Six Sigma and SPC

Recent trends and developments in the use of Six-sigma as a SPC tool for lean manufacture and improving customer satisfaction.

Six Sigma has been described as “a highly technical method using by engineers and staticians to fine-product and processes” Cavanagah, R.R. and others (2000) or “it’s a goal of near perfection in meeting customer’s requirements” Both parts are right in some aspects, more and more in the statistics bit. Six Sigma is an statisctic target. In companies where Six Sigma has been pursued and achieved, like General Electric or Motorola they agree that Six Sigma is more a change of culture.

Six Sigma is based in two interconnected factors: “total customer satisfaction and effective and efficient internal process”. The success of a company depends on the ability of satisfying customer’s quickly changing needs and how well the internal work is managed for coping with this changing demand. The ability of a succesful company for changing is not given by quick or risky decissions. It starts with the identification of the company’s key processes and manages them for being under control. Six Sigma is only a method to gain competitive advantage. Lowenthal, J.(1958)

The Voice of the Customer is very important in the Six Sigma methodology. The voice of the process is the second area of interest. Six Sigma companies must listen to both voices. The one that speaks from outside the company, and he one that speaks for the company and for the product, the process. Only by listenting both, changes can be made to the process that satisfies the customer demands. Lowenthal, J.(1958)

The fusion of Six Sigma an Lean Manufacturing is necessay because:

  • Lean itself can not bring a process under statistical control.
  • Six Sigma can not make a process faster or reduce it’s cost.

That’s why quality problems manifest themselves as scrap, waste or “muda”. A small amout of this waste can reduce the productivity of a factory a lot. The principle of Lean Six Sigma says: “The activities that cause the customer’s Critical to Quality issues and create the longest Time Delays in any process offer the greatest opportunity for improving in Cost, Quality, and Lead time”. Lean Six Sigma pretends to improve quality and customer satisfaction by reducing lack time, cost and a rapid response to the changing customer’s needs. George, L.M. (2002)

Statistical Process Control is based in the adquisition and analysis of data. Decisions are taken based in these data analysis. But the implementation of Six Sigma goes further. Is also accepted that many decissions inside companies are based in opinions and assumptions. Six Sigma reduces this random and unclear decissions by presenting two questions:

  1. What data do I really need?
  2. What do I do/analize/use this data for obtaining maximum benefit?

• Using DMAIC.

DMAIC is a structured problem-solving methodology widely used in business. The letters are an acronym for the five phases of Six Sigma improvement: Define-Measure-Analyze-Improve-Control. This strategy encourages creative thinking and aproves ideas like keeping the basic products, process and services.

  • Define- Define the team, and reach an agreement on the scoop, goals and boundaries
  • Measure-Understand and collect data from the process, speed, quality, costs. This information will be used to expose causes of problems.
  • Analyze- Here is where DMAIC comes to statistics, in this phase, the key inputs and outputs of the process have to be monitorised (The critical Xs). And perform data analysis.
  • Improve- Generate potential solutions. Prioritise and implement them, applying Six Sigma lean manufacturing best practises.
  • Control- Document standard procedures and set process control plans that permit maintain the gains

George. L et al (2005)

Using DFSS

“Is all about improving the peformance of your organization by using a structured approach for minimizing the mistakes and waste in all process” After the success of Motorola, Honeywell and GE, Six Sigma is the most popular process improving philosophy. Dr Shewart invented control charts in the early 20s and dr. Deming the Plan-Do-Check-Act problem solving strategy soon after WWII. Six Sigma concepts are invented since nearly a century. So what is new? DFSS (Design For Six Sigma) prevents future problems from appear, while DMAIC solves current problems. DFSS guarantees good products even when the key process changes. DFSS focuses in the design and development of new products and processes by selecting Critical to Quality characteristics (CTQ’s). Champions, Black Belts and Green Belts are the spine of this strategy.

Roadmap PIDOV:

  • Plan: Develope goals and metrics. Specify stakeholders and risks.
  • Identify: Identify the product concept that best satisfies the VOC.
  • Design: Design the new product and process. In this step statistics are vital to predict future performance
  • Optimize: Achieve balance between quality and cost
  • Validate: Verify the preditions from early phases and the customer requirements

Sleeper, A. (2006)

The inmediate goal of Six Sigma is the reduction in number of defect, and provide the necessary control tools to drive the process under control. Reduced defects lead to product improvement, and product improvement provides customer satisfaction. Defect reduction is intended to lead to cost reduction. It has a process focus, and aims to highlight process improvement oportunities under continuous measurements.

Some arguments agains Six Sigma is that quality needs to be created, not just monitored. That stays in line with Taguchi philosophy “quality has to be embuilt in the product, not inspected into it” Stamatis (2000)

Some companies such as Clarke American have decided not to go for the Six Sigma way. They intend to have better quality improvement systems oriented in the customer satisfactin and the employers involvement. Raisinghani, M.S. (2005)

Merck, the US pharmaceuticals company is using six sigma in redefining the R&D, finance and marketing departments. His chief executive, Dick Clark says in an interview for Financial Times on March 2006: “We got Six Sigma and black belts now working in marketing and sales…We’re finding out we can be a heck of a lot more effective than we ever were before. And so we can do a lot more with less”


  • George, L. M. (2002) Lean Six Sigma. Mc Graw Hill. Dallas, U.S.A.
  • George L. et al (2005) The Lean Six Sigma pocket toolbox. Mc Graw Hill
  • Lowenthal, J.(1958) Six Sigma Project Management, a pocket guide. ASQ Quality Press, Milwaukee. U.S.A.
  • Raisinghani, M.S. (2005) Six Sigma, concept, tools and applications in Industrial Management and Data Systems. Vol 105, nº4. Emerald Group, Texas, U.S.A.
  • Sleeper, A. (2006) Design for Six Sigma Statistics. Mc Graw Hill.

Comments are closed.

%d bloggers like this: