Six Methods To Avoid Deformation in Aluminum Alloy Machining

Aluminum alloy is an important industrial raw material. Due to its relatively small 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 eliminating internal stress of materials through pre aging treatment, from the perspective of processing technology, some measures can also be taken to minimize material processing deformation as much as possible.

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 90 millimeter thick aluminum alloy plate that needs to be milled to a thickness of 60 millimeters. If one side is immediately turned over and milled to the other side after milling, as each side is processed in one go to the final size, the continuous machining allowance is large, which will cause heat concentration problems. Therefore, the flatness of the milled aluminum alloy plate can only reach 5 millimeters. If a symmetrical machining method of repeated feeding on both sides is adopted, each surface 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 on aluminum alloy sheet parts that need to be processed, if the method of sequentially processing one cavity after another is adopted, it is easy to cause deformation of the cavity wall due to uneven stress. The best solution is to adopt a layered and multiple processing method, which means processing all cavities simultaneously, but not in one go. Instead, it is divided into several levels 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 amount

Choosing the appropriate cutting amount can effectively reduce the cutting force and cutting heat during the cutting process. In the process of mechanical machining, excessive cutting force 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 tool. Among the various factors of cutting parameters, the back cutting force has the greatest impact on cutting force. Reducing the back cutting amount is beneficial for ensuring that the parts do not deform, but it also reduces processing efficiency. The high-speed milling of CNC machining can solve this problem by reducing the back feed while correspondingly increasing the feed rate and increasing the machine speed, which can not only reduce cutting force but also ensure machining efficiency.

3. Improving the cutting ability of cutting tools

The material and geometric parameters of cutting tools have an important impact on cutting force and cutting heat. The correct selection of cutting tools is crucial for reducing part machining deformation.

① Reasonably select the geometric parameters of the cutting tool.

Front angle: While maintaining the strength of the cutting edge, selecting a larger front angle can not only sharpen the edge, but also reduce cutting deformation, making chip removal smooth, thereby reducing cutting force and cutting temperature. Avoid using negative rake angle tools.

Back angle: The size of the back angle has a direct impact on the wear of the back cutting surface and the quality of the machined surface. 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 selected. When precision milling, it is required to have a sharp edge to reduce friction between the back cutting surface and the machining surface, and to reduce elastic deformation. Therefore, a larger back angle should be selected.

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

Main deviation angle: Reducing the main deviation angle appropriately can improve heat dissipation conditions and lower the average temperature of the processing area.

② Improve tool structure.

Reduce the number of milling cutter teeth and increase the chip holding space. Due to the high plasticity of aluminum alloy materials and the large cutting deformation during processing, a larger chip holding space is required. Therefore, it is better to have a larger chip holding groove bottom radius and fewer milling cutter teeth. For example, φ Two teeth are used for milling cutters below 20mm; φ 30~ φ It is better to use three teeth for a 60mm milling cutter to avoid deformation of thin-walled aluminum alloy parts caused by chip blockage.

Precision grinding of cutter teeth: The roughness value of the cutting edge of the cutter teeth should be less than Ra=0.4um. Before using a new knife, a fine oilstone should be used to gently grind the front and back of the blade teeth a few times to eliminate any remaining burrs and slight serrations when grinding the blade teeth. 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. During 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 use 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 profile required for precision machining. Therefore, the emphasis is on processing efficiency and the pursuit of material removal rate per unit time, and reverse milling should be used. Precision machining requires higher machining accuracy and surface quality, emphasizing machining quality, and should use forward milling. Due to the gradual decrease of the cutting thickness of the cutter teeth from the maximum to zero during forward milling, the phenomenon of work hardening is greatly reduced, and it also has a certain degree of inhibitory effect on the deformation of the parts.

5. Secondary compression of thin-walled parts

When processing thin-walled aluminum alloy parts, the clamping force during clamping is also an important reason for deformation, which is difficult to avoid even with improved machining accuracy. In order to reduce the deformation of the workpiece caused by clamping, the compressed 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 slightly re compressed. The optimal point of action for secondary compression is on the supporting surface, and the clamping force should be applied in the direction where the workpiece has good rigidity. The magnitude of the clamping force should be based on its ability to clamp the workpiece without loosening, which requires a high level of experience and hand feel for operators. The compression deformation of the parts processed in this way is relatively small.

6. Drilling and 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 may even cause accidents such as tool breakage and breakage. The best method is to drill first and then mill, that is, first use a drill bit with a size not smaller than the milling cutter to drill the tool hole, and then use the milling cutter to extend into the tool hole and start milling. This can effectively solve the problems mentioned above.