Plastic Design

Plastic design is a highly specialized area of designing where continuous improvements are necessary to get high quality and low price plastic products. As polymer manufacturing is becoming the major source of our daily use necessities, this is one field of design engineering that cannot be ignored. We see the same sort of approach being applied in plastic part designing and mold tool designing, over and over again. This means that the progress in designing and manufacturing is a real minimum, where most of the companies are just concerned with getting the parts at the lowest costs. But they tend to forget that advancements in technology involves the investment of time and money for one time only, and after the research part has been completed, it reaps benefits for the whole industry for coming years. So it is essential that the manufacturing giants get together and start thinking about advancing the injection mold designs and polymer part designs. This will help all the smaller industries to follow the Plastic Design Guidelines and implement them in their system.


I personally believe that Plastic Design is a field where the mold designer working on a new part design can save time and locate the areas that require real work, i.e., innovation, with the help of his vast experience in similar design projects. He can see how others have faced and solved similar problems, while he can evaluate their results and create something even better ~ instead of “reinventing the typewriter”. One basic requirement to be met by every mold intended to run on an automatic injection molding machine is this: the molded part has to be ejected automatically and not require subsequent finishing (degating, machining to final dimensions, etc.)
For practical reasons, injection molds are best classified according to both the major design features of the molds themselves and the molding-operational features of the molded parts. These include the:

1. type of gating/runner system and means of separation .
2. type of ejection system for molded parts.
3. presence or absence of external or internal undercuts on the part to be molded.
4. the manner in which the molded part is to be released.

Important to note here that the final mold design cannot be prepared until the part design has been specified and all requirements affecting the design of the mold have been clarified. So Plastic Part Design directly determines the lead time of the whole project as well.

Types of Injection Mold Designs
There are Various types of designs which are used depending on the situation we want to use these molds in and the type of plastic components we want to produce. These may be listed as:

1. standard molds (two-plate molds)
2. split-cavity molds (split-follower molds)
3. stripper plate molds
4. three-plate molds
5. stack molds
6. hot runner molds

In normal conditions, injection molds are used in the manufacturing of following types of raw plastic materials:

1. thermoplastics
2. thermosets
3. elastomers

Just recently, elastomer injection machines have been introduced in the market and inspite of a few restrictions, they are really beating conventional elastomer molding processes by offering a lots of competitive cost advantages.
having stated that, lets describe the above mold types by their functional use. Cold runner molds for runnerless processing of thermosetting resins in analogy to the hot runner molds used for processing thermoplastic compounds and elastomers.
Runner Layout guidelines
Sometimes runners cannot be located in the mold parting plane, or each part in a multi-cavity mold has to be center-gated. In such cases, either a second parting line (three-plate mold) is required to remove the solidified runner, or the melt has to be fed through a hot runner system. In stack molds, two or more molds are mounted back-to-back in the line of closing, but without multiplying the required holding force. The prerequisite for such solutions is large numbers of relatively simple, e.g., flat molded parts, and their attractiveness comes from reduced production costs. Today’s stack molds are exclusively equipped with hot runner systems that have to meet strict requirements, especially those involving thermal homogeneity.
Conclusion to Plastic Design Guidelines
Although it is not possible to cover all the complexities and instructions related to injection mold design and plastic parts designing in this single tutorial, I will split them up into smaller and easy to read in the next few weeks and lay them out in the form of injection mold design tutorials.