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Aspects in the FMEA Grid

STRUCTURE ANALYSIS (STEP 2)

Structure Analysis aims to identify and break down the manufacturing process and represent the process flow as it physically exists. It provides the basis for the Function Analysis (Step 3)

Process Item

The Process Item of the PFMEA is at the top level of the PFMEA. In AVIX, this is always an assembly Line. 

Process Step

The process step is a workstation or a manufacturing operation. It is also considered to be the focal element of the PFMEA. In AVIX, the process step and the focus element are 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 that the 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 team can perform the function analysis, they must know the product and process functions/requirements. This information can be gathered before or during the analysis.
The description of a process function should be clear and, if possible, phrased with a verb and a noun like "Positioning rear window" or "Fasten seat".

The 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"

The functions of a Process Step

The Functions of a Process Step describes the resulting product features produced at the workstation or the process task.

The negation of a process step function will be a Failure mode in the Failure analysis (step 4)

Example: "Fasten the seat with screws"

The functions of a Work Element

The functions of a Process Work Element reflect its contribution to the Process Step (Process Task) to create the process/product features.

The negation of a work element function will be a Failure cause 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)

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

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). The team should describe a Failure effect from the customer's point of view. Failures that could impact safety or cause non-compliance should 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, and so on, like, "seat does not move")

The team should ask the following questions to help determine the potential impact of failure effects:

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

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

If so, 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 the customer facility
    • Unable to connect at the customer facility
    • Cannot bore at operation X
    • Causes excessive tool wear at operation X
    • Damages equipment at operation X
    • Endangers operator at the customer facility

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

    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 analysis team may not know the end-user effect (e.g., catalog parts, off-the-shelf products, Tier 3 components). When this information is unknown, the effects should be defined in 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 products scrapped
    • Decreased line speed
    • Increased staffing to maintain the required line rate
    • Rework and repair
    Severity

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

    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 customer and the organization should mutually agree to the evaluations of the Failure Effects.

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    If the customer impacted by a Failure Mode is the subsequent 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 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 how the process could cause the product not to deliver or provide the intended function.

    The team should assume that the product's basic design is correct; however, if design issues result in process concerns, the design issues should communicate those issues 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 the 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
    • The surface finish is too smooth
    • Misaligned connector pins
    • The connector is not fully seated
    • Pass a lousy part, reject a good part, bypass inspection operation
    • Label missing
    • Barcode not readable
    • ECU flashed with the 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. To the extent possible, identify every potential manufacturing or assembly cause for each failure mode. The cause should be listed as wholly and concisely 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 operator 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 having a facilitator who 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 manageable. Questions can be process-specific and broken down into the 4M categories. A review of previous PFMEAs can form an initial list of questions.

    Example - Assembly Process:

    Man
    1. From parts available within the process, can the 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 the 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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