Good design is essential to any manufactured product, and good design is no different for plastics. Most of the plastics we use today have been around for more than two generations. Compare that to the thousands of years we have had with metals. And in plastics it is more varied, more complex. For most designs in metals, there is no need to worry about the effects of time, temperature or environment. Unlike plastics. Plastics shrink over time, their properties change over the temperature ranges of everyday life, they can be affected by common household and industrial materials.
We can extend our thinking to define design as how to organize technology so that we don’t have to experience it. In other words, good design provides function, form, and technology in objects that meet the needs of users without demanding them. Well-designed objects provide pleasure or at least satisfaction in use, and do what they are supposed to do without undue anxiety.
Plastics are very complex and varied, always consider carefully whether the suggestions need to be tailored to your particular application.
Good design combines concept with execution. If the two are not considered together, the result will be a product that cannot be manufactured economically or that cannot be used. This is especially important for plastics. It is essential to choose the right material for the job. Then, it is equally important to adapt the design details to suit the characteristics of the material and the limitations of the production process.
Plastics come in a bewildering variety. There are hundreds or more different generic types. In addition, sophisticated techniques with catalysts and compounding are creating new alloys, blends, and molecular forms. All of these materials can have their own unique properties.
The number of different types of plastic materials available to the designer is now approaching 50,000. The importance - and difficulty - of making the right choice is clear. Plastics can be grouped into categories that behave very similarly. Thermoplastics undergo physical changes when processed; the process is reproducible. Thermosets undergo chemical changes; the process is irreversible. The main differences between thermoplastics relate to the arrangement of the molecules. Those with randomly tangled molecules are called amorphous. Those with a degree of molecular order and organization are called semi-crystalline. The differences are significant. For example, most amorphous materials can be completely transparent. And the more crystalline a material is, the less likely it is to have wide 'rubbery' processing regions, making it less suitable for stretch processes such as blow molding and thermoforming. The designer must design for the process as well as the purpose and material. In a single-surface process, for example, there is only indirect control over the shape of the second surface. The design must take these limitations into account.
