Turbochargers

Problem

Many modern passenger car and commercial vehicle engines are equipped with turbochargers. Manufacturers of these units had conventionally used inertia friction welding techniques to join the investment cast, Inconel wheel to the carbon steel shaft. Although this joining method produced a joint of adequate strength, the post-weld machining, grinding and heat treatment operations were expensive and time consuming. An alternative welding process using EB welding has been adopted by a number of leading turbocharger manufacturers.

Solution

Electron beam welding using a stream of finely focussed electrons to melt and fuse joint surfaces, was found to be the ideal solution to the problem. The welding process can be fully automated and weld parameters, such as accelerating voltage, beam current, beam focus
and traverse speed are controlled. The high heat intensity produces a narrow fusion zone, with very little distortion, so it is possible to weld together machined components in the finished condition.

Process

The characteristic electron beam weld has deep penetration, a narrow fusion zone, near parent metal strength and is carried out in a vacuum. The low heat input (typically 5% of that required for other fusion welding processes) confers small disturbance of metal near the weld zone and correspondingly small distortion of piece parts, so that finished components can be joined. Similarly, weld beads can be controlled to the extent that further finishing after joining is unnecessary. The technology permits intricate and complex fabrications to be made in a variety of materials and material combinations. The dissimilar combination of an Inconel rotor and a carbon steel shaft presents no technical problem to the electron beam welding process.

Parts are either machined with a spigot to make the joint self-locating or simply butted together before welding. Parts are welded in the finished or semi finished condition. With correct alignment of the beam at the rotor/shaft joint, accurate and repeatable welds are possible with no associated cracking.

The feature of CVE's welding process with a butt joint configuration is that neither of the two parts is machined to provide positive and precise location prior to welding. The electron beam welder is equipped with CVE designed tooling which holds the rotor and shaft accurately together during joining.

This helps to minimise the investment cost of the manufacturing cell by minimising the process steps and the number of machines required.

Examples of fast cycle machines for automotive applications include:
Turbocharger welder Includes 2 or 4 station rotary indexing table for high productivity and can be configured for both passenger car and commercial vehicle turbos. Includes quick-change precision tooling.

Today electron beam welding is an accepted production route in manufacturing turbochargers. In addition to EB welding shafts and wheels the process is also applied to other applications in turbocharger technology including variable geometry turbos.
CVE have supplied around 40 turbocharger welding systems throughout the world and the replacement of friction welding with electron beam seems set to continue.