U.S. soldiers carry loads of equipment and protective gear that can weigh anywhere from 45 to 130 pounds. This is more than enough to quickly tire even the most well-conditioned personnel, contributing to reduced mobility and impaired decision-making that could result in casualties.

Meanwhile, in the skies there has been a proliferation of unmanned aircraft and remotely controlled jet fliers. These aircraft need to travel long distances with limited fuel on board and need materials that make them “invisible” to enemy radar.

To meet the challenges of evolving – often dangerous – circumstances, and to leverage advancing technologies that provide equipment to help the military operate safer, manufacturers need to deliver products that are lighter, stronger and highly functional while simultaneously reducing the total cost of ownership (TCO) associated with their products, including design, production, delivery and maintenance.

Injection-molded plastic parts made from advanced materials are increasingly replacing metal in a variety of military applications, providing a practical solution that accommodates the needs of manufacturers, contractors and users.

Metals vs. Plastics

Metals going back to the Iron Age have been the materials of choice for equipping the military. Metals offer lower thermal expansion and high strength to survive the rugged conditions of combat.

Many metals also offer high electrical conductivity, making them ideal for shielding electronic equipment; others offer high thermal conductivity, so they are well-suited to applications requiring the rapid dissipation of heat, such as engine cooling. Finally, metal parts can be produced to very tight tolerances, though the secondary machining operations required in achieving that precision could be costly.

Today, plastics are replacing metals in military applications due to a growing number of advantages, including the following:

An automated workcell where post-molding operations are performed on a heavy vehicle pneumatic valve body.

Lower Weight

Plastics are much lighter than metals, making them a better choice for a wide variety of uses, from armor and clothing to equipment, protective gear and vehicles. Not only does plastic significantly reduce equipment carry weights – by as much as 20 pounds in some military situations – it increases vertical and horizontal user agility and safety in accord with the U.S. Department of Defense Joint War Fighting Science and Technology Plan.

Freedom of Design and Assembly

Plastics are subject to fewer assembly constraints, enabling manufacturers to consolidate multiple parts into a single, injection-molded plastic part. The ability to design plastic parts with complex geometries also means multiple parts can be assembled using the method best suited to a particular application – such as welding, heat staking or mechanical snap-fit.

Superior Durability

Today's sophisticated plastics are extremely durable and outperform comparable metals in resistance to heat, chemicals, moisture and impact. (See “Choosing the Best Plastic” and “Additives for Options” sections, below, for discussion about the characteristics of the major plastics families and how complementary materials can be added to further improve strength and durability.)

Ease of Finish

The color of equipment used in the field or in the air can be an important element of its utility – from a matte finish that decreases glare to a camouflage pattern that enables stealth. With plastics, manufacturers and molders can create virtually any color or finish during the production process and eliminate the need for expensive secondary painting or coating operations otherwise required by metal parts. Moreover, the finish color on plastics will not wear off from rugged wear.

Designers are taking body armor beyond Kevlar through the use of additives that include plastic and non-plastic materials.

Total Cost of Ownership

Taken together, the lower weight, design, assembly, durability and finishing advantages of injection-molded plastic parts result in dramatically lower total costs. Compared with metal, plastic parts do not require expensive secondary operations, such as machining or painting. In addition, because plastic parts can be designed in much more complex shapes, the manufacturer can reduce the total number of parts produced by as much as 70%.

Similarly, the weight savings created by transitioning to plastic reduces overall fuel and transportation costs. In the case of the military, this is essential since it is the world's single largest consumer of oil at more than 340,000 barrels per day, and the U.S. Department of Defense is requiring its contractors to help improve fuel efficiency.

As explained in a recent blog from Sandvik Coromant, a Sweden-based global tool supplier to the metal cutting industry:

In the modern age, the aerospace industry is also looking ahead to tougher, lighter, and more heat-resistant materials that would lessen emissions, cut fuel costs, and enable higher speeds. So far, in the aviation industry, composites have been the go-to material.

Per Dr. Eleanor Merson, the company's composite research specialist, “Thirty years ago, five to six percent of an aircraft was made up of composites; now, a plane is made up of about 50% composite material.”

Enhanced Stealth

Remaining undetected gives fighting forces an upper hand, but traditional metal components leave large electromagnetic radar/sonar echo signatures and infrared heat source footprints. A variety of non-conducting and insulating resins have been introduced to increase the stealth capabilities for military applications, including:

  • Domes constructed from polymer matrix composites that shield detection equipment and deaden position-revealing vibration on military ships and aircraft.

  • Military helicopters outfitted with polymer foam blades and Kevlar-car-bon fiber structural materials to enhance multi-spectral stealth capabilities (radar, infrared and acoustic).

  • Flexible, polymer matrix-based coatings used on a number of military vehicles to thwart “normal” and “thermal” visual detection.

Keys to Conversion

There are several considerations that impact successful metal-to-plastic conversion:

This chart contains an overview of popular plastics for military applications.