Lightweight Product Design

An Introduction to the How and Why

     Last year, I was invited to speak at a corporate “roundtable” on the subject of lightweighting.  Though the host’s unfavorable terms compelled me to decline, I do not dismiss the topic as insignificant or unimportant.  To the contrary, it is important enough to address here.  For everyone.  For free.
     Lightweight design is increasingly critical to the success of many products.  The aerospace and automotive industries are commonly-cited practitioners, but lightweighting is equally important to manufacturers of a wide variety of products.  Running shoes, health monitors, smart watches (probably dumb ones, too), various tools, and bicycles all become more appealing to consumers when weight is reduced.  Any product that is worn or carried for a significant time or distance, lifted or manipulated frequently, is shipped in large quantities, or is self-propelled is a good candidate for lightweighting.

     There are three key factors that drive manufacturers to employ lightweighting techniques in their product design process:

1. Resource use in manufacture
2. Energy use in service
3. End-of-life concerns.

 
     Resource use in manufacture includes the materials, energy, and labor consumed in production.  Material usage is the most obvious concern for manufacturers; it is purchased by the pound, after all.  Energy and labor consumption accumulate in more subtle ways.  More massive products require more massive equipment to process, lift, and transfer them.  Powerful machines are expensive to acquire and to operate.  Massive items also require more time and care in movements than their more svelte counterparts.
     Distribution costs are also lowered by reducing the weight of products.  Shipping rates are based on both weight and volume; reducing either increases a shipper’s efficiency and decreases the manufacturer’s cost.  Lower manufacturing cost can be leveraged to increase market share or profit margin.
 
     Products are often evaluated and compared on the basis of energy use in service.  Automobiles and home appliances prominently display the results of energy consumption tests.  While the weight of a dishwasher will have less impact on its appetite for energy than other factors – pump, motor, and heater efficiencies, for example – it is paramount to the performance of an automobile or aircraft.
     Consumption of fossil fuels gets the most press, but consumption of “alternative” energy also needs to be monitored and regulated carefully.  The source of energy consumed by a product may not play a significant role in customers’ satisfaction with its performance.  Electric vehicles and mobile devices can be charged from a variety of sources, but battery life expectations are unlikely to change.  In this context, lightweighting can be achieved by installing batteries with higher specific energy.
     The energy consumed by a product may also be generated by its user.  Use of many consumer goods, such as those mentioned in the opening paragraph, create a burden that the user must bear.  Reducing the burden created by a consumer product is a matter of comfort and convenience; in other applications, it may be far more critical.  Soldiers carry an ever-larger complement of gear into battle.  Additional weight in their packs causes them to become slower-moving, less agile, and more quickly fatigued; lightweight design for military applications can increase the probability of successful missions with fewer casualties.
 
     Some regulatory regimes require manufacturers to recover the products they have sold when they are no longer serviceable.  Currently, this type of requirement is most common in the electronics industry, but expansion to other industries would not be shocking.  Recycling of any number of materials may become the responsibility of manufacturers.  Recovery, recyclability, and environmental impact are typical end-of-life concerns.  The less material that is included in a product, the less that has to be processed upon its retirement.

A Simple Methodology
     Exhibit 1 presents a flowchart of a lightweighting process.  This could be called a “pure” lightweighting process, as it does not explicitly account for other factors that may need to be balanced to achieve an optimal solution.  Military applications are the most likely of those discussed to apply pure lightweighting; a premium price may be justified by the severity of operating conditions or criticality to mission success.  Disaster recovery, firefighting, or other emergency equipment may also warrant a pure lightweighting process.

Some assumptions are inherent to the process described:

• It is conducted by experienced designers and engineers capable of visualizing a design concept appropriate to the application and setting a realistic mass target.
• Those engaged in this process possess sufficient familiarity with the properties of various material classes to identify appropriate candidates for analysis.
• The types of analysis required are understood by the engineers involved.  These may include stress, thermal, vibration, or other analyses.
• How the “best” design alternative will be chosen has been established prior to launching the lightweighting initiative.

These assumptions are necessary to maintain a manageable level of complexity in the diagram and corresponding discussion.
     Dashed lines in the flowchart indicate paths that may or may not be necessary.  A thorough process will traverse these feedback loops at least once, though they are included as optional paths; an optimal solution is unlikely without utilizing them.  Lightweighting processes may be conceived in various ways; this is merely one alternative, simplified to facilitate internalization by new practitioners.

     Perhaps more common than pure lightweighting projects are those that require special attention to specific tradeoffs.  Space-limited lightweighting, as shown in Exhibit 2, is employed when mass reduction is constrained by the envelope within which the structure must fit.  The structure may be required to fit inside a defined space, or outside of it.  While it is a small modification to the “pure” lightweighting process, it provides an important reminder that both mass and volume targets often must be met in a successful design.

     Another modification to the pure lightweighting process is shown in Exhibit 3.  Perhaps the most common, cost-limited lightweighting ensures that a product remains viable in the market it is intended to serve.  A unique feature of this process is the option to estimate cost prior to, or concurrently with, structural analysis.  The impact of manufacturing process selection on a product’s total cost requires that it be evaluated earlier than in the previous processes.  Earlier review of manufacturing processes and associated costs could prevent significant analysis effort from being squandered on rejected designs.

     The flowcharts provided serve as reminders that design projects are iterative; several characteristic combinations may require evaluation before a clear “favorite” can be identified.  Design projects also include the evaluation of tradeoffs among these characteristics.  Cost, volume, and mass may need to be optimized, as discussed here.  Other factors may also be in conflict, such as material availability, process expertise, corrosion resistance, conductivity, chemical compatibility, or myriad others.  It is not practical to attempt to consider here even a fraction of the possible combinations of factors that may require analysis; design projects are diverse and unique.  The small set of process variations discussed represent near-universal scenarios and provide readers with the insight necessary to extrapolate to other situations they may encounter.  Greater detail on material choices, design methodologies, and other resources can be found in the references cited below.
 
     If you would like additional assistance with a lightweighting project, feel free to contact JayWink Solutions for guidance.  If you would like a presentation on this, or any other topic, at a corporate roundtable, panel discussion, or other function, please offer terms that are respectful of independent professionals.
 
References
[Link] “Lightweighting in Aerospace Component and System Design.” Tech Briefs, March 2019.
[Link] “Pros & Cons of Advanced Lightweighting Materials.” Tech Briefs, March 2018.
[Link] Lightweighting World
[Link] “The Road to Lightweighting: The Tech & Materials Leading the Way.”  IndustryWeek, December 10, 2018.
[Link] “Lightweighting.”  AutoForm Engineering GmbH.
[Link] NIST Center for Automotive Lightweighting
 
Jody W. Phelps, MSc, PMP®, MBA
Principal Consultant
JayWink Solutions, LLC
jody@jaywink.com