Dmitry Kalinovsky | Dreamstime
CNC milling in detail, with lubrication and coolant.

How Lubricants Enhance Tool Performance

May 17, 2024
To find the ideal solution for your workflow, consider how lubricants affect tools and materials – starting by understanding metalworking fluids’ role in the machining process.

Many metal-cutting optimization strategies focus directly on the cutting equipment. While these choices are critical, manufacturers must also pay attention to related resources and workflows. More specifically, you must use the right lubricant for the job. Your choice of metalworking fluid (MWF) has a significant impact on your equipment’s life span and efficiency. Complicating the matter, the optimal MWF varies depending on the situation. To find the ideal solution for your workflows, you must consider how these lubricants affect your tools and materials. That begins with recognizing metalworking fluids’ (MWF) role in the process.

Decreasing friction, temperature

The most obvious function lubricants perform is minimizing friction during machining. Fluids ensure smooth movement, preventing hard surfaces from touching directly. In addition to enabling a more uniform cut, friction reduction dissipates up to 96% of the heat generated by metal-to-metal contact.

By preventing mechanical damage and heat-related warping, lubricants ensure tooling ends retain their shape for longer. However, different metals have varying needs in these areas. Consequently, a lubricant that is sufficient for one material may not provide enough friction reduction for another.

Aluminum has a high friction coefficient with many other metals, so it requires MWFs with high lubricity, typically meaning less-diluted oils. By contrast, copper alloys and many steels often do not induce as much friction, so you can use lubricants with lower oil contents.

Removing debris

MWFs also clear away metal swarf, chips, and other debris from the tooling surface. Without that function, chips, dirt and other contaminants could fall into the cutting zone, creating excess friction and potentially damaging the tool end. Considering a five-axis CNC machine can cost hundreds of thousands of dollars, you want to avoid that interference as much as possible.

Debris removal is more important at higher machining speeds, as high-speed processes create chips faster. The easiest way to counter this is to adopt more viscous lubricants when debris is more of an issue. Often, that means using synthetic or semisynthetic MFWs, which have a lower oil content, promoting a higher flow rate.

High-strength metals like titanium or stainless steel are more likely to create chips. That makes high-viscosity lubricants an optimal choice for those materials, especially for processes with extended on-tool time.

Protecting equipment

Similarly, lubricants also must help to keep cutting equipment clean. Removing metal from the contact surface will provide limited long-term benefits if this debris ends up in the cutting tool itself. Many MFWs also leave residues, which can contribute to friction-related issues if they dry on surfaces.

Water-based lubricants are generally better when machine cleanliness is a concern. Glycerine, for example, is colorless and leaves no residue while providing excellent lubrication, so it will not contaminate equipment as it reduces friction.

High-end equipment or more precise end-of-arm tooling typically need these benefits more than most, as they’re more sensitive to buildup.

By contrast, silicone-based MFWs or those with a high oil content are more likely to leave behind residue. You can still use these fluids safely as long as you account for the likelihood of that build-up. Avoid using these lubricants for highly sensitive operations, and regularly clean equipment that does use them to remove residue before it thickens.

Preventing corrosion

Your choice of MFW also has a profound effect on corrosion. That applies to both the metal you’re working with and the metal on your tooling ends. Without accounting for this factor, you could use acidic or overly basic fluids that could eat away at metal and hinder the life span of your equipment and products.

Ferrous metals — especially iron and high-carbon steel — should use oil-based rather than water-based MFWs to prevent rust. Stainless steel and copper, by contrast, are more naturally corrosion-resistant, so water-based synthetics are safe to use on them. However, even stainless steel is sensitive to acids and chloride solutions, as is aluminum.

Review your lubricants’ chemical contents to identify any potential corrosive risks. Ideally, your MFWs’ pH level should be neutral or mildly alkaline, as acids or strong bases are more likely to corrode various metals. Be careful of chlorine and similar compounds when working with stainless steel and aluminum.

Reducing energy consumption

The right lubricant can help to reduce energy costs, too. Most of these savings stem from reducing corrosion and friction. Both factors will improve the smooth performance of tools on workpieces, lowering the power needed to deliver optimal results.

Reducing energy consumption is beneficial in any context but it is particularly important for materials that are typically harder to machine. These include hardened steel, titanium, and cast iron. Use a high-lubricity and corrosion-resistant lubricant when working with these metals to mitigate their difficult-to-machine nature.

A higher material removal rate also will reduce CNC energy demands despite being a higher-intensity process, thanks to its speed. Consequently, it may be most beneficial to use a lubricant with high cooling properties to promote faster, more efficient machining with harder metals.

Matching lubricants to workflows

Once you select a fluid, remember to keep it at supplier-recommended concentrations and change it as necessary to prevent contamination. As your manufacturing processes evolve, you may need to change MFWs, too.

Just as there’s no optimal material for every product, the ideal lubricant varies between workflows. Finding the right one for your needs begins with understanding the variables you must consider and how different MWFs affect them.

Emily Newton is the Editor-in-Chief of Revolutionized, an online magazine exploring the latest industrial innovations.

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