DFMEA Creation Tutorial with Example

What is DFMEA?

DFMEA is Design Failure Mode & Effect Analysis. It is the application of FMEA to a specific product/system in a disciplined manner that anticipates failures to prevent their occurrence in design.

 

 

FMEA is of  two types:

1)DFMEA

2)PFMEA (P – Process)

 

Let us go through the DFMEA creation tutorial.

 

DFMEA comes into play when

  1. New design is developed.
  2. Modifications done to an existing design.
  3. Existing design to be employed in a new application.

 

DFMEA is initiated even before finalizing the design concept and fundamentally completed before production release. In any domain, requirement and scope of work should be listed before and then their potential failure modes and causes should be identified.

Before, you get into the creation of DFMEA there are tools which help in you getting a clear idea about the crearion of DFMEA for a product. They are

  1. Boundary diagram
  2. Interface matrix
  3. P – Diagram (Paramter Diagram)

 

Let us get to know about the basics in creating a DFMEA tutorial.

A model template of how to create a DFMEA is given below. It invloves many fields so as to negate the maximum possible failure effects and failure modes in design phase.

 

Table1.: DFMEA Template

Item /

Function

Potential

Failure

Modes

Potential

Effects

of Failure

Severity

Potential Causes /

Mechanisms of Failure

Current

Design

Controls

Prevention

Occurrence

Current

Design

Controls

Detection

Detect

R.P.N.

Recomm

ended

Action

Resp

Actions

Taken

Severity

Occurrence

Det RPN

 

Let us know about each field regarding what they are and how to approach them.

Item/Function:

As the name suggests, it lists the items/parts and functions related to the part to be analyzed to meet the design intent. It is better if we list the functions separately.

Potential failure mode:

Identifying the failure mode based on parts previous history or anticipated failure by the designer of how the part will not conform to the customer requirements will be seen and necessary actions will be taken in the subsequent steps.

Potential effects of failure:

This identifies what the end customer might undergo in case of a failure. The effects may be noise, erratic operation, thermal event etc.,

Severity:

Severity is associated with effect of failure mode and ranking needs to be done based on the consensus reached by the desingner or the team assessing the failure. The ranking may vary from 1 to 10 depending upon the severity.

10 being the worst and 1 being the desirable one.

Potential causes / Mechanisms of failure:

It indicates how the design process allows the failure to happen and a clear indication how weak the design is and described in terms how it can be controlled or not.

Current Design Control Prevention:

It analyses, reviews design so as to ensure and assure design adequacy that resukts in fail-safe design and forming a closed loop resulting in establishing a lesson of meeting the design requirements.

Occurrence:

It is an index to determine a specific cause that will occur resukting in failure mode. It is related to design capabiity of the part and also depends on process capability. The ranking scale also applies here and the ranking needs to be consistent.

Current Design Control Detection:

This can be done through development tests or product validation testing, vehicle level verification tests to determine or detect the failures before reaching the end customer.

 

Detection:

It is the index associated with detection control when more than one control is identified, record the detection ranking of each control. Prevention control affects occurrence.

Note: Detection controls are the only ones which are recorded.

RPN:

RPN is Risk Priority Number. It is calculated as

RPN = Severity x Occurrence x Detection

It is a measure of how safe, reliable your design is, which can be brought down by taking necessary actions in the subsequebt steps.

Recommended actions:

Intent of this is to reduce the either occurrence, severity or detection. This is helpful to mitigate the effect and change the product design amd its effect of faliure mode on the product.

After recommended actions are taken, then rank severity, occurrence & detection and then weigh the RPN. This will yield you better results if it is followed before producing any part and reaching the end customer.
Now, we will see a real time example for better understanding

 

Table.2: DFMEA Example

Item/

Function

Potential

Failure

Modes

Potential

Effects

of Failure

Severity

Potential

Causes /

Mechanisms

of Failure

Current

Design

Controls

Prevention

Occurrence

Current

Design

Controls

Detection

Detection

R.P.N.

Actions

Needed

Resp

Actions

Taken

Severity

Occurrence

Det.

RPN

Shaft-

Transmit torque

Does not transmit

torque

Unable to drive

vehicle

 8

Inadequate strength in

Shaft material

.CAE analysis

Design reviews

 3

1. .Metallurgy inspection

2.Part Durability test

3.Vehicle level durability test

3  72

1.Mat. change

2.Increase shaft iiamter

Mr.

X

 Mat Change  3  2  2 12

 

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