What is Root Cause Analysis?

The Root Cause Analysis (RCA) is a technique that allows people to determine the reasons why a particular problem has occurred.

This technique identifies the source of the problem using precise steps and tools so that necessary steps can be taken in the future to avoid the problem from happening again. The root cause analysis is done in a systematic way. It involves different steps such as describing the existing problem, collecting the necessary data linked with the problem, identifying possible causes, identifying causes that need to be addressed to prevent the problem from recurring, identifying solutions, implementing changes, and observing the changes.

This particular tool can analyze a particular system at once. This is often used in complicated systems when multiple problems exist, and it is important to immediately get to the root cause of the problem. The current reality tree is created by listing all the undesirable events and problems observed in a particular process.

RCA is an important problem-solving tool used in quality improvement. It is one of the most useful tool in lean Six Sigma process improvement projects.

Basically, in the DMAIC approach the 3^rd phase analyse is all about analyzing the data and finding cause of problem so in that phase RCA is used to identify the root cause of problems.

RCA is not a single person approach, it is completely a team-based approach where a team of 3-4 members come together and focus on finding the root cause of the problem where they use a lot of different tea, decision-making techniques.

So that this team-based activity produces good results with consensus of all team member. Now let’s see the three basic types of causes because of which all the problem happen

There are three basic types of cause:

1. 1. Physical causes– Tangible, material items failed in some way (for example, a car’s brakes stopped working).
2. 2. Human causes– People did something wrong or did not do something that was needed. Human causes typically lead to physical causes (for example, no one filled the brake fluid, which led to the brakes failing).
3. 3. Organizational causes– A system, process, or policy that people use to make decisions or do their work is faulty (for example, no one person was responsible for vehicle maintenance, and everyone assumed someone else had filled the brake fluid).

How to perform Root Cause Analysis

The 1^st step of RCA is to identify the problematic situation and then analyze that situation to understand what’s happening there, and what are the different factors that are impacting the problematic area.

1. 2. Gather data.

A critical step in root cause analysis is the collection of relevant data about an incident or a problematic event. Documenting all the characteristics and specifications of the event will help you answer questions like What are the contributing factors? When did the problem occur? Is it a repeating event? What is the observed impact?

2. 3. Determine possible causal factors.

Creating a sequence of events is important to identify causal factors that can contribute to the observed problem or event. The project team tasked with the analysis of the problem should establish a timeline of events and brainstorm as many potential causal factors as possible by asking “Why?” questions. Using a causal graph, for instance, helps to visually represent the connection between events and enables tracking of the root cause.

3. 4. Determine the Root Cause of the Problem

This is the time to identify as many causes as possible. The analysis team can use techniques such as the 5 Whys, Fishbone analysis, or Pareto chart to narrow down the potential underlying cause or causes of the problem and the major contributing factors. During this phase, stakeholders and other relevant teams should be involved.

4. 5. Prioritize the Causes

Once the root causes are established, they need to be prioritized and tackled accordingly. To determine which cause or challenge to address first, the analysis team needs to assess what is the impact of the cause – the higher the impact, the greater its priority. Another point when prioritizing root causes is the number of causal factors triggered by a specific challenge – the greater the number of causal factors, the greater the impact of the root cause is and yields immediate addressing.

5. 6. Solution, Recommendation, and Implementation

Next step upon establishing root causes and their prioritization is finding solutions to the problem and their implementation. Brainstorming is a great way to attempt and come up with a variety of potential solution scenarios. Another approach is interviewing as many people as possible. Gathering input as well as the implementation of the solution requires involvement from everyone. On one hand, every recommendation counts, and on the other, a successful implementation is the one that sticks with everyone affected.

6 Popular root cause analysis tools

The ultimate goal of root cause analysis is to find out the root cause of the problem and organize all the cause as per their impact on the problem and then action to prevent those problems from happening again.

In this entire process of finding the root cause of the problem, RCA uses 6 powerful tools.

1. 5 Whys Analysis

The 5 Whys is a method that uses a series of questions to drill down into successive layers of a problem. The basic idea is that each time you ask why, the answer becomes the basis of the next why. It’s a simple tool useful for problems where you don’t need advanced statistics, so you don’t necessarily want to use it for complex problems.

One application of this technique is to more deeply analyze the results of a Pareto analysis. Here’s an example of how to use the 5 Whys:

Problem: Final assembly time exceeds target

• -> Why is downtime in final assembly higher than our goal? According to the Pareto chart, the biggest factor is operators needing to constantly adjust Machine A
• -> Why do operators need to constantly adjust Machine A? Because it keeps having alignment problems
• -> Why does Machine A keep having alignment problems? Because the seals are worn
• -> Why are Machine A’s seals worn? Because they aren’t being replaced as part of our preventive maintenance program
• -> Why aren’t they being replaced as part of our preventive maintenance program?

2. Failure Mode and Effects Analysis (FMEA)

The failure mode and effects analysis (FMEA) is a technique that is used to determine the failures within a particular system. A lot of companies use this RCA tool to find out which parts of the processes are faulty so that they can be corrected. It also determines the number of times the failure occurs, the actions implemented by the organization to prevent the failure from recurring, and determining areas, where actions taken, were effective. This tool is often done every time a new process or product is generated.

An FMEA chart outlines:

• -> Potential failures, consequences and causes
• -> Current controls to prevent each type of failure.

Severity (S), occurrence (O) and detection (D) ratings that allow you to calculate a risk priority number (RPN) for determining further action

3. Fault Tree Analysis

The fault tree analysis is another method of determining the root cause of a particular problem. It uses Boolean logic to determine the cause of the problem in any undesirable event. As the name implies, this tool involves creating a diagram that looks like trees where all potential causes are written down as branches.

4. Fishbone Diagram

Also called the Ishikawa diagram, a fishbone diagram is a useful tool in conducting root cause analysis. Similar to the fault tree diagram, it is named after its shape–a fishbone–and is used to group causes into different sub-categories like methods, measurements, materials and many others for easier determination of the cause.

5. Pareto Charts

A Pareto chart is a histogram or bar chart combined with a line graph that groups the frequency or cost of different problems to show their relative significance. The bars show frequency in descending order, while the line shows cumulative percentage or total as you move from left to right.

The Pareto chart example above is a report from layered process audit software that groups together the top seven categories of failed audit questions for a given facility. Layered process audits (LPAs) allow you to check high-risk processes daily to verify conformance to standards. LPAs identify process variations that cause defects, making Pareto charts a powerful reporting tool for analyzing LPA findings.

Pareto charts are one of the seven basic tools of quality described by quality pioneer Joseph Juran. Pareto charts are based on Pareto’s law, also called the 80/20 rule, which says that 20% of inputs drive 80% of results.

6. Scatter Plot diagram

A scatter plot or scatter diagram uses pairs of data points to help uncover relationships between variables. A scatter plot is a quantitative method for determining whether two variables are correlated, such as testing potential causes identified in your fishbone diagram.

Making a scatter diagram is as simple as plotting your independent variable (or suspected cause) on the x-axis, and your dependent variable (the effect) on the y-axis. If the pattern shows a clear line or curve, you know the variables are correlated and you can proceed to regression or correlation analysis.

References:

• 1. ease.io/5-root-cause-analysis-tools-for-more-effective-problem-solving/
• 2. https://www.6sigma.us
• 3. https://ashwinmore.com/how-root-cause-analysis-can-help-you-solve-complex-problems/
• 4. https://kanbanize.com/lean-management/lean-manufacturing/root-cause-analysis/perform.
• 5. https://www.mindtools.com/ag6pkn9/root-cause-analysis

What is Poka-yoke?

Poka-Yoke is a Japanese term that means “mistake-proofing” or “error prevention“. A poka-yoke is any mechanism in a process that helps an equipment operator to avoid (yokeru) mistakes (poka) and defects by preventing, correcting, or drawing attention to human errors as they occurs.

History

The term poka-yoke was applied by Shigeo Shingo in the 1960s to industrial processes designed to prevent human errors. Shingo redesigned a process in which factory workers, while assembling a small switch, would often forget to insert the required spring under one of the switch buttons. In the redesigned process, the worker would perform the task in two steps, first preparing the two required springs and placing them in a placeholder, then inserting the springs from the placeholder into the switch. When a spring remained in the placeholder, the workers knew that they had forgotten to insert it and could correct the mistake effortlessly.

Shingo distinguished between the concepts of inevitable human mistakes and defects in the production. Defects occur when the mistakes are allowed to reach the customer. The aim of poka-yoke is to design the process so that mistakes can be detected and corrected immediately, eliminating defects at the source.

Principles of Mistake-proofing / Poka-Yoke

1. Elimination (“don’t do it anymore”) is to eliminate the possibility of error by redesigning the product or process so that the task or part is no longer necessary.

2. Prevention (“make sure it can never be done wrong”) is to design and engineer the product or process so that it is impossible to make a mistake at all.

3. Replacement (“use something better “) is to substitute a more reliable process to improve consistency.

4. Facilitation (“make tasks easier to perform”) is to employ. Techniques and to combine steps to make work easier to perform.

5. Detection (“notice what is going wrong and stop it”) is to identify an error before further processing occurs so that the user can quickly correct the problem.

6. Mitigation (“don’t let the situation get too bad”) is to seek to minimize the effects of errors.

Elimination, Prevention, Replacement and Facilitation are to avoid the occurrence of mistakes. Detection and Mitigation are to minimize the effects of mistakes once they occur.

Examples Of Poka-yoke:

Implementation in Manufacturing

Poka-yoke can be implemented at any step of a manufacturing process where something can go wrong, or an error can be made. For example, a fixture that holds pieces for processing might be modified to only allow pieces to be held in the correct orientation, or a digital counter might track the number of spot welds on each piece to ensure that the worker executes the correct number of welds.

Shingo recognized three types of poka-yoke for detecting and preventing errors in a mass production system:

1. The contact method identifies product defects by testing the product’s shape, size, color, or other physical attributes.

2. The fixed-value (or constant number) method alerts the operator if a certain number of movements are not made.

3. The motion-step (or sequence) method determines whether the prescribed steps of the process have been followed.

Either the operator is alerted when a mistake is about to be made, or the poka-yoke device prevents the mistake from being made. In Shingo’s lexicon, the former implementation would be called a warning poka-yoke, while the latter would be referred to as a control poka-yoke.

Shingo argued that errors are inevitable in any manufacturing process, but that if appropriate poka-yokes are implemented, then mistakes can be caught quickly and prevented from resulting in defects. By eliminating defects at the source, the cost of mistakes within a company is reduced.

A methodic approach to build up poka-yoke countermeasures has been proposed by the Applied Problem Solving (APS) methodology, which consists of a three-step analysis of the risks to be managed:

1. Identification of the need

2. Identification of possible mistakes

3. Management of mistakes before satisfying the need

This approach can be used to emphasize the technical aspect of finding effective solutions during brainstorming sessions.

3 Rules of Poka Yoke

1. Do not wait for the perfect POKA YOKE. Do it now!

2. If your Poka-Yoke idea has better than 50% chance to succeed…Do it!

3. Do it now…. improve later!

Benefits Of poka-yoke Implementation

A typical feature of poka-yoke solutions is that they don’t let an error in a process happen. Other advantages include:

1. Less time spent on training workers.

2. Elimination of many operations related to quality control;

3. Unburdening of operators from repetitive operations.

4. Promotion of the work improvement-oriented approach and actions.

5. A reduced number of rejects.

6. Immediate action when a problem occurs.

7. 100% built-in quality control.

8. Preventing bad products from reaching customers.

9. Detecting mistakes as they occur.

10. Eliminating defects before they occur.

References:

1. Robinson, Harry (1997). “Using Poka-Yoke Techniques for Early Defect Detection”. Berry College. Archived from the original on December 27, 2014. Retrieved May 4, 2009.

2. ^ Jump up to:^a b c Shingo, Shigeo; Dillon, Andrew (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, OR: Productivity Press. ISBN 0-915299-17-8. OCLC 19740349.

3. ^ John R. Grout, Brian T. Downs. “A Brief Tutorial on Mistake-proofing, Poka-Yoke, and ZQC”. John Grout’s Mistake-Proofing Center. Archived from the original on Apr 14, 2009. Retrieved May 4, 2009.

4. ^ “The Sayings of Shigeo Shingo: Key Strategies for Plant Improvement”. QualityCoach.Net. ISBN 9781563273841. Archived from the original on January 28, 2014. Retrieved August 20, 2012.

5. ^ Jump up to:^a b “Poka Yoke or Mistake Proofing :: Overview”. The Quality Portal. Retrieved May 5, 2009.

6. ^ Jump up to:^a b Nikan (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 111. ISBN 978-0-915299-31-7.

7. ^ Ivan Fantin (2014). Applied Problem Solving. Method, Applications, Root Causes, Countermeasures, Poka-Yoke and A3. How to make things happen to solve problems. Milan, Italy: Createspace, an Amazon company. ISBN 978-1499122282

8. ^ Misiurek, Bartosz (2016). Standardized Work with TWI: Eliminating Human Errors in Production and Service Processes. New York: Productivity Press. ISBN 9781498737548.

Inventory exists in supply chain because of mismatch between demand and supply, some consider it as evil some consider it as essential. Few sector its intentional such as steel manufacturer, where it is economical to manufacture in large lots for future sales, Retail store is another such example where inventory is held in anticipation of future demand.

Another significant role that inventory plays is to reduce cost by exploiting economies of scale that may exist during production and distribution.

Inventory impacts the assets held, the costs incurred, and responsiveness provided in the supply chain. High levels of inventory in an apparel supply chain improve responsiveness but also leave the supply chain vulnerable to the need for markdowns, lowering profit margins. Low levels of inventory improve inventory turns but may result in lost sales if customers are unable to find products, they are ready to buy.

Inventory also has a significant impact on the material flow time in a supply chain. Material flow time is the time that elapses between the points at which material enters the supply chain to the point at which it exits. For a supply chain, throughput is the rate at which sales occur. If inventory is represented by I, flow time by T, and throughput by D, the three can be related using little’s law as follows:

I = DT

For example, if the flow time of an auto assembly process is 10 hours and the throughput is 60 units an hour, Little’s law tells us that the inventory is 60 x 10 = 600 units. If we were able to reduce inventory to 300 units while holding throughput constant, we would reduce our flow time to 5 hours (300/60). We note that in this relationship, inventory and throughput must have consistent units.

The logical conclusion here is that inventory and flow time are synonymous in a supply chain because throughput is often determined by customer demand.

Role in the Competitive Strategy:-

The form, location, and quantity of inventory allow a supply chain to range from being very low cost to very responsive. Large amounts of finished goods inventory close to customers allow a supply chain to be responsive but at a high cost. Centralized inventory in raw material form allows a supply chain to lower cost but at the expense of responsiveness. The goal of good supply chain design is to find the right form, location, and quantity of inventory that provides the right level of responsiveness at the lowest possible cost.

Components of Inventory Decisions:-

CYCLE INVENTORY

Cycle inventory is the average amount of inventory used to satisfy demand between receipts of supplier shipments. The size of the cycle inventory is a result of the production, transportation, or purchase of material in large lots. Companies produce or purchase in large lots to exploit economies of scale in the production, transportation, or purchasing process. With the increase in lot size, however, comes an increase in carrying costs. As an example of a cycle stock decision, consider an online book retailer. This retailer’s sales average around 10 truckloads of books a month. The cycle inventory decisions the retailer must make are how much to order for replenishment and how often to place these orders. The e-retailer could order 10 truckloads once each month or it could order one truckload every three days. The basic trade-off supply chain managers face is the cost of holding larger lots of inventory (when cycle inventory is high) versus the cost of ordering product frequently (when cycle inventory is low).

SAFETY INVENTORY

Safety inventory is inventory held in case demand exceeds expectation; it is held to counter uncertainty. If the world were perfectly predictable, only cycle inventory would be needed. Because demand is uncertain and may exceed expectations, however, companies hold safety inventory to satisfy an unexpectedly high demand.

SEASONAL INVENTORY

Seasonal inventory is built up to counter predictable seasonal variability in demand. Companies using seasonal inventory build up inventory in periods of low demand and store it for periods of high demand when they will not have the capacity to produce all that is demanded. Managers face key decisions in determining whether to build seasonal inventory, and if they do build it, in deciding how much to build. If a company can rapidly change the rate of its production system at very low cost, then it may not need seasonal inventory, because the production system can adjust to a period of high demand without incurring large costs. However, if changing the rate of production is expensive (e.g., when workers must be hired or fired), then a company would be wise to establish a smooth production rate and build up its inventory during periods of low demand. Therefore, the basic trade-off supply chain managers face in determining how much seasonal inventory to build is the cost of carrying the additional seasonal inventory versus the cost of having a more flexible production rate.

LEVEL OF PRODUCT AVAILABILITY:-

Level of product availability is the fraction of demand that is served on time from product held in inventory. A high level of product availability provides a high level of responsiveness but increases cost because much inventory is held but rarely used. In contrast, a low level of product availability lowers inventory holding cost but results in a higher fraction of customers who are not served on time. The basic trade-off when determining the level of product availability is between the cost of inventory to increase product availability and the loss from not serving customers on time.

INVENTORY-RELATED METRICS:-

Inventory-related decisions affect the cost of goods sold, the cash-to-cash cycle, and the assets held by the supply chain and its responsiveness to customers. A manager should track the following inventory-related metrics that influence supply chain performance:

Cash-to-cash cycle time is a high-level metric that includes inventories, accounts payable, and receivables.

Average inventory measures the average amount of inventory carried. Average inventory should be measured in units, days of demand, and financial value.

Inventory turns measure the number of times inventory turns over in a year. It is the ratio of average inventory to either the cost of goods sold or sales.

Products with more than a specified number of days of inventory identifies the products for which the firm is carrying a high level of inventory. This metric can be used to identify products that are in oversupply or to identify reasons that justify the high inventory, such as price discounts or being a very slow mover.

Average replenishment batch size measures the average amount in each replenishment order. The batch size should be measured by SKU in terms of both units and days of demand. It can be estimated by averaging over time the difference between the maximum and the minimum inventory (measured in each replenishment cycle) on hand.

Average safety inventory measures the average amount of inventory on hand when a replenishment order arrives. Average safety inventory should be measured by SKU in both units and days of demand. It can be estimated by averaging over time the minimum inventory on hand in each replenishment cycle.

Seasonal inventory measures the difference between the inflow of product (beyond cycle and safety inventory) and its sales that is purchased solely to deal with anticipated spikes in demand.

Fill rate (order/case) measures the fraction of orders/demand that were met on time from inventory. Fill rate should not be averaged over time but over a specified number of units of demand (say, every thousand, million, etc.).

Fraction of time out of stock measures the fraction of time that a particular SKU had zero inventory. This fraction can be used to estimate the lost sales during the stock out period.

Obsolete inventory measures the fraction of inventory older than a specified obsolescence date

Bibliography:

Supply chain management :  strategy, planning, and operation  /  Sunil Chopra, Peter Meindl