solidification of small globules, flattened from striking a cold surface at high velocities. Advantages of the twin-wire arc spray process include: • A high amount of material deposit • Wires as the feed stock material (easier to handle than powder)
• It is considered a ‘simple process’ as only a few compo- nents are necessary
• Coating without process control is possible • No extra cooling of the torch is necessary
However, the coating process requires optimal calibration
of quality-determining parameters such as current, voltage, wire feed and process gas flow. Specific advantages of the spray coating for combustion
engines are: • Weight and space advantages over liners • Favorable frictional conditions between the liner, the piston and the ring
• Fuel consumption advantages for diesel and gas engines • A very high wear resistance in-service • Manufacturability in a reliable process and at favorable costs
Due to their thermally coated cylinder liners, Nanoslide-
designed engines are superior in terms of displacement and torque, especially when compared with similar aspirated en- gines incorporating conventional lining technology. Daimler AG started development of the coating technology in 1998 with small, series production of high-performance AMG engines, including the 6.3L V8. Since 2006, Daimler has used the treatment on more than 80,000 engines.
Moving from Prototype to Series Production To provide a practical, automated process for higher pro-
duction applications, Daimler AG has entered a partnership with Heller. For its part, Heller will provide automation of pro- cesses and equipment, and develop improved processes stability
• Enhance all process steps and equipment for future requirements
• Adapt the process to different crankcases • Produce a constant surface quality with guaranteed properties
Te CBC machining process at Heller includes premachin-
ing, fine boring, coating, finish machining and finish honing the coated cylinder bore—all accomplished on the Heller MC20 four-axis machining center. Total cycle time, includ- ing part load/unload, for an eight-cylinder engine is five–six minutes. Te engine blocks may be direct-loaded into the machining center or mounted on a swiveling exchanger. A key contribution of Heller to the process is to fine-bore
the arc-sprayed cylinder coating to impart a final finish. Previ- ously this was accomplished with honing, but the Heller fine boring process takes about half the time and assures a much more consistent finish and form to the cylinder due to the ma- chining center spindle axial orientation to the bore. Tooling cost is also much lower compared to honing.
Measuring the Coating Assures Positive Results Te applied coating is measured with a Jenoptik IPS 100
bore inspection sensor system which provides a rapid, single pass automatic surface inspection of bores from 75 to 110-mm diameter, instantly providing a 360° panoramic view. Te sensor permits detection of surface defects such as
blow holes, scratches, porosities and more on bores from 75 to 110-mm diameter, to any depth. Utilizing state-of-the-art CMOS imaging technology, the IPS100 continuously scans the bore surface at high speed, creating a viewable image of the bore interior. In operation, a 360° circular optic is advanced into the bore
and generates an image of the surface. Circumferential lines in the bore are seen as rings in the image. As the sensor advances into the bore, circular scanning allows for the generation of an undistorted image of the inner surface.
Daimler AG is using the newly developed arc spraying technology for coating cylinder bore surfaces and aluminum crankcases.
strategies. Te development and demonstration of technology will be conducted at Heller’s Cylinder Bore Coating (CBC) Technology Center at its global headquarters in Nürtingen. With its global range of systems and services to support
wider application of the process beyond the limited-edition, high-performance AMG engines, Heller in cooperation with Daimler and other interested parties will automate all steps of the process and develop it into a reliable application for global markets under the name Heller CBC. Te goal of the CBC Technology Center is to: • Coat trial parts for future coating cells
“Although the technology has only been used for exclu-
sive low-volume series until now, its application in medium- volume production already provides significant competitive advantages compared to existing cylinder lining technolo- gies,” said Vincent Trampus, Heller vice president of sales. “Te technology complies with the production rules and criteria of the automotive industry. Now, it is only a small step to mass production.”
Edited by Yearbook Editor James D. Sawyer from material provided by Heller Machine Tools.
Motorized Vehicle Manufacturing 69
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