The DFE Part of DFX (Design For Environment and eXcellence)

Design for Excellence (DFX) is a concept that includes many initiatives, like design for usability, design for manufacturability and assembly, and design for environment and disassembly. It’s a focus on doing things right, exceeding customer expectations, optimizing what’s needed while minimizing costs, and continuous improvement.

Today we take a deep dive on one of those aspects: design for environment (DFE), including design for disassembly. What are reasons that a business would consider this important, and how does a design engineer fit in?

 

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Results-Driven Decisions, Faster: Accelerated Stress Testing as a Reliability Life Test

We want to ensure our designs perform reliably, as expected and intended. With today’s high-reliability products and quick release to market, we probably don’t have enough time to just test our parts at normal use rates. It would take too long, because our products ARE so reliable.  Or, we’ll miss our window of opportunity to get our product to market.

There are several ways to get reliability data to make design decisions. One of the ways is reliability life testing of our product.

This episode explores how accelerated stress testing is one subset of other reliability life testing methods, when it’s a good idea, how we can approach doing it, and what we can do with the results.

 

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When to use DOE (Design of Experiments)?

What is design of experiments, or DOE? What do we use it for and what is it all about?  We talk about when we might want to use it during the design cycle, and we do this without getting into all of the how-to and mathematical equations.

 

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Design for User Tasks using an Urgent/Important Matrix

We’ve collected all sorts of preliminary information about our users that we’re using for a new product design. We may be faced with so much data we’re not sure where to turn first, or what design feature is a priority. There’s a simple, 2-way matrix we can use to help us sort it all out: an urgent/important matrix. We may have used it to prioritize tasks for ourselves or as a management strategy for our team.  But, we can also use it to evaluate the tasks our users take when using our product.

We talk more about this matrix in the podcast, and we talk through an example of how to use it to evaluate user tasks.

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Statistical vs. Practical Significance

When we’re looking at results (like measures of a characteristic), we need to take care not to get too hung-up on what the statistics is trying to tell us.  Yes, statistical tools are a good way for us to make decisions and the results can act as proof for us. But, there’s a practical, engineering side to results, too. We need to evaluate the statistical significance along with the practical significance.

We review an example and how to document it.

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How Many Do We Need To Test?

In this episode we review sampling for design tests. We talk through a generic thought process for choosing a statistically relevant sample size and propose some basics that we can all learn about to better understand sampling.

Our goal is for us to be able to better talk through a sampling scenario with our quality and reliability engineering friends, and to better prepare for the information that they’re going to want to know when asked, “How many do we need to test?”

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Life Cycle Costing for Product Design Choices

It costs our customers to own our designed products. It costs them initially to purchase it, but it also costs them to use it, maintain it, repair it, and eventually dispose of it. And it costs our company in ways too, like processing, training requirements for customers, and warranty repair costs. 

Life cycle costing can help our team choose between design alternatives, like alternate design options, features, manufacturing methods, or suppliers.

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5 Aspects of Good Reliability Goals and Requirements

Good reliability requirements are going to drive our design decisions relating to the concept, the components, the materials, and other stuff. So, the moment to start defining reliability requirements is early in the design process. But, what makes a well-defined reliability requirement? There are five aspects it should cover: do you know what they are? 

We’ll describe what makes a good reliability requirement and examples of common (but not good) requirements.

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Using Failure Rate Functions to Drive Early Design Decisions

We have good requirements for the reliability of our design. We also have a preliminary design with ideas of how we’re going to manufacture it. Is our design idea good enough? Are there things we should do to improve its performance and reliability?

For a physical product, there are three general stages in its life cycle. In many cases the failure rates of physical products can be represented by a reliability bathtub curve. This curve is really a plot of a hazard rate function, also known as a failure rate function. We talk about data collection in the early design phase, what types of failures are typical for each phase, and design decisions we may make to improve our reliability, based on the failure rate function we plot for our system.

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Types of Design Analyses possible with User Process Flowcharts

Flowcharting isn’t just useful for manufacturing processes. We can use them in lots of ways to help us with design of products and to identify quality characteristics. After all, products are used by people, and the way in which they use them is a process.

• compare ideal vs. actual flowcharts
• identify where there is disagreement about correct sequence or steps
• identify common mistakes/problems at each step to mistake-proof the process and design
• look for holds or delays, find the critical path

We also talk about specific flowchart analyses and how they can be used to analyze the user process for design.

• Cost-of-Poor-Quality
• Critical-to-Quality
• Value-Added Analysis
• Deployment Flowchart

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Design Tolerances Based on Economics (Using the Taguchi Loss Function)

Defining tolerances for our quality characteristics is sometimes not an easy task. If we set tight tolerances, it could be costly to make with a lot of rejects and rework in the future. If we’re too sloppy with our tolerances, then it can affect the functionality of our product, leading to unhappy customers, and also possible rework and scrap. There’s economics involved in setting-up tolerances.

Genichi Taguchi related his measure of quality (variation from the target spec) with economics, called the Taguchi Loss Function. It’s used to calculate the cost (in money) of a certain deviation from a target value. It assumes that the farther our quality characteristic is from our target value, the more costly it is to us.

We talk about how we can use the Taguchi Loss Functions as a way for us to set tolerances for our designs. Scroll lower to get an interactive tool and the equations.

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How Many Controls do we Need to Reduce Risk?

When we’ve identified a risk to our design or user process – and that risk can pose a potential harm – how many controls do we need to add?

We discuss prevention vs. detection controls, ALARP, as low as possible, and some scenarios where we could (and maybe couldn’t) justify a risk as acceptable without adding additional controls.

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Solving Symptoms Instead of Causes?

How we describe and approach the issues we need to solve can affect how we react to them.  We know we’re supposed to be solving for root causes. But are we, instead, really just addressing symptoms? Are we celebrating the quick fix and then moving on without addressing the root of our issue?

“If you define the problem correctly, you almost have the solution.” – Steve Jobs

Recognize the common mishaps of us solving symptoms instead of really getting to the causes. And, clearly describe our problem in two parts (statement and description of facts) to be confident that we’re moving toward solving the causes.

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Do you have SMART ACORN objectives?

Objectives are goalposts of what it is we’re trying to accomplish. Though they’re only a part of planning a project, if we don’t have well-defined and clear objectives, it could lead to us not having the stellar project results we want. Our objective should be a SMART ACORN.  We review these two, complementing acronyms as ways to check that we’re setting up our project for success.

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Why Look to Standards

Standards are everywhere, and lots of organizations are sourcing and creating them. The U.S. Federal Trade Commission held a workshop 2019 that recently made the news, again, in July 2021. It was called “Nixing the Fix: a Workshop on Repair Restrictions”. Here’s what it’s about: manufacturers are not creating products with standard parts, or their design is created so its difficult for consumers to repair.

Are standards part of the answer? How can we proactively use them for design? Why should we?

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