Explore the parameter selection principles for CNC turning slender shafts

When CNC turning slender shafts, parameter selection needs to comprehensively consider factors such as workpiece rigidity, cutting force, and thermal deformation. The following are the specific principles:

Cutting speed

Medium-high linear speed: Usually, a medium-high linear speed is chosen, such as 80-120 m/min. High-speed cutting can reduce built-up edge, but it is necessary to avoid workpiece deformation caused by heat accumulation. The specific speed should match the material of the cutting tool and the workpiece. For example, when rough turning, the cutting speed vc can be taken as 50-60 m/min, and when finish turning, it can be taken as 60-100 m/min.

Avoid excessive speed: Excessive speed can easily cause the workpiece to bend under the action of centrifugal force, which will damage the stability of cutting. Therefore, the maximum speed should be limited according to the length-to-diameter ratio and rigidity of the workpiece.

Feed rate

Small feed rate: Select a smaller feed rate (such as 0.1-0.3mm/r) to reduce the axial cutting force and minimize the bending of the workpiece. When rough turning, the feed rate f can be taken as 0.25-0.4mm/r, and when finish turning, it can be taken as 0.08-0.12mm/r.

Balancing efficiency and quality: A feed rate that is too small will reduce efficiency, but one that is too large will increase the cutting force. A reasonable value should be selected under the premise of ensuring surface quality.

The depth of the cut

Small cutting depth: A small cutting depth (usually ≤2mm) is adopted, and the allowance on one side is turned in multiple passes to reduce the radial cutting force and avoid radial jitter of the workpiece. When rough turning, the cutting depth ap can be taken as 1.5-2mm, and when finish turning, it can be taken as 0.5-1mm.

Multi-pass machining: By making multiple passes, the allowance is gradually removed to reduce the impact of a single cutting force on the workpiece.

Geometric parameters of cutting tools

Main deflection Angle: Increasing the main deflection Angle (such as 80° - 93°) can reduce the radial cutting force and lower the risk of workpiece bending. For rough turning, take 75° - 80°; for finish turning, take 85° - 90°.

Rake Angle: Selecting a larger rake Angle (such as 15° - 30°) can reduce cutting force and cutting heat. For rough machining, take 20°, and for finish machining, take 25°.

Tool tip arc radius: Choosing a smaller radius (such as r<0.3mm) can reduce the radial component force, but it is necessary to balance the tool life and surface roughness.

Chip breaking groove: The front of the turning tool should be ground with a chip breaking groove of R1.5-3 to ensure smooth curling and breaking during cutting.

Auxiliary measures

Center rest and tool rest: Use a center rest or tool rest to increase the rigidity of the workpiece and reduce vibration. The tool rest usually adopts three supporting claws to stabilize the workpiece.

Elastic rotary center: Compensates for the thermal deformation and elongation of the workpiece to prevent bending.

Adequate cutting fluid: Reduces the cutting temperature, decreases thermal deformation, and at the same time prevents the workpiece from being scratched by the tool rest support claws.