Identification of Defects Causes: Ishikawa Diagram and 5 Whys in Theoretical and Practical Terms

Abstract

The chapter briefly presents the issue of quality and its management in production. In the relevant part of the chapter, the Ishikawa diagram, its variations, and the possibility of extending its application to new areas will be discussed. Similarly, the 5 Whys method is presented. The application of the Ishikawa diagram and how to use the 5 WHYS method are presented with practical examples, enabling them to be transferred to the operation of real enterprises. These examples concern machining, laser processing, and gluing in the context of defective products and processes. The discussion includes case studies of what defects may appear in this type of (or similar, in the field of mechanical engineering) processes, a discussion of their importance in production. Ways to improve machining and assembly operations in the presented context are shown.

1. Introduction

Production management is currently a difficult but also interesting and dynamically developing field. In production plants, with a constantly changing range of manufactured products, the challenge is to maintain a certain acceptable level of production, especially in relation to product quality. In production, the method of carrying out the production process may change; modern technologies and different devices and materials are implemented. The range of produced products can be very different at different times of the year. An example of a particular challenge may be the concept of Industry 4.0, which talks about mass-scale production of individualized, unitary products. In addition, the manufacturing process is significantly affected by the environment in which legal and normative guidelines change; various concepts of production management appear, such as Total Productive Maintenance regarding the maintenance of the machine park in efficiency, Cleaner Production expressing the need to reduce the negative impact of production on the natural environment, and implementation of a systemic approach based on ISO 9001 (quality management), 14001 (environmental management) or 45001 (occupational safety management) standards. The classic production model draws attention to the input elements, such as materials, energy, and knowledge, and to the output elements—products, services, and profit, which are processed in a specific way conditioned by technology. All these elements are somehow “fastened together” by the clamp of the management philosophy. In addition to the abovementioned concepts, decisions are also influenced by social and cultural conditions, customs, financial resources, and many other factors [1, 2].

For these reasons, quality can be perceived in different ways. In one case, it will be identified with the characteristics of the product, in another—with a specific manufacturer. In still other situations, quality may be defined as specific operating conditions, functional features, and features of the work environment, in relation to the natural environment, esthetic values, and others [3].

Despite the constant changes in the reasons for production decisions, the tools and methods of quality management known for a long time remain constant and effective. An example is the Ishikawa diagram and the 5 Whys method, which make it possible to identify the causes, places, and problems with insufficient quality, not only of products but also of defects in the broader sense. The identification process can be supported by other techniques, for instance, a kinship diagram or teamwork (like brainstorming), which trigger creativity and some freedom in defining problems and organize corrective or improvement actions [4].

2. Quality and quality management

Crosby defined quality as the fulfillment of requirements and Juran defined it as usability or applicability. Tse Li used to say that quality is “excellence, perfection of workmanship”. The EN ISO 9001:2015 standard says that quality is the extent to which a set of inherent properties meet requirements [5, 6].

Quality and the concepts related to it have evolved from antiquity to the present. Groundbreaking changes in the attitude to the quality of products and services took place thanks to the American scientists William Deming and Joseph Juran. Their work was used in Japan in 1950–1955, which, combined with Japanese culture and lifestyle, led to the concept of Total Quality Management (TQM). The concept of TQM refers to all the goals of the enterprise and is often called a management philosophy that is applied in activities related to all undertakings and processes of the organization. The main role in these processes is played by people: management, which has a leadership role, and employees who make up a team that creates quality. In this philosophical approach, quality is seen as a process of continuous improvement that applies to the entire organization, customers, and suppliers. Feedback is maintained with the client in mutual communication, and the client’s expectations and needs are taken into account in the work on quality. Suppliers are also an important element in the company’s value creation chain, as their inappropriate products or services may be the beginning of the company’s problems. The ISO 9001 standard is the basis for a systemic approach in which customer needs are defined by contract and quality management focuses on [7, 8, 9]:

• quality planning—in order to determine the requirements and goals to be pursued, for example, in the context of a product, process, or other production areas.

• production control—through the use of tools and methods of conduct, implementation of operational activities necessary to observe the process, and prevention of the occurrence of defects and noncompliant products.

• quality assurance—by planning and repeating activities carried out systematically in order to achieve customer satisfaction.

• improving quality—that is, taking actions that increase the effectiveness and efficiency of processes and activities performed.

With regard to the concept of quality, kaizen talks about the need to improve in small steps. Kaizen is synonymous with rational and skillful time management, communication, creative teamwork, as well as cost reduction by avoiding defects. Kaizen is based on foundations such as [10]:

• standardization of work,

• organization of work,

• elimination of waste.

Kaizen postulates are closely related to other concepts of production management, such as Lean Manufacturing, by striving to achieve maximum productivity, efficiency, and products without errors. This goal can be achieved, among others, by the use of a variety of quality management techniques and tools, both older and newly developed, combined with modern production management [11, 12]. Table 1 shows the quality management tools. The first column lists the so-called old ones, and the second column lists the new ones.

“Old” quality management tools	“New” quality management tools
Control sheets	Affinity diagram
Histogram	Dependency diagram
Correlation diagram	Tree diagram
Control cards	Array diagram
Cause and effect diagram	Table data analysis
Pareto-Lorenz analysis	Decision planning diagram
Block diagram	Network diagram

Table 1.

Quality management tools [11, 13].

3. Ishikawa diagram and 5 Whys

The method of analyzing the causes of various defects and irregularities, called the fishbone diagram or Ishikawa diagram, was developed by Kaoru Ishikawa in 1943. This diagram makes it possible to link the causes and effects of various technological, organizational, and economic problems in a universal way. In Ishikawa quality problems, the diagram is often used where the chain of cause and effect can be extended. The fishbone diagram makes it possible to see previously invisible or unconscious relationships and dependencies. The diagram comes in different versions, which differ in the type of analyzed areas or their number. Typical lists of areas for analysis are given in Tables 2–6; however, each time, the team can establish its own set [5, 14, 15].

Analyzed areas	Problem
Man	Is the loss of quality due to human error?
Methods	What methods of work or production were used?
Machinery	Maybe the error is generated by the machines malfunctioning?
Materials	Could the problem be in the material that the product is made of?
Management	Do problems arise from a lack of supervision, planning, and work organization; poor motivation and leadership; lack of control; and lack of conceptual, technical, and social skills?

Table 2.

5M Ishikawa diagram—basic.

Analyzed areas	Problem
5M	Basic 5M
Environment	Is the production environment, working condition, and other people a problem?

Table 3.

5M+E Ishikawa diagram.

Analyzed areas	Problem
5M	Basic 5M
Measurement	Are the measurements taken correctly?
Mother Nature	Can nature/weather influence the effects of production?
Maintenance	Is the technical condition of machines and their maintenance important for quality?

Table 4.

5M+3 M Ishikawa diagram.

Analyzed areas	Problem
Product	What kind of products will we sell?
Price	What should be the price for the products we will sell?
Promotion	Are there any promotional campaigns? How many times a year? Are they effective?
Place	Is the location from which the company operates favorable?
Process	How are the affairs of the company handled?
People	Are the employees of the company and other companies cooperating with us competent?
Procedures	Does what we do allow the company to function well?
Policies	Does the company have any rules by which it operates? Do they bring results?

Table 5.

8P Ishikawa diagram—for marketing.

Analyzed areas	Problem
Surroundings	Could the problems be related to the environment or location of the company?
Suppliers	Do suppliers deliver ordered goods of the required quality?
System	Can faulty devices, software, and processes be affected?
Skills	Are the team’s skills sufficient to achieve the desired quality?

Table 6.

4S Ishikawa diagram for services.

Table 2 shows the simplest, basic version of the five areas of analysis in the Ishikawa diagram. For each of the areas listed in the first column, a question was proposed to facilitate the general formulation of the problem (shown in the second column).

Table 3 lists the basic areas as 5M and an additional frequently used area, Environment.

Yet another version of the areas in the diagram is shown in Table 4. It is called 5M+3M because other areas, occurring in production conditions such as measurement and maintenance of machines in working order, as well as the impact of changing natural conditions, are added to the basic five areas.

A different set of areas for analysis are shown in Table 5. This is a variation of the Ishikawa diagram for situations where the product is already produced and we are not looking for reasons for the lack of quality of this product. It is intended for departments such as sales, promotion and, customer relations.

The last example shown in Table 6, on the other hand, is a suggestion for service providers who may be struggling to maintain delivery quality, logistics, and other non-production processes.

However, the principle of creating a fishbone diagram is one. In its basic form, the diagram resembles the skeleton of a fish, where the bones converge at the spine. Principal bones correspond to the causes in a given area of analysis (1 principal axis = 1 area). Major bones can have many minor bones that illustrate the possible causes of a problem with a given effect. The line of the spine is the line of the formulated problem (effect of causes) (Figure 1) [4, 16].

Figure 1.

Ishikawa diagram: (a) general concept, and (b) main and auxiliary bones.

The construction of the diagram corresponds to the original assumption of its creator. According to Ishikawa, effects, or problems, always have a cause, and in most cases, there are a number of active factors that caused them. The purpose of using the diagram is to discover, collect, and classify the causes of the problem in terms of the importance of the impact exerted.

Initially, the diagram as a tool for managing the production process was used to manage quality. It has now evolved and is used in other fields such as safety management to identify the causes of accidents or hazards, or in environmental management to identify the causes of negative environmental impact (e.g., waste generation, occurrence of industrial failures).

The cause and effect analysis should be carried out in an orderly manner:

Step 1—Creating a detailed description of the problem: What is wrong? When and where does the problem occur? How is it going?

Step 2—Creating an analysis group, that is, a team of employees who will use the “brainstorming” technique to generate as many potential causes of problems as possible. A leader should be chosen in the group, for instance, a department manager, who will coordinate the work of the team. The team should also include other competent people who come into contact with the problem due to their daily duties. Team work should take place in a calm, friendly, and creativity-enhancing atmosphere, assuming that there are no bad ideas at this stage, and you do not immediately look for a solution to the problem.

Step 3—Selecting and entering the main categories of causes into the diagram and matching the emerging proposals of their sources to them.

Step 4—Selecting the most probable causes of the analyzed problems and discussing the possibilities of remedying the situation.

The basic technique for determining the root causes of defects and process disruptions is the 5 Whys. It is a preventative technique, as opposed to the philosophy of taking action based on actual defects found. 5 Whys, originally written by Sakichi Toyoda and then developed by Taiichi Ohno, was based on the perception of a child’s curiosity about the world. It is the child who, reaching the information, repeatedly asks “Why is it the way it is?” Hence, in quality management, 5 Whys is called “a child’s play method for solving adult problems”. 5 Whys is most effective in situations concerning work organization, employee relations, cooperation between departments, disputes, and where human error may be the cause [17, 18].

The 5 Whys technique requires the following [19]:

• choose a problem for analysis,

• organize a meeting of all people affected by the problem,

• ask at least 5 “Why?” questions,

• develop corrective actions,

• assign responsibility,

• supervise the implementation.

The diagram of the analysis is shown in Figure 2.

Figure 2.

5 Whys diagram.

A variation of 5 Whys, called 5W2H, can be used to define the problem. Then, the questions are answered [20]:

1. What?—What exactly is the problem?

2. Who?—Who reported the problem?

3. When?—When did the problem start?

4. Where?—Where did he perform?

5. Why?—Why is this a problem?

6. How?—What is the effect? What are the consequences of this problem?

7. How many/How much?—What is the scale of the problem? (preferably when it is given in measurable values, e.g., % and pcs).

Then, you get full information about the nature and effects of the problem. The spreadsheet shown in Table 7 can be used to define the problem.

No	Question	Answer	Verification	Action	Deadline
1.	What ………………..?
2.	Who …………………?
3.	When ……………….?
4.	Where ………………?
5.	Why …………………?
6.	How …………………?
7.	How much ………..?

Table 7.

Problem identification and solution—5W2H sheet.

4. Ishikawa diagram and 5 Whys—case studies

In order to demonstrate the usefulness of the Ishikawa diagram and the 5 Whys method in improving production, three different examples of their application are shown. Chapter 4.1 points out the execution difficulties in machining, where technological knowledge, knowledge of the phenomena occurring during cutting, and the ability to counteract the negative effects of the cutting force component play a key role. Different ways of carrying out the analysis of 5 Whys are shown, depending on how to define the problem to ensure correctly implemented production.

Chapter 4.2 shows the possibility of modifying the Ishikawa diagram in connection with the use of a new technological device, when a laser appears instead of a metal-cutting machine tool. Instead of the typical Machine and Management areas, the Laser and PC & Software areas were proposed. An example of a situation when the typical five questions do not lead to a solution to a problem is also presented. Then, the classic method framework should be abandoned and additional questions should be asked.

Chapter 4.3, in turn, shows an example of the application of the analyzed quality tools to solve waste problems using the example of a bonding operation. The problem to be solved is not a defective product, but a defective treatment of the environment and human health. Because of the possibility of different approaches to the responsibility for total waste and hazardous waste, two ways of carrying out the 5 Whys analysis are shown.

4.1 Cutting flat bars made of polypropylene

Machining of modern construction materials on CNC stations seems to be uncomplicated. However, cutting 5 mm thick flat bars made of polypropylene turned out to be a problem due to the length of the fixed blank and the behavior of the element during processing. Loss of stiffness during machining, deflection of the element under the influence of cutting force, inadequate fixation of the workpiece, and general incorrect selection of machining conditions are important technological problems (Figure 3).

Figure 3.

Station with the problem of cutting flat bars: (a) CNC milling machine HAAS VF-1, (b) problem with cutting, and (c) problem of sticking chips.

The simplified 5W2H sheet (Table 8) was used to identify the problem.

No.	Question	Answer
1.	What is the problem?	The flat bar cannot be cut, and when appropriate stiffening is applied, the material on one side has a visible defect in the form of glued chips
2.	Who reported the problem?	Machine operator
3.	When did it happen?	At the start of production
4.	Where did it happen?	HAAS VF-1 CNC milling center
5.	Why is this a problem?	Because either the machining cannot be done or the part is not made to specification
6.	How is this happening?	The problem occurs after clamping the workpiece in a vice and trying to cut the material
7.	How many products failed to perform?	Not one so far

Table 8.

Simplified 5W2H sheet.

In order to identify the causes of problems, the Ishikawa 5M+E diagram was developed (Figure 4).

Figure 4.

Ishikawa diagram for polypropylene cutting.

Typical areas of analysis have been included in the diagram, and they have shown primarily human problems. In both Machine and Man areas, faults caused by a lack of knowledge, interest, and care and negligence were indicated. In the Method area, deficiencies in the tooling or faulty setup are indicated, but this also has its roots in human nature. The revealed difficulties should lead to rethinking whether flaccid elements should be cut at all in the presented way, for what reason this chosen position was considered justified. If, by decision of the management, CNC HAAS machining is maintained, then remedial steps will be necessary due to clear errors in the manufacturing technology. Due to the most important error, which is incorrect processing conditions, that is, incorrect mounting and loss of rigidity, the method of making the cut was first considered in 5 Whys, because so far, all products had been damaged (Figure 5). Only then were the defects verified—glued chips on the object (Figure 6).

Figure 5.

5 Whys for destroyed workpieces.

Figure 6.

5 Whys for poor quality of cut edges of workpiece.

After analyzing 5 Whys, the team came to the conclusion that the key issue is the substantive knowledge of employees. Deficiencies in this area should be made up as soon as possible through training. The second urgent task is to read and update the workstation manual, because the conditions for the implementation of the technological operation have changed dramatically along with the changed machine tool.

4.2 Laser cutting of small diameter holes

Lasers are now being used more and more commonly for various technological operations. Due to the still quite high cost of purchasing high-end devices, it is important in production to use your equipment in many different applications. The analyzed station with a fiber laser for marking and engraving was used to cut small holes in thin sheets. This method turned out to be effective, but various problems arose during the start of production (Figure 7). When developing the technological guide, it was found that with the given software, it is impossible to drill holes (you cannot apply a laser pulse multiple times in one place), but you can cut them. Cutting can be carried out according to different strategies. By setting the beam trajectory in a circle, burns are obtained at the end of cutting, depending on the beam parameters. On the other hand, the spiral trajectory allows for the gradual removal of material, but with an inaccurate definition of the spiral shape, a clear “teeth” was obtained. On the other hand, during cutting with a simultaneous circle and spiral, a deviation of ovality appeared due to the deformation of the hole under the influence of heat. Therefore, machining with clearly defined, optimal parameters, saved in the program controlling this laser model, plays a key role. The plant wants to eliminate all mistakes and defects due to the need for flexible production under the Industry 4.0 concept.

Figure 7.

Examples of poor quality during laser cutting holes: (a) wrong “spiral” cutting strategy, (b) edge irregularities and ovality, (c) edge burns.

Due to the fact that the station was new in the plant, a general Ishikawa diagram was prepared, modifying it to include the PC & Software area, due to the often signaled difficulties and impact on the course of activities at the station (Figure 8).

Figure 8.

Ishikawa diagram for hole laser cutting.

First, the laser bone was drawn in detail (Figure 9); attention was paid to the degree of detail in the construction of the device and the variety of possible problems. In this way, it was realized that knowledge about the device is necessary to maintain its efficiency. In addition, the way the laser works specifically affects the choice of method. Many parameters are adjustable, and they, ultimately affect the machining effect.

Figure 9.

Different problems in laser bone.

From the point of view of laser hole cutting, the most important issue is to maintain the optimal parameters of the laser beam. After a detailed analysis of the problem, it was determined that the employee has only one right program to run, but the thickness of the material changes. Thus, the location of the beam focus changes, which is crucial for the effective impact of the laser. An example of solving this problem is shown in Figure 10.

Figure 10.

5 Whys for holes made with defects.

The above example is also a confirmation that sometimes rigid adherence to five questions may not give a satisfactory result; in the analyzed situation, one more question, the sixth question, was needed.

In turn, the analysis of the PC & Software area made the team think about why the laser often fails to start, despite a working computer and the right program. The 5 Whys results for this problem are shown in Figure 11.

Figure 11.

5 Whys of the problem in PC & software area.

Analysis of the Ishikawa diagram and the results of 5 Whys made it possible to conclude that the overriding issue is the efficiency of the device. All employees associated with this position are required to maintain the laser in this state. The operator has the greatest contact with the laser. His knowledge and general condition, indicated by the Man area, are important in the context of determining technological parameters. In addition to him, an important role is played by service technicians, electronics engineers, and programmers as people interfering with the construction and operation of the device. People can also have an impact during transport (and thus suppliers), when damage to components may occur, during assembly and organization of the station. Fortunately, the problem that was finally identified was trivial and was quickly eliminated.

4.3 Bonding of materials

In the gluing operations, various substances are used, necessary for the proper preparation of the surface of the materials before gluing. This diversity results from the type of bonded material, surface condition, selected adhesive mixtures, and gluing technology (surface preparation baths, rinsing, method of preparing the mixture, method of applying the adhesive, and method of curing) (Figure 12).

Figure 12.

The problem of a significant amount of waste after gluing: (a) used mixing containers and brushes for applying adhesives; (b) plastic and glass packaging from degreasers and rinsing liquids; (c) metal packaging for adhesives and hardeners; and (d) plastic, glass, and pressurized packaging with various applicators for washing, preparing, and activating the surface before gluing.

The problem of waste can be perceived in different ways in a plant. The Ishikawa diagram drawn for this problem made it possible to identify a number of reasons why a lot of waste from various materials and packaging contaminated with various substances remains after gluing operations (Figure 13).

Figure 13.

Ishikawa diagram for gluing.

Reflecting on the problem, attention was first drawn to the considerable amount of total waste that comes from the gluing process. 5 Whys for this thought process are shown in Figure 14.

Figure 14.

The problem of the amount of waste after gluing.

On the other hand, by emphasizing the fact that gluing waste is hazardous waste, and additionally paying attention to its accumulation at workstations, 5 Whys may have a different course and result in other management decisions (Figure 15).

Figure 15.

The problem of hazardous waste after gluing at workstations.

5. Conclusion

The Ishikawa diagram is an effective tool for discovering the sources of problems in enterprises. It allows to classify and establish a hierarchy of a set of various statements, causes of faults, in a situation where this set is chaotic. However, it gives the opportunity to look at the production or activity of the company from the point of view of many areas that are often not suspected of affecting the broadly understood quality. When using the diagram, however, you may encounter difficulties:

• it is necessary to work in a group, so little efficiency is possible if the team leader is weak,

• for the effectiveness of the diagram, it is necessary to properly classify the causes and assign them to the appropriate areas,

• the analysis takes place in typical areas, and it is possible that the real cause of the problem is overlooked.

Difficulties can also arise when determining root causes using the 5 Whys:

• the symptom is perceived as the cause,

• the method seems trivially simple, and you might want to point out the reason right away, but in reality, it is not,

• hasty pointing of the guilty,

• lack of sincerity in the team, hiding some activities, conflicts, and fear of further employment,

• limited to 5 questions, even if the root cause has not been identified,

• conducting the analysis by one person, not a team.

The examples shown illustrate different production situations. A similar approach could be taken in many areas, for example, in the area of Man, by identifying the causes of errors inherent in the human mentality and mental and physical condition. Sometimes, the Ishikawa diagram was modified to include other issues, such as those related to computer operation and data flow. You can also encounter a situation when 5 Whys leads to a surprising discovery of the negligence of the employer, or draws attention to a seemingly insignificant problem that—as it turned out in point 4.3—can affect the health of employees.

Based on the examples, it can be concluded that the knowledge of manufacturing technology always plays a key role. However, in the production process, the subject is man, and his behavior determines the course of this process. Finally, it should be emphasized that the production process and its improvement should start with the management. The lack of awareness of the management and the lack of management skills can have a negative impact and manifest in the lack of training, motivation, and incentives for professional development of employees. Thus, it is difficult to talk about quality management of products and processes.

Conflict of interest

The author declares no conflict of interest.