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Aspects in the FMEA Grid

Structure analysis (step 2)

The purpose of Structure Analysis is to identify and breakdown the manufacturing process and is intended to represent the process flow as it physically exists. It provides the basis to the Function Analysis (Step 3)

Process Item

The Process Item of the PFMEA is the up most level of the PFMEA.  In AVIX this is always an assembly Line. 

Process Step

The process step is an work station or a manufacturing operation. It is also considered to be the focus element of the PFMEA. In AVIX the process step and the focus element is separated. The process step is the Workstation and the focus element is the Process Task.

Process Work Element

The Process Work Element is the lowest level of the process structure tree. Each work element is a potential cause that can impact a process step, or process task and should be considered separately during the FMEA. Each work element corresponds to a category, commonly used in Ishikawa causality diagrams and populated by lean manufacturing as 4M or 5M. 

Example categories:

  • Machine

  • Man

  • Material (Indirect)

  • Environment (Milieu)

  • Method

Function analysis (step 3)

The process function analysis ensures the that functions and requirements of the product/process are  taken care of. It provides the bases of the failure analysis (Step 4)

About Functions

A function describes what something is intended to do. A process item or process step can have multiple functions.

Before the function analysis can be done product and process functions / requirements needs to be known. This can be gathered prior or during the analysis.

The description of a process function should to be clear and, if possible,  phrased with a verb and an noun like: "Positioning rear window" or "Fasten seat"

Function of the Process Item

A high level function that references the Process Item in the Structure Analysis. It can take into account functions such as:

  • Internal function
  • External function
  • Customer and/or end user function

The negation of the process item functions will be the Failure effects in the Failure analysis (step 4)

Example: "Assemble front seat"

Function of Process Step

The Function of the Process Step describes the resulting product features produced at the workstation or by the process task

The negation of the process step functions will be the the Failure modes in the Failure analysis (step 4)

Example: "Fasten the seat with screws"

Function of Work Element

The Function of the Process Work Element reflects its contribution to the Process Step (Process Task) to create the process / product features.

The negation of the work element functions will be the the Failure causes in the Failure analysis (step 4)

Example: "Enter the screws into the threaded holes"
or
Example: "Tighten the screws with the right torque"

Failure Analysis (step 4)

In the Process failure analysis step failure causes, modes, and effects are identified and there relationship, the failure chain, is established.  It provides the bases of the risk analysis (Step 5)

A failure analysis is performed for each element/step in the process description (Structure Analysis/Step 2 and Function Analysis/Step 3).

Failures

Failures of a process step are deduced from product and process characteristics. Examples include:

  • non-conformities

  • inconsistently or partially executed tasks

  • unintentional activity

  • unnecessary activity

Failure Effects (FE)

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Failure Effects are related to functions of the process item (System, Subsystem, Part Element or Name of Process). Failure Effects are described from the customers point of view. Failures that could impact safety or cause noncompliance needs to be identified clearly in the PFMEA.

Customers could be:

  • Internal customer (next operation/subsequent operation/operation tar-gets)

  • External customer (Next Tier Level/OEM/dealer)

  • Legislative bodies

  • Product or Product end user/operator

Failure Effects are given a Severity rating according to:

  1. Your Plant: the effect of the failure mode assuming the defect is detected in the plant (what action will the plant take, e.g., scrap)

  2. Ship-to plant: the effect of the failure mode assuming the defect is not detected before shipping to the next plant (what action will the next plant take, e.g., sort)

  3. End user: the effect of the process item effect (what will the end user notice, feel, hear, smell, etc., e.g., window raises too slow)

The following questions should be asked to help determine the potential impact of failure effects:

  1. Does the failure mode physically impact downstream processing or cause potential harm to equipment or operators?

    This includes an inability to assemble or join to a mating component at any subsequent customer’s facility.

    If so, then identify the manufacturing impact “Your Plant" and/or "ship-to plant" in the PFMEA. If not, then go to question 2.

    Examples could include:

    • Unable to assemble at operation x

    • Unable to attach at customer facility

    • Unable to connect at customer facility

    • Cannot bore at operation X

    • Causes excessive tool wear at operation X

    • Damages equipment at operation X

    • Endangers operator at customer facility

    When parts cannot be assembled there is no impact to the End User and question 2 does not apply

  2. What is the potential impact on the End User?

    Independent of any controls planned or implemented including error or mistake-proofing, consider what happens to the process item that leads to what the End User would notice or experience. This information may be available within the DFMEA. If an effect is carried from the DFMEA, the description of the product effects in the PFMEA should be consistent with those in the corresponding DFMEA.

     

    In some cases, the team conducting the analysis may not know the end user effect (e.g., catalogue parts, off the-shelf products, Tier 3 components). When this information is not known, the effects should be defined in terms of the part function and/or process specification.

    Examples could include:

    • Noise

    • High effort

    • Unpleasant odor

    • Intermittent operation

    • Water leak

    • Rough idle

    • Unable to adjust

    • Difficult to control

    • Poor appearance

    • Regulatory System Function reduced or failed

    • End user lack of vehicle control

    • Safety effect on end user

  3. What would happen if a failure effect was detected prior to reaching the end user?

    The failure effect at the current or receiving locations also needs to be considered.

    Identify the manufacturing impact “Your Plant and/or "ship-to plant” in the PMEA.

    Examples could include:

    • Line shutdown

    • Stop shipment

    • Yard hold

    • 100% of product scrapped

    • Decreased line speed

    • Added manpower to maintain required line rate

    • Rework and repair

Severity

2. Failure Mode of Process Step

3. Failure Cause of the Work Element

Risk analysis (step 5)

Current prevention control (PC) of FC

Occurrence

Current detection control (DC) of FC

Detectability

Action priority

 

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