The fewer bumps, the better: This also holds true for slide bearings in engines, if the crank and cam shafts inside them are to rotate smoothly and thus save fuel. A new production technique considerably increases the quality of the bearings.
In order to avoid consuming unnecessary amounts of fuel, the crank and cam shafts of cars, trucks and ships must rotate as evenly as possible. They can only do this if the slide bearing bushes in which they move are sturdy and smooth. Any bumps or irregularities on the bearing slow down the crank and cam shafts. Bearing bushes are tubular and consist of a steel supporting layer and an aluminum sliding layer. After being cut to the right size from tube segments, they have to be elaborately processed to obtain their precise shape.
Researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz have developed a new method of manufacturing slide bearings. “The new bearings are ten times smoother than conventional ones – in other words, they deviate ten times less than usual from the circular form,” says IWU group manager Matthias Nagel. “The new production method drastically reduces the need for elaborate and expensive post-processing.” This not only saves costs but also speeds up production, enabling the bearings to be produced three to four times more quickly than before. An added advantage is that the slide bearings are sturdier than conventional components.
So how does the new method work? “The bearing bushes are produced as usual from flat metal sheets, which are rolled into their tubular shape inside the machine,” says Nagel. “However, we cut the sheet metal into wider strips than in conventional processes. To prevent bulges from forming or the diameter of the tube from becoming too large, we ensure that the material can only move in one direction. This produces a slightly longer bearing and a very even joint.” The surplus material generates a high tension in the metal, which then hardens. “This hardening effect makes the bearings much stronger than those produced in the conventional way,” says Nagel. Another effect of this residual stress is that the material becomes less elastic and can therefore be shaped more accurately. The machine was recently commissioned by Miba Gleitlager GmbH in Laakirchen, Austria, and should be producing twenty-one different components by the end of the year. “We expect enormous cost savings,” says Nagel, “something in the region of 150,000 euros per annum”.