Seven Methods to Prevent Deformation in Aluminum Alloy Machining

Aluminum alloy is an important industrial material. Due to its relatively low hardness and large coefficient of thermal expansion, it is prone to deformation during the machining of thin-wall or thin-plate parts. In addition to improving tool performance and using aging treatment in advance to eliminate internal stress in the material, certain measures can also be taken from the machining process perspective to minimize deformation as much as possible.

For aluminum alloy parts with large machining allowances, in order to create good heat dissipation conditions and reduce thermal deformation, heat concentration must be avoided as much as possible. The method that can be adopted is symmetrical machining. For example, if there is an aluminum alloy plate with a thickness of 90 mm, and it needs to be milled to 60 mm, milling one side and then immediately turning it over to mill the other side will cause a large amount of material to be removed continuously from each side in one operation. This leads to heat concentration and results in a flatness of only 5 mm. If the symmetrical machining method is used — milling both sides multiple times until the final dimension is reached — heat dissipation is improved, and the flatness can be controlled within 0.3 mm.

▌ Layer-by-Layer Multiple Machining Method

When there are multiple cavities on an aluminum alloy plate-type part, machining one cavity at a time will easily cause deformation due to uneven forces on the cavity walls. The best solution is the layer-by-layer multiple machining method, meaning machining all cavities simultaneously, but not completing them in one step. Instead, the machining is divided into several layers and gradually processed to the required dimensions. This way, the forces on the part are more uniform and the probability of deformation is lower.

▌ Proper Selection of Cutting Parameters

Selecting proper cutting parameters can effectively reduce cutting force and cutting heat during machining. If the cutting amount is too large during machining, the cutting force for each pass will be excessive, which easily causes part deformation and also affects the rigidity of the machine spindle and the tool’s durability. Among all cutting parameters, the factor that has the greatest influence on cutting force is the depth of cut. Reducing the depth of cut helps prevent deformation, but at the same time lowers machining efficiency. High-speed milling in CNC machining solves this problem. By reducing the depth of cut while increasing the feed rate and spindle speed accordingly, cutting force can be reduced while maintaining machining efficiency.

▌ Improving Tool Cutting Capability

The tool material and geometric parameters have a significant influence on cutting force and heat. Correctly selecting the tool is crucial for reducing part deformation.

① Reasonable selection of tool geometry:

Rake angle:
While ensuring tool edge strength, a larger rake angle should be selected. This allows a sharper cutting edge, reduces cutting deformation, facilitates chip removal, and decreases cutting force and cutting temperature. Negative rake angle tools must be avoided.

Relief angle:
The relief angle directly affects flank wear and surface quality. Cutting thickness is the important basis for selecting the relief angle. During rough milling, because of large feed and heavy cutting load generating significant heat, a smaller relief angle is required for better heat dissipation. During finish milling, a larger relief angle is required for sharper cutting edges, reduced friction on the machined surface, and reduced elastic deformation.

Helix angle:
To make milling stable and reduce milling force, the helix angle should be as large as possible.

Lead angle:
Properly reducing the lead angle improves heat dissipation and lowers the average temperature in the cutting zone.

② Improving tool structure:

Reduce the number of cutter teeth and increase chip-holding space. Aluminum alloy has high plasticity and large cutting deformation, requiring larger chip pockets. Therefore, the radius at the bottom of the flute should be larger, and fewer teeth should be used. For example, milling cutters below φ20 mm should use two flutes, and cutters φ30–φ60 mm should use three flutes to avoid chip clogging, which can cause deformation in thin-wall aluminum parts.

Finish-grinding of cutter teeth:
The surface roughness at the cutting edge must be less than Ra 0.4 μm. Before using a new tool, the cutting edges should be lightly honed with a fine oilstone to remove burrs and slight saw-tooth marks left from sharpening. This reduces cutting heat and cutting deformation.

Strict control of tool wear limits:
After tool wear occurs, surface roughness increases, cutting temperature rises, and part deformation increases. Therefore, besides selecting wear-resistant tool materials, tool wear should not exceed 0.2 mm; otherwise, built-up edge is likely to occur. During cutting, the part temperature should not exceed 100°C to prevent deformation.

▌ Proper Cutting Path Arrangement

Rough machining and finish machining should adopt different cutting paths.
Rough machining focuses on removing excess material from the workpiece surface at the fastest cutting speed within the shortest time, forming the required geometry for finishing; therefore, machining efficiency is emphasized and climb milling should be avoided. Up milling should be used.

Finish machining emphasizes machining accuracy and surface quality, so climb milling should be used. During climb milling, cutting thickness decreases gradually from maximum to zero, significantly reducing work hardening and also helping suppress deformation.

▌ Secondary Clamping for Thin-Wall Parts

For thin-wall aluminum alloy parts, clamping force is an important cause of deformation, which cannot be avoided simply by improving machining accuracy. To reduce clamping-induced deformation, the part should be loosened before final finishing to release clamping force, allowing the part to return to its natural state. Then it should be lightly clamped again. The secondary clamping point should be on a supporting surface, and the clamping force should be applied in the direction of the highest rigidity of the part. The clamping force must be just enough to prevent movement. This requires high operator experience and feel. Parts machined this way have much less clamping deformation.

▌ Drilling Before Milling Method

When machining parts with cavities, plunging directly with an end mill causes insufficient chip-holding space, leading to poor chip evacuation. This results in large amounts of cutting heat accumulating in the workpiece, causing thermal expansion and deformation, and may even cause tool chipping or breakage. The best solution is drilling before milling — using a drill with a diameter no smaller than the end mill to drill a pilot hole first, then inserting the end mill into the pre-drilled hole for milling. This effectively solves the problem mentioned above.