Learn about rolled throughput yield and how to calculate it

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In manufacturing, top-level decision-makers often view a 100% total throughput rate as a praiseworthy achievement. However, this metric alone does not reveal how much rework was necessary to achieve that seemingly perfect rate. To unveil the whole picture of a production line’s performance, business leaders need to calculate rolled throughput yield (RTY) and compare it to the final throughput percentage.

Without understanding RTY, organizations may struggle with large amounts of rework. This can drive up costs, lead to disruptions to product lines, and impact on-time delivery.

Learning about RTY can help decrease the amount of rework being performed, and organizations can address serious problem areas in the production line.

This post will explore:

What is rolled throughput yield?

Rolled throughput yield is the probability that a service or product will make it through the manufacturing process without defects. Alternatively referred to as “rolled through yield,” RTY is an easy-to-see metric that demonstrates how product defects are negatively impacting business processes.

Ideally, you want your RTY value to be 100%, as a perfect yield percentage indicates that every product makes it through the assembly line without a single defect.

Keep in mind that RTY doesn’t factor in products that have been reworked to resolve failures. Conversely, total throughput yield includes all products that pass quality control standards, even those that have been reworked.

If your rolled throughput yield is low but your total throughput yield is high, a substantial amount of rework is being performed.

Purpose of rolled throughput yield

RTY is primarily used by manufacturing managers to gauge the quality of their products and assess the efficiency of their processes, and it works quite well for these purposes. It’s part of the Six Sigma method, an organizational system for improving business processes to eliminate waste and create a more streamlined operation.

Specifically, RTY shows companies when their production lines have serious problems that must be addressed, despite their high total throughput rates.

Benefits of rolled throughput yield

Rolled throughput yield is a great way to show how rework is affecting your production line or office processes. You can combine this metric with other yield values (such as individual process yield or total throughput yield) to get a clearer picture of how poor quality affects day-to-day operations. For instance, RTY may reveal that there is a shortcoming in your current manufacturing processes. You can then examine the individual throughput yield rate of each unique process to pinpoint the cause.

RTY is also useful because it accomplishes the following:

Identifies the hidden factory

The term “hidden factory” refers to processes outside your assembly line that occur when a defect is discovered.

For example, imagine that an employee locates a defect, removes a product from your assembly line, performs rework, and places it back on the line. This series of events is part of the hidden factory.

The hidden factory creates a second line of invisible processes and labor that eat away at productivity and distract your employees from their core responsibilities. Using rolled throughput yield, you can pinpoint these processes and mitigate time loss. Additionally, RTY enables you to determine where defects are occurring so you can revamp your processes.

Rolled throughput yield is a valuable tool that can help organizations see how defects are impacting their production lines or service workflows. These insights can ultimately help address serious problem areas in production and decrease the amount of rework that must be performed.

Reveals faulty material

Reviewing rolled throughput yield is a great way to determine which phases of your process produce the most defects. Let’s say you have a yield of 100% after your first manufacturing process but a 75% yield after the second process is complete. You can infer that there’s a workmanship or material issue with your second production process.

Once you identify the source of yield shortcomings, you can make adjustments to reduce defect frequency and increase output. When using rolled throughput yield to reveal faulty material or workmanship, you’ll want to examine your processes in chronological order and reassess RTY after each round of adjustments.

Tracks improvement over time

RTY is an excellent tool for supporting continuous improvement efforts and tracking your progress over time. Each time you adjust your business processes, check RTY and monitor improvements. If a particular adjustment made little to no change to your yield, you’d know that other underlying issues are contributing to lost time or defects.

Tracking improvements over time by using RTY promotes better productivity and increased operational efficiency. Ultimately, such improvements will lead to increased profitability for your organization.

To maximize these benefits, it’s wise to combine RTY with other Six Sigma principles and techniques.

How to calculate rolled throughput yield

When calculating RTY, you only factor in the units that made it through your entire process without being reworked.

Start by multiplying the pass percentage of each stage together. Whether the failed products are reworked or scrapped isn’t relevant during this calculation, as RTY is only concerned with the items that pass the first time and make it through every stage of your process.

The rolled throughput yield formula is straightforward and features only one variable — the yield rate for each stage. It looks like this:

Rolled throughput yield = Yield 1 x Yield 2 x … Yield N (where N represents the yield of the final process step).

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“Yield” can be understood as the number of acceptable units or the total number of units entering production.

Let’s take a closer look at each step involved in calculating RTY.

  1. Calculate the yield for each unique process

To calculate the yield rate, simply divide the number of acceptable units by the total number of units entering production.

Let’s say a tool company’s adjustable wrench manufacturing process has four stages, and 2,000 wrenches are entering production. After completing the first process, the workers are forced to remove 100 wrenches from the assembly line due to material defects. The yield for stage one would be:

Yield = 1,900 / 2,000

Yield = 0.95, or 95%

Next, the wrenches move onto stage two. In our scenario, let’s say 500 wrenches are removed from production due to a defect with the knurl. The yield for stage two would be:

Yield = 1,400 / 1,900

Yield = 0.73, or 73%

During stage three, another 200 wrenches are removed due to faulty springs. The yield for stage three would be:

Yield = 1,200 / 1,400

Yield = 0.85, or 85%

In the final stage, the wrenches are finished and stamped with the manufacturer’s logo. Of the 1,200 remaining wrenches, 1,150 passed the last phase of quality inspection. The final stage yield would be:

Yield = 1,150 / 1,200

Yield = 0.95, or 95%

While all phases of the wrench manufacturing process can be improved upon, phase two has the lowest yield and makes the largest impact on RTY.

  1. Consider reworks

Calculating yield reveals how many products are getting through the entire production cycle. However, total yield doesn’t account for the number of products fixed in your hidden factory and reinserted into the production workflow.

The process of fixing defective products is known as “rework,” and it represents a major burden on your resources. By ignoring rework when assessing organizational productivity, this shortfall in your process could go unaddressed and cost you significant resources in lost time.

To account for rework in your calculation, divide the number of quality units produced without rework by the total units entering production. Using the wrench manufacturing example from above, the formula would appear as follows:

Throughput yield = 1,150 wrenches completed with no rework / 2,000 wrenches entering production

Throughput yield = 0.575, or 57.5%.

Once you determine your throughput yield (TPY), you’re ready to figure out your RTY.

  1. Combine throughput yields into your rolled throughput yield

There are two approaches to combining your throughput yields into RTY. The approach you use will be determined by the structure of your assembly model.

The first is known as the serial process. This method is used in conjunction with linear assembly lines, like in our wrench example. In that manufacturing line, each process leads directly to the next.

The equation for RTY for serial processes is as follows:

RTY = TPY of process 1 x TPY of process 2 x TPY of process 3 …

: Formula for serial process RTY file name:

You can add as many processes as necessary. The RTY for our hypothetical wrench company would be:

RTY = 0.95 x 0.73 x 0.85 x 0.95

RTY = 0.56, or 56%

The alternative approach to calculating RTY is the parallel method, which is used if you have co-occurring processes. It may be unrelated processes that occur simultaneously or functions that contribute to the same assembly line. You can calculate the rolled throughput yield of these processes by calculating the minimum. The equation is:

RTY = Min (TPY of process 1, TPY of process 2, TPY of process 3).

Formula for parallel process RTY file name:

Say that our wrench manufacturer also produces screwdrivers, and the wrench and screwdriver are sold as part of a toolset. As such, the screwdriver and wrench manufacturing processes are performed in parallel.

If 2,000 screwdrivers enter production and 1,800 make it through, the yield for stage one would be:

Throughput yield = 0.9, or 90%

The RTY for the first two production processes for wrenches and screwdrivers would be:

RTY = Min (95%, 90%)

RTY = 90%

You’d repeat this comparison for the following four stages of the wrench and screwdriver assembly lines. After identifying the minimum throughput yield for all four stages, you’d multiply those figures to determine the overall RTY.

Best practices for calculating rolled throughput yield

To calculate and use rolled throughput yield to make a measurable impact on your business, follow these three core best practices:

You can easily apply these established best practices to your RTY calculations, whether you’re managing assembly lines or overseeing service-related processes.

Improve your business processes today

Rolled throughput yield is a valuable tool that can help organizations see how defects are impacting their production lines or service workflows. These insights can ultimately help address serious problem areas in production and decrease the amount of rework that must be performed.

RTY is one of the 10 most common metrics used in Six Sigma approaches. Six Sigma helps organizations understand their processes, identify which areas that need to be optimized and how, and facilitate the implementation of process-refinement strategies to improve business outcomes.

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