How automotive foams impact vehicle design

What you'll learn:

• The different types of automotive foams and how to identify them
• Repair/replacement cautions and considerations
• Why it is important to calculate the volume of foam used in a "blind" cavity

I cautiously used the word “impact” in the subtitle. We hear that word a lot in our industry. It's used mostly to describe why cars and trucks end up in our shops. Typically, there has been an “impact” of one kind or another resulting in the need for our services, whether it be with a shopping cart, a stationary object or another vehicle. The most important aspect of the word “impact” would be that of how a repair will result in a subsequent impact. That should be our focus; too many times we focus on the “impact” of efficiency and profitability, but at the end of the day, how we repair vehicles could have the most “impact” on occupant safety. The use of foam, in various forms, is on the rise. We will dive into the role these can have on crashworthiness later, but it relates to the widespread use of thinner metal used in today's vehicles. And it’s that aspect that may very well change the role foams play during a collision.

It may seem a bit out of place to speak on occupant safety and repairing vehicles correctly after a collision when referring to automotive foams, but I feel this is an area that has not received enough attention as of late. There should be no surprise that this technology has developed along with just about every other aspect of automotive design. We will cover the types of foams, as well as where and how they are used. Some content may be a refresher for some, but all will benefit from coverage of newer technology. I will also cite some examples of repair/replacement considerations when dealing with foams. It's worth noting that typically, the foams used in automotive design are that of a closed-cell structure, unlike those in the home segment. Obviously, no home improvement-type foams should be used in the repair of vehicles. There are several types of foams we deal with daily when working with vehicles. There are the formed rigid “blocks,” such as the ones used for bumper absorbers that are located in various places throughout modern vehicles, such as doors and other inner panels. It is common to find a preformed foam block inside of a fender to help with wind/noise coming in toward the front door edge. Some foams are more of a soft variety. found inside fenders and other cavities, such as an inside quarter panel. These softer foams may even be housed in plastic bags. Those types of foams are pretty cut-and-dry when it comes to replacement. It's generally accepted to replace all of the aforementioned foams, when they are damaged, in the absence of repair procedures. It's usually more economic to replace a bumper absorber or similar preformed foam than to even attempt a repair. Hence the reason most manufacturers don't even publish repair guidelines. We won't cover those types of foams, as replacement is pretty self-explanatory.

Structural foam

An often misunderstood or misidentified type of foam is structural foam. These foams are not replaceable in the field. They are the foams typically already installed in replacement parts and are often misidentified as an adhesive. A structural foam may be sandwiched between multiple layers of metal used in a replacement frame rail or that of a pillar assembly, as an example. They may come in other forms on replacement parts as well. It's important to note here that these foams are not to be removed prior to installation. They are designed to perform a function and are not available in the aftermarket. This is why they are supplied with the new part and should be included in the replacement process as intended.

Heat-activated foam

Another type, heat-activated foam, is installed on carriers, typically plastic, that have heat-activated foam on them. During the vehicle's initial construction phase, the carriers are installed, and the foam is activated during the refinish bake cycle. As we don't achieve similar conditions in the aftermarket, most manufacturers will have a procedure for making repairs to this type of foam. An excerpt from a repair information provider shows an example for a 2014 Audi A7 Quattro is given below:

Replacement expanded foam inserts expand only after reaching 356°F (180° C). Because of this, filler foam is used for repairs.

Use filler foam (D 506 KD1 A3) for these repairs.

Since this temperature is not reached under workshop conditions, proceed as follows:

Remove excess foam from vehicle.

Reproduce the paint structure: if necessary, paint twice (wet on wet) using glass/paint primer (D 009 200 02) - minimum air drying time 10 minutes.

Precondition

Before these steps, body panel to be replaced must be prepared for installation, for example, cut, fitted, corrosion protection measures.

Replacing Molded Foam Part

Secure molded foam part on vehicle.

Apply the foam filler onto the replacement part.

Secure new part by gently press new part in foam area until it makes contact and then welding in.

The foam hardens within 25 minutes.

Do not gas-shield weld within 15 mm of foam

After painting vehicle, seal cavities in the area of the repair.

Most manufacturers have information on where and what types of foams are used in the vehicle. As virtually all the foams used today are not found in plain sight, it's imperative that the information is gathered prior to repairs beginning on the vehicle. Whether you write a repair plan or estimate, research is the key to success here. I hope it's as important to you as the construction materials, general guidelines for welding, and all other aspects of information gathering initially.

Clearing up some misconceptions

Let's first clear up some misconceptions. These categories are sometimes misunderstood because of labeling and/or changes in the products used from days past. The first topic is to explain NVH and foams. We'll tackle NVH first. NVH is an abbreviation for noise, vibration, and harshness. NVH can be used to refer to all types of foams used in a vehicle by the manufacturer, or it may be used to label a specific type of replaceable two-part foam.

The replacement foams that come in the two-part liquid form are typically one of two types, flexible or rigid. In summary, we have many types of foams we see and replace in today's vehicles: NVH type products, rigid and flexible foams, structural, and preformed foams.

NVH-type products are used to help control what they are named for: noise, vibration, and harshness. NVH foams are included in the flexible category. These materials are typically used between panels and braces. They can be used between parts such as roof panels and intrusion beams and may help control flutter on today's thinner outer sheet metal panels. An example of a typical product used in these areas is 3M’s NVH Dampening Material, PN04274. It can be used in filling small gaps where other, more dense types of foams may not be able to flow. In some instances, it can also be used to repair cut or damaged foams.

Flexible and rigid types of foams are also in more widespread use in today's vehicles. Just as with NVH type of products, they both serve functions inherent in their design. Flexible foams can move somewhat, allowing for consistent performance as the panel or whole vehicle flexes throughout its motion. Rigid foams are just that. They are rigid for a purpose. Some rigid foams play a role not only in the design of the vehicle for sound and panel rigidity but possibly in an impact. There's that “impact” word we started with. This is a very important point that is worth repeating. All the foams we have discussed this far may very well play a role in comfort, but more importantly, they may aid in the design as it relates to a subsequent collision.

As of late, vehicle manufacturers are doing a better job of providing guidelines and procedures. I separated those two areas for a reason. Please remember that “procedures” for a part/panel replacement may focus on just that task. It is as important to follow the manufacturer’s “general guidelines” or “basics” of repair.

Another consideration when it comes to automotive foams is their flammability during a welding process. For those reasons, a manufacturer may call out removal and replacement procedures. Listed below is an example. Again, the excerpt from a repair information provider found outside of a specific part/panel replacement procedure explains some of the caution and methods of dealing with their PUR foam. It's regarding a 2019 Chrysler Pacifica. The guidelines are as follows, but edited to be brief and highlight some scenarios:

PolyURethane (PUR) foam, is used in certain locations of the vehicle for Noise Vibration Harshness (NVH) purposes and structural strengthening. The PUR foam creates a hazard in the repair process as it can be flammable. Damage location and extensiveness will vary in the repairs to be performed. Therefore, it is necessary for the technician to determine if the location of the foam will create a hazard and remove it as necessary.

The locations of PUR foam, used throughout the vehicle, can be found in the Sound Deadener Locations (Refer to 31 - Collision Information/Locations/Sound Deadener Locations).

PUR foam removal options:

1. When the components to be replaced are removed from the vehicle
2. Through openings in the adjacent components

NOTE:

Only use the following options when the first two options are not possible.

Gain access by performing one of the following procedures.

Determine which procedure will work best in the situation, either the Window Access Procedure or Hole Access Procedure

Window Access Procedure

1. Remove or protect components and the surrounding areas from sparks and welding spatter as necessary.
2. With the use of a cut-off wheel, cut a “U” shaped access point (1) in the area of the PUR foam location.
3. Carefully, pry open the window to gain access to the PUR foam (2).
4. With the use of a flat bladed tool (1) or equivalent, remove the foam from the cavity.
5. Close the window back into the original position.
6. Close the access hole by either welding or alternatively with a structural adhesive patch.

Weld

The above excerpt reinforces the need for removal prior to any flammable scenarios being performed. It's important to point out these procedures can be found via a link within a specific procedure or may be listed within a category on their own. They may also be listed within the “construction material” group. The point is they are typically separate from a specific panel or part procedure and may apply even if only repairs are being made to the part/panel. Focusing on the foams that a technician will have to replace via a typical two-part system, there are several considerations to be made. Knowing how much foam to use in a “blind” cavity is critical. The volume will need to be calculated before installing the foam after a panel replacement/repair. The volume can be calculated by determining the length, width, and height. The calculation may be an estimate of course, but once the volume is known and the expansion rate is determined a calculation of material needed may be determined. Another consideration may be that of damming the area so that the foam is only expanded into the desired area. There may be several recommendations for methods to accomplish this. Prior solutions involved using balloons or plastic carriers, and other methods may be employed.

Technical Data Sheets (TDS) can also help guide the technician in the proper placement and usage. Pay close attention to what are the suitable substrates. It is unlikely any products out there will do well on bare metal or self-etching primer; a properly primed or painted surface is typically the best option. When using the popular two-part products in the market today, it's imperative to use the correct tip for that particular product. This is true for any of the two-part products in use today. Just because the tips may be able to interchange where they attach, it doesn't mean the mixing design is compatible. To be safe always read and follow the product manufacturer's guidelines, just as we do with the vehicles we repair.

There are a variety of considerations to cover when determining the proper repair/replacement of today's automotive foams. The first step is that of location and type, prior to beginning the repair process. Once that has been determined, the correct repair/replacement plan is developed and employed when necessary. As I preach often, “if the repair starts wrong, it's usually “wrong” all the way through.” My hope is that armed with this information, you will be able to make a positive “impact” when it comes to dealing with automotive foams in your shop!