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Rolled Throughput Yield


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Rolled Throughput Yield

 

Rolled Throughput Yield (RTY) - is the probability of producing a defect free product when it has to go through multiple process steps. It is the overall process yield in a multi step process or of an operation with multiple processes. It is the product of yields at each process step of the entire process / operation.

 

 

An application oriented question on the topic along with responses can be seen below. The best answer was provided by Mohan PB on 28th November 2017. 

 

 

Question

Q 54. Can a process with 100 percent Rolled Throughput Yield be considered inefficient? 

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

 
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Based on the calculated Rolled Throughput Yield of 100%, the process cannot be inefficient. But there could be assumptions that are made in this calculation which may reveal the inefficiencies in the process. These assumptions may result in some convenient omissions, which end up boosting the Rolled Throughput Yield to 100%. Sometimes, these assumptions also lower the perceived design efficiency. Some of these assumptions are:

1.    Related to available time

The equipment or plant is available for operation 24 X 7 = 168 hours in a week, but the Management chooses or there is business only for running five days a week for two shifts of eight hours each. Within this time of 80 hours per week, the plant operates at 100% rolled Throughput Yield, but from an overall time availability angle, there is already a loss of around 52% ([168 – 80] / 168).

 

2.    Related to Capacity

There could be a batch process operating in a drum, with a design capacity of 80 metric tonnes. Due to poor maintenance, some residue of the charge has solidified inside the drum reducing its usable capacity to 70 metric tonnes. The Rolled Throughput Yield on 70 metric tonnes is indeed 100%, but w.r.t. the Design Capacity, the yield loss is 10/80 = 12.5%.

 

3.    Related to Scope

For most product types, the Rolled Throughput Yield is 100%, but for some product types, the yield drops in one or more processes. But these product types are scoped out when calculating or presenting Rolled Throughput Yield calculations.

 

4.    Related to Mode of Operation

Some low yield processes get outsourced so that the “organization’s” Rolled Throughput Yield remains at 100%. But if Rolled Throughput Yield is assessed for the End-to-end process, it may go below 100%.

 

5.    Related to Changeovers

Changeovers are “Non-production” times. So, these times are not included in the available time. If considered the right way, the Rolled Throughput Yield will be less than 100%.

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Let’s discuss the definition of Rolled Throughput Yield and how it has evolved.

 

The yield from a production process is defined as the ratio of number of acceptable units to the total number of units fed into the production process.

 

The First Pass Yield is defined as the ratio of the number of first time acceptable units (excludes Reworked units) to the total number of units

 

The through put yield (TPY) is the ratio of number of defects to total number of units into production.

Note that for throughput yield it is the ‘defects’ per unit, which makes the measure more detailed that using ‘defectives’

 

When there are multiple processes involved the Rolled Throughput Yield (RTY) is a measure of the overall process yield.

 

If there are n processes connected in series,

RTY = (TPY)1 * (TPY)2 * ……….  (TPY)n

If there are n processes connected in parallel,

 

RTY = Minimum value of throughput yields of all the processes.

 

As seen above the RTY takes into account the combined effect of multiple processes, does not consider reworked units, and also uses ‘defects’ for this calculation. By all this, RTY is considered as an efficient measure for yield calculation, superior than the other measures.

 

Can a process with 100 percent Rolled Throughput Yield be considered inefficient? 

RTY can be 100% only if all the processes in the production flow are performing without any defects – which means that every unit that is fed into the production system comes out converted into the desired product with no loss. Such a process system may be considered efficient with respect to the product quality output. However, this measure does not guarantee efficiencies with respect to productivity rate, turnaround time, power consumption, or cost of production. What would need to consider other metrics that measure the efficiencies around these parameters, while the process(es) may be efficient with respect

to the Quality output.

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A process with 100% Rolled Throughput Yield (RTY) can be considered efficient or inefficient based on the way RTY is calculated.

 

Rolled Throughput Yield (RTY) is the total yield of  the entire process calculated by multiplying the yields of all the sub processes.

It can be calculated as following:

Case 1. RTY = FTY(A) * FTY(B) * FTY(C)

(or)

Case 2. RTY = FPY(A) * FPY(B) * FPY(C)

 

where A, B, C are sub-processes that constitute the process for which yield is being computed.

FTY- is First Time Yield

FPY- is First Pass yield

 

First Time Yield (FTY) – This metric is defined as ratio of number of units output of a process to the number of units Input to the process. The output may include defective parts that were repaired / rectified.

 

First Pass Yield (FPY) – This metric is defined as ratio of number of units output of a process to the number of units Input to the process. The output is before any inspections/rework and does not include defective parts that were repaired / rectified. i.e. it accounts for COPQ.

 

Example:

Sub Process

A

B

C

Input

100

100

100

Defective

20

10

10

Repaired

15

10

5

Scrap

5

0

5

Output after rework

100-20+15 =95

100-10+10 =100

100-10+5 =95

Output before rework

100-20 = 80

100-10 =90

100-10 = 90

 

 

 

 

FTY

95/100 = 0.95

100/100 = 1

95/100 = 0.95

FPY

80/100 = 0.8

90/100 = 0.9

90/100 = 0.9

 

Case 1. RTY = FTY(A) * FTY(B) * FTY(C) = 0.95*1*0.95 = 0.9025 or 90.1%

Case 2. RTY = FPY(A) * FPY(B) * FPY(C) = 0.8 *0.9 *0.9 = 0.648 or 64.8%

 

Thus, we can see that the way RTY is calculated can be very critical.

 

In the above example, if for sub process A and C, all the defective parts are reworked or repaired (i.e. scrap = 0) then calculation per Case 1 would be

RTY = FTY(A) * FTY(B) * FTY(C) = 1*1*1 = 1 or 100%.

 

 But the process is inefficient as it produces defective parts and time, man power, energy is spent in rework and repairs.

 

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Rolled Throughput Yield is the product of yield at every stage of the process. It provides the probability of producing defect free outcome in a process with multiple steps. 100 percent Rolled Throughput Yield does not indicate that process is efficient. Rolled Throughput Yield does not consider the rework associated in the process, it only accounts if the process steps have produced good outputs. So there would be hidden waste in the form of rework which makes system inefficient. First Time Right yield would be useful to analyze the efficiency of the system as it accounts for rework in the process.

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A process with 100% rolled throughput yield can be considered as insufficient. 

 

Rlooled throughput is a measure of overall quality level. In other words we can say that passing a unit of product or service through all steps without any error or defect in it so that customer does not get any defective product.  It is determined by multiplying throughput yields from each subprocess of the total process. 

We can see multiplicative effect will work against the Ray so it is better to have to first pass yield or FTY of each subprocess as high as possible. Ray is defect sensitive but FTY don't consider it. 

For example if we see one example we produced 100 componednts in a two step process to deliver to next customer after two processing,  so for production line and customer point of view we have given all good quality components to customers and for production yield is 100%but if we see in details the two processes we found that in process one 5% rework was there,  after reworking of 5 parts another process taken, there also 5% rework generated so customer got 100 components after working for 110 components.  So we add two extra station for rework and manpower to do that.  In one way we deliver all 100 components to next customer but at cost of 110 components.  So by wasting our resources we produced those components to give defect free components to customer.  So this method is not efficient for production as we need to add two station and lot more resource waste to deliver same quantity so if we see above scenario we can say that 100% Rolled throughput yield can be inefficient because we are producing the same number of units after resource wasting and by doing more work. 

In other words,  if we see From above scenario we can see difference as it is process and as is process by looking FTY and RTY,  so we can say that  rolled throughput yield points out the way where the improvement is needed in our processes so that we do maximum utilisation of resources without any wastage. 

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Understanding yield

Basically there are three types of yield

Sr.no

Traditional Yield

FTY

RTY

Definition

It is the traditional way of calculating yield, in which no of good product is divided by no of inputs.

 

First Time Yield.

It is the probability for a unit going through a process will be good product.

 

Rolled through put yield.

It is the probability for a unit going through multiple process will be a good product.

 

Formula

= Output/ Input

= (Input – Scrap – rework) / Input

= FTY1 * FTY2 * FTY3

Comments

This may be misleading because it obscures the impact of inspection and rework

This shows actual effectiveness of the process, because in this rework is also considered.

 

 

 

Taking an Example:-

There is typically 5 process in manufacturing of French fries

1.     Peeling & trimming

2.     Cutting

3.     Blanching & Drying

4.     Frying

5.     Packaging

Now input is 100 Kg of potatoes and we get 54.36 Kg of output.

Traditional Yield will be 54.36/100 = 54.36%

For each process input and the output are measured

Process

Input

Output

Traditional Yield

Peeling and trimming

100

85

85%

Cutting

85

75

88%

Blanching & Drying

74.8

64

85%

Frying

63.58

57

90%

Packaging

57.222

54

95%

Output

54.36

   

Traditional Yield for all the process are measured by formula output/input

Overall traditional yield for all the process will be 54.36/100 = 54.36%.

We will get same result if we multiply traditional yield of all the process.

As discussed before traditional yield does not consider amount of rework done.

Assuming at all different there was some rework done as shown in table.

Process

Rework

Peeling and trimming

5

Cutting

10

Blanching & Drying

10

Frying

15

Packaging

20

Output

 

Now if we calculate FTY for all the process will be get results as below table.

Process

Input

Scrap

Output

Rework

Traditional Yield

FTY

Peeling and trimming

100

15

85

5

85%

80%

Cutting

85

10.2

75

10

88%

76%

Blanching & Drying

74.8

11.22

64

10

85%

72%

Frying

63.58

6.358

57

15

90%

66%

Packaging

57.222

2.8611

54

20

95%

60%

Output

54.36

 

 

 

 

 

To calculate RTY we need to multiply FTY for each process steps, and we will get 17.42% as RTY.

 

Checking the difference between traditional yields of all process to their FTY, we can see that when rework is considered in calculation, it gives a big impact on yield.

Similarly, Traditional yield of overall process and RTY figures are having large difference.

We need to concentrate more on improving RTY, rather than traditional yield.

RTY and Traditional Yield can be same when there is no rework done in a process.

To improve RTY, we need to improve individual FTY of that process, and if we improve FTY for the initial processes, we can see a lot of improvement in RTY.

 

Now considering that one process is having a 100% RTY, which means there are no rework & no scrap produced in the entire process flow.

This does not mean the process is efficient; there can be other losses in the system. We all know 8 types of waste as per lean manufacturing. TIMWOODY (Transportation, Inventory, Motion, Over production, Over processing, Defects, Y- your skills).

 

If RTY is 100% it means one of the 8 waste is not present, but there are 7 other waste that can be eliminated.

Also the products that are 100% ok first time, does not mean that the average of all the measurement is at the target line, average might be shifted towards LSL or USL.

 

In Summary, if a process if having 100% RTY, does not mean that there is no scope of improvement in that process, there are other metrics, that needs to looked upon.

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The concept of yield in Lean management is considered as the measure of the quality of a process. The types of yields discussed or considered are First Pass Yield(FPY) & Rolled Throughput Yield(RTY). Both these measures are basically the ratio of good units produced to the number of units entering the process, where unit is any item that is being processed.

The First Pass Yield  or Throughput Yield is a unit based metric wherein the calculation occurs after any check is conducted to determine whether a unit is good or not.

For example, in a QSR,  let us look at an Offsite bulk order for 550 Burgers at a reputed Children’s charity event . Before serving the complete lot to the Children, the products are inspected for quality. It was found that 150 burgers were not up to the accepted standards, but 140 of those burgers were “reworked” upon with some fresh salads and sauce, however 10 burgers were so badly damaged during transit that they were not fit to be served at all. These 10 burgers were wasted. The FTY here will be 400 divided by 550(400/550)= 72.73%. The base is obviously the total number of Burgers sent for distribution and the 400 numerator is derived by subtracting the 150 burgers with defects. It is noteworthy that FPY does not account any rework or wastage and hence it is literally the “First Time Yield” and gives a correct picture of the efficiency of the process.

The concept of Rolled Throughput Yield (RTY) is different- It is the measure of the overall Process quality level. Every Process step (Sub process) will have a maximum and Minimum yield. RTY is at the end of the process is smaller than the lowest yield of any single process, ie. As the number of process steps increases the RTY becomes exponentially smaller.

There are 2 popular methods to calculate the RTY

Let us take an example where there are 3 process steps with each step having input units and output units, where input units are the ones which enter process steps and output units, as the term suggesta , refers to the good units(Defect free) produced by each process step.  From the above note, we know how to calculate the FPY of each process step. To calculate RTY, the FPY of each process step needs to be multiplied.

Process Step

Input

Output

FPY

1

200

180

0.90

2

180

160

0.88

3

160

150

0.94

RTY= (FPY1) X (FPY2) X (FPY3)

RTY= (0.90) X (0.88) X (0.94 )= 0.74448

Thus the RTY for all process steps is 74.44% . It goes to say that  there is a probability  that 74.44% of the input will be going out as output with no defects.

The other method of RTY calculation is more in detail and the approach is very precise. Here the RTY covers the DPU data for the process or product and then the DPU of each process step is multiplied. Let us consider yet again that there are 3 process steps. In this method, two metric ie. DPU needs to be calculated for each process step. DPU can be calculated from the DPMO also, just by dividing the DPMO by 1 million.

In each Process step the DPU is then deducted from 1- this provides us with the FPY for each process step. The logic is obvious here-  The Defects opportunities per unit (DPU) calculated in each process step is subtracted from 1.  Here 1 refers to 100% yield from each process step. Thus the 100 % yield less the DPU for each process step is equal to the Good (defect free) units produced by each process step. This is the FTY in each process step.

Then, Same like in the method above, the RTY is calculated by multiplying the FTY for each process step.

As the above methods to calculate RTY denote, RTY is a realistic view of yield (quality) of any process. Given that the calculation of RTY considers the defect level up to the unit level of the process, augments the reliability of the metric as a good measure of the quality of the process and hence is the preferred yield calculation method over the FPY. Thus, if the RTY is low, it is a sign that the process is inefficient and needs improvement. The more the value of RTY, the better is the efficiency of the process.

At 100% RTY the process efficiency is at it’s best and can be considered inefficient only if the method of measurement of the RTY is incorrect or the data used for the same is incorrect.

 

 

 

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Every product or services passes through multi steps before coming out as an output. In each and every step value gets added and the efficiency of every step may differ.

If a process consists of multi steps, any non-conformances/ defects in any steps will have impact on the final output. If you would like to find out the quality of the entire process or the probability of defect free output of the process is called rolled throughput yield (RTY). 

RTY is the proportion of conforming/defect free units that results from a series of process steps.  Mathematically, it is the product of the yields from each process step.

Consider a process is having 3 steps and each steps yield is as follow…

Step A = 90%

Step B = 91%

Step C = 99 %

The exact yield of the process will be 81.081 % (It is the product of each step yield)

If the RTY is more, the process is more efficient in terms of producing defect free products.

As per the question, whether the process having 100% RTY can be considered as inefficient.  Since 100% is the highest rolled throughput yield, hence the process is more efficient.

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Rolled Throughput yield (RTY):

 

Rolled throughput yield is the probability that a process with more than one step will produce defect free output. It is the product of the yield of each of the process steps involved in the entire process. 

In other words, a single unit passes through each of the steps of the entire process defect free.

 

RTY is a better method compared to FTY because in RTY the consideration of rejections/reworks/defectives is done to calculate the output percentage of each individual step. 

 

Say for example:-

 

Process flow below;

à B à C à D

·         100 units input at A; 10 scrap, 5 rework (total 15 defectives) = the yield is then 85/100 = .85 (85%)

·         90 units input to B (after A), 10 scrap, 3 rework (total 13 defectives) = the yield is then 77/90 = .855 (85.5%)

·         80 is the input to C, 2 scrap, 0 rework (total 2 defectives) = the yield is then 78/80 = 0.975 (97.5%)

·         78 is the input to D, 0 scrap, 0 rework (total 0 defectives) = the yield is then 100%

 

The RTY for the above process is the product of all the yields of the entire process

RTY = 0.85 X 0.855 X 0.975 X 100 == 70.85 %.

 

For the specific question on can the Process with 100% RTY be considered inefficient?

Answer:- If the process is really is having 100% RTY, then it cannot be inefficient. It is rather a very efficient process.

 

But couple of things to be considered

if the below conditions considered in RTY.

1.     We are talking about RTY where reworks/rejections/scraps are considered as out of the count while calculating the actual output at each of the process steps. Even though the rework has done & made the product fit for passing through the next step, it should still be considered as no output while calculating the yield. 

2.     This is not First Time Yield where the inputs at each of the processes are somehow made 100% to achieve the full output as desired in terms of numbers.

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RTY is stands for Rolled Throughput Yield, sometimes also referred as Final Yield, RTI is the probability which indicates that a process with multiple step will produce a flawless/defect free unit.

 

If under a process there are N number of sub-processes and the probability of getting a defect free result is n1%, n2%,  n3%, …. and n% then RTY of N = n1 * n2 * n3 * … * n.

 

Say under a process P there are four sub process and the probability of getting defect free result is 97%, 62%, 91% and 88% then RTY of P = 0.97 * 0.62 * 0.91 * 0.88  = 0.4816, that is 48% approximately.

In the above example if we have 100 items, say glass,

After 1st  sub-process:

 We have 97 defect free glasses, 3 glasses needs rework/retest/failed/scrapped.

After 2nd sub-process:

                We have 60.14 defect free glasses, 36.86 glasses needs rework/retest/failed/scrapped.

After 3rd sub-process:

                We have 54.72 defect free glasses, 5.42 glasses needs rework/retest/failed/scrapped.

After 4th sub-process:

                We have 48.16 defect free glasses, 6.56 glasses needs rework/retest/failed/scrapped.

That is we get 48% approximately and that is how it’s get calculated.

Although most of the steps have yield more than 88% but because of one step’s yield 62% it became 48%.

Same way for another process consisting of four steps each with 95% yield, RTY comes to (95%*95%*95%*95%) = 81.5%

 

95% RTY is considered ‘Good’.

 

RTY= [(1-DPI)^(s)]^(n);  s = no of inspections done, n = no of steps in production or service delivery process. 

Also can be calculated via Y = e^(-dpu)

 

Pros:  1. Its provides visibility into the yield of each process step. 2. Its expose “hidden factory” of risk defects/delays. 3. Identifies the poorest performing/greatest negative contributing process steps. 4. Helps to look into most impactful process for improvement/opportunities. 5. reflects the effect of variation on both scrap and rework. 6. Gives us a realistic view of the quality of the process.

 

Cons: 1. It is very difficult to maintain for parallel process or for offshore branches. 2. You have to know FTY of each steps.

 

RTY is TRUE yield or capabilities or reflection of a process [which has more than one steps] performance. So, if a process has RTY of 100% it’s never going to be inefficient[until and unless we have made a mistake in the beginning itself i.e assumed/gathered a wrong requirement specification and implemented that]

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Q 54. Can a process with 100 percent Rolled Throughput Yield be considered inefficient? 

Answer:

 

There are four different concepts to be understood.

Yield – Amount of material processed by the sequence of operations less the scrap. But rework is included.

1.       First time yield – is simply the good products including reworked products but not scrap from one of the process step. What gone in to come out of the step is first time yield.

2.       Final Yield – The good products including reworked items that has passed all the sequences of the process steps is called Final Yield.

3.       Throughput yield – It is a good measure of the process yield of a single sub process, which doesnot include the reworked product. It conforms the standards that are set for the product has met in terms of quality marking it as first time right without rework.

4.       Rolled throughput yield – It considers the entire process flow from beginning to end, where the product gets in and out without rework. In simple words, the throughput yield of several steps are multiplied to get the RTY.

 

 image.png.caa49fb3435a103328a4fcdb9e834e20.png

 

An ideal process must produce without defects and reworks. An appropriate measurable metric should be identified and measured frequently to expose even a smaller inefficiencies in the process to avoid unnecessary and costly efforts that is required to correct the error.

 

First time yield is not sensitive to product complexity. FTY and Final yield are classical approach to calculate the process yield but it will not reveal the inefficiencies. It will only consider the finished volumes. Corrective actions happens whenever ther errors are identified, and the same will not be recorded else where to show the process better than actually it is.

 

Eg. 100 units produced In 3 steps. Only 90 charts passed including rework. The remaining 10 are considered as scrap. Hence the final Yield is 90%

 

These two meterics does not reflect the defect rates and does n’t consider the hidden factory.

 

But throughput yield and RTY is a very good measure which also measures the inefficiencies or defects, where it will provide a detailed insight of how process is behaving and where the error is maximum. It helps us to analyse the root cause and help fixing it.

RTY allows companies to be more accurate than the final yield while assessing the performance of the process steps as quantifying the whole effects of the inefficiencies.

Rolled throughput yield is substantially less than final yield, and companies that calculated their final yield at 90 percent might find that their rolled throughput yield is only 20 percent.

 

Example 1: Low Complexity Process:

Consider a process that has 3 steps performing at a 0.94, 0.91 and 0.92 respectively. Suppose that 100 units entered the process and only 89 were good units. In this case, the final yield would be 89%, and the rolled throughput yield would be: 0.94 x 0.91 x 0.92 = 78.7%.

image.png.d01df7aefbbb19af3844753a965514cc.png

This means that even if the 3 processes are performing fairly well, one out of every 5 units will not make it through the process without being scrapped or reworked.

 

Procedure –

 

1.      Use process map as a guide to define the steps to calculate RTY

2.      Calculate Throughput Yield for each and every step

3.      Multiple the subprocess’s TPY to get the RTY.

4.      If required compare the final yield with RTY to show inefficiencies to the management.

 

Can 100% RTY process inefficient?

Ø  No. When the process is measured and it stands at 100%. The process runs with high end quality with no error and inefficiencies. If zero defect is possible , then the 100% RTY process is possible.

Ø  RTY is sentitive to the number of steps involved in production and effectiveness of the process.

Ø  RTY decreases as more the number of process steps occurs. That is why the team should have high throughput yield in each of the step to get higher RTY of the total process.

Ø  Simplification is one best idea to improve the process yield rate.

 

Conclusion:

RTY of the process is a good measure of the quality of the process. Smaller RTY reflects the room for process improvement. It is a good sign to initiate the preventive actions. Higher RTY shows that  each and every process step is achieving higher TPY  with zero defect or very minimal defect. It shows either the controls are stergnthened or the costly audit process is occurring.

When the 100% RTY process exhibits high quality, the cost involved would also be high.

Hence 100% RTY is possible when the process aims and works at zero defect or error free products at a costly audit methodology and simpler process step will yield higher RTY.

 

Reference - https://blog.masterofproject.com/rty/

 

Pizza Example - https://www.leanstrategiesinternational.com/listen-to-the-gemba/rolled-throughput-yield-rty-a-pizza-story-part-deux

 

Thanks

Kavitha

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Rolled Throughput Yield (RTY)

Also known as Rolling effect, this talks about the probability that a single unit can pass through all the steps in a process, free of defects. It is the net result of the effect of all of the steps in a process.There are few other things which need to be discussed.  Yield is one such stuff.

 

Yield

It is the percentage of units coming out of a process, free of defects.   

Now let us see why yield and RTY are important.  The moment we think or talk about a process, two things would come to our mind – most of the processes would not have a single step alone and therefore multiple steps could be there and every process would have some variation. 

Now when we talk about the variation in a process, we need to consider and take into account the cumulative effect of variation that happen in each step of a process. This is what RTY is all about.
Before we find out the RTY, we need to find the First-Time Yield (FTY).  This is needed for each of the step in a multi-step process to calculate the RTY.

 

FTY : The number of good units coming out of a process or step divided by the number of total units going into the process or step.

 

 Let us see some examples.:

Eg:1 

Let us see the common steps involved in the manufacturing of a Mobile. The steps involved in this process are Order receipt (Step 1), Material Procurement (Step2), Board Assembly process (Step 3), Final Assembly Process (Step 4), Quality check (Step 5), Rework process (Step 6), Final Quality check (Step 7), Packing and Labelling (Step 8), Shipping (Step 9)

Now let us calculate the RTY for this mobile manufacturing process. Remember each of the steps mentioned may itself contain several sub-steps which we ignore for brevity sake. We focus on the respective step’s FTY.

 

RTY = FTY of Step1 * FTY of Step2 * FTY of Step3 * FTY of Step4 * FTY of Step5 * FTY of Step6 *  FTY of Step7 * FTY of Step8 * FTY of Step9

 

Now let us assume that yield of all steps is 99.379% (0.99379) which is at 4 sigma

[Note: putting each steps’s sigma at the same level for providing easy DPMO values (for easy understanding)]

Then RTY = 0.99379 * 0.99379 * 0.99379 * 0.99379 * 0.99379 * 0.99379 * 0.99379 * 0.99379 *    0.99379 = 0.945478.

 

Step 1

 

Step 2

 

Step 3

 

Step 4

 

Step 5

 

Step 6

 

Step 7

 

Step 8

 

Step 9

 

RTY

 

0.99379

0.99379

0.99379

0.99379

0.99379

0.99379

0.99379

0.99379

0.99379

0.945478

 

RTY of 94.54 % means that 94.5 % chance of getting through the mobile manufacturing process without any defect. But the sigma level is down to around 3.1sigma.  This is far off, from the probability percentage for each of the step.  At 4 sigma, Defects Per Million Opportunities (DPMO) would be 6210 and for around 3.1 sigma range, it would be around 50000.  So how many steps are needed for a RTY to be acceptable?   The answer is that fewer the steps, better or higher will be the RTY.

 

Eg:2

In a software development project, for delivering the code , a team had a five-step process to deploy to UAT environment (Customer)

Step 1

Step 2

Step 3

Step 4

Step 5

Development (Coding)

Code Review

Unit Testing

Unit Testing Review

Fix System Testing defects

 

Assuming if the steps are operating at 3 sigma, then the RTY for this would be at around 2 sigma.

Step 1

 

Step 2

 

Step 3

 

Step 4

 

Step 5

 

RTY

 

0.9332

0.9332

0.9332

0.9332

0.9332

0.70774

 

Now the next question is that can a process have RTY as 100% and even if it is so, can it be considered inefficient?

 

Because is a net result of the effect of all steps in a process, RTY being 100% is virtually difficult impossible at a macro level.   At a micro level for each step, this could be possible to some extent, but when it comes at the overall steps at macro level, this may be difficult to achieve.  Also to arrive to such a maturity in process, it may take quite some time.   That maturity might come from reducing steps (Eliminating waste) and also improving processes / process steps. 

 Now if there is a process is available with RTY as 100 %, then it can be considered effective (outcome) but not be efficient (process of doing that).  

 

 Say for instance, a process has 10 steps and all steps have a yield of 100% and hence the RTY is 100%.  Assume, now customer wanted some change in the process flow. Unfortunately for the current month, the team could not achieve 100% in all the steps with this changed process flow. The team found that they can eliminate few steps and minimize the potential variation that could happen and increase the RTY value back to 100% sooner.  So the bottom line is even if RTY is 100%, as and when change happens to the process, there could be impact on the RTY.  So in such a case, lesser the steps in a process, greater will be the chance of RTY being still in 100%.  Then only we can consider a process with an effective RTY (with 100%) deemed as a process with an efficient RTY.

 

Conclusion

Better First Time Yield (FTY) will give higher Rolled Throughput Yield (RTY).  The most influencing factor would be the process steps involved in a process. Lesser the steps, greater the chance, for increasing the RTY. Greater the RTY, will result in lesser variation.

Edited by R Rajesh
alignment of para and addition
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Rolled Throughput Yield:

Throughput Yield:

It is a measurement taken taken at each step of the process, based on the No. of defects, the No. of Unit processed & the no. of defects opportunities per unit.

(Total No.of Units processed - No.of Actual defects) / Total no.of Unit Processed

 

Rolled Throughput Yield:

It is a Process by metric used to express the Probability that the given Unit will make it through the Whole System without producing a Defect part. It is calculated by multiplying out all of the individual through put yields. RTY Provides us a chance to look into the Cumulative effects of the Ongoing Process. It measures the Yield for each of Several process steps & provides us the Probability that a unit will come through the process defect free.

 

RTY helps us to understanding the Hidden factors by giving us a Visibility into the yield of each process step. This helps us to identify the Poorest performing Process steps  - REWORKS & gives us idea to where to look to find out the most impact process improvement opportunities.

 

Calculation of RTY:

In a Process there are multiple processes comes together to deliver the Final product.These Processes may be placed in a row or operate parallel & deliver output to a single process. To calculate the overall Throughput yield of the Process, the Rolled Throughput Yield is being used. 

RTY uses two different formulas for the Serial Process & for the Parallel Process:

- For a serial Process, RTY is calculated by multiplying the Through Put Yield of all the individual Processes

- For a Parallel Process, RTY is calculated by selecting the Minimum of all the individual processes operating parallel

 

The Calculation of RTY for the following yields are 0.994, 0.987, 0.951 & 0.990

RTY =  0.994 * 0.987 * 0.951* 0.990 = 0.924

 

If we simply count all the defects & divide by total units we would get a mean DPU for our Process. This is different but not necessarily less value than RTY. RTY helps us to find the Probability that a unit comes through Process defect free.

 

Can a process with a 100% RTY can be Considered as inefficient:

The process which can be produce a part involves all the sub processes to make it a complete process. In such condition there are possibilities for error to occur. A 100% RTY process will be efficient one if it satisfies all the necessary condition to be a defect free process. once a Process has achieved 100% RTY, then automatically it is considered an efficient process.

 

 

 

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RTY is the percent good in a process with sub-steps. Hence, when RTY is 100%, it is an indication of "effectiveness" and not "efficiency". This effectively means that even though a process may attain higher values of RTY, it may not necessarily be efficient. 

 

Keeping the differentiation between effectiveness and efficiency in mind, the three best answers are those of Mohan PB, Venugopal R and Ronaaq. Mohan's answer is the chosen best answer owing to the apt and crisp verbiage, and the multiple examples provided.

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