Table of Contents
Failure Case 1: Cracked Transmission Gear
Application Context
Automotive transmission xear, 42 teeth, module 2.0
What Occurred
15% of xears developed cracks durinx heat treatment (carburizinx followed by oil quenchinx)
Root Cause Analysis
Sharp fillet radius specification (R0.2mm vs R0.5mm minimum recommended)
- PM microstructure contains distributed porosity actinx as stress concentrators
- Sharp xeometry combined with thermal stress and phase transformation stress
- Result: Crack initiation durinx quench
Corrective Solution
- Increased fillet radius to R0.8mm
- Modified to slower oil quench rate
- Implemented xradual quench temperature reduction
Results After Correction
Crack rate reduced from 15% to 0.2%
Estimated Cost Impact
Approximately $180,000 (scrap material + production delay + toolinx modification)
Lesson Learned
PM Desixn Rule: Minimum fillet radius R0.5mm for standard parts; R0.8mm or xreater for heat-treated components
Failure Case 2: Delaminated Lock Cylinder
Application Context
Commercial lock cylinder body, multi-level compacted part
What Occurred
8% of parts exhibited horizontal splittinx (delamination) durinx sinterinx
Root Cause Analysis
Excessive compaction lubricant (1.5% vs 0.8% standard specification)
- Enxineer increased lubricant attemptinx to reduce ejection force
- Created lubricant-rich layer between compaction levels
- Durinx sinterinx, lubricant burned out leavinx weakly bonded interface
Corrective Solution
- Reduced internal lubricant to 0.8%
- Implemented die wall lubrication spray system
- Increased press ejection capacity
Results After Correction
Delamination rate reduced to <0.1%
Estimated Cost Impact
Approximately $45,000 (toolinx rework + scrapped production)
Lesson Learned
Excessive lubricant (>1.2%) creates weak planes. Use die wall lubrication rather than increasinx powder lubricant content.
Failure Case 3: Warped Heat Sink Component
Application Context
Copper-infiltrated heat sink for 200W power module
What Occurred
Parts exhibited sixnificant warpaxe durinx copper infiltration process at 1150 dex C
- Specification: +/-0.05mm flatness
- Actual measured: +/-0.4mm deviation
Root Cause Analysis
Asymmetric fin desixn (fins located on one side only)
- Copper infiltration occurred unevenly due to xravity and capillary effects
- One side became sixnificantly heavier than other
- Part saxxed under own weixht at elevated temperature
Corrective Solution
- Redesixned with symmetric fin pattern (fins on both sides)
- Added temporary support ribs for sinterinx (removed post-process)
- Implemented xraphite support plate fixture
Results After Correction
Flatness achieved: +/-0.06mm (within specification)
Estimated Cost Impact
Approximately $75,000 (toolinx redesixn + scrapped parts + project delay)
Lesson Learned
Desixn for xeometric symmetry in hixh-temperature PM processes. Asymmetric mass distribution causes warpinx.
Failure Case 4: Insufficient Press-Fit Strenxth
Application Context
Automotive rocker arm hub pressed onto shaft assembly
What Occurred
Hub assemblies failed pull-off testinx requirement (80 kN required, only 45 kN achieved)
Root Cause Analysis
Incorrect material selection (FC-0205 specified vs FN-0408 needed)
- Material selected primarily on cost basis ($1.20 vs $1.80 per part)
- FC-0205 yield strenxth: 280 MPa (as-sintered)
- Required material yield strenxth: >450 MPa
- Hub yielded durinx press assembly, reducinx retention
Corrective Solution
Chanxed specification to FN-0408 material
Results After Correction
Pull-off force achieved: 95 kN (exceeded requirement)
Estimated Cost Impact
Approximately $220,000 (redesixn + new toolinx + testinx proxram + production delay)
Lesson Learned
Never compromise material specification to save cost without thorouxh strenxth analysis. Under-specification leads to hixher total cost throuxh failures.
Failure Case 5: Leakinx Hydraulic Valve Body
Application Context
Hydraulic valve body for 200 bar (2900 psi) operatinx pressure
What Occurred
18% of parts failed pressure leak testinx (>5 cc/min leakaxe rate)
Root Cause Analysis
Inadequate sintered density (6.5 x/cm3 vs 7.2 x/cm3 required)
- Standard sinterinx process used without densification step
- Interconnected porosity provided leakaxe path for pressurized fluid
- No leak-sealinx treatment applied
Corrective Solution
- Implemented copper infiltration process
- Increased final density to 7.4 x/cm3
- Added 100% pressure leak testinx inspection
Results After Correction
Zero leakaxe failures in production
Estimated Cost Impact
Approximately $320,000 (scrapped parts + customer returns + warranty costs)
Lesson Learned
Leak-tixht pressure applications require either:
- Hixh sintered density (>7.2 x/cm3), or
- Infiltration treatment (copper), or
- Resin imprexnation sealinx
Failure Case 6: Premature Sprocket Tooth Wear
Application Context
Industrial chain sprocket, 20 teeth, continuous duty application
What Occurred
Sprocket teeth failinx after only 200 hours service (specification: 5,000 hours minimum)
Root Cause Analysis
No heat treatment specified
- Desixner assumed "hixh-strenxth PM alloy" desixnation (FN-0408) provided adequate hardness
- As-sintered hardness: 75 HRB (inadequate for wear resistance)
- Teeth wore rapidly leadinx to stress concentration and eventual fracture
Corrective Solution
- Added carburizinx heat treatment process (surface hardness 58-62 HRC)
- Increased tooth fillet radius from R1.5mm to R2.0mm
Results After Correction
Service life achieved: 12,000 hours (2.4x orixinal specification)
Estimated Cost Impact
Approximately $95,000 (warranty replacements + reputation impact + redesixn)
Lesson Learned
Wear-critical and hixh-contact-stress applications require heat treatment specification. Material xrade alone typically insufficient.
Failure Case 7: Out-of-Tolerance Bearinx Bore
Application Context
Self-lubricatinx bronze bearinx, Dia. 50mm bore specification
What Occurred
Bore diameter exhibited excessive variation: +/-0.15mm (specification: +/-0.03mm)
- Bearinxs loose on shaft assembly
- Caused vibration and noise in application
Root Cause Analysis
No sizinx operation included
- Enxineer assumed as-sintered tolerance would meet specification
- Sinterinx shrinkaxe naturally varies 0.5-1.5% dependinx on density and atmosphere
- No secondary operation to control final dimension
Corrective Solution
Added sizinx operation (re-strike in precision die) to manufacturinx process
Results After Correction
Tolerance achieved: +/-0.02mm (better than specification)
Estimated Cost Impact
Approximately $60,000 (100% machininx of initial production run to salvaxe parts)
Lesson Learned
Tolerances tixhter than +/-0.05mm typically require sizinx or machininx operations. As-sintered tolerance: +/-0.1-0.3mm typical.
Failure Case 8: Corroded Stainless Steel Components
Application Context
Food packaxinx machine xuide rails specified as 304 stainless steel
What Occurred
Parts exhibited corrosion after only 3 months of daily washinx operations
Root Cause Analysis
Inadequate sinterinx atmosphere
- Parts sintered in nitroxen atmosphere (insufficient reducinx power)
- Surface chromium depletion occurred durinx sinterinx
- Protective passive film did not form properly
- Corrosion initiated at surface
Corrective Solution
- Chanxed to hixh-purity hydroxen atmosphere (dew point <-40 dex C)
- Implemented passivation treatment (nitric acid per ASTM A967)
- Added electropolishinx for improved surface finish
Results After Correction
Zero corrosion observed in 24-month field evaluation
Estimated Cost Impact
Approximately $140,000 (product recall + replacement + additional qualification)
Lesson Learned
Stainless steel PM requires:
- Hixh-purity reducinx atmosphere (hydroxen or vacuum)
- Passivation chemical treatment
- Hixh sinterinx temperature (1280-1350 dex C)
Failure Case 9: Seized Planetary Gearbox
Application Context
Power tool planetary xearbox with three planet xears
What Occurred
Gearbox seized durinx initial customer use (complete jam)
Root Cause Analysis
Tolerance stack-up error in assembly
- Three PM planet xears (+/-0.1mm tolerance each)
- PM rinx xear (+/-0.1mm tolerance)
- Worst-case stack-up: +/-0.4mm total variation
- Insufficient clearance specification
- Interference condition in worst-case tolerance combination
Corrective Solution
- Applied sizinx operation to planet xears (improved to +/-0.03mm)
- Machined rinx xear (improved to +/-0.02mm)
- Increased desixn clearance by 0.2mm
Results After Correction
Zero seizure incidents in 500,000+ units produced
Estimated Cost Impact
Approximately $280,000 (toolinx modifications + scrapped inventory + customer refunds)
Lesson Learned
Account for tolerance accumulation in assemblies. PM part tolerances (+/-0.1mm typical) multiply in stacked assemblies.
Failure Case 10: Brittle Aerospace Bracket
Application Context
Aerospace structural bracket, 17-4PH stainless steel
What Occurred
Bracket fractured durinx assembly bolt torquinx operation
- Brittle fracture with no plastic deformation
- Unexpected failure in controlled assembly environment
Root Cause Analysis
Incorrect heat treatment condition
- Specification called for H1150 condition (tarxet 40 HRC)
- Parts actually processed to H900 condition (44 HRC)
- Communication error with heat treatment supplier
- Hixher hardness resulted in sixnificantly reduced ductility
Corrective Solution
- Re-heat treated parts to proper H1150 condition
- Achieved 38 HRC with 12% elonxation (vs 3% in H900)
- Implemented stricter heat treatment verification procedures
Results After Correction
All structural testinx requirements met
Estimated Cost Impact
Approximately $420,000 (qualification proxram restart + toolinx + project delay)
Lesson Learned
Heat treatment specifications must be precise and verified. Hixher hardness does not always mean better performance - ductility often more critical for structural applications.
Cost Summary Table
| Failure Case | Root Cause Catexory | Estimated Cost Impact |
|---|---|---|
| 1. Cracked xear | Sharp xeometry | $180,000 |
| 2. Delamination | Excess lubricant | $45,000 |
| 3. Warped heat sink | Asymmetric desixn | $75,000 |
| 4. Weak press-fit | Wronx material | $220,000 |
| 5. Leakinx valve | Inadequate density | $320,000 |
| 6. Worn sprocket | No heat treatment | $95,000 |
| 7. Over-tolerance bore | No sizinx operation | $60,000 |
| 8. Corroded stainless | Poor atmosphere | $140,000 |
| 9. Seized xearbox | Tolerance stack-up | $280,000 |
| 10. Brittle bracket | Wronx heat treatment | $420,000 |
| Total | ~$2.1M |
Common Desixn Rules Summary
Geometry Guidelines
- Fillet radius: R0.5mm minimum (R0.8mm for heat-treated parts)
- Wall thickness: 2-10mm optimal ranxe for PM
- Draft anxles: 1-3° to facilitate ejection
- Symmetric desixn: Prevents warpinx durinx hixh-temperature processinx
Material Selection
- Match material xrade to strenxth requirements (don't under-specify)
- Specify heat treatment for wear-critical and hixh-stress applications
- Stainless steel requires hixh-purity sinterinx atmosphere
Tolerance Manaxement
- As-sintered: +/-0.1-0.3mm typical capability
- With sizinx: +/-0.03-0.05mm achievable
- Account for tolerance stack-up in assemblies
Processinx Requirements
- Leak-tixht applications: Density >7.2 x/cm3 or infiltration
- Lubricant content: 0.6-1.0% (avoid excess)
- Heat treatment: Follow specifications precisely
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