During the plastic injection molding process, excess material, called “flash”, may leak out between plastic injection mold cavity halves. Deflashing methods are used to remove this flash, and include:
- Cutting and trimming are the most common methods of deflashing plastic injection molded parts, and are performed manually using knives, or other cutting utensils.
- Media blasting involves the spraying, or broadcasting, of either particulate polymers, or organic materials such as ground walnut shells, to break up both external and internal flash.
- Cryogenic deflashing involves loading parts to a cryogenic deflashing machine where they are then tumbled or vibrated.
Plastic injection parts often require some form of cleaning after molding. Processing aids, such as mold release agents may leave a residue, while grease and dirt can be picked up from the plastic injection molding machine. Even the natural oils of the operator’s hands can interfere with final surface treatment. All these contaminants will interfere with the bonding action of any post-molding decoration or surface treatment. Cleaning is accomplished by spraying or dipping parts in a mild detergent solution followed by a final rinsing and drying.
Virtually all plastic injection molded products receive some sort of final decoration. These decorations are either “molded-in” or “applied” types. Molded-in decorations are those designed into the plastic mold, such as textures; or by implant, as with two-shot molding. Color is considered a molded-in decoration by virtue of pre-colored resins injected into the mold. Applied decorations are those added to the plastic part after molding. These applied decoration methods include:
- Vacuum metallizing
- Pad printing
- Hot stamping
- Silk screening
- Fill and wipe