Thermal spray technology for engine blocks

Reducing vehicle weight and frictional losses in the power- train can help improve overall vehicle efficiency, which is one reason why many manufacturers are adopting aluminum alloy engine blocks as an alternative to traditional cast iron blocks.

Aluminum reduces weight, and many automakers have spent significant time engineering solutions that are capable of addressing the tribological deficiencies introduced with aluminum cylinder blocks.

One solution has been to sleeve the cylinder bores of an aluminum block with cast iron. This solution compensates for the missing tribological characteristics of aluminum, however, packaging the liner into the block and the weight and thickness of the liner itself are problems. The most significant disadvantage, however, concerns thermodynamic properties. Even if the insertion of the liner to the block material is ideal, thermal conductivity and thermal capacitance can hamper the ability to maintain efficient piston and bore temperatures for optimal combustion.

A more recent solution to address this issue is to use plasma transferred wire arc (PTWA) thermal spray coating to coat aluminum cylinder bores with a fine spray of molten steel particles at an extremely high speed. The ComauSmartSpray system transforms the aluminum engine block into a monolithic mass that reduces the weight of the engine, increases endurance, and lowers energy consumption. The cell is available with one or two robots.

Comau’s spray technology integrates into high-volume production lines because it essentially substitutes one process with another. PTWA eliminates the setup and processes needed to insert the cast iron sleeves in the aluminum casting, which translates to a reduced number of process steps. At the same time, the machining process of the PTWA-coated aluminum engine is identical up through the final bore steps. Here, instead of finishing boring, the cylinder bores are roughened and sprayed with a 0.10mm-to-0.15mm layer of molten steel. Once sprayed, the process continues as before with the final washing and honing process.

PTWA coated cylinders are more durable than non-coated cylinders, and the treatment can ensure a reduction up to 0.5kg per cylinder according to the engine’s geometry. In terms of thermodynamics and tribology, PTWA reduces friction and knock and improves noise, vibration, and harshness performance. Performance enhancements include reduced heat loss, emissions, and fuel efficiency.

Because it can coat cylinder bores measuring from 70mm to 120mm in diameter, new engine models can be inserted into the line with minimal modification of the PTWA production cell. At most, there may be minor adjustments related to the interfaces with the new block.

Whether designing a new line or retrofitting an existing one, thermal spray coated cylinder bores is becoming an essential solution for advanced light-alloy engine production.

Comau LLC

www.comau.com