Coating & Machining for Better Bores

Spray arc process of cylinder bores in aluminum blocks is preceded and followed by machining on a Heller machining center. Eliminates the need for iron liners in the bores.

Here’s a block that has been processed with the Heller Cylinder Bore Coating process. What you can’t see is a ferrous coating on the ID of the bores, which allows aluminum pistons to be run.

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Aluminum blocks without cast iron cylinder sleeves? Yes. And not just for high-performance engines. In fact, a cylinder bore coating process that Daimler AG has been working on since 1998, is being developed by Daimler, other partners, and Gebr. Heller Maschinefabrik GmbH—parent company of Heller Machine Tools (heller-us.com)—for mass-production applications by companies that don’t put the three-pointed star on the hoods of their vehicles.

Yes, the Daimler process is going commercial.

The process uses a twin-wire arc spray that melts iron/carbon wires, then uses nitrogen gas to propel the particles onto the surface of the cylinder bores at a velocity of from 60 to 80 m/sec. The particles are at a temperature of up to 2,000°C. The resulting surface provides both wear-resistance and lubricity.

Daimler has been using its NANOSLIDE process in low-volume production, for, primarily, AMG engines.

But now Heller is working on productionizing what it calls “CBC”—Cylinder Bore Coating. In other words, it is developing the processes and equipment such that this can be applied in high-production engine operations.

There are two pieces of equipment involved. The twin arc spray device, and a Heller MC20 horizontal machining center. The cylinders are prepared via the machining center, then sprayed. Subsequently, there are rough honing, finish honing, and finish machining performed. Whereas in the previous process honing was used in place of the fine boring process, but the boring is faster and imparts a more consistent finish and form to the cylinder. The cycle time to process an eight-cylinder block is six minutes or less.

Vincent Trampus, Heller vp of Sales, said, “Although the technology has only been used for exclusive low-volume series until know, its application in medium-volume production already provides significant competitive advantages compared to existing cylinder lining technologies. The technology complies with the production rules and criteria of the automotive industry. Now, it is only a small step to mass production.”