Process Failure Mode and Effect Analysis

STANDARD PRACTICE PROCEDURE SPP-329 PROCESS FAILURE MODE AND EFFECT ANALYSIS 1. PURPOSE The purpose of this procedure is to define the steps involved in carrying out a Process Failure Mode and Effect Analysis (PFMEA) for the assessment and reduction of risk of failures in a process / product and to apply to continuous improvement methodologies to improve processes. 2. SCOPE This procedure applies to the review of processes and products considered to have significant impact on the quality of outcomes. It applies specifically to new or changed processes, but also to the existing processes with known issues or when investigating opportunities for improvements. 3. REFERENCES AS 3960 Australian Standard - Guide to reliability and maintainability program management QS 9000 Potential Failure Mode and Effect Analysis Handbook 4. DEFINITIONS Process Failure Mode and Effect Analysis An analytical technique by which potential failure modes in a process / product are analysed and actions to eliminate or to reduce the chance of the potential risk to occur are identified and implemented. In a PFMEA, each failure mode identified is ranked according to the combined influence of its likelihood of occurrence and the severity of its consequences. Failure Mode Analysis: A study of the system and the working interrelationships in order to determine the manner in which the process / product could potentially fail to meet process requirements. Failure Effect Analysis: A study of the potential effects of the failure on the customer, in order to determine the severity of each failure effect in terms of a probable safety, environmental hazard / non-compliance with government regulations, unacceptable degradation of performance, loss of operation or disruptions of process. Potential Failure Mode Potential Failure Mode can be defined as the manner in which a process, component, sub-system or system could potentially fail to meet the process requirements. It is a description of the non-conformance of the specific operation. Typical failure modes are, but not restricted to the following: Oversized / undersized Bent Cracked Deformed Dirty Handling damage Chipped Missing Burred Potential Failure Modes should be described in “physical” or technical terms, not as a symptom noticeable by the customer. Potential Effect (s) of Failure Potential Effects of Failure are defined as the effects of the failure mode on the function, as perceived by the customer. The customer in this content should be the next operation, subsequent operations or locations and the end customer. Typical effect(s) are, but not restricted to the following: Poor appearance Inoperative Unpleasant odour Excessive effort required Noise Does not match / fit Does not connect Potential Causes / Mechanisms of Failure: Typical examples for cause are but not restricted to the following: Over / under torque Improper heat treatment (time/temperature) Weld quality unacceptable Improper weld process (current, time, pressure) no / inadequate lubrication Machining process inadequate Inadequate casting Inaccurate gauging Current Process Controls Current process controls are a description of the controls that either prevent the failure mode from occurring or detect the failure mode, should it occur. There are three types of Process Controls to consider: a) prevent the cause / mechanism or failure mode from occurring or reduce the rate of occurrence, b) detect the cause/mechanism and lead to corrective actions, and c) detect the failure mode. The preferred approach is to use the type (1) controls if possible, second is to use type (2) controls, and third is to use the type (3) controls. Risk Priority Number (RPN) = (severity) x (occurrence) x (detection). Special Process / Product Characteristics Those characteristics that significantly affecting fit / function or ability to build. Critical Process / Product Characteristics Those characteristics affecting safety or compliance with regulations 5. PROCESS FLOWCHART The process flowchart for this procedure is available in Appendix 1 of this document. 6. PROCESS AND RESPONSIBILITIES 6.1 Application 6.1.1 PFMEA shall be carried out with a purpose of identifying and eliminating potential failures or poor process controls in a new manufacturing processes, significantly changed processes or existing processes known to have past quality issues to improve process controls and outcomes. 6.1.2 The Process FMEA shall be initiated by the Quality Department. A Process flowchart shall be used with each Process FMEA. 6.1.3 The PFMEA shall include representation from manufacturing, quality assurance, engineering and other departments, supplier, customer, as applicable. 6.1.4 Where appropriate or as required by DEDIR Quality department, subcontractors should be required to provide Downer EDI Rail with PFMEA in respect of the scope of their supply. 6.2 PFMEA Procedure The following discrete steps shall be employed when performing PFMEA and the results shall be recorded on the Process Failure Mode and Effects Analysis (Form:SPP3291): 6.2.1 Defining the Process to be analysed - Complete a process definition including identification of relevant process steps, expected performance, process requirements. Develop a process flow for process PFMEA analysis. Use historical information and past performance and non-conformance information to select a process to be analysed through PFMEA. 6.2.2 Identify potential failure modes within each process selected for analysis and define their effect on the customer (being the next operation, the end customer or both). 6.2.3 Assign severity classification following evaluation of the worst potential consequences (effect) of a failure mode (Table 1). Assign classification of process / product characteristics (critical, major) 6.2.4 Analyse potential causes or mechanism of failure. 6.2.5 Assign occurrence ranking (Table 2). 6.2.6 Analyse current process controls considering their type (error proof type, gauging, manual inspection). 6.2.7 Identify failure detection methods and compensating provisions of each failure mode (Table 3). 6.2.8 Assign failure probability classification of the identified failure mode (RPN number). 6.2.9 Identify recommended corrective actions to eliminate the failure, control the risk or improve process controls (detection levels). Corrective actions should be first directed at the highest ranked concerns and critical items. The intent of any recommended action is to reduce any one or all of the occurrence, severity, and / or detection rankings. An increase in process validation / verification actions will result in a reduction in the detection ranking only. A reduction in the Occurrence ranking can be effected only by removing or controlling one or more of the causes / mechanisms of the failure mode through a process revision. NOTE: Severity ranking can not be changed by process revisions or additional process controls, only a design revision can bring about a reduction in the severity ranking. If no actions are recommended for a specific cause, indicate this by entering a “None” in the Actions Column in the Process Failure Mode and Effects Analysis (Form:SPP3291). 6.2.10 After the corrective actions have been identified, estimate and record the resulting severity, occurrence and detection rankings. Calculate and record the resulting RPN. All resulting RPN(s) should be reviewed to determine if further actions are required. Summarise the problem which could not be corrected by process change or design and identify special process controls which are necessary to reduce failure risk. In general practice, regardless of the resulting RPN, special attention should be given to high severity areas and/or poor detection areas. 6.3 Criticality Analysis - Qualitative Approach to Prioritize Failure Risk (RPN) This approach (qualitative) should be used when specific failure rate data is not available. Failure modes identified by the PFMEA process are assessed by their probability of occurrence. To establish qualitative measures of occurrence, severity, and detection, criteria must be established that subjectively relate to the overall effect on the process. The product of the measures of occurrence, severity and detection is called the Risk Priority Number (RPN). The numbers or criteria assigned to any particular ranking system are at the discretion of the user. 6.3.1 Ranking The ranking system in PFMEA is a numerical rating of effect(s) of failure based on the probability of frequency of occurrence, level of severity and likelihood of failure getting detected, based on the existing controls & past experience. The ranking system shall be in accordance with QS 9000 PFMEA standard (Process FMEA). 6.3.2 Severity Severity is an assessment of the seriousness of the effect of the potential failure mode if it occurs. Severity applies to the effect only. A reduction in Severity Ranking can be effected only through a design change. It is estimated on a scale of 1 to 10. All potential causes of failures for a particular effect of failure should receive the same severity ranking. Evaluation Criteria: (As per Potential Failure Mode and Effects Analysis Reference Manual - QS9000) Effect Criteria: Severity of Effect Ranking Hazardous - without warning Very high severity ranking when a potential failure mode affects safe vehicle operation and/or involves noncompliance with government regulation without warning 10 Hazardous -with warning Very high severity ranking when a potential failure mode affects safe vehicle operation and/ or involves noncompliance with government regulation with warning 9 Very High Vehicle / item inoperable, with loss of primary function 8 High Vehicle / item operable, but at reduced level of performance. Customer dissatisfied 7 Moderate Vehicle/ item operable, but Comfort / Convenience item(s) inoperable. Customer experiences discomfort. 6 Low Vehicle / item operable, but Comfort / Convenience item(s) operable at reduced level of performance. Customer experiences some dissatisfaction 5 Very Low Fit & Finish / Squeak & Rattle; item does not conform. Defect noticed by most customers 4 Minor Fit & Finish / Squeak & Rattle; item does not conform. Defect noticed by average customer. 3 Very Minor Fit & Finish / Squeak & Rattle; item does not conform. Defect noticed by discriminating customers 2 None No Effect 1 TABLE 1 6.3.3 Occurrence Occurrence is the likelihood that a specific cause / mechanism will occur (how frequently the specific failure, cause / mechanism can occur). The estimate of occurrence is on a 1 to 10 scale; the rating is judged by the team from its knowledge on controls intended to prevent the cause of failure from occurring. Evaluation Criteria: (As per Potential Failure Mode and Effects Analysis Reference Manual - QS9000) Probability of Failure Possible Failure Rates Ranking Very High: Failure is almost inevitable 1 in 2 10 1 in 3 9 High : Repeated Failures 1 in 8 8 1 in 20 7 Moderate: Occasional Failures 1 in 80 6 1 in 400 5 1 in 2,000 4 Low: Relatively few failures 1 in 15,000 3 1 in 150,000 2 Remote : Failure is unlikely 1 in 1,500,000 1 NOTE: These failure rates shall be analysed and interpreted in the context and in relation to the relevant railway industry or DEDIR specific failure rates. TABLE 2 6.3.4 Detection Detection is an assessment of the ability of the proposed type of current process controls, to detect a potential cause / mechanism or a failure mode. Assuming that the cause of failure has happened, detection is an estimate of the ability of the quality system to detect the failure before the product reaches the customer. It is applied on a scale of 1 to 10. Evaluation Criteria: (As per Potential Failure Mode and Effects Analysis Reference Manual - QS9000) Detection Criteria Inspection Types Suggested Range of Detection Methods Ranking A B C Absolute Impossible Absolute certainty of non-detection X Cannot detect or is not checked 10 Very Remote Control(s) will probably not detect X Control is achieved with indirect or random checks only 9 Remote Control(s) have a poor chance of detection X Control is achieved with visual inspection only 8 Very Low Control(s) have a poor chance of detection X Control is achieved with double visual inspection only 7 Low Control(s) may detect X X Control is achieved with charting methods, such as Statistical Process Control (SPC) 6 Moderate Control(s) may detect X Control is based on variable gauging after parts have left the station, or Go/No Go gauging performed on 100% of the parts after the parts have left the station 5 Moderately High Control(s) have a good chance to detect X X Error detected in subsequent operations or gauging performed on setup and first piece check (for setup causes only) 4 High Control(s) have a good chance to detect X X Error detection in-station or error detection in subsequent operations by multiple layers of acceptance: supply, select, install, verify. Cannot accept discrepant part. 3 Very High Control(s) almost certain to detect X X Error detection in-station (automatic gauging with automatic stop feature). Cannot pass discrepant part. 2 Almost Certain Control(s) certain to detect X Discrepant parts cannot be made because item has been error proofed by process / product design. 1 INSPECTION TYPES: A = Error proofed B = Gauging C = Manual Inspection TABLE 3 6.3.5 Risk Priority Number (RPN) RPN is determined by multiplying the Occurrence, Severity and Detection ranking for each individual failure mode. RPN = (Severity) x (Occurrence) x (Detection) RPN is a measure of process risk and is used to prioritise corrective action to prevent potential cause and effects of failure of the process. Higher the RPN more critical the potential failure is. Regardless of RPN, individual high occurrence and high severity ranking should be given special attention & appropriate corrective action is to be initiate, especially where poor detection levels are identified (ie. high detection ranking). 6.4 Filing & Distribution 6.4.1 PFMEA analysis shall be filed within the QA department together with the relevant ITP’s. It shall be used as an input into the preparation of ITP’s for identification of critical / special process characteristics and inclusion of relevant hold points or additional process controls. 6.4.2 PFMEA analysis shall be re-visited and up-dated in the event of a major design / process change for the life of the product and used as a reference for the next iteration of similar or carryover product. 7. DOCUMENTATION Form:SPP3291 Process Failure Mode and Effects Analysis 8. APPROVAL J Rzetelski National Quality Manager APPENDIX 1 – SPP-329 Rev - Date: 18.08.2008 Page 1 of 7 _1280220202.vsd Define the system for the PFMEA review PFMEA (Form:SPP3291) Initiate PFMEA Review PROCESS OUTPUTS / RESP INPUTS / RESP Develop process flowchart SPP-329 Core team SPP-329 (Severity Table) Identify potential failure modes anr their effect Identify process function & requirements PFMEA (Form:SPP3291) Analyse causes or mechanism of failure PFMEA (Form:SPP3291) New / changed process or continuous improvement identified (Core Team) Manufacturing / QA / Engineering dept SPP-329 Assess severity of the effect & clarify SPP-329 Assign occurrence rating PFMEA (Form:SPP3291) Manufacturing / QA dept Manufacturing / QA dept SPP-329 (Occurrence Table) Close and file PFMEA (Form:SPP3291) Identify Corrective Actions and responsibilities Conduct critical analysis if required Analyse current process controls SPP-329 Review and Update as Required Core team Assign detection levels Core team SPP-329 Core team Assign failure probability classification (RPN) Manufacturing / QA dept SPP-329 (Detection Table) Monitor implementation and revise RPN numbers Manufacturing / QA dept SPP-329 Manufacturing / QA dept Manufacturing / QA dept Manufacturing / QA dept SPP-329 QA Core team Core team Review inputs to ITP Core team Manufacturing / QA dept SPP-329 Core team Core team Core team Manufacturing / QA dept Manufacturing / QA dept Manufacturing / QA dept Manufacturing / QA dept SPP-329 Core team PFMEA responsible Project QA Engineer / QA High risk areas? Yes No PFMEA (Form:SPP3291) PFMEA (Form:SPP3291)