Grinding workpieces on a lathe
Grinding a workpiece on a lathe is a machining method that combines lathe and grinding processes. It is suitable for workpieces that are inconvenient to machine on a grinding machine, or when high-precision grinding requires the lathe’s rotational accuracy. This method fully utilizes the lathe’s equipment resources, expands its processing range, and enables both turning and grinding on the same machine, improving production efficiency and machining accuracy. Grinding a workpiece on a lathe requires addressing issues such as grinding tool installation, grinding parameter selection, and cooling and lubrication to ensure grinding quality.
The key to grinding workpieces on a lathe lies in the installation and adjustment of the grinding tools. Commonly used grinding tools include a grinding wheel holder, abrasive belt grinding device, and specialized grinding heads. The grinding wheel holder can be mounted on the lathe slide via a flange or a specialized fixture, and moves longitudinally and transversely with the slide. The main axis of the grinding wheel holder must be parallel to the lathe spindle to ensure surface straightness. During installation, a dial indicator should be used for alignment, ensuring radial runout of the grinding wheel holder spindle does not exceed 0.01mm. The belt grinding device consists of an abrasive belt, abrasive belt wheel, and a tensioning mechanism. It is mounted on the lathe tool post. The belt can be driven by the lathe spindle through a transmission mechanism or by a separate motor. Belt grinding is suitable for workpieces with low surface roughness requirements, offering high grinding efficiency and excellent surface quality. Specialized grinding heads are typically electric and mounted on the lathe tool post. The grinding head has an adjustable speed (generally 3,000-10,000 rpm) and is suitable for precision grinding of small workpieces. Regardless of the type of grinding tool used, it must be ensured that it is securely mounted and does not vibrate during the grinding process, otherwise the surface quality will be affected.
The process characteristics of grinding a workpiece on a lathe differ from those of grinding on a grinder. The appropriate grinding method and parameters must be selected based on the workpiece material and processing requirements. The main grinding methods include external cylindrical grinding, internal cylindrical grinding, and face grinding. During external cylindrical grinding, the workpiece is rotated by the lathe spindle, and the grinding wheel is fed longitudinally. Either longitudinal grinding or plunge grinding can be used. Longitudinal grinding is suitable for slender shafts, while plunge grinding is suitable for short, thick workpieces. For internal cylindrical grinding, a small grinding wheel is required. The diameter of the grinding wheel should be smaller than the diameter of the workpiece’s inner hole. During grinding, the grinding wheel rotates and feeds laterally, while the workpiece is rotated by the spindle. For face grinding, the grinding wheel axis is perpendicular to the workpiece axis, and the grinding wheel feeds laterally to grind the workpiece’s end face. Grinding parameters include grinding wheel speed, workpiece speed, feed rate, and grinding depth. Grinding wheel speed is generally 3,000-10,000 rpm, workpiece speed is 50-200 rpm, feed rate is 0.05-0.2 mm/r, and grinding depth is 0.01-0.05 mm. For high-hardness materials (such as hardened steel), a lower grinding speed and smaller grinding depth are required to avoid grinding wheel clogging and workpiece burns. For non-ferrous metals, a softer grinding wheel and a larger grinding depth are required to improve grinding efficiency.
Cooling and lubrication of workpieces ground on a lathe are crucial, as the grinding process generates a significant amount of heat. Failure to cool the workpiece promptly can cause burns and deformation on the workpiece surface, and even shorten the life of the grinding wheel. Cooling lubricants must possess excellent cooling and lubricating properties. Commonly used cooling lubricants include emulsions, extreme-pressure cutting oils, and specialized grinding fluids. Emulsions offer excellent cooling properties and are suitable for grinding general materials; extreme-pressure cutting oils offer excellent lubrication and are suitable for grinding high-hardness materials; specialized grinding fluids offer excellent rust prevention and cleaning properties and are suitable for precision grinding. The cooling lubricant should be supplied using high-pressure jetting, spraying the coolant directly into the grinding area at a flow rate of at least 15 L/min to ensure adequate cooling. Grinding chips and grinding wheel debris generated during grinding must be promptly removed to prevent them from mixing with the coolant and scratching the workpiece surface or clogging the cooling lines.
Precision control for workpiece grinding on a lathe requires careful attention to multiple aspects, including equipment, tools, and processes. The lathe’s spindle’s rotational accuracy directly impacts the workpiece’s roundness error. Therefore, radial runout and axial play of the lathe’s spindle must be maintained within 0.005mm. The lathe should be calibrated as necessary. The precision of the grinding tool also requires strict control. The grinding wheel or belt must be balanced to the required accuracy. Excessive imbalance can cause grinding vibration, affecting surface quality. A static balance test should be performed before installing the grinding wheel. Regarding the process, a reasonable grinding sequence should be adopted, generally starting with rough grinding and ending with fine grinding. Rough grinding removes most of the excess material, while fine grinding ensures accuracy and surface quality. The grinding depth during fine grinding should be less than the workpiece’s surface roughness value to avoid introducing new surface defects. For external cylindrical grinding of slender shafts, a steady rest or steady rest is required to prevent workpiece bending and deformation. The steady rest’s support jaws must maintain good contact with the workpiece surface and be properly lubricated.
Grinding different workpiece types on a lathe requires different precautions. When grinding external cylindrical workpieces, ensure the workpiece is securely clamped. For irregularly shaped workpieces, a dedicated fixture is required to prevent the workpiece from loosening during grinding. When grinding internal cylindrical workpieces, due to the smaller grinding wheel diameter and lower grinding speed, the workpiece rotation speed should be appropriately reduced and the number of grinding passes increased to ensure surface quality and dimensional accuracy of the inner hole. At the same time, the clearance between the grinding wheel and the inner hole wall should be carefully considered to prevent collisions between the grinding wheel and the workpiece. When grinding end faces, the grinding wheel axis must be perpendicular to the workpiece end face. This can be achieved by adjusting the angle of the grinding wheel holder. The grinding feed should be uniform during the grinding process to avoid creating bosses or depressions in the center of the end face. Furthermore, the workpiece temperature should be closely monitored during grinding. If excessive heating is detected, grinding should be stopped immediately and allowed to cool before resuming to prevent thermal deformation that could affect accuracy. By properly selecting grinding tools, optimizing grinding parameters, and ensuring effective cooling, lubrication, and precision control, high-quality grinding can be achieved on a lathe to meet production requirements.
