Slender austenitic stainless steel screws are widely used in the chemical and mechanical industries due to their excellent corrosion resistance and mechanical properties. However, their turning process presents numerous challenges. These screws have a large aspect ratio and poor rigidity, making them prone to bending, deformation, and vibration during turning, impacting machining accuracy and surface quality. First, during the preparatory stage for turning, the tool material must be carefully selected. Due to the poor thermal conductivity and severe work hardening of austenitic stainless steel, high-speed steel tools are insufficient. Carbide tools, such as tungsten-cobalt-titanium (YT15) or tungsten-cobalt (YG8), are preferred. YT15 offers excellent red hardness, making it suitable for higher cutting speeds and effectively minimizing the adverse effects of work hardening. Furthermore, determining tool geometry is crucial. A rake angle of 10°-15° and a relief angle of 6°-8° are generally recommended to reduce cutting forces and minimize vibration risk. Furthermore, the blank must be inspected to ensure that its straightness meets the required standards, and straightening performed if necessary to lay a good foundation for subsequent turning.
The selection of cutting parameters during the turning process is directly related to the processing effect. The turning speed of austenitic stainless steel slender screw should not be too high, and is usually controlled at 80-120m/min. If the speed is too high, the cutting temperature will rise sharply, aggravating tool wear and possibly causing thermal deformation of the workpiece. The feed rate should be reasonably set according to the processing accuracy requirements. 0.2-0.3mm/r can be selected for rough turning, and it needs to be reduced to 0.1-0.15mm/r for fine turning to ensure surface roughness. The selection of back cutting amount needs to be combined with the blank allowance. It can be appropriately increased during rough turning, generally 2-3mm, and controlled at 0.1-0.5mm during fine turning to avoid bending of the workpiece due to excessive cutting force. In actual operation, the cutting parameters must be adjusted in time according to the tool wear to ensure a stable processing process.
To address the lack of rigidity when turning slender screws, effective auxiliary support measures must be implemented. Common methods include the use of a steady rest and a steady rest. The steady rest is mounted on the lathe’s large carriage and moves with the tool, effectively supporting the workpiece and reducing vibration and deformation. For particularly long screws, a steady rest is also required in the middle. The steady rest is fixed to the lathe bed and contacts the workpiece via three adjustable support claws, further enhancing the workpiece’s rigidity. When installing the steady rest and steady rest, pay attention to the gap between the support claws and the workpiece. Too large a gap will provide no support, while too small a gap will damage the workpiece surface. A suitable gap is generally 0.05-0.1mm. Lubrication of the support claws is also necessary to reduce friction and wear.
Cooling and lubrication during the turning process are also crucial. Austenitic stainless steel generates significant cutting heat during turning. Failure to cool the tool in a timely manner can lead to excessive tool temperatures, increased wear, and thermal deformation of the workpiece, affecting machining accuracy. Therefore, it is essential to select a suitable cooling lubricant, typically an emulsion. Emulsions offer excellent cooling and lubricating properties, effectively lowering cutting temperatures and minimizing friction between the tool and workpiece. The cooling lubricant should be supplied adequately and sprayed directly into the cutting area through a nozzle to ensure adequate cooling of the tool and workpiece. Furthermore, the cooling lubricant must be replaced regularly to maintain cleanliness and prevent excessive impurities from affecting the cooling effect and workpiece surface quality.
Finally, after turning, the slender screw requires necessary testing and treatment. Testing primarily covers dimensional accuracy, form and position tolerances, and surface roughness. This testing can be performed using tools such as micrometers, dial indicators, and roughness meters. Areas that do not meet these requirements require rework. Furthermore, the screw requires stress relief. Internal stresses generated during turning can cause deformation during use if not promptly eliminated. Stress relief typically involves aging, heating the screw to a specific temperature, holding the temperature for a period of time, and then slowly cooling it to eliminate internal stresses. These measures ensure the turning quality of austenitic stainless steel slender screws, ensuring they meet actual operational requirements.
