As I have pointed out in past articles, there are many different reasons for spring fractures. When designing springs, every effort is put forth to prevent premature spring failures. Infinite life for springs has been defined as successfully lasting over 10 million cycles. This definition has been “second guessed” and I’ve read some articles that have stated that “eventually” everything breaks.
Well, I for one wouldn’t want to foot the cycle testing bill for “eventually.” But I have seen high frequency cycle testing exceed 100 million and even one billion cycles. Most springs don’t need to last over 10 million cycles to perform properly. Therefore, designing to that criterion would be a waste of money.
Due to high operating loads, environmental conditions, and space constraints some springs must be periodically replaced in anticipation of failure. For springs in particularly corrosive environments, for example, a successful design is one that lasts for one year and is replaced regardless of how many cycles.
A successfully made spring is one that performs satisfactorily over its operating life. Three basic elements are needed to achieve this goal: 1) a good design, 2) quality processing procedures and 3) a predictable operating environment. I’ve taken note over the past four years that most spring failures are the result of the latter factors; processing procedures and operating environment. I’ve often referred to the operating environment as “the black box.”
I usually report about springs that have broken in service due to some extraordinary event, like embrittlement or improper processing. With only one major exception, most spring failures are not the result of poor design. This exception is in the hook design on extension springs.
I am reminded of this as Dick Carter and I just completed teaching the annual SMI Spring Design class, August 12-13 in Naperville, Ill. The class was well attended and bought together springmakers from across the country (pictured above and on the following page) who wanted to learn the essentials of spring design. We added some information to the class pertaining to common causes of spring failures and some simple, yet effective, countermeasures. Many attendees presented real life spring problems that were resolved during class to the benefit of all.
As with every other industry today, computers and software programs are making tasks, which were previously considered tedious and arduous, streamlined and accurate. SMI has a history of not only providing the needed spring design technology but of also consistently improving upon it.
The first attempt was a DOS-based software that has been long superseded by the Advanced Spring Design (ASD) 6.0. This software combines the spring design technical expertise from SMI with the software and problem-solving capabilities of Universal Technical Systems (UTS) based in Rockford, Ill.
SMI is dedicated to improving the software models and performance to meet the expanding needs of the spring industry. This dedication will manifest itself as a new version of the ASD software that is scheduled for release near the end of this year. This upgrade will be free for all current users of the software.
The author would like to thank all the attendees of the Spring Design class and special thanks to Dick Carter of Michigan Spring and Stamping for his invaluable assistance.
