|Year : 2011 | Volume
| Issue : 2 | Page : 107-112
Relevance of Six Sigma Line of Attack in SMEs: A Case Study of a Die Casting Manufacturing Unit
Department of Mechanical Engineering, UIET, MD University, Rohtak, Haryana, India
|Date of Web Publication||24-Oct-2011|
Department of Mechanical Engineering, UIET, MD University, Rohtak, Haryana
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Six Sigma within small- and medium-sized enterprises (SMEs) is rapidly emerging as the new wave of change in Six Sigma. The methodology adopted is Define, Measure, Analyze, Improve, and Control (DMAIC) of Six Sigma which had been mostly successful so far in large-scale industries. The methodology has been applied to reduce the rejection rate of the engine mounting bracket (EMB) by reducing defects inherent in the processes. The application of Six Sigma project recommendation brought up the process sigma level to 5.24 from 1.64 by reduction in EMB hole diameter variation in the process of machining after die casting. This increase in the sigma level is equivalent to a monitory saving of Rs. 0.260 million per annum which is a noteworthy figure for an industry of such level. This paper provides documented evidence of Six Sigma implementation in a die casting manufacturing unit which has been taken as a representative of a small- and medium-size industry.
Keywords: Define, Measure, Analyze, Improve, and Control, DPMO, engine mounting bracket, Six Sigma, SMEs
|How to cite this article:|
Kaushik P. Relevance of Six Sigma Line of Attack in SMEs: A Case Study of a Die Casting Manufacturing Unit. J Eng Technol 2011;1:107-12
|How to cite this URL:|
Kaushik P. Relevance of Six Sigma Line of Attack in SMEs: A Case Study of a Die Casting Manufacturing Unit. J Eng Technol [serial online] 2011 [cited 2020 Jan 27];1:107-12. Available from: http://www.onlinejet.net/text.asp?2011/1/2/107/86644
| 1. Introduction|| |
Sigma is a Greek letter representing the standard deviation or the amount of variation within a given process  . According to Harry and Schroeder, Six Sigma is a powerful breakthrough business improvement strategy that enables companies to use simple and powerful statistical methods for achieving and sustaining operational excellence  . Park described that Six Sigma implies three things: Statistical measurement, management strategy, and quality culture  . It is a measure of how well a process is performing through the statistical measurement of the quality level. The goal of Six Sigma is to design processes that do what they are supposed to do with very high reliability, ultimately producing very consistent products and services  . The numerical goal of Six Sigma is reducing defects less than 3.4 parts per million (PPM) also known as "defects per million opportunities" (DPMO), reducing cycle time and reducing costs dramatically which impact the bottom line , .
Although Six Sigma has been implemented with success in many large corporations, there is still less documented evidence of its implementation in smaller organizations  . The increasing demand for high-quality products and highly capable business processes by large organizations has left no choice for the small- and medium-sized enterprises (SMEs) but to consider the introduction of the Six Sigma business strategy  . Being able to link compensation to Six Sigma implementation is much easier in small companies compared to a large company  .
| 2. Research Background|| |
Wessel and Burcher in their study identified the specific requirements for the implementation of Six Sigma based on a sample of SMEs in Germany  . This study also examines how Six Sigma has to be modified to be applicable and valuable in an SME environment. This is the first study of its kind to be carried out on a Six Sigma survey in SMEs. Burton proposed alternative Six Sigma deployment models that allow SMEs to implement Six Sigma at a pace where they can digest the methodology and achieve benefits, without significant resource commitment and overhead structure of the traditional Six Sigma  . Snee and Hoerl argue that there is nothing inherent in Six Sigma that makes it more suitable for large companies. They also suggest that the greatest barrier to implementation in small companies to date has been the way the major Six Sigma training providers have structured their offerings  . Once an owner of the business (in small firms) is convinced of the advantages conferred by Six Sigma and visualizes the benefits, it is much easier to implement Six Sigma at smaller firms and to realize its benefits  . They suggest that the initial focus on SMEs can be to reduce quality costs or waste in the system. Effort and investment, as well as results in smaller companies, are more visible within a short time. Tennant argues that, in small organizations, if one visible and important person is actively against Six Sigma, then this attitude must change or the initiative must be a nonstarter  .
| 3. About the Case Study|| |
The present study was carried out in a SME unit manufacturing die casting products in Noida in Uttar Pradesh (India). The main product of the unit is manufacturing (engine mounting bracket) EMB as shown in [Figure 1].
The tolerance limit of one of the EMB hole diameters is 10.50 ± 0.10 mm as shown in [Figure 1]. The initial observations showed a very high rejection rate in the machining process of the EMB hole. The rejection rate of EMB was 5.2% because of a high variation in the EMB hole diameter. This hole was working as a reference point for many other projections in its drawing. So, there was a great need to reduce the rejection rate of EMB by reducing defects inherent in the processes.
| 4. Application of Six Sigma DMAIC Methodology|| |
For solving any problem, the methodology adopted must cover all possible causes of the problem. If the methodology of problem solving is not comprehensive enough, the solution obtained at completion will not be correct and the problem will resurface sooner or later. A process flow chart is prepared to proceed in a sequential manner and to present a one-shot picture of the entire methodology, as shown in [Figure 2].
In this paper, the high rejection problem of EMB was studied in depth and all the five phases in the Six Sigma methodology, i.e., DMAIC has been successfully implemented to achieve the existing sigma quality level from 1.64 to 5.24 which are explained as follows.
The problem and what the customer requires are defined  . In the define phase, a high-level process map - a SIPOC (Supplier, Input, Process, Output, Customer) - was drawn for EMB as shown in [Figure 3]. This diagram was used to identify the process or product for improvement.
In the measure phase, a measurement system analysis (MSA) is conducted which includes the gauge repeatability and reproducibility (Gauge R&R) studies. The purpose of the Gauge R&R study is to ensure that the measurement system is statistically sound. Gauge repeatability and reproducibility studies determine how much of the observed process variation is due to the measurement system variation. Two persons are needed to perform this experiment, which in this case were the operator on line and the investigator. The sample size was 10 and 2 readings were taken on each sample, thereby making a total of 40 readings. The gage used for this experiment was a Vernier calliper. From the results of the Gauge R&R study, repeatability and reproducibility comes out to be 29.73% and 0.00%, respectively, which put the percentage study variation at 29.73%, which is less than 30%, indicating that the measurement system was correct.
Many statistical tools were used to carry out the analysis which are explained as follows.
4.3.1 Process capability analysis
Process capability analysis was performed to find out the actual state of the process. Rational subgrouping was done and 20 samples were drawn, in a group of 5. Minitab was used to draw the process capability analysis curve for the EMB hole diameter as shown in [Figure 4].
|Figure 4: Process capability analysis of EMB rejection data before implementing the DMAIC methodology|
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The Z-bench sigma value of the process was found to be 1.64 and the existing DPMO level of the process came out to be 50270.39, which is remarkably high and this shows that there are a lot of opportunities for improvement in the process.
4.3.2 Fishbone diagram
Using process capability analysis, the DPMO level and sigma level of the EMB hole diameter rejection were known. Now it was the time to find out the causes of EMB rejection. Using expert experience and critical analysis of the actual process, a fishbone diagram [Figure 5] was drawn to find out the causes of more EMB rejections.
In the two-sample t-test, three important factors were taken for the study identified from the fishbone diagram. In the first case, a two-samplet-test was done for operator skills (unskilled and skilled) by taking the sample size of 50 each for skilled and unskilled operators. In the second case, a two-sample t-test was done for drilling tool replacement (after 96 h and after 140 h) by taking the sample size of 50 each for tool replacement after 96 h and 140 h. In the third case, a two-sample t-test was done for the EMB holding mechanism, i.e., fixtures (old and new) by taking the sample size of 50 each for old and new mechanisms.
In the improve phase, design of experiments was done to find out the optimum conditions for the vital few factors found out after the two-sample t-test.
These experiments were conducted to optimize the value of the parameters tool replacement and EMB holding mechanism. A 2×2 experiment was designed, i.e., an experiment with two factors on each level. [Table 1] shows the significant vital factors for EMB hole diameter variation.
Minitab was used to plot the main effects plot and interaction plot between the vital few factors (tool replacement and EMB holding mechanism). [Table 2] shows the readings of significant factors at various levels.
Sample 1 was taken for the unskilled operator.
Sample 2 was taken for the skilled operator.
Using Minitab, the two-samplet-test showed that as the P-value for the EMB hole diameter came out to be greater than 0.05; therefore, operator skill cannot be a factor for EMB rejection.
Sample 1 was taken for tool replacement after 96 h
Sample 2 was taken for tool replacement after 140 h
Since the P-value for tool replacement came out to be less than 0.05; therefore, this might be a factor for EMB rejection.
Sample 1 was taken for the new EMB holding mechanism.
Sample 2 was taken for the old EMB holding mechanism.
Since the P-value for the EMB holding mechanism came out to be less than 0.05; therefore, this might be a factor for EMB rejection.
The main effect plot [Figure 6] suggests that tool replacement and EMB holding mechanism both are major factors.
The interaction plot [Figure 7] shows that the lines are parallel to each other so there are no interactions present between the factors. The change in the response mean from the low to the high level of tool replacement does not depend on the level of the EMB holding mechanism.
In the control phase, an X bar/R control chart was drawn to visualize the presence of an assignable cause of variation after implementing the changes in factors proposed by DOE and for ensuring that the process continues to be in a new path of optimization. A 100-sample size was taken for drawing the X bar/R chart. The X bar/R chart is as shown in [Figure 8].
| 5. Improvement Results|| |
The application of project recommendation brought up the sigma level to 5.24 with a DPMO level of 0.08 as shown in [Figure 9], which is equivalent to the monitory saving of Rs. 0.260 millions (refer appendix I) which is substantial for a small organization. The machining process had been chosen in the EMB manufacturing unit because it represents the general process of a manufacturing unit operating in a SME environment. The success of the Six Sigma application in this case study can definitely encourage the other manufacturing units to use Six Sigma as a quality tool to reduce the losses in their processes and reap rich benefits from it.
|Figure 9: Process capability analysis of EMB rejection data after improvement|
Click here to view
| 6. Conclusion|| |
The Six Sigma tool for SMEs is an emerging topic among many academics and Six Sigma practitioners over the last 2-3 years. Very few studies have been reported about the successful applications of Six Sigma in SMEs. As small companies are more agile, it is much easier to buy in management support and commitment, as opposed to large organizations. The education and training component is much harder for smaller companies. Moreover, small companies do not have the slack to free up top talented people to engage in training followed by the execution of Six Sigma projects as they are crucial to the day-to-day operations and problem solving within the company.
This paper is an attempt to justify the highly useful role of management techniques like Six Sigma for SMEs which are normally presumed to be in the domain of large industries. Hole diameter variation is found to be a common problem in any manufacturing industry. The application of Six Sigma project recommendations brought up the sigma level to 5.14, and the estimated saving from the project after implementation is expected to be around Rs. 0.259 millions per annum which is substantial for any small manufacturing industry.
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| Authors|| |
Dr. Prabhakar Kaushik is working as Assistant Professor in Mech. Engg. Dept at UIET, MD University, Rohtak, Haryana. He has completed his PhD from NIT, Kurukshetra. His area of interest includes Quality Management techniques, Six Sigma, SQC etc. He has number of publications in International and in national journals.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2]