Is using ANSI/ASQ Z1.4-2008 the correct sampling plan to determine Pass/Fail of Apparel measurements?

Sokat

Registered
Hello,

This relates to Apparels industry. We had an inspector appointed by the customer to do a Pre Shipment Inspection.

They used ANSI/ASQ Z1.4-2008 sampling level II for what they call 'visual' inspection which was essentially attributes inspection. Major 2.5 and Minor 4.0. Based on the lot size of 2000 pcs they inspected 125 pcs as the random sample size. So far so good.

They then used special inspection level S4 for measurements of the garments and selected 32 garments with Accept as 2 and reject 3.

I was not convinced that this was right as would have thought that to determine conformance, they should have used variable sampling plan Z1.9 based on MIL-STD-414 and should do the standard deviation calculation to determine percent conformance/ non-conformance.

They chose 7 measure points. 1. Chest width 2. Body length 3, Shoulder width 4. Bottom opening (sweep) 5. Hood height 6. Sleeve length and 7. cuff opening.

They classified a garment as defective if any one of the measurement was out of tolerance on any one garment. For e.g. body length is specified to be 27 inches. The process tolerance given is +/- ½ inch. Thus if any one garment measured + or - ¾ inch it was counted as one defective piece. They ended up counting 22 out of 32 in this way and failed it.

The overall report was PASS for Visual FAIL for Measurement.

My view was that their measurement inspection was not correct. If they were counting out of tolerance points then statistically they are asking a score of 2 out of 32x7 = 224 points and not 2/32. If they have to convert their variable into attribute then the garment should count as a defect if it falls under 'Major' classification, and a length of +¼ inch does not make a garment fall in that definition and should not be counted. Hood is cinched for functionality and its measure of +½ inch or ¼ inch over tolerance is not 'Major'

Below is a part of the report that shows the sizes, tolerances and what they measure. The yellow highlights are out of tolerance and is considered major defect. This is a pullover, not a dress shirt.

In the table below they inspected 3 pcs size XS, 4 pcs size S, 4 pcs Size M, 4 pcs size L, 4 pcs size XL and 4 pcs size XXL. Total 23 garments and their count was major = 20. I Have not included the table for the rest of 9 pcs but it looks similar.

Screenshot 2020-08-01 at 18.51.34.jpg

So my questions are:
1. Is using Z1.4 attributes sampling valid for variable inspection as above?


2. If answer to Q1 is Yes, then Is their classification of 'Major' count correct?
 

William55401

Quite Involved in Discussions
What were the pre-determined quality requirements? What features were identified as important / critical to quality? Did supplier and customer agree as part of order acceptance?
 

Sokat

Registered
What were the pre-determined quality requirements? What features were identified as important / critical to quality? Did supplier and customer agree as part of order acceptance?

Thanks William. The question here is not of compliance with any agreements or legal standing. My question is more to do with the methodology. Technically, what is the correct application of sampling plans to evaluate a process variable, regardless of any commercial agreements.
 

William55401

Quite Involved in Discussions
Understand. My point was that sampling (and analysis) methodology can also be pre-determined. Good luck.
 

Sokat

Registered
Understand. My point was that sampling (and analysis) methodology can also be pre-determined. Good luck.
Yes, your point is spot on and well taken. There should be a more detailed agreement on sampling and methodology. But what I am trying to learn from everyone here is if Z1.9 sampling should have been used for variables to establish conformance/non-conformance of what is essentially a process variation and not attribute.
 

vzepeda

Registered
Applying ANSI/ASQ Z1.4 Inspection Level II, does that mean I have to inspect 100% of all characters of the sample size?
 

vzepeda

Registered
We manufacture castings. I am not 100% sure but I feel we are inspecting Attributes, if I understand it correctly. Our customer has flowed down the sampling plan that i have addressed and they say based off of the lot size, sample is 80, which I agree, but 100% of all characters of that 80 are to be inspected, not sure that I agree
 

Mike S.

Happy to be Alive
Trusted Information Resource
What's your lot size and AQL?

Here's an example: Let's say you are required to measure length, width, thickness, and a hole size. Lot size is 1000, AQL is 1%, sample size is 80, inspection by attributes.

You determine pass/fail for each of the 4 characteristics on the 80 pieces. If the number of defects is </= AC number, you pass the lot of 1000.
 
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