Austenitic stainless steel shafts are widely used in the field of mechanical manufacturing due to their excellent corrosion resistance and high-temperature strength, and deep hole drilling is a difficult process in the machining process. The core challenge of deep hole drilling is that the depth to diameter ratio of the hole is usually more than 5 times, and it is difficult for the cutting fluid to effectively reach the cutting area, resulting in heat dissipation difficulties. At the same time, poor chip removal can easily cause tool wear and scratches on the hole wall. Austenitic stainless steel itself has high toughness and high plasticity, and is prone to severe work hardening during drilling, which causes a sudden increase in the cutting force of the tool and further aggravates tool wear. In addition, the thermal conductivity of the material is low, about 1/3 of that of 45 steel. The cutting heat accumulates in large quantities at the tip of the tool, which not only affects the tool life, but may also cause deformation of the workpiece and reduce machining accuracy.
When selecting tools for deep-hole drilling in austenitic stainless steel shafts, it’s important to consider both material properties and processing requirements. While high-speed steel tools are less expensive, they have poor heat resistance and easily lose hardness due to high temperatures during high-speed cutting. Therefore, they are only suitable for low-speed, small-diameter, shallow hole machining. Carbide tools, especially ultrafine-grained carbide with a high cobalt content, offer high hardness and wear resistance, maintaining cutting performance at higher cutting speeds, making them the preferred choice for deep-hole drilling. The design of the tool’s geometric parameters is equally critical. The drill’s top angle should be appropriately reduced, generally to around 118°, to reduce axial cutting forces. The helix angle should be increased to 30°-40° to improve chip evacuation. Furthermore, the cutting edge should be properly chamfered to reduce the impact of work hardening on the tool.
Properly setting cutting parameters is crucial for ensuring high-quality deep-hole drilling of austenitic stainless steel shafts. Excessively high cutting speeds can lead to a sharp increase in cutting temperature, exacerbating tool wear; excessively low speeds can reduce machining efficiency and easily cause extrusion deformation. Practice has shown that when using carbide tools, a cutting speed of 80-120 m/min is ideal. The feed rate should balance machining efficiency and surface quality. Excessive feed rates can easily result in rough hole walls and drill bit breakage, while too low a feed rate can prolong machining time. A typical feed rate is 0.1-0.2 mm/min. Furthermore, the selection and supply of cutting fluid are crucial. Extreme-pressure emulsions or sulfurized cutting oils should be used, and the fluid should be injected through the drill bit’s internal channels via a high-pressure pump to ensure adequate cooling and lubrication, while also assisting with chip removal.
In the actual drilling process, operating skills and process control have a significant impact on the processing effect. When starting to drill, a low feed rate should be used for positioning. After the drill bit stably cuts into the workpiece, the feed speed should be gradually increased to avoid the offset of the hole due to inaccurate initial positioning. For holes with greater depth, segmented drilling is required. After drilling to a certain depth, the drill bit should be withdrawn, the chips should be cleared and the tool should be cooled to prevent chip accumulation from causing drill jamming or tool overheating damage. At the same time, pay close attention to the sound and vibration during the drilling process. If abnormal sounds or severe vibrations occur, the processing should be stopped immediately, and the tool should be checked for wear and the workpiece should be checked for looseness. The fault should be eliminated in time before continuing the operation. In addition, the size and verticality of the hole should be measured regularly, and the cutting parameters should be adjusted according to the measurement results to ensure that the processing accuracy meets the requirements.
After processing is completed, the quality inspection and subsequent processing of the deep hole of the austenitic stainless steel shaft are equally important. First, check the surface roughness of the hole. If defects such as scratches and cracks are found, analyze the cause and take appropriate repair measures, and reprocess if necessary. Secondly, measure the actual size and tolerance of the hole to ensure that it meets the design requirements. For holes that are out of tolerance, they can be corrected by reaming or boring. At the same time, clean the chips and cutting fluid remaining in the hole to prevent corrosion of the workpiece surface. Finally, maintain and maintain the tool, clean the oil and chips on the tool, check the wear of the tool, and sharpen or replace the tool with severe wear in time to ensure the smooth progress of subsequent processing. Through strict quality inspection and reasonable subsequent processing, the processing quality and service life of the deep hole of austenitic stainless steel shaft can be effectively improved.
