Development of Six Sigma methodology to improve grinding processes: A change management approach

Behrooz Noori (Department of Industrial Engineering, West Tehran Branch, Islamic Azad University, Tehran, Iran)
Mana Latifi (Islamic Azad University, Tehran, Iran)

International Journal of Lean Six Sigma

ISSN: 2040-4166

Publication date: 5 March 2018

Abstract

Purpose

This paper aims to deploy the Six Sigma methodology to facilitate defect reduction and enhance the bottom-line results of an automotive industry.

Design/methodology/approach

Six Sigma is a business process improvement strategy widely used in manufacturing field for enhancing organizational performance. Six Sigma enables the attainment of defects reduction. In this study, the Six Sigma methodology has been developed with the integration of change management tools.

Findings

Six Sigma has been successfully implemented in the grinding process in automotive engine manufacturing organization. The proposed Six Sigma methodology has been applied to facilitate defect reduction. The developed methodology with linkage of DMAIC (define, measure, analyze, improve and control) and change management techniques reduces defects.

Research limitations/implications

The developed methodology has been implemented in an automotive industrial complex. In future, more number of studies could be conducted, i.e. for mistake proofing. Furthermore, advanced tools and techniques could be included in the methodology for increasing the effectiveness of change management.

Practical implications

The proposed Six Sigma methodology has been successfully implemented in a grinding process of automotive manufacturing organization; in future, the approach could be applied in different industrial sectors with addition of new tools and techniques for improving its effectiveness.

Originality/value

The Six Sigma methodology has been designed and implemented in the grinding process. Researchers have not treated Six Sigma in much detail in the automotive industry. Moreover, previous studies on Six Sigma have not dealt with the grinding process. Besides, most studies in the field of Six Sigma have focused only on DMAIC, but this study adds change management approach to DMAIC.

Keywords

Citation

Noori, B. and Latifi, M. (2018), "Development of Six Sigma methodology to improve grinding processes", International Journal of Lean Six Sigma, Vol. 9 No. 1, pp. 50-63. https://doi.org/10.1108/IJLSS-11-2016-0074

Download as .RIS

Publisher

:

Emerald Publishing Limited

Copyright © 2018, Emerald Publishing Limited


1. Introduction

Increased competition at international level is one of the most important achievements of economic globalization. The speed and quality to achieve superior performance in a competitive world are dependent on selecting proper methods, the use of organization ability and its key competencies. Automotive industry is one of the most active industries involved in the quality improvement, lower production cost and continuous improvement activities (Habidin et al., 2016).

Establishment of quality management (QM) systems, which has evolved day by day, has a direct impact on the management of organizations and the clarification of qualitative objective, considering that the process management and the use of improvement cycles have changed the organization situation. The improved quality of processes and quality improvement of products is one of the most important modern business strategies. Development and implementation of an effective quality strategy is an important factor in the long-term success of an organization (Gijo et al., 2014). In this regard, the Six Sigma methodology is a project-oriented approach to reduce the process variation and defect, and in other words, to increase the process capability (Montgomery and Woodall, 2008). Six Sigma was developed for the first time in Motorola Inc. in 1986. Six Sigma is a powerful method to improve the quality and reduce the defect rate. Over the years, Six Sigma is greatly developed in both manufacturing organizations and service organizations. Six Sigma is one of the best techniques to improve business processes. Six Sigma is a teamwork-based project, and solves the main problems of customers and processes.

Six Sigma can help the engineers in dealing with multitasking issues with uncertain solutions. In many cases, the root causes are unclear and should be identified systematically using the DMAIC (define, measure, analyze, improve and control) methodology.

Researchers have not treated Six Sigma in much detail in the automotive industry. Moreover, previous studies on Six Sigma have not dealt with the grinding process. Besides, most studies in the field of Six Sigma have focused only on DMAIC but this study has used change management approach in improvement implementation. There is a hope that this article encourages the car manufacturers’ managers and car industry suppliers in using Six Sigma to solve the difficult problems, especially when the root of the problem is not clear.

This article has used Six Sigma instead of Kaizen or quality circles to solve the problem of the increased processing defects because Six Sigma integrated a series of techniques and tools regularly. This article presents the application of the DMAIC methodology in an automotive supplier company based in Iran to reduce the defects in shaft manufacturing process. This article has explored that the grinding process parameters are the key factors affecting the runout significantly. Runout is critical to customer feature. Then, the optimum process parameters are determined by means of the DOE method, and the control chart is adopted to monitor the effect of process improvement. The specific objective of this study is to improve first-pass yield significantly in the grinding processes.

The rest of the article is organized as follows. The second section presents related words. The third section provides information about the company and the nature of the problem. The next section provides the use of modified DMAIC methodology and expression of techniques used in the problem-solving process. The final section provides discussion, the results and main lessons learned during project implementation.

2. Background

Six Sigma has several dimensions such as philosophy, which results in low defects in operation; statistical measurement, which helps the accuracy of product, service and process measurement; measurement tool, which establishes the measurement system; and finally a business strategy because high quality reduces the business costs. Using effective techniques proposed in the Six Sigma methodology causes identification of the strong and weak points of the processes and paves the way to improve the production and service processes. Supporting techniques, which is also named as Six Sigma tools such as cause and effect analysis, have appropriate performance in dealing with issues and problems, help in the identification of the problems and provide certain image from the company performance to the authorities for further investigation.

Much of the current literature on Six Sigma pays particular attention to industrial processes. Kumaravadivel and Natarajan (2013) applied the Six Sigma methodology to the flywheel casting process. Kumaravadivel and Natarajan (2013) found that the efficiency and performance level of the sand-casting process can be improved by adopting the Six Sigma approach. Swarnakar et al. (2016) designed and successfully implemented the Lean Six Sigma methodology to facilitate defect reduction in an automotive component manufacturing organization. There has been 50 per cent reduction in DPU. Srinivasan et al. (2016) indicated that the implementation of Six Sigma will pave the way for achieving the Six Sigma level quality in the companies with little revenue. During the conduct of the research reported in this paper, the case of rejecting the furnace nozzles because of the deviation in the diameter of the furnace nozzle hole was considered as the main problem. To overcome this problem, the Six Sigma phases were applied. Moreover, Pugna et al. (2016) applied the DMAIC methodology to the riveting process. Process capability was substantially improved on short and long terms: Cpk increased from 0.96 to 1.72. In another major study, Uluskan et al. (2016) integrated the Six Sigma practices into traditional QM theory by investigating its relation to traditional QM practices as well as its direct effect on the organizational performance.

So far, very little attention has been paid to the role of Six Sigma in the automotive industry (Kumar et al., 2007; Vinodh et al., 2011; Pyle and Liker, 2014; Garza-Reyes et al., 2014; Gijo and Scaria, 2014; Jirasukprasert, et al., 2014; Zhang et al., 2015; Rocha-Lona et al., 2015). Orbak (2012) explained a detailed application of the Six Sigma methodology for reducing the shell scrap of foam production and lamination process. As a result of the approach, the process capabilities and the Sigma levels increased, and shell scrap percentage decreased. The average decrease is around 3.5 per cent which is greater than the project target of 2 per cent. In addition, the financial benefit of this project is approximately $45,000 per year. Gijo et al. (2014) illustrated the power of the Six Sigma methodology in improving the first-pass yield of a high-precision grinding process. Moreover, Gijo and Scaria (2014) presented the successful implementation of the Six Sigma methodology in an automotive part manufacturing company. Gijo and Scaria (2014) implemented the Six Sigma approach and resulted in the reduction of process capability-related problems and improved the first-pass yield from 94.86 to 99.48 per cent.

Although there are reluctant managers to implement the Six Sigma process, Venkatesh et al. (2014) showed that the efforts put for implementing Six Sigma in the form of DMAIC process resulted in financial gain and improved customer satisfaction. Furthermore, quality requirements for, in particular, ground components are increasing all the time, while the integrity of the cylindrical grinding process also remains an important criterion (Oliveira et al., 2009). Overall, these studies highlight the need for addressing Six Sigma in the automotive industry, and pay particular attention to the grinding processes.

3. Problem definition

The case study examined a motor supplier of a large car manufacturing company based in Iran. The major products of this supplier are engines, gearboxes and axles (Plate 1). This company has a strong emphasis on improvement of business processes. One of the ways to achieve this purpose is removing non-value-added activities and improving the production efficiency through reducing the defect and reworking. The problem is related to the motor shaft defect. The process capability (Cpk) of the new shaft production process was reported 0.29. The new shaft production process was not capable of meeting the customers’ requirement. The off-limit components reported by the quality control unit were observed, and the SPC committee and engineering unit were responsible to examine the problem.

This problem causes customer dissatisfaction and has negative impact on the business performance . To find a solution for this unknown problem and minimizing the costs related to the irregular solution implementation, the use of systematic methodology was necessary. The company decided to use the Six Sigma methodology to solve the problem. The problem has high priority for the organization and it is clear that solving the problem greatly helps in achieving the quality objectives. In addition, the management knows that an effective solution will have great impact on the costs reduction.

Critical-to-quality (CTQ) characteristics are the important measurable characteristics of product or process for which performance standards or specification limits must be satisfied (Eckes, 2002). In this study, the team decided to consider the “runout” as the CTQ characteristic for the shaft production process. Plate 2 shows the initial shaft. If CTQ is less than 0.0015, the defect occurs. Many factors can influence the amount of runout in a shaft. Grinding process is generally the last step in the shaft manufacturing. The grinding process generates significant heat that is localized at the point where the grinding wheel touches the shaft (Plate 3). Runout value is a combination of several types of error motions, form errors and form factors, e.g. drive bearing performance, machine structure and drive alignment. After accurate examination of the processes related to the nonconformance of intermediate quality control unit, the shaft grinding step was identified as the effective factor on the runout parameter.

4. Six Sigma methodology

4.1 Define

In this phase, the first step is to determine project scope and project objectives based on the customer requirement. An eight-member team that included a quality consultant was formed and the role and responsibility of the members were determined. The common understanding of the problem and the important steps of this project were also defined. The engineering manager was the team leader, and the team members were two quality control engineers, production supervisor, quality assurance supervisor and three operators from the production line. The operators have long professional background and technical knowledge on the production process. The team leader was responsible to ensure the completion of the project in the specified time limit. The champion was also responsible to select and confirm the project and monitor the project implementation. Consultant held the required trainings for the team, and provided the necessary instructions for the project successful implementation. He was also responsible for the output examination and assessment of each Six Sigma phase.

The first step was the development of project charter, including all required details such as the composition of the team and the project schedule. The Define phase checklist helped the executive team to accurately understand the project objectives, duration, required resources, responsibilities and roles, scope and project boundaries and the anticipated results of the project, which creates a common vision and sense of ownership among the project team.

The objective of the project was to increase the grinding process capability. The initial flowchart of the grinding process was provided on the basis of the SIPOC (supplier-input-process-output-customer) model to establish a clear vision of the project. The SIPOC provided a big picture of the required measures to meet the process output.

4.2 Measure

The objective of the Measure phase in a Six Sigma project is to evaluate the baseline performance of the process with respect to the CTQs identified during the Define phase. The phase is related to selecting product characteristics, examining and evaluating measurement system accuracy, data entry and establishing a baseline for process capability. CTQ or shaft runout was measured per millimeter. This feature should be less than 0.0015 mm. For the validation and verification of the measurement system, the Gage R&R study was performed (Knowles et al., 2003). Two measurement experts and ten components were used in this study. Measurement tool is shown in Plate 4. The measurement system variation was estimated about 20 per cent. The measurement system can be acceptable when the Gage R&R is less than 30 per cent (Antony et al., 1999). The data collection strategy was also developed, which included the number of samples and data collection process. Sixty observations were collected over the eight weeks. The data normality was examined using Minitab software. The results are shown in Figure 1. According to the current process Cpk, further analyses were required to identify the causes of process incapability as well as the main drivers that could be improved.

4.3 Analysis

To address process incapability, cause and effect analysis of the new process was performed. The analysis target is to determine the root cause of the defects or main sources of variation and develop the initial solutions. The brainstorming session in connection with the causes and effects of the problem was held. The cause and effect analysis output is shown in Figure 2. The cause and effect diagram was used to find the root causes. The important point in cause and effect analysis is that the causes listed in the diagram should be validated. For validation, the data related to the causes must be collected. On the basis of the data related to a cause, consultant and team can have a discussion. Finally, all the causes were examined (Table I), and validated root causes were addressed in Table II.

4.4 Manage change and improve

In the case of this study, solutions were generated through a brainstorming session (Garza-Reyes et al., 2016). For optimization of the machinery parameters specified in the previous phase, it was determined to emphasize on the most important root cause based on Pareto analysis, therefore, the agreement was obtained on optimization of the tailstock. In addition, it was decided to design the experiments. Thus, ANOVA was used to evaluate the main cause effects. Solution testing was performed correctly. Beside, cost–benefit analysis on solutions was addressed (Table II). After experiments, dead center was considered as a main solution.

Six Sigma is arguably a very high-minded methodology, but that is not to say that all of its components are complete. We used tools and concepts of the change management to improve the process of improvement implementing. Researchers have not analyzed the Six Sigma change efforts in industrial cultures. We integrated the change management philosophy and the Six Sigma method. We need to empower all our management team and especially the quality assurance supervisor who have to be engaged and committed to the success of the Six Sigma program. In this respect, we can say that Six Sigma is more a change management and cultural change program than a technical one. Change management techniques that were considered in this study were collaboration on a solution with everyone impacted, identifying improvement stakeholders, communicating the proposed solution and benefits, learning organization, training and development of knowledgeable staff, increasing data collection efficiency and celebrating the success. Successful change management requires awareness of improvement and effective communication and the involvement of people who will be affected (Hughes, 2007; Crawford and Nahmias, 2010). Therefore, the traditional DMAIC methodology has been modified, by including an additional phase called “management of change” (M), to reduce the conflicts and increase the efficiency of implementation (Figure 4).

Process capability analysis was carried out to evaluate the effect of the improvement made on the process capability index. Minitab was used to perform the process capability analysis, and the results are presented in Plate 5. In general, the results showed major improvement in the process capability index.

4.5 Control

The objective of this phase is to keep and maintain the improvements which resulted in the previous phase. Because of different inter-organizational reasons such as job rotation, the maintenance of the improvements is very difficult. One of the useful tools in this regard is the use of standard of operation (SOP). Furthermore, the process changes should be documented in form of the procedures in the QM system. This greatly helps the standardization of the improvements in a Six Sigma project. In addition, CTQ was added to the process audit checklist and validated by internal auditors in a few audit sessions.

In addition, if there were any changes reported in the process, the corrective measures will be performed. Control chart was another powerful and useful tool to ensure the improvement sustainability during the time (Figure 3). The mean and range control chart was used to monitor the process along with the control plan to deal with specific causes. The instructions are also considered for those involved in the new improved process using new methods to increase their skill. Control charts and metrics were established correctly (Figure 4). Moreover, financial savings were verified and new standard operating procedure was signed-off by the process owner (Figure 5).

5. Discussion

This paper presented a successful case study of defects reduction in an engine manufacturing process by applying the Six Sigma methodology. Therefore, this paper can be used as a reference for industrial managers to guide specific process improvement projects in their organizations, similar to the one presented in this paper. By considering this, a reduction in the amount of defects was obtained by determining the optimum technology. In terms of the Six Sigma level, the concept literally refers to reaching a Sigma level of 6, or in other words, 3.4 DPMO. The improvement project presented in this paper has not been able to take the organization studied to achieve a Six Sigma level. However, moving from one Sigma level to another does take considerable time. In addition, this study considered a pilot project that was conducted to empirically demonstrate the Iranian organization studied that the Six Sigma problem-solving methodology is an effective approach capable of improving its manufacturing process by reducing the amount of defects. This demonstrated that as long as the organization continues embracing Six Sigma and change management within its continuous improvement culture and applies its concepts and principles to systematically solve the quality problems, it is believed that benefits such as cost savings, increase in product quality and customer satisfactions will be achieved.

6. Conclusion

Six Sigma is one of the most important strategies to decrease the defect and improve the process capability. This case study was implemented to improve the grinding process output from 27 to 93.3 per cent. A multidisciplinary team was formed to examine the process defects and the Six Sigma methodology was performed by the corresponding team. After implementation of this project, the defect costs were decreased sharply. In Table III, a comparison of before and after Six Sigma implementation is shown. The saving that resulted from this project is estimated at $40,000, and also no one can deny the improvement effects of customer perceptions. This case study opened the management eye on the efficiency of Six Sigma. Although, high-level technical capabilities are required to achieve the benefits of Six Sigma, correct adjustment of objectives, correct selection of team members and correct atmosphere for project implementation are important factors in the project success. In fact, both technical and managerial aspects are effective in the project success. This paper has presented a case study where DMAIC has been modified and adapted to the specific needs and improvement. In particular, a “management of change” (M) phase has been integrated to the DMAIC methodology.

Moreover, the improvement in the grinding process with the Six Sigma methodology is an appropriate benchmark which can meet the expected results for the company. The most important lessons learned in this project are as following:

  • Six Sigma showed the power of using a systematic method in the studied company.

  • Accurate data collection is a main factor for the project success, but data collection should be done by considering the important points of the study. Another point is that no data collection should be done without Gage R&R study.

  • Data collection must structurally be focused on the root causes of a problem.

  • Management found that Six Sigma is a good strategy to discover the root causes; therefore, it can reduce the quality costs greatly.

  • Management issues related to data collection should be considered carefully. For example, the fear from blame should be removed from the corporate culture, and the open corporate culture must be replaced.

  • Use of change management approach in improvement implementation.

Vinod et al. (2015) suggested Poka-Yoke, which is a tool that can be used to achieve zero defect manufacturing, has the potential to support the implementation of Six Sigma. So far, very little attention has been paid to the role of Poka-Yoke in Six Sigma. Future studies on the Poka-Yoke are therefore recommended.

Figures

Gage R&R report

Figure 1.

Gage R&R report

Cause and effect diagram for runout variation

Figure 2.

Cause and effect diagram for runout variation

Process capability after improvement

Figure 3.

Process capability after improvement

DMAIC model

Figure 4.

DMAIC model

Grinding process monitoring

Figure 5.

Grinding process monitoring

Engine

Plate 1.

Engine

Initial shaft

Plate 2.

Initial shaft

Tailstock with live center before improvement

Plate 3.

Tailstock with live center before improvement

Measurement tool (dial indicator)

Plate 4.

Measurement tool (dial indicator)

Grinding machine after improvement

Plate 5.

Grinding machine after improvement

Cause validation plan

No. Causes Validation method
1 Gauge damage Gemba
2 Low precision of micrometer Calibration
3 Low precision of operator Evaluation
4 Not optimum machining parameters Design of experiments
5 Improper feed and speed rate Process audit
6 Part place is not clean Gemba
7 Part adjustment not OK Gemba
8 CP machine adjustment not done properly SOP
9 Drive changing Gemba
10 Low precision of machine R&D
11 Using dead center or live center Design of experiments
12 Improper grinder change Gemba
13 Stopping and restart of machine for various Gemba
14 Unsatisfied worker Motivation plan
15 Worker rotation Gemba
16 Worker skill Gemba

Validated root causes and solutions

No. Validated root cause Solution
1 Improper feed and speed rate Adjustment procedure implementation
2 CP machine adjustment not done properly Shaft adjustment with MAE machine
3 Drive changing This is introduced as a parameter to be checked in machine preventive maintenance checklist
4 Using dead center or live center Introduced dead center through DOE
5 Stopping and restart of machine for various Introduced operator before restarting of the machine

Comparison of results before and after the project

Measures Before After
DPMO 725,747 66,807
First yield (%) 27.4 93.3

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Acknowledgements

The authors would like to thank Mr Javidmehr and Mr Dehghani for their contributions and information to the preparation of the paper. The authors also gratefully acknowledge the helpful comments and suggestions given by anonymous referees.

Corresponding author

Behrooz Noori can be contacted at: bnoori@gmail.com