**1. Introduction**

In manufacturing industries, waste refers to the activities that consume resources but that do not directly add value to the product or service for the customer [1]. According to the literature review, there are seven categories of waste in manufacturing that negatively affect the quality of products, delivery times, and unit cost [2,3]. These wastes are overproduction, inventory, over-processing, motion, waiting, transport, and defects [4,5]. Regarding the defects, during the manufacturing processes, companies receive material or components from their suppliers. Then, those materials or components

are changed to obtain a final product, which must be delivered to customers on time and without defects [6]. However, defects continue being present in the manufacturing industry nowadays. In fact, several authors mention that defects are the main cause of damages in final products or other components [7–10], which represent a critical situation for the industrial and manufacturing sector [11].

Moreover, customer satisfaction is a requirement that must be considered for any distributor business that is intending to remain globally competitive [12,13]. Nevertheless, if managers want to fulfill customer needs, an appropriate product design process must be included [14]. In this sense, one of main customer needs is a non-defective, quality product [15], since product defects lead to customer dissatisfaction, sales decreases, low financial profits, and greater unit costs [16,17]. In order to improve the effectiveness and efficiency of the production process, offer quality products, and avoid the latest problems, manufacturing companies rely on a wide range of methods and techniques for production improvement [18], including the six sigma management philosophy, DMAIC (i.e., define, measure, analyze, improve, and control) [19], process flow charting (PFC) [20], the Deming or PDCA cycle (i.e., plan, do, check, act) [21,22], and the eight disciplines (8Ds) method [23], among others.

Specifically, the 8Ds are focused on: (D1) develop a team, (D2) describe the problem, (D3) develop an interim containment action, (D4) determine and verify root causes, (D5) Choose/verify permanent corrective actions, (D6) implement and validate corrective actions, (D7) prevent recurrences, and (D8) recognize and congratulate teamwork as well as individual contributions, which is a powerful method because it helps with creating appropriate activities in order to identify the root causes of a problem, and provides permanent solutions to eliminate them. In addition, the 8Ds method is a special tool of ISO/TS 16949:2009 that has been broadly applied in automotive industry for service, including the issues concerning supplier qualification confirmation, process deviations, maintenance, customer complaints, and purchases.

The 8Ds method has been adopted widely in the manufacturing world [24]. For instance, several authors have applied it to solve problems of defects. Some of these authors are: Mitreva et al. [25], who applied it for solving a problem in a LED diode that does not perform its function in a circuit board. Likewise, Titu [26] implemented the 8Ds method to reduce complaints about a defective part; consequently, 60 days after corrective actions were implemented, no other product was identified with this type of defect, and customers decided to withdraw the complaint. Additionally, Kumar and Adaveesh [24] conducted a study in a spring and stamping manufacturing plant for solving a high rejection rate (i.e., 17.07%) of valve springs due to defects. In order to solve this problem, the 8Ds method was applied, and as a result the rejection rate decreased significantly in 6 months, by 4.91%.

### *Research Problem*

A maquiladora is a factory that operates under preferential tariff programs established in Mexico that has headquarters in other countries and performs assembly operations with high hand labor required. Materials, assembly components, and production equipment used in maquiladoras are allowed to enter Mexico duty-free. Currently, in Mexico there are 5144 maquiladoras giving 2,678,633 direct jobs. However, Baja California state has 914 (17.76% from national) maquiladoras giving 333,392 direct jobs [27].

Those companies are using several techniques and methodologies for solving manufacturing problems in production lines. This paper reports a case study applied in a manufacturing company located in Tijuana, Mexico, dealing with the manufacturing of electric custom cables. Each cable is tested for quality through a series of computer-assisted programs for a complete inspection. This strategy allows the company to build and maintain long-term relationships with its customers, thereby helping the company reach its goals and be successful. However, the company has lately experienced problematic defects; as a result, customers are complaining due to 67 returned assemblies.

The problem concerns a stepper motor (see Figure 1), one of the main assembly components, which has a part number that will be called part number A. Customers provide the motors to the company, which introduces them into the production process; next, the motor cables are cut at a specific

length, and the plate and terminals are riveted; then, the terminals are inserted into connector units in which a functional test is performed; finally, some defects that are found in this assembly process include cable inversion, incorrect cable length, and lack of an ID tag. In order to solve these problems, the 8Ds method is implemented to decrease the rate of defective products, and to increase customer satisfaction. Therefore, the objective of this paper is to prove the efficiency of the 8Ds method through a case study.

**Figure 1.** Stepper motor.

A case study is conducted because according to Easton [28], the critical realism approach (CRA) states that a single case study research method is enough to generalize theoretical and empirical findings, giving a new, rigorous, and coherent philosophical position that helps develop the theoretical and research process. Similarly, Tsang [29] states that CRA highlights the impacts of a case study on the theoretical process, empirical generalization, and theoretical evidence. Additionally, Tsang presents the fallibility of knowledge, which establishes that all developed theory requires being subjected to empirical evidence and evaluations; in that sense, case studies are appropriate research strategies to illustrate and analyze proposed theories. Therefore, only one case study is enough to generalize results [30]. Recently, several case studies in the manufacturing sector have been published in journals with a high impact factor. These case studies include the application of methodologies such as value-stream mapping [31,32], the plan-do-check-act (PDCA) cycle [22], lean six sigma [19], and standardized work [33], to mention few.

Specifically, this research implements the single case study approach, since the main contribution is that it allows generalizing the positive impact of the 8Ds methodology on defect reduction in the manufacturing processes with a single case study, which is supported by the CRA. Then, this paper contributes to illustrating how a single and easy technique can be applied for improving a production system in the maquiladora industry.

The rest of the paper is organized into five sections: Section 2 reports the literature review about the 8Ds method and its successful implementations from case studies; Section 3 addresses a description of materials and methods that are implemented in the present case study; Section 4 shows the findings obtained; and finally, Section 5 presents the conclusions and industrial implications regarding the 8Ds implementation.

#### **2. Literature Review**

The 8Ds is a teamwork-oriented problem-solving method that aims at identifying the root cause of a problem to solve it through a corrective-action-guided procedure [23]. From a business perspective, the 8Ds method seeks to find the main problems' root causes, identify their possible solutions, and assess their impacts on companies [34]. Originally, the 8Ds method was developed at Ford Motor Company; it was introduced in 1987 to a manual entitled "Team Oriented Problem Solving" (TOPS) [35]. Since then, the method has been applied mainly in automotive industries to solve product and service-related problems, such as defects, customer complaints, manufacturing process deviations, returned purchases, poor machinery maintenance, and supplier qualification issues, among others [34,35].

According to Chelsom et al. [36] and Vargas [37], the 8Ds method can be applied to any type of problem or activity in order to provide assistance to achieving effective communication among departments that share a common objective. However, the 8Ds method is popularly applied to solve quality problems; it is typically required when at least one of the following events are presented [38]:


The literature review mentions several successful case studies wherein the 8Ds method was applied. For instance, Mitreva et al. [25] implemented the 8Ds method to solve the problem of an LED diode that did not perform its function in a circuit board; they reported a decrease of operational defects after its implementation, and an increase the efficiency of software packages in the application of statistical methods and techniques. In the same way, Bremmer [39] applied the 8Ds method and other techniques to analyze Scania's global supply chain; how the company could guarantee the quality of products was demonstrated. As a result, this author found the problem and its root causes.

Similarly, Pacheco-Pacheco [40] sought to optimize delivery times of alteration clothing (Alto de basta and Alto de camisa) products in a tailor shop by implementing the 8Ds method. It was found that production times decreased by 2.46% in two mix products. In both products, delivery delay times decreased by 33.33%. Finally, Zasadzie ´n [41] employed the 8Ds method to reduce machine downtimes that were caused by bottlenecks. In summary, Table 1 presents the successful case studies wherein the 8Ds method was implemented.


**Table 1.** Recent case studies applying the 8Ds method.


**Table 1.** *Cont.*


**Table 1.** *Cont.*

Although the 8Ds method is flexible—it can be adapted to different situations—and has several successful applications, it has some disadvantages, such as [50]:


#### **3. Materials and Methods**

In order to conduct the present case study, the following materials were used: Microsoft Excel® spreadsheets [51], AutoCAD® [52], Visual Basic® [53] software programs, a PDCA form, and a visual aid form. As for the methodology, the 8Ds method was applied and its steps are presented in Figure 2.

**Figure 2.** Steps for the 8Ds problem-solving process. Adapted from Joshuva and Pinto [35].

Some similar case studies to this research have used the Kano model as a tool to classify and prioritize customer needs based on how they affect customer satisfaction [54]. However, according to experts, the Kano model has several deficiencies, which discouraged its use in this case study. For instance, it is known that, to conveniently quantify the Kano model, customer satisfaction or dissatisfaction levels toward a product or service must be measured by using the customer satisfaction scale (see Table 2) of positive or negative comments with product or service attributes [55,56]. However, some experts claim that the satisfaction scale is asymmetric, since a positive answer is stronger than a negative answer, which reduces the impact of a negative assessment [54,55].

**Table 2.** Satisfaction scale of positive and negative comments.


Another inconvenience with the Kano model is that it does not consider customer perceptions towards a product or service attributes. Particularly, it provides limited decision support for designers [57], and it is administered through a reduplicative survey, which is time-consuming. In addition, the classification obtained after analyzing the survey results is based merely on subjective assessments; therefore, it may be biased. Finally, it has been claimed that Kano's different classification schemes may influence resource allocation and product design strategy, not only customer satisfaction, and it inherently emphasizes customer and market perspectives, but does not consider the capacity of the company [54,57].

An alternative to the Kano model is the 8Ds method, which relies on facts rather than opinions [37,58]. Specifically, the 8Ds method adopts an objective approach, whereas the Kano model is based on a subjective approach. In this case study, the 8Ds method is applied to solve the identified problem.

### *3.1. Develop a Teamwork (D1)*

Proper planning will always guarantee a better start; therefore, the following criteria should be applied before integrating 8Ds teamwork [38]:

• Collect information regarding symptoms, such as the ID number and description of the claimed part, failure date, customer and supplier numbers, and a short, descriptive analysis of the problem [39,59,60].


Moreover, the 8Ds method involves organizing a cross functional teamwork that must have enough knowledge about the product/process to successfully deal with customer complaints or quality deviations in the problem-solving phase [23,35]. Additionally, the teamwork must be interdisciplinary—integrated by operators from several departments (i.e., manufacturing, engineering, and marketing) and different knowledge fields to create a solid task force [61], because the experience of the members is a key element to implementing any problem-solving method [62].

In addition, a teamwork leader is assigned, who ensures that all activities are being carried out and the 8Ds report is regularly updated. Additionally, there should be a champion; this is a person in a management position with enough authority to assist and lead the teamwork when it encounters difficulties or in case additional resources are required [59]. Similarly, any permanent solution may require subsequent teamwork involvement [36]. Based on these facts, manufacturing companies employ hundreds, or even thousands of people with different types of skill sets, ideas, and values, who must be useful for the company.
