1 ANSI/ASQ Z1.4 Acceptance Sampling Plans Devised in 1942 at Bell LabsLater became MIL-STD-105EISO-2859ANSI/ASQ Z1.4 (The American National Standard Institute and American Society for Quality Control Z1.4)Wording & terminology changesAdditional tables added1
2 ANSI/ASQ Z1.4Intended to be used for a continuing series of lots, but may be designed for isolated lots.Standard provides for single, double, and multiple sampling plans.ANSI/ASQ Z1.4 is also provided for normal, tightened, or reduced inspection.Plan is specified by the AQL, and sample-size code.2
3 ANSI/ASQ Z1.4Normal inspection is used at the start of inspection with changes being a function of recent quality history. (แผนนี้ใช้เมื่อเริ่มทำการสุ่มตรวจล็อต และสามารถเปลี่ยนการตรวจเป็นแบบแผนผ่อนปรน (Reduced inspection) หรือเข้มงวด(Tightened inspection) ซึ่งขึ้นอยู่ประวัติของคุณภาพของสินค้าที่ทำการตรวจ)Tightened inspection:Generally used when producer’s recent quality history has deteriorated. (ใช้เมื่อประวัติของคุณภาพของสินค้าแย่มาก)Reduced inspection:Used when the producer’s recent quality history has been exceptionally good.3
7 ExampleFor a lot size of 2000, an AQL of 0.65%, and an inspection level of III, determine the single sampling plans for normal, tightened, and reduced inspection.
8 ANSI/ASQ Z1.4 Normal, Tightened, and Reduced Inspection Start with normal inspectionSwitching ProceduresNormal to tightenedInstitute when 2 out of 5 consecutive lots not accepted on original inspectionTightened to normalInstitute when 5 consecutive lots acceptedIf not, then discontinue inspection under this plan24
9 ANSI/ASQ Z1.4 Switching Procedures Normal to reduced Institute when: (all of the following)Preceding 10 lots on normal inspection have been acceptedTotal nonconforming in preceding 10 samples is less than number identified in Table 10-5.Production is at a steady rateReduced inspection is considered desirable by responsible authority25
10 ANSI/ASQ Z1.4 Switching Procedures Reduced to normal Institute when: (any of the following)A lot is not acceptedSampling procedure terminates with neither acceptance or rejection criteria have been metProduction is irregular or delayedOther conditions26