Modelling Yearly Cyclical Failures

R

RelEng

Hi,

We have some parts that are only used during the winter months, so that the fault arising chart is a wave pattern, with crests starting around October, rising to a peak in December-January, then tailing off towards March.

Failures do still occur between March and October, but they are less than 5% of the winter rate.

The parts are only used momentarily, the root cause of the failure is known, and it's fairly certain that the failure will occur if the assembly was built during a known period in the past.

Can you recommend a suitable method to model this, so that a reasonable warranty forecast can be made?
 

Miner

Forum Moderator
Leader
Admin
Your choice of analytical approaches will depend greatly on the type of information available to you. Do you only have quantity and date of return information, or do you also have date of manufacture, quantities shipped by period, operating hours, etc.?
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
Hi,

We have some parts that are only used during the winter months, so that the fault arising chart is a wave pattern, with crests starting around October, rising to a peak in December-January, then tailing off towards March.

Failures do still occur between March and October, but they are less than 5% of the winter rate.

The parts are only used momentarily, the root cause of the failure is known, and it's fairly certain that the failure will occur if the assembly was built during a known period in the past.

Can you recommend a suitable method to model this, so that a reasonable warranty forecast can be made?

I attended a session at the 2012 WCQI where the presenter put the data into an Excel grid - columns are month of failure, rows are month of manufacture, and have a failure rate in each cell. This triangular grid could show various patterns. I made the suggestion to tie that in with a Chi Square analysis to see if there were cells that were significantly higher or lower than the rest. I'll see if I can dig up the spreadsheet suggestion I made, but never did hear back from the person.
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
Found the file on my home computer. It has a random number generator in it to simulate different results. Hit f9 to generate a new set of data.
 

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