Joining Mechanisms in BIW

Joining methods play a critical role in the BIW industry. It, directly and indirectly, influences critical aspects of the vehicle viz., the weight, fuel consumption, structural integrity, strength, and cost of the vehicle. Joining methods can be thermal (Arc welding, MIG Welding, Laser brazing) and non-thermal (clinching, glueing, riveting, etc.) in nature.

This article will take you through the popular joining methods in the BIW industry viz. Spot Welding, MIG Welding (Arc Welding), Laser Brazing and Clinching

Spot Welding

Also called Resistance Spot Welding, spot welding continues to be the main choice of joining processes in the body shop ( it constitutes close to 40% of all joining processes).

• It is a solid-state welding method and is used for joining overlapping sheet metals in projects where strength and durability are not pressing.
• Workpieces are held together under the force exerted by electrodes.
• Typically, the sheets are of the order the 0.3 to 6 mm thickness.
• The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets. This forces the large current through the spot, which will melt the metal and form the weld.
• Spot welding has fewer applications and tends to harden and warp workpiece materials. 
• Low-carbon steel is the most suitable material for spot welding.

 Advantages:

• Time-saving compared to TIG or MIG welding.
• Very suitable for high volume & automated production.
• It does not require grinding after welding (to remove slag formation).
• Minimal material distortion.
• Non-consumable electrode, unlike MIG Welding.
• No slag formation after welding.

Arc Welding

Arc welding is one of the most prominent types of welding. Arc processes involve using the concentrated heat of an electric arc to join metal materials (Fusion welding)

• The arc can be either manually or mechanically guided along the line of the join, while the electrode either simply carries the current or conducts the current and melts into the weld pool at the same time to supply filler metal to the
• Since the metals react chemically to oxygen and nitrogen in the air when heated to high temperatures by the arc, protective shielding gas or slag is used to minimize the contact of the molten metal with the air. Once cooled, the molten metals solidify to form a metallurgical bond.

Categories of Arc Welding

MIG Welding

MIG Welding is the most widely used arc welding technique in BIW joining. Aluminium parts have been largely joined by means of MIG (Metal Inert Gas) welding in lightweight car manufacturing.

This technique is principally used to make joints between castings, extruded sections, and sheet-metal parts.

Advantages

• High-strength weld with a great appearance
• Little need for sanding or cleaning
• Relatively quicker process due to operability at a continuous rate due to the use of shielding.
• MIG welding can be used on any metal surface and can weld materials as thin as 26 gauge.

Metal Inert Gas Welding

MIG welders use a tool called a spool gun, which feeds a spooled wire electrode at a selected speed. The gun also emits a shielding gas as it lays the weld. This gas protects the weld area from atmospheric gases such as nitrogen and oxygen, which can cause problems if they come in contact with the electrode, the arc, or the welding metal.

The final result of an optimal MIG Welding process

Laser Brazing

• Welding vs Brazing

A brazed joint is made in a completely different manner from a welded joint. Brazing does not melt the base metals since the temperature is invariably lower than the melting points of the base metals. Brazing temperatures are significantly lower than welding temperatures for the same base metals, using less energy.

A brazed joint has a smooth, favourable appearance compared to a welded joint and reduced cost since there is no need to perform any finishing operations after Brazing is performed.

Laser Brazing

• Laser Brazing or Laser Soldering is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal.
• The filler material, typically a wire with a diameter of 1.0 mm, is fed to the process. The laser beam melts the wire, and the melt penetrates the gaps in the joint and wets the joint surfaces. The filler solidifies and forms a smooth joint. The filler wire can be preheated to increase the processing speed.

• Compared to laser welding or spot welding, laser brazing has improved geometrical tolerances and improves the joint's aesthetics.
• The consumer gets a lighter, quieter, stiffer, and safer car as the final that doesn’t have extra plastic parts.

Clinching

• Clinching(press-joining) is a bulk-sheet metal-forming process for joining thin metal sheets without additional components, using special tools to plastically form an interlock between two or more sheets.
• The process is generally performed at room temperature, but in some special cases, the sheets can be pre-heated to improve the material ductility and thereby avoid the formation of cracks during the process.

Advantages

• Riveting without rivets
• Fast, clean, and easy joining process
• High static and dynamic strength
• Energy savings since it does not require electricity
• No contamination of workpieces
• Used widely in the automotive industry, where it often replaces spot welding.

Clinching Tong for Robotic arms