Image of The Vital Role of Metalworking Fluids in Precision Manufacturing

The Vital Role of Metalworking Fluids in Precision Manufacturing

Metalworking fluids are liquids used in various machining processes, such as turning, milling, drilling, and grinding. They provide lubrication & cooling and remove debris generated during the machining process.

Some of the fundamental properties of metalworking fluids include the following:

  • Lubrication: Metalworking fluids reduce friction and wear on cutting tools and machine components. This improves tool life and reduces heat generated during machining.
  • Cooling: Metalworking fluids help regulate tool temperatures and reduce thermal stress on cutting tools. This improves the quality and accuracy of machined parts.
  • Debris removal: Metalworking fluids help remove chips and debris generated during machining. This improves surface finish and prevents clogging of coolant systems.
  • Corrosion protection: Some fluids also provide corrosion protection to machine components and cutting tools, extending their service life.
  • Biodegradability: Some metalworking fluids, such as synthetic fluids, are formulated to be more biodegradable and environmentally friendly than others.

All metal removal processes generate a tremendous amount of heat. Reducing this aids in improving productivity and parts quality. The cooling effect provided by a metalworking fluid gives the cutting tool or grinding wheel a longer life and helps to prevent burning and smoking.

Lubrication is necessary at the point where the tool is in contact with the machined part. This reduces friction which improves tool life and better finishes on your metal cut.

Metalworking fluids also provide corrosion protection for the newly machined part and the tool bit. Water-miscible metalworking fluid formulations (those fluids that are meant to be diluted with water) include components that slow or prevent corrosion. MWFs also help remove chips or swarf (an accumulation of fine metal and abrasive particles) from the cutting zone.

The type of metalworking fluid used depends on the specific requirements of the machining operation, raw materials, cutting speed, and environmental factors. Carefully consider the benefits and drawbacks of different types of metalworking fluids to determine the best choice for a particular application.

What Are the Different Types of Metalworking Fluids?

There are four major classes of metalworking fluids widely available:

  • Straight Oil
  • Soluble Oil
  • Semi-Synthetic
  • Synthetic

Many metalworking fluids, except straight oils, are mixed with water for use. Each has additives such as surfactants, biocides, extreme pressure agents, anti-oxidants, and corrosion inhibitors to improve performance and increase fluid life.

Let’s break these down:

Straight Oil:

These mineral oils provide lubrication and excel in high-speed machining operations. It is made from mineral (petroleum) or vegetable oils. Petroleum oils used for these fluids today can be “severely solvent refined” or “severely hydrotreated”. This is a refining process that reduces cancer-causing substances called polynuclear aromatic hydrocarbons [PAHs] present in crude oil.

Straight oils’ recognizable features are an oily appearance and a viscous feel. These materials may contain chlorinated and sulfur additives. This type of coolant is not diluted with water before use.

Straight-oil metalworking fluids are generally used for processes that require lubrication rather than cooling. They perform best when used at slow cut speeds, high metal-to-metal contact, or with older machines explicitly made for use with straight oils. In addition, Straight-oil MWF systems may require fire protection.

Tips to remember:

  • Have a higher viscosity compared to other types of fluids
  • Provide good lubrication but limited cooling
  • It can leave a residue on machined parts
  • They have limited biodegradability, potentially harmful to the environment

Soluble Oil:

Soluble oil is also emulsifiable oil. These emulsions of oil in water provide lubrication and cooling and are often used for general-purpose machining operations. They are primarily composed with 30 to 85 percent of severely refined lubricant base oil and emulsifiers to help disperse the oil in water.

The fluid concentrate usually includes other additives to improve performance and lengthen the fluid’s life. Soluble oil products are supplied as concentrates diluted with water to obtain the working fluid. In addition, they may have colorants added.

Soluble oils generally provide good lubrication and are better at cooling than straight oils. Drawbacks in using soluble oils, however, are that they sometimes have poor corrosion control, are sometimes “dirty”. For example, machine tool surfaces and nearby areas become covered with oil or difficult-to-remove product residues. They also may smoke because they do not cool as well as semi-synthetics and synthetics. Finally, they may have poor mix stability or short sump life.

Tips to remember:

  • Are an emulsion of oil and water
  • Provide both lubrication and cooling
  • Can leave a residue on machined parts and may require more frequent cleaning in your parts washer
  • Generally, have a higher biodegradability than straight oils


Semi-synthetic fluids are a type of metalworking fluid that combines the properties of mineral oil and synthetic fluids. They are formulated by blending mineral oils with synthetic additives. This enhances performance, such as improved cooling and reduced residue.

Semi-synthetic fluids offer some of the benefits of both mineral oils and synthetic fluids, such as good lubrication and improved cooling performance. They are also more cost-effective compared to synthetic fluids. However, they may provide a different level of performance than synthetic fluids. Also, their properties may not be as consistent as fully synthetic fluids.

Your semi-synthetic fluids depend on the specific requirements of your machining operation. Make sure you know the trade-off between cost and performance.

This type of metalworking fluid contains less severely refined base oil, for example, 5-30 percent in the concentrate. Semi-synthetics offer good lubrication, reduce heat, have decent rust control, have longer sump life, and are cleaner than soluble oils. They comprise many of the same ingredients as soluble oils and contain a more complex emulsifier package.

Tips to remember:

  • Improved Lubrication: Semi-synthetic fluids blend mineral oil and synthetic additives that provide improved lubrication compared to straight oils, reducing friction and wear during machining operations.
  • Enhanced Cooling: Semi-synthetic fluids provide improved cooling compared to straight oils. This helps regulate tool temperatures and reduce thermal stress on cutting tools.
  • Reduced Residue: The synthetic additives in semi-synthetic fluids helps reduce the residue left on machined parts. This makes post-processing operations easier and improves surface finish.
  • Cost-effectiveness: Compared to fully synthetic fluids, semi-synthetic fluids offer a decent balance between performance and cost. This makes them a more economical option for many machining operations.

It’s important to note that the benefits of using semi-synthetic fluids will depend on the specific requirements of your machining operation and the trade-off between cost and performance. A semi-synthetic fluid may not be your best choice for every application. It’s essential to carefully consider the specific benefits and drawbacks in your decision-making process.


Synthetic fluids are manufactured from chemically-derived compounds. They are formulated to provide specific properties such as improved cooling, reduced residue, and reduced odor. They are often used for demanding machining operations or in applications where environmental concerns are a priority.

These metalworking fluids do not contain any petroleum oil. Instead, they have detergent-like components to help “wet” the part and other additives to improve performance. Like the different classes of water-miscible fluids, synthetics are engineered to be diluted with water.

Among the four types of fluids, synthetic metalworking fluids generally are the cleanest. They offer the best heat reduction, have excellent rust control, and provide longer sump life. This type of metalworking fluid is transparent so the operator sees the work.

Tips to remember:

  • Chemically derived and have consistent properties formulated to meet specific requirements
  • Provide good lubrication and cooling
  • Leave minimal residue on machined parts
  • Have a low odor and biodegradability compared to other types of metalworking fluids
  • Can be more expensive than other fluid types

The type of fluid used will depend on the machining operation and material requirements, the cutting speed, and environmental concerns.

The best tip is to consult with your coolant distributor to find the best available coolant for your job type. If you have any further questions, feel free to reach out to us. We are happy to help you!



About Zebra Skimmers:

Our mission has always been simple. It is to provide the metal working industry with the oil skimmers and metalworking fluid management systems they need to complete jobs quickly and efficiently. Innovative and affordable solutions have gained us many accolades. Our continued growth is due in no small part to our excellent customer service… Not to mention our satisfaction guarantees and the performance of our tools.

Among our diverse options of oil skimmers and metal working fluid management systems, you can expect to find: