Although the material selection process is generally a successful one, there are a few pitfalls to avoid. For instance, it is human nature to remain loyal to tried and true methods that worked satisfactorily in the past. But, in today’s fast-paced materials industry, ongoing technology changes have produced new materials that may better address the requirements of a particular application. The challenge is to find a balance between proven materials and innovative but potentially riskier ones. Material suppliers recommend careful, upfront research from information that is readily available from them and online. Suppliers’ R&D departments work at the leading edge of specific material technologies and can provide guidance.

Here is a nut of an electromechanical transport mechanism with lubricant applied. This situation arose when the designer selected a new, inherently lubricated material for the spindle with limited data from the field. Although inherent lubrication is cleaner and avoids problems such as dust adhesion, often the material ends up being noisy and requires topical lubrication. This could have been avoided by selecting a steel spindle with lubricant added.

The photo of a television back cover shows the high-gloss surface of the part coming out of production. The photo shows abrasion and scratches after wiping off dust with a standard cloth. This quality issue occurred because the material is not scratch-resistant. The manufacturing process was not appropriate.

Examples of new materials and processes include non-conductive, decorative foils, and heat-activated foils (HAFs) for mobile phones and handheld devices, and soft-touch lacquering, which accommodates display bezel printing and other features.

Immature technology drawbacks
You may be looking for a new material, but there may not be enough testing documentation readily available to answer all your questions. The new material may work well in a validation environment, for instance, but during mass production when processing windows are narrower, it may exhibit flaws. Take plastics for example. Although they are replacing sheet metal in diverse applications due to its advantages of design freedom, part integration, light weight, and lower cost, it is more difficult to get maximum tolerances under control versus metal. The influence of temperature over time, issues with material flow and brittleness at screw connections, diverse notching effects, and other factors can cause the product to fail in the field. For example, lubricated plastics and coatings can be attractive alternatives to traditional lubricants for wear resistance. However, they can end up producing unwanted noise when highly stressed.

Another example is hot and cold molding which may offer a beautiful and unique surface finish for a competitive advantage. Yet, it may exhibit unacceptable damage from scratching and marring during product testing. The problem may lie in relying on lab test results that offer better consistency than real-world mass production.

In some cases, problems only occur under combinations of processing parameters. Therefore, thousands of parts may be manufactured before the problems become apparent.

If you select a new material, apply risk management principles to evaluate the probability of failure, the severity of the implications of a failure, and how visible a defect will be. If risk is high across all categories, find a replacement material.

This is the top cover of a mobile phone. A display frame is meant to adhere properly to the top cover. In this case, it failed to do so because the processing parameters for the heat-activated foil (HAF) were not fully under control (the top cover was not sufficiently flat as seen here on the right). This quality issue could have been avoided by selecting a standard process and material. The HAF technology was not mature enough for this complex geometry.

However, if the risk appears low, you might wait until the material has undergone a year of full-scale production and field testing. It is best not to accept a new material without an agreement on a validation and testing program. Another prudent measure is to seek the manufacturer’s guarantee of performance while performing independent audits and checks of critical components and parameters.

Global supply issues
In today’s manufacturing arena, products may be designed in one region, manufactured in another, and assembled at a third. This reality has implications for material selection due to variations in climate, particularly temperature and humidity. Sheet metal can be susceptible to environmental conditions. For example, stamped edges can corrode, anti-fingerprint coatings can blur, and laminations can be marred. To avoid such problems, you should include climate and environmental tests in validation plans in your design specifications.

In addition, with the increasing interest in environmentally responsible products, more materials that are recyclable or biodegradable are emerging. Today, many plastics manufacturers offer products that incorporate recycled materials. This trend can complicate the selection process.

Specify the maximum percentage of recycled material to be used when molding a part. This information gives the component manufacturer some latitude in the amount of recycled plastic to use – between none and the maximum allowed.

However, part testing is often based on that maximum value that is assumed to be the weakest. The risk is that parts with lower percentages of recycled plastic may perform differently. Test plans should cover all possible variations in recycled content with particular emphasis on stress loading to reveal any potential design issues.

Sometimes, material selection decisions are based on all the bells and whistles that a supplier may tout about its product. All the while, another more appropriate and not as expensive material may suit your application better. Another risk of selecting the latest and greatest is being limited to a single source of supply, which can drive up costs and potentially result in shortages and delays.

Testing, testing, testing
Depending on where the product will be marketed, different national and international tests may come into play. The material should meet all anticipated tests and standards. Typically, the customer defines the standards based on where the product will be sold. If these are general industry standards, information can be found in the public domain. However, if the application targets a niche market or is a unique product, the customer may need to provide additional specifications.

The use of standard parts is another aspect of testing. All parts ordered from catalogs have tolerances. Do not assume that standard parts from one manufacturer can automatically be substituted for those from another. All possible brands of parts should be tested and validated at the beginning so that substitutions can be made at a later stage.