Importance of Robust FMEA Development in Reducing Heat Treat Product Issues

Ms. Suranjeeta Dhar Ms. Medina Kaknjo Ford Motor Company

Overview

• Heat Treat Systemic Issues • Two (2) case studies will be presented that exemplify

the significance of FMEA in mitigating risks of heat treat systemic issues

• Key inputs for consideration in developing robust Heat Treat PFMEA

• Risk Mitigation Tool - AIAG CQI-9 Special Process: Heat Treat System Assessment

• Linkage of Heat Treat PFMEA to CQI-9 Requirements • Data from NHTSA and automotive company databases

showing improvement in heat treat related issues

Introduction

• Improperly heat treated product is not easily discernible in form and appearance from properly heat treated product

• Robust process and product control is critical to ensure all parts meet product specifications

• Comprehensive review and development of a robust FMEA is key input in defining the process and product controls.

• AIAG CQI-9 Heat Treat System Assessment is a constructive resource for evaluating process and product control systems in heat treating

Key Heat Treat Systemic Issues

CASE STUDIES

Case Study #1 – Fastener Issue

• Vehicles unable to start due to broken ground cable bolts • Bolts were neutral hardened in a continuous heat treat

shaker furnace • The broken bolts exceeded the hardness specification • Microstructure analysis of the broken bolts revealed

untempered martensite which resulted due to improper tempering operation

Case Study #1 – Fastener Issue

• Investigation of the process revealed the flat hearth of the shaker furnace allowed free movement of some of the bulk loaded bolts.

• The unintended free movement of the bolts prevented them from being processed adequately through the tempering operation in the furnace.

• Inadequately tempered bolts were unintentionally mixed with properly tempered bolts.

SYSTEMIC ROOT CAUSES

• The heat treater did not perform adequate advanced quality planning to identify criticality of furnace part handling design.

• Failure mode not identified in the process FMEA.

• Process controls critical to quality were not identified.

• Furnace design (DFMEA) did not consider different failure modes, severity and occurrence for handling small parts of various design.

Case Study #2 – Induction Hardening Issue

• Parts were found broken in vehicle upon delivery to dealership.

• Investigation of broken part revealed crack initiated at OD.

• Cause of crack was determined to be overheating during induction hardening.

Case Study #2 – Induction Hardening Issue

• Review of heat treat process control at process owner revealed the following issues: – Dwell time and power were allowed to be adjusted by the

operator after setup verification – Rotation speed was not monitored nor measured.

• In addition the following characteristics were not properly checked: – Hardness and case depth were not being checked in the critical

radius or the transition from a large to small diameter. – Longitudinal sections were not obtained consistently from the

center of the bearing journal for macro case depth inspection.

SYSTEMIC ROOT CAUSES

• The heat treater did not perform adequate advanced quality planning to identify critical location for heat treat pattern check.

• Failure mode not identified in the process FMEA.

• Process controls critical to quality were not identified and did not meet minimum requirements.

• Control plan did not include checking of microstructure at the minimum required frequency.

KEY TAKEAWAYS

• Most of the Heat Treat systemic issues can be directly related to failure modes and key operational steps not identified in the FMEA.

• Heat Treat characteristics are “Pass-Thru” in nature. This means heat treat defects are difficult to detect through subsequent assembly processes and can be passed on to the end customer.

• Most heat treat characteristics can be verified through destructive methods only. Hence having a good understanding of heat treat failure modes associated with each process step is crucial in order to have robust controls.

• Driving robustness in FMEA development is the critical to mitigate risks related to heat treat issues.

KEY CONSIDERATIONS FOR ROBUST FMEA AND BEST PRACTICE

HEAT TREAT FMEA FUNDAMENTALS

• Following the AIAG PFMEA guidelines, Heat Treat FMEA should include identification and evaluation of both process and product failure modes.

• Evaluation of process failure modes should begin with developing a detailed process map.

• For robustness, Heat Treat FMEAs should be inclusive of all operational steps from part receipt to shipment as key process inputs, such as: Receiving Product Staging Product Handling Pre-Treatment Loading/Fixturing/Positioning Pre-wash/Rinsing

Austenizing/Solutionizing Transfer time Quenching Tempering/Aging Post-wash

KEY PROCESS EVALUATION METHOD

One method is to map key process inputs to corresponding outputs. Each Key Process Input should be further evaluated for sub functions. EXAMPLE KPI (KEY PROCESS INPUT) #1 • X = Product Handling

– x1 = Product Identification – x2 = Product Traceability – x3 = Control of non-conforming product – x4 = Identification of trap points – x5 = Inspection of containers for foreign material – x6 = Product segregation during equipment emergency

For every KPI, the Key Process Outputs should be similarly evaluated. KPO (KEY PROCESS OUTPUT) #1 • Y = Mixed Product

– y1 = Green parts mixed with heat treated parts – y2 = Improperly heat treated parts mixed with good parts – y3 = Foreign parts mixed with good parts

KEY PROCESS EVALUATION METHOD

P-Diagrams that are typically used to develop DFMEA’s can also be effectively used to determine both Key Process Inputs as well as Outputs.

HEAT TREAT PROCESS P-DIAGRAM

Example of a P-Diagram For Induction Heat Treated Shaft

Induction Heat TreatShaft

Special Characteristics

SC17 - Shaft alignment between shaft OD and nose IDSC18 - Shaft Static Torsional Break Torque

Noise Factors

N1: Incoming material N1.1: CompositionN1.2: Surface HardnessN1.3: ToughnessN1.4: Torsional StrengthN1.5: Fatigue Strength

N2: Equipment wear/ Coil leakageN3: Quench

N3.1: Concentration variation, contaminationN3.2: TemperatureN3.3: Flow Variation

N4: Power supply variationN5: Part temperature variationN6: Delay in temperN7: Coil resistivity change over time

Key Process Inputs

1. Power/Frequency2. Quenching3. Heating4. Part Loading5. Tempering 6. Coil (Type and condition)7. Material Chemistry8. Part to Coil Position

Expected Process Outputs

Y1: Acceptable microstructure, case depth, pattern and hardnessY2: No evidence of overheating or cracksY3: Meets torsional strength (torque requirement)Y4: Meets expected fatigue life (B10)

Output Monitoring Methods

Y1-1: Check for hardness (surface, case, core) and case depth per control plan*Y1-2: Check for case pattern from longitudinal section(s) per control plan* Y1-3: Verify microstructure through metallurgical section(s)*Y2: Visually inspect for cracksY3: Conduct torque testing on assembly per control plan

Error States

E1: Cracked part E5: Part distortion E2: Broken shaftE3: Noisy compressor due to premature wear of shaftE4: Mixed part (unheatreated/scrap/setup part mixed with good) impacting large suspect volume

Manufacturing Control Factors

X1: Energy X2: Quench

X2.1: Flow X2.2: PressureX2.3: Level X2.4: DelayX2.5: Temperature X2.6: ConcentrationX2.7: TimeX2.8: PM for quench plenum, quench linesX2.9: Quench alarm

X3: Heat X3.1: Cycle timeX X3.2: Rotation speed X3.3: Travel speed/distance X3.4: Process alarms

X4: Part loadingX5: Temper

X5.1: Delay X5.2: TemperatureX5.3: Time X5.4: Process alarms

X6: Coil managementX6.1: Type X6.2: DimensionX6.3: Condition X6.4: Traceability

X7: Material X7.1: Chemistry X7.2: Hardenability

X8: First piece setup verification with correct process recipeX9: Heat Treat Lot Control

Process Control/Monitoring Methods

X1: Continuous Energy monitoring with set control limits*X2: Automatic recipe driven control of Quench within set limits, verification of quench alarm.X3: Set recipe to control X3, following first piece setup , process deviation alarms and verification of alarms.X4: Part loading procedure/work instruction/visual aids X5: Set recipe for Temper Control following first piece setup verification process deviation alarms and alarm verificationX6: Coil identification and tracking, tracking of coil rebuilds, verification of coil dimension to print/design. X7: Verification of the material certification to specification for chemistry and hardenability.

X8: Position verification through 1st piece setup, gages (calipers, thickness gage etc.) and sensors (optical, proximity switches)*

X9: Heat treat lot control procedure and work instructions for part segregation in the event of process deviation, interruption and power failure*

HEAT TREAT PROCESS P-DIAGRAM

Example of a P-Diagram For Gaseous Nitrocarburizing Process

ROBUST IDENTIFICATION OF TYPES OF FAILURE MODES Four types of Failure Modes occur as listed below. The first and second types are commonly applied whereas, the third and fourth types are typically missed when identifying failure modes. 1.NO FUNCTION. 2.PARTIAL/OVER FUNCTION/DEGRADED OVER TIME. 3.INTERMITTENT FUNCTION. 4.UNINTENDED FUNCTION A good check to discover “hidden” functions is to match all possible failures with the appropriate functions.

BEST PRACTICE

• Heat Treat FMEAs can be developed as part specific, process specific or part family based FMEA.

• Development of the Heat Treat FMEA should begin with a detailed process map.

• Tools such as Input/Output Function, P-Diagrams help drive robustness in evaluating key process inputs and outputs to be included in the FMEA.

• Ensuring all types of failure modes are taken into consideration in order to account for “hidden” functions.

• Industry standard, AIAG CQI-9, serves as an additional reference for guidance to key process inputs and outputs for specific heat treat processes.

AIAG CQI-9 SPECIAL PROCESS: HEAT TREAT SYSTEM ASSESSMENT

AIAG SPECIAL PROCESS: HEAT TREAT SYSTEM ASSESSMENT

Project Team Organization

Quality Steering Committee

Special Processes Sponsors

Special Processes Project Team

Heat Treat Work Group (CQI-9)

Plating Work Group (CQI-11)

Coatings & Pretreatment Work Group(CQI-12)

Welding Work Group (CQI-15) Soldering (CQI-17)

Technical Experts

Manage & Implement

CQI – 9 HEAT TREAT WORK GROUP

• Core Members – Phil Mikula (Chair) – TRW – Madhu Chatterjee – Bodycote – Rick Metcalf & Dave Paluch – GM – Medina Kaknjo & Suranjeeta Dhar – Ford

NA – Peter Schiefer – Ford Europe – Stefan Bruder – Bodycote Europe – Pete Batche – Akebono NA – Dean Higdon – Acument – Virender Choudhri – Delphi – Werner Schwan – Bosch Europe – Darrell Rydzewski – Control Services – Thomas Ruecker – Invensys Europe

• Supporting Members – Mike Wiezbowski – Chrysler – Mike Oberg – Induction

Services – Jeff Martin – ZF – Leonard Gadzinski –

Acument

CQI-9 – Applicable Processes

• Carburizing (including low pressure or vacuum) • Carbonitriding • Carbon Correction • Neutral Hardening (Quench & Tempering) • Nitriding (Gas and Ion or Plasma) • Ferritic Nitrocarburizing (FNC – Gas or Salt) • Sinter Hardening (powder metal) • Aluminum Solution Treating / Age Hardening • Precipitation Hardening • Austempering • Martempering • Tempering • Induction Heat Treating • Normalizing, Annealing, & Stress-Relieving

CQI-9 Summary

• 1st edition released March 2006 • 2nd edition released 3rd Quarter 2007 • 3rd edition available now; effective for 2012 CQI-9

assessments – Added process tables – Revised/added element questions – Eliminated reference to AMS 2750 – Miscellaneous Changes

CQI-9 Goals

• Reduction of campaigns, spills, recalls and warranty claims related to heat treated components

• Focus on specific technical process control for implementation of quality systems

• Standardize heat treat surveys within the automotive industry

Typical Utilization of CQI-9

CQI-9 Process Flow – High Level

CQI-9 HEAT TREAT FMEA REQUIREMENTS

CQI-9 3rd Edition HTSA Question # 1.3 • Question:

Are heat treat FMEA’s up to date and reflecting current processing?

• Requirements and Guidance: The organization shall incorporate the use of a documented Failure Mode and Effects Analysis (FMEA) procedure and ensure the FMEA’s are updated to reflect current part quality status. The FMEA shall be written for each part or part family or maybe process-specific and written for each process. In any case, they shall address all process steps from part receipt to part shipment and all key heat treat process parameters as defined by the organization. A cross-functional team shall be used in the development of the FMEA. All special characteristics, as defined by the organization and its customers, shall be identified, defined, and addressed in the FMEA.

INFLUENCE ON HEAT TREAT RISK MITIGATION

NHSTA Data

• The recall data base from NHTSA was reviewed. • Recalls between 1999 and 2005 were compared to recalls between 2006

and 2012. • The number of recalls due to improper heat treat, the number of vehicles

recalled, and the average number of vehicles per year were determined.

Note: Although number of recalls increased during this period, the total number vehicles affected were significantly reduced suggesting

better lot control.

NHSTA Data

Down by

288,775 vehicles

Down by 76,608

vehicles/year by 2

Analysis of data was limited to 6 years prior and

post implementation of CQI-9 requirements

Automotive Data

• Number of field occurrences and suspended shipments from 1999 to 2012 were analyzed.

• The data shows a decrease of heat treat related issues since CQI-9 was introduced globally

Automotive Data

65% Improvement

30% Improvement

38% Improvement

Analysis of data was limited to 6 years prior and

post implementation

of CQI-9 requirements

Summary

• Two (2) case studies were presented to show the importance of developing robust FMEA.

• Key inputs to Heat Treat PFMEA, some Best Practices and the linkage to Heat Treat Industry Standard, AIAG CQI-9 was discussed.

• AIAG CQI-9 Special Process: Heat Treat System Assessment was described and typical utilization of CQI-9 was presented.

• Lastly, NHTSA data and automotive company data showed the improvement in heat treat related issues since the implementation of CQI-9 in 2006.

Conclusion

• Robust FMEA development is the key to mitigating heat treat related product issues.

• Global implementation of CQI-9 helped mitigate some of the risks through standardizing heat treat requirements in the industry

• Global implementation of CQI-9 significantly reduced heat treat related issues

• CQI-9 provides proper guidance to avoid improper heat treated parts from being produced or shipped to the customer

References

• ASM International Materials Handbook, Volume 4, 10th Edition p. 573 - 586 • Unpublished research by S. Dhar, Ford Motor Company, Dearborn, MI, USA • Ford FMEA Handbook v4.2 • AIAG, CQI-9 Special Process: Heat Treat System Assessment 3rd edition, p.6 • http://www-odi.nhtsa.dot.gov/downloads/flatfiles.cfm, Federal Department

of Transportation, National Highway Safety Association, FLAT_RCL.zip, last modified July 10, 2013

• Reducing Heat Treat Product Issues in the Global Automotive Heat Treat Supply Chain – S. Dhar, M. Kaknjo, P. Mikula, T. Buck, ASM HT Conference 2013.