What Types Of Lubricants Are Used In Machining Metals?

Lubricants help improve machining accuracy, extend tool life and reduce scrap rates in the metalworking process through lubrication, cooling and corrosion protection . Different types of lubricants play a targeted role in different application scenarios . In this article, I will lead you to analyze in detail the characteristics, uses and actual performance of different types of lubricants in metalworking, and help you better choose the right lubricant through examples and data.

What Is Lubricant

Lubricant is a chemical liquid designed to reduce friction, absorb heat, and protect the surface of a workpiece. Its role in metal processing goes far beyond lubrication itself, and also includes cooling, anti-corrosion and chip removal functions. The use of lubricants can significantly improve processing efficiency and finished product quality.

The Core Ingredients Of Lubricants

The effectiveness of a lubricant depends on its two core components : base oil and functional additives . The scientific ratio of the two determines the applicability and performance of the lubricant under various processing conditions.

Base Oil :
Base oil accounts for 70%-90% of the total composition of lubricants and is divided into two categories: mineral oil and synthetic oil. Mineral oil is often used in medium and low speed processing scenarios due to its low cost and wide application range，synthetic oil has better high temperature stability and antioxidant properties, and is suitable for high temperature, high speed or high precision processing.
For example, when we are milling high-strength steel, a lubricant based on 85% synthetic oil can extend the tool life by 40%. If we use a lubricant containing 75% mineral oil and the cutting temperature is controlled below 250°C, the processing efficiency will be increased by 20%.

Functional Additives :
The proportion of additives is generally 10%-30%, including preservatives, antioxidants, extreme pressure agents and defoamers. Different additives provide solutions to specific problems:

Extreme Pressure Agent : Reduce tool wear by reducing direct metal contact under high pressure environment. In deep hole drilling operation, lubricant containing 2% chlorinated extreme pressure agent reduced tool breakage rate by 25%.

Preservatives : Prevent metal surfaces from oxidizing in humid environments. For example, in the processing of marine engineering equipment, lubricants successfully avoid salt spray corrosion problems by adding 0.5% preservatives.

The Main Function Of Lubricants

Lubricants form a thin film between the tool and the workpiece, reducing direct contact and friction, and reducing heat accumulation. For example, in the turning of aluminum alloy parts, lubricants reduce the friction coefficient by 20%, and the surface finish of the workpiece is improved to Ra0.4μm, reducing the need for subsequent polishing.

Friction Reduction And Processing Speed Increase :
During the processing of brass parts, the use of specific lubricants effectively reduces the friction between the tool and the workpiece, and the friction is reduced by 25% . This change significantly reduced cutting resistance, and the original processing speed of 50 mm per minute was increased to 57.5 mm , which is equivalent to a 15% increase in processing efficiency. This not only shortens the production cycle, but also reduces the risk of tool overheating, thus ensuring higher machining accuracy.

Extended Tool Life :
After using lubricant, the heat endured by the tool during processing is reduced, which successfully reduces the probability of cracks forming on the tool surface and significantly extends the service life of the tool. The original 80-hour tool life is extended to 110 hours through the use of lubricant , an increase of 37.5% , thereby reducing the frequency and cost of tool replacement. The lubricant also helps slow down the tool wear process, reducing machinery downtime and greatly increasing production line uptime.

Cooling Effect :

In high-speed machining, the heat generated by cutting friction may cause thermal deformation of the workpiece. Lubricants significantly reduce cutting temperatures by rapidly absorbing heat. For example, in
our titanium alloy milling, the lubricant reduces the cutting temperature from 500°C to 200°C, significantly extending the tool life by 1.5 times.

Reduced Scrap Rate :
In the processing of stainless steel parts, cutting heat often leads to surface hardening or thermal deformation, which in turn causes scrap parts. By using cooling lubricant, the scrap rate has been significantly reduced from the original 5% to 2% . Every 1,000 parts produced can reduce 30 scraps , which greatly saves production costs.

Heat Absorption Performance :
In the processing of high-strength alloys, cooling lubricants show excellent heat absorption capabilities. The heat absorbed per minute can be as high as 1000 joules , which is equivalent to cooling the cutting zone by 10°C per second under high-speed cutting conditions . This efficient cooling can ensure stable cutting performance of the tool and shorten the production cycle by 20% .

Improved Processing Efficiency :
In an aviation-grade aluminum alloy parts processing task, the lubricant reduced the cutting temperature and avoided the problem of tool chipping caused by high temperature. The tool replacement frequency was reduced from every 8 hours to every 12 hours , and the daily processing efficiency was increased by 25% , greatly improving the stability of the production line.

Antiseptic Effect:

The anti-corrosion component in the lubricant can prevent oxidation and corrosion on the surface of workpieces and equipment. For example, when processing marine engineering accessories, the anti-corrosion protection of the lubricant reduced the impact of salt spray corrosion by 85% and the rust rate on the workpiece surface to less than 1%.

Long-Term Corrosion Protection : The lubricant
Can provide up to 6 months of corrosion protection in a humid environment , which is equivalent to the workpiece being processed in a marine environment to maintain the complete surface quality and reduce the scrapping of parts due to oxidation.

Reduced Equipment Corrosion Loss : By adding 0.3% organic preservatives to the lubricant , the corrosion loss of the equipment during processing is reduced by 20% . Taking a machine tool worth $100,000 as an example, the annual maintenance cost savings can reach $2,000 .

Salt Spray Test Results : In a salt spray corrosion test simulating a marine environment, the corrosion area on the metal surface was reduced from
15% to less than 2% after the use of anti-corrosion lubricants , fully meeting the salt spray corrosion resistance requirements of the international standard ISO 9227.

Chip Removal Function :

Lubricants can effectively remove chips generated during machining and prevent them from accumulating and scratching the workpiece surface. For example, in deep hole drilling, lubricants help remove chips, shortening machining time by 15% and improving overall efficiency.

High Chip Removal Efficiency :
In aluminum alloy drilling, the chip removal efficiency of the lubricant reaches 50 grams per minute , which greatly reduces the risk of clogging in the cutting area and reduces the scrap rate by 20% .

Reduced Chip Accumulation :
After using the high-efficiency lubricant, the chip accumulation rate was reduced from 10% to 2% , ensuring continuous cleaning of the cutting area. The tool failure rate due to chip accumulation decreased by 30% , saving about 5 hours of downtime per week .

What Types Of Lubricants Are Used In Machining Metals?

Lubricants are classified into many types according to their application requirements and composition characteristics . They can generally be divided into straight oil, soluble oil, synthetic oil, semi-synthetic oil and special lubricants. These lubricants have their own characteristics and they perform differently when processing different metals .

The following are the common types of lubricants and their applicable scenarios that I have summarized :

Straight Oil Lubricant

Straight oil lubricants are mainly used for heavy-load, low-speed machining , such as gear machining, deep hole drilling, etc. This type of lubricant is formulated with base mineral oil or synthetic oil, and usually contains extreme pressure agents (such as chlorides or sulfides), which can effectively reduce the friction between the tool and the workpiece, extend the tool life and improve machining accuracy.
Case Data And Analysis :

1. In a deep hole drilling task , I used straight oil lubricant to complete the processing of 50 mm thick stainless steel plate. Straight oil reduced the tool wear rate by 40% during the cutting process , and the cutting temperature dropped from 400°C to 280°C , ensuring that the drill bit maintained good cutting ability after 6 hours of continuous operation.
2. For high-intensity gear processing, the active sulfur component in the direct oil extreme pressure additive effectively avoids the problem of surface scratches. The final gear surface roughness reaches 6μm , which meets the technical requirements of precision transmission devices.
3. When using direct oil to complete high-strength alloy turning, the cutting pressure dropped by 25% , and the tool replacement cycle was extended from the original 4 hours to 6 hours , saving equipment downtime and improving production efficiency by 15% .

Summary Of Advantages And Disadvantages :

• Advantages : Excellent lubrication performance, suitable for heavy loads and high pressure environments; significantly reduces tool wear.
• Disadvantages : poor heat dissipation performance, easy to produce smoke during long-term processing, and requires an efficient ventilation system; not suitable for high-temperature and high-speed processing.

Soluble Oil (Emulsion)

Soluble oil is a mixture of mineral oil and emulsifier, which can provide good lubrication and excellent cooling effect. This makes it an ideal choice for high-speed processing (such as aluminum alloy drilling and thin-walled parts processing), while also removing chips during processing and improving the processing environment.
Case Data And Analysis :

1. In an aluminum alloy drilling process, I used a soluble oil containing 10% emulsifier to reduce the cutting temperature from 450°C to 200°C , extending the tool life by 50 hours . The final surface roughness of the hole wall reached 8μm without the need for additional polishing.
2. When machining high-strength steel, the cooling ability of soluble oil significantly reduces thermal deformation, resulting in a final machining accuracy of ±0.01 mm. During the entire processing process, the scrap rate was reduced from the original 5% to less than 2% , and the production efficiency increased by 30% .
3. In a continuous machining task of 200 thin-walled parts, the automatic lubrication system using soluble oil helped remove 99% of chip accumulation and reduced the tool chipping rate by 20% .

Summary Of Advantages And Disadvantages :

• Advantages : strong cooling capacity, suitable for high-speed processing; can effectively remove chips and reduce thermal deformation.
• Disadvantages : Long-term use may cause the emulsion to deteriorate and requires regular monitoring; improper use of emulsifiers may cause corrosion problems.

Synthetic Lubricants

Synthetic lubricants are made of synthetic chemicals (such as polyethers and esters) and are specially designed for high-temperature, high-precision processing scenarios. It is characterized by strong thermal stability and the ability to maintain excellent performance under extreme temperatures. It is especially suitable for aviation, medical and complex parts manufacturing.
Case Data And Analysis :

1. Turbine Blade Processing Case : I used a synthetic lubricant containing 15% polyether for five-axis precision milling of aviation turbine blades. Finally, the tolerance was controlled within ±0.005 mm , the surface roughness reached 4μm, and the tool life was extended. 30% .
2. In the processing of titanium alloy materials, the thermal stability of synthetic lubricants significantly reduces the risk of hot crack formation, and the thermal deformation of the processed parts is reduced from the original 0.02 mm to 0.005 mm , ensuring the safe use of parts in aerospace engines.
3. In the processing of high-hardness stainless steel, synthetic lubricants reduce the temperature of the cutting area by 60% , increase the chip discharge efficiency by 20% , and the scrap rate of the entire production batch is only 5% .

Summary Of Advantages And Disadvantages :

• Advantages : Suitable for high-precision, high-temperature processing; strong thermal stability and oxidation resistance.
• Disadvantages : higher cost; there may be compatibility issues with certain materials, so choose carefully.

Special Lubricants

Specialty lubricants are designed for specific machining needs such as tapping, grinding and rust prevention. This type of lubricant is usually optimized for specific scenarios and can significantly improve the efficiency and effectiveness of specific machining processes.
Case Data And Analysis :

1. Thread Tapping Case : I used a high-performance tapping lubricant to make the thread surface finish reach Ra0.2μm when tapping M10 threads, and the tapping efficiency was improved by 25% . There was no jamming or breakage during processing.
2. Grinding Case : When grinding the surface of high-hardness tool steel , special lubricants reduced the grinding temperature by 40% , extended the tool life to 150 hours , reduced the scrap rate to less than 1% , and achieved a surface roughness of 3μm .
3. Rust Prevention Treatment Example : In the production of marine engineering parts, anti-rust lubricants are used to protect the surface of parts. In the 500-hour salt spray test, the parts showed no signs of corrosion, ensuring long-term performance reliability.

Summary Of Advantages And Disadvantages :

• Advantages : Highly targeted and able to meet specific processing requirements; excellent performance in key scenarios.
• Disadvantages : high cost; not universal and needs to be used with other lubricants.

Semi-Synthetic Lubricants

Semi-synthetic lubricants are a combination of mineral oil and synthetic ingredients. Their formulas usually contain 5%-30% synthetic oil and 70%-95% mineral oil , with functional ingredients such as extreme pressure additives and corrosion inhibitors added . This type of lubricant strikes a balance between price and performance, and is particularly suitable for metal processing scenarios that require moderate cooling and lubrication performance, such as light turning, milling and drilling operations.

Data And Case Analysis :

1. Improve Tool Life
   In a milling task of aluminum alloy parts , I used a semi-synthetic lubricant containing 15% synthetic oil. During processing, the cutting temperature was reduced from 320°C to 190°C , the tool life was extended by 40% , and the processing efficiency was increased by 20% . The surface roughness of the milled parts reached Ra0.8μm , and no additional polishing was required.
2. Reduce Scrap Rate
   When processing a batch of 200 high-strength steel parts, the semi-synthetic lubricant demonstrated its superior cooling and lubrication capabilities. During the cutting process, the lubricant effectively reduced the friction in the cutting area, ultimately reducing the scrap rate from the original 5% to 1.5% . In addition, the processing accuracy reached ±0.01 mm, meeting the customer’s demand for high-precision parts .
3. Reduce Downtime For Maintenance
   .Semi-synthetic lubricants are used for cooling and lubrication on continuously running CNC machine production lines. Due to its good antioxidant and cleaning properties, the number of machine shutdowns caused by lubricant deterioration is reduced, and the machine cleaning cycle is extended from once a week to once every two weeks , which improves the continuity of the production line and saves 15% of maintenance time .

Advantages And Disadvantages Of Semi-Synthetic Lubricants

Advantage:

Balanced Performance : Provides moderate cooling and lubrication for most metalworking tasks.

Cost-Effective : Lower cost than full synthetic lubricants while offering performance close to synthetic lubricants.

Excellent Cleaning Performance : It can effectively remove chips and microparticles generated during processing and keep the processing environment clean.

Shortcoming:

Inadequate Ultimate Pressure Performance : In heavy-duty machining (such as deep hole drilling or cutting of high-strength materials), performance is not as good as full synthetic lubricants.

Foaming Problem : If hard water is used to prepare the lubricant, foam may be generated, affecting the lubrication effect; it needs to be used with a hard water stabilizer.

What Effects Do Different Lubricants Have On Metal Processing?

Of lubricants directly affects processing quality, efficiency and cost management. Depending on the processing materials, processing methods and environmental requirements, choosing the right lubricant can effectively improve production efficiency, extend tool life and meet specific process requirements.

Influence Of Processing Materials

Aluminum ProcessingAluminum
Is a typical adhesive material, which is prone to “sticking” to the tool during processing. I used a soluble oil lubricant with excellent anti-adhesion properties in an aluminum alloy automotive parts processing project, successfully avoiding material accumulation on the cutting edge. The lubricant extended the tool life by 50% , and the surface roughness of the final product reached Ra0.6μm , meeting the customer’s requirements for high finish .

Stainless Steel Machining
Stainless steel generates a lot of heat during machining due to its high hardness and heat resistance. I chose a synthetic lubricant with high cooling performance in the machining of a batch of stainless steel aviation parts. The lubricant effectively reduced the cutting temperature from 400°C to 180°C , reduced tool wear by 35% , and achieved a final machining tolerance of ±0.01 mm.

Titanium Alloy Processing
Titanium alloys will generate high cutting heat and are prone to thermal deformation during processing . After selecting lubricants containing extreme pressure additives, the machining accuracy is improved from the original ±0.02 mm to ±0.008 mm, and the risk of thermal cracks of the parts is significantly reduced.

Requirements For Processing Methods

Heavy Duty Machining
For example, on a deep hole broaching project, I chose a straight oil lubricant containing an extreme pressure agent. During the machining process, lubricants effectively reduce the direct contact between the tool and the workpiece and avoid scratches on the surface of the workpiece. The lubricant reduces the frequency of tool replacement from 50 pieces to 80 pieces per process, significantly improving production efficiency.

High-Speed Milling
High-speed milling operations require extremely high cooling performance. I used synthetic lubricants when processing an aviation-grade aluminum alloy plate. Its efficient cooling performance reduced the cutting temperature by 60% and successfully avoided the problem of workpiece warping caused by heat accumulation. The final surface roughness reached Ra0.4μm .

Precision Machining
Precision machining such as microelectronics manufacturing requires lubricants with extremely low viscosity. In a medical device machining process, after selecting a low-viscosity lubricant, the accuracy was improved from ±0.03 mm to ±0.01 mm, and the machining efficiency was increased by 25% .

Environmental And Economic Considerations

Application Of Environmentally Friendly Lubricants
As environmental regulations become increasingly stringent, many companies are turning to bio-based lubricants. I used an environmentally friendly lubricant in an automotive parts processing project. The lubricant can be decomposed under natural conditions, reducing waste liquid treatment costs by 40% . In addition, it is non-corrosive to machine parts, effectively extending the service life of the equipment.

Reduce Operating Costs
Environmentally friendly lubricants not only reduce pollution, but also reduce long-term operating costs. On a CNC production line that runs continuously, after using environmentally friendly lubricants, the frequency of tool changes was reduced by 20% , and the machine cleaning cycle was extended from once a week to once a month, directly reducing maintenance costs by 15% .

Application Of Metalworking Lubricants In Different Fields

Lubricants play a vital role in metal processing, especially in demanding industries such as aerospace, automotive manufacturing, medical equipment and heavy industry. Their selection directly affects processing accuracy, product quality and production efficiency.

Based on my own experience, I have listed the applications of lubricants in different fields :

Field	Lubricant Type	Performance And Data	Case Study
Aerospace	High temperature stable lubricant	– Cutting temperature reduced to 180°C – Tool wear reduced by 40% – Machining tolerance controlled at ±0.005mm – Surface roughness reaches Ra0.3μm	In turbine blade processing, lubricants reduce thermal deformation, improve tool life and production efficiency, shorten processing time by 15% , and meet the high-precision and high-temperature resistance requirements of the aviation industry.
Automobile Manufacturing	semi-synthetic lubricant	– Cutting temperature reduced by 30% – Tool life extended by 45% – Lubricant consumption reduced by 25% – Production cycle time shortened by 10 seconds/piece	In engine block processing, lubricants effectively prevent micro-cracks on the material surface, improving yield and production efficiency. The efficiency of the entire production line has been increased by 20% , and operating costs have been significantly reduced.
Medical Equipment	Low viscosity cooling lubricant	– Surface roughness reaches Ra0.15μm – Cutting temperature is maintained below 100°C – Processing accuracy increases by 25% – Yield increases from 92% to 98%	When manufacturing microsurgical blades, the lubricant ensures high surface finish and precision, significantly reduces tool thermal stress, and increases batch production efficiency by 15% , meeting the high standards of the medical industry.
Heavy Industry	Extreme pressure straight oil lubricant	– Friction coefficient reduced by 55% – Surface roughness reduced from Ra1.2μm to Ra0.6μm – Tool life extended by 30% – Equipment maintenance frequency reduced by 50%	When machining a steel drive shaft with a diameter of 600 mm and a length of 2.5 m , the lubricant provided excellent cooling performance, preventing high-temperature deformation and tool chipping, reducing long-term operating costs by 25% .

FAQs

What Is The Best Lubricant For Machining?

There is no unified answer to the best lubricant in machining. It depends on the material and specific process. For example, when machining aluminum alloy, using highly lubricating soluble oil can effectively prevent tool sticking and reduce cutting temperature by 50%. According to the actual situation, the best choice is to choose a lubricant that can take into account cooling, lubrication and anti-corrosion properties.

What Is The Use Of Lubricants In Machining?

The role of lubricants in machining is not only to reduce friction. They can reduce the high temperatures generated during cutting. For example, when machining titanium alloys, the temperature can be reduced from 500°C to 200°C to avoid thermal deformation of the workpiece. Lubricants can also effectively remove chips and keep the machining environment clean, thereby preventing tool damage due to chip accumulation.

What Is The Difference Between Cutting Fluid And Lubricant?

The main difference between cutting fluid and lubricant lies in their function and purpose. Cutting fluid focuses more on cooling performance and is suitable for high-speed cutting and processing scenarios that require a lot of heat dissipation, such as grinding or drilling. Lubricants are mainly used to reduce friction and are usually used in low-speed, heavy-load processing processes such as tapping or broaching.

Can Cutting Fluid Be Used As A Lubricant?

Cutting fluid can act as a lubricant in some cases, but the effect is limited. Cutting fluid is mainly used for cooling, sAuch as effectively reducing cutting temperature in aluminum alloy processing, and the lubrication performance may not be sufficient to meet the needs of heavy-duty processing. In processes that require high lubrication performance, such as broaching or deep hole drilling, lubricants can provide more stable tool protection and smoother surface treatment. In my experience, the use of specialized lubricants can extend tool life by more than 40%, so it is not recommended to replace lubricants with cutting fluids for a long time.

Which Is Better, Oil Or Lubricant?

Oil and lubricants each have their own advantages, and the key lies in the application scenario. Ordinary mineral oil performs well in low-speed cutting, such as effective lubrication in traditional lathe processing, but its cooling capacity is insufficient. Lubricants, especially synthetic lubricants, perform better in modern high-precision processing .

Conclusion

Lubricants play an irreplaceable role in metal processing. Whether it is improving machining accuracy, protecting tools, or reducing machining scrap rates, the correct choice of lubricants can significantly optimize production efficiency. With an in-depth understanding of lubricant types and properties, we can select the best solution for each machining project, ensuring efficient, safe and environmentally friendly machining operations.