One hundred years ago, vehicles were built without consideration for noise, vibration, and harshness (NVH) control, or occupant protection. These vehicles were designed for function alone, which was primarily to transport people and goods from one place to another. As vehicles evolved through the years, they were built with more attention to creature comforts and accommodated the passengers by increasing occupant crash protection and reducing NVH.

Figure 1. Though a two-part material, dispensed sound dampening material resembles windshield urethane.

Figure 2. Flexible foam is compressible, unlike rigid- type foam.

Figure 3. With no cell structure, structural foam is a material with virtually no expansion.

Though many different techniques and materials have been used over the years, foams seem to be the latest innovation used throughout the vehicle for the ultimate benefit of the occupants. Foam materials used during vehicle repairs are typically two-part materials that can change in state and shape after they are dispensed. Along with the introduction of two-part foam materials came the need for technicians to learn how to determine the required foam quantity, and to develop the ability to hold the material at specific locations on the vehicle.

NVH foam categories

Some of the first foam materials were used for NVH control. NVH foam materials are currently broken into four categories: sound-dampening material, flexible, rigid-type, and structural. Rigid-type foam is also broken into three sub-categories.

Sound-dampening material is an NVH foam used for covering or sealing small openings that are easily accessible, and for reattaching existing foam. This is a two-part product that is black, heavy bodied, and non-expanding, much like windshield urethane or seam sealer when compared to common two-part expanding NVH foam (see Figure 1).

Another NVH material is flexible foam. Flexible foam is soft, compressible, and re-turns to its original shape without retaining permanent deformation (see Figure 2).

Rigid-type foam is the NVH material that currently has three sub-categories. These sub-categories include rigid, semi-rigid, and pillar foam. Each material has distinct characteristics as an NVH control product. Rigid foam reacts differently than flexible foam when compressed. Rigid materials have a much lower compression rate when a force is applied and may remain permanently deformed when the force is removed. The main difference between rigid and semi-rigid is the strength of the material. Pillar foams are typically rigid foams with unique foam times and flow rates. This allows them to be used in situations where foam placement is difficult.

The latest material introduced to the foam family is referred to as structural foam. Structural foam is used for stiffening parts of a vehicle chassis/body and for increasing occupant protection in the event of a collision (see Figure 3).

Foam replacement considerations

Along with identifying the material originally used in the vehicle, there are other considerations that affect installing replacement foam. These include determining the amount of material to be installed, how to get the material to a specific location, and how to get the foam to adhere in a specific location. Expansion rate, viscosity, and foam time are among the variables that must be considered.

The expansion rate of a foam product is typically given as a maximum amount. Products may have expansion rates listed as "up to ten times." The actual expansion rate of the foam may change based on many variables, some of which technicians can control. To determine how much material should be installed in a part, the volume of the void to be filled should be calculated. After determining the volume of the void, and matching that to the approximate expansion rate of the material being used, the proper amount of two-part foam can be determined.

Knowing the viscosity and foam time of different foams can be helpful when determining how to place the foam in specific areas. Sometimes, due to location and access, it is difficult to hold foam in specific areas. When this is the case, dams can be used. Depending on where the dam is to be placed, it can be installed either before or after parts are assembled. There are many different acceptable materials that can be used as dams. The most important consideration for using a dam is determining its ability to retain moisture. Do not use materials that have the ability to retain moisture.

New I-CAR program

To learn more about working with automotive foams, I-CAR has a new program coming soon. Look for Automotive Foams (FOM01) being offered in your area in the near future. Some key information contained in this program includes:

• OEM-used materials.

• identifying OEM and replacement materials.