have developed standards primarily through relationships with the injection molding machinery manufacturers.

The ten (10) most frequently cited standards for plastic injection molders* were:

1910.147 The control of hazardous energy (lockout/tagout)
1910.212 General requirements for all machines
1910.1200 Hazard Communication
1910.305 Electrical, Wiring Methods, Components, and Equipment
1910.134 Respiratory Protection.
1910.178 Powered Industrial Trucks
1910.303 Electrical Systems Design, General Requirements
1910.219 Mechanical Power-Transmission Apparatus
1910.215 Abrasive Wheel Machinery
1910.95 Occupational Noise Exposure

*During the period of 10.02 through 09.02

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