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ME 333 Manufacturing Process I
© 2006 Prof. B. Ravi, Mechanical Engineering Department, Indian Institute of Technology, Bombay.
Lecture 09
Casting Defects
• Types of Defects • Inspection Methods • Moulding Related Defects • Filling Related Defects • Solidification Related Defects• Defects Analysis
Types of Defects
Based on Location:ExternalInternal
Based on Type:GeometricIntegrity
Based on Size/Severity:Small/MinorLarge/Major
Based on Process:Moulding-relatedFilling-relatedSolidification-related.
Based on Cause:Raw materialsProduct design Tooling designProcess parametersProcess control
Based on Stage:CastingRough machiningFinish machiningService
Based on Reparability:RepairableIrreparable
Inspection Methods
Destructive: Sectioning, MachiningMechanical testingChemical testing
Non-Destructive: Visual: large external defectsDimensional: size defects Pressure testing: leakage Radiography: internal holes Ultrasound: internal discontinuities Eddy current: hardness, structure Magnetic Particle: sub-surface discontinuitiesDye Penetrant: defects with opening to surface.
Moulding-related Defects
Improper ClosureAcross parting plane: flash Along parting line: mismatch
FLASHMISMATCH
[Atlas of Casting Defects, Institute of British Foundrymen]
Filling-related Defects
Incomplete Filling: cold shut, misrun.Gaseous Entrapments: blow hole, gas porosity.Solid Inclusions: sand inclusion, slag inclusion.
COLD SHUT MISRUN BLOW HOLE GAS POROSITY[Atlas
of
Cas
ting D
efec
ts,
Inst
itute
of
British
Foundry
men
]
Solidification/Cooling-related Defects
Solidification Shrinkage: cavity, porosity, centerline, sink.Hindered Cooling Contraction: hot tear, crack, distortion.
SHRINKAGE CAVITY POROSITY
SINK CORNER SHRINKAGE CRACK
[Atlas
of
Cas
ting D
efec
ts,
Inst
itute
of
British
Foundry
men
]
Defects Analysis
Individual Defect: Defect identificationCause identificationRemedy specification
Defects over a batch/period: Quality control charts Defect frequency (histogram)Defect spectrum (pattern over time)
Expert Systems for Defects Analysis Knowledge base (IF-THEN rules with confidence)Inference Engine
Summary
Casting defects are significant: typically 1-10% About 20 major types of casting defects:
Flash, mismatch, cold shut, misrun, blow hole, gas porosity,shrinkage cavity, porosity, centerline, sink, hot tear, crack,
scab, swell, metal penetration, rough surface.Other defects: improper composition and properties.
Implications:Minor defects can be repaired, with cost increase.
Major defects lead to rejection, with loss of productivity.
Status and Progress:Quality control and defects analysis: experts/systems. Quality certification and assurance gaining importance.Responsibility shifting to manufacturer; legal implications. Toward zero defects: prevention is better than cure!
Home Exercise
• Draw the cause-effect (Ishikawa) diagram for the following defects:Shrinkage porosity, Blow hole, Mismatch. Include causes related to moulding, filling and solidification.
• For each of above group of causes, identify the sub-causes (ex. improper filling), and sub-sub-causes (ex. ingate too small).
• Write the IF-THEN rules for identifying and troubleshooting (cause)the following defects: shrinkage porosity, gas porosity.