Q. 66.  Can a key output of a process also be a key input for the same process? Give some examples and explain how this creates unique advantages or challenges in such situations. 

 

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A key process input variable (KPIV) is a process input that provides a significant impact on the output variation of a process or a system or on the key process output variable (KPOV) of a product. This means that the KPOV is determined by the KPIV; so, if the KPIV is held constant, then it would yield a predictable and consistent output. As such, the KPIV determines the overall quality of the KPOV or, simply, the quality of the output of either a process or a product.

 

In many cases the output and input of a process might be similar. For example in a oil heater we are using heat itself as an input to generate the temperature. here the heat is acting both as an input as well output in the system. Similarly in a milk vending machine we are pouring milk and the same is processed inside the machine and we can get hot milk as an output

 

The KPIV determines the output of a process or product, which is the KPOV. For example, if the KPOV is the traction provided by a certain model of a car tire, then the KPIVs would be the width of the tire and the compound used to make it. Certain combinations of the two KPIVs will result in a particular KPOV (traction), so if the KPIVs are kept constant, then they will yield a specific traction rating, and if these variables are changed, then the tire model obtained will either have a high traction, which can be more expensive, or have a low traction yet more affordable, and these two variations will fill different segments of the market.

Another good example of KPIV is the size and number of transistors that are placed in a microchip. These two directly affect the capacity, speed and power consumption of the chip. As the size gets smaller, the power consumption of each transistor also decreases and it allows for more transistors to be placed in the same small space. This results in a more efficient and powerful chip that consumes less power.

The challenge is in determining the correct KPIV in a product or system that would yield the most favorable results for the selected KPOVs. This can be done through experimentation, but this would cost too much and would be too imprecise. Design of experiments (DOE) is a tool used for conducting a structured and scientific experimentation in order to efficiently model different process behaviors and understand the underlying cause-and-effect relationships that link KPIV and KPOV.

Examples of KPIV:

• The number of transistors in a microchip
• The size of the components of a microchip
• The surface area of a heat sink
• The shape of cooling fan blades

In many cases if there is a defect generating out of a process that would also be used as an input through change control unless it is processed error free.

Yes, Key output can become key input for the same process. And that is what "Feedback" is. It can do miracles in keeping the process output in required/desired state and level. Key output of a process can be compared with "desired output", deviation can be known, and that deviation can be used as "input" to adjust or re-set the key process parameters. This type of process design helps to keep the process outcome in desired levels by taking continuous references of "actual outcome" and "desired outcome" and use as "input".

 

Example - 1. Teacher can ask Student to prepare a topic and teach a class on sample basis. This way teacher is using his outcome (who is student), in the process (teaching), as an input, to improve his teaching process. By doing this, teacher judges whether his student has understood the concepts upto the expectations, accordingly improves his own teaching process.

2. Second example could be financial products, like investments, Money earned out of investments can also be used as investment and more money can be earned through same process.

3. In foundry, left out metal after casting (like gates, cleaned off parting line material from casting) is added casting process, as an ingredient.

4. Process of making Curd by adding small amount of curd into milk - Lactobacillus is a genus of bacteria which can convert sugars into lactic acid by means of fermentation. Milk contains a sugar called lactose, a disaccharide (compound sugar) made by the glycosidic bonding between glucose and galactose (monosaccharides). When pasteurized milk is heated to a temperature of 30-40 °C, or even at room temperature or refrigerator temperature, and a small amount of old curd or whey added to it, the lactobacillus in that curd or whey sample starts to grow. These convert the lactose into lactic acid, which imparts the sour taste to curd. Raw milk naturally contains lactobacillus.

 

It is clear from above examples that, It creates Unique advantage like continuous improvement of process and maximum use of inputs & resources.

Sometimes it helps in stabilizing the process. 

However it can also create some challenges like "Intentional" addition of smaller variation &  impurities in process inputs.

 

The first example that comes to my mind is process of developing a control chart. The output of the process, which is the measure of variation becomes the input for determining the control limits.

 

Machine learning is a process used to train a computer driven automation application continuously, where the outputs are used as inputs to build and improve the algorithms used for the automation.

 

A reinvestment deposit employs a process where the output in the form of periodic interest, is fed back as inputs into the deposit scheme for a accumulated benefit.

 

There are instances where a partial output is recycled as input to the same process. Eg: the extra material that gets generated in a plastic molding process like the runners, risers, flashes, are recycled in controlled quantities. (however, we may not call it as key input).

 

Certain machining processes require multiple passes, when the same job which passes out as output of a process, will have to be re-fed into the same process for the subsequent processing.

 

 

One of the best examples that we use at our home is curdle the curd (dahi jamaana). In order to get the curd, you need small amount of curd (output becomes input).

 

Being in the chemical process industries, I have observed that many times, the output of the process is being used as the key input to the same process. The usage of the output as the main input is for the Crystallization or as Seeding material.  For instance, in Zinc Smelting (Hydrometallurgical route) process, one of the major outputs is Jarosite. But for the Jarosite production, Crystallization/ seeding of Jarosite is required, which is being done by the output (Jarosite) only via recirculation piping. Also, for the production of Sulphuric acid (i.e. output), Sulphuric acid (at low concentration) is used as input in the Absorption towers and Drying towers.

 

The main challenge of the Crystallization/ Seeding process is how to proceed from scratch, i.e. how to commission it first time.  Moreover, material balance poses a big hassle. Due to the complexity of the Mass flow diagram, it requires extensive training to train and get the team at the same platform.