Lecture Operations management: Creating value along the supply chain (Canadian edition) - Chapter 3S

Quality contracts require producer’s risk of 0.05 with an AQL of 1% defective and a consumer’s risk of 0.10 with a LTPD of 5% defective.. Average Outgoing Quality (AOQ)[r]

Robert S Russell, Bernard W Taylor III, Ignacio Castillo, Navneet Vidyarthi

CHAPTER 3 SUPPLEMENT

Acceptance Sampling

OPERATIONS MANAGEMENT:

Creating Value Along the Supply Chain,

Canadian Edition

Lecture Outline

—Single-Sample Attribute Plan

—Operating Characteristic Curve

—Developing a Sampling Plan with Excel

—Average Outgoing Quality

—Double - and Multiple-Sampling Plans

Acceptance Sampling

—Accepting or rejecting a production lot based on the number of defects in a sample

—Not consistent with TQM or Zero Defects

philosophy

— producer and customer agree on the number of

acceptable defects

— a means of identifying not preventing poor quality

— percent of defective parts versus PPM

—Sampling plan

— provides guidelines for accepting a lot

Single–Sample Attribute Plan

• Single sampling plan

• N = lot size

• n = sample size (random)

• c = acceptance number

• d = number of defective items in sample

• If d ≤c, accept lot; else reject

Producer’s and Consumer’s Risk

—AQL or acceptable quality level

— proportion of defects consumer will accept in given lot

— or producer’s risk

— probability of rejecting a good lot

—LTPD or lot tolerance percent defective

— limit on the number of defectives the customer will accept

—β or consumer’s risk

— probability of accepting a bad lot

Producer’s and Consumer’s Risk

Sampling Errors

Producer’ Risk

Type II Error

Operating Characteristic (OC) Curve

—Shows probability of accepting lots of different

quality levels with a specific sampling plan

—Assists management to discriminate between good and bad lots

—Exact shape and location of the curve is defined by

the sample size (n) and acceptance level (c) for the

sampling plan

OC Curve

Developing a Sampling Plan

with OM Tools

ABC Company produces mugs in lots of 10,000

Quality contracts require producer’s risk of 0.05 with

an AQL of 1% defective and a consumer’s risk of

0.10 with a LTPD of 5% defective What size

sample and what acceptance number should ABC

use to achieve performance measures called for in

the sampling plan?

N = 10,000

α = 0.05

β = 0.10 AQL = 1%

LTPD = 5%

n = ? C=?

Average Outgoing Quality (AOQ)

—Expected number of defective items that will pass

on to customer with a sampling plan

—Average outgoing quality limit (AOQL)

— maximum point on the curve

— worst level of outgoing quality

AOQ Curve

Double-Sampling Plans

— Take small initial sample

— If # defective ≤ lower limit, accept

— If # defective > upper limit, reject

— If # defective between limits, take second sample

— Accept or reject based on 2 samples

— Less costly than single-sampling plans

Multiple-Sampling Plans

— Uses smaller sample sizes

— Take initial sample

— If # defective ≤ lower limit, accept

— If # defective > upper limit, reject

— If # defective between limits, resample

— Continue sampling until accept or reject lot based

on all sample data

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