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A New Plastic Molding Process? - Dip Molding

Date: 07/14/2004, 20:59:13

A New Plastic Molding Process?

While dip molding may trace it roots to the ancient art of candle making, it is fair to say that the current capabilities in the plastic dip molding industry have increased exponentially. In fact, so many dynamic improvements have been made that dip molded parts are now competing with injection molded parts on design and not just cost.

How dip molding works.

Dip molding is a plastic manufacturing process whereby heated metal molds are immersed or “dipped” in a tank of liquid plastisol. The heat from the mold attracts the cool plastisol and the part is formed around the mold. The molds are extracted from the liquid and run through a baking process to cure the plastisol. From there, the parts are cooled and stripped from the molds in preparation for shipment or secondary operations.

So what is so new about dip molding?

While the basic process has remained the same there have been two major technical advances over the past decade that have expanded the popularity of dip molding as an option for design engineers.

Multi-dipping capabilities were ushered into mainstream products when “dual-walled” beverage can coolers were designed to combine a durable and slick inside liner with an insulating, cushioned foam exterior. Since then the double and triple dipping process has been utilized for numerous design projects when two or three different materials characteristics are needed for a single product. For example, tool companies have designed hand grips with hard inside liners that fit tightly and provide durability while covering the outside layer with more consumer friendly materials that are more comfortable and have a better feel. An added bonus is the ability to make these in different colors and give the product an upscale look.

Material development in the plastisol industry has also evolved significantly in the past decade. Historically, dip molded plastics had been limited to being smooth and shiny in feel and appearance. Advances in the formulation, dipping, and curing processes have led to numerous new materials including both closed and open celled foams, textured and matte finish formulations, and materials that simulate the look and feel of suede or expensive rubber compounds.

Limitations of dip molding.

As with every process, there are limitations. The dip molding process is an extremely flexible process in that one set of tooling can make parts with different wall thicknesses and lengths. However, with the exception of internal dimensions, tolerances are often much higher than on injection molded parts. Further, the internal molding process limits exterior design possibilities and control.

Dip molded tooling typically consists of numerous metal molds that are affixed to channels or plates. Typically, the more molds one can dip at a time, the lower the per piece cost will be. This, however, is limited to the size of the machine on which the parts will be run and machine sizes vary greatly in the industry.

As a general rule, dip molded tooling is less expensive and faster to make than injection molding tooling and this is one advantage that the industry likes to exploit. This is especially true in the case of prototypes where single molds can be used to make actual products in days.

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