Parameter optimization for CNC turning of stainless steel materials
When CNC turning stainless steel materials, parameter optimization can start from aspects such as cutting parameters, tool parameters, and cooling strategies. The following are the specific contents:
Cutting parameter optimization
Rotational speed: Excessively high rotational speed can easily cause high temperature, leading to tool oxidation; while too low rotational speed will accelerate work hardening. It is recommended to use a medium speed during rough machining, such as 80-120m/min. The fine processing can be increased to 150-180m/min. For example, for stainless steel workpieces with an outer diameter of 20 millimeters or less, rough machining can choose around 1200 RPM, and fine machining can choose around 1500 RPM. If the outer diameter of the workpiece is larger, the rotational speed needs to be reduced accordingly. For example, for a workpiece with an outer diameter of 50 millimeters, the rough machining rotational speed can be set at 1000 RPM or 800 RPM.
Feed rate: It needs to be determined in combination with the surface quality requirements. Rough machining is recommended at 0.15-0.3mm/r, and finish machining should be controlled at 0.05-0.1mm/r. For example, when processing austenitic stainless steel, a feed rate of less than 0.08mm per cut should be avoided.
Cutting depth: It should be avoided to be too small to prevent the accumulation of work hardening layers. Rough machining is recommended at 2-4mm, and finish machining at 0.2-0.5mm. The total cutting allowance for processing can be set at approximately 0.1mm. The first cutting depth should be 150-200% of the tool tip radius (R), and the maximum should not exceed 0.5mm.
Tool parameter optimization
Tool material: Hard alloy coated tools (such as TiAlN, AlCrN coating) can extend their service life by more than 30% by reducing the coefficient of friction and heat insulation. You can also choose YG type (tungsten-cobalt type, with high cobalt content, good toughness and strong impact resistance, suitable for intermittent cutting of stainless steel) or YW type (tungsten-titanium-tantalum-cobalt type, with balanced heat resistance and wear resistance, suitable for continuous cutting) carbide tools according to the working conditions.
Tool geometric Angle:
Rake Angle: Under the premise of ensuring that the tool has sufficient strength, a larger rake Angle should be selected to reduce the plastic deformation of the metal being cut, lower the cutting force and cutting temperature, and at the same time decrease the depth of the hardened layer. The rake Angle for turning various stainless steels is approximately 12° - 30°. For martensitic stainless steel (such as 2Cr13), the rake Angle can take a larger value. For austenitic and austenitic + ferritic stainless steels, the rake Angle should be taken as a smaller value. For stainless steel that has not undergone quenching and tempering treatment or has a relatively low hardness after quenching and tempering, a larger rake Angle can be adopted. For workpieces with smaller diameters or thin walls, a larger rake Angle is recommended.
Relief Angle: Increasing the relief Angle can reduce the friction between the rear tool face and the machined surface, but it will lower the strength and heat dissipation capacity of the cutting edge. The reasonable value of the relief Angle depends on the cutting thickness. When the cutting thickness is small, a larger relief Angle should be selected. Stainless steel turning tools or boring tools usually have a relief Angle of 10° - 20° (for finish machining) or 6° - 10° (for rough machining).
Main deflection Angle, secondary deflection Angle and tool tip arc radius: Reducing the main deflection Angle can increase the working length of the cutting edge, which is beneficial for heat dissipation. However, during the cutting process, it increases the radial force and is prone to vibration. The main deflection Angle is usually set at 45° - 75°. If the rigidity of the machine tool is insufficient, it can be appropriately increased. The secondary deflection Angle is usually taken as 8° to 15°. To strengthen the tip of the tool, a tip arc of 0.5-1.0mm should generally be ground out.
Edge Angle: To enhance the strength of the tool tip, the edge Angle is generally set at -8 ° to -3 °. When cutting intermittently, a larger value of -15 ° to 5° is adopted. Double-edge inclined turning tools can also be used. The first edge inclination is ≥0°, and the second edge inclination is approximately -20 ° near the tip of the tool. The length of the second edge inclination is about 1/3 of the cutting depth.
Cooling strategy optimization
Micro-lubrication (MQL) technology: Precisely spray 5-50 ml /h of atomized cutting oil onto the cutting area, reducing thermal deformation and lowering liquid consumption by 90%.
High-pressure internal cooling system: By directly flushing the tool tip with 5-10 mpa high-pressure coolant, it effectively suppresses built-up edge and accelerates chip removal.
Low-temperature cooling: The use of liquid nitrogen or CO₂ cold air (-50℃ to -30 ℃) can reduce the temperature in the cutting zone by more than 200℃, which is particularly suitable for the processing of high-hardness stainless steel.
