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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Getting the Voice of the Customer

Before we can link customer needs to design, production, and service of our products, we need to listen to and understand the voice of the customer.  We review 6 common VOC collection strategies, and talk about their pros and cons. We also discuss an affinity diagram process, which may help our team organize all of the data to get to customer needs.

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The Way We Test Matters

We can look at test methods like a product in and of itself. Because tests also have requirements and need to produce usable results, we validate against those requirements. Validating our test method also ensures that they are precise and accurate.

We talk about things to consider when looking at product tests: tying test methods to the product’s use environment, standards, and cumulative effects of testing.

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Designing Specs for QA

Creating specs for suppliers and producers is generally at the forefront of our thoughts about the activity. But, it’s also important to design for our QA friends, too, for inspection.

We talk about what acceptance sampling is all about. We also step through a thought process for identifying and creating design features for inspection using FMEA.

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Every Failure is a Gift

When designs fail we can take on damaging mindsets while we’re deciding our next steps, and this can lead us to bad decisions. We explore this and give some examples of pitfalls. We also talk about what to do within the design-realm to prepare for and combat those mindsets. Finally, I share my mantra when designing activities get tough with failures.

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Understanding the Purposes behind Kaizen

In the quality world, kaizen is a tool for continuous improvement under the umbrella of a Lean philosophy. The quality-tool kaizen is just one layer of a larger, overarching idea that we benefit from small, incremental improvements made consistently.

Kaizen as a tool involves all employees of the company toward continuous improvement. The way kaizen events are done helps to promote the continuous improvement philosophy throughout the business through its effect on culture, time, proof, and teamwork. We talk more about how this all fits together in the podcast.

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Fishbone Diagram: A Supertool to Understand Problems, Potential Solutions, and Goals

A Fishbone Diagram is named for its looks because it resembles the bones of a fish drawn on paper. Its less creative names are Cause-and-Effect Diagram and Ishikawa Diagram. It’s popularly known to help with root cause analysis. But, we can also use it to help with goals and to evaluate a potential solution.

Why is it a Supertool? Just creating its headings helps us to better define our question. Writing it out as a graphical organizer helps organize jumbled thoughts. And, when paired with a 5W2H approach and the 5-whys, it can help us dig to the root causes.

I’ve included some abbreviated examples of fishbone diagrams; click the thumbnail for a larger version (notice that my root causes follow the 5-whys). And, listen to the podcast (or read the transcript) to learn more about Fishbones and their construction and uses.

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What is ‘Production Equivalent’ and Why Does it Matter?

We’re in the middle of our design process and we’re getting some of the first parts in hand, from prototyping or benchtops or our manufacturing cell. Let’s test them and finish our verification testing! Maybe we shouldn’t.

We talk about the concept of production equivalent: what it means and when it’s important to consider.

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About Visual Quality Standards

“A picture is worth a thousand words” is an old saying, and it holds true! Visual standards, visual aids, and quality standards are a great tool, especially in design when communicating the limits of acceptability. This episode explores areas to capture this type of information and how it can be used not just for Quality Assurance and Production, but also for design verification protocols, FMEA, root cause analysis, and future field defect investigations (to name a few).

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