In CNC machining of metal housings, thermal deformation is one of the key factors affecting machining accuracy. During cutting, the workpiece and tool generate a large amount of heat due to friction. If not cooled effectively and promptly, this can lead to localized temperature increases in the workpiece, causing dimensional changes or shape distortion, ultimately reducing machining accuracy. Therefore, selecting the appropriate cooling method is crucial for ensuring machining quality.
Coolant cooling is the most commonly used cooling method in CNC machining due to its high efficiency and controllability. A circulating system precisely sprays coolant onto the cutting area, rapidly removing heat and reducing the coefficient of friction. Water-based coolants, with their excellent thermal conductivity, are suitable for machining most metal materials; while oil-based coolants, with their good lubrication, are more suitable for difficult-to-machine materials such as cemented carbides or high-temperature alloys. Furthermore, the coolant concentration needs to be adjusted according to the material being machined. For example, the concentration needs to be reduced when machining aluminum alloys to avoid corrosion, while the concentration needs to be increased when machining stainless steel to enhance rust prevention.
The coolant spraying method directly affects the cooling effect. Traditional unidirectional spraying can easily lead to uneven cooling, while multi-angle composite spraying technology, by optimizing the nozzle layout, allows the coolant to cover a wider cutting area, making it particularly suitable for machining complex curved surfaces or thin-walled structures. For example, when machining the metal frame of a mobile phone, a dual-nozzle design can simultaneously cool both the cutting tool and the workpiece, effectively reducing deformation caused by heat buildup. Furthermore, pulse jet technology, by intermittently releasing coolant, reduces energy consumption and avoids workpiece surface vibration caused by continuous jetting.
Coolant temperature control is another crucial factor in preventing thermal deformation. If the coolant temperature is too high, its heat absorption capacity decreases, leading to a temperature rise in the workpiece; if the temperature is too low, thermal stress may cause the workpiece to crack. Therefore, a constant temperature control system is needed to maintain the coolant temperature within a reasonable range. For example, when machining heat-sensitive materials such as titanium alloys, the coolant temperature must be strictly controlled between 20-30℃ to avoid changes in material properties due to temperature fluctuations. Simultaneously, the coolant circulation system must be equipped with a high-efficiency filter to promptly remove chips and impurities, preventing nozzle clogging or scratching of the workpiece surface.
Dry cooling technology uses high-pressure gas or low-temperature nitrogen instead of traditional coolant, making it suitable for machining scenarios with extremely high cleanliness requirements. For example, in the machining of metal casings for optical components or semiconductor devices, dry cooling avoids the impact of coolant residue on surface quality. Furthermore, liquid nitrogen cooling, with its extremely low temperature, can rapidly freeze the cutting area, significantly reducing the risk of thermal deformation, but requires a closed-loop circulation system to prevent condensation. However, dry cooling has relatively low efficiency and usually needs to be combined with optimized cutting parameters (such as reducing cutting speed and increasing feed rate) to compensate for heat generation.
The choice of cooling method needs to be optimized in conjunction with machining process parameters. For example, in high-speed milling, high cutting speeds exacerbate heat generation, requiring high-pressure coolant (pressure ≥7MPa) to enhance penetration and ensure coolant reaches the cutting edge directly. For low-cutting-force scenarios such as micro-machining, micro-volume lubrication (MQL) technology can be used, achieving precise cooling through a small amount of atomized coolant while reducing environmental pollution. In addition, the choice of tool material and coating must also match the cooling method; for example, coated tools can reduce the coefficient of friction, reduce heat generation, and thus reduce dependence on the cooling system.
The maintenance and management of the cooling system are equally important. Regularly changing the coolant can prevent performance degradation due to additive failure, while timely chip removal can prevent blockages in the circulation system. For precision machining, the pH and conductivity of the coolant should also be tested regularly to ensure its chemical stability. In addition, operators need to receive professional training to master the methods of adjusting cooling parameters, such as dynamically switching cooling modes according to the workpiece material and machining stage to achieve the best cooling effect.
