Fators impacting to root causes of manufacturing defects by fuzzy ahp method a case of chang shin vietnam

Trang 1 CAPSTONE PROJECTMAJOR: INDUSTRIAL MANAGEMENT FACTORS IMPACTING TO ROOT CAUSES OFMANUFACTURING DEFECTS BY FUZZY AHP METHOD:A CASE OF CHANG SHIN VIETNAM ADVISOR: NGUYEN PHAN ANH H

Reason of choosing a topic

According to Grand View Research (2022), the Sports Shoes Market is predicted to increase at a CAGR of 4.63% from 111.65 billion USD in 2023 to 140 billion USD in 2028 People began to experience health difficulties over a year after the COVID-19 epidemic, owing to the work-from-home culture Everyone is gaining weight and developing ailments such as high blood pressure, cholesterol, and diabetes People have become more aware of the benefits of exercise as a result of these factors, and countries have boosted involvement in sporting activities Following the pandemic, mountaineering and trekking expeditions rose around the world, raising demand for sports shoes and, as a result, fueling the expansion of the sports shoes industry In 2021, 58.7 million people hiked in the United States, according to the 2022 Outdoor Participation Trends Report

The increased awareness of the value of fitness is driving the market Consumer purchasing habits have shifted substantially in recent years, owing primarily to greater disposable income and increased expenditure on self-improvement products Demand for sports shoes has increased due to an increase in the number of specialty and franchised footwear stores, as well as collaboration between footwear producers and other retail chains Many growing trends in various areas are predicted to benefit the sports footwear business in the next years Furthermore, developments in product development by market players, such as smart footwear that calculates calories burned, could have an impact on the athletic footwear business

In the context of deepening international integration, Vietnam is becoming a destination for investors and production relocation of major manufacturers when it is considered as a potential market for development That, has attracted two major men in the Althetic Footwear Industry in the world to set foot in Vietnam, Nike and Adidas The proportion of Nike’s footwear processing and exporting in Vietnam in recent years has attained impressive numbers, with 50% of Nike products being manufactured, that is, every 2 pairs of Nike shoes put on the market In the international market, there is 1 pair made in Vietnam With the entry of two giants from the footwear industry, Vietnam's footwear manufacturing industry has acquired a certain foothold in the US market Each year, the US market imports about 1.8 billion pairs of shoes, while Vietnam exports over 300 million pairs of shoes to this market, mainly export athletic shoes

The success of any organization depends on the effective implementation of quality management strategies in line with its purpose and objectives The AHP method is a useful tool for evaluating factor effects to production quality The analytical Hierarchy Process (AHP) technique is one of the methods used to determine the relative importance of a set of attributes or criteria AHP is designed to solve complex multi-criteria problems Vaidya & Kumar (2006) reviewed about 150 applied articles under three themes: (i) selection, evaluation, cost-benefit analysis, allocation, planning and development, prioritization and ranking and decision-making, (ii) forecasting, health and related fields, and (iii) AHP combined with quality functional implementation and application areas such as personal, social, domain manufacturing, politics, engineering, education, industry, government and other fields They critically analyzed 27 articles and found that most of the applications involved the context of selection and evaluation They also found that AHP is used primarily in the technical, personal and social domains

Companies are competing with each other in many different ways, but in general, reducing production costs and ensuring product quality are the top factors However, there are presently no studies that apply Fuzzy AHP model to evaluate the factors affecting quality in the athletic footwear industry With all the above reasons, the author decided to choose the topic: “ Factors impacting to root causes of manufacturing defects by Fuzzy AHP method:

A case of Chang Shin Vietnam ” to research and evaluate the factors affecting product quality products at Chang Shin Vietnam

The purpose of this study is to contribute to minimizing and rectifying errors in the production process In addition, offering solutions to create conditions to achieve the highest efficiency, meet the requirements of consumers and save production costs for businesses.

Purpose, objectives and scope of research

Purpose of research

The article employs theoretical research methods, practical observations, combined with company And apply the AHP method to rank the influencing factors to enhance performance, increase productivity and competitiveness, and improve From there, propose some disarmament to increase production efficiency and product quality.

Objectives and scope of research

- Identifying important criteria and sub-criteria of sewing line and bonding shoes quality failure in Chang Shin Vietnam company

- Evaluating criteria and sub-criteria of sewing line and bonding shoes base quality failure based on AHP method and using fuzzy number

Research scope: Chang Shin Vietnam company

Research method

The article uses the theoretical research method and applies the data collection method through expert consultation, to collect data to evaluate each relationship between the criteria The experts participating in the interview process are all individuals with knowledge and experience in assessing the factors affecting quality in the althetic footwear industry From there, propose a number of disarmament to increase management efficiency

In this thesis, the method of Hierarchical Analysis Process will be applied and combined with fuzzy numbers to evaluate the root cause defects of manufacturing.

Structure of report

The thesis is divided into the following 6 chapters:

Chapter 1: Introduction of the company

Chang Shin Vietnam is introduced in this chapter with a history of development, a multinational factory network, and a preliminary introduction of shoe production lines

Presentation of outlining concepts and theories about athletic footwear industry, quality management, Ishikawa diagram, basic theory of AHP and fuzzy number

As well as listing previous studies, along with actual combinations from the company to indicate the criteria and build a research model for the article Detailed description of the research methodologies In particular, the method is deployed based on the combination of AHP and Ishikawa to develop a research model

Employing the techniques described, together with fuzzy AHP method, to analyze and interpret data derived from interviews, and ranking the sub-criteria

Following the findings of the ranking of influence elements, this chapter will offer some remedies

In order to determine the root causes of manufacturing defects at Chang Shin Vietnam, this study used the Fuzzy AHP approach The decision-maker will feel more confidence thanks to this method's ability to provide a more accurate result.

INTRODUCTION OF THE COMPANY

History of Formation and Development

Changshin is the exclusive footwear manufacturer for Nike that was founded in 1981 Current revenue is $1.3 billion, with a worldwide employee total of 72,129 In 1995, the first multinational factory was established in Vietnam, followed by China; Indonesia in 2010 In addition, the company’s manufacturing competitiveness has been enhanced by establishing a global network connecting Korea-Vietnam-China-Indonesia

As the leader of the Korean footwear industry, Changshin has become an international enterprise with sustainable growth capabilities based on a robust global network, management that pursues challenges and innovation, lengthy experience years and accumulated technology

In 1997, Changshin first applied the Toyota Production System (TPS) in the footwear industry which has become the foundation of the “LEAN Enterprise Management” that is applied to this day The system helps to optimize the efficiency of the company's production methods through minimizing waste and reducing costs by implementing LEAN management to each manufacturing plant Moreover, Changshin is progressively becoming a world-class manufacturer by promoting an audacious investment in equipment, technical innovation, and diversification of business lines

Changshin Vietnam Company is the primary factory with approximately 40,000 employees Capable of manufacturing over 60,000 pairs of shoes a day, the primary factory is located in Thanh Phu Commune, Vinh Cuu District, Dong Nai Province (50km from Ho Chi Minh City) If in 1995, the initial investment capital of Chang Shin Vietnam was only 11 million USD, now it has increased to more than 219 million USD After 29 years of production and business activities, despite many difficulties, especially the financial crisis in 2010-2012, Chang Shin Vietnam Company has gradually risen to overcome difficulties, stand firm and continue invest in expanding production development, attracting more workers to work, contributing to promoting economic growth of Dong Nai province in particular and Vietnam in general

On March 29, 2013, the second factory is Changshin Long Thanh in Loc An Industrial Park - Binh Son, Loc An Commune, Long Thanh District, Dong Nai Province was placed into operation

On February 22, 2019, Chang Shin Vietnam marked a new development stride with the Groundbreaking Ceremony of Chang Shin Vietnam Manufacturing Factory in Tan Phu Industrial Park This is an investment project that has just been granted a Registration Certificate with a total registered investment capital of 100 million USD, the factory scale has a capacity of more than 27 million pairs of products/year erected on an area of 14.3 hectares of land in Tan Phu industrial zone When placed into operation, the factory will generate jobs for more than 10,000 workers, contributing to the socio-economic development of the mountainous district of Tan Phu, Dong Nai province

Changshin Company was awarded the third-class Labor Medal by the Vietnamese government and many other certificates of merit for social activities, environment, labor safety, well implementation of state policies

Changshin Inc is the primary company situated in Korea – the company that manufactures shoes exclusively for Nike Established in December, 1981, at 242, Jangpyeong-ro, Saha-gu, Busan, Republic of Korea Currently, the corporation is producing jobs for 1,125 employees Changshin is the first manufacturing company to implement Toyota Production Systerm (TPS) in the footwear industry, thereby optimizing production efficiency, minimizing waste and production costs

Changshin Technology was established in March 2001 at 85, Jangnimbeonyeong-ro, Saha-gu, Busan, Republic of Korea, with the number of personnel of 578 individuals Changshin Technology is the primary affiliate that supplies Nike shoe molds for factory production In order to enhance the competitiveness of mold production, Changshin Technology established CSTV in

VJ is Changshin’s first shoe factory in Vietnam, established in June, 1994 VJ is the foremost manufactory in Nike's manufacturing chain which is evaluated at gold level by Nike’s Manufacturing Index (MI) The company has been awarded

“Employment and Welfare Grand Prize of 2018”, “Korea-Vietnam Diplomatic Relations CSR Grand Prize”, and supporting the photovoltaic business community Currently, the scope of the company has expanded two more branches in Long Thanh and Tan Phu, Dong Nai province With a total personnel of more than 42,000 individuals

Qingdao is a shoe manufacturing located in No 6, Guan Zhou Road, Jiao Zhou City, Qingdao, China Established in March,

1995 with a staff of 6,042 employees The factory employs the LEAN Production system, which was assessed as silver by the Beyond Compliance audit in 786 manufacturing partners operating with Nike in 2013 China's High Tech Hub, the hub for the shoe industry, lead the way Tech Cascading by incorporating technological innovation into running shoes and more The company set the groundwork for shoe trends with a collaboration between Nike and influential designers In particular, based on Nike's unique product strategy of High - Performance TRACK & FIELD, which plays an essential role in bringing athletes to victory

JJ is a pioneer factory manufacturing high-tech jogging products in the Indonesian Nike factory chain The factory was established in October, 2010, at Jl Dusun Gintungkolot Rt 16/04, Gintungkerta, Karawang with a staff of up to 18,385 employees The factory has satellite optimized the operation and efficiency of the shoe factory based on the integrated operation of the C2.0 system With a humane working environment that has brought many awards such as “the Best Employers For Women”, “Excellent Health Insurance Provider”, “Excellent labor benefit provider for pregnant women”, and “Excellent benefit program provider for Women”

RJ is the second manufacturing facility established in Indonesia RJ is the factory that powers Nike’s foundation with a new development strategy based on the experience of the JJ factory The factory was established and in February 2020, at Jl.Raya Leles No.134 Ciburial, Kec.Leles,kabupaten Garut, Jawa Barat, with the staff size (10,162) positions third in the total number of Changshin factories

Production line of Nike shoes

1.2.1 The diagram of Nike shoes production line

Figure 1.1 The diagram of Nike Running shoes

To have a contemporary pair of sports shoes, satisfying the demands of the feeble market as well as the quality requirements of consumers, the shoes need to go through a number of various phases and can be done for a long time The production line is initiated with the preparation of the input materials, a specified number of details will be processed through the material rolling stage, to create a suitable composite material with the characteristic properties of the product that want to target The materials are then carried to the cutting stage, where the material is cut with special pointed blades manufactured particularly for the details of the shoe In addition, at the stage of preparing materials for production input, there will also be stages to perform such as edge honing, detailing, attaching reinforcement for details, etc,

Laminated material Cut component of product Prepare input

Packing depending on the design of the product And particularly, for the Running shoe line, the No- sew pressing procedure will be applied to the decorative details of the upper shoes After the preparatory stages have been completed, it will be transferred to the stitching stage of the upper body During this period, preparation for the sole (midsole and outsole) will also be done To have a complete pair of shoes, the assembly stage is indispensable Here, the upper body and sole will be thoroughly assembled by using specialized apparatus and technical processes And lastly, the completed shoes will be packaged according to Nike standards, ready to be distributed by Nike throughout the market

1.2.2 Analyze each stage of production line

Table 1.2 Sample of material in laminated process

Tongue Aero moneylon, rec (100%), DJT – 995 -

Tongue Soft PU backing foam (001), 4MM #

Tongue lining (PM) Lining, knit, matte, micro,

Tongue lining Soft PU backing foam (001), 2MM #

Tongue lining Tricot, 1 tone, rec, 44” #

Collar lining Tricot, 1 tone, rec, 44” #

Collar lining (PM) Lining, knit, matte, micro,

Collar lining Firm PU backing foam (003), 2mm, 44” #

The laminated material process will be carried out in a specialized workshop in the factory The input materials, after being imported into the warehouse, will be subjected to a rolling process for a number of specified details The material will be used with thermoplastic powder and dispersed using a Powder Scattering Device (PSD) This powder sprayer is installed in front of the dough roller and helps to evenly spread the thermal paste over the material Next comes an infrared heater, which heats up the dough a little so it ‘sticks’ better The next step in the process is to heat and press the layers of material together A pressure roller is used to precisely adjust the right amount of pressure to fuse two materials

The shoe production process starts with cutting the materials Shoe parts are generally cut by steel dies in a hydraulic press Every shoe part requires it’s own cutting die Every part for every size needs its own die, but some special cases are using group size for optimal production and minimize cost These shoe parts are called the shoe pattern To support the production of high-volume shoes in popular sizes, often many die sets are required

Table 1.3 Some sample of cutting component

Component name Picture Cutting die

The cutting dies are placed on the leather or fabric materials by hand, then using specialized machine to make the cuts After the parts are cut, a worker will carefully remove excess cut and arrange a shoe parts into shelves The parts will then be inventoried in quantity and organize the parts into kits for the stitching department à In presents, company are using “ Atom SP588/3 25T” machine by ATOM ITALY S.P.A for cutting process

Dimension length, width, and height

Net weight with oil 1430 kg

Source: Xiangdi machine CO., LTD

Figure 1.3 The diagram of No-sew process

No-sew pressing procedure is the process of applying pressure to adhere decorative details on the upper of shoes without applying stitching This technique is often employed in the footwear process Each detail will be combined with high and low-temperature fusion TPU film To carry out this procedure, a pallet will be required to establish the position of the detailing on the exterior of the shoe The details need to be pressed under the correct temperature because the upper material is a knitted fabric, which will be affected under high temperatures that will cause the material to shrivel

In order for the pressed details to be fixed on the upper, workers will cut the adhesive films in the shape of the details that will be attached on the upper This type of film, under the influence of heat, will melt and firmly adhere the details on the upper

Using heat gun to fixed component

Put silicon pad and insulating paper

Heat press in 54s Top: Silicon 8mm/

Upper: Surface up with pin-plate

Remove silicon pad and replace another

Take out and aging time 3-5s in silicon pad à Material using to attaching decorated detail in process

Color Transparent, semi-transparent, colored, embossed

Source: Shenzhen Tunsing Plastic Products CO., LTD

Figure 1.4 The diagram of Stitching process

After the details of the shoe have been prepared, there will be stitching to shape the body During the sewing phase, activities will be divided into basic steps, each worker will be assigned a task to complete Each of the above details will be sewn by a worker such as when a worker finishes sewing zigzag lines to shape the heel of the shoe, it will be transferred to the next worker to label the heel of the shoe With each task assigned to a worker, the quality control staff can quickly find any problems From there, it can be changed in time, helping to

Stitching and 3D No-sew heel

Attaching and stitch heel label

Turnover and attach collar lining

Pressure: 3kg/𝑐𝑚 ! minimize the loss of finished products The division of business also helps employees quickly master their profession

Figure 1.5 The diagram of Stockfitting process

The stockfitting process is a process where assembly is performed outside of the main process Stand-alone components: Midsole and Outsole will be assembled on a pre-assembled line before they are sent to the main assembly line Assembling the base parts separately

Preparation: Input sole component and put sole on conveyor

Primer: Midsole (Adding 1-2% black tone if M/S and O/S is black color)

Attaching and Pressing by hand tool

Inprection and close the carpentry date stamp reduces main line operations, making the main line run smoother and faster Assembling the base outside the main assembly line allows for easy detection of quality checks and other complex issues that would not be possible on the main line

Step Detail Temperate Press Time

2 Toe pre-molding process 65 ~ 75°C 2kg/𝑐𝑚 ! 20 sec

8 Flatting strobel by press machine 30 ~ 40 kg/𝑐𝑚 !

9 Go thourgh heating box 60 ~ 65°C 2 ~ 3 min

10 Gauge marking for attaching sole 2kg/𝑐𝑚 !

( Add 1~ 2% black toner if upper has black color )

Once the upper details are complete, the upper is ready to be bonded to the outsole Before the outsole can be affixed, the upper must be fixed to the form First, the upper will be shaped into the tip and heel form by a special machine Next, workers will sew the strobel into the upper and are set to go to the stage of installing the sole Upper will be fixed form by the last inserted in the upper Inserting last causes the upper to stretch to its correct shape, producing the desired shoe shape To ensure that no metal shards or needles are lost during sewing, the shoe body is passed through a metal detector Here, the parts of the shoe that do not satisfy the standards will be removed immediately Then, the upper will be taken to the step of drawin gauge marking for attaching sole, with a temporary marking pen, whose writing can be wiped off swiftly by water easily

Figure 1.6 Picture of gauge making for attaching sole

With the upper in position, will continue to move on the pass, to the next stage The base has been prepared from the previous stage, and the upper will be attached on the line In this procedure, parts of the shoe move inside a heat tunnel to dry the glue before the final bonding stage In order for the upper and the sole to satisfy the adhesive standards, the temperature before attaching should not be lower than 48 degrees Celsius Finally, the shoes will be reinforced with a press, to make sure that the upper and the sole is firmly bonded In the end this process, the shoe travels inside a cool tunnel to dry the glue before the packing process The final stages are QC and packing

The finishing department is the last stage in the entire production chain While the departments involved in the previous phases were attempting to develop a shoe with optimal comfort, the packaging department was mainly concerned with completing the appearance Once the shoe has chilled to the requested temperature, it proceeds through the packaging process The socks liner will be inserted, and the laces will also be threaded to the standard

In order to keep the shoes in the finest condition, each shoe will be kept folded with paper At this stage, an end-of-process quality control personnel will be arranged to thoroughly inspect the product before canning So every pair of shoes that depart the factory, will always be in the finest standard condition

Provide readers with a comprehensive overview of Chang Shin Vietnam This chapter details the history and development of Chang Shin Vietnam, and outlines the company’s area of expertise in shoe manufacturing for its exclusive partner Nike In addition, viewers also get an overview of the company’s production process.

LITERATURE REVIEW

Athletic Footwear Industry

According to Merk (2008) only a limited number of brands dominate the athletic shoe market Nike alone accounts for 35% and the 20 largest companies account for more than 92% of global wholesale sales In the summer of 2005, Reebok was taken over by Adidas As a result, the sector will be even more concentrated, with only two companies (Nike and Adidas) controlling more than 50% of the market The industry is also geographically volatile For example, in 1989, Nike (the brand with the largest market share in the United States) had about 2% of their shoes manufactured by subcontracts based in China: in 1993, almost a part Four of their shoes will come from Chinese factories Although countries of origin continue to change, the majority of athletic footwear production continues to take place in Southeast Asia Three U.S companies that account for more than 60% of sales in the United States have manufacturing facilities there (Barff & Austen, 1993)

Since sneakers are designed for a wide variety of sports, it is necessary to take into account the different respective requirements Thus, each sport can be thought of as an individual genre, resulting in a large number of genres Integrated approaches identify sports and disciplines that share similar mobility and movement characteristics, resulting in shared overlapping needs These sports are then grouped into broader and comprehensive categories (Sterzing et al., 2012) Besides issues of comfort, performance and injury prevention, aspects of durability need to be taken into account, which refers to the expected and, targeted life span of the shoe (Wang et al., 2010) The demand for athletic footwear product is increasing significantly owing to their usage in various conditions Various types of athletic footwear available in the market are prepare from high-quality raw types, such as leather, foam, and plastic, which involve the use of complex chemical additives

With a strong growth of fitness trends and increasing awareness of people’s health Besides, people also recognize the importance of selecting the right shoes for various sports activities to avoid injuries such as muscles, legs, knees, etc So that, production quality should be paid more attention.

Quality Management

Quality management (QM) has become a management philosophy that has a comprehensive pervasive power and is applied to most countries and business sectors Led mostly by practitioners, QM adopted a strong normative stance during the early stages of indoctrination (primarily the 1980s and early 1990s) with practices that were commonly advocate is universally applicable to organizations In addition, the emergence of awards such as the Malcolm Baldrige National Quality Award and the European Quality Award reinforced the popular profile of QM practice at this time (Sousa, 2003)

The application of multi-criteria decision making methods in selecting the most effective option has been widely applied in the quality management system of many industries For the food industry, Radaev & Bochkov, (2009) applied the AHP method to formulate and analyze the problem and define the goal of improving the quality of food products and increasing the efficiency of the company’s management Nguyen (2021) determined the quality of hotel service by using Fuzzy Hierarchical Analysis Process (FAHP) and SERVQUAL method In the petroleum industry, Yazdani et al., (2013) have found the factors affecting the success in implementing Total Quality Management for Pars Oil and Gas Company by using AHP method by Expert choice software In the heathycare industry, to rank the hospital with the best service in the Indian state of Punjab, Singh & Prasher, (2019) integrated Fuzzy AHP and SERVQUAL method to measure the service quality of four hospitals In addition, using a combined multiple criteria decision making (MCDM) methodology containing fuzzy analytic hierarchy process (AHP) and fuzzy technique for order performance by similarity to ideal solution (TOPSIS), to analyze electronic service quality in healthcare industry (Bỹyỹkửzkan & ầifỗi, 2012) Besides, the AHP method is also applied to select and evaluate quality in many other industries such as e-service quality and in-flight service quality in airline industry (Bakır

& Atalık, 2021; W Li et al., 2017), quality of processes and products in bakery (Serpa et al.,

2023), port service quality (T Q Nguyen et al., 2022), etc There is many research about evaluating in factor effects to quality management in many industry, however, there is not research to perform product quality assessment in the athletic industry footwear.

Ishikawa Diagram

The Ishikawa diagram was popularized in the 1960s by Kaoru Ishikawa, who pioneered quality management processes at the Kawasaki shipyard, and in the process became one of the founders modern management methods The Ishikawa chart, also known as a fishbone diagram or cause and effect diagram, is a traditional quality management tool because it permits visualization (Lira et al., 2017) The Ishikawa chart is a simple graphical tool for understanding the causes of quality defects and is used to analyze the relationship between a problem and all possible causes Ishikawa diagrams have been applied to analyze problems and identify potential causes contributing to their occurrence.

However, the mathematical way to assess the validity of the relationship between potential causes has not been analyzed, and such an approach may better indicate which cause is the true root cause of the problem subject Furthermore, the subjectivity of those who were establishing potential causes of the problem during the brainstorming session was not taken into account A large number of factors affected by subjectivism can be analyzed by applying fuzzy multi-criteria hierarchical analysis to decision problems (Fuzzy Analytic Hierarchy

Se con da ry ca us e

Process) (Pacana & Siwiec, 2020) In a case study conducted in a soap production line, specifically the Tage Company, it was identified that increased waste in the production process was a major issue By using a fishbone (or cause and effect) diagram, the causal relationship between the phenomena of the problem becomes clear Finally, by using process analysis hierarchical analysis and prioritizing possible solutions, an effective decision will be made and implemented (A.-A Yazdani & Tavakkoli-Moghaddam, 2012) Therefore, it is reasonable to assume that the integration of the Ishikawa method and the FAHP method allows to accurately identify the main causes of the problem numerically and to consider the subjectivity of the decision maker.

Fuzzy Set Theory

Human assumptions are often biased and difficult to represent using numbers, which makes it difficult to estimate or compare the value of existing assumptions Traditional AHP uses explicit numbers (1, 3, 5, 7 and 9) to distinguish between two elements However, it is difficult to express the ambiguity to account for the difference between the two factors To surmount this uncertainty, Zadeh, (1965) proposed fuzzy set theory A fuzzy set is the designed to represent the uncertain and imprecise character of human thought in mathematical form Therefore, fuzzy sets are extensively applied in relation to management decisions regarding ambiguous or imprecise information (Ordoobadi, 2009)

A fuzzy set is a collection of elements with fluid boundaries, in which transmission from membership to non-membership is gradual rather than abrupt According to Wibowo et al.,

(2018), Fuzzy Set enable membership functions to have values in the range [0,1] Zero (0) indicates that the element is out of scope ( no members), while One (1) indicates that the element has full membership levels in the range If the value is between 0 and 1, it signifies the constituent has a certain membership level in the range

Fuzzy set theory is an element that can be part of a fuzzy set Let X represent the set of

𝑥 items The membership function 𝜇 𝒜($) coupled with a real integer in the interval [0; 1] for each element 𝑥 in X, to indicate the “membership” of 𝑥 in 𝒜, characterizes the fuzzy set 𝒜 of the discourse set U Triangular membership functions are frequently utilized to improve computing efficiency and data collecting A triangular fuzzy number C determined by the membership function shown below (Wu et al., 2004)

(1) which can be represent as triplet (𝒶, 𝒷, 𝒸), with 𝒶 ≤ 𝒷 ≤ 𝒸

Parameters a and c represent the lower and upper boundaries of the evaluation data availability region, respectively, while 𝒷 represents the “average” of the fuzzy number C corresponding to the top of its membership function (ie 𝜇 𝒜($) = 1) As a result, the triangular fuzzy number C (𝒶, 𝒷, 𝒸) can be read as an “approximately 𝒷” fuzzy quantity whose value cannot be less than 𝒶 or greater than 𝒸

Figure 2.2 A triangular membership function of the fuzzy number

There are many evaluation studies on quality management using different variations of fuzzy sets in the literature In education, Lin (2010) developed an evolutionary model that integrates triangular fuzzy numbers and AHP to develop a fuzzy evaluation model This reseach reviewed the course website quality literature to come up with 16 sub-criteria along with 4 criteria used to measure course website quality Combines the use of the Matlab (Matrix Laboratory) program system with its toolboxes Simulink and Fuzzy Logic to evaluate the

1 lower point upper point mean point commerce, a system model based on TRIZ method is proposed to generate innovative solution to improve service quality, combined with Fuzzy Quality Function Deployment ( QFD) to indentify the key determinants related to customer satisfaction by Su & Lin, (2008) In a case study of airline industry, Nejati et al., (2009) introduced a fuzzy TOPSIS approach along with a survey questionnaire from SERVQUAL model to rank the service quality aspects of the aviation industry according to customer needs, in order to entice customer trust Besides, in this study of Mohammad Kazem Ghorbani et al (2021), a WLA optimization model using the constraints of wastewater treatment costs along with the objective function of the mean NSFWQI and the fuzzy method was proposed From there, water resources planning and management can be done using a more integrated and complete approach

However, there are many studies in the performance of quality management assessment in many industries, but no research has used the fuzzy analytic hierarchy process (FAHP) method to perform product quality assessment in the athletic industry footwear.

The Analytic Hierarchy Process (AHP)

AHP is one of the multi-objective decision making methods proposed in 1980 by Thomas L Saaty – an Iraqi mathematician It is widely used in various disciplines, including operational research, management, engineering and social sciences, to solve complex problems and make an informed choice between different alternatives AHP is a quantitative method, used to arrange decision alternatives and select an alternative that satisfies the provided criteria On the basis of pairwise comparison, AHP can be described with 3 main principles: analysis, evaluation and synthesis AHP answers questions like “Which option should we choose?” or “Which option is best?” by selecting the best alternative that satisfies the decision maker's criteria on the basis of comparing pairs of alternatives and a specific calculation mechanism

The main advantage of the AHP is its inherent ability to handle intangibles, which are present in any decision-making process Also, the AHP less cumbersome mathematical calculations and it is more easily comprehended in comparison with other methods

Triantaphyllou & Lin, (1996) and Durán & Aguilo, (2008) summarized the following advantages for AHP:

1) It is the only known multicriteria decision making model that can measure the consistency in the decision maker’s judgments

2) The AHP can also help decision makers to organize the critical aspects of a problem in a hierarchical structure, making the decision process easy to handle

3) Pairwise comparisons in the AHP are often preferred by the decision makers, allowing them to derive weights of criteria and scores of alternatives from comparison matrices rather than quantify weights/scores directly

4) AHP can be combined with well-known operation research techniques to handle more difficult problems

5) AHP is easier to understand and can effectively handle both qualitative and quantitative data

In the early 1980s, American mathematician Thomas L Saaty invented a multi-criteria decision support method called AHP Its goal is to quantify the priority relationships of a given set of alternatives on a scale based on opinions and to emphasize the importance of the decision maker’s intuitive judgments and consistency in comparing alternatives through a pairwise comparison process In addition, AHP also combines both sides of human thinking, both qualitative and quantitative The qualitative is expressed through a hierarchical arrangement, while the quantitative is expressed through the description of evaluations, preferences through numbers that can be used to describe people’s judgments on all tangible physical and intangible issues, describe emotions, and intuitive judgments of people

The Analytical Hierarchy Process (AHP) is performed according to the following steps:

Step 1 : Define the issue and determine what knowledge is needed to resolve it

Step 2 : Building an AHP model based on evaluation criteria collected from experts’ opinions A hierarchical structure diagram begins with the goal, which is analyzed through major criteria and component criteria, the final level often includes possible alternatives

Figure 2.3 The structure diagram of AHP

Step 3 : Evaluate the priority of each decision criterion by using Saaty’s pairwise comparison scale

Table 2.1 Saaty’s pairwise comparison scale

2, 4, 6, 8 Intermediate values between the two adjacent judgments

Source: Saaty (1980) Step 4 : After setting up the evaluation matrix, will proceed to calculate the weights for the criteria by summing the values of the matrix by column, then taking each value of the matrix divided by the sum of the corresponding column

The weighted statistics shown here shouldn’t be regarded as the last word; instead, it's crucial to confirm that the experts’ assessments are consistent

Step 5 : Measure inconsistency To check the consistency of the expert's assessment, ensure the science of the assessment The consistency ratio (CR) is determined as follows:

• RI is Random Consistency Index

Equation to calculate consistency index CI :

In there, 𝜆 &'$ is the highest eigen value of matrix, and n is the number of elements that are compared in pairs in a single computation is the size of the calculated matrix

Table 2.2 The random index corresponding to the number of selection criteria considered ( Saaty, 1980 ) n 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Saaty (2008) indicates that a consistency ratio (CR) less than or equal to 10% is acceptable In other words, there is a 10% possibility that the experts answer the queries completely at random If the CR is greater than 10% it indicates an inconsistency in the assessment and needs to be re-evaluated and recalculated

Figure 2.4 An 8-step of fuzzy AHP flowchart

Summary of related work

The athletic footwear industry is a dynamic sector characterized by evolving consumer preferences and intense competition Within this context, ensuring high-quality products is paramount to maintaining market share and customer loyalty The application of the AHP model will increase the ability to elucidate the complex relationships between the determinants, providing a comprehensive understanding of their relative meanings By integrating the Fuzzy AHP method, this study seeks to elucidate the factors that shape quality management in the athletic footwear industry, contributing to a practical understanding for industry practitioners

Step 1: Formulate the hierarchic tree

Step 2: Create fuzzy pairwise comparison matrix (𝐽#)

Step 3: Check for consistency rate (CR)

Step 4: Calculate the fuzzy weight

Step 8: Rank and desicion making

Table 2.3 Summary of related work in quality management

Radaev & Bochkov (2009) AHP Food Industry

Hung Nguyen (2020) Fuzzy AHP and

Yazdani et al (2013) AHP Petroleum Industry

Singh & Prasher (2019) Fuzzy AHP and

Healthcare Service Industry Kurilovas &Vinogradova (2016) Fuzzy AHP Education

Ordoobadi (2009) Fuzzy AHP Supply Chain

Hsieh et al (2004) Fuzzy MCDM or

Serpa et al (2023) Fuzzy AHP and

Bakır & Atalık (2021) Fuzzy AHP and

Fuzzy MARCOS Airline Industry Nguyen et al (2022) Fuzzy AHP and IPA Port Service

Li et al (2017) Fuzzy AHP and 2- tuple fuzzy linguistic Airline Industry

Bỹyỹkửzkan & ầifỗi (2012) Fuzzy AHP and

Mardani et al (2016) Fuzzy Hybrid MCDM Hotel

Stella et al (2012) Fuzzy Logic and

Su et al (2008) Fuzzy QFD and TRIZ E-commerce

Nejati et al (2009) Fuzzy TOPSIS and

SERVQUAL Airline Industry Mohammad Kazem Ghorbani et al

Fuzzy Logic, WLA and NSFWQI Water Resources

In the context of the changing business environment, people increasingly appreciate product quality To my knowledge, there is a lack of research to evaluate the root cause of manufacturing defects in the athletic footwear industry using Fuzzy AHP model, the author develops a decision-making model with fuzzy number to solve the problem of evaluating factors affecting quality

This section aims to present a preliminary background on theory, applied models and previous research papers on the assessment of factors affecting the quality and application of research in various industries Understanding the necessity and practice of researching the factors influencing the quality as well as having few research on the athletic footwear industry, the author has implemented this topic.

METHODOLOGY

Research Framework

The proposed method

Figure 3.2 Flowchart for interview with experts

The author interviewed experts in the field to collect the necessary information, to select sub-criteria based on the experts’ evaluation criteria, through searching from articles and actuality from the company From there, the author identifies the two most typical defects in products It’s a matter of the quality of the sewing on the upper and the quality of the bonding And synthesize all potential causes through the use of Ishikawa (Cause and Effect) diagram The problem is shown on the main bone and the cause of the problem is shown on its five primary branches, respectively And the results are shown figures in Figure 3.3 and Figure 3.4

Figure 3.3 Sewing Line Quality Failure

Smoothness of material Sewing thread dynamics

Sewing details wrong operation Poor monitoring

Figure 3.4 Shoe Bonding Quality Failure

Process quality management is an essential aspect to ensure product excellence and customer satisfaction in various industries In this discipline, the use of effective tools and methods is essential to accurately identify the key factors affecting quality results Therefore, the author applies the Ishikawa chart method (Cause and Effect), to construct criteria and sub- criteria for the AHP model

Material factor (A1, C1): One of the first factors considered when evaluating the quality of a product is the raw materials to make that product Involves the materials, components and inputs used in the production process

Machine factor (A2, C2): In order to produce quality products, the important factor is the machine This can include problems related to equipment breakdown, machine performance and quality during production

Elasticity of sole is not properly meet standard Quality of glue

Heating box temperature is unstable Temp and joule UV machine are unstable

Inspection of worker in each step Poor monitoring

Not following the standard 10mm bonding margin

Man factor (A3, C3): Human resources involved in the production process include workers, operators, managers and managers The impact of the human factor on production can be significant and play an important role in determining the performance and quality of a product

Method (A4, C4): The manufacturing methods and processes used in the manufacturing process will affect the overall quality of the final product

Environment (A5, C5): Referring to the work environment where production takes place, factors such as temperature, lighting, and overall workplace conditions have an impact on production performance and employee efficiency

3.2.2.1 Criteria for Sewing Line Quality failure

Table 3.1 Criteria for evaluating Sewing Line Quality failure

Material such as leather, imitation leather or knit fabric, etc will significantly affect the sewing process

Smoother material produce better stitching quality, more evenly spaced and less wrinkled

Thread’s elasticity, tensile strenghth, and friction coefficient all affect how it behaves during sewing

More difficult to control component, which can lead to mistakes

A sewing machine that is not properly maintained can produce poor stitching quality

Can lead to injuries to worker when perform the sewing operation, as well as need to replace the needle and re-stitch the component

Not follow the correct processes, they are less likely to be productive

Negligence of management’s supervision in the sewing process

Poor stitching manipulate leads to many mistakes

Inconsistent control settings can lead to variations in seam allowances and seam placements

Setting the target too high will put pressure on workers, sewing operations will be affected

Using the wrong needle for the material can result in missed stitches, uneven or wrinkled stitches, affecting the overall appearance and strength of the seam

Workers are not able to see clearly, they are less likely to be productive

High temperatures can cause heat stress for workers Heat stress can impair concentration of worker

Increase ability to make mistakes, affect labor productivity

3.2.2.2 Criteria for Shoe Bonding Quality failure

Table 3.2 Criteria for Shoe Bonding Quality failure

Elasticity of sole is not properly meet standard

The sole is not elastic enough, which can cause the sole to crack and split when workers make adjustments when attach upper to sole

Quality glue is more resistant to degradation from factors such as, temperature changes, moisture, etc

Beatrix & Triana (2019) Sreenivasulu Reddy A et al

Any impurities on the surface can act as a barrier, reduces the bonding of glue

Unstable presses can lead to uneven pressure distribution during pressure process

Beatrix & Triana (2019) Sreenivasulu Reddy A et al

Heating box temperature is unstable

In shoe manufacturing typically require a specific temperature range to keep the glue in the best adhesive state If the heating box temperature is not maintained within the recommended range, the adhesive may not fully activate

UV light is used to induce a photochemical reaction that promotes adhesion of the glue When the UV machine doesn’t work stably, the bonding will be weakened

Worker applies thin or uneven glue, the bond between upper and sole may be weaker

Beatrix & Triana, (2019) Jor et al.,

Inspection of worker in each step

Step by step inspection allows early detection of any error or error made by workers during the assembly process

Negligence of management’s supervision in the assembly process

If the drying time is too short, the adhesive not have enough time to fully dry and achieve optimal bond strenghth

Not following the standard 10mm bonding margin

Insufficient bonding margin can result in the adhesive not have enough surface area to create a strong bond

The upper material should have a surface that is compatible with the adhesive used for bonding

In some case, giving a slightly roughened surface to upper can improve the adhesion of glue ( such as leather and imitation leather)

The workspace is not clean, leading to dust and debris from the surrounding environment falling into the glue

Affects the temperature in the heating box, leading to the possibility of inconsistencies in the bonding

Reducing focus and attention to detail, leading to increase ability to make mistakes

With the theoretical basis, refer to the research experience of experts in the company related to quality management for the production line Combined with the application of the Ishikawa diagram (Cause and Effect) is the basis for the author to apply to his research model The author proposes two hierarchical models for evaluating sewing line and bonding quality failure, with evaluation objectives with 5 criteria and 15 sub-criteria for each

3.2.3.1 Hierarchy structure for Sewing Line quality failure

• Material (A1) : Consists of 3 sub-criteria are thickness of material (A11), smoothness of material (A12) and sewing thread dynamics (A13)

• Machine (A2) : Consists of 3 sub-criteria are setting of speed (A21), poor condition

• Man (A3) : Consists of 3 sub-criteria are sewing details wrong operation (A31), poor monitoring (A32) and unskilled worker (A33)

• Method (A4) : Consists of 3 sub-criteria are improper control setting (A41), work target

(A42) and improper selection of needle (A43)

• Environment (A5) : Consists of 3 sub-criteria are insufficient light intensity (A51), high- temperature room (A52), and uncomfortable working condition (A53)

Figure 3.5 The hierarchy structure of Sewing Line quality failure

(A12) Smoothness of material (A13) Sewing thread dynamics

(A51) Insufficient light intensity (A52) High-temperature room

3.2.3.2 Hierarchy structure for Bonding shoes quality failure

• Material (C1) : Consists of three sub-criteria are elasticity of sole is not properly meet standard (C11), quality of glue (C12) and upper material quality (C13)

• Machine (C2) : Consists of three sub-criteria are pressure machine is unstable (C21), heating box temperature is unstable (C22) and temp and joule UV machine are unstable

• Man (C3) : Consists of three sub-criteria are unskilled worker (C31), inspection of worker in each step (C32) and poor monitoring (C33)

• Method (C4) : Consists of three sub-criteria are drying time (C41), not following the standard 10 mm bonding margin (C42) and upper preparation (C43)

• Environment (C5) : Consists of three sub-criteria are high-temperature room (C51), improper cleaning(C52), and uncomfortable working condition (C53)

Figure 3.6 The hierarchy structure of Shoes Bonding quality failure

(C22) Heating box temperature is unstable

(C23) Temp and joule UV machine are unstable

(C32) Inspection of worker in each step

(C42) Not following the standard 10mm bonding margin

(C11) Elasticity of sole is not properly meet standard

Definition 1: According to Lehmann et al., (1992), if the set X is a set of members shared by x, then a fuzzy set 𝒜 in X is a set of pairs of numbers denoted as follows:

In there, à 𝒜( (𝓍) is a membership function that maps X into the space of M With sup à 𝒜( (𝓍) = 1: normalized fuzzy set

Definition 2: According to Socorro Garcia & Teresa Lamata (2007), a real fuzzy number, denoted as 𝒜, is characterized as any fuzzy subset of the real line ℛ with a membership function 𝔣 𝒜 that exhibits the following characteristics :

1) 𝔣 𝒜 (𝓍) is is a continuous mapping from ℛ to the closed interval [0, 𝓌], where

2) 𝔣 𝒜 (𝓍) = 0 for all x in the range (-∞, 𝒶]

3) 𝔣 𝒜 (𝓍) is strictly increasing over the interval [𝒶,𝒷]

4) 𝔣 𝒜 (𝓍) = 1 for all 𝓍 in the range [𝒷, 𝒸]

5) 𝔣 𝒜 (𝓍) is strictly decreasing over the interval [𝒸, 𝒹]

6) 𝔣 𝒜 (𝓍) = 0, for all x in the range (𝒹, ∞], where 𝒶, 𝒷, 𝒸, 𝒹 represent real numbers For the purposes of this context, unless otherwise stated, 𝒜 is assumed to be both convex and bounded, expressed by the constraints −∞ < 𝒶, 𝒹 < ∞ fuzzy numbers [𝒶, 𝒷, 𝒸, 𝒹; 1] will be represented by the four previously defined values, while [𝒶, 𝒷, 𝒸, 𝒹; 𝓌] will be used for numbers unusual fuzzy [𝒶, 𝒷, 𝒸, 𝒹; 𝓌] can be expressed as −𝒜 = [−𝒹, −𝒸, −𝒷, −𝒶; 𝓌]

Definition 3: Boral et al., (2020) let 𝒜= = [ 𝒶 ℓ , 𝒶 𝓂 , 𝒶 𝓊 ] and ℬA = [ 𝒷 ℓ , 𝒷 𝓂 , 𝒷 𝓊 ] be two fuzzy numbers, where 𝒶 ℓ ≤ 𝒶 𝓂 ≤ 𝒶 𝓊 and 𝒷 ℓ ≤ 𝒷 𝓂 ≤ 𝒷 𝓊 Their operations are provided as Equations (2) to (6)

3.2.4.2 Step in Fuzzy Analytic Hierarchy Process

The hierarchy is divided into two level The upper level of the structure that describes in detail the heat of the problem is called the dimension while the second level of the hierarchy explain the properties or criteria of the dimension

Step 2: Constructing a pairwise comparison matrix Fuzzy

The metamorphosis scale is applied to convert the language variable into a Fuzzy number This study used a scale from 1 to 9 (H X Li et al., 2013) shown in Table 3.3

Table 3.3 Fuzzy AHP ranking scale

Linguistic variable Fuzzy number Fuzzy number scale

From there, the Fuzzy pairwise comparison matrix is built as follows: Α = #

Step 3: Check the consistency rate of fuzzy matrices A

According to Han, W J., & Tsay, (1998) explain that the value of 𝜆 &'$ is necessary to calculate the consistency ratio The 𝜆 &'$ obtained by calculating the matrix product of the pairwise comparison matrix and the weight vectors and then adding all the elements of the resulting vector Formula to calculate consistency index (CI):

The final consistency ratio has been determined by division of the Consistency Index (CI) with the Random Index (RI)

Step 4: The following equation illustrates how multiple decision makers priority is aggregate out by (Chou et al., 2019)

Step 5: Use the geometric mean method to synthetic jugdments of aspects by Davies (1994)

In there: ∁Z 01 is be the aggregated relative importance of ∁ 0 over ∁ 1 judged by experts

Step 6: Calculate Fuzzy weights for each criterion Apply fuzzy weight method by (Chou et al., 2019)

In there:𝔴f 1 is fuzzy weights of the jth criteria

With 𝔴f 1 = ( ℒ 𝔴 & , 𝑀 𝔴 & , 𝑈 𝔴 & ), ℒ 𝔴 & , 𝛭 𝔴 & and 𝑈 𝔴 & represent the lowest, average and highest values of the Fuzzy weights of the jth criterion

Step 7: Calculate the normalized weight criteria

Because 𝔴f 1 is still a fuzzy number, we proceed to normalized by the average method according to the following formula by (Chou et al., 2019)

In there: 𝑁 1 is normalized weight of the jth criteria

Step 8: Calculate the defuzzified weight criteria by Thắm et al., (2020)

Step 9: Calculate the global weight of sub-criterion

The priority of each criterion contributes to the priority of the goal, and the priority of each sub-criteria contributes to the priority of its parent The global weight of each sub-criteria is calculated by multiplying the weight of the criterion with weight of each sub-criteria by U- Dominic et al., (2021)

In there: 𝒮 :; is sub-criteria priority

Step 9: Ranking of the sub-criteria based on data has been calculated on

Combining from the implementation of the Ishikawa model combined with the theoretical background and previous studies, the author provides two hierarchical model that includes 5 main criteria with 15 sub-criteria to evaluate and rank the most affecting element, has been consulted by experts In addition, this chapter offers the preliminary formulas and steps of the fuzzy AHP approach.

RESULT

Data description

Based on the flowchart above Figure 3.2, carry out the process of interviewing experts to collect data Collecting data from experts is limited due to time constraints for doing research, as well as the nature of the job and experience of the experts Only seven experts with in-depth knowlegde of quality management and knowledge of the athletic footwear industry provided input to the author Using prepared questionnaires and employing direct interview method to collect data The responses were used as data for research paper The application of the direct interview method can guide and answer questions to limit blunders in the interview process Post-interview data will be analyzed be applying the Fuzzy AHP method

Table 4.1 Group of experts participating in interview

Expert Gender Work experience Job position

1 Female More than 3 years of experience in tracking processes to ensure compliance with Nike’s regulatory and quality requirements

Categories Quality Management in Chang Shin Vietnam

2 Female More than 6 years of experience in final product quality assessment

Quality Assurance in Chang Shin Vietnam

3 Male More than 6 years of experience in testing and evaluating the quality of input materials and finished shoes

LAB Department in Chang Shin Vietnam

4 Female 5 years of experience in support tracking and quality assurance for the production line of new codes

5 Female 3 years of experience in developing and testing production processes for new codes

Development in Chang Shin Vietnam

6 Male 6 years of experience in monitor and control shoes bonding issues

Chemical Engineer in Chang Shin Vietnam

7 Female More than 4 years of experience in support tracking and quality assurance for the production line of new codes

Data analytic result

4.2.1 Data analytic result of Sewing line quality failure

Step 1: Construct a hierarchical framework of criteria and sub-criteria designed from the mentioned issues as shown in Figure 3.5

Step 2: Using expert judgments combined with a language-to-numeric conversion (Table 3.3), pairwise comparison matrices are generated Equation (7) is used to determine the symmetric equivalences of language evaluations in a pairwise comparison matrix

Step 3: Use the consistency rate formula (9) to check the validity of expert judgments This value is below the 10% threshold and therefore the judgment matrix is accepted

Table 4.2 Consistency rate of 6 experts in main criteria (A1-A5)

Step 4: Using the fomula (10) to aggregate multiple decision makers priority The results of the table compiling the opinions of the experts are displayed below

Table 4.3 Aggregate pairwise comparison matrix of main criteria (A1-A5)

Step 5: Use the geometric mean method to define the fuzzy geometrical geomean for main criteria by fomula (11)

Table 4.4 Fuzzy geometrical geomean for main criteria (A1-A5)

Step 6: To calculate the fuzzy weights, normalization, and the weighted defuzzification by equation (12), (13) and (14) The result is given below

Table 4.5 The fuzzy weights of main criteria (A1-A5)

Step 7: Repeat steps 4 to 6 above for the sub-criteria Pairwise comparison matrices, normalized weights, and important weight of sub-criteria are presented in the tables

Table 4.6 Aggregate pairwise comparison matrix of sub-criteria ( A11-A13 )

Table 4.7 Fuzzy geometrical geomean of sub-criteria ( A11-A13 )

Source: Author Table 4.9 Fuzzy geometrical geomean of sub-criteria ( A21-A23 )

Source: Author Table 4.10 Aggregate pairwise comparison matrix of sub-criteria ( A31-A33 )

Source: Author Table 4.14 Aggregate pairwise comparison matrix of sub-criteria ( A51-A53 )

Table 4.16 The fuzzy weights of sub-criteria (A11-A53)

Step 8: Calculate the global weight of each sub-criteria

The priority of each criterion contributes to the priority of the goal, and the priority of each sub-criteria contributes to the priority of its parent Using equation (15), the global priority of each sub-criteria is calculated as follows:

Table 4.17 The global weight of each sub-criteria (A1-A5)

Criteria Sub – criteria Global weight

Step 9: Ranking the global weight of sub-criteria

Table 4.18 Derived factor priorities for the sewing line quality failure

Factors Global weight Rank Factors Global weight Rank

Poor condition 0,1625 2 Uncomfortable working condition

Broken sewing needle 0,1207 3 Sewing thread dynamics 0,0236 11

Poor monitoring 0,1138 4 Thickness of material 0,0232 12

Improper selection of needles 0,0688 5 High-temperature room 0,0206 13

Setting of speed 0,0653 6 Insufficient light intensity 0,0117 14

Improper control setting 0,0628 7 Smoothness of material 0,0061 15

Based on Table 4.18, it can be see that unskilled worker (A33) is the highest sub-criteria with 19,12%, followed by poor condition (A22) and broken sewing needle (A23) with 16,25% and 12,07%, respectively Additionally, there are low-weight sub-criteria including insufficient light intensity (A51), 1,17%, and smoothness of material (A12), 0,61% The criteria with the biggest volume shown that regarded to have a highest relevance

4.2.2 Data analytic result of Shoes bonding quality failure

Step 1: Construct a hierarchical framework of criteria and sub-criteria designed from the mentioned issues as shown in Figure 3.6

Step 2: Applying the same method as the first model, pairwise comparison matrices are generated Equation (7) is used to determine the symmetric equivalences of language evaluations in a pairwise comparison matrix

Step 3: Use the same formula to calculate consistency rate (9) to check the validity of expert judgments This value is below the 10% threshold and therefore the judgment matrix is accepted

Table 4.19 Consistency rate of 6 experts in main criteria (C1-C5)

Step 4: Using the same method as the first model to calculate the aggregate pairwise comparison matrix for main criteria

Table 4.20 Aggregate pairwise comparison matrix of main criteria (C1-C5)

Step 5: Define the fuzzy geometrical geomean for main criteria by fomula (11)

Table 4.21 Fuzzy geometrical geomean for main criteria (C1-C5)

Step 6: Using the same equation as first model to calculate the fuzzy weights of main criteria, normalization, and the weighted defuzzification The result is given in

Table 4.22 The fuzzy weights of main criteria (C1-C5)

Step 7: Repeat steps 4 to 6 above for the sub-criteria Pairwise comparison matrices, normalized weights, and important weight of sub-criteria are presented below

Table 4.23 Aggregate pairwise comparison matrix of sub-criteria ( C11-C13 )

Table 4.24 Fuzzy geometrical geomean of sub-criteria ( C11-C13 )

Source: Author Table 4.26 Fuzzy geometrical geomean of sub-criteria ( C21-C23 )

Source: Author Table 4.27 Aggregate pairwise comparison matrix of sub-criteria ( C31-C33 )

Source: Author Table 4.31 Aggregate pairwise comparison matrix of sub-criteria ( C51-C53 )

Table 4.33 The fuzzy weight of sub-criteria (C11-C53)

Step 8: Use equation (15), to calculate the global priority of each calculated sub-criteria shown below

Table 4.34 The global weight of each sub-criteria (C1-C5)

Criteria Sub – criteria Global weight

Step 9: Ranking the global weight of each sub-criteria is presented below

Table 4.35 Derived factor priorities for the bonding shoes quality failure

Factors Global weight Rank Factors Global weight Rank

Upper preparation 0,1478 1 Inspection of worker in each step

Pressure machine is unstable 0,1337 2 Elasticity of sole is not properly meet standard

Heating box temperature not stable

Temp and joule UV machine are unstable

Drying time 0,1103 6 Upper material quality 0,0110 14

Unskilled worker 0,0558 7 High-temperature room 0,0057 15

Based on Table 4.35, it can be see that upper preparation (C43) is the highest sub-criteria with 14,78%, followed by pressure machine is unstable (C21) and heating box temperature is unstable (C22) with 13,37 % and 13,31%, respectively Additionally, there are low-weight sub-criteria including upper material quality (C13), 1,10%, and high-temperature room

(A52), 0,57% The criteria with the biggest volume shown that regarded to have a highest relevance

Priority factors were identified, such as unskilled worker (A33) at 19,12% highlighting the urgent importance of investing in employee training Similarly, in the context of bonding shoes quality failures, the most important sub-criteria of upper preparation (C43) with a rate of 14,78% signals the important role of this stage By addressing these root causes, the company can significantly reduce errors and improve overall product quality

This chapter gives us the results of the evaluation of the factors affecting the causes of quality defects The results show that the factors of unskilled worker (A33) and upper preparation (C43) are the priority factors identified for sewing line and bonding shoe quality failure.

RECOMMENDATION

Improve skilled for worker

Numberous surveys have consistently demonstrated that placing the right individuals in suitable roles not only enhances overall workforce efficiency but also enables employees to effectively exhibit their competencies and fulfill their job responsibilities This complementary relationship between job suitability and employee performance significantly contributes to enhancing product output Allocating resources based on appropriate qualifications and skills to guarantee that workers’ resources are employed effectively to meet the company’s production goals for each product code The first step is to determine the product code’s requirements in terms of worker qualifications and competencies This is accomplished by examining the job requirements of each task in the code The knowledge, abilities, experience, and other attributes required to execute the task are included in the job criteria The next stage is to examine employee competency profiles in order to find individuals who possess the experiences and skills required by the product code The employee’s job experience and operational skills are included in the competency profile Finally, after identifying the product code's demands and studying the worker's competency profile, create a resource allocation plan (list of activities to be performed, qualifications and skills required to complete each activity, and a list of personnel assigned to each task) To guarantee that the resource allocation plan is consistent with the real situation of the production line, it must be monitored and updated on a regular basis

Furthermore, the implementation of comprehensive human resource training programs offers diverse benefits in the manufacturing process The implementation of skill development training initiatives creates a greater understanding of the complexities skill in manufacturing methods, hence reducing the frequency of errors These training programs also act as a catalyst for the growth of the company’s human resources, aiding in the discovery and nurturing of high-potential talents through participation in such programs’ healthy competitive atmosphere Acquiring new abilities through training fosters strategic thinking, encourages creativity in making timely decisions, and increases the possibility for return on investment

And the expansion of diverse training programs is needed in multinational companies According to Ali Asghar & Mohtsham Saeed, (2012), diversity training is all about focuses on understanding difference on the various backgrounds of employees, like their ages, races, ethnicities, genders, and how much they earn This type of training affects employee performance, significantly impacting the overall effectiveness of the organization When organizations are lack of diversity training programs, they are essentially leaving their employees vulnerable to bias and stress because everyone is so different And when people are treated unfairly, they tend to walk away, and that costs the organization a lot of money

In addition, strong communication skills are essential in the manufacturing process When used correctly, competent communication allows for the smooth distribution of information For example, effective communication between production supervisors and workers allows the latter to freely express their opinions and solve issues encountered during job performance This open communication allows management to improve scheduling and maintain smooth production advancement To become fluent and effective communicators, workers must focus on a variety of key aspects Firstly, it is critical to listen carefully and respect other people’s perspectives Before offering your own viewpoint or criticism, make sure you comprehend what others are saying Second, communicating confidence is a key aspect Workers must talk clearly and coherently while avoiding speaking too quickly or too slowly Furthermore, employees need to utilize language relevant to the communication setting in order to convey their thoughts readily and clearly Finally, paying attention to body language and gestures is essential in communication Understanding and efficiently using body language can assist boost confidence and efficacy in a conversation Regular communication practice, as well as listening to feedback from colleagues or consultants, will help employees become more fluent and confident in all communication circumstances

5.1.2 Tools to help prevent errors

Single Wheel Roller Presser: This specialized tool ensuring the precise alignment of materials during stitching By preventing material slippage and maintaining uniform edge positioning A single wheel roller presser aids to perfectly performer seams and minimizing the possibility of crooked or mismatched components Worker can handle curving shapes and complex design patterns with increased precision thanks to its handling of diverse materials, from soft leather to synthetic fabrics

Figure 5.1 Picture of Single wheel roller presser

Presser Feet : Pressure feet tools, such as navigation feet or even-feed feet, help control the movement of layers of fabric This helps to ensure that when sewing stretchy or slip-on fabrics, the presser foot can help prevent the fabric from slipping or stretching unevenly This tool ensures both upper and lower fabric move together, reducing the risk of distortion or mismatched seams, resulting in consistent stitch lengths The worker does not need to manually adjust the fabric, reducing the risk of uneven or missed stitches

Figure 5.2 Picture of Presser feet

TPU pieces : With shoe models, there will be stitching details with high difficulty The application of TPU (polyurethane thermoplastic) pieces is recommended to help align the seam to ensure that the stitches are sewn in the correct position and according to the intended seam The TPU pieces will be cut to a shape and dimension to match the pattern and template of the applicable part When the worker starts stitching, simply place the TPU piece in the position where the seam alignment is desired In order to secure the placed TPU piece accurately and firmly so that it does not move during sewing, the TPU pad will be attached with a sticker underneath (without affecting the product)

Figure 5.3 Picture of TPU pieces

Improve bonding shoes quality

An effective solution to improve shoe adhesion quality is to focus on improving the upper preparation procedure It is essential to ensure that the upper material has a surface suitable for the adhesive used in the bonding By carefully selecting and applying appropriate surface treatments to the upper material, such as controlled sanding techniques, footwear manufacturers can create optimal conditions Improve the compatibility between the upper and the sole This approach not only enhances the overall adhesive strength but also contributes to the longevity and quality of the finished shoes, ultimately leading to enhanced customer satisfaction and brand reputation

Surface treatment can help create a more uniform and even surface, minimizing the appearance of cracks that can interfere with bonding Conversely, inadequate or incompatible surface treatments can lead to insufficient adhesion, resulting in the quality of the final product being affected Below are two commonly used physical and chemical treatment methods: a) Cleaning

To get a good adhesive bond, it is important to start with a clean adhesive surface Foreign materials such as dirt, oil, moisture and weak oxide layers must be removed; on the other hand, the binder will bond to these weak boundary layers rather than to the substrate Solvent wiping is the most common method and is sufficient to remove most organic contaminants There are a range of cleaning solvents used for surface treatments, each suited to specific materials and methods Some typical types of cleaning solvents include: acetone, metanol, isopropanol và metyl etyl xeton (MEK) (Broughton & Lodeiro, 2002; Khan M Majbaur, 2015) b) Roughing surface

For the case of materials used including materials such as leather or leatherette, the use of a slightly roughened surface can considerably enhance the adhesive bond This surface modification promotes better adhesion of the adhesive, resulting in a stronger and more reliable bond between the upper and the sole So, it can be affected by a number of negative factors such as pressure from time, fatigue, and decreased concentration when working under extended hours This can contribute to inconsistencies in product quality and increase the risk of defects

Applying deployment using robotic technology, by assigning roughing surface operations, manufacturers can ensure consistent and controllable surface textures, eradicating the risk of human error Thereby optimizing the adhesion ability and overall durability of the final product

Figure 5.4 Automatic roughing for upper and sole by DESMA

5.2.2 Adhesives and surface treatments suitable for each type of material

In the footwear industry, there are many different types of glue that can be used for different activities in the footwear manufacturing process These glues can be classified based on their method of application There are three main groups that are most suitable for use in the footwear industry (UNIT 2 Sustainable Materials and Components for Footwear, 2016; Paiva et al., 2016) ị Solvent-based adhesive: These adhesives include polymer solutions, such as Natural

Rubber, Polychloroprene (PCP) and Polyurethane (PU) Polychloroprene-based adhesives use a mixture of solvents such as toluene, light hydrocarbons, and methyl ethyl ketone (MEK) Polyurethane-based adhesives use solvents such as acetone or MEK and other solvents such as toluene and ethyl acetate to improve their properties While effective in bonding footwear materials, these adhesives release volatile organic compounds (VOCs) during the bonding process, posing a health hazard to workers and contribute to environmental pollution ị Water-based adhesive: This heading includes polymer solutions such as polyurethane (PU) and polychloroprene (PCP) Water-based polyurethane adhesives contain natural or synthetic rubber that is dispersed in water and is commonly used for sewing work Unlike solvent-based adhesives, water-based adhesives pose no health or environmental hazards due to their water composition ị Hot-melt adhesive: Hot melt adhesives are completely solid at room temperature, but they change to a liquid state when exposed to higher temperatures To use them, a suitable application device is needed that will heat them, then reduce the temperature, causing the adhesive to solidify and achieve optimal adhesive strength Because of their benefits over solvent or water-based adhesives, they facilitate rapid manufacturing processes, thereby reducing the time required for assembly tasks However, they require specific application equipment, low permeability on porous surfaces, and are expensive

These glues, especially solvent-based and water-based adhesives, play an important role in the footwear industry While solvent-based adhesives have good adhesion performance but pose health and environmental risks, water-based types offer safer and more environmentally friendly options Hot melt adhesives are a combination of effective adhesive performance and no risk from solvents, despite the need for specific application equipment and high costs This classification highlights the complex choice that manufacturers must make to balance performance, safety and environmental responsibility in the footwear manufacturing process

Table 5.1 The adhesives and surface treatments for upper material

Upper material Surface treatment Adhesive

Leather Roughening ( strong or weak depend on the thickness of leather )

Greasy leather Strong roughening 2K PU

Finished leather Strong roughening PCP or PU

Solvent wipe PCP or PU

Source: Orgilés-Calpena et al., 2019

Based on the influence evaluations of sub-criteria as unskilled worker (A33) and upper preparation (C43), the author recommends some solutions according to my knowledge, and based on data collection from research papers.

CONCLUSION

Conclusion

In conclusion, the application of the Fuzzy AHP approach to study the elements influencing the root cause of production defects in the instance of Chang Shin Vietnam has provided an in-depth picture of a comprehensive context to identify and prioritize these critical factors This study revealed the efficiency of Fuzzy AHP in examining the complex and linked factors that contribute to manufacturing errors by using a systematic and quantitative method These findings emphasized the nature of the manufacturing process andunderscored the importance of considering multiple factors - both tangible and intangible - to resolve problems at the source This study’s findings have significant significance for optimizing the quality control approach and decision-making process in the industrial industry

This study encourages the integration of the fuzzy AHP method into quality control frameworks and decision-making processes in the manufacturing industry The flexibility of the fuzzy AHP method to handle ambiguities and increases its application in this context, as manufacturing processes often involve complex factors that are difficult to pinpoint

Adopting cutting-edge methods like Fuzzy AHP not only provides a deep grasp of complexity, but also opens the door to continual improvement and growth in an ever-changing industry landscape Development that is long-term The Fuzzy AHP becomes a helpful tool for minimizing manufacturing faults, increasing performance, and improving overall manufacturing operations excellence.

Implication

The Fuzzy AHP approach was used by the company to determine the root cause of manufacturing failures The AHP technique aids in the prioritization of factors based on their relative influence on manufacturing failures As a result, the organization more efficiently allocates labor and resources, allowing it to handle essential problems first and eliminate production errors

Practical application of these implications at Chang Shin Vietnam requires the implementation of targeted measures Upskilling personnel on a regular basis, modernizing facilities to maintain safe working conditions, and performing routine equipment maintenance can all result in considerable reductions in production failures Incorporate a solid quality management system that handles even seemingly little elements that can have a substantial impact on a product’s overall quality

Furthermore, Chang Shin Vietnam has more options in applying eco-friendly solvents for cleaning and surface treatment, which is in stutable with modern sustainable practices

This is not only advantageous to the environment, but is also in line with consumer expectations for eco-friendly products

In conclusion, the implications acquired from the analysis of root cause failures in the sewing and shoe bonding processes provide Chang Shin Vietnam with actionable information to improve the manufacturing process and product quality By addressing root causes, maintaining equipment and adopting a holistic quality management approach, the company can enhance operational performance and customer satisfaction in the footwear industry

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Appendix 1: Questionnaire to evaluation criteria (A1-A5) More important than Equal Less important than

A1 MMI MI LMI EI LLI LI MLI A2

M u ch m or e im p or tan t M or e im p or tan t A li tt le m or e im p or tan t Mu ch le ss im p or tan t

A lit te l le ss im p or tan t Le ss im p or tan t

Appendix 2: Questionnaire to evaluation criteria (C1-C5) More important than Equal Less important than

C1 MMI MI LMI EI LLI LI MLI C2

M u ch m or e im p or tan t M or e im p or tan t A li tt le m or e im p or tan t E q ual im p or tan t A lit te l le ss im p or tan t Le ss im p or tan t Mu ch le ss im p or tan t

Tiêu đề	Factors Impacting to Root Causes of Manufacturing Defects by Fuzzy AHP Method: A Case of Chang Shin Vietnam
Tác giả	Nguyen Mai Thao
Người hướng dẫn	Nguyen Phan Anh Huy, PhD
Trường học	Ho Chi Minh City University of Technology and Education
Chuyên ngành	Industrial Management
Thể loại	thesis
Năm xuất bản	2023
Thành phố	Ho Chi Minh City

Định dạng
Số trang	100
Dung lượng	15,15 MB