Table of Contents
1) PFMEA header filled out completely including traceable unique number,
Team leader and key date.
and Effects Analysis
Don’t Let This Happen To YOU!
Potential Failure Mode and Effects Analysis
• To understand the role and function of the FMEA
• To understand the concepts and techniques of Design FMEA and how to apply it
• To understand the concepts and techniques of Process FMEA and how to apply it
• To understand the role and function of FTA
• To understand the concepts of Zero Quality Control or Mistake-Proofing (e.g. Poka-Yoke) and its implications for FMEA
What Is An FMEA
A tool used to evaluate
potential failure modes and their causes.
• Prioritizes Potential Failures according to their Risk and drives actions to eliminate or reduce their likelihood of occurrence.
• Provides a discipline/methodology for documenting this analysis for future use and continuous process improvement.
• By its self, an FMEA is NOT a problem solver. It is used in combination with other problem solving tools. ‘The FMEA presents the opportunity but does not solve the problem.’
How FMEA Fits With Elements of TQM
• Customer Requirements
• Engineering Specifications
• System and Components Specifications
• Process and Supplier Requirements and Control
• Develop System Design and Process FMEA
• Eliminate Potential Failures
• Improve Upon Design and Process
• Design is The Critical Element
FMEAs Have Failure Modes
• The team developing the FMEA turns out to be one individual.
• The FMEA is created to satisfy a customer or third party requirement, NOT to improve the process.
• The FMEA is developed too late in the process and does not improve the product/process development cycle.
• The FMEA is not reviewed and revised during the life of the product. It is not treated as a dynamic tool.
• The FMEA is perceived either as too complicated or as taking too much time.
• Failure Mode Effects and Criticality Analysis
• 1950’s Origin - Aerospace & US Military
• To categorize and rank for focus
• Targeted prevention as a critical issue
• Addressed safety issues
• Failure Mode and Effects Analysis - 1960’s and 70’s
• First noticed & used by reliability engineers
• System of various group activities provided through documentation of potential failure modes of products and/or processes and its effect on product performance.
• The evaluation and documentation of potential failure modes of a product or process. Actions are then identified which could eliminate or reduce the potential failure
History of the FMEA
• The FMEA discipline was developed in the United States Military. Military Procedure MIL-P-1629, titled Procedures for Performing a Failure Mode, Effects and Criticality Analysis, is dated November 9, 1949. It was used as a reliability evaluation technique to determine the effect of system and equipment failures. Failures were classified according to their impact on mission success and personnel/equipment safety.
• The term "personnel/equipment", taken directly from an abstract of Military Standard MIL-STD-1629, is notable. The concept that personnel and equipment are interchangeable does not apply in the modern manufacturing context of producing consumer goods. The manufacturers of consumer products established a new set of priorities, including customer satisfaction and safety. As a result, the risk assessment tools of the FMEA became partially outdated. They have not been adequately updated since.
History of the FMEA
• In 1988, the International Organization for Standardization issued the ISO 9000 series of business management standards.
• The requirements of ISO 9000 pushed organizations to develop formalized Quality Management Systems that ideally are focused on the needs, wants, and expectations of customers.
• QS 9000 is the automotive analogy to ISO 9000. A Task Force representing Chrysler Corporation, Ford Motor Company, and General Motors Corporation developed QS 9000 in an effort to standardize supplier quality systems.
• In accordance with QS 9000 standards, compliant automotive suppliers utilize Advanced Product Quality Planning (APQP), including design and process FMEAs, and develop a Control Plan.
History of the FMEA
• Advanced Product Quality Planning standards provide a structured method of defining and establishing the steps necessary to assure that a product satisfies the customer’s requirements. Control Plans aid in manufacturing quality products according to customer requirements in conjunction with QS 9000. An emphasis is placed on minimizing process and product variation. A Control Plan provides "a structured approach for the design, selection, and implementation of value-added control methods for the total system." QS 9000 compliant automotive suppliers must utilize Failure Mode and Effects Analysis (FMEA) in the Advanced Quality Planning process and in the development of their Control Plans.
8-D Eight Disciplines of Problem Solving
AIAG Automotive Industry Action Group
APQP Advanced Product Quality Planning
ASQC American Society for Quality Control
DOE Design of Experiments
FMEA Potential Failure Mode and Effects Analysis
FTA Fault Tree Analysis
ISO International Organization for Standardization
QFD Quality Function Deployment
QOS Quality Operating System
RFTA Reverse Fault Tree Analysis
RPN Risk Priority Number
SPC Statistical Process Control
Cause A Cause is the means by which a particular element of the design or process results in a Failure Mode.
Critical Characteristics Critical Characteristics are Special Characteristics defined by Ford Motor Company that affect customer safety and/or could result in non-compliance with government regulations and thus require special controls to ensure 100% compliance.
Criticality The Criticality rating is the mathematical product of the Severity and Occurrence ratings. Criticality = (S) ¥ (O). This number is used to place priority on items that require additional quality planning.
Current Controls Current Controls (design and process) are the mechanisms that prevent the Cause of the Failure Mode from occurring, or which detect the failure before it reaches the Customer.
Customer Customers are internal and external departments, people, and processes that will be adversely affected by product failure.
Detection Detection is an assessment of the likelihood that the Current Controls (design and process) will detect the Cause of the Failure Mode or the Failure Mode itself, thus preventing it from reaching the Customer.
Effect An Effect is an adverse consequence that the Customer might experience. The Customer could be the next operation, subsequent operations, or the end user.
Failure Mode Failure Modes are sometimes described as categories of failure. A potential Failure Mode describes the way in which a product or process could fail to perform its desired function (design intent or performance requirements) as described by the needs, wants, and expectations of the internal and external Customers.
FMEA Element FMEA elements are identified or analyzed in the FMEA process. Common examples are Functions, Failure Modes, Causes, Effects, Controls, and Actions. FMEA elements appear as column headings in the output form.
Function A Function could be any intended purpose of a product or process. FMEA functions are best described in verb-noun format with engineering specifications.
Occurrence Occurrence is an assessment of the likelihood that a particular Cause will happen and result in the Failure Mode during the intended life and use of the product.
Risk Priority Number The Risk Priority Number is a mathematical product of the numerical Severity, Occurrence, and Detection ratings. RPN = (S) ´ (O) ´ (D). This number is used to place priority on items than require additional quality planning.
Severity Severity is an assessment of how serious the Effect of the potential Failure Mode is on the Customer.
Cause and Effect Cascade
The FMEA Process
An Early FMEA
Where and Why
QS9000 paragraph 4.2
Cited in the AIAG APQP Manual
• Process Safety Management Act (PSM)
CFR 1910.119999999 lists the process FMEA as one of about 6 methods to evaluate hazards
Example: ICI Explosives - Hazardous Operability Studies
• FDA - GMPs
One of several methods that should be used to verify a new design (21CFR Part 820). Inspector’s check list questions cover use of the Design FMEA.
• ISO 9001/2
Requires Preventative Actions. The utilization of FMEAs is one continuous improvement tool which can satisfy the requirement (ISO9001, Section 4.14)
Can be used to evaluate potential hazards and their accompanying risks.
Types of Automotive FMEAs
Types of Automotive FMEAs
Machinery FMEA – is used to analyze low-volume specialty machinery (equipment and tools), that allows for customized selection of component parts, machine structure, tooling, bearings, coolants, etc.
--> Focuses on designs that improve the reliability and maintainability of the machinery for long-term plant usage.
--> Considers preventive maintenance as a control to ensure reliability.
--> Considers limited volume, customized machinery where large scale testing of a number of machines is impractical prior to production and manufacture of the machine.
--> Considers parts that can be selected for use in the machine, where reliability data is available or can be obtained before production use.
Concept FMEA – is used to analyze concepts for systems and subsystems in the early stages.
° Focuses on potential failure modes associated with the functions of a concept proposal caused by design decisions that introduce deficiencies.
° Includes the interaction of multiple systems, and interactions between the elements of a system at concept stages.
° Would apply to all new machinery concepts that have never been done before, all new plant machinery layout, new architecture for machinery, etc.)
System FMEA – is used to analyze planned / proposed systems.
° Intended to transform an operational need into a description of system performance parameters and system configuration through the use of an interactive process of functional analysis, synthesis, optimization, design, test, and evaluation.
Design FMEA – is used to analyze products, high volume tools or standard machines, machine components, standard production tooling, etc., before they are released to production.
° Focuses on potential failure modes of products caused by design deficiencies.
° Focuses on parts that can be prototyped and tested or modeled before high volume production of the product is launched.
Process FMEA – is used to analyze manufacturing and assembly processes.
° Focuses on potential product failure modes caused by manufacturing or assembly process deficiencies.
° Useful in analyzing process steps that can influence the design of machinery, including selection of appropriate tooling and machinery component parts.
Types of Automotive FMEAs
Relationships of Automotive FMEAs
Automotive FMEA Timeline
Some Key FMEA Terms
• Customer Input
• Team - Team Selection (Cross-Functional)
• Ranking - Ranking of Decisions
• Risk Priority Assessment
• Design Process
• Production Process
• AIAG: Automotive Industry Action Group
• APQP: Advanced Product Quality Planning
• DFMEA: Design Failure Mode and Effects Analysis
• DOE: Design of Experiments
• FMA: Failure Modes Analysis
• FMEA: Failure Mode and Effects Analysis
• KCC: Key Control Characteristic
• KPC: Key Product Characteristic
• PFMEA: Process Failure Mode and Effects Analysis
• PPAP: Production Part Approval Process
• PSW: Product Submission Warrant
• QFD: Quality Function Deployment
Verbiage and Definitions
How many ways can you say
• CHARACTERISTIC: A distinguishing feature, dimension or property of a process or its output (product) on which variable or attribute data can be collected. (P39 APQP)
• CHARACTERISTIC, CRITICAL, CHRYSLER DEFINITION: Characteristics applicable to a component, material, assembly, or vehicle assembly operation which are designated by Chrysler Corporation Engineering as being critical to part function and having particular quality, reliability and/or durability significance. These include characteristics identified by the shield, pentagon, and diamond. (49 PPAP)
• CHARACTERISTIC, CRITICAL (INVERTED DELTA), FORD DEFINITION: Those product requirements (dimensions, performance tests) or process parameters that can affect compliance with government regulations or safe vehicle/product function, and which require specific supplier, assembly, shipping, or monitoring and included on Control Plans. (P49 PPAP)
• CHARACTERISTIC, CRITICAL, GM DEFINITION: See Key Product Characteristic. (P49 PPAP)
• CHARACTERISTIC, KEY CONTROL (KCCs): Those process parameters for which variation must be controlled around a target value to ensure that a significant characteristic is maintained at its target value. KCCs require ongoing monitoring per an approved Control Plan and should be considered as candidates for process improvement. (P49 PPAP)
• CHARACTERISTIC, KEY PRODUCT (KPC): Those product features that affect subsequent operations, product function, or customer satisfaction. KPCs are established by the customer engineer, quality representative, and supplier personnel from a review of the Design and Process FMEA’s and must be included in the Control Plan. Any KPCs included in customer-released engineering requirements are provided as a starting point and do not affect the supplier’s responsibility to review all aspects of the design, manufacturing process, and customer application and to determine additional KPCs. (P49 PPAP)
• CHARACTERISTIC, PROCESS: Core team identified process variables (input variables) that have a cause and effect relationship with the identified Product Characteristic(s) which can only be measured at the time of occurrence. (6.3 #20 APQP)
• CHARACTERISTIC, PRODUCT: Features or properties of a part, component or assembly that are described on drawings or other primary engineering information. (6.3 #19 APQP)
• CHARACTERISTIC, PRODUCT, CRITICAL (D), CHRYSLER DEFINITION: A defect which is critical to part function and having particular quality, reliability, and durability significance. (QS-9000)
• CHARACTERISTIC, PRODUCT, MAJOR, CHRYSLER DEFINITION: A defect not critical to function, but which could materially reduce the expected performance of a product, unfavorably affect customer satisfaction, or reduce production efficiency. (QS-9000)
• CHARACTERISTIC, PRODUCT, MINOR, CHRYSLER DEFINITION: A defect, not classified as critical or major, which reflects a deterioration from established standards. (QS-9000)
• CHARACTERISTIC, PRODUCT, SAFETY/EMISSION/NOISE (S), CHRYSLER DEFINITION: A defect which will affect compliance with Chrysler Corporation and Government Vehicle Safety/Emission/Noise requirements. (QS-9000)
• CHARACTERISTIC, SAFETY, CHRYSLER DEFINITION “Shield <S>: Specifications of a component, material, assembly or vehicle assembly operation which require special manufacturing control to assure compliance with Chrysler Corporation and government vehicle safety requirements. (QS-9000)
• CHARACTERISTIC, SAFETY, CHRYSLER DEFINITION: Specifications which require special manufacturing control to assure compliance with Chrysler or government vehicle safety requirements. (P50 PPAP)
• CHARACTERISTIC, SIGNIFICANT, CHRYSLER DEFINITION: Special characteristics selected by the supplier through knowledge of the product and process. (QS-9000)
• CHARACTERISTIC, SPECIAL: Product and process characteristics designated by the customer, including governmental regulatory and safety, and/or selected by the supplier through knowledge of the product and process. (P104 APQP)
• CHARACTERISTIC, SPECIAL, CHRYSLER DEFINITION “Diamond” <D>: Specifications of a component, material, assembly or vehicle assembly operation which are designated by Chrysler as being critical to function and having particular quality, reliability and durability significance. (QS-9000)
• CHARACTERISTIC, SPECIAL, CHRYSLER DEFINITION “Diamond” <D>: Specific critical characteristics that are process driven (controlled) and therefore require SPC to measure process stability, capability, and control for the life of the part. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, CHRYSLER DEFINITION “Pentagon” <P>: Limited to highlighting Critical characteristics on (Production) part drawings, tools and fixture, and tooling aid procedures where ongoing process control is not automatically mandated. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, CHRYSLER DEFINITION “Shield” <S>: Engineering designated specifications or product requirements applicable to component material, assembly operation(s) which require special manufacturing control to assure compliance with governmental vehicle safety, emissions, noise, or theft prevention requirements. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, FORD DEFINITION “Critical Characteristic” <Inverted Delta>: Those product requirements (Dimensions, Specifications, Tests) or process parameters which can affect compliance with government regulations or safe Vehicle/Product Function and which require specific producer, assembly, shipping or monitoring actions and inclusion on the Control Plan. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, FORD DEFINITION “Significant Characteristic - SC” <None>: Those product, process, and test requirements that are important to customer satisfaction and for which quality planning actions shall be included in the Control Plan. (Appendix C QS-9000)
• CHARACTERISTIC, SPECIAL, FORD DEFINITION “Significant/Characteristic - S/C” <None>: Characteristics that are important to the customer and that must be included on the Control Plan. (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, GM DEFINITION “Fit/Function” <F/F>: Product characteristic for which reasonably anticipated variation is likely to significantly affect customer satisfaction with a product (other than S/C) such as its fits, function, mounting or appearance, or the ability to process or build the product. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, GM DEFINITION “Safety/Compliance” <S/C>: Product characteristic for which reasonably anticipated variation could significantly affect customer the product’s safety or its compliance with government regulations (such as: flammability, occupant protection, steering control, braking, etc. . .), emissions, noise, radio frequency interference, etc. . . (Appendix C QS-9000)
• CHARACTERISTIC, SPECIAL, GM DEFINITION “Safety/Compliance” <S>: Product characteristic for which reasonably anticipated variation could significantly affect customer the product’s safety or its compliance with government regulations (such as: flammability, occupant protection, steering control, braking, etc. . .), emissions, noise, radio frequency interference, etc. . . (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, GM DEFINITION “Standard” <None>: Product characteristic for which reasonably anticipated variation is unlikely to significantly affect a product’s safety, compliance with governmental regulations, fit/function. (Appendix C QS-9000) & (Appendix C APQP)
• CHARACTERISTIC, SPECIAL, PROCESS (e.g., CRITICAL, KEY, MAJOR, SIGNIFICANT): A process characteristic for which variation must be controlled to some target value to ensure that variation in a special product characteristic is maintained to its target value during manufacturing and assembly. (P57 FMEA)
• CHARACTERISTIC, SPECIAL, PRODUCT: Core team compilation of important product characteristics from all sources. All Special Characteristics must be listed on the Control Plan. (6.3 #19 APQP)
• CHARACTERISTIC, SPECIAL, PRODUCT (e.g., CRITICAL, KEY, MAJOR, SIGNIFICANT): A product characteristic for which reasonably anticipated variation could significantly affect a product’s safety or compliance with governmental standards or regulations, or is likely to significantly affect customer satisfaction with a product. (P55 FMEA)
• CHARACTERISTIC, SPECIAL, TOOLING, CHRYSLER DEFINITION “Pentagon” <P>: Critical tooling symbol used to identify special characteristics of fixtures, gages, developmental parts, and initial product parts. (QS-9000)
• CONTROL ITEM PART, FORD DEFINITION: Product drawings/specifications containing Critical Characteristics. Ford Design and Quality Engineering approval is required for changes to Control Item FMEA’s and Control Plans. (QS-9000)
• Flow CHART, Preliminary Process
Description of anticipated manufacturing process developed from preliminary bill of material and product/process assumptions. (P10 #1.10 APQP) & (P104 APQP)
• Flow DIAGRAM, Process
Depicts the flow of materials through the process, including any rework or repair operations. (P50 PPAP)
FMEA & Failure Terms
• FMEA: FAILURE MODE and EFFECTS ANALYSIS - Systematized technique which identifies and ranks the potential failure modes of a design or manufacturing process in order to prioritize improvement actions. (P22 SS) & (P49 PPAP)
• FAILURE CAUSE, POTENTIAL: How the failure could occur, described in terms of something that can be corrected or can be controlled. (P37 #14 FMEA)
• FAILURE MODES ANALYSIS (FMA): A formal, structured procedure used to analyze failure mode data from both current and prior processes to prevent occurrence of those failure modes in the future. (P103 APQP)
• FAILURE MODE, POTENTIAL: The manner in which the process could potentially fail to meet the process requirements and/or design intent. A description of the non-conformance at that specific operation. (P31 #10 FMEA)
• FMEA, DESIGN: Analytical technique used by a design responsible engineer/team as a means to assure, to the extent possible, that potential failure modes and their associated causes/mechanisms have been considered and addressed. (P103 APQP)
• FMEA, MACHINE/EQUIPMENT: Same as process FMEA, except machine/equipment being designed is considered the product. (P29 FMEA)
• FMEA, PROCESS: Analytical technique used by a manufacturing responsible engineer/team as a means to assure that, to the extent possible, potential failure modes and their associated causes/mechanisms have been considered and addressed. (P104 APQP)
• Before or After
• Individual or Team Approach
Typical Automotive Trilogy Development
Automotive Document Development
Control Plan / Process Flow Combination Example
Control Plan / Process Flow Combination Example
One Document Or More
Example Discussion II
Example Discussion III
° Develop Recommendation for a "Standard FMEA Approach"
The team defined two different types of Process FMEAs as defined below:
° Device FMEA (a single FMEA that defines a single Device Flow (from start to completion).
° Process FMEA, which defines the process for either an equipment set or a "Cost Block" (e.g., probe).
Example Discussion IIIa
• Device FMEA "PRO's":
Defines a single flow.
Allows identification of Process Interaction Failure Modes.
Allows identification of "Critical Processes".
Opens communication between Device and Process Engineers.
• Device FMEA "CON's":
Less detail on Process Failure Modes.
Document control is unmanageable.
Diffuses ownership responsibilities.
• Process FMEA "PRO's":
More user friendly.
TPM/Cross Functional Team Enabler.
• Process FMEA "CON's":
Doesn't exhibit Process Interaction Failure Modes.
More difficult to identify critical processes.
Example Discussion IIIb
Based on this information the team made the following recommendations:
° As a minimum, Process FMEAs should be used.
° Device FMEAs should be used as tool to introduce new Platforms to manufacturing.
FMEAs must be reviewed and updated as detailed below:
° Process Changes.
° Customer Incidents (IFAR/EFAR).
° Whenever the process produces significant line scrap as determined by each manufacturing site.
° Ensure that the FMEAs links with the Control Plans.
QS9000:1998 - FMEAs
4.2.3 - Quality Planning
Process Failure Mode and Effects Analysis (Process FMEAs)
• Process FMEAs shall consider all special characteristics. Efforts shall be taken to improve the process to achieve defect prevention rather than defect detection. Certain customers have FMEA review and approval requirements that shall be met prior to production part approval (see customer specific pages). Refer to the Potential Failure Mode and Effects Analysis reference manual.
Quality Planning - 4.2.3.S
During the advanced quality planning processes, the supplier shall include all processes from the incoming material through shipping and warehousing
Failure Mode and Effects Analysis and Control Plan documents shall include these processes.
The supplier shall *consider* all processes. But - does it mean that all process shall be included in the FMEA and Control Plan
• “A control plan is a written description of the system for controlling parts and processes”
• “In effect, the Control Plan describes the actions that are required at each phase of the process including receiving, in-process, out-going, and periodic requirements to assure that all process outputs will be in a state of control”
“ Process Potential FMEA”
Is “...a summary of engineer’s/team’s thoughts (including an analysis of items that could go wrong based upon experience and past concerns) as a process is developed.”
“A process FMEA should begin with a flow chart/risk assessment of the general process. This flow chart should identify the product/c characteristics associated with each operation.”
General Benefits of FMEAs
• Prevention Planning
• Identifies change requirements
• Cost reduction
• Increased through-put
• Decreased waste
• Decreased warranty costs
• Reduce non-value added operations
Concept FMEA Benefits
-> Helps select the optimum concept alternatives, or determine changes to System Design Specifications.
-> Identifies potential failure modes caused by interactions within the concept.
-> Increases the likelihood all potential effects of a proposed concept’s failure modes are considered.
-> Helps generate failure mode Occurrence ratings that can be used to estimate a particular concept alternative’s target.
-> Identifies system level testing requirements.
• Helps determine if hardware system redundancy may be required within a design proposal.
Design FMEA Benefits
-> Aids in the objective evaluation of design requirements and design alternatives.
-> Aids in the initial design for manufacturing and assembly requirements (known as Design for Manufacturing/Assembly – DFM/DFA).
-> Increases the probability that potential failure modes and their effects on system and vehicle operation have been considered in the design/development process.
-> Provides additional information to aid in the planning of thorough and efficient design test and development programs.
-> Develops a list of potential failure modes ranked according to their effect on the “customer,” thus establishing a priority system for design improvements and development testing.
-> Provides an open issue format for recommending and tracking risk reducing actions. Can be a reporting tool.
-> Provides future reference to aid in analyzing field concerns, evaluating design changes and developing advanced designs.
-> Helps to identify potential Critical Characteristics and Significant Characteristics.
• Helps validate the Design Verification Plan (DVP) and the System Design Specifications (SDSs).
Process FMEA Benefits
-> Identifies potential product related process failure modes.
-> Assesses the potential customer effects of the failures.
-> Identifies the potential manufacturing or assembly process causes and identifies process variables on which to focus controls for occurrence reduction or detection of the failure conditions.
-> Develops a ranked list of potential failure modes, thus establishing a priority system for corrective action considerations.
-> Documents the results of the manufacturing or assembly process.
-> Identifies process deficiencies to enable engineers to focus on controls for reducing the occurrence of producing unacceptable products, or on methods to increase the detection of unacceptable products.
-> Identifies confirmed Critical Characteristics and/or Significant Characteristics and aids in development of thorough Manufacturing or Assembly Control Plans.
-> Identifies operator safety concerns.
• Feeds information on design changes required and manufacturing feasibility back to the design community.
• Concept FMEAs are used to analyze concepts for systems and subsystems in the early stages.
∞ Focus on potential failure modes associated with the proposed functions of a concept proposal caused by design decisions that introduce deficiencies (these include “design” decision about the process layout).
∞ Include the interaction of multiple systems and the interaction between the elements of a system at concept stages (this may be operation interaction in the process).
• Design FMEAs are used to analyze products before they are released to production.
-> Focus on potential failure modes of products caused by design deficiencies.
-> Identify potential designated characteristics called “Special Characteristics.”
• Process FMEAs are used to analyze manufacturing and assembly processes.
∞ Focus on potential product failure modes caused by manufacturing or assembly process deficiencies.
∞ Confirm the need for Special Controls in manufacturing and confirm the designated potential “Special Characteristics” from the Design FMEA.
° Identify process failure modes that could violate government regulations or compromise employee safety.
• Concept FMEA Outputs
∞ A list of potential concept failure modes.
∞ A list of design actions to eliminate the causes of failure modes, or reduce their rate of Occurrence.
∞ Recommended changes to SDSs.
∞ Specific operating parameters as key specifications in the design.
° Changes to global Manufacturing Standards or Procedures.
• Design FMEA Outputs
∞ A list of potential product failure modes.
∞ A list of potential Critical Characteristics and/or Significant Characteristics.
∞ A list of design actions to reduce Severity, eliminate the causes of product failure modes, or reduce their rate of Occurrence, or improve detection.
∞ Confirmation of the Design Verification Plan (DVP).
° Feedback of design changes to the design committee.
• Process FMEA Outputs
∞ A list of potential process failure modes.
∞ A list of confirmed Critical Characteristics and/or Significant Characteristics.
∞ A list of Operator Safety and High Impact Characteristics.
∞ A list of recommended Special Controls for designated product Special Characteristics to be entered on a Control Plan.
∞ A list of processes or process actions to reduce Severity, eliminate the causes of product failure modes, or reduce their rate of Occurrence, and to improve product defect detection if process capability cannot be improved.
° Changes to process sheets and assembly aid drawings.
• Select proper team and organize members effectively
• Select teams for each product/service, process/system
• Create a ranking system
• Agree on format for FMEA matrix (Typically set by AIAG)
• Define the customer and customer needs/expectations
• Design/Process requirements
• Develop a process flow chart **
• What is a team
Two or more individuals who coordinate activities to accomplish a common task or goal.
• Maintaining Focus
A separate team for each product or project.
Brainstorming (the Team) is necessary as the intent is to discover many possible possibilities.
• Are management directed and focused
• Build their own identity
• Are accountable and use measurements
• Have corporate champions
• Fit into the organization
• Are cross-functional
Basic Team Rules
• Determine if there should be a meeting
• Decide who should attend
• Provide advance notices
• Maintain meeting minutes or records
• Establish ground rules
• Provide and Follow an agenda
• Evaluate meetings
• Allow NO interruptions
Team Ground Rules
• Ground Rules are an aid to “self-management”
• Team must develop their own ground rules
• Once developed, everyone must live by them
• They can modify or enhance the rules as they continue to meet
Team Meeting Responsibility
• Stay on track
• Manage time
• Test for consensus
• Evaluate meeting process
Decision Criteria / Model
• One person makes the decision
• One person consults the group, then makes the final decision
• Team or group makes decision based upon majority rule or consensus
Design FMEA Team
• Start During Prototype Stage
• Design Engineer - Generally the Team Leader
• Test Engineer
• Reliability Engineer
• Materials Engineer
• Field Service Engineer
• Component Process Engineer
• Vehicle Process Engineer
• Styling Engineer
• Project Manager or Rep.
• Quality Engineer
• Customer Contact Person
• Others, including Mfg., Sales, Mkting, QA/QC, Process, Pkging
Process FMEA Team Members
• Process Engineer - Generally the Team Leader
• Production Operator
• Industrial Engineer
• Design Engineer
• Reliability Engineer
• Tooling Engineer
• Maintenance Engineer
• Styling Engineer
• Project Manager or Rep.
• Quality Engineer
• Others including Supplier, Sales, QA/QC, Mfg.
Defining the Customer
Design FMEA Customer
--> End User; person who uses the product
This can help in Repair manuals & Field Service
More in the DFMEA section herein...
Process FMEA Customer
End User; person who uses the product
More in the DFMEA section herein...
Do NOT mix up:
Design Failures & Causes
Process Failures & Causes
Risk Assessment (RPN) Factors
RPN = (S) X (O) X (D)
S = Severity
O = Likelihood of Occurrence
D = Likelihood of Detection
Prevention vs Detection - Automotive Expectations:
1000 is the Maximum and 75 is considered “OK”
High and low numbers are the important ones to consider
Segregation and Relationships
A Design FMEA is an analytical technique utilized primarily by a Design FMEA team to ensure potential failure modes and their associated causes are identified, considered and addressed.
Reference page 8 in the AIAG FMEA Reference Manual
This systematic approach parallels, formalizes and documents the mental discipline that an engineer normally goes through in any design process.
Design FMEA Foci
• End User
• Repair Functions
• Dealership or other Sales Outlet
• Designer of the next level system or product
• Process Engineers
• Assembly Engineers
• Test Engineers
• Product Analysis
Typical Design Considerations
Design FMEA Benefits
• Aids in the objective evaluation of design requirements and alternatives.
• Increases the probability that potential failure modes and their effects on the system / product have been considered.
• Aids in the planing of design test and development programs.
• Aids in analyzing field concerns, design changes and in developing advanced designs.
• Ranks potential failure modes according to their effect on the customer, thus prioritizing improvements and development testing.
• Provides an open issue format for recommending and tracking risk reducing actions.
• Can reduce product development timing, production startup problems, reduce costs and enhance product quality, reliability and safety.
More Design FMEA Considerations
• The Design FMEA is a living document and should be initiated at, or by, design concept completion.
• The Design FMEA should be continually updated as changes occur throughout all phases of product development.
• The Design FMEA should be fundamentally complete along with the final product drawings.
• The Design FMEA addresses the design intent and assumes the design will be manufactured / assembled to this intent.
• The Potential Failure Modes/Causes which can occur during manufacturing or assembly process are covered by the Process FMEA and therefore should NOT be included in a Design FMEA.
Design Failure Causes
Design Failure Cause Examples
• Improper Tolerancing
• Incorrect Stress Calculations
• Wrong Assumptions
• Wrong Material Call Out
• Lower Grade Component
• Lack of Design Standards
• Improper Heat Treatment
• Improper Torque Call Out
Design Block Diagram Example
DFMEA Basic Columns
Generic Design FMEA Severity
Generic DFMEA Occurrence
Generic DFMEA Detection
Design Control Examples
• Reliability Tests / Prototype Testing
• Design Reviews
• Worst Case Stress Analysis
• Robust Design
• Environmental Stress Testing
• Designed Experiments
• Finite Element Analysis
• Variation Simulation
• FT Analysis
• Component Derating (60% to 80%)
• 100,000 Mile Pilot Test
• When the failure modes have been ranked by their RPN, corrective actions should be first directed at the highest ranked concerns and critical items identified.
• The intent of any recommended action is to reduce one or more (or all) of the occurrence, severity and/or detection rankings.
• Only a design revision can bring about a reduction in the severity ranking. If no actions are recommended for a specific cause, this should be indicated.
• A reduction in the occurrence ranking can only be effected by removing or controlling one or more of the causes of the failure mode through a design revision.
• An increase in design verification actions will result in a reduction in the detection ranking ONLY.
• Design FMEA doesn’t rely on process controls to overcome potential weaknesses in the design; however, it does take technical and physical limitations of a process into consideration (Design Rules)
What is a Machinery FMEA
° A Machinery Failure Mode and Effects Analysis is a standardized technique for evaluating equipment and tooling during its design phase to improve the operator safety, reliability and robustness of the machinery.
What are the Purposes of a Machinery FMEA
° To identify potential failure modes
° To identify effects of the failure mode
° To rate the severity of each effect
° To determine the potential causes of the failure starting with the highest severity rating
° To identify robust designs or controls that will prevent the failure from occurring
° To identify corrective actions required to prevent, mitigate, or improve the likelihood of detecting failures early
° To establish a priority for design improvement actions
What are the Benefits of a Machinery FMEA
• Improves the safety, reliability, and robustness of equipment and tooling
• Allows design changes to be incorporated early to minimize machinery cost and delivery delays
• Minimizes the risk of delaying product programs
• Reduces overall life cycle costs
When is a Machinery FMEA Started
A Machinery FMEA must be started early in the design phase when:
• The equipment and tooling being specified is able to take advantage of revisions in order to derive the desired benefits.
• When GDT information on component parts are available and Critical/Special Characteristics are identified.
Normally, Design FMEAs on the products that are being manufactured and Process FMEAs on the steps used during the manufacture will be available.
Machinery FMEA Form
Machinery FMEA (MFMEA)
What are the Key Differences Between a Product Design FMEA and a Machinery FMEA
• Product Design FMEAs are intended for high production systems/subsystems and components.
• Prototype or surrogate part testing is used to verify design intent.
• Machinery FMEAs are used for relatively low volume designs, where statistical failure data on prototypes is not practical to be obtained by the manufacturer.
• Machinery FMEAs are targeted for long-term, repetitive cycles, where wear out is a prime consideration. For example, machinery running at two 10-hour shifts per day, 50 weeks per year, will accumulate 120,000 hours of operation in twenty years. This would be equivalent to a vehicle being driven 600,000 miles at an average speed of 50 mph.
• The severity, occurrence, and detection tables used are tailored to meet the needs of the machinery design engineer in order to maintain a standard interpretation across a wide variety of machinery designs.
What are the Similarities Between a Product Design FMEA and a Machinery FMEA
• Both emphasize operator/passenger safety as the first consideration of the design.
• Both emphasize robustness in designs to prevent problems before they occur.
• Both use 1-10 ranking scales for calculating Risk Priority Numbers.
• Both emphasize taking corrective actions based first on severity and then on overall RPN .
• Both use a standardized form to document the FMEA analysis.
MFMEA Sub-System Name
Terminology Equipment Hierarchy
° Part (lowest serviceable level)
MFMEA Function & Performance
• Enter, as concisely as possible, the function of the subsystem being analyzed to meet the design intent. Include information regarding the environment in which this subsystem operates (e.g., define environmental conditions, machine performance specification). If the subsystem has more than one function with different potential modes of failure, list all the functions separately.
• Start by listing the wants, needs or requirements of the system. Function analysis should be used to insure requirments are defined in terms that can be measured.
• Describe the function in terms that can be measured. A description of the function should answer the question: “What is this subsystem supposed to do” It is helpful to describe the function using a verb-noun phrase. However, avoid the use of verbs like “provide, facilitate, allow,” which are too general.
MFMEA Function and Performance
• When a subsystem must function under certain conditions, it is helpful to describe the conditions. Conditions may include environmental parameters, engineering requirements, and/or machine performance specifications (i.e., operating temperature, capability, cycle time, mean-time-between-failure (MTBF), mean-time-to-repair (MTTR) or other measurable engineering attributes).
• The function(s), conditions and requirements of the subsystem being analyzed. When the subsystem has many functions with different potential failure modes for each function, list each function separately.
Examples: Function Condition-Requirement
Load part 120 JPH
Index head MTBF > 300 hrs.
Control flow-hydraulic cubic centiliters/second
Position subsystem angle of rotation
Drill hole 1st run % – 99.9%
Potential MFMEA Failure Modes
Potential Failure Mode is defined as the manner in which machinery could potentially fail to meet its intended function. The potential failure mode may also be the cause of a potential failure mode in a system, subsystem, or component. Machinery failure is an event when machinery is not available to produce parts at specified conditions when scheduled or is not capable of producing parts or performing scheduled operations to specification. For every potential failure, an action is required to bring the machinery back to its intended production capability. Machinery failure modes can occur three ways:
--> (1) A type of machinery component defect contributing to a failure (hard failures; i.e., bearing seized, shaft broke).
--> (2) The manner by which machinery system failure is observed or the way the failure occurs (degraded performance; i.e., slow cycle time, excessive process variation).
--> (3) The abnormality of performance that constitutes the machinery system to be classified as failed (quality defects; i.e., high micro due to vibration, concentricity due to worn shaft bearing diameter).
Potential MFMEA Failure Modes
List each potential failure mode for the particular subsystem function. The assumption is made the failure could occur, but may not necessarily occur. A recommended starting point is a review of maintenance logs, downtime reports, field service reports, warranty documents, scrap reports and group “brainstorming.”
The task of identifying subsystem failure modes can take either of two approaches:
--> Functional approach: involves listing each subsystem, its functions, and the failure modes leading to the loss of each function. The functional approach is used most often in the preliminary design stages when machinery design detail is not complete. When taking a functional approach, it may be necessary to list the cause(s) in column 14 before listing the effect(s) first in column 11. This could assist in selecting the appropriate severity rating.
--> Hardware approach: involves listing each part, and its probable failure modes. The hardware approach is used most often when detailed part design information is available.
Potential MFMEA Failure Modes
Review historical and surrogate Machinery FMEAs, test reports, warranty data, field maintenance logs, field service reports, and other applicable documents. Identify known design failure modes.
Brainstorm potential failure modes by asking:
--> In what way can this subsystem fail to perform its intended function
--> What can go wrong although the subsystem is manufactured/assembled to print
--> If the subsystem function were tested, how would its failure mode be recognized
--> How will the environment contribute to or cause a failure
--> In the application of the subsystem, how will it interact with other subsystems
Potential MFMEA Failure Modes
• Fault Tree Analysis (FTA) can be used to help determine component failure modes. As-sume the top level event of the Fault Tree is how a component may fail to meet its intended function. Then the next level down will identify the causes as part failure modes.
• Enter the potential failure mode(s) for each function listed in Column 9. Potential failure modes should be described in “physical” or technical terms, not as a symptom noticeable by the operator. (To track the failure modes, it may be beneficial to assign them a number.) Do not enter trivial failure modes, i.e., failure modes that will not, or cannot, occur.
• General types of failure modes for the functional approach include:
° Failure to operate at the prescribed time
° Failure to stop operating at the prescribed time
° Intermittent operation
° Wear out
• General types of failure modes for the hardware approach include:
° Fractured l Warped
° Corroded l Loose
° Sticking l Cracked
° Short circuit l Leaking
Potential MFMEA Failure Effects
• Potential Effects of Failure are defined as the consequence(s) of the failure mode on the subsystem, described in terms of Safety and the “7 Big Losses.” The “7 Big Losses” are as follows:
° Setup and Adjustment
° Idling and Minor Stoppages
° Reduced Cycle
° Start-up Losses
° Defective Parts
• Note: If a functional approach is used, it may be necessary to list the cause(s) in column 14 before listing the effect(s) first in column 11.
• Review historical and surrogate FMEAs, warranty data, concern reports, field reports, and other applicable documents. Identify historical failure mode effects.
Definitions of Losses
• Breakdowns – Losses that are a result of a functional loss (mechanical, chemical, or electrical) or function reduction (e.g., one spindle not operating on a multi-spindle drill) on a piece of equipment requiring maintenance intervention.
• Setup and Adjustment – Losses that are a result of setup procedures such as retooling, changeover, die/mold change, etc. Adjustments include the amount of time production is stopped to adjust process or machinery to avoid defect and yield losses, requiring operator or jobsetter intervention.
• Idling and Minor Stoppage – Losses that are a result of minor interruptions in the process flow, such as a process part jammed in a chute or a limit switch sticking, etc., requiring only operator or jobsetter intervention. Idling is a result of process flow blockage (downstream of the focus operation) or starvation (upstream of the focus operation). Idling can only be resolved by looking at the entire line/system.
• Reduced Cycle – Losses that are a result of differences between the ideal cycle time of a piece of machinery and its actual cycle time. Ideal cycle time is determined by: a) Original design speed; b) Optimal conditions: and c) Highest cycle time achieved on similar machin-ery.
• Start-up Losses – Losses that occur during the early stages of production after extended shutdowns (weekends, holidays, or between shifts), resulting in decreased yield or increased scrap and rejects. (This may also include non-value activities required prior to production, such as bringing process to temperature.)
• Defective Parts – Losses that are a result of process part quality defects resulting in rework, repair, and/or non-useable parts.
• Tooling – Losses that are a result of tooling failures/breakage or deterioration/wear (e.g., cutting tools, fixtures, welding tips, punches, etc.).
• Severity is a rating corresponding to the seriousness of the effect(s) of a potential equipment failure mode. Severity is comprised of three components: safety considerations to equipment operator or downstream customer, equipment downtime, and defective parts. A reduction in Severity Rating index can be effected only through a design change.
• Assess the seriousness of each effect listed in Column 11. Safety of the personnel is the primary criteria in determining the rating.
• Note: If a functional approach was used, it may be necessary to list the cause(s) in column 14 before listing the effect(s) first in column 11. This could assist in selecting the appropriate severity rating.
• Subsystem functions can be prioritized by rating the severity of the effect that will result from loss of the subsystem function. Estimate the Severity of failure of the subsystem function and enter the rating in the subsystem function worksheet. Rank the functions in descending order. Begin the analysis with the highest ranked functions. Generally, these will be the functions that affect safe equipment operation, government regulations, and customer specification (downtime, defective parts).
• The FMEA Team should consent on Severity ratings for each effect listed. The effects on downtime and defective parts are independent events, and the team should select the highest rating that meets the individual criteria (i.e., downtime of 4 hours or defective part loss of 2 to 4 hours of production, select rating of 7; downtime of 40 minutes, or loss of 40 minutes of production, select 5).
• Enter the rating for the most serious (highest) effect.
Potential Failure Cause Mechanism
The cause of a failure mode is:
° 1) a design deficiency, or
° 2) machinery process variation that can be described in terms of something that can be corrected or can be controlled.
Identification of causes should start with those failure modes with the highest severity rating.
Review historical test reports, warranty data, concern reports, recalls, field reports, and other applicable documents listed in Appendix II. Also review surrogate FMEAs. List the known causal factors of the failure modes listed in Column 14.
Brainstorm potential cause(s) of each failure mode by asking questions, such as:
° What could cause the subsystem to fail in this manner
° What circumstance(s) could cause the subsystem to fail to perform its function
° What can cause the subsystem to fail to deliver it intended function
• Identify all first level causes. A first level cause is the immediate cause of the failure mode. It will directly make the failure mode occur. In a Cause and Effect Diagram, it will be an item on the major “fishbone” of the diagram. In a Fault Tree Analysis (FTA), it will be the first cause identified below the failure mode.
• A Root Cause(s) may be below the first level cause. For example, consider the illustration:
• For failure modes whose effects have a severity rating of 9 or 10, identify the Root Cause(s) of the failure mode. Root Causes are sometimes below the first level cause, and there may be more than one lower level root cause. Techniques such as TOPS (8D), Cause and Effect Diagram, or Fault Tree Analysis (FTA) can be used to help determine Root Causes.
Design Deficiency Equipment Process Variation
Switch rocker cracked Inadequate or no lubrication
Incorrect algorithm Part mis-located
• Occurrence is a rating corresponding to the likelihood that a particular failure mode will occur within a specific time period.
• Note: Controls can be used to prevent or minimize the likelihood that failure cause(s) will occur. In this event, the presence or application of the control should be considered when estimating the Occurrence rating.
• For each cause listed in Column 14, estimate the possible failure rates and/or mean time between failure.
• The occurrence of failure can be based upon historical data, including the service history, warranty data, and maintenance experience with similar or surrogate parts.
Current Design/Machinery Controls
Design/Machinery Controls are methods, techniques, devices, or tests used to:
° Prevent the Cause/mechanism or Failure Mode from occurring, or reduce rate of occurrence.
° Detect the Cause/mechanism and lead to corrective design actions, and
° Detect the Failure mode.
• Identification of Design/Machinery Controls should begin with those failure mode combinations that have the highest Severity and Occurrence ratings.
• Design/Machinery Controls used to prevent the cause/mechanism or failure mode/effect from occurring, or reduce their rate of occurrence may affect the Occurrence rating. If this is the case, these Controls should be taken into account when estimating the Occurrence rating (Column 15). Only Controls that are used before engineering release are to be considered when estimating the Detection rating.
Design Controls Machinery Controls
Worst Case Analyses Proximity Sensors
Derating Temperature Sensors
Tolerance Studies Oil Pressure Light
Simulations Studies Timing Sensors
Design Reviews Proactive Maintenance*
Safety Margins Vibration Sensor
• * Proactive Maintenance actions are key preventive, predictive, and visual management tools to control the reliability of machinery. Preventive maintenance schedules, procedures, and in-plant resources are valid design controls to reduce the occurrence ratings of the machinery FMEA, only if they have been developed as part of the design process, and are included in the machinery user’s manual.
• Note: The Machinery Design Engineer’s goal is to make the design robust so that machinery controls are not required. The Machinery Design Engineer must not rely on machinery controls or control plans to overcome potential design weaknesses.
• Detection is an assessment of the ability of the Design/ Machinery Controls to detect a potential cause/mechanism or to detect the potential failure mode.
• Estimate the effectiveness of each Design/Machinery Control listed in Column 16 to detect the cause/mechanism or the failure mode. Assume the failure mode has occurred. When several controls are listed, estimate a Detection rating for each control and then select the best (lowest) rating to enter into column 17.
MFMEA Risk Priority Number
• The Risk Priority Number (RPN) is the product of the Severity (S), Occurrence (O), and Detection (D) ratings.
RPN = (S) x (O) x (D)
• Remember, ratings and RPN numbers, in themselves, have no value or meaning.
• Ratings and RPN numbers should be used only to prioritize the potential design weaknesses (root causes) for consideration of possible design actions to reduce criticality and/or to make the design more robust (less sensitive to manufacturing variation).
MFMEA Recommended Actions
• Design actions taken to reduce the Severity, Occurrence, and/or Detection ratings.
• Remedial design actions should be considered in the following order:
° A Failure Mode has an effect with a Severity rating of 9 or 10.
° A Failure Mode/Cause combination has a high Severity and Occurrence rating (based on Team consensus).
° A Failure Mode/Cause/Design Control and Machinery Control combination has a high RPN rating (based on Team consensus).
• The intent of design actions is to reduce the Severity, Occurrence and Detection ratings, in that order.
• Whenever failure mode/cause combinations have Severity ratings of 9 or 10, design actions must be considered before engineering release to eliminate a safety concern. For these ratings, the goal is to reduce criticality below conditions that could adversely affect the safety of the operator.
MFMEA Recommended Actions
• The Machinery Design engineer’s goal is to make the design robust so that equipment controls are not required. Remember, the Equipment Design engineer CANNOT rely on machinery controls or control plans to overcome potential weaknesses.
• Emphasis should be placed upon design actions aimed at preventing or reducing the severity of the efforts of failure modes, or preventing or reducing the occurrence of causes. Detection does not decrease criticality.
• In order to track and follow up design actions, it may be helpful to assign a number to them. If no actions are recommended, it is desirable to enter “No action at this time” in the column. This prevents someone interpreting a blank space as an oversight or an incomplete resolution.
• List the actions that can be taken to prevent or reduce the occurrence of the causes of a failure mode, or to detect the failure mode. Enter a design action. If no actions are recommended, then enter “No action at this time.”
MFMEA Actions Taken
• After an action has been implemented, enter a brief description of the actual action and effective date.
• FOLLOW UP: The need for taking actions with quantified benefits, and following up all recommended actions cannot be overemphasized. A thorough Machinery FMEA will be of limited value without positive and effective actions to eliminate machine downtime or prevent part defects.
• The supplier is responsible for updating the Machinery FMEA. The Machinery FMEA is a living document. It should reflect the latest design level and latest design actions.
• In addition, any machinery design changes need to be communicated to the customer so that Process FMEAs, Control Plans and Process sheets can be updated.
• After an action has been taken, enter a brief description of the action, and its effective or actual completion date.
MFMEA Resulting RPN
• After design actions are taken, the ratings for Severity, Occurrence, and/or Detection are revised by the FMEA Team. Calculate and rate the revised RPNs. The Machinery FMEA Team Engineer will review the revised RPNs and determine if further design actions are necessary. If so, then Columns 19-22 should be repeated.
• After design actions are taken, reestimate and enter the ratings for Severity, Occurrence, and Detection. Calculate and enter the resultant RPN. If no actions are listed, leave these columns blank.
° Higher Level Assembly
° System Design Specification
° Engineering Specification
° Manufacturing/Process Specifications
° Equipment Performance Specification
° Dimensional Control Plans
Previous or Similar Data
° Warranty Data
° Reliability Data
° Recall Data
° Field Service Data
° Quality Function Deployment (QFD)
° Competitive New Vehicle Quality (CNVQ)
° National New Car Buyer’s Study (NNCB)
° Durability Tracking Study (DTS)
° EAO Quality Audit Survey (QAS)
° EAO Quality Telephone Study (QTS)
° EAO Van Quality Panels
• The practice of limiting the stresses on components/subsystems to levels well within their specified or proven capabilities in an effort to improve reliability.
• An event when machinery is not available to produce parts at specified conditions when scheduled or is not capable of producing parts or performing scheduled operations to specification. For every failure, an action is required to bring the machinery back to its intended production capability.
Mean Time Between Failures (MTBF)
• The average time between failure occurrences. The sum of the operating time of a machine divided by the total number of failures.
• The average time to restore machinery to specified conditions.
Proactive Maintenance [Preventive and Predictive]
• Preventive maintenance are all actions performed in an attempt to retain a machine in specified condition by providing systematic inspection, detection, and prevention of incipient failures.
• Predictive maintenance are techniques used to detect potential failures so that action can be taken to avoid the consequences which could occur if they degenerate into functional failures.
Machinery FMEA Check List
The Process FMEA Identifies
Critical and Significant Characteristics
and is therefore the
Use a Process Flow Chart!
• You want to understand your current process
• You are looking for opportunities to improve
• You want to illustrate a potential solution
• You have improved a process and want to document the new process
Let’s Try A Process Flow Chart
Creating a Process Flow Chart
1. Identify the process or task you want to analyze. Defining the scope of the process is important because it will keep the improvement effort from becoming unmanageable.
2. Ask the people most familiar with the process to help construct the chart.
3. Agree on the starting point and ending point. Defining the scope of the process to be charted is very important, otherwise the task can become unwieldy.
4. Agree on the level of detail you will use. It’s better to start out with less detail, increasing the detail only as needed to accomplish your purpose.
Creating a Process Flow Chart
5. Look for areas for improvement
• Is the process standardized, or are the people doing the work in different ways
• Are steps repeated or out of sequence
• Are there steps that do not ad value to the output
• Are there steps where errors occur frequently
• Are there rework loops
6. Identify the sequence and the steps taken to carry out the process.
7. Construct the process flow chart either from left to right or from top to bottom, using the standard symbols and connecting the steps with arrows.
8. Analyze the results.
• Where are the rework loops
• Are there process steps that don’t add value to the output
• Where are the differences between the current and the desired situation
Early Process Flow Diagram
GM Example Process Flow Chart
Basic Flow Chart Example
Basic Flow Chart Example
How To Use The Flow Chart
• Use to help determine who should be involved by identifying all the work areas in a process
• Use as a job aid to remind people about process standards
• Use as a check list to collect data on where problems occur
• Use to investigate why rework is occurring at a certain place in the process
• Use the ‘ideal process’ flow chart data to communicate your proposed solution
Flow Chart Tips
• If a process step or box has two output arrows, consider whether a decision box is needed
• Remember that the people closest to the work know it best. Make sure people are involved in developing the flow chart
• Software packages make flow chart production easy.
The Process Potential FMEA
• Identifies potential product-related failure modes
• Assesses the potential customer effects of the failures
• Identifies the potential internal and external manufacturing or assembly process causes and identifies process variables on which to focus controls for occurrence reduction and/or detection of the failure condition(s)
• Develops ranked list of potential failure modes, thus establishing a priority system for corrective action considerations
• Documents the results of the manufacturing or assembly process
Process Potential FMEA
• A Process Potential FMEA is an analytical tool utilized by a Process FMEA team as a means to ensure potential failure modes and their associated causes are identified, considered and addressed.
• Teams should be run by the owner of the process or someone who understands the process well.
• Defines reasons for rejection at specific operations.
• In preparation for the FMEA, the assumption should be made that the incoming parts and materials are correct.
• A comparison of similar processes and a review of customer claims relating to similar components is a recommended starting point. A knowledge of the purpose of the design is necessary.
• It can be cause-associated with a potential failure mode in a subsequent operation or an effect associated with a potential failure in a previous operation.
• Each potential failure mode for the particular operation should be listed in terms of a part or process characteristic.
FMEA White Space Issues
Process FMEA Foci
• End User
• Next Manufacturing or Process Step
• Process Engineers
• Assembly Engineers
• Repair Functions
• Test Engineers
• Product Analysis
• Dealership or other Sales Outlet
Process FMEA Benefits
• As a systematic approach, the Process Potential FMEA parallels and formalizes the mental discipline that an engineer goes through in any manufacturing planning process.
• The Process Potential FMEA identifies potential product related process failure modes.
• The Process Potential FMEA assesses the potential customer effects of the failures.
• The Process Potential FMEA identifies potential manufacturing and/or assembly process causes.
• The Process Potential FMEA identifies significant process variables to focus controls for occurrence reduction and detection of failure conditions.
• The Process Potential FMEA develops a list of potential failure modes ranked according to their affect on the customer, thus establishing a priority system for corrective and preventive action considerations.
More Process FMEA Considerations
• The Process FMEA is a living document.
• The Process FMEA should be continually updated as changes occur throughout all phases of product development and on into and through to the end of production.
• The Process FMEA should begin with a flow chart of the processes - from receiving through shipping and warehousing.
• The Potential Failure Modes/Causes which can occur during manufacturing or assembly process are covered by the Process FMEA but some information (severity rankings, identification of some effects) may come from the Design FMEA.
A reduction in occurrence ranking can only be achieved by implementing a process change that controls or eliminates one or more causes of the failure mode.
Generic Process FMEA Basic Columns
Generic PFMEA Severity
Generic PFMEA Occurrence
Generic PFMEA Detection
Process Failure Causes
1. Omitted processing
2. Processing errors
3. Errors setting up work pieces
4. Missing parts
5. Wrong parts
6. Processing wrong work piece
8. Adjustment error
9. Equipment not set up properly
10. Tools and/or fixtures improperly prepared
Process Control Examples
1. Standardized work instructions/procedures
2. Fixtures and jigs
3. Mechanical interference interfaces
4. Mechanical counters
5. Mechanical sensors
6. Electrical/Electronic sensors
7. Job sheets or Process packages
8. Bar coding with software integration and control
10. Training and related educational safeguards
11. Visual Checks
12. Gage studies
13. Preventive maintenance
14. Automation (Real Time Control)
Typical Process Documents
• SPC records
• Visual aides
• Work instructions
• Inspection instructions/records
• Equipment operating instructions
• Training records
• Traceability records
• Corrective Action should be first directed at the highest concerns as rank ordered by RPN.
• The intent of any recommended action is to reduce the occurrence, severity and/or detection rankings.
• If no actions are recommended for a specific cause, then this should be indicated.
• Only a design revision can bring about a reduction in the severity ranking.
• To reduce the probability of occurrence, process and/or specification revisions are required.
• To increase the probability of detection, process control and/or inspection changes are required. Improving detection controls is typically costly. The emphasis should be placed on preventing, rather than detecting, defects.
Action On Severity
• The question of action should be based on the RPN, not severity alone. If the severity is high, we at least think about any changes that might be made.
• Often times, we have no control on what the vehicle does when our parts fail… This is determined by the car companies and we all know they are infinitely wise in areas of quality and safety. If changes are not feasible, we then focus on occurrence and detection to bring the RPN into an acceptable level.
The Role and Function of FTA
• Fault-tree analysis is a deductive process especially useful for analyzing failures, when the causes of failures have not been identified
• Reliability engineering tool
FMEA vs FTA
Fault Tree Symbols
• The Ellipse
The top event, the ellipse, contains the description of the system-level fault or undesired event. This symbol appears at the head or top of the tree and is included only once in any tree. The input to the ellipse is from a logic gate.
• The Rectangle
The fault event, the rectangle, contains a brief description of a lower-level fault. This description should be short without being vague. Fault events appear throughout the tree and have both their input and output from a logic gate.
• Logic Gates
Logic Gate inputs and outputs, except for the Inhibit Gate, which is addressed below, have similar connections. The output from a logic gate is to any fault event block or to a Transfer Out function. The input is from any fault event block or from a Transfer In function. The AND Gate is the logic gate in which the output occurs only if all inputs exist.
The OR Gate is the logic gate in which the output occurs only if one or more of the input events occur.
Fault Tree Fundamentals
1. Defining the Undesired Event(s) (Major Fault(s))
a. The undesired event is most often the fault which, upon occurrence, results in complete failure of the system, the failure of a back-up system, degradation, or an undetected failure. This is considered catastrophic failure. The major fault is a failure which causes loss of availability through the degradation or system shut-down and/or poses a safety hazard to operators and/or maintenance personnel. The undesired event, however, may be an unusual failure at a sub-system level, the root cause of which is unknown. Any observable event may be chosen as the “undesired event”. The analyst must recognize that the FTA will not identify failures unrelated to the chosen event.
b. To define the undesired event, the normal system operation and environment must be known in order to allow the analysis to show the undesired event as a failure. When defining the undesired event, care must be taken to prevent the range of the faults from becoming too broad. For example, “Failure to complete trip”, for an automobile, is not specific enough to allow for ease of analysis. This is because failure could vary from an air conditioning fault, which caused discomfort, to loss of engine power, which caused loss of mobility. Both faults could be considered failure; however, loss of mobility is obviously a much more severe fault than losing air conditioning.
Fault Tree Fundamentals (Continued 1)
2. Defining Types of Faults
Faults fall into two basic categories: operational and component.
The operational fault is one which occurs when a component is operating as it was designed to, but at an inappropriate time or place. An example is a failure of a control valve to close or to interrupt the introduction of a reactant into a chemical process due to an inappropriate signal from another device.
The component fault can be further divided into two sub-categories: primary and secondary. A Primary component fault occurs when a component fails to function in its intended environment. Example: A radar unit designed for use in aircraft which fails due to vibration. A Secondary component failure occurs when a component fails to function in an environment other than the environment for which it is intended. Example: A radar unit designed for a cargo aircraft fails in a fighter aircraft due to vibration.
Fault Tree Fundamentals (Continued 2)
3. Comparison of Fault Occurrence and Fault Existence
The term Fault Occurrence refers to the fact that an undesired event has taken place and may or may not still exist. Fault Existence, however, implies that the fault has occurred and continues to exist. Therefore, the fault can be described as being either transient or permanent.
During the construction of the fault tree, all systems analysts should use Fault Occurrence, rather than Fault Existence, as the focus of interest.
4. Comparison of Failure Causes and Fault Effects
A failure is considered to be an inability to perform a normal function. Example: Valve does not open. A fault is a higher level Occurrence which is usually preceded by a lower-level failure, such as a casing cracking due to overheating because of a lack of coolant induction due to an inoperable valve (lower level of failure). However, a fault may also occur when no failure is present. Example: Coolant valve operates properly, but the signal to operate it encounters a delay. A fault has occurred, but there is no valve failure. Because of this, it can be stated that any failure causes a fault, but not every fault is caused by a failure.
Failure Categories: a. Component, b. Environment, c. Human, d. Software.
Fault Tree Construction Steps Summary
• Determine the level to which the examination should be constructed
• Begin with the system-level fault
• Fully describe all events which immediately cause this event
• With each lower-level fault, continue describing its immediate causes until a component level failure or human error can be attributed to the fault
Fault Tree Construction Steps Summary (continued)
• Fully define each branch of the tree before beginning another branch
• During the construction of the tree, it is advisable to use a block diagram of the system to simplify determining the main branches
• If the results of the FMECA on the system are available at the time of the FTA it is advisable to use the results in defining the top event(s)
Analyzing the Fault Tree
1. Determine the minimal cut-sets to simplify the tree (qualitative analysis).
2. Determine the probability of each input event
3. Combine the probability inputs to logic gates as follows:
a. AND Gate - The probability of output is the product of the probabilities of the inputs (P0=Pi1• Pi2...•Pin)
b. OR Gate - The probability of output is the sum of the probabilities of the inputs (P0=Pi1+ Pi2...•Pin)
4. Combine the gate input probabilities until the probability of the top event is determined.
Fault-Tree Analysis Procedures
• Identify the system or equipment level fault state(s) [undesired event(s)]
• Construct the fault tree
• Perform the analysis to the component level
Criteria for Identifying the Undesired Event
• The top event must be measurable and definable
• The top event must be inclusive of the lower events
• The top event is the result of the lower events
Zero Quality Control
Clues about Causes
• Can any equipment failures contribute to this effect
• Material faults
• Human errors
• Methods and Procedures
• Software performance
• Maintenance errors or the absence of maintenance
• Inaccuracies or malfunction of measurement device(s)
• Environments such as chemicals, dust, vibration, shock and/or temperature
Almost all errors are caused by human error.
• Forgetfulness - Sometimes we forget things when we are not concentrating. Example: A person forgets to set his/her alarm clock at night. Safeguard: Establish a routine which includes checking before going to bed.
• Errors due to misunderstanding - Sometimes we make mistakes when we jump to the wrong conclusion before we’re familiar with the situation. Example: A person used to a stick shift pushes the brake petal in an automatic thinking it is the clutch. Safeguards: Training, checking in advance, standardizing work procedures.
• Errors in identification - Sometimes we misjudge a situation because we view it too quickly or are too far away to se it clearly. For example, a $1 bill is mistaken for a $10 bill. Safeguards: Training, attentiveness, vigilance.
Five Methods of Mistake-Proofing
• Variation control using assembly aids
• Identification by visual techniques
• Standardized work and workplace organization
• Self-check (in-process)
• Emphasizes Prevention!
∞ Build into processes
∞ Eliminate inadvertent errors
∞ Stop doing it wrong - Do It Right!
∞ Work Together
∞ Find True Cause!
∞ Guide for part (fixture)
∞ Error detection alarm
∞ Limit switch
∞ Check List
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