Sandwich molding

Other. Laminated plastic (industrial laminate), sandwich molding, filled plastic, cellular plastic, glass reinforced plastic (GRP), carbon fiber reinforced plastic (CFRP). 

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. 

Two-component injection machines, using separate injection units for each of the two components perform the standard sandwich molding process. This process is characterized by a sequential injection of the two components using the same gating system. After filling the mold partially with the skin material with one injection unit the core component will be injected by the second injection unit. In order to avoid flow marks on the part surface a simultaneous phase is inserted between the injection of skin and core components. The final packing phase may be performed either with the core or the skin component. 

In 1992, a new sandwich injection molding concept, called monosandwich, was developed by Jaroschek and Thoma (Ferromatic Milacron). In contrast to the standard sandwich molding process, this technology uses only one injection unit for both skin and core components with an extruder. 

FIGURE 2.14 Three stages of co-injection (sandwich) molding, (a) Short shot of skin polymer melt (shown in black) is injected into the mold (b) injection of core polymer melt until cavity is nearly filled and (c) skin polymer melt is injected again, pushing the core polymer away from the sprue. 

A system for sandwich molding developed by Aron Kasei uses fiber-reinforced ABS as the outer skin and a PLS conductor (see below) as the inner core. Applications include keyboard housings, printer housings, CRT enclosures, and medical equipment housings. 

Special method, by which at least two materials are injected by the skin-core molding process. The outer skin-injected first-consists of the more expensive material, whereas the core may even be of regrind. It is injected to fill the skin, hence sandwich molding. A cost-saving... 

See also foamed plastic structural foam molding sandwich molding. 

One of the major advantages of the sandwich molding process is that two different resins may be used for the skin and core. Thus a hard, relatively expensive material can be used for the outer skin and an inexpensive resin, or even regrind, may be used for the core. The two resins used should be chemically and physically compatible. 

Sandwich foam molding, also called coinjection molding may be considered a special form of sandwich molding. Two injection units are used to produce the skin and core as separate operations. First the skin material is injected then, through the same sprue, the core foamant is injected. The mold cavity expands, allowing the core to foam. This is a process that has been patented by ICl of Great Britain. 

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