All entries for November 2013

November 30, 2013

Steps of drawing SPC

As I mentioned on my previous post, SPC is the one of the important tools for monitoring the system behaviour. SPC can be seen as a six sigma tool; however, the people can use it without any 6 sigma knowledge as well.

Okay , let’s come to draw a SPC chart.

Assume that we work on the quality department and we take regularly 2 samples for checking the dimensions of the products. And we do this observation 3 times: at 11am, 3pm, and 6.30pm in a typical working day (Totally we can say that we measure 6 products a day). Moreover, customer told us that the parts suppose to be (150,00mm- 151,00mm) in those dimensions. Okay I am going to create my own measurement chart step by step.


I wrote the every sample which is collected from production. Firstly I wrote down the difference between highest number and the lowest in the same day. And then I calculated the average of difference by adding whole ranges of days and then dividing to 6. And it is 1,035(Range_bar). X_bar means that average of samples which are collected in same day. After I calculated X_bar, I can reach X_bar_bar easily which is average of average of samples.

Finally, the Upper Control Limit equals to X_bar_bar+ (0,483*Range_bar). And Lower control limit equals to X_bar_bar – (0,483*Range_bar).

[0,483 is a constant and can be founded on almost every tables.] My n is 6, so it is 0,483



I drew my own SPC chart according to assumed values. Actually we can use this tool for almost every application on the industry. As you can see Brown line was our “upper control limit” and green one is “lower control limit”. And Blue demonstrates the system behaviour.

As you can see from the graph the system behaviour stays in the limit; however, the limits are not capable of customer tolerances which is 150,00-151,00, even though the flow is stable.

On the next post, I am going to calculate capabilities!

Important Note: Before reduce the common variations in the system, system or application should be removed from any special causes.

November 23, 2013

Why does industry need 6σ?

Six sigma was developed by Motorola engineers in 1980s. Motorola saved more than $ 16 billion as a result of six sigma effort. So how did Motorola save that much money? And what is the aim of the six sigma? Before Process Improvement using 6 sigma (PIUSS) lectures started completely, I always thought like that this 6 sigma methodology must be a miracle. The exact aim of the six sigma is reducing the defect levels by eliminating the variances in the system. By reducing the defects level on the production, we use Statistical Process Chart (SPC) in order to monitor the volume of production. Before we start to reduce common variances in the production, the system must be stable which means that there has to be no special cause. Special causes can be emerged by either passing the upper /lower control limits or stays on the almost same level for 8 measurements. After we understand special causes on the system and solve them by using cause and effect diagram (fish bone method), we are ready to investigate the common variances that affect system behaviour. We need at least 20 points for drawing a real SPC. I will talk about SPC more on the next post!

Industry needs 6 sigma, because it reduces defects by decreasing the variances. Moreover, the most important point on the six sigma ideology is that industry does not reduce its number of defected parts by producing more products (they do not affect to overproduction) and spending more money. On the contrary, 6 sigma helps company saves money by reducing the some types of wastes (defect, inventory, motion, etc). Actually six sigma creates by According to six sigma levels, if a typical industry reaches 6 sigma levels; it means that they can run maximum 3.4 defected parts into in a million! It sounds like a dream! For instance, one of the significant users of 6 sigma methodology in industry is General Electric. GE announced that they saved around $ 350 million in 1998. A Fortunearticle stated that “of 58 large companies that have announced Six Sigma programs, 91 percent have trailed the S&P 500since”.

By the way, I am really interested in 6 sigma methodology and I think that I will apply green belt to PMI in order to gain more knowledge about it.

November 20, 2013

CBE reflection

Although I have some brief knowledge about excellence pathway for industry implications, it was an interesting and informative module. After Paul and Chris Hakes explained how organisations should achieve excellence rank, it attracted my attention more and the class presentations and games foster me to learn more. And I finally focus more on continuous improvements which seem like difficult but are very essential for being sustainable and having quality management. Also I agree with Paul’s idea that hierarchy in the organisation from the lowest rank worker to executives should be changed!! But how? And then we decide to implement it reversely in order to create collaboration environment in business instead of competition; therefore, each rank must be ask and help its one lower rank in terms of knowledge and experience sharing. On the other hand, one of other significant points is building learning organisations which are open-minded to learn more and more and keep its mistakes in mind. All in all, CBE is going to form the foundation of this master degree and other modules are going to be give richness.

November 2013

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