Aluminum alloy turning tools
Aluminum alloys, due to their low density, high strength, and corrosion resistance, are widely used in aerospace, automotive, and electronic equipment applications. The choice of turning tools for aluminum alloys directly impacts machining efficiency and surface quality. The cutting characteristics of aluminum alloys differ significantly from those of ferrous metals like steel. While they have lower hardness (generally between HB50 and 150), they exhibit greater plasticity and a higher thermal conductivity (approximately 3 to 5 times that of steel). This makes them susceptible to built-up edge (BUE) during cutting, and chips tend to adhere to the tool surface, impacting surface quality. Furthermore, aluminum alloys have a low melting point (approximately 660°C). Inadequate heat dissipation during high-speed cutting can easily lead to burns on the workpiece surface or increased tool wear. Therefore, tools used for turning aluminum alloys require excellent wear resistance, adhesion resistance, and heat dissipation.
The main tool materials used for turning aluminum alloys include high-speed steel, cemented carbide, and diamond tools. Different tool materials are suitable for different machining applications. High-speed steel tools (such as W18Cr4V) offer excellent toughness and a sharp cutting edge, making them suitable for low-speed precision turning of aluminum alloys, especially for parts with complex shapes. However, their poor heat resistance makes them unsuitable for high-speed cutting. Carbide tools are a common choice for turning aluminum alloys. Tungsten-cobalt cemented carbides (such as YG3 and YG6) offer excellent toughness and adhesion resistance, making them suitable for machining aluminum alloys. Ultrafine-grained carbides with added elements such as titanium and tantalum offer even greater wear resistance and can be used for high-speed cutting. Diamond tools (natural diamond and artificial polycrystalline diamond PCD) are ideal tools for machining aluminum alloys. They have high hardness, good wear resistance, low affinity with aluminum alloys, are not prone to built-up edge, and can achieve extremely high surface quality (Ra can reach 0.02~0.1μm). They are suitable for machining high-precision, high-finish aluminum alloy parts, such as aluminum alloy components for aircraft engines. However, they are relatively expensive and brittle, making them unsuitable for intermittent cutting or machining aluminum alloys with hard spots.
Tool geometry significantly impacts aluminum alloy turning performance and requires optimization based on the alloy’s characteristics. The rake angle should be large (15°-25°) to reduce cutting forces and friction, ensuring smooth chip evacuation while also increasing cutting edge sharpness and minimizing built-up edge. The clearance angle should be 8°-12° to minimize friction between the tool’s flank and the workpiece surface, improving surface quality. The lead angle is generally between 45° and 90°. A tool with a 90° lead angle produces low radial cutting forces, making it suitable for machining thin-walled aluminum alloy parts and preventing workpiece deformation. A tool with a 45° lead angle is suitable for general external turning, providing better heat dissipation. The tool nose radius should be small (0.2-0.8mm) to reduce cutting forces and vibration. For fine turning, the nose radius can be even smaller (0.1-0.3mm) to achieve a smoother surface. Furthermore, the rake and flank faces of the tool should be finely ground and polished to reduce surface roughness and minimize chip adhesion.
The cutting parameters for turning aluminum alloys must be appropriately set based on the tool material and machining requirements to maximize tool performance and improve machining efficiency. In terms of cutting speed, high-speed steel tools typically have a cutting speed of 50-100 m/min; carbide tools can increase this to 100-300 m/min; and diamond tools can operate at even higher speeds (300-1000 m/min). High-speed cutting not only improves efficiency but also reduces built-up edge and improves surface quality. The feed rate should be selected based on both surface quality and machining efficiency. For rough turning, the feed rate can be 0.1-0.3 mm/r, while for finish turning, it can be 0.05-0.15 mm/r. A smaller feed rate can produce better surface roughness. The depth of cut is determined based on the machining allowance: 1-5 mm for rough turning and 0.1-0.5 mm for finish turning. This is to avoid workpiece deformation or increased tool wear due to excessive cutting depth. At the same time, the selection of cutting fluid is also very important. Emulsion or kerosene is generally used as cutting fluid for turning aluminum alloys. Emulsion has good cooling performance and is suitable for high-speed cutting; kerosene has good lubrication performance, can reduce the friction between the tool and the chips, and improve the surface quality, and is especially suitable for precision turning.
Techniques and precautions for turning aluminum alloys are equally important for ensuring machining quality. Before machining, clean the workpiece surface of scale and oil to prevent hard spots from damaging the tool cutting edge. When clamping the workpiece, avoid over-tightening, which can cause deformation. For thin-walled aluminum alloy parts, use specialized fixtures or add support, such as soft jaws or filler materials inside the workpiece. During turning, maintain sharp tool edges and replace worn tools promptly to avoid built-up edge (BUE) and scratches on the workpiece surface caused by tool wear. For slender or thin-walled aluminum alloy parts prone to deformation, symmetrical machining and segmented machining should be employed to reduce the effects of cutting forces and thermal deformation. After machining, chips should be cleaned promptly to prevent scratches caused by friction between the chips and the workpiece surface. For parts requiring precision, dimensional measurements and surface quality inspection should be performed to ensure they meet design requirements. By selecting the right tool material, optimizing geometric parameters, setting appropriate cutting parameters, and employing the right machining techniques, efficient and high-quality turning of aluminum alloy parts is possible.
