Injection molding process sequence

Two polymers can be used in sequence to fill the mold, forming skin-core sandwich molded articles. Air can also be introduced in partially melt-filled molds, and pressurized to form a polymer skin-air core sandwich structure, through the gas-assist injectionmolding process. In all injection molding processes, the polymer is melted, mixed, and injected from the injection unit of the machine. 

Figure 2-10 Injection-compression molding process sequence...

In certain processes (such as rubber tire manufacture and plastic injection molding operations), it is common for a valve sequencing system to first provide hot steam followed by cold cooling water and thus for cross-contamination to occur. The result may be the stripping of passivated cooling system surfaces by steam and for the condensate to be infiltrated by cooling water. 

The shaping and vulcanization steps are combined in a number of processes such as transfer or injection molding or may be separated as in the extrusion and subsequent vulcanization sequence. An outline of these steps is given in Figure 18.4. 

Co-injection molding involves injecting two or more different materials into a mold, generally in sequence. To accomplish this, molding machines are fitted with multiple injection units (Figure 14-53). Two-shot molding, the most common version, often utilizes an indexing mold. In this process, the mold is rotated 180° after the first shot fills a portion of the cavity, then the second shot finishes the part... 

In this process the parison is injection molded rather than extruded. In one system, for example, the parison is formed as a thick-walled tube around a blowing stick in a conventional injection-molding machine. The parison is then transferred to a second, or blowing, mold in which the parison is inflated to the shape of the mold by passing compressed air down the blowing sticL The sequence is shown in... 

Blow molding is a process for converting thermoplastics into hollow objects. Like injection molding, the process is discontinuous or batchwise in nature, involving a sequence of operations that culminates in the production of a molding. This sequence or cycle is repeated automatically or semi-automatically to produce a stream of molded parts. 

T. Hanemann, W. Pfleging, 1. Haubelt, K. H. Zum, Laser micromachining and Ught induced reaction injection molding as suitable process sequence for the rapid fabrication of microcomponents . Microsystem Technologies, 7, 209-214 (2002). 

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