**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**).

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

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

#### **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.*

*Identification of Defects Causes: Ishikawa Diagram and 5 Whys in Theoretical and Practical… DOI: http://dx.doi.org/10.5772/intechopen.113990*


#### **Table 8.**

*Simplified 5W2H sheet.*

#### **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.

*Identification of Defects Causes: Ishikawa Diagram and 5 Whys in Theoretical and Practical… DOI: http://dx.doi.org/10.5772/intechopen.113990*

**Figure 7.**

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

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.

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**).

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 8.** *Ishikawa diagram for hole laser cutting.*
