Aluminum is a valuable industrial raw material. However, due to its poor hardness and high thermal expansion coefficient, it is easily deformed when machined into thin-walled and thin-plate parts. In addition to increasing tool performance and removing internal material stress in advance, there are numerous methods that can be taken to limit material deformation as much as feasible.
To improve heat dispersion and prevent thermal deformation in aluminum parts with a large processing allowance, an excessive concentration of heat must be avoided. The approach that can be used to do this is known as symmetrical processing.
Consider a 90 mm thick aluminum plate that needs to be reduced to 60 mm thick. Because each surface is treated to the final size if the milling side is immediately changed over to the other side, the continuous processing allowance will be enormous, causing heat concentration and limiting the flatness of the alloy plate to 5 mm.
However, if the symmetrical two-sided processing method is employed regularly, each surface can be treated at least twice until the ultimate size is attained, which is good for heat dissipation and flatness can be controlled at 0.3 mm.
Because of the uneven strain, it is simple to twist the cavity wall when there are several cavities on the aluminum alloy plate sections. The optimum solution is to use a layered multiple processing method, which involves processing all of the cavities at the same time.
Rather than completing the part all at once, it might be separated into layers and processed to the desired size layer by layer. The force exerted to the pieces will be more uniform, reducing the likelihood of deformation.
Cutting force and heat generated as a result of cutting can be decreased by using the right cutting parameters. If the cutting parameters are larger than normal, it will result in excessive cutting force, which can easily cause deformation of the parts, as well as compromising the rigidity of the spindle and the tool's longevity.
The quantity of back cutting depth has the greatest influence on cutting force of all cutting parameters. However, while limiting the number of cutting tools is good for ensuring that parts are not distorted, it reduces processing efficiency.
This issue can be solved with numerical control machining's high-speed milling. Machining can reduce cutting force and ensure processing efficiency by reducing back cutting depth, boosting feed, and enhancing machine speed.
Cutting force and cutting heat are heavily influenced by the material and geometric parameters of cutting instruments. The proper selection of cutting tools and parameters is thus critical for reducing part machining distortion.
Tool geometric parameters that can affect performance:
To maintain blade strength, the front angle must be appropriately set, or the sharp edge may wear off. Setting the front angle correctly can help reduce cutting distortion, assure smooth chip removal, and lower cutting force and temperature. Use the negative front angle tool at your own risk.
Cutting thickness is a key element to consider when designing the rear angle since it has a direct effect on both flank wear and machined surface quality. Because of the high feed rate, significant cutting load, and high heat generated during rough milling, the tool must accommodate for heat dissipation. As a result, the rear angle should be reduced. Sharp edges, on the other hand, are necessary in precision milling to reduce friction between the flank and the machined surface and to reduce elastic deformation. The back corner should be larger in these circumstances.
The helix angle should be as large as feasible to ensure stable milling and minimise milling force.
Reduced the primary deflection angle properly can increase heat dissipation and lower the average temperature of the processing area.
When machining aluminum alloy, reducing the number of milling cutter teeth can boost capacity. Because of the qualities of aluminum alloy, cutting deformation is greater, necessitating a big capacity for chip space.
The radius of the tank bottom should be increased, and the number of milling cutter teeth should be reduced. To avoid distortion of thin-walled aluminum alloy parts caused by chip blockage, two cutter teeth are utilized in milling cutters smaller than 20 mm and three cutter teeth in milling cutters larger than 30 mm.
The cutting edge roughness of cutter teeth should be less than Ra=0.4um. Use fine oil stones to gently grind the front and back edges of the teeth to remove burrs and slight zigzag patterns before using the new knives. Not only can cutting heat be decreased in this manner, but cutting deformation can also be reduced.
Workpiece surface roughness, cutting temperature, and workpiece deformation all rise as tools wear. As a result, in addition to selecting tool materials with high wear resistance, the tool wear standard should be less than 0.2 mm, or built-up nodules will form. To avoid distortion, the temperature of the workpiece during cutting should not exceed 100 degrees.
Different procedures are required for rough cutting and finishing. Rough machining entails removing extra material from the blank surface as quickly as possible with the fastest cutting speed, establishing the geometric contour required for finishing. The emphasis here is on processing efficiency and material removal rate.
Finishing machining, on the other hand, necessitates more machining precision and surface quality. The importance of milling quality should not be underestimated. As the cutting thickness of the cutter teeth drops from maximum to zero, the machining hardening phenomena is considerably decreased, and component deformation can be controlled to some amount.
Clamping force can induce deformation when cutting thin-walled aluminum alloy parts. To decrease workpiece deformation induced by clamping, unclamp pressed components before finishing the final dimension, releasing pressure and restoring parts to their original shape before reapplying pressure a second time.
The second pressing action point on the supporting surface is preferable, and the clamping force should be directed in the direction of highest rigidity. If everything is in order, the compression force should be able to keep the workpiece in place without slipping. This procedure necessitates the use of an experienced operator, but it can ensure that distortion of machined parts is kept to a minimum.
Machining items with cavities brings its own set of challenges. Cuttings will not be smooth if the milling cutter is placed immediately to parts due to insufficient debris space. This causes a high amount of cutting heat to accumulate, part expansion and distortion, and even probable part or knife breaking.
The best way to deal with this issue is to pre-drill and then mill. This entails drilling the hole with a tool no smaller than the milling cutter, then inserting the milling cutter to begin milling.