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Origin of the Zero Defect Concept: Philip B. Crosby, known as the “father of zero defects” and “global quality management guru,” introduced the concept of “zero defects” in the early 1960s and promoted the zero defects movement in the United States.
Later, the idea of zero defects spread to Japan, where it was comprehensively promoted in the manufacturing industry, leading to a rapid improvement in product quality and placing Japanese manufacturing ahead of global standards, further expanding into all areas of industry and commerce.
The core of the zero defect theory is: “Do it right the first time.”
The so-called “zero defect” sampling plan simply means that regardless of your batch size and sample size, the acceptance number for sampling inspection is Ac=0, i.e., “0 accept, 1 reject.”
Example:
A certain client specifies in their “Supplier Quality Manual” that finished product acceptance uses the C=0 sampling plan. The C=0 sampling plan, commonly referred to as the zero defect sampling plan, means that only if all sampled products pass inspection can the entire batch be accepted; if even one defective item is found during acceptance, the entire batch will be deemed nonconforming.
This requirement raised concerns among some colleagues within the company, who wondered if such a demand was too strict. They believed the company could not meet it, and some even considered it a “bullying” clause from the client.
In fact, the C=0 sampling plan is widely used in the country today. It does not have a strict or lenient concept in itself, similar to the GB/T2828.1-2012 sampling plan commonly used in China.
When applying GB/T2828.1-2012, the strictness of a sampling plan depends on our choice of AQL.
A smaller AQL value results in a stricter sampling plan;
A larger AQL value results in a more lenient sampling plan.
Similarly, the C=0 sampling plan also specifies a series of AQL values identical to those in GB/T2828.1-2012, and the choice of AQL value is entirely up to our selection and negotiation with the client.
Therefore, the assertion that the “C=0 sampling plan is too strict” is completely unfounded; this misunderstanding arises simply from a lack of understanding of the C=0 sampling plan.
It should be noted that the client’s “Supplier Quality Manual” is established based on IATF16949:2016, which explicitly requires that the acceptance level must be zero defects.
(IATF16949:2016 Clause 8.6.6 Acceptance Criteria: The organization shall determine acceptance criteria, which shall be approved by the customer when required. For attribute data sampling, the acceptance level shall be zero defects.) Therefore, the client’s requirement is justified and does not constitute any “bullying” demand.
Number 01 .
Introduction to Sampling Inspection
Sampling inspection, also known as statistical sampling inspection, refers to the process of randomly selecting several units from a batch of products for inspection and making quality judgments about the entire batch based on the inspection results of the sample.
We know that inspection does not create value, so how to conduct inspections more economically and quickly directly relates to production costs and efficiency. The theory of statistical sampling inspection was established in 1929 by Dodge and Romig at Bell Labs in the United States, and along with the statistical process control (control charts) proposed by Shewhart in 1924, it is regarded as one of the two landmark achievements marking the transition of quality management from quality inspection to statistical quality control. The emergence of statistical sampling inspection theory changed the previous reliance on large-scale inspections to ensure product quality.
Since the U.S. military issued the MIL-STD-105 sampling standard in 1950, statistical sampling inspection has gradually been promoted worldwide. The upgraded and extended versions of MIL-STD-105 have been adopted by the International Organization for Standardization and many national standards. The U.S. military’s MIL-STD-105 standard has gone through five versions from A to E and has now been abolished by the military.
Number 02 .
Two Types of “Zero Defect” Sampling Plans
In 1965, an American professor, Nicholas S. Stogdill, published the C=0 sampling plan, which has undergone several revisions, with the latest version being the fourth edition. The C=0 sampling plan is modified from MIL-STD-105, with the acceptance criteria limited to “0 accept, 1 reject,” hence it is also referred to as the “zero defect” sampling plan.Although the C=0 sampling plan is not yet an international or national standard in any country, the concept of “zero defects” has become deeply ingrained, and with explicit requirements in IATF16949:2016, it has been widely applied in the business sector.In 1994, the three major American automakers (General Motors, Ford, and Chrysler) released the QS9000 quality system standard, which explicitly required that acceptance criteria must be zero defects in clause 4.10.1.1.This requirement in QS9000 facilitated the rapid promotion and application of the C=0 sampling plan. After QS9000 was adopted as an international standard IATF16949:2016, the application of the C=0 sampling plan further expanded.In 2005, to honor Professor Nicholas S. Stogdill for his outstanding contribution to the creation of the C=0 sampling plan, the American Society for Quality awarded him the Shainin Medal.The American Society for Quality stated in the citation: His greatest contribution was developing a practical, easy-to-use, and economical zero defect sampling plan. His method has saved millions of dollars in military and commercial applications. Because his method has proven to be practical, simple, and economical, it has been widely accepted.In 1996, the U.S. military introduced a new version of the sampling standard, MIL-STD-1916. Like the C=0 sampling plan, MIL-STD-1916 also limits its acceptance criteria to “0 accept, 1 reject,” so MIL-STD-1916 can also be called a zero defect sampling plan.MIL-STD-1916 no longer emphasizes sampling techniques like MIL-STD-105 but instead requires suppliers to establish preventive quality systems and effective process quality control systems. MIL-STD-1916 emphasizes prevention over inspection.Since IATF16949:2016 only requires that “the acceptance level should be zero defects” and does not specify whether to use the C=0 sampling plan or MIL-STD-1916, companies can decide which “zero defect” sampling plan to use based on their own circumstances and specific customer requirements.
Number 03 .
Application of Domestic Sampling Standards
In 1981, China began to formulate its statistical sampling standards GB/T2828 based on ISO2859 (i.e., MIL-STD-105D).GB/T 2828 has undergone three revisions in 1987, 2003, and 2012, with the latest version being GB/T2828.1-2012, which is the most widely used in the country.Although MIL-STD-105 has been abolished in the United States, many companies in China still use this standard, and some even use earlier versions like MIL-STD-105D.Currently, the C=0 sampling plan is widely used in many automotive industry companies and other enterprises voluntarily adopting the IATF16949 standard.Number 04 . The Concept of “Zero Defects”The “zero defect” (C=0) sampling plan is modified from MIL-STD-105, and the concepts related to statistical sampling are derived from the same source as GB/T 2828. The definitions of terms related to GB2828 can be used in the “zero defect” (C=0) sampling plan. To highlight the important concept of “zero defects,” the “zero defect” (C=0) sampling plan modifies the terms “nonconforming” and “nonconforming products” in GB/T 2828 to “defects” and “defective products.” Since the judgment criteria of the “zero defect” (C=0) sampling plan are limited to “0 accept, 1 reject,” as long as one defective product appears, regardless of batch size or sample size, the entire batch can be deemed nonconforming. Emphasizing the concept of “zero defects” can promote an increase in quality awareness.Another consideration of the “zero defect” (C=0) sampling plan is: if your quality is quite poor, having an acceptance number greater than 0 is not very helpful; when your sampling plan allows for an acceptance number greater than zero, you are authorizing your inspectors to accept some potentially useless products; zero defects enforce action on any nonconformance; if you are striving for zero defects, how can you allow your sampling plan to permit defects?We see many companies often use the concept of “zero defects” for quality promotion, but how can the spirit of “zero defects” be implemented? If we promote “zero defects” on one hand while still using the GB/T 2828.1-2012 sampling plan to accept defective products on the other, that is inherently a contradictory joke.Number 05 . The Simplicity of the “Zero Defect” (C=0) Sampling PlanCompared to GB/T 2828.1-2012, the “zero defect” (C=0) sampling plan does not have transfer regulations between strict, lenient, and normal inspections, nor does it have secondary or multiple sampling plans. The “zero defect” (C=0) sampling plan only uses one main sampling table, greatly simplifying the process compared to the dozens of sampling tables in GB/T 2828.1-2012, making it easier to learn and manage. Additionally, the “zero defect” (C=0) sampling plan is suitable for both batch inspections and isolated batch inspections.Number 06 . Benefits of Implementing the “Zero Defect” (C=0) Sampling Plan1 . Helps to Form a Rigorous and Pragmatic Work StyleAlthough most companies currently have finished product inspection standards that specify sampling plans for functional parameter inspections as nonconforming products GB/T 2828.1-2012 II AQL=0.65%, while appearance inspection items are specified as nonconforming products GB/T 2828.1-2012 II AQL=1.0%. However, whether inspections are strictly conducted according to the sampling plan is still a question. Inspectors often respond that they inspect products according to GB/T 2828.1-2012, but which level of inspection standard are we following? What AQL values are selected for various quality characteristics? No one can answer that.In fact, how many samples should be taken during the inspection of a batch of products? And how to determine whether they are conforming or not? Often, it is the supervisors who rely on intuition and personal experience to make these decisions. The problem with this approach is that the sampling work lacks rationality, the judgment of conformity lacks fairness, and the control of quality risk for outgoing products is not scientific.Whether we choose GB/T 2828.1-2012 or the “zero defect” (C=0) sampling plan, once the standard is established, it must be ensured that inspections are conducted according to the standard. We must change the bad habit of relying on subjective experience for judgments and promote rigor in work. The ease of learning and use of the “zero defect” (C=0) sampling plan further helps us to form a rigorous and pragmatic work style.2 . Choosing the “Zero Defect” (C=0) Sampling Plan is More EconomicalWith the same AQL value, the sampling risk probability of the “zero defect” (C=0) sampling plan is similar to that of GB/T2828.1-2012, while the amount of sampling is greatly reduced.Like GB/T2828.1-2012, the application of the “zero defect” (C=0) sampling plan also requires specifying different AQLs (acceptance quality limits) for different categories of quality characteristics.The “zero defect” (C=0) sampling plan is suitable for: expecting that the produced products fully meet the specification requirements. For some non-critical characteristics, it is hoped to use fewer inspections.For example, Huawei’s mobile base station equipment focuses on key quality characteristics such as networking, calling, data transmission, and stability, which are of primary concern to customers and must meet “zero defects”; however, for secondary quality characteristics such as appearance, customers typically do not scrutinize them as they would with craft products, so it is unnecessary to maintain a large amount of sampling, which would clearly be uneconomical.3 . Will Help Us Establish a “Zero Defect” Quality Awareness and Improve Product Quality LevelsSince the judgment criteria of the “zero defect” (C=0) sampling plan are limited to “0 accept, 1 reject,” as long as one defective product appears, the entire batch can be deemed nonconforming, necessitating full inspection and return measures. In the initial implementation phase, this will undoubtedly increase efficiency and cost pressure, thereby prompting the entire company to truly establish the concept of “zero defects” and not tolerate a single defective product. When each of us develops an intolerance for defective products and work errors, we believe that our product quality levels will also improve accordingly.4 . Helps to Enhance Customer Confidence and Expand Overseas MarketsSince Philip B. Crosby introduced the concept of “zero defects” in the early 1960s, the quality concept of “zero defects” has become popular worldwide. If we hope to enter mature high-end markets in Europe, America, and Japan, we must use the “zero defect” quality language that customers can understand to connect with them.5 . The “Zero Defect” (C=0) Sampling Plan Aligns with the Company’s Business PhilosophyThe company’s work culture of “innovation and transformation, meticulous cultivation, and service-oriented” aligns perfectly with the requirements of these twelve words.At the same time, the “Quality Manual” (No: YXQM-01) is the guiding document for the company’s quality management work, and its content complies with IATF 16949:2016 (Quality Management System – Special Requirements for Organizations Applying ISO9001:2015 for Automotive Production and Related Services), and should also meet the quality management requirements of “zero defects.”In summary, “zero defects” is the current trend in enterprise quality management, and we should transform customer requirements into opportunities for internal improvement, actively facing challenges: implementing the C=0 sampling plan and establishing a zero defect awareness! Practicing the concept of “doing it right the first time.”
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