Non-ferrous and non-metal turning
Compared to ferrous metal turning, turning nonferrous and nonmetallic materials has unique processing characteristics and requirements, which are closely related to their physical and mechanical properties. Nonferrous metals such as copper, aluminum, magnesium, and their alloys have good thermal conductivity, high plasticity, and low hardness. Nonmetallic materials such as plastics, rubber, and wood have low hardness, poor wear resistance, and are prone to thermal deformation. These characteristics dictate the need for selecting appropriate tool materials, cutting parameters, and cooling methods during the turning process to ensure processing quality and efficiency. Understanding the turning characteristics of nonferrous and nonmetallic materials is crucial for improving product quality and reducing production costs.
Turning non-ferrous metals requires selecting appropriate tools and cutting parameters based on the material’s characteristics. For copper and copper alloys, due to their high plasticity and susceptibility to built-up edge (BUE), sharp tools should be selected, primarily made of high-speed steel or carbide. A large rake angle (15°-25°) and a clearance angle (8°-12°) should be used to reduce cutting forces and friction. Cutting speeds should be high, generally 100-300 m/min, to avoid BUE at low and medium speeds, which can affect surface quality. Feed rates can be increased to improve machining efficiency, but care must be taken to avoid workpiece deformation. Aluminum and aluminum alloys have lower hardness and lower cutting forces, but are prone to tool sticking. Therefore, tools should be kept sharp, and cutting speeds as high as 300-600 m/min can be used. Kerosene or an emulsion should be used as a cutting fluid to cool and lubricate the tool and prevent sticking . For magnesium alloys, due to their flammability, a large amount of cutting fluid must be used during turning, while avoiding excessively high cutting temperatures. The cutting speed is generally controlled at 100~200 m/min.
Turning non-metallic materials presents different challenges than turning metals. When turning plastics, due to their poor thermal conductivity, cutting heat tends to concentrate in the cutting area, causing the material to soften and melt, impacting surface quality. Therefore, high cutting speeds (200-500 m/min) and low feed rates (0.05-0.2 mm/rev) should be selected to reduce cutting heat generation. Tool materials can be high-speed steel or carbide, with a rake angle of 10°-20° and a relief angle of 10°-15°. The tool edge should be sharp to avoid tearing the material. Compressed air or kerosene can be used as a cutting fluid to cool and remove chips. Turning rubber requires a lower cutting speed (50-100 m/min), as high-speed cutting can cause rubber to heat up and age. Feed rates should also be low to prevent elastic deformation. When turning wood, the tool should have a large rake angle (25°~35°) and a sharp cutting edge to obtain a smooth surface. The cutting speed can be selected according to the hardness of the wood, generally 100~300 m/min. No cutting fluid is required, but chips must be removed in time to avoid clogging.
The clamping method for turning non-ferrous and non-metallic materials also needs to be adjusted according to the material properties. Non-ferrous metal materials are usually soft in texture, and excessive clamping force should be avoided during clamping to prevent deformation of the workpiece. Soft jaws can be used, or soft materials such as copper and aluminum can be placed between the jaws and the workpiece to protect the workpiece surface and reduce deformation. For thin-walled non-ferrous metal parts, special fixtures can be used or auxiliary supports can be added to increase the rigidity of the workpiece. Non-metallic materials such as plastics and wood have low hardness and high brittleness. During clamping, the clamping force should be applied evenly to prevent the workpiece from breaking or plastic deformation. For example, when turning plastic pipe fittings, an expansion mandrel can be used for clamping so that the clamping force is evenly distributed on the inner wall of the pipe to prevent the pipe from being clamped flat.
Common problems and solutions in the turning process of non-ferrous and non-metallic materials are as follows. Built-up edge, a common problem in non-ferrous metal turning, can be addressed by increasing cutting speeds, using cutting fluids with good lubricity, or coating the tool. If surface roughness is unsatisfactory, replace the tool with a sharper one or reduce the feed rate. Plastic melting and tool sticking in the turning of non-metallic materials can be improved by lowering the cutting temperature, using compressed air cooling, or selecting an appropriate cutting fluid. If burrs appear on the surface of wood, the tool edge can be trimmed to ensure a sharp edge and the cutting speed can be increased appropriately. Furthermore, since the chip morphology of non-ferrous and non-metallic materials differs from that of ferrous metals—for example, aluminum chips form ribbons and plastic chips form powder—effective chip removal measures, such as installing chip flutes or using compressed air to blow off chips, are necessary to prevent chips from accumulating on the workpiece surface or around the tool, which can affect machining quality and operator safety. By properly selecting tools, cutting parameters, and clamping methods, as well as implementing effective process measures, it is possible to ensure the turning quality of non-ferrous and non-metallic materials and meet the machining requirements of different products.
