Key points of end mills in the processing of aluminum alloy materials

Aluminum alloy materials are widely used in aerospace, automotive and 3C fields due to their low density, high thermal conductivity and easy machinability. However, problems such as chip sticking, deformation and poor surface quality are prone to occur during processing. As the core tool, the end mill needs to achieve efficient and precise processing through the three-dimensional coordination of tool design optimization, cutting parameter matching and process strategy adjustment. The following analyzes the key points from the perspective of the combination of technical principles and engineering practice:

First, tool geometry structure: Break through the bottleneck of chip adhesion and deformation

Edge passivation and polishing

Aluminum alloy processing is prone to generating fine chips. The traditional sharp cutting edge is likely to cause the curling radius of the chips to be too small and lead to adhesion. Passivation with a T-shaped cutting edge of 0.01-0.03mm and mirror polishing (Ra≤0.1μm) can reduce the frictional resistance of the cutting edge to the chip. For instance, when processing 6061-T6 aluminum alloy, end mills with blunt cutting edges have a 40% higher chip removal efficiency and a 70% lower tool sticking phenomenon compared to those without blunt cutting edges.

Helical Angle and core thickness design

A large helix Angle (40°-45°) can enhance the chip curling effect, but it needs to be matched with a high-rigidity core thickness. For example, when processing 2024-T351 aviation aluminum alloy, end mills with a helix Angle of 42° and a core thickness ratio of 65% were used. At a cutting speed of 200m/min, the fluctuation of cutting force was reduced by 25% compared with conventional tools, avoiding the elastic deformation of the workpiece caused by sudden changes in cutting force.

Optimization of the rake Angle and rake Angle

Aluminum alloy has a high thermal conductivity (200W/m·K). It is necessary to reduce cutting heat by using a large rake Angle (12°-18°), and at the same time, a large relief Angle (15°-20°) should be used to avoid friction between the rear tool face and the machined surface. For instance, when processing 7075-T6 high-strength aluminum alloy, a end mill with a rake Angle of 15° and a relief Angle of 18° can reduce the cutting temperature to below 280℃, which is 30% lower than that of conventional tools, thus avoiding the peeling of the surface hardening layer caused by thermal softening.

Second, coating technology: Building an anti-sticking and lubricating barrier

Selection of super-lubricating coatings

In view of the chemical reactivity of aluminum alloys, coatings with a low coefficient of friction (μ≤0.3) should be adopted. For instance, the DLC (diamond-like carbon) coating, due to its graphitization property, has a friction coefficient of only 0.15 when processing aluminum alloys, which is 50% lower than that of the TiAlN coating. This can reduce the tendency of cold welding between chips and tools. In addition, the CrAlSiN coating still maintains low friction characteristics at a high temperature of 600℃, making it suitable for high-speed dry cutting.

The coating thickness and toughness are balanced

In aluminum alloy processing, the coating needs to take into account both hardness and toughness. For example, the 5μm AlTiN coating deposited by PVD has a hardness of up to 3200HV. Meanwhile, through the design of the nano-multilayer structure, the toughness of the coating is increased by 30%, avoiding coating peeling caused by chip impact. When processing ADC12 die-cast aluminum alloy, the service life of this coated end mill cutter is 8 times longer than that of the uncoated tool.

Coating surface texture control

The microstructure of the coating surface can affect the chip flow. For instance, by applying a nano-scale corrugated structure coating, the contact area between the chip and the tool is reduced by 40%, lowering the risk of chip adhesion. When processing 5083-H116 Marine aluminum alloy, the end mill with this coating remained clean on the tool surface after continuous processing for 2 hours, while the conventional coated tool had developed a 0.3mm thick built-up edge.

Third, cutting parameters: Match the material properties with the tool’s capabilities

The coordination of cutting speed and feed

Aluminum alloy processing requires a combination of high cutting speed (Vc≥150m/min) and large feed (fz≥0.15mm/ tooth) to achieve a cutting mode dominated by shear slip. For example, when processing 6082-T6 aluminum alloy, by adopting the parameters of Vc=220m/min and fz=0.2mm/ tooth, the cutting force can be reduced to 60% of the conventional parameters, and at the same time, the brittle fracture of chips caused by too low cutting temperature can be avoided.

The golden ratio of cut depth to cut width

Aluminum alloy is prone to form a work hardening layer (with a depth of approximately 0.05mm). It is necessary to penetrate the hardening layer through a cutting depth (ap) of ≥0.1mm, while controlling the cutting width (ae) to reduce the fluctuation of cutting force. For instance, when processing the 7003-T5 aluminum alloy for the middle frame of a mobile phone, parameters such as ap=0.2mm and ae=0.8D (where D is the tool diameter) are adopted to keep the surface roughness stable within Ra0.8μm and avoid vibration marks caused by periodic changes in cutting force.

Precise supply of cooling and lubrication

In aluminum alloy processing, it is necessary to avoid the reaction between coolant and chips to form a hydrogen embrittlement layer. It is recommended to use micro-lubrication (MQL) or cold air cutting. For example, when processing 2219-T851 aluminum alloy for aerospace, the use of 5μm grade plant oil-based MQL can increase the tool life by three times compared with dry cutting, and at the same time reduce the surface hardness fluctuation to ±5HV.

Fourth, process strategy: Suppress deformation and enhance efficiency

Climb milling priority and pre-drilling

Aluminum alloys have high plasticity, and climb milling can reduce the friction between chips and the machined surface. For example, when processing thin-walled aluminum alloy cabins, the adoption of climb milling strategy can control the wall thickness deformation within 0.02mm, which is 60% lower than that of climb milling. Meanwhile, pre-drilling a φ0.8D lead hole before deep groove processing can reduce the peak cutting force by 30% and avoid tool deflection caused by entry impact.

Layered milling and allowance control

In view of the characteristic that aluminum alloys are prone to deformation, stepped layer-by-layer milling should be adopted. For instance, when processing 20mm thick aluminum alloy structural components, the cutting is carried out in three layers (each layer is 6-7mm), with a 0.1mm allowance left for each layer for the final finishing. This ensures that the overall flatness error is controlled within 0.05mm, which is four times more accurate than a single milling operation.

Vibration suppression of the tool path

Vibration caused by sudden changes in the tool path should be avoided during aluminum alloy processing. For instance, when machining curved surfaces, a combined path of helical feed and contour milling is adopted to reduce the fluctuation of tool acceleration to within 2m/s², thus avoiding surface ripples caused by vibration. When processing the wings of a certain brand of unmanned aerial vehicle, this strategy has increased the consistency of surface roughness to more than 90%.