Plastic Mold Construction

Injection molding caused a high fiber attrition resulting in an average fiber length of 390 and 350 µ m for formulations with and without coupling agent, respectively. The effect of jute fibers on the tensile and bending strengths was poor when there was no coupling agent. The addition of MAPP as coupling agent improved the composite performance by enhancing the adhesion between jute fibers and PP. The improved adhesion did partially offset the fiber attrition and the associated strength loss that resulted from injection molding. Fiber orientation occurred mainly in the melt-flow direction.

About 2 years ago I purchased a tool set. It came with a wonderful set of tools, but a really low end, thin and hollow plastic injection molding case that belies the namesake and tradition. Needless to say, the case finally gave up the ghost this past week. I began shopping for a replacement tool box for the old set that has since grown to over 200 pieces. Wanting some level of organization that is needed on the trail while off roading, the plastic tool box intrigued me due to its thick plastic construction and it's similarity to a larger tool chest with extendable drawers. Its size and depth allowed me to place it in the same spot as where I held the old plastic injection molding case in my truck.

Thermoplastic injection molding is the most widely used of all plastic processing methods. The injection molding machine reduces pelletized raw material and colorants into a hot liquid. This "melt" is forced into a cooled mold under tremendous pressure. After the material solidifies, the mold is unclamped and a finished part is ejected. Injection molding offers the lowest piece prices available, plastic but tooling prices are generally the highest. Thermoset injection molding is similar to thermoplastic injection molding except that uncured thermoset resins are mixed, injected, and held in the mold until cured. As with thermoplastic molding, the price per piece can be low, but the tooling prices are generally very high.

Over-mold injection molding and two-shot injection molding are two distinctly different molding methods even though both are used to combine multiple polymers into a single part. Because of this similarity, the two are often confused or misapplied by the design engineer. The more finite capabilities of these two molding methods differ as much as their required tooling, machines and often, the resulting part cost. Choosing the right method can mold be a critical factor in achieving targeted features, cost and time-to-market. Both methods can be used to create the soft-touch products popular in today's marketplace. However, both methods can be applied to other applications where multiple polymers must be combined into a single part. Over-mold injection molding is used for parts that do not require fine detail and can absorb the higher cost of machine time and labor. 2-shot injection molding is reserved for parts requiring fine detail and low part cost.