Six Sigma is a management methodology used to help businesses improve, current processes, products or services by discovering and eliminating defects. The goal is to streamline quality control in manufacturing or business processes so there is little to no variance throughout.
It was trademarked by Motorola in 1993, but Six Sigma references the Greek letter sigma, which is a statistical symbol that represents a standard deviation. Motorola used the term because a Six Sigma process is expected to be defect-free 99.999666 percent of the time — can allow for 3.4 defective features for every million opportunities. Motorola initially set this goal for their own manufacturing operations, but it quickly became a buzzword and widely adopted standard for all.
Six Sigma is specifically designed to help large organizations with a quality management system. In 1998, Jack Welch, CEO of GE, started helped thrust Six Sigma into the limelight by donating upwards of $1 million as a thank you to the company, recognizing how Six Sigma positively impacted GE’s operations and promoting the process for large organizations. After then, Fortune 500 companies followed suit and Six Sigma has been popular with large organizations ever since.
Suggested Read: Quality assurance in six sigma
Six Sigma principles
The goal in any Six Sigma project is very specific to identify and eliminate any defects that are causing variations in quality by defining a sequence of steps around a certain target. The most common examples you’ll find use the targets “smaller is better, larger is better or nominal is best.”
- Smaller is Better creates an “upper specification limit,” such as having a target of zero for defects or rejected parts.
- Large is Better involves a “lower specification limit,” such as test scores — where the target is 100 percent.
- Nominal is Best looks at the middle ground — a customer service rep needs to spend enough time on the phone to troubleshoot a problem, but not so long that they lose productivity.
The process aims to bring data and statistics into the mesh to help objectively identify errors and defects that will impact quality. It’s designed to fit a variety of business goals, allowing organizations to define objectives around specific industry needs.
Six Sigma methodologies
In practice, Six Sigma mainly follow one of two sub-methodologies: DMAIC and DMADV:
Six Sigma DMAIC
The Six Sigma DMAIC project methodology includes five phases, each represented as a letter in the DMAIC acronym. These include:
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- Define the problem, the customer, the project requirements and the ultimate goals and expectations of the customer.
- Measure the performance of the current process by establishing a data collection plan to determine defects and gather metrics.
- Analysis of the process to establish the root cause of variations and defects to identify issues with the current strategy that stand in the way of the end goal.
- Improve the process by eliminating the root causes of defects through innovative solutions.
- Control the new process to avoid falling into old habits and to ensure it stays on track.
Six Sigma DMADV
The Six Sigma DMADV, also known as the Design For Six Sigma (DFSS), includes five stages:
- Define realistic goals that suit the customer’s requirements or business strategy.
- Measure and identify the customer’s critical to quality (CTQ) requirements and translate them into clear achievable project goals.
- Analyze multiple options and alternatives for the customer along with the estimated total life cycle of the project.
- Design the process at a high level before moving onto a more detailed version that will become the prototype to identify errors and make modifications.
- Verify that the final iteration of the product or process is approved by all customers and clients — whether internal or external.
DMAIC vs. DMADV
These methodologies seem similar but they have different use cases. The DMAIC methodology is designed for existing process or products that aren’t meeting customers’ needs or performing to standards. When a business needs to develop a product or process that doesn’t already exist or when a product has been optimized but still falls short, that’s when you want to use DMADV.
Also read: Principles of six sigma process
Determining a Six Sigma project
To find projects in any organization that would benefit from Six Sigma they need to fit some criteria:
- Each project needs to have a clear process of inputs and outputs.
- Don’t go into the project with a pre-determined solution — that means you already know the fix.
- Focus on reducing operation of variation to make it easier for untrained operators.
- Project needs to be approached with knowledge of variations in process inputs and how to control and eliminate defects.
Six Sigma offers the example of a slow cycle time at Station 30 due to defective parts coming from Station 20. A non-Six Sigma solution would attempt to rebalance the assembly line while re-doing the work, keeping cycle time low and not spending on labor.