ACCEPTANCE SAMPLING 1 Acceptance Sampling Student’s Name Professor’s Name Course Name and Number Date ACCEPTANCE SAMPLING 2 Table of Contents Abstract/Introduction .................................................................................................................................... 3 Acceptance Sampling.................................................................................................................................... 4 Relationship between acceptance sampling and the improvement of quality ........................................... 4 Advantages of acceptance sampling ......................................................................................................... 5 Disadvantages of acceptance sampling ..................................................................................................... 6 Acceptance sampling plans ....................................................................................................................... 6 Single sampling ..................................................................................................................................... 7 Double sampling ................................................................................................................................... 7 Sequential sampling .............................................................................................................................. 8 Operating characteristics curves ........................................................................................................... 9 References ................................................................................................................................................... 10 ACCEPTANCE SAMPLING Abstract/Introduction Product quality assurance is notably a major problem for industrial engineering. Nonetheless, there is the need to ensure compliance in regard to the minimum standards in product manufacturing so as to augment design performance capability. It is at this instance where acceptance criteria as well as acceptance sampling come into play. Particularly, acceptance sampling is a principle component of quality control. It is a useful tool utilized when the testing costs are higher in comparison to the cost of passing a defective item or in some instances when the testing of the product is destructive. Therefore, it is notable that acceptance sampling is a compromise when it comes to choosing between 100% inspection and no inspection at all (Wetherill, 2013). The research paper will detail the definition of acceptance sampling, its relationship with quality improvement, the pros and cons of acceptance sampling, and acceptance sampling plans. 3 ACCEPTANCE SAMPLING 4 Acceptance Sampling Acceptances sampling can be termed as a statistical measure that is utilized in quality control. Most of the organizations are not in a position to test all their products, probably due to large volumes or the potential for ruining of destructing the products. Therefore, acceptance sampling helps solve this consideration through the testing of sample of products to check for any defects. It is a statistical process that involves testing of batch size, sample size and detailing the number of defects that can be acceptable within a batch. Through this process, an organization is in a position to measure the quality of a batch with a specified statistical certainty without the need to test every product units. Using the t-statistic, the statistical reliability can be measured for accuracy purposes (Wetherill, 2013). Relationship between acceptance sampling and the improvement of quality Most people might question how organizations have the ability to ensure that suppliers are in compliance with the critical quality standards. In most instances, organization have their reliance on inspection for the incoming materials. The results of the delivery are compared to the quality standards of the organization whereby if they do not conform to the acceptable standards, they are rejected (Mitra, 2016). Majorly, organizations utilize acceptance sampling procedures and are critical in the minimization of the inspection costs, helps in the management of risks and the prevention of non-conforming quality features from having their entry into the production process. It can be said that acceptance sampling is somewhere between no inspection and 100% inspection. Acceptance sampling plans are utilized as sources of quality data. In this case, there is the use of Pareto charts, statistical analytical tools, histograms, and control charts in the analysis of the use of inspection data. A comparison is usually made between the suppliers. This way, there is the ACCEPTANCE SAMPLING 5 identification of substantial time-based changes in parts with regard to per million defect rates. If there is a lack of control or any control in the processes of the suppliers, then it is identified (Mitra, 2016). Therefore, such information is useful in ensuring a collaborative effort between suppliers and organizations in enhancing the quality of products. Essentially, utilization of the measurement data along with either accepting or rejecting shipment allows acceptance sampling procedures to complement the emblematic improvement efforts. The specific supplier quality levels are accurately quantified and such information is utilized significantly to improve supplier quality as well as the reduction of quality costs when it comes to the supplier chain (Mitra, 2016). Advantages of acceptance sampling Acceptance sampling procedures are widely utilized in organizations that produce large volumes of products. This is due to the fact that an organization utilization an already set production procedure. Besides, acceptance sampling is economical and is utilized under the assumptions when the quality characteristics of an item are under control and there is homogeneity in production. It is, therefore, evident that acceptance sampling saves time as well as money and resources in the overall evaluation of the quality of products. The savings brought about by acceptance sampling can be measured in terms of the reduction in labor, the reduction in the product part movement and a short product manufacturing inspection throughout. There is no complicated training for those involved in acceptance sampling procedures and since they can be easily imparted training. Few staff are also involved in the inspection process. In the cases of destructive products, they can be easily inspected through the use of acceptance sampling. ACCEPTANCE SAMPLING 6 Moreover, with acceptance sampling, it involves a quick inspection process. In this case, scheduling and delivery times are improved. Also, computation work in the statistical measure is comparatively very small. There is still less fatigue and boredom in the acceptance sampling procedures. Finally, acceptance sampling procedures put more pressure to the suppliers to ensure quality improvement efforts are enhanced rather than the rejection of items. Disadvantages of acceptance sampling Acceptance sampling has its limitations. First, the conclusion on the quality of the products is usually based on the sample size selected. In this case, there is a high probability of making the wrong inference with regard to the overall quality of the products. This risks goes down to the producers and the consumers (Aslam, Kundu & Ahmad, 2010). Besides, the success of the scheme is dependent on the sample randomness, the quality features of the products being tested and the criteria being utilized for acceptance sampling. Without proper and accurate assessment, it can lead to the wrong inferences on the nature and the quality of the products delivered. This has an implication that there is no 100% assurance that the specifications of the products are in order. This, thus, increases the probability of drawing wrong inference with regard to the quality of the batch sampled (Aslam, Kundu & Ahmad, 2010). Acceptance sampling plans Particularly, items can be inspected in different ways. The acceptance sampling plan is usually defined by the lot size, the sample size and the acceptance number (Rao, Durgamamba & Kantam, 2014).The sampling plans are a way of offering the producer’s and the consumer’s risk. The available sampling plans include; ACCEPTANCE SAMPLING 7 Single sampling A single sampling plan is a type of decision rule where rejecting or accepting a lot size is dependent on the results of a single random sample from the lot. In this case, the random sample size is taken and each item is inspected. In the cases where the number of defects identified do not go beyond the sample size, the consumer can accept the lot size. Therefore, the defects identified can be repaired or rejected and hence returned to the producer. At the instances where the number of defects is higher than what is expected, the consumer can subject the entire products to 100% inspection or decide to reject the entire lot and take it back to the producer. It is the easiest acceptance sampling plan that can be used (Rao, Durgamamba & Kantam, 2014). Figure 1: Single sampling demonstrated Double sampling In double sampling, it is the work of the management to give two sample sizes as well as two acceptance numbers. At the instances where the quality of the lot is very good, the consumer can accept the lot on the basis of the first sample. On the other hand, where the quality of the lot is bad, the consumer can reject the lot still on the basis of the first sample. With the use of double sampling, it aids in the reduction of the inspection costs in comparison to the single-sampling ACCEPTANCE SAMPLING plan. However, this applies for the lot sizes that have either low or high proportion defective. This is because there is the option of making a decision after taking a first sample (Rao, Durgamamba & Kantam, 2014). Sequential sampling Sequential sampling is seen as a refinement of the double sampling plan. There is the random selection of items from the lot size. These are inspected one by one. When an item is inspected, a decision can be made to reject the lot size, accept the lot size and continue with sampling. These decisions are usually based on the cumulative results for the random samples. The individual inspecting usually plot the number of defectives against the cumulative sample size. When the number of defects are less than the given acceptance number, the consumer is usually free to accept the lot. However, in the instances where the number of defects are greater than the given acceptance, the consumer is supposed to reject the lot. At times, the number derived for the acceptance criteria can be between the two instances. In this case, there is the requirement to ensure the inspection of another item (Fallah Nezhad, Akhavan Niaki & Abooie, 2011). Figure 2: Sequential sampling demonstrated 8 ACCEPTANCE SAMPLING 9 Operating characteristics curves The figure below shows a typical operating characteristics curve Figure 3: typical operating characteristics curve The operating characteristics curve details how well an acceptance plan differentiates between the good and the bad lot sizes. It is a specific plan. It combines the acceptance level with the sample size. The function of the operating characteristic curve is to indicate the probability that the plan will accept different lots of different quality levels (Rao, Durgamamba & Kantam, 2014). ACCEPTANCE SAMPLING 10 References Aslam, M., Kundu, D., & Ahmad, M. (2010). Time truncated acceptance sampling plans for generalized exponential distribution. Journal of Applied Statistics, 37(4), 555-566. Fallah Nezhad, M. S., Akhavan Niaki, S. T., & Abooie, M. H. (2011). A new acceptance sampling plan based on cumulative sums of conforming run-lengths. Journal of Industrial and systems engineering, 4(4), 256-264. Mitra, A. (2016). Fundamentals of quality control and improvement. John Wiley & Sons. Rao, R. S., Durgamamba, A. N., & Kantam, R. R. L. (2014). Acceptance Sampling Plans: Size Biased Lomax Model. Universal Journal of Applied Mathematics, 2(4), 176-183. Wetherill, G. B. (2013). Sampling inspection and quality control (Vol. 129). Springer.
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