Lapping and Polishing Inconel for High Surface Finish

Precision lapping is a critical process in achieving desired surface finishes and ensuring proper sealing performance in high-precision components. The primary goal in this test trial was to match and lap Inconel components to identify whether RA (reduced angle) or ER (extended radius) configurations provide better sealing. Achieving a highly polished surface finish with an Ra of 0.1 µm was essential for enhancing sealing efficiency and minimising potential leakage.

The following equipment and materials were employed during the process:

• Kemisphere II
• Custom Tooling specially designed fixtures to securely hold and align the parts during the lapping process
• C0-42 Cleaning Fluid
• Diamond Paste (6, 3, and 1 micron sizes, Type KD) utilised in successive steps to progressively refine the surface finish

The following steps outline the lapping procedure:

• Each Inconel part was loaded into the chuck of the Kemisphere II machine. The lap arbour was secured using a locating pin to ensure precise alignment during the lapping process. Custom tooling provided additional stability and repeatability.
• Diamond compound abrasives were applied in descending grades of coarseness (6 µm, 3 µm, and 1 µm).
• The parts were lapped for one minute clockwise (CW) followed by one minute counterclockwise (CCW) to ensure uniform material removal and minimise surface asymmetry.
• Each assembly underwent 18 minutes of total lapping time, equally distributed among the abrasive grades to achieve progressive surface refinement.
• Following lapping, the parts were meticulously cleaned using C0-42 cleaning fluid to eliminate any residual diamond compound. The surface finish was then measured using a profilometer to ensure compliance with the target Ra of 0.1 µm.

Results and Observations: After the completion of the lapping process, the final measured surface finish was Ra = 0.1063 µm, slightly exceeding the target. This result demonstrates the effectiveness of the lapping procedure and the capability of the Kemisphere II in achieving near-target precision. The evaluation of sealing performance between Reduced Angle (RA) and Extended Radius (ER) configurations is ongoing. Preliminary observations suggest that the surface finish plays a significant role in improving the seal integrity, but detailed analysis is required to determine the superior configuration.

After Processing

Inconel is a family of nickel-chromium-based superalloys known for their exceptional resistance to oxidation, corrosion, and extreme temperatures. These properties make Inconel an indispensable material in industries that require high-performance components operating under harsh environments. The main applications of Inconel include:

• Aerospace and Aviation: Inconel is extensively used in jet engines, turbine blades, exhaust systems, and afterburners, where components must endure high-temperature exposure without losing mechanical strength or succumbing to oxidation.
• Power Generation: Inconel is crucial in gas turbines, heat exchangers, and steam generators, particularly in nuclear power plants, due to its ability to withstand both heat and radiation while maintaining structural integrity.
• Chemical and Petrochemical Processing: The material is highly resistant to corrosive chemicals, making it suitable for use in heat exchangers, reactors, and piping systems exposed to acids, alkalis, and high pressures.
• Oil and Gas: Inconel's durability and resistance to chloride stress-corrosion cracking make it ideal for downhole tubing, wellhead components, and other equipment exposed to sour gas or seawater environments.
• Marine Applications: The material’s exceptional resistance to saltwater corrosion makes it valuable in shipbuilding, offshore platforms, and underwater exploration equipment.

By enhancing the surface characteristics of Inconel parts, lapping and polishing not only improve their functionality but also extend their operational life, making them even more reliable in the demanding environments where they are deployed.