The "specialness" of milling aluminum: A complete guide to defect prevention and efficiency improvement

Milling aluminum and its alloys may seem simple on the surface, but it hides three major problems: "low melting point sticking to the tool", "high thermal conductivity and heat dissipation" and "high plastic deformation". How to avoid tool chipping and surface scratches while ensuring a high material removal rate? This article will take you through the core elements of milling aluminum alloys from material properties, tool geometry to machine tool selection, and help you establish an efficient and stable milling process system.

1. Basic cognition: Why is milling aluminum "special"?

(1) How do the material properties of aluminum affect milling?

1) Sticking and built-up edge problems caused by low melting point (660℃)

The melting point of aluminum and its alloys is only about 660℃. It is very easy to melt locally in the high-speed cutting zone, thereby adhering to the blade to form a built-up edge. The built-up edge is constantly disassembled and regenerated, resulting in tool edge failure, deterioration of surface roughness, and cutting vibration and tool breakage.

Formation of stacked edges on the cutting edge when milling aluminium

2) The influence of high thermal conductivity on cutting heat distribution

The thermal conductivity of aluminum alloy is usually between 160–230 W/(m·K), which is several times higher than that of steel. This makes it easy for cutting heat to be quickly transferred to the workpiece and chips, rather than concentrated on the front edge of the tool.

Experiments show that a large amount of heat is carried away with the chips, which helps to reduce the temperature rise of the tool, but it also puts higher requirements on chip removal and cutting fluid cooling.

3) Risk of surface scratches and deformation caused by high plasticity and low hardness

Aluminum alloy has good plasticity and a hardness of only about HV50–100. It is easy to scratch or deform under the action of cutting force. Especially when milling aluminum thin-walled parts, it is necessary to control the cutting force and fixture rigidity to avoid processing deformation and dimensional deviation.

(2) Differences in processing performance of commonly used aluminum alloys (6061/7075/5052, etc.)

5052: Non-heat-treated alloy, high fatigue strength and corrosion resistance; due to its softness, it is prone to tool sticking, but the processing torque is small, and it is often used in marine and light-load structural parts.

6061-T6: Heat-treated strengthened alloy, with good balance performance, easy welding, good thermal conductivity and machinability, it is a universal "universal alloy".

7075-T6: High-strength aviation alloy, with strength close to that of steel, but high processing hardness and fast tool wear, requiring sharper tools and stable cutting conditions.

2. In which industries is milling aluminum most widely used? What are the typical scenarios?

(1) 3C electronics

The mass production of thin-walled, high-finish parts such as mobile phone middle frames and notebook shells requires wall thickness ≤2.5 mm, high consistency and Ra ≤0.6 µm. Vacuum adsorption or special elastic clamps are often used in combination with MQL cooling.

(2) Automobile

Motor housings, chassis connectors, radiators, etc. require efficient batch processing and meet torque load and structural strength requirements. 5-axis linkage machine tools and high-efficiency carbide or PCD tools are usually used.

Motor housings

(3) Aerospace

High-strength structural parts, fuselage skins, fasteners, etc. require high precision (±0.01 mm) and fatigue resistance. Typical alloys are 7075, 2024, etc. PCD or coated carbide tools are used to improve tool life.

(4) Medical devices

Lightweight implants and precision catheter interfaces require a processing accuracy of Ra≤0.2 µm to ensure the quality of subsequent biocompatible surface treatment, and require no tool marks and burrs. High-precision CNC and ultra-fine tools are commonly used.

3. Technical practice: How to choose tools and parameters when milling aluminum?

(1) The core logic of tool selection

Comparison of applicable scenarios of carbide, DLC coating, and PCD tools:

Carbide: High cost performance, suitable for general aluminum alloy rough processing.

DLC (diamond-like carbon) coating: reduces aluminum adhesion and is suitable for semi-finishing to finishing.

PCD (polycrystalline diamond): extremely high wear resistance, tool life is more than 10 times that of ordinary cemented carbide, and can maintain high-quality surface at high cutting speeds.

(2) The influence of tool geometry parameters (front angle/back angle/helix angle) on milling aluminum

Rake angle: A larger front angle helps reduce cutting resistance and improve surface quality;

Back angle: An appropriate back angle ensures the tool edge inclination angle and reduces the risk of workpiece scratches;

Helix angle: A high helix angle (30°–45°) helps chips to be discharged smoothly, reducing vibration and chip accumulation.

(3) Edge passivation vs. sharp edge: How to balance efficiency and surface quality

Sharp edges can reduce cutting forces and scratches, but are easy to damage; passivated edges are more stable and durable, but may sacrifice some surface finish, which needs to be weighed according to batch and quality requirements.

Case: Why is the tool life of PCD 10 times longer than that of ordinary carbide when machining 7075-T6?

PCD has extremely high hardness and wear resistance, and can be cut stably under high cutting parameters without significant wear due to the "sticking tool" effect of aluminum; carbide tools will quickly form accumulated edges and break under the same conditions.

4. How to adjust the cutting parameters for milling aluminum? What are the common misunderstandings?

(1) Advantages and risks of critical speed (above 10,000 rpm) of high-speed milling (HSM)

High speed can reduce chip thickness and improve surface quality, but if it exceeds the dynamic balancing capacity of the machine tool, it is easy to cause vibration, surface chatter marks and shorten tool life.

(2) Quantitative effect of feed rate on surface roughness

Classic formula: Ra≈f2 /8re​​

Where f is the unit tooth feed (mm/tooth) and re is the tool arc radius (mm). Actual measurements show that for every 0.01 mm/tooth increase in f, Ra increases by about 20%.

(3) Cutting depth stratification strategy: how to improve efficiency in roughing and how to control deformation in fine machining

Roughing: large cutting depth (2–4 mm), low-precision tools, focus on MRR;

Fine machining: shallow cutting depth (≤0.2 mm), high-precision tools and paths, minimize cutting force to control workpiece deformation.

Precision milling of aluminium

(4) Guide to avoiding pitfalls: Vibration caused by too high speed, sticking caused by too low feed rate

There is a big misunderstanding in this sentence. It is not absolutely judged by the speed, but by many factors. In fact, aluminum is suitable for high-speed milling.

The root cause of sticking: too low cutting temperature, improper tool coating selection, lack of cutting fluid, etc.;

Prevention of built-up edge: Use DLC/CrN coated tools + MQL or dry cutting combination to reduce adhesion and timely chip removal;

Surface vibration mark inspection: Confirm that the spindle dynamic balance reaches G1.0 level, and the tool extension does not exceed 3 times the diameter to avoid resonance.

5. Equipment and process for milling aluminum: how to build an efficient processing system?

(1) What are the key indicators for machine tool selection? How to make choices with a limited budget?

High-speed electric spindle (24,000 rpm+): suitable for 3C thin-walled high-finish parts;

Heavy-duty spindle (high torque): suitable for large automotive and aviation structural parts;

Motor spindle rotates the tool for cutting

Linear motor: fast response, no screw pitch error, suitable for high-precision small parts;

Ball screw: low cost, good rigidity, suitable for general medium and large machining centers.

● Case: A small factory processes 6061 aluminum alloy and recommends core parameters for purchasing a 100,000 yuan machine tool:

Spindle speed ≥ 18,000 rpm;

Dynamic balancing level G2.5;

12,000 N lateral rigidity;

Support MQL and internal cooling;

4-axis or 5-axis linkage module.

(2) How to optimize the clamping and cooling solution?

Clamping of thin-walled parts (wall thickness ≤ 1 mm): vacuum adsorption provides uniform clamping force; elastic clamp (soft pad + positioning pin) reduces local stress concentration.

Cooling and lubrication options:

Dry cutting: environmentally friendly, but requires PCD + DLC coating support;

MQL: trace oil mist, taking into account both cooling and environmental protection;

High-pressure internal cooling: essential for deep cavity processing, significantly extending tool life.

● Money-saving tips: How to achieve high-precision clamping with ordinary vises

Use locating pins + thin metal gaskets to adjust the height and level of the workpiece;

Install flexible pads on both jaws of the vise to distribute the clamping force.

Clamping and cooling of the part

(3) Process strategies for different processing stages (roughing/semi-finishing/finishing)

Roughing: maximize MRR, refer to typical parameters - cutting speed 300-500 sfpm, feed 0.006-0.010 ipt, cutting depth 2-4 mm;

Semi-finishing: reduce cutting depth to 1 mm, increase feed appropriately, and balance efficiency and surface;

Finishing: mirror processing Ra≤0.2 µm, use spiral milling or multi-tool overlapping pass, step distance ≤0.05 mm.

● Case: How to reduce the number of tool changes by using composite tools in the processing of automotive aluminum alloy cylinders

Using end and side milling composite tools, rough, semi-finishing and finishing can be completed in one clamping, which improves efficiency by 40% and reduces error accumulation.

6. Conclusion

Although milling aluminum and its alloys seems simple, it contains many traps: from the sticking of the tool caused by the low melting point of the material to the challenge of cutting thermal management due to high thermal conductivity, and then to the profound impact of tool and machine tool selection on efficiency and quality.

Mastering the processing characteristics of different grades of aluminum alloys, combining reasonable tool materials and geometric shapes, precise cutting parameters, and targeted machine tool and fixture configuration, can achieve a balance between high efficiency and low cost while ensuring high surface quality. It is hoped that the systematic analysis of this article can provide practical and feasible guidance ideas for relevant industry personnel on the road to optimizing the milling aluminum alloy process.