Robust Plastic Product Design: A Holistic Approach

1.1	Causes of Plastics Failure

In his book Failure of Plastics and Rubber [1], David Wright conducted an analysis on 5,000 failed parts and came up with the causes for the failures shown in Figure 1.1.

 

Therefore, a designer may conclude that he or she is responsible for only twenty percent of the failures. As will be shown in the following chapters, what appears as materials, processing, tooling, or misuse issues may be traced back to fundamental design issues that may manifest themselves as the former.

Let us assume for the moment that design issues do cause only twenty percent of the failures, and the designer proactively makes sure that this 20% has been reduced to zero. Even then, in order to be certain that the product meets all the functional and cost requirements, someone needs to take responsibility for ensuring that the other three areas are optimized. The presence of designated materials, tooling, and processing specialists in the organization notwithstanding, that someone is still the designer!

1.2	The Holistic Approach

Let us look at the classical definition of the word "holistic" [2]:

holistic

adjective ho·lis·tic \hō-ˈlis-tik\

1: of or relating to holism

2: relating to or concerned with wholes or with complete systems rather than with the analysis of, treatment of, or dissection into parts; holistic medicine attempts to treat both the mind and the body; holistic ecology views humans and the environment as a single system

In the case of a well-designed plastic part or assembly, the parts are:

• Material

• Design

• Tooling

• Processing

• Secondary operations

The analogy I have used over my years of conducting training on this subject is that material, design, tooling, and processing are like the four wheels of a high performance car.

 

One bad wheel and...

 

On the other hand, if all of the four wheels are taken care of, one can have a product that can last for years and withstand a lot of so-called "abuse." During my training sessions I often show the video 1 of a handheld terminal 2 with proper consideration to the four "wheels." In the video this terminal is tossed to the high ceiling of a warehouse multiple times, dropping back each time on a hard concrete floor. It is also kicked around and used as a hammer on the concrete floor. At the end of the video, there is no crack or break and the terminal functions normally.