Session: 03-05-01: 8th Symposium on Fastening and Joining Research and Advanced Technology

Paper Number: 109836

109836 - A Thorough Characterization Study of the Critical Al-Fin Bond Between the Ni-Resist Insert and Aluminum Base Material in a Heavy-Duty Engine Piston 

The need to reduce emissions while increasing power output necessitates high loads and temperatures within an engine. This in turn places more stress on the high temperature resistant cast-iron insert that reinforces the top ring groove of piston in a reciprocating engine. This insert is an engineered component in which the nickel content is optimized to match the coefficient of thermal expansion of the high silicon aluminum of the piston. 

The Ni-Resist insert used in the INNIO Waukesha VHP piston is bonded to the piston during casting by the Al-Fin bond process.  The Al-Fin bond between the Ni-Resist insert and cast piston material is critical to the manufacture and performance of pistons used in heavy duty industrial engines.  Iron has a strong solubility in the molten aluminum but does not at room temperature.  The typical preparation of the Ni-Resist inserts to be installed in a piston mold prior to filling the mold is to immerse the insert in a bath of molten aluminum for a predetermined amount of time.  The dissolution of alloys from the Ni-Resist insert into the bath make control of the bath composition a critical parameter.  Negligent bath maintenance can result in the potential of forming undesirable intermetallics in the bond region.  The material structures in the bond can be complex with metastable phases developing.  This means the Al-Fin bond can be brittle and sensitive to variation in tooling pressure during machining. 

In the INNIO Waukesha design, the loading on the piston is not great enough to damage the bond during routine service.  However, any flaws in the bond during piston casting or machining can propagate during engine operation and result in a power cylinder failure, leading to collateral damage of other engine components and a lengthy repair time.  The disciplined use of ultrasonic inspection in the rough machined and the finished piston catches defects and prevents faulty pistons from being released to a customer.  However, if problems are identified at these aforementioned late stages, they can result in product delivery delays and even the shutting down of the engine factory assembly line.  Since the raw casting used to produce the piston can be sourced from several different foundries around the world, it is important to have a robust method to ensure the integrity of the Al-Fin bond.

This paper highlights the modern material characterization methods used to identify a satisfactory bond.  The understanding of the challenging nature of the bond between the Ni-Resist insert and the piston material has been gained through these methods. This knowledge has helped resolve problems by both quickly getting to their root cause and taking corrective action.  This minimizes production delays and works toward the INNIO Waukesha gas engine goal of meeting its customers’ needs.

Presenting Author: Subha Kumpaty Milwaukee School Of Engrg

Presenting Author Biography: Dr. Kumpaty is a professor of mechanical engineering at Milwaukee School of Engineering. He collaborates with INNIO Waukesha Engines on various materials characterization studies.

Authors:

Subha Kumpaty Milwaukee School Of Engrg
Nolan Coen INNIO Waukesha Gas Engines
Liam Coen INNIO Waukesha Engines