Electron beam welding in the automotive industry

The qualities of speed and precision make EBW a favoured joining process in a number of automotive applications. Both vacuum and non-vacuum process derivatives have been widely industrially employed. TWI's EB group has helped to prototype and develop a large number of automotive applications. In many ways EB welding is well-suited to mass production as it is a non-contact joining technology, with little in the way of moving or wearing parts to worry about. Although the equipment is rarely inexpensive, consumables costs are typically low, making the process extremely cost-effective. Some examples of typical automotive applications are given below;

Gear welding

Both continuous and intermittently loaded gear components are welded via EBW. Of the latter variety, synchromesh rings are welded to gears in their millions. EB machines that perform this task usually have small chambers with rapid pump-downs. They may also employ a pre-evacuation strategy so that unwelded parts are made ready to be welded, and the electron gun is more effectively utilised.

EB welding is often used to make gears that are difficult or impossible to make via normal mass-production machining techniques. This can result in smaller, lighter gears, or it may simply reduce costs. Auto-gearboxes frequently utilise EB welding for the manufacture of gears, planetary gear hubs, and other parts.

Turbochargers

Modern high specific output diesel engines invariably utilise turbocharging as a means of improving power output and fuel consumption figures. At one end of a shaft, a compressor wheel forces the air into the engine; this is driven by a turbine wheel spinning at up to ~200000rpm, propelled by the exhaust gases. This sounds like some form of perpetual motion, but it isn't- it is just one method of achieving forced induction, by which means the overall efficiency of an engine may be increased. The compressor wheel operates at relatively low temperatures, so is normally made of an aluminium alloy. But the turbine wheel sees very high temperatures, and must be made from a heat resistant alloy. Typically this is a Ni base alloy, of a type that until recently would only be found inside a jet engine. These alloys are inherently expensive, and materials costs are saved here if the wheel can be welded to an inexpensive steel shaft. EB welding is a favoured process here, providing welding speed, integrity, and very low distortion. The narrow angle EB is able to weld in relatively inaccessible locations, even on the largest diameter impellers, unlike competing technologies, e.g. laser welding techniques. EB welding has an excellent track record, having made millions of sound, cost-effective welds in this application.

Typical turbocharger wheel and shaft welding installation Courtesy of CVE

Other applications

Non-Vacuum (NVEB) welding has been used for over thirty years to make a variety of welds at extremely high production rates, typically in thinner section parts. Power outputs of 30kW are readily attained, giving extremely high joint completion rates. In total it is estimated that several billion automotive components have now been NVEB welded.

NVEB is also favoured for high speed welding of automotive structural components. Its ability to accommodate joint fit-up gap variations, even at welding speed in excess of 30m/min, make it highly suitable for such mass production applications.

EB systems have also been deployed for many other automotive applications, including leather perforation, camshaft hardening, etc. There is surely a multitude of other future developments.

The following are of particular interest to the automotive industry:

• Enhancements to power beam welding processes for land transport
• Review of electron beam and friction technologies from 2001
• Comeld ^TM - joining composite materials to metals

Contact: electronbeam@twi.co.uk