Ford Workshop Service and Repair Manuals

Normal strength steels

Normal strength steels are most often used in body construction. They are relatively soft and are therefore particularly suitable for the deep drawing processes used in body manufacturing. As well as very good reshaping properties, the panels also have a relatively high rigidity.

High strength steel panels

The strength of the material and the nature of the surface can be changed as required by different engineering processes. In order to achieve suitable configuration and a good match between construction specifications and what is possible in production, a large range of high strength panels is available.

The range of the minimum yield strength is from 180 N/mm² to 460 N/mm². High strength thin steel panels usually have a surface finish. Electrolytic surface sealing is preferred.

Within the group of high strength steels, various types of steel are used in body construction:

• Micro-alloyed high strength steels for very difficult drawn components such as fenders, the internal components of doors, hoods and luggage compartment lids or load bearing components such as sidemembers, crossmembers etc.
• Bake-hardening steels and phosphorus alloyed steels for external panel components with higher draw depth and subject to higher operational demands.
• Isotropic materials for flat shaped outer steel panels on doors, hoods, luggage compartment lids, roofs.

Ultra-high-strength steels

These steels are predominately used for body structural components which are relevant to safety. Despite the reduced thicknesses of the panels used, weight reduction is often achieved together with greater strength.

As with high-strength steels, special types of steel are used in the ultra-high-strength steels group:

• Complex phase steels are used for door side impact carriers, bumper carriers and body components relevant to crashes. Besides high strength, they have good cold reshaping properties and are easily welded.
• Dual phase steels have the same properties as complex phase steels. Because of their high strengthening properties they are suitable for body reinforcements.
• Residual austenite steels and martensite phase steels have very high strength levels of up to 1200 N/mm² and are mostly used in body structures relevant to crashes.

Because of the use of such steels, some special points must be taken into account during body repair:

• Increased force required during straightening.
• Strong springback tendency during alignment work.
• Cutting tools have a shorter useful life.
• 

  NOTE:High-strength and ultra-high-strength steel panels must not be heated during straightening work.
  Work without applying heat when carrying out straightening work. Losses of strength will occur at temperatures as low as 400°C.

The basic working methods and the tools to be used are the same however.

Coated steel panels

In a similar way to high-strength steel panels, coated steel panels are finding more applications because of the better corrosion protection which they offer. There are basically two different process which are used to apply a zinc layer:

• Hot dip zinc coating (no longer used in vehicle construction).
• Electrolytic zinc plating.

The following points must be noted when welding:

NOTE:Welding fumes are harmful to health. Make certain that the workspace is well ventilated and use welding fume extraction.

• Zinc starts to melt at about 420°C.
• The zinc vaporizes at a temperature of about 900°C.
• The amount of heating determines the damage to the zinc coating, and therefore to the corrosion protection.
• 

  NOTE:Coated panels have a higher electrical resistance, but this can be compensated for by increasing the welding current by 10 - 20% .
  Resistance spot welding is particularly suitable for welding zinc-coated panels, because no widespread warming occurs.
• With electrolytically zinc-plated panels there is no need for any special preparation because the zinc coating does not need to be removed.

Tailored blanks

Tailored blanks are panels which are made up of at least two separate panels with different material thicknesses and/or material properties. The panels are joined together by a laser weld seam and then shaped in a press.

This technique allows panel shapes to be produced which meet special requirements with regard to deformation behavior, strength and weight.

Laser weld seams at the sidemember

NOTE:No cutting, no welding and therefore no sectional repairs are permitted in the immediate area of the laser weld seams. The model specific requirements are documented in the respective Body Repair Manuals.

Typical examples of application are:

• Sidemember.
• Door inner reinforcement/door frames.
• Wheelhouses.
• Rocker panel inner reinforcement.
• Roof rail inner reinforcement.

When repairing the vehicle body, pay special attention that such a connection is never separated. The possible cut line locations are given in the respective repair manuals.

Aluminum

Aluminum is becoming ever more important in body construction because of the trend to reduce weight. Doors, hoods and body outer panels are increasingly being made of aluminum alloy panels.

Although at the time of publication of this document, Ford of Europe has not yet introduced any aluminum body or aluminum body components, this topic is briefly described in this section.

NOTE:Fine aluminum dust may catch fire if a flame or spark touches it. All persons working in the workshop should pay special attention to this danger.

All the tools needed for body repair must be suitable for working aluminum, and they must be only used on aluminum.

The main properties of aluminum are:

• Low weight.
• High resistance to corrosion.
• High strength.
• High deformation rigidity.
• Very good heat conductivity.
• Very good electrical conductivity.

NOTE:When working aluminum components pay particular attention to avoid the danger of contact induced corrosion. The workplace must be free of steel swarf, and tools which have worked steel panels must not be used.

In the electrochemical potential series, aluminum has a negative potential of 1.23V in relation to steel. Because of this, when aluminum and steel touch and an electrolyte is present, contact corrosion occurs.

The following points should therefore be noted:

• Use only checked and coated connecting components (bolts, nuts, washers etc.).
• Always use new bolts.
• Use adhesives and sealants which are tolerant towards aluminum.
• No steel swarf in the workplace. Clean the workplace and pay attention to any steel-sanding dust from neighboring workplaces.
• Use a separate set of aluminum working tools.
• Use wire and rotating brushes made of stainless steel.

NOTE:In-depth knowledge and skill in panel beating techniques are the basic requirements for the repair of aluminum panels.

In the main, aluminum panels can be worked using the same processes as used for steel panels. There are however some special features to pay attention to:

• Do not use steel hammers or sharp-edged panel beating tools.
• Only use hammers with smooth surfaces.
• Working cold aluminum leads quickly to embrittlement. For this reason, perform more extensive mechanical deformation removal under exact temperature controlled heating.

NOTE:If uncontrolled heating is used on an aluminum panel, it will very quickly be destroyed, and a new one must then be installed. The necessary specialist knowledge cannot be given in theory, special courses must be attended instead.

In contrast to steel, aluminum does not display any surface color change when heated. This therefore means that the level of heating of the material cannot be seen.

Only once the material is overheated does a change in the material structure of the surface occur. By the time this has occurred, the structure of the material is already seriously damaged, and its strength very much reduced.

Overheated aluminum components must always be replaced.

Aluminum welding

Aluminum welding requires a welder which is specially designed to meet these requirements.

NOTE:As a rule, vehicle manufacturers require that persons who wish to weld aluminum must show evidence of having completed special training in aluminum welding. Please study the guidelines.

Both repair welding processes are based on fusion welding.

• MIG welding (metal-inert gas welding).
• MAG welding (metal-active gas welding).

Success of aluminum welding partly depends on how well the surface oxidation can be removed. Because aluminum oxide remains solid at the melting point of pure aluminum, it is important to remove it before welding.

• Melting point of aluminum (approx. 660 °C).
• Melting point of aluminum oxide (approx. 2040 °C).

The aluminum surface must be cleaned before welding. Cleaning improves the later fusion penetration and prevents contamination of the welding wire.

NOTE:If a stainless steel brush is used, it must never come into contact with steel components, so that it does not become contaminated.

The following three steps are to be performed in preparation:

• Clean the surface. Use a chemical cleaner to remove all traces of wax and other contaminants.
• Remove the oxide. This can be done using abrasive paper or a stainless steel brush.
• Wipe the oxide dust away with a lint-free cloth.

Aluminum oxide forms very quickly, therefore steps 2 and 3 should be performed immediately before welding.

Before working on the vehicle body, create a test seam on scrap which is made of identical material. Test the test piece visually and destructively, to make certain that all welding parameters are correctly set, and an acceptable weld seam can be achieved.

An optimum weld can be recognized by the following quality features:

• All visible weld surfaces are clean, light and have the same profile.
• The weld seam should have the same height and width over its complete length.
• There must have been complete melting between the surfaces of the work piece and the weld metal.
• The correct penetration has been achieved when a thin continuous line can be seen on the reverse side.