The term metal forming includes a diverse variety of manufacturing processes and applications. This can include the use of one ton mechanical presses down to wire drawing processes. All of these come down to moving metal into a desired geometry. Metal is plastically deformed through force applied that will exceed the yield strength of the metal itself. During this deformation process, friction and heat are generated.
The challenge in formulating fluids for metal forming is not to work against heat and friction, but to work with them. The primary functions of removal fluids are:
Lubricate: Reduce friction and wear, thus improving tool life and reducing forces and energy consumption
Cool: Cool the forming zone, reducing temperature and distortion
Wash: Clear debris away from the forming zone and dies
Protect: Prevent corrosion on newly-machined surfaces
All this is done through a precise balance of base fluid and additives to produce fluids with the desired characteristics to apply to each particular process.
Base Fluids
Metal forming fluids can use mineral base stocks, synthetic or renewable base stocks derived from seeds or vegetables. A few decades ago, water-based synthetic lubricants gained favor in the metal forming process. They were environmentally-friendly and reduced costs in post-process. They represented an overall savings over the fluids they replaced. Plus, as suppliers refined the fluids, they produced a better product. Today, more advanced metal compounds often require increased tool forces which lead to more heat and friction. This, along with the desire from customers to use waterless fluids, has caused synthetic emulsions to lose some of their dominance.
Oil vs. Emulsion
Oils have good anti-weld properties and high lubricity. So, in general, neat oils are used in applications where:
• Speeds are low
• Pressures are great
• Metal is tough
Water cools better than oil, so emulsions are used where:
• Speeds are high
• Pressures are lighter
• Stock removal is lower
The Chemistry
In the petroleum industry additives are often explained to the laymen as the ingredients that make oil “work.” In forming fluids, these additives generally consist of phosphorous, fats, sulfur, polymers, soaps and chlorinated paraffins. With the diversity of metals and metal forming applications, the proper selection of additives becomes more dependent on understanding the actual application than in other areas of metalworking fluids. The necessary ability to balance boundary versus hydrodynamic lubrication in the fluid means that multiple additives are often needed. The added emphasis on moving away from chlorinated paraffins for regulatory issues along with the desire for more easily cleaned final parts is making the formulation of forming fluids increasingly difficult. Many advancements have been made with additives for the following areas:
1) Meet increasingly stringent regulatory issues
2) Increase additive solvency in water-diluted fluids
3) Match the demands of newer forming techniques
4) Provide increased performance with the increasing amount of non-ferrous metals, especially aluminum, titanium, and magnesium
5) Easier to clean off after forming
6) Provide corrosion prevention during and after forming
7) Pre-lubes that minimize fluid use and disposal
Metal Forming Processes
Bulk deformation and sheet metal working processes are the two major groups of metal working. Bulk deformation has a low surface area to volume ratio, meaning only small areas of the stock are being worked. Sheet metal has a high surface area to volume ratio meaning large areas of the metal are worked at once.
Bulk deformation processes include:
• Rolling deforms the metal by use of rolls. These processes include rotary tube piercing, roll piercing, thread rolling, gear rolling flat rolling and shape rolling
• Forging uses dies to compress and shape metal into the desired form and can be done “cold” as with many heading operations, or “hot” at temperatures above 2000 degrees F
• Extrusion forces metal through a die opening creating a length of work with a consistent cross section
• Drawing is similar to extrusion except the drawing process pulls the material through the die opening instead of pushing it
Sheet Metal Working
• Shearing involves cutting the metal and includes punching holes or shapes
• Bending is the deformation of metal around a certain axis
• Deep Drawing is a process where a sheet of metal is drawn into a cavity to create a shape
Again, the term metal forming applies to a wide variety of metals, processes to move that metal, pressures to move the metal, and temperatures at which the metal is moved. The most highly-compounded fluid with the greatest additives and base fluids in the world may be effective in one application but perform poorly in another. The selection of the proper fluid must include normal parameters such as the part and tool metallurgy, but must also include an understanding of the proper application techniques, proper application amounts, and proper timing for application. A strong technical approach to fluid selection is needed to form an optimum solution. Pun intended.
