May 2025 Volume 7

EQUIPMENT & TECHNOLOGY

PUSHING THE LIMITS OF FORGING: Technical Advancements in Lubricant Engineering By Frank Sobnosky

A s forging operations evolve to and extreme forming environments, lubrication remains a critical variable in process efficiency, die life, and part quality. Recent developments in modifying lubricant tribology—the science of friction, wear, and lubrication—are reshaping how the industry approaches lubricant selection, accommodate increasingly complex geometries, aggressive cycle times, In forging, lubrication is far more than an ancillary consideration. It directly affects metal flow, life, energy consumption, and surface finish. A nuanced understanding of tribological principles is essential, particularly as die temperatures rise, cycle times shorten, and the demand for dimensional consistency and production volume intensifies. Forging lubricants today must serve multiple functions: reduce die-workpiece friction, dissipate heat, prevent part sticking in the die, enable proper metal flow, and do so while minimizing environmental impact and operational downtime. Modern Lubricant Classes and Their Applications While there are several types of forging lubricants used for various purposes today, the main classes of lubricants will be discussed in this article. The choice of class is key for each forging operation, however, what may be even more important is tailoring each product to specific operational needs and forming conditions. The Stribeck Curve (figure 1) governs the tribological interactions between the tooling and workpiece. Each category discussed in this article relates directly to a formulation, and application. Lubrication as a Strategic Engineering Variable

lubrication regime in the Stribeck Curve. A properly controlled coefficient of friction is the ultimate goal of forging lubrication, not the lowest possible coefficient of friction. Too little friction between the tool and workpiece can lead to metal overflow and improperly formed parts. Choosing an optimized lubricant which the correct lubrication regime leads directly to successful forging. Graphite in Water A widely used boundary lubricant, graphite-in-water systems utilize graphite as the functional material and water as the carrier. Organic binders ensure adhesion to hot die surfaces, creating a protective film that enables clean separation between the tool and workpiece. Water simply exists in these lubricants to deliver the graphite and binders to the die surface, where they create a boundary film to lubricate and part the tooling and workpiece. This is the right-most category on the Stribeck Curve (boundary lubrication), also called “dry film lubrication”. The coefficient of friction between the tool and the workpiece is higher than a hydrodynamic lubricant. This is needed to control metalflow and provide just enough lubricity to flow metal to the end of the impression. Recent innovations in dispersion techniques have improved the performance of these graphite dispersions. Properly controlled graphite particle sizing and graphite type choice, as well as optimized dispersion techniques have contributed to these improvements significantly. These enhancements have extended metal flow performance in deep-draw and extrusion operations, improved die protection, and reduced total lubricant consumption. Additionally, soft-film formulations have been developed that provide excellent die coverage with minimal overspray,

improving cleanliness and reducing interference with automation systems. Graphite in Oil and Emulsions Graphite in oil-based systems remain indispensable for high-temperature, long metalflow forging, especially with non-ferrous materials and aerospace components. These lubricants perform well above 600°F, where water-based carriers fail due to the Leidenfrost effect. Oil not only serves as a carrier but also contributes to lubrication itself. These lubricants operate under both the hydrodynamic and boundary regimes. The oil carrier not only delivers graphite to the die surface but also provides hydrodynamic lubrication to lower the coefficient of friction. The graphite serves as a boundary lubricant in a comparable manner to graphite in water products. The combination of these regimes in both graphite in oil and emulsion lubricants. Hybrid emulsion systems—where oil is emulsified and graphite is dispersed in water—balance thermal insulation and cooling. These are particularly effective in overcoming steam barriers at elevated temperatures when properly engineered. Advances in graphite particle sizing control, wetting agents, and film formation technologies have made these systems viable for more extreme applications with reduced environmental trade-offs compared to pure oil-based formulations. Synthetic (Salt-Based) Lubricants Salt-based synthetic lubricants are created through acid-base reactions and are primarily used in warm forming. While they offer limited metal flow support, they excel in die cooling and minimizing sticking. This makes them ideal for forming components like pinions, yokes, and joints where localized

FIA MAGAZINE | MAY 2025 14