Autobody Metals and How it Affects Paintless Dent Repair and Pricing
This is rough draft material that I used as a general guide. I will update and clean this material up at some point. Right now my main focus is getting the many videos that I need out.
Autobody Metals and How it Affects Paintless Dent Repair.
What kinds of Metals do you have on your vehicle that affect Paintless Dent Repair.
Terminology utilized to categorize steel products differs significantly across the globe, the metals used on most American cars is the World Auto Steel format. Each grade of steel is recognized by metallurgical type, minimum tensile strength (in MPa), and minimum yield strength (in MPa).
What kinds of Metals do you have on your vehicle that affect Paintless Dent Repair. There are Three Primary Categories
1. Steel
2. Aluminum
3. High Strength Steel
But before we get into that we need to look at four other factors that affect all three of these types of metals.
As it relates to PDR we are looking at metal based upon four primary categories.
1. Tensile Strength
2. Ductility
3. Gauge
4. How Its Formed
1. Tensile Strength which is essentially the measure of force per unit defined at one newton per square meter. This is pounds-force per square inch or PSI, which you might recognize from your tire pressures PSI.We convert this into MPA’s and that’s how we are viewing the metal. At around 550 mpa’s or pascal (PA) and Megapascal (Mpa’s), or a newton per square meter (N/m2) This affects the amount of pressure the technician must use.
2. Ductility and malleability. Ductility is essentially a metals ability to be stretched into a thin wire without becoming weaker or more brittle in the process. It's the metals ability to withstand plastic deformation before rupture.
A. This is absolutely critical when dealing with stretched dents. This is where
B. It deals with how well the metal will take a strike downward with a topdown. We call this malleability.
C. It affects the temperature at which the metal should be repaired at: The ductile–brittle transition temperature DBTT. If a metal is cooled below this temperature it increases it chance to shatter instead of bending or deforming in the way that we need it to.
“In metallic bonds valence shell electrons are delocalized and shared between many atoms. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.”
3. The Gauge of the metal. 18-22. The larger the number with auto body sheet metal is thiner with the lower number is thicker. Older cars from the 50-60’s used 18 guage and more modern cars use 20-22. However, there are certain places on a vehicle where thicker gauges are used, depending on the year, make and model.
4. How Formed
Hot Rolled Steel vs Cold Rolled Steel affects our ability to push it. Hot rolled is far more denser and much harder to push with a lower ductility rating and cold rolled is far easier to manipulate, irregardless of the same exact metal and gauge thickness. There are many other’s but these are the two most common methods that we can physically and visually see a difference in when pushing.
Note: Bonding: How these various metals bond with paint affects our limitations and our limitations.
Ok, now lets get into the types of metals.
1. Steel: This is typically cheaper to work because of its great ductility regardless depending on Gauge. We typically charge more for thicker gauges but for the most part these prices are relatively similar.
A. It is an Iron Alloy
B. Almost all Iron by weight but has small amounts of carbon and other materials in it. At the atomic level, the additional elements change the way the material behaves in dramatic fashion. The way the carbon is managed during the production of steel is also key to its properties.
2. Aluminum: Aluminum typically costs between 20-50% more depending on the gauge and how it was formed.
Aluminum is less ductile than steel. Furthermore, thicker gauges compound this problem further by producing uneven or what I like to call the “black eye pea” affect when trying to push it as a technician. Many technicians are confused by this at first, because some Aluminum seems to be easy to work with while others are far more difficult. Its not the aluminum itself, its the gauge thickness that really creates the problem.
3. High strength steel. Usually costs 50-100% more.
One way to think of high-strength steel is to think of it as low-carbon steel. In conventional steel, the carbon content is about 1.4%. In high-strength steel it is about 1/6th that amount. Typically this is going to also be thicker in gauge which makes pushing it far more difficult. For example this bedside on a GMC Dooley is HHS and its gauge thickness is 18 on the flair. Regardless of that, simply understanding its Tinsel Strength, Ductility, and Gauge helped me determine if and how to deal with that category.
3. How Formed
Hot Rolled Steel vs Cold Rolled Steel affects our ability to push it. Hot rolled is far more denser and much harder to push with a lower ductility rating and cold rolled is far easier to manipulate, irregardless of the same exact metal and gauge thickness. This is why there is so much variety between similarly gauged and types, when manipulating it. Without realizing why it, many experienced techs have simply mastered all of these across a wide spectrum of vehicles.
If you would like to learn more than you ever want to know on this subject refer them to the book.
There is an entire body of work that im not covering here with several subcategories within this but its the general and only what’s related to Paintless Dent Repair.