Podcast Episode 8: Design for Manufacturability

In this episode I discuss Design for Manufacturability related to component fabrication and joining components by welding, brazing, or soldering. Design for manufacturing is concerned with designing components and assemblies that can be repeatedly produced with consistent good quality without hassles, and at low-cost.

DFM applies to primary component fabrication processes, secondary processing (coating, heat treating), and joining. Primary component fabrication processes include casting, extruding, stamping and other cold forming, forging, and machining. Secondary processes include heat treating, machining, and coating by painting, electroplating, anodizing and other processes. And joining includes welding, brazing, soldering, and using adhesives.

Here's a link to the episode. The episode is about 10 minutes long.

Subscribe to the Metal Conversations podcast series on Spotify, Google Podcasts, Apple Podcasts, Amazon Music, Pocket Casts, Overcast, Castbox, and Stitcher.

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Failure Mode and Mechanism

In a previous article I discussed the degradation of materials due to exposure to stressors (use conditions) and how to identify stressors. Cracks form and grow in axles and shafts due to cyclic stress, steel screws corrode when exposed to water, some plastics become brittle when exposed to sunlight, and coatings on surfaces can wear away. When too much degradation occurs, components and joints fail, leading to product failure.

Things to consider during design

If you’re someone who likes to design reliable products, you must think about the stressors and their effects. When designing a product, we must identify the following things

• The stressors that will be acting on the components and joints
• Potential degradation mechanisms
• The amount of degradation that is acceptable
• Whether the degradation will lead to component or joint failure
• The failure mode

This information guides decisions about the mechanical form and materials to use components and joints, the control measures to put in place to ensure that components and joints are fabricated properly, and testing to evaluate product reliability.

I already discussed stressors in a previous article. Two important terms in this list are failure mode and failure mechanism. Understanding their difference and keeping them straight is important.

Attend our January 26 workshop to learn how to prevent galvanic corrosion. CLICK HERE for information

Failure mechanism

Failure mechanism is the physical process of materials degradation that leads to failure. Here are some examples of failure mechanisms:

• Cracking of a support member exposed to cyclic stress from vibration
• Intergranular corrosion of 304 stainless steel pipe exposed to water
• Crevice corrosion of a bolt and washer exposed to water and road salt
• Fretting wear of a circuit board pad and contact during thermal cycling
• Adhesive wear of two rollers moving against each other

Circuit board wear

Intergranular corrosion

These are just a few of the many different degradation and failure mechanisms. Notice that for corrosion and wear there is more than one degradation mechanism. So, saying that a component will fail by corrosion or wear is not specific enough to understand the actual mechanism and make design decisions to prevent the degradation.

Failure mode

Failure mode is how a component or joint stops functioning. So, for the previous examples we have the following failure modes:

• Fracture
• Leak
• Loss of clamping force
• High electrical resistance
• Change in surface profile

Identifying stressors, failure mode, and failure mechanism

A valuable engineering tool used to identify the information is Failure Modes and Effects Analysis (FMEA). The tool helps focus engineering teams on the factors that influence their products’ reliability and how to address the factors through design decisions, specifications and other control measures, and testing to evaluate reliability.

Using FMEA requires discipline because the process can seem arduous, though it’s really just boring. However, the benefits are tremendous when the efforts result in products that pass reliability testing the first time and field failures don’t occur.

Learn about one common failure mechanism. Attend the January 26 workshop to learn about galvanic corrosion and how to design to prevent it.

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New workshop series

People like simple guidelines and rules to follow when making decisions, especially when there are unpleasant consequences for uniformed decisions. This is especially true for designing the components and joints for a product.

Many product failures due to the degradation of materials are avoidable by using well-known approaches when selecting the form (size, shape, features) and materials for components and joint. It's also helpful to understand the degradation mechanisms to help put the rules in context.

There are many degradation mechanisms and each has several rules to follow and approaches to use to prevent them from occurring. Learning about all of them can seem overwhelming.

But, it's not necessary to be an expert. Though, it is necessary to be informed about the basics of the degradation mechanisms (why and how) and the rules and approaches to avoid failures. There's no way around it. Some investment is required. Picking up bits and pieces of information (correct and incorrect) as you go along is not a recipe for success.

So, we're putting together a new workshop series geared to design engineers to teach about the many degradation mechanisms and the rules and approaches to avoid failures.

Because we want to make it easy for people to learn and get the benefits, each workshop will be:

• Focused on a single, specific degradation mechanism such as galvanic corrosion, adhesive wear, or hydrogen embrittlement. So, no worries about being overwhelmed.
• 45 minutes long: 30 minute presentation + 15 minutes for attendee questions.
• Available on video for 14 days.
• Accompanied by slide handouts.
• Once a month.
• Taught by an expert

Use the sign-up form above to receive email notices about these workshops.

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Presentation: What is Accelerated Life Testing?

Accelerated life testing. Sounds simple … right? We simply test faster! Great! But what does this get us?

Many organizations are faced with a dilemma when it comes to testing to measure reliability. If we test an amazing new product in ‘at use’ conditions, it might take many years before it will fail. This is time we simply don’t have when it comes to product development.

So how do we test faster? One obvious answer is to increase the stress. Turn the temperature up. Increase the vibration. Use more voltage. But how do we get this right? How can we know that (for example) one week of accelerated testing is equivalent to 10 years of actual use?

This presentation will introduce you to Accelerated Life Testing or ALT to help you and your organization make reliability testing a reality.

January 24, 2023, at 8 am US Pacific time.

Presenter: Chris Jackson from Acuitas Reliability

REGISTER HERE to attend this virtual presentation. There's no fee to attend.

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Presentation - Stressors and reliability

The materials in a product's components and joints can degrade due to exposure to use conditions - steel screws corrode when exposed to water, some plastics become brittle when exposed to sunlight, and coatings on surfaces can wear away.

If their materials degrade too much, components and joints will stop functioning as required . This is a problem if it leads to reduction or loss of product performance before the end of a product’s expected life. Identifying the conditions to which materials are exposed and selecting materials that can withstand the exposure is critical for designing products that have good reliability.

A few weeks ago, I gave a presentation through Accendo Reliability about stressors and the materials degradation they can cause. I discussed stressors that act on components and joints, material degradation mechanisms, five sources of stressors, and evaluating the effects of stressors.

The presentation recording is at this link. Viewing the presentation requires the Accendo free membership login

The audio version of the presentation is at this link.

Need help selecting materials that won't degrade during use and that will give your components and joints the reliability needed for your products? Contact us. in**@im*****.com, 847.528.3467, or complete this form.

Original post here: Presentation - Stressors and reliability

Fatigue

Fatigue is a common degradation and failure mechanism. It involves localized, permanent damage to metals exposed to cyclic stress. The stress can be uniaxial, bending, or torsional resulting from a variety of sources including an applied force, vibration, acceleration and deceleration, and differences in thermal expansion between mating components exposed to heating and cooling cycles. Localized means the damage is confined to a portion of a component or joint.

The reason fatigue is sometimes unexpected is because the nominal stress acting on a component or joint is less than its yield strength. However, at a fatigue crack initiation site, the stress is greater than the nominal stress due to the presence of a stress concentration. More on this later.

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Three requirements

There are three requirements for fatigue to occur:

• Cyclic stress
• The stress must be tensile
• The local stress must exceed the metal’s yield strength

Three stages

Fracture due to fatigue consists of three stages:

• Stage 1: Crack initiation. Microcracks less than 0.001 mm long form as the material cycles between the upper and lower stress. As the cycling continues the microcracks grow and coalesce, forming one or more larger cracks. 
• Stage 2: Crack growth. The larger cracks grow into the material. As the cracks grow the nominal stress on the uncracked portion of the metal increases.
• Stage 3: Finally, when a critical amount of the cross section has cracked, the remaining uncracked material cannot bear the load and fractures by overload.

Fracture surface

This is a diagram of a fracture surface where a crack started by fatigue. The crack started at the component’s surface. Once the crack formed it grew with each successive stress cycle. Finally, the crack grew so large that the uncracked material could not support the load, and it cracked during a single stress cycle.

In many cases, beachmarks are present on the fracture surface that can be seen visually or with a low-power microscope. Beachmarks start at the crack origin and expand in the direction of crack growth and are helpful for identifying the crack origin.

This scanning electron image shows the fracture surface of an aluminum component. The striations are a result of the fatigue crack growing with each stress cycle. Each striation formed during a stress cycle, thus indicating the amount the crack grew with each stress cycle. Not all fatigue failures have striations on the fracture surface.

Stress concentrations

Fatigue damage occurs even though the nominal stress on a metal is less than its yield strength. Stress concentrations cause an increase of the stress, resulting in a localized stress that exceeds the yield strength of the material. Stress concentrations include notches, identification markings, and metal defects (non-metallic inclusions, voids, laps).

It is possible for a fatigue crack to form in a metal with a smooth surface and no apparent stress concentrations. However, more cycles are required to initiate a crack in such a metal compared to the same metal with an apparent stress concentration.

Interested in learning metallurgy principles? Check out our Principles of Metallurgy online course.

Factors that influence fatigue life

The fatigue life of a component or joint is often expressed as the number of cycles to failure, which is equal to the sum of the number of cycles to initiate a crack and the number of cycles for the crack to grow to failure. In some cases, failure is when a crack grows to a pre-determined length, at which point the component or sub-assembly is removed from service. In other cases, failure is when a component or joint fails, and the failure is often unexpected.

Several design, material, and fabrication factors influence component and joint fatigue life, including the following:

• Mechanical design features that are stress concentrators
• Alloy strength
• Non-metallic inclusions and manufacturing defects
• Surface residual stress
• Surface roughness
• Metal fracture toughness

These factors and approaches to improve fatigue resistance will be discussed in more detail in future articles.

Need help designing a component that will be exposed to fatigue condition or figuring out the cause of a fatigue failure? Contact us info@imetllc.com, 847.528.3467, or complete this form.

This article was originally published on the Accendo Reliability website https://accendoreliability.com/fatigue/

Original post here: Fatigue

Podcast Episode 7: Failure Analysis

In this episode I discuss failure analysis of component and joint failures during product testing or use and manufacturing problems such as supplier quality problems and manufacturing output that doesn't meet specifications. 

Failure analysis is part of performing a root cause analysis to identify the action, event, or decision that led to a failure or manufacturing problem. The information from a root cause analysis is used to either fix a problem - in the case of product design and manufacturing - or assign blame - in the case of an insurance claim or litigation.

The discussion includes the steps of a failure analysis, how a metallurgists works with other engineers on a failure analysis and root cause analysis, examples of failure analyses (including one where it was raining in someone's living room), and the analyses performed.

Here's a link to the episode. The episode is about 20 minutes long.

You can subscribe to the Metal Conversations podcast series on Spotify, Google Podcasts, Apple Podcasts, Amazon Music, Pocket Casts, Overcast, Castbox, and Stitcher.

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