Laser honing boosts engine performance
Big Three discover its benefits
Racing has been the proving ground for technical developments in the automotive industry since the early days of dirt tracks and race cars with mechanics on board. When a racing team, in any given racing season, suddenly pulls away from the pack, it’s usually a sign that they’re on to something new.
This happened just a year or so ago when laser honing was “discovered” by racing teams on several of the major racing circuits. Engine performance and race results improved dramatically when the process was used to finish the cylinders of these high-performance engines.
“Laser honing of cylinders produces a superior surface match With piston rings that reduces friction blowby and wear,” explains Olaf Tessarzyk, president and CEO, Gehring L.P., Farmington Hills, MI. “The laser honing process gave the racers who adopted it a big competitive edge.”
Its potential for engines has not gone unnoticed by the Big Three automakers who are integrating the process into their transfer machining lines in the U.S. and Europe. Initially they have targeted diesel engines because of the ability of laser honing to dramatically reduce emissions.
Introduced in 1997 by Maschinenfabrik Gehring GmbH, Ostfildern, Germany, the laser honing process combines laser structuring with conventional honing to produce a microstructure in the cylinder wall for both high bearing capacity and excellent gliding properties. It also produces an open structure to ensure lubricant retention.
The microstructure comprises pockets (either spiral or cup structures) that are drilled into the cylinder wall by a laser beam. After laser machining, the cylinders are finish honed to remove the buildup of any molten mass on each side of the groove. The new automotive production sequence is rough honing, semifinish honing, laser structuring and finish honing.
The benefits of laser honing cylinders are dramatic, says Tessarzyk. “They include reduction of oil consumption, improvement of emissions, reduction of wear and a subsequent increase of service life, higher degree of efficiency and reduced friction losses resulting in lower fuel consumption.”
The simple explanation is that the lubricant adheres better to a laser– honed surface for optimal tribological conditions for bearing and lubricating qualities. As a result, any stressed component that can benefit from a better design for lubrication offers good potential. Typically, pieces like guideways, slide bushings, axial face seals, control bushings, drawing tools or control pistons can benefit from laser honing by reducing wear from abrasion and adhesion.
The wear rates of these components are determined by the complex interaction of many parameters. The factors include component load, kinetic conditions, relationship of hardness between the component materials, and topography of the interacting surfaces that are in relative motion. Bearings and gears are typical of such “stressed components.”
Piston engines offer potential because of the desire to optimize fuel consumption and minimize emissions to the environment. In laser honing cylinders, only the top third of the cylinder has to be laser honed because that’s the point of highest pressure, Tessarzyk points out, where a better surface match can do the most good.
Laser honing is an alternative to the universally used method of plateau honing. The limitation of plateau honing is that irregularities are caused by the variance of grain size and grain distribution in the honing stone. As a result, the match of cylinder and piston can only be so close.
For the automakers, adding the laser honing process to a transfer line is as easy as adding another station. The laser is located in a spindle where rotary and stroke movements are NC controlled. The high-energy Nd-YAG beam is focused on the bore wall in a cylinder block where it strikes the surface of the workpiece and is partially reflected and absorbed. As a result of the absorption of the beam energy, the material is heated up to the vapor phase.
The stock removal is determined by the parameters of pulse frequency, power, mode panel and feedrate-all of which are NC controlled. As a result of the steep temperature gradients and the high power density, the local and temporal action of the beam on the workpiece is extremely limited. The total temperature rise is insignificant. Adhering dirt and cooling lubricant residues vaporize or bum and consequently have no influence on the quality of the machined surface.
The potential for the laser honing process extends well beyond diesel, gasoline and race car engines.. Laser honing can be beneficial wherever two mechanical surfaces are in contact for critical bearings and gears, for example. “In applications where maintenance and safety are critical considerations such as aircraft gears and turbines, laser honing can have a dramatic impact,” Tessarzyk concludes.
Gehring L.P., Farmington Hills, MI, www.RSLeads.com/?201tp-173 or circle 173
By Jim Lorincz
Copyright Nelson Publishing Jan 2002
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