The purpose of rolled throughput yield in six sigma would not be to:
|
Often, management and financial reporting can contain bias. When a sample of business processes is taken to determine production success, the most-successful part of a sample might be reported to the public and shareholders to paint a picture of success that is greater than reality. Show
The possibility of biased reporting is especially present in the realm of manufacturing, for example, where businesses must report how many units make it through an assembly line without defect and how many units had to be scrapped and/or reworked. A part of Six Sigma provides a helpful process to fairly and accurately report production success. This process is called the Rolled Throughput Yield calculation, or RTY. To explain, we will first look at one traditional way that companies might report “success” and then look at how RTY helps reveal the real data. Our Example ModelLet’s use an example of a manufacturing company that produces motherboards for computers. Each motherboard consists of a board with electrical circuits printed on it and hundreds of tiny components including modules, capacitors, resistors, ribbon wires, and more. The possibility of multiple boards reaching the end of the line with defects and malfunctioning is very high given the number of parts and the complex processes they must be able to perform. Some units will be scrapped if reworking the defects is not possible or not worth the cost. Others will be reworked. Let’s say that the factory performs five runs each day of 100 motherboards. With each run, only a certain number of boards make it through without defect and are shipped out the door. Here are the results of five runs on a random day: A Traditional ApproachWithout an honest system of reporting, bias could lead management to report on financial reports and to shareholders a number from the above example that skews reality and creates false positivity. Say that shareholders want to know what the daily number of units shipped and assembly-line success rate are. A traditional approach might lead a manager to pull out their favorite of the above five runs. Favoring Run 3 above, the manager reports to the shareholders that the daily success rate is and whopping 98% with 98 units being shipped per day. The Rolled Throughput Yield (RTY) ApproachThe honest approach would take the less-successful runs into account. The Rolled Throughput Yield (RTY) approach does this. It is a combined approach. To calculate RTY, simply take the success percentage from all five runs and multiply them: 89% x 70% x 98% x 86% x 91% = 48% Success As you can see, this is a drastic difference. It is not even half of the 98% that was reported using the traditional approach above. In ClosingWhen reporting numbers that impact financial, investment, operational, and other significant business decisions, it is critical to be honest. Reporting a false reality could lead to investors chipping in on bad investments and other problems. Instead report accurately and view the honest, negative reports and critical pieces of information that lead to strategizing how to improve. That is a primary purpose of systems like Six Sigma and RTY. In Lean training courses, the concept of yield is discussed as a measure of the quality of a process. Yield is an important term for 6 Sigma. There are two types of yield: first pass yield or FPY and rolled throughput yield or RTY. Free Lean Six Sigma training debates whether FPY or RTY is the best measure of yield. This article compares rolled throughput yield vs first pass yield. Also, it explains how to calculate each method according to the Six Sigma approach. Attend our 100% Online & Self-Paced Free Six Sigma Training.  We will go through the Yield, also known as first-pass yield metric of Lean Six Sigma by looking at the following sections:
Definition of Yield in LEANLet’s talk about one of the key metrics in LEAN methodology. It is the concept of yield. Yield or first pass yield or throughput yield in LEAN is simply the ratio of good units produced to the number of units entering the process. Here’s a reminder of the term ‘unit.’ A unit is any item that is being processed. Two Types of YieldFirst-pass yield (FPY)There are different ways to define yield, or you can also call it as types of yield. The first one is the first-pass yield, which is abbreviated as FPY. It is also known first-time yield or throughput yield. It is a unit-based metric. The disadvantage of the first-time yield is that it ignores or does not account for any rework of scrap products carrying one or multiple defects. In this case, the calculation occurs after any “inspection” is conducted to determine whether a unit is good or not. Let us have a look at an illustration on the first-time yield or throughput yield formula. We are looking at an email response process in a BPO company which works as a service provider for a Utilities and Energy Company. We are looking at the number of emails i.e. 550; which was responded by a team of customer service associates. Before sending those emails to customers, all of them were inspected, or quality checked. During the quality audit, 203 emails were found to be carrying numerous errors or defects. As a part of correction exercise, out of 203 emails, 190 were reworked and sent back into the email process queue. Moreover, 13 emails were so badly responded that they could not be sent to the customer at all. Therefore; the first time yield or throughput yield formula for this process would be 347 divided by 550. And this gives us 0.630 or 63.09%. How did we arrive at 347? It is the result of 550 (total number of emails) minus 203 (defects). When we want to count the number of emails that were eventually sent to the customers we subtract the number of defectives (13) from the total number of emails. Rolled-throughput Yield (RTY)Let us now discuss the concept of rolled throughput yield. The acronym is RTY. What RTY means? RTY is a measure of the overall process quality level. It summarizes DPMO data for a process or product by multiplying the DPMO of each process step. rolled-throughput yield is the preferred yield calculation method over the first-pass yield. RTY is smaller than the lowest yield of any single process. Every process step will always have a minimum and maximum yield. As the number of process steps increases, the RTY becomes exponentially smaller. Let us have a look at an illustration of RTY now. We’ll discuss two formulas to calculate RTY. Let’s have a look at the first one. Illustrations of RTYFirst method to calculate RTYWe’ve got 5 process steps in this example. Each step has got input units and output units. Input units are the ones entering each process step, and output units refer to good units produced by each process step. With the help of a formula, we’ve got the first pass yield for each process step. To calculate RTY, multiply the FPY of each process steps to get the answer. In this case, your equation will be the multiplication of five FPY values which will result in 0.6372. In other words, your RTY for all process steps is 63.72%. That was the first throughput yield formula. Second method to calculate RTYLet us have a look at the second method of RTY calculation. We’ve again got 5 process steps in this example. To use this method; you need to have two metrics i.e. DPMO and DPU calculated for each process step. We will now review the calculations to determine the DPU and DPMO. Calculation of DPU
Calculation of DPMO
Another simple way to calculate DPUIn this example, we’ve calculated DPU using another quick formula. We’ve divided DPMO figure by 1 million to get DPU for each process step. Why did we do that? DPMO incorporates 1 million defect opportunities, and we need to know defect opportunities for each unit. That is why we divided DPMO by 1 million. Calculating the RTY from the DPUIn the next column, we have deducted DPU from 1 to get the first-pass yield (FTY) for each process step. The 1 refers to 100%. The logic here is simple. The 100% yield for each process step minus defect opportunities per-unit for each process step is equivalent to good units produced by each process step. In this method, the RTY is calculated by multiplying the FTY for each process as determined in the previous step to get the RTY. RTY is a realistic view of the yield of any process, looking at all the process steps. The RTY of a process is a good measure of the quality of a process. If the RTY is too low, then a problem-solving team needs to investigate how the process can be improved. What is rolled throughput yield used for?Rolled Throughput Yield (RTY) is a process performance measure that provides insight into the cumulative effects of an entire process. RTY measures the yield for each of several process steps and provides the probability that a unit will come through that process defect free.
What is the difference between first time yield and rolled throughput yield?First Time Yield (FTY): The ratio of the number of good “units” coming out of the process to the number of “units” going in. Rolled Throughput Yield (RTY): The probability that the process produces a good “unit” the first time through.
What is the best definition of RTY?Rolled throughput yield (RTY) in production economics is the probability that a process with more than one step will produce a defect free unit. It is the product of yields for each process step of the entire process.
What is the yield in a Six Sigma process?Q: What is the definition of “yield?” A: From a Lean Six Sigma perspective, it is the percentage of improvement achieved on an activity or process. It is determined by dividing the total improvement by the total number of efforts expended on that activity or process.
|
