Once the package design is completed, the prototype package system is tested to ensure that all design goals were met.
Shock – Package Testing
The package must be able to fall from the design drop height, set in STEP 1, and transmit less than the critical acceleration to the unit. An accelerometer mounted to a rigid portion of the product near the center of gravity can be used to monitor the acceleration level transmitted through the cushioning material into the product. A rigid location is selected so that the input to the product as a whole can be observed during the impact, and thus directly compared to the results of the Step Acceleration test. It may be desirable to monitor additional locations during the tests, such as certain critical components, however the only effective way evaluate package performance is to monitor a rigid location. Packaging itself does not directly change the response of the product to a given input, but it can modify the input which eventually reaches the product.
Flat drops are usually thought to be the most severe drops possible in terms of the acceleration level transmitted to the product. Flat drops focus all of the input along one axis of the unit and little energy is lost to the crushing of corners or edges of the package, or to package rotation. Flat drops, therefore, are used to measure the performance of the package system.
Corner and edge drops, however, often cause damage to the structure of the package which similar flat drops do not. These types of drops are often used as part of a test sequence to verify the package’s ability to hold together during shipment.
Vibration – Package Testing
Ideally, the package system will attenuate or filter out vibration at those frequencies where the unit is most sensitive. To accomplish this most effectively, the package system should have a natural frequency less than one half that of the product’s lowest natural frequency.
To run the package response vibration tests, the product is again fitted with a response accelerometer attached at a rigid location. The product is then placed in the prototype package system and secured to the table of a vibration test machine. The package is subjected to a low level sinusoidal input over the same frequency range which was used to test the bare product. In this test, however, it is the response of the package system rather than the product components which is monitored. A transmissibility plot of the package response is generated and used to verify that the package is working properly.
Once the package resonant frequencies have been determined, dwell tests are performed at those frequencies. In addition, dwell tests may be performed at each of the product resonant frequencies. Random vibration tests may also be conducted in which the vibration system is programmed to mimic the real world motions of transportation vehicles.