Lecture 26 Quality inspection systems

Quality Inspection Systems  There are four systems which are used in industry – 4-point system – 10 point system – Clock-wise garment inspection system – Acceptance Sampling

4-point system  This is a fabric inspection method for different type of faults. This is issued by The American Society for Testing and Materials with reference to the designation:(ASTM D )  Faults are scored with penalty points of 1, 2, 3 and 4 according to their size and significance.

4-point system Size of defect (Length in inches) Penalty points and above 4  We can also assess fabric fault/defect rates against other systems as required by the client, for example jersey fabrics are often expressed in meters per fault/defect.

10-point system  This is an old system and not being used now a days

Clock-wise garment inspection system  See last page (Photocopy is attached)

Acceptance sampling  This a different technique.  This technique was first time used in 2 nd world war  This is a time saving technique  But in this technique there is a possibility of type-I error (Producer’s risk) and type-II error (Consumer’s risk)

Acceptance Sampling Plans …  Single sampling plans  Double sampling plans  Multiple sampling plans  Sequential sampling plans  Skip lot sampling plans

Important definitions …  Acceptance quality level (AQL)  Lot tolerance percent defectives (LTPD)  OC Curve (Operating Characteristic)  Average outgoing quality (AOQ)

OC Curve  OC curve means operating characteristic curve  X-Axis : % non-conformity  Y-Axis : Probability of acceptance

Inspection Levels…  Special Inspection Levels – There are 4 levels (S1, S2, S3, S4) – They are used for small sample sizes  General Inspection Levels – There are 3 levels (I, II, III)

Acceptable Quality Levels for Normal Inspection (% defective) Lot Size/ Sample Size Lot Acceptance (Ac) Number (maximum number of rejects to accept the lot) LS=2 to 8 SS= LS=9 to 15 SS= LS=16 to 25 SS= LS=26 to 50 SS= LS=51 to 90 SS= to 150 SS=

151 to 280 SS= to 500 SS= to 1200 SS= to 3.2K SS= to 10K SS= K SS= K SS= K SS=