Cutting parameters for turning aluminum and its alloys
Aluminum and its alloys are widely used in aerospace, automotive, and other fields due to their low density, excellent thermal conductivity, and high plasticity. However, the selection of cutting parameters for turning aluminum and its alloys differs significantly from that for steel. Cutting parameters include cutting speed, feed rate, and depth of cut. Properly setting these parameters can fully utilize the machining properties of aluminum and its alloys, reduce tool wear, and improve surface quality. Due to their low hardness (HB20-100) and high plasticity, aluminum and its alloys are prone to tool sticking and built-up edge (BUE) during turning. Therefore, cutting parameters must be optimized around the three core objectives of suppressing BUE, ensuring smooth chip evacuation, and improving machining efficiency.
The choice of cutting speed significantly impacts the turning quality of aluminum and its alloys. The thermal conductivity of aluminum and its alloys is 3-5 times that of steel, and cutting heat is easily carried away by the workpiece and chips. Therefore, higher cutting speeds, generally between 200-800 m/min, are suitable. High-speed cutting rapidly raises the cutting temperature above the softening point of aluminum (approximately 300°C), reducing adhesion between the tool and the chips and effectively suppressing the formation of built-up edge. For example, when turning pure aluminum, the cutting speed can be controlled at 400-600 m/min. When turning high-strength aluminum alloys (such as 2A12), due to the increased strength of these alloying elements such as copper and magnesium, the cutting speed can be reduced to 200-400 m/min. However, the cutting speed should not be too high. When it exceeds 800m/min, tool wear will be aggravated, especially for carbide tools, which have limited heat resistance and are prone to blade cracking. Therefore, it needs to be adjusted according to the tool material – high-speed steel tools are suitable for 200-400m/min, carbide tools are suitable for 400-800m/min, and ceramic tools can reach 800-1200m/min.
The feed rate setting must balance surface quality and machining efficiency. Aluminum and its alloys have high plasticity. If the feed rate is too small, the contact time between the tool and the workpiece is prolonged, which can easily lead to built-up edge. Excessive feed rate will increase cutting forces and cause tearing or burrs on the workpiece surface. During rough turning, the feed rate is generally 0.2-0.5mm/r to quickly remove the blank allowance. At this time, the chips are ribbon-shaped or spiral-shaped, and the chip flute design must be used to ensure smooth discharge. During finish turning, the feed rate needs to be reduced to 0.05-0.15mm/r to reduce the extrusion of the tool on the workpiece surface and achieve a surface roughness of Ra1.6μm or less. For thin-walled aluminum alloy parts, the feed rate should be further reduced to 0.05-0.1mm/r to avoid workpiece deformation due to excessive cutting forces. In addition, the feed rate and cutting speed need to be adjusted in coordination. A smaller feed rate is used for high-speed cutting (such as 0.08-0.12mm/r at 600m/min), and a larger feed rate is used for medium-speed cutting (such as 0.2-0.3mm/r at 300m/min) to form the best match.
The depth of cut should be determined based on the machining stage and workpiece structure. When rough turning aluminum and alloys, a depth of cut of 2-5mm is recommended for maximum efficiency. The primary consideration here is the tool’s load capacity. Carbide tools can withstand greater cutting depths, while high-speed steel tools should be limited to 2-3mm. For finish turning, a depth of cut of 0.1-0.5mm is generally recommended to remove surface defects left by roughing and ensure dimensional accuracy. For aluminum alloy parts with stepped surfaces, the depth of cut should be gradually reduced, leaving a 0.5-1mm margin at the base of the step to prevent tool impact on the step. It is important to note that aluminum and its alloys have low strength, and excessive depth of cut can cause plastic deformation in the workpiece, especially in thin-walled and slender parts. Therefore, the cutting depth should be adjusted based on the rigidity of the workpiece—a higher value for workpieces with good rigidity and a lower value for workpieces with poor rigidity.
Optimizing cutting parameters requires comprehensive consideration of cooling and lubrication conditions. When turning aluminum and its alloys, the choice of cutting fluid is crucial for suppressing built-up edge and improving surface quality. Kerosene or an emulsion (5%-8% concentration) is generally used. Kerosene offers excellent lubrication and effectively reduces tool-chip adhesion, making it particularly suitable for finish turning. Emulsions offer excellent cooling properties, making them suitable for rough turning and high-speed cutting. When using cutting fluid, cutting speeds can be increased by 10%-20%, and feed rates can be appropriately increased. For example, a cutting speed of 400 m/min can be increased to 450-500 m/min. Furthermore, cutting parameters vary between different aluminum alloy types. For example, cast aluminum alloys (such as ZL102) have better cutting performance than wrought aluminum alloys (such as 6061). Therefore, the cutting speed and feed rates for cast aluminum alloys can be slightly higher than those for wrought aluminum alloys. Through continuous experimentation and adjustment, the optimal cutting parameter combination for a specific aluminum alloy can be found, achieving efficient production while ensuring machining quality.
