Why is it necessary to use cutting fluid when CNC machining parts?
Table of Contents :
Chapter 1. The core role of cutting fluid
Chapter 2. If cutting fluid is not used, the possible consequences include
Chapter 3 : Special needs in different processing scenarios
Chapter 4 : Special cases where cutting fluid is not used
Chapter 5 : Selection and use of cutting fluids
Chapter 6: Summary
When processing related CNC parts, we will see that there will be flowing liquid on the machines and parts to cooperate with the processing of related parts. These flowing liquids are the cutting fluids used on CNC machines. As a professional CNC machining center with 17 years of experience, we share with you the role of cutting fluid plays in CNC processing as below ?
Chapter 1. The core role of cutting fluid
It is critical to use the cutting fluid ( coolant ) during CNC machining. It is not an optional auxiliary, but one of the core elements to ensure machining quality, efficiency and equipment life. The following are its key roles:
1.1: Cooling effect: reducing machining thermal damage
Due to the liquid properties of the cutting fluid itself, it has the ability to cool down. Its cooling function can significantly reduce the temperature generated when the CNC part is cut, reduce tool wear, and increase tool life. At the same time, temperature control may also effectively prevent the CNC part from thermal expansion, warping, etc., which affect the machining accuracy, and cool the already processed surface to inhibit the generation of thermal metamorphic layers.
Principle: When CNC machines are processing metal parts or plastic part, they need to run at high speed, and the tool and the part need to rub and work violently, which will generate a lot of heat (the local temperature can reach hundreds of degrees Celsius). The heat is absorbed and taken away by the circulation of cutting fluid to reduce the temperature of the cutting area.
Key effects:
Protect the tool: prevent the tool from softening, wearing or breaking due to high temperature, and extend the service life (for example, the life of high-speed steel tools can be increased by 3-5 times under cutting fluid cooling).
Reduce CNC Part deformation: Prevent high temperature from causing thermal expansion and deformation of the CNC part material, which is especially important for high-precision parts (such as aerospace structural parts).
Maintain machine tool accuracy: Reduce thermal deformation of machine tool spindles, guide rails and other components to ensure long-term machining accuracy stability.
1.2. Lubrication: Improve friction state
In addition to cooling, cutting fluid can also play a lubricating role. During processing, the cutting fluid can reduce the friction, wear, melting and adhesion between the front cutting edge and the cutting, and the back cutting edge and the CNC part surface. Under certain conditions, the front and rear friction of the tool can be reduced by using high-quality cutting fluid, thereby extending the tool life and obtaining better surface quality of the CNC part. Most importantly, it can also reduce the generation of built-up edge.
Working principle: The cutting fluid forms an extremely thin lubricating film between the tool and the CNC part and the chips, reducing direct friction and reducing cutting force.
Key effects:
Improve surface quality: Reduce scratches, burrs and roughness on the machined surface (for example, when cutting aluminum alloys, the use of cutting fluid can reduce the surface roughness Ra from 1.6μm to below 0.8μm).
Reduce cutting power consumption: The cutting force can be reduced by 15%-30%, especially in high-load scenarios such as deep hole processing and tapping.
Suppress built-up edge: Avoid chips from accumulating on the tip of the tool to form built-up edge, preventing it from damaging the machining dimensional accuracy and surface finish.
1.3 Cleaning function: remove chips and impurities
During the processing of CNC parts, some debris, metal powder, or grinding wheel powder will be generated. These things will adhere to the tool, or between the part processing surface and the moving parts of the machine tool. When the adhesion amount increases, mechanical scratches and wear will occur, which will have a bad impact on the surface quality of the product, reduce the accuracy of the machine tool and the life of the tool. Therefore, when selecting cutting fluid, it is required to have a cleaning function, and it will be pressurized when used to increase the flushing capacity of the cutting fluid, so as to facilitate the timely flushing of these fine chips and powders.
Principle: High-pressure cutting fluid flow can flush the processing area, take away fine chips (such as aluminum chips, powder chips) and abrasive particles, and prevent them from being retained and causing tool wear or part scratches.
Typical scenarios:
Deep cavity / narrow gap processing: such as mold cavity, gear box hole, etc., to avoid chip accumulation affecting processing efficiency and accuracy.
Automatic production line: cooperate with chip removal system to achieve continuous chip removal and ensure the continuity of automated processing.
1.4 Anti-rust effect: protect machine tools and CNC metal part
During machine tool processing, machine tools and CNC metal part are very prone to rust due to the invasion of moisture, hand sweat, oxygen and other substances in the surrounding environment. Especially in the summer when the temperature is high and the humidity is high, it is more prominent. Therefore, according to these actual conditions, when processing metal products and the processing time is long, the cutting fluid must have the function of anti-rust. In this way, it can not only prevent the CNC metal part from rusting, but also prevent the machine tools and tools from rusting.
Principle: Add rust inhibitors to the cutting fluid to form a protective film on the metal surface to prevent rust in a humid environment (especially suitable for semi-finished products or machine tool guides that are stored for a long time).
Application example: The anti-rust performance of water-based cutting fluid can be adjusted through the formula to meet the anti-rust requirements of different processing cycles (such as short-term anti-rust from 72 hours to 30 days).
Cutting fluid plays a huge role in the metal cutting process. Therefore, when choosing cutting fluid, it is necessary to reasonably select the most suitable and high-quality cutting fluid, so that the four major functions of cutting can be perfectly exerted, and it can extend the life of the tool, ensure processing accuracy, prevent rust, improve cutting efficiency, reduce survival costs and many other benefits.
Chapter 2. If cutting fluid is not used, the possible consequences include
| Problem | Performance | Performance |
| Increased tool wear Blade cracking | life reduction Cost increase | frequent tool change |
| CNC size instability | Thermal expansion leads to precision error | Increased scrap rate |
| Poor surface roughness Burrs | burns | and roughening Affect product quality |
| Low processing efficiency | Reduce speed and feed for conservative processing | Extended working hours |
Special note:
Different cutting methods (such as high-speed milling, deep hole drilling, turning, etc.) have different requirements for the best type of cutting fluid (oily, water-soluble) and injection method (cooling spray, oil mist, internal cooling channel).
In some special materials (such as aluminum alloy, titanium alloy) or dry cutting processes, the use method will be optimized or a special formula cutting fluid will be selected.
Chapter 3 : Special needs in different processing scenarios
| Processing type | Cutting fluid selection focus | Typical cases |
| High-speed cutting (such as steel parts | Focus on cooling performance, choose high water-based or semi-synthetic cutting fluid | Processing 45# steel shaft parts, reduce the temperature of the cutting area to prevent tool annealing |
| Precision processing (such as aluminum alloy) | ocus on lubrication and cleaning, choose low-viscosity fully synthetic or oil-based cutting fluid Processing of aviation aluminum alloy | Processing of aviation aluminum alloy thin-walled parts to avoid sticking and chip residue |
| Difficult-to-process materials (such as titanium alloy) | Focus on lubrication and cleaning, choose low-viscosity fully synthetic or oil-based cutting fluid | Titanium alloy impeller processing, reduce tool adhesion and wear |
| Grinding | Focus on cleaning and cooling, low foam, high permeability cutting fluid is required | Ceramic bearing ring grinding, prevent |
Chapter 4 : Special cases where cutting fluid is not used
Not all CNC processing must use cutting fluid. Dry cutting or minimal lubrication (MQL) can be considered in the following scenarios:
4.1. Scenarios with extremely high environmental protection requirements: such as medical device processing, to avoid residual pollution of cutting fluid
4.2. Special material processing: such as some metals that are easy to react chemically with cutting fluids (such as magnesium alloys, which are easy to burn when exposed to water).
4.3. Ultra-high-speed processing: When the cutting speed exceeds the critical value (such as titanium alloy>150m/min), the cutting heat is mainly taken away by the chips, which can reduce the use of cutting fluids.
4.4. Minimum quantity lubrication technology (MQL): through compressed air + a small amount of lubricating oil mist, quasi-dry cutting is achieved, which is suitable for low-load processing such as aluminum alloys and copper alloys.
Chapter 5 : Selection and use of cutting fluids
5.1 According to material matching:
5.2 Steel/cast iron: Preferentially choose semi-synthetic or fully synthetic cutting fluids containing extreme pressure additives.
5.3 Aluminum alloy: Choose chlorine-free, low pH cutting fluids to prevent corrosion.
5.4 Stainless steel/high-temperature alloys: Extreme pressure cutting fluids with high lubricity are required (such as sulfur-phosphorus additives).
5.5 Pay attention to concentration and maintenance:
5.6 The concentration of water-based cutting fluid is usually 5%-15% (8%-12% is recommended for processing steel parts). The pH value should be tested regularly (7.5-9.5 is the normal range) to prevent bacteria from growing and stinking.
5.7 Waste fluid treatment:
5.8 It must comply with environmental regulations, give priority to biodegradable cutting fluids, and waste fluids must be discharged after professional treatment.
Chapter 6: Summary
Cutting fluid is an "invisible tool assistant" in CNC processing. Its combined effects of cooling, lubricating, cleaning, and rust prevention directly determine the processing efficiency, cost, and quality. Reasonable selection and use of cutting fluids can not only improve processing performance, but also extend equipment life and reduce environmental burden. With the development of green manufacturing technology, low-pollution, high-performance cutting fluids (such as nano-lubricating cutting fluids and bio-based cutting fluids) are becoming a future trend.