Parameter control for CNC turning of thin-walled aluminum alloy parts

Tool parameter control

Tool material: Due to the softness of aluminum alloy, built-up edge is prone to form during cutting. Therefore, the tool should have good wear resistance and anti-adhesion properties. Although high-speed steel cutting tools are low in cost, they have poor wear resistance. When processing thin-walled aluminum alloy parts, the tools wear out quickly, which affects the processing accuracy and surface quality. Hard alloy cutting tools have high hardness and good wear resistance, and are commonly used for processing thin-walled aluminum alloy parts. In addition, diamond tools have extremely high hardness and wear resistance. When processing aluminum alloys, they can achieve excellent surface quality and dimensional accuracy. However, they are relatively expensive and are generally used in situations where processing quality is highly demanded.

Tool geometric Angle:

The rake Angle: Appropriately increasing the rake Angle can reduce the cutting force, lower the cutting temperature, and decrease the formation of built-up edge. For the processing of thin-walled aluminum alloy parts, the rake Angle is generally taken as 15° - 25°. If the rake Angle is too small, the cutting force increases and thin-walled parts are prone to deformation. If the rake Angle is too large, the tool strength will decrease and it is prone to chipping.

Relief Angle: The relief Angle mainly affects the friction between the rear face of the tool and the machined surface of the workpiece. When processing thin-walled aluminum alloy parts, it is advisable to take the relief Angle of 8° to 12°. If the clearance Angle is too small, the friction intensifies and the tool wears out quickly. If the clearance Angle is too large, the wedge Angle of the cutting tool will decrease and the strength will be reduced.

The main deflection Angle and secondary deflection Angle: Reducing the main deflection Angle and secondary deflection Angle can decrease the height of the residual cutting area and lower the surface roughness. However, if the main deflection Angle is too small, the radial cutting force will increase, and thin-walled parts are prone to deformation. The main deflection Angle is generally 45° - 75°, and the secondary deflection Angle is 5° - 10°.

Edge tilt Angle: The edge tilt Angle can control the chip flow direction. When processing thin-walled aluminum alloy parts, the cutting edge Angle should be set at 0° - 5° to ensure that the chips flow towards the surface to be processed and avoid scratching the already processed surface.

Cutting parameter control

Cutting speed: Cutting speed has a significant impact on processing efficiency and surface quality. Increasing the cutting speed can enhance production efficiency, but an excessively high cutting speed will raise the cutting temperature, accelerate tool wear, and may also cause thermal deformation of thin-walled parts. Generally speaking, when roughly machining thin-walled aluminum alloy parts, the cutting speed can be taken as 200-400 m/min, and when finely machining, it can be taken as 400-800 m/min. For instance, when processing thin-walled aluminum alloy shaft parts with a diameter of 50mm, the rotational speed for rough machining can be selected as 1200-2500r /min, and for finish machining, it can be selected as 2500-5000r /min.

Feed rate: Excessive feed rate will increase the cutting force and cause deformation of thin-walled parts. If the feed rate is too small, the production efficiency will be low, and the surface quality may be affected due to the intensified friction between the tool and the workpiece. The feed rate can be taken as 0.1-0.3mm/r during rough machining, and 0.05-0.15mm/r during finish machining. For instance, when precisely turning the outer circle of thin-walled aluminum alloy parts, it is more appropriate to control the feed rate within 0.08-0.12mm/r.

Cutting depth: Aluminum alloy thin-walled parts have poor rigidity. If the cutting depth is too large, it will cause significant deformation. During rough machining, the cutting depth can be taken as 1-3mm, and during finish machining, it can be taken as 0.05-0.2mm. For example, when performing fine machining on thin-walled cylindrical parts made of aluminum alloy with a wall thickness of 2mm, the cutting depth should be controlled within 0.1mm to reduce deformation.

Fixture parameter control

Clamping force: If the clamping force is too large, it will cause elastic deformation of thin-walled parts. After processing, the deformation will recover, affecting the dimensional accuracy. If the clamping force is too small, the workpiece is prone to loosening under the action of the cutting force, resulting in processing errors. The magnitude of the clamping force should be comprehensively considered based on factors such as the shape, size, material and cutting force of the workpiece. Generally, the appropriate clamping force can be determined through experiments or empirical formulas. Under the premise of ensuring the reliable clamping of the workpiece, the clamping force should be reduced as much as possible. For instance, the test can be conducted by gradually increasing the clamping force to observe the deformation of the workpiece and determine the appropriate clamping force magnitude.

Clamping method: Evenly distributed clamping points should be adopted to ensure uniform force distribution on the workpiece and reduce deformation. For circular thin-walled parts, open expansion sleeves or elastic chucks can be used for clamping. For square thin-walled parts, a pressure plate can be used to press them evenly. Meanwhile, the clamping part should be as close as possible to the processing part to minimize the influence of the clamping force on the processing accuracy.

Cooling and lubrication parameter control

Coolant selection: Aluminum alloys are prone to chemical reactions with certain coolants at high temperatures, leading to corrosion. Therefore, coolant that has no corrosive effect on aluminum alloy should be selected, such as emulsion, kerosene, etc. The emulsion has excellent cooling and lubricating properties, which can effectively reduce the cutting temperature, decrease tool wear and improve the quality of the machined surface. Kerosene has good lubricating performance and is suitable for fine processing with high requirements for surface quality.

Cooling method: High-pressure cooling or spray cooling can be adopted to ensure that the coolant fully penetrates the cutting area and enhances the cooling effect. High-pressure cooling can spray the coolant onto the cutting edge at a relatively high pressure, promptly removing the cutting heat and reducing the cutting temperature. Spray cooling involves atomizing the coolant and spraying it onto the cutting area, which can both cool and lubricate, reducing the friction between the tool and the workpiece.

Coolant flow rate: The coolant flow rate should be moderate. If the flow rate is too small, the cooling effect will be poor. Excessive flow will cause waste and may also affect the processing environment. Generally speaking, the coolant flow rate should be adjusted according to factors such as cutting parameters, tool type and workpiece material to ensure that the cutting area can be adequately cooled and lubricated.