Auto Body Frame Basics


I had finally got an answer from the Auto Body Repair College on where to find the test information for the license exemption. I need to visit my ministry representative to get the information I need, I will be doing that this week and will know exactly what I need to study. Until then I just ran through some of the basics, it’s a little dull but I thought I’d write out some of what I’ve been brushing up on.
Recently I’ve been just reviewing the basics and going over some modern vehicle construction principles. I’ve been looking at drive line configurations, vehicle styles, frame styles..etc
So starting with frame styles the most common would be the “unibody” platform which incorporates in the entire vehicle structure. Typically it would consist of two front and rear rails that weld into the body, the rails take up majority of the impact in a front or rear collision. The other main platform is “body on frame” , this is not very common on passenger vehicles anymore but was before unibody came about. It is still fairly common on larger suv and pickup trucks.
There are many different types of metals used, high strengths, aluminum…etc which will be talked about more in the repair portions. It\’s also worth noting there are many new configurations on the horizon as well as in the developmental stages such as a composite unibody frames and currently used space frames which incorporates a composite wrapped around the metal. Other unibody hybrids exist where the front and rear use a bolt up frame into a unibody.
Having a better look at the main platform (unibody), it was designed based off an aircraft and uses an “egg shell” design. The passenger compartment was designed disperse collision energy along the rest of the vehicle. A unibody utilizes crush zones in the front and rear that are made to be weaker and collapse in a collision to reduce the impact to the passenger compartment. Torque boxes are also used along the sides to crush and absorb energy in a twisting or crushing action. A unibody is also made up of various cross members that add to the structure of the vehicle. One downside to unibody is they require extra sound deadening measures as the body will amplify vibrations more.
Looking at a “body over frame” design the frame is a completely separate part of the vehicle, attaching with bolts. This design uses rubber isolators to reduce the drivetrain and suspension noises / vibrations so the sound deadening requirements aren’t as great compared to a unibody. A “body on frame” design would typically make for a stronger vehicle, however with that comes greater weight. They allow vehicles to be made with stonger towing capacities, smoother rides and allow greater energy to be absorbed in a collision through the frame. They both have there pro’s and con’s.

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