Explore the parameter strategies for CNC turning of polyhedral parts

Exploration of Parameter Strategies for CNC Turning of Polyhedral Parts

When CNC turning polyhedral parts, the parameter strategy needs to comprehensively consider factors such as tool selection, cutting parameters, processing sequence and rigidity of the process system to ensure processing accuracy, efficiency and surface quality. The following is the specific strategy analysis:

First, tool selection strategy

Tool type adaptation

Polyhedral parts usually feature planes, inclined planes and curved surfaces, and the cutting tools should be selected according to the type of processing surface. For instance, for planar processing, carbide end mills can be selected, while for inclined or curved surface processing, ball-end mills or ring mills should be used.

For complex polyhedrons, modular tools are preferred as they facilitate the quick replacement of tool heads to meet different processing requirements.

Optimization of tool geometric parameters

The main deflection Angle needs to be adjusted according to the slope of the machined surface. For example, when machining a 45° inclined surface, the main deflection Angle should be close to 45° to reduce the radial cutting force.

The radius of the tool tip arc should match the machining allowance. During finish machining, the radius of the tool tip arc should be taken as 0.1 to 0.2mm to reduce the surface roughness.

Second, the strategy of cutting parameters

Back cut depth (ap) control

During rough machining, the depth of cut can be taken as 2 to 5mm, but it needs to be dynamically adjusted according to the rigidity of the process system. For example, when processing slender shafted polyhedrons, the depth of cut on the back should be reduced to 1 to 2mm to avoid vibration.

During fine machining, the depth of cut should be controlled within 0.1 to 0.3mm to ensure dimensional accuracy and surface quality.

Feed rate (f) optimization

During rough machining, the feed rate can be taken as 0.3-0.8mm/r, while during finish machining, it needs to be reduced to 0.05-0.2mm/r.

When processing thin-walled or easily deformable polyhedrons, the feed rate should be further reduced, for example, by using 0.05 to 0.1mm/r to lower the cutting force.

Selection of cutting speed (Vc)

The cutting speed needs to be adjusted according to the hardness of the material. For instance, when processing 45 steel, the cutting speed for rough machining can be set at 80 to 100m/min, and for finish machining, it can be increased to 120 to 150m/min.

When processing high-hardness materials (such as quenched steel), the cutting speed should be reduced to 50 to 80m/min to extend the tool life.

Third, processing sequence and technological strategy

Processing sequence planning

Following the principle of "from the inside to the outside and from coarse to fine", prioritize processing the inner hole or reference surface, and then gradually expand to the outer contour. For example, when processing polyhedral shaft parts, the center hole is turned first, and then each outer cylindrical surface and end face is processed in sequence.

For symmetrical polyhedrons, the "layered cutting" strategy can be adopted, with each cutting depth not exceeding 0.5mm, gradually approaching the final size.

The rigidity of the process system has been enhanced

The "one clamp, one top" clamping method is adopted, for example, one end is clamped with a three-jaw chuck and the other end is supported by a top, to enhance the rigidity of polyhedral parts with a large length-to-diameter ratio.

When processing thin-walled polyhedrons, auxiliary supports can be added or liquid-filled fixtures can be used to prevent deformation caused by cutting force.

Cutting fluid and cooling strategy

Fully pour high-pressure cutting fluid (pressure ≥5MPa) and directly impact the cutting area to reduce the temperature. For example, when processing titanium alloy polyhedrons, it is necessary to ensure that the cutting fluid flow rate is ≥15L/min to avoid thermal deformation.

For materials that are prone to sticking to the tool (such as aluminum alloy), the micro-lubrication (MQL) technology can be adopted to reduce chip adhesion.

Fourth, dynamic adjustment and optimization of parameters

Cutting force monitoring and feedback

The cutting force is monitored in real time through a power sensor. When the fluctuation of the cutting force exceeds 15%, the depth of cut is automatically reduced by 10% to 20%. For example, if a sudden increase in the spindle power is found during the processing, immediately reduce the depth of cut from 3mm to 2.4mm.

The cutting vibration is monitored by using a vibration sensor. When the vibration amplitude exceeds 0.05mm, the feed rate or cutting speed is adjusted.

Tool wear compensation

When the wear of the rear face of the tool reaches 0.2mm, reduce the depth of cut by 10% to extend the tool life. For example, the original depth of cut of 2mm was adjusted to 1.8mm, and the cutting speed was increased by 5% at the same time to compensate for the efficiency loss.

Regularly inspect the condition of the cutting edge of the tool. If chipping or built-up edge is found, immediately replace the tool and adjust the cutting parameters.

Multi-objective optimization model

Establish an optimization model with the goals of "processing efficiency, surface quality and tool life", and solve the optimal parameter combination through genetic algorithm or particle swarm optimization algorithm. For example, after optimization, the cutting speed increases by 10%, the feed rate decreases by 5%, and the surface roughness drops from Ra1.6μm to Ra0.8μm.