Reasons for Deformation in Aluminum Alloy Machining

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When machining multiple cavities on an aluminum alloy plate, sequentially machining one cavity at a time can easily cause uneven stress on the cavity walls, leading to deformation. The solution is to use a layered multi-pass machining method, where all cavities are machined simultaneously but not in a single pass. Instead, the machining is done in multiple layers, gradually reaching the required dimensions. This ensures more uniform stress distribution on the part, reducing the likelihood of deformation.

Choosing appropriate cutting parameters can effectively reduce cutting forces and heat during the machining process. Excessive cutting parameters in mechanical machining can lead to high cutting forces in a single pass, easily causing part deformation and affecting the rigidity of the machine tool spindle and tool durability.

Among the various elements of cutting parameters, the depth of cut has the most significant impact on cutting force. While reducing the depth of cut helps prevent part deformation, it also lowers machining efficiency. High-speed milling in CNC machining can address this issue. By reducing the depth of cut while correspondingly increasing the feed rate and raising the machine tool's rotational speed, cutting forces can be reduced without compromising machining efficiency.

The material and geometric parameters of the tool significantly impact cutting forces and heat. Selecting the right tool is crucial for reducing part deformation.

3.1 Rational Selection of Tool Geometric Parameters

Rake Angle: Under the condition of maintaining cutting edge strength, a larger rake angle should be selected. This allows for a sharper cutting edge, reduces cutting deformation, facilitates smooth chip evacuation, and lowers cutting forces and temperatures. Avoid using tools with negative rake angles.

Relief Angle: The relief angle directly affects flank wear and machined surface quality. Cutting thickness is an important factor in selecting the relief angle. During rough milling, due to high feed rates and heavy cutting loads, significant heat is generated, requiring good heat dissipation conditions. Thus, a smaller relief angle should be chosen. For finish milling, a sharp cutting edge is needed to reduce friction between the flank face and the machined surface, minimizing elastic deformation. Therefore, a larger relief angle should be selected.

Helix Angle: To ensure stable milling and reduce milling forces, the helix angle should be as large as possible.

Lead Angle: Appropriately reducing the lead angle can improve heat dissipation conditions, lowering the average temperature in the machining area.

3.2 Improving Tool Structure

Reduce the number of milling teeth and increase chip space. Due to the high plasticity of aluminum alloy, cutting deformation is significant during machining, requiring ample chip space. Therefore, a larger chip groove radius and fewer teeth are preferable.
For example:

Use two teeth for milling cutters below Φ20mm.

Use three teeth for milling cutters between Φ30mm and Φ60mm to avoid chip clogging and deformation of thin-walled aluminum alloy parts.

Precision grinding of teeth: The roughness value of the cutting edge should be less than Ra=0.4μm. Before using a new tool, lightly rub the front and back of the teeth with a fine oilstone to remove burrs and minor serrations left during sharpening. This not only reduces cutting heat but also minimizes cutting deformation.

Strictly control tool wear standards: Worn tools increase surface roughness, raise cutting temperatures, and lead to greater part deformation. Therefore, in addition to selecting wear-resistant tool materials, the tool wear standard should not exceed 0.2mm; otherwise, built-up edges are likely to form. During cutting, the workpiece temperature should generally not exceed 100°C to prevent deformation.

Roughing and finishing should employ different tool path sequences. Roughing aims to remove excess material from the blank surface at the highest cutting speed in the shortest time, forming the geometric contour required for finishing. Thus, efficiency is prioritized, pursuing the material removal rate per unit time, and climb milling should be used.

Finishing, on the other hand, demands higher precision and surface quality, emphasizing machining accuracy. Conventional milling should be used here. Since conventional milling gradually reduces the cutting thickness to zero, it significantly reduces work hardening and somewhat suppresses part deformation.

When machining thin-walled aluminum alloy parts, clamping force is a major cause of deformation, which is difficult to avoid even with improved machining accuracy. To reduce clamping-induced deformation, the clamped part can be loosened before the final finishing pass to release the clamping force, allowing the part to return to its original shape. It can then be reclamped lightly.

The secondary clamping point should ideally be on the support surface, with the clamping force applied in the direction of the part's highest rigidity. The clamping force should be just enough to secure the part without loosening, which requires considerable experience and feel from the operator. This method minimizes clamping deformation in the machined part.

When machining parts with cavities, directly plunging a milling cutter into the part can cause poor chip evacuation due to insufficient chip space, leading to accumulated cutting heat, thermal expansion, and deformation. In severe cases, tool chipping or breakage may occur. It is advisable to use the drill-before-mill method: first, drill a pilot hole with a drill bit no smaller than the milling cutter, then extend the milling cutter into the pilot hole to begin milling. This effectively addresses the issues mentioned above.

By applying these aluminum alloy machining methods, deformation issues in thin-walled aluminum alloy products can be effectively resolved. Deformation in finished aluminum alloy products is influenced by various factors, so making improvements in machining methods can significantly reduce the likelihood of aluminum alloy deformation.

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