Automotive Subassembly Engineers Face A Multitude Of Challenges

It used to be that automotive companies took ownership for all aspects of the finished vehicles. Scores of engineers worked on the improvements and innovation that put American automotive companies at the top of the industry for decades. In today’s market, however, automotive companies have evolved into professional assemblers. Automotive companies have passed the burden of design, performance, longevity, aesthetics, warranty, and most importantly, cost reductions, to their suppliers, and the suppliers in turn have passed much of this burden to their suppliers. The resulting shakeout has created some interesting dynamics for engineers, as they are weighed down with having to engineer sub-assembled products (such as specialty o-rings) which may or may not be in their specialty. Rubber and plastics often come into play in these circumstances, as both rubber and plastics are somewhat unique in the broad field of industrial engineering.

The first consideration for engineers in this predicament is to qualify the physical demands of the application, for instance of automobile or aircraft o rings in a given program.

Automotive engineering is generally more complex than most industrial engineering, as there are so many physical, environmental, and longevity considerations, as well as numerous constraints. If the sub-assembled unit goes under the hood, for example, vibration, heat, cold, exposure to hydrocarbon oils or fuel must be considered. Since auto o rings as well as other rubber and plastics are normally used to control the flow of fluids or gasses, they must be engineered to seal out any foreign media. ASTM standards for tensile strength, elongation, heat aging, compression set, and media exposure have to be kept in line with performance requirements. There are several established specifications for rubber and plastic materials, depending on the OEM, and most will establish the specification and provide a drawing only. The required dimensions and associated tolerances of specialty rubber o-rings, for example, will also have an impact on material choice, as the processing method and tooling considerations can vary widely based on the material. It is then up to the project engineer for the sub- assembler to choose and qualify a material to meet this criterion.

The next step is to narrow down the material choices based on the physical demands of the application. Qualifying the physical requirements of the application will normally limit the field of materials. If the application demands high temperature resistance as well as resistance to hydrocarbon oils, for example, the only realistic choices are FKM or FS rubber. If the application demands high temperature resistance without hydrocarbon resistance, then silicone rubber will normally be suitable. If the temperature does not exceed 240°F or so, then NBR or HNBR may be used, and thermoplastic materials may come into play. Once material choices have been filtered down and qualified against required specifications, the picture becomes much more finite. For additional information on automotive and mechanical engineering topics, please visit http://www.real-seal.com/ to learn more.

Important Things Come In Small Packages: Engineered Thermoplastic Components

Polyurethane is generally the material of choice to create longevity in products due to its resistance to abrasion and performance in harsh environments. Components used in specialty seals and other sealing systems that were traditionally metallic in nature have largely been replaced with thermoplastic materials that offer greater resilience, improved frictional properties, improved resistance to wear, weathering and oxidation, and overall improved aesthetics.

Rubber has its own unique array of available materials and associated properties, and can be produced in almost any conceivable configuration, including bonding to metal components and various application-specific seal systems. Rubber materials possess some physical properties that are superior to many plastics, and can provide several advantages, including compression set resistance, thermal conductivity, and resistance to fluid swell.

High performance o-rings are arguably one of the simplest yet most engineered, precise, and useful seal designs ever developed. Though tiny compared to other machine components, o-rings are one of the most common and important elements of machine design. They are available in various metric and inch standard sizes. Sizes are specified by the inside diameter and the cross section diameter (thickness).

In the United States the most common standard inch sizes are per SAE AS568B specification (i.e. AS568-214). ISO 3601-1:2008 contains the most commonly used standard sizes, both inch and metric, worldwide. The UK also has standards sizes known as BS sizes, typically ranging from BS001 to BS932. Several other size specifications also exist.

Successful o-ring joint design depends on rigid mechanical mounting that applies a predictable deformation to the o-ring. This introduces a calculated mechanical stress at the o-ring contacting surfaces. As long as the pressure of the fluid being contained does not exceed the contact stress of the rubber o-rings San Diego experts explain, leaking cannot occur. Fortunately, the pressure of the contained fluid transfers through the essentially incompressible o-ring material, and the contact stress rises with increasing pressure. For this reason, an o-ring can easily seal high pressure as long as it does not fail mechanically. The most common failure is extrusion through the mating parts.

Seals are designed to have a point contact between the o-ring and sealing faces. This allows a high local stress, able to contain high pressure, without exceeding the yield stress of the o-ring body. The flexible nature of o-ring materials accommodates imperfections in the mounting parts. But it is still important to maintain good surface finish of those mating parts, especially at low temperatures where the seal rubber reaches its glass transition temperature and becomes increasingly crystalline. Surface finish is also especially important in dynamic applications. A surface finish that is too rough will abrade the surface of the o-ring, and a surface that is too smooth will not allow the seal to be adequately lubricated by a fluid film. For additional information about sealing systems and machine components, please visit http://www.real-seal.com/ to learn more.