1. Linear Yard basis:
Acceptable tolerance=20 points per 100 linear yard
2. Square yard basis:
Points/100 sq. yd= Total Points scored in the bulk X 100 X 36
Width of the roll(inch) X total yds inspected
a. 28 points per 100 sq. yd. for each individual roll.
b. 20 points per 100 sq.yd. for average of rolls inspected.
1st Quality: Penalty points not exceed the acceptable tolerance.
2nd Quality: Penalty points exceed the acceptable tolerance.
Sampling method represents on which sampling level the inspection carries out and on which mathematical theories it is based. DQC uses the MIL-STD-105E as sampling method, which is recognized international quality control standard and the most widely accepted sampling method by every industrial company. This standard now has equivalents in all nationals and international standardization organizations such as BS 6001, ABC 105, ANSI/ASQ Z1.4, NFX 06-022, ISO 2859, DIN 40.080.
They are based on mathematical theories of probability and offer the advantage of clearly defining the number of samples to be drawn for inspection from a given lot or consignment. They also suggest the maximum number of defective items allowed in the sample size.
Unless otherwise instructed, DQC uses the Single Sampling Plan Normal Level II (according to the MIL-STD-105E standard). This is generally the common requirement for products manufactured in China.
You can use the AQL Table to calculate the number of sample drawn depending on the lot or consignment quantity.
You can also specify a very simple sampling method by percentage of the consignment quantity or the given lot, for example 5%, 10%, even more…(in this case, you need also specify acceptable quality level such as 4% for Major defectives, 8% for Minor defectives...)
Acceptable Quality Level (AQL)
As MIL-STD-105E is based on random sampling, therefore a few defectives are considered acceptable. The AQL is the maximum defective rate that, for purposes of sampling inspection, can be considered satisfactory as a process average. Different AQL may be designated for different defects such as critical, major and minor defects. The AQL should be agreed upon between buyer and supplier before the start of production.
The following AQL are usually applied by DQC unless otherwise instructed by the client: