Copper alloy turning
Copper alloys, as a metallic material with excellent electrical and thermal conductivity and plasticity, are widely used in machinery manufacturing, electronics, and other fields. The turning of copper alloys differs significantly from that of materials like steel and cast iron. Their unique physical and mechanical properties place special demands on turning tools, cutting parameters, and machining processes. Mastering the key technologies for copper alloy turning is crucial to ensuring machining quality and efficiency.
The primary challenge in turning copper alloys lies in the high plasticity and low hardness of the material. Most copper alloys (such as brass and copper) have low hardness and high elongation, which easily lead to large plastic deformation during the turning process, resulting in chips that are difficult to break and form continuous ribbon-like chips. Such chips will wrap around the tool or workpiece, which not only affects the machining accuracy but also may cause safety hazards. To solve this problem, it is necessary to reasonably select the tool geometry parameters. Usually, a larger rake angle (15°-25°) and back angle (8°-12°) are used to reduce cutting force and friction and promote chip curling and breaking. At the same time, the tool’s blade inclination angle should be adjusted according to the chip flow requirements. For materials that are easy to stick to the tool, such as copper, a positive blade inclination angle can be used to make the chips flow to the surface to be machined of the workpiece to avoid scratching the machined surface.
The choice of cutting parameters significantly impacts the turning quality of copper alloys. Because copper alloys have good thermal conductivity, heat generated during cutting is easily dissipated by the workpiece and chips, allowing for higher cutting speeds. For example, when turning brass, cutting speeds can reach 100-300 m/min; when turning copper, cutting speeds typically range from 80-200 m/min. However, it should be noted that excessively high cutting speeds can lead to increased tool wear, especially when machining copper alloys containing silicon and lead, where hard particles can cause abrasive wear on the tool edge. The feed rate and depth of cut should be determined based on the required machining accuracy. For roughing, a higher feed rate (0.2-0.5 mm/r) and depth of cut (2-5 mm) can be used to improve efficiency. For finishing, a lower feed rate (0.05-0.15 mm/r) and depth of cut (0.1-0.5 mm) are recommended to ensure surface roughness (typically Ra 1.6-3.2 μm).
The proper selection of tool materials is crucial for copper alloy turning. Commonly used tool materials include high-speed steel (HSS), cemented carbide, and cubic boron nitride (CBN). High-speed steel tools offer high toughness and wear resistance, making them suitable for low-speed turning or forming. However, due to their poor heat resistance, they are not suitable for high-speed cutting. Carbide tools (such as YG tungsten-cobalt alloys) offer excellent wear and heat resistance and are the preferred material for copper alloy turning. YG8 is suitable for roughing, while YG6 is suitable for semi-finishing and finishing. For high-strength copper alloys or high-precision machining, coated carbide or CBN tools can be used. Coatings (such as TiN and TiAlN) can effectively reduce tool-chip adhesion and extend tool life. Furthermore, tool edge preparation is crucial. A sharp edge can reduce material extrusion deformation, but the edge strength must be compatible with the cutting conditions. Appropriate chamfering can be applied if necessary.
Surface quality problems are prone to occur during the turning process of copper alloys, such as tool sticking, excessive surface roughness, or built-up edge. The tool sticking phenomenon is mainly due to the high plasticity of copper alloys. The intense friction between the chips and the front cutting edge of the tool will cause the material to stick to the cutting edge, forming a built-up edge, which in turn affects the quality of the processed surface. In order to avoid tool sticking, in addition to the reasonable selection of tool materials and geometric parameters, it is also necessary to use a suitable cutting fluid. Emulsions or extreme pressure cutting oils are usually used for copper alloy turning. The cutting fluid not only cools down the temperature, but also has a lubricating effect, reducing friction and adhesion. For those with higher surface quality requirements, oil-based cutting fluids can be used. Their lubrication performance is better than that of water-based cutting fluids, but the cooling effect is slightly worse, and the selection needs to be weighed according to the specific situation. In addition, regularly cleaning the adhesive on the tool and keeping the cutting edge sharp are also important measures to ensure surface quality.
The turning processes for different types of copper alloys vary, requiring tailored adjustments to the machining plan. Brass (such as H62) offers excellent machinability and is relatively easy to turn. However, high zinc content can generate zinc vapor, which can be harmful to both the user and the tool. Therefore, ventilation should be maintained and wear-resistant tools should be used during machining. Red copper (T2) exhibits exceptional plasticity, resulting in chips that are less prone to breakage. Therefore, tools with a larger rake angle, higher cutting speeds, and ample cutting fluid should be used when turning. Bronze (such as tin bronze and aluminum bronze) exhibits high hardness and strength, particularly aluminum bronze, which generates significant cutting forces. Therefore, stronger carbide tools (such as YG10) should be used, with appropriate reductions in cutting speeds and increases in feed rates. While lead-containing copper alloys exhibit excellent machinability, lead is highly toxic, requiring protective measures to avoid inhalation of lead dust during machining . In summary, copper alloy turning requires a customized process plan tailored to the material’s characteristics to achieve efficient and high-quality machining.
