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Seven Methods to Avoid Part Deformation in Aluminum Alloy Processing

Aluminum alloy is an important industrial raw material. Due to its relatively low hardness and high coefficient of thermal expansion, it is prone to deformation in the mechanical processing of thin-walled and thin plate parts. In addition to improving tool performance and pre using aging treatment to eliminate internal stress in materials, from the perspective of processing technology, some measures can also be taken to minimize material deformation during machining.

For aluminum alloy parts with large machining allowance, in order to create better heat dissipation conditions and reduce thermal deformation, it is necessary to avoid excessive heat concentration as much as possible. The method that can be adopted is symmetrical machining. For example, there is a 90mm thick aluminum alloy plate that needs to be milled to a thickness of 60mm. If one side is milled and immediately turned over to mill the other side, since each side is machined to the final size at once, the continuous machining allowance is large, which will cause heat concentration problems. As a result, the flatness of the milled aluminum alloy plate can only reach 5mm. If a symmetrical machining method with repeated cutting on both sides is adopted, each side should be machined at least twice until the final size is reached, which is beneficial for heat dissipation and the flatness can be controlled at 0.3 millimeters.

1. Layered multiple processing method

When there are multiple cavities that need to be processed on aluminum alloy sheet parts, if the method of processing one cavity after another is adopted, it is easy to cause deformation of the cavity wall due to uneven force distribution. The best solution is to adopt a layered multiple processing method, which means that all cavities are processed simultaneously, but not in one go. Instead, they are divided into several layers and processed layer by layer to the required size. This way, the force on the parts will be more uniform and the probability of deformation will be smaller.

2. Proper selection of cutting parameters

Choosing appropriate cutting parameters can effectively reduce cutting forces and cutting heat during the cutting process. In the process of mechanical processing, excessive cutting parameters can lead to excessive cutting force in one pass, which can easily cause deformation of the parts and affect the rigidity of the machine tool spindle and the durability of the cutting tools. Among the various elements of cutting parameters, the back cutting amount has the greatest impact on cutting force. In theory, reducing the amount of back cutting is beneficial for ensuring that the parts do not deform, but at the same time, it will also reduce machining efficiency. High speed milling in CNC machining can solve this problem by reducing the back cutting amount, increasing the feed rate accordingly, and increasing the machine speed. This can reduce cutting force while ensuring machining efficiency.

3. Improve the cutting ability of cutting tools

The material and geometric parameters of cutting tools have a significant impact on cutting force and cutting heat. Choosing the right tool is crucial for reducing machining deformation of parts.

① Reasonably select the geometric parameters of the cutting tool.

Fore angle: While maintaining the strength of the blade, choosing a larger front angle can not only sharpen the edge, but also reduce cutting deformation, facilitate chip removal, and ultimately lower cutting force and temperature. Never use tools with negative front angles.

Rear corner: The size of the rear corner has a direct impact on the wear of the rear cutting surface and the quality of the machined surface. The cutting thickness is an important condition for selecting the back angle. During rough milling, due to the large feed rate, heavy cutting load, and high heat generation, it is required that the tool has good heat dissipation conditions. Therefore, a smaller back angle should be chosen. When precision milling, it is required that the cutting edge be sharp, reduce the friction between the back cutting surface and the machining surface, and minimize elastic deformation. Therefore, the back angle should be chosen to be larger.

Spiral angle: In order to ensure smooth milling and reduce milling force, the spiral angle should be selected as large as possible.

Lead angle: Reducing the lead angle appropriately can improve heat dissipation conditions and lower the average temperature in the processing area.

② Improve the tool structure.

Reduce the number of milling cutter teeth and increase the chip space. Due to the high plasticity of aluminum alloy materials and significant cutting deformation during processing, a larger chip space is required. Therefore, it is preferable to have a larger chip groove bottom radius and fewer milling cutter teeth. For example, milling cutters with a diameter of less than 20mm use two teeth; It is better to use three teeth for milling cutters with a diameter of 30-60mm to avoid deformation of thin-walled aluminum alloy parts caused by chip blockage.

Precision sharpening teeth: The roughness value of the cutting edge of the teeth should be less than Ra=0.4 μ m. Before using a new knife, it should be lightly ground with a fine oilstone in front and behind the teeth to eliminate any burrs and slight serrations left during sharpening. In this way, not only can cutting heat be reduced, but cutting deformation is also relatively small.

Strict control of tool wear standards: After tool wear, the surface roughness value of the workpiece increases, the cutting temperature rises, and the deformation of the workpiece increases accordingly. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not exceed 0.2mm, otherwise it is easy to produce chip deposits. When cutting, the temperature of the workpiece should generally not exceed 100 ℃ to prevent deformation.

4. The order of cutting is particular

Rough machining and precision machining should adopt different cutting sequences. Rough machining requires the fastest cutting speed to remove excess material from the surface of the blank in the shortest possible time, forming the geometric contour required for precision machining. Therefore, the emphasis is on processing efficiency, pursuing material cutting rate per unit time, and reverse milling should be used. Precision machining has higher requirements for machining accuracy and surface quality, emphasizing machining quality and using sequential milling. Due to the gradual decrease in cutting thickness from maximum to zero during sequential milling, the phenomenon of work hardening is greatly reduced, and there is also a certain degree of suppression on the deformation of the parts.

5. Secondary compression of thin-walled components

When processing thin-walled aluminum alloy parts, the clamping force during clamping is also an important cause of deformation, which is difficult to avoid even if the processing accuracy is improved. In order to reduce the deformation of the workpiece caused by clamping, the clamped part can be loosened before reaching the final size during precision machining, releasing the clamping force to allow the part to freely return to its original state, and then re tightened slightly. The optimal point for secondary compression is on the supporting surface, and the clamping force should be applied in the direction of good rigidity of the workpiece. The magnitude of the clamping force should be based on the ability to clamp the workpiece without loosening, which requires a high level of experience and tactile sensation from the operator. The compression deformation of the parts processed in this way is relatively small.

6. Drilling before milling method

When machining parts with cavities, if a milling cutter is used to directly insert the part downwards, it will cause poor chip removal due to insufficient chip space of the milling cutter, resulting in the accumulation of a large amount of cutting heat and expansion deformation of the part, and even possible accidents such as tool breakage and fracture. The best method is to drill first and then mill, that is, first drill the tool hole with a drill bit that is not smaller than the milling cutter, and then insert the milling cutter into the tool hole to start milling. This can effectively solve the problems mentioned above.