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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.