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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 applyapply.

  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

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

Severity is a rating number associated with the most serious effect for a given failure mode for the process step being evaluated. It is a relative rating within the scope of the individual FMEA and is determined without regard for Occurrence or Detection.

2.For process-specific effects, the Severity rating should be determined using the criteria in evaluation Table P1. The table may be augmented to include corporate or product line specific examples.

The evaluations of the Failure Effects should be mutually agreed to by the customer and the organization.

If the customer impacted by a Failure Mode is the next manufacturing or assembly plant or the product user, assessing the severity may lie outside the immediate process engineer’s/team’s field of experience or knowledge. In these cases, the Design FMEA, design engineer, and/or subsequent manufacturing or assembly plant process engineer, should be consulted in order to comprehend the propagation of effects.

 

Process General Evaluation Criteria Severity (S)

Potential Failure Effects rated according to the criteria below.

S

Effect

Impact to Your Plant

Impact to Ship-to Plant (when known)

Impact to End User (when known)

10

High

Failure may result in an acute health and/or safety risk for the manufacturing or assembly worker

Failure may result in an acute health and/or safety risk for the manufacturing or assembly worker

Affects safe operation of the vehicle and/or other vehicles, the health of driver or passenger(s) or road users or pedestrians.

9

Failure may result in in-plant regulatory noncompliance

Failure may result in in-plant regulatory noncompliance

Noncompliance with regulations.

8

Moderatly high

100% of production run affected may have to be scrapped. Failure may result in in-plant regulatory noncompliance or may have a chronic health and/or safety risk for the manufacturing or assembly worker

Line shutdown greater than full production shift; stop shipment possible; field repair or replacement required (Assembly to End User) other than for regulatory noncompliance. Failure may result in in-plant regulatory noncompliance or may have a chronic health and/or safety risk for the manufacturing or assembly worker.

Loss of primary vehicle function necessary for normal driving during expected service life.

7

Product may have to be sorted and a portion (less than 100%) scrapped; deviation from primary process; decreased line speed or added manpower

Line shutdown from 1 hour up to full production shift; stop shipment possible; field repair or replacement required (Assembly to End User) other than for regulatory noncompliance.

Degradation of primary vehicle function necessary for normal driving during expected service life.

6

Moderatly low

100% of production run may have to be reworked off line and accepted

Line shutdown up to one hour

Loss of secondary vehicle function.

5

A portion of the production run may have to be reworked off line and accepted

Less than 100% of product affected; strong possibility for additional defective product; sort required; no line shutdown

Degradation of secondary vehicle function.

4

100% of production run may have to be reworked in station before it is processed

Defective product triggers significant reaction plan; additional defective products not likely; sort not required

Very objectionable appearance, sound, vibration, harshness, or haptics.

3

Low

A portion of the production run may have to be reworked in-station before it is processed

Defective product triggers minor reaction plan; additional defective products not likely, sort not required

Moderately objectionable appearance, sound, vibration, harshness, or haptics.

2

Slight inconvenience to process, operation, or operator

Defective product triggers no reaction plan; additional defective products not likely; sort not required; requires feedback to supplier

Slightly objectionable appearance, sound, vibration, harshness, or haptics.

1

Very low

No discernible effect

No discernible effect or no effect

No discernible effect

 

Failure Mode of Process Step

A (Process) Failure Mode is defined as the manner in which the process could cause the product not to deliver or provide the intended function.

3.The team should assume that the basic design of the product is correct; however, if there are design issues which result in process concerns, those issues should be communicated to the design team for resolution.

Assume that the failure mode could occur but may not necessarily occur. Failure modes should be described in technical terms, not as a symptom noticeable by the customer.

Verification of completeness of the failure modes can be made through a review of past things-gone-wrong, reject or scrap reports, and group brainstorming. Sources for this should also include a comparison of similar processes and a review of customer (end user and subsequent operation) claims relating to similar components.

There are several categories of potential failure modes including:

  • Loss of process function/operation not performed

  • Partial function - Incomplete operation

  • Degradation of process function

  • Overachieving process function - Too much too high.

  • Intermittent process function - operation not consistent

  • Unstable operation

  • Unintended process function - wrong operation

  • Wrong part installed

  • Delayed process function - operation too late

Typical failure modes could be, but are not limited to:

  • Hole too shallow, too deep, missing or off location.

  • Dirty surface

  • Surface finish too smooth

  • Misaligned connector pins

  • Connector not fully seated

  • Pass a bad part, or reject a good part, bypass inspection operation

  • Label missing

  • Barcode not readable

  • ECU flashed with wrong software.

Failure Cause of the Work Element

A failure cause is an indication of why a failure mode could occur. The consequence of a cause is the failure mode. Identify, to the extent possible, every potential manufacturing or assembly cause for each failure mode. The cause should be listed as concisely and completely as possible so that efforts (controls and actions) can be aimed at appropriate causes.

Typical failure causes may include the classic Ishikawa’s 4M, but are not limited to:

  • Man: set-up worker, machine operatori associate, material associate, maintenance technician etc.

  • Machine/Equipment: robot, hopper reservoir tank, injection molding machine, spiral conveyor, inspection devices, fixtures, etc.

  • Material (Indirect): machining oil, installation grease, washer concentration, (aid for operation), etc.

  • Environment (Milieu): ambient conditions such as heat, dust, contamination, lighting, noise, etc.

 

In preparing the FMEA, assume that the incoming part(s)/material(s) are correct. Exceptions can be made by the FMEA team where historical data indicate deficiencies in incoming part quality.

One method to help reveal/uncover failure causes is to have a facilitator that leads the team through "Thought Provoking Stimulation Questions." These questions can be broad category questions, enough to stimulate the process experts thought process, while keeping the number of questions to a manageable level. Questions can be process specific and broken down into the 4M categories. Initial list of questions can be formed by reviewing the Failure Causes in previous PFMEA’s.

Example - Assembly Process:

Man

  1. From parts available within the process, can wrong part be applied?

  2. Can no part be applied?

  3. Can the parts be loaded incorrectly?

  4. Can parts be damaged - From pickup to application?

  5. Can wrong material be used?

Machine

  1. Can automated process be interrupted?

  2. Can inputted data be entered incorrectly?

  3. Can machine be run in manual mode, bypassing automated controls?

  4. Is there a schedule to confirm prevention and detection controls?

Material (indirect)

  1. Can too much / too little / no material be used?

  2. Can material be applied to a wrong location?

EnvironMent (Milieu)

  1. Is lighting adequate for task?

  2. Can parts used within the process, be considered foreign material?

The description of the failure cause needs to be clear. Terms such as "defective, broken," "operator failure," non-fulfillment or “not OK" and so on are insufficient to comprehensively assign the failure cause and mode and to determine actions.

Risk analysis (step 5)

Current prevention control (PC) of FC

Occurrence

Current detection control (DC) of FC

Detectability

Action priority

 

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