Parameter optimization methods for deep hole parts in CNC turning
When performing CNC turning on deep hole parts, to optimize parameters, the following aspects can be considered
Optimization of cutting parameter parameters
Depth of cut: Under the condition that the rigidity of the process system and the power of the machine tool permit, a larger depth of cut should be selected as much as possible to reduce the number of feed cycles. During rough machining, in addition to leaving the finishing allowance, all the allowance should be removed as much as possible in one pass. The machining allowance for fine machining is generally small and can be removed at one time. For instance, on medium-power machine tools, the depth of cut for rough machining can reach 8-10mm, for semi-finish machining it is 0.5-5mm, and for finish machining it is 0.2-1.5mm. When the precision requirements for parts are relatively high, it is necessary to consider leaving a finish turning allowance. The finish turning allowance left is generally smaller than that left during ordinary turning, and is usually taken as 0.1-0.5mm.
Feed rate: The selection of feed rate should be adapted to the depth of cut and the spindle speed. Under the premise of ensuring the processing quality of the workpiece, a higher feed rate (below 2000mm/min) can be selected. When cutting, turning deep holes or performing fine turning, a lower feed rate should be selected. When performing rough turning, f is generally taken as 0.3-0.8mm/r; For fine turning, f is often taken as 0.1-0.3mm/r. When cutting, f = 0.05-0.2mm/r.
Cutting speed: When turning the outer circle, the spindle speed should be determined based on the diameter of the workpiece on the part, as well as the cutting speed allowed by the material of the part and the tool, and the nature of the processing, etc. In addition to calculation and table lookup, the cutting speed can also be determined based on practical experience. It should be noted that the low-speed output torque of the AC variable frequency speed regulation CNC lathe is small, so the cutting speed cannot be too low. After the cutting speed is determined, the spindle speed n (r/min) is calculated using the formula n = 1000vc/πd.
Optimization of deep hole processing command parameters
Instruction selection: Most CNC systems offer deep hole processing instructions. For instance, the FANUC system provides two instructions, G73 and G83. G73 is the high-speed deep hole reverse chip removal drilling command, and G83 is the deep hole reverse chip removal drilling command. For deep hole processing, especially for those with a large length-to-diameter ratio, to ensure smooth breaking and chip removal, the G83 instruction should be given priority.
Instruction parameter setting: In the instruction format, X and Y represent the positions of the holes to be processed. Z represents the coordinate value at the bottom of the hole (if it is a through hole, the drill tip should extend beyond the bottom surface of the workpiece). R is the coordinate value of the reference point (point R is 2-5mm higher than the top surface of the workpiece). Q represents the processing depth for each time; F represents the feed rate (mm/min); G98 is for returning to the initial plane after drilling is completed. G99 is the return to the reference plane (i.e., the plane where point R is located) after the drilling is completed.
Optimization of cooling and lubrication parameters
Cooling system selection: High-pressure internal cooling is the preferred choice for deep hole machining. The coolant passes through the interior of the tool and directly reaches the cutting zone, serving both cooling and chip removal functions. The pressure is usually between 2 and 10MPa. The flow rate should be designed to match the tool specification and hole diameter to avoid overheating of the tool or chip blockage due to insufficient cooling. For processing with large hole diameters or extremely deep depths, an external cooling auxiliary system is sometimes adopted, that is, coolant is sprayed from the outside of the hole opening while internal cooling is carried out through the inner hole of the tool.
Selection of cutting fluid: Commonly used coolants in deep hole machining include water-based emulsions, mineral oil-based cutting fluids, and special deep hole machining oils. The emulsion has good cooling properties, but its lubricity is slightly poor. Deep hole oil has excellent lubrication performance and is more suitable for high-precision and long-cycle processing.
Cutting fluid management: To ensure the stable operation of the cooling system, it is necessary to configure a filtration, constant temperature and circulation system to prevent the mixture of chip impurities in the cutting fluid and avoid blockage. For BTA or jet suction systems, it is also necessary to ensure that the cooling pipelines have good sealing performance to prevent pressure drop.
Optimization of special working condition parameters
For thin-walled deep hole parts: When turning thin-walled workpieces, to avoid clamping deformation, the axial clamping method is preferred. The workpiece is axially clamped by the end face of the axial clamping sleeve, and the clamping force F is distributed along the axial direction of the workpiece. When performing rough turning, the depth of cut and feed rate can be slightly larger. When performing finish turning, the depth of cut should be controlled at 0.1-0.2mm/r, and the cutting speed should be 6-120m/min. In addition, process ribs can be added. To enhance the rigidity of thin-walled deep-hole workpieces at their clamping positions, several process ribs can be specially made at the clamping positions, allowing the clamping force to act on the process ribs to reduce the deformation of the workpiece. After processing is completed, the process ribs can be removed.
Different depth feed adjustment: Different depths and different feeds can be achieved through programming. For example, in MasterCAM, select the advanced transfer in the milling machine's tool path, choose the hole center, determine the tool, select the appropriate drill bit, determine the parameter Settings, add segments, and set the feed speed for different depths.
