Failure chain appears in the context of risk management. Risk management is only possible when it is quantified. Depending on the type of risk, different risk measures (e.g. diffusion, sensitivity) and analysis methods (e.g. quantitative, qualitative) are used. Referring to its quantitative definition, it will be the greater the more the tolerance limit is exceeded and the greater the probability of the event occurring. You can read more about risk management in the article here.
Fast reminder – what is the risk?
ISO 9000: 2015 in clause 3.7.9 defines risk as “the influence of uncertainty”. Further is this clause it is said that it is “the impact of uncertainty causing deviation from expectations”. Uncertainty, on the other hand, is defined as “a state, (…), lack of information related to the understanding or knowledge of an event, its consequences or probability”.
Therefore, risk is often presented as a combination of the event consequences and the associated probability of occurring. This approach can be observed in one of the risk management tools, namely in the FMEA. In this method, risk is quantified based on severity, occurrence, and detection rated on a 10-point scale.
FMEA according to AIAG-VDA
The new AIAG and VDA Handbook (FMEA) was developed by a global team of OEM subject matter experts and Tier 1 suppliers. Design / Process / MSR FMEA is an analytical system and function analysis methodology for both product and process. The manual does not define the requirements, it only explains the steps, procedures, tools necessary for the technical creation of an FMEA.
What are its most essential elements?
- new 7-step approach to FMEA development,
- Significantly revised Severity, Occurrence and Detection (SOD) tables,
- new methodology for Action Priorities (AP) and Tables identifying Risk priorities as High, Medium, Low
- resignation from RPN = risk priority number.
Failure chain – what is it?
In the case of FMEA (Failure Mode and Effects Analysis), which is a quality management tool, the “Failure chain” is a sequence of events that can lead to the appearance of potential defects or non-conformities in a product or process. Within the FMEA, it is possible to construct a failure chain that describes how successive factors can lead to a defect or nonconformity. If we wanted to graphically represent the failure string as FMEA does, it would look like this:
This approach makes it very easy to identify key points where corrective actions should be taken to minimize the risk of failures and ensure high quality.
In this way, the FMEA failure chain analysis allows you to systematically identify potential problems in the process and solve them at an early stage, which contributes to improving the quality of the final product or service.
Failure chain in FMEA according to AIAG-VDA
Here is an example failure table. This table lists seven different failures that can occur in car manufacturing. For each failure, the table shows the cause and effect, i.e. typical elements of failure analysis.
NOTE: In order to easily understand the concept of failure chain, the table uses very general language that should be avoided when working with FMEA.
|1||Deficiencies in the engine manufacturing process||Improper process parameters||Imperfect performance|
|2||Failures in chassis assembly||Improper part fastening||Steering system problems|
|3||Inaccurate painting||Improper painting conditions||Aesthetic defects|
|4||Failures in interior assembly||Improper connections and fastenings||Ergonomic and aesthetic defects|
|5||Improperly adjusted wheels||Inaccuracy in the adjustment of axles and wheels||Handling and tire wear issues|
|6||Faulty ABS system software||Failures in software coding||Braking problems|
|7||Failure to conduct quality tests before the product leaves the factory||Insufficient quality control||Hidden defects, safety issues|
However, the failure chain in the FMEA analysis according to the combined AIAG – VDA approach according to the figure presented above is characterized by even more precise logic.
If we swap some columns like below, we’ll have a clearer link to our potential failure with the 7-step analysis. In addition, we will gain a more accurate possibility of analysis according to the reasoning logic of cause – failure – effect, as well as ease of assessment based on severity, occurrence, and detection.
|1||Imperfect performance||Deficiencies in the engine manufacturing process||Improper process parameters|
|2||Steering system problems||Failures in chassis assembly||Improper part fastening|
|3||Aesthetic defects||Inaccurate painting||Improper painting conditions|
|4||Ergonomic and aesthetic defects||Failures in interior assembly||Improper connections and fastenings|
|5||Handling and tire wear issues||Improperly adjusted wheels||Inaccuracy in the adjustment of axles and wheels|
|6||Braking problems||Faulty ABS system software||Failures in software coding|
|7||Hidden defects, safety issues||Failure to conduct quality tests before the product leaves the factory||Insufficient quality control|
Let us remember that in the FMEA AIAG – VDA:
- The effect of the failure is defined as the consequences of the type of failure. For DFMEA, the effect on the next level of product integration (internal or external) and on the end user who will drive the vehicle (external) and government regulations (regulatory) should be described if applicable. The failure effects for the PFMEA refer to the function of the process element (system, subsystem, part element or process name). The effects of the failure are described in terms of what the customer may notice or experience.
Customers could be:
- Internal customer (next operation/subsequent operation)
- External customer (Next Tier Level/OEM/dealer)
- Legislative bodies
- Product or Product end user/operator
2. The failure mode is defined as how a component/process may fail to perform or deliver its intended function.
3. Failure cause is an indication of why the failure mode might have occurred. The consequence of the cause is the failure mode.
Failure chain sum up:
Failure chain analysis allows you to identify key points where changes or improvements should be made to minimize the risk of failures and ensure high quality of the final product.
If you want to learn more about FMEA analysis according to AIAG-VDA, I invite you to familiarize yourself with the Qualitywise training offer.
Take part in my survey and get the complete list of FMEA in IATF 16949:2016
I invite you to complete a quick survey about “20 examples of incorrectly implemented FMEA according to AIAG-VDA causing non-compliance in IATF 16949 audits in the automotive industry.”
In this survey I collected my experiences that I want to present to you. They can also be helpful for you in avoiding potential nonconformities during your IATF 16949 audit. However, I would like to hear from you if you have any other issues/observations while working with FMEA.
As a thank you, after completing the survey, I have prepared a complete list of FMEA in IATF 16949:2016 for you.
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Thank you for your presence.
Agata Lewkowska Ph.D.
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For people who want to know more:
Knowledge must have a solid foundation to avoid information noise. Therefore, the article was based on the following literature:
IATF 16949: 2016 Requirements for quality management systems in serial production and the production of spare parts in the automotive industry, 1st edition, 2016
ISO 9000:2015 Quality management systems — Fundamentals and vocabulary
FMEA AIAG-VDA, 1st edition, 2019
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