How to Choose a Metalworking Fluid (MWF): Practical Selection by Operation, Metal and Working Conditions

A metalworking fluid (MWF) should not be selected only by product name or concentrate price. Proper selection should take into account the machining operation, workpiece material, machining load, machine type and speed range, MWF delivery method, water quality, condition of the circulation system, and operating temperature.
The guide below provides a practical selection framework for the Novohim range. It helps define the operating requirements first and then narrow the choice to a specific product.

Quick Selection Guide

Application / conditions	First options to consider	Comment
Grinding	Biol Universal 4–5%; Biol 4–5%; Biol ECO 2–3%	These concentrations apply specifically to grinding.
Standard machining	Biol, Biol Universal, Defender Ultra	Confirm against metal, load, water and machine conditions.
Heavy-duty machining with circulation	Defender Pro	Primary option for demanding operating conditions.
Copper, brass and bronze	Defender Ultra M	Specialized water-miscible MWF for copper and copper alloys.
Heavy local machining	Defender Zoom → Master Rez → Defender Oil 210	Selection depends on the metal and severity of the operation.
Band saw machine	Defender Pro	With hard or problematic water, consider Defender Ultra separately.
Low- and medium-speed machines	Biol or Defender products depending on the operation	A wider range can be considered; check metal, load and water.
Modern high-speed machines, including CNC	Defender Pro; Defender Ultra in selected conditions	Pay particular attention to circulation and foaming.
Operation at temperatures down to −20 °C	Winter-grade MWFs	Select according to the confirmed low-temperature specification of the particular product.

Start with the Machining Operation

The same MWF will not necessarily perform equally well in turning, grinding, deep drilling or threading. As the load in the machining zone and the need for lubrication increase, correct product and working-concentration selection becomes more important.
Do not select an MWF simply on the assumption that a higher oil content is always better. Performance depends on the complete formulation, working concentration, workpiece material, water, cutting conditions and system condition.

Consider the Machine Type and Speed Range

MWF selection should include not only the operation and workpiece material but also the machine itself. The same operation performed on an older low-speed machine and on modern high-speed equipment may impose different requirements on the fluid.
For practical selection, distinguish between older low-speed machines, medium-speed equipment and modern high-speed machines, including CNC machines.
For low- and medium-speed equipment, the choice is broader. Depending on the operation, metal and load, products from the Biol and Defender ranges, conventional emulsifiable oils and other suitable MWFs can be considered.
For modern high-speed machines, requirements are higher. Among Novohim water-miscible products, Defender Pro is the primary recommendation. Defender Ultra can be considered under selected conditions, but the final choice also depends on the operation, material, load, water and circulation-system characteristics.

Foaming on High-Speed Equipment

High machine speeds, intensive circulation and strong MWF delivery can contribute to increased foaming. Foam behaviour is influenced by the MWF itself, working concentration, water quality, circulation conditions, delivery method and air entrainment.
If excessive foam occurs, first check the actual concentration, water, correct preparation of the working fluid, circulation and delivery conditions, and possible air intake or intensive air entrainment.
If the cause cannot be eliminated by correcting the operating conditions, a separate antifoam agent may be used. Recommended addition to the working emulsion is 0.1–0.5%. Before addition, dilute the antifoam agent with water at a ratio from 1:1 to 1:10.
An antifoam agent should not be used as a substitute for correcting the underlying cause of persistent foaming.

Selection by Operation

Grinding

For grinding, our primary practical recommendation is Biol Universal at a working concentration of 4–5%.
Biol at 4–5% and Biol ECO at 2–3% can also be used for grinding. These concentration recommendations apply specifically to grinding and should not automatically be transferred to other operations.

After Grinding and Inter-Operation Storage of Parts

If parts need longer storage after grinding, a 10% Biol Lemon solution can be used as an additional process step. Parts are immersed in the solution, kept in it for a period of time, then removed and dried.
For inter-operation storage, Biol ECO can also be used at a concentration of 10% or higher: immerse the parts and dry them before storage or the next operation.
The actual storage period depends on the part material, surface condition, indoor environment, humidity and packaging method. Therefore, no universal guaranteed storage period is stated.

Deep Drilling and Heavy-Duty Machining

Where the MWF is supplied through a circulation system, Defender Pro should normally be considered first for deep drilling and other heavy-duty operations.
Defender Ultra also covers a broad range of operations; however, under high loads and difficult machining conditions, Defender Pro is the preferred option.
If additional local lubrication is needed in the cutting zone, select the local product separately. A circulation system does not prevent the use of a local product directly at the point of highest load.

Threading and Heavy Local Drilling

Three products have distinct practical roles for local application.
Defender Zoom is a water-washable product for demanding operations. It can be used over a wide concentration range, from undiluted product to working solutions of approximately 3%. Technically, it can also function as a conventional water-miscible MWF, but continuous circulation at a low concentration is often economically impractical for this specialized product.
Master Rez is a stronger local option and is particularly convenient for non-ferrous metals. It is not water-washable, so entry into the main circulation system should preferably be minimized.
Defender Oil 210 is the primary option for the heaviest local operations, including drilling and threading. It is a ready-to-use neat-oil product and should likewise not be introduced in significant quantities into a water-miscible MWF system.

How to Select an MWF by Metal

Steel and Cast Iron

For standard conditions, Biol, Biol Universal and Defender Ultra can be considered. As the machining load increases, selection shifts toward Defender Light, Defender Standard and, above all, Defender Pro for heavy-duty machining.
For plants that prefer conventional oil-containing emulsions, TUV-95 remains a separate option.
Stainless and High-Alloy Steels, Difficult Machining
Here it is especially important to consider the operation as well as the material. For high-load operations with circulating MWF supply, Defender Pro is the main candidate. Defender Oil 210 can additionally be used for heavy local drilling, threading and similar operations.

Aluminium

Biol Universal is one of the proven practical options for aluminium. Other products may also be suitable depending on the operation and load, so aluminium alone is not a sufficient selection criterion.

Copper, Brass and Bronze

Among water-miscible MWFs, Defender Ultra M is our primary recommendation for these materials. It is a specialized option for copper and copper alloys.
For local machining, Master Rez is the more straightforward practical choice. Defender Oil 210 can also be used for short-duration local machining of non-ferrous metals if the product is removed promptly from the surface after the operation.

TUV-95: When a Cost-Effective Conventional Emulsifiable Oil Is Required

TUV-95 is a conventional oil-containing water-miscible MWF. It is a strong practical option for plants accustomed to traditional emulsifiable oils and looking for pronounced lubricating properties at an accessible concentrate cost.
Working concentration can be adjusted according to load. For higher and heavy-duty operating conditions, the concentration can be increased to 10–15% to increase the lubricating properties of the working emulsion.
At higher concentration the working emulsion becomes more oil-rich in practical behaviour, but different MWFs do not become identical: stability, biostability and behaviour in water depend on the formulation.
TUV-95 requires disciplined operation, including attention to water quality, removal of tramp oil from the surface, filtration and system cleaning, prolonged shutdowns, and signs of biological contamination.

Defender Oil Strong or Defender Pro

Defender Oil Strong should be considered when a plant specifically requires a water-miscible MWF with very high oil content and a distinctly oil-rich emulsion.
Higher oil content in the concentrate does not by itself guarantee a better result in every operation. Where the main objective is stable performance in heavy-duty machining, we generally prefer Defender Pro.
TUV-95 remains a cost-effective and flexible conventional option whose concentration can be increased as the machining load rises.

Ready-to-Use Neat Oils

A water-miscible MWF is not required for every operation. For some processes, a ready-to-use non-water-miscible neat oil is more appropriate. These products are not diluted with water, so there is no water-based working-emulsion concentration or water-quality requirement for preparation.
Defender Oil 200 is a ready-to-use neat oil for demanding operations.
Defender Oil 205 is a low-viscosity neat oil intended primarily for honing and finishing operations.
Defender Oil 206 / sulfofrezol is a conventional non-water-miscible oil-type MWF.
Defender Oil 210 is also a ready-to-use oil product, but its main role in this selection system is local use for particularly demanding drilling and threading operations.

Which MWF to Choose for a Band Saw Machine

Defender Pro is our primary recommendation for band saw machines. If the plant has hard or problematic water, Defender Ultra should be considered separately. This does not mean that Defender Ultra is automatically suitable for water of any hardness; water quality should be assessed independently.

MWFs for Winter Operation and Unheated Workshops

A conventional water-based working fluid should not automatically be considered suitable for sub-zero operation. Special winter-grade products should be used where low-temperature performance is required.
The range includes Biol ECO −20 °C, Biol Universal −20 °C and Defender Ultra WINTER −20 °C. Where required for copper, brass and bronze, Defender Ultra M −20 °C can be manufactured.
Neat oils do not contain a water phase, but this does not mean that every neat oil can automatically be specified for −20 °C. Viscosity increases as temperature falls, and pumpability and equipment operation depend on the particular product.

Water Quality Matters

For a water-miscible MWF, the concentrate is only one part of the system; the other is water. Excessive hardness, high dissolved-salt content, mechanical contamination, source instability or microbiological contamination can affect working-emulsion behaviour.
Very soft or demineralized water is not always optimal either: with some MWFs it may contribute to increased foaming. Particular attention to water quality is required with conventional emulsifiable oils such as TUV-95.

Do Not Ignore System Condition

Even a correctly selected MWF cannot compensate for a contaminated system. Control working concentration, remove chips and sludge, prevent accumulation of a tramp-oil layer on the surface, maintain circulation and filtration, and monitor changes in odour and appearance.
Where biological contamination is present in the circulation system, a 10% Biol Lemon solution can be used for cleaning. Protective gloves are required when working with this solution. After cleaning, drain the Biol Lemon solution and rinse the system with a 10% Biol ECO solution before preparing it for further operation.

MWF for Stone Processing

MWFs intended for metalworking should not automatically be transferred to stone processing. Defender Stone is a separate specialized product for this task.
Defender Stone is intended for mechanical processing of stone, including marble and granite. The product is colourless, which is important where the natural colour of the stone needs to be preserved.

Common MWF Selection Mistakes

• Selecting only by concentrate price. Working concentration, machining conditions and actual performance also matter.
• Assuming that higher oil content is automatically better. MWF performance depends on the complete formulation.
• Ignoring the workpiece material, particularly for copper, brass and bronze.
• Ignoring water quality.
• Increasing concentration without a technological reason.
• Charging new MWF into a contaminated system without proper preparation.

Short Selection Algorithm

1. What operation is being performed? Turning, milling, drilling, grinding, threading, honing, band sawing or another operation.
2. What material is being machined? Steel, cast iron, stainless or alloy steel, aluminium, copper, brass, bronze or another material.
3. What type of machine is used? Determine whether it is an older low-speed machine, medium-speed equipment or a modern high-speed machine, including CNC. For high-speed equipment, consider Defender Pro first and Defender Ultra under selected conditions.
4. What is the machining load? Standard or heavy-duty; deep drilling, heavy milling, threading or another demanding operation.
5. How is the MWF supplied? Through a circulation system, locally, or by a combination of circulating and local application.
6. What water is used? For water-miscible MWFs, consider hardness and other relevant water characteristics.
7. Is foaming a problem? This is particularly important on high-speed equipment with intensive circulation.
8. At what temperature does the equipment operate? For unheated facilities, check whether a winter-grade MWF is required.
9. Select the specific product and working concentration. Compare products only after the technological requirements have been defined.
10. Check the selection using the MWF category filters. Use the selected parameters to narrow the product list and open the relevant product pages.

Self-Selection Using Category Filters

Once the main requirements have been defined, specific products can be selected in the MWF (Metalworking Fluids) category.
The category includes product filters that allow customers to narrow the range independently and compare relevant options.
Products can be filtered by MWF brand, MWF type, consistency, machining operation, workpiece material, cutting speed, biostability and operating conditions. A separate filter is available for MWFs intended for operation at temperatures down to −20 °C.
A practical approach is to define the operation, material, machine type and operating conditions using this guide first, and then use the category filters to narrow the selection to specific products.

FAQ

Is there one best MWF for every metalworking operation?
No. Selection depends on the metal, machining load, machine, delivery method, water and operating conditions.
What should I choose for heavy-duty machining?
For heavy-duty machining with circulation, Defender Pro is one of the primary options. For particularly demanding local drilling and threading, consider Defender Oil 210.
Which MWF should I use for grinding?
The primary practical option is Biol Universal at 4–5%. Biol at 4–5% and Biol ECO at 2–3% can also be used.
Which MWF should I choose for copper and brass?
Among water-miscible products, Defender Ultra M is our primary recommendation. For local machining, consider Master Rez.
Can TUV-95 concentration be increased for heavy-duty operations?
Yes. For higher and heavy-duty loads, TUV-95 can be increased to 10–15%, while monitoring emulsion condition, water and system cleanliness.
Which is better: TUV-95, Defender Oil Strong or Defender Pro?
They serve different roles. TUV-95 is a cost-effective conventional emulsifiable oil; Oil Strong is intended where a very oil-rich water-miscible emulsion is specifically required; for heavy-duty circulating operations we generally prefer Defender Pro.
Can a neat-oil MWF be used in winter?
The absence of water eliminates freezing of a water phase, but oil viscosity increases as temperature falls. The minimum permissible temperature must be confirmed for the specific product.
Which MWF should I choose for a modern high-speed CNC machine?
Among Novohim water-miscible MWFs, Defender Pro is the primary recommendation. Defender Ultra can be considered under selected conditions. With intensive circulation, foaming should also be monitored. Recommended antifoam addition to the working emulsion is 0.1–0.5%, with pre-dilution in water at 1:1 to 1:10.

Conclusion

An MWF should be selected as part of the machining process rather than as a universal consumable.
For standard operations, Biol, Biol Universal or Defender Ultra can be considered first. As machining load increases, selection moves toward products with stronger lubricating performance, with Defender Pro becoming one of the primary options for heavy-duty circulating applications.
Defender Ultra M is available for copper and its alloys; Defender Zoom, Master Rez and Defender Oil 210 cover heavy local machining; TUV-95 serves plants that prefer conventional emulsifiable oils; and the Defender Oil range covers honing and other neat-oil applications.
After selecting the product, always consider water quality, concentration, system cleanliness and the actual operating conditions of the equipment.