Forging Lubricants Explained - Part 1
It All Comes Down to the Right Choice of Lubricant
by Mr. Marius Schmid (Forging Products Specialist, oelheld GmbH) and Dr. Marcel Eberle (R&D, oelheld GmbH)
Why Are There Lubricants in Forging?
Every employee in the forging value chain has a different answer to this question, and yet they all have one thing in common: all the answers are correct. The advantages for using a lubricant in forging range from reduced wear of the press, to the surface finish of the forged product, to cost savings due to a longer die life.
In detail, the advantages become clearer. Due to reduced friction, the press force can be set lower, which reduces the load on the machine and its components. With an improved sliding effect of the material in the die, wear and small cracks are delayed. This not only extends the service life, but also improves the surface quality of the components over the life cycle of a die. Finally, yet importantly, it is also possible to shape difficult-to-flow alloys, e.g. chrome, nickel or titanium, in a forging process so that all corners and shapes of the finished component are completely filled. So, one thing can be said with great certainty: Die forging cannot be done without a lubricant/release agent.
What Properties Does a Lubricant Need for Forging?
The criteria that a die lubricant needs to match are numerous. The most important are a good sliding effect, excellent separating properties and a temperature resistance that corresponds to the process. Besides the fact that a smooth production process must be established, the well-being of the employees and the environment should also be considered.
What Types of Lubricants Are There in Forging?
In order to better divide the selection of a suitable lubricant, lubricants are roughly categorized into three groups: Coatings; Graphite Products; and Synthetic Products.
1. Coatings
Turbine forged with coating product
Coatings are protective films that seal the surface of the alloys. The closed protective layer reduces hot gas diffusion, which improves the surface quality of the manufactured component. In addition, the heat is better retained in the component and cooling during transport between the furnace and the press is prevented. Glass Coating range is most commonly used in aerospace applications. The glass protects the titanium or nickel alloys from the reactive oxygen and a clean and, above all, defect-free surface is achieved after forging. The glass coatings are applied to the workpieces by brushing, spraying or even by an electrostatic application process. The user can adjust the thickness of the applied glass coating to the respective process by diluting the product with water to the appropriate consistency on site.
2. Graphite Products
Black products get their color from the graphite they contain. This naturally black solid has excellent properties that make it valuable for lubricants. In addition to a good lubricating effect, these also include outstanding separation performance. With graphite-containing lubricants, the carrier fluid can be varied; there are both water- and oil-based products.
Crankshaft forged with black graphite product
2.1. Water Graphite
The water used is cooling the parts which it comes in contact with and prevents the die from overheating. These products can be mixed with water on site, allowing the user to mix his own suitable concentration depending on the complexity of the part, quality of the die, and application method.
2.2. Oil Graphite
An oil graphite, as the name implies, brings with it the benefits of graphite and also lubricates slightly better than a pure water graphite does, due to the oil content. In addition, the machine is protected against corrosion. Depending on the requirements, products with different viscosities are available.
2.3. Hybrids
Practical experience has shown that there is a need for lubricants that can cover both processes with and without graphite. These products are called hybrids.
The fact that the degree of deformation of the produced parts varies is often the reason for using several lubricants. Hybrids are lubricants that combine the advantages of graphite-free and graphite-containing lubricants. They are therefore particularly suitable for forging companies with a wide range of products. Hybrids can be matched in such a way that by introducing them into production, one lubricant can be used for all forging processes. This ensures that all components can be lubricated with just one medium. This not only helps employees, as there is now only one product on the shop floor, but also reduces costs in terms of inventory and ordering procedures. In addition, a lower proportion of graphite in hybrids means that fewer particles are left in the circulating air, the periphery of the press and on the surface of the components.
3. Synthetics
Many forging companies are willing to "remove" graphite from production and give white products a chance. White products are applicable to steel and steel alloys, aluminium, titanium and titanium alloys, and nickel and nickel alloys. The advantages of "white lubricants" are mainly a cleaner production environment and less post-processing due to cleaner surfaces with almost identical lubricating properties compared to graphite products. The type of products varies, depending on the material used and the application. You can also run our salt product in circulation.
3.1. Transparent
The water-based transparent lubricants form a white release film in the die. They are pigment-free and very well miscible with water and can therefore be applied in good doses by automatic spraying machines or also manually. The contained ingredients ensure good wetting of the die. Due to its excellent driving and release properties over a wide temperature range, it is ideally suited for demanding hot and semi-hot forming operations.
3.2. White Lubricants
Water-based white synthetic lubricants are available specifically for hot forming of aluminium. These can be diluted by the customer to the required application concentration and then applied with all standard spray equipment.
3.3. Circulating Lubricants
Special transparent fluids are available for horizontal high speed forging. They are very well miscible with water and produce colourless solutions. Good wetting of the components is ensured by the very low foaming behaviour circulating.