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

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Solidification/Cooling-related Defects

Solidification Shrinkage: cavity, porosity, centerline, sink.Hindered Cooling Contraction: hot tear, crack, distortion.

SHRINKAGE CAVITY POROSITY

SINK CORNER SHRINKAGE CRACK

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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.