Introduction

SPS07-STMAN1-E INTRODUCTION

Topic A. Obligations To The Customer Throughout the damage analysis and repair process, And Liability the repairer and insurer must communicate with each other and the customer. They must be in agreement with each other and the customer on how repairs will be performed. The customer must be informed of any changes in the repair plan from the original repair agreement and explain the changes and why they have to be made.

The Collision Repair Industry has an obligation to correctly repair the customer’s vehicle. Collision repairs must be performed using:

 recommended or tested procedures from vehicle makers, I‑CAR, and other research and testing organizations. To reduce liability, make sure that all repairs are  quality replacement parts and materials. performed thoroughly and correctly. Perform the  repair processes and parts as written and agreed repairs as listed in the damage report and have upon in the repair order. documentation of required repairs available for customers. Be sure of the proper procedures. If items on the repair agreement are not consistent Technicians are considered the experts and are with the repair order, it can be considered fraud. expected be knowledgeable on how to perform a quality repair. Performing proper collision repairs requires using parts and procedures that keep remaining warranties Liability insurance that covers the repair facility may intact. Collision repairs must restore: not always cover all damages. For example, the policy may not cover faulty repairs, leaving liability  safety. responsibility completely on the facility. A shop  structural integrity. owner may find that repair facility liability coverage  durability. may not cover the full amount awarded in a  performance. lawsuit. The shop owner would have to pay the  fit. difference.  finish.

© 2007–2012 Inter-Industry Conference On Auto Collision Repair 2 It is difficult to reduce the risk of liability exposure. Keeping thorough records includes more than The part that the repairer can control is the chance recording the date, mileage, and pre-existing damage. of being found at fault. Chances can be minimized Record keeping also includes: by using recommended or tested procedures from the vehicle makers, I‑CAR, or other research and  making sure all notes are legible. testing organizations. It is also important to use  verifying the repairs that were made or not quality replacement parts and materials that restore made. fit, finish, durability, and perform at least as well  having the customer sign a waiver for repairs as the original. Lastly, keep thorough records that that they do not want performed. Repairers document the repair process. must determine their liability on not repairing safety systems such as restraint and anti-lock brake systems.  keeping computer printouts or worksheets on file showing wheel alignment readings or vehicle dimensions before and after repairs.  keeping scan tool printouts and records of computer codes for airbag, anti-lock brake, emission, and powertrain control module (PCM) systems.  attaching the OEM procedure printout to the vehicle repair order.  keeping receipts for all sublet work performed.

® IMPORTANT NOTICE

This material provides general directions for collision damage repair using tested, effective procedures. Follow- ing them will help assure the reliability of the repair.

I-CAR cannot accept responsibility for any individual repair, nor can it warrant to the quality of such repair. Anyone who departs from the instructions in this program must first establish that neither personal safety nor the integrity of the repair of the vehicle is compromised by the choice of methods, tools, or supplies.

I-CAR does not endorse or recommend any brands or makes of vehicles, repair equipment and supplies or other products. The appearance of various makes and brand names in any I-CAR material is purely coincidental and is based on the availability of those products at the time of production.

All recommendations presented in this program are based upon research programs or upon tests conducted by laboratories, manufacturers, or selected collision repair facilities. If performed as outlined, these recommendations will provide the basis for a thorough, professional repair.

Module 1–Steel Strength And Unitized Structures Repair...... 4 A. Vehicle Features And Functions...... 4 B. Steel Strength...... 8 C. Mechanical Properties Of Steel...... 16 D. Heat Affects On Steel...... 20 E. Identifying Steel Types...... 21 F. Metallurgical Designation...... 23 G. Review...... 32 Module 2–New Construction Processes...... 33 Topic A. Front Structures...... 33 Topic B. Laminated Steel...... 34 Topic C. Tailored Blanks...... 38 Topic D. Hydroformed Parts...... 41 Topic E. Multiple Layer Construction...... 42 Topic F. Foams...... 46 Topic G. Weld Bonding...... 49 Topic H. MIG Brazing...... 50 Topic I. Summary...... 51

Topic A. Vehicle Features And Functions

A-3 New unitized structures are designed to maximize occupant protection during collisions.

A-2 Like most new vehicles, this late model Mercedes Benz CLK sedan is loaded with safety and convenience features that add weight to the Passive safety for unitized structures includes: vehicle. n controlling collision energy forces for optimized New vehicles have many features and functions that occupant protection. This is done by designing the vehicles of just a decade or less ago did not. This the structure to optimize both collision energy includes: absorption and collision energy transfer characteristics. n additional electronics, including an increasing n maintaining the integrity of the passenger com- number of computers and the wiring associated partment in collisions. This is critical to limit with them. intrusion injuries to the vehicle occupants. The n increased noise, vibration, and harshness (NVH) passenger compartment is the strongest portion control. of the vehicle. n increased collision energy management. The structures of late model vehicles have been designed with collision energy management and occupant protection as one of the primary goals. n additional restraints and other safety systems for increased occupant protection in collisions.

All of these added features and functions add weight to the vehicle.

Side

Side Dodge Caliber

A-4 The deformation of this front frame rail is an example of how unitized A-5 These illustrations show how collision energy is transferred through structures absorb collision energy during collisions. the structure of a vehicle during a collision.

Collision energy absorption: Collision energy transfer: n is achieved through deformation of parts of the n characteristics are incorporated into the struc- structure. As a part deforms or crushes, energy is ture through build geometry and increased part dissipated. This energy absorption through part strength. deformation is designed into the structure by n helps to disperse energy around the passenger including collapse or crush zones in the part. As compartment and other critical areas of the parts crush and energy is absorbed the decelera- vehicle. tion rate of the vehicle is also slowed down. This n occurs in the stronger portions of the frame rails, helps in controlling g-forces experienced by the closer to the passenger compartment, and in the vehicles occupants. pillars and roof rails. n occurs mostly in the front or rear section of the vehicle, though other areas of the vehicle may aide in the process to a lesser extent. Part deformation in the center section of the vehicle is limited to help maintain the shape of the passenger compartment and limit intrusion injuries to vehicle occupants.

A-6 This offset-front crash test was done to analyze the collision energy A-7 The center section of the B-pillar on this vehicle maintained its shape management of the vehicles during a common frontal collision. during a side collision, helping to avoid intrusion injuries to the vehicle occupants. Collision energy management during frontal colli- Collision energy management during side-impact sions: collisions: n includes the front portions of the long front frame n includes very limited part movement and crush. rails crushing to absorb collision energy and Because of the limited space between the side of slow the rate of vehicle deceleration. The space the vehicle and the passengers, the pillars have between the passenger compartment and the to be very strong and have minimal deflection in front of the vehicle is where the majority of part the center portions. B-pillars on newer vehicles deformation and energy absorption is designed are designed to maintain their shape in the center to take place in a frontal collision. and deflect in very small amounts at the top and n requires the stronger portions of the vehicle bottom where they connect to the rocker panels structure close to, and including the passenger and roof structure. compartment, to maintain their shape and transfer n is mostly done through energy transfer. The side the collision energy throughout the entire vehicle pillars transfer energy into the strong rocker structure through the rocker panel, roof rails, panels, floor reinforcements, and roof structure pillars, and floor pan. The passenger compart- where it is dispersed throughout the passenger ment is designed to maintain its size and shape. compartment and absorbed in softer parts of the Damage may radiate into weaker parts of the structure. Collision energy is also dissipated by the core structure that do not allow a reduction of vehicle sliding sideways on the road surface. area inside the passenger compartment.

A-9 This Dodge Caliber uses high-strength and ultra-high-strength steel, as well as new construction methods to maximize passenger safety and Ford Mustang comfort while controlling vehicle weight.

A-8 During a rear collision, the rear portion of this vehicle deformed significantly behind the passenger compartment to absorb collision How are newer steel unitized vehicles designed to energy. provide maximum occupant protection and comfort while dealing with the increased weight these Collision energy management during rear-impact features add? collisions: n includes the long, rear frame rails and body structure behind the passenger compartment crushing to absorb collision energy. n requires the stronger portion of the structure close to the passenger compartment to maintain its shape and transfer collision energy throughout the structure and around the passenger compartment and fuel tank.

Rear structures tend to be made of lower strength steels when compared to front structures and will typically collapse more as a result. Crossmembers and reinforcements near the fuel tank and passenger compartment use higher strength steel to resist collapse and transfer energy to portions of the structure away from passengers and the fuel tank.

B-2 This tensile test machine is used to determine the ultimate tensile strength of metal samples. Buick Enclave

B-1 The inner B-pillar on this Buick Enclave uses ultra-high-strength steel reinforcements to provide maximum strength without adding consider- Steel types can be classified by the: able weight to the vehicle. n strength of the steel. Steel strength may be listed In recent years, new steel types have been designed as tensile strength, yield strength, or both. that allow: n mechanical properties of the steel. The mechanical properties include those things that determine n parts to be made stronger without the addition the workability of the metal. of reinforcements. n metallurgical designation or name of the steel. n parts to be made thinner and lighter, but still have The metallurgical designation is determined by the same strength. the build process and alloy of the steel. n for added control of collision energy management. Mechanical properties of new steels allow the collision energy management of a part to be fine-tuned for added energy absorption and transfer as needed.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 8 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Low-Strength Ultra-High-Strength 70 Steels High-Strength Steels (> 700 MPa) (< 270 MPa) Steels 60

50 IF

IF-HS 40 MILD IS 30 BH TRIP 20 CMn HSLA DP-CP 10 MART Total Elongation (%) Total 0 0 200 500 800 1100 1400 1700

Tensile Strength (MPa)

B-3 This chart shows different types of automotive steels and the basic strength categories that they fall into.

Steel strength classifications for vehicles include: n mild steel. Mild steel is typically any steel that has B-5 A molten steel mixture is being poured from one vessel to another less than 270 MPa tensile strength and 210 MPa during the steel making process. yield strength. Increasing the strength of steel can be done by: n high-strength steel (HSS). HSS typically has a tensile strength between 270 and 700 MPa and n altering the manufacturing process. The amount a yield strength between 210–550 MPa. and rate of heating and cooling of the steel, and n ultra-high-strength steel (UHSS), which has a ten- the pressures used as it is manufactured can have sile strength over 700 MPa and a yield strength a drastic effect on the strength of the finished over 550 MPa. steel. n alloying of the steel. The percentage of carbon 70

60 mixed into the iron that steel is made from is AHSS one of the main contributing factors to its final 50 IF 40 IF-HS strength. Other metals are also added in small MILD IS 30 amounts to alter the properties and strength of BH TRIP 20 CMn the steel. HSLA DP-CP 10 MART Total Elongation (%) Total 0 0 200 500 800 1100 1400 1700

Tensile Strength (MPa)

B-4 This chart highlights the steels that may be called advanced high- strength steel (AHSS).

Newer types of high-strength steel, especially those in the upper strength ranges, may be called advanced high-strength steel (AHSS).

800 (Austenite) Body Centered (9 Atoms) 700

600 Pearlite

500 Baninite Baninite 400 Temperature (C) Temperature 300 Martensite

200 Martensite B-6 This illustration shows the basic body-centered cubic structure of 100 ferrite phase or mild steels. 0 0.1 1 10 102 103 104 10 5 Time (Seconds) Ferrite phase steels are typically considered mild steels and: B-7 This temperature-to-time graph shows how the cooling rate affects the final phase and composition of steel. n have a body-centered cubic crystal structure. The spaces between the iron atoms in a body- Austenite phase steels are stronger than ferrite phase steels and are: centered cubic crystal structure are too small to hold carbon atoms. n made by heating the steel above 727oC (1,340oF) n have a very small percentage of dissolved carbon where more carbon atoms dissolve in the iron in the iron base. atoms of the structure. The amount of carbon that n are the softest and most basic of the steel struc- remains dissolved in the iron is affected by rate tures. of heating and cooling, as the carbon falls out of the solution as it cools. The faster the steel is cooled, the more carbon atoms that will remain suspended with the iron atoms. n a face-centered cubic crystal structure. The spaces between the iron atoms in a face-centered cubic crystal structure are just large enough to hold the carbon atoms.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 10 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Series Alloy % Carbon Steels Face Centered 10xx Plain Carbon 11xx Resulfurized (14 Atoms) 12xx Resulfurized And Rephosphorized Manganese Steels 13xx Mn 1.75 Nickel Steels 23xx Ni 3.5 25xx Ni 5.0 Nickel Chromium Steels 31xx Ni 1.25 Cr 0.65-0.80 32xx Ni 1.75 Cr 1.07 33xx Ni 3.50 Cr 1.50-1.57 34xx Ni 3.00 Cr 0.77 Chromium Molybdenum Steels 41xx Cr 0.50-0.95 Mo 0.12-0.30 B-8 This illustration shows the basic face-centered cubic structure of Nickel Chromium Molybdenum Steels martensite phase steel. 43xx Ni 1.82 Cr 0.50-0.80 Mo 0.25 47xx Ni 1.05 Cr 0.45 Mo 0.20-0.35 86xx Ni 0.55 Cr 0.50 Mo 0.20 Nickel Molybdenum Steels Martensite phase steels are stronger than austenite 46xx Ni 0.85-1.82 Mo 0.20 48xx Ni 3.50 Mo 0.25 steels and are: Chromium Steels 50xx Cr 0.27-0.65 51xx Cr 0.80-1.05 n made by quick quenching austenite steel. The rapid cooling traps the carbon atoms inside the B-9 This chart shows the very small percentage of alloying elements that are added to various types of steel. iron atoms in the face-centered cubic crystal structure of the austenite. Alloying elements that are added to steel when it is n typically very hard and brittle. made:

n are added in very small percentages. The percentage depends on the element added and the desired properties of the steel, but are typically in the 0.1 to 5.0 percent range. n affect the microstructure and grain size of the finished steel. n affect the temperature where the austenite and martensite phases of the steel happen.

B-10 The high-strength steel frame rail on this Honda Accord cracked B-11 The floor pan, cowl, and other outer closure panels that are color- when it was subjected to straightening forces. coded black on this Volvo XC90 body shell are all made from mild steel. As the strength of steel increases, it typically Mild steel: becomes:

n is easily formed and is the most repairable of the n harder. The Rockwell hardness of steel typically steel types used in vehicle structures. increases as the tensile strength is increased. This n typically can be heated during repairs as long as makes the steel less workable and harder to form the limits for maximum temperature and time are or straighten. The Rockwell hardness scale uses observed. a testing method based on indention testing that n usage for structural parts is becoming limited on measures the steels resistance to deformation. late model unitized structures. n more brittle. The harder and stronger a steel is, the more prone it becomes to cracking when it is worked. n more heat sensitive. The properties of HSS and UHSS are changed by heat much more than mild steels.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 12 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Yellow, Aqua, Blue–HSS Red–UHSS B-12 The yellow, aqua, and blue structural parts on this Volvo XC90 body shell are all made from various strengths and types of high-strength B-13 The parts of this Volvo XC90 body shell that are color coded red steel. are made from boron-alloyed steel.

High-strength steel: Ultra-high-strength steel: n is made in numerous different types. Each type n is very hard and strong. may have unique mechanical properties and n usage is becoming more common. UHSS is typi- strength characteristics. cally used to reinforce areas and limit passenger n is commonly used for structural parts because compartment deformation in a collision. it can be thinner, lighter, and stronger than the n has its strength destroyed by heat. same part made from a mild steel. n is typically not straightened at all due to its strength n is heat sensitive and is typically cold straightened. and the high degree of brittleness that it has. Heat can dramatically affect the strength and properties of HSS and therefore, is not recommended.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 13 © 2007–2012 Inter-Industry Conference On Auto Collision Repair B-14 Forces applied during structural straightening must exceed the yield B-15 This tensile test machine measures the force necessary to fracture strength of the steel part. a metal sample.

Yield strength: Tensile strength: n is the stress limit where plastic deformation starts. n is the maximum tension load reached before Yield strength is the minimum force required to the metal fractures, and is measured in force per achieve permanent deformation of the steel. unit of cross section area. Tensile strength can be n can be described as the minimum force necessary described as the maximum force the metal can to form or straighten the metal. be subjected to before it tears or breaks. n of a metal typically increases with work harden- n increases with work hardening, but typically at a ing. As a part is formed or straightened, the yield lesser rate than yield strength. strength increases due to work hardening and the part becomes more difficult to straighten. Tensile and yield strength values are typically listed as MPa or megapascals. One megapascal is one million pascals and is equal to about 145 psi.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 14 © 2007–2012 Inter-Industry Conference On Auto Collision Repair B-16 The high-strength steel front frame rail on this Honda Accord is Honda Accord being initially straightened prior to its replacement. B-17 The structural damage to this Honda Accord is greater than indicated What effects does the increased strength of the HSS by outward visual damage indicators. and UHSS used in the parts of a unitized structure have on the collision repair process? The inclusion of higher strength steels in vehicle structures has led to changes in the way vehicles are damaged during collisions. These changes include:

n less passenger compartment deformation and fewer visible damage indicators. n more collision energy transfer into the vehicle structure. Damage may radiate deeper into the structure and cause deformation of the softer parts of the structure, well away from the area of the primary damage.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 15 © 2007–2012 Inter-Industry Conference On Auto Collision Repair BRITTLENESS OF ULTRA-HIGH STRENGTH STEEL Refer to screen B-19v of your CD-ROM for a video on the brittleness of ultra-high strength steel.

Topic C. Mechanical Properties Of Steel

Energy Load Transfer/ 70 Absorption Ultra-High-StrengthCrush Resistance Steels (> 700 MPa) 60

50 IF B-18 Straightening high-strength steel structural parts may require increased 40 IF-HS MILD IS pulling force and additional anchoring to avoid collateral damage to 30 other parts of the vehicle. BH TRIP 20 CMn HSLA DP-CP 10 Total Elongation (%) MART

HSS and UHSS structural parts add some consider- 0 ations to the structural straightening process. These 0 200 500 800 1100 1400 1700 considerations include that: Tensile Strength (MPa)

C-1 This chart shows the basic strength ranges where energy absorption n increased force is required to straighten a dam- and energy transfer occur. aged HSS part. Most UHSS parts that are damaged should not be straightened and will require Mechanical properties of steel include: replacement. n kink vs. bend may not apply to damaged parts n total elongation, which is the percentage that the made of higher strength steels. The kink vs. bend metal will stretch before it fractures or breaks. rule was made when most structural parts were n the work hardening exponent, which is the rate made of mild steel, or conventional high-strength that the metal work hardens. steel that falls into the lower strength range of the n the toughness of the metal. Toughness is a com- group. With newer advanced HSS and UHSS, even bination of strength and ductility. For a metal to minor visible damage may be hard to repair. be considered very tough, it has to have high n collateral damage to anchoring points or attached strength along with a high degree if ductility. parts is more of a concern. The part that is being Many very strong metals are not considered tough straightened may be of a higher strength than the because they are very brittle, while many of the parts that it is attached to. This will cause the pulling very ductile metals are not tough because they forces to be transferred to the lower strength parts, lack strength. which could cause unwanted damage. Careful monitoring during the straightening process can help avoid causing collateral damage. Additional anchoring points will also help to avoid collateral damage. Another helpful technique is to use heat when stress relieving. However, this should only be done on HSS and UHSS parts that are going to be replaced.

Fracture Stress X

Plastic Region

Elastic Region

Strain

C-2 These mild steel samples show the amount of elongation and neck- C-3 This illustration shows the stress strain curve of a metal, with the ing that occurs before fracture when the sample is pulled beyond its stress indicating an applied force to the metal and the strain indicating yield strength. the amount of deformation caused by the force.

The yield strength-to-tensile strength ratio: Total elongation:

n indicates the ductility of the steel. A lower number n is related to the ductility of the metal or material. indicates a higher ductility of steel. “1” indicates A very hard and brittle material, like concrete, no ductility at all. would have a total elongation percentage close n affects the formability and repairability of the steel. to or at zero. There would be no flex or give to If a steel has a yield strength that is very close to the material before it breaks. A very soft and form- the tensile strength, it is considered unrepairable. able material, like a putty, would have a very high This is because when there is enough force put total elongation percentage. A total elongation on the steel to move it plastically, it will typically of 100% would indicate that the material can crack. stretch to twice its length before breaking. n causes necking of the material after reaching the maximum tensile strength, which reduces the total force needed to fracture the material. Once the material with good ductility reaches its YIELD-TO-TENSILE STRENGTH RATIO Select the Demonstration icon found on maximum tensile strength, it will stretch to the screen C-3 of your CD-ROM for examples of point that the cross section the force is exerted materials with high and low yield-to-tensile on becomes thinner. This is called necking. The strength ratios. total force exerted on the material will then go down and the actual fracture point will occur at a lower force than the maximum tensile strength of the material. Brittle material, with low total elongation percentages, will tend to break once the force applied reaches the maximum tensile strength of the material.

900 800

700 600

500

Timeline Strain (MPa) Timeline 400

300 200 0.001 0.01 0.1 1 10 100 1000 10000 Strain Rate (MPa) Yield Strength 1200 1000

900 800

700 DP 500/800 600 DP 350/600 500 TRIP 350/600

Timeline Strain (MPa) Timeline 400 HSLA 350/450 300 200 0.001 0.01 0.1 1 10 100 1000 10000 Strain Rate (MPa)

C-4 These charts show the difference between the work hardening effect C-5 Resistance spot welding may be the preferred welding method on on the yield and tensile strength of a steel. new unitized structures.

What considerations do the different mechanical Work hardening: properties of some newer steels add to the collision repair process? n describes the tendency of steel to increase in strength as it is worked. Work hardening affects both the yield and tensile strength of steel, but tends to affect yield strength at a higher rate than tensile strength. This leads to an increase in the brittleness of the steel as it is work hardened. n rate differs by steel type. Some steel types work- harden at a much faster rate than others.

WORK HARDENING Select the Demonstration icon found on screen C-4 of your CD-ROM for an example of the affects of work hardening.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 18 © 2007–2012 Inter-Industry Conference On Auto Collision Repair STRAIGHTENING HIGH-STRENGTH STEEL STRUCTURES Refer to screen C-7v of your CD-ROM for a video on structural straightening of a high- strength steel unitized structure.

C-6 Because of the strength of the B-pillar, the side collision damage to this vehicle radiated deep into the floor pan.

Straightening considerations added by the different mechanical properties of newer steels include: n that high yield-to-tensile strength ratios will cause cracks when straightening and because of this, parts made from steels with this property are not repairable. The closer the yield-to-tensile ratio is to “1,” the less likely it is that a part can be straightened without cracking. n the high work hardening rate of some steels. Some of the newer steels used in unitized structures gain a good deal of their final strength through work hardening when parts are formed. Collision damage further work hardens the part and the straightening process adds to it again. This limits the amount of straightening that should be done because even if the part is restored to its correct shape, the mechanical properties and strength of the part may be significantly different than intended. Work hardening also tends to make a part more brittle and prone to cracking when straightened. n the high heat sensitivity of HSS and UHSS.

GM STEEL REPAIRABILITY CHART Select the Demonstration icon found on screen C-6 of your CD-ROM for an example of the General Motors Steel Repairability Chart.

D-2 The front structure of this vehicle is being straightened with multiple pulls and no heat.

Heating considerations for HSS and UHSS include:

D-1 The strength and mechanical properties of steel may be changed by the application of heat. n UHSS parts should not be straightened unless OEM documentation states that it can be straight- The effect of heat on steel: ened. n HSS parts should be straightened cold unless OEM n varies depending on the type of steel and other documentation states that heat can be used. variables. n observing the limits for both maximum tempera- n alters the strength of the part. Heat tends to ture and length of time that a part can be heated. strengthen mild steels, weaken high-strength If a vehicle maker has heating recommendations, steel, and completely destroy the strength of they typically include a maximum temperature most ultra-high-strength steels. A good analogy and the amount of time that the part can be is that it was not the physical structural damage subjected to heat. of the collisions with the planes that brought n using heat on parts that are going to be replaced the World Trade Center towers down, but it was during initial straightening. This may help to reduce heat damage from the fires to the HSS used in collateral damage to adjacent parts. This allows the building structures. the entire structure to be returned to proper n changes the mechanical properties. The amount dimensions without having to apply excessive of heat and rate at which it is applied, as well force to remove damage to HSS and UHSS parts as the cooling rate, can have a dramatic effect that are going to be replaced. on the mechanical properties of the steel. Mild steels tend to become more brittle when heated while some of the higher strength steels may become softer and more formable. This may lead to a part that was intended to transfer collision energy actually absorbing it instead and a part that should absorb energy may either crack or be hard enough to transfer the energy instead.

Steel Unitized Structures Technologies And Repair v.9.4.a–Module 1 20 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Topic E. Identifying Steel Types HEAT AFFECT ON STEEL Refer to screen D-3v of your CD-ROM for a video on the affects of heat on the strength GM Lambda Body Structure and mechanical properties of various types of steel.

Ultra-High-Strength Steel Dual-Phase Steel High-Strength Steel

Bake Hardenable Steel Laminated Steel Mild Steel

E-1 This illustration shows the locations of different types of steel in the General Motors Lambda body structure.

How can we determine what type of steel a structural D-4 This GMA (MIG) weld shows the relatively wide heat-affect zone part is made of? created by this welding process.

Considerations for welding HSS and UHSS include: n the heat affect zone (HAZ) that welding creates. The strength and mechanical properties of the steel can be greatly changed by the extreme heat in the HAZ. HAZ softening typically increases as the steel strength increases. Because of this, when welding on HSS and UHSS, the amount of heat input into the metal should be held to the minimum necessary to make a quality weld. Methods that can help control the heat input include making stitch welds where long continuous welds are needed, and using welding equipment that utilizes the pulse-spray transfer method. n that STRSW may be the preferred welding method to use on HSS and UHSS. STRSW equipment may have separate HSS and UHSS settings that also help to reduce the HAZ of the weld. These setting may work by pulsing the current input into the weld.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 21 © 2007–2012 Inter-Industry Conference On Auto Collision Repair E-2 This vehicle maker service information shows the location of high- E-3 This technician is using bench top hardness testing equipment to strength and ultra-high-strength steel in a vehicle’s structure. determine the Rockwell hardness of a steel sample.

Ways of identifying what type of steel a structural Hardness testing: part is made of include: n may be done with fixed or bench mounted equip- n looking up the name or metallurgical designation ment that requires a small piece to be removed of the steel in vehicle maker service information. from the part. Some collision repair manuals may include infor- n may be done with portable equipment. This allows mation on the types of steel used to make the testing without having to cut sections out of the structure and body panels of a vehicle. vehicle parts. n hardness testing to categorize as mild, HSS, or n for comparison readings should be done with the UHSS. Typically hardness testing will give numbers same equipment. Do not compare results from that can be compared to that of a known steel. one piece of equipment to those taken with a This will allow the steel to be placed into a basic different piece of equipment. strength category based on this comparative data.

VEHICLE MAKER STEEL IDENTIFICATION Select the Demonstration icon found on screen E-2 of your CD-ROM for an example of vehicle maker steel identification information.

50 IF

IF-HS 40 MILD IS 30 BH TRIP 20 CMn HSLA DP-CP 10 MART Total Elongation (%) Total 0 0 200 500 800 1100 1400 1700

Tensile Strength (MPa)

F-1 This chart shows the metallurgical designations for the steels commonly used in vehicle structures.

The metallurgical designation: F-2 This illustration is a magnification of the grain structure of a typical mild steel.

n is the scientific name given to different categories of steel based on the build process or alloy Names used for soft ferrite phase or mild steels content used. include: n categorizes steels by common mechanical properties. Typically steels that are made with the same n conventional steels. build process and alloy content will have similar n drawing steel (DS). mechanical properties. n deep drawing steel (DDS). n only loosely categories the strength of the steel. n interstitial free (IF). The strength range within the categories can be very wide. These common mild steels have a very low carbon content and low tensile strengths but tend to have good ductility.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 23 © 2007–2012 Inter-Industry Conference On Auto Collision Repair F-3 Mild steel is typically used for outer body panels. F-4 This illustration is a magnification of the grain structure of a typical high-strength steel. Typical mild steel usage on unitized structures includes: Commonly used conventional HSS: n outer body panels. n have had the ferrite structure converted to aus- n underbody closure panels, including center floor tenite structure through heat treatment. pans, trunk floors, and cowl panels. n may fall into the bake hardenable designation. The n some outer unisides and pillars. strength of steels that may be called bake hardenable overlaps the mild steel strength range. n may fall into the high-strength low alloy (HSLA) designation. The strength range of HSLA steels overlaps the UHSS range.

Honda Accord Front Frame Rail F-5 This Honda Accord frame rail is an example of the type of structural part that may be made from high-strength steel.

Typical conventional high-strength steel usage on unitized structures includes: Martensite Ferrite F-6 This illustration shows the pockets of hard martensite steel that are intermixed with the softer ferrite steels in dual-phase steel. n some outer body panels. Outer body panels may be made of HSS to allow them to be made thinner and lighter. Dual-phase (DP) and complex-phase (CP) steels: n all major structural parts. HSS may be used any- where on a vehicle. The presence of HSS may n are made by taking a soft ferrite steel and inter- vary from the vehicle maker model and year mixing it with pockets of a hard martensite steel. and should not be assumed based on previous The percentage of martensite added depends on years or different models from the same vehicle the desired properties of the finished steel, but maker. is typically in the 20–70% range. n reinforcements for structural parts. n have high strength along with good formability and energy absorption properties. This is due to the fact that the soft ferrite phase steel portions can deform and absorb energy, while the hard martensite portion increases the strength of the total part. n have a high initial work hardening rate. This is one of the reasons why the steel is very formable and strong. A lot of the strength of the finished part comes from work hardening when the part is formed. This high work hardening rate also makes DP and CP steels difficult to straighten.

1000 900 800 700 600 500 400 True Stress True 300 200 100 0 0 0.05 0.1 0.15 0.2 0.25 True Strain

DUAL-TEN 780/800 DP500 DUAL-TEN 590/600 HSLA 340 DQSK HSLA 550

F-7 This chart shows a comparison of the yield strength of different grades F-8 This Chrysler Sebring has dual-phase steel in the front frame rails, of dual-phase steel and high-strength low alloy steel. inner rocker panels, and floor pan reinforcements.

Dual-phase and complex-phase steel: Examples of dual-phase steel usage in vehicles include the: n comes in many different types depending on the desired strength and mechanical properties. n 2007–2008 Chrysler Sebring in the front frame n use is becoming common on front frame rails rails, inner rocker panels, and floor pan reinforce- and other structural parts of unitized structures ments. because it offers both good strength and energy n 2006–2008 Honda Civic, which uses 590 MPa absorption, making it a tough steel. DP steel in the frame rails, rocker panels, pillars, roof structure and floor pan reinforcements. n 2005–2008 General Motors Lambda platform vehicles. The Lambda platform includes the 2008 Buick Enclave, 2007–2008 GMC Acadia, and 2005–2008 Saturn Outlook. These vehicles use DP steel in the front frame rails, and reinforcements of the floor pan, rocker panels, and B-pillars.

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Martensite Ferrite

F-9 This illustration shows the austenite and martensite steels that are intermixed with the ferrite steel in TRIP steel. F-10 This illustration is a magnification of the grain structure of a typical martensite steel. Transformation induced plasticity (TRIP) steel: Martensitic (MART) steels: n is mostly a mixture of ferrite and austenite steels with a small amount of martensite steel. They are n have had the austenite structure converted to similar to DP and CP steels in that a percentage martensite structure. of it is a soft ferrite steel and the remainder is n are very strong and hard with tensile strengths harder and stronger austenite steel and martensite up to 1700 MPa. steel. n typically have low ductility, low total elongation n has tensile strengths in the 500–1050 MPa percentages, and high yield strength-to-tensile range. strength ratios. This makes them hard to form n has similar mechanical properties as DP steels, and very difficult to straighten when damaged. but with slightly more ductility due to the presence of austenite steel instead of the martensite steel which is used for making DP steel.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 27 © 2007–2012 Inter-Industry Conference On Auto Collision Repair F-11 The inner and outer rocker panels and center floor pan crossmember of this General Motors Lambda body structure are made from a martensitic steel. F-12 Using pinchweld clamps in conjunction with fixtures helps to avoid collateral damage when straightening high-strength steel structures. The 2005–2008 General Motors Lambda platform vehicles use martensitic steel in the: Collision repair considerations with AHSS steels such as DP and MART include: n rocker panels. Both the inner and outer rocker panels are made from martensitic steel, making n that parts made from them are very strong. They a fully enclosed martensitic structure that maxi- are designed to transfer energy and therefore, will mizes energy transfer in front, rear, and side transfer damage also. The high strength of these collisions. parts also makes straightening them difficult, and n center floor crossmember that runs between UHSS should not be straightened unless OEM the lower B-pillars. This helps to transfer collision documentation allows it. The high strength of energy from one side of the passenger compart- parts made from these steels also increases the ment to the other and keep the distance between possibility of collateral damage to other parts of the left and right side rocker panels from changing. the vehicle when doing structural straightening. In conjunction with a strong B-pillar, this helps n the location and function of parts that are typically avoid intrusion of the B-pillar into the passenger made from these steels. These parts are typically compartment. in the main load-carrying path of the vehicle and have functions that are critical to protecting passengers during collisions.

60 2 50

30 1 20

10 3 Total Elongation (%) Total 0 0 200 500 800 1100 1400 1700

Tensile Strength (MPa)

1: Before Heating 2: After Heating 3: After Stamping And Quenching

F-13 Advanced high-strength steel should not be heated during F-14 This chart shows the strength change that a typical boron-alloyed repairs. steel goes through during the heating and quenching cycles of the hot stamping process.

Other considerations with DP and MART steels Hot stamped parts: include: n are made by stamping the sheet steel while n their heat sensitivity. Parts made from these steel it is very hot. The parts are then quenched to should not be heated unless OEM documentation cool while still in the dies. This is done for two allows it or the part is going to be replaced. The reasons, one to add increased formability with HAZ when welding should also be considered. higher strength steels, and two, the heating and Use only enough heat to make a sound weld. quenching process can actually increase the Make practice welds that are destructively tested steel strength due to conversion of austenite to to verify the quality of the weld. martensite. n the yield-to-tensile strength ratio. The closer the n are typically made from boron-alloyed steels. The yield-to-tensile strength ratio is to “1,” the less strength of a boron-alloyed steel part can increase repairable the steel is. A frame rail that cracks as much as 250% during the hot stamping process, when pulled back into position is likely made making a very strong part. from a steel with a high yield-to-tensile ratio. DP n are typically not galvanized because the high steels tend have a lower yield-to-tensile ratio than heat used during stamping would destroy the MART steels, but have high work hardening rates galvanized coating. that increase the ratio as the part is damaged and repaired. n that they may have high work hardening ratio. DP steels have good formability and energy absorption, but tend to have high work hardening ratios. A steel with a high work hardening ratio cannot tolerate much straightening before it will crack, making anything more than minor straightening or moving of the position of these parts very difficult.

Steel Unitized Structures Technologies And Repair v.9.4.a–Module 1 29 © 2007–2012 Inter-Industry Conference On Auto Collision Repair F-15 This very strong and hard boron-alloyed B-pillar was cut using a F-16 The parts of this Volvo XC90 body shell that are color coded red chop saw with a special blade. are made from boron-alloyed steel.

Boron-alloyed steel: Locations on unitized structures where boron-alloyed steel parts may be found include: n is made by adding a small percentage of boron to the steel. n door intrusion beams. n is very strong and hard, with tensile strengths up n bumper reinforcements. to 1600 MPa. n roof structures. n typically has low ductility, low total elongation n pillar inner panels and reinforcements. percentages, and high yield strength-to-tensile n rocker panel reinforcements. strength ratios. It is typically recommended that n rear body panels. boron alloyed steels not be straightened. Examples include the 2003–2008 Volvo XC90, which Boron-alloyed steels may be called by different uses boron-alloyed steel in the B-pillar reinforcement, names. center roof bow, and the inner rear body panel. The 2007–2008 Dodge Caliber uses boron-alloyed steel in the roof rail reinforcement and pillar reinforcements. The 2007–2008 Mercedes-Benz S-class uses a type of boron-alloyed steel called Usibor in the pillars of the vehicle.

Steel Unitized Structures Technologies And Repair v.9.4–Module 1 30 © 2007–2012 Inter-Industry Conference On Auto Collision Repair SECTIONING BORON-ALLOYED PARTS Refer to screen F-18v of your CD-ROM for a video on sectioning parts made from boron- alloyed steel.

F-17 A cutoff wheel is being used to cut through this boron-alloyed B-pillar on a Volvo XC90.

Boron-alloyed part considerations include that: n they should not be sectioned without a vehicle maker procedure. Volvo has sectioning proce- F-19 Grinding with a cutoff wheel or using a plasma cutter are two ways dures for the boron-alloyed rear body panel and of removing spot welds from boron-alloyed steel. B-pillar reinforcement on the XC90. n they should be cut with a cutoff wheel. A boron- Ways of removing spot welds from boron-alloyed alloyed steel part is harder than a saw blade and parts include: will remove the teeth from the blade almost immediately. n grinding through the weld with a cut-off wheel. n rivet bonding may be recommended for their n using a plasma cutter. Some plasma cutters have replacement. Mercedes-Benz has recommenda- a setting that allows the cut to be made through tions to replace some of the Usibor parts on their only one layer of a multiple layer assembly. Check vehicles using rivet bonding instead of welding. vehicle maker recommendations to ensure that they do not warn against the use of a plasma Follow vehicle maker procedures for the replacement cutter. of damaged boron-alloyed steel parts. n drilling the weld using a special hardened bit turning low rpm’s and remaining perpendicular to the weld. Welds can also be drilled from the backside or through the non-boron alloyed part. If you have access to the spot weld on the part that is not a boron-alloyed part, and it is acceptable to have holes in that part, this allows the weld to be drilled out in the conventional manner. Make sure that it will not be a problem having holes in the part that will remain on the vehicle before using this method.

Review Refer to screens G-1 and G-2 of your CD-ROM for review questions on steel strength and unitized structures repair.

Grade 590 340 11% 440 270

38% 19% 50% 68%

9% 2%

3% HSS Usage Rate: 50% HSS Usage Rate: 32%

F-20 This illustration shows the difference in high-strength steel usage between the 2005 and 2006 Honda Civic.

The usage rate for HSS, UHSS, and AHSS in unitized vehicle structures is increasing every model year. An example of this is the Honda Civic. The 2005 Honda Civic structure was made up of 32% higher strength steels with 11% being DP 590. The 2006 Honda Civic structure is made up of 50% higher strength steels with 38% being DP 590.

Topic A. Front Structures

Nissan 350Z A-3 Because it will break in a collision, the composite radiator core support on this vehicle will not transfer as much collision energy from Ford Taurus side-to-side as a welded steel radiator core support. A-2 The composite radiator core support on this vehicle bolts to the upper and lower front frame rails. Composite radiator supports: Composite radiator core supports are a new trend in n do not transfer as much collision energy from vehicle design. Composite radiator core supports: side-to-side as a welded steel radiator core support. This may help to keep minor front damage n allow for an open design front structure. The head- isolated more to the side of the collision. lamps, coolers, and the hood latch are typically n are typically not repaired when damaged. Dam- attached and can be removed as an assembly with aged composite radiator core supports are typi- the composite radiator support assembly. Once cally replaced. the assembly is removed, it allows access to the drivetrain and other front structural parts. n are typically light weight compared to their steel counterparts. n bolt on to both the lower frame rails and the upper rails.

Volvo S40

A-4 The crush tube on this front module assembly from a Volvo S40 is B-1 Laminated steel is made by bonding two steel sheets together with made from lower strength steel than the boron-alloyed inner bumper an inner polymer layer. reinforcement. Laminated steel: Front crush tubes: n is two steel sheets bonded together with an n may be found between the bumper reinforcement inner polymer layer. It is primarily used for NVH and front frame rails. They may be separate bolt-on control, as the polymer layer absorbs any sound parts or may be part of the bumper reinforcement waves that are passing through the metal. assembly. This assembly may be called a front n plays a role in weight reduction of the vehicle as module assembly. it allows good NVH control with the use of less n are designed to absorb collision energy. They are insulation and padding. typically made of lower strength steel than the n is found mostly on the cowls of vehicles, but bumper reinforcement and frame rails and are may be used on storage tubs or rear floor pan considered a sacrificial part. Damaged front crush areas. tubes should be replaced and not straightened. n use is becoming more common.

LAMINATED STEEL Select the Demonstration icon found on screen B-1 of your CD-ROM for an example of laminated steel

Dodge Caravan B-2 This Chevrolet Cobalt cowl panel and the Stow ‘n Go seat storage B-3 The edges of this laminated steel part show the three layers. tubs on this Chrysler Town & Country minivan are both made of laminated steel. Ways of identifying laminated steel include: Laminated steel is used on a wide variety of parts including: n checking service information. Laminated steel may be called Quiet Steel by some vehicle makers. n cowl panels. n tapping on the panel. Tapping on laminated steel n upper and lower plenums. produces a dull, non-resonating thud with very n floor pan storage tubs. little sound transfer. n a visual inspection of panel edges. If the panel Some examples of laminated steel usage include edges can be seen, it may be possible to visually the 2005–2007 Jeep Grand Cherokee dash panel detect the laminate between the two layers of and inner rear wheelhouse reinforcements, the steel. 2002–2006 Ford Explorer/Mercury Mountaineer cowl panel, and the 2006–2007 Cadillac DTS cowl panel. The cowl on the 2004–2008 Ford F-150 is made of laminated steel.

Steel Unitized Structures Technologies And Repair v.9.4–Module 2 35 © 2007–2012 Inter-Industry Conference On Auto Collision Repair B-4 Minor damage to laminated steel parts, such as this, can be cold B-5 Plug welds and rivet bonding are two repair methods used to fasten straightened. replacement parts to laminated steel.

Collision repair considerations for laminated steel Collision repair considerations for laminated steel panels include that: panels include that: n minor straightening can be done, but should be n they are typically attached with STRSW at the done without the use of heat. Heat will destroy the factory, but are typically not fastened with STRSW polymer core between the steel sheets, reducing in the field. the NVH control of the panel. Also, do not use n recommendations for replacing attached parts weld-on pull tabs or other weld-on straightening vary by vehicle maker. Ford recommends GMA equipment on laminated steel parts. (MIG) plug welding when replacing parts attached n they may be serviced with regular mild steel to a laminated steel cowl panel and General replacement parts. Cowl and plenums may be Motors recommends that the parts be replaced serviced with mild steel parts that require the with rivet bonding. The laminated steel storage application of sound deadening material after tubs for the Stow ‘n Go seat storage tubs on they are installed. the 2005–2007 Chrysler Town & Country and Dodge Caravan/Grand Caravan are replaced with adhesive bonding.

B-6 These GMA (MIG) plug welds have been made through the laminated B-7 Rivets and adhesive were used to fasten the replacement frame rail steel part into the non-laminated steel replacement part. and extension to this laminated steel cowl panel.

When welding to laminated steel: When rivet bonding parts to laminated steel: n GMA (MIG) plug welds are the preferred method. n follow the vehicle maker procedure for the repair. Some vehicle makers may not recommend weld- Since the attachment of the service part is differ- ing to the laminated steel, so check the service ent than the factory attachment method, vehicle information before making repairs. The plug weld makers will typically have very specific service hole is typically put in the laminated steel part. This information for the procedure. can be done by drilling completely through both n large 7 mm (1/4") rivets are typically used. The panels when removing the factory spot welds. The rivets are used to replace the factory spot welds plug weld is then made through the laminated and are typically put in the same location. steel into the new part. Some procedures may n structural adhesive is used along with the rivets. Be call for sectioning of the attached part to avoid sure to use the adhesive specified in the service disturbing the flange where the laminated steel procedure, or one with equivalent properties if and regular steel are attached. the specified adhesive cannot be sourced. n STRSW of parts attached to laminated steel cowls is typically limited by access of the welding tips Rivet bonding may also be used for application other to the flange. than laminated steel but the procedures for doing it will be similar.

RIVET BONDING TO LAMINATED STEEL Refer to screen B-8v of your CD-ROM for a video on rivet bonding a front frame rail to a laminated steel cowl panel.

0.8 mm/270 MPa

1.2 mm/590 MPa Lexus IS 300 C-2 The laser weld on the tailor-welded blank front frame rail of this Honda Civic Lexus IS300 is clearly visible. C-1 This illustration shows the different strength and thickness of steel used in the tailor-welded blank on the cowl of a Honda Civic. Tailored blanks:

Tailored blanks are another fairly new construction n are used to provide control of collision energy method that is seeing increased usage in unitized management. They allow the part to transition structure construction. Tailored blanks: from energy absorption to energy transfer. n reduce the need to add reinforcements where n are two or more different thicknesses or strengths a part needs to be made stronger. This helps to of steel in one continuous part. The metal sheet reduce vehicle weight and improve corrosion that the part is made from is first formed from protection because it reduces overlapping panels the two different strengths or thicknesses of steel, where reinforcements are added. and then the part is stamped from this blank. n may be of different thicknesses or strengths that are laser welded together. These are called tailor- welded blanks and typically have a visible laser weld seam. n may be rolled blanks which are only different thicknesses of the same strength steel. In a tailor-rolled blank, there is no seam at all and the different thicknesses are made by rolling the sheet blank thinner at one end than the other.

1.6 mm

1.2 mm 1.4 mm

Saturn Aura Honda Civic C-3 Tailor-welded blanks may be used for both front and rear frame C-4 This illustration of the front frame rails from a Honda Civic shows rails. the three different thicknesses of the same strength steel that are used in their construction. Tailored blanks are becoming more common and may be found in a wide variety of locations including: Examples of vehicles using tailor-welded blanks include the: n upper and lower frame rails. Tailored blanks may be used in either front or rear frame rails to tailor n 2007–2008 Saturn Aura, which has both the the collision energy management of the parts. front and rear frame rails made from tailor-welded n cowl panels. Cowl panels may be thicker or made blanks. of stronger steel in the bottom portion where the n 2006–2008 Honda Civic, whose front frame rails, front frame rails are attached to them. An example cowl, door inner panels, and B-pillar reinforcement of this is the 2006–2008 Honda Civic, which has are all made from tailor-welded blanks. a cowl made from a tailor-welded blank that is both thicker (0.8 mm compared to 1.2 mm) and TAILOR-WELDED BLANK LASER WELD a higher strength steel (270 MPa compared to Select the Demonstration icon found on screen 590 MPa) on the bottom half. C-4 of your CD-ROM for an example of a tailor- n side body structures. Both the outer and inner welded blank laser weld. rocker panels and pillars may be made from tailored blanks.

1.85–1.05 mm

1.9 mm

1.65–1.85 mm

1.6 mm 1.75–1.65 mm Transition Zone 1.8 mm

1.0 mm Mild Steel Lexus IS 300 Dodge Caliber C-6 A tailor-welded blank frame rail may deform in front of the laser weld and maintain its shape behind it. C-5 This illustration of the tailor-rolled B-pillar on a Dodge Caliber shows the different thickness of the part. Considerations with tailored blanks include: Examples of vehicles using tailor-rolled blanks include the: n that parts may deform at the transition point between the two strengths or thicknesses of n 2007–2008 Dodge Caliber. Tailor-rolled blanks steel. are used in the B-pillar reinforcements. n collateral damage during straightening to the n 2006–2008 Audi A3. Tailor-rolled blanks are used weaker or thinner portion of the part. If straighten- in the rocker panel reinforcements. ing is being done to the thicker or stronger portion, carefully monitor the part for unwanted collateral damage during the straightening process. n the laser weld is typically not a sectioning joint. Never section a tailor-welded blank at the laser weld unless called for in a vehicle maker procedure.

Tube Hydroforming

A B

C D

E F

D-2 Roof rails and pillar reinforcements are two locations where hydroformed parts may be found on unitized structures.

D-1 This illustration shows the process used to hydroform a tube part. Typical applications of hydroformed parts on unitized structures include: Hydroforming is another construction method used on vehicles. Hydroformed parts: n pillar reinforcements. Hydroformed pillar reinforcements are used to resist roof crush and may n are made using hydraulic pressure to push the be part of an inner pillar assembly. metal against a die. n roof side rails. Hydroformed roof rails are typi- n may be tube or sheet parts. Hydroformed tube cally one-piece front to back and may be serviced parts are shaped by forcing the tube outward as part of a uniside assembly. The 2004–2005 against a 360° die with hydraulic pressure from Chrysler Pacifica has a one-piece hydroformed the inside. Sheet hydroformed parts are made by rail that runs the entire length of the passenger forcing a metal sheet onto a one sided die. compartment. n are one-piece structures with no flanges. The lack of flanges and seams or multiple pieces offers increased corrosion protection. n have a uniform thickness. Stamped parts tend to have thin spots where the metal is stretched around corners between the two dies. Because of this, the entire part is typically made a little thicker so that the thin spots have adequate strength. Since hydroforming can produce a uniform thickness, parts can be made thinner and lighter while maintaining the proper strength.

Volvo C70

D-3 The hydroformed A-pillar reinforcement on this Volvo C70 convert- ible would make straightening the pillar very difficult. Volvo XC90

Considerations with hydroformed parts include: E-1 This B-pillar reinforcement is sandwiched very close to the outer panel. n that they are difficult to straighten. Because of Inner reinforcements: their closed tube design, straightening visible damage is very difficult. Leaving a buckle in the n are used to add strength to a part. They are typi- side of a tubular part will create a collapse zone cally placed where the part is intended to transi- at that point if exposed to forces from the right tion from energy absorption to energy transfer. direction. n may be in multiple locations on the frame rails n part replacement issues. Hydroformed rails are of modern vehicles. Inner reinforcements may often large parts that are behind multiple seams be found spaced along the entire length of the from adjacent assemblies. Replacing pillars or rail and may be used to help design crush zones portions of unisides that have hydroformed into the part. reinforcements or rails may require sectioning of n are typically made from HSS or UHSS. the hydroformed part. An example of this is the 2004–2005 Chrysler Pacifica uniside, which is supplied as a partial front or back assembly and contains a hydroformed roof rail reinforcement that requires sectioning when replacing either portion.

Steel Unitized Structures Technologies And Repair v.9.4–Module 2 42 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Volvo XC90 2005 Subaru Forester E-2 This rear frame rail has multiple staggered reinforcements located E-3 This Subaru forester B-pillar has multiple layered reinforcements in inside of it. order to create a very strong part.

Considerations with inner reinforcements include: Structural parts may have multiple reinforcements inside them. Reinforcements may: n that they limit the amount of straightening that can be done. Areas that have HSS or UHSS reinforce- n be staggered through the part to help create col- ments inside will be so stiff and strong that it is lapse zones. This is especially true of frame rails. often not practical to straighten visible damage The areas that are reinforced will be very strong in these areas. Straightening of rails or pillars in and transfer collision energy while the areas reinforced areas is limited to minor movement between the reinforcements will be weaker and of the part that does not show visible deforma- will collapse to absorb energy. tion. n be layered on top of each other in a part. This n limits to sectioning locations for the part. Heat is done to add strength to the part and to keep input from welding is a consideration because it from collapsing. Layered reinforcements are inner reinforcements are typically made from typically found in A-, B-, and C-pillars. higher strength steels. Reinforcements are typically n not be serviced as separate parts. Typically, rein- not serviced as separate parts, but are included forcements are not serviced separately but are with, and spot welded to, the part that they are supplied with the part that they reinforce. reinforcing. This can make it difficult to make a cut through the outer panel without cutting into the reinforcement. n corrosion protection considerations because of limited access to parts that are buried deep within an assembly.

E-4 This illustration shows the location of nylon reinforcement inserts used on the Saturn Aura. E-5 This cutaway shows how the roof and side structures can be layered over each other. Reinforcement inserts: Repair considerations created by panel layering include: n may be made from nylon or aluminum. n must be replaced if damaged. They are designed n outer panels layered over inner panels. For to absorb collision energy and then transfer it to example, a roof skin and rails may be layered a specific location once they have collapsed. If a over pillars and uniside assemblies, requiring roof reinforcement insert is damaged and not replaced, removal to replace the entire uniside. Upper front it will not perform this function in a subsequent frame rails may also be layered over the radiator collision. core support. n are typically adhesively bonded. When replac- n that the build sequence affects access to joints that ing an adhesively bonded reinforcement insert, require separation for the replacement of parts. thoroughly clean off any old or loose adhesive The order that overlapping panels were put on from the structure and use the recommended at the factory may affect how parts are replaced adhesive. during repairs. The outer layer may be larger or smaller than the underlying parts, causing joints to be covered by the next panel out. n that sectioning of parts may be limited by multiple layers. As an example, a B-pillar that is made with five layers might require windows to be cut into three of the layers to section the entire B-pillar, thus making it impractical. In other instances, multiple layers may lead to the vehicle maker developing unique sectioning procedures to avoid removing undamaged parts during repairs. An example of this is the 2005–2007 Saturn Outlook B-pillar.

E-6 This multi-layered B-pillar, from a 2002 Subaru Legacy Outback, would E-7 This technician is stress relieving while pulling to help avoid collateral be very difficult to straighten if bent. damage to the structure.

Straightening considerations for parts that have mul- Additional straightening considerations include: tiple layers include: n collateral damage to other parts of the vehicle n limited access to the inside layers. If a multi-layer when pulling. A multi-layered pillar or uniside B-pillar is bent, the inside layers may be damaged will typically be the strongest part of a vehicle. as well as the outer layers. The damage may have Because of this strength difference, pulling these been pushed from one panel to the next as the assemblies with structural straightening equip- panels collapse against each other. Pulling and ment may break spot welds where the assembly straightening the outside panel may not transfer is connected to weaker parts of the vehicle. Some the corrective forces to the inner panels, making outer unisides may also be considered non-struc- them impossible to straighten without removing tural by the vehicle maker and be made of lower the outer panels. strength steel than the inner and reinforcements. n that damaged reinforcements may hold damage This makes moving the inner panels by pulling in the outer panels of an assembly. Reinforce- on the outer panels difficult to do without further ments may be made from higher strength steel damaging the outer panel. than the part they are inside of. Because of this, n that cutting windows to access inner panels the straightening force that can be applied to and reinforcements is considered a sectioning the outer panels without damaging them is not procedure. There may be vehicle maker proce- great enough to move the damage to the inner dures for sectioning of outer side structures and reinforcement. There is also typically not enough trunk floors that can be used to aid in access for access to the inside to properly stress relieve the straightening. damaged reinforcement.

Steel Unitized Structures Technologies And Repair v.9.4–Module 2 45 © 2007–2012 Inter-Industry Conference On Auto Collision Repair LAYERED B-PILLAR REPLACEMENT Refer to screen E-9v of your CD-ROM for a video on replacing a layered B-pillar inner reinforcement assembly without removing the roof.

Topic F. Foams

Chevrolet Cobalt E-8 This prop shows the pre-sleeved service part that is used for sectioning the upper frame rails when replacing the radiator core support on a Chevrolet Cobalt.

The build sequence of a vehicle affects the repair process: n because of overlapping panels. The build sequence of a front structure may cause the radiator core support to be on top of or underneath the upper frame rails. Overlapping panels are more Buick LaCrosse common on vehicle side structures than front F-1 NVH foam is used where the upper frame rail connects to the A-pillar structures. The side structure may be overlapped to block the movement of air through the parts. on top of the roof skin, or the roof skin may be overlapped on top of the side structure. NVH foam: n and may require undamaged part removal or sectioning of outer panels when replacing certain n is used in vehicles to control noise and vibration parts. When replacing a complete uniside that and to block air movement that may cause drafts is layered underneath a roof skin, the roof skin or wind noise. may require replacement also. Because of build n may fill sections of pillars and rocker panels. Rocker geometry and layering, upper frame rails may panels can be completely filled with foam or they require removal to replace a radiator core sup- may have small sections filled. Pillars are typically port that they are layered over. An example of filled towards the bottom or in small sections along this is the 2005–2007 Chevrolet Cobalt, which their length to block air movement through door requires partial replacement of both outer upper hinge fasteners. rails when replacing the radiator core support. n may be flexible or rigid, but is typically a low density product in either case.

Steel Unitized Structures Technologies And Repair v.9.4–Module 2 46 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Chrysler 300M F-2 The center part of the rocker panel on this Chrysler 300M is completely filled with NVH foam.

Collision repair considerations for NVH foam include that it: Ford Expedition (Upper B-Pillar) F-3 This structural foam carrier is used in the top of this B-pillar to add strength to the area. n is combustible and will burn if exposed to enough heat. Typically, cured foam will melt if exposed Structural foam may be found in the front rails and to heat higher than 300°C (575°F). When cured pillars of some unitized structures. Structural foam foam begins to melt, it generates toxic chemicals, may be used to: including carbon monoxide and cyanide gas. Because of this, it is recommended to remove n stiffen a part and reduce flex, which helps to foam from the immediate area where welding or control work hardening and stress cracking. heating will be done. n modify the collision energy management of a n limits access to the backside of parts that it is part. The structural foam will reduce deformation installed in. of the part in the area where it is installed and n can be reused if not damaged. If the outer skin will aid in energy transfer. of an assembly that is filled with foam is being replaced, the foam can remain with the vehicle and be reused as long as it is not damaged. When removing the panel, a heat gun can be used to release the foam from the damaged part. A ure- thane adhesive, seam sealer, or additional foam can be used to reattach the existing foam to the new part. n must be replaced where it has been removed.

Steel Unitized Structures Technologies And Repair v.9.4–Module 2 47 © 2007–2012 Inter-Industry Conference On Auto Collision Repair Kent Ure-Foam does not list a flash point for non-cured part A. Part B has a non-cured flash point of 254°C (490°F). According to the MSDS, if this material catches fire, the recommend fire fighting materials include carbon dioxide, dry chemical, foam, alcohol foam, or water fog. According to the MSDS, special fog nozzles are recommended if water is to be used for extinguishing a fire.

Fusor 1908 structural foam and Motorcraft® structural foam, have a flash point of the non-cured material of 93°C (201°F) for non-cured material. According Cadillac DTS to the MSDS, if this material catches fire, the recom- F-4 The rear portion of the service front frame rail for a Cadillac DTS is filled with structural foam. mended fire fighting materials include carbon dioxide, dry chemical, foam, or water fog. According to the Collision repair considerations for structural foam MSDS, special fog nozzles are recommended if water include: is to be used for extinguishing a fire. n the fact that it may be supplied pre-installed in the service part for some frame rails. n if it is broken loose and rattling that vehicle maker recommendations for repair may differ. This may require replacement of the frame rail on some vehicles while for others the loose foam may be reattached by full filling the area with additional structural foam. Check vehicle maker service information for the proper procedure for the application.

Ford says to reattach loose structural foam by full filling with additional foam. Loose structural foam in the frame rail of a Cadillac DTS requires frame rail replacement due to limited access.

NVH AND STRUCTURAL FOAM SAMPLES Select the Demonstration icon found on screen F-4 of your CD-ROM for examples of NVH and structural foam.

G-2 This Chrysler publication gives recommendations for welding and weld bonding on their vehicles. Chrysler 300M

G-1 This outer rocker panel is being installed using weld bonding. Considerations for weld bonded side structures include: Weld bonding: n vehicle maker recommendations for part replace- n is a combination of resistance spot welds and ment. Recommendations vary from vehicle maker structural adhesive for attaching parts. Weld to vehicle maker with some recommending weld bonding is being used more and more on vehicle bonding for repair and others recommending structures as the finished joint is stronger than a increasing the number of spot welds used and joint that is only spot welded. The adhesive also leaving the adhesive out. Follow the recommenda- adds additional benefits such as NVH control tion for the vehicle being repaired when factory and corrosion protection to the joint. weld bonding is present. n can typically be found on the vehicle side struc- n that part removal may be aided by using heat to ture. loosen the adhesive. Also remember that adhe- sives have poor peel strength so using a chisel to peel apart the flange works better than trying to pull the part straight off.

WELD BONDING Refer to screen G-3v of your CD-ROM for a video on weld bonding.

GMA (MIG) Welding

MIG Brazing

H-1 This illustration shows the difference between the fusion GMA (MIG) welding process and the non-fusion MIG brazing process. H-2 This pulse MIG welding machine has pre-programmed parameters for MIG brazing. MIG brazing: MIG brazing: n is a non-fusion joining process. Factory MIG brazed joints are found on some cosmetic exte- n is done using GMA (MIG) welding equipment. rior panel joints such as the quarter panel to roof Because the electrode wire is softer than steel seam, and may also be found in limited areas of wire, plastic cable liners and half-round smooth the vehicle structure. drive rolls are typically used. Pulse MIG equip- n uses much lower heat than GMA (MIG) welding ment yields the best results as it provides the and therefore, damages much less of the factory lowest heat input into the metal and produces zinc coating. The reduced heat input will also almost spatter free welds. Some machines may create a much narrower heat affect zone, result- have pre-programmed parameters for MIG brazing in less damage to the strength of the steel ing. being joined. n uses copper-silicon (CuSi3) or bronze alloy (CuAi8) electrode wire. Copper-silicon is the most common electrode wire for MIG brazing sheet steel. n typically uses 100% argon for the shielding gas. Shielding gas flow rates are typically set in the 25–30 cfh range.

Mild Steel High-Strength Steel Extra-High-Strength Steel Ultra-High-Strength Steel

Land Rover Ranger Rover Sport

H-3 This illustration shows the location of the MIG braze slot welds made when replacing the outer A-pillar on the Land Rover Range Rover Sport. Volvo S40

MIG brazing for collision repairs is fairly new, vehicle I-1 This illustration shows the steel types used on the Volvo S40 body maker recommendations vary including: shell. n no mention of the process. Vehicle design and construction processes are: n duplicating factory MIG brazed joints during the repair process. Toyota has numerous references n changing rapidly with passenger safety at the in their collision repair manuals to brazing roof forefront of many. Vehicles are being designed panel-to pillar joints and quarter panel to rear and built different from what we have become body panel at the drip channel joint. used to working on. n replacing factory GMA (MIG) welds with MIG n using many new steels that were not in vehicles brazing. Currently, most of the recommendations of just a few years ago. for using MIG brazing on structural parts apply n using new build geometries to help control and to European vehicles that are not available in transfer collision energy around the passenger North America, including the Vauxhall Vectra C compartment of the vehicle. Opel, the Volkswagen Golf, and the PSA Peugeot n using new construction methods to attach parts. Citroen1s. One North American Example is the The increased use of HSS and UHSS, as well outer A-pillar to UHSS inner panel joint on the as the desire for increased NVH and corrosion 2006 Land Rover Range Rover Sport. MIG braze control, has led to the vehicle makers adopting slot welds are made through the replacement new construction methods for the attachment A-pillar to the UHSS inner panel. of some parts.

MIG BRAZING SAMPLE Select the Demonstration icon found on screen H-3 of your CD-ROM for an example of MIG brazing.

I-2 The ultra-high-strength steel inner reinforcements are being slid up I-3 New steels and construction techniques are leading to less structural into a portion of the inner B-pillar assembly that remains on this Buick straightening and more complete part replacement. Encalve when replacing the B-pillar.

The way vehicles are built is changing and it is impact- Because of the new higher strength steels and ing the repair process. Collision repairs: designs being used in vehicles, collision repairs are involving: n are changing along with the way vehicles are built. The vehicle makers’ emphasis on comfort n less structural straightening. With parts being and safety has to become a part of the thinking made from steels 2–3 times stronger than in the we use during repairs also. past, and with reinforcements and multiple layer- n on new vehicles may use new techniques and ing of panels, straightening of structural parts is procedures that weren’t part of the process just becoming more difficult. a few years ago. n more structural part replacement. Since parts n may require new skills and equipment that didn’t are more difficult to straighten, more parts are exist a few years ago. being replaced. Structural parts can be sectioned n are being supported by the vehicle makers at where there is a procedure, but may have to be a greater level that ever before. Vehicle maker replaced in their entirety because of design or part replacement and sectioning procedures are vehicle maker recommendations. becoming more common on the newer design vehicles.