The bathtub curve is characterized by three periods
Mar 14, 2024 0:28:15 GMT -5
Post by account_disabled on Mar 14, 2024 0:28:15 GMT -5
Decide where is the “sweet spot” between designing products (made of components) that last a long time vs those that fail earlier. One critical question is “should we design (and make) all the components to fail at the same time and incur the extra cost and, likely, over design, or should we let one or more components fail earlier and then reuse the remaining components as with remanufacturing?
Engineers have been dealing with the tradeoff between product design, quality and failure for a long time. This is usually discussed as part of product reliability. Dennis Wilkins (retired from HP) explains that reliability engineers characterize the lifetime of a population of products using a graphical representation called the “bathtub curve.”
A product life: an infant mortality period (early failure)
with a decreasing failure rate, then a normal CG Leads life period (also known as “useful life”) with a low, relatively constant failure rate, and ending up with a wear-out period of accreted failure exhibiting an increasing failure rate. Engineers try to reduce failures at each stage of product life by efforts such as “burn-in” or running the product for some time to catch early failures or other tests to attempt to screen out infant mortality failures. Design and manufacturing choices can reduce (or increase!) failures at any stage – depending on quality of components and design and production.
Professor Sami Kara and colleagues at the University of New South Wales in Australia have studied this problem, as applied to appliances, for some time. The studies explore the useful life of components with the thought to identifying those that have significant use in a second life versus those that fail with the appliance. This can drive the economic models for re-manufacturing but is dependent on simple ways to estimate which components have life left and, importantly, how to assess this easily and reliably.
Challenges include the cost of testing procedures that might increase labor costs for remanufacturing or re-use, necessity for disassembly of an appliance to access the component to assess its condition, inaccurate test data with respect to condition, degradation or remaining life and questions about number of samples that need to be tested to get reliable data.(see “Reliability assessment of components in consumer products – a statistical and condition monitoring data analysis strategy” by Mazhar, Kara and Kaehernick, ).
Kara describes some of their studies showing that some very inexpensive components of large appliances fail early and render the appliance unusable – and often it would be very inexpensive to improve these components for a dramatically longer product life. One that comes to mind is the door seal on a residential refrigerator. But when is “good enough” for a product component good enough?!
So, that’s one consideration in design, production and life of the product.
Engineers have been dealing with the tradeoff between product design, quality and failure for a long time. This is usually discussed as part of product reliability. Dennis Wilkins (retired from HP) explains that reliability engineers characterize the lifetime of a population of products using a graphical representation called the “bathtub curve.”
A product life: an infant mortality period (early failure)
with a decreasing failure rate, then a normal CG Leads life period (also known as “useful life”) with a low, relatively constant failure rate, and ending up with a wear-out period of accreted failure exhibiting an increasing failure rate. Engineers try to reduce failures at each stage of product life by efforts such as “burn-in” or running the product for some time to catch early failures or other tests to attempt to screen out infant mortality failures. Design and manufacturing choices can reduce (or increase!) failures at any stage – depending on quality of components and design and production.
Professor Sami Kara and colleagues at the University of New South Wales in Australia have studied this problem, as applied to appliances, for some time. The studies explore the useful life of components with the thought to identifying those that have significant use in a second life versus those that fail with the appliance. This can drive the economic models for re-manufacturing but is dependent on simple ways to estimate which components have life left and, importantly, how to assess this easily and reliably.
Challenges include the cost of testing procedures that might increase labor costs for remanufacturing or re-use, necessity for disassembly of an appliance to access the component to assess its condition, inaccurate test data with respect to condition, degradation or remaining life and questions about number of samples that need to be tested to get reliable data.(see “Reliability assessment of components in consumer products – a statistical and condition monitoring data analysis strategy” by Mazhar, Kara and Kaehernick, ).
Kara describes some of their studies showing that some very inexpensive components of large appliances fail early and render the appliance unusable – and often it would be very inexpensive to improve these components for a dramatically longer product life. One that comes to mind is the door seal on a residential refrigerator. But when is “good enough” for a product component good enough?!
So, that’s one consideration in design, production and life of the product.