Methods for improving the surface quality of CNC turning precision turning

The improvement of the surface quality of CNC turning precision turning requires comprehensive measures from multiple dimensions such as process parameter optimization, tool management, machine tool status control and processing environment guarantee. The following are the specific methods and key points of implementation:

Process parameter optimization

The cutting speed is matched with the feed rate

Cutting speed: Appropriately increasing it within the allowable range of the tool material (for example, 80-150 m/min for carbide tools) can reduce the fluctuation of cutting force and lower the surface roughness. However, it is necessary to avoid excessive speed causing built-up tumors or vibration.

Feed rate: During finish turning, it should be controlled at 0.05-0.2 mm/ R. If it is too high, it will accelerate tool wear and cause vibration marks. If it is too low, it may lead to work hardening due to too thin chips.

Back cut depth: Usually 0.1- 0.5mm, it needs to be adjusted according to the rigidity of the workpiece to avoid excessive cutting depth causing vibration.

Selection and use of cutting fluid

Emulsion: Suitable for general steel, it can lower the cutting temperature and reduce friction.

Extreme pressure cutting oil: It is used for difficult-to-machine materials (such as stainless steel and titanium alloy), and can form a lubricating film to reduce adhesive wear.

Spray method: A combination of high-pressure internal cooling and external cooling is adopted to ensure that the cutting area is fully cooled and to prevent secondary scratches on the workpiece by chips.

2. Tool management

Optimization of tool geometric parameters

Rake Angle: Increasing the rake Angle (such as 10°-15°) can reduce the cutting force, but if it is too large, it will lower the tool strength.

Relief Angle: Appropriately increasing the relief Angle (such as 6°-8°) can reduce the friction between the rear tool face and the workpiece, but it is necessary to avoid making it too large to prevent insufficient edge strength.

Edge grinding: Small arc edge (R0.1- 0.3mm) or chamfering treatment is adopted to enhance the edge strength and reduce chipping.

Tool wear monitoring

Regular inspection: After processing a certain number of workpieces, check the tool wear condition, with particular attention to the wear width of the rear tool face (VB value).

Timely replacement: When the VB value exceeds 0.3mm, the cutting tool needs to be replaced to avoid a decline in surface quality due to intensified wear.

3. Machine tool status control

Spindle accuracy adjustment

Radial runout: The radial runout of the main shaft should be controlled within 0.005mm, which can be achieved by adjusting the preload of the main shaft bearing or replacing the worn bearing.

Axial movement: The axial movement should be less than 0.01mm to avoid steps during end face processing.

Maintenance of guide rails and lead screws

Guide rail cleaning: Regularly remove debris from the surface of the guide rail and apply grease to reduce friction.

Lead screw clearance compensation: Adjust the reverse clearance of the lead screw through the numerical control system to ensure feed accuracy.

4. Optimization of processing environment and fixtures

Workpiece clamping stability

Clamping force control: The clamping force should be evenly distributed to prevent workpiece deformation. For example, the use of soft jaws or hydraulic chucks can reduce clamping stress.

Auxiliary support: For slender shafts or thin-walled parts, add a center rest or tool rest to reduce vibration.

Environmental temperature control

Constant-temperature workshop: Keep the workshop temperature at 20±2°C to prevent dimensional changes in workpieces caused by thermal expansion and contraction.

Workpiece preheating: For large-sized workpieces, they can be placed in the workshop in advance to balance the temperature and reduce thermal deformation during the processing.

5. Optimization of processing strategies

Layer-by-layer cutting and finishing

Layer-by-layer cutting: For workpieces with large allowances, a layer-by-layer processing method of rough turning - semi-finish turning - finish turning is adopted to gradually reduce the fluctuation of cutting force.

Finishing process: After fine turning, adding rolling or vibration polishing processes can further reduce the surface roughness (Ra value can be below 0.2 μm).

Programming skills

Circular interpolation: Use circular arc transitions at corners to avoid impact caused by right-angle cutting.

Constant linear speed control: For workpieces with variable diameters (such as conical surfaces), enable the G96 constant linear speed command to ensure a stable cutting speed.

6. Summary of Key implementation points

Give priority to solving the vibration problem: Vibration is the primary cause of surface quality decline and can be eliminated by adjusting the cutting parameters, enhancing the rigidity of the workpiece or reducing the spindle speed.

Pay attention to the shape of the chips: The ideal chips should be continuous band-shaped or short helical. If chipping or long band-shaped chips occur, the cutting parameters or tool Angle need to be adjusted.

Establish standardized processes: Form operation instructions for tool selection, parameter setting, clamping methods, etc., to ensure operational consistency.

Through the comprehensive application of the above methods, the surface quality of CNC precision turning can be significantly improved to meet the requirements of high-precision processing.