Implementation of the Six Sigma Methodology for Reducing Fabric Defects on the Knitting Production Floor: A Sustainable Approach for Knitting Industry

Reducing fabric faults in the textile knitting industry is one of the main challenges for knit fabric production. Due to the fabric defects, the sigma level of knit fabric production is between 3 to 3.5. This study aims to increase the sigma level of knit fabric productions. Here, we implement a six sigma strategy in the textile knitting industry. The Six Sigma methodology is applied step by step on the knitting fabric production floor. The DMAIC approach is clearly stated through the phases of defining, measurement, analysis, improvement and control. The types and reasons for different fabric defects are identified by using the cause and effect diagram. The Pareto chart showed that the highest percentages (51%) of defects are related to yarn quality. In the improvement phase, the defects are eliminated by utilizing the Six Sigma methodology. Then, the sigma level of our knit fabric production went to 4. The risk priority number was calculated and suggestions for preventive actions were analysed in the control phase. Implementing the six sigma methodology on the knitting production floor also reduces the cost of production. As a result, this real time study on the knitting production floor has proved to be an economically sustainable production of knit fabric.

https://doi.org/10.31881/TLR.2022.29 Implementation of the Six Sigma Methodology for Reducing Fabric Defects on the Knitting Production Floor: A Sustainable Approach for Knitting Industry

INTRODUCTION
One of the world's most globally interconnected industries is the textile and apparel business, which is crucial to human existence.The demand from developed countries has increased significantly, resulting in higher output and employment, increased growth in the agricultural sector, and an Dhaka, 1000, People's Republic of Bangladesh Shanghai 201620, People's Republic of China Bashundhara R/A, Dhaka-1212, People's Republic of Bangladesh https://doi.org/10.31881/TLR.2022.29 increase in the amount of foreign currency generated for developing economies [1].Textile industries are the contributions of different part-by-part industries [2].The fabric manufacturing industries are divided into two main categories [3].One is the weaving industry [4] and another is the knitting industry [5].The knit fabrics are produced by the textile knitting industries.The word "knitting" came into use in the middle of the 16th century, with earlier words like "cnyttan" and "nahyat" being less precise.This suggests that knitting came from knotting and Coptic knitting [6].At present, the knitting industries employ the warp knitting and the weft knitting process.There have been many potentials for fabric manufacturing by using the knitting process [7,8].Knitting has a unique loop structure that makes it possible to use a small number of yarns, change the size of the loops, and make loops that change shape when under tension.This makes it possible to knit single-face, double-face, open-work, and surface-interest structures, as well as to make different types of loops in different widths and depths [9].The production efficiency of knitted fabric is decreased due to the occurrence of knitting faults on the production floor.The reduction of knitting faults and the increase of the knitting production efficiency is one of the key challenges on the knitting production floors.To reduce the faults, Six Sigma approach can be used as a sustainable approach to knitted fabric production.
Six Sigma is frequently used to guide overall organizational advancement activities because of its structured project strategy that includes a vast range of problem-solving tools that are easy to apply.
It is intended for eliminating defective products and other wastes from operational processes by applying the Define, Measure, Analyse, Improve, and Control (DMAIC) methodology in a disciplined and data-driven manner [10].While Six Sigma was originally created for and employed in industrial environments, its application has expanded to include a wide range of other industries.In fact, the services industry is the second most prevalent sector to employ this practice [11].Using the DMAIC approach, for example, considerable performance improvements have been achieved in service operations, such as banking and finance, education, government, and healthcare.Specific examples of its application in healthcare include lowering the length of clinic appointments, reducing the number of insurance claim denials, and cutting the time it takes to dispatch medical reports.Consulting, communications, human resources, information technology, and marketing are just a few of the professional services where this technique has been used successfully in the past [12].The introduction of Six Sigma into the industrial field in the early 1980s by Motorola was a watershed moment in the expansion of the scope and application of quality systems in today's business environment [13].The application of Six Sigma in the textile industries can increase the production efficiency of textile manufacturing.
Numerous studies have been conducted in various areas of textiles to improve product quality and defect reduction through the application of Six Sigma methodologies [14].Adikorley et al. reported on https://doi.org/10.31881/TLR.2022.29 the implementation and completion of Lean Six Sigma (LSS) projects and programs in the textile and apparel industries [15].Bongomin et al. described a technique for increasing the efficiency of garment assembly lines through line balancing [16].Prasad et al. documented the implementation of lean manufacturing in the Indian textile industry in their studies [17].Mukhopadhyay et al. used the Six Sigma methodology to minimize yarn packing defects [18].Karthi et al. presented a case study of lean Six Sigma implementation in a textile mill using an ISO 9001:2008-based quality management system [19].Hussain et al. demonstrated the application of Six Sigma methodology in reducing defects in Pakistan's textile weaving industry [20].Although some reports have analysed the Six Sigma methodology in relation to the knitting industry, the ultimate objects and their findings are far from our study.For example, (a) Ortega et al. developed dynamic model of the system for the manufacture of knitted textiles using Six Sigma, but they only increased the sigma level from 1.3 to 1.9.[21]; (b) Kurnia et al. studied the amount of sigma faults in sock knitting and give solutions for minimizing the percentage of socks with defects, which is mainly conducted in the garments industries [22].Hence, there has been no study attempted to date that can provide a cost-effective and sustainable approach to six sigma application in the textile knitting industry.
Therefore, this study is conducted with the aim of implementation of the Six Sigma methodology on the knitting production floor.Industrial applications using DMAIC approaches are introduced part by part.The different phases are clearly stated and the cost of production after implementing Six Sigma are calculated.During the control phase, the risk priority number is calculated and possible preventive measures are examined.As a consequence of this real-time investigation on the knitting manufacturing floor, it is clear that knit fabric production will be economically sustainable.

Materials
There are several types of knitting machines in the industry, such as single-jersey knitting machines.

Methodology
In this particular research piece, the methodology used is a case study.The "X Knitting Industry Limited" in Gazipur, Bangladesh, was selected as the location for the case study.An initial analysis of the knitted floor section with illustrations is presented.It has come to our attention that the knitting area contains many defects and rework concerns.Based on prior research findings, several different industries use the DMAIC method in combination with the Six Sigma method to fix defects.In addition to that, this study will also measure the level of sigma in the knitting industry.There is no study to this date that provides a cost-effective and sustainable approach to six sigma application in the knitting industry.
The study decided to use the DMAIC approach for the Six Sigma methodology to reduce the defect percentage on the knitting floor by a significant margin.The factory's management furnished secondary data on the knitting division and only Plants' data was gathered.Using the data provided by the management, we were able to identify a few quality-related issues in the knitting department.The collected data and information was organized in a way that would allow for further investigation and analysis.In our research, we used the Pareto Analysis and the Cause-and-Effect Diagram.Our team needed to perform a Failure Modes and Effects Analysis [FMEA] during the control stage in order to identify potential failure modes, the effects and severity of those failures, as well as the causes, risk priority numbers [RPN], and preventive measures.This research employed FMEA to improve quality with the Six Sigma method.It is undertaken in stages, as illustrated in Figure 1.

RESULTS AND DISCUSSION: APPLICATION OF THE SIX SIGMA DMAIC METHODOLOGY Defining Phase
In the defining step of the Six Sigma approach, the problem, the scope of the research, the objective, the research team, and the timetable are all defined.This study's problem was defined as a high percentage of B-grade and C-grade knitted fabrics production in the knitting sector due to a large number of faults in the fabric.The study's objective was to reduce the production of B-grade fabric.A team of people from the fabric manufacturing department, quality control workers, management, and researchers were assembled to accomplish the work.Figure 2 shows the flow chart of the knitting process.Initially, yarn was purchased from the manufacturers as per the merchandiser provided for every particular order.Then the knitting production person ordered the required yarn.In the meantime, the yarn testing team tested the yarn to see if it could fulfil the requirements of the physical and chemical properties or not.They checked for various imperfections to match the reports provided by the yarn manufacturers to produce good fabrics.If yarns were not able to meet the requirements, they were sent back to the manufacturers.As per order, yarn was placed on the machine and then into the creel of the machine by a one-by-one system.After that, yarn was fed into the yarn feeder through an inching motion.Then, as per the order requirement, fabric design and stitch length were checked.If the design was okay, then GSM was checked as per stitch length.Finally, the machine was prepared for production.The roll of the fabric was withdrawn and the weight of the fabric measured.
Furthermore, the quality department inspected the fabric and numbered the roll of the fabric as per grading.If the fabric was grade A and B, it was marked separately.Moreover, C-grade fabric was rejected.To fulfil the quantity, they again ordered the yarn to makeover the production quantity.

Measurement Phase
Each identified problem was alternated with a measurable phase in the measurement phase.An evaluation was made in light of the information gathered on these issues.Over the course of a week, all of the knitted fabrics on display were thoroughly inspected.Same as in the assessment, A-grade, B-grade and rejected (C-grade) fabrics were identified.During fabric grading, all the fabrics were counted as major and minor problems.The fabrics that were characterized by major defects would not be considered as acceptable for customers.In between, these fabrics would be considered as rejected.
The rest of the inspected fabrics with minor defects would have a fair chance of acceptance.
The established sigma level of the knitting procedures was determined as follows, based on the data After calculating the findings from the table, the existing sigma level was 3.5.

Analysis Phase
After the measurement phase, we analysed the diagram of cause and effect using brainstorming with the purpose of identifying all the factors that affect knitted fabric performance.Figure 3 shows the cause-and-effect diagram.The chart below gives a clear overview of all the potential problems, along with the areas of improvement, respectively.The fabrics were inspected and all faults were recorded; the causes and the severity of the faults were also recorded in Table 1.According to the table below, the total length of the inspected fabric was 22910 meters and the total length of major and minor faults was 4149 and 4057 meters, respectively.

Improvement Phase
The improvement phase assures the tasks of elimination of the root causes of the faults, the design of improved processes and their implementation.The risk matrix in this table depicts the likelihood, the impact, and the risk of the potential knitted fabric faults shown in Table 2.All of the above-mentioned issues were noted and possible solutions were devised.The major areas of concern found by the Pareto  The manufacturer of the circular knitting machine advised proper machine setting during each design change into single-or double-jersey fabrics.The technical and maintenance teams always follow those kinds of machine settings to ensure preventive maintenance.However, in some cases, companies use needles, cams, sinkers, or other machine parts, beyond their life span, which affects the quality in the long run.Mostly, it causes rejection.In order to maintain proper quality, the maintenance of machines and the parts needs to be done properly.This would reduce 90% of the faults related to the machine.
Proper training for workers is essential in order to ensure proper quality.There is also a proverb, 'workers are the best quality'.Training is the first and foremost tool for ensuring proper quality, making every worker aware of the long-term issues that may affect the quality.This would reduce material handling problems by 70%.
Along with the above-mentioned corrective actions, some other related corrective actions were implemented which are referred to in the risk matrix table.
 In the case of all problems related to yarn quality, spinning technology was improved.Testing of yarns should be given more priority to identify more excellent yarns before knitting.
 Ensure more of the preventive measures before the machine runs any new program.
 Set up a training zone for new workers so that they get proper knowledge about the machine and the materials.
 Focus on quality along with quantity.
 Performance based incentives for all workers were ensured so that they could motivate themselves for the bigger aspects of the manufacturer.https://doi.org/10.31881/TLR.2022.29 After eliminating all kinds of major defects in knitted fabrics related to yarns, machine setting, and material handling, the quantity of rejected and B-grade fabrics was reduced.After implementing Six Sigma, the improved sigma level of the knitting process was calculated as follows: Total After implementing, the improved sigma level is 4.

Cost Calculation
From the implementation of Six Sigma methodologies, the total amount of cost savings is summarized below.We have observed that after implementing the above measures, the knitting charge per kg of fabric is reduced.This scenario in Table 3 shows how this method can enhance the effectiveness of the products in the industry.Because of the increasing cost of yarn purchase and less increment in buyer's purchasing rate, Six Sigma methodology shows a positive tendency to decrease the cost of the production.The annual savings for single-jersey plain, loose knit, heavy jersey, pique, full-feeder Lycra,

Control Phase
A procedure is adjusted, monitored, and regulated in such a way that the integrated improvements from the preceding measure phase are sustained in the control phase.The control phase covered all processes, including the control strategy (Poka Yoke), statistical process control (SPC), and failure mode and effect analysis (FMEA) [18].We executed the FMEA at the measurement control stage, for all specific issues having do with potential failure, probable failure modes, their impacts and severity, causes, risk priority numbers (RPN), and preventive actions.In order to do FMEA, it was required to collect all the data relating to errors that occurred during the knitting process throughout the entire process.In Table 4, the results of the completed FMEA are shown.
Here, S stands for Severity, which indicates the impact of failure mode.It is scored from 1 to 10, where

CONCLUSION
This research started because of the increasing defects of the knitting production floor.We were prompted to reduce the defects to increase the productivity and efficiency.Proper data collection was the most important part of identifying the accurate solution for any problem.In this study, we collected https://doi.org/10.31881/TLR.2022.29 accurate data and recognized major areas that need improvement.During data collection, we focused on all the possible defects along with the areas related to that particular defect.The collected data steered us towards the fruitful identification of the faults and towards the solutions for improvement.
The identified defects were observed in the analysis phase and dealt with in the improvement phase.
The entire knitting production team was also investigated and informed of the respective corrective measures taken, so that they could be seasoned continuously to keep the knitting process in control.
The main recommendations of our research are: strategy in the textile industry is a sustainable approach that also reduces the cost of production.As a result, the Six Sigma methodology in the textile industry will reduce the knitted fabric defects as well as an increase of production efficiency.

Figure 1 .
Figure 1.Schematic diagram of the implementation of Six Sigma

Figure 4 Figure 3 .Figure 4 .
Figure4illustrates a Pareto chart of the notable faults.We could easily distinguish the 'vital view' from the 'trivial many' in the Pareto chart.It was observed that 51% of the defects were related to yarn quality, 30% to machine setting and the rest of the defects came from machine maintenance and material handling.
chart are yarn quality, machine setting, machine maintenance, material handling viz.count mix, lot mix, tension variation, Lycra cut, cylinder and dial placement, congested floor, and lack of operator consciousness, respectively.All possible machine configurations and machine maintenance procedures were investigated, and the improved results were implemented in consultation with the machine manufacturer and the well-equipped, well-trained technical personnel.Before deciding on a better quality yarn, the research and development team should be more proactive about the yarn, yarn manufacturers, and factory quality.Human Resources and Development department should deliver better operators by ensuring proper knowledge about production and quality for the purpose of reducing faults.

3 -
thread fleece, and terry fabrics are 620, 170, 250, 64, 340, 148 and 86 US dollars, respectively.The annual savings are 77, 232, 114, 150, and 127 US dollars, respectively.Therefore, overall savings per annum of 2378 US dollars shows the improvement of fabric production in comparison with the conventional production method.As a result, the level of improvement of the sigma level was increased to 4 from 3.5 and the profit per annum was increased to 2378 US dollars.https://doi.org/10.31881/TLR.2022.29

( 1 )
new circular knitting machine setting should be noted, implemented, and instructed on routinely; (2) proper yarn quality has to be ensured before knitting; (3) training of the new workers and follow up on the performance is required for setting up the benchmark performance of workers; (4) online quality check panel should be established for reducing faults; (5) overall equipment efficiency needs to be established for every machine.The finding of the research, along with the proper remedies to the problems, resulted in improvement.The initial findings of the sigma level were 3.5 and that was improved to 4 at the end of the study.The end result reduced the rejection of the knitted fabric to around 50%.The implementation of the Six Sigma

Table 1 .
Defects identified after knit fabric inspection

Table 3 .
Identification of risk matrix table

Table 4 .
1 is the lowest impact mode and 10 is the highest impact mode.O means Occurrence, which indicates the frequency of the failure mode.It ranges from 1 to 10, where 1 is the lowest occurrence and 10 is the highest occurrence of the failure mode.D means Detection, which indicates the ability to detect the failure mode during process control.It is scored from 1 to 10.The low scores indicate that the failure mode is easily detectable, high scores indicate the opposite.RPN means Risk Priority Number, which indicates the total risk score of the mode.If the mode shows high RPN then it needs immediate action, while low RPN is vice versa.It is calculated using the equation [1].Identification of FMEA for knit fabrics tension of yarn https://doi.org/10.31881/TLR.2022.29