Overview

Design for Six Sigma focuses on new process design principles. It's focus in on fully redesigning or creating new products or processes instead of on improving a current process or makign incremental changes to a product design.

Theory of Inventive Problem Solving (TRIZ)

The Theory of Inventive Problem Solving (TRIZ) is a technique for problem solving that observes commonalities in solutions discovered in the past. It is primarily based on the work of the Russian Genrich Altshuller and is based on a systematic view of the technological world. The many tools and techniques of TRIZ centre around two major ideas: First, that all innovation can be classified (and is described by Altshuller's 40 inventive principles. Second, that innovation fundamentally solves inherent or imposed conflicts.

Taguchi Methods

Taguchi - seek the design parameters to minimize the impact of the noise factors on variation.

• Robust design
• Functional requirements
• Noise factors

Taguchi suggests the following guidelines for robust design:

• Identify the ideal function for the product or process.
• Select quality characteristics that are continuous variables.
• Select characteristics that add quality.
• Quality characteristics should cover all aspects of the ideal function.
• Quality characteristics should be easy to measure.

Taguchi Robustness

Taguchi - seek the design parameters to minimize the impact of the noise factors on variation.

• in Taguchi robustness concepts, signal factors strongly affect the mean response of the process, but are controllable and have little affect on variation in the output response
• Noise factors influence the variation in the output

Taguchi’s suggested guidelines for robust design:

•  Identify the ideal function for the product or process.
•  Select quality characteristics that are continuous variables.
•  Quality characteristics should be easy to measure.

A product or process is controlled by three primary factors: noise (events and parameters not controllable by designer, things like outside temperature), signal (things like a thermostat), and control

The factors that cause variability in product functions are called error factors or noise.

• Factors due to environmental conditions – outer noise (ex: variations in raw materials; mental state of operators)
• Factors due to deterioration – inner noise 
• Factors due to variation among products – inner noise (humidity, dust, vibrations)

To study each factor independently,  the plan consists of two orthogonal arrays – the inner array and the outer array. The inner array consists of control factors, and the outer array consists of noise and signal factors.

Statistical tolerance defines the amount of variance in the process: 

Define-Measure-Analyze-Design-Verify (DMADV) 

A Define-Measure-Analyze-Design-Verify (DMADV) approach is appropriate when a product or process is not in existence and one needs to be developed or when a current product/process exists and has been optimized but still doesn’t meet customer and/or business needs. When using the DMADV methodology, in the final phase you should verify design performance and its ability to meet customer needs. Another version of this is Define, Measure, Analyze, Design, Optimize, and Verify (DMADOV)

BATHTUB CURVE

A bathtub curve is useful for reliability engineering and deterioration modelling and is used to improve maintenance programs and efficiency. The first area of a bathtub curve is generated by mapping the rate of early life failures (sometimes called infant mortality) when the manufacturing process is first introduced. This second segment is generated by mapping the faiures during the products useful life, and the last segment shows the rate of wear out failures adn the product exceeds its design lifetime. The region most impacted by changes in the manufacturing process control is the early life region.

Design for X (DFX)

Describe design constraints, including design for cost, design for manufacturability and producibility, design for test, design for maintainability, etc.

axiomatic design (AD)

Axiomatic design (AD) is a series of activity steps to analyze systematically the transformation of customer needs into functional requirements, design parameters and process variables. AD identifies four domains within design: customer, functional, physical and process.

An axiom is a self-evident truth upon which other knowledge must rest, thus serving as a starting point for deducing other truth

Customer needs serve as the foundation of axiomatic design in six sigma

Entitlement refers to the best performance level for a process, product, service, or transaction.

Design for X (DFX)

Design for cost, design for manufacturability, design for assembly, design for producibility, design for test, design for maintainability/servicability, design for safety

Mean time to failure (MTTF - measure of reliability for nonrepairable), mean time to repair (MTTR), and mean time between failures (MTBF - measure of reliability for repairable) are indicators of a unit’s reliability. The greater the MTTF and MTBF, the less likely a unit is to fail and the higher the reliability. 

DFX toolbox

•  Design for Cost
•  Design for Maintenance
•  Design for Tolerance