Key points of parameter control for CNC turning of thin-walled parts

When CNC turning thin-walled parts, the core of parameter control lies in balancing the cutting force, thermal deformation and workpiece rigidity. It is necessary to optimize it in a coordinated manner from multiple dimensions such as cutting parameters, tool geometry parameters, clamping methods and process strategies. The following are the specific control points:

First, control of cutting parameters

Cutting depth (depth of cut)

During rough machining, the depth of cut should be 0.2 to 2mm to prevent workpiece deformation caused by excessive cutting force.

During finish machining, the depth of cut should be controlled within 0.2 to 0.5mm to ensure surface quality and dimensional accuracy.

It needs to be dynamically adjusted according to the material characteristics of the workpiece. For example, for plastic materials, a smaller value should be taken, while for brittle materials, it can be appropriately increased.

Feed rate

During rough machining, the feed rate can be taken as 0.12-0.25mm/r, taking into account both efficiency and cutting force control.

During fine machining, the feed rate should be controlled at 0.08 to 0.15mm/r to reduce the surface roughness.

It is necessary to pay attention to the synergistic relationship between the feed rate and the depth of cut to avoid a sudden increase in cutting force due to the simultaneous increase of both.

Cutting speed

During rough machining, the cutting speed should be 6 to 80m/min. The specific value needs to be determined in combination with the material of the workpiece and the type of cutting tool.

During finish machining, the cutting speed can be increased to 6 to 120m/min, but it is necessary to avoid excessive speed to prevent thermal deformation.

High-speed machining helps to reduce cutting force and remove cutting heat, but it is necessary to ensure the rigidity matching between the tool and the workpiece.

Second, optimization of tool geometric parameters

Front Angle and rear Angle

The rake Angle should be set at 5° to 20°. Increasing the rake Angle can reduce the cutting force, but it is necessary to avoid making it too large, which may lead to insufficient tool strength.

The relief Angle should be set at 4° to 12°. Increasing the relief Angle can reduce the friction force, but both the tool strength and heat dissipation performance need to be taken into account.

During fine machining, the relief Angle can be appropriately increased to improve the surface quality.

Principal deflection Angle and secondary deflection Angle

The main deflection Angle should be set at 30° to 90°. When turning the inner and outer circles of thin-walled parts, taking a larger main deflection Angle can reduce the radial cutting force.

The secondary deflection Angle should be set at 8° to 15°. During fine machining, it can be appropriately increased to reduce the surface roughness.

The main deflection Angle needs to be dynamically adjusted according to the rigidity of the workpiece to avoid deformation caused by uneven distribution of cutting force.

Radius of the arc at the tip of the knife

The radius of the tool tip arc should be taken as a smaller value to reduce the cutting force and decrease the internal stress of the workpiece.

During fine machining, the radius of the tool tip arc should match the length of the finishing edge to ensure surface quality.

Third, clamping methods and process strategies

Clamping method

Axial clamping is preferred to avoid deformation of the workpiece caused by radial clamping.

Slit sleeves or soft jaws can be used to increase the clamping contact surface, so that the clamping force can be evenly distributed.

For workpieces with a large length-to-diameter ratio, a center rest or a tool rest can be used to enhance rigidity.

Process strategy

Rough machining and finish machining should be carried out in stages. A allowance of 0.2 to 0.5mm should be left for finish machining to remove.

The processing of the inner hole should precede that of the outer circle to avoid affecting the accuracy of the outer circle due to the deformation of the inner hole.

Shaft protection auxiliary processing can be adopted to ensure that the workpiece does not deform during the outer circle processing.

Use of cutting fluid

Fully pour the cutting fluid to lower the cutting temperature and reduce thermal deformation.

The cutting fluid should evenly cover the cutting area to avoid dimensional errors caused by local overheating.

Fourth, the rigidity of the tool and the workpiece should be matched

Tool rigidity enhancement

Increase the cross-sectional area of the tool holder to position the tool tip at the centerline of the tool holder and enhance the rigidity of the inner hole turning tool.

The extension length of the tool holder should be 5 to 8mm longer than that of the workpiece to reduce cutting vibration.

The length of the finishing edge of a finish turning tool should be 0.2 to 0.3mm, and the edge should be sharp to reduce the cutting force.

Rigidity enhancement of the workpiece

Add process ribs at the clamping position to enhance the local rigidity of the workpiece.

After processing is completed, remove the process ribs to ensure the dimensional and shape accuracy of the workpiece.

For thin-walled tube parts, special fixtures can be used for fixation to avoid vibration and deformation.