铸造缺陷- 9

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 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 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. 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] 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 [ A t l a s o f C a s t i n g D e f e c t s , I n s t i t u t e o f B r i t i s h F o u n d r y m e n ] 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 [ A t l a s o f C a s t i n g D e f e c t s , I n s t i t u t e o f B r i t i s h F o u n d r y m e n ] 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 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! 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.