Optimization strategy for rough turning parameters in CNC turning
The optimization of rough turning parameters in CNC turning is a key link to improve processing efficiency and reduce tool wear. Systematic adjustments need to be made in combination with the characteristics of the process system, material properties and processing goals. The following specific strategies are developed from three dimensions: cutting parameter selection, tool path planning, and process system optimization:
First, the optimization strategy for cutting parameters
Hierarchical control of the depth of cut (ap)
During the rough turning stage, a larger depth of cut should be given priority to reduce the number of tool passes, but it needs to be dynamically adjusted according to the rigidity of the machine tool and the allowance of the workpiece. For instance, when the total allowance is 6mm, it can be cut in three steps (2mm each time) to avoid excessive impact load on the tool due to a single deep cut. When processing castings and forgings or when there is a hard skin on the surface, the depth of the first cut should be appropriately increased to ensure that the cutting edge penetrates into the material and prevent the surface from being uneven.
The balance between feed rate (f) and surface roughness
The feed rate should be matched with the depth of cut. Generally, 0.3 to 0.8mm/r is taken for rough turning. When the stiffness of the process system is insufficient or there are large corners in the workpiece contour, the feed rate needs to be reduced to avoid overtravel errors. For example, the feed rate at the contour corner can be reduced to 0.2mm/r, while when the tool is idle travel, it can be increased to the maximum value allowed by the machine tool to shorten the non-cutting time.
Dynamic adaptation of cutting speed (vc)
The cutting speed should be determined in combination with the material of the cutting tool and the characteristics of the workpiece material. For example, when turning 45 steel with carbide tools, the cutting speed can be referred to as 60 to 120m/min. If coated tools are adopted, the cutting speed can be increased to 150m/min. It should be noted that when cutting at low speed (such as when the spindle speed is lower than 500r/min), vibration caused by insufficient torque should be avoided. At this time, the cutting speed can be appropriately reduced to 80m/min.
Second, optimization of tool paths and processing strategies
Reuse of precision vehicle programs and parameter adjustment
By reusing the geometric path of the finish turning program, rough turning can be achieved only by adjusting the cutting parameters. For example, the depth of cut during finish turning was increased from 0.5mm to 2mm, the feed rate was raised from 0.1mm/r to 0.3mm/r, and the spindle speed was reduced from 1200r/min to 800r/min. During the final finishing process, retain the precision turning parameters of the last tool pass to ensure the surface finish.
Endpoint control of layer-by-layer cutting
When performing layer-by-layer cutting, it is necessary to avoid each tool terminating at the same axial position to prevent the main cutting edge of the tool from chipping due to the instantaneous heavy load impact. For example, when using a 90° main deflection Angle tool, the cutting end point of each tool should be advanced by 0.05mm successively to disperse the cutting force and extend the tool life.
The coordinated control of cutting force and heat
During the rough turning process, the cutting temperature needs to be reduced by coolant, and at the same time, the cutting parameters should be optimized to reduce heat accumulation. For instance, when the cutting speed exceeds 100m/min, high-pressure coolant should be used to directly impact the cutting area to prevent the tool from softening due to heat and causing accelerated wear.
Third, optimization of the process system and auxiliary strategies
Tool geometric parameters and material selection
For rough turning tools, high-strength and high-wear-resistant materials should be given priority, such as cemented carbide or ceramic-coated tools. In terms of tool geometry parameters, the rake Angle can be taken as 5° to 15° to reduce the cutting force, and the relief Angle can be taken as 6° to 8° to avoid wear on the rear tool face. For deep holes or long shaft workpieces, negative rake Angle tools should be used to enhance the strength of the cutting edge.
Rigidity and vibration suppression of the process system
The rigidity of the process system is enhanced by optimizing the clamping method. For instance, hydraulic chucks are used instead of mechanical chucks to reduce clamping deformation. For slender shaft workpieces, a tool rest or center rest can be added to suppress vibration. In addition, the accuracy of the machine tool guide rails and spindles should be inspected regularly to ensure that the positioning error does not exceed 0.01mm.
Tool life monitoring and chip breaking control
Establish a tool life monitoring system to assess the tool status in real time through cutting force sensors or power monitoring devices. When the cutting force fluctuates by more than 10%, the cutting tool needs to be replaced in time. In terms of chip breaking, the chip shape can be controlled by adjusting the parameters of the chip-breaking groove on the rake face of the tool (such as a width of 2mm and a depth of 0.5mm) to prevent long strip-shaped chips from entangling the workpiece.
Fourth, multi-objective optimization and verification
The cutting parameters are comprehensively optimized through the multi-objective genetic algorithm or the linear weighted sum method. For example, on the premise of ensuring the surface roughness Ra≤1.6μm, the cutting ratio energy can be reduced from 9.91J/mm³ to 7.33J/mm³. After optimization, the validity of the parameters needs to be verified through trial cutting, and the parameters should be fine-tuned according to the actual processing results. For instance, when vibration marks are found on the surface of the workpiece, the cutting speed can be reduced by 10% and the feed rate increased by 5% to improve the cutting condition.
Through the coordinated implementation of the above strategies, the rough turning efficiency can be increased by 20% to 30% while ensuring the processing quality, and the tool wear can be reduced by more than 15% at the same time. In practical applications, dynamic adjustments need to be made in combination with the specific workpiece material, machine tool characteristics and tool performance.
