The package designer now has all the information necessary to adequately protect the product during distribution. Step 1 defined the types of inputs that the package will receive during shipment. Step 2 determined the ruggedness of the product and thus its ability to withstand the environmental inputs. Step 3 evaluated the ruggedness to allow for product redesign. Step 4 defined the performance characteristic of packaging materials. Its now time to combine this information into a package design.
Shock – Package Design
First, gather together cushion curves for the selected cushion materials. It is important to check that the drop height at which the cushion curves were generated is the same as the design drop height selected in step 1. Next, locate the critical acceleration level determined in step 2 on each of the cushion curves. Draw a horizontal line across the plots through this point. Any portion of the curve which falls below critical acceleration line indicates the static loading range where the material should transmit less than the critical acceleration, see figure 12.
Vibration – Package Design
For vibration consideration, we need to collect amplification/attenuation curves for the selected materials. Locate the lowest product natural frequency on each of the curves and draw a horizontal line across the plot. Any portion of the line which extends into the attenuation zone indicates the static loading range where the material should attenuate vibration at the frequencies where the product is most sensitive, see figure 13.
Once the static loadings which appear to provide adequate shock and vibration protection have been identified, material and thickness selections can be made. The actual static loading which is chosen for the package is dependent upon several factors, however designing at the highest possible static loading means using less material. When other considerations such as compressive creep are important, designing at the lowest possible static loading may be warranted. Figure 14 displays the method for calculating the amount of material which must be used around a product to reach a desired static loading.
Package Design Considerations
The package design must be able to achieve both the shock protection requirements and the vibration protection requirements of the unit. This can sometimes present a challenge since the best design from a shock standpoint is rarely the best design from a vibration standpoint, and vice versa. Often times, due to material limitations, compromises need to be made. When this is the case, intelligent decisions can be based upon the facts and techniques used for Steps 1 and 2. We know, for instance, that vibration is a certainty. We will encounter vibration no matter which method of shipment is used because it is inherent to vehicles as they travel. Drops, on the other hand, have a certain probability associated with them. Not all packages will be dropped and certainly not all will be dropped from the design drop height. In addition, the critical acceleration of the unit was determined in a conservative manner. The package system will most likely not transmit a rectangular waveform to the product. Thus the product should be able to withstand somewhat higher accelerations than were predicted by the step acceleration test because the actual transmitted waveform is less damaging. What this means is that it is usually best to lean toward vibration protection when compromises need to be made. Of course this will depend upon the individual situation, however, in general this is the optimum approach.