Critical Parameter Development and Management (CPD&M) is a process that aligns within a product development process, or as a stand-alone post-launch process, to discover and manage parameters that control the functions of any engineered system. A critical parameter is one that carries significant risk during development or post-launch life-cycle management of a product, including the processes that make, package and maintain the product. CPD&M is a form of Systems Engineering and is done collaboratively between a cross-functional team of engineers and their technical support staff.

Initially, CPD&M defines all the parameters of the design, and then only those that pose high risk to the performance of the design -- the critical parameters -- are isolated and improved or controlled. The objective is to manage these critical parameters throughout the product's lifecycle. CPD&M is the basis for creating a Design Guide that explains how and why any engineered system works and to what it is sensitive. CPD&M is the science-based rationale for controlling costs and minimizing the undesirable effects of unwanted variation.

When a parameter is suspected to be critical, it is subjected to a series of measurements to discover how well the parameter is understood. The metrics used to designate a parameter as critical are called The Big 7. They measure seven essential elements of how the parameter is learned about and understood over time based upon physics and statistical analysis. The critical parameters are divided into two parts: the measured inputs, the X variables, which control a design's function; and the measured outputs, the Y variables. Both Ys and Xs are assessed across the Big 7 metrics.

The Big 7 metrics include 1) Measurability of Ys and Xs; 2) Stability of both Y and the controlling Xs over time; 3) Adjustability of Y by specific Xs over desired ranges of performance; 4) Independence, Interactivity & Statistical Significance of Xs; 5) Hyper-sensitivity between Ys and their controlling Xs under nominal conditions; 6) Robustness of Ys to unwanted sources of variation under stressful conditions (leveraging interactivity between X_Controllable *X_Noises); and 7) Capability (Cp & Cpk) under both nominal and stressful conditions.

If all seven metrics cannot be achieved satisfactorily, the parameter officially becomes critical and is carefully managed. The goal is to process the candidate critical design parameters through the Big 7 metrics and thereby improve their performance, understand them as much as possible in the context of the rest of the design and (perhaps) be able to move them off the "critical" list. Furthermore, subjecting the candidate parameters to the Big 7 metrics may also reveal that the design will never work, thus preventing wasting more resources on a doomed design.

CPD&M can be applied proactively during technology and product/process development, or reactively during post-launch production and product/process life-cycle management. CPD&M can be used to back-derive an existing design's governing parameters, isolating the CPs for cost reduction and life-cycle management decisions when making changes or improvements. If the product does not have a CP-enhanced Design Guide, then it is likely that the effect of changes for a given X will be poorly understood, forcing high-risk estimates as to what might happen, thus enabling the "Law of Unintended Consequences".

CPD&M is a powerful method for forensic analysis of potential or actual safety problems to uncover the cause of a catastrophic failure if it is unknown. The method leaves no stone unturned. It is entirely objective, scientific and data-driven. CPD&M is regarded as a strong enabler to engineering credibility.

CPD&M: The Process

The process of CPD&M has 12 steps within 5 phases to develop and document all the parameters, and then identify the critical few that must be controlled as the product or system is developed and transferred into sustained life-cycle management. The following steps guide a post-launch CPD&M project to derive a CP database and produce a Design Guide when it was not done during the development of the product.

Phase

CPD&M Phase Alignment with the Product Development Process

Below are links to each of the prior newsletters with CPD&M Quick Guides: 

The CPD&M Quick Guide TOC (Nov 2013)