Plastic Molds

Cast kirksite cavities from SLA models can provide excellent rapid tools for prototype and bridge to production injection molding parts. Parts can be molded in two to three weeks in any thermoplastic production resin, this technology has been around for many years, but with the growth of stereolithography and the need for rapid turnaround of plastic parts in the correct production material, the kirksite approach has re-emerged. More complex parts can be made using handloads. Injection molding tapers are important and are best incorporated in the master file. One of the advantages of kirksite aluminum/zinc alloy moulds is the ease of making geometry modifications by either welding or adding inserts. Another main benefit is the ability to mold most materials.

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.

The wonderful thing about plastic injection molding is the low cost of the parts being produced when you need a large volume of parts. The downside is the cost of injection molding tooling. The toolings, or the molds, range in price anywhere from $2000 for a simple one, to over a hundred thousand dollars for a big and complex injection mold. The way the injection molders figured out how much to charge per part was to weigh the part complete with runner to determine how much plastic resin is used for each part. The size of the part determines what size injection molding machine must be used, and how big the mold is etc.

Making polymers is a fantastic science. Then there is the matter of shaping the plastic into useful objects....another fantastic science. One of the most common methods of shaping plastic resins is a process called injection molding. Injection molding is accomplished by large machines called injection molding machines. A type of mold used in the process of injection molding. The mold usually comprises two sections held together by a clamping device with sufficient strength to withstand the pressure of the injected, molten plastic. The mold is provided with channels for heating, cooling and venting.