Selecting the appropriate cooling strategy in CNC machining is one of the most important technological decisions, affecting not only the quality of the workpiece but also tool life, production costs and the stability of the entire process. In manufacturing practice, there is no single universal solution – dry machining and machining with coolant each have their own clearly defined areas of application. In this guide, we explain in detail when each method works best.
In this article, you will learn:
- exactly what dry machining involves and when it is advisable to use it,
- what functions coolant serves and what types there are,
- in which situations cooling is essential and when it is optional,
- how to choose a cooling strategy for a specific material,
- how cooling affects tool life, production costs and the environment.
Dry machining – advantages and limitations
Dry machining refers to a cutting process carried out without the use of a conventional coolant (emulsion or oil). In practice, this means that the heat generated during machining is not actively dissipated by a liquid, but must be dispersed by the chips, the tool and the air. In many cases, only a stream of compressed air is used, the purpose of which is to remove chips and prevent them from coming into contact with the cutting edge again.
CNC dry machining is usually carried out using appropriately selected cutting parameters, namely:
- higher speeds,
- shallower cutting depths
- and the use of modern tools with high heat resistance.
The key principle here is that most of the heat should be ‘removed’ along with the chips. This is precisely why dry machining is often combined with modern tool coatings and stable, rigid machine tools.
Materials suitable for dry machining
Of course, not all materials react to the absence of coolant in the same way. The materials that perform best with this technology are those that dissipate heat well and do not tend to stick to the cutting edge. Typical examples include cast iron, certain aluminium alloys and selected plastics. In many cases, dry machining of plastics helps to avoid problems such as material swelling or surface contamination by coolant.
At the same time, it should be borne in mind that materials with low thermal conductivity or high ductility (e.g. stainless steel) are rarely suitable for this machining technology.
Reduced costs and environmental impact
One of the greatest advantages of dry machining is the elimination of the costs associated with purchasing, filtering and disposing of coolant. This is significant because, in many industrial plants, the costs associated with coolant management account for a significant proportion of the production budget. Doing away with emulsions also means lower energy consumption, no need to wash workpieces, and improved working conditions for operators.
From an environmental perspective, too, this solution is particularly attractive – the reduction in hazardous waste and chemical consumption is in line with sustainable production strategies, which is often of great importance to modern businesses.
Requirements for coolant-free tools
Dry machining requires tools with high thermal resistance and coatings that reduce friction. Popular coatings include AlTiN, TiAlN and DLC, which remain stable at high temperatures. Tools must also be designed to effectively remove chips and minimise contact between the cutting edge and the heated material.
The basics of cooling in CNC machining
Cooling in CNC machining involves supplying a cooling and lubricating medium to the cutting zone in order to lower the temperature, reduce friction and improve chip removal. Many modern workshops utilise state-of-the-art machinery with spindle cooling, which allows coolant to be delivered directly to the cutting edge under high pressure.
Functions of coolant in the machining process
Coolant for machining plays a vital role, as it enables:
- a reduction in temperature at the cutting zone,
- a reduction in friction between the tool and the workpiece,
- chip removal,
- corrosion protection,
- and an improvement in the surface quality of the workpiece.
Without these functions, many processes would be unstable or economically unviable.
Types of coolant: emulsion, oil-based, MQL
Emulsion coolants are among the most commonly used solutions. This is because a mixture of oil and water provides good cooling and moderate lubrication.
Oil-based coolants, on the other hand, provide very good lubricating properties and are used in operations requiring the highest surface quality.
At this point, it is also worth mentioning the MQL (Minimum Quantity Lubrication) method, which involves minimal lubrication using an oil mist. Consumption of the coolant is exceptionally low here, and the process itself is more environmentally friendly (though not always sufficient for more demanding materials).
When is a coolant necessary?
It should be emphasised that in many processes, the use of a coolant is not a choice but a prerequisite for stable production. To quote Łukasz Mazur, one of the process engineers at our company, RADMOT:
“In certain operations, the absence of coolant leads to rapid tool wear and a loss of production repeatability – this applies, for example, to the machining of difficult-to-machine materials or the drilling of deep holes. In such cases, cooling is not an option, but a technological requirement.”
Difficult-to-machine materials requiring cooling
Nickel alloys, titanium and stainless steel generate enormous amounts of heat and tend to stick to the tool. An example of a demanding process is turning stainless steel with optimised coolant, where the correct choice of coolant is crucial for tool life and process stability.
Deep holes and finishing operations
Deep-hole drilling and finishing operations require effective chip removal and cooling. Without this, the risk of tool seizure or damage to the workpiece increases dramatically.
Cooling in the machining of various materials
The choice of cooling strategy must always take into account the physical and thermal properties of the material. Differences in thermal conductivity, ductility or the tendency to stick to tools mean that the same cooling method can produce completely different results depending on the material being machined. Matching the technology appropriately to the material allows for a significant increase in process stability, reduced tool wear and improved surface quality of the workpieces.
Aluminium – cooling versus dry machining
Aluminium can be machined both dry and with a coolant. In mass production, aluminium milling with a cooling system is often used, which prevents chips from sticking and improves surface quality.
Stainless steel and cooling requirements
Stainless steel almost always requires coolant due to its low thermal conductivity and high ductility.
Plastics and the problem of overheating
Plastics can melt and deform. In many cases, dry machining with air blowing works better.
The effect of cooling on tool life
The first key aspect is reducing the temperature of the cutting edge. Excessive temperature leads to accelerated wear of coatings and a loss of tool hardness. Consistent cooling can significantly extend tool life.
The second important aspect is the reduction of friction. Lubrication reduces cutting forces, which minimises micro-damage to the cutting edges and improves process stability.
Attention must also be paid here to thermal shocks. Sudden temperature changes can cause micro-cracks and chipping of the cutting edges; therefore, the method of coolant supply must be well controlled.
Economic and environmental aspects
The costs of coolant at the production plant level are often underestimated. They include not only the purchase of the concentrate, but also the preparation of the emulsion, filtration, monitoring of parameters, system maintenance, as well as the working time of the operators responsible for maintaining the system. In many companies, the total annual cost of coolant operation accounts for a significant proportion of the production department’s operating costs.
On the other hand, appropriate cooling can significantly reduce tool wear, minimise production defects and improve the stability of mass production processes. In large-scale production, even a slight increase in tool life translates into tangible savings amounting to tens of thousands of zlotys per year. Therefore, a cost-benefit analysis of cooling should always take into account the full cost picture, rather than just the expenditure associated with purchasing the coolant.
From an environmental perspective, the disposal of used emulsions and the reduction of oil mist emissions are of key importance. Companies are increasingly investing in filtration systems, oil separators and MQL technologies to reduce the environmental impact of production. Responsible coolant management is becoming an integral part of ESG strategies and a competitive advantage within the industrial sector.
The choice of cooling strategy should be based on an analysis of the material, the workpiece geometry and quality requirements. Explore our range, request a quote and get in touch with us.
FAQ – frequently asked questions about cooling in CNC machining
Is it possible to mill aluminium without cooling?
Yes, but mainly when using the correct parameters and tools. In mass production, cooling improves process stability.
What cutting parameters should be used for dry machining?
Higher cutting speeds and shallower depths are usually employed so that heat is carried away with the chips.
Does dry machining reduce tool life?
Not always – with the right choice of tools, it can be just as effective as machining with coolant.
What coolant should be chosen for stainless steel?
Most commonly, emulsions or oils with high lubricating properties.
Will MQL replace traditional cooling?
In many applications, yes, but for difficult-to-machine materials, conventional cooling remains the standard.
