About Casting Defects Die Casting defects and its remedies

1. 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

2. Types of Defects
ƒ Based on Location:
¾ External
¾ Internal
ƒ Based on Type:
¾ Geometric
¾ Integrity
ƒ Based on Size/Severity:
¾ Small/Minor
¾ Large/Major
ƒ Based on Process:
¾ Moulding-related
¾ Filling-related
¾ Solidification-related.
ƒ Based on Cause:
¾ Raw materials
¾ Product design
¾ Tooling design
¾ Process parameters
¾ Process control
ƒ Based on Stage:
¾ Casting
¾ Rough machining
¾ Finish machining
¾ Service
ƒ Based on Reparability:
¾ Repairable
¾ Irreparable

3. Inspection Methods
ƒ Destructive:
¾ Sectioning, Machining
¾ Mechanical testing
¾ Chemical testing
ƒ Non-Destructive:
¾ Visual: large external defects
¾ Dimensional: size defects
¾ Pressure testing: leakage
¾ Radiography: internal holes
¾ Ultrasound: internal discontinuities
¾ Eddy current: hardness, structure
¾ Magnetic Particle: sub-surface discontinuities
¾ Dye Penetrant: defects with opening to surface.

4. Moulding-related Defects
ƒ Improper Closure
ƒ Across parting plane: flash
ƒ Along parting line: mismatch
FLASH
MISMATCH
[Atlas of Casting Defects, Institute of British Foundrymen]

5. Filling-related Defects
ƒ Incomplete Filling: cold shut, misrun.
ƒ Gaseous Entrapments: blow hole, gas porosity.
ƒ Solid Inclusions: sand inclusion, slag inclusion.
COLD SHUT MISRUN BLOW HOLE GAS POROSITY
[Atlas
of
Casting
Defects,
Institute
of
British
Foundrymen]

6. Solidification/Cooling-related Defects
ƒ Solidification Shrinkage: cavity, porosity, centerline, sink.
ƒ Hindered Cooling Contraction: hot tear, crack, distortion.
SHRINKAGE CAVITY POROSITY
SINK CORNER SHRINKAGE CRACK
[Atlas
of
Casting
Defects,
Institute
of
British
Foundrymen]

7. Defects Analysis
ƒ Individual Defect:
¾ Defect identification
¾ Cause identification
¾ Remedy specification
ƒ Defects over a batch/period:
¾ Quality control charts
¾ Defect frequency (histogram)
¾ Defect spectrum (pattern over time)
ƒ Expert Systems for Defects Analysis
¾ Knowledge base (IF-THEN rules with confidence)
¾ Inference Engine

8. Summary
ƒ Casting defects are significant: typically 1-10%
ƒ 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.
ƒ Implications:
¾ Minor defects can be repaired, with cost increase.
¾ Major defects lead to rejection, with loss of productivity.
ƒ Status and Progress:
¾ Quality control and defects analysis: experts/systems.
¾ Quality certification and assurance gaining importance.
¾ Responsibility shifting to manufacturer; legal implications.
¾ Toward zero defects: prevention is better than cure!

9. 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.