In the process of CNC milling aluminum, aluminum is widely used due to its good plasticity, thermal conductivity and lightweight properties, but aluminum milling is prone to poor surface quality, insufficient dimensional accuracy, and fast tool wear. The following summarizes common problems and solutions based on processing principles and practical experience.
1. Surface quality problems and solutions
Aluminum has strong plasticity. If the feed speed does not match the spindle speed, burrs are easy to occur; if the tool edge is worn or the cutting parameters are unreasonable, obvious tool marks will be left. The solution needs to start from two aspects: the parameters adopt the "high speed and low feed" mode, and the recommended spindle speed for aluminum milling is 3000-8000r/min and the feed rate is 0.1-0.2mm/r; the tool should choose a sharp ultra-fine grain carbide tool, and the edge should be passivated (edge radius 0.01-0.03mm) to avoid edge cracking and burrs.
When the temperature of the cutting area is too high, aluminum chips will adhere to the blade to form built-up edge, resulting in deterioration of surface roughness. The cooling system needs to be optimized, high-pressure cooling (pressure ≥ 5bar) is used to directly flush the cutting area, and special aluminum alloy cutting fluid containing extreme pressure additives is selected; at the same time, the cutting temperature is controlled. When processing 6061 aluminum alloy, the cutting speed should not exceed 150m/min. If necessary, intermittent cutting is used to allow the tool to cool down naturally.
2. Dimensional accuracy problems and solutions
The thermal expansion coefficient of aluminum is large (about 23×10⁻⁶/℃), and the temperature rise during processing will cause the workpiece to deform. It is necessary to reserve thermal deformation compensation in the program (0.02-0.03mm for every 100mm length); use layered cutting to reduce cutting force, leave 0.5-1mm margin for rough processing, and pass the tool in 2-3 times for fine processing; use soft claws or rubber pads when clamping to avoid deformation rebound caused by rigid clamping.
Thin-walled aluminum parts are prone to vibration deformation due to cutting force. To solve this problem, the clamping method needs to be optimized, and vacuum suction cups or multi-point support tooling should be used to ensure uniform clamping force; reduce radial cutting force, select large rake angle tools (rake angle 12°-15°), and reduce cutting depth (finishing ≤0.5mm); add a retraction pause in the program to allow the workpiece to release stress before the next cut.
3. Tool-related issues and solutions
Although the hardness of aluminum chips is low, friction and adhesion during high-speed cutting will accelerate wear. Tool materials should preferably be titanium-containing cemented carbide (such as WC-Co-TiC series) or coated tools (AlTiN coating can improve wear resistance); the cutting fluid should be kept clean, and aluminum chips should be filtered regularly to remove particles to avoid abrasive wear; when the wear of the back face of the tool reaches 0.2mm, it should be replaced in time.
A tool bar that is too long or has a large overhang will cause chatter. The tool overhang should be controlled (no more than 3 times the tool diameter), and a damping tool bar should be used when necessary; down milling should be used to reduce cutting force fluctuations. When down milling, the tool cutting direction should be consistent with the workpiece feed direction, which can reduce vibration by more than 50%; check the spindle runout to ensure that it is ≤0.01mm. Excessive runout will aggravate tool vibration.
4. Other common problems and solutions
Aluminum chips are easy to wrap around the tool handle in a ribbon shape, affecting the circulation of cutting fluid. A chip breaker groove can be opened on the tool (groove width 0.5-1mm), or an end mill with a helix angle of 30°-45° can be used to discharge the chips upward with a spiral blade; chip breaking instructions can also be set in the program to achieve chip segmentation by pausing the feed.
The release of internal stress in aluminum can cause deformation after processing. It is recommended to perform aging treatment after rough machining (6061 aluminum alloy can be kept at 120℃ for 2 hours); adopt the "separate rough and fine" process, place it for 24 hours after rough machining and then fine machining to fully release the stress; for complex structural parts, a symmetrical machining path can be used to balance the deformation caused by cutting force.
In short, the core of CNC milling aluminum is to control the three major elements of "temperature, cutting force, and chip removal". By reasonably matching cutting parameters, optimizing tools and tooling, and strengthening cooling and stress control, common problems can be effectively solved and high-quality machining can be achieved. In actual production, the process plan needs to be flexibly adjusted according to the aluminum grade (such as pure aluminum, aluminum alloy) and the workpiece structure.