Stellite, a cobalt-chromium superalloy with applications in aerospace, automotive, and biomedical industries, presents machining hurdles due to its formidable hardness, toughness, work hardening, and limited thermal conductivity. Challenges include excessive tool wear, poor surface finish, and dimensional inaccuracies. Addressing these demands strategic solutions, including specialized tool materials, applying coolant flood in specific locations, speed and feed optimization, rigidity reinforcement, and automation. Conquering these challenges requires a nuanced grasp of Stellite’s properties, ensuring the cost-effective manufacturing of high-performance components across various applications through purpose-driven machining methodologies.
Research Highlights
- Successful Stellite machining, a superalloy with a hardness range of 30 to 48 HRC, was achieved.
- Innovative methods were introduced to overcome the machining challenges associated with Stellite in this project.
- The project’s insights were applied to successfully machine a pelletizing cutter made from Stellite.
Challenges
Machining Stellite, known for its hardness (30-48 HRC), presents intricate challenges. Its hardness leads to swift tool wear, hindering precision. The cobalt binder imparts toughness but elevates cutting forces and temperatures, risking plastic deformation. Stellite’s age-hardening nature exacerbates complications by rapidly work-hardening during machining, escalating forces and wear. Additionally, Stellite’s poor thermal conductivity, just 1/8th of steel, intensifies challenges. Heat buildup in cut zones accelerates tool wear, impacting the process. These hurdles manifest in issues like excessive wear, poor finish, inaccuracies, high temperatures, and forces causing problems such as chatter, tool breakage, and part defects.
Our Solution
To tackle these challenges, strategic solutions and optimization techniques were deployed. The selection of ceramic cutting tools and the application of TiAlN significantly extended tool life. Precise coolant application, utilizing high-pressure, high-volume flood coolant directed precisely at the tool-stellite interface (Figure 1), proved effective in maximizing heat removal and lubrication.
Enhancing efficiency in Stellite machining involved strategic adjustments in speed and feed parameters, prioritizing lower speeds and moderate feeds compared to conventional steel machining. Reducing setup overhang, ensuring secure part fixturing, and utilizing short, stiff tools on robust machining platforms contributed to increased rigidity, minimizing vibration and deflection. Additionally, automation elements, including part manipulators, pallet changers, and tool changers, facilitated extended unmanned operations, improving overall efficiency, especially considering Stellite’s slower metal removal rates. The successful machining of a Stellite pelletizing cutter implying the mentioned strategies is shown in Figure 2.
Machining steps for a pelletizing cutter manufactured by laser deposition of Stellite are demonstrated in Figure 3, applying the findings from this project.
Outcomes
- Overcoming challenges in Stellite machining through a deep understanding of its properties and behavior.
- Implementing purpose-driven approaches, including specialized tools, precise coolant application, optimized machining parameters, and automation, for effective Stellite machining.
- Successful resolution of Stellite machining challenges, enabling cost-effective production of high-performance components like the palletizing cutter.